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2012-06-01 | Elastic-plastic steel damper (EPSD) is a new device controlling seismic responses. The mechanical principle of EPSD was presented and a comparison was conducted between the theoretical formulas and finite element (FE) simulation of damper units. The verified force-displacement hysteretic curve of the damper system was obtained with reference to tests. The Nanjing Jiangxinzhou Bridge (NJB) was subsequently taken as the case to investigate the seismic response control effect of EPSDs on single-tower self-anchored suspension bridges. A 3-dimensional FE model of the bridge was established in ANSYS and the dynamic and static analyses of the bridge were conducted, the control effect of EPSDs under different seismic waves was further investigated through nonlinear time-history analysis based on the validated model. Results showed that both the simplified theoretical and FE simulation methods can preferable reflect the mechanical performance of EPSD, and that seismic responses of NJB with EPSDs are better than those with elastic connection device or fluid viscous damper. However, the control effect of EPSDs is influenced by seismic wave characteristics. | Study on seismic response control of a single-tower self-anchored suspension bridge with elastic-plastic steel damper | 10.1007/s11431-012-4826-5 |
2012-05-01 | Organic hybrids of polyacrylate emulsion (PAE)/hindered phenol (3,5-bis(1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid thiodi-2,1-ethanediyl ester, abbreviated as Irganox-1035) have been prepared in this study. The dynamic mechanical properties, denoted by storage modulus (E′) and loss factor (tanδ), of this binary system have been investigated. Dynamic mechanical analysis (DMA) results show that by adding Irganox-1035, the tanδ peak maximum of the hybrids are remarkably increased up to 4.2, demonstrating PAE/Irganox-1035 hybrids are promising damping materials. The damping mechanism of the hybrids has also been systematically investigated through Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), X-ray diffraction (XRD), DMA and scanning electronic microscope (SEM). The experimental results indicate no hydrogen bonding is formed between polyacrylate matrix and Irganox-1035 molecules and PAE has a good compatibility with Irganox-1035 existing in the amorphous form in the hybrids. Meanwhile, DMA results show amorphous Irganox-1035 has a super-high viscoelastic property (tanδ=20.7), which improves the damping performance of this compatible hybrids system. Irganox-1035 has a positive effect on damping performance of PAE/Irganox-1035 hybrids. When the Irganox-1035 amount in PAE/Irganox-1035 hybrids increases from 0 to 70 phr, the tanδ values increase from 2.2 to 4.2, demonstrating PAE/Irganox-1035 hybrids are promising damping materials. Meanwhile, the single loss factor also indicates Irganox-1035 has a good compatiblity with PAE. | Studies on the damping properties of polyacrylate emulsion/hindered phenol hybrids | 10.1038/pj.2012.6 |
2012-05-01 | The literature includes a variety of analytical and semi-analytical models to describe squeeze-film damping in MEMS perforated structures. Even if many of them have been validated by means of numerical simulations, nobody seems to have discussed about the accuracy of numerical approaches in this field. In the present paper, we apply both the main analytical models and a commercial finite element software, COMSOL Multiphysics, to solve a good number of squeeze-film problems. They refer to some cases, which were experimentally investigated during the past by different authors. The tested structures are rigid rectangular plates fabricated with different material, different perforation ratio (i.e., the ratio of the hole side to the holes pitch) and different number of perforations. We compare both the analytical and the numerical results with the available experimental data, in order to have an overview about their effectiveness. Numerical simulations offer in all the considered cases valuable agreement with experiments. | Analytical and numerical modeling of squeeze-film damping in perforated microstructures | 10.1007/s10404-011-0931-1 |
2012-04-13 | This study investigates the existence of global solutions to a class of nonlinear damped wave operator equations. Dividing the differential operator into two parts, variational and non-variational structure, we obtain the existence, uniformly bounded and regularity of solutions. Mathematics Subject Classification 2000 : 35L05; 35A01; 35L35. | Global solutions to a class of nonlinear damped wave operator equations | 10.1186/1687-2770-2012-42 |
2012-04-01 | In the present paper we establish results concerning the decay of the energy related to the damped Korteweg–de Vries equation posed on infinite domains. We prove the exponential decay rates of the energy when a initial value problem and a localized dissipative mechanism are in place. If this mechanism is effective in the whole line, we get a similar result in H ^ k -level, k ∈ℕ. In addition, the decay of the energy regarding a initial boundary value problem posed on the right half-line, is obtained considering convenient a smallness condition on the initial data but a more general dissipative effect. | Decay of Solutions to Damped Korteweg–de Vries Type Equation | 10.1007/s00245-011-9156-7 |
2012-04-01 | This work proposes an image-based visual servoing scheme applied to a class of overactuated planar parallel robots with revolute joints. A Proportional Derivative algorithm computes torques for the robot active joints. The Derivative action operates at the joint level and the Proportional action works at the visual level. A linear filter provides velocity estimates from active joint position measurements, and Lyapunov Stability theory allows concluding closed loop stability. Experimental results on a laboratory prototype show that the proposed approach permits using higher gains compared with a control law relying on velocity estimates generated using visual measurements; moreover, these experiments also show that the closed loop system is robust in face of kinematic uncertainty. | Visual Control of Planar Parallel Robots Without Using Velocity Measurements | 10.1007/s10846-011-9609-x |
2012-04-01 | This study examines the small-strain dynamic properties of mixtures composed of sandy and gravelly soils with granulated tire rubber in terms of shear modulus (G_O), and damping ratio in shear (D_min). Torsional resonant column tests are performed on dry, dense specimens of soil-rubber mixtures in a range of soil to rubber particles size 5:1–1:10 and rubber content from 0 to 35% by mixture weight. The experimental results indicate that the response of the mixtures is significantly affected by the content of rubber and the relative size of rubber to soil particles. Concering the small-strain shear modulus, an equivalent void ratio is introduced that considers the volume of rubber particles as part of the total volume of voids. Based on a comprehensive set of test results a series of equations were developed that can be used to evaluate the shear modulus and damping ratio at small shear strain levels if the confining pressure, the content of rubber by mixture weight, the grain size of soil and rubber particles, and the dynamic and physical properties of the intact soil are known. | Small-Strain Shear Modulus and Damping Ratio of Sand-Rubber and Gravel-Rubber Mixtures | 10.1007/s10706-011-9473-2 |
2012-04-01 | Context Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material. Aims The objective is to contribute to overcoming the critical lack of data on the diversity of wood dynamic mechanical/viscoelastic vibrational properties by testing lesser known species and categorising sources of variability. Methods Air-dry axial specific dynamic modulus of elasticity ( E′ / γ ) and damping coefficient (tan δ ) were measured on a wide sampling (1,792 specimens) of 98 wood types from 79 species. An experimental device and protocol was designed for conducting systematic (i.e. rapid and reproducible) characterisations. Results Diversity at the specimens’ level corroborates the “standard” relationship between tan δ and E′ / γ , which is discussed in terms of orientation of wood elements and of chemical composition. Diversity at the species level is expressed on the basis of results for normal heartwood, with specific gravity ( γ ) ranging from 0.2 to 1.3. Axial E′ / γ ranges from 9 to 32 GPa and tan δ from 4 × 10^−3 to 19 × 10^−3. Properties distribution follows a continuum, but with group characteristics. The lowest values of tan δ are only found in certain tropical hardwoods. Results can also suggest alternative species for musical instruments making. Conclusion The variations in specific gravity, in stiffness or in “viscosity” appear to be predominantly linked to different levels of diversity: between species or between wood types (reaction wood or taxonomy-related differences in heartwood extractives). | Characterisation and categorisation of the diversity in viscoelastic vibrational properties between 98 wood types | 10.1007/s13595-011-0166-z |
2012-04-01 | This paper utilizes the Discrete Element Method to characterize energy dissipation mechanisms in cyclically loaded soils based on micromechanical considerations. Computational simulations of consolidated undrained cyclic triaxial tests were conducted at various relative densities and were subjected to cyclic loading of different frequencies and shear strain amplitudes. The different components of microscale energies were monitored during the course of the simulations and characterized into input and dissipated energies. A comparison is made between the dissipated energy computed from microscopic energy components and macroscopic energy calculated based on the area of the deviator stress-axial strain loops. These energies are then used to obtain the specific damping capacity defined as the ratio of dissipated energy during one cycle to the maximum stored elastic energy during the same cycle. The conducted simulations highlight the importance of calculating actual stored energy in the system as opposed to approximating it to be that calculated as the triangular area under the secant modulus. Finally, a series of simulations that resulted in liquefaction are discussed, and the amount of energy dissipated to liquefaction is examined based on these results. | Microscale Energy Dissipation Mechanisms in Cyclically-Loaded Granular Soils | 10.1007/s10706-011-9472-3 |
2012-04-01 | In this paper, we focus on studying approximate solutions of damped oscillatory solutions of the compound KdV-Burgers equation and their error estimates. We employ the theory of planar dynamical systems to study traveling wave solutions of the compound KdV-Burgers equation. We obtain some global phase portraits under different parameter conditions as well as the existence of bounded traveling wave solutions. Furthermore, we investigate the relations between the behavior of bounded traveling wave solutions and the dissipation coefficient r of the equation. We obtain two critical values of r , and find that a bounded traveling wave appears as a kink profile solitary wave if | r | is greater than or equal to some critical value, while it appears as a damped oscillatory wave if | r | is less than some critical value. By means of analysis and the undetermined coefficients method, we find that the compound KdV-Burgers equation only has three kinds of bell profile solitary wave solutions without dissipation. Based on the above discussions and according to the evolution relations of orbits in the global phase portraits, we obtain all approximate damped oscillatory solutions by using the undetermined coefficients method. Finally, using the homogenization principle, we establish the integral equations reflecting the relations between exact solutions and approximate solutions of damped oscillatory solutions. Moreover, we also give the error estimates for these approximate solutions. | Approximate damped oscillatory solutions for compound KdV-Burgers equation and their error estimates | 10.1007/s10255-012-0147-5 |
2012-04-01 | Several damping materials have been employed to reduce the vibration of marine structures. In this paper, a new method of identifying system matrices for non-proportional damping structures using modal parameters is proposed. This method has two advantages. First, the mass and stiffness matrices do not need to be calculated using the FEM, so errors due to the inaccuracy of these matrices can be reduced. Second, various indirect methods can be used to identify modal parameters such as natural frequencies, modal damping ratios and mode shapes. Three case studies of lumped mass systems with non-proportional damping are carried out to verify the performance of the proposed method in this study. | Direct identification of non-proportional modal damping matrix for lumped mass system using modal parameters | 10.1007/s12206-012-0221-1 |
2012-04-01 | The process of damping oscillations of a rod consisting of two dissimilar segments and fixed at one end is considered. The damping is carried out by means of a boundary control at the other end of the rod. | On the complete damping of oscillations of an inhomogeneous rod by means of a boundary control at one end | 10.1134/S0081543812020083 |
