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2015-01-01 | Cables are structural elements designed to bear tensile forces and experience vibration problems due to their slenderness and low mass. In the field of civil engineering, they are mostly used in bridges where the vibrations are mainly induced by wind, rain, traffic and earthquakes. This paper proposes the use of a tuned-inerter-damper (TID) system, mounted on cables to suppress unwanted vibrations. These are to be attached transversally to the cable, in the vicinity of the support, connected between the deck and the cable. The potential advantage of using a TID system consists in the high apparent mass that can be produced by the inerter. Our analysis showed that the modal damping ratio obtained is much higher than in the case of traditional dampers or tuned mass dampers, leading to an improved overall response. An optimal tuning methodology is also discussed. Numerical results are shown with a cable subjected to both free and forced vibrations and the TID performance is improved when compared with equivalent dampers. | Performance Analysis of Cables with Attached Tuned-Inerter-Dampers | 10.1007/978-3-319-15248-6_44 |
2015-01-01 | Vehicle suspension design is primarily characterised by conflicting targets concerning ride comfort, demanded handling performance qualities and save driving. Recent developments in the field of active and semi-active vehicle suspensions – aiming to dissolve these conflicts as far as possible – derive both from technological innovation as well as from corresponding theoretical studies. Although many active systems have been introduced to premium cars in recent years, the importance of well-designed passive systems is likely to remain for the foreseeable future, in particular for economyclass vehicles. | Virtual chassis tuning with emphasis on the damper characteristics – a method for optimal integrative damper adjustment by means of vertical and lateral dynamics simulation and evaluation criteria | 10.1007/978-3-658-09711-0_22 |
2015-01-01 | This study aims to evaluate the seismic performance of steel frames upgraded with shape memory alloy (SMA)-based self-centering viscous dampers. The proposed Superelastic Viscous Damper (SVD) relies on SMA elements for re-centering capability and employs viscoelastic (VE) damper that consists of two layers of a high damped (HD) blended butyl elastomer compound to augment its energy dissipation capacity. First, experimental tests are conducted to characterize behavior of SMA elements and VE damper and to assess the influence of various parameters such as displacement amplitude and loading frequency on their mechanical response. A prototype of the SVD is designed and fabricated. Then, an analytical model of a four-story steel special moment frame building with the installed SVDs is developed to determine the dynamic response of the structure. The incremental dynamic analysis is used to evaluate the behavior of controlled and uncontrolled buildings under 18 different ground motion records. The analytical results indicate that the buildings upgraded with the proposed passive control device effectively mitigate the peak interstory drifts and residual story drifts. | Seismic Performance Assessment of Steel Frames Upgraded with Self-Centering Viscous Dampers | 10.1007/978-3-319-15248-6_43 |
2015-01-01 | The vehicle semi-active suspension with magneto-rheological damper(MRD) has been a hot topic since this decade, in which the robust control synthesis considering load variation is a challenging task. In this paper, a new semi-active controller based upon the inverse model and sliding mode control (SMC) strategies is proposed for the quarter-vehicle suspension with the magneto-rheological (MR) damper, wherein an ideal skyhook suspension is employed as the control reference model and the vehicle sprung mass is considered as an uncertain parameter. According to the asymptotical stability of SMC, the dynamic errors between the plant and reference systems are used to derive the control damping force acquired by the MR quarter-vehicle suspension system. The proposed modified Bouc-wen hysteretic force-velocity ( F - v ) model and its inverse model of MR damper, as well as the proposed continuous modulation (CM) filtering algorithm without phase shift are employed to convert the control damping force into the direct drive current of the MR damper. Moreover, the proposed semi-active sliding mode controller (SSMC)-based MR quarter-vehicle suspension is systematically evaluated through comparing the time and frequency domain responses of the sprung and unsprung mass displacement accelerations, suspension travel and the tire dynamic force with those of the passive quarter-vehicle suspension, under three kinds of varied amplitude harmonic, rounded pulse and real-road measured random excitations. The evaluation results illustrate that the proposed SSMC can greatly suppress the vehicle suspension vibration due to uncertainty of the load, and thus improve the ride comfort and handling safety. The study establishes a solid theoretical foundation as the universal control scheme for the adaptive semi-active control of the MR full-vehicle suspension decoupled into four MR quarter-vehicle sub-suspension systems. | Semi-active sliding mode control of vehicle suspension with magneto-rheological damper | 10.3901/CJME.2014.0918.152 |
2015-01-01 | In the present chapter some of the most relevant applied forces and joint reaction forces are introduced. There are many types of forces that can be present in multibody systems, such as gravitational forces, spring-damper-actuator forces, normal contact forces, tangential or frictional forces, external applied forces and moments, forces due to elasticity of bodies, and thermal, electrical and magnetic forces. However, only the first six types of forces are relevant in the multibody systems of common application. | Force Elements and Reaction Forces | 10.1007/978-3-319-16190-7_11 |
2015-01-01 | One of the tasks within the FP7-SERIES project was the creation of a European Platform for Geographically Distributed Tests. This platform was envisioned to be able to deal with different protocols and algorithms so that its users and facilities would not be restricted to one specific protocol. The platform should also prove the possibility of performing geographically continuous distributed tests since up to now such tests were stop and go. However, through the use of an efficient substructure algorithm, continuous tests can be performed using standard network connections. With that in mind, several activities were performed at the University of Kassel that involved major earthquake engineering facilities around the world. With each partner, continuous time-scaled hybrid simulation tests with a non-linear substructure were performed exploring the available protocols. In addition, preliminary tests using Large Numerical models and a Linux cluster were also performed in order to assess the extensibility of the platform to more complex and larger models. | Geographically Distributed Continuous Hybrid Simulation Tests Using Shaking Tables | 10.1007/978-3-319-10136-1_8 |
2015-01-01 | Coupling of adjacent dissimilar buildings connected by semiactive dampers involving base isolation is one of the more viable techniques against seismic hazards mitigation through which counter-acting forces exert one upon another in addition to isolation effect. The proposed study two buildings of dissimilar in dynamic characteristics from these, two coupled building models are considered that is, first model (Model-1) consisting of taller building (Building-1) and shorter building (Building-2) are connected in-line variable friction dampers whereas second model (Model-2) is same as first except taller building is isolated by laminated rubber bearing at base. The seismic response analysis of these two models is compared with normal buildings of same characteristics. The seismic response analysis is carried out by exciting under unidirectional excitation due to Kobe 1995 earthquake. The governing equation of motion of these models and normal buildings are solved by state space method. The dynamic behavior of laminated rubber bearing is studied by Wen’s model whereas predictive control law used as control algorithm to predict the dynamic behaviour of variable friction damper. The seismic responses of these buildings are simulated through coding using MATLAB® computing software. The proposed study conclude that seismic performance of coupled building Model-2 work very significantly in reducing seismic response than Model-1 but Model-1 works effectively in avoiding pounding effects by adjacent buildings. Further, there is significant reduction in responses of Building-1 whereas marginal reduction is observed in Building-2. | Comparative Study of Seismically Excited Coupled Buildings with VF Damper and LR Bearing | 10.1007/978-81-322-2193-7_86 |
2015-01-01 | Loss of personal mobility is a large and growing issue that can be caused by a variety of medical problems. Knee pain, muscle weakness, and their associated conditions are among the most common causes of impaired walking. Currently, conventional solutions include simple braces, canes, and medication. In more extreme cases, surgery is also routine. We propose a design for a novel quasi-passive orthotic knee brace which combines a smart support system employing magnetorheological (MR) fluid with a passive load reduction system. To work in concert with the walking motion of the knee, we have designed a four-bar linkage in conjunction with a compliant mechanism. The resulting orthotic knee brace will alleviate common symptoms related to knee pain and restore lost mobility, most notably in cases of osteoarthritis. | Novel Quasi-Passive Knee Orthosis with Hybrid Joint Mechanism | 10.1007/978-3-319-10723-3_6 |
2015-01-01 | A solution procedure is proposed to approximate the probability density function (PDF) solution of high-dimensional non-linear systems under Poisson impulses. The PDF solution yields the generalized Fokker–Planck–Kolmogorov (FPK) equation. First a state-space-split method is proposed to reduce the high-dimensional generalized FPK equation to a low dimensional equation. After that, the exponential–polynomial closure method is further adopted to solve the reduced FPK equation for the PDF solution. In order to show the effectiveness of the proposed solution procedure, a two-degree-of-freedom coupled pitch–roll ship motion system and a 10-degree-of-freedom mass–spring–damper system are investigated, respectively. Compared to the simulated results, the proposed solution procedure is effective to obtain the PDF solution, especially in the tail region which is very important for reliability analysis. | Approximate Probability Density Function Solution of Multi-Degree-of-Freedom Coupled Systems Under Poisson Impulses | 10.1007/978-3-319-07167-1_19 |
2015-01-01 | Within this contribution, a linear-elastic Laval/Jeffcott rotor is considered, which is symmetrically supported in two identical semi-floating ring bearings. Run-up simulations and bifurcation analyses are carried out to investigate the stability and bifurcation phenomena of the rotor-bearing system. In particular, the methods of numerical continuation are applied to identify the nonlinear phenomena (jump phenomena, coexistence of solutions, etc.) and the corresponding bifurcations. The occurrence of subsynchronous oscillations is examined, which is caused by an oil whirl/whip instability due to the inner oil films. In this case, the main damping is provided by the outer oil films so that the oscillation amplitudes usually remain moderate. Besides these well-known subsynchronous oscillations with moderate amplitudes (oil whirl/whip instability due to the inner oil films), it is shown that self-excited oscillations with very high amplitudes also exist. This effect resembles Total Instability known from rotors in full-floating ring bearings. A detailed bifurcation analysis proves the coexistence of a so-called critical limit cycle with high amplitudes in the case of the perfectly balanced rotor which represents Total Instability. Finally, a variation of rotor and bearing parameters shows the influence on both the subsynchronous oscillations of tolerable amplitudes and the critical limit cycle oscillations. | Stability and bifurcation phenomena of Laval/Jeffcott rotors in semi-floating ring bearings | 10.1007/s11071-014-1759-5 |
2015-01-01 | The goal of this paper is to concentrate on dynamics and vibration attenuation of the electromechanical system flexibly coupled with a baseplate and damped by a double impact element. The model is constructed with four degrees of freedom in the mechanical oscillating part, three translational and one rotational. The system movement is reported by five mutually coupled second-order ordinary differential equations. There are the most important nonlinearities: stiffness of the support spring elements and internal impacts. As the main results it is shown that the double impact damping device massively attenuates vibrations of the rotor frame for a suitable choice of mass of the impact elements in dependence of the excitation amplitude of the baseplate. | Vibration Attenuation of the Electromechanical System by a Double Impact Element | 10.1007/978-3-319-21206-7_3 |
2015-01-01 | Squeeze Film Dampers (SFDs) are effective means to reduce shaft vibration and eliminate instabilities in high performance rotating machinery. Presently there is a need to characterize the performance of ultra-short length SFDs for aero jet engines where overall weight and space are at a premium. The paper presents force coefficients and dynamic film pressures measured in an open ends SFD with slenderness ratio L/D = 0.2 and for two film clearances c _ A = 0.129 mm and c _ B = 0.254 mm. The film land length L = 25.4 mm and diameter D = 125.7 mm. ISO VG2 lubricant flows into the axial mid-plane of the film land through three orifices spaced 120^o. The journal has end grooves (width and depth = 2.5 × 3.8 mm) for the installation of piston rings, and hence the total wetted length L _ tot = 36.8 mm. A static loader pulls the bearing cartridge (BC) to a set static eccentricity ( e _ s ), and two shakers, orthogonally positioned, exert dynamic loads on the BC to create circular orbits of amplitude ( r ) over a range of whirl frequencies ( ω ). In the current tests, the end seals are not in place. Comparing the dynamic forced performance of the open ends SFDs, the small clearance damper generates about four times more damping than the one with a larger clearance, whereas the inertia coefficients are approximately twice as large. The test results modestly agree with the theoretical ratios, where damping scales with ~1/ c ^3 and inertia with ~1/ c . The measurements also evidence significant dynamic pressures at the end grooves, which amplify the test elements’ inertia coefficients. The test results continue to demonstrate the paramount effect of grooves on enhancing the dynamic forced response of SFDs. | Dynamic Forced Performance of Short Length Open-Ends Squeeze Film Damper with End Grooves | 10.1007/978-3-319-06590-8_70 |
