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2019-01-01 | We address the problem of a transition front propagation in chains with a bi-stable nondegenerate on-site potential and a nonlinear gradient coupling. For a generic nonlinear coupling, one encounters a special regime of transitions, characterized by extremely narrow fronts, far supersonic velocities of the front propagation, and long waves in the oscillatory tail. This regime is qualitatively associated with a shock wave. In this case, the front propagation can be described with the help of a simple reduced-order model; the latter delivers a kinetic law, which is almost not sensitive to the fine details of the on-site potential. Besides, it is possible to predict all main characteristics of the transition front, including its velocity, as well as the frequency and the amplitude of the oscillatory tail. Numerical results are in a good agreement with the analytical predictions. The suggested approach allows one to consider the effects an on-site damping. When the damping is moderate, it is possible to consider the shock propagation in the damped chain as a perturbation of the undamped dynamics. This approach also yields reasonable predictions. When the damping is high, the transition front enters a completely different asymptotic regime of a subsonic kink. The gradient nonlinearity generically turns negligible, and the propagating front converges to the regime described by simple exact solution for continuous model with a linear coupling. | Shockwaves and Kinks in Exothermic Nonlinear Chains | 10.1007/978-3-319-92234-8_19 |
2019-01-01 | The paper treats the control problem of the locomotion phases in a jumping cycle of a robot. The mechanical architecture of the leg with elastic lower segment (ATHLETE MODEL) is discussed. The dynamic model of the motion in stance phase is determined. The touch-down sequence, when the elastic foot hits the ground, is discussed and the control system is analyzed for two cases: actuator as passive damper system and actuator as semi-active damper system with ground-hook damper model. The transmissibility characteristics are analyzed. An active damper with ER fluids actuator and a skyhook viscosity controller is proposed to avoid the vibrations in the mechanical structure that can disturb the evolution of the robot. The control parameters are determined by using the circle criterion. The take-off sequence conditions in the stance phase are inferred by using the energy concept. | Hybrid Control Strategies for Jumping Robots | 10.1007/978-3-030-00232-9_20 |
2019-01-01 | A major decisive task in power system stability enhancement is optimal setting of damping controller parameters. This work proposes small signal stability enhancement of power system using UPFC-based optimal PI-lead-lag controller, whose parameters are optimized by modified Grey Wolf Optimizer technique. Lead-lag structure has been very much popular in UPFC damping controller design but in this work the efficacy of lead-lag controller has been improved by proportional–integral (PI) structure. The modified GWO technique proposed here has been compared with GWO-optimized lead-lag controller and PSO, DE-optimized PI-lead-lag controller to justify its supremacy. ITAE criterion is selected for minimization problem considering an increase in input mechanical power to generator. The system eigenvalues, speed and line power deviations subjected to disturbance in power system show that the proposed PI-lead-lag controller performs better than conventional lead-lag controller and is much better in comparison to other optimization techniques to tune the controller parameters for enhancing stability of power system. | Small Signal Stability Enhancement of Power System by Modified GWO-Optimized UPFC-Based PI-Lead-Lag Controller | 10.1007/978-981-13-1595-4_21 |
2019-01-01 | Metal mesh isolator is made of metallic wires. It has been widely used in vibration control engineering applications such as isolation mounting of machine tools. To investigate the performance of the metallic wires material, a set of dynamic tests was conducted for a range of frequencies and amplitudes of loading. The experimental results has demonstrated that the output of the isolator is revealed to the loading amplitude, however, slightly dependent to the loading frequency. As the loading amplitude increases, the dynamic mechanical property exhibits asymmetrical characteristic. Therefore, a model that includes the asymmetric non-linear elastic force, viscous damping and hysteretic coulomb friction is setup to describe the dynamic general restoring force. In this paper, an experimental identification methodology is presented to determine the unknown parameters of the constitutive mechanical model. The Bouc-Wen model was implemented to identify the unknown parameters of the hysteretic damping force. In order to measure the equivalent loss factor of nonlinear material, a damping capacity measurement method, based on the decomposition of the hysteresis loop, is brought forward. The equivalent loss factor of the metallic-wires material at different loading frequencies and amplitudes were measured through a damping capacity measurement method, based on the decomposition of the hysteresis loop. The results show that this material has excellent damping performance with loss factor about 0.4–0.5 for lower frequency and amplitude. | Experimental Characterization of Metal-Mesh Isolator’s Damping Capacity by Constitutive Mechanical Model | 10.1007/978-3-030-11220-2_24 |
2019-01-01 | The hydrodynamic bearings are used to support rotors for their high loading capacity, simple design, and quiet operation. To increase stability limit of lateral vibration of rotating machines, the hydrodynamic bearings are combined with classical squeeze film dampers. This technological solution is widely used to support rotors of high speed turbomachinery. The amount of damping in the rotor supports influences suppression of the vibration amplitude and magnitude of the force transmitted between the rotor and its stationary part. A simple dynamical analysis shows that to achieve optimum performance of the damping elements of rotors working in a wide range of operating speeds, their damping effect must be adaptable to the current angular velocity. This is possible if the classical squeeze film dampers are replaced with controllable damping devices. The presented article deals with a proposal and investigation of a new type of such support element that is a combination of a hydrodynamic bearing and of a magnetorheological squeeze film damper and with its application for rigid rotors. The computational simulations show that higher damping is needed for lower rotor velocities and lower one for higher speeds to achieve optimum compromise between the vibration attenuation and minimization of the force transmitted between the rotor and the stationary part. The results also show that damping in the rotor supports has almost no influence on the rotor oscillation amplitude for higher angular velocity. The proposal of the novel controllable rotor support element, the development of its mathematical model, and learning more on its effect on vibration attenuation and on the force transmission are the principal contributions of the research work carried out. | Controllable magnetically sensitive rotor support element for reducing oscillation and force transmission | 10.1007/978-3-030-20131-9_334 |
2019-01-01 | This chapter presents the validity of the extended rod theory proposed in the previous chapter to various high-rise buildings. The effectiveness of the extended rod theory proposed here is examined by comparing with the numerical results obtained from NASTRAN (MSC Software Corporation) and SNAP (Structural Systems, Inc.) which are general-purpose software for three-dimensional frame analysis, and dynamic Pro (SS3 abbreviation Union Co., Ltd.) for the lumped mass system. | Simplified Analysis of High-Rise Buildings by the Extended Rod Theory | 10.1007/978-981-13-7185-1_5 |
2019-01-01 | Large amplitude vibrations from hand held impact machines might bring serious health problems for users in long term. Here, a vibration absorber which works based on the nonlinear tuned mass damper concept is applied to mitigate unpleasant vibrations in a hand held impact machine. A global sensitivity analysis is carried out using multiplicative dimensional reduction method to scrutinize the effects of different components on the hand held impact machine dynamics response and attenuate the number of input parameters for optimization. Based on the global sensitivity analysis results, the nonlinear tuned mass damper components are chosen as the design parameters subject to optimization. A multiobjective optimization problem is formulated and solved using genetic algorithm to reduce vibrations and total weight of the machine. The Pareto optimized solutions are robust against the exciting force amplitude and frequency. The global sensitivity analysis results revealed that it is possible to run the simulations with a constant exciting force amplitude and extend the obtained solutions for the case with a variable exciting force amplitude while the same order of accuracy in the results can be observed. This significantly reduced the computational burden of the optimization. Closed form expressions for the optimal values of the tuned mass damper parameters as well as system response in terms of the auxiliary mass are developed by using the nonlinear least squares method. The results revealed that the proposed technique can significantly suppress the vibrations induced by the hand held impact machine. This makes it possible for users to operate the machine for a longer time period with lower health risks. | Pareto Optimization of a Nonlinear Tuned Mass Damper to Control Vibrations in Hand Held Impact Machines | 10.1007/978-3-319-74280-9_4 |
2019-01-01 | Metallic yielding device is one of the passive energy dissipation devices. It has good energy dissipation capacity, high initial stiffness along with high ductility. In this study, 0.4-scale single-story single-bay non-ductile gravity load design frame has been tested under cyclic load; later on, the damaged frame has been strengthened with the help of steel caging and metallic yielding damper. In this paper, the experimental results are validated numerically using OpenSees . The numerical model has the capability of predicting of failure and nonlinear behavior of reinforced concrete frame. The numerical model predicted the hysteresis behavior, stiffness, and energy dissipation with adequate accuracy. | Numerical Evaluation of Cyclic Performance of Damaged RC Frames Using Passive Devices | 10.1007/978-981-13-0365-4_58 |
2019-01-01 | The trends in the automotive field aim at providing all users with a high level of safety and a high degree of comfort. Current technologies combine increasingly judicious optimal control of most systems in the their componing. Thus, the highest level electronic equipment permanently adjusts the various systems and subsystems of the vehicles. The aim of the research is to determine optimal MRD functionality to reduce extreme shock and vibration values at the driver’s seat during unbuilt or very rough roads. Also, the identifying of these values its to view of correctly determining the supply current of the shock absorber coil so that the magnetic force created can efficiently absorb the accelerations produced beyond the limits allowed by the international standards in force. Carrying out the research involves multiple laboratory tests on MRD using the Hidropuls type, but also some references to vertical seat accelerations values recorded in the real world. The expected results are to reduce physical activity on the spine, as well as increasing the comfort of the seated staff. | Experimental Research on the Use of MRD to Reduce Shocks and Vibrations in Light Car Seats | 10.1007/978-3-319-94409-8_19 |
2019-01-01 | Bolts, screws, rivets, and pins can significantly complicate the prediction of damping, stiffness, and resonance frequencies of built-up systems. Because the interaction of interfacial joints is not well understood, current predictive models incorporating fastened joints often require over-designing for safety. To better understand the behavior of fastened joints, several experiments have been performed on a built-up structure with two rectangular 1/4″ plates fastened together by two screws on a 1/2″ thick flange. The structure was excited via acoustic excitation, and acceleration was measured at multiple locations on the flange and plate during and after ensonifying. While the energy input to the system may be lower for acoustic excitations than other direct contact methods, the results in this paper show that ensonifying the structure has two important advantages over traditional impact hammer and shaker methods. First, resonances of the structure can be excited and analyzed individually in both steady state and free-decay conditions, which is an advantage over impact excitation. Second, the excitation method is non-intrusive and does not change the system properties, which is an advantage over shaker excitation. The proposed method is shown to be an effective way to excite structures for both steady-state and decay measurements. | Acoustic Excitation of a Flanged Joint | 10.1007/978-3-319-74280-9_23 |
2019-01-01 | In this work, we investigate the possibility of using a piezoelectric element connected to an external electric RL-circuit for passive vibrations damping of a cantilevered plate interacting with a quiescent fluid. The behavior of piezoelectric elements is described by the equations of electrodynamics of deformable electroelastic media within the framework of quasi-static approximation. The motion of an ideal fluid in the case of small perturbations is considered in the framework of acoustic approximation. Small strains in a thin plate are determined using the Reisner–Mindlin theory. A mathematical formulation of the problem of electroelasticity elastic body with external electric circuits is based on the Lagrange variational principle, which includes the expression for hydrodynamic pressure. The acoustics equations together with the boundary conditions and the impermeability condition are converted to a weak form using the Bubnov–Galerkin method. The numerical implementation of the problem is carried out using an original approach, which is based on the ANSYS finite element package integrated with the program that implements the algorithm for solving the non-classical eigenvalue problem by the Muller method. This allows us to evaluate the values of the parameters of the external RL-circuit, which could provide the most effective damping of vibrations at a certain frequency. | Damping of Hydroelastic Vibrations of the Plate Using Shunted Piezoelectric Element. Part I: Numerical Model | 10.1007/978-3-030-21894-2_63 |
2019-01-01 | Floating offshore wind turbines are envisaged to undergo a significant development in the near future, due to their advantages with respect to the onshore or nearshore counterparts, in terms of greater available wind power, reduction of the land occupation and minimization of the visual impact of the turbines. Although many numerical codes have been developed for the representation of the dynamic behaviour of such structures, few experimental data have been collected up to now. These data would be useful for the validation of the codes and to give practical indications for the design of floating offshore wind turbines. This paper reports some results based on experimental data collected during an at-sea experiment on a 1:30 model of the OC3-Hywind spar support for floating offshore wind turbines, in parked rotor conditions. The experiment was carried out at the Natural Ocean Engineering Laboratory (NOEL) of Reggio Calabria (Italy), between July 2015 and March 2016. Heave and yaw representative response spectra of the structure, obtained for local wind-generated waves, are shown, and the corresponding damping estimations are performed. The results obtained could be useful for design purposes and motivate further elaborations of the experimental data collected during the experiment, to be realized in the near future. | Experimental Study on Heave and Yaw Motions of a 1:30 Spar Support for Offshore Wind Turbines | 10.1007/978-981-13-3134-3_63 |
