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2015-12-01 | Thermoelastic damping (TED) is a fundamental dissipation mechanism in micro/nano-scale resonators. Therefore, it is crucial to minimize this dissipation in design of these resonators. The problem has been formulated by the nonlocal theory of elasticity to take into account the small scale effect. Moreover, the Timoshenko beam model has been used to capture the transverse shear deformation and rotary inertia effects. The coupled thermoelastic equations have been derived using the generalized thermoelasticity theory based on dual-phase-lagging heat conduction model for transverse vibration of an electrostatically deflected short beam. A step-by-step linearization method has been used to escape from the nonlinearity. Afterwards, the Galerkin’s weighted residual method has been applied to discretize the coupled dynamic equations of a beam resonator with both ends clamped and isothermal. Then, the complex-frequency approach has been utilized to obtain eigenvalue solution and TED ratio. The numerical results addressing importance of the nonlocal effect on the TED ratio of the short beam resonators have been presented. | Analysis of bias DC voltage effect on thermoelastic damping ratio in short nano-beam resonators based on nonlocal elasticity theory and dual-phase-lagging heat conduction model | 10.1007/s11012-015-0171-7 |
2015-12-01 | Visco-elastic material models with fractional characteristics have been used for several decades. This paper provides a simple methodology for Finite-Element-based dynamic analysis of structural systems with viscosity characterized by fractional derivatives of the strains. In particular, a re-formulation of the well-known Newmark method taking into account fractional derivatives discretized via the Grünwald–Letnikov summation allows the analysis of structural systems using standard Finite Element technology. | Dynamic Finite Element analysis of fractionally damped structural systems in the time domain | 10.1007/s00707-015-1454-8 |
2015-12-01 | The two critical issues of robust control are stable controller synthesis and control performance guarantee in the presence of model uncertainties. Inside all robust stable solutions, small modeling parametric uncertainties lead to better performance controllers. However, the cost to develop an accurate hydrodynamic model, which shrinks the uncertainty intervals, is usually high. Meanwhile, when the robot geometry is complex, it becomes very difficult to identify its dynamic and hydrodynamic parameters. In this paper, the main objective is to find an efficient modeling approach to tune acceptable control design models. A control-oriented modeling approach is proposed for a low-speed semi-AUV (Autonomous Underwater Vehicle) CISCREA, which has complex-shaped structures. The proposed solution uses cost efficient CFD (computational fluid dynamic) software to predict the two hydrodynamic key parameters: The added mass matrix and the damping matrix. Four DOF (degree of freedom) model is built for CISCREA from CFD and verified through experimental results. Numerical and experimental results are compared. In addition, rotational damping CFD solutions are studied using STAR-CCM+ ^TM. A nonlinear compensator is demonstrated to tune linear yaw model for robust control scheme. | Modeling of a Complex-Shaped Underwater Vehicle for Robust Control Scheme | 10.1007/s10846-015-0186-2 |
2015-12-01 | We consider the vibrations of a cantilever structure modeled by the standard linear flexible model of viscoelasticity coupled to an expectedly dissipative effect through heat conduction. It is shown that the amplitude of such vibrations is bounded under some restriction of the disturbing force. Using multiplier technique, an uniform exponential stability of the system is obtained directly, when the disturbing force is insignificant. | Stability of the vibrations of an inhomogeneous flexible structure with thermal effect | 10.1007/s40435-014-0113-6 |
2015-12-01 | In the early Universe up to hydrogen recombination in the Universe, the radiation pressure was much greater than the pressure of baryons and electrons. Moreover, the energy density of cosmic microwave background (CMB) photons was greater than or close to the energy density contained in the rest mass of baryonic matter, i.e., the primordial plasma was a radiated-dominated one and the adiabatic index was close to 4/3. The small density perturbations from which the observed galaxies have grown grew as long as the characteristic perturbation scales exceeded the horizon of the Universe сt at that time. On smaller scales, the density perturbations were standing sound waves. Radiative viscosity and heat conduction must have led to the damping of sound waves on very small scales. After the discovery of the cosmic microwave background, J. Silk calculated the scales of this damping, which is now called Silk damping, knowing the CMBtemperature and assuming the density of baryons and electrons. Observations with the South Pole Telescope, the Atacama Cosmology Telescope, and the Planck satellite have revealed the predicted damping of acoustic peaks in the CMB power spectrum and confirmed one important prediction of the theory. In 1970, R.A. Sunyaev and Ya.B. Zeldovich showed that such energy release in the early Universe should lead to characteristic deviations of the CMB spectrum from the Planck one. The development of the technology of cryogenic detectors of submillimeter and millimeter wavelength radiation has made it possible to measure the CMB spectral distortions at 10^−8 of its total intensity (PIXIE). This has sharply increased the interest of theoretical cosmologists in the problem of energy release when smallscale sound waves are damped. We have derived a relativistic formula for the energy of a standing sound wave in a photon–baryon–electron plasma from simple hydrodynamic and thermodynamic relations. This formula is applicable for an arbitrary relation between the energy density of photons and the rest energy density of baryons and their thermal energy density. It continuously describes the transition between the two extreme cases. We obtain the expression for a radiation-dominated plasma in one limit and return to the expression for a gas of classicalmassive particles in the other limit. We have derived the relations that relate the amplitudes of velocity, baryon number density, and temperature perturbations in a radiation-dominated plasma of photons, baryons, and electrons. | Energy density of standing sound waves at the radiation-dominated phase of the universe expansion (hydrodynamic derivation) | 10.1134/S106377371512004X |
2015-12-01 | An experimental study is conducted on fully grouted reinforced masonry shear walls (RMSWs) made from concrete blocks with a new configuration. Ten RMSWs are tested under reversed cyclic lateral load to investigate the influence of different reinforcements and applied axial stress values on their seismic behavior. The results show that flexural strength increases with the applied axial stress, and shear strength dominated by diagonal cracking increases with both the amount of horizontal reinforcement and applied axial stress. Yield displacement, ductility, and energy dissipation capability can be improved substantially by increasing the amount of horizontal reinforcement. The critical parameters for the walls are derived from the experiment: displacement ductility values corresponding to 15% strength degradation of the walls reach up to 2.6 and 4.5 in the shear and flexure failure modes, respectively; stiffness values of flexure- and shear-dominated walls rapidly degrade to 17%–19% and 48%–57% of initial stiffness at 0.50 D _max (displacement at peak load). The experiment suggests that RMSWs could be assigned a higher damping ratio (∼14%) for collapse prevention design and a lower damping value (∼7%) for a fully operational limit state or serviceability limit state. | Experimental studies on behavior of fully grouted reinforced-concrete masonry shear walls | 10.1007/s11803-015-0030-5 |
2015-12-01 | 目 的 基于三维线性势流理论, 通过在近距两浮体间的自由液面上引入“粘性耗散系数”, 建立计及粘性影响的波浪中近距两浮体水动力干扰效应分析数值计算方法, 以准确分析两浮体的干扰力及浮体间液面升高;并探讨“粘性耗散系数”的确定方法、两浮体间流体共振频率及共振模式的数值计算方法。 方 法 1. 通过理论分析, 在三维线性势流理论基础上, 引入流体“粘性耗散”(公式2、10∼12、18和19)以准确模拟近距两浮体波浪中的水动力及浮体间液面抬升;2. 采用雷诺应力平均方程(RANSE)方法或试验方法确定“粘性耗散系数”(图2 和3);3. 采用数值计算和理论分析的方法给出近距两浮体间的流体共振模式(图8)及共振频率估算方法(公式21∼ 25)。 结 论 1. 采用三维线性势流理论并引入流体“粘性耗散系数”可较为准确地计算得到近距两浮体波浪作用下的受力及浮体间液面抬升;“粘性耗散系数”可通过RANSE 方法或试验方法获得;2.相比于其它因素(浪向角等), 近距两浮体间的干扰效应受横向间距影响较大;3. 采用类似于“月池”中流体共振频率分析方法获得的共振频率计算公式可用于估算近距两浮体间的流体共振频率, 同时不同共振频率时浮体间的流体共振模式得到了数值计算结果的验证。 In this study, we conducted numerical simulations of fluid resonance in-between two floating structures based on potential theory assessing the effect of fluid viscosity by including the artificial damping force. The numerical results of two adjacent Barges systems and Barge & Wigley systems were compared with experimental data of those of the viscous fluid model based on Reynolds average Navier-Stokes equations (RANSE). It can be observed that the conventional potential flow model (without artificial damping force) significantly over-estimated the wave height and forces around the resonant frequencies. Results of the present method with an appropriate damping coefficient supported the available data, confirming the importance of the viscous damping effect on strong hydrodynamic interaction between the floating structures. Furthermore, influences of lateral clearances, wave heading angles, and ships’ motions on the wave surface elevations were analyzed. Validation and application of methods to estimate the fluid resonant frequencies and modes were also conducted. Generally speaking, Molin’s simplified theory can give an accurate estimation of resonant frequencies and serve as a practical tool to analyze the fluid resonant phenomena of gaps in-between a two Barge system and Wigley & Barge system in close proximity. | Modeling of fluid resonance in-between two floating structures in close proximity | 10.1631/jzus.A1500017 |
2015-12-01 | In this work, we address experimentally the determination of the dynamical properties, in particular natural frequencies and damping factors, of laminated structural glass. Various specimens, coming from different productions and manufactures, are investigated. Damped free vibrations experiments are performed, where the excitation is provided by an instrumented hammer. The boundary conditions are free–free (the specimens lay on a very flexible sponge substrate). The dynamical characteristics are determined by last squares fitting of time histories, a technique that is very simple, fast and provides very good results. Finally, two theoretical models (a two-layer beam model and a 2D finite element model) are employed to interpret the experimental results, and to determine the (dynamical) elastic properties of the interlayer (which in the present case is made of PVB), which are very difficult to be determined directly. | On the experimental determination of dynamical properties of laminated glass | 10.1007/s12356-015-0040-z |
2015-12-01 | In this paper the projected gradient method is applied as an effective gradient-based topology optimization algorithm in order to direct energy propagation through the desired region of composites microstructure. Rayleigh Damping model is also used in order to take the effect of internal damping mechanisms into account and thus, to fill in the gap between the designed layouts and those in reality. The success of the proposed algorithm is illustrated through several numerical experiments by revealing a set of various designed optimal layouts besides their corresponding energy distributions. | Energy management through topology optimization of composites microstructure using projected gradient method | 10.1007/s00158-015-1295-z |
2015-12-01 | In this paper, we propose an augmented Lagrangian method based on the accelerated proximal gradient (APG) strategy for an inverse damped gyroscopic eigenvalue problem (IDGEP), which is a special case of the classical inverse quadratic eigenvalue problem. Under mild conditions, we show that the whole sequence of iterations generated by the proposed algorithm converges to the unique solution of the IDGEP. In view of the iteration-complexity, the proposed algorithm requires at most $$O(\log (\varepsilon ^{-1}))$$ O ( log ( ε - 1 ) ) outer iterations and at most $$O(\varepsilon ^{-1})$$ O ( ε - 1 ) APG calls to obtain an $$\varepsilon $$ ε -feasible and $$\varepsilon $$ ε -optimal solution of the IDGEP. Numerical results indicate that the proposed algorithm can solve the test problems efficiently. | The augmented Lagrangian method based on the APG strategy for an inverse damped gyroscopic eigenvalue problem | 10.1007/s10589-015-9757-1 |
2015-12-01 | Vibro-impacts of gear pairs in a torsion system inherently occur under the steady state torque input condition since clearance type nonlinearities are related to the torsional vibration induced by the firing stroke of an engine. In order to investigate the dynamic characteristics of gear rattle, front engine and front wheel drive configuration of the manual transmission is investigated under both wide open throttle and coast conditions. This configuration is examined using 6 degree-of-freedom system model, embedded by the relevant nonlinearities such as multi-staged clutch dampers, gear backlash and drag torques. This article focuses on the relationship of vibro-impacts with key parameters of clutch dampers, where the gear rattle phenomena are defined by “sing-sided”, “double-sided” and “no-impact” along with different clutch dampers. Thus, the mathematical model of the multi-staged clutch dampers is developed by including the asymmetric transition angles and pre-load effect. Based upon this nonlinear model, three real-life clutch dampers are employed and simulated results are compared with limited experimental measurements conducted on a vehicle. Also, the dynamic characteristics of gear motions under the coast condition are investigated. This coast condition is explained corresponding to different input torque conditions and its simulations show the main reasons of vibro-impacts induced by the clutch stopper well. Finally, modified clutch damper concepts for rattle-free transmission are proposed along with dynamic clutch design guidelines. | Analysis of vibro-impacts in a torsional system under both wide open throttle and coast conditions with focus on the multi-staged clutch damper | 10.1007/s12206-015-1117-7 |