2015-01-01 | Tuned-Mass-Damper (TMD) is a passive control device for vibration control Vibration control of structures. However, the requirement of higher mass ratio restricts its applicability for seismic excitations. The improved performance of TMD is attempted herein by supplementing it with nonlinear restoring devices made of Shape-Memory-Alloy (SMA) Shape memory alloy (hence referred as SMA-TMD), motivated by its energy dissipation capability through micro-structural phase transitional hysteresis under cyclic loading. Extensive numerical simulations are conducted based on nonlinear random vibration analysis. A design optimization Optimization based on minimizing the root mean square displacement of the main structure is also carried in search for the optimal design parameters, latter validated through its performance under recorded ground motions. Significant improvements of the control efficiency and reduction of TMD displacement at a much reduced mass ratio is achieved by the SMA-TMD. | Shape Memory Alloy-Tuned Mass Damper (SMA-TMD) for Seismic Vibration Control | 10.1007/978-81-322-2193-7_108 |
2015-01-01 | A model for a Magneto-Rheological ( MR ) damper based on Artificial Neural Networks ( ANN ) is proposed. The design of the ANN model is focused to get the best architecture that manages the trade-off between computing cost and performance. Experimental data provided from two MR dampers with different properties have been used to validate the performance of the proposed ANN model in comparison with the classical parametric model of Bingham . Based on the RMSE index, an average error of 7.2 % is obtained by the ANN model, by taking into account 5 experiments with 10 replicas each one; while the Bingham model has 13.8 % of error. Both model structures were used in a suspension control system for a Quarter of Vehicle ( QoV ) model in order to evaluate the effect of its accuracy into the design/evaluation of the control system. Simulation results show that the accurate ANN -based damper model fulfills with the control goals; while the Bingham model does not fulfill them, by concluding erroneously that the controller is insufficient and must be redesigned. The accurate MR damper model validates a realistic QoV model response compliance. | Nonparametric Modeling of an Automotive Damper Based on ANN: Effect in the Control of a Semi-active Suspension | 10.1007/978-3-319-11271-8_19 |
2015-01-01 | Energy based seismic analysis is expected to provide better idea for design and damage assessment of structure subjected to seismic load compared to displacement based analysis as former can take care of repeated plastic deformations. However, the approach based on energy concepts has not been explored in depth. At the same time, use of dampers in structures is also being investigated in order to protect the structures from adverse effects from earthquake. Herein, formulation for energy dissipated by friction damper and energy balance approach has been established for friction damped medium and high-rise buildings. Also, it has been observed that friction dampers not only can reduce the input energy but also dissipate major part of the input energy. The effect of friction damper on kinetic energy and strain energy has also been studied. | Energy Assessment of Friction Damped Two Dimensional Frame Subjected to Seismic Load | 10.1007/978-81-322-2193-7_100 |
2015-01-01 | In the last three decades, there has been great deal of interest in the use of control systems to mitigate the effects of dynamic environmental hazards like earthquake and strong winds on the civil engineering structures. A variety of control systems have been considered for these applications that can be classified as passive, semi-active active or hybrid. In the present study, Viscoelastic damper as a structural protective system has be implemented to mitigate the damaging effects from the seismic and wind forces acting on the benchmark building. The dynamic behavior of the structural system supported on viscoelastic damper, the optimum parameters of the damper and effect of damper properties on the free vibration characteristics of the structure subjected to seismic and wind forces are investigated. The seismic force considered for study is El-Cento and wind force as simulated onsite wind velocity from the results obtained from the wind tunnel test. It is observed from the study that vicoelastic damper is very effective in reducing the reposes of benchmark building due to seismic and wind forces with respect to uncontrolled structure. | Seismic and Wind Response Reduction of Benchmark Building Using Viscoelastic Damper | 10.1007/978-81-322-2193-7_112 |
2015-01-01 | Since hysteretic dampers have nonlinear restoring-force characteristics with sensitive plastic flow and input earthquake ground motions propagating random media are extremely random in time and frequency domains, the seismic response of a building structure with hysteretic dampers deviates greatly depending on the installed quantity and location of dampers. This characteristic could become a barrier and difficulty to the reliable formulation of optimal placement problems of such dampers. In order to overcome such difficulty, a new optimization method including a variable adaptive step length is proposed. The proposed method to solve the optimum design problem is a successive procedure which consists of two steps. The first step is a sensitivity analysis by using nonlinear time-history response analyses, and the second step is a modification of the set of damper quantities based upon the sensitivity analysis. Numerical examples are presented to demonstrate the effectiveness and validity of the proposed design method. | Optimal Placement of Hysteretic Dampers via Adaptive Sensitivity-Smoothing Algorithm | 10.1007/978-3-319-18320-6_13 |
2015-01-01 | The dynamic properties of automotive chassis are affected by several different factors. Especially with respect to transmission of structure-borne sound, flexible bearings in chassis play an important role. In contrast to elastomer bushings, friction afflicted ball joints have not yet been studied with regard to this specific aspect [1]. In order to analyse their dynamic properties, a component test bench was developed, which is used to measure the rotational motion behaviour of ball joints in-depth. Based on vehicle test runs, a specific excitation range was defined to meet realistic boundary conditions for the experimental examinations. The experimental results show conditions of sticking and sliding due to specific operating states depending on low frequency vibrations. These results form the background of the ball joint model. In this context, the biggest challenge is to describe the nonlinear component characteristics in time domain simulation. To identify parameters and to improve the understanding of mechanisms in moving ball joints, a numerical model approach was further developed which considers nonlinear effects. The comparison of experimental and simulation results show the ability of the model to calculate the ball joint behaviour in time domain simulation. Figure 1.1 shows the structure of the used approach. | Motion behaviour of ball joints in automotive chassis with respect to structure-borne sound | 10.1007/978-3-658-08844-6_91 |
2015-01-01 | Nowadays, proportional integral derivative (PID) controller is the most popular control algorithm applied in engineering systems and has been generally accepted in industrial control. Recent developments in commercial vehicles have heightened the need for improving the ride comfort. The application of magnetorheological (MR) dampers in a seat suspension has been shown to provide significant benefits in this area. In most research on seat MR dampers the control application was not quite suitable for the semi-active and nonlinear hysteretic nature of MR dampers. This paper introduces an investigation into the use of a controlled MR damper for a semi-active seat suspension for commercial vehicle, enabling more suitable control. The proposed control system comprises a system controller that computes the desired damping force using a PID controller tuned using genetic algorithm (GA), and a continuous state damper controller that provides a direct estimation of the command voltage that is required to track the desired damping force. A mathematical model of a six degree-of-freedom semi-active seat suspension with human body model using an MR damper is derived. The proposed semi-active seat suspension is compared to a passive seat suspension for prescribed base displacements. These inputs are representative of the vibration of the body (sprung) mass of a passive quarter–vehicle suspension under bump and random-profile road excitation. Control performance criteria such as seat travel distance and head acceleration are evaluated in both time and frequency domains, in order to quantify the effectiveness of the proposed semi-active control technique. The simulated results indicate that the proposed genetic PID of the semi-active MR seat suspension provides a significant improvement in ride comfort. | Vibration Control of Semi-active MR Seat Suspension for Commercial Vehicles Using Genetic PID Controller | 10.1007/978-3-319-09918-7_64 |
2015-01-01 | Humanoid robot requires a robust prevention system against external disturbances to protect itself from falling to the ground and to perform its tasks completely. In this paper, a Falling Prevention System for humanoid robot is proposed to avoid falling from the disturbances, and helps humanoid robot recover its balance from external force by taking a step. The algorithm for the Falling Prevention System consists of two processes. First, humanoid robot can perceive whether it is falling or not by using an IMU sensor, and if falling, the center of mass (CoM) and swinging leg trajectories are calculated for the robot to take a step. The CoM and swinging leg trajectories are also used to acquire all joint angles of lower body by inverse kinematics. Furthermore, designed foot trajectory helps humanoid robot minimize its yawing moment. Next, mass-spring-damper system for the robot’s legs is modeled to reduce large impact force from the ground. The effectiveness of the proposed method is demonstrated through computer simulations for a humanoid robot. | Falling Prevention System from External Disturbances for Humanoid Robots | 10.1007/978-3-319-16841-8_10 |
2015-01-01 | Magneto-rheological (MR) fluid damper is a semi-active control device that has recently received more attention because they offer the adaptability of active control devices without requiring the associated large power sources. But inherent nonlinear nature of the MR fluid damper is one of the challenging aspects for utilizing this device to achieve the high performance. So development of an accurate MR fluid damper model is necessary to take the advantages from its unique characteristics. The focus of this paper is to develop an alternative method for modeling a MR fluid damper by using a so-called self-tuning Lyapunov-based fuzzy model (STLFM). Here, the model is constructed in the form of a center average fuzzy interference system, of which the fuzzy rules are designed based on the Lyapunov stability condition. In addition, in order to optimize the STLFM, the back propagation learning rules are used to adjust the fuzzy weighting net. Firstly, experimental data of a damping system using this damper is used to optimize the model. Next, the optimized model is used to estimate online the damping performance in the real-time conditions. The modeling results prove convincingly that the developed model could represent satisfactorily the behavior of the MR fluid damper. | Hysteresis modeling of magneto-rheological damper using self-tuning Lyapunov-based fuzzy approach | 10.1007/s12541-015-0004-6 |
2015-01-01 | Rail dampers are designed to reduce the rail component of rolling noise by increasing the attenuation with distance along the rail (decay rate, DR). There is no standardized method to assess the performance of rail dampers. The method described here, developed during the Franco-German STARDAMP project, uses laboratory tests and computer simulation to avoid the need for expensive and time-consuming field trials. The premise of the method is that the DRs of a damped track can be found from summing the DRs of a short-section of damped ‘freely supported’ rail and the DRs of an undamped track. Reasonable predictions of the decay rates of a test track have been made using this method. Software has been produced that implements TWINS-like predictions of rolling noise with and without rail dampers to predict the damper effect. The effect of rail pad stiffness on the effectiveness of rail dampers has been considered for track constructions typical in the UK and a regional train travelling at 120 km/h. For track fitted with ‘soft’ 120 MN/m rail pads, the dampers are predicted to reduce the total level by 2.5 dB(A) while with the ‘stiff’ 800 MN/m pads a 0.7 dB(A) reduction is expected. | Estimating the Performance of Rail Dampers Using Laboratory Methods and Software Predictions | 10.1007/978-3-662-44832-8_7 |
2015-01-01 | This article considers the dynamic analysis and semiactive vibration control on a building-like structure, excited on its base through an external force generated by an electromechanical shaker providing harmonic and seismic motion at the base of the overall structure. The mathematical model of the overall system is obtained using Euler-Lagrange methods, which is validated by means of experimental modal analysis techniques. In fact, the external force excites the first three (lateral) vibration modes of the building-like structure. Therefore, to suppress and/or attenuate the undesirable vibrations on the structure, it is proposed a semiactive vibration control scheme considering a Magneto-Rheological damper directly coupled between the base and the first floor. The hysteretic behavior of the Magneto-Rheological damper is modeled by means of the polynomial approach proposed by Choi-Lee-Park. Finally, a Multi Positive Position Feedback controller combined with Sliding-Mode Control techniques is synthesized, using as output the position provided by an accelerometer collocated on the first floor. Some experimental results are presented to show the dynamic performance of the overall building-like structure. | Semiactive Vibration Control in a Three-Story Building-Like Structure Using a Magnetorheological Damper | 10.1007/978-3-319-15248-6_48 |