2012-04-01 | Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry ( Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tan δ ), storage (elastic) modulus ( E ′) and specific modulus ( E ′/ γ ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low E _L′/ γ but its tan δ was smaller than expected, and the anisotropy of tan δ and E ′/ γ was very low. Removal of extractives caused tan δ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tan δ _L by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E ′/ γ was nearly unchanged after extraction in methanol or hot water, while tan δ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance. | Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba) | 10.1007/s10086-011-1225-7 |
2012-03-01 | From a macroscopic perspective, saturated porous materials like soils represent volumetrically interacting solid–fluid aggregates. They can be properly modelled using continuum porous media theories accounting for both solid-matrix deformation and pore-fluid flow. The dynamic excitation of such multi-phase materials gives rise to different types of travelling waves, where it is of common interest to adequately describe their propagation through unbounded domains. This poses challenges for the numerical treatment and demands special solution strategies that avoid artificial and numerically-induced perturbations or interferences. The present paper is concerned with the accurate and stable numerical solution of dynamic wave propagation problems in infinite half spaces. Proceeding from an isothermal, biphasic, linear poroelasticity model with incompressible constituents, finite elements are used to discretise the near field and infinite elements to approximate the far field. The transient propagation of the poroacoustic body waves to the infinity is thereby modelled by a viscous damping boundary, which, for stability reasons, necessitates an appropriate treatment of the included velocity-dependent damping forces. | Dynamic wave propagation in infinite saturated porous media half spaces | 10.1007/s00466-011-0647-9 |
2012-03-01 | The paper presents some findings of numerical investigations of torsional vibrations in steam turbine shafting in the turbogenerator abnormal operation modes (short circuit, random paralleling start, etc.). The shafting vibrations are shown to be essentially dependant on the reaction torque surge parameters (magnitude, duration, and form). For three types of the reaction torque surge a comparative hazard analysis is performed from the standpoint of initiation of cyclic damage in the rotor material and the risk of shafting failure. | Torsional vibrations in steam turbine shafting in turbogenerator abnormal modes of operation | 10.1007/s11223-012-9370-9 |
2012-03-01 | In this paper, the controllability problem is discussed for the damped second-order impulsive neutral functional differential systems with infinite delay in Banach spaces. Sufficient conditions for controllability results are derived by means of the Sadovskii fixed point theorem combined with a noncompact condition on the cosine family of operators. An example is provided to illustrate the theory. | Controllability of Damped Second-Order Impulsive Neutral Functional Differential Systems with Infinite Delay | 10.1007/s10957-011-9926-z |
2012-03-01 | The damping of the relaxation modulus under step shear deformation is weaker for multi-branched polymers such as comb polymers than for linear polymers. This weak damping has been related to the hierarchical relaxation, the branched arm relaxation occurring prior to the backbone relaxation and dilating the entanglement network for the backbone relaxation/contraction. A corresponding model has been proposed and favorably compared with the data for the damping function. However, the enhancement of dilation due to large deformation, known to occur for linear polymers to affect the chain contraction rate, was not considered in the model. Thus, in this paper, we investigated the dilation for a comb polymer under deformation with the aid of a 3D multichain sliplink simulation that naturally accounts for the dilation due to the constraint release through the many chain dynamics. The simulation was confirmed, to the first time, to reproduce the linear and nonlinear viscoelastic data for a comb polyisoprene (Kirkwood et al., Macromolecules 42:9592–9608, 2009 ). A magnitude of dilation under deformation was examined for the survival probability of the sliplinks. It turned out that the dilation for the comb backbone activated by the arm relaxation is enhanced by the deformation at short times but not at long times where the backbone relaxes and the damping function is defined. This result lends support to the conventional model. | Primitive chain network simulations for comb-branched polymer under step shear deformations | 10.1007/s00397-011-0574-x |
2012-03-01 | Nonlinear dust-acoustic (DA) shock waves are addressed in a nonextensive dusty plasma exhibiting self-consistent nonadiabatic charge variation. Our results reveal that the amplitude, strength and nature of the DA shock waves are extremely sensitive to the degree of ion nonextensivity. Significant differences in the potential function occur for very small changes in the value of the nonextensive parameter. Stronger is the ions correlation, more important is the charge variation induced nonlinear wave damping. | Nonextensive collisioneless dust-acoustic shock waves in a charge varying dusty plasma | 10.1007/s10509-011-0905-5 |
2012-03-01 | This paper deals with the problem of the bounded traveling wave solutions’ shape and the solution to the generalized Whitham-Broer-Kaup equation with the dissipation terms which can be called WBK equation for short. The authors employ the theory and method of planar dynamical systems to make comprehensive qualitative analyses to the above equation satisfied by the horizontal velocity component u ( ξ ) in the traveling wave solution ( u ( ξ ), H ( ξ )), and then give its global phase portraits. The authors obtain the existent conditions and the number of the solutions by using the relations between the components u ( ξ ) and H ( ξ ) in the solutions. The authors study the dissipation effect on the solutions, find out a critical value r *, and prove that the traveling wave solution ( u ( ξ ), H ( ξ )) appears as a kink profile solitary wave if the dissipation effect is greater, i.e., | r | ≥ r *, while it appears as a damped oscillatory wave if the dissipation effect is smaller, i.e., | r | < r *. Two solitary wave solutions to the WBK equation without dissipation effect is also obtained. Based on the above discussion and according to the evolution relations of orbits corresponding to the component u ( ξ ) in the global phase portraits, the authors obtain all approximate damped oscillatory solutions ( ũ ( ξ ), $\tilde H$ ( ξ )) under various conditions by using the undetermined coefficients method. Finally, the error between the approximate damped oscillatory solution and the exact solution is an infinitesimal decreasing exponentially. | Shape analysis of bounded traveling wave solutions and solution to the generalized Whitham-Broer-Kaup equation with dissipation terms | 10.1007/s11401-012-0697-0 |
2012-02-01 | In this paper, a viscoelastic equation with nonlinear boundary damping and source terms of the form $$\begin{array}{llll}u_{tt}(t)-\Delta u(t)+\displaystyle\int\limits_{0}^{t}g(t-s)\Delta u(s){\rm d}s=a\left\vert u\right\vert^{p-1}u,\quad{\rm in}\,\Omega\times(0,\infty), \\ \qquad\qquad\qquad\qquad\qquad u=0,\,{\rm on}\,\Gamma_{0} \times(0,\infty),\\ \dfrac{\partial u}{\partial\nu}-\displaystyle\int\limits_{0}^{t}g(t-s)\frac{\partial}{\partial\nu}u(s){\rm d}s+h(u_{t})=b\left\vert u\right\vert ^{k-1}u,\quad{\rm on} \ \Gamma_{1} \times(0,\infty) \\ \qquad\qquad\qquad\qquad u(0)=u^{0},u_{t}(0)=u^{1},\quad x\in\Omega, \end{array}$$ is considered in a bounded domain Ω. Under appropriate assumptions imposed on the source and the damping, we establish both existence of solutions and uniform decay rate of the solution energy in terms of the behavior of the nonlinear feedback and the relaxation function g , without setting any restrictive growth assumptions on the damping at the origin and weakening the usual assumptions on the relaxation function g . Moreover, for certain initial data in the unstable set, the finite time blow-up phenomenon is exhibited. | General decay and blow-up of solutions for a viscoelastic equation with nonlinear boundary damping-source interactions | 10.1007/s00033-011-0151-2 |
2012-02-01 | An automatic control system for electrically driven hoisting devices is investigated. An acceleration sensor for the calculation of the coordinate of the engine moment, the speed of movement, and the displacement angle is proposed. Synthesis of the system of the subordinate regulation adapted to the operating mode is carried out. To define the requirements for the sensors used, the sensitivity of the system components to the variations in the parameters is analyzed. | Synthesis of a control system for hoisting devices | 10.3103/S1068371212020046 |
2012-02-01 | Vibrating wire viscometers rely on the principle that the viscosity of the fluid surrounding the wire provides the dominant damping action on the motion of the wire. However, some residual damping is always present due to other effects such as internal friction of the wire (anelastic relaxation), losses through the wire supports, and magnetic damping. Magnetic damping is a physical mechanism that has received relatively less attention than internal friction in the context of viscometers. The phenomenon arises because the current induced by the motion of the wire contributes to the magnetic field in such a way as to oppose its own motion. For a test circuit using a 40 μm diameter tungsten wire in a 0.3 T magnetic field, surprisingly, the effect of magnetic damping was found to be of a similar order of magnitude to other non-viscous damping effects. The effect can be accounted for by including the internal impedance of the oscillating voltage source in the model and it disappears completely for a perfect oscillating current source. | Magnetic Damping Effects in Forced-Oscillation Vibrating-Wire Viscometers | 10.1007/s10765-012-1157-5 |
2012-02-01 | In this paper, thermoelastic damping (TED) in a micro-beam resonator with a pair of piezoelectric layers bonded on its upper and lower surfaces is investigated. Equation of motion is derived and the thermoelasticity equation is governed using two dimensional non-Fourier heat conduction model based on continuum theory frame. Applying Galerkin discretization method and complex-frequency approach to solve the equations of coupled thermoelasticity, we study TED of a clamped-clamped micro-beam resonator. The presented results demonstrate that thickness of the piezoelectric layers and application of DC voltage to them can affect the TED ratio and the critical thickness value of the resonator. | Thermoelastic Damping in a Micro-Beam Resonator Tunable with Piezoelectric Layers | 10.1016/S0894-9166(12)60008-1 |
2012-02-01 | Through a box model of the subpolar North Atlantic, we examine the genesis and predictability of the Atlantic Multidecadal Variability (AMV), posited as a linear perturbation sustained by the stochastic atmosphere. Postulating a density-dependent thermohaline circulation (THC), the latter would strongly differentiate the thermal and saline damping, and facilitate a negative feedback between the two fields. This negative feedback preferentially suppresses the low-frequency thermal variance to render a broad multidecadal peak bounded by the thermal and saline damping time. We offer this “differential variance suppression” as an alternative paradigm of the AMV in place of the “damped oscillation”—the latter generally not allowed by the deterministic dynamics and in any event bears no relation to the thermal peak. With the validated dynamics, we then assess the AMV predictability based on the relative entropy—a difference of the forecast and climatological probability distributions, which decays through both error growth and dynamical damping. Since the stochastic forcing is mainly in the surface heat flux, the thermal noise grows rapidly and together with its climatological variance limited by the THC-aided thermal damping, they strongly curtail the thermal predictability. The latter may be prolonged if the initial thermal and saline anomalies are of the same sign, but even rare events of less than 1% chance of occurrence yield a predictable time that is well short of a decade; we contend therefore that the AMV is in effect unpredictable. | A minimal model of the Atlantic Multidecadal Variability: its genesis and predictability | 10.1007/s00382-011-1007-3 |
2012-02-01 | In turbomachinery, the perfect detuning of turbine blades in order to avoid high cycle fatigue damage due to resonant vibration is often unfeasible due to the high modal density of bladed disks. To obtain reliable predictions of resonant stress levels of turbine blades, accurate modeling of friction damping is mandatory. Blade root is one of the most common sources of friction damping in turbine blades; energy is dissipated by friction due to microslip between the blade and the disk contact surfaces held in contact by the centrifugal force acting on the blade. In this paper, a method is presented to compute the friction forces occurring at blade root joints and to evaluate their effect on the blade dynamics. The method is based on a refined version of the state-of-the-art contact model, currently used for the nonlinear dynamic analysis of turbine blades. The refined contact model is implemented in a numerical solver based on the harmonic balance method able to compute the steady-state dynamic response of turbine blades The proposed method allows solving the static and the dynamic balance equations of the blade and of the disk, without any preliminary static analysis to compute the static loads acting at the contact interfaces. | Numerical assessment of friction damping at turbine blade root joints by simultaneous calculation of the static and dynamic contact loads | 10.1007/s11071-011-0119-y |
