publicationDate stringlengths 10 10 | abstract stringlengths 0 37.3k | title stringlengths 1 5.74k | doi stringlengths 11 47 ⌀ |
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2014-07-01 | The features of an elastic object controlled by an electric drive in the frequency region are considered, which is followed by an analysis of transitional processes in the electric drive during damping of elastic vibrations. Emphasis is laid on the basic components of the electric drive that enable it to absorb elastic vibrational energy and, therefore, largely determine its damping capacity. A case study of the calculation of the regenerative capacity of the electric drive is proposed, and possible means of improving this capacity are given. | Evaluating the damping capacity of a recitifier drive with elastic couplings | 10.3103/S1068371214070049 |
2014-07-01 | The magnetoelectric-damper geometry and influence of mechanical parameters onthe axial forces and on the electromagnetic processes in the damper are investigated. An analytic method for determining the magnetoelectric-damper axial forces is developed, and bases are given for a rotor with projections designed for minimizing axial forces is proved. Magneto electric-damper three-dimensional computer modeling using the final-elements method was carried out to confirm the theoretical data. | An investigation on the influence of rotor geometry on axial forces in the magnetoelectric damper of a suspension system | 10.3103/S1068371214070062 |
2014-07-01 | We obtain an exact solution to the problem of damped rotation of a solid cylinder and the surrounding viscous liquid which is at rest at infinity. We uncover a series of nontrivial characteristics of the dynamics of this hydromechanical system and establish in particular that the liquid can move faster than the boundary of the body. | On a damped motion of a hydromechanical system | 10.1134/S1990478914030120 |
2014-06-01 | Dynamic and static magnetizations of an exchange biased bilayer system which is constructed as a proximity of a CoO layer on an Fe-layer grown on the (100) oriented MgO substrate by ion beam sputtering technique have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The room-temperature FMR measurements reveal that the Fe layer is epitaxially grown on MgO substrate with four-fold magnetocrystalline anisotropy and the hard magnetization axis of the sample is the [100] crystallographic directions of MgO substrate. We have determined the g -value, effective magnetization, magnetocrystalline anisotropy constants and contributions to FMR linewidth due to the intrinsic Gilbert damping and inhomogeneity of magnetization by using Landau–Lifshitz–Gilbert (LLG) equation. We observed an unusual FMR line shape attributed to impedance switching of resonance cavity and complex component of conductivity of sample system. The low-temperature FMR measurement shows asymmetric hysteretic behavior of resonance field related to magnetic coupling of ferromagnetic and antiferromagnetic layers. From both FMR and VSM measurements between 10–300 K, the magnetocrystalline anisotropy is observed to dominate above blocking temperature, while unidirectional anisotropy is observed to dominate below blocking temperature over internal magnetic anisotropy. FMR spectra have a comparatively small linewidth between 40–100 Oe, which indicates to a high crystallinity of the Fe film. Gilbert constant was calculated as 0.007 from the linewidth fitting of FMR spectra. This small value is a suitable for reducing the critical switching current used in magnetic tunneling junction. Detailed exchange bias studies were carried out for hard and easy axis of the sample in the temperature range of 10–300 K. From both low-temperature FMR and VSM measurements, the blocking temperature of the system was determined as ∼60 K. | Ferromagnetic Resonance Studies of Exchange Biased CoO/Fe Bilayer Grown on MgO Substrate | 10.1007/s10948-013-2464-1 |
2014-06-01 | In this paper, an interconnected wave-ODE system with K-V damping in the wave equation and unknown parameters in the ODE is considered. It is found that the spectrum of the system operator is composed of two parts: Point spectrum and continuous spectrum. The continuous spectrum consists of an isolated point $$- \tfrac{1} {d}$$ , and there are two branches of the asymptotic eigenvalues: The first branch is accumulating towards $$- \tfrac{1} {d}$$ , and the other branch tends to −∞. It is shown that there is a sequence of generalized eigenfunctions, which forms a Riesz basis for the Hilbert state space. As a consequence, the spectrum-determined growth condition and exponential stability of the system are concluded. | Spectral analysis and stabilization of a coupled wave-ODE system | 10.1007/s11424-014-2219-5 |
2014-06-01 | This paper presents a theoretical investigation of squeeze film flow in systems employing microplates parallel to a substrate and undergoing large amplitude normal vibration. Most previous models of squeeze film damping assume small oscillation amplitude with linear system behavior, but it is often unclear how small the vibrations must be to actually elicit this response. In addition, fluid inertia effects are usually overlooked. This study provides a compact nonlinear solution for the incompressible hydrodynamic forces with specific terms describing fluid inertia and viscous damping. Numerical analysis (the explicit Runge-Kutta method) is applied to solve the nonlinear governing equation. The effects of frequency, oscillation amplitude, aspect ratio (of gap to length), and Reynolds number on the dynamic response of the system are investigated. The overall system response depends strongly on the actuation frequency and system properties. It is found that a simple criterion of validity for the linear system assumption is not possible. Near resonance, the vibration input amplitude (relative to the initial gap) must be very small indeed for linearity (∼0.001), while in other cases the relative amplitude can be greater than one. | Limits of linearity in squeeze film behavior of a single degree of freedom microsystem | 10.1007/s10404-013-1278-6 |
2014-06-01 | A numerical solution based on the Steffensen stable point iterative method is proposed to resolve the transcendental frequency equation of a stay cable-damper system. The frequency equation, which considers clamped supports and flexural rigidity of the cable, is intended to investigate the influence of the parameters of the cable damper system on its dynamic characteristics. Two factors involved in the design and construction phases, the damping coefficient induced by external dampers and the cable tension, are the focus of this study. Their impact on modal frequencies and damping ratios in these two phases of cable-damper systems are investigated by resolving the equation with the proposed solution. It is shown that the damping coefficient and cable tension exert more noticeable effects on the modal damping ratios than on the modal frequencies of stay cable-damper systems, and the two factors can serve as design variables in the design phase and as adjustment factors in the construction phase. On the basis of the results, a roadmap for system-level optimal design of stay cable-damper systems that can achieve global optimal vibration suppression for the entire bridge is proposed and discussed. | Dynamic properties analysis of a stay cable-damper system in consideration of design and construction factors | 10.1007/s11803-014-0233-1 |
2014-06-01 | This paper investigates mathematical modelling of response amplitude operator (RAO) or transfer function using the frequency-based analysis for uncoupled roll motion of a floating body under the influence of small amplitude regular waves. The hydrodynamic coefficients are computed using strip theory formulation by integrating over the length of the floating body. Considering sinusoidal wave with frequency ( ω ) varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed, analytical expressions of RAO in frequency domain is obtained. Using the normalization procedure and frequency based analysis, group based classifications are obtained and accordingly governing equations are formulated for each case. After applying the fourth order Runge-Kutta method numerical solutions are obtained and relative importance of the hydrodynamic coefficients is analyzed. To illustrate the roll amplitude effects numerical experiments have been carried out for a Panamax container ship under the action of sinusoidal wave with a fixed wave height. The effect of viscous damping on RAO is evaluated and the model is validated using convergence, consistency and stability analysis. This modelling approach could be useful to model floating body dynamics for higher degrees of freedom and to validate the result. | Mathematical modelling of response amplitude operator for roll motion of a floating body: Analysis in frequency domain with numerical validation | 10.1007/s11804-014-1249-7 |
2014-06-01 | In this paper, we consider the complex Ginzburg–Landau equation $${u_t = e^{i\theta} [\Delta u + |u|^\alpha u] + \gamma u}$$ u t = e i θ [ Δ u + | u | α u ] + γ u on $${\mathbb{R}^N}$$ R N , where $${\alpha > 0,\,\gamma \in \mathbb{R}}$$ α > 0 , γ ∈ R and $${-\pi /2 < \theta < \pi /2}$$ - π / 2 < θ < π / 2 . By convexity arguments, we prove that, under certain conditions on $${\alpha,\theta,\gamma}$$ α , θ , γ , a class of solutions with negative initial energy blows up in finite time. | Finite-time blowup for a complex Ginzburg–Landau equation with linear driving | 10.1007/s00028-014-0220-z |
2014-06-01 | Based on known theoretical developments in linear dynamics of homogeneous beams, two homogenization approaches of composite beams are developed further to an anterior work using two equivalent properties: the physical and the mechanic–geometrical properties. Further to the assumption of Euler–Bernoulli beams, dynamic parameters are needed. Equations of a given beam structure subjected to free un-damped and/or damped vibration are established. The natural frequency responses of the first five modes are obtained from both approaches, and then compared with those obtained from a finite element model approach, taking into account different slenderness and boundary conditions. The result shows good agreement. An extension to the equivalent physical parameter homogenization method using the behaviour law in nonlinear state is presented here. Thus, the homogenization is extended to an elastically equivalent model elaboration for a system having an elastic–plastic and bilinear behaviour. The aim is to use analytical expressions from an elastically equivalent model for a nonlinear system of multilayer beam type to obtain the new corrected dynamic parameter. Based on the ductility factor method combined with the secant method that uses a substitute structure and secant stiffness to account for nonlinear behaviour, we developed a formula using global effective flexural modulus $${E_{\rm s}^*}$$ E s ∗ , the equivalent mass density ρ ^*, as well as the two types of viscous damping parameter (these types include a viscous resistance to transverse displacement C ^* of the beam and a viscous resistance to straining of the beam material $${C_{\rm S}^{*})}$$ C S ∗ ) which can be incorporated into the formula without difficulty. The nonlinear analysis shows that the degradation of rigidity decreases the frequencies response curve, which tends to increase the vibration periods giving an additional storage space for the structure capacity to accumulate displacements of a higher degree compared to those of the elastic case. The importance of the nonlinearity assumption is shown, which fits better with the real mechanical performances of the structure. | Simplified Method Using Homogenization Approach for Nonlinear Dynamic Analysis of Dissipative Energy in Multilayered Beams | 10.1007/s13369-014-1036-4 |
2014-06-01 | In this paper, soft tissue is modeled by a mass–spring–damper system and tissue deformations under the compression of surgical instruments are simulated. For this purpose, soft tissue confined in a cubic plastic mold is studied using a nonlinear viscoelastic model. Displacements resulting from probe insertions are measured and modeled for use in robotic surgery. Data is collected on bovine sirloin using the Instron hardness tester. The model’s dynamic equations are obtained in the form of ordinary differential equations. The external force is considered as the input and the resulting deformation as the output of the model. Simulation results are compared with laboratory findings, and the nonlinear model’s unknown parameters are estimated. The threshold force and displacement before the tearing of the soft tissue are respectively determined by analyzing the force–time and displacement–time diagrams obtained for the test samples. | A new fast nonlinear modeling of soft tissue for surgical simulation | 10.1007/s11701-013-0444-x |
2014-06-01 | The influence of the gravitational radiation damping on the evolution of the orbital elements of compact binary stars is examined by using the method of perturbation. The perturbation equations with the true anomaly as an independent variable are given. This effect results in both the secular and periodic variation of the semi-major axis, the eccentricity, the mean longitude at the epoch and the mean longitude. However, the longitude of periastron exhibits no secular variation, but only periodic variation. The effect of secular variation of the orbit would lead to collapse of the system of binary stars. The deduced formulae are applied to the calculation of secular variation of the orbital elements for three compact binary stars: PSR19 13 + 16, PSR J0737-3039 and M33X-7. The results obtained are discussed. | Gravitational Radiation Damping and Evolution of the Orbit of Compact Binary Stars (Solution by the Second Perturbation Method) | 10.1007/s12036-014-9275-z |