2015-12-01 | Because of the rapid progress in the state-of-the-art R&D technology in the semiconductor and optical instruments industry, the microvibration performance requirements for high-technology facilities and R&D institutes have become increasingly severe. Therefore, the microvibrations of high-technology facilities due to nearby road and rail traffic has attracted considerable attention. A smart base isolation system was developed to protect structures from seismic excitation. The research presented thus far showed that a smart base isolation system effectively reduced both the structural responses and isolator displacements. On the other hand, the control performance of a smart base isolation system for microvibration has not been studied. Therefore, this study evaluated the microvibration control performance of a smart base isolation. An MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. The microvibration control performance was compared with that of a passive lead rubber bearing (LRB) isolation system. A train-induced ground acceleration was used as the excitation source for microvibration. A fuzzy logic control algorithm (FLC) was used to effectively control the smart base isolation system and a multi-objective genetic algorithm was employed to optimize the FLC. A sky-hook control algorithm was used as a comparative algorithm. The numerical simulation results showed that the smart base isolation system can effectively reduce the microvibrations of a high-technology facility subjected to train-induced excitation. | Evaluation of microvibration control performance of a smart base isolation system | 10.1007/s13296-015-1220-8 |
2015-11-18 | The aim of this paper is to investigate oscillatory properties of a class of second-order nonlinear differential equations with damping. Employing the generalized Riccati transformation and a class of functions, several oscillation criteria are presented that improve the results obtained in the literature. Two examples are presented to demonstrate the main results. | Some oscillation results for nonlinear second-order differential equations with damping | 10.1186/s13662-015-0688-z |
2015-11-01 | A prismatic semiquadratic element with a nonclassical approximation of its displacements is suggested for modeling the composite and soft layers of a torsion bar and multilayered plate-rod structures. The stiffness, weight, damping, and geometric stiffness matrices of the above-mentioned element are obtained. Expressions for computing stresses in the finite element under the action of static loads and vibrations in the resonance zone are presented. Test examples confirming the validity of the element suggested are given. An example of finite element determination of the dynamic response of a multilayered torsion bar in the resonant mode is considered. | Modeling the Elastic and Damping Properties of the Multilayered Torsion Bar-Blade Structure of Rotors of Light Helicopters of the New Generation. 1. Finite-Element Approximation of the Torsion Bar | 10.1007/s11029-015-9531-6 |
2015-11-01 | The linear plane problem of oscillations of an elliptic cylinder in an ideal incompressible fluid of finite depth in the presence of an ice cover of finite length is solved. The ice cover is modeled by an elastic plate of constant thickness. The hydrodynamic loads acting on the body are determined as functions of the oscillation frequency and the positions of the cylinder and plate. | Oscillations of a cylindrical body submerged in a fluid with ice cover | 10.1134/S002189441506019X |
2015-11-01 | Damping effect of the overland of a sub-basin has significant impact on the simulation accuracy of large-scale routing models; however, traditional large-scale routing models have often ignored this impact. To address this problem, we propose a sub-basin response function by combining unit hydrograph theory and sub-basin kinematic wave routing. Specifically, supposing that 10 mm net rainfall input in the sub-basin, the kinematic wave is used to route the net rainfall to the outlet pixels based on high resolution routing network, and the outlet discharge are normalized as sub-basin response function. Meanwhile, the geomorphic function was established to determine the river routing parameters based on observed data. The results of model application demonstrate that the model has satisfactory simulation accuracy both in outlet discharges and in spatial distribution. And simulation with different grid scales brings similar results, illustrating that the model is scale independent. Particularly, the outlet simulation accuracy of the routing model involving sub-basin response function is higher than before. | Development of a Large-Scale Routing Model with Scale Independent by Considering the Damping Effect of Sub-Basins | 10.1007/s11269-015-1115-7 |
2015-11-01 | We study large deviations in the Langevin dynamics, with damping of order $$\epsilon ^{-1}$$ ϵ - 1 and noise of order 1, as $$\epsilon \downarrow 0$$ ϵ ↓ 0 . The damping coefficient is assumed to be state dependent. We proceed first with a change of time and then we use a weak convergence approach to large deviations and its equivalent formulation in terms of the Laplace principle, to determine the good action functional. Some applications of these results to the exit problem from a domain and to the wave front propagation for a suitable class of reaction diffusion equations are considered. | Large Deviations for the Langevin Equation with Strong Damping | 10.1007/s10955-015-1346-2 |
2015-11-01 | The effect of constraints for the travel of the working body of a roller damper on its tuning parameters is studied. A simple procedure for determining the tuning parameters of a roller damper with such constraints is proposed. A numerical experiment is conducted to obtain nomograms representing the dependence of the tuning parameters on the constraints. It is shown that the tuning parameters of the roller damper differ considerably from those of the roller without the constraints | Determining the Tuning Parameters for a Roller Damper with Constraints | 10.1007/s10778-015-0726-2 |
2015-11-01 | The initiation and propagation of damage such as cracks in an engineering structure under dynamic loadings is a nonlinear process. Strictly speaking, conventional eigenvalue and eigenvector extraction-based damage identification approaches are suitable for linear systems only. Due to the unique nonlinearities associated with each civil engineering structure, it would be inefficient to attempt to express the nonlinear restoring force (NRF) of an engineering structure such as a reinforced concrete structure in a parametric form. Consequently, it is highly desirable to develop a general nonlinear identification approach to achieve structural damage detection in both qualitative and quantitative ways without the assumption on the parametric model of the hysteretic behavior. In this paper, based on a double Chebyshev polynomial function, a time-domain identification approach is proposed for identifying both the structural NRF and the mass distribution for multi-degree-of-freedom (MDOF) structures under incomplete dynamic loadings. As a typical nonlinear material, shape memory alloy (SMA) is introduced to a MDOF structural model to mimic the nonlinear behavior under dynamic loadings. The feasibility and robustness of the proposed approach is validated via (1) a numerical MDOF structure model equipped with a SMA damper whose restoring force is described by a double-flag-shaped nonlinear model, and (2) an experimental study on a four-story shear building structure model equipped with an in-house design of a SMA damper used to mimic the structural NRF under incomplete impact loadings. The identified NRF is compared with the theoretical values and the measurements in experiment. Both numerical and experimental results show that the proposed approach is capable of identifying both the mass distribution and structural nonlinearity under dynamic loadings, and could be potentially used for damage initiation and propagation monitoring during vibration of engineering structures under dynamic excitations. | Model-free nonlinear restoring force identification for SMA dampers with double Chebyshev polynomials: approach and validation | 10.1007/s11071-015-2257-0 |
2015-10-01 | In this paper, the phenomenon of stochastic resonance (SR) in a harmonic oscillator with fractional-order external and intrinsic dampings under the external periodic force is investigated. Applying the Shapiro–Loginov formula, fractional Shapiro–Loginov formula, generalized fractional Shapiro–Loginov formula and the Laplace transform technique, we obtain the analytic expressions of the first moment and the amplitude of the output signal. By studying the impacts of the driving frequency, system parameters and the noise parameters, we find the non-monotonic behaviors of the output amplitude. The results indicate that the bona fide SR, the generalized SR and the conventional SR phenomena occur in the proposed model. Furthermore, the numerical simulations are presented to verify the effectiveness of the analytic result. | Stochastic resonance in a harmonic oscillator with fractional-order external and intrinsic dampings | 10.1007/s11071-015-2174-2 |
2015-10-01 | Machining vibrations are harmful to workpiece surface quality and tool life, especially for thin-walled parts. A lightweight damping device is proposed by utilizing eddy current damping, and it can be easily attached onto the workpiece surface by glue. The cylindrical device is mainly composed of a magnet, an aluminum cylindrical conductor, and two springs. An induced repulsive force due to the machining vibration is generated and transmitted to the workpiece and then contributed to the vibration attenuation. Dynamic response evaluation on a cantilever beam by hammer tests demonstrates that the device is able to damp vibration mode and the effect of additive mass on the beam dynamics is investigated by roving the attaching point. Moreover, the device is applied to damp multiple modes and attenuate machining vibration of a thin-walled frame. Machining tests under different configurations of cutting parameters are carried out, and its effectiveness of wide band and adaptability to the varying machining processes are validated. | Milling vibration attenuation by eddy current damping | 10.1007/s00170-015-7239-3 |
2015-10-01 | The equation of motion for the response of SDOF systems is presented in terms of energy for a general class of hysteretic relationships that include stiffness degrading inelastic and bilinear elastic behavior, for systems subjected to earthquake ground motions in the presence or absence of P-delta effects. The evaluation of expended energy is presented in a continuous form, along with the evaluation of input energy associated with second-order geometric effects. Examples illustrate the dissipation of energy through damping and hysteretic response and the increase in input energy associated with P-delta effects. | Energy components in nonlinear dynamic response of SDOF systems | 10.1007/s11071-015-2208-9 |
2015-10-01 | We investigate the practice of regularization (also termed damping) in inverse problems, meaning the use of prior information to supplement observations, in order to suppress instabilities in the solution caused by noisy and incomplete data. Our focus is on forms of regularization that create smooth solutions, for smoothness is often considered a desirable—or at least acceptable—attribute of inverse theory solutions (and especially tomographic images). We consider the general inverse problem, in its continuum limit. By deconstruction into the part controlled by the regularization and the part controlled by the data kernel, we show the general solution depends on a smoothed version of the back-projected data as well as a smoothed version of the generalized inverse. Crucially, the smoothing function that controls both is the solution to the simple data smoothing problem. We then consider how the choice of regularization shapes the smoothing function, in particular exploring the dichotomy between expressing prior information either as a constraint equation (such as a spatial derivative of the solution being small) or as a covariance matrix (such as spatial correlation falling off at a specified rate). By analyzing the data smoothing problem in its continuum limit, we derive analytic solutions for different choices of regularization. We consider four separate cases: (1) the first derivative of the solution is close to zero, (2) the prior covariance is a two-sided declining exponential, (3) the second derivative of the solution is close to zero, and (4) the solution is close to its localized average. First-derivative regularization is put forward as having several attractive properties and few, if any, drawbacks. | Relationship Between Data Smoothing and the Regularization of Inverse Problems | 10.1007/s00024-015-1059-0 |
2015-10-01 | A numerical solution was derived to determine wave field in a converging channel bounded by rubble-mound jetties. The solution was achieved by applying boundary element method. The model was applied to analyze the effect of channel convergence, the cross-section of the jetties and their physical and damping properties on wave field in the channel. The study reveals numerous non-intuitive results specific for jetted and convergent channels. The analysis shows that wave reflection is usually low and is of secondary practical importance. Wave transmission strongly depends on the channel geometry and transmitted waves may be higher than incident waves, despite reflection and damping processes. Moreover, wave transmission depends on physical and damping properties of rubble jetties and the results show that wave transmission may increase with the increasing damping properties of jetties, which is a non-intuitive feature of wave fields in jetted channels. The analysis reveals several novel results of practical importance. It is shown that the rubble-mound jetties should be constructed from the material of high porosity, which ensures low transmission. More attention should be devoted to hydraulic properties of porous materials. It is recommended to use the material of moderate damping properties. The material of high damping properties often increases the wave transmission. It is possible, by a selection of rubble-mound material, to obtain lower transmission level for steep waves than for waves of moderate steepness. A series of laboratory experiments were conducted in the wave flume to verify the theoretical results. The comparisons show that theoretical results are in fairly good agreement with experimental data. | Wave propagation in a converging channel of arbitrary configuration | 10.1007/s13344-015-0054-7 |
