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2020-01-01 | Active vibration dampers can reduce or eliminate unwanted vibrations, but determining a good control policy can be challenging for highly nonlinear systems. For these types of systems, reinforcement learning is one method to optimize a control policy with only limited prior knowledge of the system dynamics. An experimental system was constructed by attaching a permanent magnet to the end of a pendulum and positioning an electromagnetic actuator below the resting position of the pendulum. The pendulum was excited with a sinusoidal force applied horizontally at the pivot point, and the control input was the applied voltage across the electromagnet. Due to the geometric arrangement and the strong dependence of magnetic force on distance, the relationship between the position of the pendulum and the actuation torque for any control input was highly nonlinear. A generalized version of the PILCO reinforcement learning algorithm was used to optimize a control policy for the electromagnet with the objective of minimizing the distance between the end of the pendulum and the downward position. After 16 s of interaction with the experimental system, the resulting learned policy was able to substantially reduce the amplitude of oscillation. This experiment illustrates the applicability of reinforcement learning to highly nonlinear active vibration damping problems. | Reinforcement Learning for Active Damping of Harmonically Excited Pendulum with Highly Nonlinear Actuator | 10.1007/978-3-030-12391-8_15 |
2020-01-01 | Damping plays an important role in the simulation of the mechanical system. Various damping models are used such us non-viscous damping, coulomb damping, and hysteresis damping. For mathematical convenience, Rayleigh damping is usually used in a gear system to model damping. Rayleigh damping coefficients (RDCs) can be identified using the frequencies when the degree of freedom of the system is low. However, for complex systems, problems of selecting the frequencies of the RDCs are presented. The classical methods used only a constant damping ratio for all modes can underestimate the dynamic response. Continuous wavelet transforms (CWT) method is recently used to identify the modal parameters such as the natural frequencies and the damping ratios. This study presents initial research into the use of the CWT method to select the optimal frequencies of the Rayleigh damping formulation to identify RDCs. The RDCs are identified using the modes contributing to the dynamic response of the two-stage gear system. The modes that remarkably affect the dynamic responses are determined on the basis of the modes corresponding to the maximum values of the wavelet spectrum. The proposed method is validated using the simulated responses of a two-stage gear system and compared with the classical methods. | Rayleigh Damping Coefficients Identification Using the Wavelet Transform on Two Stage Gear System | 10.1007/978-3-030-24247-3_23 |
2020-01-01 | The fast mechanical switch equipped with the Thomson-coil actuator is one of the key devices in hybrid HVDC circuit breaker. And electromagnetic damping technology can solve the problems of high-speed damping operation without adding additional mechanical parts. In order to make the opening/closing operation process as unified as possible, the driving and damping voltages are the same in the previous research. In this paper, the effects of different combinations of driving and damping voltages on the travel characteristics have been studied. Voltage combinations are divided into three types. The first type is to change the driving and damping voltage at the same time; the second is to keep the damping voltage constant and change the driving voltage; the last type is to keep the driving voltage constant and change the damping voltage. In order to ensure that the contacts system can move to the isolating distance in 3 ms, the driving voltage should not be reduced. At the same time, in order to ensure a better damping effect, the buffer start time range should be as large as possible. Therefore, it is suggested that the damping voltage is 2%–4% lower than the driving voltage. A fast simulation method based on equivalent circuit method, which avoids lots of test operations, has been proposed in this paper. It can provide reliable references for the application and improve the feasibility and reliability of fast mechanical switch in engineering. | Effect of Voltage on Thomson-Coil Actuator for Fast Mechanical Switch | 10.1007/978-3-030-31680-8_129 |
2020-01-01 | We consider the following Cauchy problem for a wave equation with time-dependent damping term b ( t ) u _ t and mass term m ( t )^2 u , and a time-dependent non-linearity h = h ( t , u ): u t t − Δ u + b ( t ) u t + m 2 ( t ) u = h ( t , u ) , t ≥ 0 , x ∈ ℝ n , u ( 0 , x ) = f ( x ) , u t ( 0 , x ) = g ( x ) . $$\displaystyle \begin {cases} u_{tt}-\Delta u+b(t)u_t+m^2(t)u=h(t,u), & t\geq 0, \ x\in \mathbb R^n,\\ u(0,x)=f(x), \quad u_t(0,x)=g(x). \end {cases} $$ Here, we consider an effective time-dependent damping term and a time-dependent mass term, in the case in which the mass is dominated by the damping term, i.e. m ( t ) = o ( b ( t )) as t → ∞ . Under suitable assumptions on the non-linearity h = h ( t , u ) (Hypothesis 1.3), we prove the global existence of small data solutions in a supercritical range p > p ̄ $$p>\bar p$$ , assuming small data in the energy space ( f , g ) ∈ H ^1 × L ^2. | Small Data Solutions for Semilinear Waves with Time-Dependent Damping and Mass Terms | 10.1007/978-3-030-36138-9_14 |
2020-01-01 | This paper presents the full spectrum analysis of a cracked Jeffcott rotor with the internal and external damping. In this study, a mathematical model is developed for a Jeffcott rotor considering both external and internal damping, crack force, and unbalance force. The crack in the rotor model is considered as switching crack function in the form of a rectangular shape, which provide forces that generate the forward and backward whirls at varied harmonics. The assumption of weight dominance simplifies the switching crack model to a linear one; however, it gives rise to the internal damping due to rubbing on crack faces. The rotor model is numerically simulated to provide responses from two orthogonal directions to obtain the full spectrum analysis to show both forward and backward whirls. | A Full Spectrum Analysis of a Jeffcott Rotor with Switching Crack in the Presence of Internal and External Damping | 10.1007/978-981-15-5693-7_9 |
2020-01-01 | Abstract An asymptotic method for investigating small oscillations of fluids in cylindrical tanks with longitudinal damping partitions is presented. The effect of the number and width of partitions on the hydrodynamic parameters and the damping coefficients of fluid oscillations is studied in detail for the case of a circular cylindrical enclosure with a plane bottom. The numerical results are obtained using the finite element method. Basing on the asymptotic theory of vortex resistance a perturbation method applicable for determining the fluid oscillation damping in tanks of arbitrary shape with partitions of small relative width is developed. | Fluid Oscillations in Cylindrical Tanks with Longitudinal Damping Partitions | 10.1134/S001546281906003X |
2020-01-01 | The article is dedicated to the study of anti-vibration properties of vehicle suspension at optimal instantaneous damping control in oscillation cycle. These suspensions in foreign literature are called “semi-active control suspensions.” However, its vibration isolation properties have not been thoroughly analyzed. This article presents ineffective damper zones in the oscillation cycle, mathematical models of vehicle suspension, and the results of theoretical and experimental study of vibration isolation properties of one- and two-mass oscillation systems simulating a suspension at optimal instantaneous damping control in the oscillation cycle. The results in the form of amplitude-frequency characteristics of sprung and unsprung masses displacement and accelerations, waveforms of resonant oscillations and elastic-damping characteristics of oscillation systems at resonance proved that optimal instantaneous damping control does not improve vibration isolation properties in response to shocks and noise in the suspension, thus setting a problem of searching and studying the ways of a smooth damping change in the oscillation cycle. | Vibration Isolation Properties of Vehicle Suspension at Optimal Instantaneous Damping Control in Oscillation Cycle | 10.1007/978-3-030-22041-9_87 |
2020-01-01 | The logarithmic decrement method is perhaps the most common technique for estimating the damping ratio of linear systems with viscous damping. The approach directly relates the damping ratio to two samples collected from peaks of a recorded free oscillation. These peaks are separated by one or more oscillation periods and are inherently influenced by experimental uncertainty. Literature on the method indicates that improved estimates are sometimes obtained with more periods between samples. However, it is unknown when improvements can be expected for a given data set because there is a trade-off between the chosen number of periods and measurement noise. A guideline for selecting the number of periods which minimizes uncertainty in estimated damping is desired. In this work, an analytical expression is derived for the optimal number of periods between peaks. This expression, obtained from an uncertainty analysis of the logarithmic decrement equation, is shown to be a function of only one system parameter: the damping ratio. This suggests that for linear systems with viscous damping there is a unique, damping-dependent period choice which guarantees minimum uncertainty in the estimated damping ratio. This result is used to obtain an optimal amplitude ratio which offers a simple, accurate, and easy to implement guideline for selecting a second sample. The derived expressions are applied to a set of numerical systems to confirm their validity. | Optimizing Logarithmic Decrement Damping Estimation via Uncertainty Analysis | 10.1007/978-3-030-12243-0_3 |
2020-01-01 | In this chapter, we study the electrostatic boundary-value problems involving planar two-dimensional electron gas layers. The main interest and the key first applications of presented boundary-value problems concern doped graphene, while keeping in mind the analysis can be applied to semiconductor inversion layers, high electron mobility transistor, and potentially other planar two-dimensional electron gas systems. For brevity, in many sections of this chapter the exp ( − i ω t ) $$\exp (-i\omega t)$$ time factor is suppressed. Furthermore, all media under consideration are nonmagnetic and attention is only confined to the linear phenomena. | Electrostatic Problems Involving Two-Dimensional Electron Gases in Planar Geometry | 10.1007/978-3-030-43836-4_6 |
2020-01-01 | In acoustoelectric and piezotronic devices, the redistribution or motion of charge carriers is caused or affected by mechanical loads through the electric field produced via piezoelectric coupling. This coupling can also happen in composite structures of piezoelectric dielectrics and nonpiezoelectric semiconductors. In this chapter we study a few problems of this type. | Composite Structures | 10.1007/978-3-030-48206-0_6 |
2020-01-01 | Frequency spectra of torsional vibration and contact force are very important to understand the dynamic behavior of a horizontal axis wind turbine drivetrain system (WTDS). The drivetrain has three gear stages, namely one planetary and two parallel gear stages. Hence, a mathematical model is developed to understand the dynamic behavior of the system using a lumped parameter model. Governing equations of motion are derived using Lagrange’s formulation by taking the kinetic and potential energy of the system into Lagrange’s function. The equations of motion include time varying parameters like time varying gear mesh stiffness and damping coefficient, which are estimated by analytical approach. The concept of mesh phasing is incorporated in the first stage of drivetrain. Steady-state dynamic responses are computationally obtained using Houbolt method and responses are analyzed in time and frequency domain. Thus, effect of damping on WTDS has been studied. | Dynamic Analysis of Wind Turbine Drivetrain Under Constant Torque | 10.1007/978-981-15-4032-5_55 |
2020-01-01 | Large-capacity wind farms may increase the risk of torsional vibration of turbine generator shafts in the wind-thermal-bundled power transmitted by series-compensated system, therefore the analysis and suppression strategy of sub-synchronous oscillation (SSO) in such system needs to be thoroughly studied. In this paper, the mechanism of electromechanical torsional interaction and the influence of wind farm integration on system oscillation are analyzed. In order to suppress the SSO, the mechanism of electromagnetic torque increment produced by additional damping control of static synchronous compensator (STATCOM) is studies, based on which, a SSO damping controller is designed. Based on the complex torque coefficient approach and time domain simulation approach simulation cases are built in DIgSILENT/PowerFactory. The results show the impact of wind farm integration and series compensation degree on system damping and verify the suppression effect of STATCOM on system SSO. | Analysis and Suppression Strategy of Sub-synchronous Oscillation for Wind-Thermal-Bundled Power Transmitted by Series-Compensated System | 10.1007/978-981-13-9783-7_1 |
2020-01-01 | High Quality factor ( Q factor) resonator is a mandatory requirement for very fine resolution Hemispherical Resonator Gyroscope (HRG). It is a measure of damping. This paper discusses the role of Thermo Elastic Dynamic Damping (TEDD) when the resonator is operating in its functional vibration mode. Finite Element (FE) method is used to solve the coupled thermal and mechanical equations. A sensitive analysis of the effect of different parameters like resonator material properties, operating temperature, size, geometry, conductive metallic coating materials, multilayer coating, and coating thickness is carried out. The uniqueness of the present work is the sensitivity study of ultrathin coating (volume fraction of 0.01%), multilayer coating, and different partial coating configurations. The coating can reduce Q factor by orders compared to uncoated shell. It is found that the coating material selection and the coating configuration are very important factors and a Q factor of 5.5 × 10^6 in the final optimum coating configuration is achieved. | Design of Inertial Class Gyroscope Resonator with Ultrahigh Quality Factor for Interplanetary Space Missions | 10.1007/978-981-15-0124-1_95 |
2020-01-01 | In most of the applications of vibration compared to the elastic and inertia forces, the magnitude of damping forces is small. Under certain circumstances, these small forces may, however, create great influence. Damping is one of the important parameters in the study of dynamic systems. It is generally measured under conditions of cyclic motion and is defined as the energy dissipation in a mechanical system whose free oscillations decrease with time, resulting in a decrease in its amplitude of vibration. From a theoretical point of view, there are two different methods to measure damping, i.e., time response methods and frequency response methods. In rotating machinery, the measurement of damping by applying time response methods and frequency response methods is very difficult. Due to that reason, there is a lack of experiments to measure damping in rotating machinery. This paper discussed Kelvin–Voigt approach for measuring damping in mechanical systems. The mechanical system analyzed in this thesis is a rotating shaft. In general, damping can be explicit through different parameters as damping ratio ( ζ ) or loss factor ( η ). Therefore, the objective about this paper is to determine one of these parameters by means of measuring simple variables such as forces or displacements. | Analysis of Internal Damping in Rotating Shaft | 10.1007/978-981-15-1124-0_60 |