2012-02-01 | The PZT thin films were prepared on (111)- Pt/Ti/SiO_2/Si substrates by sol-gel method, and lead acetate [Pb(CH_3COO)_2], zirconium nitrate [Zr(NO_3)_4] were used as raw materials. The X-ray diffractometer (XRD) and scanning electron microscopy (SEM) were used to characterize the phase structure and surface morphology of the films annealed at 650 °C but with different holding time. Ferroelectric and dielectric properties of the films were measured by the ferroelectric tester and the precision impedance analyzer, respectively. The PZT thin films were constructed with epoxy resin as a composite structure, and the damping properties of the composite were tested by dynamic mechanical analyzer (DMA). The results show that the films annealed for 90 minutes present a dense and compact crystal arrangement on the surface; moreover, the films also achieve their best electric quality. At the same time, the largest damping loss factor of the composite constructed with the 90 mins-annealed film shows peak value of 0.9, higher than the pure epoxy resin. | Influence of annealing time on the microstructure and properties of Pb(Zr_0.53Ti_0.47)O_3 thin films | 10.1007/s11595-012-0413-7 |
2012-02-01 | A novel intelligent semi-active control system for an eleven degrees of freedom passenger car’s suspension system using magnetorheological (MR) damper with neuro-fuzzy (NF) control strategy to enhance desired suspension performance is proposed. In comparison with earlier studies, an improvement in problem modeling is made. The proposed method consists of two parts: a fuzzy control strategy to establish an efficient controller to improve ride comfort and road handling (RCH) and an inverse mapping model to estimate the force needed for a semi-active damper. The fuzzy logic rules are extracted based on Sugeno inference engine. The inverse mapping model is based on an artificial neural network and incorporated into the fuzzy controller to enhance RCH. To verify the performance of the NF controller (NFC), comparisons with existing semi-active techniques are made. The typical control strategy are linear quadratic regulator (LQR) and linear quadratic Gaussian (LQG) controllers with clipped optimal control algorithm, while inherent time-delay and non-linear properties of MR damper lie in these strategies. Simulation results demonstrated that the NFC has better control performance and less control effort than the optimal in improving the service life of the suspension system and the ride comfort of a car. | Intelligent semi-active vibration control of eleven degrees of freedom suspension system using magnetorheological dampers | 10.1007/s12206-011-1007-6 |
2012-01-01 | Since material losses of many engineering materials are known to be independent on frequency, the viscous damping is not always appropriate model of damping. In the case of structures, the effect of damping is usually small far from the system resonance. Unlike the case of structures, the material damping of rotor can lead to system instability. Traditional concept of hysteretic damping introduced by complex modulus of elasticity has serious drawback of its inapplicability in the time domain. Also it is inconsistent when frequency of vibration tends to zero, what is the case of rotor undergoing synchronous forward precession. In this paper, the Maxwell-Weichert material model is used to approach hysteretic material damping of rotor systems. Presented finite element model of Timoshenko rotating beam with non-viscous internal damping with exponential kernel is suitable for time domain solutions as well as for calculation of decay rates and Campbell plots of rotor systems. | Exponential Damping as an Approach to Internal Hysteretic Damping of Rotor Systems: FEM Model of Timoshenko Rotating Beam with Maxwell-Weichert Damping Model | 10.1007/978-94-007-5125-5_34 |
2012-01-01 | While hopping, 12 subjects experienced a sudden step down of 5 or 10 cm. Results revealed that the hopping style was “terrain following”. It means that the subjects pursued to keep the distance between maximum hopping height (apex) and ground profile constant. The spring-loaded inverse pendulum (SLIP) model, however, which is currently considered as template for stable legged locomotion would predict apex-preserving hopping, by which the absolute maximal hopping height is kept constant regardless of changes of the ground level. To get more insight into the physics of hopping, we outlined two concepts of energy management: “constant energy supply”, by which in each bounce—regardless of perturbations—the same amount of mechanical energy is injected, and “lost energy supply”, by which the mechanical energy that is going to be dissipated in the current cycle is assessed and replenished. When tested by simulations and on a robot testbed capable of hopping, constant energy supply generated stable and robust terrain following hopping, whereas lost energy supply led to something like apex-preserving hopping, which, however, lacks stability as well as robustness. Comparing simulated and machine hopping with human hopping suggests that constant energy supply has a good chance to be used by humans to generate hopping. | Energy management that generates terrain following versus apex-preserving hopping in man and machine | 10.1007/s00422-012-0476-8 |
2012-01-01 | Friction mechanism has an extensive usage in many different fields for energy dissipation. It is also used at buildings to reduce the displacement that is caused by ground acceleration during an earthquake. Despite friction damper is a simple device to use on structures, due to its nonlinear characteristic, analysis and design of a structure equipped with a friction damper is difficult. In this paper, Harmonic Balance Method (HBM) is employed to represent the frictional contact as a nonlinear complex stiffness in order to find the steady state displacement of each story of a multi-story building under harmonic ground acceleration. Application of HBM results in a set of nonlinear algebraic equations in frequency domain which can be solved by an iterative method. As a result of this, the solution method presented reduces the computational effort compared to time integration methods; therefore, optimization of friction dampers can be performed in a reasonable time. Accuracy and validation of the presented method is demonstrated on a single-story shear building model equipped with a single friction damper by comparing the frequency domain solution with time marching results. A multi-story building is considered as a case study where the slip force of each dry friction damper is optimized in order to minimize the relative displacement between the stories. | Frequency Domain Optimization of Dry Friction Dampers on Buildings Under Harmonic Excitation | 10.1007/978-1-4614-2413-0_12 |
2012-01-01 | The idea of using the distributed-order differential equation first proposed by Caputo in (1969) is at least mathematically interesting as demonstrated in the previous chapters. However, people may question its usefulness in engineering practice. In this chapter, we included two generic applications. One is on distributed order signal processing and the other is on optimal distributed damping. We hope these two initial applications can serve as motivating examples to further the investigation in distributed order dynamics systems, signal processing, modeling and controls. | Distributed-Order Filtering and Distributed-Order Optimal Damping | 10.1007/978-1-4471-2852-6_4 |
2012-01-01 | Nonlinear elastic effects play an important role in the dynamics of microelectromechanical systems (MEMS). A Duffing oscillator is widely used as an archetypical model of mechanical resonators with nonlinear elastic behavior. In contrast, nonlinear dissipation effects in micromechanical oscillators are often overlooked. In this work, we consider a doubly clamped micromechanical beam oscillator, which exhibits nonlinearity in both elastic and dissipative properties. The dynamics of the oscillator is measured in both frequency and time domains and compared to theoretical predictions based on a Duffing-like model with nonlinear dissipation. We especially focus on the behavior of the system near bifurcation points. The results show that nonlinear dissipation can have a significant impact on the dynamics of micromechanical systems. To account for the results, we have developed a continuous model of a geometrically nonlinear beam-string with a linear Voigt–Kelvin viscoelastic constitutive law, which shows a relation between linear and nonlinear damping. However, the experimental results suggest that this model alone cannot fully account for all the experimentally observed nonlinear dissipation, and that additional nonlinear dissipative processes exist in our devices. | Nonlinear damping in a micromechanical oscillator | 10.1007/s11071-011-0031-5 |
2012-01-01 | The dynamic analysis is an important part of basic research of complex planetary transmission systems with split power flow. The bifurcation characteristics of the resonance courses especially for high-speed weakly and strongly non-linear parametric and in the damping time-heteronymous systems are highly sensitive to their parameters, i.e. to the quality and quantity of their bifurcation features and ambiguities. In the case of mass discretization, their analytical—numerical solution leads to complex integro-differential equations with solving kernels in the form of Green’s resolventes and complex simulation models in MATLAB/Simulink. The case of one branch of the planetary transmission system with six degrees of freedom is analysed in terms of internal dynamics in this paper, i.e. the causes of the quantity and quality of resonance bifurcation curves and formation of ambiguity characteristics of relative motion in gear meshes. | Dynamic Analysis of Resonance: Bifurcation Characteristics of Non-linear Parametric Systems | 10.1007/978-94-007-5125-5_25 |
2012-01-01 | The single degree-of-freedom system subject to mass and base excitation is used to model an elastic system to determine the frequency-domain effects of squeeze film air damping and viscous fluid damping. This model is also used to determine the important response characteristics of electrostatic attraction and van der Waals forces, the maximum average power from piezoelectric and electromagnetic coupling, and to illustrate the fundamental working principle of an atomic force microscope. The two degree-of-freedom system is introduced to examine microelectromechanical filters, atomic force microscope specimen control devices, and as a means to increase the input to piezoelectric energy harvesters. An appendix gives the details of the derivation of a hydrodynamic function that expresses the effects of a viscous fluid on a vibrating cylinder. | Spring-Mass Systems | 10.1007/978-94-007-2672-7_2 |
2012-01-01 | A nonlinear model of monotube hydraulic dampers is presented with an emphasis on the shim stack properties and their effects on the overall damper performance. There has been no published detailed analysis of the effects of shim stack design in a hydraulic damper to date. Other damper models have used simplifying assumptions for the shim stack deflection and effects of the shim stack have not been completely studied. Various parameters affecting the nonlinear characteristics of monotube dampers such as the hysteresis region are studied. The model presented in this paper can be used for design purposes and helps in developing controllable valvings based on shim stacks. It can also be used to design controllable bypasses in hydraulic dampers. The mathematical model is validated by comparison against experimental test results carried out on an OHLINS CCJ 23/8 monotube damper, in CVeSS test facilities. | Nonlinear modeling and experimental characterization of hydraulic dampers: effects of shim stack and orifice parameters on damper performance | 10.1007/s11071-011-0079-2 |
2012-01-01 | Extremum seeking is realized via a state regulator that drives the state along a convergent set point sequence generated by a numerical optimization algorithm. In this chapter, we propose an asymptotic state regulator design for state feedback linearizable systems, where we trade off finite time state regulation to obtain flexibility in designing a robust extremum seeking controller. Existing techniques such as nonlinear damping and nonlinear adaptive control are then used to deal with input disturbance and unmodeled plant dynamics. Simulation examples illustrate the effectiveness of the basic and robust extremum seeking schemes, and design guidelines are provided for engineering applications. We also show that the NOESC scheme allows a large design flexibility for general nonlinear systems and performance functions, where the key is having the ability to design a robust regulator. | Asymptotic State Regulator Design | 10.1007/978-1-4471-2224-1_5 |
2012-01-01 | Chapter 10 studies the optimal non-delayed fractional-order damping, time-delayed fractional-order damping, and optimal distributed order fractional damping based on ISE, ITSE, IAE and ITAE performance criteria. The comparisons of the step responses of the integer-order and the three types of fractional-order damping systems indicate that the optimal fractional-order damping systems achieve much better step responses than optimal integer-order systems in some instances, but sometimes the integer-order damping systems performs as well as fractional-order ones. Furthermore, time delay can sometimes be used to gain benefit in control systems, and, especially, the fractional-order damping plus properly chosen delay can bring outstanding performance. Time-delayed fractional-order damping systems can produce a faster rise time and less overshoot than others. | Optimal Fractional-Order Damping Strategies | 10.1007/978-1-4471-2233-3_10 |