2015-10-01 | In this work, a new dissipative contact force model, based on the foundation of Hertz contact law, is presented for impact analysis in multibody dynamics. A hysteresis damping force is introduced in the model for capturing the energy loss during the contact process. An approximate function, representing the relationship between the deformation velocity and deformation, is used to calculate the energy loss due to the damping force. The difference between the compression phase and restitution phase during the contact process is taken into account in the energy loss calculation. For illustration, four different contact force models are applied in a numerical example to compare their behaviors. The results are presented in the form of dynamic simulations in a multibody system, which allow comparison of the differences and similarities among the four contact models. They show the validity of our model for soft or hard contact problems. | A dissipative contact force model for impact analysis in multibody dynamics | 10.1007/s11044-015-9453-z |
2015-10-01 | In this research, a series of epoxy-silicone copolymers were prepared from methyl phenyl silicone intermediates (PMPS) with a bisphenol A type epoxy resin (E-51) by condensation with dilaurate dibutyltin acting as catalyst. The chemical structure of the siloxane-bridged epoxy resin was characterized by Fourier transform infrared spectroscopy (FTIR), ^1H-NMR and an epoxy equivalent weight (EEW) test. The modified epoxy resins showed better elongation at break and izod notched impact strength than neat resin. TGA results revealed that the residue at 600 °C of the modified epoxy resin increased with the increase of siloxane content. DMA tests displayed that the addition of silicone effectively enhanced the damping properties. Morphology studies indicated that the increase in izod notched impact strength is due to the suitable diameter of silicone phases because of the silicone toughening effect. | Silicone modified epoxy resins with good toughness, damping properties and high thermal residual weight | 10.1007/s10965-015-0852-x |
2015-10-01 | Finite element simulations are being more and more applied when studying the crash-worthiness of vehicles during impact. This paper deals with setting up such a simulation and discusses several ways to simplify and verify a simulated crash. For this purpose, a notch impact-testing machine will be released from a certain angle and crash into a model constructed with three different wall thicknesses. The plastic and elastic deformation is measured in the front of the model and is then used for validation of the simulation. In the end, the simulation was found to be in good agreement with the real crash data. | Development and validation of a nonlinear dynamic impact model for a notch impact | 10.1007/s00170-015-7144-9 |
2015-10-01 | Based on the dynamic characteristics obtained with a three-dimension finite element method, a reduced mechanical model and parameters for the ship lift can be modified and obtained. Simulated analysis shows that the reduced mechanical model can adequately represent the dynamic characteristics of the ship lift. The wind-induced vibrations and seismic responses of the structure were calculated respectively. A fuzzy semi-active control strategy for seismic response reduction using a magnetorheological damper was presented. A roof intelligent isolation system was also proposed. Simulation analysis results show that the fuzzy semi-active control with a magnetorheological smart damper is beneficial in suppressing the seismic whiplash effect on the top workshop and confirm that the fuzzy semi-active control strategy is valid in this scenario. | Fuzzy semi-active control and analysis of wind-induced vibration of a ship lift | 10.1617/s11527-014-0400-x |
2015-09-01 | Discontinuous deformation analysis (DDA) is a numerical method for analyzing the deformation of block system. It employs unified dynamic formulation for both static and dynamic analysis, in which the so-called kinetic damping is adopted for absorbing dynamic energy. The DDA dynamic equations are integrated directly by the constant acceleration algorithm of Newmark family integrators. In order to have an insight into the DDA time integration scheme, the performance of Newmark time integration scheme for dynamic equations with kinetic damping is systematically investigated, formulae of stability, bifurcation, spectral radius, critical kinetic damping and algorithmic damping are presented. Combining with numerical examples, recognition and suggestions of Newmark integration scheme application in the DDA static and dynamic analysis are proposed. | Performance of DDA time integration | 10.1007/s11431-015-5893-1 |
2015-09-01 | Both the friction caused by the preload in locked joints and the impact caused by clearance in unlocked joints cause energy dissipation in jointed deployable structures. The energy dissipation of locked joints is studied by analyzing the force on the infinitesimal body of the joint. The jointed beam with an unlocked joint is simplified into an impact mass-spring model with clearance, which considers the coefficient of restitution of impact. The energy dissipations of the joint caused by friction and clearance are transformed into damping ratios by Taylor expansion. Then, the effects of pressure, clearance and the dynamic parameters on the damping of joints are analyzed by utilizing the damping ratio formulation. The damping ratio increases with the preload and the clearance. To validate the damping ratio formulation of joints, experiments on a single jointed beam with preload and double jointed beams with clearance are conducted. Comparison between the experimental results and the model simulation results shows that the friction and impact damping models are accurate for the dynamic calculation of deployable structures. Furthermore, the damping ratio formulations can be directly introduced into the design and dynamic analysis of deployable structures. | Damping formulations for jointed deployable space structures | 10.1007/s11071-015-2119-9 |
2015-09-01 | In combination with a wave action balance equation, a damping model for sea waves covered by oil films of a finite thickness is proposed. The damping model is not only related to the physical parameters of the oil film, but also related to environment parameters. Meanwhile, the parametric analyses have been also conducted to understand the sensitivity of the damping model to these parameters. And numerical simulations demonstrate that a kinematic viscosity, a surface/interfacial elasticity, a thickness, and a fractional filling factor cause more significant effects on a damping ratio than the other physical parameters of the oil film. From the simulation it is also found that the influences induced by a wind speed and a wind direction are also remarkable. On the other hand, for a thick emulsified oil film, the damping effect on the radar signal induced by the reduction of an effective dielectric constant should also be taken into account. The simulated results are compared with the damping ratio evaluated by the 15 ENVISAT ASAR images acquired during the Gulf of Mexico oil spill accident. | The damping model for sea waves covered by oil films of a finite thickness | 10.1007/s13131-015-0729-1 |
2015-09-01 | This paper discusses the new concept of a hybrid damper for application in low-frequency accelerometers. A hybrid damping structure is proposed in which an air damping principle and an eddy current damping principle are integrated into one damping structure. A prototype of the hybrid damper was fabricated and applied to a low-frequency accelerometer structure. A free-vibration test was conducted on the accelerometer structure in various damping configurations: air-damped, eddy-current-damped and hybrid-damped. The experimental results indicate that the proposed hybrid damper exhibits good damping performance in comparison with single-damped cases while still maintaining their original advantages, such as their low cost, simple structure and nonsealing, nonelectric system. The proposed hybrid damping system will be useful for other small machinery devices in real applications. | An experimental study on a new air-eddy current damper for application in low-frequency accelerometers | 10.1007/s12206-015-0805-7 |
2015-09-01 | We consider the memory relaxation of an Euler–Bernoulli plate equation with nonlinear source term and internal frictional damping of arbitrary polynomial growth. The main focus is the existence of a smooth global attractor for the associated dynamical system. | Existence of smooth global attractors for nonlinear viscoelastic equations with memory | 10.1007/s00028-014-0270-2 |
2015-09-01 | The problem of the forced axisymmetric vibrations and self-heating of a hinged cylindrical shell with piezoelectric layers (sensor and actuator) is solved. The mechanical and electric excitation of vibrations is considered. The possibility of damping the mechanical vibrations by applying the appropriate voltage to the actuator electrodes is examined. The effect of the temperature dependence of the viscoelastic properties of the materials on the frequency dependence of the deflections and self-heating temperature and the sensor voltage is studied when the shell is harmonically loaded in the range of the fundamental resonance of its bending mode | Resonant Axisymmetric Vibrations and Vibrational Heating of a Viscoelastic Cylindrical Shell with Piezolayers Subject to Electromechanical Excitation | 10.1007/s10778-015-0712-8 |
2015-09-01 | A numerical implementation of system identification from non-linear and non-stationary signals is presented. The continuous wavelet transform (CWT) along with the complex Morlet wavelet skeleton curve extraction and Hilbert Transform (HT)-based methodologies are used for identification purposes. A comparison of the advantages of each technique in the analysis of non-stationary free decay systems is presented and improvements to the current methodologies are proposed. The HT approach offered good results in the estimation of the instantaneous amplitude in low damping and non-noisy signals. However, it is highly sensitive to impulses and irregularities in the signal, which affects the proper detection of frequency and amplitude parameters in real-life signals. The CWT exhibited better results for the analysis of noisy signals, from the resulting wavelet map the noise content can be distinguished from the actual system response. That is, the modes show a distinctive pattern in the map allowing proper modal extraction. However, for highly damped non-stationary decaying signals, the results are affected by the decay rate, round-up errors, and edge effects. | On the identification of damping from non-stationary free decay signals using modern signal processing techniques | 10.1007/s40091-015-0096-3 |
2015-09-01 | We investigate the dynamic stability of a pipe that conveys fluid, clamped or pinned at one end and with an intermediate support, thus exhibiting an overhang. The model of the pipe incorporates both Euler–Bernoulli and Bresse–Timoshenko schemes as well as transverse inertia. Material and external damping mechanisms are taken into account, while the conveyed fluid is supposed to be in fully turbulent flow. The pipe can rest on a linear elastic Winkler soil. The influence of all the physical quantities and of the overhang length on the critical velocity of the fluid front is investigated. Some numerical results are presented and discussed. | A contribution to the stability of an overhanging pipe conveying fluid | 10.1007/s00161-014-0357-6 |
2015-09-01 | This paper presents a new concept of multi-axis wave energy converter (WEC), which can capture wave energy from multiple directions of motion. It describes the modelling of the multi-axis WEC and presents the results of laboratory experiments on the power capture of the multi-axis WEC in a wave tank subjected to synthesized scaled sea waves. The experiments investigate the influence of parameters such as buoy structure, damping and inertia modification (ballasting) on the hydrodynamic performance. The experimental results indicate that the multi-axis WEC yields very good performance under a variety of wave conditions. It is also demonstrated that, by utilizing more than one direction of motion, the multi-axis WEC proves capable of supplying more power than a single-axis WEC. This work constitutes a preliminary step towards the development of an advanced concept of WEC. | Wave tank experiments on the power capture of a multi-axis wave energy converter | 10.1007/s00773-015-0306-5 |
2015-09-01 | The amplitude-frequency characteristic equations of a nonlinear vibroprotection system with an isochronous roller damper are obtained in the first approximation. On the basis of these equations, we carry out a numerical experiment and propose a numerical-graphical method for determining the optimal tuning parameters of such a damper. It is shown that the natural damper tuning frequency in the nonlinear setting does not coincidewith the natural damper tuning frequency in the linear setting. Numerical analysis is also used to determine that the maximum amplitudes of the bearing body in the nonlinear problem exceed themaximumamplitudes of the bearing body in the linear problem. It is shown that the use of the new isochronous roller damper permits dramatically decreasing the forced vibration amplitudes of bearing bodies. | Derivation of the amplitude-frequency characteristic equations of a vibroprotection system with an isochronous roller damper (a nonlinear model) | 10.3103/S0025654415050015 |