2014-06-01 | The paper presents the results of in-situ and laboratory tests aimed at defining the cyclic properties of soils and soft rocks of the Central Archeological Area of Rome in the framework of the seismic microzonation study of the area. The small-strain shear modulus $$\text{ G }_{0}$$ (or analogously shear wave velocity $$\text{ V }_\mathrm{S}$$ ) and the curves expressing shear modulus G and damping ratio D variation with shear strain amplitude were investigated. A large amount of in-hole tests integrated with active surface wave tests were utilized to characterize the small-strain stiffness of the lithotypes identified in the area. Small-strain stiffness values determined by geophysical tests were further compared with those measured in the laboratory showing different behaviors of soils and soft rocks. The effects of sample disturbance and degree of jointing, for soils and soft rocks, respectively, was invoked to explain the observed differences. The shear modulus and damping ratio versus shear strain amplitude curves were determined by means of resonant column and cyclic shear tests, both simple and torsional. The experimental results were compared with literature data on similar soils highlighting some peculiar behaviors. In particular the role of fine matrix in sandy soils and organic matter content of clays on the cyclic properties was stressed. The results showed that an increase in fine matrix and organic content results in a stronger linearity and lower damping ratio. | Dynamic characterization of soils and soft rocks of the Central Archeological Area of Rome | 10.1007/s10518-013-9452-5 |
2014-06-01 | In this study, energy absorption capacity, flexural and dynamic properties of flax fibre reinforced epoxy polymer composite (FFRP) tubes are investigated. The energy absorption capacity of the tubes is investigated under uniaxial compression. Flexural behaviour of the tubes is studied under four-point bending and the dynamic properties (i.e., natural frequency and damping characteristics) are evaluated by impact hammer vibration testing of the tube specimens. The damping characteristics of the tubes are determined by using both a logarithmic decrement curve and the half-peak bandwidth method. The influence of tube laminate thickness and specimen size on the mechanical properties of FFRP tubes is determined. Compressive testing indicates that the FFRP tube provides a specific absorbed energy of 22 J/g, which is close to the conventional metal energy absorption materials, i.e. stainless steel and aluminium tubes. Flexural study shows that the FFRP tube exhibits a brittle failure as similar to that of the FFRP composites in a flat-coupon tension. The load carrying capacity and deflection of the tube increase with an increase in the tube thickness. Impact loading test concludes that an increase in tube thickness leads to a reduction in natural frequency and damping ratio of the tubes. The FFRP tubes have sizedependent dynamic properties, i.e. an increase in tube size increased the natural frequency but reduced the damping ratio of the specimens remarkably. However, all FFRP tubes have high damping ratios, thus reducing the effect of dynamic loading on the structural response. Therefore, this study suggests that FFRP tubes could be used in several structural applications, i.e. in automotive as energy absorbers and in civil infrastructure as poles. | On energy absorption capacity, flexural and dynamic properties of flax/epoxy composite tubes | 10.1007/s12221-014-1270-0 |
2014-06-01 | This paper presents the ground motion amplification scenario along with fundamental frequency ( F _0) of sedimentary deposit for the seismic microzonation of Kolkata City, situated on the world’s largest delta island with very soft soil deposit. A 4th order accurate SH -wave viscoelastic finite-difference algorithm is used for computation of response of 1D model for each borehole location. Different maps, such as for F _0, amplification at F _0, average spectral amplification (ASA) in the different frequency bandwidth of earthquake engineering interest are developed for a variety of end-users communities. The obtained ASA of the order of 3–6 at most of the borehole locations in a frequency range of 0.25–10.0 Hz reveals that Kolkata City may suffer severe damage even during a moderate earthquake. Further, unexpected severe damage to collapse of multi-storey buildings may occur in localities near Hoogly River and Salt Lake area due to double resonance effects during distant large earthquakes. | Computation of ground motion amplification in Kolkata megacity (India) using finite-difference method for seismic microzonation | 10.2478/s11600-013-0169-2 |
2014-06-01 | Plan asymmetric buildings are very susceptible to earthquake induced damage due to lateral torsional coupling, and the corners of these systems suffer heavy damage during earthquakes. Therefore, it is important to investigate the seismic behavior of an asymmetric plan building with MR dampers. In this study, the effectiveness of MR damper-based control systems has been investigated for seismic hazard mitigation of a plan asymmetric building. Furthermore, the influence of the building parameters and damper command voltage on the control performance is examined through parametric study. The building parameters chosen are eccentricity ratio and frequency ratio. The results show that the MR damper-based control systems are effective for plan asymmetric systems. | Earthquake response of asymmetric building with MR damper | 10.1007/s11803-014-0232-2 |
2014-06-01 | This paper presents exact analytical solutions for a novel damped outrigger system, in which viscous dampers are vertically installed between perimeter columns and the core of a high-rise building. An improved analytical model is developed by modeling the effect of the damped outrigger as a general rotational spring acting on a Bernoulli-Euler beam. The equivalent rotational spring stiffness incorporating the combined effects of dampers and axial stiffness of perimeter columns is derived. The dynamic stiffness method (DSM) is applied to formulate the governing equation of the damped outrigger system. The accuracy and efficiency are verified in comparison with those obtained from compatibility equations and boundary equations. Parametric analysis of three non-dimensional factors is conducted to evaluate the influences of various factors, such as the stiffness ratio of the core to the beam, position of the damped outrigger, and the installed damping coefficient. Results show that the modal damping ratio is significantly influenced by the stiffness ratio of the core to the column, and is more sensitive to damping than the position of the damped outrigger. The proposed analytical model in combination with DSM can be extended to the study of structures with more outriggers. | Dynamic characteristics of a novel damped outrigger system | 10.1007/s11803-014-0231-3 |
2014-05-23 | Damping is a critical design parameter for miniaturized mechanical resonators used in microelectromechanical systems (MEMS), nanoelectromechanical systems (NEMS), optomechanical systems, and atomic force microscopy for a large and diverse set of applications ranging from sensing, timing, and signal processing to precision measurements for fundamental studies of materials science and quantum mechanics. This paper presents an overview of recent advances in damping from the viewpoint of device design. The primary goal is to collect and organize methods, tools, and techniques for the rational and effective control of linear damping in miniaturized mechanical resonators. After reviewing some fundamental links between dynamics and dissipation for systems with small linear damping, we explore the space of design and operating parameters for micromechanical and nanomechanical resonators; classify the mechanisms of dissipation into fluid–structure interactions (viscous damping, squeezed-film damping, and acoustic radiation), boundary damping (stress-wave radiation, microsliding, and viscoelasticity), and material damping (thermoelastic damping, dissipation mediated by phonons and electrons, and internal friction due to crystallographic defects); discuss strategies for minimizing each source using a combination of models for dissipation and measurements of material properties; and formulate design principles for low-loss micromechanical and nanomechanical resonators. | Design strategies for controlling damping in micromechanical and nanomechanical resonators | 10.1140/epjti5 |
2014-05-09 | In this paper, we consider a class of non-periodic damped vibration problems with superquadratic nonlinearities. We study the existence of nontrivial ground state homoclinic orbits for this class of damped vibration problems under some conditions weaker than those previously assumed. To the best of our knowledge, there has been no work focused on this case. MSC: 49J40, 70H05. | Ground state homoclinic orbits of damped vibration problems | 10.1186/1687-2770-2014-106 |
2014-05-01 | The friction behavior of steel/steel contacts lubricated with glycerol, 150NS and PAO4 is investigated using a new technique. Then, three additives are used in PAO4 lubricant: oleic, linoleic and stearic acids. The experiments are performed at different temperatures. Moreover, nearly all the systems operate in either the mixed or boundary lubrication regime. The experimental methodology is able, with a high accuracy and without any force transducer, two contributions of friction: μ _0, velocity-independent contribution and μ _1, velocity-dependent one. This study shows that glycerol is the most effective in reducing friction among the three pure lubricants. In addition, only glycerol affects the viscous damping of the system at some operating conditions. Using the additives in PAO4, the friction is reduced. More precisely, the unsaturated fatty acids are more significant in reducing the friction than saturated acids. Moreover, the viscous damping of the apparatus is slightly affected as additives are used in PAO4. | Effect of Temperature on Lubricated Steel/Steel Systems With or Without Fatty Acids Additives Using an Oscillating Dynamic Tribometer | 10.1007/s11249-014-0323-2 |
2014-05-01 | This paper presents a numerical method based on a three dimensional boundary element–finite element (BEM–FEM) coupled formulation in the time domain. The proposed model allows studying soil–structure interaction problems. The soil is modelled with the BEM, where the radiation condition is implicitly satisfied in the fundamental solution. Half-space Green’s function including internal soil damping is considered as the fundamental solution. An effective treatment based on the integration into a complex Jordan path is proposed to avoid the singularities at the arrival time of the Rayleigh waves. The efficiency of the BEM is improved taking into account the spatial symmetry and the invariance of the fundamental solution when it is expressed in a dimensionless form. The FEM is used to represent the structure. The proposed method is validated by comparison with analytical solutions and numerical results presented in the literature. Finally, a soil–structure interaction problem concerning with a building subjected to different incident wave fields is studied. | A 3D time domain numerical model based on half-space Green’s function for soil–structure interaction analysis | 10.1007/s00466-013-0949-1 |
2014-05-01 | Knowledge of critical points is important to determine the phase behavior of a mixture. This work proposes a reliable and accurate method in order to locate the liquid–vapor critical point of a given mixture. The theoretical model is developed from the rigorous definition of critical points, based on the SRK equation of state (SRK EoS) or alternatively, on the PR EoS. In order to solve the resulting system of $$C+2$$ C + 2 nonlinear equations, an improved method is introduced into an existing Newton–Raphson algorithm, which can calculate all the variables simultaneously in each iteration step. The improvements mainly focus on the derivatives of the Jacobian matrix, on the convergence criteria, and on the damping coefficient. As a result, all equations and related conditions required for the computation of the scheme are illustrated in this paper. Finally, experimental data for the critical points of 44 mixtures are adopted in order to validate the method. For the SRK EoS, average absolute errors of the predicted critical-pressure and critical-temperature values are 123.82 kPa and 3.11 K, respectively, whereas the commercial software package Calsep PVTSIM’s prediction errors are 131.02 kPa and 3.24 K. For the PR EoS, the two above mentioned average absolute errors are 129.32 kPa and 2.45 K, while the PVTSIM’s errors are 137.24 kPa and 2.55 K, respectively. | An Improved Computational Method for the Calculation of Mixture Liquid–Vapor Critical Points | 10.1007/s10765-014-1680-7 |
2014-05-01 | This paper is aimed to extend a certain damped technique, suitable for the Broyden–Fletcher–Goldfarb–Shanno (BFGS) method, to the limited memory BFGS method in the case of the large-scale unconstrained optimization. It is shown that the proposed technique maintains the global convergence property on uniformly convex functions for the limited memory BFGS method. Some numerical results are described to illustrate the important role of the damped technique. Since this technique enforces safely the positive definiteness property of the BFGS update for any value of the steplength, we also consider only the first Wolfe–Powell condition on the steplength. Then, as for the backtracking framework, only one gradient evaluation is performed on each iteration. It is reported that the proposed damped methods work much better than the limited memory BFGS method in several cases. | Damped Techniques for the Limited Memory BFGS Method for Large-Scale Optimization | 10.1007/s10957-013-0448-8 |
2014-05-01 | Diurnal wind (DW) and nonlinear interaction between inertial and tidal currents near the Xisha Islands of the South China Sea (SCS) during the passage of Typhoon Conson (2010) are investigated using observational data and a damped slab model. It is found that the DWs, which are dominated by clockwise wind components, are prominent at our observational site. The DWs increase after the passage of the typhoon from 1 to about 4 m/s, which may be due to the decrease of the sea surface temperature caused by the passage of the typhoon. Kinetic energy spectra and bicoherence methods reveal nonlinear interactions between the inertial currents and the 2MK_3 tidal constituent at our observational site. The slab damped model reproduces the inertial currents successfully induced by the total observed winds, and it is shown that the inertial currents induced by DWs are positively proportional to the DWs speed. Even though the observed inertial currents are distinct, the proportion of inertial currents induced by DWs to those induced by the total observed winds is just 0.7%/4% before/after the passage of typhoon. This shows that the inertial currents induced by the DWs are unimportant near the Xisha Islands during the typhoon season. | Diurnal wind and nonlinear interaction between inertial and tidal currents in the South China Sea during the passage of Typhoon Conson | 10.1007/s13131-014-0467-9 |