2014-12-12 | PACS: 07.10.Cm (Micromechanical devices and systems), 46.40.Ff (Resonance and damping of mechanical waves), 07.79.-v (Scanning probe microscopes and components), 07.07.Df (Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing). Background The functionality of atomic force microscopy (AFM) and nanomechanical sensing can be enhanced using higher-mode microcantilever vibrations. Both methods require a resonating microcantilever to be placed close to a surface, either a sample or the boundary of a microfluidic channel. Below a certain cantilever-surface separation, the confined fluid induces squeeze-film damping. Since damping changes the dynamic properties of the cantilever and decreases its sensitivity, it should be considered and minimized. Although squeeze-film damping in gases is comprehensively described, little experimental data is available in liquids, especially for higher-mode vibrations. Methods We have measured the flexural higher-mode response of photothermally driven microcantilevers vibrating in water, close to a parallel surface with gaps ranging from ~200 μm to ~1 μm. A modified model based on harmonic oscillator theory was used to determine the modal eigenfrequencies and quality factors, which can be converted into co-moving fluid mass and dissipation coefficients. Results The range of squeeze-film damping between the cantilever and surface decreased for eigenfrequencies (inertial forces) and increased for quality factors (dissipative forces) with higher mode number. Conclusions The results can be employed to improve the quantitative analysis of AFM measurements, design miniaturized sensor fluid cells, or benchmark theoretical models. | Influence of squeeze-film damping on higher-mode microcantilever vibrations in liquid | 10.1140/epjti/s40485-014-0010-6 |
2014-12-01 | Present guidelines indicate the need to deorbit new satellites launched into low Earth orbit (LEO) within 25 years from their end of life. Our research task is to develop a new technology suitable to deorbit a satellite at the end of life with as small an impact as possible on the mass budget of the mission. An alternative to the traditional chemical rockets consists in using an electrodynamic tether that, through its interaction with the Earth ionosphere and magnetic field, can take advantage of Lorentz forces for deorbiting purposes. However, Lorentz forces produce a low and yet continuous injection of energy into the system that, in the long run, can bring the tether to instability. This paper addresses this issue through the analysis of the benefits provided by an elastic-viscous damping device installed at the attachment point of the tether to the spacecraft. The analysis carried out by means of linearization of dynamics equations and numerical simulations show that a well-tuned damper can efficiently absorb the kinetic energy from the tether thus providing system stability during deorbiting. | Two-bar model for free vibrations damping of space tethers by means of spring-dashpot devices | 10.1007/s12567-014-0065-x |
2014-12-01 | To maximize stability in a constant-speed hydromechanical system, close attention must be paid to parameter selection in the dynamic vibrational damper within the centrifugal regulator. | Dynamic vibrational damping within a constant-speed hydromechanical system | 10.3103/S1068798X14120259 |
2014-12-01 | We consider the Timoshenko model for vibrating beams under effect of two nonlinear and localized frictional damping mechanisms acting on the transverse displacement and on the rotational angle. We prove that the damping placed on an arbitrarily small support, unquantitized at the origin and without assuming equal speeds of propagation of waves , leads to uniform decay rates (asymptotic in time) for the energy function. This result removes the necessity (as long as both transverse displacements and rotational angles are minimally damped) of the assumption on equal speeds which has been imposed in the prior literature. The proof of this result relies on the method introduced in Daloutli et al. (Discret Contin Dyn Syst 2(1):67–94, 2009 ), which reduces the nonlinear stabilization to the observability inequality established for the associated linear problem. The latter is important on its own rights within the context of internal and localized controllability/observability of free linear systems. | Uniform decay rates for the energy of Timoshenko system with the arbitrary speeds of propagation and localized nonlinear damping | 10.1007/s00033-013-0380-7 |
2014-12-01 | A displacement-based design (DBD) procedure aiming to proportion hysteretic damped braces (HYDBs) in order to attain, for a specific level of seismic intensity, a designated performance level of a structure is proposed for the retrofitting of framed buildings. A key step for the reliability of the DBD procedure is the selection of the equivalent viscous damping in order to account for the energy dissipated by the damped braced frame. In this paper, expressions of the equivalent damping are obtained considering the energy dissipated by the HYDBs and the framed structure. To this end, dynamic analyses of an equivalent single degree of freedom system, whose response is idealized by a trilinear model, are carried out considering real accelerograms matching, on the average, Eurocode 8 (EC8) response spectrum for a medium subsoil class. Then, a three-storey reinforced concrete (r.c.) framed structure of a school building, designed in a medium-risk seismic region according to the Italian code in force in 1975 , is supposed as retrofitted as if in a high-risk seismic region of the current seismic code (NTC08) by the insertion of HYDBs. Nonlinear static analyses are carried out to evaluate the vulnerability of the primary structure, characterized by the lack of interior girders along the floor slab direction, and to select optimal properties of the HYDBs. The effectiveness of the retrofitting solutions is checked referring to nonlinear dynamic analyses, considering artificially generated accelerograms whose response spectra match those adopted by NTC08 for the earthquake design levels corresponding to the serviceability and ultimate limit states. | Equivalent viscous damping for displacement-based seismic design of hysteretic damped braces for retrofitting framed buildings | 10.1007/s10518-014-9601-5 |
2014-12-01 | This paper is devoted to studying the effects of a vanishing structural damping on the controllability properties of the one dimensional linear beam equation. The vanishing term depends on a small parameter ɛ ∈ (0, 1). We study the boundary controllability properties of this perturbed equation and the behavior of its boundary controls $${v_\varepsilon }$$ as ɛ goes to zero. It is shown that for any time T sufficiently large but independent of ɛ and for each initial data in a suitable space there exists a uniformly bounded family of controls $${({v_\varepsilon })_\varepsilon }$$ in L ^2(0, T ) acting on the extremity x = π . Any weak limit of this family is a control for the beam equation. This analysis is based on Fourier expansion and explicit construction and evaluation of biorthogonal sequences. This method allows us to measure the magnitude of the control needed for each eigenfrequency and to show their uniform boundedness when the structural damping tends to zero. | Uniform controllability for the beam equation with vanishing structural damping | 10.1007/s10587-014-0140-7 |
2014-12-01 | Single machine infinite bus (SMIB) power system and multi-machine power system (MMPS) stability improvement by tuning of static var compensator (SVC) based controller parameters are investigated in the proposed method. The design problem is formulated as an optimization problem with a time-domain simulation-based objective function and real-coded genetic algorithm is used for searching optimal controller parameters. SMIB power system and MMPS models are developed using MATLAB’s SIMULINK which incorporates SVC controller. A fault is created on the transmission line. The simulation results of SMIB power system and MMPS without SVC controller and with SVC controller are presented. The simulation results are analyzed which show that the power system becomes unstable on the occurrence of the fault if SVC controller is not used. This paper proves the effectiveness of the proposed design. Thus the proposed method enhances the power system stability. | Improvement of power system stability using genetically optimized SVC controller | 10.1007/s13198-014-0233-6 |
2014-12-01 | This paper deals with the analysis of active constrained layer damping (ACLD) of large amplitude vibrations of smart magneto–electro–elastic (MEE) doubly curved shells. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composite (PZC). The constrained viscoelastic layer of the ACLD treatment is modeled by using the Golla–Hughes–McTavish method in the time domain. A three-dimensional finite element model of the overall smart MEE doubly curved shells has been developed taking into account the effects of electro–elastic and magneto–elastic couplings, while the von Kármán type nonlinear strain displacement relations are used for incorporating the geometric nonlinearity. Influence of the curvature ratio, the curvature aspect ratio, the thickness aspect ratio on the nonlinear frequency ratios of the MEE doubly curved shells has been investigated. Effects of the location of the ACLD patches and the edge boundary conditions on the control of geometrically nonlinear vibrations of paraboloid and hyperboloid MEE shells have been studied. Particular attention has been paid to investigate the performance of the ACLD treatment due to the variation of the piezoelectric fiber orientation angle in the 1–3 PZC constraining layer of the ACLD treatment. | Active control of large amplitude vibrations of smart magneto–electro–elastic doubly curved shells | 10.1007/s10999-014-9252-3 |
2014-12-01 | Highly concentrated colloidal suspensions exhibit a discontinuous shear-thickening behaviour. The transition from a low to a high viscosity state is associated to a large energy dissipation. This effect could find applications in structural damping while the viscosity increase brings added stiffness. In the present work, highly concentrated suspensions of monodisperse spherical silica particles in polyethylene glycol were selected for their strong thickening at low critical shear rates. Their damping properties were characterized by measuring the energy dissipated per cycle at low frequency (below 2 Hz) during oscillatory tests using a rheometer. The influence of parameters such as particle concentration, size and frequency was investigated. Damping was found to overcome that of benchmark elastomeric materials only in high frequencies and high strain domains. | Energy dissipation in concentrated monodisperse colloidal suspensions of silica particles in polyethylene glycol | 10.1007/s00396-014-3378-6 |
2014-12-01 | Relaxation time spectra (RTS) derived from time domain induced polarization data (TDIP) are helpful to assess oil reservoir pore structures. However, due to the sensitivity to the signal-to-noise ratio (SNR), the inversion accuracy of the traditional singular value decomposition (SVD) inversion method reduces with a decrease of SNR. In order to enhance the inversion accuracy and improve robustness of the inversion method to the SNR, an improved inversion method, based on damping factor and spectrum component residual correction, is proposed in this study. The numerical inversion results show that the oscillation of the RTS derived from the SVD method increased with a decrease of SNR, which makes it impossible to get accurate inversion components. However, the SNR has little influence on inversion components of the improved method, and the RTS has high inversion accuracy and robustness. Moreover, RTS derived from core sample data is basically in accord with the pore-size distribution curve, and the RTS derived from the actual induced polarization logging data is smooth and continuous, which indicates that the improved method is practicable. | A time domain induced polarization relaxation time spectrum inversion method based on a damping factor and residual correction | 10.1007/s12182-014-0367-9 |
2014-12-01 | Hydrodynamic coefficients due to horizontal oscillation in surge motion for a floating, hollow cylinder placed above a fixed, coaxial, bottom-mounted cylinder are investigated within the framework of linear, water wave theory. This problem of radiation by this specific pair of two cylinders can be considered as a wave energy device consisting of two coaxial cylinders: the upper one hollow and the lower one solid. The energy that is created and transferred by this device finds use in a number of practical applications. We use the method of separation of variables to obtain the analytical expressions for the corresponding radiated potentials in clearly identified regions. By using the matching conditions which ensure the continuity of velocity and pressure along the virtual vertical boundaries of the regions, a system of linear equations for the unknown coefficients is derived and solved. The analytical expressions of the radiated potentials allow us to obtain the hydrodynamic coefficients, namely, the added mass and damping coefficients, which play a vital role for a structure in motion, however small. A set of values of added mass and damping coefficients is obtained for different radii of the fixed cylinder and for different gaps between the cylinders (i.e., also for different drafts of the floating cylinder) for the same fixed radii of the cylinders. It is observed that changes in values in radius and the gap have significant effect on the hydrodynamic coefficients. We also compute the coefficients due to different gaps between the cylinders with the radii of both taken to be different. The behaviour of both the added mass and damping coefficients is observed to be steady in the lower frequency range. However, fluctuations are observed for both coefficients due to resonance in the neighbourhood of a specific frequency. These results are depicted graphically and compared with available results. Comparison is carried out with numerical data presented by other investigators by considering the case of a hollow cylinder floating over an even sea bottom, i.e., without the coaxial cylindrical caisson underneath. Good agreement is observed from this comparison. A numerical verification is also carried out for the body boundary condition satisfied at the boundary of both the cylinders. | Hydrodynamic coefficients in surge for a radiating hollow cylinder placed above a coaxial cylinder at finite ocean depth | 10.1007/s00773-014-0280-3 |