2020-01-01 | We study the linearized Vlasov equations and the linearized Vlasov–Fokker–Planck equations in the weakly collisional limit in a uniform magnetic field. In both cases, we consider periodic confinement and Maxwellian (or close to Maxwellian) backgrounds. In the collisionless case, for modes transverse to the magnetic field, we provide a precise decomposition into a countably infinite family of standing waves for each spatial mode. These are known as Bernstein modes in the physics literature, though the decomposition is not an obvious consequence of any existing arguments that we are aware of. We show that other modes undergo Landau damping. In the presence of collisions with collision frequency $$\nu \ll 1$$ ν ≪ 1 , we show that these modes undergo uniform-in- $$\nu $$ ν Landau damping and enhanced collisional relaxation at the time-scale $$O(\nu ^{-1/3})$$ O ( ν - 1 / 3 ) . The modes transverse to the field are uniformly stable and exponentially thermalize on the time-scale $$O(\nu ^{-1})$$ O ( ν - 1 ) . Most of the results are proved using Laplace transform analysis of the associated Volterra equations, whereas a simple case of Yan Guo’s energy method for hypocoercivity of collision operators is applied for stability in the collisional case. | The Linearized Vlasov and Vlasov–Fokker–Planck Equations in a Uniform Magnetic Field | 10.1007/s10955-019-02441-x |
2020-01-01 | In boring process, casted, forged, or extruded holes in components are finished with a boring bar having cutting insert at its frontend. Dynamic and static deflections are always there in the boring bar due to its slenderness. The generating force for chatter is supplied by the cutting process itself, so it creates problems in achieving desired productivity. The main goal of this research work is to amend the rendition of boring tool with the help of shim having good damping capacity, which is placed under the tool insert. Here, brass shim is used and experiments are performed with and without shim one by one on CNC machine. Whole experimental data of acceleration is collected using CoCo80 dynamic signal analyzer. Using this data, various plots like time response plot, frequency response plot, Poincare plot, orbit plot are obtained to check for motion behavior. Surface roughness is also measured using surface roughness tester. The proposed concept shows effective chatter suppression strategy in boring operation. | Experimental Investigation of Chatter in Boring Operation Using Shim | 10.1007/978-981-15-3746-2_23 |
2020-01-01 | An algorithm for controlling the hydraulic damping of an innovative articulation for an articulated vehicle was tested with respect to the stability of the vehicle movement while avoiding a road obstacle at 50 km/h by a double change of the lane. Related maneuvers were simulated using LabVIEW software. Two testing methods were employed - with the steering wheel motion being dependent or independent on delays introduced into the control loop. Simulation results according to the first method proved that the mean absolute slip angle of all the tires and the mean absolute lateral acceleration of the rear car centre of mass did not exceed, respectively, 0.65° and 0.55 m/s^2, whereas for the second method these values were lower than 0.85° and 0.75 m/s^2. In both methods the results depended on the delay in signal transmission. It was concluded that the control loop delay should be kept lower than 0.1 s. Moreover, this delay should be monitored and used as an input to the control algorithm, as in certain conditions deactivating the articulation damping in presence of excessive delays can be confusing to the driver. | Selected Tests of a Control System for an Articulated Vehicle with Innovative Articulation | 10.1007/978-3-030-29993-4_9 |
2020-01-01 | This paper presents a novel arrangement of a current blocking shunt circuit for the mitigation of multiple structural resonances. The number of required electrical components is reduced compared to the previous versions of this circuit proposed in the literature. This paper also proposes a tuning methodology for the electrical parameters of this circuit based on the evaluation of the electromechanical coupling between the electrical circuit and the structure. Effective mitigation performance can be expected with little knowledge of the host structure. A comparison with the solutions in the literature demonstrates the efficiency of the proposed approach. | A Simplified Current Blocking Piezoelectric Shunt Circuit for Multimodal Vibration Mitigation | 10.1007/978-3-030-12243-0_4 |
2020-01-01 | In order to avoid damage to mechanical structure, the vibration damping is necessary. The conventional methods of damping are less effective as well as tedious. This paper deals with passive techniques of vibration damping using piezoelectric material. Piezoelectric materials called as smart materials are bonded to structure and can be used as actuator as well as sensor. By rigorous variations of R and L values, a RLC circuit is designed, which nullifies the vibrations at the frequency of resonance. It results in 80% of vibration damping as compared to conventional methods. | Effective Vibration Damping Using Self-tuning Smart Material | 10.1007/978-981-15-2329-8_7 |
2020-01-01 | This paper presents preliminary experimental results from a novel shaking table testing campaign investigating the dynamic response of a two-degree-of-freedom (2DOF) physical specimen with a grounded inerter under harmonic base excitation and contributes a nonlinear dynamic model capturing the behavior of the test specimen. The latter consists of a primary mass connected to the ground through a high damping rubber isolator (HDRI) and a secondary mass connected to the primary mass through a second HDRI. Further, a flywheel-based rack-and-pinion inerter prototype device is used to connect the secondary mass to the ground. The resulting specimen resembles the tuned mass damper inerter (TMDI) configuration with grounded inerter analytically defined and numerically assessed by the authors in a number of previous publications. Physical specimens with three different inerter coefficients are tested on the shake table under sine-sweep excitation with three different amplitudes. Experimental frequency response functions (FRFs) are derived manifesting a softening nonlinear behavior of the specimens and enhanced vibration suppression with increased inerter coefficient. Further, a 2DOF parametric nonlinear model of the specimen is established accounting for non-ideal inerter device behavior and its potential to characterize experimental response time-histories, FRFs, and force-displacement relationships of the HDRIs and of the inerter is verified. | Shake Table Testing of a Tuned Mass Damper Inerter (TMDI)-Equipped Structure and Nonlinear Dynamic Modeling Under Harmonic Excitations | 10.1007/978-3-030-41057-5_122 |
2020-01-01 | Vibrating flip-flow screens provide an effective solution for screening highly viscous or fine materials. However, only linear theory has been applied to their design. Yet, to understand deficiencies and to improve performance an accurate model especially of the rubber shear springs equipped in screen frames is critical for its dynamics to predict, e.g. frequency- and amplitude-dependent behaviour. In this chapter, the amplitude dependency of the rubber shear spring is represented by employing a friction model in which parameters are fitted to an affine function rather constant values used for the classic Berg’s friction model; the fractional derivative model is used to describe its frequency dependency and compared to conventional dashpot and Maxwell models with its elasticity being represented by a non-linear spring. The experimentally validated results indicate that the proposed model with a non-linear spring, friction and fractional derivative model is able to more accurately describe the dynamic characteristics of a rubber shear spring compared with other models. | A Non-linear Model of Rubber Shear Springs Validated by Experiments | 10.1007/978-3-030-34713-0_32 |
2020-01-01 | Reduction of the vibration amplitude is often problem in mechanical and civil engineering. Damping of the oscillation could be done by changing the mass and stiffness. This approach often requires a change in the constructive system solution. The alternative is active vibration damping systems, which, depending on the vibration states of the system they are part of, can induce the vibrations that by superimposition lead to their reduction. This paper presents an overview the vibration damping system (active and passive) and the principle of the mechatronic system for active vibration damping. | Systems for Passive and Active Vibration Damping | 10.1007/978-3-030-18072-0_10 |
2020-01-01 | Surface treatments on aluminum substrates are introduced to improve the bonding characteristics between rubber and aluminum components that are widely used in automotive industries. This present work involves the modification of surface roughness of aluminum plates either by sand blasting or anodizing or graphene coating followed by primer coating. Finally, rubber was vulcanized on these surfaces and aluminum-rubber interface were characterized. Sand blasted aluminum surface sample provides the best damping performance with a capacity of 50% damping. Although, aluminum treated with graphene has not been shown better damping properties, aluminum treated with sand blasting and graphene shows equivalent damping performance as that of sand blasted sample with similar average surface roughness (Ra) of 3.2 µm. | Effect of Aluminum Surface Treatment on the Damping Properties of Aluminum-Rubber Bonding System | 10.1007/978-981-15-0950-6_76 |
2020-01-01 | One of the greatest challenges to the optimization of assembled systems is a lack of understanding of how jointed interfaces augment system dynamics. Thus, a design tool that can assess the nonlinearity of a joint prior to manufacturing and experimentation will lead to significant savings in qualification testing and improved performance in terms of dynamic properties and failure rates. This paper explores the a priori metric hypothesis for jointed structures, which states that the strength of a nonlinearity (SNL) can be estimated by a metric derived from both the magnitude and uniformity of contact pressure within an interface and the modal strain energy at an interface’s location. | A Priori Methods to Assess the Strength of Nonlinearities for Design Applications | 10.1007/978-3-030-12391-8_35 |
2020-01-01 | In order to further improve the average off-road speed of special vehicles, a semi-active oil and gas spring design scheme is proposed, and the multi-stage damping adjustable function can be realized by parallel proportional throttle valve. Based on the physical model of oil and gas springs, the series-parallel relationship of adjustable damping throttling is extracted, and the derivation of analytical equations between flow and differential pressure is carried out; In addition, the flow characteristics of the proportional throttle valve were fitted by least squares fitting, and the exact correspondence between current and flow coefficient was obtained. Combined with the actual gas state equation, the simulation results of the oil and gas springs under different currents are simulated and compared with the experimental data to verify the correctness of the model; Finally, the analysis of the influencing factors of the performance characteristics was carried out, which laid the foundation for the design of oil and gas springs. | Modeling and Simulation Analysis of Semi-active Oil and Gas Spring Characteristics | 10.1007/978-3-030-34387-3_51 |
2020-01-01 | Abstract The mechanical and damping characteristics of titanium–aluminum foam composite materials obtained via casting of a mold with aluminum filled with pore-forming granules and titanium fittings are investigated in this work. Titanium reinforcement of aluminum foam is shown to increase the strength of a foamed material, slightly increasing its density. The damping properties of titanium–aluminum foam composites are close to those of a solid metal at an increase in the titanium content in the composite. | Mechanical and Operational Characteristics of Layered Titanium–Aluminum Foam Composite Materials | 10.1134/S2075113320010244 |
2020-01-01 | Perturbed Markov chains are popular models for description of information networks. In such models, the transition matrix $$\mathbf {P}_0$$ of an information Markov chain is usually approximated by matrix $$\mathbf {P}_{\varepsilon } = (1 - \varepsilon ) \mathbf {P}_0 + \varepsilon \mathbf {D}$$ , where $$\mathbf {D}$$ is a so-called damping stochastic matrix with identical rows and all positive elements, while $$\varepsilon \in [0, 1$$ ] is a damping (perturbation) parameter. We perform a detailed perturbation analysis for stationary distributions of such Markov chains, in particular get effective explicit series representations for the corresponding stationary distributions $$\bar{\pi }_\varepsilon $$ , upper bounds for the deviation $$| \bar{\pi }_{\varepsilon }- \bar{\pi }_0 |$$ , and asymptotic expansions for $$\bar{\pi }_{\varepsilon }$$ with respect to the perturbation parameter $$\varepsilon $$ . | Perturbation Analysis for Stationary Distributions of Markov Chains with Damping Component | 10.1007/978-3-030-41850-2_38 |
2020-01-01 | The objective of this work is to establish an accurate non-linear parametric model which relates the physical parameters with the damping characteristics of the hydraulic damper before relieving. A new non-linear parametric model including the sub-models of the orifice, hydraulic fluid, pressure chambers, reservoir chamber, etc. is established based on the theory of the fluid mechanics. Subsequently, a new force element of the hydraulic damper based on the new non-linear model is developed with Fortran language in the secondary development environment of the multi-body dynamics software SIMPACK. Used the force element, the force-displacement and force-velocity characteristics of the modified yaw damper with the base diameter of 0.4 and 0.6 mm are calculated under different amplitudes and frequencies of the sinusoidal excitation. Comparing with the experimental results obtained under the same condition, it shows that the new model can accurately model the nonlinear static and dynamic characteristics. Furthermore, the leakages for the high frequency, the air release and cavitation for the modelling of the fluid shortage, the non-constant flow coefficient of the orifice and the dynamic states of the fluid should be included in the modelling of the hydraulic damper before relieving. The non-linear parametric model proposed in this paper is more applicable to the railway vehicle system dynamics simulation and individual system description of the hydraulic damper. | Study on the Non-linear Parametric Model of Hydraulic Dampers Before Relieving for Railway Vehicles | 10.1007/978-3-030-38077-9_72 |