2012-01-01 | In order to enhance the low voltage ride through (LVRT) capability of full power converter, an improved control strategy was proposed. LCL filter was used to reduce the harmonics. An active damping method was introduced for the passive damping producing great quantity losses. A lead-lag element was added to enhance the damping. The traditional control strategy was improved, voltage and reactive power combined to work as reference for producing reactive power. Proportional-Resonant (P-R) regulator was used to extend the parameter limit and improve response fast. The simulation verified the feasibility and correctness. | LVRT Control Strategy of Full Power Converter with LCL Filter | 10.1007/978-3-642-26001-8_43 |
2012-01-01 | The investigated semiactive damping element works on the principle of squeezing two lubricating layers formed by classical and magneto rheological oils. The damping effect is controlled by the change of intensity of magnetic field passing through the layer of magneto rheological lubricant. The developed mathematical model of the studied element, in which the oils are represented by Newtonian and Bingham materials, was implemented into the computational algorithm for determination of the frequency response characteristic of a flexible rotor and of the dependence of magnitude of the force transmitted between the rotor and its casing on angular speed of the rotor rotation. A trigonometric collocation method was applied to calculate the steady state response. Advantage of the proposed damping element is that it does not require an expensive and complicated control system for its operation. | Reducing the Steady State Vibrations of Flexible Rotors by Squeezing Thin Layers of Normal and Magneto Rheological Oils | 10.1007/978-94-007-5125-5_36 |
2012-01-01 | Damping and loss factor assessment of high damped materials is a challenging task addressed in the past by several researchers, one of the most important is H. Oberst who defined a standard method to tackle the issue. In this paper a sandwich beam composed of two aluminium layers separated by the damping material has been studied. First the beam made only of aluminium layer has been tested and then the composite beam has been assembled by using as damping layer a sheet of styrene-butadiene rubber (SBR). The highly damped behaviour of the test sample makes the test very difficult; great care must be taken in the setting up the test itself. In particular the excitation system has been studied in depth by comparing the results obtained with a traditional non-contact impact test and an electro-dynamic system. Being the impact excitation invasive as well when considering light structures as the object under test, a non-contact electro-magnetic system has been developed in order to limit the influence of the excitation device on the structure behaviour. | Damping Properties Assessment of Very Highly Compliant Sandwich Materials: Are Traditional Methods Really Too Old? | 10.1007/978-1-4614-2425-3_6 |
2012-01-01 | A new type of electromagnetic function material named magneto-thixotropic gel (MTG) is proposed in this chapter. Based on the material, the author proposed a new working model—the wedge-squeezing model which can improve the mechanical properties of the damping devices. By calculating and analyzing the model, it is found that the damping force associated with the wedge-squeezing model mainly consists of two parts and the squeezing viscosity and wedge angle are key parameters to affect the damping force of electromagneto-thixotropic damping devices. The analysis analysis results show that the wedge-squeezing model based on the MTG will have a promising application in electromagneto-thixotropic damping devices. | Modeling and Analysis of High-efficiency Wedge-squeezing Model for Electromagneto-thixotropic Damping Devices | 10.1007/978-1-4419-8849-2_50 |
2012-01-01 | This chapter presents a systematic method to describe a large class of switched-mode power converters within the Brayton–Moser (BM) framework, a framework that has proven to be useful for analysis and control purposes. The approach forms an alternative to the switched Lagrangian and (port-)Hamiltonian formulations. The proposed methodology allows for the inclusion of often encountered devices like diodes, nonlinear (multi-port) resistors, and equivalent series resistors, a feature that does not seem feasible in the switched Lagrangian formulation. Additionally, and besides the fact that the BM equations allow for almost any type of nonlinear resistor, the framework constitutes a practical advantage since in most control applications the usual measured quantities are voltages and currents—instead of fluxes and charges as with the Lagrangian or (port-)Hamiltonian approaches. The application of the proposed framework to stability analysis, new passivity properties and control is briefly highlighted. | Power-Based Modelling | 10.1007/978-1-4471-2885-4_8 |
2012-01-01 | This paper explores methods that can be used to characterize weakly nonlinear systems, whose natural frequencies and damping ratios change with response amplitude. The focus is on high order systems that may have several modes although each with a distinct natural frequency. Interactions between modes are not addressed. This type of analysis may be appropriate, for example, for structural dynamic systems that exhibit damping that depends on the response amplitude due to friction in bolted joints. This causes the free-response of the system to seem to have damping ratios (and to a lesser extent natural frequencies) that change slowly with time. Several techniques have been proposed to characterize such systems. This work compares a few available methods, focusing on their applicability to real measurements from multi-degree-of-freedom systems. A beam with several small links connected by simple bolted joints was used to evaluate the available methods. The system was excited by impulse and the velocity response was measured with a scanning laser Doppler vibrometer. Several state of the art procedures were then used to process the nonlinear free responses and their features were compared. First the Zeroed Early Time FFT technique was used to qualitatively evaluate the responses. Then, the Empirical Mode Decomposition method and a simple approach based on band pass filtering were both employed to obtain mono-component signals from the measured responses. Once mono-component signals had been obtained, they were processed with the Hilbert transform approach, with several enhancements made to minimize the effects of noise. | Identifying the Modal Properties of Nonlinear Structures Using Measured Free Response Time Histories from a Scanning Laser Doppler Vibrometer | 10.1007/978-1-4614-2416-1_22 |
2012-01-01 | This paper discusses the improvements in small signal performance of a multi machine power system under the impact of Power System Stabilizer (PSS) and Static Compensator (STATCOM) devices. Parameters of both devices are optimized independently using MATLAB control system tools. PSS lead-lag network is designed using bode plot technique by analyzing Single Machine Infinite Bus (SMIB) based Heffron-Phillips model of network generators. STATCOM voltage regulator is optimized using a reduced STATCOM-Infinite bus model. The proposed designs are tested on a modified IEEE 14 bus system using MATLAB/SIMULINK. Simulations reveal that the system gains an appreciable damping ability against local modes of oscillation with PSS employed while STATCOMs increase this strength further. Results have validated the effectiveness of these SMIB based approximate modeling techniques in a multi machine environment where comprehensive system modeling is complex and often require information about whole power system which is sometimes hard to achieve. | Improvement of Small Signal Performance of Multi Machine Power System Using SMIB Based PSS and STATCOM Designs | 10.1007/978-3-642-28962-0_19 |
2012-01-01 | We consider issues related to the design of mechanical systems that feature nonlinear vibratory behavior. Designs that account for, and also exploit, nonlinear dynamics are considered. The chapter provides a brief overview of general considerations related to these issues, and then considers in detail the case of vibration absorbers that are used to reduce torsional vibrations in rotating systems. These absorbers, which are being developed for use in automotive engines, consist of centrifugally driven masses that ride on user-specified paths relative to a rotor that is being driven by a fluctuating torque. The absorbers are used to reduce the torsional vibrations of the rotor by providing a torque on the rotor that counteracts, at least partially, the applied torque. The mathematical model of this system represents, under assumptions on the system parameters consist with practical applications, a system of N identical nonlinear oscillators with weak damping, weak global coupling, and weak near-resonant excitation. The nonlinearity in the oscillators depends on the path, and the goal of this nonlinear dynamic design problem is to select a path that provides good vibration reduction over a specified range of torque amplitudes. The desired response has all N absorbers behaving identically, that is, in a synchronous manner. However, the structure of this system leads to two distinct types of dynamic instabilities, and both must be avoided for a given design to be feasible. In this work we examine the synchronous absorber response in terms of vibration reduction, torque range, and stability. It is shown that a particular epicycloidal path provides good performance, and can be made stable. These results are a summary of previous work described in (30). | Designing Nonlinear Torsional Vibration Absorbers | 10.1007/978-3-7091-1187-1_4 |
2012-01-01 | The chapter deals with autoparametric vibrations of a system composed of a nonlinear oscillator with an attached pendulum. Dynamics of the mechanical structure is studied analytically around the principal parametric resonance region, numerically and experimentally for a wide range of parameters. The influence of damping, nonlinear stiffness (hard and soft), amplitude and frequency of excitation on the system’s behaviour is analysed in details. The obtained results show that the pendulum can be applied as a dynamical absorber. However, for selected parameters, near the main parametric resonance, instability, which transits the pendulum to chaotic oscillations or to a full rotation, occurs. Therefore, the application of a magnetorheological (MR) damper and a nonlinear spring is proposed to improve the dynamics and to control the response online. Periodic vibrations, chaotic motions or a full rotation of the pendulum obtained numerically are confirmed by the experiment. The chaotic nature of motion is determined from real signals by the attractor reconstruction and the recurrence plot calculation. The results show that the semi-active suspension may reduce dangerous motion and it also allows to maintain the pendulum at a given attractor or to jump to another one. | Autoparametric Vibrations of a Nonlinear System with a Pendulum and Magnetorheological Damping | 10.1007/978-94-007-2473-0_1 |
2012-01-01 | For oscillation damping of a multi link flexible arm under gravity this paper exploits the image data already acquired by an eye-in-hand camera used for visual servoing. It replaces commonly applied distributed strain measurements in a model free oscillation damping control concept. Based on simulations and experiments the paper compares three predictive signal processing approaches to compensate for the sensor inherent delay. Damping results for oscillations induced by joint motions as well as sudden load changes are presented in three different unstructured scenes. | Predictive Delay Compensation for Camera Based Oscillation Damping of a Multi Link Flexible Robot | 10.1007/978-3-642-33503-7_10 |
2012-01-01 | Our recent analysis on nonlinear nonextensive dust-acoustic waves (DA) [Amour and Tribeche in Phys. Plasmas 17:063702, 2010] is extended to include self-consistent nonadiabatic grain charge fluctuation. The appropriate nonextensive electron charging current is rederived based on the orbit-limited motion theory. Our results reveal that the amplitude, strength and nature of the nonlinear DA waves (solitons and shocks) are extremely sensitive to the degree of ion nonextensivity. Stronger is the electron correlation, more important is the charge variation induced nonlinear wave damping. The anomalous dissipation effects may prevail over that dispersion as the electrons evolve far away from their Maxwellian equilibrium. Our investigation may be of wide relevance to astronomers and space scientists working on interstellar dusty plasmas where nonthermal distributions are turning out to be a very common and characteristic feature. | Nonextensive dust acoustic waves in a charge varying dusty plasma | 10.1007/s10509-011-0830-7 |