2015-09-01 | As a novel structural control strategy, tuned mass damper (TMD) inspired passive and semi-active smart building isolation systems are suggested to reduce structural response and thus mitigate structural damage due to earthquake excitations. The isolated structure’s upper stories can be utilized as a large scaled TMD, and the isolation layer, as a core design point, between the separated upper and lower stories entails the insertion of rubber bearings and (i) viscous dampers (passive) or (ii) resettable devices (semi-active). The seismic performance of the suggested isolation systems are investigated for 12-story reinforced concrete moment resisting frames modeled as “10 + 2” stories and “8 + 4” stories. Passive viscous damper or semi-active resettable devices are parametrically evaluated through the optimal design principle of a large mass ratio TMD. Statistical performance metrics are presented for 30 earthquake records from the three suites of the SAC project. Based on nonlinear structural models, including P-delta effects and modified Takeda hysteresis, the inelastic time history analyses are conducted to compute the seismic performances across a wide range of seismic hazard intensities. Results show that semi-active smart building isolation systems can effectively manage seismic response for multi-degree-of freedom (MDOF) systems across a broader range of ground motions in comparison to uncontrolled case and passive solution. | Aseismic smart building isolation systems under multi-level earthquake excitations: Part I, conceptual design and nonlinear analysis | 10.1007/s11709-015-0307-9 |
2015-08-28 | In this paper, a kind of half-linear impulsive delay differential equations with damping is studied. By employing a generalized Riccati technique and the impulsive differential inequality, we derive several oscillation criteria which are either new or improve several recent results in the literature. In addition, we provide several examples to illustrate the use of our results. | Oscillations of even order half-linear impulsive delay differential equations with damping | 10.1186/s13660-015-0791-4 |
2015-08-01 | This article is a continuation of our earlier work in Grobbelaar-Van Dalsen (Z Angew Math Phys 63:1047–1065, 2012 ) on the polynomial stabilization of a linear model for the magnetoelastic interactions in a two-dimensional electrically conducting Mindlin–Timoshenko plate. We introduce nonlinear damping that is effective only in a small portion of the interior of the plate. It turns out that the model is uniformly exponentially stable when the function $${{{\mathbf{p}}}({\mathbf{x}},{\mathbf{U}}_t)}$$ p ( x , U t ) , that represents the locally distributed damping, behaves linearly near the origin. However, the use of Mindlin–Timoshenko plate theory in the model enforces a restriction on the region occupied by the plate. | Exponential stabilization of magnetoelastic waves in a Mindlin–Timoshenko plate by localized internal damping | 10.1007/s00033-015-0507-0 |
2015-08-01 | The vibration amplitude, damping ratio and viscous damping force in capacitive micromachinedultrasonic transducers (CMUTs) with a perforated membrane have been calculated theoretically and compared with the experimental data on its vibration behavior. The electrical bias of the DC and the AC voltages and the operation frequency conditions influence the damping effect because leads to variations in the gap height and the vibration velocity of the membrane. We propose a new estimation method to determine the damping ratio by the decay rate of the vibration amplitudes of the perforated membrane plate are measured using a laser vibrometer at each frequency, and the damping ratios were calculated from those results. The influences of the vibration frequency and the electrostatic force on the damping effect under the various operation conditions have been studied. | Air damping effect on the air-based CMUT operation | 10.3938/jkps.67.486 |
2015-08-01 | Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids ( D _50,r/ D _50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10^-4% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D _50,r/ D _50,s causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice. | Shear modulus and damping ratio of sand-granulated rubber mixtures | 10.1007/s11771-015-2853-7 |
2015-08-01 | In this work we investigate the global existence, decay, and blow up of solutions for a quasilinear hyperbolic equation. We prove the decay estimates of the energy function by using Nakao’s inequality. Also, we obtain the blow up of solutions and lifespan estimates in three different ranges of the initial energy. | On the decay and blow up of solutions for a quasilinear hyperbolic equations with nonlinear damping and source terms | 10.1186/s13661-015-0395-4 |
2015-08-01 | A study on long wavelength propagation of shear and compression waves across jointed rocks is important as this condition exists in field. Wave propagation velocities and damping of waves across a jointed rock mass depend on many factors and orientation of rock joints is one of them. The experimental study on influence of joint orientation during wave propagation is carried out using resonant column apparatus. The jointed Plaster of Paris samples with and without infill material have been used to simulate the jointed rock mass with different orientations. The experiments and analyses are centered on propagation of shear and compression waves in jointed rocks with different orientations. Wave velocities and wave attenuations across frictional and filled rock joints are obtained for different strain levels and confining pressures. The results show that propagation of shear waves is dependent on joint orientation. Shear waves are attenuated more than compression waves and confining pressure decreases this influence of joint orientation. Results show that filled joints can damp the waves more easily than frictional joints. The joints oriented perpendicular to direction of wave propagation are more effective in damping compared to joints oriented parallel to the direction of wave propagation. | Long Wavelength Propagation of Elastic Waves Across Frictional and Filled Rock Joints with Different Orientations: Experimental Results | 10.1007/s10706-015-9874-8 |
2015-08-01 | This paper presents the use of a state of the art damper for high-precision motion stages as a sliding plate rheometer for measuring linear viscoelastic properties in the frequency range of 10 Hz–10 kHz. This device is relatively cheap and enables to obtain linear viscoelastic (LVE) fluid models for practical use in precision mechanics applications. This is an example of reversed engineering, i.e., turning a machine part into a material characterization device. Results are shown for a high-viscosity fluid. The first part of this paper describes the damper design that is based on a high-viscosity fluid. This design is flexure-based to minimize parasitic nonlinear forces such as hysteresis and stick-slip. In the second part of the paper, LVE fluid characterization by means of the damper setup is presented. Measurements are performed and model parameters are fitted by a non-convex optimization algorithm in order to obtain the frequency-dependent behavior of the fluid. The resulting fluid model is validated by comparison with a second measurement with a different damper geometry. This paper shows that LVE fluid characterization between 10 Hz and 10 kHz for elastic high-viscosity fluids is possible with a motion stage damper for which the undamped behavior is known. | Linear viscoelastic fluid characterization of ultra-high-viscosity fluids for high-frequency damper design | 10.1007/s00397-015-0862-y |
2015-08-01 | Concern about the effects of climate change have set in motion a search for flood protection measures to adapt coastlines to the foreseen accelerated sea level rise. In this context, the potential role of salt marshes to adapt the Wadden Sea’s flood defences was explored in the Netherlands Wadden Region Delta Programme. This paper provides an overview of the steps taken by the programme in developing a climate change adaptation strategy so that others might learn from its experiences. The second aim is to summarize the knowledge generated by the programme on the potential role of salt marshes as part of a climate change adaption strategy. Explorative modelling results indicate that Wadden Sea salt marshes affect wave heights, even under extreme conditions. Therefore, a salt-marsh zone in front of the Wadden Sea dikes that could keep pace with sea level rise may result in a reduced dike reinforcement task. A salt marsh potential map gives a rough impression of locations that are potentially interesting for salt marsh conservation and development, based on the current situation, on available information about abiotic conditions for salt marsh formation and the habitats present in the coastal zone. Besides elongated stretches were seminatural salt marshes are already present or developing, several stretches along the Dutch Wadden Sea coast have favourable abiotic conditions for salt marsh development. However, the prospects for integrating salt marshes into flood defences depend also on other aspects. Various nature conservation agreements are in effect with their associated obligations. Furthermore, the foreseen value of salt marsh development compared to traditional reinforcements, in terms of both costs and benefits, must be considered. | Salt marshes to adapt the flood defences along the Dutch Wadden Sea coast | 10.1007/s11027-015-9640-5 |
2015-08-01 | A design of offshore floating structure is mainly based on the extreme response analysis due to the forces experienced. The extreme response can induce the negative air gap response and potential impact to the deck bottom of floating structure. It is important to predict the slamming load in order to check the strength of local structures which withstand the wave slamming. In recent years, studies of the effects of wind load on air gap response and slamming load are ignored. When the platform suffers the extreme wave, the wind is also harsh. Moreover, the wind load can affect the motion response of the platform. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Though the model test results are not accurate enough for air gap and slamming load evaluation due to the loss of wind effect, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. This paper aims at presenting the sensitivity analysis results of wave slamming load with respect to the wind load for the design of semi-submersible platform. As an example of semi-submersible drilling platform design, the wind tunnel test has been carried out, and the sea-keeping model test is also performed in towing tank, while the wind load effect is ignored. According to the model test results, a numerical model is tuned and validated by ANSYS AQWA. Sensitivity analysis studies of the relative velocity between water particle and platform surface and the wave slamming load with respect to the wind load are performed in time domain by the tuned numerical model. Five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design. | Sensitivity analysis of wave slamming load with respect to wind load for semi-submersible platform design | 10.1007/s12204-015-1619-6 |
2015-08-01 | In this study, the stirred casting with various processing parameters, such as stirring temperature and stirring speeds, was carried out on the Al–Pb monotectic alloys in order to make Pb particles distribute much more uniformly. More importantly, their damping capacities were systematically studied. The results show that mechanical stirring can not only make Pb in the aluminum matrix uniformly distribute but also dynamically influence the damping capacity of this alloy system. The Al–Pb alloy was prepared under a slow speed at solid–liquid temperature region, wherein high volume fraction of Pb in alloy could be obtained. The high volume fraction of Pb gives high overall damping capacity. The dislocation damping and interface damping theories are mainly dominated to the alloys. | Stirred casting Al–Pb monotectic alloys with high damping capacity | 10.1007/s12598-014-0312-5 |
2015-08-01 | This paper presents laboratory experiments of wave-driven hydrodynamics in a three-dimensional laboratory model of constructed coastal wetlands. The simulated wetland plants were placed on the tops of conically-shaped mounds, such that the laboratory model was dynamically similar to marsh mounds constructed in Dalehite Cove in Galveston Bay, Texas. Three marsh mounds were placed in the three-dimensional wave basin of the Haynes Coastal Engineering Laboratory at Texas A&M University, with the center of the central wetland mound located in the center of the tank along a plane of symmetry in the alongshore direction. The experiments included two water depths, corresponding to emergent and submerged vegetation, and four wave conditions, typical of wind-driven waves and ocean swell. The wave conditions were designed so that the waves would break on the offshore slope of the wetland mounds, sending a strong swash current through the vegetated patches. Three different spacings between the wetland mounds were tested. To understand the effects of vegetation, all experiments were repeated with and without simulated plants. Measurements were made throughout the nearshore region surrounding the wetland mounds using a dense array of acoustic Doppler velocimeters and capacitance wave gauges. These data were analyzed to quantify the significant wave height, phase average wave field and phase lags, wave energy dissipation over the vegetated patches, mean surface water levels, and the near-bottom current field. The significant wave height and energy dissipation results demonstrated that the bathymetry is the dominant mechanism for wave attenuation for this design. The presence of plants primarily increases the rate of wave attenuation through the vegetation and causes a blockage effect on flow through the vegetation. The nearshore circulation is most evident in the water level and velocity data. In the narrowest mound spacing, flow is obstructed in the channel between mounds by the mound slope and forced over the wetlands. The close mound spacing also retains water in the nearshore, resulting in a large setup and lower flows through the channel. As the spacing increases, flow is less obstructed in the channel. This allows for more refraction of waves off the mounds and deflection of flow around the plant patches, yielding higher recirculating flow through the channel between mounds. An optimal balance of unobstructed flow in the channel, wave dissipation over the mounds, and modest setup in the nearshore results when the edge-to-edge plant spacing is equal to the mound base diameter. | Experimental study of wave dynamics in coastal wetlands | 10.1007/s10652-014-9384-x |