2014-12-01 | This paper presents the results of nonlinear finite element analyses conducted on stainless steel shear links. Stainless steels are attractive materials for seismic fuse device especially for corrosion-aware environment such as coastal regions because they are highly corrosion resistant, have good ductility and toughness properties in combination with low maintenance requirements. This paper discusses the promising use of AISI 316L stainless steel for shear links as seismic fuse devices. Hysteresis behaviors of four stainless steel shear link specimens under reversed cyclic loading were examined to assess their ultimate strength, plastic rotation and failure modes. The nonlinear finite element analysis results show that shear links made of AISI 316L stainless steel exhibit a high level of ductility. However, it is also found that because of large over-strength ratio associated with its strain hardening process, mixed shear and flexural failure modes were observed in stainless steel shear links compared with conventional steel shear links with the same length ratio. This raises the issue that proper design requirements such as length ratio, element compactness and stiffener spacing need to be determined to ensure the full development of the overall plastic rotation of the stainless steel shear links. | Numerical study of the cyclic load behavior of AISI 316L stainless steel shear links for seismic fuse device | 10.1007/s11709-014-0276-4 |
2014-12-01 | This article extends a signal-based approach formerly proposed by the authors, which utilizes the fractal dimension of time frequency feature (FDTFF) of displacements, for earthquake damage detection of moment resist frame (MRF), and validates the approach with shaking table tests. The time frequency feature (TFF) of the relative displacement at measured story is defined as the real part of the coefficients of the analytical wavelet transform. The fractal dimension (FD) is to quantify the TFF within the fundamental frequency band using box counting method. It is verified that the FDTFFs at all stories of the linear MRF are identical with the help of static condensation method and modal superposition principle, while the FDTFFs at the stories with localized nonlinearities due to damage will be different from those at the stories without nonlinearities using the reverse-path methodology. By comparing the FDTFFs of displacements at measured stories in a structure, the damage-induced nonlinearity of the structure under strong ground motion can be detected and localized. Finally shaking table experiments on a 1:8 scale sixteen-story three-bay steel MRF with added frictional dampers, which generate local nonlinearities, are conducted to validate the approach. | Experimental validation of a signal-based approach for structural earthquake damage detection using fractal dimension of time frequency feature | 10.1007/s11803-014-0271-8 |
2014-12-01 | The transfer matrix method is a rather unusual strategy of modeling linear multibody systems, however, it is able to elegantly model systems including both discrete and continuous elements and to solve such kind of problems with any precision required. This is achieved by transforming differential to algebraic equations and summarizing all system information in an overall system of linear equations independent of the degrees of freedom. Nontrivial solutions representing vibration modes then require the coefficient matrix to be singular. Thus, the precision of solutions is associated with the ability of finding zeros for the determinants of these coefficient matrices, which may be nonlinear or transcendental, real or complex functions of natural vibration frequencies or complex eigenvalues. The paper reduces the zero search to a minimization problem and suggests two simple, but robust algorithms which are much more efficient than direct enumeration. Further, the problem of noisy determinant computation is addressed and the complex transfer matrix of a rod for damped vibrations is derived. Three basic examples serve for demonstrating the concept and for showing the robustness of the proposed approach. For a rod-damper system, the solution with jumping frequencies for a critical damping value can be proven analytically. | Recursive eigenvalue search algorithm for transfer matrix method of linear flexible multibody systems | 10.1007/s11044-013-9399-y |
2014-11-28 | In this paper, we are concerned with a nonlinear coupled viscoelastic wave equations with initial-boundary value conditions and nonlinear damping and source terms. Under suitable assumptions on relaxation functions, damping terms, and source terms, by using the energy method we proved a global nonexistence result for certain solutions with negative initial energy. | Global nonexistence of solutions for nonlinear coupled viscoelastic wave equations with damping and source terms | 10.1186/s13661-014-0250-z |
2014-11-01 | The effects of annealing on the Gilbert damping constant and the magnetic properties are investigated in CoFeB films sandwiched by either Ta, Ru, or Pd layers. As the annealing temperature increases, the damping constant is found to be slightly decreased first and then, rapidly increased. The minimum damping constant is, thus, obtained with a 300 °C-annealed Ta/CoFeB/Ta film while the samples with Ru and Pd layers exhibit their minimum at 200 °C. The coercive field also exhibits a behavior similar to the damping constant; thus, an empirical correlation between them is proposed. | Optimization of the Gilbert damping constant by annealing CoFeB films sandwiched by Ta, Ru, and Pd layers | 10.3938/jkps.65.1611 |
2014-11-01 | The logarithmic decrement of damped vibrations of materials is determined using a theoretical-experimental method. The method is based on measuring the deflection amplitudes of flat cantilever test specimens during their damped vibrations according to the first resonance mode, on the description of internal viscous friction of materials by known models both in linear and nonlinear approximations, on theoretical determination of the aerodynamic constituent of damping, and on a theoretical investigation of damping vibrations of test specimens by employing equations of motion constructed with a corresponding degree of accuracy and pithiness. To determine the vibration decrement of a soft material in tension-compression, sandwich test specimens with a steel core and external layers made of the soft material were used, but in transverse shear — with a core made of the soft material and steel external layers. A considerable effect of external aerodynamic forces on the vibration decrement of the specimens is revealed. Two methods for identification of the parameters of internal damping are proposed on the basis of data of the experimental investigations performed. | Theoretical-Experimental Method for Determining the Parameters of Damping Based on the Study of Damped Flexural Vibrations of Test Specimens. 3. Identification of the Characteristics of Internal Damping | 10.1007/s11029-014-9451-x |
2014-11-01 | We explore the notion of resonant absorption in a dynamic time-dependent magnetised plasma background. Very many works have investigated resonance in the Alfvén and slow MHD continua under both ideal and dissipative MHD regimes. Jump conditions in static and steady systems have been found in previous works, connecting solutions at both sides of the resonant layer. Here, we derive the jump conditions in a temporally dependent, magnetised, inhomogeneous plasma background to leading order in the Wentzel–Kramers–Billouin (WKB) approximation. Next, we exploit the results found in Williamson and Erdélyi ( Solar Phys. 289 , 899, 2014 ) to describe the evolution of the jump condition in the dynamic model considered. The jump across the resonant point is shown to increase exponentially in time. We determined the damping as a result of the resonance over the same time period and investigated the temporal evolution of the damping itself. We found that the damping coefficient, as a result of the evolution of the resonance, decreases as the density gradient across the transitional layer decreases. This has the consequence that in such time-dependent systems resonant absorption may not be as efficient as time progresses. | Resonant Damping of Propagating Kink Waves in Time-Dependent Magnetic Flux Tube | 10.1007/s11207-014-0569-8 |
2014-11-01 | After a brief review of the history of viscosity from classical to quantal fluids, a discussion of how the shear viscosity η of a finite hot nucleus is calculated directly from the width and energy of the giant dipole resonance (GDR) of the nucleus is given in this paper. The ratio η / s with s being the entropy volume density, is extracted from the experimental systematic of GDR in copper, tin and lead isotopes at finite temperature T . These empirical results are compared with the results predicted by several independent models, as well as with almost model-independent estimations. Based on these results, it is concluded that the ratio η / s in medium and heavy nuclei decreases with increasing T to reach ( 1.3 − 4 ) × ℏ / ( 4 π k B ) $(1.3 - 4) \times \hbar /(4\pi k_{\mathrm {B}})$ at T = 5 MeV, which is almost the same as that obtained for quark-gluon plasma at T > 170 MeV. | Viscosity: From air to hot nuclei | 10.1007/s12043-014-0857-8 |
2014-11-01 | This paper proposes the use of the non-time based control strategy named Delayed Reference Control (DRC) to the control of industrial robotic cranes. Such a control scheme has been developed to achieve two relevant objectives in the control of autonomous operated cranes: the active damping of undesired load swing, and the accurate tracking of the planned path through space, with the preservation of the coordinated Cartesian motion of the crane. A paramount advantage of the proposed scheme over traditional ones is its ease of implementation on industrial devices: it can be implemented by just adding an outer control loop (incorporating path planning) to standard position controllers. Experimental performance assessment of the proposed control strategy is provided by applying the DRC to the control of the oscillation of a cable-suspended load moved by a parallel robot mimicking a robotic crane. In order to implement the DRC scheme on such an industrial robot it has been just necessary to manage path planning and the DRC algorithm on a separate real-time hardware computing the delay in the execution of the desired trajectory suitable to reduce load swing. Load swing has been detected by processing the images from two off-the-shelf cameras with a dedicated vision system. No customization of the robot industrial controller has been necessary. | A Non-Time Based Controller for Load Swing Damping and Path-Tracking in Robotic Cranes | 10.1007/s10846-014-0036-7 |
2014-11-01 | This paper proposes a variable walking trajectory generation method for biped robots based on redundancy analysis. In designing a bipedal trajectory for locomotion, maintaining locomotion stability without falling down and natural patterns of the locomotion are important. First, the positions and orientations of the feet and body of a robot are chosen as the reference factors, whose trajectories are predetermined. The augmented Jacobian method is used at the acceleration level with differential equation of the reference factors and the ZMP equation to secure stable walking motions. A virtual spring-damper system is implemented as an additional task in the null-space of the augmented Jacobian to make a balanced cyclic configuration of the robot. For a more stable trajectory generation, the condition to avoid kinematic singularity is also used. Computer simulations were conducted for various situations, for example, with locomotion speed changes or an asymmetrical mass distribution, which showed that the proposed trajectory generation method was very effective in generating various walking motions for biped robots. | Variable walking trajectory generation method for biped robots based on redundancy analysis | 10.1007/s12206-014-1007-4 |
2014-11-01 | This paper presents a novel method, based on the particle impact damping (PID), for the attenuation of regenerative vibration in boring operation. A specially designed boring bar having a cavity near machining-end for partial filling of spherical particles has been developed. Characteristics of boring bar with and without PID have been found from impact and shaker tests. After identifying appropriate particle size and filling volume, experiments are conducted to evaluate the performance in actual boring operations. Additional boring experiments are also conducted to confirm the performance by changing particle size and filling volumes. The collision of the particles in PID is found to attenuate regenerative vibration by the energy dissipation and thus effectively enhances stability of the boring operation. Analysis of effect of PID on surface topography in terms of chatter marks, surface roughness, and roundness of bored holes shows that the proposed method results in improvement of bore quality when compared with a boring bar without PID. It is also established that radial vibration of the boring bar has a significant influence on the surface topography obtained in boring operation. | Investigation into effect of particle impact damping (PID) on surface topography in boring operation | 10.1007/s00170-014-6201-0 |
2014-11-01 | The flexural and vibration properties were examined in order to evaluate the anti-vibration characteristics of rubber modified reinforced concrete beam. The rubberised mixtures were produced by replacing 5, 7.5, and 10 % by mass of the fine aggregate with 1–4 mm scrap truck tyre crumb rubber particles. A series of reinforced concrete beam (1,200 × 135 × 90 mm^3) was tested in a free vibration mode and then subsequently in a four point flexural tests. The input and output signals from vibration tests were utilised to calculate various dynamic parameters such as natural frequencies, frequency response function, dynamic modulus of elasticity and damping ratio. The results showed that compared to control mixture, gradual reductions of natural frequencies in first six modes of all rubberised beams with the highest being in the mixture with 10 % rubber contents. In addition, despite the reduction in overall strength, rubberised mixtures showed flexibility under loading due to the higher energy absorption capacity of rubber particles. Compared to control mixture, the results also showed a uniform global decrease in the dynamic modulus over the span. The reduction was found as high as 26 % in the mixture with 10 % rubber content. The results indicated that the rubberised concrete exhibits better anti-vibration properties and could be a viable alternative to use as vibration attenuation material where resistance to impact or blast is required such as in railway buffers, jersey barriers (a protective concrete barrier used as a highway divider and a means of preventing access to a prohibited area) and bunkers. | Anti-vibration characteristics of rubberised reinforced concrete beams | 10.1617/s11527-013-0151-0 |