2020-01-01 | We investigate the nonlinear dynamic response of a device made of two electrically coupled cantilever microbeams. The vibrations of the microbeams triggered by the electric actuation lead to the redistribution of the air flow in the gap separating them and induce a damping effect, known as the squeeze-film damping. This nonlinear dissipation mechanism is prominent when encapsulating and operating the microstructure under high gas pressure. We present different modeling approaches to analyze the impact of the squeeze-film damping on the dynamic behavior of the microsystem. We first develop a nonlinear multi-physics model of the device by coupling Euler–Bernoulli beam equations with the nonlinear Reynolds equation and use the Galerkin decomposition and differential quadrature method to discretize the structural and fluidic domains, respectively. We consider also another modeling approach based on approximating the squeeze-film damping force by a nonlinear analytical expression. This approach is widely used in the literature and referred to as partially coupled model in this paper. We conduct a comparative study of the nonlinear dynamic responses obtained from the two models under different operating conditions in terms of electric actuation and applied pressure. The simulated frequency and force-response curves show the limitations of the partially coupled model to capture properly the microsystem dynamics, especially when approaching the onset of the pull-in instability and exciting the microsystem with an AC voltage near resonance. As such, we propose a correction factor to the partially coupled model which is much less computationally demanding to obtain good match with the fully coupled model. The selection of the correction factor depends on the thickness ratio, the ambient pressure, and the excitation frequency. The influence of the ambient pressure and the thickness ratio between the two microbeams were also examined. We observe that operating the microsystem at a reduced ambient pressure or when reducing one of the microbeams’ thickness can lead to a premature instability of the dynamic solution which reduces the maximum amplitude of the vibrating microbeams. This feature can be exploited for switching applications but it constitutes an undesirable effect for resonators. | Multifidelity modeling and comparative analysis of electrically coupled microbeams under squeeze-film damping effect | 10.1007/s11071-019-04928-4 |
2020-01-01 | To study the transient interaction between the transformers and the power system is essential use very accurate transformer models considering the dependence of damping with frequency. In this work the fundamentals of transformer parameters calculation for high frequency transients using finite elements method (FEM) are reviewed and a promissory time-domain equivalent circuit is proposed based in the analysis of transient measurements results obtained by the CIGRE JWG A2/C4.52 in two transformers manufactured by WEG in Mexico. | Calculation of Circuit Parameters of High Frequency Models for Power Transformers Using FEM | 10.1007/978-981-15-5600-5_14 |
2020-01-01 | The Gilbert damping parameter $$\alpha$$ represents the rate of energy dissipation associated with magnetic dynamics, characterizing the relaxation of magnetic dynamics to its equilibrium state. In Chap. 2 , it is assumed that $$\alpha$$ of ferrimagnetic GdFeCo is constant in the temperature range across $${T}_{\mathrm{A}}$$ . However, this assumption of constant $$\alpha$$ is in contrast with earlier experiments reporting that the effective $$\alpha$$ of ferrimagnets, estimated from the FiMR linewidth, increases remarkably as the temperature approaches $${T}_{\mathrm{A}}$$ and diverges at $${T}_{\mathrm{A}}$$ . Recently, a theoretical study by Kamra et al. has suggested that the drastic increase in the FiMR linewidth in the vicinity of $${T}_{\mathrm{A}}$$ can be attributed to the change in the nature of the magnetic dynamics from ferromagnetic (significantly away from $${T}_{\mathrm{A}}$$ ) to antiferromagnetic (at $${T}_{\mathrm{A}}$$ ) rather than the increase in the effective $$\alpha$$ . In Chap. 3 , $$\alpha$$ of ferrimagnetic GdFeCo is investigated using the field-driven DW mobility extracted from the DW motion experiment in Chap. 2 . It is confirmed that $$\alpha$$ of ferrimagnets is almost insensitive to temperature across $${T}_{\mathrm{A}}$$ , supporting the validity of the theoretical study by Kamra et al. and the analysis in Chap. 2 . | Gilbert Damping Parameter of Ferrimagnets Probed by Domain Wall Motion | 10.1007/978-981-15-9176-1_3 |
2020-01-01 | This paper proposes a novel fully integrated digitally controlled active inductor for damping of ultrasonic transducer. Using new grounded inductor simulator (GIS) topology, the work addresses number of design challenges to demonstrate a feasibility of active damping of a transformer-less ultrasonic distance measurement sensor. The topology is described and basic parameters are derived in the paper. Presented GIS topology is suitable for full integration, and achieves low distortion, high input voltage dynamic range, and can digitally be tuned in a wide range from 1.1 to 75 mH with a step less than 1%. Presented design was manufactured in 0.18 um CMOS technology and occupies area of 0.216 mm^2. Measurement results confirming key parameters are presented to support this work. | A fully integrated digitally controllable grounded inductor simulator with a large inductance range for damping of ultrasonic transducers | 10.1007/s10470-019-01396-z |
2020-01-01 | The study of both linear and nonlinear structural vibrations routinely circles the concise yet complex problem of choosing a set of coordinates which yield simple equations of motion. In both experimental and mathematical methods, that choice is a difficult one because of measurement, computational, and interpretation difficulties. Often times, researchers choose to solve their problems in terms of linear, undamped mode shapes because they are easy to obtain; however, this is known to give rise to complicated phenomena such as mode coupling and internal resonance. This work considers the nature of mode coupling and internal resonance in systems containing non-proportional damping, linear detuning, and cubic nonlinearities through the method of multiple scales as well as instantaneous measures of effective damping. The energy decay observed in the structural modes is well approximated by the slow-flow equations in terms of the modal amplitudes, and it is shown how mode coupling enhances the damping observed in the system. Moreover, in the presence of a 3:1 internal resonance between two modes, the nonlinearities not only enhance the dissipation, but can allow for the exchange and transfer of energy between the resonant modes. However, this exchange depends on the resonant phase between the modes and is proportional to the energy in the lowest mode. The results of the analysis tie together interpretations used by both experimentalists and theoreticians to study such systems and provide a more concrete way to interpret these phenomena. | Transient dynamics, damping, and mode coupling of nonlinear systems with internal resonances | 10.1007/s11071-019-05198-w |
2020-01-01 | Synchronous static compensator (STATCOM) can also be used to improve the dynamic performance of a power system apart from being used for reactive power compensation. This article performs a comparative study for robust STATCOM control designs based on graphical loop-shaping and simultaneous tuning using Particle Swarm Optimization (PSO) for a single machine infinite bus system (SMIB) equipped with STATCOM. The power system working at various operating conditions is considered as a finite set of plants. Fixed parameter robust controllers were designed considering the voltage magnitude of the voltage source converter (VSC), a part of the STATCOM system, as the input and speed deviation of the generator as the system output. Simulation studies are conducted on a simple power system which indicates that the designed robust controllers by the two methods provide very good damping properties over a wide range of operating conditions, but the simultaneous tuning method using particle swarm optimization is easy to implement compared to the cumbersome graphical loop-shaping technique. | Comparative Study for Robust STATCOM Control Designs Based on Loop-Shaping and Simultaneous Tuning Using Particle Swarm Optimization | 10.1007/978-981-15-4775-1_45 |
2020-01-01 | Detection of inadequate tightening in bolted joints is quintessential to ensure structural rigidity and to prevent catastrophic failure. Studies show that 30% of assembly failures occur due to inadequate tightening. In the present study, three vibration-based techniques are presented and compared to detect inadequate tightening of bolted joints. Variation in the damped natural frequency, variation in the damping ratio, and variation in the dynamic joint stiffness are studied with varying tightening torques in the bolted joint. The results show that all the three dynamic parameters vary with the tightness of the bolted joint. Dynamic joint stiffness varies significantly as opposed to the damping ratio and damped natural frequency as tightening torque reduces. In order to verify the results of dynamic stiffness method, ANSYS is used to model and analyze the joint. The experimental setup used to calculate the parameters consists of two Euler–Bernoulli beams connected with single lap bolted joint. | Modeling and Experimental Studies on the Dynamics of Bolted Joint Structure: Comparison of Three Vibration-Based Techniques for Structural Health Monitoring | 10.1007/978-981-15-5693-7_21 |
2020-01-01 | In order to improve the efficiency of damping characteristic adjustment for vehicle suspension shock absorber, the control system with a magnetorheological (MR) damper was proposed to realize the adjustable damping characteristic. The Bingham model of a MR damper was establish based on the damping force of the MR damper under different sinusoidal excitations and different currents. The force-velocity curves of dampers were described with a mathematics model. The whole slope and the curvature of the damping force-velocity curves were represented by separate parameters and could be adjusted independently. An embedded control system was developed to adjust damping characteristic with a speed sensor, a microprocessor, a damping characteristic adjustment module, a MR damper and a current driver. The current driver was designed by taking the voltage Pulse Width Modulation (PWM) as the excitation signal. The verification experiment shows that the overall slope and the rate of curvature change for the peak damping force-velocity curve could be adjusted in a little time delay by this control system. | Realization of Adjustable Damping Characteristic Based on a Magnetorheological Damper | 10.1007/978-3-030-38077-9_194 |
2020-01-01 | The use of shape memory alloys (SMA) is really promising in the field of vibration mitigation. Indeed, several works are already available in the literature, describing how to exploit the special features of SMAs in order to design and build dampers and tuned mass dampers (TMD). Regarding TMDs, the features of SMA materials allow to design adaptive TMDs able to change their eigenfrequencies in order to keep the TMD tuned on the primary system to be damped in case of changes of the dynamic features of the primary system (e.g. changes of the eigenfrequency due to thermal shifts). The possibility to ensure the tuning between the TMD and the primary system allows to achieve an optimal damping action. The adaptive TMDs based on SMAs described in the literature are usually able to work on a single eigenfrequency of the primary system. Conversely, this paper proposes a new adaptive TMD able to change more than one eigenfrequency at the same time with a given level of independence. This allows to work on at least two eigenfrequencies of the primary system, thus realizing a multi-modal adaptive TMD. The paper explains that this multi-modal adaptive TMD is based on a special configuration made from a system of masses and SMA wires. Particularly, each mass is connected to the adjacent masses by SMA wires. The possibility to tune more than one eigenfrequency is achieved by heating/cooling the different SMA wires independently. Indeed, this allows to change the geometry of the adaptive TMD and, at the same time, the tensile load into the SMA wires. This double effect is suitable for building multi-modal adaptive TMDs. The paper first describes the working principle of the adaptive TMD. Then, simulations are presented in order to show the effectiveness of the proposed device. | Adaptive Multi-modal Tuned Mass Dampers Based on Shape Memory Alloys: Design and Validation | 10.1007/978-3-030-12676-6_14 |
2020-01-01 | In Chap. 3 , the Gilbert damping parameter $$\alpha $$ is obtained from the field-driven domain wall mobility and is found to be temperature-insensitive across the angular momentum compensation temperature, $${T}_{\mathrm{A}}$$ . Here, it should be noted that the most common experimental method to determine $$\alpha $$ is the ferromagnetic resonance. The previous study on the ferrimagnetic resonance (FiMR) concluded that the effective Gilbert damping parameter $${\alpha }_{\mathrm{eff}}$$ significantly increases as the temperature approaches $${T}_{\mathrm{A}}$$ and diverges at $${T}_{\mathrm{A}}$$ . However, a recent theoretical study has provided a new perspective on $$\alpha $$ of ferrimagnets; the temperature dependence of FiMR is attributed to that of magnetic dynamics, not to that of $$\alpha $$ . This chapter presents a macroscopic theory and experimental results on FiMR, providing an additional evidence of temperature-insensitive $$\alpha $$ of ferrimagnets. The theory, which considers both the antiferromagnetic-like and ferromagnetic-like dynamics, can describe FiMR in a wide temperature range across $${T}_{\mathrm{A}}$$ without divergence of $$\alpha $$ . The experiment on FiMR excited by spin–orbit torque is performed, and the spectral analysis based on the theory reveals that $$\alpha $$ is insensitive to temperature. | Gilbert Damping Parameter of Ferrimagnets Probed by Magnetic Resonance | 10.1007/978-981-15-9176-1_4 |
2020-01-01 | Operational Modal Analysis (OMA) is one of the most used technique to study structures under environmental excitations, for the purpose of structural health monitoring, acceptance test and model updating. In OMA, the modal parameters are obtained only from the measured data using environmental vibrations as unknown input (e.g. wind load, micro-tremors, traffic) and without any artificial excitations applied on the structure. One of the advantages of OMA technique is the possibility to test large-scale structures, which are impossible to test by using artificial excitations, and to provide a modal model under operating conditions, meaning within true boundary conditions, actual forces and vibration levels. Other advantages of OMA are the velocity and cheapness to make the tests, and the possibility to detect close-spaced modal shapes. One of the most used methods in OMA is the Stochastic Subspace Identification (SSI). It relies on an elegant mathematical framework and robust linear algebra tools to identify the state-space matrix from raw data. As a result, non-linear optimization problems are avoided. Moreover, the use of well-known tools from numerical linear algebra, such as Singular Value Decomposition and LQ Decomposition, leads to a numerically very efficient implementation. In order to obtain accurate modal parameters estimations, some user-defined parameters need to be properly set. In this paper, Data-Driven Stochastic Subspace Identification (DD-SSI) method and its sensitivity to two user-defined parameters are investigated. These parameters are, namely, the number of block rows in Hankel matrix and the selection of the length of the data acquired and used in the identification process. In order to establish a standardization on the use of these parameters for reliable system parameters identification, a sensitivity analysis has been conducted on real scale building vibration data. | Influence of User-Defined Parameters Using Stochastic Subspace Identification (SSI) | 10.1007/978-3-030-41057-5_127 |