2012-01-01 | The dynamics of a system of coupled oscillators possessing strongly nonlinear stiffness and damping is examined. The system consists of a linear oscillator coupled to a strongly nonlinear, light attachment, where the nonlinear terms of the system are realized due to geometric effects. We show that the effects of nonlinear damping are far from being purely parasitic and introduce new dynamics when compared to the corresponding systems with linear damping. The dynamics is analyzed by performing a slow/fast decomposition leading to slow flows, which in turn are used to study transient instability caused by a bifurcation to 1:3 resonance capture. In addition, a new dynamical phenomenon of continuous resonance scattering is observed that is both persistent and prevalent for the case of the nonlinearly damped system: For certain moderate excitations, the transient dynamics “tracks” a manifold of impulsive orbits, in effect transitioning between multiple resonance captures over definitive frequency and energy ranges. Eventual bifurcation to 1:3 resonance capture generates the dynamic instability, which is manifested as a sudden burst of the response of the light attachment. Such instabilities that result in strong energy transfer indicate potential for various applications of nonlinear damping such as in vibration suppression and energy harvesting. | Dynamic instabilities in coupled oscillators induced by geometrically nonlinear damping | 10.1007/s11071-011-0028-0 |
2012-01-01 | On February 27, 2010 one of the largest magnitude earthquake ever registered occurred in Chile. Although, several tall buildings suffered damage without collapse, the response of these buildings, in general, has been considered a success. Several studies have been carried out to understand the seismic response of these damage buildings, in order to develop appropriate retrofit strategies. We have selected one building located in the coastal city of Viña del Mar for instrumentation. This area suffered strong shaking with peak ground acceleration close to 0.35 g and more than 180 s of motion. The structure is a residential shearwall building with 17 stories and one basement level. The main structural system was damaged at the basement and first floor levels. The main damage was concrete crushing of walls, along with longitudinal reinforcement buckling at wall boundaries and severe cracking of slabs and lintel beams. An array of 12 accelerometers was deployed in the building to evaluate its modal properties variations, recording five aftershocks. This publication presents the structural damage in the building and the preliminary system identification results from strong motion records. Variations of the modal parameters are correlated with motion amplitudes and compared with ambient vibration conditions. | Modal Parameter Variation of an Earthquake Damaged Building | 10.1007/978-1-4614-2413-0_39 |
2012-01-01 | The sensitivity of the response characteristics of a bolted interface to the bolt preload level used in the joint can often cause the dynamic properties of a system to be difficult to predict. A bolted interface test fixture was fabricated to investigate the effects of preload changes on the system dynamic response characteristics, and experimental results indicated that increases in bolt preload led to increases in modal frequency and decreases in modal damping. Furthermore, the system demonstrated a nonlinear behavior that resulted in the increase in modal frequency due to increases in impact amplitude when preload levels were low. The experimental results motivated the creation of a simplified low order nonlinear system model to represent the two dominant modes of the system. A model was used to describe the relationship between static stiffness and preload to account for the changes in initial bolt preload, and cubic stiffness terms were included to account for the amplitude dependent nonlinearity that was observed. The resulting model was able to accurately simulate system frequencies and general trends, but was unable to match some response characteristics of the system due to the lack of force information for the high amplitude loading used in the experiments. | Simplified Nonlinear Modeling Approach for a Bolted Interface Test Fixture | 10.1007/978-1-4614-2416-1_7 |
2012-01-01 | A new type of generalized Lax-Friedrichs scheme for the convective-diffusion equation u _ t + au _ x = εu _ xx ( a ∈ R , ε > 0) is given and analyzed. For the convection term, the scheme use generalized Lax-Friedrichs scheme. For the diffusion term, it uses implicit central difference scheme. The scheme is discussed by applying modified equation analysis, in order to find the relative phase error, numerical dissipation, numerical viscosity, numerical damping and oscillations. | Generalized Lax-Friedrichs Scheme for Convective-Diffusion Equation | 10.1007/978-3-642-34038-3_44 |
2012-01-01 | In this paper, an infinite family of solutions describing solitary wave packets with a finite number of nodes is presented. These structures arise from the study of damping in the framework of non-linear ordinary differential equations with oscillatory behaviour. Usually one expects to find effects of this kind in physical systems described by a set of partial differential equations. The standard argument is that the non-linear term acts against the dispersive flux and this balance explains the appearance of solitary waves. Here we show that the non-linear oscillatory behaviour can also balance the effect of damping in special cases. The theory used to discriminate among the various possibilities is plain Painlevé analysis. Several physical applications are briefly discussed. | Solitary wavepackets from oscillatory non-linear equations with damping | 10.1007/s11071-011-9957-x |
2012-01-01 | A new Modular Recurrent Trainable Neural Network (MRTNN) has been used for system identification of two-mass-resort-damper nonlinear oscillatory plant. The first MRTNN module identified the exponential part of the unknown plant and the second one - the oscillatory part of the plant. The plant has been controlled by a direct adaptive neural control system with integral term. The RTNN controller used the estimated parameters and states to suppress the plant oscillations and the static plant output control error is reduced by an I-term added to the control. | Recurrent Neural Identification and an I-Term Direct Adaptive Control of Nonlinear Oscillatory Plant | 10.1007/978-3-642-33185-5_24 |
2012-01-01 | The objective of this research is aimed to design and implement a Wearable Hybrid Assisted Lower Limb Orthosis (HALLO), which could provide up to 10% of knee torque support. The proposed device adopted a specially designed M-shaped flexible mechanism to store the potential energy due to different human body gestures, such as stand-to-sit, a DC motor would act as a variable damper to control the releasing rate of potential energy. To provide a proper trajectory tracking, a discrete-time output feedback sliding-mode controller design [7] is adopted to perform efficient tracking. Finally, wearing the device to perform a variety of basic movements is demonstrated through experiments. | On the Design and Implementation of a Wearable Hybrid Assisted Lower Limb Orthosis | 10.1007/978-3-642-28314-7_6 |
2012-01-01 | Let’s extend the two degree of freedom free vibration analysis from Chap. 4 to include externally applied forces so that we can analyze two degree of freedom forced vibration. The general case is that a separate harmonic force is applied at each coordinate; see Fig. 5.1. However, we are considering only linear systems, so we can apply superposition . This means that we can determine the system response due to each force separately and then sum the results to find the combined effect. | Two Degree of Freedom Forced Vibration | 10.1007/978-1-4614-0460-6_5 |
2012-01-01 | The present paper deals with a brief review on different modeling techniques used to model friction dampers in turbomachinery. It is not the intention of the author to provide a detailed survey on all the approaches. However, the main concentration is on finite element modeling and bondgraph modeling. The main purpose of this paper is to provide a detailed survey on various modeling approaches adopted in turbomachinery, especially kinematics modeling, finite element modeling, parametric modeling, harmonic balance analysis and bondgraph modeling. The usefulness of bondgraph modeling technique is underlined in this paper presenting several considerations in the model. The bondgraph is one of the most convenient ways to represent a system form the physical aspects in foreground. It has advantages of putting together multi-energy domain of the system in a single representation in a unified manner. A case study of bondgraph modeling of turbine blade has been presented along with friction damper. | A Brief Review on Modeling Approaches of Friction Dampers Used in Turbomachinery | 10.1007/978-81-322-0491-6_31 |
2012-01-01 | The physical and thermodynamic properties of a repulsive clathrate used as a working body for the dissipation, storage, and conversion of energy in thermomechanical systems are studied. In repulsive clathrates, use is made for the first time of the molecular repulsive forces acting in large interfacial areas in a system consisting of a fluid and a capillary-porous matrix not wetted by this fluid. Based on experimental studies of a car damper with a repulsive clathrate, a rheological model of energy dissipation was developed which can be used to design compact high-performance dampers for different purposes and anti-seismic systems of new generation. | Rheology and dynamics of repulsive clathrates | 10.1134/S0021894412010130 |
2012-01-01 | The optimal design of the magnetorheological (MR) dampers is important to meet the engineering applications and obtain better performance compared with the conventional design methods. In this chapter, a multiobjective optimization method, based on Parallel-plate Model and genetic algorithms, is proposed to obtain the optimal structural parameters for the MR damper. The algorithm indicates that the most important influential factors of the damping force and its adjustable ratio are the gap between the cylinder and piston and the effective length of the piston. The results demonstrate the effectiveness and feasibility of the proposed optimization approach. | Multiobjective Optimization of Structural Parameters Designing for Magnetorheological Damper Based on Genetic Algorithms | 10.1007/978-1-4419-8849-2_187 |
2012-01-01 | ^1Research in this article was carried out at Washington State University (WSU) while the author was a visiting scholar at WSU. This article proposes an algorithm denoted Frequency-Domain Optimization (FDO) for real-time modal estimation of power system oscillatory modes based on multiple synchronized Phasor Measurement Units (PMUs). The proposed method combines Fast Fourier Transform (FFT) with least-square optimization to estimate the mode parameters of electromechanical oscillations in power systems. Multiple signals are analyzed simultaneously to improve the accuracy of estimation, and the mode shape can also be determined from analyzing these multiple signals. Results from simulated and measured ambient PMU data show that this FDO method is able to estimate the system modal parameters results effectively. | Multi-Dimensional Modal Analysis in Large Power Systems from Ambient Data Based on Frequency-Domain Optimization | 10.1007/978-1-4614-1605-0_8 |
2012-01-01 | Alfalfa Alfalfa ( Medicago sativa Medicago sativa L.) is affected by several pathogens; however, those that attack crown and roots, such as Macrophomina phaseolina Macrophomina phaseolina , directly define the longevity or productive period of the plant. Use of microorganisms with biological control capacity constitutes an alternative to chemical products. In this chapter, we have gathered some studies on this subject; in addition, we contribute data from our own researches on in vitro and in vivo antifungal activity of rhizobacteria isolated from alfalfa rhizosphere against the causal agent of damping-off, M. phaseolina . In vitro tests consisted in culturing a bacterium and the pathogen on Potato Dextrose Agar (PDA) medium. In vivo tests were carried out in pots containing soil infested with M. phaseolina sclerotia. Alfalfa Alfalfa seeds were inoculated with each selected isolate (single inoculation treatments) or co-inoculated with Sinorhizobium meliloti Sinorhizobium meliloti strain B399 (mixed inoculation treatment); also, non-inoculated seeds were sown in infested soil (control treatment). Experiments were conducted in a growth chamber for 30 days and the evaluated parameters were: germination percentage, damping-off at 5 and 8 days, number of surviving plants at 15 and 30 days, and number of nodules. The pathogen incidence was high in the control treatment, with a low germination rate, high occurrence of damping-off and death of all of the plants at the end of the experiment. Pseudomonas Pseudomonas sp. Ch2 performed the best, since singly inoculated seeds reached a germination percentage of 83.3%; in addition, there was no damping-off incidence after 5 and 8 days neither in single inoculation nor in mixed inoculation treatments. The number of surviving plants at 15 days was 9/18 for the Pseudomonas Pseudomonas sp. Ch2 treatment and 15/18 for the Pseudomonas Pseudomonas sp. Ch2- S. meliloti B399 treatment. At 30 days, the number of surviving plants was 9/18 for both treatments. Pseudomonas Pseudomonas sp. Ch2 showed antifungal activity against the alfalfa pathogen M. phaseolina in the in vitro as well as in the in vivo assays. | Isolation and Characterization of Rhizobacteria Antagonistic to Macrophomina phaseolina (Tassi) Goid., Causal Agent of Alfalfa Damping-Off | 10.1007/978-94-007-1591-2_10 |