2014-05-01 | Histones are DNA-binding proteins and are involved in chromatin remodeling and regulation of gene expression. Histones can be released after tissue injuries, and the extracellular histones cause cellular damage and organ dysfunction. Regardless of their clinical significance, the role and relevance of histones in ocular diseases are unknown. We studied the role of histones in eyes with retinal detachment (RD). Vitreous samples were collected during vitrectomy, and the concentration of histone H3 was measured by enzyme-linked immunosorbent assay. The location of the histones and related molecules was examined in a rat RD model. The release of histones and their effects on rat retinal progenitor cells R28 and ARPE-19 were evaluated in vitro . In addition, the protective role of the vitreous body against histones was tested. The intravitreal concentration of histones was higher in eyes with RD (mean, 30.9±9.8 ng/ml) than in control eyes (below the limit of detection, P <0.05). In the rat RD model, histone H3 was observed on the outer side of the detached retina and was associated with photoreceptor death. Histone H3 was released from cultured R28 by oxidative stress. Histones at a concentration 10 μ g/ml induced the production of interleukin-8 in ARPE-19 cells (2.5-fold increase, P <0.05) that was mediated through the ERK1/2- and p38 MAPK-dependent pathways and Toll-like receptor 4. Histones were toxic to cells at concentrations of ≥20 μ g/ml. Vitreous body or hyaluronan decreased toxicity of histones by inhibiting diffusion of histones. These results indicate that histones are released from retinas with RD and may modulate the subretinal microenvironment by functioning as damage-associated molecular pattern molecules, thereby inducing proinflammatory cytokines or cell toxicity. In addition, the important role of the vitreous body and hyaluronan in protecting the retina from these toxic effects is suggested. | Toxic effects of extracellular histones and their neutralization by vitreous in retinal detachment | 10.1038/labinvest.2014.46 |
2014-04-29 | It is well known that the vibration of washing machines is a challenging issue to be considered. This research work focuses on the optimal design of a flow-mode magneto-rheological (MR) damper that can replace the conventional passive damper for a washing machine. Firstly, rigid mode vibration of the washing machine due to an unbalanced mass is analyzed and an optimal positioning of the suppression system for the washing machine is considered. An MR damper configuration for the washer is then proposed considering available space for the system. The damping force of the MR damper is derived based on the Bingham rheological behavior of the MR fluid. An optimal design problem for the proposed MR brake is then constructed. The optimization is to minimize the damping coefficient of the MR damper while the maximum value of the damping force is kept being greater than a required value. An optimization procedure based on finite element analysis integrated with an optimization tool is employed to obtain optimal geometric dimensions of the MR damper. The optimal solution of the MR damper is then presented with remarkable discussions on its performance. The results are then validated by experimental works. Finally, conclusions on the research work are given and future works for development of the research is figured out. | Optimal design and performance evaluation of a flow-mode MR damper for front-loaded washing machines | 10.1186/2196-1166-1-3 |
2014-04-23 | Background Sterile inflammation occurs in the absence of live pathogens and is an unavoidable consequence of ischemia-reperfusion (IR) injury in the central nervous system (CNS). It is known that toll-like receptor 4 (Tlr4) contributes to damage and sterile inflammation in the CNS mediated by IR. However, the mechanism of Tlr4 activation under sterile conditions in ischemic tissue is poorly understood. We performed this study to clarify the mechanism. To this end, we focused on the extracellular heat shock protein 70 (Hsp70), the prototypic Tlr4 ligand. Methods Tlr4-, Myd88- and Trif-knockout animals, as well as C57BL/6 mice, were used for the wild type control. For the in vivo study, we used a mouse model of retinal IR injury. To test the role of protein kinase C (PKC) in IR injury, IR retinas were treated with the PKC inhibitors (polymyxin B and Gö6976) and retinal damage was evaluated by directly counting neurons in the ganglion cell layer of flat-mounted retinas seven days after IR. Primary retinal neurons (retinal ganglion cells) and glial cells were used for in vitro experiments. Quantitative RT-PCR, ELISA and western blot analysis were used to study the production of pro-inflammatory factors in IR retinas and in primary cell cultures. Results We found significant accumulation of extracellular Hsp70 in a model of retinal IR injury. We noted that PKC was involved in Tlr4 signaling, and found that PKC inhibitors promoted neuroprotection by reducing pro-inflammatory activity in ischemic tissue. To put all of the pieces in the signaling cascade together, we performed an in vitro study. We found that PKC was critical to mediate the Hsp70-dependent pro-inflammatory response. At the same time, the contamination of Hsp70 preparations with low-dose endotoxin was not critical to mediate the production of pro-inflammatory factors. We found that extracellular Hsp70 can promote neuronal death at least, by mediating production of cytotoxic levels of tumor necrosis factor alpha, predominantly due to the Tlr4/Myd88 signaling cascade. Conclusions Our findings suggest that PKC acts as a switch to amplify the pro-inflammatory activity of Hsp70/Tlr4 signaling, which is sufficient to mediate neuronal death. | Putative role of protein kinase C in neurotoxic inflammation mediated by extracellular heat shock protein 70 after ischemia-reperfusion | 10.1186/1742-2094-11-81 |
2014-04-01 | The goal of this paper is to investigate the finite time blow-up of solutions with supercritical boundary/interior sources and nonlinear boundary/interior damping. First, we prove that if the interior and boundary sources dominate their corresponding damping terms, then every weak solution blows up in finite time with positive initial energy. Second, without any restriction on the boundary source, we prove the finite time blow-up of solutions, provided that the interior sources dominate both interior and boundary damping and the initial energy is nonnegative. A similar result has been shown when the boundary source is absent. Moreover, in the absence of the interior sources, we prove that the solution grows as an exponential function. | Blow-up of Positive Initial Energy Solutions for A System of Nonlinear Wave Equations with Supercritical Sources | 10.1007/s10883-014-9210-2 |
2014-04-01 | The shape memory alloys present unusual thermo-mechanical properties. The most important of them are pseudo-elasticity and memory effect. The paper investigates this behaviour for the Ni-Ti wires under static (v < 50 mm/s) and dynamic conditions (v > 50 mm/s) at different temperatures. Ni-Ti actuator and pseudoelastic wires with diameter between 0.1 mm to 0.5 mm are being tested. For dynamic investigation a new testing plant able to satisfy the testing conditions is created. This new testing plant is still under development and the reported results originate from the first tests on this new machine. The new device is designed to reach speeds higher than 50 mm/s. These speeds can be achieved using a drop weight which will hit a bottom plate and by this the kinetic energy is transferred to the sample. Because the weight is dropped, the stroke for the sample is measured in two points. The force of this impact will be in-line measured and, if the sample will be electrically activated during this test, it is also possible to log the electrical voltage. To widen the application range of the shape memory alloys it is necessary to study their behaviour in the dynamic region. With the new testing facility, it is expected to test the damping properties of SMA wires. In that case, these results can generate the basis for finding new applications for shape memory alloys especially in the automotive safety industry. | Future applications of Ni-Ti alloys in automotive safety systems | 10.1007/s12239-014-0049-z |
2014-04-01 | The focus of this paper is on studying an inverse second-order cone quadratic programming problem, in which the parameters in the objective function need to be adjusted as little as possible so that a known feasible solution becomes the optimal one. We formulate this problem as a minimization problem with cone constraints, and its dual, which has fewer variables than the original one, is a semismoothly differentiable ( SC ^1) convex programming problem with both a linear inequality constraint and a linear second-order cone constraint. We demonstrate the global convergence of the augmented Lagrangian method with an exact solution to the subproblem and prove that the convergence rate of primal iterates, generated by the augmented Lagrangian method, is proportional to 1/ r , and the rate of multiplier iterates is proportional to $1/\sqrt{r}$ , where r is the penalty parameter in the augmented Lagrangian. Furthermore, a semismooth Newton method with Armijo line search is constructed to solve the subproblems in the augmented Lagrangian approach. Finally, numerical results are reported to show the effectiveness of the augmented Lagrangian method with both an exact solution and an inexact solution to the subproblem for solving the inverse second-order cone quadratic programming problem. | The augmented Lagrangian method for a type of inverse quadratic programming problems over second-order cones | 10.1007/s11750-011-0227-3 |
2014-04-01 | Non-linear tidal dynamics are investigated in a network that consists of a semi-enclosed main channel and a secondary channel at an arbitrary position. The water motion, governed by the one-dimensional shallow water equations, is forced by an incoming tidal wave. Solutions are obtained with the method of characteristics. The overall aim is to quantify and understand the spatial structure of different tidal harmonics (the principal tide and its non-linear overtides) and of tidal asymmetry for both the vertical and the horizontal tide in the main channel for different locations of the secondary channel. This is of practical interest in the context of possible construction of secondary channels to reduce tidal range in estuaries. Moreover, tidal asymmetry is an important factor in driving net sediment transport. Analysis of the different tidal harmonics shows that their characteristics are similar to those obtained with an earlier linear model. In particular, amplitudes of the harmonics are reduced landward of the secondary channel if the latter is positioned less than a quarter wavelength of the respective tidal wave away from the landward boundary. Thus, the distortions of the tide due to the presence of the secondary channel are generated locally and afterwards propagate through the network. Tidal asymmetry is quantified by examining tidal range, flood-to-ebb ratio and the duration of the falling tide and the duration between maximum flood and maximum ebb. A spatial non-uniform reduction in tidal range is observed that shows very localised increase and decrease depending on the position of the secondary channel. The changes in the velocity characteristics induce changes in net sediment transport. It turns out that the direction of the peak current, derived from the flood-to-ebb ratio, is not sensitive to the position of the secondary channel, whereas the duration between flood and ebb can change from more to less than half the tidal cycle. However, the changes in the velocity asymmetries are confined to a small region. | Effect of a secondary channel on the non-linear tidal dynamics in a semi-enclosed channel: a simple model | 10.1007/s10236-014-0690-0 |
2014-04-01 | This paper proposes an optimization procedure based on eigenvalues to carry out the stabilization function of the Gate-Controlled Series Capacitor (GCSC) in a power system. It is aimed to provide a reliable damping framework by means of a GCSC based multi-objective damping controller. The proposed method employs Particle Swarm Optimization (PSO) to search for optimal parameter settings of a widely used multi-objective lead-lag damping controller. The eigenvalue analysis is considered as the cornerstone of the performed studies in order to investigate the multi-objective methodology in which the unstable or lightly damped modes are scheduled to effectively shift to some prescribed stability zones in the s-plane. The effectiveness of the suggested approach in damping local and interarea oscillations modes in a multi-machine power system, over a wide range of loading conditions, is confirmed through eigenvalue analysis and time simulation. | Design of multi-objective damping controller for gate-controlled series capacitor | 10.1007/s12046-013-0213-6 |
2014-04-01 | Conventional steel-based rubber bearings are being replaced by fiber reinforced elastomeric isolators (FREI) due to their high weight and manufacturing cost. Compared to existing rubber bearings, FREIs have superior performance and as a result can control the seismic response of structures more efficiently. This study aims to simulate the performance of rectangular carbon FREIs (C-FREIs) produced through a simple and cost-effective manufacturing process. Additionally, the effect of different factors including the number and the thickness of rubber layers, as well as the thickness of carbon fiber reinforced sheets are investigated on the performance of C-FREIs through sensitivity analyses based on the results obtained from finite element simulations. The results show that by increasing the number and thickness of rubber layers, the efficiency of C-FREIs degrades in terms of vertical strength and damping capacity, however, the performance improves in terms of lateral flexibility. Another important observation is that the increasing thickness of fiber-reinforced layers can increase the vertical rigidity of the base isolator. The vertical stiffness has the most sensitivity to the thickness of elastomeric layers and the thickness of CFR sheets while, when the number of rubber layers increases, the effective lateral stiffness is mostly affected. | Sensitivity analysis of carbon fiber-reinforced elastomeric isolators based on experimental tests and finite element simulations | 10.1007/s10518-013-9556-y |