2015-08-01 | The dynamic mechanical properties of environment-friendly elastomeric composites consisting of reclaimed rubber (r-rubber), a waste product of roller processing of textile mill, and organic hindered phenol compound 4,4′-thio-bis(6- tert -butyl- m -methyl phenol) (AO-300) were investigated. With incorporation of AO-300 into the r-rubber, the storage modulus (E′) and loss modulus (E′′) of r-rubber were found to increase sharply, the maximum loss factor (tan δ ) peak value increased from 0.49 to 1.01, and tan δ peak position was significantly shifted from 6.19 to 34.42 °C, indicating that r-rubber/AO-300 composite is a promising damping material. Furthermore, r-rubber/AO-300 systems exhibited an exceptional damping performance in the wide temperature range and with increasing AO-300 content, the effective temperature range increased from 55.32 to 63.14 °C. Meanwhile, the presence of intermolecular hydrogen bonds in the composite was confirmed by FTIR. Furthermore, from the SEM analysis of various r-rubber/AO-300 systems, it could be seen that by introduction of a small amount of AO-300 to the r-rubber, a typical complex morphology and hybrid state were coexistent in the composites. When the AO-300 content was larger than the critical value, more excess AO-300 molecules were crystallized. Thus, a new type of environment-friendly r-rubber based high-performance damping materials with a broad temperature range of damping behavior was developed. | Processing and characterization of reclaimed rubber composite materials | 10.1007/s13726-015-0356-x |
2015-08-01 | We suggest to apply the Bubnov–Galerkin method to solving control problems for bilinear systems. We reduce the solution of a control problem to a finite-dimensional system of linear problem of moments. We show a specific example of applying this procedure and give its numerical solution. | The Bubnov–Galerkin method in control problems for bilinear systems | 10.1134/S0005117915080032 |
2015-08-01 | This paper tries to find the reasons of differences between results from semiactive suspension simulations and from real measurements. Simulations of semiactive algorithms which have already been published in many scientific papers have showned a great potential for improvement of the suspension quality. However, experiments with suspension controlled by semiactive algorithms which are supposed to improve grip did not bring any benefits. The reason of algorithm failure seems to be the response time of the damper used in the suspension. This paper compares the quality of suspension using three different semiactive algorithms (Skyhook, Groundhook, modified Groundhook) and passive settings for different damping levels. All the simulations were conducted for three different response times of MR damper: 1.5, 8 and 20 ms. Response time 20 ms is usual for commercial MR dampers control. Response time 8 ms corresponds to commercial MR dampers which are controlled by the newly developed PWM controller. Response time 1.5 ms corresponds to the fastest available MR devices. Simulations show a significant influence of the MR damper response time on the suspension quality if semiactive algorithms are used. The simulations are confirmed by measurements on a quarter car suspension controlled by modified Groundhook algorithm using MR damper with response time 8 and 20 ms. | Influence of MR damper response time on semiactive suspension control efficiency | 10.1007/s11012-015-0139-7 |
2015-07-01 | In this paper, we consider the damped harmonic oscillator with a time-dependent damping constant and a time-dependent angular frequency, which is actually the generalized Caldirola-Kanai Hamiltonian. For some choices of the time-dependent damping constant and the time-dependent angular frequency, we investigate the exact solutions. We also obtain the corresponding conserved quantities and finally discuss the quantum damped harmonic oscillator with a time-dependent damping constant and a time-dependent angular frequency. | On the exact solutions of the damped harmonic oscillator with a time-dependent damping constant and a time-dependent angular frequency | 10.3938/jkps.67.404 |
2015-07-01 | Friction is the primary concern of all mechanical systems having contacting surfaces in relative motion and is a major source of loss of power and performance. Friction introduces vibrations in a system; stick-slip induced vibration is one of them. Stick-slip can result when friction coefficient decreases with velocity, usually at low velocity. In most practical sliding applications, fluctuations of the sliding velocity are detrimental and so objectionable. Stick slip is critical in determining the lower performance bounds of a machine. One of the ways to eliminate stick slip from a system is to incorporate it with proper damping. A complete and universal analytical explanation of these observations is an important area of research in the field of system dynamics and control. In this work, the problem of dynamic behavior of a mass being dragged on a dry surface is studied in detail in the light of stiction friction models. The objective of this work is to identify proper damping for the set of other influencing parameters to eliminate stick slip from the system. In order to examine this range, numerical simulation is conducted on a model consisting of a spring-mass-damper system, dragged with constant velocity on a rough surface. | Proposed Critical Damping for a Spring Mass System to Avoid Stick Slip | 10.1007/s40032-015-0173-1 |
2015-07-01 | We consider the existence, both locally and globally in time, as well as the asymptotic behavior of solutions for the Cauchy problem of the sixth-order Boussinesq equation with damping term. Under rather mild conditions on the nonlinear term and initial data, we prove that the above-mentioned problem admits a unique local solution, which can be continued to a global solution, and the problem is globally well-posed. Finally, under certain conditions, we prove that the global solution decays exponentially to zero in the infinite time limit. | Existence and asymptotic behavior of solution of Cauchy problem for the damped sixth-order Boussinesq equation | 10.1007/s10255-012-0174-2 |
2015-07-01 | The present work is motivated by the asymptotic control theory for a system of linear oscillators: the problem is to design a common bounded scalar control for damping all oscillators in asymptotically minimal time. The motion of the system is described in terms of a canonical system similar to that of the Pontryagin maximum principle. We consider the evolution equation for adjoint variables as a perturbed observable linear system. Due to the perturbation, the unobservable part of the state trajectory cannot be recovered exactly. We estimate the recovering error via the L _1-norm of perturbation. This allows us to prove that the control makes the system approach the equilibrium state with a strictly positive speed. | Perturbation theory of observable linear systems | 10.1134/S0001434615070226 |
2015-07-01 | Vibratory systems that are used in linear optical scanners are significantly influenced by the properties of the surrounding fluid. Although, the dominant energy loss in scanner vibrations is caused by viscous effects, especially in non-microelectromechanical system (MEMS) scanners, the relative importance of viscous damping model is not well studied. In this study, a piece-wise method for calculating the damping ratio with logarithmic decrement to produce a numerical model which is able to predict the free response of a linear optical scanner is developed. The damping ratio function used in the model was derived by comparing and minimizing the deviation between the amplitude predicted by numerical model and the experimental data. The efficiency of this approach was tested on the basis of a torsional spring scanner. The results show significant improvement whereby the proposed model predicted the free response with a deviation of only 8% while the general exponential damping model produced a deviation of 20%. | An approach for nonlinear damping characterization for linear optical scanner | 10.1111/j.1747-1567.2012.00855.x |
2015-07-01 | Acoustic and damping properties of known and test chromium steels are investigated after heat treatment. Test metal microstructure and physicomechanical properties are studied. The increase in sound energy attenuation for a martensitic structure is determined. As a result of steel quenching, attenuation is reduced due to dislocation annihilation. | Development of Iron-Based Alloys with Improved Damping Capacity and Good Mechanical Properties | 10.1007/s11015-015-0089-2 |
2015-07-01 | Oscillations occurring in elastic structures and long mechanical transmissions of operating machines lead to an increase in regulation errors of the controlled coordinates and increase in the dynamic loads in electromechanical systems with elastic connections (EMSs with ECs), which decreases the quality of the manufactured products and reliability and long-term operation of the mechanisms and leads to significant economic damage. Determination of the limit capabilities of the electric drive (ED) while damping the oscillations of elastic mechanisms is of practical interest. A mathematical model of the electromechanical systems with elastic connections in the form of a Mason directed graph is considered. The main factors influencing the efficiency of damping of the electric oscillations of operating machines’ mechanical transmission by the ED are defined. The conditions of optimization and reasonable parameters of regulators of the slave regulation system (SRS) providing the smallest amplitude of the oscillations of the elastic mechanisms by the electric drive are found. The efficiency of the suggested recommendations on implementation of regulators of electromechanical systems with elastic connections has been confirmed in practice during modernization of an AT-500-230-1 roller electric drive processing plastic materials and balanced manipulators of MP-100 type. It is shown that the efficiency of damping the oscillations on the elastic mechanical transmissions of operating machines by the electric drove depends on the structure and parameters of the regulators of the slave regulation systems, the rational values of which should be determined taking into account the resonance frequency of an EMS with an EC. Settings are proposed of slave regulation systems permitted providing the minimum possible amplitude of oscillations of the torque in the elastic transmissions of the mechanisms caused by the change of the disturbing action. | Conditions of optimization and efficiency of damping of oscillations of elastic mechanisms by an electric drive | 10.3103/S1068371215070111 |
2015-07-01 | The insertion of damped braces proves to be very effective for enhancing the performance of a framed building under seismic loads. For a widespread application of this technique suitable design procedures are needed. In this paper a design procedure which aims to proportion damped braces to attain a designated performance level of the structure, for a specific level of seismic intensity, is proposed. In particular, a proportional stiffness criterion, which assumes the elastic lateral storey-stiffness due to the braces proportional to that of the unbraced frame, is combined with the displacement-based design, in which the design starts from a target deformation. To check the effectiveness and reliability of the design procedure, a six-storey reinforced concrete plane frame, representative of a medium-rise symmetric framed building, is considered as primary structure. This, designed in a medium-risk seismic region, has to be retrofitted as in a high-risk seismic region by the insertion of braces equipped with either metallic-yielding dampers or viscoelastic ones. Nonlinear dynamic analyses of unbraced and damped braced frames are carried out, under real (set A) and artificially generated (set B) ground motions, by a step-by-step procedure. Frame members and hysteretic dampers are idealized by bilinear models, while the viscoelastic dampers are idealized by a six-element generalized model describing the variation of the mechanical properties depending on the frequency, at a given temperature. | Displacement-based design procedure of damped braces for the seismic retrofitting of r.c. framed buildings | 10.1007/s10518-014-9709-7 |
2015-07-01 | The explicit equations of motion for a general $$n$$ n -body planar pendulum are derived in a simple and concise manner. A new and novel approach for obtaining these equations using mathematical induction on the number bodies in the pendulum system is used. Assuming that the parameters of the system are precisely known, a simple method for its control that is inspired by analytical dynamics is developed. The control methodology provides closed-form nonlinear control and makes no approximations/linearizations of the nonlinear system. No a priori structure is imposed on the controller. Globally, asymptotic Lyapunov stability is achieved along with the minimization of a user-provided control cost at each instant of time. This control methodology is then extended to include uncertainties in the parameters of the system through the use of an additional continuous controller. Simulations showing the simplicity and efficacy of the approach are provided for a 10-body pendulum system whose model is only known imprecisely. The ease with which the uncertain system can be controlled to move from any initial state to various final so-called inverted configurations is demonstrated. | Dynamics and control of a multi-body planar pendulum | 10.1007/s11071-015-2034-0 |