2020-01-01 | Based on the post-inhibitory rebound (PIR) spike induced by inhibitory current pulse, in the present paper, a novel counterintuitive phenomenon that the inhibitory autapse with time delay can induce the resting state changed to stable spiking pattern is identified near subcritical Hopf bifurcation of Hodgkin–Huxley model. The delayed inhibitory autaptic current pulse induced by the preceded action potential can induce the preceding PIR spike via the hyperpolarization, rebound, and depolarization processes, which is compared with spiking induced by excitatory autapse via only a depolarization process. The threshold of inhibitory or excitatory autaptic conductance to induce spiking with increasing time delay, and the threshold curve of inhibitory or excitatory pulse current to evoke a spike exhibit damping oscillations can be well interpreted with the damping dynamics of focus near subcritical Hopf bifurcation. However, due to PIR mechanism, the threshold conductance of inhibitory autapse is stronger than that of excitatory autapse, and the spiking period for inhibitory autapse, which is composed of time delay and durations of the other three processes, is longer than the one for excitatory autapse, which is composed of time delay and duration of only a depolarization process. Therefore, a linear correlation between spiking period and time delay is identified, which shows that autapse can modulate the spike timing related to temporal coding. The results present a novel viewpoint and a potential function that inhibitory autapse can facilitate spiking like the excitatory autapse and provide effective measures to modulate neuronal spiking pattern, which is related to subcritical Hopf bifurcation. | Different dynamics of repetitive neural spiking induced by inhibitory and excitatory autapses near subcritical Hopf bifurcation | 10.1007/s11071-019-05342-6 |
2020-01-01 | This work explores the role of asymmetrical damping and geometrical nonlinearities in the suspension system of a simplified vehicle model in order to improve comfort. Improving comfort for passengers is a constant challenge for the automotive industry. Although technologies have been introduced for this purpose, many vehicles still use suspension systems which are less effective in vibration isolation due to cost restrictions. To improve comfort at relatively low cost, the use of asymmetrical suspension dampers has been explored. It has been shown that different asymmetry ratios can be advantageous to improve comfort at different frequency ranges. Models which include the suspension geometry can help to better understand the vehicle dynamical response, as it also depends on the geometrical arrangement of its components. As a contribution to the current literature, this paper proposes a study on asymmetrical damping considering a Double Wishbone suspension geometry. A nonlinear single-degree-of-freedom system subject to harmonic base excitation is used. The combination of asymmetry and geometry nonlinearities is investigated for varying asymmetry ratio, geometrical parameters and vehicle velocity. The numerical and experimental results show that the geometrical nonlinearity induces changes in the spring and damping forces because of different inclinations of the spring–damper assembly during expansion and compression, resulting in changes in acceleration amplitude and resonance frequency. This effect is superimposed on the effect of asymmetrical damping coefficient alone, ultimately influencing the acceleration of the suspended mass. Therefore, these two effects must be considered carefully when designing a suspension system with comfort criteria. | Interaction between asymmetrical damping and geometrical nonlinearity in vehicle suspension systems improves comfort | 10.1007/s11071-019-05374-y |
2020-01-01 | Identification of modal parameters, when a structure is under operational conditions is termed Operational Modal Analysis (OMA). Current OMA techniques are based on the assumption of linear time-invariant systems, and thus have limited applicability when applied to structures known to violate these assumptions. The present study investigates how the Random Decrement (RD) technique can improve robustness of OMA methods when friction-induced nonlinear damping is present in a system. This is done by estimating the amplitude dependent damping. A friction mechanism is introduced in a model of a structure, and by applying the RD technique at different amplitudes of simulated responses, RD signatures are produced, that represent the system vibrating with these amplitude levels. This allows the modal parameters to be estimated based on RD signatures computed with each amplitude level, using time domain parameter estimation methods, and the amplitude dependency of the damping is identified. | Output-Only Estimation of Amplitude Dependent Friction-Induced Damping | 10.1007/978-3-030-12115-0_3 |
2020-01-01 | This chapter gives a comprehensive review on R&D efforts to develop bio-based thermosetting resins and biocomposites for use in critical applications such as aircraft fabrication, rail transportation, and construction by a Chinese research consortium in collaboration with international teams. This work was initially motivated by the fact that, on one hand, environmental and resource-related benefits of bio-sourced materials are still compromised by limited standards of technical performance and material life. On the other hand, in the air and ground transportation sectors, new environmental regulations and societal concerns have triggered a search for new products and processes that complement not only environment but also resources. To address this issue, novel bio-sourced materials, including bio-sourced epoxies, continuous plant fibers, textiles and prepregs, and neat and hybrid biocomposite laminates, were developed. These materials were characterized, modified, and evaluated in terms of their interfacial properties, flammability, and hydrothermal stability levels. Quasi-structural and structural damping biocomposite structures were finally designed and manufactured using technologies that have been fully adapted to state-of-the-art industrial composite processes. It is also found that developing function-integrated plant-fiber-fabric-reinforced biocomposites and corresponding hybrid structures appears to be more essential and feasible than the mere development of “high-performance” biocomposites for applications. At the end of the chapter, structural damping and decorative quasi-structural composites for use in aircraft, rail transportation, and civil engineering sectors are presented. | Biopolymers and Biocomposites | 10.1007/978-3-030-35346-9_9 |
2020-01-01 | Recently, a new algorithm was presented (Festjens et al., Int J Mech Sci 75 (2013) 170–177) that allows one to predict the effective natural frequency and damping ratio as a function of amplitude for a structure with bolted joints. This paper applies a variant on that algorithm to a finite element model of the “S4 Beam” (two C-shaped beams bolted together on their ends) and compares the results with the measurements described in (Singh et al., IMAC 2019). The algorithm, which is here referred to as Quasi-Static Modal Analysis (QSMA), is applied to a detailed finite element model of the beam in the commercial software package, Abaqus^®. Coulomb friction is assumed to govern the contact interface. Amplitude dependent damping and natural frequency curves are calculated for the structure and compared to experimental measurement. Several studies are included which explore the solver tolerances and preload values needed to reach agreement with experimental measurements. Additionally, the shape of the actual contact interfaces is measured using a profilometer and fed into the model to quantify the effect of slight curvature in the contact. | Predicting S4 Beam Joint Nonlinearity Using Quasi-Static Modal Analysis | 10.1007/978-3-030-12391-8_5 |
2020-01-01 | Structural damping ratio which quantifies the energy dissipation of civil structures under external excitations plays a critical role in the seismic design and assessment of civil structures. In existing building design provisions and guidelines, however, the structural damping ratio is only suggested either as a single fixed value or as an optional value for the general structure type adopted. For example, damping ratio 5% is commonly recommended for all reinforced concrete (RC) structures in practical seismic design, which may not be sufficient to represent the realistic damping features of different RC structures under ground motions with different amplitudes. This research explored deeper understandings on the structural damping features of different RC structures under actual ground motion excitations. A series of seismic response records of RC structures were collected from the “Center for Engineering Strong Motion Data” (CESMD) database. These records were then categorized into three typical lateral resisting systems: moment-resisting frame systems, shear wall systems, and moment-resisting frame plus shear wall systems. The equivalent structural damping ratios for different systems of RC structures were then estimated based on the categorized response records with different amplitudes. Finally, an empirical statistical relationship was established, offering a refined basis for civil engineers to reasonably choose the equivalent damping ratios during the design and post-earthquake assessment of the RC structures. | Damping Ratios of Reinforced Concrete Structures Under Actual Ground Motion Excitations | 10.1007/978-3-030-12115-0_36 |
2020-01-01 | Scrap Tire Derived Materials (STDM) mixed with soil are often being used as geomaterials in civil engineering projects for reducing dynamic loads acting on geo-structures and soil liquefaction remediation purposes. On the other hand, any soil dynamic analysis involving STDM needs an estimation of dynamic characteristics of these materials. Predicting dynamic properties of STDM-soil mixture is a complicated task because there are large numbers of factors affecting dynamic properties of mixture, which might have complex relationships with each other within the soil-STDM system. There have been several attempts to evaluate and predict dynamic characteristics of STDM-soil mixtures using simple mathematical expressions. However, all those studies have been focused on case studies of some specific types of STDM and soil mixtures without considering various aspects of their dynamic behavior. This study presents application of artificial intelligence technique in predicting dynamic properties of gravel-tire chips mixtures (GTCM). Two Artificial Intelligence (AI) techniques, Support Vector Machine (SVM), and Artificial Neural Networks (ANN) were employed for modeling shear modulus and damping ratio of TDGM. Test results have shown that shear modulus and damping ratio of the granular mixtures are remarkably influenced by gravel fraction in GTCM. Furthermore, shear modulus was found to increase with the mean effective confining pressure and gravel fraction in the mixture. It was found that a feedforward multilayer perceptron model with backpropagation training algorithm have better performance in predicting complex dynamic characteristics of granular mixture than SVM one. | An Artificial Intelligence Approach for Modeling Shear Modulus and Damping Ratio of Tire Derived Geomaterials | 10.1007/978-981-15-0890-5_49 |
2020-01-01 | This manuscript deals with a fractional PID controller which is proposed for inverted pendulum on a cart system (IPCS). The mathematical equivalent of the system is done by Euler–Lagrange’s method with the consideration controller and system frequency response specifications controller parameters like $$K_{p}$$ , $$K_{i}$$ , $$K_{d}$$ ; λ and µ are determined using FPID optimization toolbox. Compared to classical optimization techniques, this FPID technique provides better phase and gain margins for the system. FPID optimization tuning helps to obtain iso-damping property. It is a property where the open-loop phase https://en.wikipedia.org/wiki/Bode_plotis constant, means the derivative of open-loop phase is zero at a frequency called tangent frequency ( $$\omega_{c}$$ ). Open-loop phase is flat which indicates that the plant exhibits the property of robustness for gain variations. Systems which exhibit iso-damping properties, overshoots the closed-loop step signal have nearly constant for assorted values of the system gain. This ascertains that the system demonstrates the robustness properties to gain variations. | Control Quality Enhancement of Inverted Pendulum Using Fractional Controller | 10.1007/978-981-15-2256-7_64 |
2020-01-01 | In this study, a nonlinear mathematical model for drum-type washing machines is developed considering rotating unbalance type excitation. Nonlinear differential equations of motion are converted into a set of nonlinear algebraic equations by using harmonic balance method (HBM). The resulting nonlinear algebraic equations are solved by using Newton’s method with arc-length continuation. Several case studies are performed in order to observe the effects of orientation angles of springs and dampers supporting the drum. In order to reduce the steady-state vibration amplitude of the drum and transmitted force through springs and dampers, suitable spring and damper orientation angles are identified. Moreover, in order to further reduce the vibration amplitude of the drum, dry friction dampers are introduced to the system. It is clearly observed that dry friction dampers are solving the walking problem of washing machines. | Vibration Analysis of Washing Machines in the Drum Plane | 10.1007/978-3-030-34713-0_54 |
2020-01-01 | Inerter-based tuned mass dampers (TMDs) have been developed recently with the goal of improving upon the performance of traditional TMDs. However, studies investigating the response of single-degree-of-freedom (SDOF) systems with inerter-based TMDs have been primarily limited to ones considering harmonic loads and stationary random excitation. Various relevant random loads have non-stationary characteristics (their frequency contents and/or amplitude change with time); therefore, these load types should be considered in the design of inerter-based TMDs. This paper presents an investigation to evaluate the mean squared response of SDOF systems with inerter-based TMDs that are subjected to a random non-stationary excitation. The non-stationary excitation considered is an evolutionary spectrum of the ground acceleration. The results of this study are used to determine the influence of the non-stationary excitation on the optimal damper properties in comparison to designs considering a stationary process. | Response of a SDOF System with an Inerter-Based Tuned Mass Damper Subjected to Non-stationary Random Excitation | 10.1007/978-3-030-12115-0_27 |
2020-01-01 | A simplified physical model of a high-speed train yaw damper is developed which has the ability to reproduce its dynamic performance with less computational efforts. It is then suitably validated with experimental results considering static and dynamic conditions. At last, comparisons of vehicle dynamics relevant to vehicle stability are carried out, by integrating the proposed model and conventional Maxwell model into a three dimensional MBS model of a high-speed railway vehicle. In the case of low conicity, the proposed model and Maxwell model show good consistency. This is because the F-D characteristics of the proposed model approximately follow an elliptical and symmetry shape in low excitation frequencies, like the Maxwell model. However, in the case of high conicity, vehicle dynamics are quite different comparing the two damper models. This is because the F-D characteristics of the damper studied in this paper are nonlinear and asymmetrical in high excitation frequencies, and cannot be described by the elliptical and symmetry characteristics of the Maxwell model. It is concluded that the proposed model could be used to study the dynamics of railway vehicle under various operating conditions. | A Simplified Yaw Damper Model for Use in Dynamics Simulation | 10.1007/978-3-030-38077-9_69 |