2012-01-01 | This paper presents a theory describing the fluid mechanics of whale flukeprints. It contains excerpts of a longer paper recently published in the International Journal of Non-Linear Mechanics special issue on biological structures. Whale flukeprints are smooth oval-shaped water patches that form on the surface of the ocean behind a swimming or diving whale. The prints persist up to several minutes and can be used to track whales cruising near the ocean surface. The motion of the fluke provides a mechanism for shedding vortex rings. The subsequent interaction of the vortex ring with the ocean surface damps the short wavelength capillary waves in the print. The theory suggests that the role of natural surfactants are of secondary importance in the early formation of flukeprints. We describe potential directions for future research, including collection of quantitative data from real flukeprints. | Formation of Ocean Surface Patterns by Cetacean Fluke Oscillations | 10.1007/978-1-4614-3997-4_11 |
2012-01-01 | Recent vibration serviceability problems of many structures have drawn researchers’ attention to the walking-induced vibration modelling and assessment of floors and footbridges. Stochastic nature of human-induced vibration and its dependency on numerous conditions significantly reduce the accuracy of the current non-stochastic design procedures and consequently the level of confidence on them. This paper tends to study the performance of two of the most recent design guidelines, UK National Annex to Eurocode 1 (2008) [1] and French Sétra guideline (2006) [2], on real structures and to highlight their advantages and disadvantages. These methods are used to calculate dynamic reactions of a slender and lightly damped pre-stressed concrete slab strip and an as-built footbridge using various loading scenarios such as group loading, spatially unrestricted flow of pedestrians, and crowd loading. The calculated structural responses under first and second harmonics of walking load are further compared with their corresponding experimentally acquired reactions to examine their accuracy and efficiency. Various potential sources of discrepancy in the results of these procedures in comparison with the experimental data, such as missing human-structure interaction effects (e.g. damping), invalid ‘perfect periodicity’ assumption, limited applicability and unrealistic people correlation are then discussed. Finally the effects of using stationary pedestrians’ added damping on performance of considered design models are investigated and briefly discussed. The results of this analysis can provide a comprehensive insight into current design procedures’ accuracy and shall be taken as a good starting point for future researches in this area. | Comparative Evaluation of Current Pedestrian Traffic Models on Structures | 10.1007/978-1-4614-2413-0_5 |
2012-01-01 | Chapter 8 deals with nonoscillation problems for a scalar linear delay differential equation of the second order including explicitly a term with the first derivative which is usually called “a damping term”. Most of publications deal with equations not containing the term with the first derivative; for these equations, positivity of the coefficients and a solution on the semiaxis implies that its derivative is nonnegative. This fact is very important, and it is employed in most investigations on second-order delay differential equations. If the first derivative is included in the equation explicitly, i.e. the equation contains the damping term, then a sign of a solution does not uniquely define the sign of its derivative, which makes the study of oscillation properties of the equations with the damping term more complicated. This is the reason why such equations are much less studied than equations without the damping term. The main result of the chapter is the following: if a generalized Riccati inequality has a nonnegative solution, then the differential equation has a positive solution with a nonnegative derivative, and the fundamental function of this equation is positive. If the damping term is not delayed, this immediately yields that the following four properties are equivalent: nonoscillation of solutions of this equation and the corresponding differential inequality, positivity of the fundamental function and existence of a nonnegative solution of the generalized Riccati inequality. The generalized Riccati inequality is applied to compare oscillation properties of two equations without comparing their solutions. These results can be considered as a natural generalization of the well-known Sturm comparison theorem for a second-order ordinary differential equation. The chapter also contains explicit nonoscillation conditions which are obtained by substituting specific solutions of the generalized Riccati inequality. | Second-Order Delay Differential Equations with Damping Terms | 10.1007/978-1-4614-3455-9_8 |
2012-01-01 | Two psychophysical experiments are conducted to identify masking effects for the perception of damping. The results indicate that the just noticeable difference for damping increases with the magnitude of additional masking stimuli. This is the case for environments consisting of a damping/stiffness and environments consisting of a damping/inertia. This has implications for the design and evaluation of haptic human-system interfaces, telepresence systems and haptic rendering algorithms. | Masking Effects for Damping JND | 10.1007/978-3-642-31404-9_25 |
2012-01-01 | We investigate the death of entanglement and the purity loss of a two qubits–field system in the dispersive regime with a reservoir. For an alternative entanglement measure, we calculate the negativity of the eigenvalues of a partially transposed density matrix and compare it with the mutual entropy. A new measure related to the mutual entropy, namely, the index of entropy, is proposed to measure the degree of entanglement, and this agrees well with the negativity. We found that the entanglement has a strong sensitivity to the phase damping. The asymptotic behavior of the field states, the two qubits, and the total system fall into a mixed state. We treat the phenomena of death of entanglement and purity as they arise from the effect of phase damping. | Death of entanglement and purity in a two qubits–field system induced by phase damping | 10.1007/s10946-012-9256-0 |
2012-01-01 | In China, the construction of passenger dedicated line is in progress on a large scale. As the important infrastructure of passenger dedicated line, the fastener damping of ballastless turnout influences the vibration and noise of the track. In order to study the mutative fastener damping’s impact on the vibration and noise of ballastless turnout, The method for determining the fastener damping was established by using the vehicle-turnout coupling dynamic analysis, and the noise prediction method for ballastless turnout was stated from three parts of the excitation of wheel-rail roughness, the sound radiation efficiency and the calculation of wheel-rail radiated noise. From both aspects of vibration decrease and noise reduce, the reasonable fastener damping of ballastless turnout was determined by using the above method. The research results showed that the damping of 0.15~0.225 to the fastener of ballastless turnout was reasonable for vibration decrease and noise reduction. | The Reasonable Fastener Damping of Ballastless Turnout’s Vibration Decrease and Noise Reduction of 350 km/h Passenger Dedicated Line | 10.1007/978-3-642-27960-7_3 |
2012-01-01 | Any mechanical system possesses its own vibrating characteristics from which functioning can be understood and foreseen. Modal parameters such as natural frequencies and damping ratios are the main examples. This paper presents homemade numerical analyzer for characterizing them. The procedure is based on complex Morlet wavelet transform with particular use of translated version for better detection of closed modes. The code has been successfully tested through simulated signals. Experimental validation was carried out through the modal analysis of a gear motor on which repeatable and reliable results were obtained. | Numerical Tool for Extraction of Modal Parameters Based on Continuous Wavelet Transform | 10.1007/978-3-642-28768-8_37 |
2012-01-01 | Long-span bridges can undergo vibrations during both construction and service phases, due to their flexibility and lightness. Moreover, they can be sensitive to environmental dynamic actions. The internal damping of this kind of structures is moderate, therefore vibration damping is frequently obtained by using dedicated devices, as an example tuned mass dampers (TMD). On the other hand, TMD’s performance strongly depends on their constitutive parameters and on the external loads. In this paper the adaptive use of a new electro-mechanical damper (EMD) is presented, made of an oscillating mass around the axis of an alternator, whose output is connected to a resistor: in this way the kinetic energy of the oscillating pendulum is transformed into electrical energy dissipated. An application is made of this EMD to a cable-stayed bridge steel model. The internal parameters of this new damper are constant or variable according to a semi-active control law. The experiments show that the adaptive semi-active control strategy makes effectiveness of this EMD independent on the excitation characteristics. | Some Applications of Passive and Semi-active Control Devices for Harmonic Vibrations Damping in Cable-Stayed Bridges | 10.1007/978-3-642-24638-8_33 |
2012-01-01 | This chapter will briefly review some of the existing applications of model predictive control for vibration attenuation or its closely related fields. The application of model predictive control as a vibration reduction strategy is not common, and there are only a handful of available publications related to this field. | Applications of Model Predictive Vibration Control | 10.1007/978-1-4471-2333-0_9 |
2012-01-01 | The Distributed Tuned Mass Damper system, which is defined as the multiple Tuned Mass Damper design based on one specific vibration mode of the main structure, is investigated in this study. As those for single TMD design cases, the challenge work in this area is to attain the best vibration suppression performance through an optimally designed DTMD system. In the traditional DTMD or TMD design, the general approach is to focus on the attached spring(s) and damper(s). In this study, a novel DTMD design methodology will be proposed, in which the design parameters are the attached masses in the DTMD system under assumed constant spring(s) and damper(s). The presented method provides a simple and straight-forward way to design the DTMD system, and may provide a more cost-efficient approach in manufacturing, installation and also maintenance than the traditional design. The numerical examples will be presented to illustrate the validity and effectiveness of the proposed DTMD design approach. | A Novel Distributed Tuned Mass Damper Design Approach | 10.1007/978-3-642-33503-7_27 |
2012-01-01 | The magneto-rheological (MR) damper has been widely explored in the study of vibration suppression for vehicle suspension and constructional systems, etc. Aiming at semi-active controllable hysteretic nonlinear property of the MR damper depending on direct magnetic field, the generation mechanism of conducted and radiated electromagnetic interference (EMI) noises for intelligent vehicle system with MR dampers are initially proposed in this paper, which includes strong nonlinearities arisen from the semi-active control strategy, road surface shock excitations, high-frequency devices in control circuit, environmental electromagnetic (EM) field coupling to excitation coil, and excitation coil impedance mismatch of the MR damper. Upon above studies, both the conducted EMI noise model and the radiated EMI noise model are generally proposed for the MR damper and its control system, and the far field characteristic of radiated EM field generated from excitation coil of the MR damper is further analyzed. The results of simulation and experiment show correctness of the proposed EMI noise models, which will play an important role in future application study for the EMI noise suppression of intelligent vehicle suspension design with MR dampers. | Modeling of Electromagnetic Interference Noise Mechanism for Magneto-Rheological Damper | 10.1007/978-3-642-33515-0_16 |
2012-01-01 | The geometric telegrapher’s process has been proposed in 2002 as a model to describe the dynamics of the price of risky assets. In this contribution we consider a related stochastic process, whose trajectories have two alternating slopes, for which the random times between consecutive slope changes have exponential distribution with linearly increasing parameters. This leads to a process characterized by a damped behavior. We study the main features of the transient probability law of the process, and of its stationary limit. | On the damped geometric telegrapher’s process | 10.1007/978-88-470-2342-0_21 |
2012-01-01 | Although major improvements have been made in the field of hybrid simulation, the numerical models used in the tests are fairly simple, reaching only an order of ten Dynamic Degrees of Freedom (DDOF). However, the presence of large computational facilities along with the implementation of a Platform for Geographically Distributed Seismic Tests (PGDSTs) provides the possibility to use large and complex numerical models, maybe consisting of a couple of thousand DDOF, within the context of continuous hybrid simulations that work with acceptable time scale factors. However, the use of these facilities requires some approach from both parts in order to solve major issues such as the operating mode and thread to transfer data between facilities, or adapting the substructure algorithms to work in a parallel fashion through the use of special libraries and specifications among others. This paper presents ongoing work within SERIES to assess the extensibility of the PGDSTs to use HPC facilities as well as adapting the substructure algorithm developed by Dorka, which has been used successfully not only in Earthquake Engineering but also in aerospace applications. | Use of Large Numerical Models and High Performance Computers in Geographically Distributed Seismic Tests | 10.1007/978-94-007-1977-4_11 |