2019-01-01 | Purposes: This paper aims to clarify the effects of the changes in detection probe external damping resistance on the transient electromagnetic method and detect the trenchless underground pipeline corrosion resolution. Methods and Process: A corrosion model was designed, multiple sets of tests were performed indoors, and online fixed points were selected and analyzed. Changes in external damping resistance were investigated to shut off the time, and the influence of the size of induction electromotive force was explored. According to the survey line profile and the relative error of test analysis, the effects of external resistance on detecting resolution were examined. Based on analysis of the influence of corrosion wall thickness change, and then compared with standard pipe groove in thickness. Results, Observations, and Conclusions: Changes in damping resistance affect the transient electromagnetic method to detect buried pipeline corrosion. Under the same test conditions, pipeline residual wall corrosion exacerbates as external damping resistance increases. The variation of residual wall thickness can determine the size of the corrosion of the resolution, and accuracy can be determined whether to confirm the requirements of the test, to identify the position of buried pipeline corrosion of high accuracy, and to provide a basis for on-site real-time detection convenient recognition. Technical Contributions: This paper confirms that using the transient electromagnetic method can be used to detect buried pipeline corrosion, and changes in damping resistance affect corrosion resolution and measure accuracy. Thus, appropriate damping resistance should be selected to obtain accurate test results. | Influence of Probe External Resistance on the Detection of Buried Pipeline Corrosion Through Transient Electromagnetic Method | 10.1007/978-981-10-7560-5_113 |
2019-01-01 | The results of solving the problem of finding the optimal synthesizing control function of the damping process in the vibration isolation system are given. It is established that the optimal control determines the intermittent damping process. The damper is activated when the sign of the object’s speed changes and is switched off when the object’s displacement sign is changed. The results of the simulation of dynamic processes in a controlled system of vibration isolation indicate that intermittent damping eliminates resonant phenomena and provides a monotonic decrease in the dynamic coefficients with increasing frequency of power disturbance. In this case, the transient processes decay within the same period of forced oscillations. | Control of Damping Process in System of Vibration Isolation | 10.1007/978-3-319-95630-5_37 |
2019-01-01 | Damping and vibration protection systems of equipment are necessary for industrial applications. In many respects, the existing fluid supports’ constructions for damping and vibration damping meets the requirements of industrial standards; they have some limitations and constructive disadvantages. The use of magnetorheological damping systems eliminates many disadvantages which are inherent to hydraulic dampers, but this leads to new operational problems, and they are inherent only to magnetorheological systems. The solution of these problems will improve efficiency and universalize magnetorheological dampers. Main disadvantages of magnetorheological systems are dependence on temperature stability of performances and significant heating of magnetorheological fluid in electromagnetic fields. The research paper presents methodological approaches to constructive solutions to these problems. It is considered as the original design of an adaptive combined rheological damper with magnetorheological chamber, which is control element of construction. Damping and vibration damping processes of a combined rheological damper includes magnetorheological, rheological and mechanical effects. It reduces the dependence on working environment temperature of performances. The effective method of combating environment heating is thermostating. The structure of a damping system has original rheological throttle-thermostat construction. The combination of new design solutions needs to create control algorithms, improve layout of devices and develop hardware implementation of control system and feedback. For ease of control and feedback implementation, there are selected devices which permist electrical measurements for non-electrical parameters. The text describes sensor arrangement in system and control algorithms for original devices. Component definition basics of multiparametric control and correction signals are considered. These relevant proposals allow simplifying and speeding up of sensor interrogation processes and correction of signals. | Hardware Implementation of Automatic Control System for New Generation Magnetorheological Supports | 10.1007/978-3-319-95630-5_239 |
2019-01-01 | The paper presents a problem of soldiers’ lower limbs safety in military vehicles during high impact loads derived from explosion of Improvised Explosion Devices (IED) charges. The numerical studies concerned the function of combat boots as an element of the soldier’s equipment. The model of a lower limb with cooperation with a sole was prepared as a multibody dynamic system. For this model the governing equations have been prepared and solved numerically with the Runge-Kutta method. The results were obtained for the load acting on the sole as the velocity generated proportionally in relation to the mass of an IED charge. The changes of material property for the sole were analysed to select the best parameters for protection of both a foot and a whole leg. The results show the conditions for increasing the safety of a passenger’s feet formulated as damping properties for soles and were compared with the similar data from an experimental study. | Analysis of the Lower Limb Model Response Under Impact Load | 10.1007/978-3-319-97286-2_14 |
2019-01-01 | ZJUNlict became the Small Size League Champion of RoboCup 2019 with 6 victories and 1 tie for their 7 games. The overwhelming ability of ball-handling and passing allows ZJUNlict to greatly threaten its opponent and almost kept its goal clear without being threatened. This paper presents the core technology of its ball-handling and robot movement which consist of hardware optimization, dynamic passing and shooting strategy, and multi-agent cooperation and formation. We first describe the mechanical optimization on the placement of the capacitors, the redesign of the damping system of the dribbler and the electrical optimization on the replacement of the core chip. We then describe our passing point algorithm. The passing and shooting strategy can be separated into two different parts, where we search the passing point on SBIP-DPPS and evaluate the point based on the ball model. The statements and the conclusion should be supported by the performances and log of games on Small Size League RoboCup 2019. | Champion Team Paper: Dynamic Passing-Shooting Algorithm of the RoboCup Soccer SSL 2019 Champion | 10.1007/978-3-030-35699-6_39 |
2019-01-01 | This paper investigates the effects of mixing ratio, cement content and curing time on the transient electrical and mechanical properties of sand-cement-inorganic binder mixture adopting two non-destructive testing (NDT) methods, electrical resistivity (ER) test and Free Free resonant Column test (FFRC). Due to the environmental issues related to cement, the reduction of cement usage is requesting. Inorganic binder is then introduced in this paper as alternative to reduce the use of cement contents for ground improvement. The results reveal that mixing ratio and curing time have considerable effects on electrical and mechanical properties of the mixture, and it is expected that sufficient strength can be obtained with the increase of inorganic binder content, confirming that the usage of cement can be reduced to some extent. | Geophysical Properties of Sand-Cement-Inorganic Binder Mixture: Electrical Resistivity and Elastic Wave Velocity | 10.1007/978-3-319-95759-3_9 |
2019-01-01 | Prosthetic knee is the most important component of lower limb prosthesis. This work aims to design a novel knee joint prosthesis and provide theoretical model of the hydraulic microprocessor-controlled prosthetic knee. The intelligent knee prosthesis with hydraulic damper is designed. Innovative valve structure is proposed to realize damping adjustment with single motor. The dynamics model of the lower limb prosthesis is established. Motion simulation is done to verify the correctness of the knee joint structure. The flexion and extension damping can be adjusted continuously and independently. The simulation shows that the motion of the knee joint is steady. It means that the structure of the knee joint prosthesis is reasonable. | Structure Design and Motion Simulation of a Microprocessor-Controlled Prosthetic Knee | 10.1007/978-981-13-2481-9_14 |
2019-01-01 | This paper presents the possibility to apply distributed vibration absorbers to reduce the vibration amplitude in axially symmetric components. The kind of metastructures here presented does not require complicated and expensive production processes such as additive manufacturing, but can be manufactured with more conventional means, for example with wire electrical discharge machining (EDM). Flexible rotating structures have a lot of natural frequencies in the operative range and the geometry changing approach is often not sufficient to improve the dynamic behavior. Using structural damping becomes fundamental to increase the transmitted power and the system life. In the present paper, the authors investigate the possibility to apply different geometrical configurations, each designed and tuned to suppress a particular mode shape, by means of the metastructure concept applied to flexible rotating devices. Their performances are analyzed with and without a balanced mistuning added to the metastructure. A number of distributed absorbers is set in order to act on each mode to be damped. Their vibration amplitude is firstly compared by keeping the total mass constant with respect to the original component, but also cases with higher and lower mass are analyzed. The frequency response of the proposed configurations is obtained from three-dimensional (3D) finite element models and some interesting results are evinced. | On the Implementation of Metastructures in Rotordynamics | 10.1007/978-3-319-74693-7_5 |
2019-01-01 | Rigid-body resonances used to be the only known vibration phenomena to occur in washing machines. However, lately there have been unexpected incidences of excessive, self-destructive vibrations. It is not clear how these incidents can be explained and reliably prevented. It is presumed that design changes evoke or shift vibrational phenomena which did not occur in the operating speed range of previous machines. Rotordynamic theories might be a suitable explanatory approach for these effects. However, since these effects have yet not been an issue, rotordynamic theories have never been applied to washing machines, even though they are obviously a rotor system and effects are well known for other applications. This paper investigates and highlights rotordynamic effects in frontloaders with a horizontal axis of rotation. To do so, a numerical multi-body model is utilized for dynamical analysis. Potential causes for rotordynamic effects in washing machines are discussed and included in the model. Numerical analyses of eigenvalues and transient displacements show several rotordynamic effects, their rough speeds and their dependency of different parameters. It is discussed how likely each effect is to shift into the operating speed range because of design changes, and thus how likely it is to become a threat. This gives a supplemented overview of the dynamic behavior of washing machines. | Rotordynamic Instabilities in Washing Machines | 10.1007/978-3-319-99268-6_27 |
2019-01-01 | Despite the hundreds of wind tunnel studies executed every year on tall- and super-tall buildings globally, the number of full-scale measurements conducted on these structures is still somewhat limited. Full-scale measurements, even for a short duration, have in fact tremendous value as they can be used to validate the structural frequencies predicted during the design stage through Finite Element Model (FEM) analysis and, at the same time, they can provide very valuable information on the level of damping these structures can inherently exhibit once built. In the assessment of the wind-induce response of tall- and super-tall buildings, damping does in fact constitute one of the most uncertain variables. In this technical paper, the findings of a 3-month full-scale monitoring campaign conducted on a 63-storey high-end residential tall building will be presented and discussed in detail. | Full-Scale Measurements of the Structural Response of a 63-Storey Mixed-Use High-Rise Under Wind Loading | 10.1007/978-3-030-12815-9_13 |
2019-01-01 | Design optimization has already become an important tool in industry. The benefits are clear, but several drawbacks are still present, being the main one the computational cost. The numerical simulation involved in the solution of each evaluation is usually costly, but time and computational resources are limited. Time is key in industry. The present communication focuses on the methodology applied to optimize the installation and design of a Tuned Mass Damper. It is a structural device installed within the tower of a wind turbine aimed to stabilize the oscillations and reduce the tensions and the fatigue loads. The paper describes the decision process to define the optimization problem, as well as the issues and solutions applied to deal with a huge computational cost. | Industrial Application of Genetic Algorithms to Cost Reduction of a Wind Turbine Equipped with a Tuned Mass Damper | 10.1007/978-3-319-89890-2_27 |
2019-01-01 | A well-designed SFD must deliver enough damping to aid in decreasing rotor amplitudes of motion. Piston rings (PRs) and O-rings (ORs) are commonly used as end seals in dampers for commercial and military gas turbine engines, respectively. The paper details dynamic load tests conducted on a short length SFD ( L / D = 0.2) sealed with either (a) PRs or (b) ORs and the experimentally estimated damping and inertia force coefficients. Lubricant (ISO VG2) flows thru one feedhole at the land middle plane with supply pressure increasing from 0.7 bar(g) to 6.2 bar(g). In the PR-SFD, oil leaves the film land through the rings’ abutted ends making a slit. The OR-SFD effectively seals any leakage; hence, lubricant flows out through a discharge hole at a location halfway of the film (upper) land length. Multiple sets of single frequency (10 Hz–100 Hz) dynamic loads produced circular centered orbits with amplitude ( r ) equal to 30% of the radial clearance. For both PR-SFD and OR-SFD, the viscous damping coefficient diminishes quickly as the lubricant supply pressure drops below 3 bar(g). The added mass coefficient, on the other hand, remains nearly constant for the PR-SFD and slightly increases for the OR-SFD. The OR-SFD delivers ~10% more viscous damping than the PR-SFD albeit it demands of a larger flow rate. Analysis of the recorded film dynamic pressures shows their peak - peak magnitude increases with whirl frequency. However, operation at the lowest oil supply pressure, 0.7 bar(g), generates film peak pressures not increasing as the excitation frequency rises, thus evidencing the presence of air ingestion and entrapment, as vividly shown by recorded film dynamic pressure waves, in particular for the PR-SFD. | Effect of Lubricant Supply Pressure on SFD Performance: Ends Sealed with O-rings and Piston Rings | 10.1007/978-3-319-99262-4_26 |
2019-01-01 | The helicopter rotor lead-lag damper dynamic characteristic modeling has the important role and significance for helicopter rotor system dynamic analysis in all three major research fields that are structural loads, motion response and system stability. The difficult part of this work is the variety of dampers means different working principle and the nonlinearity of the stress-strain relationship. The existing model can’t cover all those problems above and the lacking of a unified form both has brought inconvenience to rotor system dynamic modeling. The approach of helicopter lead-lag damper dynamic characteristic modeling based on the fractional calculus theory is attempted to cover elastomeric damper, fluid-elastomeric damper and MRFE damper. By adding the initial order variable function, the influence of current amplitude on MRFE damper dynamic characteristic is considerate. And the possibility of using fractional derivative damper model in research on fluid-elastomeric damper and MRFE damper dynamic characteristic is validated. | Helicopter Lead-Lag Damper Modeling Using Fractional Derivative Methods | 10.1007/978-981-13-3305-7_236 |