2014-04-01 | In superfluid ^3He-B externally pumped quantized spin-wave excitations or magnons spontaneously form a Bose-Einstein condensate in a 3-dimensional trap created with the order-parameter texture and a shallow minimum in the polarizing field. The condensation is manifested by coherent precession of the magnetization with a common frequency in a large volume. The trap shape is controlled by the profile of the applied magnetic field and by the condensate itself via the spin-orbit interaction. The trapping potential can be experimentally determined with the spectroscopy of the magnon levels in the trap. We have measured the decay of the ground state condensates after switching off the pumping in the temperature range (0.14÷0.2) T _c. Two contributions to the relaxation are identified: (1) spin diffusion with the diffusion coefficient proportional to the density of thermal quasiparticles and (2) the approximately temperature-independent radiation damping caused by the losses in the NMR pick-up circuit. The measured dependence of the relaxation on the shape of the trapping potential is in a good agreement with our calculations based on the magnetic field profile and the magnon-modified texture. Our values for the spin diffusion coefficient at low temperatures agree with the theoretical prediction and earlier measurements at temperatures above 0.5 T _c. | Relaxation of Bose-Einstein Condensates of Magnons in Magneto-Textural Traps in Superfluid ^3He-B | 10.1007/s10909-013-0946-y |
2014-04-01 | Vibrations on gears are mainly induced by the gear mesh contact. Resonance conditions of the gear may occur during service if the mesh frequency is close to the natural frequencies of the system at the designed speed of the shaft. Since detuning is not always possible in gears, the response level must be reduced by increasing the damping of the system. In this paper, a passive approach based on the application of a ring damper to reduce the vibration level is presented. The ring damper is placed in a groove underneath the outer rim of the gear. The contact is guaranteed by the preload due to the elasticity of the ring damper itself and above all by the centrifugal force that presses the damper against the groove during rotation. The relative motion of the two components at the contact interface dissipates energy by friction, and hence damping is generated. The vibration amplitude is reduced by optimizing the material and geometrical properties of the ring damper. One of the most important parameters in the determination of the amount of damping due to friction phenomena is the static normal load at the contact, which depends on the mass, the shape, and the material of the ring damper. A numerical method is presented, which couples the static and dynamic equilibrium equations of the assembly. The core of the proposed method is the contact element that takes into account local stick–slip–lift off of the contact and determines the contact forces in terms of static and dynamic loads, which are then used to solve the coupled static and dynamic equilibrium. Since the ring damper has a cut that breaks its continuous circular shape in order to be fitted on the groove, the hypothesis of cyclic symmetry for the gear/ring–damper assembly fails. As a consequence, an appropriate reduced-order modeling is presented to allow the forced response calculations. The algorithm is applied to a dummy bevel gear and to a ring damper having a flat punch contact area. The forced response calculations are performed to highlight the nonlinear interaction between the gear and damper by varying the parameters that mainly affect the amount and distribution of the contact forces and therefore the response level. | Passive control of vibration of thin-walled gears: advanced modelling of ring dampers | 10.1007/s11071-013-1125-z |
2014-04-01 | The aim of this study is to develop a general model for beams and rods with fractional derivatives. Fractional time derivatives can represent the damping term in dynamical models of continuous systems. Linear differential operators with spatial derivatives make it possible to generalize a wide range of problems. The method of multiple scales is directly applied to equations of motion. For the approximate solution, the amplitude and phase modulation equations are obtained in terms of the operators. Stability boundaries are derived from the solvability condition. It is shown that a fractional derivative influences the stability boundaries, natural frequencies, and amplitudes of vibrations. The solution procedure may be applied to many problems with linear vibrations of continuous systems. | Linear dynamical analysis of fractionally damped beams and rods | 10.1007/s10665-013-9642-9 |
2014-04-01 | In this paper, we show how to obtain decay estimates for the damped wave equation on a compact manifold without geometric control via knowledge of the dynamics near the undamped set. We show that if replacing the damping term with a higher-order complex absorbing potential gives an operator enjoying polynomial resolvent bounds on the real axis, then the “resolvent” associated to our damped problem enjoys bounds of the same order. It is known that the necessary estimates with complex absorbing potential can also be obtained via gluing from estimates for corresponding non-compact models. | From resolvent estimates to damped waves | 10.1007/s11854-014-0006-9 |
2014-04-01 | We focus on growth of solutions of the problem Under condition p > max ( m − 1, k + 1, l + 1, ϑ + 1, ϱ + 1), with positive initial energy, we will prove that the solutions of (1) satisfies $\lim _{t \to \infty } \sum\nolimits_{i = 1}^2 {\left\| {u_i } \right\|_{p + 1} \to \infty } $ . | Growth of solutions with positive initial energy to system of degeneratly damped wave equations with memory | 10.1134/S1995080214020139 |
2014-04-01 | This paper deals with the Cauchy problem of a nonlinear wave equation with damping and source terms. By the exact Gagliardo–Nirenberg inequality connected with the classic nonlinear elliptic equation, we establish new invariant sets of the problem. Then we get the exact conditions of blow-up and global existence. | Exact conditions of blow-up and global existence for the nonlinear wave equation with damping and source terms | 10.1007/s11071-013-1116-0 |
2014-04-01 | This paper deals with the studies for determining the degree of seismic hazard of grounds by taking into account all possible most important factors that influence their seismic hazard degree. The procedure, which is developed by the author on the basis of new approaches to solve this problem multilaterally, is presented. The characteristics of the behavior and quantitative estimate of seismic intensity amplification of soft and stiff grounds under seismic effects are shown. | New procedure for assessing the seismic hazard and behavior of soft and stiff grounds caused by the multifactor seismic effect | 10.3103/S0747923914020030 |
2014-04-01 | Study of intermediate mass fragments (IMFs) and light charged particles (LCPs) emission has been carried out for a few reactions involving α -cluster and non- α -cluster systems to see how the emission processes are affected by nuclear clustering. Li, Be, B and α -particles have been studied from α -clustered system ^16O + ^12C for 117, 125, 145 and 160 MeV bombarding energies respectively. The enhanced yields of near-entrance channel fragment B and large quadrupole deformation of the produced composite ^28Si^∗ extracted from LCP spectra indicate the survival of orbiting-like process in ^16O + ^12C system at these energies. The same IMFs emitted from the α -cluster system ^12C (77 MeV) + ^28Si and nearby non- α cluster ^11B (64 MeV) + ^28Si and ^12C (73 MeV) + ^27Al (all having the same excitation energy of ∼67 MeV) have also been studied. The fully energy damped (fusion–fission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time-scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value. | The effect of nuclear structure in the emission of reaction products in heavy-ion reactions | 10.1007/s12043-014-0724-7 |
2014-04-01 | In this paper, a class of damped vibration problems with impulsive effects is considered. An existence result is obtained by using the variational method and the critical point theorem due to Brezis and Nirenberg. The obtained result is also valid and new for the corresponding second-order impulsive Hamiltonian system. Finally, an example is presented to illustrate the feasibility and effectiveness of the result. | Existence of nonzero solutions for a class of damped vibration problems with impulsive effects | 10.1007/s10492-014-0046-6 |
2014-04-01 | The basic purpose of a damper is to reduce the vibration and to have a better ride comfort, road handling and safety to the rider. Recent developments show that an active vibration damper can effectively work much better than a passive damper. The effectiveness and reliability can be further enhanced by using hybrid dampers, which is a combination of active and passive dampers. But the need to have energy optimization in any field need not be stressed. Consequently, novel suspension concepts are required, not only to improve the vehicle’s dynamic performance, but also to see that the energy generated during vibration can be harvested by utilizing regeneration functions. Hence if a hybrid damper with energy harvesting capability be designed, it would serve both purposes. In the hybrid damper a combination of hydraulic damper to act as a passive damper and an electromagnetic (EM) damper to act as an active damper is considered. The hydraulic system has more reliability and is time tested and the EM system acts as a dynamic vibration system as well as energy harvester. In this study a hybrid EM damper is modeled, analyzed and validity is shown for frequency response functions and energy balance for its active use. It is also shown how the effectiveness of the suspension system can be enhanced by using a hybrid damper. | A Study on Design and Analysis of Hybrid Vibration Damper with Energy Harvesting and Optimal Damping Effect | 10.1007/s40032-014-0115-3 |
2014-04-01 | Structural damping is an important parameter in system identification and assessment of structural systems. Due to its variable nature, especially in highway bridges, precise estimation of damping poses challenges both from the computational point of views as well as complexity of operations. Survey of technical literature indicates that several methodologies have been developed over the past few decades for the determination of structural damping parameters. The present study determines damping in an operational highway bridge using two approaches, namely, the decay of motion direct measurement and the natural excitation technique. A two-span concrete box girder bridge was instrumented with various types of fiber optic Bragg grating sensors. Series of live load tests were performed on the bridge using a calibrated truck. Estimated damping was implanted in a detailed finite element model of the bridge. Live load on the actual bridge was replicated on the finite element model and the calculated results correlated with measured data at site. | Field tests and verification of damping calculation methods for operating highway bridges | 10.1007/s13349-013-0067-y |
2014-04-01 | This paper is focused on the study of an earthquake protection system, the tuned liquid damper (TLD), which can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated TLD, subjected to a sinusoidal excitation at its base, with different displacement amplitudes, was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses. | Tuned liquid dampers simulation for earthquake response control of buildings | 10.1007/s10518-013-9528-2 |
2014-04-01 | This paper deals with the damped superlinear oscillator $$x'' + a(t)\phi_p\bigl(x' \bigr) + b(t)\phi_q\bigl(x'\bigr)+ \omega^2x = 0, $$ where a ( t ) and b ( t ) are continuous and nonnegative for t ≥0; p and q are real numbers greater than or equal to 2; ϕ _ r ( x ′)=| x ′|^ r −2 x ′. This equation is a generalization of nonlinear ship rolling motion with Froude’s expression, which is very familiar in marine engineering, ocean engineering and so on. Our concern is to establish a necessary and sufficient condition for the equilibrium to be globally asymptotically stable. In particular, the effect of the damping coefficients a ( t ), b ( t ) and the nonlinear functions ϕ _ p ( x ′), ϕ _ q ( x ′) on the global asymptotic stability is discussed. The obtained criterion is judged by whether the integral of a particular solution of the first-order nonlinear differential equation $$u' + \omega^{p-2}a(t)\phi_p(u) + \omega^{q-2}b(t)\phi_q(u) + 1 = 0 $$ is divergent or convergent. In addition, explicit sufficient conditions and explicit necessary conditions are given for the equilibrium of the damped superlinear oscillator to be globally attractive. Moreover, some examples are included to illustrate our results. Finally, our results are extended to be applied to a more complicated model. | Global Dynamics of Froude-Type Oscillators with Superlinear Damping Terms | 10.1007/s10440-013-9839-y |
2014-04-01 | This paper presents a simple method to control the motion of a quadruped robot in unknown rough terrain using a full dynamic model. First, using the stiffness control method, the behavior of the four legs is approximated using four 3D spring damper systems. In this way, the dynamic model can be derived in Cartesian space. Based on this model, a control strategy is proposed to preserve the asymptotical stability of the system. In addition, a reflex motion control is introduced to cope with the rotational disturbance of the robot body. Finally, dynamic simulations and experiments of a quadruped walking robot were performed on unknown rough terrain to verify the proposed method. | Motion control of a quadruped robot in unknown rough terrain using 3D spring damper leg model | 10.1007/s12555-013-0053-5 |
2014-03-01 | We consider the Cauchy problem in R ^ n for the system of elastic waves with structural damping. We derive (almost) optimal decay rates in time for the L ^2-norm and the total energy which improves previous results for this system. To derive the estimates for elastic waves, we employ an improvement in a method in the Fourier space, which was developed in our previous works. Our estimates came from those for a generalized energy of α-order in the Fourier space. | Optimal decay rates for the system of elastic waves in R
^
n
with structural damping | 10.1007/s00028-014-0216-8 |
