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2016-10-01 | Resonance period is a key parameter in the seismic design of a structure, thus dynamic parameters of buildings in Beirut (Lebanon) were investigated based on ambient vibration method for risk and vulnerability assessment. Lebanon is facing high seismic hazard due to its major faults, combined to a high seismic risk caused by dense urbanization in addition to the lack of a seismic design code implementation. For this study, ambient vibration recordings have been performed on 330 RC buildings, period parameters extracted and statistically analyzed to identify correlations with physical building parameters (height, horizontal dimensions, age) and site characteristics (rock sites or soft sites). The study shows that (1) the building height or number of floors (N) is the primary statistically robust parameter for the estimation of the fundamental period T; (2) the correlation between T and N is linear and site dependent: T ≈ N/23 for rock sites and N/18 for soft sites; (3) the measured damping is inversely proportional to the period: the taller the building the lower is the damping; (4) a significant overestimation of the period exists in current building codes. However part of the large discrepancy with building code recommendations may be due to the very low level of loading. | Seismic response of Beirut (Lebanon) buildings: instrumental results from ambient vibrations | 10.1007/s10518-016-9920-9 |
2016-10-01 | This paper proposes a new criterion for the occurrence of stick–slip vibration in an oscillator excited by a moving belt. Equations of motion were derived for a single-degree-of-freedom oscillator excited by the friction between the oscillator mass and a moving belt, considering two types of velocity-dependent friction models: exponential and polynomial. Based on the derived equations, dynamic responses were analyzed for various damping values, and it was found that the damping value determines the classification of oscillator motion among stick–slip, pure slip, and damped slip motions. Furthermore, a criterion for the occurrence of stick–slip motion, expressed in an integral form, was derived in terms of friction and damping forces. Using the least squares method, closed forms for the damping values to determine the occurrence of stick–slip vibration were obtained as functions of normal force, relative speed between contact surfaces, and friction parameters. In addition, the effects of the belt speed and of friction parameters on the occurrence of stick–slip vibration were also investigated. | Stick–slip vibration of an oscillator with damping | 10.1007/s11071-016-2887-x |
2016-10-01 | Attenuation of a bulk wave, generated by a point source, propagating in an isotropic medium, is due to the geometry and nature of the material involved. In numerical simulations, if the complete domain of propagation is modeled, then it captures the attenuation of a wave caused due to its geometry. To model the attenuation of the wave caused due to the nature of the material, it is required to know the material’s attenuation coefficient. Since experimental measurement on attenuation of a wave involves both the effects of geometry and material, a method based on curve fitting to estimate the material’s attenuation coefficient from effective attenuation coefficient, is proposed. Using the material’s attenuation coefficient in the framework of Rayleigh damping model, numerical modeling on attenuation of both the bulk waves - longitudinal and shear excited by a point source was carried out. It was shown that the proposed method captures the attenuation of bulk waves caused on account of geometry as well as nature of the material. | Attenuation modelling of bulk waves generated by a point source in an isotropic medium | 10.1007/s12206-016-0917-8 |
2016-10-01 | In this paper, we propose a methodology to tune power system stabilizers and thyristor-controlled series capacitor damping controllers simultaneously. The particle swarm optimization algorithm is incorporated into a power system model to tune the parameters of supplementary damping controllers. A test power system of 10 generators, 39 buses and 46 transmission lines is simulated to validate the use of this optimization algorithm. The tuning of supplementary damping controllers using the proposed methodology increases their performance to provide additional damping to low-frequency oscillation modes in the simulated power system. The controller position is determined by the participation factors (power system stabilizers) and the distance between the interest pole and the zero of the open-loop transfer function of the power oscillation damping controller (thyristor-controlled series capacitor-power oscillation damping). The results show the operating efficiency of the power system after using the optimization technique to tune damping parameters, thereby improving power system integrity. The power sensitivity model is used for the simulations presented in this work focusing on the analysis small-signal stability. | Design of PSS and TCSC Damping Controller Using Particle Swarm Optimization | 10.1007/s40313-016-0257-z |
2016-10-01 | Of concern is a structure consisting of two identical beams of uniform thickness. The beams are fastened tightly but still allowing an interfacial slip between the two components. This means that we are in presence of a longitudinal displacement and at the same time keeping a continuous contact of the layers. These beams are also subject to rotatory inertia and shear forces. We prove uniform stability of the system when a viscoelastic damping acts on the effective rotation and in the slip. This extends previous works where boundary controls were used in addition to a frictional damping in the dynamic of the slip. | Uniform Stability of a Laminated Beam with Structural Memory | 10.1007/s12346-015-0147-y |