2019-01-01 | In this article, modelling of the magnetorheological (MR) damper and its finite element analysis (FEA) is presented. The axisymmetric FEM (finite element method) model of the MR damper was built using ANSYS Maxwell software. The MR damper was modelled using the geometrical parameters which were selected using the literature survey and then magnetic flux density was calculated and studied at the clearance space of the MR damper. The developed FEM model was used for determining the damping force of an MR damper with selected geometrical parameters. This article demonstrates that the developed FEM model for the MR damper can be used for predicting its damping force. The data gathered from this article will help the future researchers to know in depth the FEM modelling of MR damper and also provides a procedure to estimate the damping force. | Modelling and Analysis of Magneto-Rheological Damper for Maximizing the Damping Force | 10.1007/978-981-13-6469-3_7 |
2019-01-01 | Vibrations, considered one of the major problems in the engineering applications, are analyzed to predict their detrimental effects on the equipment and structures. The metal mesh isolator has become widely applied to mitigate the disturbing vibration due to its special production techniques. The metal mesh isolator is a kind of novel style porous damping material that is manufactured via a process of wire-drawing, weaving and compression molding. The influencing laws of the manufacturing parameters including the relative density and the working condition together with the excitation direction dependence should be taken into account in the characterization of the metallic wires material. In this paper, the mechanical properties of three models with different relative density will be investigated under different preload masses and for three acceleration levels. A number of experiments can be examined by changing the direction of excitation in order to describe the compression and non-compression molding direction effect on the dynamic behavior. A modal analysis is performed using the rational fraction polynomial method to determine the stiffness and the damping ratio from the measured transmissibility data. According to the reported experimental results, the major factor affecting the mechanical characteristics (stiffness and damping) is the sliding friction that exists at the contact-points between wires. | Experimental Investigation of Normal/Lateral Excitation Direction Influence on the Dynamic Characteristics of Metal Mesh Isolator | 10.1007/978-3-319-94616-0_23 |
2019-01-01 | Brake squeal is a typical problem of “Noise, Vibration, Harshness” (NVH) phenomena in the automotive world leading to potential customer complaints. This high frequency noise in the audible frequency range of approximately 1 kHz to 15 kHz is induced by self excitation resulting from the frictional contact between brake pad and disk. A typical industrial countermeasure to address this problem is the mounting of thin composite structures consisting of elastomer and steel layers, so called shims, on the pad backplates. They are applied to increase the damping and to influence the vibration shapes. The computational modeling of shims using Finite Elements is still a complex task and shows significant potential for improvement. To avoid problems resulting from element sizes of the partially very thin layers a classical homogenization theory from literature is considered. This homogenization approach maps shim properties in an improved manner which contributes to substantially smaller model sizes as well as less simulation effort and time. Therefore, analytical approaches for constrained layer damping structures are introduced and corresponding theoretical results are presented. To validate these theoretical results, experimental investigations are carried out on shims bonded to structures, especially steel plates and brake pads. | On Brake Pad Shim Characterization: a Homogenization Approach and Finite Element Analysis | 10.1007/978-3-030-13307-8_30 |
2019-01-01 | The present study focuses on a means of improving the performance of transmission towers under high-intensity winds in the form of cyclonic winds through the use of shape memory alloy (SMA) dampers installed in the bracings of the tower. The cyclonic wind field is modelled as per the guidelines of the World Meteorological Organization, and the Harris power spectral density function (PSDF) is used to characterize the fluctuating component of the cyclonic wind velocity. Nonlinear time history analysis of a single circuit lattice transmission tower is carried out under the cyclonic wind load time histories generated for each node of the tower. Results indicate that the recentering and energy dissipation properties of superelastic SMA bar dampers are capable of significantly mitigating the tower’s response to cyclonic wind loads. | Cyclone Wind Response Mitigation of Transmission Towers by SMA Dampers | 10.1007/978-981-13-0365-4_35 |
2019-01-01 | In this study, a new graphical user interface (GUI), VC4OWT, is developed to evaluate the structural response of National Renewable Energy Laboratory (NREL) 5-MW offshore wind turbine (OWT) subjected to seismic excitations. Finite element model of OWT has been modelled and analyzed using the Opensees simulation platform. Performances of structure with and without friction damper considering soil-structure interaction (SSI) have been studied to reduce the effects of seismic load. The diagonal-bracing friction damper system is added at platform for the vibration purpose. The obtained outputs demonstrate that VC4OWT is a functional and efficient software to simulate and study the vibration control of OWT. | VC4OWT: MATLAB Interface for Vibration Control of Offshore Wind Turbine | 10.1007/978-981-13-2306-5_75 |
2019-01-01 | Small-scale, quickly executed modal surveys can yield an incredible amount of useful information. Electrodynamic shakers and especially impact hammers have been the excitation methods of choice for these tests because of their ease of use. However, large low-frequency structures with highly damped modes are difficult to excite due to exciter stroke limitations or inability to apply long duration pulse inputs. Hydraulic actuation allows large displacements at low frequencies, but it is expensive and challenging to install in a short amount of time. Similarly, while step-relaxation techniques allow large force and displacement inputs, setup, using a reaction structure, and execution is complicated by the need to reset the system multiple times. In order to overcome some of these drawbacks, ATA developed a modal handle to apply a manual excitation while measuring the input levels of the excitation force. This paper presents results of using this modal handle to perform a modal survey on a test article to evaluate the effect of different dampers and damper configurations on the test article primary torsion mode. This inexpensive and efficient excitation method proved to be successful in quickly completing over eighty test configurations needed to down select to a final damper configuration. | Using Manual Excitation for Large Displacement on a Highly Damped System | 10.1007/978-3-319-74700-2_30 |
2019-01-01 | The paper deals with the analytical investigation of the behaviour of the harmonically excited physical pendulum suspended on the nonlinear spring. The asymptotic method of multiple scales (MS) has been used to derive approximate solutions in the analytical form. The applied approach allows one to perform a qualitative analysis of the behaviour of the system. MS method gives possibility, among others, to recognize resonance conditions which can appear in the system. | Plane Motion of a Rigid Body Suspended on Nonlinear Spring-Damper | 10.1007/978-3-319-92234-8_10 |
2019-01-01 | Most of the studies on the control of building frame using MR damper are investigated for far-field earthquake records, and a considerable reduction in responses is shown. However, MR dampers have some significant drawbacks like the saturation of MR dampers and its performance variability with respect to the ground motions. It has been found that when the predominant frequency of the earthquake is much away from the natural frequency of the structure, the response reduction becomes significantly less. The reason for this may be attributed to the less values of relative displacement and velocities of the floors which primarily influence the force generated in the damper for a given voltage. The characteristics of the near-field ground motion are distinctly different from the far-field ground motion. The performance of the MR damper for the near-field earthquake is not well investigated. In the present study, the performance of the MR dampers is studied for two types of near-field earthquakes, namely Bam (directivity effect) and Chichi (fling step effect) earthquakes. A limited number of MR dampers are employed for response reduction. | Performance of Semi-actively Controlled Building Frame Using MR Damper for Near-Field Earthquakes | 10.1007/978-981-13-0365-4_34 |
2019-01-01 | Many lightly damped flexible structures suffer from unwanted vibrations. Typically a tuned-mass-damper (TMD) can be used to reduce unwanted vibrations of a specific mode of vibration. The inerter is a novel passive vibration control device offering a wide range of potential applications in engineering practice. It has been analytically proven to be an effective device for controlling unwanted vibrations in structural systems. One of the most effective control strategies employing an inerter is the tuned inerter damper (TID) whose inerter element is connected in series with parallel connected spring-damper. When the inerter element is in parallel with the damper element, it is then called Parallel Viscous Damper Inerter (PVID). In this paper, we will introduce a new passive modal vibration control strategy for the PVID based on a fluid inerter combined with a linear spring connected in parallel. The fluid inerter produces inertance by the acceleration of the fluid inside a helical pipe coiled around the outside of the main fluid chamber. The fluid inerter has both inertance and damping in one device and these properties are coupled to each other. Hence, it is a particular challenge to tune both parameters to fit with optimized values resulting from a design analysis. In this paper, a new analysis will be presented for this device that demonstrates how the PVID with a fluid inerter can be modelled to achieve the targeted parameters. | The Realisation of an Inerter-Based System Using Fluid Inerter | 10.1007/978-3-319-74421-6_16 |
2019-01-01 | It is a well-known fact that soil–structure interaction plays vital role in governing the response of building during seismic activities. Also, for better stability of buildings during earthquakes, energy dissipation devices are widely used. This paper is an attempt to gather the work done by researcher to study the influence of soil–structure interaction and friction dampers. From the available literature, it was concluded that friction dampers which are designed and placed based on rigid base hypothesis may not perform same under consideration of soil–structure interaction. So, it is needed to study the performance of friction damper considering soil–structure interaction with suitable assumptions. | A Review on: ‘Performance of Friction Damper for Response Control of Buildings Considering Effect of Soil–Structure Interaction’ | 10.1007/978-981-13-6148-7_34 |
2019-01-01 | This paper investigates the potential of tuned mass dampers (TMDs) coupled with inerter devices in different tuned mass dampers inerter (TMDI) topologies to dissipate oscillations in tall buildings due to vortex shedding in the across wind direction while generating electric energy. The TMDI is first optimized for minimizing peak accelerations for serviceability purposes in a 74 storey benchmark steel building under different wind intensity levels. It is seen that TMDI stiffness and damping optimal parameters are robust to design/reference wind velocity and, therefore, to potential climate change effects, while achieving same level of performance using significantly smaller attached mass compared to the classical TMD. Then, a regenerative electromagnetic motor (EM) is added to the TMDI allowing for varying the TMDI damping property as well as transforming part of the dissipated kinetic energy to electricity. It is shown that by increasing TMDI damping above the optimal value for vibration suppression and/or by reducing the inerter property increases the available energy for harvesting at the expense of larger floor accelerations. Therefore, it is concluded that by relaxing serviceability limit state requirements associated with occupancy considerations renders possible an increase in energy generation in wind-excited tall buildings. | Simultaneous Vibration Suppression and Energy Harvesting in Wind Excited Tall Buildings Equipped with the Tuned Mass Damper Inerter (TMDI) | 10.1007/978-3-030-12815-9_42 |
2019-01-01 | This article introduces a new type of active damper—elastic support/dry friction damper (ESDFD) for vibration control of rotor systems and its performances. The basic operation principle of ESDFD in rotor system was introduced. In particular, a two-dimensional friction model-ball/plate model was proposed, by which a dynamic model of rotor systems with ESDFD was established and verified. The damping performance of the ESDFD has been studied numerically. The simulation results show that the damping performance of ESDFD is closely related to the characteristics of the rotor’s mode. For obtaining the damper’s best performance, the damper should be located at the elastic support in which the vibration energy is concentrated. And the damper not only provides external damping to the rotor system, but also increases extra stiffness into the rotor system. The stiffness of the stationary disk and the tangential contact stiffness of the contact interface are connected in series between the moving disk and the mounting base of the stationary disk. The larger of this combined stiffness, the better of the damper’s damping performance. The application of ESDFD to the vibration suppression of a rotor system is investigated experimentally. A switch control scheme for the damper is introduced; the effectiveness and control characteristics with control scheme for attenuating the vibration of rotor systems are experimentally investigated. | An Active Elastic Support/Dry Friction Damper: New Modeling and Analysis for Vibration Control of Rotor Systems | 10.1007/978-3-319-99270-9_2 |
2019-01-01 | This paper focuses on constructing a Matlab/Simulink program of vibration model with 2 DOF horizontal washing machine. The key point of this paper is using a strong nonlinear friction force - velocity (F-V) relationship of dampers which is obtained from experiment as an input for the simulation. The suitability and high reliability of the model were proved by comparing simulation and experimental results. The model was used to study the effect of damper configurations on the vibration characteristics of horizontal washing machines and then to propose several suitable damper configurations. | The Effect of Damper Configurations on the Vibration of Horizontal Washing Machines | 10.1007/978-3-030-04792-4_40 |
2019-01-01 | Today, a number of researchers are broadly studying the effective implementation of supplemental seismic energy dissipation systems to improve seismic behavior of structures during earthquakes. The current article studies the impacts of employing Viscous Wall Damper devices to couple two adjacent structures on seismic response of the new system. An exclusive finite element algorithm capable of modeling and analyzing structures equipped with special damper systems was used in order to perform a nonlinear time history analysis subjected to seismic excitation. Two ten-story RC framed structures are modeled adjacently in 11 different cases, each representing existence or damping coefficient of the Viscous Wall Damper device. A parametric study has been conducted in each case to assess the effectiveness of implementing Viscous Wall Damper devices on improving seismic behavior of the coupled structure. The considered metrics include rotation and displacement amplitude, plastic hinge formation, and induced element forces. It has been proved that the proposed damper system substantially diminishes and dissipates induced seismic response of the system. Also, it is indicated that the extent to which Viscous Wall Damper device contributes in mitigating seismic responses is highly correlated with the damping coefficient. | Preventing Seismic Pounding of Adjacent Structures Using Viscous Wall Damper Device | 10.1007/978-981-10-8016-6_44 |