2014-03-01 | Seismic Damage Avoidance Design (DAD) principle that incorporates rocking wall with armoured steel wall to foundation seat details are presented for a class of warehouse type building. The walls consist of a mix of seismic wall panels and non-seismic infill cladding panels. The seismic wall panels are used to seat the rafters. Lateral loads are transmitted via diaphragm action through a roof truss. This design procedure involves seven steps. A key step of this procedure is the evaluation of total effective damping which includes intrinsic, hysteretic and radiation damping arising from rocking of the wall panels. Damping reduction factors for short, medium and long periods for the seismic design demand spectrum are also considered. The design is confirmed and validated using nonlinear time-history analysis under various earthquake ground motions. | Damage avoidance design for buildings | 10.1007/s12205-014-0016-2 |
2014-03-01 | Certain exact solutions to the linear differential-difference heat and mass transfer equations with a finite relaxation time are specified. The exact solution to the one-dimensional Stokes problem with the periodic boundary condition when a first-order volume chemical reaction occurs is given. A wide class of exact solutions to the nonlinear differential-difference heat-conduction equation with the following source is described: $$\Theta _t = div[f(T)\nabla T] + g(\Theta ), = T(r,t + \tau ),$$ where T = T ( r , t ) is temperature and τ is the relaxation time. Certain more complex heat conduction models with a variable relaxation time that can depend on time and a temperature gradient are also considered. | Exact solutions to differential-difference heat and mass transfer equations with a finite relaxation time | 10.1134/S0040579514020110 |
2014-03-01 | Based on a three-component description of partially ionized plasmas (i.e., electrons, ions, and neutral atoms), effects of inelastic collisions between ions (neutrals) and electrons on Alfvén waves (AWs) in a partially ionized plasma are studied. It is shown that for a fixed ionizability ( $$\epsilon_i$$ ϵ i ) or a fixed inelastic collision parameter ( χ , i.e., the ratio of the inelastic to elastic collision frequency), the damping rate of AWs has a peak value round k _z v _A/ ν _in ∼1, where k _z is the parallel wavenumber of AWs, v _A is the Alfvén velocity, and ν _in is the elastic collision frequency between ions and neutrals. On the other hand, the damping rate of AWs decreases monotonously with the ionizability $$\epsilon_i$$ ϵ i for a fixed inelastic collision parameter, but has a peak value when the inelastic collision parameter varies for sufficiently small ionizability ( $$\epsilon_i<0.1$$ ϵ i < 0.1 ). For sufficiently large ionizability ( $$\epsilon_i>0.1$$ ϵ i > 0.1 ), it is found that the damping rate decreases with the inelastic collision parameter. The results may help us to understand the physics of AWs in partially ionized plasmas. | Effects of inelastic collisions on Alfvén waves in partially ionized plasmas | 10.1007/s11434-013-0021-8 |
2014-03-01 | In this paper we consider the propagation of Rayleigh surface waves in an exponentially graded half-space made of an isotropic Kelvin-Voigt viscoelastic material. Here we take into account the effect of the viscoelastic dissipation energy upon the corresponding wave solutions. As a consequence we introduce the damped in time wave solutions and then we treat the Rayleigh surface wave problem in terms of such solutions. The explicit form of the secular equation is obtained in terms of the wave speed and the viscoelastic inhomogeneous profile. Furthermore, we use numerical methods and computations to solve the secular equation for some special homogeneous materials. The results sustain the idea, existent in literature on the argument, that there is possible to have more than one surface wave for the Rayleigh wave problem. | Rayleigh Surface Waves on a Kelvin-Voigt Viscoelastic Half-Space | 10.1007/s10659-013-9447-0 |
2014-03-01 | The chain/wire rope/chain combination is a common choice for mooring offshore floating platforms. However, data of the drag coefficients of chain links are rather limited, resulting in uncertainties with the calculations of the drag force, and hence the damping of the mooring system. In this paper, the importance of the selection of the drag coefficient is first investigated. The computational fluid dynamics (CFD) method is then used to determine the drag coefficients of a studless chain under steady flows. Numerical model validation is first completed by simulating a smooth circular cylinder under steady flows. In particular, the performance of different turbulence models is assessed through the comparisons between the calculations and the experimental results. The large eddy simulation (LES) model is finally selected for the simulation of steady flows past a chain. The effects of the Reynolds number on the drag coefficient of a stud-less chain is also studied. The results show that the calculated drag coefficients of a stud-less chain are fairly consistent with the available experimental data. | Numerical investigation of mooring line damping and the drag coefficients of studless chain links | 10.1007/s11804-014-1235-0 |
2014-03-01 | In this study, a novel rotational damper called a Rotational Friction Viscoelastic Damper (RFVD) is introduced. Some viscoelastic pads are added to the Rotational Friction Damper (RFD) in addition to the friction discs used in this conventional device. Consequently, the amount of energy dissipated by the damper increases in low excitation frequencies. In fact, the input energy to the structure is simultaneously dissipated in the form of friction and heat by frictional discs and viscoelastic pads. In order to compare the performance of this novel damper with the earlier types, a set of experiments were carried out. According to the test results, the RFVD showed a better performance in dissipating input energy to the structure when compared to the RFD. The seismic behavior of steel frames equipped with these dampers was also numerically evaluated based on a nonlinear time history analysis. The numerical results verified the performance of the dampers in increasing the energy dissipation and decreasing the energy input to the structural elements. In order to achieve the maximum dissipated energy, the dampers need to be installed in certain places called critical points in the structure. An appropriate approach is presented to properly find these points. Finally, the performance of the RFVDs installed at these critical points was investigated in comparison to some other configurations and the validity of the suggested method in increasing the energy dissipation was confirmed. | Performance evaluation of a novel rotational damper for structural reinforcement steel frames subjected to lateral excitations | 10.1007/s11803-014-0213-5 |
2014-03-01 | Surface wave methods are becoming increasingly popular in many geotechnical applications and in earthquake seismology due to their noninvasive characteristics. Inverse surface wave dispersion curves are a crucial step in most surface wave methods. Many inversion methods have been applied to surface wave dispersion curve inversion, including linearized inversion and nonlinearized inversion methods. In this study, a hybrid inversion method of Damped Least Squares (DLS) with Very Fast Simulated Annealing (VFSA) is developed for multi-mode Rayleigh wave dispersion curve inversion. Both synthetic and in situ field data were used to verify the validity of the proposed method. The results show that the proposed method is superior to the conventional VFSA method in aiming at global minimum, especially when parameter searching space is adjacent to real values of the parameters. The advantage of the new method is that it retains both the merits of VFSA for global search and DLS for local search. At high temperatures, the global search dominates the runs, while at a low temperatures, the local search dominates the runs. Thus, at low temperatures, the proposed method can almost directly approach the actual model. | A hybrid inversion method of damped least squares with simulated annealing used for Rayleigh wave dispersion curve inversion | 10.1007/s11803-014-0208-2 |
2014-03-01 | This paper constitutes the second part of the article Kinematically excited parametric vibration of a tall building model with a TMD. Part 1: numerical analyses (ACME, in press) by K. Majcher and Z. Wójcicki, which presents the results of theoretical research. This paper presents the experi¬mental verification of those results. The experimental studies were carried out with the use of an especially designed physical model of a tall building, which rested on an earthquake simulator — a shaking table — created for this project. The simulator was used to generate several types of kinematic excitations: harmonic ones, superpositions of harmonic ones and, finally, ones generated on the basis of real seismograms. Vibrations were kinematically excited in the horizontal and vertical directions independently and simultaneously. The vertical component of the earthquake causes the pendulum suspension point to vibrate, thus exciting the pendulum parametrically. The theoretical study indicated a significant influence of this parametric excitation (parametric resonance) on the effectiveness of the Pendulum Tuned Mass Damper (PTMD). Therefore, the experimental analyses were especially focused on the parametric effects’ impact on the PTMD’s ability to reduce the building’s vibration, and: the possibility of parametric resonance of the building due to parametric resonance of the PTMD. | Kinematically excited parametric vibration of a tall building model with a TMD—Part 2: Experimental analyses | 10.1016/j.acme.2013.09.003 |
2014-02-14 | In this paper we are interested in studying the effect of the fractional-order damping in the forced Duffing oscillator before and after applying a discretization process to it. Fixed points and their stability are discussed for the discrete system obtained. Finally, numerical simulations using Matlab are carried out to investigate the dynamic behavior such as bifurcation, chaos, and chaotic attractors. We note that on increasing the value of the fractional-order parameter, the resulting discrete system is stabilized. | Discretization of forced Duffing system with fractional-order damping | 10.1186/1687-1847-2014-66 |
2014-02-01 | Let $\mathcal{M}\subset\mathbb{R}^{3}$ be an oriented compact surface on which we consider the system: $$\left \{ \begin{array}{l@{\quad}l} u_{tt} - \Delta_{\mathcal{M}} u + a(x)g_{0}(u_{t})=0 & \text{in } \mathcal{M}\times\mathopen{]} 0,\infty[ ,\\ \partial_{\nu_{co}}u +u + b(x)g(u_t)=0 & \text{on } \partial \mathcal {M}\times\mathopen{]}0,+\infty[. \end{array} \right . $$ If $\mathcal{M}$ along with the localizers a , b and the nonlinear feedbacks g , g _0 satisfy certain conditions then uniform (but not necessarily exponential) decay rates of the finite energy of solutions can be established. We present a unified approach that bridges and extends a number of earlier results on stabilization of 2nd-order hyperbolic equations on manifolds. The methodology captures geometric requirements for damping acting simultaneously on subsets of the interior and of the boundary, and shows how placements of these feedbacks can complement each other depending on the underlying surface. In addition, the results conveniently incorporate the existing theory that allows elimination of geometric conditions from the controlled boundary (in absence of nearby interior damping), and elimination of damping entirely from certain boundary neighborhoods. The model also admits feedbacks that grow sub- or super-linearly not only at the origin, but also at infinity and demonstrates an interplay between the regularity of solutions and asymptotic energy decay rates. | Unified Approach to Stabilization of Waves on Compact Surfaces by Simultaneous Interior and Boundary Feedbacks of Unrestricted Growth | 10.1007/s00245-013-9218-0 |
2014-02-01 | This paper investigates how changes in chatter amplitude and frequency depend on process damping effect in dynamic turning process. For this purpose, the two degrees of freedom (TDOF) cutting system was modeled, and for an orthogonal turning system, the process damping model with a new simple approach was developed. To further explore the nature of the TDOF cutting model, a numerical simulation of the process was developed by this model. This simulation was able to overcome some of the weaknesses of the analytical model. The equations of motion for this cutting system were written as linear and nonlinear in the τ -decomposition form. The variation in the process damping ratios for different work materials was simply obtained by solving the nonlinear differential equations. A series of orthogonal chatter stability tests were performed for the identification of dynamic cutting force coefficients, using AISI-1040, Al-7075, and Al-6061 work materials, at a constant spindle speed. Finally, the experimental results were analyzed and compared with the simulation model, and it was observed that the results obtained through the experiments comply with the simulation model results. | A simple approach to analyze process damping in chatter vibration | 10.1007/s00170-013-5307-0 |
2014-02-01 | Two different methods to model a point absorber wave energy converter (WEC) with direct drive linear power take-off (PTO) are proposed in the present study: the frequency domain (FD) method and the time domain (TD) method. In the FD analysis, the frequency response function (FRF) of the WEC device is obtained via the equation of motion, and the expressions of power capture width in regular and random waves are derived as well. In the TD modeling, based on a state space approximation of the convolution term in the motion equation, both regular wave and random wave simulations are carried out. The regular wave simulation results indicate that the state space approximation is sufficiently accurate and the capture width reaches the maximum in the vicinity of the natural frequency. In the random wave simulations, the effects of buoy size, the PTO damping and wave climate on the power capture width are discussed in detail, which leads to the conclusion that the capture widths are influenced by the natural frequency of the WEC device, peak frequency of the wave spectrum, the amplitude of FRF and PTO damping. Furthermore, the increase of the capture width is at the cost of a relatively large buoy size and PTO damping when control is not included. | Frequency/time domain modeling of a direct drive point absorber wave energy converter | 10.1007/s11433-013-5200-8 |