2020-01-01 | Power systems stabilizers (PSSs) have been extensively used as supplementary excitation controllers to damp out the low-frequency oscillations in the range of 0.2–3 Hz. These controllers are able to provide additional damping to enhance the overall system stability. However, conventional PSS (CPSS) performance deteriorates as the operating conditions change, and require re-tuning. It is therefore desirable to design a PSS that is robust with respect to the changes in operating conditions. This chapter describes the application of two evolutionary algorithms (differential evolution—DE and population-based incremental learning—PBIL) to optimize PSS parameters and provide adequate performance for a wide range of operating conditions. The three PSSs were designed and tested on two power system models, namely, the single machine infinite bus (SMIB) and the two-area multimachine system. Using simulations, the performances of DE-PSS, PBIL-PSS, and CPSS were compared. In addition, the performance of DE was improved through the use of self-adaptive DE (or jDE). | Application of Evolutionary Algorithms to Power System Stabilizer Design | 10.1007/978-3-030-37830-1_2 |
2020-01-01 | The paper presents a study on adaptive vibration control applied in a semi-active vehicle suspension. The simulation-based analysis is dedicated to laboratory tests conducted for an experimental all-terrain vehicle subjected to mechanical exciters emulating road-induced vibration. The implemented simulation environment consists of a full-car model which exhibits seven degrees of freedom (7 DoFs), equipped with magnetorheological dampers. The MR damper model based on hyperbolic tangent function was included in the vehicle model. The front wheels of the model were subjected to sinusoidal excitation with constant frequency within the range 0.5–25 Hz. The FxLMS (Filtered-x Least Mean Squares) algorithm is adopted and used for controlling the MR dampers where the vertical velocity of excitation is assumed as a reference signal of the control algorithm. The goal of the algorithm is to attenuate vertical velocity of the front middle vehicle body part. The proposed FxLMS was compared to passive suspension controlled with constant control current and Skyhook algorithm. Comparison of different suspension configurations based on transmissibility characteristics and quality indices confirm usefulness of FxLMS with respect to vibration control, suspension deflection and adaptability features. | FxLMS Control of an Off-Road Vehicle Model with Magnetorheological Dampers | 10.1007/978-3-030-50936-1_63 |
2020-01-01 | This paper presents the seismic control problem of a broad Liquefied Natural Gas (LNG) storage tank using Sliding Mode Control (SMC) with base isolation technique. To reduce seismic forces, the LNG tank is isolated from base by laminated isolation bearing made from intrinsic rubber. In order to control excessive displacement of LNG tank at isolation level, magneto-rheological (MR) dampers are installed. The Magneto-rheological (MR) dampers are admired by robust sliding mode control designed using constant rate reaching law. The stability condition for closed-loop system is derived using Lyapunov Approach. The robustness of the designed controller is proved and compared with uncontrolled system for different seismic ground motion. The simulation results substantiated that the sliding mode control (SMC) strategy is more effective in reducing the structural responses as compared to uncontrolled system. | Design of Sliding Mode Control for LNG Storage Tank System | 10.1007/978-981-15-0226-2_2 |
2020-01-01 | Most classical substructuring methods yield great approximation accuracy if the underlying system is not damped. One approach is a fixed interface method, the Craig-Bampton method. In contrast, many other methods (e.g., MacNeal method, Rubin method, Craig-Chang method) employ free interface modes, (residual) attachment modes, and rigid body modes. None of the aforementioned methods takes any damping effects into account when performing the reduction. If damping significantly influences the dynamic behavior of the system, the approximation accuracy can be very poor. One procedure to handle arbitrarily viscously damped systems and to take damping effects into account is to transform the second-order differential equations into twice the number of first-order differential equations resulting in state-space representation of the system. Solving the corresponding eigenvalue problem allows the damped equations to be decoupled; however, complex eigenmodes and eigenvalues occur. The complex modes are used to build a reduction basis that includes damping properties. The derivation of different Craig-Bampton substructuring methods (fixed interface) for viscously damped systems was presented in Gruber et al. (Comparison of Craig-Bampton approaches for systems with arbitrary viscous damping in dynamic substructuring). In contrast, we present here the derivation of different free interface substructuring methods for viscously damped systems in a comprehensible consistent manner. Craig and Ni suggested a method that employs complex free interface vibration modes (1989). De Kraker and van Campen give an extension of Rubin’s method for general state-space models (1996). Liu and Zheng proposed an improved component modes synthesis method for nonclassically damped systems (2008), which is an extension of Craig and Ni’s method. A detailed comparison between the different formulations will be given. Liu and Zheng’s method can be considered as a second-order extension of Craig and Ni’s method. We propose a third-order extension and a generalization to any given higher order. Moreover, a new method combining the reduction basis of Liu and Zheng’s approach with the primal assembly procedure applied by de Kraker and van Campen is proposed. The presented theory and the comparison between the methods will be illustrated in different examples. | Overview of Free Interface Substructuring Approaches for Systems with Arbitrary Viscous Damping in Dynamic Substructuring | 10.1007/978-3-030-12184-6_11 |
2020-01-01 | In this chapter, the problems of the fifth chapter are fully solved, in detail and step-by-step. In solving the problems of this chapter, all the subjects of the previous chapters are applied. Moreover, the concepts of quality factor, circuit responses, impulse function, time-dependent second-order homogeneous and nonhomogeneous differential equations, characteristic equation, and general solution of a second-order differential equations are explained. | Solutions of Problems: Second-Order and Higher-Order Circuits | 10.1007/978-3-030-50711-4_6 |
2020-01-01 | The measurement and diagnosis of high-voltage cables as part of commissioning tests On-Site is a particular challenge. To circumvent the problems of high reactive power delivery On-Site, resonant testing systems are widely used to perform an AC voltage test. As an alternative for resonance testing, the Damped AC (DAC) method becomes more and more accepted. Since the resulting test voltage shape in case of a Damped AC system is not fully comparable with the operational AC voltage, the influence of the DAC voltage on defects of the cable system needs to be investigated. The general question is: is the Damped AC test voltage capable to detect service endangering defects in cables and accessories and what are the appropriate voltage levels and durations for On-Site tests. In previous experiments, the needle defect was chosen to investigate the performance of a DAC test voltage to detect severest inhomogeneity’s inside the insulation. Indeed, the needle defect represent the most extreme form of an inner cable failure but can be designed the different levels and performed on full scale cable specimen reproducibly. In addition, other cable system defects such as termination or joint failures also have to be investigated to compare the capability of DAC with AC to detect such defect under On-Site test conditions. For this purpose, investigations where performed to create a reproducible and scalable artificial accessory failure on full scale MV and later HV cable specimen. First, the ratios of the electric field within a high-voltage cable are converted by means of FEM (Finite Element Method) to a surface discharge arrangement according to EN 60343-70. First step was to perform comparable investigations of DAC and AC on the surface discharge behaviour in general. After calculating the required geometry, XLPE (Cross-linked Polyethylene) discs are tested in the surface discharge arrangement. The main focus of investigation is laid on the partial discharge characteristics under a test voltage. After demonstrating the reproducibility of the PD-results of this setup, the tests are performed with AC and DAC voltage. The main subjects of this study is the comparison of the PD characteristics of the two different voltage types. | Comparative Investigations on Surface Discharge at a Surface Discharge Arrangement Under AC and Damped AC (DAC) | 10.1007/978-3-030-31680-8_111 |
2020-01-01 | In this paper by using the Poincaré compactification of R^3 we make a global analysis of the model x′ = − ax + y + yz, y′ = x − ay + bxz, z′ = cz − bxy. In particular we give the complete description of its dynamics on the infinity sphere. For a + c = 0 or b = 1 this system has invariants. For these values of the parameters we provide the global phase portrait of the system in the Poincaré ball. We also describe the α and ω -limit sets of its orbits in the Poincaré ball. | On the global dynamics of a three-dimensional forced-damped differential system | 10.1080/14029251.2020.1757232 |
2020-01-01 | This paper presents an adaptive optimal control strategy for an adaptive two-degree-of-freedom quarter car model with magnetorheological dampers. The method assumes the system is fitted with sensors to “read” the road profile ahead of the vehicle. The main objective of the adaptive optimal control is to minimise the root mean square acceleration of the sprung mass. Pointwise constraints (upper and lower suspension travel and minimum tyre vertical force) are considered instead of incorporating the constraints to the cost function via penalty methods. The implemented gradient optimisation routine, the so-called Method of Moving Asymptotes, shows very good performance for optimal controls subjected to large numbers of constraints. For the adaptive approach considered in this paper, the optimal intensity supplied to the MR damper remains constant unless either the quality of the road or the vehicle velocity change. The results obtained show that the adaptive optimal control obtains comfort improvements up to 63% with respect to the best passive constraint–abiding configuration. | Comfort Improvement of an Adaptive Vehicle Suspension via Pointwise-Constrained Optimal Control | 10.1007/978-3-030-38077-9_200 |
2020-01-01 | Calculation of the time course and speed of the oscillation motion dampened by centripetal force typically represented by sliding friction is rather complicated mathematical task, which is unnecessary to solve repeatedly for individual stages of the given oscillations until they are completely subdued. Using classical mathematics is a rather lengthy calculation when the results obtained for one of the examined oscillations are simultaneously the initial conditions for the following oscillations. The fact that said damping friction force changes its direction of action depending on the direction of movement of the mechanism considerably complicates given solution. It is rather complicated to solve the given calculation by classical programming in the available mathematical software. To solve the motion equation of such a mechanism, the mathematical software MAPLE using the signum function is being used. The values obtained by calculation are further verified on a model of low-energy device for the transfer of objects in a material flow designed on the principle of Karakuri mechanism. | Solution of Damped Oscillations by Coulomb Friction at the Karakuri Mechanism Using MAPLE Software | 10.1007/978-3-030-33146-7_44 |
2020-01-01 | In high-speed rotating machinery, the internal damping becomes predominant that further aggravates the appearance of cracks in the rotor due to severe unstable vibrations. The internal damping comes into existence in thick shafts when the fibers of the material are alternately compressed and stretched due to the asynchronous whirling motion. The presence of internal damping in rotors is also influenced by the appearance of the crack due to rubbing of fatigue crack fronts during its opening and closing, which has an additional effect of reducing the stiffness of the shaft. The aim of the present paper is to actively control through magnetic bearings (MB), the unstable vibrations induced by the internal damping in the presence of switching crack and unbalances in a rotor system. Equations of motion of a simple Jeffcott rotor are derived considering both external and internal damping, switching crack model, unbalance force, and active MB force. The chosen crack model gives multiple harmonics not only in the forward whirl but also in the backward whirl. The active MB system, which is used here as a controller and not for supporting the rotor static load, utilizes PID control law, which requires tuning of control law parameters for stable control of the rotor system. Rotor responses are obtained through a numerical simulation to study interplay between instability of rotor due to internal damping and its active control through the MB. Full (or directional) spectrum plots are utilized to demonstrate both the forward and backward harmonics of the rotor whirling at different rotor speeds due to the presence of switching crack with and without active MB. Nyquist plots are provided to check the stability of the rotor system at different operating speeds. | Active Control of Internal Damping Instabilities in a Cracked Rotor with Magnetic Bearing | 10.1007/978-981-15-5693-7_10 |
2020-01-01 | Shutdown System Shutdown system constitutes a part of reactor safety system of Indian Pressurized Heavy Water Reactor (IPHWR). The system is required to be seismically qualified to demonstrate its capability of functioning and maintaining structural integrity during and after a seismic Seismic event. Experimental studies have been carried out on full-scale shutdown system Shutdown system assembly to evaluate the responses under multi-support excitation. Dynamic characterization and functionality test of the assembly have been carried out simulating rock site and alluvium soil condition. Critical parameters, viz. added mass coefficient Added mass coefficient and damping factor Damping factor have been evaluated for the submerged structure from the experiments, and analytical studies have been carried out incorporating these parameters. Dynamic responses from experimental and analytical studies have been compared and are found to be in good agreement. Studies concluded that shutdown system Shutdown system can perform its intended safety function even when subjected to extremely strong earthquake motion. | Seismic Performance of Shutdown System of Indian Pressurized Heavy Water Reactors | 10.1007/978-981-13-8767-8_70 |
2020-01-01 | This paper introduces the details of a transient damping feature extracting method based on the bridge monitoring data with the aid of the frequency slice wavelet transform (FSWT) which is a time-frequency space analysis tool and its application to damage detection of the bridges. The proposed method via the state representation methodology (SRM) algorithm has been verified by the state probably density distribution using the vibration signal from a laboratory bridge monitoring system. As a result, the system state vector as a non-parametric state variable will be able to apply to assess the state change (damage) of the bridge structures by expression of the state probably density distribution. | A Damage Detection Method by Transient Damping Feature Based on Monitoring Data | 10.1007/978-981-13-8331-1_3 |