2019-01-01 | The energetic boundary element method (BEM) is a discretization technique for the numerical solution of wave propagation problems, introduced and applied in the last decade to scalar wave propagation inside bounded domains or outside bounded obstacles, in 1D, 2D, and 3D space dimension. The differential initial-boundary value problem at hand is converted into a space–time boundary integral equations (BIEs), then written in a weak form through considerations on energy and discretized by a Galerkin approach. The paper will focus on the extension of 2D wave problems of hard scattering by open arcs to the more involved case of damped waves propagation, taking into account both viscous and material damping. Details will be given on the algebraic reformulation of Energetic BEM, i.e., on the so-called time-marching procedure that gives rise to a linear system whose matrix has a Toeplitz lower triangular block structure. Numerical results confirm accuracy and stability of the proposed technique, already proved for the numerical treatment of undamped wave propagation problems in several space dimensions and for the 1D damped case. | Energetic BEM for the Numerical Solution of 2D Hard Scattering Problems of Damped Waves by Open Arcs | 10.1007/978-3-030-04088-8_14 |
2018-12-15 | The understanding of physical processes over submerged reefs represents an important ongoing research topic when considering wave energy dissipation and coastal protection that these environments provide. Detailed analyses are required to assess wave damping based on the contribution of reef roughness and wave breaking. For this purpose, the CFD (computational fluid dynamics) toolbox OpenFOAM^® is applied to simulate the wave energy dissipation process over reefs with explicit accounting for the complexities of coral shape instead of commonly applied parameterized approaches for bottom roughness and wave breaking. Model validation was performed through comparison with field measurements over a reef profile of Tesoro Island in the Colombian Caribbean. Quantitative analysis of wave damping caused by wave breaking and reef roughness was conducted for (1) moderate and extreme wave conditions, (2) smooth and rough seabed configurations and (3) changes in the water depth over the reef crest. Wave height attenuation is found to vary along the reef profile reaching differences of up to 55% between smooth and rough reef surface scenarios, particularly for moderate wave conditions. Wave breaking, high turbulent flows and detachment of undertow currents are among the reef roughness effects on hydrodynamics. The fore-reef terrace and the reef crest are identified as the most critical zones where dissipation takes place. Wave breaking from rough seabeds provides a global wave attenuation of 75.4–94.8%, with the reef roughness alone accounting for ~ 4–14%. Under extreme wave height scenarios, the wave damping from reef roughness is not significant. Further predictions regarding roughness effects on the reef hydrodynamics, wave set-up and undertow currents for moderate and extreme wave climate conditions are also shown. Directions for future research using CFD are presented to address limitations that arise from the limited span-wise domain in our approach that prevents development of large lateral coherent structures. | CFD modelling of wave damping over a fringing reef in the Colombian Caribbean | 10.1007/s00338-018-1736-4 |
2018-12-13 | We consider a system of acoustic wave equation possessing lower-order perturbation terms in a bounded domain in R 2 $\mathbb{R}^{2}$ . In this paper, we show the system is well-posed and stable with energy decays introducing a local discontinuous Galerkin (LDG) method. Also, we study an a priori L 2 $L^{2}$ -norm error estimate for the semi-discretized LDG method for the system under additional regularity assumptions. Further, numerical tests are presented to support the theoretical analysis. | Error estimates of a semi-discrete LDG method for the system of damped acoustic wave equation | 10.1186/s13662-018-1919-x |
2018-12-07 | The global LR04 δ^18O, the tropical ODP Site 846 sea surface temperature (SST), and the global ΔSST stack records were investigated using the advanced method for time-series decomposition singular spectrum analysis to outline the quantitative role of orbital forcings and to investigate the nonlinear dynamics of the Pliocene and Pleistocene climate system. For the first time, a detailed quantitative evaluation is provided of the δ^18O and SST variance paced by long-period orbital modulation, short eccentricity, obliquity, precession, and half-precession cycles. New insights into the nonlinear dynamic of the orbital components suggest considering astronomical signals as composite feedback lagged responses paced by orbitals and damped (Early Pliocene) or amplified (Mid-Late Pleistocene) in a range of − 100 to + 400% the forcing. The Early Pliocene asymptotic decay of the δ^18O and SST response sensitivity up to − 100% observed for the first time in all orbital responses is interpreted as damping effect of a wide global forest cover along with a possible high ocean primary productivity, through the CO_2-related negative feedbacks during time of global greenhouse. An anomalous post-Mid-Pleistocene Transition (MPT) sharply declines to near-zero in obliquity response sensitivity observed in both global δ^18O and tropical SST, suggesting an attenuation mechanism of the obliquity driving force and a reduction of the related feedback amplification processes. It is hypothesized the post-MPT obliquity damping has contributed to the strengthening of the short eccentricity response by mitigating the obliquity “ice killing”, favoring a long-life ice sheet sensitive to a synergistic ~ 100-kyr amplification of positive feedback processes during the time of a global icy state. The global δ^18O, the tropical SST, and the global ΔSST trend components, all explaining ~ 76% of the Plio-Pleistocene variance and significantly modifying the mean climate state, appear to be related to the long-term pCO_2 proxies, supposedly controlled by plate tectonics through the global carbon cycle (CO_2 outgassing, explosive volcanism, orography and erosion, paleogeography, oceanic paleocirculation, and ocean fertilization). Finally, singular spectrum analysis provides a valuable tool in cyclostratigraphy with the remarkable advantage of separating full-resolution time series by variance strength. | δ^18O and SST signal decomposition and dynamic of the Pliocene-Pleistocene climate system: new insights on orbital nonlinear behavior vs. long-term trend | 10.1186/s40645-018-0236-z |
2018-12-01 | In nonlinear dynamic analysis, damping models are used to represent the un - modelled dissipation. Till now, majority of nonlinear dynamic analysis tools for seismic engineering uses the classical Rayleigh damping and its variations. Though these models perform well in linear dynamic analysis, their adaptation to nonlinear dynamic analysis is accompanied with severe penalties. In quest of developing a better modelling approach to mimic the so observed un - modelled dissipation phenomenon in nonlinear dynamic analysis, the authors have recently proposed a new approach of inherent damping modelling by formulating the damping matrix at an element level. In this paper, the new approach is further applied into more mathematically rigorous continuum damping models based on local elasticity. In the present paper, these models are called local continuum damping models mainly because the damping stress at a point in space is a function of the strain history at that point only. Semi-discretization procedures and time domain implementation schemes are outlined in detail. It has been shown that these models can be easily incorporated into the existing commercial software framework with minor modifications. The performance of the proposed adaptations of these models is illustrated by conducting nonlinear dynamic analysis on a four-story RC frame designed to Eurocodes. The incremental dynamic analysis study presented outlines the fact that the proposed models perform in a more reliable manner in comparison to the classical damping models in capturing the damping phenomenon. | Application of local elasticity continuum damping models in nonlinear dynamic analysis | 10.1007/s10518-018-0424-7 |
2018-12-01 | In order to have a more generic representation of the damping phenomenon in seismic analysis of structures, in this paper, the already existing nonlocal elasticity continuum damping models have been adapted and extended to the inelastic domain. Adaptations of two nonlocal elasticity based damping models, Russell’s spatial hysteresis model and the extended Sorrentino model, into the nonlinear dynamic analysis is presented. Galerkin based finite element schemes are developed and the numerical implementation of the models are outlined. The performances of the nonlocal elasticity-based damping models are illustrated by studying the nonlinear dynamic responses of a four-story Reinforced Concrete frame designed to the Eurocodes. The incremental dynamic analysis study presented illustrates the fact that the proposed models are devoid of the large spurious damping actions commonly exhibited by the popular classical Rayleigh damping model. It has also been shown that in a nonlinear dynamic analysis, the proposed adaptation of the nonlocal elasticity continuum damping models might be a more realistic alternative to the popular classical Rayleigh damping model. The proposed models may be easily implemented in an existing software framework capable of solving both ordinary and integro-differential equations without adding markedly to the computational effort. | Application of nonlocal elasticity continuum damping models in nonlinear dynamic analysis | 10.1007/s10518-018-0412-y |
2018-12-01 | We consider the 2D Navier–Stokes equation on $$\mathbb T \times \mathbb R$$ T × R , with initial datum that is $$\varepsilon $$ ε -close in $$H^N$$ H N to a shear flow ( U ( y ), 0), where $$\Vert U(y) - y\Vert _{H^{N+4}} \ll 1$$ ‖ U ( y ) - y ‖ H N + 4 ≪ 1 and $$N>1$$ N > 1 . We prove that if $$\varepsilon \ll \nu ^{1/2}$$ ε ≪ ν 1 / 2 , where $$\nu $$ ν denotes the inverse Reynolds number, then the solution of the Navier–Stokes equation remains $$\varepsilon $$ ε -close in $$H^1$$ H 1 to $$(e^{t \nu \partial _{yy}}U(y),0)$$ ( e t ν ∂ y y U ( y ) , 0 ) for all $$t>0$$ t > 0 . Moreover, the solution converges to a decaying shear flow for times $$t \gg \nu ^{-1/3}$$ t ≫ ν - 1 / 3 by a mixing-enhanced dissipation effect, and experiences a transient growth of gradients. In particular, this shows that the stability threshold in finite regularity scales no worse than $$\nu ^{1/2}$$ ν 1 / 2 for 2D shear flows close to the Couette flow. | The Sobolev Stability Threshold for 2D Shear Flows Near Couette | 10.1007/s00332-016-9330-9 |
2018-12-01 | The movement of the simplest model of a statically unbalanced rotor under the condition of the action of a constant external torque is considered, taking into account the forces of external and internal damping. Two modes of stationary motion of the rotor are investigated: synchronous whirling and asynchronous self-excited oscillations. Using the system of equations that describes the rotor dynamics in polar coordinates, conditions for the existence and stability of both types of stationary modes are obtained. | Synchronous Whirling and Self-oscillations of a Statically Unbalanced Rotor in Limited Excitation | 10.3103/S0025654418050047 |
2018-12-01 | We consider an optimization problem related to semi-active damping of vibrating systems. The main problem is to determine the best damping matrix able to minimize influence of the input on the output of the system. We use a minimization criteria based on the ℋ 2 $\mathcal {H}_{2}$ system norm. The objective function is non-convex and the associated optimization problem typically requires a large number of objective function evaluations. We propose an optimization approach that calculates ‘interpolatory’ reduced order models, allowing for significant acceleration of the optimization process. In our approach, we use parametric model reduction (PMOR) based on the Iterative Rational Krylov Algorithm, which ensures good approximations relative to the ℋ 2 $\mathcal {H}_{2}$ system norm, aligning well with the underlying damping design objectives. For the parameter sampling that occurs within each PMOR cycle, we consider approaches with predetermined sampling and approaches using adaptive sampling, and each of these approaches may be combined with three possible strategies for internal reduction. In order to preserve important system properties, we maintain second-order structure, which through the use of modal coordinates, allows for very efficient implementation. The methodology proposed here provides a significant acceleration of the optimization process; the gain in efficiency is illustrated in numerical experiments. | Damping optimization of parameter dependent mechanical systems by rational interpolation | 10.1007/s10444-018-9605-9 |
2018-12-01 | This paper is concerned with long-time dynamics of laminated beams modeled from the well established Timoshenko system. Of particular interest is a model of two-layered beam proposed by Hansen and Spies which describes the slip effect produced by a thin adhesive layer uniting the structure. In a more general setting, involving a nonlinear foundation, we establish the existence of smooth finite dimensional global attractors for the corresponding solution semigroup. | Dynamics of Laminated Timoshenko Beams | 10.1007/s10884-017-9604-4 |
2018-12-01 | This paper improves upon experience mapping based predictive controller (EMPC) for an under-damped type 1 system which is a fairly new concept presented in literature. EMPC has been earlier demonstrated for an under-damped type 1 system. However, the earlier EMPC controller did not address changes in system parameters and hence the performance in terms of rise time and overshoots deteriorated with change in friction and inertia. This paper develops a theoretical basis for EMPC presented earlier. An adaptation technique is proposed for EMPC to control under-damped type 1 systems for variations in load friction and inertia. The present control action is decided based on the steady state error due to the previous control action. The general nth order type-1 under-damped system is simulated and the results of simulation for system variation and various demands are presented. EMPC is shown to perform robustly with adaptation. Adaptive EMPC controller is shown to outperform proportional derivative controller and a Model reference based adaptive controller. The system is also simulated and practically implemented with a PMDC motor based positioning system coupled to a load through a flexible shaft. The results of these simulations and experiments are presented and it is observed experimentally that adaptive EMPC performs well. | Adaptive experience mapping based predictive controller for under-damped type 1 systems | 10.1007/s40435-018-0396-0 |
2018-12-01 | In this communication, we propose a nonlocal fractional viscoelastic model of a nanobeam resting on the fractional viscoelastic foundation and under the influence of the longitudinal magnetic field and arbitrary number of attached nanoparticles. Size effects are taken into account using the differential form of the nonlocal constitutive relation together with the fractional Kelvin–Voigt model. The governing equation for the free vibration of a nanobeam is derived, where Maxwell’s equations are used in order to represent the effect of the longitudinal magnetic field. We propose an analytical solution of the problem based on the Laplace transform, Mellin–Fourier transforms, and residue theory. From the validation study, it is shown that the obtained complex roots of the characteristic equation, where the imaginary part is the damped frequency and the real part is the damping ratio, are approximated eigenvalues of the system. In the parametric study, several numerical examples are given to investigate the influence of different parameters on complex roots as well as different masses and numbers of nanoparticles on the damped vibration behavior of a nanobeam system. | Fractional-order model for the vibration of a nanobeam influenced by an axial magnetic field and attached nanoparticles | 10.1007/s00707-018-2263-7 |