2014-02-01 | In this paper, we study the initial-boundary value problem for a coupled system of nonlinear viscoelastic wave equations of Kirchhoff type with Balakrishnan–Taylor damping terms. For certain class of relaxation functions and certain initial data, we prove that the decay rate of the solution energy is similar to that of relaxation functions which is not necessarily of exponential or polynomial type. Also, we show that nonlinear source of polynomial type is able to force solutions to blow up in finite time even in presence of stronger damping. | On a system of nonlinear wave equations with Balakrishnan–Taylor damping | 10.1007/s00033-013-0324-2 |
2014-02-01 | Revolute joints in applications always show clearance between pin and bushing due to manufacturing tolerances, the need of relative motion or progressing wear. Many researchers developed and investigated methodologies to calculate the dynamic behavior of mechanisms with such imperfect joints. Very often they use a simple slider-crank mechanism to test or demonstrate the capability of their approaches. In this paper, a methodology for simulating a slider-crank mechanism with an imperfect revolute joint in RecurDyn, a commercial multibody simulation tool, is presented. Therefore, a thorough investigation of existing contact, damping and friction force models as well as different ways of modeling revolute joints in RecurDyn was conducted. For the investigation of the damping models, a special program for calculating the model parameters for a given coefficient of restitution was developed. Only one damping model was capable of reproducing the experimental results, which were found in literature. Some characteristic results of the slider-crank mechanism are presented in a way that they can be compared to results in other papers. Thereby. a good correlation was achieved, demonstrating the capabilities of the methodology. | Modeling planar slider-crank mechanisms with clearance joints in RecurDyn | 10.1007/s11044-012-9339-2 |
2014-02-01 | In a companion article Akkar et al. (Bull Earthq Eng, doi: 10.1007/s10518-013-9461-4 , 2013a ; Bull Earthq Eng, doi: 10.1007/s10518-013-9508-6 , 2013b ) present a new ground-motion prediction equation (GMPE) for estimating 5 %-damped horizontal pseudo-acceleration spectral (PSA) ordinates for shallow active crustal regions in Europe and the Middle East. This study provides a supplementary viscous damping model to modify 5 %-damped horizontal spectral ordinates of Akkar et al. (Bull Earthq Eng, doi: 10.1007/s10518-013-9461-4 2013a ; Bull Earthq Eng, doi: 10.1007/s10518-013-9508-6 , 2013b ) for damping ratios ranging from 1 to 50 %. The paper also presents another damping model for scaling 5 %-damped vertical spectral ordinates that can be estimated from the vertical-to-horizontal (V/H) spectral ratio GMPE that is also developed within the context of this study. For consistency in engineering applications, the horizontal and vertical damping models cover the same damping ratios as noted above. The article concludes by introducing period-dependent correlation coefficients to compute horizontal and vertical conditional mean spectra (Baker in J Struct Eng 137:322–331, 2011 ). The applicability range of the presented models is the same as of the horizontal GMPE proposed by Akkar et al. (Bull Earthq Eng, doi: 10.1007/s10518-013-9461-4 2013a ; Bull Earthq Eng, doi: 10.1007/s10518-013-9508-6 , 2013b ): as for spectral periods $$0.01 \hbox { s}\le \,\hbox {T}\le \,4\hbox { s}$$ 0.01 s ≤ T ≤ 4 s as well as PGA and PGV for V/H model; and in terms of seismological estimator parameters $$4\le \hbox {M}_\mathrm{w} \le 8, \hbox { R} \le 200 \hbox { km}, 150\hbox { m/s}\le \hbox { V}_\mathrm{S30}\le $$ 4 ≤ M w ≤ 8 , R ≤ 200 km , 150 m/s ≤ V S 30 ≤ 1,200 m/s, for reverse, normal and strike-slip faults. The source-to-site distance measures that can be used in the computations are epicentral $$(\hbox {R}_\mathrm{epi})$$ ( R epi ) , hypocentral $$(\hbox {R}_\mathrm{hyp})$$ ( R hyp ) and Joyner–Boore $$(\hbox {R}_\mathrm{JB})$$ ( R JB ) distances. The implementation of the proposed GMPEs will facilitate site-specific adjustments of the spectral amplitudes predicted from probabilistic seismic hazard assessment in Europe and the Middle East region. They can also help expressing the site-specific design ground motion in several formats. The consistency of the proposed models together with the Akkar et al. (Bull Earthq Eng, doi: 10.1007/s10518-013-9461-4 2013a ; Bull Earthq Eng, doi: 10.1007/s10518-013-9508-6 , 2013b ) GMPE may be advantageous for future modifications in the ground-motion definition in Eurocode 8 (CEN in Eurocode 8, Design of structures for earthquake resistance—part 1: general rules, seismic actions and rules for buildings. European Standard NF EN 1998-1, Brussels, 2004 ). | Compatible ground-motion prediction equations for damping scaling factors and vertical-to-horizontal spectral amplitude ratios for the broader Europe region | 10.1007/s10518-013-9537-1 |
2014-02-01 | In a rotor bearing system operating with constant angular acceleration, after passing through the critical speed, typical beat characteristics are observed because the transverse vibration response contains both excited and natural motion, and shortly after passing resonance, vibrations with close frequencies appear. The present study explains a method for estimating damping of rotor bearing systems from transient beat vibration signals observed during run up stage. A mathematical derivation to prove that a part of run-up vibration of the rotor system consists of beat phenomenon when the system crosses critical speed. It is also observed from the mathematical model that the beat vibrations depend on the damping in the system. This beat response is considered for Hilbert analysis and the damping is estimated. Increase in angular acceleration of the rotor will increase the damping. This paper investigates how the damping varies with respect to different angular acceleration values of the rotor bearing system. Experimental validation of the beat phenomenon and damping estimation are done for the rotor system. The proposed method is validated by using half-power band width method applied to run-up response. | Damping identification in rotors from run-up beat responses using Hilbert transforms | 10.1007/s12206-013-1106-7 |
2014-02-01 | An analytical model is developed to estimate the two-phase damping ratio for upward cross-flow through horizontal tube bundles. The present model is formulated based on Feenstra’s model (2000) for void fraction and various models (homogeneous, Levy, Martinelli-Nelson and Marchaterre) for two-phase friction multiplier. The analytical results of drag coefficient on a cylinder and two-phase Euler number are compared with the experimental results by Sim-Mureithi (2013). The correlation factor between frictional pressure drop and the hydraulic drag coefficient is evaluated by considering the experimental results. The two-phase damping ratios given by the analytical model are compared with existing experimental results. The model based on Marchaterre’s model is suitable for air-water mixture, whereas the Martinelli-Nelson’s model is suitable for steam-water and Freon mixtures. The two-phase damping ratio is independent of pitch mass flux for air-water mixture, but is more or less influenced by the mass flux for steam-water/Freon (134) mixtures. The two-phase damping ratios given by the present model agree well with experimental results for a wide range of pitch mass ratio, quality, and p/d ratios. | A two-phase damping model on tube bundles subjected to two-phase cross-flow | 10.1007/s12206-013-1122-7 |
2014-02-01 | A new tamping device which is driven by an electrohydraulic exciter was proposed to overcome the limitations of mechanically driven devices. The double-rod oscillation cylinder drives the tamping arm to realize vibration. A new spin valve was designed in order to fulfill dynamic state requirements of the oscillation cylinder. Parametric analysis was carried out by establishing mathematic model. Then, the relationships among the structure of valve port and the frequency, amplitude, output shock force of the cylinder were researched. An experimental device of the electrohydraulic exciter was established to validate the theoretical results. The signals were acquired by AVANT dynamic signal analyser of vibration. The results show that new tamping device can satisfy all kinds of complex working conditions with the flexible adjustment of frequency and amplitude. | Mechanism of electro-hydraulic exciter for new tamping device | 10.1007/s11771-014-1969-5 |
2014-02-01 | Many engineering structures are required to minimize vibrations. Vibrations in a system can be reduced by changing the design of the structure or by using a new material which has better mechanical damping. Damping materials are desirable as they convert mechanical energy to heat. As most engineering structures are load bearing, the material used needs to have high stiffness as well. Hence, a new material developed for the use of engineering structures should have both high stiffness and high damping. This paper discusses a variety of materials that were uniquely developed to achieve the aforementioned objectives. The new manganese bronze C86500 based samples were alloyed with different indium alloys (In, InSn, and BiSn) and classified according to the type of heat treatment, amount of cold working, and alloy composition by weight percentage. A dynamic mechanical analyzer (DMA) was used to find the complex modulus and loss tangent (tan δ ) values of the created samples. These values were then used to evaluate and compare the various samples and their relative damping capacities across different frequencies at a particular temperature and strain. Most of the alloying compounds showed an average increase of 120 % in the low frequency range (0.01–0.1 Hz), without significantly compromising its stiffness. BiSn was found to be the most effective alloying compound for the new manganese bronze C86500 with 30 % cold working. | Improvement of viscoelastic damping by using manganese bronze with indium | 10.1007/s11043-013-9223-3 |
2014-02-01 | Machining dynamic stability has been enhanced through a damping coating based on a novel carbon-based nanocomposite material. The coating was synthesized using a plasma enhanced chemical vapor deposition method, and deposited on to the round-shank boring bar used for internal turning and tested during machining. Comparisons between an uncoated and a coated boring bar were carried out at 0.25 mm and 0.5 mm depth of cut using a five times length to diameter ratio overhang, which are typical conditions known to generate detrimental mechanical vibrations. From sound pressure measurement it was found that the measured absolute sound level during process could be reduced by about 90% when using the tool coated with damping layer. Surface roughness measurements of the processed workpiece showed decreased Ra values from approximately 3-6 μm to less than 2 μm (and in 50% of the cases <1 μm) when comparing an uncoated standard tool with its coated counterpart. Moreover, it was found that the addition of an anti-vibration coating did not adversely affect other tool properties, such as rigidity and modularity. | Anti-vibration Engineering in Internal Turning Using a Carbon Nanocomposite Damping Coating Produced by PECVD Process | 10.1007/s11665-013-0781-y |
2014-02-01 | Dynamic thermomechanical analysis (DTMA) of unfilled as well as particle-filled poly(dimethylsiloxane) and poly(norbornene) was performed to compare their behavior as dampers. PDMS and PNB were filled with varying contents of spherical iron particles (aspect ratio of 1) and also different hardness formulations of the materials were characterized. The wicket-plot (tan δ vs. storage modulus) was considered therefore and all frequency- and temperature-dependent results were presented. Linear dependencies were observed for PDMS, even though the material did not reveal thermorheologically simple behavior. However, tan δ of PNB was a unique function of its storage modulus and so the material exhibited thermorheologically simple behavior. A linear shift factor over frequency–temperature and frequency–internal pressure (Fe-content) was found for PDMS. Master curves of PNB were constructed and reasonable results were achieved, which were due to their thermorheologically simple material behavior. | Applicability of elastomer time-dependent behavior in dynamic mechanical damping systems | 10.1007/s11043-013-9219-z |
2014-01-01 | Damping forces are typically ignored during the Finite Element Analysis (FEA) of mechanical structures. In most real structures, it can be assumed that there are several damping mechanisms at work, but they may be difficult to identify, and even more difficult to model. Since both mass & stiffness matrices are available during an FEA, a common method of modeling viscous damping is with a proportional damping matrix. That is, the viscous damping matrix is assumed to be a linear combination of the mass & stiffness matrices. Therefore, in order to model viscous damping with a proportional damping matrix, the two constants of proportionality must be determined. In this paper, a least-squared-error relationship between experimental modal frequency & damping and the proportional damping constants of proportionality is developed. An example is included in which experimental modal parameters are used to calculate the constants of proportionality. The modal parameters of an FEA model with proportional damping are then compared with the original experimental modal parameters. | Proportional Damping from Experimental Data | 10.1007/978-1-4614-6585-0_17 |
2014-01-01 | The traditional measurement techniques to acquire the linear dynamic response of a single component are well established and have been in use for many decades to provide reliable input data for model updating. The measurement of assembled structures normally follows a very similar approach, although the presence of joints can introduce a nonlinear dynamic behaviour, which impacts the measurement results. Applying traditional linear test methods to a highly nonlinear structure, such as a dovetail joint in an aircraft engine blade-disk connection, does not necessarily take the special features of the nonlinear response into account and may lead to unreliable data. This is particularly true, if modal information such as damping are required. The influence of the measurement setup and the test procedures must be well understood for an accurate measurement. In this paper the influence of the different measurement components on a simple clamped beam and a compressor blade dove tail test rig will be investigated. A particular focus will be on the support of the test rig, the location and control of the excitation and the influence of the accelerometer on the response. Based on the findings an approach will be recommended that allows a reliable measurement of the dynamic behaviour of this heavily nonlinear structure. | Test Method Development for Nonlinear Damping Extraction of Dovetail Joints | 10.1007/978-3-319-04501-6_21 |