2020-01-01 | Past experience of earthquakes has shown the importance of asymmetry effects on the severity of the damage sustained by structures. In order to mitigate torsional response of asymmetric structures under seismic loads, employing passive energy dissipating equipment, such as viscous dampers, has been investigated by many researchers during recent years. One decisive factors contributing to the seismic behaviour of asymmetric structures is the torsional component of strong ground motion. The main purpose of this research is to compute a damping eccentricity which minimizes torsional response of asymmetric structures. To this end, several one-storey, three-dimensional steel moment frames with various stiffness and strength eccentricities are studied. Due to the limitations in recording torsional component of earthquakes, translational components are used to develop torsional counterparts. Models were analyzed using time history analysis method under 7 records of strong ground motions. Results indicate that incorporating viscous dampers could not only mitigate structural response, but it also could suppress torsional deflections due to asymmetry in structures. Results showed by increasing the asymmetry of the structure, optimal damping eccentricity should be shifted towards the flexible edge to reduce the displacement difference considerably. | On the Response of Asymmetric Structures Equipped with Viscous Dampers Subjected to Simultaneous Translational and Torsional Ground Motion | 10.1007/978-3-030-33532-8_28 |
2020-01-01 | This study investigates the effect of a tool holder with a metallic damping alloy on both vibration reduction and surface finish improvement for use in an end-milling process. Two different configurations of damping alloys are designed: a collet and a sleeve inside a conventional tool holder. To determine the system characteristics including damping effects, an experimental verification was organized, after that actual machining tests are conducted. The damping effects of each tool holder are compared through machining tests on carbon-fiber reinforced plastics (CFRP) and mold steel respectively. Additionally, a chatter vibration suppression test using thin aluminum workpiece concludes that the metallic damping alloy is comparable to other damping methods. The results show that damping alloy can reduce machining vibration regardless of workpiece materials or the form of it, and the sleeve type tool holder improves the surface roughness significantly in an end-milling process for both workpiece materials. | Surface finish improvement using a damping-alloy sleeve-insert tool holder in the end milling process | 10.1007/s00170-019-04757-0 |
2020-01-01 | In order to study the phenomenon of sub-synchronous oscillation (SS0) in thermal power plants considering different topologies, based on the IEEE first standard model, this paper uses the PSCAD simulation platform to build models of different topological structures of thermal power plants. The complex torque coefficient (CTC) analysis method is used to obtain the electrical damping (De) in each topology. The analysis shows that the topology will affect the sub-synchronous oscillation, if the system topology is more complex, the system’s ability to withstand the sub-synchronous oscillation will be stronger, and it is verified by time-domain simulation.. | Research on SSO Influence with Consideration of Topology Structure Based on CTC Analysis Method | 10.1007/978-3-030-62483-5_2 |
2020-01-01 | This article proposes a method of selecting the damping factor (DF) based on finding the boundaries of the range of the domain of the DF for a model of effective controls, reflecting the spread of influence on the directed weighted signed graphs. The graph model is a fuzzy cognitive map (FCM). Two ranges of the subset values of the domain of the DF are proposed: (i) the admissible range, within which the co-directionality of the response and impact vectors is guaranteed to prevail, and (ii) the resonance range, within which there is a rapid rearrangement and reversal of the ranks of the vertices. An interpretation of the resonance surge for this model of the spread of influence is proposed. | Effect of Resonance in the Effective Control Model Based on the Spread of Influence on Directed Weighted Signed Graphs | 10.1007/978-3-030-50097-9_28 |
2020-01-01 | The paper discusses the classical methods of surface damping of bending vibrations in thin-walled structures. Furthermore, the perspective integral version of a damping coating has been proposed. Such coating consists of two layers of material with pronounced viscoelastic properties with a thin reinforcing layer of high modulus material between them. Dynamic tests of cantilevered duralumin specimens under the damped bending vibrations were carried out using the created experimental setup. The purpose of these tests is to compare the effectiveness of the known and proposed methods of surface vibration damping. The influence of aerodynamic drag forces on the vibration damping of specimens is noted. A refined finite element model of an elongated plate with an integral layer damping is constructed on the basis of the four-layer finite element. This model allows taking into account the effect of transverse compression of damping layers under high-frequency deformation. The analysis of the stress-strain state of the damping layers of a simply supported elongated plate under resonance vibrations in several lower eigenmodes has been carried out. The analysis showed a significant increase in the transverse compression stresses of the damping layers with frequency increasing. | Vibration of the Plate with Integral Layer Damping: Experimental and Theoretical Studies | 10.1007/978-3-030-47883-4_46 |
2020-01-01 | Daily increase in plastic waste amounts is a serious environmental problem and it is among the major challenges worldwide. Reusing this waste material can be therefore an appropriate solution to overcome this problem. Besides, recycling plastic waste as reinforcing material has become a cheap and viable alternative for soil improvement schemes. In the current study, PET plastic waste strips (water bottles) were randomly mixed with sandy soil to improve the soil strength parameters. Due to the lack of comprehensive seismic studies on soils reinforced with PET strips, a series of 1-g shaking table tests was performed to evaluate the dynamic properties of the sand-PET mixtures with different PET contents (0%, 0.5%, 0.75% and 1% by the sand weight) and aspect ratios (1 and 5). Effect of various parameters, including excitation amplitude, PET strip content and PET strip aspect ratio on response of the mixtures were elaborated. It was found that addition of the PET strips to the sand, could reduce the soil brittleness under low overburden pressures. Therefore, at the inclusion ranges used in this study, increase of the PET strips content or aspect ratio, caused an increase in the damping ratio and decrease in the shear modulus values compared to the plain sand model. Opposite trends of PET strips inclusion contribution were reported under the influence of high overburden pressures through carrying out some cyclic large-scale direct shear tests. | Shaking Table Study on PET Strips-Sand Mixtures Using Laminar Box Modelling | 10.1007/s10706-019-01057-y |
2020-01-01 | Abstract This paper considers a possible approach to the embodiment of a gantry crane motion control while moving cargo. Two different methods for determining the controlling acceleration that provides vibration damping of the cargo are proposed. The first method is based on the application of the classical Pontryagin maximum principle. The second method using the Gauss principle is based on modern research in nonholonomic mechanics. The new method relies on the results of the classical one and can be exploited as an entirely independent approach to various control problems. | Motion Control of a Loaded Gantry Crane by Prescribing Its Acceleration | 10.1134/S1063454120010100 |
2020-01-01 | Dynamic Mechanical Analysis is carried out on treated and untreated kenaf, thespesia lampas and okra fiber polyester composites. Results indicate that composites with fibers treated by sodium hydroxide have higher storage modulus, decreased loss modulus and damping factor Best properties are noted for treated okra fiber composite with highest storage modulus and glass transition temperature and lowest damping factor. The Scanning Electron Microscopy results indicate a superior interfacial bonding for treated kenaf fiber composite. Improved interfacial bonding upon treatment causing hindrance to the mobility of molecular chains can be seen clearly in the micrographs. The effect of chemical modification of the fibers in enhancing the dynamic mechanical properties is well demonstrated for kenaf, thespesia lampas and okra fiber composites in this paper. | Dynamic Mechanical Properties of Kenaf, Thespesia Lampas and Okra Fiber Polyester Composites | 10.1007/978-3-030-43690-2_52 |
2020-01-01 | The importance of placing the piezoelectric patch at the optimal location for getting the maximum vibration control using the shunt circuit technique is discussed here. A shunt circuit damper converts the mechanical vibration to the electrical energy, which is then dissipated as heat using resistors. The energy dissipated by the device increases with respect to the energy absorbed by the piezoelectric patch in the circuit. Hence, placing the patch in a location where it can produce maximum electric potential results maximum energy dissipation. Performance of this device is investigated on an aluminium cantilever beam for three types of shunt circuit conditions by optimising the design variables using genetic algorithm and fmincon in MATLAB. Further, sensitivity analysis shows that the arbitrary placing of the patch causes detuning at some locations and induces negative damping to the system. The numerical study indicates that at the optimal location, the performance of the device improves significantly in terms of percentage reduction in tip velocity. Moreover, a considerable reduction in the resistance value is obtained by the use of genetic algorithm. | Optimal Location of Piezoelectric Patch in Passive Vibration Control | 10.1007/978-981-15-5693-7_40 |
2020-01-01 | In maximizing the power transmission from solar electricity to the grid, the use of power converters is very essential. In the early days, the problems in terms of power quality (PQ) have meant that both the voltage quality and current quality of the PV system linked to the grid are becoming increasingly crucial, particularly as nonlinear equipment has been widely used. This paper presents a PV-based DSTATCOM with LCL filter in power distribution network to reduce the power quality problem as a harmonic distortion presents in network. Low-frequency-induced harmonics can be reduced by an LCL filter and a satisfying grid-side current can be generated with a relative low induction in comparison with the L filter. The new poles implemented by LC part lead to resonance in the scheme, leading to stability problems. This paper introduces a compensation technique using the SRF theory to enhance such issues so that efficiency in the constructed LCL filter scheme can be enhanced. The use of the active damping technique can rectify this issue. The proposed system is simulated in MATLAB/SIMULINK to improve the performance of the system by harmonic distortion reduction. | Design and Analysis of PV-Based DSTATCOM with LCL Filter for Localized Distribution System | 10.1007/978-981-15-2256-7_35 |
2020-01-01 | Lanzhou–Xinjiang high-speed railway has passed through several wind areas, and it is necessary to study pantograph–catenary coupling under wind environment. In this paper, SS400 + pantograph used in Lanzhou–Xinjiang line is utilized to study the pantograph–catenary parameter matching. Firstly, the sliding vibration law of the pantograph is analyzed considering pantograph–catenary coupling. Secondly, a three-mass pantograph model considering wind damping is established. Then, the Laplace transform is applied to the pantograph model, and the relation between the pantograph–catenary contact force and the pantograph head displacement is established. Finally, under the different pantograph parameters, the optimal amplitude–frequency characteristic matching test is carried out for ensuring the smooth coupling of pantograph–catenary system. | Optimal Matching of High-Speed Pantograph Parameters Considering Catenary Suspension Irregular Point and Wind Damping | 10.1007/978-981-15-2862-0_51 |
2020-01-01 | The body vibration damping process with a dynamic shock vibration damper containing a system of successive shock pairs in which the colliding elements are magnets is considered. The projected parameters’ effect of the vibration damper on the body oscillations is considered. The features of setting up the system in the mode of wideband vibration damping are described. | Damping of Oscillations by a Vibro-Impact System with Serial Magnetic Impact Pairs | 10.1007/978-3-030-38708-2_25 |
2020-01-01 | Numerical wave tanks are widely-acknowledged tools in studying waves and wave-structure interactions. They can generate waves under realistic scales and offers more information on the fluid field. However, most numerical wave tanks suffer from issues known as the numerical dissipation and numerical dispersion. The former causes wave energy to be slowly dissipated and the latter shifts wave frequencies during wave propagation. This paper proposes a simple method of depressing numerical dissipation effects on the basis of solving Euler equations using the finite difference method (FDM). The wave propagation solutions are solved analytically taking into account the influence of the damping terms. The main idea of the method is to append a source term to the momentum equation, whose strength is determined by how strong the numerical damping effect is. The method is verified by successfully depressing numerical effects during the simulation of regular linear waves, Stokes waves and irregular waves. By applying the method, wave energy is able to be close to its initial value after long distance of travel. | A simple method of depressing numerical dissipation effects during wave simulation within the Euler model | 10.1007/s13131-019-1524-1 |
2020-01-01 | The article compares robustness of five selected speed control systems to the changes in the controlled plant, which is a two mass system with backlash introduced between the motor and the linking shaft. Authors propose a test procedure which will take into account typical dynamical and steady states occurring in electrical drives. Moreover, modified quality indicators also are proposed in order to measure the influence of varying object parameter to the control process. During the research, authors changed the moment of inertia of the motor and the load as well as the backlash width. The results are summarized in tables in order to enable clear comparison between investigated methods. | Comparison of Robustness of Selected Speed Control Systems Applied for Two Mass System with Backlash | 10.1007/978-3-030-50936-1_114 |
2020-01-01 | The paper is concerned with a laboratory study on wave damping efficiency of structures of this type, needed for their functional design. Systematic test series of dikes without and with piles were carried out to evaluate wave energy dissipations by the porous base and rows of piles are evaluated separately so that they can flexibly be combined into a general formulation for the structure as a whole. The derived formulation shows very good agreement with the laboratory data. | Wave Damping Efficiency of Porous Piled Dikes on a Mangrove Foreshore | 10.1007/978-981-15-0291-0_118 |