2018-12-01 | The machining of complex geometries and deep cavities requires the use of long projecting tool holders. However, due to their high length-to-diameter ratio, these tool holders have a high degree of static and dynamic compliance. High dynamic compliance reduces process stability and thus productivity. A new approach to lessen this is to increase the damping of long projecting tool holders by using friction dampers integrated into the tool holder shaft. The mathematical description and experimental testing of large friction-damped tool holders are the subject of this paper. With the aid of experimental modal analysis and cutting tests, the dynamic compliance and maximal cutting depth were determined. Due to the integration of friction segments in the tool holder shaft, the maximal depth of cut could be increased about 75% compared to a reference tool holder with the same diameter and length configuration. | Frictionally damped tool holder for long projection cutting tools | 10.1007/s11740-018-0847-7 |
2018-12-01 | A precise tangential contact damping model is proposed, which includes the lateral contact of the upper–lower asperities and the interaction of adjacent asperities. The effects of the normal static preload, frequency, and amplitude of tangential displacement on the tangential contact damping were analyzed by simulation, respectively. Furthermore, the results of simulation are verified by experiment. The tangential contact damping of considering the interaction and lateral contact of asperity is very close to the experimental results. | A Model of Tangential Contact Damping Considering Asperity Interaction and Lateral Contact | 10.1007/s10338-018-0050-6 |
2018-12-01 | A regenerative semi-active control system based on self-tuning Fuzzy proportional-derivative (PD) control strategy is applied to suppress the vortex-induced vibrations (VIV) of an elastically supported circular cylinder at low Reynolds numbers. Of particular interest was the effect of control parameter and capacitance on the VIV reduction and energy regeneration capabilities of adopted semi-active control system. A collaborative simulation which couples a Fuzzy PD controller along with the adjustable electromagnetic (EM) damper and corresponding energy harvesting circuit (implemented in MATLAB/Simulink) to the computational fluid dynamic (CFD) plant model (implemented in Fluent) is employed. It appears that the cylinder displacement amplitude, capacitor charging speed, and maximum stored electrical energy vary with the controller parameters and capacitance value. It is shown that the selected regenerative semiactive control system can store maximum energy in a capacitor in prescribed limiting time, along with the highest level of cylinder oscillation reduction which is the primary goal of current work. | Regenerative semi-active vortex-induced vibration control of elastic circular cylinder considering the effects of capacitance value and control parameters | 10.1007/s12206-018-1104-x |
2018-12-01 | Gravity waves are prominent physical features that play a fundamental role in transport processes of stratified aquatic ecosystems. In a two-layer stratified basin, the equations of motion for the first vertical mode are equivalent to the linearised shallow water equations for a homogeneous fluid. We adopted this framework to examine the spatiotemporal structure of gravity wavefields weakly affected by the background rotation of a single-layer system of equivalent thickness $$h_{\ell }$$ h ℓ , via laboratory experiments performed in a cylindrical basin mounted on a turntable. The wavefield was generated by the release of a diametral linear tilt of the air–water interface, $$\eta _{\ell }$$ η ℓ , inducing a basin-scale perturbation that evolved in response to the horizontal pressure gradient and the rotation-induced acceleration. The basin-scale wave response was controlled by an initial perturbation parameter, $${\mathcal{A}}_{*} = \eta _{0}/h_{\ell }$$ A ∗ = η 0 / h ℓ , where $$\eta _{0}$$ η 0 was the initial displacement of the air–water interface, and by the strength of the background rotation controlled by the Burger number, $${\mathcal{S}}$$ S . We set the experiments to explore a transitional regime from moderate- to weak-rotational environments, $$0.65\le {\mathcal{S}} \le 2$$ 0.65 ≤ S ≤ 2 , for a wide range of initial perturbations, $$0.05\le {\mathcal{A}}_{*}\le 1.0$$ 0.05 ≤ A ∗ ≤ 1.0 . The evolution of $$\eta _{\ell }$$ η ℓ was registered over a diametral plane by recording a laser-induced optical fluorescence sheet and using a capacitive sensor located near the lateral boundary. The evolution of the gravity wavefields showed substantial variability as a function of the rotational regimes and the radial position. The results demonstrate that the strength of rotation and nonlinearities control the bulk decay rate of the basin-scale gravity waves. The ratio between the experimentally estimated damping timescale, $$T_{d}$$ T d , and the seiche period of the basin, $$T_{g}$$ T g , has a median value of $$T_{d}/T_{g}\approx 11$$ T d / T g ≈ 11 , a maximum value of $$T_{d}/T_{g}\approx 10^{3}$$ T d / T g ≈ 10 3 and a minimum value of $$T_{d}/T_{g}\approx 5$$ T d / T g ≈ 5 . The results of this study are significant for the understanding the dynamics of gravity waves in waterbodies weakly affected by Coriolis acceleration, such as mid- to small-size lakes. | Evolution and decay of gravity wavefields in weak-rotating environments: a laboratory study | 10.1007/s10652-018-9609-5 |
2018-12-01 | The use of CFRP transmission shaft has positive effect on the weight and flexural vibration reduction of drive-line system. However, the application of CFRP transmission shaft will greatly reduce the torsional stiffness of the drive-line, and may cause strong transient torsional vibration. Which will seriously affect the performance of CFRP drive-line. In this study, the forced torsional vibration of the CFRP drive-line system is carried out using the lumped parameter model. In addition, the effect of rotary inertia, internal damping, coupling due to the composite laminate, and excitation torque are incorporated in the modified transfer matrix model (TMM). Then, the modified TMM is used to predict the torsional frequency and forced torsional vibration of a CFRP drive-line with three-segment drive shafts. The results of modified TMM shown that the rotational speed difference of the CFRP transmission shaft segment is much larger than metal transmission shaft segment under excitation torque. And compared the results from finite element simulation, modified TMM and torsional vibration experiment respectively, and it has shown that the modified TMM can accurately predict forced torsional vibration behaviors of the CFRP drive-line system. | Study on Forced Torsional Vibration of CFRP Drive-Line System with Internal Damping | 10.1007/s10443-017-9668-7 |
2018-12-01 | An economical solution to reduce building motions to an acceptable level, under dynamic loadings, is to provide additional damping. A passive damping device shown to be effective as a vibration control mechanism is tuned liquid damper (TLD). A TLD is a passive control system which utilizes fluid-sloshing motion to dissipate the lateral excitation energy. In this paper, the TLD was modeled as an equivalent nonlinear-tuned mass damper. Furthermore, the validity of the numerical procedure in predicting the structural response equipped with TLD under seismic loading is also investigated with two studies. To study the effectiveness of implementing TLDs, three existing intermediate steel moment-resisting frames were taken into consideration, and nonlinear response history analysis was carried out for structural models with and without TLDs. It was observed that TLDs can be utilized as seismic response mitigation devices and can also be employed for seismic rehabilitation of the existing steel structures. Even though the natural frequency of the TLD is always chosen to match the natural frequency of the structure, any change in the frequency of the primary structure or amplitude-dependent frequency of the TLD results in a detuned TLD system. Therefore, this paper also evaluates the efficiency of a detuned TLD system for some tuning ratios (0.8–1.2) by sensitivity analysis. The results showed that tuning ratio in the range of 0.9–1.1 has a slight influence on the seismic response of the structure. | Seismic performance evaluation of steel frame structures equipped with tuned liquid dampers | 10.1007/s42107-018-0082-8 |
2018-12-01 | Timber structures are characterized by a pinching phenomenon that leads to reduced dissipative capability. A few hysteretic models have been proposed to simulate the mechanical behavior of timber structures, among which the one composed of a bilinear element and a slip element in parallel has been popular in practice. Based on this model, this paper expands on the existing seismic control design methodology to determine the capacity of hysteretic dampers for multi-story timber structures. The equivalent linearization method for a single-degree-of-freedom timber structure with added hysteretic damper is established and is verified through nonlinear timber history analysis over a wide range of structural parameters. The design formulas for determining the damper capacity for a multi-degree-of-freedom system are derived, based on the concept of adjusting the distribution of equivalent stiffness of structure. The seismic control design is applied to many buildings with randomly generated parameters and the effectiveness is confirmed through a nonlinear time history analysis with four sets of seismic excitations. An extended study has shown that the shear force pattern plays an important role in the seismic control design results and thus the performance of structures. The effectiveness of the control of residual deformations by adding dampers is also studied. | Optimum hysteretic damper design for multi-story timber structures represented by an improved pinching model | 10.1007/s10518-018-0437-2 |
2018-12-01 | Chatter is a very common phenomenon and severely affects the productivity and quality of workpiece during milling. However, it is very difficult and expensive to suppress chatter directly in machining. The main method involves avoiding chatter by predicting chatter stability. Tool wear is a difficult and unavoidable problem in micromilling and significantly affects the prediction of chatter stability, but it was neglected in the currently available chatter stability prediction methods. To establish the relationship between tool wear and chatter stability, models were established for the process damping coefficients and gamma process of tool wear with cutting edge radius. Based on these models, equations were derived for the time-varying chatter stability and reliability of micromilling systems. In the proposed method, the stability lobe diagram (SLD) increases with the cutting time, maintaining the accuracy of chatter stability prediction at different cutting times. The method also can concisely express the position relationship between the axial depth of cut and critical depth with the number of chatter reliability, more accurate than the traditional methods. The corresponding experimental verification was carried out. The results show that the process damping force and critical depth of micromilling systems gradually increase with the cutting time, and the proposed method is consistent with the results. | Prediction of time-varying chatter stability: effect of tool wear | 10.1007/s00170-018-2582-9 |
2018-12-01 | An integrated optimal structural design method for a diagrid structure and control device was developed. A multi-objective genetic algorithm was used and a 60-story diagrid building structure was developed as an example structure. Artificial wind and earthquake loads were generated to assess the wind-induced and seismic responses. A smart tuned mass damper (TMD) was used as a structural control system and an MR (magnetorheological) damper was employed to develop a smart TMD (STMD). The multi-objective genetic algorithm used five objectives including a reduction of the dynamic responses, additional stiffness and damping, mass of STMD, capacity of the MR damper for the integrated optimization of a diagrid structure and a STMD. From the proposed method, integrated optimal designs for the diagrid structure and STMD were obtained. The numerical simulation also showed that the STMD provided good control performance for reducing the wind-induced and seismic responses of a tall diagrid building structure. | MOGA-Based Structural Design Method for Diagrid Structural Control System Subjected to Wind and Earthquake Loads | 10.1007/s13296-018-0055-5 |
2018-12-01 | The main role of the suspension system is to achieve ride comfort by reducing vibrations generated by the road roughness. The active damper is getting much attention due to its reduced cost and ability to enhance ride comfort especially when the road ahead is measurable by an environment sensor. In this study a preview active suspension control system was developed in order to improve ride comfort when the vehicle is passing over a speed bump. The control system consists of a feedback controller based on the skyhook logic and a feedforward controller for canceling out the road disturbance. The performance limit for the active suspension control system was computed via trajectory optimization to provide a measure against which to compare and validate the performance of the developed controller. The simulation results indicated that the controller of this study could enhance ride comfort significantly over the active suspension control system employing only the skyhook feedback control logic. Also the developed controller, by displaying similar control pattern as the trajectory optimization during significant time portions, proved that its control policy is legitimate. | Development of Preview Active Suspension Control System and Performance Limit Analysis by Trajectory Optimization | 10.1007/s12239-018-0097-x |
2018-12-01 | The synergy between Mantua Diocese, Direzione Regionale per i beni culturali e paesaggistici della Lombardia and Politecnico di Milano enabled the elaboration of a strategic conservation plan for some Mantova buildings of great significance to the city and to the owners: the planning of monitoring activities necessary to the conservation has experienced a further development as regards the structural aspects, after the earthquake, to improve performances vis-à-vis the updated seismic risk level. The collaboration between stakeholder bodies made it possible to systematise the resources needed to access available funds for scheduled conservation and innovative diagnostics over the last decade. The aim is to bring about the necessary conditions for an in depth examination of case studies pretty much representative of local building materials and techniques, for which to identify the best practices for conservation. The networks the bodies belong to permit the dissemination of the results achieved to a vast number of observers, stakeholders, owners, and other local bodies. The paper relates to the diagnostics part, including the innovative techniques employed alongside the more traditional and standardised ones, with a view to drawing up a program of checks and a plan of preventive actions, despite of a limited number of interventions. The monitoring measures and the inspections aim to mitigate some risk factors, among them the (up to now) advanced state of decay of some elements in the oldest buildings, whose maintenance would aggravate the conservation conditions, especially as regards decorated surfaces. Out of the analysed buildings, the case study herein described concerns the Basilica Concattedrale di Sant’Andrea Apostolo in Mantova, a mankind architectural heritage and, obviously, a city monument. | Monitoring as strategy for planned conservation: the case of Sant’Andrea in Mantova (Mantua) | 10.1007/s12518-018-0240-4 |