2014-01-01 | First, this article analyzes the basic principles of supplementary subsynchronous damping controller (SSDC) inhibiting SSO caused by the DC control system. Second, based on the principle of phase compensation, a multi-mode SSDC is designed in accordance with the maximum phase compensation method. Third, test signal method is used to analyze SSDC’s compensation role in improving the system electrical damping. Finally, the availability of SSDC designed in this paper is simulated and verified in an actual power system model. | Design of Direct Current Subsynchronous Damping Controller (SSDC) | 10.1007/978-3-319-01273-5_76 |
2014-01-01 | This chapter aims at presenting basic ideas and main insights of the energy-based control approach for power electronic converters. Thus, two control methods based on concepts of energy will be here detailed: the so-called stabilizing control – based upon Lyapunov control design methods – and passivity-based control , relying upon specific structural properties – for example, passivity and dissipativity – and on control methods that exploit these properties. | Energy-Based Control of Power Electronic Converters | 10.1007/978-1-4471-5478-5_12 |
2014-01-01 | In this paper we consider the critical exponent problem for the semilinear damped wave equation with time-dependent coefficients. We treat the scale invariant cases. In this case the asymptotic behavior of the solution is very delicate and the size of coefficient plays an essential role. We shall prove that if the power of the nonlinearity is greater than the Fujita exponent, then there exists a unique global solution with small data, provided that the size of the coefficient is sufficiently large. We shall also prove some blow-up results even in the case that the coefficient is sufficiently small. | Critical Exponent for the Semilinear Wave Equation with Scale Invariant Damping | 10.1007/978-3-319-02550-6_19 |
2014-01-01 | The dynamic model of a vehicle seat with magnetorheological damper is established in this paper, which is established with the finite element analysis software. On the basis of single degree of freedom spring-damping system, the established model simulates the working characteristic of the magnetorheological damper. Based on the established model, the dynamic analysis is carried out. The results of the simulation experiments verify the effectiveness of the established model and show that performance of the dynamic model of a vehicle seat with magnetorheological damper is better than the dynamic model with spring. | Research on the Dynamic Model with Magnetorheological Damper | 10.1007/978-3-642-54236-7_36 |
2014-01-01 | Structures with mechanical joints are difficult to accurately model; even when the natural frequencies of the system remain essentially constant, the damping introduced by the joints is often observed to depend nonlinearly on amplitude. Although models for individual joints have been employed with some success, the modeling of a structure with many joints remains a significant obstacle. This work explores whether nonlinear damping can be applied in a modal framework, where instead of modeling each discrete joint within a structure, a nonlinear damping model is used for each mode of interest. This approach assumes that the mode shapes of the structure do not change significantly with amplitude and that there is negligible coupling between modes. The nonlinear Iwan joint model has had success in modeling the nonlinear damping of individual joints and is used as a modal damping model in this work. The proposed methodology is first evaluated by simulating a structure with a small number of discrete Iwan joints (bolted joints) in a finite element code. A modal Iwan model is fit to simulated measurements from this structure and the accuracy of the modal model is assessed. The methodology is then applied to actual experimental hardware with a similar configuration and a modal damping model is identified for the first few modes of the system. The proposed approach seems to capture the response of the system quite well in both cases, especially at low force levels when macro-slip does not occur. | Investigation of Modal Iwan Models for Structures with Bolted Joints | 10.1007/978-1-4614-6540-9_2 |
2014-01-01 | We study the asymptotic behaviour of the wave equation with viscoelastic damping in presence of a time-delayed damping. We prove exponential stability if the amplitude of the time delay term is small enough. | Exponential Stability of the Wave Equation with Memory and Time Delay | 10.1007/978-3-319-11406-4_1 |
2014-01-01 | This chapter addresses the most important issues on the virtual synchronous generator (VSG) concept with the relevant past achievements. The most important VSG design frameworks and topologies are described. An overview of the key issues in the integration of VSGs in the MGs and power grids, and their application areas that are of most interest today is presented. Then the chapter focuses on the potential role of VSGs in the grid frequency control task. Finally, the need for further research on the more flexible and effective VSGs, and some other related areas, is emphasized. | Virtual Inertia-Based Frequency Control | 10.1007/978-3-319-07278-4_12 |
2014-01-01 | The most employed and useful model of a vehicle suspension system is a quarter car model, shown in Figure 15.1. We introduce, examine, and optimize the quarter car model in this chapter. | ⋆ Quarter Car Model | 10.1007/978-1-4614-8544-5_15 |
2014-01-01 | In this work, an efficient FE-modeling technique for assembled metallic structures is presented. Linear thin-layer elements containing damping and stiffness parameters are placed on the interfaces of bolted joints. The interface parameters are identified experimentally on an isolated lap joint and then used as an input for the FE-simulation. Since the presented modeling technique is linear, it delivers acceptable results only for small relative displacements in the joint interface, i.e. microslip. Therefore investigations on the transition from micro- to macroslip are conducted. A promising approach to detect macroslip is based on the significant increase of higher harmonic frequency generation. The application of this criterion results in a linear relation between the normal force and the maximum tolerable tangential force. | Microslip Joint Damping Prediction Using Thin-Layer Elements | 10.1007/978-3-319-04501-6_22 |
2014-01-01 | The paper at hand shows how structural damping and stiffness parameters in shrunk joints can be determined by a generic joint experiment. With thin-layer elements these parameters from the joint experiment are coupled to the structures finite element model. Equivalent modal damping factors can be determined by performing a complex numerical modal analysis, by which the stability of the rotor can be tested. The two-disc rotor is examined as an application sample. This rotor consists of a shaft with two shrunk-on discs. With the above mentioned approach, and by considering structural damping added to material damping, the modal damping of the first torsional eigenfrequency is calculated and then compared to the results of an experimental modal analysis. The paper shows that the presented approach leads to a reliable approximation of the examined structure’s dissipation properties. It serves as a prediction tool for the response behavior of a turbo-generator. | Experimental Identification and Simulation of Rotor Damping | 10.1007/978-3-319-04501-6_19 |
2014-01-01 | In simple terms, noise is unwanted sound. Noise can disturb human’s work, rest, sleep and communication, and it can damage hearing. Indeed, the most important issue is industrial noise problem and a need for noise control and hearing conservation programs. This chapter provides guidelines comprising: (a) Brief explanation of the principle and essential standards for noise emitted by machineries and equipment. (b) Brief explanation of the principle underlying standards for noise in workplace areas, and noise control procedures in plants/complexes, offices, conference rooms, etc. (c) Brief explanation of the principle for vibration control. | Noise Pollution Control | 10.1007/978-3-319-01234-6_4 |
2014-01-01 | In this chapter, the response characteristics for material, hysteretic, and friction damping mechanisms are examined for a single-degree-of-freedom (SDOF) system. The concept of equivalent viscous damping is introduced and is used to express viscoelastic, structural, and hysteretic damping in terms of their equivalent viscous counterpart. Numerical simulations are presented to demonstrate the validity of this concept for SDOF systems subjected to seismic excitation. This introductory material is followed by a discussion of the influence of distributed viscous damping on the deformation profiles of multi-degree-of-freedom systems. The damping distribution is initially taken to be proportional to the stiffness distribution generated in the previous chapter, and then modified to allow for non-proportional damping. Numerical results and deformation profiles for a range of structures subjected to seismic loading are presented, and the adequacy of this approach for distributing damping is assessed. | Optimal Passive Damping Distribution | 10.1007/978-3-319-06281-5_4 |
2014-01-01 | Human interaction with structural systems is not totally understood, leading to either overdesign or extreme vibrations. Different numerical models have been proposed to represent this interaction. Most of these models use masses, springs and dampers to model the human. One could argue that the interaction between structural system and human is more complicated, specially, that the human might react with the structure even though he or she is still at a particular location. This paper proposes the use of a close loop controller system to model the human–structure interaction. The model is updated in a probabilistic sense using experimental data collected in the laboratory. | Modeling Human–Structure Interaction Using a Close Loop Control System | 10.1007/978-3-319-04546-7_12 |
2014-01-01 | Characterizing frictional behavior of viscoelastic joints is investigated in the present work. A new visco-tribological model was developed by coupling the rheological Generalized Maxwell model (GMM) and Dahl friction model. Parameters of the proposed model are identified from Dynamic Mechanical Analysis (DMA) tests for different excitation frequencies. Comparison between measurements and simulations of hysteretic friction of the viscoelastic component has been carried on. | Dynamic Characterization of Viscoelastic Components | 10.1007/978-3-319-07170-1_15 |
2014-01-01 | The mechanical response of a viscoelastic material to external loads combines the characteristics of elastic and viscous behavior. On the other hand, as we know from experience, springs and dashpots are mechanical devices which exhibit purely elastic and purely viscous response, respectively. It is then natural to imagine that the equations that relate stresses to strains in a viscoelastic material could be represented with an appropriate combination of equations which relate stresses to strains in springs and dashpots. To develop this idea, Sect. 3.2 examines the response of the linear elastic spring and linear viscous dashpot to externally applied loads. The response equations for these simple mechanical elements are formalized in Sect. 3.3 , with the introduction of so-called rheological operators. As it turns out, because combinations of springs and dashpots require the addition and multiplication of constant and first derivative operators, it turns out that the constitutive equation of general arrangements of springs and dashpots, such as are needed to reproduce observed viscoelastic behavior, must be represented by linear ordinary differential equations whose order depends on the number, type, and specific arrangement of the springs and dashpots. The physical significance of the coefficients in the resulting differential equations is examined also, and the proper form of the initial conditions established. As will be seen, the mere presence or absence of some of the coefficients of a differential equation reveals whether the particular arrangement of springs and dashpots it represents will model fluid or solid behavior, and whether it will exhibit instantaneous, elastic response. A general approach to establishing rheological models is presented in Sect. 3.4 , and applied in Sects. 3.5 through 3.7 to develop the differential equations, and examine the behavior of simple and general rheological models. | Constitutive Equations in Differential Operator Form | 10.1007/978-1-4614-8139-3_3 |
2014-01-01 | With the rapid development of femtosecond laser and micro/nano processing techniques, researchers face great challenges in thermal management and analysis under the extreme conditions. As the theoretical basis of heat transfer, Fourier’s law may break down at femtosecond temporal scales and nanometer spatial scales. In 1822, Fourier stated in his book “Analytical theory of heat” that the mechanical principles could not be applied to study the thermal phenomenon, which used concepts that differed from other fields of study [ 1 ]. But the heat transport in metals can be analogous to the charge transport according to the Wiedemann–Franz (WF) law [ 2 ], it shows internal connection between thermal science and other branches of physics. Guo has developed a novel thermomass theory to analyze the heat conduction using Newtonian mechanics [ 3 ], creating a new path for thermal analysis under the extreme conditions. | Thermomass Theory for Non-Fourier Heat Conduction | 10.1007/978-3-642-53977-0_2 |