2020-01-01 | The frequency response analysis (FRA) is a known highly sensitive method to detect mechanical and electrical defects in power transformers. Investigations already showed, that this technique is applicable to detect broken windings or shorted turns in rotor and stator of rotating machines. Here, the applicability of FRA to other defects was investigated, like broken rods of damping windings in synchronous machines or in a squirrel cage of induction motors, which often can be detected only by disassembling the machine. The reason lies in the design: damping windings as well as the squirrel cages have no accessible outer terminal, which can be used for electrical measurements. As the FRA method is capable to measure also capacitive or inductive couplings, it might be a possible low effort alternative. This investigation focuses on the reliability of failure detection. For a clear conclusion, numerous tests were performed on rotating machines of different types. It was found, that the frequency response can be measured on assembled rotating machines highly reproducible up to 1 MHz in different setups. Main factors to be considered are a good connection technique and a clear description of the measurement setup for later tests. A comparative analysis is only possible for the same phase configuration as well as the same rotation angle of the rotor. Similar to power transformers a time-based comparison is preferred. Different phases have not exactly the same frequency responses. For the investigation described in this contribution, broken rods in a squirrel cage of a 55 kVA induction motor and in the damping winding of a 37 kVA synchronous machine were reproduced. It was found, that the FRA method is sensitive enough to identify even single defects. | Reliable Diagnostics on Rotating Machines Using FRA | 10.1007/978-3-030-31676-1_70 |
2020-01-01 | We focus this study on the dynamics of a Rubber-Layer Roller Bearing (RLRB) for vibrational base isolation. By exploiting viscoelastic friction arising from rigid cylinders rolling on concave rigid plates padded with rubber layers, the device is able to provide a nonlinear damping behavior. Specifically, we consider the case of a two degrees of freedom system, in which an inertial mass is base-isolated from ground motion by mean of RLRB. We firstly investigate the system dynamic response under sinusoidal ground motion, then we focus on a real earthquake excitation. In both cases, the system equipped with nonlinear RLRB device presents smaller inertial load and displacement compared to the case of a system exploiting linear damping. Further, we show that an optimization can be performed on the physical parameters of the device (i.e. the viscoelastic material relaxation time and the cylinders spacing) in order to further enhance the system dynamic behavior. | Rubber-Layer Roller Bearings (RLRB) for Base Isolation: The Non-linear Dynamic Behavior | 10.1007/978-3-030-41057-5_109 |
2020-01-01 | The hybrid solution of natural-synthetic fibres can be an effective option to enhance the moisture resistance of natural fibre reinforced polymer composites. This work aims at studying the effect of long-term water immersion of hybrid composites on their mechanical and damping properties. These properties were investigated using free vibrations from samples composed of quasi-unidirectional flax and glass layers and epoxy resin. The results showed that the saturation mass uptake and the diffusion coefficient of the composites were strongly dependent on the stacking sequence between the flax and glass layers. For instance, less than 25 days were necessary to reach the water saturation when flax fibre reinforcements were in the outer layers, whereas it took over 10 months when these reinforcements were in the inner layers. Compared to the flax fibre reinforced composite, the flax-glass hybrid laminate with two inner flax layers and two outer glass layers was the most efficient for a specification where damping and bending modulus are the main criteria. This one enabled a significant increase in bending and specific bending moduli (+38 % and +79 % respectively compared to the unaged flax laminate), a considerable slowing down of the diffusion phenomenon, while limiting the decrease in damping property with ageing (−20 %). | Long-term Immersion in Water of Flax-glass Fibre Hybrid Composites: Effect of Stacking Sequence on the Mechanical and Damping Properties | 10.1007/s12221-020-9494-7 |
2020-01-01 | This paper experimentally investigates the static and dynamic properties of polypropylene fiber reinforced concrete (PPFRC). And also, the main objective of this present study is to examine the dynamic behavior of damaged and undamaged PPFRC beams in free-free constraints. The static properties have been carried out by conducting compression, splitting tensile and flexural strength. In addition to this, dynamic properties such as damping ratio, mode shape and fundamental frequency of PPFRC beams were also determined experimentally. In this paper, the influence of 0.1, 0.2, 0.3 and 0.4% variation of fiber contents by volume fraction of concrete with constant water-cementitious ratio of 0.31 was investigated for M50 grade of concrete. In order to determine the effect of polypropylene fibers in concrete and to compare, the properties of plain concrete have also been studied. The test results emphasize that the addition of fibers reduces the fundamental frequency and increase the damping ratio of concrete. Damping of PPFRC beams increases with the increase of damage while the fundamental natural frequency decreases with an increase of damage. The changes of fundamental natural frequency and damping values have been correlated to the damage degree of the prismatic beam experimentally. | Experimental Modal Analysis of Polypropylene Fiber Reinforced Concrete | 10.1007/978-981-13-9008-1_42 |
2020-01-01 | A key aspect of the seismic performance of bridges is the energy dissipation mechanism. The most usual mechanisms are the formation of plastic hinges in the piers, seismic isolation, and the addition of supplemental damping devices (such as hydraulic or hysteretic dampers). The present study assesses the feasibility of an energy dissipation device that has not been used in bridges before, consisting of special steel links installed at the abutments. First, the behaviour of these devices is evaluated, and an analytical (finite element) model is developed, informed by test results. Then the response of an actual railway bridge to a number of input motions is studied; in one case the bridge is equipped with hydraulic dampers and in the second with the proposed steel links. It is found that the energy dissipation and the performance of the bridge are similar in both cases, which is a first indication that the proposed system, which has a lower cost than hydraulic dampers, is worth exploring further as an alternative option for providing supplemental energy dissipation in bridges. | Alternative solutions for supplemental energy dissipation in bridges | 10.1007/s10518-019-00733-x |
2020-01-01 | This paper focus on the nature of a high-damping soft elastic material based on Eucommia ulmoides gum (EUG) obtained by epoxidation of EUG first and then in situ reaction between epoxy group and sodium bisulfite. The influence of degree of modification ( M mol%) and degree of sulfonation ( S mol%) of the product sulfonated E. ulmoides gum (SEUG) on the melting–crystallization behavior, tensile properties and dynamic mechanical properties is analyzed mainly. The results show that M mol% is the key factor in controlling the aggregation structure and static or dynamic mechanical behavior of SEUG, while the introduced sodium bisulfite groups show strengthening and toughening effect to some extent. Besides, the SEUG with high M mol% shows dramatically high tan δ value. With M mol% increasing, the tensile strength and Shore A hardness of SEUG decrease sequentially, while the elongation at break increases visibly. SEUGs with M mol% above 20.3 display soft and elastic stress–strain behavior. At similar M mol% level, SEUG with higher S mol% shows higher tensile strength and lower elongation at break than the one with lower S mol% value. These are attributed to the transformation of the aggregate structure and the introduction of ion interaction. The maximum tan δ value of SEUG reaches up to 2.19. The removal of the restriction effect of crystal region on the molecular motion of amorphous and the increased intermolecular interaction are thought to be main causes. | Preparation of high-damping soft elastomer based on Eucommia ulmoides gum | 10.1007/s00289-019-02723-0 |
2020-01-01 | Tuned liquid column dampers (TLCDs) have an extensive usage as effective vibration absorbers to enhance the structure response under the effect of seismic or wind loads. In this study, parameter optimization of nonlinear model of a TLCD in frequency domain under harmonic excitation is proposed in order to improve the performance of TLCDs. The nonlinearity in the model is due to the head-loss caused by the orifice resulting in velocity squared damping. A six-story building with a TLCD is considered as a case study. Describing function method (DFM) is used to model the nonlinear effects in frequency domain which results in a set of nonlinear algebraic equations. The resulting set of nonlinear equations is solved by Newton’s method utilizing Homotopy Continuation. The effect of change of TLCD parameters (cross-sectional area, head loss coefficient, total length, horizontal length) on the overall system response is investigated through the developed nonlinear model. TLCD parameters are optimized utilizing genetic algorithm and gradient descent optimization methods. Response of the optimized and non-optimized models is compared in frequency domain. The linear and nonlinear models are also compared, and the necessity of introducing nonlinearity to the frequency domain model is addressed. | Frequency Domain Nonlinear Modeling and Analysis of Liquid-Filled Column Dampers | 10.1007/978-3-030-34747-5_5 |
2020-01-01 | The aim of the study is to demonstrate a couple of special states which can be encountered at the system of a ball moving in a spherical cavity working as a passive tuned mass damper (TMD) of slender engineering structures. The system includes six degrees of freedom with three non-holonomic constraints being under horizontal additive kinematic excitation. The Appell–Gibbs approach is used to deduce the governing differential system. Uniaxial and biaxial types of kinematic excitation are considered. Among biaxial, a special attention is paid to circular setting. Influence of the rolling and spinning damping in contact of the ball with cavity is discussed. Under uniaxial excitation is the system auto-parametric and posses multiple solutions. The individual response branches can be identified when the excitation frequency is swept up or down with respect to setting up of initial conditions. Among stable branches reveal those with very low and sometimes zero approaching stability level. Although the accessibility of relevant trajectories is often very subtle due to effect of the dynamic stability, these post-critical phenomena accumulate a lot of energy. Hence, they can be very dangerous for TMD and other important engineering systems. Some general recommendations for practice are formulated. | Stable and unstable solutions in auto-parametric resonance zone of a non-holonomic system | 10.1007/s11071-019-04948-0 |
2020-01-01 | The implementation, operation and efficacy of semi-active (SA) structural control systems based on the adoption of magnetorheological (MR) devices are still object of research. For a such system, generally a complex electronic equipment is required to acquire then elaborate then generate signals to properly command the smart devices in real time. Given this, the effectiveness of these control systems in reducing the seismic response of structures is often called into question. And one wonders about the performance of these systems in the long term, i.e. when called to respond to seismic actions after many years since their installation. Will the devices be ready to respond? Is their dissipative capacity still that exhibited before their installation? This work attempts to present a comprehensive description and offer suitable solutions for a number of specific aspects that characterize the implementation of SA control systems. Authors also highlight undesired and unavoidable effects and provide insights on the way to reduce their incidence. The performance of such system is then showed via a shaking table test of a full-scale steel structure. These tests allowed to measure the actual short-term effectiveness of this system. After 10 years of inactivity of those MR devices, these have been subjected characterization tests once again, in order to assess the evolution of their mechanical behaviour over time and the decay of performance. The long-term response in terms of readiness, dissipative capacity and reaction force was measured, leading to positive conclusions about the reliability of the control system after years of inactivity. | Use, Effectiveness and Long Term Reliability of MR Dampers for Seismic Protection of Framed Structures | 10.1007/978-3-030-41057-5_143 |
2020-01-01 | In this paper a model-based method for estimating the damper excitations and velocity amplitudes by means of synthetic road irregularities are shown. They are based on a stationary white noise process with power density 1. With two 1^st order filters it is possible to generate realistic synthetic road irregularities which are limited to an adequate magnitude level for both, small frequencies and higher frequencies. To estimate the damper excitations and velocity amplitudes two methods are presented. The first method is based on the standard deviation method, which takes the appearance probability of 99.7% of simulated damper excitations and velocity amplitudes into account. The main disadvantage of these method, no information of the amount of amplitudes can be extracted, can be overcome with the second method. It is based on the relative frequency of the damper excitations and velocity amplitudes. Three different synthetic roads based on the road types highway, main road and urban road, with an equivalent road surface quality index are generated. With a quarter vehicle model, which consists of a nonlinear so called VDA-characteristic simulations are presented to estimate the damper excitations and velocity amplitudes by means of the two described methods. | Model-Based Estimation of Damper Excitations and Velocities Due to Road Surface Irregularities with Focus on Ride Comfort | 10.1007/978-3-030-38077-9_202 |
2020-01-01 | Natural hazards like landslides, tsunami, earthquake, cyclone and volcanic eruption are most rigorous natural hazards in the environment that causes damage to structures. These natural calamities produce a potent remembrance because of heavy damage to the environment. Accordingly, a structural engineer faces a challenge of designing the structure which can tolerate the natural forces and protect all the structural member and dwellers, to all environmental forces like wind load, earthquakes, cyclones and tsunamis. In recent years, all the structures are designed with the earthquake protective system like passive protective system, active protective system and semi-active protective system for structural control. The semi-active protective system is preferred over others since it adopts the advantage of two systems as consistency of passive protective system and flexibility of active protective system. In this work, magnetorheological damper is chosen to regulate the vibration of a three-story benchmark structure. The damper is placed in between the ground and the first floor to produce required force by the structure which is excited for Kobe earthquake. This paper has considered the earthquake as uncertainty. Therefore, a robust controller is preferred because it produces the required controlled voltage to suppress the structural vibration even in the presence of the uncertainty. These controller parameters are tuned by ultimate gain method in MATLAB and Simulink. Current driver is used to convert the controlled voltage to controlled current and is applied to magnetorheological damper. This produces the controlled force which further is applied to the benchmark structure which is considered. Results obtained by robust controller and classical Proportional Integral Derivative (PID) controller are compared, and superiority of robust controller is presented. | Robust Controller for Seismic Response Mitigation | 10.1007/978-981-15-4676-1_12 |