2018-12-01 | Hysteresis steel dampers are widely used in earthquake-resistant structures, where some of them are anisotropic and capable of sustaining earthquake-induced bidirectional deformation. In this paper, a simplified analytical model is proposed for simulating the hysteretic behavior of U-shaped steel dampers with horizontal bidirectional deformation. The proposed model is composed of a series of shear springs with different nonlinear characteristics in a radial configuration, and the Menegotto–Pinto hysteresis model is employed to represent the hysteretic characteristics of the springs. The mechanical and shape-related parameters of the hysteresis model are set according to the multi-directional deformation characteristics of steel dampers. With the aim of validating the effectiveness and applicability of the analytical model, a U-shaped steel damper was used as an example. The pseudo-static hysteretic characteristics of the steel damping element were analyzed and the elasto-plastic seismic response of a curved bridge featuring a steel hysteresis device was investigated. The results showed that the proposed model is sufficiently accurate to simulate the hysteretic behavior of U-shaped steel dampers, and thus provides a practical method to assess U-shaped steel dampers through seismic response analysis. | A simplified analytical model for U-shaped steel dampers considering horizontal bidirectional deformation | 10.1007/s10518-018-0407-8 |
2018-12-01 | Tuned mass dampers (TMDs) are a subclass of dynamic vibration absorbers that consist of a mass-spring-damper unit that is attached to a structure to adjust its response to seismic and wind loads. The efficacy, performance and optimum design of a TMD strongly depend not only on its mass, stiffness and damping as well as the input energy and the structure characteristics, but also on the structural response parameter(s) that the TMD is intended to mitigate. In that respect, this study evaluates the suitability of four objective functions for the optimum design of the TMD of an inelastic, steel moment-resisting frame (SMRF) under an artificial, white-noise excitation. The objective functions include 1) the maximum roof lateral displacement, 2) the maximum drift, 3) the root mean square of drifts and 4) the cumulative hysteretic energy of the SMRF. The results indicate that the SMRF equipped with a TMD optimized using the cumulative hysteretic energy of the SMRF as the objective function exhibits the best seismic response under the artificial earthquake. Further examining the response of the TMD-equipped SMRF under four historic earthquake records shows that equipping a structure with a TMD optimized using an artificial earthquake will not warrant that the structure will exhibit a better seismic performance in all measures compared with when no TMD is used. Put other way, while the minimization of cumulative hysteretic energy could be the best objective function for a case subjected to an artificial earthquake, under real earthquakes, none of the objective functions consistently results in a better seismic performance. This behavior is attributed to detuning effects arising from major structural damages and significant period shifts that occur during strong earthquakes. | Seismic energy dissipation-based optimum design of tuned mass dampers | 10.1007/s00158-018-2033-0 |
2018-11-27 | Temperature is one of the variables that influence the elasto-plastic behavior and integrity of rock outcrops. Fluctuations in temperature can trigger alteration of some of the mineral properties and impact the brittle-plastic transition. Initiation and propagation of thermally induced tension cracks tend to weaken most rock types. The principal goal of this study was to anticipate impacts of thermal stress-strain cycles on the dynamic response of representative rock units exposed in the Khewra Gorge of the Salt Range Punjab of Pakistan. Ten types of sedimentary rock units were sampled, including marl, dolomite, three types of limestone, and five different sandstones exhibiting varying characteristics in outcrop. Boulder specimens were collected from the field and transported to the laboratory to prepare 50 drill cores that could be subjected to thermal cycling between 50 and 200 °C in increments of 50 °C. Room temperature core samples were tested using an Erudite resonance frequency meter to measure their Q-factors and the resonance frequency (F_r) at an applied loading frequency of 7 KHz with 0.01 V output voltage. Results suggest that thermal cycling tends to reduce the dynamic Young’s modulus (E_d) and Q-factor. Other parameters, such as damping ratio ( ξ ), specific damping capacity ( Ψ ), and loss factor ( Ƞ ) appeared to increase with increasing temperature cycles, likely as a result of developing thermally induced tensile fractures. The resultant values of the null hypothesis (t-critical and t-stats) suggests that the null hypothesis can be discarded because there was no observable difference between the measured and expected values for the cores tested. The observations and data emanating from this study might be useful in designing low-level radioactive waste landfills, nuclear waste repositories, and deep underground excavations where the increased temperature could alter the mechanical behavior of the parent rock mass. | Effect of heat treatment on dynamic properties of selected rock types taken from the Salt Range in Pakistan | 10.1007/s12517-018-4058-5 |
2018-11-21 | We study a nonlocal evolution equation modeling the deformation of a bridge, either a footbridge or a suspension bridge. Contrarily to the previous literature, we prove the exponential asymptotic stability of the considered model with a small amount of damping (namely, on a small collar around the whole boundary) which represents less cost of material. | Stabilization of a suspension bridge with locally distributed damping | 10.1007/s00498-018-0226-0 |
2018-11-21 | A keen interest towards technological implications of spin-orbit driven magnetization dynamics requests a proper theoretical description, especially in the context of a microscopic framework, to be developed. Indeed, magnetization dynamics is so far approached within Landau-Lifshitz-Gilbert equation which characterizes torques on magnetization on purely phenomenological grounds. Particularly, spin-orbit coupling does not respect spin conservation, leading thus to angular momentum transfer to lattice and damping as a result. This mechanism is accounted by the Gilbert damping torque which describes relaxation of the magnetization to equilibrium. In this study we work out a microscopic Kubo-Středa formula for the components of the Gilbert damping tensor and apply the elaborated formalism to a two-dimensional Rashba ferromagnet in the weak disorder limit. We show that an exact analytical expression corresponding to the Gilbert damping parameter manifests linear dependence on the scattering rate and retains the constant value up to room temperature when no vibrational degrees of freedom are present in the system. We argue that the methodology developed in this paper can be safely applied to bilayers made of non- and ferromagnetic metals, e.g., CoPt. | Another view on Gilbert damping in two-dimensional ferromagnets | 10.1038/s41598-018-35517-x |
2018-11-20 | We consider the Cauchy problem of the semilinear wave equation with a damping term $$\begin{aligned} \left\{ \begin{array}{ll} u_{tt} - \Delta u + c(t,x) u_t = |u|^p,&{}(t,x)\in (0,\infty )\times {\mathbb {R}}^N,\\ u(0,x) = \varepsilon u_0(x), \quad u_t(0,x) = \varepsilon u_1(x),&{} x\in {\mathbb {R}}^N, \end{array}\right. \end{aligned}$$ u tt - Δ u + c ( t , x ) u t = | u | p , ( t , x ) ∈ ( 0 , ∞ ) × R N , u ( 0 , x ) = ε u 0 ( x ) , u t ( 0 , x ) = ε u 1 ( x ) , x ∈ R N , where $$p>1$$ p > 1 and the coefficient of the damping term has the form $$\begin{aligned} c(t,x) = a_0 (1+|x|^2)^{-\alpha /2} (1+t)^{-\beta } \end{aligned}$$ c ( t , x ) = a 0 ( 1 + | x | 2 ) - α / 2 ( 1 + t ) - β with some $$a_0 > 0$$ a 0 > 0 , $$\alpha < 0$$ α < 0 , $$\beta \in (-1, 1]$$ β ∈ ( - 1 , 1 ] . In particular, we mainly consider the cases $$\begin{aligned} \alpha< 0, \beta =0 \quad \text{ or } \quad \alpha < 0, \beta = 1, \end{aligned}$$ α < 0 , β = 0 or α < 0 , β = 1 , which imply $$\alpha + \beta < 1$$ α + β < 1 , namely, the damping is spatially increasing and effective. Our aim is to prove that the critical exponent is given by $$\begin{aligned} p = 1+ \frac{2}{N-\alpha }. \end{aligned}$$ p = 1 + 2 N - α . This shows that the critical exponent is the same as that of the corresponding parabolic equation $$\begin{aligned} c(t,x) v_t - \Delta v = |v|^p. \end{aligned}$$ c ( t , x ) v t - Δ v = | v | p . The global existence part is proved by a weighted energy estimates with an exponential-type weight function and a special case of the Caffarelli–Kohn–Nirenberg inequality. The blow-up part is proved by a test-function method introduced by Ikeda and Sobajima [ 15 ]. We also give an upper estimate of the lifespan. | Critical exponent for the semilinear wave equations with a damping increasing in the far field | 10.1007/s00030-018-0546-2 |
2018-11-12 | Computing is not understanding. This is exemplified by the multiple and discordant interpretations of Landau damping still present after 70 years. For long deemed impossible, the mechanical N -body description of this damping, not only enables its rigorous and simple calculation, but makes unequivocal and intuitive its interpretation as the synchronization of almost resonant passing particles. This synchronization justifies mechanically why a single formula applies to both Landau growth and damping. As to the electrostatic potential, the phase mixing of many beam modes produces Landau damping, but it is unexpectedly essential for Landau growth too. Moreover, collisions play an essential role in collisionless plasmas. In particular, Debye shielding results from a cooperative dynamical self-organization process, where “collisional” deflections due to a given electron diminish the apparent number of charges about it. The finite value of exponentiation rates due to collisions is crucial for the equivalent of the van Kampen phase mixing to occur in the N -body system. The N -body approach incorporates spontaneous emission naturally, whose compound effect with Landau damping drives a thermalization of Langmuir waves. O’Neil’s damping with trapping typical of initially large enough Langmuir waves results from a phase transition. As to Coulomb scattering, there is a smooth connection between impact parameters where the two-body Rutherford picture is correct, and those where a collective description is mandatory. The N -body approach reveals two important features of the Vlasovian limit: it is singular and it corresponds to a renormalized description of the actual N -body dynamics. | Basic microscopic plasma physics from N-body mechanics | 10.1007/s41614-018-0021-x |
2018-11-01 | Along with the increasing penetration of distributed generation with voltage-source converters (VSCs), there are extensive concerns over the potential virtual rotor angle stability, which is characterized by oscillations of power and frequency during the dynamic process of synchronization in the grid. Several control strategies have been developed for VSCs to emulate rotating inertia as well as damping of oscillations. This paper classifies these strategies and provides a small-signal modeling framework including all kinds of VSCs in different applications for virtual rotor angle stability. A unified perspective based on the famous Phillips–Heffron model is established for various VSCs. Thus, the concepts of equivalent inertia and the synchronizing and damping coefficients in different VSCs are highlighted, based on the similarities with the synchronous generator (SG) system in both physical mechanisms and mathematical models. It revealed the potentiality of various VSCs to achieve equivalence with the SG. This study helps promote the unity of VSCs and traditional SGs in both theories and methods for analyzing the dynamic behavior and enhancing the stability. Finally, future research needs and new perspectives are addressed. | Modeling framework of voltage-source converters based on equivalence with synchronous generator | 10.1007/s40565-018-0433-1 |
2018-11-01 | Abstract —A study of the temperature and frequency dependences of the mechanical loss factors and elastic moduli of polymeric materials allows one to calculate the efficiency of vibration-damping coatings on substrates of metals and rigid composites under specified operating conditions. The calculated and experimental data for different compositions of vibration-damping materials are compared. The studies are performed using polymer compositions on the basis of modified epoxy resins and reinforcing fillers. | Temperature and Frequency Dependences of Dissipative Properties of Rigid Vibration-Damping Coatings | 10.1134/S2075113318060151 |
2018-11-01 | The damping modification factors are utilized to alter the design spectral ordinates for constructions whose damping differs significantly from 5%, this being the level that is routinely considered by most codes. Such factors are habitually evaluated after suites of historical inputs representing the local seismicity. However, such records may not be readily available, due either to moderate seismicity or to limited seismological network; in such cases, representative artificial accelerograms might be used instead. This paper proposes a methodology for establishing damping modification factors after artificial inputs generated to match the 5% design spectra; this approach can be used for countries, regions or cities. The proposed methodology is based on performing dynamic analyses on underdamped and overdamped SDOF linear systems by using the aforementioned selected accelerograms. Although previous studies have highlighted the differences among factors generated after natural and artificial inputs, it has been observed that such discrepancies are mainly due to the longest significant (Trifunac) duration of the artificial accelerograms. Therefore, the artificial inputs are generated as their duration fits those of the available local strong motion records. An application to Colombia is presented; the results are compared with those for some available Colombian records. The sensitivity of the calculated factors to the soil type, period and seismic zone is investigated; matching expressions are provided. Such expressions are compared with the prescriptions of major design codes and with other studies. The suitability of the proposed formulation is further verified in an example on an isolated hospital building. | Generating damping modification factors after artificial inputs in scenarios of local records scarcity | 10.1007/s10518-018-0406-9 |
2018-11-01 | This work is concerning with the study of the thermoelastic damping of a nanobeam resonator in the context of the two-temperature generalized thermoelasticity theory. An explicit formula of thermoelastic damping has been derived when Young’s modulus is a function of the reference temperature. Influences of the beam height and Young’s modulus have been studied with some comparisons between the Biot model and the Lord–Shulman model (L–S) for one- and two-temperature types. Numerical results show that the values of the thermal relaxation parameter and the two-temperature parameter have a strong influence on thermoelastic damping at nanoscales. | The reference temperature dependence of Young’s modulus of two-temperature thermoelastic damping of gold nano-beam | 10.1007/s11043-017-9365-9 |
2018-11-01 | Particles impact damping is one of the promising technologies used for the passive mitigation of vibrations. Through the dynamic impact and friction between particles, particles impact damper is able to reduce or eliminate vibratory energy under kinetic shape. Due to the simplicity of this type of damper and the operating frequency band, it is widely used in civil engineering. On the other hand it can operate in aggressive environments including high temperature or humidity. In this paper, the dynamic behaviour and efficiency of this process to reduce vibrations are highlighted. Using a simple analytical model, a clamped-free beam coupled to a particles impact damper, the influence of some system parameters is investigated. The proposed model is, then, validated through a comparison of simulated responses with experimental results established in a previous work. It is noticed that the nonlinear behaviour and the large number of their design parameters make the determination of its participation in damp very complicated. For this reason, it is crucial to seek optimal design parameters of the particles impact damper. In this context, an optimized method based on a genetic algorithm is proposed. The obtained results demonstrate the satisfactory side of this approach to identify the optimal parameters of the considered particles impact damper. Consequently, the developed approach may be constitutes an aid, for the engineer, to choose particles impact damper parameters according to the characteristics of the vibrating structure to be studied. | Design parameters optimization of a particles impact damper | 10.1007/s12008-018-0463-y |