2014-11-01 | Continuing on the recent observation that sudden death of entanglement can occur even when a single qubit of a 2-qubit state is exposed to noisy environment (Yashodamma and Sudha in Results Phys 3:41–45, 2013 ), we examine the local action of a noise on bipartite qubit–qutrit and qutrit–qutrit systems. We show that depolarizing noise causes sudden death of entanglement in both qubit–qutrit and qutrit–qutrit systems even when it acts only on one part of the system. While generalized amplitude damping noise also causes finite-time disentanglement in qubit–qutrit states, the entanglement sudden death occurs much faster due to depolarizing noise. This result strengthens the observation (Yashodamma and Sudha in Results Phys 3:41–45, 2013 ) that depolarizing noise is more effective than other noise models in causing sudden death of entanglement. | Effectiveness of depolarizing noise in causing sudden death of entanglement | 10.1007/s11128-014-0812-0 |
2014-11-01 | The paper is devoted to description of certain ways of extending the domain of convergence of Newton’s method. This paper is a survey of contributions of representatives of Soviet and Russian mathematical school, namely, Kalitkin, Puzynin, Madorskij and others. They introduced different kinds of damping multiplier and showed that their usage may be helpful and beneficial while solving different nonlinear equations and systems starting with “bad” zero estimate. We have also paid attention to the problem of degeneracy of Jacobian matrix and the ways it was solved by named researchers. Finally, we have tested the presented iterative schemes on some examples in order to check their effectiveness. All complete strict proofs of key theorems can be found both in Russian and English in the provided bibliography. | Modifications of Newton’s method to extend the convergence domain | 10.1007/s40324-014-0020-y |
2014-11-01 | Vibrations generated by blasting carried out during the quarrying of material induce dynamic stresses that can give rise to damage of diverse considerations in surrounding buildings and structures. The adverse effects of vibrations caused by explosives used in mining and civil works can be controlled by suitably planning blasting operations, appropriately managing and optimising the equipment used, and monitoring the processes that cause these vibrations. The aims of the present study were to discuss and test the existence of a damping of underground vibrations, besides defining a transmission law for such vibrations which will depend on the directionality between the blast and the measurement point. Besides, the damages that vibrations can produce on the rock mass are evaluated. Their effects are very similar to those produced by an earthquake that disconnects the rock mass integral blocks. | Influence of depth and geological structure on the transmission of blast vibrations | 10.1007/s10064-014-0595-7 |
2014-11-01 | Absorption systems observed along the line of sights to distant quasars are observed at all redshifts and the full range of the electromagnetic spectrum is needed to recover the variety of transitions of different elements. However, some important elements are found within the Lyman forest and their absorption line profiles need to be analyzed against the presence of possible Ly- α contamination. Considering the cosmological evolution of the number density of hydrogen clouds, the probability to detect uncontaminated metal lines is higher in the UV-Optical region exploited by CUBES. The list of these elements includes some important ones such as D, H_2, O i , N i , O vi , Ar i , P ii , C ii , S ii and B ii . The determination of some of them in the Damped Ly- α galaxies and their astronomical interest are briefly discussed. | DLA abundances in the CUBES’s spectral window | 10.1007/s10509-014-2017-5 |
2014-10-16 | We study periodic solutions of the suspension bridge model proposed by Lazer and McKenna with a periodic damping term. Under the Dolph-type condition and a small periodic damping term condition, the existence and the uniqueness of a periodic solution have been proved by a constructive method. Two numerical examples are presented to illustrate the effect of the periodic damping term. MSC: 34B15, 34C15, 34C25. | Periodic oscillation in suspension bridge model with a periodic damping term | 10.1186/s13661-014-0231-2 |
2014-10-16 | The long time behavior of the solutions for the strongly damped wave equation is considered with nonlinear damping, a nonlinear forcing term, and with a periodic boundary condition. We prove that the global attractor which captures all trajectories in H 1 ( Ω ) × L 2 ( Ω ) is a compact set in H 2 ( Ω ) × H 1 ( Ω ) . MSC: 35B40, 34A35, 37L30. | Regularity of the attractor for strongly damped wave equations with nonlinearity | 10.1186/1029-242X-2014-396 |
2014-10-01 | Accurate determination of the squeeze-film damping in rare air is crucial for the design of high- Q MEMS devices. In the past, for the MEMS structures with no perforations, there have been two approaches to treating the squeeze-film damping in rare air: the approach based on the continuum assumption and the approach using molecular dynamics (MD) method. The amount of squeeze-film damping can be controlled by providing perforations in microstructures. To model perforation effects on squeeze-film damping, many methods have been proposed. However, almost all the previous methods are based on the continuum assumption. Only one paper focuses on analytical modeling of squeeze-film damping of a perforated microplate using the MD method. Hutcherson and Ye (J Micromech Microeng 14:1726–1733, 2004 ) developed a novel MD method to model the squeeze-film damping in free molecular regime. The method possesses high computational efficiency. However, their work is valid only for non-perforated rectangular microplate. This paper presents a numerical MD approach for calculating the squeeze-film damping of a perforated rectangular plate and a perforated circular plate in free molecular regime. In Hutcherson and Ye’s work, the microplate is non-perforated. After each collision with the non-perforated plate, all the molecules are reflected to the substrate. In this paper, the plate is perforated. For the molecules in the air gap striking the surface of the perforated microplate, some of the molecules are reflected to the substrate. The rest leave the air gap through the perforations. This paper is an extension of the work done by Hutcherson and Ye (J Micromech Microeng 14:1726–1733, 2004 ). The accuracy of the present numerical MD approach is verified by comparing its results with the experimental results available in the literature and the finite element method results. | A numerical molecular dynamics approach for squeeze-film damping of perforated MEMS structures in the free molecular regime | 10.1007/s10404-014-1349-3 |
2014-10-01 | The initial boundary value problem for nonlinear wave equations of Kirchhoff systems with memory type in a bounded domain is considered. By modifying the method introduced in a work by Autuori et al. (Arch Rational Mech Anal 196:489–516, 2010 ), we establish the nonexistence result of global solutions with the initial energy controlled above by a critical value, that is, when the initial data belong to a specific region in the phase plane. This improves earlier results in the literatures. | Global nonexistence for nonlinear Kirchhoff systems with memory term | 10.1007/s00033-013-0367-4 |
2014-10-01 | A nonlinear impact damping model of single-degree-of-freedom spur cylindrical gear with backlash and time-varying stiffness was established. Systematic analyses of the dynamic responses were performed. First, the nonlinear damping coefficient was considered as a constant parameter with two types of compliance exponent, meanwhile, dynamic factors were adopted to depict the dynamic characteristics. Second, the bifurcation graphs were plotted, where the damping coefficient was obtained along with the impact velocity and coefficient of restitution. The results show that light and heavy load conditions have an effect on the responses when the compliance exponent is integer. On the contrary, when the compliance exponent is non-integer, the dynamic responses are slightly affected, namely the system is more stable than the former situation. | Effect of nonlinear impact damping with non-integer compliance exponent on gear dynamic characteristics | 10.1007/s11771-014-2355-z |
2014-10-01 | We study oscillatory properties of solutions to a class of nonlinear second-order differential equations with a nonlinear damping. New oscillation criteria extend those reported in [ROGOVCHENKO, Yu. V.—TUNCAY, F.: Oscillation criteria for second-order nonlinear differential equations with damping , Nonlinear Anal. 69 (2008), 208–221] and improve a number of related results. | Oscillation of second-order nonlinear differential equations with damping | 10.2478/s12175-014-0271-1 |
2014-10-01 | Particle damping is a derivative of impact damping, which can be used to achieve structural damping. Real-time applications of particle damping are scarce in literature. For this study, a boring bar, filled with various metal particles, was used for internal turning operation, and the impacts on the surface roughness were studied. The influences of particle parameters on the surface roughness of machined surface are investigated in this study. In spite of the simplicity of the experiments conducted, the results provide us with a fundamental understanding of the parameters influencing particle damping. | Impact of Particle Damping Parameters on Surface Roughness of Bored Surface | 10.1007/s13369-014-1209-1 |
2014-10-01 | The authors study decay properties of solutions for a viscoelastic wave equation with variable coefficients and a nonlinear boundary damping by the differential geometric approach. | General decay rate estimates for viscoelastic wave equation with variable coefficients | 10.1007/s11424-014-1056-x |
2014-10-01 | This paper estimates fundamental translational period and damping ratio parameters and examines the changes in dynamic characteristics of a set of low-to-medium rise buildings in Lorca town (SE of Spain) affected by the May 11th, 2011 earthquake. These building parameters have been calculated analysing structural dynamic response from ambient vibration measurements recorded at top RC buildings pre- and post earthquake, using the Fast Fourier Transform and the Randomdec technique. The empirical expression relating period $$(T)$$ ( T ) and number of floor $$(N)$$ ( N ) here obtained analysing ambient noise recorded on 59 healthy buildings before the earthquake is $$T= (0.054\pm 0.002)\, N$$ T = ( 0.054 ± 0.002 ) N , very similar to others empirical period–height relationships obtained for RC structures in the European built environment but quite different from code provisions. Measurements performed in 34 damaged buildings show a period elongation after the quake according to $$T^{*} =(0.075\pm 0.002)\,N$$ T ∗ = ( 0.075 ± 0.002 ) N expression. Moreover, we found a rise of the fundamental period with the EMS’s grade of damage of buildings. In contrast to natural frequency, damping ratio $$(\xi )$$ ( ξ ) do not shows a significant variation with earthquake damage degree and the product $$\xi \, T$$ ξ T remains near constant. | Changes in dynamic characteristics of Lorca RC buildings from pre- and post-earthquake ambient vibration data | 10.1007/s10518-013-9489-5 |
2014-10-01 | The equation considered in this paper is $$x'' + h(t)\:x'|x'| + \omega^2\sin x = 0,$$ x ′ ′ + h ( t ) x ′ | x ′ | + ω 2 sin x = 0 , where h ( t ) is continuous and nonnegative for $${t \geq 0}$$ t ≥ 0 and ω is a positive real number. This may be regarded as an equation of motion of an underwater pendulum. The damping force is proportional to the square of the velocity. The primary purpose is to establish necessary and sufficient conditions on the time-varying coefficient h ( t ) for the origin to be asymptotically stable. The phase plane analysis concerning the positive orbits of an equivalent planar system to the above-mentioned equation is used to obtain the main results. In addition, solutions of the system are compared with a particular solution of the first-order nonlinear differential equation $$u' + h(t)u|u| + 1 = 0.$$ u ′ + h ( t ) u | u | + 1 = 0 . Some examples are also included to illustrate our results. Finally, the present results are extended to be applied to an equation with a nonnegative real-power damping force. | Asymptotic stability of a pendulum with quadratic damping | 10.1007/s00033-013-0361-x |
2014-10-01 | Studies of thermal fluctuations in discocytes, echinocytes, and spherocytes suggest that the coupling between lipid bilayer and cytoskeleton can affect viscoelastic behavior of single erythrocyte membranes. To test this hypothesis, we developed a 3D constitutive model describing viscoelastic behavior of erythrocyte membranes, at long relaxation times $$t \in [0.20\,\mathrm {s}, 1.05\,\mathrm {s}]$$ t ∈ [ 0.20 s , 1.05 s ] and short relaxation times $$t \in [0.03\,\mathrm {s}, 0.20\,\mathrm {s}]$$ t ∈ [ 0.03 s , 0.20 s ] . The model was constructed using combination of spring and spring pot rheological elements arranged in parallel. The rearrangement of cytoskeleton induced by changing the bending state of lipid bilayer was described by a modified Eyring model. The model predictions point to an anomalous nature of energy dissipation and an ordered harmonic nature of the coupling mechanism described by a series of fractional derivatives of the order n $$\alpha $$ α (where $$ n \in [- 1, 2]$$ n ∈ [ - 1 , 2 ] ). As a result, the stress generated within the lipid bilayer is related to the rate of change of the irreversible stress within the cytoskeleton. | Modeling analysis of the lipid bilayer–cytoskeleton coupling in erythrocyte membrane | 10.1007/s10237-014-0559-7 |