2014-01-01 | This chapter analyzes the two most popular classes of transducers used in active vibration control: the electromagnetic transducer known as voice coil , and the piezoelectric transducer. The first part of the chapter discusses the theory of the transducers and the second part discusses some applications in structural control. | Electromagnetic and Piezoelectric Transducers | 10.1007/978-3-7091-1821-4_4 |
2014-01-01 | This chapter deals with the theory of viscoelasticity and the discrete models such as, for example, the Kelvin and Maxwell models. The aim of this chapter is to assess the dynamic behavior of viscoelastic dissipative bracing systems taking into account the presence of the brace. In fact, the viscoelastic damper is modeled as the Kelvin model, whose behavior is dependent, in itself, on frequency; the viscoelastic damper-brace component can be studied through the Poynting-Thomson model which presents even more dependence on the frequency. Similarly, the viscous (linear or non-linear) damper-brace component can be studied through the Maxwell model, characterized by a frequency dependent dynamic response. In both cases, because of the frequency dependence, in the dynamic field, dynamic “reduced” magnitudes correspond to the static magnitudes of the viscoelastic dissipative bracing system, in other terms, between the static and dynamic behavior, there is a reduction in the effectiveness of the viscoelastic dissipative bracing system. | Modeling of Viscoelastic Dissipative Bracing Systems | 10.1007/978-3-319-02615-2_4 |
2014-01-01 | The United States Eastern Interconnection (EI) has been going through some profound changes due to the increasing penetration of wind power in this bulk grid, including the worsening of the frequency response and inter-area oscillation. However, the fast response speed of electronics devices makes it possible that the kinetic energy stored and/or wind power reserve (if it exists) in variable-speed wind generators could be injected into the power grid in a fast manner. This portion of fast-injected active power could contribute to frequency regulation or oscillation damping of the EI significantly if implemented with appropriate control schemes. In this chapter, a user-defined wind electrical control model with fast active power controllers is built in PSS®E. Then, based on the 16,000-bus EI system dynamic model, the potential contributions of variable-speed wind generators to the EI frequency regulation and oscillation damping are evaluated respectively. Simulation results have demonstrated that current and future penetrations of wind generation are promising in providing frequency regulation and oscillation damping in the EI. | Contribution of Variable-Speed Wind Generators to Frequency Regulation and Oscillation Damping in the United States Eastern Interconnection | 10.1007/978-981-4585-27-9_8 |
2014-01-01 | By subsuming experimental modal and radiation analysis results on many violins, boundary element method computations for a violin undergoing soundpost removal, nearfield acoustical holography for port ( f -holes) radiation, and statistical energy analysis into a generalized structural acoustics framework it is possible to construct a dynamic filter model for the averaged-over-sphere radiativity of the traditional, properly setup violin over the frequency range from 0.2 to 6 kHz. This model treats the low frequency “deterministic” region below 660 Hz—where all violins show two cavity and three body modes—three always radiating strongly through the f -holes, two with strong surface radiation, one hardly radiating, and one requiring induced surface motion to radiate—as a simplified dual -Helmholtz resonator where two low-lying bending modes “pump” the lowest Helmholtz-resonator-like cavity mode. The mid-high frequency region uses a band-averaged, “statistical” structural acoustics approach built on a distributed-excitation statistical mobility function (SEA) to incorporate bridge filter and critical frequency effects. Both regions were rejoined at 630 Hz where all violin quality classes had a common value. This dynamic filter model is capable of simulating the effects on violin radiativity of top-back plate and bridge tuning, holding the violin or soundpost removal, singly or in combination. | EMA-BEM-NAH-SEA Path to a Dynamic Filter Model for Violin Radiativity | 10.1007/978-3-319-04753-9_32 |
2014-01-01 | This paper derives exact results for the maximum achievable accuracy when estimating modal parameters from free vibration and forced vibration signals contaminated by Gaussian white noise. These limits are found through the Cramer-Rao lower bound. The paper proposes a simple yet accurate expression to determine the ratio between the coefficient of variation of damping and frequency. This expression can be useful to compute the variance of the damping using limited number of vibration tests. The paper presents results that verify and validate the derived expressions using laboratory and field experiments. | Uncertainty Quantification of Identified Modal Parameters Using the Fisher Information Criterion | 10.1007/978-3-319-04552-8_17 |
2014-01-01 | The aim of this paper is to understand the influence of the interplay between a time-dependent increasing speed of propagation and a timedependent coefficient in the dissipation on qualitative properties of solutions to the wave model $$u_{tt}-a^2(t)\bigtriangleup\mathrm{u}+ b(t)u_t=0,\,u(0,x)=u_1(x),u_{t}(0,x)=u_{2}(x).$$ Our considerations are focused to energy estimates. The main difficulty is to find a good description of non-effective and effective dissipations depending on a given speed of propagation. The obtained energy estimates are optimal as special examples will show. At the end we will sketch very briefly how to get scattering and over-damping results. So, we propose a classification of different damping terms which is motivated by the thesis of J. Wirth for the case $$a\equiv1$$ | The Interplay Between Time-dependent Speed of Propagation and Dissipation in Wave Models | 10.1007/978-3-319-02550-6_2 |
2014-01-01 | This chapter is concerned by tuned-mass damping systems. We start with an introductory example of a tuned-mass damper (TMD) design and a brief description of some of the implementations of TMDs in building structures. A rigorous theory of TMDs for single-degree-of-freedom (SDOF) systems subjected to harmonic force excitation and harmonic ground motion is discussed next. Various cases including a damped TMD attached to an undamped SDOF system, and a damped TMD attached to a damped SDOF system are considered. Time history responses for a range of SDOF systems connected to optimally tuned TMD and subjected to harmonic and seismic excitations are presented. The theory is then extended to multi-degree-of-freedoms systems where the TMD is used to dampen out the vibrations of a specific mode. Lastly, a theory for tuned liquid column dampers is presented and design procedures are suggested. | Tuned Mass Damper Systems | 10.1007/978-3-319-06281-5_5 |
2014-01-01 | The pendulum chain with torsional spring coupling represents a physical system that is described exactly by the spatially discrete sG equation. In order to study its solutions experimentally, however, we have to drive the system to counteract the inevitable dissipation we face in experiments. In fact, it is important to model the main sources of energy dissipation realistically; here we find that both on-site and intersite contributions to dissipation are relevant. We show that lattice solitons, also known as discrete breathers (DB) or intrinsic localized modes (ILMs), can be produced and stabilized in this system in the presence of driving (forcing) and damping. One way to do this is by exploiting the modulational instability of the uniform mode. Once a discrete soliton has been phase-locked to the driver, it persists indefinitely, and its properties can be studied, as can the range of its stability in parameter space and the types of instability outside of it. We also explore in some detail the interesting effect of which there exists no analogue in continuous media: the existence of two types of discrete solitons of different symmetry—the one-site centered and the two-site centered ILM. Furthermore, we find an exchange of stability between those two breather types as certain system parameters are varied. Comparison to analytical work based on realistic model parameters will be discussed as well. | Experimental Results for the sine-Gordon Equation in Arrays of Coupled Torsion Pendula | 10.1007/978-3-319-06722-3_5 |
2014-01-01 | This chapter discusses base-isolation systems. A set of simple examples are presented to identify the key parameters and illustrate the quantitative aspects of base isolation. This material is followed by a discussion of practical aspects of seismic base isolation and a description of some seismically isolated buildings. The remaining sections deal with the behavioral and design issues for base isolated multi-degree-of-freedom structural systems. Numerical results illustrating the level of performance feasible with seismic base isolation are included to provide a basis of comparison with the other motion control schemes considered in this text. | Base Isolation Systems | 10.1007/978-3-319-06281-5_6 |
2014-01-01 | A finite element model calibration procedure that uses frequency response function data and relies on damping equalization is presented. In this, the dampings of the finite element model and the corresponding experimental model are set equal before calibration. The damping equalization is made to avoid the mode pairing problem that normally needs to be solved in other model updating procedures. It is demonstrated that one particular use of frequency response data gives a calibration deviation metric that is smooth in the variation of model parameters and give a large radius of convergence to the calibration minimum. The method is combined with model reduction for increased speed and employs a minimizing procedure that employs randomized multiple starting points in the parameter space to get to the calibration solution. The performance of the calibration procedure is demonstrated by two numerical examples. | FEM Calibration with FRF Damping Equalization | 10.1007/978-3-319-04552-8_26 |
2014-01-01 | This study presents an operational modal analysis of rotating Carbon Nanotube (CNT) infused composite beams in order to explore the effect of CNT’s on the natural frequencies and damping characteristics of the composite structure during rotation. Engineering applications with rotating components made from composites often suffer from excess vibrations because of the inherent high stiffness to weight ratio of the composite material and the oscillating loads from rotation. Previous research has demonstrated that the addition of CNT’s to composite resins increases the damping characteristics of the resulting material, and several of these works have suggested that CNT-infused composites may be useful in rotor design as a means of passive vibration suppression. The present work aims to address this suggestion with an experimental investigation using composite beams fabricated with CNT’s embedded in an epoxy resin matrix along with several layers of reinforcing carbon fiber fabric. An experimental apparatus is designed and constructed to hold two cantilever composite beams on opposite sides of a rotating central shaft controlled via a DC servo motor and a PID control loop. White noise is generated and added to the input motor RPM signal to randomly excite the base of the structure during rotation, and the Eigensystem Realization Algorithm (ERA) is used to analyze the data measured from the vibrating beam in order to determine the modal parameters of the system. The extracted modal parameters are presented as a function of the angular speed and weight percentage CNT loading in order to gain insight into application areas involving vibration suppression in rotating composite structures such as helicopter rotors and wind turbine blades. | Modal Analysis of Rotating Carbon Nanotube Infused Composite Beams | 10.1007/978-1-4614-6585-0_52 |
2014-01-01 | The scope of this paper is to investigate the damping performance of metal swarfs in hollow structures and to compare its vibration suppression performance with existing granular damping technologies. The effectiveness in suppressing vibrations in a hollow aluminum beam using aluminum, mild steel and stainless steel swarfs is compared to that of rubber spheres. Performance is compared using swept sine wave across a range of amplitudes from 0.1 g to 10 g for both first and the second modes of the beam. Considerable vibration suppression is observed for both modes, and the effect of filler type on damping and natural frequency variation is presented. | Damping performance of metal swarfs in a horizontal hollow structure | 10.1007/s12206-013-0980-3 |
2014-01-01 | A base isolated three storey 3-D building is semi-actively controlled not to exceed the maximum allowable base displacement. Large displacements are likely to cause failure in the isolation system, and hence, failure in the superstructure is expected. If a base isolated structure is positioned next to a very long fault line, such as the North Anatolian Fault, the structure will mostly undergo far field type excitations. Near field effects will be seen less occasionally, but design considerations should be made to account for both types of excitations. In case of nearby seismic action, the isolated building should be smart enough to modify its isolation impedance to resist against large ground displacement and velocities. For this study, an isolated three storey building model together with four dampers, which are all placed at the base level, is considered. The dampers have controllable orifices (damping coefficients) and the magnitudes of these damping coefficients are assigned by using a linear quadratic regulator (LQR). During an earthquake excitation, the storey displacements and velocities are used as feedback in the calculation of the optimal control force that is producible by viscous dampers, at each time step. This force, however, is applied only at times when critical displacements and/or velocities occur. The performance of the set of controllers is presented via time simulations of the system for three recorded earthquakes. In addition, these records are time shifted five folds to see the effect of near field action. The results indicate that the control effectively reduces the maximum displacements of the isolation system, while maintaining a reasonable isolation to the superstructure. | Hybrid Control of a 3-D Structure by Using Semi-Active Dampers | 10.1007/978-3-319-00458-7_18 |
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