2018-11-01 | Background Global agriculture is undergoing a phase of agroecological transition. This transition will be characterized by adoption of agroecological cropping practices and by an increased diversity of soil management/tillage practices. However, very little is known as to whether or not crop seed germination and seedling emergence (hereafter referred to as SGE) will be affected under these cropping practices. Scope This paper first proposes a conceptual scheme which integrates key abiotic and biotic factors affecting crop SGE. Subsequently, the key mechanistic factors affecting SGE (i.e. intrinsic factors related to the seeds, and extrinsic factors related to the biotic and abiotic conditions of the seedbed), and how crop management practices can influence SGE through alterations of these direct mechanistic factors are discussed. This is done with special emphasis on how agricultural practices, particularly those related to agro-ecology, may impact SGE. Conclusions Crop SGE are affected by five major groups of drivers, namely seed and seedling characteristics, seedbed physical components, seedbed chemical components, seedbed biological components, and cropping systems. Although the crop SGE failure frequently occurs under field conditions, very little quantitative information is available in the literature on the real economic impact, the precise cause/s and ranking of factors associated with this failure. Re-seeding is often practiced for a number of crops to compensate the lack of SGE with significant direct and indirect costs for farmers. Little information exists in the literature concerning how SGE will be affected under agroecological cropping systems, such as conservation agriculture, or organic farming, or under climate-driven changes. Field observation, experimental and modeling studies are needed to fill the current knowledge gaps on the economic impact, precise cause/s and ranking of different stress factors associated with SGE failure. | Abiotic and biotic factors affecting crop seed germination and seedling emergence: a conceptual framework | 10.1007/s11104-018-3780-9 |
2018-11-01 | High rotating speed milling operation is the most essential mean of implementing high-speed milling. To improve and enhance the dynamic performances of cutting system, a large number of creative spindle-tool systems with high damping performance are designed and applied, in which larger rotational damping (or internal damping) occurs. In this regard, since the system generally operates at supercritical speed, there are two different types of instability, namely rotational damping instability and chatter instability. In this paper, the effect of rotational damping on stability is proposed according to Routh-Hurwitz stability criterion, and comparisons between rotational damping instability and chatter instability are investigated in the subcritical and supercritical speed ranges. Some critical results and comments are analyzed and discussed. And three different types of experiments are performed to verify the numerical results. | Influence of rotational damping on stability in end milling processes | 10.1007/s00170-018-2554-0 |
2018-11-01 | Abstract Fuel consumption control in a combustion chamber of an air-breathing engine is carried out by a metering device (dispenser). The metering needle of the dispenser is driven by a hydraulic cylinder. The hydraulic cylinder is controlled by a spool-valve amplifier of an electromechanical device. The idea of fuel consumption control in the combustion chamber is to position the metering needle with a given accuracy. An adaptive astatic fuzzy controller of the metering needle position is designed for controlling the dispenser. The controller consists of a fuzzificator, a unit for correcting the fuzzificator’s grade of membership, a defuzzificator, and an integrator. The fuzzificator consists of a set of linear terms (negative small, negative medium, normal, positive small, positive medium). The last ones are multiplied in addition to synapses tuned by an adapting unit with comparison element and built-in adder for correcting the fuzzificator’s grade of membership. The adaptation procedure is performed by step-by-step learning with the help of recurrent formula. The defuzzificator, consisting of a set of five unimodal membership functions, is used for transforming the fuzzy information into clear information. Defuzzification is performed by the centroid method. The loop for controlling the dispenser is an integral part of the loops for controlling parameters of the air-breathing engine. | A Way to Design an Adaptive Fuzzy Controller for the Dispenser Position of an Air-Breathing Engine | 10.3103/S1068371218110068 |
2018-11-01 | The power system dynamic response is impacted by uncertainties in the system operation such as load variation and large penetration of intermittent generation. This paper presents a method based on the solution of the nonlinear Riccati equation for the design of coordinated robust damping controllers for power systems. The resulting robust controller is of practical application (fixed-order) with a performance guarantee based on quadratic stability. The method is applied to the 68-bus 5-area benchmark test system and the designed controllers are assessed by modal analysis and nonlinear time simulation. The obtained results show better performance of the proposed method compared to benchmark controllers. | Robust design of coordinated decentralized damping controllers for power systems | 10.1007/s00170-018-2646-x |
2018-11-01 | Users of structural analysis software commonly apply the Rayleigh damping model as a default option for analyzing of structures. When a distributed plasticity model is utilized in the numerical models, the structural responses are not found to be sensitive to the damping models; even the Rayleigh damping model leads to the reasonable seismic results. Moreover, the lower bounds and upper bounds of the demands are sensitive to the type of damping model. In this paper, the effects of viscous damping models in the seismic demands of moment and concentrically braced steel frames are carefully investigated. For this purpose, seven viscous damping models are considered using the different forms of the stiffness matrices in the finite-element modeling. The declared structural systems are modeled against several strong ground motion records in OpenSees environment. Then, the seismic responses such as drifts, accelerations and base shears are compared for the aforementioned damping models. The main result of this research is that applying Rayleigh damping model, as a default option for structural analyzing software will produce underestimated responses. In addition, it is shown that no matter which type of stiffness matrix is used in the stiffness proportional damping model. Therefore, using initial stiffness matrix is cost efficient, particularly in time-consuming nonlinear analyses. | Selection of Viscous Damping Model for Evaluation of Seismic Responses of Buildings | 10.1007/s12205-018-0860-6 |
2018-11-01 | This study dealt with investigating the seismic performance of the smart and shape memory alloy (SMA) and magnets plus rubber-spring (MRS) dampers and their effects on the seismic resistance of multiple-span simply supported bridges. The rubber springs in the MRS dampers were pre-compressed. For this aim, a set of experimental works was performed together with developing nonlinear analytical models to investigate dynamic responses of the bridges subjected to earthquakes. Fragility analysis and probabilistic assessment were conducted to assess the seismic performance for the overall bridge system. Fragility curves were then generated for each model and were compared with those of as-built. Results showed dampers could increase the seismic capacity of bridges. Furthermore, from system fragility curves, use of damper models reduced the seismic vulnerability in comparison to the as-built bridge model. Although the SMA damper showed the best seismic performance, the MRS damper was the most appropriate one for the bridge in that the combination of magnetic friction and pre-compressed rubber springs was cheaper than the shape memory alloy, and had the similar capability of the damper. | Investigation of MRS and SMA Dampers Effects on Bridge Seismic Resistance Employing Analytical Models | 10.1007/s13296-018-0125-8 |
2018-11-01 | We consider the L ^2-critical nonlinear Schrödinger equation with an inhomogeneous damping coefficient a ( x ). We prove the global existence of the solution in H ^1( R ^ d ) and we give the minimal time of the blow up for some initial data. | On the Nonlinear Schrödinger Equation with a Variable Damping Term | 10.1134/S1995080218090378 |
2018-11-01 | A bandwidth method based on power ratio is proposed to evaluate the system damping by using frequency response functions. For single-degree freedom systems, exact formula for calculating damping ratio from displacement frequency response function is established. Additionally, an approximate formula to estimate the damping ratio from acceleration frequency response function is also derived. Both are represented in terms of the power ratio and the bandwidths relative to the corresponding peak frequencies. In contrast to the well-known half-power method, the proposed method can be used for relatively large damping ratios by selecting a corresponding high power ratio. The accuracy of the proposed formulas in damping estimation is investigated for a four-degree of freedom system by numerical experiments. The results show that by increasing the power ratio, the estimation errors in damping ratios for the four-degree of freedom system can be significantly reduced. | A damping estimation method based on power ratio | 10.1007/s00419-018-1434-2 |
2018-11-01 | In structural control, appropriate control parameters and a stable closed-loop mechanism are required for a controller to achieve optimal performance, particularly in the presence of uncertain structural parameters under external excitation. In this study, an optimum model reference adaptive control (OMRAC) algorithm combining the Linear quadratic regulator method and Model Reference Adaptive Control based on Lyapunov stability is proposed. The OMRAC algorithm is implemented and applied to the response control of a base-isolated structure equipped with magneto-rheological dampers under earthquake excitations. The results from a series of numerical simulations that consider the effects of uncertainty within structural parameters are reported. The performance of the OMRAC algorithm is compared with that of other control algorithms in terms of effectiveness and stability. The results suggest that the proposed OMRAC method can successfully compensate for uncertainties in structural parameters, leading the controlled structure to adaptively track the optimal response of the reference model. | An optimum model reference adaptive control algorithm for smart base-isolated structures | 10.1007/s10518-018-0403-z |
2018-10-29 | The problem of chatter vibration is associated with adverse consequences that often lead to tool impairment and poor surface finished in a workpiece, and thus, controlling or suppressing chatter vibrations is of great significance to improve machining quality. In this paper, a workpiece and an actuator dynamics are considered in modeling and controller design. A proportional-integral controller (PI) is presented to control and actively damp the chatter vibration of a workpiece in the milling process. The controller is chosen on the basis of its highly stable output and a smaller amount of steady-state error. The controller is realized using analog operational amplifier circuit. The work has contributed to planning a novel approach that addresses the problem of chatter vibration in spite of technical hitches in modeling and controller design. The method can also lead to considerable reduction in vibrations and can be beneficial in industries in term of cost reduction and energy saving. The application of this method is verified using active damping device actuator (ADD) in the milling of steel. | Active Damping of Milling Vibration Using Operational Amplifier Circuit | 10.1186/s10033-018-0291-9 |
2018-10-01 | This paper presents an ant lion optimizer (ALO) that is used to solve the robust and coordinated tuning of power system stabilizers (PSS) and the power oscillation damping (POD) controller of flexible AC transmission system (FACTS) devices in the presence of remote signals in multimachine power systems. The remote signals are used for the damping of interarea oscillation modes and are modeled by Padé approximation. The static var compensator and thyristor-controlled series capacitor, two FACTS most deployed in practical applications, were considered in this study. The ALO algorithm mimics the hunting mechanism of ant lions in nature: where four steps of hunting prey such as entrapment of ants in traps, random walk of ants, elitism and catching preys/re-building traps are implemented. The two test systems which have been used for the application of the proposed methodology for tuning of PSS and FACTS-PODs are the New England–New York 16-generator 68-bus system, and the Brazilian equivalent system modeled with 24 synchronous machines and 107 buses. Results from these simulations demonstrate the applicability of the proposal in which the efficiency of ALO is highlighted as compared to other algorithms used for design of PSS and FACTS-PODs such as particle swarm optimization and sequential quadratic programming. | Robust and Coordinated Tuning of PSS and FACTS-PODs of Interconnected Systems Considering Signal Transmission Delay Using Ant Lion Optimizer | 10.1007/s40313-018-0408-5 |
2018-10-01 | High-rise buildings are usually considered as flexible structures with low inherent damping. Therefore, these kinds of buildings are susceptible to wind-induced vibration. Tuned Mass Damper (TMD) can be used as an effective device to mitigate excessive vibrations. In this study, Artificial Neural Networks is used to find optimal mechanical properties of TMD for high-rise buildings subjected to wind load. The patterns obtained from structural analysis of different multi degree of freedom (MDF) systems are used for training neural networks. In order to obtain these patterns, structural models of some systems with 10 to 80 degrees-of-freedoms are built in MATLAB/SIMULINK program. Finally, the optimal properties of TMD are determined based on the objective of maximum displacement response reduction. The Auto-Regressive model is used to simulate the wind load. In this way, the uncertainties related to wind loading can be taken into account in neural network’s outputs. After training the neural network, it becomes possible to set the frequency and TMD mass ratio as inputs and get the optimal TMD frequency and damping ratio as outputs. As a case study, a benchmark 76-story office building is considered and the presented procedure is used to obtain optimal characteristics of the TMD for the building. | Application of artificial neural networks in optimal tuning of tuned mass dampers implemented in high-rise buildings subjected to wind load | 10.1007/s11803-018-0483-4 |
2018-10-01 | We study both analytically and numerically the localized modes in long Josephson junctions with phase shift formations, so-called $$0{-}\pi {-}0$$ 0 - π - 0 and $$0{-}\kappa $$ 0 - κ junctions. The system is described by an inhomogeneous sine-Gordon equation with a variety of time-periodic drives. Perturbation technique, together with multiple-scale expansions, is applied to obtain the amplitude of oscillations. It is observed that the obtained amplitude equations decay with time due to radiative damping and emission of high harmonic radiations. It is also observed that the energy taken away from the internal mode by radiation waves can be balanced by applying either direct or parametric drives. The appropriate external drives are applied to re-balance the dissipative and radiative losses. We discuss in detail the excitation by direct and parametric drives with frequencies to be either in the vicinity or double the natural frequency of the system. It is noted that the presence of external applied drives stabilizes the nonlinear damping, producing stable breather modes in long Josephson junctions. It is also noted that in the presence of parametric drives, the amplitudes of the driving forces are much more sensitive than in the case of external ac drives; that is, in the case of parametric drives, a small change in the amplitudes of the driving forces can make a drastic change in the system behavior and the system becomes unstable as compared to the case of the direct ac driving. Furthermore, we noticed that, in the presence of external driving, the driving effect is stronger for the case of driving frequency nearly equal to the system frequency as compared to that of the driving frequency nearly equal to twice the frequency of the oscillatory mode. | Localized modes in a variety of driven long Josephson junctions with phase shifts | 10.1007/s11071-018-4355-2 |