2014-10-01 | In this work, we study the synchronization of two coupled chaotic oscillators. The uncoupled system corresponds to a mass attached to a nonlinear spring and driven by a rolling carpet. For identical oscillators, complete synchronization is analyzed using Lyapunov stability theory. This first analysis reveals that stability area of synchronization increases with the values of the coupling coefficient. Numerical simulations are shown to illustrate and validate stick-slip and chaos synchronization. Some cases of anti-synchronization are detected. Curiously, amplification of fixed point either regular or chaotic is observed in the area of anti-synchronization. Furthermore, phase synchronization is studied for nonidentical oscillators. It appears that for certain values of the coupling coefficient, coincidence of the phases is obtained, while the amplitudes remain uncorrelated. Contrarily to the case of complete synchronization, it does not exist a threshold of the coupling from which phase synchronization could appear. Besides, when we add the modified tuned mass damper on the structure, the behavior of the system can change including the appearance of synchronization, particularly in the region of fixed point. More precisely, complete synchronization is improved in the region of fixed point, while the damage of synchronization is observed when the velocity of the carpets is less than $$0.30$$ 0.30 . | Effect of coupling, synchronization of chaos and stick-slip motion in two mutually coupled dynamical systems | 10.1007/s11071-014-1504-0 |
2014-10-01 | Analysis of experimental data shows that the nature of the oscillating motion of an aircraft does not depend uniquely on the value of the coefficients of aerodynamic damping derivatives. The present work makes an attempt to explain this phenomenon and develops a methodology to adequately characterize the oscillating motion of aircraft based on the analysis of the coefficients of aerodynamic damping derivatives. | Method determining the nature of oscillating motion of the aircraft based on the analysis of coefficients of aerodynamic damping derivatives | 10.1134/S0869864314050060 |
2014-10-01 | Nonlinear damping suspension is a promising method to be used in a rotor-bearing system for vibration isolation between the bearing and environment. However, the nonlinearity of the suspension may influence the stability of the rotor-bearing system. In this paper, the motions of a flexible rotor in short journal bearings with nonlinear damping suspension are studied. A computational method is used to solve the equations of motion, and the bifurcation diagrams, orbits, Poincaré maps, and amplitude spectra are used to display the motions. The results show that the effect of the nonlinear damping suspension on the motions of the rotor-bearing system depends on the speed of rotor: (a) For low speeds, the rotor- bearing system presents the same motion pattern under the nonlinear damping ( $$p=0.5, 2, 3$$ p = 0.5 , 2 , 3 ) suspension as for the linear damping ( $$p=1$$ p = 1 ) suspension; (b) For high speeds, the effect of nonlinear damping depends on a combination of the damping exponent and damping coefficient. The square root damping model ( $$p=0.5$$ p = 0.5 ) shows a wider stable speed range than the linear damping for large damping coefficients. The quadratic damping ( $$p=2$$ p = 2 ) shows similar results to linear damping with some special damping coefficients. The cubic damping ( $$p=3$$ p = 3 ) shows more stable response than the linear damping in general. | Effects of nonlinear damping suspension on nonperiodic motions of a flexible rotor in journal bearings | 10.1007/s11071-014-1526-7 |
2014-10-01 | In order to solve fretting instability problem of gear shaft shoulder due to torsional vibration in mechanical system, the mathematical model of fretting instability vibration of gear shaft shoulder was established by adopting the method of combining kinematics and tribology, and the numerical analysis was applied to the fretting instability mechanism of gear shaft shoulder by introducing the friction instability damping ratio. The numerical results show that the main factors causing the unstable and vibrating gear shaft shoulder are the large tightening torque and too large static friction coefficient. The reasonable values of the static friction coefficient, the amount of interference and tightening torque can effectively mitigate the fretting instability phenomenon of gear shaft shoulder. The experimental results verify that damping plays a significant role in eliminating the vibration of gear shaft control system. | Fretting instability characteristics for gear shaft shoulder | 10.1007/s11771-014-2358-9 |
2014-10-01 | Most of modern tall buildings using lighter construction materials with high strength and less stiffness are more flexible, which occurs excessive wind-induced vibration, resulting in occupant discomfort and structural unsafety. It is necessary to predict wind-induced vibration response and find out a method to mitigate such an excessive wind-induced vibration at the preliminary design stage. Recently, many studies have been conducted in using actuator control force based on the linear quadratic optimum control algorithm. It was accepted as a common knowledge that the performance of passive tuned mass damper (TMD) could increase by incorporating a feedback active control force in the design of TMD, which is called active tuned mass damper (ATMD). However, the fact that ATMD is superior to TMD to reduce wind-induced vibration of a tall building is still a question. The effectiveness of TMD for mitigating the along-wind vibration of a tall building was investigated. Optimum parameters of tuning frequency and damping ratio for TMD under a random load which has a white noise spectra were used. Fluctuating along-wind load acting on a tall building treated as a stationary Gaussian random process was simulated numerically using the along-wind load spectra. And using this simulated along-wind load, along-wind responses of a tall building with and without TMD were calculated and the effectiveness of TMD in mitigating the along-wind response of a tall building was found out. | Passive control of along-wind response of tall building | 10.1007/s11771-014-2388-3 |
2014-10-01 | In this paper, we obtain the critical exponent for a wave equation with structural damping and nonlinear memory: $$ u_{tt}-\triangle u + \mu\,(-\triangle)^{\frac12} u_t = \int\nolimits_0^t (t-s)^{-\gamma}\,|u(s,\cdot)|^p\,ds,$$ u t t - ▵ u + μ ( - ▵ ) 1 2 u t = ∫ 0 t ( t - s ) - γ | u ( s , · ) | p d s , where μ > 0. In the supercritical case, we prove the existence of small data global solutions, whereas, in the subcritical case, we prove the nonexistence of global solutions for suitable arbitrarily small data, in the special case μ = 2. | A wave equation with structural damping and nonlinear memory | 10.1007/s00030-014-0265-2 |
2014-10-01 | The problem of minimizing the dynamics response of a damped cantilever Timoshenko beam subjected to earthquake excitation is investigated in this paper. The ground acceleration is expressed in terms of a Fourier series that is modulated by an enveloping function. The method of lines and modal approach are developed for analyzing the eigenvalues and the flexural vibrations. A magneto rheological damper is proposed to reduce the vibration of the structure. The device is localized at a specific point of the beam. A modal shape which characterizes the vibration of the uncontrolled and controlled system is obtained. The condition of stability of the controlled system is derived using the Routh–Hurwitz criterion. | Dynamics and magneto-rheological control of vibration of cantilever Timoshenko beam under earthquake loads | 10.1007/s11071-014-1429-7 |
2014-09-10 | This paper is concerned with the Cauchy problem of nonlinear wave equations with potential, strong, and nonlinear damping terms. Firstly, by using variational calculus and compactness lemma, the existence of standing waves of the ground states is obtained. Then the instability of the standing wave is shown by applying potential-well arguments and concavity methods. Finally, we show how small the initial data are for the global solutions to exist. | Standing waves and global existence for nonlinear wave equations with potential, strong, and nonlinear damping terms | 10.1186/s13661-014-0144-0 |
2014-09-01 | The experimental equipment, model, test conditions, and methods used for determining the streamwise damping on a setup with free oscillations on rolling bearings are described. Characteristics of aerodynamic damping of the model with two positions of the rotation axis and Mach numbers M_∞ = 2, 4, and 6 are measured. Irregular oscillations of the model with a greater displacement of the rotation axis with respect to the longitudinal axis are found to arise at M_∞ = 2. | Damping characteristics of a reentry vehicle at hypersonic velocities | 10.1134/S0021894414050162 |
2014-09-01 | The dynamic Hartree-Fock theory with point-like interaction is used to calculate the speed of sound and damping factor of a zero-sound wave propagating in a degenerate Fermi gas. This wave propagates slower than Fermi velocity. It is shown, that if the interaction is weak and density is small, then the damping of such a wave can be small. A possibility of discovering such waves in ultracold Fermi gases is discussed. | “Slow” wave of zero-sound in degenerate Fermi gas | 10.2478/s11534-014-0491-6 |
2014-09-01 | An analytical model based on a nonlinear deflection equation and the Reynolds equation is proposed to describe the dynamic behavior of an electrically actuated micro-beam with two piezoelectric layers. The proposed model takes explicit account of the fringing field effect, the axial stress effect, the residual stress effect, and the squeeze-film damping effect between the micro-beam and the lower electrode. The nonlinear governing equation of the micro-beam is solved using a hybrid computational scheme comprising the differential transformation method and the finite difference method. The validity of the analytical model and numerical solution procedure is demonstrated by comparing the result obtained for the pull-in voltage of a micro-beam actuated by a DC voltage only with that presented in the literature. It is shown that the nonlinear dynamic response of the micro-beam can be controlled using a combined driving scheme consisting of both the magnitude and the frequency of the AC actuating voltage and a DC driving voltage. The effects of the AC/DC actuating conditions, micro-beam geometry parameters, and squeeze-film damping force on the center-point displacement of the micro-beam are systematically examined. In addition, the actuating conditions which ensure the stability of the micro-beam are identified by means of phase portraits and Poincaré maps. In general, the results show that the analytical model and hybrid numerical scheme provide a feasible means of analyzing the dynamic response of a variety of electrostatically-actuated microstructures. | Analysis of nonlinear dynamic behavior of electrically actuated micro-beam with piezoelectric layers and squeeze-film damping effect | 10.1007/s11071-014-1384-3 |
2014-09-01 | This paper deals with the nonlinear vibration of a beam subjected to a tensile load and carrying multiple spring–mass–dashpot systems. The nonlinearity is attributable to mid-plane stretching, damping, and spring constant. Explicit expressions are presented for the frequency equations, mode shapes, nonlinear frequency, and modulation equations. The validity of the results is demonstrated via comparison with results in the literature. Parametric studies are conducted on beams with varying boundary conditions to investigate the effect of the location and magnitude of the spring–mass–dashpot system, as well as the role of the tension. | Nonlinear vibration of an axially loaded beam carrying multiple mass–spring–damper systems | 10.1007/s11071-014-1402-5 |
2014-09-01 | The Hopf and double Hopf bifurcations analysis of asymmetrical rotating shafts with stretching nonlinearity are investigated. The shaft is simply supported and is composed of viscoelastic material. The rotary inertia and gyroscopic effect are considered, but, shear deformation is neglected. To consider the viscoelastic behavior of the shaft, the Kelvin–Voigt model is used. Hopf bifurcations occur due to instability caused by internal damping. To analyze the dynamics of the system in the vicinity of Hopf bifurcations, the center manifold theory is utilized. The standard normal forms of Hopf bifurcations for symmetrical and asymmetrical shafts are obtained. It is shown that the symmetrical shafts have double zero eigenvalues in the absence of external damping, but asymmetrical shafts do not have. The asymmetrical shaft in the absence of external damping has a saddle point, therefore the system is unstable. Also, for symmetrical and asymmetrical shafts, in the presence of external damping at the critical speeds, supercritical Hopf bifurcations occur. The amplitude of periodic solution due to supercritical Hopf bifurcations for symmetrical and asymmetrical shafts for the higher modes would be different, due to shaft asymmetry. Consequently, the effect of shaft asymmetry in the higher modes is considerable. Also, the amplitude of periodic solutions for symmetrical shafts with rotary inertia effect is higher than those of without one. In addition, the dynamic behavior of the system in the vicinity of double Hopf bifurcation is investigated. It is seen that in this case depending on the damping and rotational speed, the sink, source, or saddle equilibrium points occur in the system. | Hopf bifurcation analysis of asymmetrical rotating shafts | 10.1007/s11071-014-1367-4 |
2014-09-01 | Ring-opening copolymerization of caprolactone and glycidyl methacrylate can generate cyclic and linear double-bond-functionalized copolymers. These polymers can be cross-linked by thiol–ene click reaction, and/or radical copolymerized with 2-hydroxyethyl methacrylate. Networks having interesting and variable damping properties were obtained. Poly(caprolactone-co-glycidyl methacrylate), p(CL-co-GMA), was prepared by ring-opening copolymerization in a one-step solvent-free process. 1,5,7-Triazabicyclo[4,4,0]dec-5-ene, stannous octoate and 4-hydroxybenzenesulfonic acid were tested separately as catalysts, and the copolymerization parameters were optimized. Analyses of the obtained copolymers, principally by matrix-assisted laser desorption/ionization–time of flight, confirmed the copolymerization, as macrocycles and linear chains were detected. Networks of p(CL-co-GMA) were prepared using 2-hydroxyethyl methacrylate and/or multi-mercapto coupling agents. Thermomechanical analyses of the obtained networks were conducted. Of particular importance, damping over a wide range of temperatures was observed for some materials. | Cross-linking and damping properties of poly(caprolactone-co-glycidyl methacrylate) | 10.1038/pj.2014.29 |