2012-01-01 | The aim of this chapter is to emphasize the interest of the LPV methodology for suspension modeling and control. Indeed, the main features of a semi-active automotive suspensions are: The damper can only dissipate energy. The damper has a nonlinear behavior which is important to account for in the control design step. New methodologies have been recently designed to separately cope with these constraints (Do AL et al., An LPV control approach for semi-active suspension control with actuator constraints, 2010; Poussot-Vassal et al., Contr Eng Pract 16(12):1519–1534, 2008; Savaresi et al., Semi-active suspension control for vehicles, 2010). In this study, recent developments are presented to: First, develop an LPV model for an automotive suspension system starting from a nonlinear semi-active damper model. Second, using an original LPV representation of the dissipativity of the semi-active damper, develop an ad hoc H _ ∞ ∕ LPV controller. The whole LPV model is used to design a polytopic H _ ∞ controller for an automotive suspension system equipped with a Magneto-Rheological semi-active damper. This controller aims at improving ride comfort and/or road holding, depending on the required specifications. Some simulation results are given on realistic vehicle and damper models (whose validation on real data has been performed), allowing to show the efficiency of the approach. | LPV Modeling and Control of Semi-active Dampers in Automotive Systems | 10.1007/978-1-4614-1833-7_15 |
2012-01-01 | In this Chapter the control and exploitation of nonlinearity are considered when applied to so called ‘smart structures’. Here we consider how active control can be applied to structures particularly in the presence of nonlinearity. We also consider how snap-through structures can potentially be exploited as hinges in morphing applications. | Control and exploitation of nonlinearity in smart structures | 10.1007/978-3-7091-1187-1_6 |
2012-01-01 | Magneto- Rheological (MR) damper is a new generation of dampers, filled up with a MR fluid. This fluid, when exposed to a magnetic field, will transform regularly from a slipper linear viscous fluid to a semi rigid state. In this article, semi-active control of structures equipped with MR damper is studied. For this purpose, fuzzy control theory is used to determine appropriate command voltage applied to MR damper; and genetic algorithm is used to optimize the fuzzy rules. Then, generated fuzzy rules database will improve fuzzy control system performance relative to experimental fuzzy rules database. Consequently, with applying an appropriate command voltage through an optimized fuzzy control system will decrease vibrations of the structures. The results show that, in the presence of optimized fuzzy rules through genetic algorithm, the amplitude of vibrations is decreased significantly. | Semi-active Control of Structure Vibrations with MR Damper Using Fuzzy Control System (FLC) and Optimization through Genetic Algorithm (GA) | 10.1007/978-3-642-25541-0_74 |
2012-01-01 | CindyScript offers a wide range of very versatile functions for the generation of audio output. These audio functions cover the generation of music (via a built-in synthesizer), as well as the generation of algorithmically generated audio samples (how, for instance, does a function sound?). They can be used to serve many different purposes, e.g.... | Music Support: Syntherella | 10.1007/978-3-540-34926-6_14 |
2012-01-01 | The vibration analysis of n -dof systems is the subject of this chapter, the focus being undamped systems, while only outlining the analysis of damped systems in Sect. 6.6. The analysis of n -dof undamped systems parallels that of their two-dof counterparts, the only difference being that the calculations that were possible in graphical form for the latter are not possible for the former. Hence, the analyst has to resort to a numerical procedure to implement these calculations. The widespread availability of pertinent mathematical software, however, eases the analysis tremendously. Therefore, frequent mention will be made to suitable software, as the need arises. | Vibration Analysis of n-dof Systems | 10.1007/978-1-4419-1027-1_6 |
2012-01-01 | Since the initiation of 200 km·h^− 1 High Speed Railway (HSR) in the Japanese Shinkansen, the lateral stability solutions of High Speed Rolling Stocks (HSRS) have been developed and improved through the theoretical and practical courses, especially the novel theory of anti-hunting wide-band absorption is presented and put into Chinese 300 km·h^− 1 HRS practices. The lateral vibrations of some motor-vehicle coaches are experienced during the test running of 16-vehicle train with CRH380B bogies in Jinghu HSR line. Based on the contrastive data from anti-hunting damper testrig, the determining criterion was formulated definitely for the in-series stiffness. After the comparison with the acceptance tests, it is further pointed out that the radical reason for the above coaches’ lateral vibrations is that the in-series stiffness of anti-hunting dampers is too hard so that the stability margin of rear bogie is reduced much, and the direct factors are due to the wind load interactions and longitudinal eccentric loads which cause their wheel sideslips. The anti-hunting soft-constraint technique strategy is therefore proved to be the successful and effective solution, in which there exists a theoretical optimal value of the in-series stiffness to trade off the stability of trailer bogies and the handling performance of motor bogies. | Theoretical and Practical Study on High-Speed Bogie Stability Margin Regulations | 10.1007/978-3-642-27960-7_10 |
2012-01-01 | Magneto-rheological damper is a nonlinear system. In this case study, system has been identified using Neural Network tool. Optimization between number of neurons in the hidden layer and number of epochs has been achieved and discussed by using multilayer perceptron Neural Network. | Nonlinear System Identification Using Neural Network | 10.1007/978-3-642-28962-0_13 |
2011-12-01 | The aim of the present study was to find and describe the relationship between damping properties and both the number of layers and the fiber orientation in wood-veneer-composite specimens. The testing apparatus was a simple torsional pendulum in which the frequencies of the resulting free vibrations were maintained between 13 and 23 Hz. Cross-sectional (30 × 30 mm) specimens with a total length of 250 mm were used. The specimens were cut from manufactured wood-veneer-composite panels (both 0°/90° and 0°/0° oriented) with up to 13 layers. Existing problems such as nonlinearities, which are often responsible for weighting results, were taken into account by using several mathematical approaches. The results led to a consistent picture of the damping properties across the measured range. We found that the damping ratio increased for the 0°/90° orientation with increasing numbers of layers in a cross-sectional specimen of constant outer dimensions. This effect could not be reproduced for specimens oriented 0°/0°. | Damping and layer configuration in wood veneer composites | 10.1007/s10086-011-1206-x |
2011-12-01 | This work is concerned with a system of two viscoelastic wave equations with nonlinear damping and source terms acting in both equations. Under some restrictions on the nonlinearity of the damping and the source terms, we prove that, for certain class of relaxation functions and for some restrictions on the initial data, the rate of decay of the total energy depends on those of the relaxation functions. This result improves many results in the literature, such as the ones in Messaoudi and Tatar (Appl. Anal. 87(3):247–263, 2008 ) and Liu (Nonlinear Anal. 71:2257–2267, 2009 ) in which only the exponential and polynomial decay rates are considered. | General decay of solutions of a nonlinear system of viscoelastic wave equations | 10.1007/s00030-011-0112-7 |
2011-12-01 | This paper focuses on the dynamic stiffness and overall equivalent damping of an air spring connected to an orifice and an auxiliary reservoir, with respect to the displacement excitation frequency, orifice area, and auxiliary reservoir volume. A theoretical model of this air spring with its auxiliary reservoir is derived by utilizing the energy conservation equation, gas state equation, and orifice flow rate equation. Simulation results from the presented model reveal that, when the air spring is subject to harmonic displacement excitation, its dynamic stiffness increases with an increase in excitation frequency and decrease in orifice area. Smaller orifice areas and lower excitation frequencies result in higher overall equivalent damping. A validation experiment is also implemented. When compared with experimental results, simulations show consistent varying trends of the dynamic stiffness and overall equivalent damping. The model developed here can correctly describe the behavior of the air spring with auxiliary reservoir, indicating that it is reasonable and feasible. | Model development and experimental research on an air spring with auxiliary reservoir | 10.1007/s12239-011-0096-7 |
2011-12-01 | Dispersion relations for a coupled thermoelasticity problem including a hyperbolic heat conduction equation are derived, and their asymptotic analysis is performed. Dependences of the wave number and characteristics of the vibration damping rate on frequency are obtained and compared with similar diagrams in the classical model. | Analysis of dispersion relations of a coupled thermoelasticity problem with regard to heat flux relaxation | 10.1134/S0021894411060125 |
2011-12-01 | The Reynolds equation coupled with an effective viscosity model is often employed to predict squeeze-film damping of plate resonators in a low vacuum. Due to the lack of a sound theoretical foundation, a study is carried out to evaluate the performance of such an approach in the free-molecule regime and results are presented in this paper. An experimentally validated Monte Carlo simulation approach for the simulation of air damping is developed and employed for this study. First, effective viscosity models are developed for a parallel-plate resonator and a rotational resonator based on experimental measurements. These models are then coupled with Reynolds equation and employed to simulate air damping of resonators of the same type but with differing dimensions. The results are compared with Monte Carlo simulation results. It has been found that the modified Reynolds equation approach cannot accurately compute air damping for a general class of resonators and hence cannot serve as a predictive tool. The deficiency lies in the effective viscosity model that is assumed to be a function of Knudsen number only. Possible extensions of the modified Reynolds equation approach in the highly rarefied regime are also discussed. | On the modified Reynolds equation model for the prediction of squeeze-film gas damping in a low vacuum | 10.1007/s10404-011-0840-3 |
2011-12-01 | The scientific basis for the design of self-lubricating self-aligning sliding bearings with reciprocal motion is presented for the first time. The bearings are used as seismic dampers for bridges, industrial and civil buildings, and oil and gas offshore structures; they are superior to known bearings in carrying and damping capacities. An original experimental-calculation method for determining the life of a frictional pendulum sliding bearing used as a seismic damper is elaborated. It implies the use of the dependences for the wear rate presented in generalized variables. A method for estimating the friction coefficient of frictional pendulum bearings is also developed. The outlook for domestic development of an antifriction self-lubricating coating with preset tribological characteristics is analyzed and the present state of the art is discussed. The studies are based on known developments in the field of tribological materials with account for modern advances in nanotribology. The most promising heat-resistant polymers and fillers, as well as combined mixed antifriction fabrics on their basis, are considered. | Sliding bearings used as seismic dampers with composite self-lubricating materials | 10.3103/S1068366611060043 |
2011-12-01 | Considering the direct and converse piezoelectric effect, expressions of piezoelectric membrane internal forces in the piezoelectric constrained layer were given. The control equations of the piezoelectric constrained layer and host plate were obtained in according with the thin plate theory. Based on the layer wised principle, the integrated first order differential equation of an active constrained layer damping (ACLD) plate was derived for the simply supported boundary condition. Then, this method was expanded to the ACLD plate with cantilever boundary condition by virtue of geometric analogy method. Employing the extended homogeneous capacity precision integration approach, a high precision semi-analytical method was proposed to analyze the dynamic characteristics of the ACLD plate with various boundary conditions. The comparison with the literature results has verified the accuracy and effectiveness of the present method. | Dynamic characteristics analysis of active constrained layer damping plate with various boundary conditions | 10.1007/s11465-011-0240-0 |