2015-07-01 | This paper deals with the solution of modified-Duffing ordinary differential equation for large-amplitude vibrations of imperfect rectangular plate with viscous damping. Lindstedt's perturbation technique and Runge-Kutta method are applied. The results for both methods are presented and compared for a validity check. It is proved that Lindstedt’s perturbation technique only works accurately for a small range of vibration amplitude. For a structure with a sufficiently large geometric imperfection, the well-known softenspring to harden-spring transforming backbone curve is confirmed and better developed. Although the softening to hardening behavior occurs twice in one backbone curve, the turning points share the same vibration frequency. Yet the amplitude for turning points varies due to the existence of imperfection. Moreover, the effect of damping ratio on vibration mode and vibration amplitude is studied. The usual nonlinear vibration tends to behave more linearly under the effect of large damping. | Accurate backbone curves for large-amplitude vibrations of imperfect rectangular plate with viscous damping | 10.1007/s12205-015-0114-9 |
2015-07-01 | A model of a medium consisting of parallel layers of elastic rectangular blocks separated by deformable viscoelastic interlayers is considered. The model is proposed for describing the lowfrequency part of the spectrum in waves propagating in media with such a structure. For a twodimensional assembly consisting of 36 blocks, the results of numerical calculations are compared with experimental data. | Wave propagation in two-dimensional block media with viscoelastic layers (Theory and experiment) | 10.1134/S0021894415040161 |
2015-07-01 | It is generally accepted that the generation of antibodies proceeds due to immunization of an organism by alien antigens, and the level and affinity of antibodies are directly correlated to the presence of immunogen. At the same time, vast experimental material has been obtained providing evidence of antibodies whose level remains unchanged and affinity is constant during a lifetime. In contrast to the first, adaptive immunoglobulins, the latter are named natural antibodies (nAbs). The nAbs are produced by B1 cells, whereas adaptive Abs are produced by B2. This review summarizes general data on nAbs and presents in more detail data on antigens of carbohydrate origin. Hypotheses on the origin of nAbs and their activation mechanisms are discussed. We present our thoughts on this matter supported by our experimental data on nAbs to glycans. | Hypotheses of the origin of natural antibodies: A glycobiologist’s opinion | 10.1134/S0006297915070032 |
2015-07-01 | The influences of Ca addition on the microstructures and damping capacities of AZ91-(0∼2)%Ca casting alloys were investigated, on the basis of the results of X-ray diffractometry, optical microscopy, scanning electron microscopy and vibration tests in a single cantilever mode. The amount of intermetallic compounds decreased with increasing Ca content up to 0.5%, above which it increased; the average cell size showed the opposite tendency. All alloys exhibited similar damping levels in the strain-amplitude independent region. Considering the very low solubility of Ca in the matrix, and that most of the Ca elements are consumed by the formation of the Al_2Ca phase and incorporation into the Mg_17Al_12 phase, this would be ascribed to the almost identical concentrations of Ca solutes distributed in the matrix. In the strain-amplitude dependent region, however, the AZ91-0.5%Ca alloy possessed the maximum damping capacity. From the viewpoint of microstructural evolution with Ca addition, the number density of compound particles is considered to be the principal factor affecting the damping behavior in the strain-amplitude dependent region. | Effect of Ca addition on the damping capacity of Mg-Al-Zn casting alloys | 10.1007/s12540-015-4367-0 |
2015-07-01 | We establish a new Kamenev-type theorem for a class of second-order nonlinear damped delay dynamic equations on a time scale by using the generalized Riccati transformation technique. The criterion obtained improves related contributions to the subject. An example is provided to illustrate assumptions in our theorem are less restrictive. | Kamenev-type criteria for nonlinear damped dynamic equations | 10.1007/s11425-015-4974-8 |
2015-07-01 | The magnetorheological (MR) damper is one of the utmost progressive applications of asemi-active damper. Uninterrupted controllability in both on and off state is an important factor of its plenitude application. Current research is attempting to make the damper more effective and efficient by minimizing the existing limitations such as MR fluid’s sedimentation, power consumption and temperature rising, and design optimization. We have broadly analyzed the optimization of MR dampers design with finite element simulation where various parameters of the MR damper have been considered for more accurate results. A prototype MR fluid has been prepared by coating the carbonyl iron particles with xanthan gum to reduce sedimentation. The SEM and Turbiscan results noticeably verify the improved sedimentation stability. In addition, a power-saving MR damper model has been developed by finite element analysis using ANSYS software. Prolonged operation raises the damper’s body temperature and degrades the performance. However, in this energy-saving MR damper model the temperature is not rising to a higher value compared to the conventional dampers, and consequently promotes damper efficiency. | ANSYS finite element design of an energy saving magneto-rheological damper with improved dispersion stability | 10.1007/s12206-015-0608-x |
2015-06-17 | We investigate the features of weakly nonlinear waves in a collisional dense plasma consisting of ultra-relativistic degenerate electrons and non-relativistic degenerate ions. In weak dissipation limit, the dynamics of low frequency nonlinear ion (solitary) wave is described by solving a damped Korteweg-deVries equation. The analytical and numerical analysis shows the existence of weakly dissipative solitons evolving with time. The characteristics of soliton evolution with plasma number density and slow ion-neutral collision rate are discussed with some detail. The relevance of the study with degenerate plasmas in ultra-dense astrophysical objects, particularly white dwarf stars is also pointed out. | Weakly dissipative solitons in dense relativistic-degenerate plasma | 10.1007/s10509-015-2415-3 |
2015-06-01 | Dynamic properties of two timber floor specimens are experimentally evaluated by the impact method. Each specimen uses one specified type of connectors, either screws or nails. A numerical model is developed using constrained degrees-of-freedom for the modeling of connectors. Numerical analyses have been performed, and show good agreement with experimental results. A procedure is written using the finite element software Abaqus to predict material damping from a strain energy approach. Estimation of structural damping is performed as the difference between the experimentally evaluated total damping and the predicted material damping. The contribution from floor members to material damping is extensively investigated. | Prediction of material damping in timber floors, and subsequent evaluation of structural damping | 10.1617/s11527-014-0286-7 |
2015-06-01 | The mechanical design of turbine blades aims at verifying the structural integrity against High Cycle Fatigue damage. For this reason Forced Responses are simulated in order to evaluate the distribution of variable stress in the blade. When resonant excitation can not be avoided in service, the mechanical damping is enhanced to reduce blade vibrations by the design of friction joints which dissipate energy by the slip of the contact surfaces. In this paper a test campaign is presented in order to collect a database of the nonlinear Frequency Response Functions (FRF) of a dummy blade by varying the normal contact load and the amount of excitation of the system. Two different geometries of blade root joints are tested: the dovetail and the crowned joint. Commissioning of the exciter and of the measurement system is described and discussed in order to define the fastest and most reliable FRF measurement. | Experimental Investigation on the Damping Effectiveness of Blade Root Joints | 10.1007/s11340-015-0001-9 |
2015-06-01 | The paper deals with a thermo-mechanical problem for a slender microbeam subjected to an electric actuation; the purpose of the study is to improve the knowledge of loss mechanisms in micro-electro-mechanical devices and to predict accurately the dynamical behaviour. The thermoelastic damping in microbeam resonators is strictly correlated to the mechanical behaviour, and the thermoelastic response of the structure changes significantly near critical frequencies. To fully understand the thermoelastic coupling effects, we add the description of the thermal phenomena to the mechanical problem obtaining a system of two coupled PDEs. The proposed governing equations, by making use of a unified model, are able to describe the response by using the classical thermoelastic formulation and two distinct generalized theories, namely, the Lord–Shulman and the Green–Lindsay models. The study is carried out by means of a spectral approximation method and numerical simulations. The results show the influence of the relaxation times and the presence of dissipation peaks in the different formulations. | Vibration frequency analysis of an electrically-actuated microbeam resonator accounting for thermoelastic coupling effects | 10.1007/s40435-014-0132-3 |
2015-06-01 | Performance of rotational friction dampers with two and three units was evaluated experimentally because of a lack of research data on performance of these dampers with multi units. Results of multi-unit dampers were compared with the results of one-unit damper. Increasing trend in dissipating energy was observed. Then, the behavior of these dampers in frames of 3, 7 and 12 stories was studied by modeling the damper directly. Nonlinear time history dynamic analysis was used. It was observed that by increasing the number of stories in the buildings, dampers with multi units should be used to perform properly against earthquake. The equivalent damping method was also investigated to consider the effects of this damper without direct modeling of the damper. Effective damping of the frames equipped with this type of damper was estimated and used in nonlinear time history dynamic analysis and it was observed that the responses of these structures with dampers can be approximated by the responses of moment resisting frames without damper but with damping equal to the effective damping due to rotational friction damper. | Experimental and numerical investigation of rotational friction dampers with multi units in steel frames subjected to lateral excitation | 10.1016/j.acme.2014.05.009 |
2015-06-01 | This paper deals with the investigation of the performance of the skew or the rectangular patches of the active constrained layer damping (ACLD) treatment for active damping of geometrically nonlinear vibrations of skew doubly curved laminated composite shells. Developing a three-dimensional nonlinear electro-mechanical finite element model, the performance of the patches is examined for different configurations of their placements on the top surface of the skew substrate shells. The investigation reveals that the patches of the ACLD treatment significantly improves the active damping characteristics of the skew doubly curved laminated composite shells over the passive damping for suppressing their geometrically nonlinear vibrations. It is suggested that even though the substrate shells are skew, a rectangular patch of the ACLD treatment located at the centre of the top surface of the substrate shells should be used for achieving optimum damping of geometrically nonlinear vibrations of skew doubly curved laminated composite shells irrespective of the skew angles and boundary conditions. The effects of variations of the piezoelectric fiber orientation angle in the constraining layer of the ACLD patches and the skew angle of the substrate shells on the control authority of the ACLD patches have been extensively investigated. | Performance of skew or rectangular smart patches for active damping of nonlinear vibrations of skew doubly curved laminated composite shells | 10.1007/s10999-014-9290-x |
2015-06-01 | When a model for quantum noise is exactly solvable, a Kraus (or operator-sum) representation can be derived from the spectral decomposition of the Choi matrix for the channel. More generally, a Kraus representation can be obtained from any positive-sum (or ensemble) decomposition of the matrix. Here we extend this idea to any Hermitian-sum decomposition. This yields what we call the “operator-sum-difference” (OSD) representation, in which the channel can be represented as the sum and difference of “subchannels.” As one application, the subchannels can be chosen to be analytically diagonalizable, even if the parent channel is not (on account of the Abel-Galois irreducibility theorem), though in this case the number of the OSD representation operators may exceed the channel rank. Our procedure is applicable to general Hermitian (completely positive or non-completely positive) maps and can be extended to the more general, linear maps. As an illustration of the application, we derive an OSD representation for a two-qubit amplitude-damping channel. | The operator-sum-difference representation of a quantum noise channel | 10.1007/s11128-015-0965-5 |