2014-09-01 | Using the IWOP technique, Wigner function theory and TFD theory, the quantization of a mesoscopic biological cell equivalent circuit is proposed, The quantum fluctuations of the mesoscopic biological cell are researched in thermal vacuum state and vacuum state. It is shown that the IWOP technique, Wigner function theory and Umezawa-Takahashi’s TFD theory play the key role in quantizing a mesoscopic biological cell at finite temperature and the fluctuations and uncertainty increase with increasing temperature and decrease with prolonged time. | The IWOP Technique and Wigner-Function Approach to Quantum Effect of Mesoscopic Biological Cell | 10.1007/s10773-014-2114-9 |
2014-09-01 | The problems of optimal design of structure-inhomogeneous thermostabilizing constructions have been investigated. Variational problems of the optimal design of structure-inhomogeneous thermostabilizing constructions have been formulated. The parameters determining the physicomechanical and geometric structures of the construction were varied. The quality functional in the variational problem determines the level of decrease in the temperature field intensity. On the basis of the necessary optimality conditions in the variational formulation asound structure of layerinhomogeneous constructions realizing the limiting possibilities for lowering the intensity level of the temperature field has been investigated. | Methods of Investigating the Limiting Possibilities of Structure-Inhomogeneous Thermostabilizing Constructions | 10.1007/s10891-014-1104-3 |
2014-09-01 | Magnetorheological (MR) damper is one of the most advanced applications of semi active damper in controlling vibration. Due to its continuous controllability in both on and off state its practice is increasing day by day in the vehicle suspension system. MR damper’s damping force can be controlled by changing the viscosity of its internal magnetorheological fluids (MRF). But still there are some problems with this damper such as MR fluid’s sedimentation, optimal design configuration considering all components of the damper. In this paper both 2-D Axisymmetric and 3-D model of MR Damper is built and finite element analysis is done for design optimization. Different configurations of MR damper piston, MR fluid gap, air gap and Dampers housing are simulated for comparing the Dampers performance variation. From the analytical results it is observed that among different configurations single coil MR damper with linear plastic air gap, top and bottom chamfered piston end and medium MR fluid gap shows better performance than other configurations by maintaining the same input current and piston velocity. Further an experimental analysis is performed by using RD-8041-1 MR Damper. These results are compared with the optimized MR Damper’s simulation results, which are clearly validating the simulated results. | Optimal design of Magneto-Rheological damper comparing different configurations by finite element analysis | 10.1007/s12206-014-0828-5 |
2014-09-01 | An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring (FVSS), can be widely used, especially in tuned mass dampers (TMDs) with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper bounds through a small change of distance between its supports. This special feature results in lower time-lag errors and readjustment in shorter time intervals. The governing equations of the device are derived and simplified for a symmetrical FVSS with similar elements. This device is then used to control a single-degree-of-freedom (SDOF) structure as well as a multi-degree-of-freedom (MDOF) structure via a semi-active TMD. Numerical simulations are conducted to compare several control cases for these structures. To make it more realistic, a real direct current motor with its own limitations is simulated in addition to an ideal control case with no limitations and both the results are compared. It is shown that the proposed device can be effectively used to suppress undesirable vibrations of a structure and considerably improves the performance of the controller compared to a passive device. | A novel semi-active TMD with folding variable stiffness spring | 10.1007/s11803-014-0258-5 |
2014-09-01 | Isolation bearings and dampers are often installed between piers and superstructures to reduce the seismic responses of bridges under large earthquakes. This paper presents a novel steel damper for bridges. The damper employs steel plates as energy dissipation components, and adopts a vertical free mechanism to achieve a large deformation capacity. Quasi-static tests using displacement-controlled cyclic loading and numerical analyses using a finite element program called ABAQUS are conducted to investigate the behavior of the damper, and a design methodology is proposed based on the tests and numerical analyses. Major conclusions obtained from this study are as follows: (1) the new dampers have stable hysteresis behavior under large displacements; (2) finite element analyses are able to simulate the behavior of the damper with satisfactory accuracy; and (3) simplified design methodology of the damper is effective. | Development of steel dampers for bridges to allow large displacement through a vertical free mechanism | 10.1007/s11803-014-0249-6 |
2014-09-01 | An improved hydraulic yaw damper model with series in-service clearance and comprehensive stiffness was proposed by Wang et al. (Nonlinear Dyn 65(1–2):13–34 2011 ). In order to study how in-service parameter variations to the hydraulic yaw damper affect the dynamics of a Chinese $$\hbox {SS}_{9}$$ SS 9 locomotive, this study continued that research by establishing a multibody system (MBS) model of the $$\hbox {SS}_{9}$$ SS 9 locomotive–rail coupling system, and then validating the MBS model using field test data from the $$\hbox {SS}_{9}$$ SS 9 . Extensive simulations were performed, and the results demonstrated that both the effective stiffness and the small clearance accumulated between two ends of the damper due to wear and lack of maintenance had remarkable impacts on the locomotive’s critical speed and on its normal operation. The results also influenced the locomotive’s ride comfort, but the effect of the small clearance was more remarkable than that of the effective stiffness in this regard, and these parameters had little to no influence on the locomotive’s curve-negotiation performance. The small clearance and effective stiffness are usually omitted or simplified in engineering, and so it was important to apply the proposed in-service nonlinear damper model with series clearance and stiffness to a vehicle dynamics study and improve the accuracy of vehicle design. The study was also useful for setting pertinent vehicle maintenance standards in engineering to control the influence of such in-service parameter variations. | A locomotive’s dynamic response to in-service parameter variations of its hydraulic yaw damper | 10.1007/s11071-014-1393-2 |
2014-08-20 | In the case where nonlinearities are superquadratic at infinity, we study the existence of ground state homoclinic orbits for damped vibration systems without periodic conditions by using variational methods. Here the (local) Ambrosetti-Rabinowitz superquadratic condition is replaced by a general superquadratic condition. MSC: 49J40, 70H05. | Ground state homoclinic orbits of superquadratic damped vibration systems | 10.1186/1687-1847-2014-230 |
2014-08-01 | We present an experimental study about the vortex dynamics in liquid metal flow under the influence of confined non-homogeneous magnetic field, so-called magnetic obstacle. A permanent magnet installed on a moving rail beneath a cell, filled with eutectic alloy GaInSn, moves with constant velocities with the corresponding Reynolds number from $$Re = \text{125 to 2000}$$ R e = 125 to 2000 . The liquid metal flow patterns are recorded using a camera moving with the magnet. Small bubbles, which are a product of hydrochloric acid and GaInSn oxide reaction, illuminate the streamlines which are to be presented here. As the velocity and hence Reynolds number and interaction parameter change, complicated phenomena are visible inside the channel including formation of vortices or their suppression, symmetry breakdown, vortex duplication and vortex shedding. The vast number of instability-related phenomena present in the flow past a magnetic obstacle make it worth investigating. This leads to a better understanding of magnetic obstacle or even turbulence. Since it is impossible to present all the observed phenomena in detail in one paper, here we present only a few illustrative examples to provide an overall view of the phenomena occurring. We conclude with a discussion of the flow instabilities and comparison between the results of our experiments and the theoretical predictions of the reference literature. | Vortex dynamics in the wake of a magnetic obstacle | 10.1007/s12650-014-0204-7 |
2014-08-01 | A series of shake-table tests was conducted by inserting and replacing 4 different types of dampers, or by removing them in a full-scale 5-story steel frame building. The objective is to validate response-control technologies that are increasingly adopted for major Japanese buildings without being attested to-date by a major earthquake. Test results are briefly described, and good performance of the dampers and frame demonstrated. The concepts of the full-scale building tests and various contributions are discussed. The difficulty associated with full-scale dynamic testing is explained. | Full-scale dynamic testing of response-controlled buildings and their components: concepts, methods, and findings | 10.1007/s11803-014-0246-9 |
2014-08-01 | The dissipative properties of most structural materials are usually described by a viscous damping parameter determining the rate of energy dissipation. The parameter stem from the traditionally adopted rheological Kelvin model. However, the analytical description of the dynamic properties of modern structural materials, including biological materials, often poses difficulties, due to the fact that the stress–strain dependence in these materials is not linear. Therefore a method of determining of nonlinear form of dissipative characteristic $$ D\left( {x,\dot{x}} \right) $$ D x , x ˙ (is presented. As it is assumed, mathematical function of the characteristic consist of nonlinear term g ( x ) of arbitrary form and so called mixed term κ ( x ) v where κ ( x ) is a function of deformation x and v —velocity of deformation. The deformation of a viscoelastic element which is made of tested material can be measured as displacement x of a single mass m in relative to a point of a complex vibratory system. The proper analysis of the mass m movement allows to evaluate the form of the functions g ( x ) and κ ( x ) what is a fundamental aim of the presented method. Beside of analytical method description some computer examples are presented. The method can be useful in evaluation of modern structural material properties (e.g. composites). | An identification of nonlinear dissipative properties of constructional materials at dynamical impact loads conditions | 10.1007/s11012-014-9931-z |
2014-08-01 | The membranous utricle sac of the red-eared turtle was mounted in a piezoelectric actuated platform mounted on the stage of a light microscope. The piezoelectric actuator oscillated the base of the neuroepithelium along a linear axis. Displacements were in the plane of the utricle and consisted of a linear sinusoidal-sweep signal starting at 0 and increasing to 500 Hz over 5 s. This inertial stimulus caused measurable shear displacement of the otoconial layer’s dorsal surface, resulting in shear deformation of the gelatinous and column filament layers. Displacements of the otoconial layer and a reference point on the neuroepithelium were filmed at 2,000 frames/s with a high-speed video camera during oscillations. Image registration was performed on the video to track displacements with a resolution better than 15 nm. The displacement waveforms were then matched to a linear second-order model of the dynamic system. The model match identified two system mechanical parameters—the natural circular frequency ω _n and the damping ratio ζ —that characterized the utricle dynamic response. The median values found for the medial-lateral axis on 20 utricles with 95 % confidence intervals in parenthesis were as follows: ω _n = 374 (353, 396) Hz and ζ = 0.50 (0.47, 0.53). The anterior-posterior axis values were not significantly different: ω _n = 409 (390, 430) Hz and ζ = 0.53 (0.48, 0.57). The results have two relevant and significant dynamic system findings: (1) a higher than expected natural frequency and (2) significant under damping. Previous to this study, utricular systems were treated as overdamped and with natural frequencies much lower that measured here. Both of these system performance findings result in excellent utricle time response to acceleration stimuli and a broad frequency bandwidth up to 100 Hz. This study is the first to establish the upper end of this mechanical system frequency response of the utricle in any animal. | Experimental Measurement of Utricle System Dynamic Response to Inertial Stimulus | 10.1007/s10162-014-0456-x |
2014-08-01 | The analytic function of relativistic nonextensive distribution is given, and employed to solve the Landau damping of longitudinal oscillation in ultra-relativistic plasmas. The unified expression of Landau damping which reduces to the result in relativistic Maxwellian distributed plasmas in the extensive limit is obtained, and find that Landau damping is relevant to both the number and energy of resonant particles, which described by temperature and nonextensive parameters in relativistic nonextensive distribution. | Landau damping of longitudinal oscillation in ultra-relativistic plasmas by analytic function of nonextensive distribution | 10.1007/s10509-014-1917-8 |
2014-08-01 | A numerical study of an application of magnetorheological (MR) damper for semi-active control is presented in this paper. The damper is mounted in the suspension of a Duffing oscillator with an attached pendulum. The MR damper with properties modelled by a hysteretic loop, is applied in order to control of the system response. Two methods for the dynamics control in the closed-loop algorithm based on the amplitude and velocity of the pendulum and the impulse on–off activation of MR damper are proposed. These concepts allow the system maintaining on a desirable attractor or, if necessary, to change a position from one attractor to another. Additionally, the detailed bifurcation analysis of the influence of MR damping on the number of periodic solutions and their stability is shown by continuation method. The influence of MR damping on the chaotic behavior is studied, as well. | Magnetorheological damping and semi-active control of an autoparametric vibration absorber | 10.1007/s11012-014-9892-2 |