2020-01-01 | This paper discusses averaging and vibrational control of mechanical control-affine systems with piecewise linear damping and high-frequency inputs. The results are used for dynamic analysis and vibrational control of a three-degree-of-freedom, planar, horizontal pendulum. The system has non-symmetric, linear viscous damping, and the pivot point of the pendulum moves along a prescribed elliptical path with “high” frequency. The dynamic analysis shows that the presence of non-symmetric damping results in change of periodic orbits or equilibria of the system or instability of an otherwise stable system. This paper presents the stability conditions of the system in terms of the physical parameters of the pendulum and the prescribed path. Using the results of dynamic analysis, the paper also discusses vibrational control of the system of horizontal pendulum. The analysis can be extended to mechanical control systems with nonlinear viscous forces, dry friction, or inviscid flow forces. | Vibrational control of mechanical systems with piecewise linear damping and high-frequency inputs | 10.1007/s11071-019-05361-3 |
2020-01-01 | Abstract Outbreaks of individual species populations are important phenomena in many aspects and are not alike in terms of the theory of multispecies community dynamics. Outbreaks of insect populations develop more quickly with long-lasting effects experienced by the forest industry. These events are considered as extreme unbalanced and transient processes. The mechanisms of the development and subsidence of insect outbreaks differ in different taxonomic groups of pests. The duration and occurrence of repeated outbreaks of psyllids and forest moths, which affect deciduous or coniferous forests in the same region, are different. Computational simulation is needed for understanding the dynamics of insect outbreaks. For the mathematical description of the outbreaks of forest tent caterpillar, in addition to the threshold version of the development of the insect outbreak, it is interesting to modify continuous computational models for the analysis of fluctuation dynamics. In this paper, we simulate the dynamics of spontaneously damping oscillations under a specific scenario during a population outbreak using a continuous model with delayed regulation and nonlinear counteraction by the biotic environment. The scenario described by the new phenomenological equation, which consists of a series of maxima of different sizes and final attenuation of peaks near balance, occurs for the pest tent caterpillar, Malacosoma disstria , which affects deciduous forests in North America leading to large-scale defoliation. The new scenario is qualitatively different from our model of the threshold development and subsidence of outbreaks of the psyllid Cardiaspina albitextura in Australia. | A Continuous Model for Oscillating Outbreaks of the Population of a Phytophagous Moth, the Tent Caterpillar, Malacosoma disstria (Lepidoptera, Lasiocampidae) | 10.1134/S0006350920010169 |
2020-01-01 | The present work investigates the effectiveness of Magnetorheological Damper (MR) damper coupled with the smart self-powered system, MR damper acts as electromagnetic induction (EMI) device in controlling seismic vibration. The proposed smart damping system with an EMI device is capable of converting vibration energy into electrical energy. Thus, the EMI device attached with MR damper can be used as an effective and alternative power source for the MR damper, making it a self-powering system. The primary aim of the experimental study is to identify the performance of the proposed smart damping system using time history loading (El Centro earthquake). For experimentation, the MR damper with EMI was designed and fabricated. To reduce sedimentation, nano Fe3O4 was used in the preparation of MR fluid. The performances of the proposed smart damping system are compared with the passive, semi-active and active control system in force and displacement to evaluate the effectiveness of the self-powered smart damping system in reducing seismic vibration. The experimental results show that the self-powered smart damping system produces more damping force and reduction in displacement. The maximum damping force obtained is 0.67 kN. In an active system, a force was increased by 12.9% and displacement was reduced by 13.4% when compared with the semi-active control system. The results revealed that the proposed EMI can act as a sole power source for the damping system. | Experimental Investigation of a Self-powered Magnetorheological Damper for Seismic Mitigation | 10.1007/978-981-15-0802-8_61 |
2020-01-01 | An innovative application of a new corrugated steel plate damper (CSPD) in steel arch bridges is proposed to enhance their seismic performance. The mechanical properties of the CSPD were investigated by static and quasi-static parametric analysis using ABAQUS software, and validation of the CSPD finite element models was conducted by comparing the numerical results with published experimental results. The results indicate that the CSPD has desirable mechanical properties and hysteretic performance when the geometric design parameters lie within a reasonable range. Then a selected CSPD with reasonable geometric design parameters was installed on the side piers of upper-deck type steel truss arch bridge to explore the resulting improvement in the seismic behaviour of the original arch bridge. The displacement and force responses indicate that the selected CSPD can improve energy dissipation and the seismic behaviour of the arch bridge in transverse and longitudinal directions in major earthquakes. | The Mechanical Properties of a New Corrugated Steel Plate Damper and Its Application in a Steel Arch Bridge | 10.1007/s12205-020-0888-2 |
2020-01-01 | In this paper, a Proportional Integral Derivative (PID) controller is designed to mitigate the vibration response of the structure. The simulation is done for three degrees of freedom system under different earthquakes using MATLAB and Simulink. Different earthquakes are considered to find the capability of the controller used. The controller is designed using tuning rules of Zeigler–Nichols ultimate gain method. The controller proposed will reduce the vibrations of the structure as compared to the vibrations obtained without controller. The controller output is given to Magneto-rheological (MR) damper which gives necessary force output, which will be applied to the structure to damp out its vibrations. | Classical PID Controller for Semi-active Vibration Control of Seismically Excited Structure Using Magneto-Rheological Damper | 10.1007/978-981-13-9213-9_19 |
2020-01-01 | We consider the damped wave equation with the energy critical power type nonlinearity. It is known that the global solution with a finite space-time norm decays to 0 as time goes to infinity. In the present paper, we give the asymptotic order that the solution goes to a solution of the linear heat equation. | Remark on Asymptotic Order for the Energy Critical Nonlinear Damped Wave Equation to the Linear Heat Equation via the Strichartz Estimates | 10.1007/978-3-030-58215-9_10 |
2020-01-01 | Chapter 8 is dedicated to the topic of controlled and uncontrolled responses to trauma, that is, wound healing and polytrauma, a topic that has been experiencing a paradigm change of medical thinking during the past 15 years. At first, the DAMP-promoted wound healing process as a classical homeostatic defensive function of the innate immune system, as well as its dysregulation in the form of keloid formation and chronic, nonhealing wounds is presented. The theme is followed by a burning topic of intensive care medicine, the polytrauma that, in its modern pathogenetic interpretation, is characterized by two emerging models that are proposed and discussed in detail. The first model refers to severe trauma-induced emission of DAMPs in excess, which trigger hyperinflammatory pathways known as systemic inflammatory response syndrome (SIRS), most often associated with multiple organ dysfunction/failure. The second tentative but clinically still unproven model refers to severe trauma-induced emission of suppressing DAMPs (SAMPs) in excess, which—by operating in parallel, only slightly delayed—may trigger counterbalancing hyperinflammation-resolving/immunosuppressive pathways known as compensatory antiinflammatory response syndrome (CARS), often associated with increased susceptibility of patients to infections. The various DAMPs and putative SAMPs so far reported to be involved in these two scenarios are described in detail. Finally, the emerging field of DAMPs and SAMPs in diagnosis, prognosis, and therapy in severely traumatized, acutely critically ill patients is discussed by focusing on a theoretical framework in the future exploitation of DAMPs and SAMPs as therapeutic targets in polytrauma. | DAMP-Controlled and Uncontrolled Responses to Trauma: Wound Healing and Polytrauma | 10.1007/978-3-030-53868-2_8 |
2020-01-01 | This paper presents the neuro-fuzzy modeling approach to analyze the test results of MR damper. Every Electric current in provides to MR Fluid will have a different output. On the other hand, the meandering type valve has a different output and calculation. Therefore, the prototype of MR Damper that has been made was taken to a laboratory to test using Dynamic Testing Machine. The data test result will be analyzed using Neuro-Fuzzy. This paper aims to find a correlation between every variable is there in the testing of MR Damper. For the hysteresis modeling purpose, some parts of the data are taken as the training data source for the optimization parameters in the Neuro-Fuzzy model. The performance of the trained Neuro-Fuzzy model is assessed by validating the model output with the remaining measurement data and benchmarking. The assigned membership function results in a minimum error of 0.16 from 3000 epoch from 3 sets of data given as training data. | Neuro-fuzzy Hysteresis Modeling of Magnetorheological Dampers | 10.1007/978-981-15-4481-1_59 |
2020-01-01 | Abstract Ribosomal genes encode ribosomal RNA (rRNA), which is an integral part of ribosomes. The main function of ribosomal genes in the cell is the synthesis of rRNA. However, ribosomal genes can also perform other functions in the body. It was found that DNA of ribosomal genes (rDNA) is an active biomolecule, which can be attributed to the family of DAMPs (danger-associated molecular patterns). Three unusual characteristics of rDNA confer to it the properties of a DAMP molecule: (1) high content of unmethylated CpG motifs—ligands of DNA sensing TLR9; (2) low oxidation potential; and (3) resistance to fragmentation under the accumulation of single-strand breaks in rDNA chains. Owing to these properties, rDNA fragments are accumulated as a part of circulating extracellular DNA and stimulate the TLR9–MyD88–NF-kB signaling pathway in various cells of the body. Oxidized rDNA permeates into the cells, where it can stimulate other DNA sensors (AIM2, RIG1, STING). Extracellular oxidized rDNA reaches the structures of the nucleolus and affects the level of rRNA in the cell. The body defends itself against the excess of extracellular rDNA by producing antibodies to rDNA, which form much stronger complexes with rDNA than common antibodies to double-stranded DNA. It is reasonable to further study extracellular rDNA as a potential target in the treatment of autoimmune, oncological, and cardiovascular diseases. | Noncanonical Functions of the Human Ribosomal Repeat | 10.1134/S1022795420010044 |
2020-01-01 | Under-platform damper is used to attenuate resonant response and further prevent high cycle fatigue failure of turbine blades. The aim of this work is to improve the representation of contact interfaces in modeling an asymmetrical under-platform damper. A new reduced-order contact model with a lumped parameter form is proposed, which is based on a modification of the classical Iwan model. This model can explicitly consider the normal contact pressure on line contact. In modeling process, a method to relate the physical Hertzian normal contact pressure with the probability density function (PDF) of slider sliding force for continuous Iwan model is developed. Experimental results from a laboratory asymmetrical under-platform damper test rig are employed to validate the proposed model. For comparison, different normal contact pressure distributions are considered. The out-of-phase motion of the damper is numerically investigated, and the results show that the proposed model can give an accurate prediction of the damper’s nonlinear mechanics behavior. | Reduced-Order Modeling Friction for Line Contact in a Turbine Blade Damper System | 10.1007/978-3-030-34747-5_20 |
2020-01-01 | Multiple pantograph operation is an unfavourable condition for current collection, since the trailing pantograph is subjected to high vibrations and elevated contact force variations, due to the perturbation induced on the overhead line by the leading pantograph. In a previous work it was shown that a diversification of preloads of front and rear pantographs, achievable using pressure regulation systems driven by electronic units, can have beneficial effects on current collection quality of the trailing pantograph. This paper investigates the concepts of differentiating the leading and trailing pantograph damping, and of varying the pantograph damping as a function of speed. A plan of numerical simulations is first performed considering a number of permutations of leading and trailing pantograph damping values, obtaining a map of optimal damping values for different train speeds. The numerical model of an electro-hydraulic damper, able to adapt its damping parameter is then proposed and integrated in the PCaDA model for the simulation of the dynamic interaction between pantograph and catenary. The numerical results corroborate the idea that the regulation of damping values as a function of train speed and orientation would allow improving the system performances and extending the operating speeds. | Semi-active Dampers for Multiple Pantograph Operation | 10.1007/978-3-030-38077-9_27 |
2020-01-01 | The influence of the nonlinearity of pendulum-tuned mass dampers (PTMD) on vibration control of H-section hangers was studied analytically. Firstly, the coupled system of a slender H-section hanger and an attached PTMD was simplified to a two-degree-of-freedom (2-DOF) system. The equations of motion were derived for the system under free vibration and forced excitation. Both linear and nonlinear results were obtained. Results show that the free vibration responses of the system are significantly different for linear and nonlinear solutions when the hanger subjects to the large initial displacements. A small structural damping of the H-section hanger has significant effects on enhancement of the pendulum motion stability. For the case of forced vibration, the displacement responses of the primary structure solved by nonlinear solution are smaller than that solved by the linear solution when the excitation amplitude is less than 0.3. However, the displacement responses of the primary structure considering pendulum nonlinearity are larger than the linear responses when the dimensionless excitation amplitude is gradually increased. | Nonlinear Behavior of Pendulum-Tuned Mass Dampers for Vibration Control of H-Section Hangers | 10.1007/978-3-030-34747-5_7 |
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