2018-10-01 | In this article, we consider the oscillation of a class of third-order nonlinear damped delay dynamic equation on time scales of the form $$\begin{aligned} \left( r_2(r_1(y^\Delta )^\alpha )^\Delta \right) ^\Delta (t)+p(t)(y^\Delta )^\alpha (\sigma (t))+q(t)f(y(g(t)))=0. \end{aligned}$$ r 2 ( r 1 ( y Δ ) α ) Δ Δ ( t ) + p ( t ) ( y Δ ) α ( σ ( t ) ) + q ( t ) f ( y ( g ( t ) ) ) = 0 . We offer a new description of oscillation of the third-order equation in terms of the nonoscillation of a related well studied second-order dynamic equation $$\begin{aligned} \left( r_2z^\Delta \right) ^\Delta (t)+\frac{p(t)}{r_1(\sigma (t))}z(\sigma (t))=0. \end{aligned}$$ r 2 z Δ Δ ( t ) + p ( t ) r 1 ( σ ( t ) ) z ( σ ( t ) ) = 0 . Using generalized Riccati transformation and integral averaging technique, some new sufficient conditions which insure that any solution of the equation oscillates are established. | Oscillation of third-order nonlinear delay dynamic equation with damping term on time scales | 10.1007/s12190-017-1158-4 |
2018-10-01 | Mechanical damping of composites reinforced by randomly distributed particles due to interfacial sliding is analyzed. The matrix is elastically isotropic, and the particles are assumed rigid and of identical radii. An auxiliary problem is solved at first for the steady-state response of an infinite matrix containing a single inclusion to a harmonic external load. The result is then used to derive the explicit expression of the specific damping capability of the composite by using Mori–Tanaka’s mean-field method. Numerical results are given and discussed in detail. It is concluded that the overall damping of the composite depends on several factors, including volume fraction of particles, Poisson’s ratio of matrix and a dimensionless parameter that incorporates the combined effects of particle size, matrix stiffness, interfacial viscosity and vibration frequency. The result is expected to be helpful in tailoring the damping performance of particle-reinforced composites. | Damping of Particle-Reinforced Composites Due to Interfacial Sliding | 10.1007/s10338-018-0051-5 |
2018-10-01 | Structural vibration and noise control of a cavity-backed three-layered smart piezo-coupled rectangular panel system under harmonic or transient loads is achieved by using purely active, passive, and hybrid active/passive piezoelectric shunt networks. Problem formulation is based on the classical lamination plate theory, Maxwell’s equation for piezoelectric materials, linear circuit theory, and wave equation for the enclosed acoustic domain. The orthogonal mode expansions along with the modal coupling theory are employed to obtain the coupled differential equations of the electro-mechanical-acoustic system, which are then put into the convenient state-space form, and subsequently solved numerically in both frequency and time domains. A triple-mode hybrid RLC shunt circuit, in series with an external active voltage source and connected to a single electroded piezoelectric segment, is tuned to the dominant resonance frequencies of the composite structure. The linear quadratic optimal control (LQR) theory is adopted for obtaining the active control gains. The frequency and time domain performances of the passive, active and hybrid multi-modal piezoelectric systems are calculated and discussed in terms of sensor output voltage, local sound pressure, and control effort. It is found that the hybrid control methodology with properly tuned circuit parameters can be an excellent candidate for simultaneous vibration and structure-borne noise control of the cavity-coupled smart panel with decreased control effort. Also, the active control strategy integrated in the hybrid control system is demonstrated to enhance the overall system damping characteristics and improve the control authority at frequencies where the passive shunt network performs weakly. Limiting cases are considered and correctness of the mathematical model is verified by using a commercial finite element software as well as by comparisons with the literature. | Assessment of shunted piezoelectric devices for simultaneous noise and vibration reduction: comparison of passive, active and hybrid networks | 10.1007/s11012-018-0885-4 |
2018-10-01 | A new approach to solving the problem of expanding the functionality of the rotor vibratory gyroscope is presented. Its motion equations are analyzed under modulated damping. Numerical solutions and analytical dependences are obtained, on the basis of which recommendations on technical improvement of the device are proposed. | Modulation of Damping in the Rotor Vibratory Gyroscopes | 10.3103/S1068799818040141 |
2018-10-01 | This paper describes the method of numerical solution of decaying vibration equations for heterogeneous composite structures. The system of algebraic equations is generated by applying the Ritz method with Legendre polynomials as coordinate functions. First, real solutions are found. To find complex natural frequencies of the system, the obtained real natural frequencies are taken as initial values, and then, by means of the third-order iteration method, complex natural frequencies are calculated. The paper discusses the convergence of numerical solution of the differential equations describing the motion of layered heterogeneous structures, obtained for an unsupported rectangular two-layered plate. The bearing layer of the plate is made of unidirectional CRP, its elastic and dissipation properties within the investigated band of frequencies and temperatures are independent of vibration frequency. The bearing layer has one of its outer surfaces covered with a layer of “stiff” isotropic viscoelastic polymer characterized by a temperature-frequency relationship for the real part of complex Young’s modulus and loss factor. Validation of the mathematical model and numerical solution performed through comparison of calculation results for natural frequencies and loss factor versus test data (for two composition variants of a two-layered unsupported beam) has shown good correlation. | Energy Dissipation during Vibrations of Heterogeneous Composite Structures: 2. Method of Solution | 10.3103/S106345411804012X |
2018-10-01 | Abstract Wave properties of damped solitons in a collisional unmagnetized four-components dusty fluid plasma system contains superthermal distributed electrons, mobile ions, and negative-positive dusty grains have been examined. To study dissipative DIA mode properties, a reductive perturbation (RP) analysis is used under convenient geometrical coordinate transformation, three-dimensional damped Kadomtsev–Petviashvili (3D-CDKP) equation in cylindrical coordinates is obtained. Effects of collisional parameters on damped soliton pulse structures are studied. More specifically, the impact of axial, radial, and polar coordinates with the time on solitary propagation are examined. This investigation may be viable in plasma of the Earth’s mesosphere. | Cylindrical Damped Solitary Propagation in Superthermal Plasmas | 10.1134/S1063776118100138 |
2018-10-01 | As an effort to minimize material utilization, seismic steel dampers designed to deform inelastically in an in-plane flexural mode have attracted serious attention recently. This paper presents a new type of metallic yielding damper referred to as the in-plane arch-shaped damper modified from its portal frame-shaped counterpart by replacing the straight beam with a circular arch to minimize the effects of stress concentration and warping, and therefore to avoid premature failure. Component tests of both the portal frame-shaped and arch-shaped in-plane dampers were conducted for comparison. Hysteresis loops obtained from the component tests under cyclic loads indicate substantial improvement on the energydissipative characteristics of the proposed damper. Moreover, seismic performance assessment of the proposed damper was carried out further via shaking table tests of a five-story model frame. Encouraging results have been achieved in terms of acceleration reduction, damping enhancement and peak suppression of the frequency response functions, suggesting the potential of the proposed device to be used in earthquake-resisting systems. | An experimental study of in-plane arch-shaped dampers | 10.1007/s11803-018-0480-7 |
2018-10-01 | Friction-based dampers can be considered as one of the suitable passive control systems for seismic strengthening and rehabilitation of existing substandard structures due to their high adjustability and good energy dissipation capability. One of the main issues in the design of these systems is to obtain the magnitude of the maximum slip force and the distribution of slip forces along the height of the building. In this study, a practical performance-based optimisation methodology is developed for seismic design of RC frame buildings with friction energy dissipation devices, which allows for an accurate solution at low computational cost. The proposed method aims at distributing the slip loads of the friction dampers to achieve a uniform distribution of damage along the height of the building. The efficiency of the method is evaluated through the optimum design of five different low to high-rise RC frames equipped with friction wall dampers under six natural and six synthetic spectrum-compatible earthquakes. Sensitivity analyses are performed to assess the reliability of the method using different initial height-wise slip load distributions, convergence parameters and earthquake records. The results indicate that optimum frames exhibit less maximum inter-storey drift (up to 43%) and global damage index (up to 75%), compared to uniform slip load distribution. The method is then developed to obtain the optimum design solution for a set of earthquakes representing a design spectrum. It is shown that the proposed method can provide an efficient tool for optimum seismic design of RC structures with friction energy dissipation devices for practical purposes. | Performance-based optimisation of RC frames with friction wall dampers using a low-cost optimisation method | 10.1007/s10518-018-0380-2 |
2018-10-01 | Viscoelastic (VE) dampers, with their stiffness and energy dissipation capabilities, have been widely used in civil engineering for mitigating wind-induced vibration and seismic responses of structures, thus enhancing the comfort of residents and serviceability of equipment inside. In past relevant research, most analytical models for characterizing the mechanical behavior of VE dampers were verified by comparing their predictions with performance test results from small-scale specimens, which might not adequately or conservatively represent the actual behavior of full-scale dampers, especially with regard to the ambient temperature, temperature rise, and heat convection effects. Thus, in this study, by using a high-performance testing facility with a temperature control system, full-scale VE dampers were dynamically tested with different displacement amplitudes, excitation frequencies, and ambient temperatures. By comparing the analytical predictions with the experimental results, it is demonstrated that adopting the fractional derivative method together with considering the effects of excitation frequencies, ambient temperatures, temperature rises, softening, and hardening, can reproduce the design performance of full-scale VE dampers very well. | Experimental and analytical study on design performance of full-scale viscoelastic dampers | 10.1007/s11803-018-0469-2 |
2018-10-01 | Concrete is a type of quasi-brittle material with high compressive strength and low tensile strength. To obtain the complete tensile stress-deformation curve of massive concrete specimens, a specially designed loading machine is proposed with a pair of hydraulic oil dampers parallel to the direction of the tensile loading. The dampers were designed with valves to modify the stiffness of the loading machine, enhancing the stiffness of the machine before the applied stress reaches 90% of the ultimate stress of the concrete. Several experiments were conducted with the proposed loading machine on prism-shaped specimens (size: 1350 mm× 450 mm × 450 mm), and the stress-deformation curves and mechanical parameters of the concrete were obtained. Finally, an empirical formula is presented and compared with the experimental results. | Experimental Study on the Complete Tensile Stress-Deformation Curve of Fully Graded Concrete | 10.1007/s40799-018-0250-5 |
2018-10-01 | A method for analyzing the influence of temperature on the dynamic characteristics of structures with viscoelastic dampers is proposed in this paper. Dampers which are described by so-called fractional rheological models are considered. The temperature–frequency superposition principle is used to describe the influence of temperature on the dynamic characteristics. The concept of continuous dependence of damping on an artificially introduced parameter is adopted for solving, in an approximate way, the nonlinear eigenvalue problem from which dynamic characteristics are determined. The correctness and effectiveness of the method was verified by means of two examples. | Approximate method for temperature-dependent characteristics of structures with viscoelastic dampers | 10.1007/s00419-018-1394-6 |
2018-09-28 | Purpose of Review Allergen is an umbrella term for irritants of diverse origin. Along with other offenders such as pathogens, mutagens, xenobiotics, and pollutants, allergens can be grouped as inflammatory agents. Danger-associated molecular patterns (DAMPs) are altered metabolism products of necrotic or stressed cells, which are deemed as alarm signals by the innate immune system. Like inflammation, DAMPs play a role in correcting the altered physiological state, but in excess, they can be lethal due to their signal transduction roles. In a vicious loop, inflammatory agents are DAMP generators and DAMPs create a pro-inflammatory state. Only a handful of DAMPs such as uric acid, mtDNA, extracellular ATP, HSPs, amyloid β, S100, HMGB1, and ECM proteins have been studied till now. A large number of DAMPs are still obscure, in need to be unveiled. The identification and functional characterization of those DAMPs in inflammation pathways can be insightful. Recent Findings As inflammation and immune activation have been implicated in almost all pathologies, studies on them have been intensified in recent times. Consequently, the pathologic mechanisms of various DAMPs have emerged. Following PRR ligation, the activation of inflammasome, MAPK, and NF-kB is some of the common pathways. Summary The limited number of recognized DAMPs are only a fraction of the vast array of other DAMPs. In fact, any misplaced or abnormal level of metabolite can be a DAMP. Sophisticated analysis studies can reveal the full profile of the DAMPs. Lowering the level of DAMPs is useful therapeutic intervention but certainly not as effective as avoiding the DAMP generators, i.e., the inflammatory agents. So, rather than mitigating DAMPs, efforts should be focused on the elimination of inflammatory agents. | Danger-Associated Molecular Patterns (DAMPs): the Derivatives and Triggers of Inflammation | 10.1007/s11882-018-0817-3 |
2018-09-27 | This article is concerned with the decay and blow-up properties of a nonlinear viscoelastic wave equation with strong damping. We first show a local existence theorem. Then, we prove the global existence of solutions and establish a general decay rate estimate. Finally, we show the finite time blow-up result for some solutions with negative initial energy and positive initial energy. | General decay and blow-up of solutions for a nonlinear viscoelastic wave equation with strong damping | 10.1186/s13661-018-1072-1 |
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