2014-08-01 | Metal passive energy dissipation dampers are widely used in building structures, but research into their use in high-voltage electrical installations has been limited. This paper employs the passive energy dissipation method for a high-voltage arrester as an example. Metal energy dissipation dampers are designed using the bilinear restoring force model. The factors affecting the damper, including the yield force, yield displacement and ratio between initial and postyield stiffness, which affect the damping efficiency, were analyzed in finite element numerical simulation. The dampers were designed with the optimum parameters found in numerical simulation and were installed at the bottom of an arrester in shake table tests. The dynamic reactions of the arrester with and without dampers were analyzed under the excitation of a resonance wave and artificial waves E and T. Results of simulation and tests show that the dampers designed with the optimum parameters significantly reduced the strain of the bottom of the porcelain bushing, and the damping efficiency increased with the acceleration peak. | Damping Efficiency Analysis of Metal Dampers for a High-Voltage Electrical Arrester | 10.1007/s13369-014-1291-4 |
2014-08-01 | Damping performance of a passive constrained layer damping (PCLD) structure mainly depends on the geometric layout and physical properties of the viscoelastic damping material. Properties such as the shear modulus of the damping material need to be tailored for improving the damping of the structures. This paper presents a topology optimization method for designing the microstructures in 2D, i.e., the structure of the periodic unit cell (PUC), of cellular viscoelastic materials with a prescribed shear modulus. The effective behavior of viscoelastic materials is derived through the use of a finite element based homogenization method. Only isotropic matrix material was considered and under such assumption it is found that the effective loss factor of viscoelastic material is independent of the geometrical configuration of the PUC. Based upon the idea of a Solid Isotropic Material with Penalization (SIMP) method of topology optimization, the relative material densities of the elements of the PUC are considered as the design variables. The topology optimization problem of viscoelastic cellular material with a prescribed property and with constraints on the isotropy and volume fraction is established. The optimization problem is solved using the sequential linear programming (SLP) method. Several examples of the design optimization of viscoelastic cellular materials are presented to demonstrate the validity of the method. The effectiveness of the design method is illustrated by comparing a solid and an optimized cellular viscoelastic material as applied to a cantilever beam with the passive constrained layer damping treatment. | Topology optimization of microstructures of viscoelastic damping materials for a prescribed shear modulus | 10.1007/s00158-014-1049-3 |
2014-08-01 | Silica gel, a typical desiccant widely used in industry to absorb moisture, is a porous inert colloid with different sizes in beaded or angular shape. The mixture of silica gel and pore fluid of matched refractive index has been used as transparent media to mimic the behavior of sand. Previous studies have been focused on the static properties of transparent soil. In the current study, the dynamic properties of silica gel, including small-strain shear modulus and damping ratio, were examined through a series of resonant column tests. Four different gradations of silica gel were tested under confining pressures of 50, 100, 200, 300, and 400 kPa. The test results fully displayed the dynamic behavior of the silica gel. The test data also revealed that silica gel has a certain similar dynamic behavior as those of natural soils. With the test findings, silica gel could be used as a surrogate for natural soils in dynamic transparent soil model tests. | Investigation on the shear moduli and damping ratios of silica gel | 10.1007/s10035-014-0495-3 |
2014-08-01 | This paper presents the design, formulation, and performance optimization of a new hybrid electromagnetic damper in response to the demand for a tunable, regenerative and fail-safe damping device for various applications. Damping in a multitude of engineering applications has a variable threshold requirement based on system excitation. Since system excitation is also variable; dampers are such that an adequate amount of damping is provided, opposed to an optimal amount as a function of excitation. In this research it was shown that, by implementing a hybrid damper design based on a bias component provided through a hydraulic medium and a variable component provided by electromagnetics, an optimal damping quantity can be obtained for a given excitation. The produced damping force and electrical power were formulated based on the structure’s geometry and input displacement. The presented design was optimized for a scooter scaled application and it was shown that the damping and regenerative characteristics can be adjusted for different requirements. Furthermore, it was illustrated that this design has the potential to be scaled for other applications as well. | Hybrid variable damping control: design, simulation, and optimization | 10.1007/s00542-014-2214-8 |
2014-08-01 | Clay soils are very useful as liners in geotechnical structures such as landfill sites, dams, water channels, etc. Swelling is a common problem in clay liners, however. To better understand swelling properties, in the present study clay nanocomposites were produced by means of the sol gel method, using a hydrophobic clay, polymers (locust bean gum, latex, glycerine, vinyl acrylic copolymer), and rubber powder. The study focused on the swelling and dynamic properties (secant shear modulus and damping ratio) of the clay nanocomposites researched experimentally in laboratory conditions. The dynamic tests were conducted on samples compacted using two different compaction energy levels. The test results were compared with those of natural clay and hydrophobic organo-clay. The test results revealed that the damping ratios and secant shear modulus of clay nanocomposites without rubber (CNC) and with rubber (CNCr) that were compacted with both the E1 and E2 energy levels were increased and decreased, respectively. In addition, with increasing percentage of vinyl acrylic in nanoclay composites, the secant shear modulus values were decreased and damping ratio values were increased. Consequently, the test results found that the swelling and dynamic properties of clay nanocomposites can be optimized in order to attenuate the negative effects of dynamic loads on clay liners. | The Dynamic Shear Modulus and Damping Ratio of Clay Nanocomposites | 10.1346/CCMN.2014.0620405 |
2014-08-01 | Fluid viscous dampers are extensively adopted as efficient and cheap energy dissipation devices in structural seismic protection. If we consider the usefulness of these passive control devices, the exact recognition of their mechanical behavior is of outstanding importance to provide a reliable support to design a very efficient protection strategy. In scientific and technical applications, many different constitutive models have been proposed and adopted till now to represent fluid viscous dampers, with different levels of complexity and accuracy. This paper focuses on parameter identification of fluid viscous dampers, comparing different existing literature models, with the aim to recognize the ability of these models to match experimental loops under different test specimens. The identification scheme is developed evaluating the experimental and the analytical values of the forces experienced by the device under investigation. The experimental force is recorded during the dynamic test, while the analytical one is obtained by applying a displacement time history to the candidate mechanical law. The identification procedure furnishes the device mechanical parameters by minimizing a suitable objective function, which represents a measure of the difference between the analytical and experimental forces. To solve the optimization problem, the particle swarm optimization is adopted, and the results obtained under various test conditions are shown. Some considerations about the agreement of different models with experimental data are furnished, and the sensitivity of identified parameters of analyzed models against the frequency excitation is evaluated and discussed. | A comparative study on parameter identification of fluid viscous dampers with different models | 10.1007/s00419-014-0869-3 |
2014-08-01 | This paper deals with a novel type of the friction damping brace systems and its development using slip resistance for seismic retrofitting of damaged structures. In the system, slotted bolt holes are placed on the shear faying surface with a view to dissipating a considerable amount of passive energy. Superelastic shape memory alloy (SMA) wire strands that enable self-centering mechanism and enhanced energy dissipation capacity are also installed between brace members. Self-centering friction damping braces (SFDBs) treated in this study have the desirable potential to efficiently reduce residual inter-story drifts in the braced frames during seismic events as compared to conventional passive damping systems. The SFDB system mechanism is described, and then its parametric study accounting for recentering capability and dissipative energy is carried out using numerical models that are calibrated with experimental data. Based upon the parametric investigation, this study suggests an optimal design methodology for establishing the smart self-centering bracing system. | Performance-based optimal design of self-centering friction damping brace systems between recentering capability and energy dissipation | 10.1007/s12206-014-0721-2 |
2014-07-30 | This paper proposes designing of Static Synchronous Series Compensator (SSSC) based damping controller to enhance the stability of a Single Machine Infinite Bus (SMIB) system by means of Invasive Weed Optimization (IWO) technique. Conventional PI controller is used as the SSSC damping controller which takes rotor speed deviation as the input. The damping controller parameters are tuned based on time integral of absolute error based cost function using IWO. Performance of IWO based controller is compared to that of Particle Swarm Optimization (PSO) based controller. Time domain based simulation results are presented and performance of the controllers under different loading conditions and fault scenarios is studied in order to illustrate the effectiveness of the IWO based design approach. | Design of static synchronous series compensator based damping controller employing invasive weed optimization algorithm | 10.1186/2193-1801-3-394 |
2014-07-01 | Every transducer needs some deconvolution operation to return the original signal. In the seismometer’s case, this is usually done by using the pole-zero instrument models. This method assumes that the seismometer can be described by a linear model that can be schematized by a ratio of polynomials of the Laplace variable s . This paper shows a deconvolution method that uses the mechanic-electric model of a transducer. Such a model can also give a better description of a transducer since it can also take into account nonlinear behavior which cannot be included in pole-zero models. Examples of deconvolution of both linear and nonlinear transfer functions are shown, and some considerations about friction damping and the electromechanical analogies used to perform the simulations are included in the appendix. | Deconvolving seismic signals with a SPICE model of the seismometer | 10.1007/s10950-014-9425-4 |
2014-07-01 | The aerodynamic component of damping of a vibrating plate in the range of parameters characteristic of damped flexural vibrations of test specimens is investigated. On the basis of a large series of numerical simulations in the dynamics of two-dimensional flow of gas around a plate, we managed to suggest a unified approximating equation for the damping constant in terms of dimensionless parameters of the process considered. | Theoretical-Experimental Method for Determining the Parameters of Damping Based on the Study of Damped Flexural Vibrations of Test Specimens 2. Aerodynamic Component of Damping | 10.1007/s11029-014-9413-3 |
2014-07-01 | NiTi exhibits distinct damping properties associated with the martensite-austenite transformation. We fabricated net-shape NiTi parts layer-by-layer using a laser beam that locally melted the NiTi powder. The damping properties of such NiTi parts were analyzed by the decay of cantilever vibrations in comparison to conventionally prepared NiTi. The dynamic modulus as a function of the temperature was derived from the resonant frequency. We found that the two cantilevers showed a damping ratio of about 0.03 at temperatures below austenite start, maximal values of up to 0.04 in the transformation regions and low values of about 0.005 above austenite finish. The results indicate that selective-laser-melted NiTi qualifies for the fabrication of shock-absorbing medical implants in the same manner than conventionally produced NiTi. | Damping of Selective-Laser-Melted NiTi for Medical Implants | 10.1007/s11665-014-0889-8 |
2014-07-01 | For structures deployed in space using cables where vibration damping is critical for structural stability, cable damping is significant to structural performance. To provide a better understanding of damping mechanism of carbon fiber cables, this paper describes the tests of cable damping under different experimental configurations (different cable length, tension and type), and presents an analytical method for modeling and therefore predicting cable damping. The method is developed using simplified but physically realistic assumptions on material constitutive properties and geometric compatibility conditions, and considered the contact forces and friction between helical wires. The results of the proposed method and several related issues are discussed and compared with those from experiments. These results show that the proposed method is useful and applicable for predicting cable damping value and its variation with cable tension, length and type of the cables. | Experimental and Analytical Investigation of Carbon Fiber Cable Vibration Damping | 10.1007/s11340-014-9878-y |
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