2011-12-01 | This two-part paper deals with impact interaction of ships with one-sided ice barrier during roll dynamics. The first part presents analytical and numerical studies for the case of inelastic impact. An analytical model of a ship roll motion interacting with ice is developed based on Zhuravlev and Ivanov non-smooth coordinate transformations. These transformations have the advantage of converting the vibro-impact oscillator into an oscillator without barriers such that the corresponding equation of motion does not contain any impact term. Such approaches, however, account for the energy loss at impact times in different ways. The present work, in particular, demonstrates that the impact dynamics may have qualitatively different response characteristics to different dissipation models. The difference between localized and distributed equivalent damping approaches is discussed. Extensive numerical simulations are carried out for all initial conditions covered by the ship grazing orbit for different values of excitation amplitude and frequency of external wave roll moment. The basins of attraction of safe operation are obtained and reveal the coexistence of different response regimes such as non-impact periodic oscillations, modulation impact motion, period added impact oscillations, chaotic impact motion and rotational motion. The second part will consider experimental validations of predicted results. | Inelastic impact dynamics of ships with one-sided barriers. Part I: analytical and numerical investigations | 10.1007/s11071-010-9937-6 |
2011-12-01 | In this study, we consider the vibration mitigation problem for a structural system using a magneto-rheological (MR) damper. For this purpose, through the use of Lyapunov-based design techniques, a nonlinear adaptive controller which can compensate the parametric uncertainties related to both the structural system and the MR damper has been constructed. To overcome effects of the unmeasurable internal dynamics of the MR damper on the controller, a filter-based design has been utilized. Experimental results performed on a six-degree-of-freedom (DOF) structure installed on a shaking table, illustrating the viability and the performance of the proposed method are also included. | A new semiactive nonlinear adaptive controller for structures using MR damper: Design and experimental validation | 10.1007/s11071-011-9946-0 |
2011-12-01 | If a discrete elastic system with frictional interfaces is subjected to periodic loading, the eventual steady-state response may depend on the initial condition or an initial transient phase of the loading history. In cases where shakedown is possible, it is known that it will occur for all initial conditions if there is no coupling between slip displacements and normal contact tractions, but that when coupling is present, counter-examples can be developed where the steady-state depends on the initial conditions. In this paper, we explore the conjecture that this is a special case of a more general theorem that the time-varying terms in the steady-state solution for an uncoupled system are always independent of initial conditions. In such problems, the ‘memory’ of previous events can only be stored in the slip displacements at nodes that are presently strictly within the friction cone. If all the nodes slip at some point in the cycle, this memory must be continually exchanged between nodes, with a consequent degradation, or loss of memory, resulting in an asymptotic approach to a unique steady state. This behaviour is illustrated using a simple two-node example. When there exists a set of ‘permanently stuck nodes’, these constitute a repository for the system memory, but in uncoupled problems the displacements at these nodes have no effect on the normal tractions at the slipping nodes and hence on the time-varying terms in the solution These arguments are illustrated in the context of two examples: a random distribution of frictional microcracks in a block loaded in plane strain and a generalized Hertzian contact problem with friction. | Frictional systems subjected to oscillating loads | 10.1007/s12356-011-0017-5 |
2011-12-01 | The active damping of the resonant vibrations of a flexible cylindrical panel with rectangular planform and clamped edges is considered. The damping is done with distributed piezoelectric sensors and actuators. It is shown that the amplitude of the resonant vibrations can be substantially decreased by choosing the appropriate feedback factors. The combined effect of geometrical nonlinearity and dissipative properties of the material on the effectiveness of damping is analyzed | Active damping of the resonant vibrations of a flexible cylindrical panel with sensors and actuators | 10.1007/s10778-011-0497-3 |
2011-12-01 | The main aim of this paper is to investigate the effect of various constrained layers (viscoelastic layer (VEL), electro-rheological fluid (ERF), and magneto-rheological fluid (MRF)) over natural frequency and the damping loss factor with two different fiber orientations (0° and 90°) for a Graphite/Epoxy (GR/E) composite sandwich shaft disc system. The finite element technique is used to investigate the natural frequency and loss factor for various combinations. Furthermore, the vibrational characteristics of the composite sandwich shaft disc system are compared with those of the base structure without constrained layers. The study shows that introducing various constrained layers reduces the magnitude of natural frequency by up to 80%. The results also show that GR/E composite with 90° fiber orientation acquires the highest frequency reduction. Among the proposed layers, VEL has the highest damping loss factor. | Effect of constrained layers on vibrational characteristics of a composite sandwich system—A finite element based critical investigation | 10.1007/s10999-011-9166-2 |
2011-12-01 | By extending the numerical technique suggested by the author for the dynamic contact problem having a very stiff spring on the contact point, it is shown that the dynamic contact problem having a very stiff damper as well as a spring on the contact point can be time integrated without instability by imposing the time-differentiated constraints with the unconditionally stable Newmark time integration rule. It is also shown that the dynamic contact involving the repeated impacts and separations can be solved without instability by using the same time-differentiated constraints, and that the spring-damper deformation (i.e., penetration) on the contact point at the time of impact (i.e., at the first time step of contact) can be most reasonably determined by the displacement contact constraint. The special features of the present technique to solve the impact problem having a very stiff spring-damper on the contact point are that the equation of motion may be time integrated with any convenient ODE technique, and that the time step size reduction or the penetration threshold need not be considered at the time of impact. | A short note for numerical analysis of dynamic contact considering impact and a very stiff spring-damper constraint on the contact point | 10.1007/s11044-011-9257-8 |
2011-11-01 | Numerical simulations of spontaneous shear rupture on a planar fault using a slip-weakening model in a three-dimensional uniform elastic medium were conducted using a parallel FE code, GeoFEM, which was originally developed for the solid-Earth simulations on the Earth Simulator. The aim was to evaluate the accuracy and applicability of GeoFEM to earthquake rupture. The present numerical results are compared with published results obtained using a finite-difference (FD) method and a boundary integral (BI) method for rupture times and time functions of slip, slip rate, and shear stress at two particular points on the fault plane. The effects of mesh size and damping on the attenuation of spurious oscillations were also examined in a range of simulations. The appropriate degree of damping depends on mesh size and must be introduced in order to obtain reliable numerical solutions; weak damping leads to significant oscillation and strong damping to artificially low rupture speeds and low slip rates. Our results indicate that mesh size should be sufficiently small to allow the inclusion of a few grids in the cohesive zone, as shown in other numerical methods. The solutions by GeoFEM that have the appropriate mesh size and damping are quite similar to those obtained using the FD and BI methods, the difference between them being generally less than 2% in terms of the rupture time and 5.2% in terms of the peak slip rate. | Assessment of the finite element solutions for 3D spontaneous rupture using GeoFEM | 10.5047/eps.2011.06.041 |
2011-11-01 | Procedural questions related to the construction of mathematical models that establish a quantitative relationship between certain characteristics of the temperature field and the indicator of damping of the pulse electromagnetic field in a layer of the annual temperature fluctuations of built-up areas of the cryolithic zone of Yakutia are considered. Recommendations are given for practical application of the mathematical models based on an analysis of the errors that arise when calculating the temperature of frozen ground found with the use of the models. | Calculation of the temperature of frozen ground on the basis of mathematical models of the temperature dependence of ground penetrating radar signals | 10.1007/s11018-011-9829-2 |
2011-10-01 | Internal vibration of the valve spring is a critical factor in determining the dynamic characteristics of high-speed valve train systems. Because precise prediction of the spring surge amplitude is a difficult problem, especially for nonlinear variable-pitch springs, the development stage requires a process of trial and error. In the present study, a new method that considers the variable natural frequency and variable damping ratio is proposed to predict the spring surge amplitude. First, the change in the natural frequency and damping ratio caused by compression is predicted from the initially given pitch curve at the free height. Second, the spring surge amplitude is estimated by solving the wave equation with nonlinear variable coefficients. The surge amplitudes of typical valve springs are also measured using a motoring test rig and are compared with theoretical results predicted by the spring drawing and cam profile data. | Estimation of valve spring surge amplitude using the variable natural frequency and the damping ratio | 10.1007/s12239-011-0073-1 |
2011-10-01 | Damping constitutes a major source of uncertainty in dynamic analysis and an open issue to experimental and analytical research. After a thorough review of the current views and approaches existing in literature on damping and its appropriate modelling, this paper focuses on the implications of the available modelling options on analysis. As result of a series of considerations, a damping modelling solution for nonlinear dynamic analyses of cantilever RC walls is suggested within the frame of Direct Displacement-Based Design, supported by comparative analyses on wall structures. | Modelling of elastic damping in nonlinear time-history analyses of cantilever RC walls | 10.1007/s10518-011-9286-y |
2011-10-01 | The purpose of this paper is to establish strong lower energy estimates for strong solutions of nonlinearly damped Timoshenko beams, Petrowsky equations in two and three dimensions and wave-like equations for bounded one-dimensional domains or annulus domains in two or three dimensions. We also establish weak lower velocity estimates for strong solutions of the nonlinearly damped Petrowsky equation in two and three dimensions. The feedbacks in consideration have arbitrary growth close to the origin. These results improve the strong lower energy decay rates obtained in our previous papers (Alabau-Boussouira in J Differ Equ 249:1145–1178, 2010 ; J Differ Equ 248:1473–1517, 2010 ) for strong solutions of the nonlinearly locally damped wave equation and extend to systems and to Petrowsky equation the method of Alabau-Boussouira (J Differ Equ 249:1145–1178, 2010 ; J Differ Equ 248:1473–1517, 2010 ). These results are the first ones for Timoshenko beams and Petrowsky equations. | Strong lower energy estimates for nonlinearly damped Timoshenko beams and Petrowsky equations | 10.1007/s00030-011-0108-3 |
2011-10-01 | An experimental apparatus designed specifically for fretting experiments on mechanical lap joints is presented. A piezoactuator is used to impose fretting motion, and a tri-axial load cell is used to measure tangential force as well as possible misalignment forces. A laser nanosensor is employed to measure the relative motion between the joint halves. No post-processing and filtering of the data is needed to obtain the fretting response using this apparatus. Instead, raw data obtained from experiments with monolithic and 1-bolt aluminum and steel joints under various loading conditions suggest that noise, misalignment, stiffness and damping associated with the apparatus are minimal, and thus the fretting behavior of the mechanical lap joints is accurately captured. Analyses of typical fretting loops obtained by the proposed apparatus suggest that normal preload and maximum tangential displacement influence the critical joint parameters of stiffness and damping. Aluminum joints show a more compliant behavior with more energy dissipation compared to steel joints. | Development of a Lap Joint Fretting Apparatus | 10.1007/s11340-010-9458-8 |
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