2015-06-01 | Accurate prediction of dynamic soil properties is very important to basic understanding of soil behavior and also practical soil modeling. Shear modulus and damping ratio play a vital role in the design of geotechnical structures subjected to dynamic loads. In this study, artificial neural network (ANN), and adaptive neuro-fuzzy inference system (ANFIS) were employed for prediction of damping ratio of fine-grained soils. Most effective factors that affect this parameter include shear strain, plasticity index, and effective confining pressure. A wide-ranging database of soil element tests was used to develop an advanced model, capable of predicting soil damping ratio accurately. Results of geotechnical centrifuge tests were also involved during the training process for adequate generalization of the algorithm for future predictions. Contributions of the effective variables were evaluated through a parametric study. It was found that the ANN model developed with feed-forward back propagation (FFBF) algorithm exhibits higher performance in prediction of soil damping ratio than those developed by radial basis function (RBF) and ANFIS. The results indicate that the soft computing-based model could provide accurate and reasonable predictions, compared with the available practical charts. | Predicting damping ratio of fine-grained soils using soft computing methodology | 10.1007/s12517-014-1493-9 |
2015-06-01 | ^15N longitudinal relaxation rates are extensively used for the characterization of protein dynamics; however, their accurate measurement is hindered by systematic errors. ^15N CSA/^1H–^15N dipolar cross-correlated relaxation (CC) and amide proton exchange saturation transfer from water protons are the two main sources of systematic errors in the determination of ^15N R_1 rates through ^1H–^15N HSQC-based experiments. CC is usually suppressed through a train of 180° proton pulses applied during the variable ^15N relaxation period (T), which can perturb water magnetization. Thus CC cancellation is required in such a way as to minimize water saturation effects. Here we examined the level of water saturation during the T period caused by various types of inversion proton pulses to suppress CC: (I) amide-selective IBURP-2; (II) cosine-modulated IBURP-2; (III) Watergate-like blocks; and (IV) non-selective hard. We additionally demonstrate the effect of uncontrolled saturation of aliphatic protons on ^15N R_1 rates. In this paper we present an optimized pulse sequence that takes into account the crucial effect of controlling also the saturation of the aliphatic protons during ^15N R_1 measurements in non-deuterated proteins. We show that using cosine-modulated IBURP-2 pulses spaced 40 ms to cancel CC in this optimized pulse program is the method of choice to minimize systematic errors coming from water and aliphatic protons saturation effects. | An optimized method for ^15N R_1 relaxation rate measurements in non-deuterated proteins | 10.1007/s10858-015-9937-4 |
2015-06-01 | We analyze two identical qubits interacting with a single-mode quantized radiation field, taking into account the influence of phase damping. The qubits are assumed to be initially in a superposition of the excited and the ground states, and the field is in a coherent state. The effects of the damping on the purity loss of the system and different bipartite partitions of the system [field-two qubits, qubit–(field + qubit)] through the tangles are considered. The effect of the damping on the entanglement of field qubits state is evaluated by the negativity. It is noted that the phenomenon of death and rebirth of the entanglement appears. With the increase in the phase parameter, this phenomenon disappears. | Effects of a phase-damping cavity on entanglement and purity loss in two-qubit system | 10.1007/s11128-015-0952-x |
2015-06-01 | Model-based feedforward–feedback tracking control has been shown as one of the most effective methods for real-time hybrid simulation (RTHS). This approach assumes that the servo-hydraulic system is a linear time-invariant model. However, the servo-control closed-loop is intrinsically nonlinear and time-variant, particularly when one considers the nonlinear nature of typical experimental components (e.g., magnetorheological dampers). In this paper, an adaptive control scheme applying on a model-based feedforward–feedback controller is proposed to accommodate specimen nonlinearity and improve the tracking performance of the actuator, and thus, the accuracy of RTHS. This adaptive strategy is used to estimate the system parameters for the feedforward controller online during a test. The robust stability of this adaptive controller is provided by introducing Routh’s stability criteria and applying a parameter projection algorithm. The tracking performance of the proposed control scheme is analytically evaluated and experimentally investigated using a broadband displacement command, and the results indicates better tracking performance for the servo-hydraulic system can be attained. Subsequently, RTHS of a nine-story shear building controlled by a full-scale magnetorheological damper is conducted to verify the efficacy of the proposed control method. Experimental results are presented for the semi-actively controlled building subjected to two historical earthquakes. RTHS using the adaptive feedforward–feedback control scheme is demonstrated to be effective for structural performance assessment. | Adaptive model-based tracking control for real-time hybrid simulation | 10.1007/s10518-014-9681-2 |
2015-05-21 | In this present paper, the existence of pullback attractors for the 2D Navier-Stokes equation with weak damping and continuous delay is considered; by virtue of the classical Galerkin method, we derive the existence and uniqueness of global weak and strong solutions. Using the Aubin-Lions lemma and some energy estimate in the Banach space with delay, we obtain the uniform bound and the existence of a uniform pullback absorbing ball for the solution’s semi-processes, and we conclude to the global attractors via verifying the pullback asymptotical compactness by the generalized Arzelà-Ascoli theorem. | Pullback attractors of 2D Navier-Stokes equations with weak damping and continuous delay | 10.1186/s13661-015-0344-2 |
2015-05-01 | This paper presents a solution of the boundary-value problem of the stress–strain state of a friction unit placed in the gap between rigid rotating cylinders. It is assumed that the two-layer incompressible material of these unit has elastic, viscous, and plastic properties and different values of the elastic moduli, stress limit, and viscosity. The conditions of the occurrence of viscoplastic flow, motion of the elastoplastic boundary in a deformable medium, and interaction of the latter with the contact boundary of the materials were determined. Limiting values of the characteristic rotation parameters at which the damping layer of the friction unit is not deformed plastically are given. The velocity and stress fields for acceleration and deceleration of the lubricant flow are calculated. | Accounting for the elastic properties of viscoplastic lubricant between coaxial rotating cylinders | 10.1134/S0021894415030244 |
2015-05-01 | The paper summarizes the results of approximate calculation of the influence of amplitudedependent dissipation of energy on vibrodiagnostic parameters of the presence of a closing mode I edge crack in beams of rectangular cross-section for different end restrain conditions and different cases of harmonic excitation of subharmonic resonance in any natural mode. | The Influence of Amplitude-Dependent Damping on Vibrodiagnostic Parameters of the Presence of a Closing Crack in a Beam Under Subharmonic Resonance | 10.1007/s11223-015-9668-5 |
2015-05-01 | A 3D time-domain Rankine source method is developed to study the hydrodynamic loads and motions of a moored ship in shallow water waves in head sea conditions. Both the wave steepness and ship motions relative to the ship’s draft are assumed small and the exact free-surface and body-boundary conditions are expanded about the mean surface by a Taylor series. A formulation correctly to second order in the wave steepness is adopted. A fourth-order Runge–Kutta method is used to time integrate the boundary conditions and the six degree of freedom motion equations. It is found that the water depth has significant effects on the hydrodynamic coefficients, especially on the vertical modes of motions. The linear horizontal motions of a moored ship have distinct increment in shallower water depth in the low-frequency domain. Further, the horizontal slow-drift excitation forces increase significantly with decreasing water depth and the second-order velocity potential gives dominant contribution in a frequency range of importance for moored ships in shallow water. Lastly, the slowly varying motions of an LNGC is simulated and the satisfactory agreements with experiments demonstrate that the present method can predict the slowly varying motions of a moored ship in finite-amplitude shallow water waves with acceptable results. | A numerical investigation of second-order difference-frequency forces and motions of a moored ship in shallow water | 10.1007/s40722-015-0014-6 |
2015-05-01 | Trypanosoma cruzi infection and Chagas disease remains among the most neglected of the neglected tropical diseases. Despite this, studies of the immune response to T. cruzi have provided new insights in immunology and guidance for approaches for prevention and treatment of the disease. T. cruzi represents one of the very best systems in which to study CD8^+ T cell biology; mice, dogs, and primates (and many other mammals) are all natural hosts for this parasite, the robust T cell responses generated in these hosts can be readily monitored using the full range of cutting edge techniques, and the parasite can be easily modified to express (or not) a variety of tags, reporters, immune enhances, and endogenous or model antigens. The infection in most hosts is characterized by vigorous and largely effective immune responses, including CD8^+ T cells capable of controlling T. cruzi at the level of the infected host cells. However, this immune control is only partially effective and most hosts maintain a low level infection for life. This review addresses the interplay of highly effective CD8^+ T cell responses with elaborate pathogen immune evasion mechanisms, including the generation and simultaneous expression of highly variant CD8^+ T cell targets and a host cell invasion mechanisms that largely eludes innate immune detection. | CD8^+ T cells in Trypanosoma cruzi infection | 10.1007/s00281-015-0481-9 |
2015-04-01 | The design and numerical simulation of a linear generator for use in an automobile shock absorber are presented in this paper. The conceived linear generator employs high-performance rare earth permanent magnets with compact size to ensure efficient energy recovery. Finite element analysis and Matlab simulation are utilized to derive the generator configurations for the satisfactory utilization of magnets and optimized functioning. Experimentation was performed on a linear generator prototype and electromagnetic shock absorber to validate the numerical analysis. The numerical model is then utilized in the design of a full-scale energy-harvesting shock absorber with fluid damping and a linear generator. A novel feature of the presented work is the use of fluid amplification to simultaneously achieve energy dissipation and velocity amplification. Fluid amplification does not affect the dynamics of the system and increases the coil velocity by approximately eight times. Smooth variation in damping force, improved fail-safe characteristics, and absence of transmission elements, such as mechanical gears, are additional advantages of the system. Matlab Simscape evaluation is employed to analyze comfort, safety, and energy-harvesting characteristics, which are then compared with that of the conventional fluid shock absorber. Simulation with actual road excitation data indicates that the presented system harvests 15 W of the average power from each wheel. Lastly, the layout for integrating the presented shock absorber in McPherson suspension is discussed. | Design and analysis of energy-harvesting shock absorber with electromagnetic and fluid damping | 10.1007/s12206-015-0331-7 |
2015-04-01 | Low-yield-strength steel (LYS100, yield stress 100 N/mm^2) is utilized here to design a shear panel damper for its high ductility. Deformation capacity of the low-yield-strength steel shear panel damper (LYSPD) is known to be affected by out-of-plane buckling which denies precise prediction by the buckling ratio obtained using empirical equations. Therefore, a preliminary investigation into the relationships between the buckling ratio and the deformation capacity of LYSPD is made via static increment tests. A modified equation is proposed to address plastic deformation for the design. As the loading speed of LYSPD goes rather high with large deformation capacity, dynamic tests are conducted to ascertain whether the out-of-plane buckling is affected by the loading speed. Test results reveal that the influence of loading speed on the LYSPD’s out-of-plane buckling is negligible and high deformation capacity is advisable for the application of LYSPD to the design of the damper. | The performance of low-yield-strength steel shear-panel damper with without buckling | 10.1617/s11527-013-0228-9 |
2015-04-01 | To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams (RCCDs), mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary (VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam. However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes, combination quality of the RCC layers should be significantly ensured. | Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams | 10.1007/s11771-015-2669-5 |
2015-04-01 | In the present day scenario, materials with high damping capacity and good mechanical properties are significant to suppress mechanical vibrations. In pure metals or alloys, even though the mechanical properties are fairly good, the damping capacity was found to be stumpy. Composites are a better choice which simultaneously exhibits good mechanical properties and high damping values. In the present review, the damping behavior of metals, alloys and its composites is summarized and presented. | Damping Behavior of Metal Matrix Composites | 10.1007/s12666-014-0462-z |
2015-04-01 | Methods are proposed for determining the logarithmic decrements (damping coefficients) of structural vibrations from the experimental amplitude-frequency characteristics and the imaginary and real components of the frequency characteristics of the displacements, velocities, and accelerations. | Determining the logarithmic decrements in resonant tests of structures | 10.3103/S1068798X15040061 |
2015-04-01 | We investigate energy decay for solutions to the wave equation $\partial_{t}^{2}u+a(x)\partial_{t}u-\Delta u=0$ , with damping coefficient a ≥0, where Δ is the Laplace–Beltrami operator on a compact Riemannian manifold M . We make a weak regularity hypothesis on the metric tensor of M , though one that guarantees the unique existence of the geodesic flow. We then establish exponential energy decay under the natural hypothesis that all sufficiently long geodesics pass through a region where a ( x )≥ a _0>0, extending the scope of previous work done in the setting of a smooth metric tensor. | Wave Decay on Manifolds with Bounded Ricci Tensor, and Related Estimates | 10.1007/s12220-013-9454-1 |
2015-04-01 | Many material and mechanical systems, such as magnetorheological (MR) dampers used for reducing vibration in engineering systems, have long-standing modeling and control problems because of their nonlinear hysteresis behavior. Existing hysteresis models, including discontinuous and piecewise-continuous functions, are nonideal for numerical computation, stability analysis, and control design. This study links the hysteresis characteristics of a Duffing-like equation and an input–output system through a very subtle observation. Thus, the hysteresis dynamics are approximated using a traceable, second-order nonlinear ordinary differential equation with an inertial element. In addition, the hysteresis stability associated with energy dissipation can be analyzed using the Lyapunov method in a more deterministic and systematic manner than has previously been possible. Experimental work and hysteresis identification of a realistic MR damper device are presented to illustrate the proposed Duffing-like modeling techniques. | Continuous hysteresis model using Duffing-like equation | 10.1007/s11071-015-1926-3 |
2015-04-01 | The performance assessment and optimal design of fluid viscous dampers through life-cycle cost criteria is discussed in this paper. A probabilistic, simulation-based framework is described for estimating the life-cycle cost and a stochastic search approach is developed to support an efficient optimization under different design scenarios (corresponding to different seismicity characteristics). Earthquake losses are estimated using an assembly-based vulnerability approach utilizing the nonlinear dynamic response of the structure whereas a point source stochastic ground motion model, extended here to address near-fault pulse effects, is adopted to describe the seismic hazard. Stochastic simulation is utilized for estimation of all the necessary probabilistic quantities, and for reducing the computational burden a surrogate modeling methodology is integrated within the framework. Two simplified design approaches are also examined, the first considering the optimization of the stationary response, utilizing statistical linearization to address nonlinear damper characteristics, and the second adopting an equivalent lateral force procedure that defines a targeted damping ratio for the structure. These designs are compared against the optimal life-cycle cost one, whereas a compatible comparison is facilitated by establishing an appropriate connection between the seismic input required for the simplified designs and the probabilistic earthquake hazard model. As an illustrative example, the retrofitting of a three-story reinforced concrete office building with nonlinear dampers is considered. | Performance assessment and optimization of fluid viscous dampers through life-cycle cost criteria and comparison to alternative design approaches | 10.1007/s10518-014-9646-5 |
2015-04-01 | In service robotics, control systems allowing for skillful manipulation and dexterity constitute one of the most valuable technologies. Recently, control approaches inspired by humans or animals have attracted widespread attention, due to their merit of allowing various tasks to be performed naturally without precisely calculating their behaviors. This work, thus, focuses on the embodiment of a notable control method for a multi-DOF robotic system considering a human physical activity. In contrast to the traditional approaches, in the proposed control, the linear superposition of four control terms is exploited. These consist of joint spring-damping and virtual spring-damper terms in the joint and Cartesian spaces, respectively. Remarkably, the joint spring term is newly designed for the consideration of the simple passive muscle stiffness effect under gravity to guarantee motion repeatability and avoid the problem of ill-posedness. In the experiment, various abilities with respect to position control and compliant behavior are exposed through a real robot. Additional experiments are performed for the verification of the motion repeatability and energy-efficient motion under DOF redundancy. | Task space control considering passive muscle stiffness for redundant robotic arms | 10.1007/s11370-015-0165-2 |
2015-03-31 | Background Magneto-rheological (MR) damper is one of the most promising semi-active devices. The MR dampers offer a reliability of a passive system yet maintain the versatility and adaptability of the fully active control devices. Methods In this paper, an optimization process is developed to optimize the geometrical parameters of an MR damper using finite element method (FEM) coupled with Taguchi approach which is rarely available in the literature. The damping force of the MR damper is selected as an objective function. To achieve this objective, 18 FEM models, based on Taguchi orthogonal array, are developed on ANSYS platform. Results These results have been analyzed by using the design of experiment (DoE) methodology and an optimized solution is then arrived. The optimal solution is validated experimentally as well as through FEM for 95% confidence level. These results are found to be in good agreement with each other. Conclusions This paper establishes that numerical technique results, e.g . , FEM, can be used over the real experimental results for the geometric parameter optimization of an MR damper. The proposed methodology will save time and resources for designing an optimized MR damper for automotive and other applications. | Geometric parameter optimization of magneto-rheological damper using design of experiment technique | 10.1186/s40712-015-0031-1 |
2015-03-26 | This paper is concerned with oscillations of certain second-order Emden-Fowler variable delay functional dynamic equations with damping and neutral of the form [ A ( t ) φ ( y Δ ( t ) ) ] Δ + b ( t ) φ ( y Δ ( t ) ) + P ( t ) F ( φ ( x ( δ ( t ) ) ) ) − Q ( t ) f ( φ ( x ( γ ( t ) ) ) ) = 0 $$\bigl[A(t)\varphi\bigl(y^{\Delta} (t)\bigr)\bigr]^{\Delta} + b(t) \varphi\bigl(y^{\Delta} (t)\bigr) + P(t)F\bigl(\varphi\bigl(x\bigl(\delta(t) \bigr)\bigr)\bigr) - Q(t)f\bigl(\varphi\bigl(x\bigl(\gamma(t)\bigr)\bigr)\bigr) = 0 $$ on an arbitrary time scale T , where y ( t ) = x ( t ) + B ( t ) x ( τ ( t ) ) $y(t) = x(t) + B(t)x(\tau (t))$ and φ ( u ) = | u | λ − 1 u $\varphi(u) = |u|^{\lambda- 1}u$ ( λ > 0 $\lambda> 0$ ). By using the generalized Riccati transformation and the inequality technique, some new oscillation criteria for the equations are established. Our results extend and improve some known results, but they also unify the oscillation of second-order Emden-Fowler delay differential equations with damping and second-order Emden-Fowler delay difference equations with damping. Examples are given to illustrate the importance of our results. | Oscillation criteria for certain second-order Emden-Fowler delay functional dynamic equations with damping on time scales | 10.1186/s13662-014-0338-x |
2015-03-04 | In this paper, we present a new approach via variational methods and critical point theory to obtain the existence and multiplicity of solutions to a class of damped vibration problems with impulsive effects on time scales. By establishing a proper variational set, two existence results and two multiplicity results are obtained. Finally, one example is presented to illustrate the feasibility and effectiveness of our results. | An application of variational approach to a class of damped vibration problems with impulsive effects on time scales | 10.1186/s13661-015-0305-9 |
2015-03-01 | Structures consisting of concrete and steel parts, which are irregular in damping ratios are investigated. This investigation is a code-based seismic design of such structures. Several practical difficulties encountered, due to inherent differences in the nature of dynamic response of each part, and the different damping ratios of the two parts. These structures are irregular in damping ratios and have complex modes of vibration so that their analysis cannot be handled with the readily available commercial software. Therefore, this work aims to provide simple yet sufficiently accurate constant values of equivalent damping ratios applied to the whole structure for handling the damping irregularity of such structures. The results show that the equivalent damping ratio changes with the height of the building and the kind of the structural system, but it is constant for all accelerations values. Thus, available software SAP2000 applied for seismic analysis, design and the provisions of existing seismic codes. Finally, evaluation of different kinds of structural system used in this research to find the most energy dissipating one found by finding the best value of quality coefficient. | Parametric study on equivalent damping ratio of different composite structural building systems | 10.1007/s13296-015-3001-9 |
2015-03-01 | The SMA was studied for their macroscopic application in damping for civil engineering. The study is a synthesis and includes an outline of the models required for the SMA simulation and some case studies using the finite element analysis methods. This work is an overview that focuses in the mitigation of the oscillations in structures induced by earthquakes, and for a reduction of the oscillations amplitude in stayed cables under the action of rain, wind or traffic. The analysis needs the required conditions for each application determining the working conditions. The study includes the number of working cycles, the temperature effects and the cooling actions and, for instance, the action of the cycling frequency. The main target relates the appropriateness of the SMA for each purpose, and the suitability of the SMA device is always experimentally guaranteed. Furthermore, the applicability of the obtained results for SMA and the practical behavior of the SMA dampers were studied in international facilities. The paper includes appropriate suggestions for a correct preparation of the SMA dampers. This work outlines the effects of stress and temperature aging in NiTi, describes the particular structural effects between 18 R and 6 R , introduces a first attempt in the dynamic properties of the CuAlBe single crystals and summarizes some recent suggestions for damping using SMA. | Shape memory alloys as an effective tool to damp oscillations | 10.1007/s10973-015-4405-7 |
2015-03-01 | Owing to the interactions among the complex terrain, bottom materials, and the complicate hydrodynamics, typhoon waves show special characteristics as big waves appeared at the high water level (HWL) and small waves emerged at low and middle water levels (LWL and MWL) in radial sand ridges (RSR). It is assumed that the mud damping, sandy bed friction and wave breaking effects have a great influence on the typhoon wave propagation in this area. Under the low wave energy, a mud layer will form and transport into the shallow area, thus the mud damping effects dominate at the LWL and the MWL. And high Collins coefficient ( c around 1) can be applied to computing the damping effects at the LWL and the MWL. But under the high wave energy, the bottom sediment will be stirred and suspended, and then the damping effects disappear at the HWL. Thus the varying Collins coefficient with the water level method (VCWL) is implemented into the SWAN to model the typhoon wave process in the Lanshayang Channel (LSYC) of the RSR, the observed wave data under “Winnie” (“9711”) typhoon was used as validation. The results show that the typhoon wave in the RSR area is able to be simulated by the VCWL method concisely, and a constant wave breaking coefficient (γ) equaling 0.78 is better for the RSR where wide tidal flats and gentle bed slopes exist. | The study on the bottom friction and the breaking coefficient for typhoon waves in radial sand ridges—the Lanshayang Channel as an example | 10.1007/s13131-015-0637-4 |
2015-03-01 | In the present paper a vibrational differential equation governing on a rigid beam on viscoelastic foundation has been investigated. The nonlinear differential equation governing on this vibrating system is solved by a simple and innovative approach, which has been called Akbari-Ganji’s method (AGM). AGM is a very suitable computational process and is usable for solving various nonlinear differential equations. Moreover, using AGM which solving a set of algebraic equations, complicated nonlinear equations can easily be solved without any mathematical operations. Also, the damping ratio and energy lost per cycle for three cycles have been investigated. Furthermore, comparisons have been made between the obtained results by numerical method (Runk45) and AGM. Results showed the high accuracy of AGM. The results also showed that by increasing the amount of initial amplitude of vibration ( A ), the value of damping ratio will be increased, and the energy lost per cycle decreases by increasing the number of cycle. It is concluded that AGM is a reliable and precise approach for solving differential equations. On the other hand, it is better to say that AGM is able to solve linear and nonlinear differential equations directly in most of the situations. This means that the final solution can be obtained without any dimensionless procedure. Therefore, AGM can be considered as a significant progress in nonlinear sciences. | Solving nonlinear differential equation governing on the rigid beams on viscoelastic foundation by AGM | 10.1007/s11804-015-1284-z |
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