2016-10-01 | The effect of the damping insertion due to viscoelastic material (VEM) on the dynamic behavior of aluminum panels is assessed in this work. Dynamic mechanical analysis tests are carried out, aiming at characterizing the rheological behavior of a VEM compound. The time–temperature superposition principle is applied and the VEM compound master curve is built over a large frequency range. The parameters of the fractional derivative model are identified from the obtained master curve, and then input in the model. A distributed coating of constrained VEM applied to a homogeneous aluminum plate is considered in this study. In a first step, the responses of this sandwich structure are calculated by using finite element method (FEM). Free and clamped boundary conditions configurations are modeled. In a second step, tests are performed using the KULeuven test facilities by reproducing the same modeled configurations and the experimental frequency response functions (FRF) are measured. To validate the built FEM models, numerical vs. experimental FRF comparisons are done. Despite a slight underestimation of the damping, good agreements were observed in the whole frequency range. | Validating the modeling of sandwich structures with constrained layer damping using fractional derivative models | 10.1007/s40430-016-0533-7 |
2016-10-01 | Effects of temporally correlated infiltration on water flow in an unsaturated–saturated system were investigated. Both white noise and exponentially correlated infiltration processes were considered. The moment equations of the pressure head ( ψ ) were solved numerically to obtain the variance and autocorrelation functions of ψ at 14 observation points. Monte Carlo simulations were conducted to verify the numerical results and to estimate the power spectrum of ψ ( S _ ψψ ). It was found that as the water flows through the system, the variance of the ψ ( $$ \sigma_{\psi }^{2} $$ σ ψ 2 ) were damped by the system: the deeper in the system, the smaller the $$ \sigma_{\psi }^{2} $$ σ ψ 2 , and the larger the correlation timescale of the infiltration process ( λ _ I ), the larger the $$ \sigma_{\psi }^{2} $$ σ ψ 2 . The unsaturated–saturated system gradually filters out the short-term fluctuations of ψ and the damping effect is most significant in the upper part of the system. The fluctuations of ψ is non-stationary at early time and becomes stationary as time progresses: the larger the value of λ _ I , the longer the non-stationary period. The correlation timescale of the ψ ( λ _ ψ ) increases with depth and approaches a constant value at depth: the larger the value of λ _ I , the larger the value of λ _ ψ . The results of the estimated S _ ψψ is consistent with those of the variance and autocorrelation function. | Effects of temporally correlated infiltration on water flow in an unsaturated–saturated system | 10.1007/s00477-015-1119-0 |
2016-10-01 | An approach that can be used for modeling the situation of unanticipated yaw is presented. A software is developed that allows us to obtain the helicopter equilibrium attitude at an arbitrary speed and consider the helicopter dynamics under influence of a certain disturbing factor. | On a certain approach to modeling aerodynamics and dynamics of spatial motion of single rotor helicopters | 10.3103/S1068799816040103 |
2016-10-01 | The stationary response analysis of stochastic vibro-impact (VI) dynamical system with a unilateral nonzero offset barrier and viscoelastic damping under additive and multiplicative random excitations is explored. First, the conversion of the original stochastic VI system coupled with viscoelastic damping into an equivalent stochastic VI system without viscoelastic damping terms is performed by adding the equivalent stiffness and damping. Then, the equivalent stochastic VI system is studied according to the level of system energy instead of non-smooth transformation of the previous literature; thus, description on effects of impacts draws support from the loss of the system energy. The energy loss at each impact is found to be related to the restitution factor and the energy level before impact. Furthermore, the probability density functions of the equivalent VI system based on assumption of the weak damping and random perturbation is produced by the application of the stochastic averaging of energy envelope. The effectiveness of the suggested method is verified by comparing the analytical results with those from Monte Carlo simulations. | Stationary response analysis of vibro-impact system with a unilateral nonzero offset barrier and viscoelastic damping under random excitations | 10.1007/s11071-016-2931-x |
2016-10-01 | The eavesdropping attacks applied in the quantum secret sharing (QSS) protocols through a phase-damping noisy environment are very easy to be realized. In fact, the QSS fidelity has an ordinary behaviour with just one peak according to the noise rate value for many values of the quantum message amplitude. The present work employs a Fock cavity field in such protocols to complicate any eavesdropping attacks through a phase-damping noisy environment. Indeed, only the legitimate users who can adjust the cavity parameters to reach periodically the fidelity peaks. | Exploiting a Fock Cavity Field to Enhance Quantum Secret Sharing Through a Phase-Damping Noisy Channel | 10.1007/s10773-016-3078-8 |
2016-10-01 | In order to reduce structural vibrations in narrow frequency bands, tuned mass absorbers can be an appropriate measure. A quite similar approach which makes use of applied piezoelectric elements, instead of additional oscillating masses, are the well-known resonant shunts, consisting of resistances, inductances, and possibly negative capacitances connected to the piezoelectric element. This paper presents a combined approach, which is based on a conventional tuned mass absorber, but whose characteristics can be strongly influenced by applying shunted piezoceramics. Simulations and experimental analyses are shown to be very effective in predicting the behavior of such electromechanical systems. The vibration level of the absorber can be strongly attenuated by applying different combinations of resistant, resonant, and negative capacitance shunt circuits. The damping characteristics of the absorber can be changed by applying a purely resistive or resonant resistant shunt. Additionally, the tuning frequency of the absorber can be adapted to the excitation frequency, using a negative capacitance shunt circuit, which requires only the energy to supply the electric components. | Tuning of a vibration absorber with shunted piezoelectric transducers | 10.1007/s00419-014-0972-5 |
2016-10-01 | The Bouc–Wen model was used to investigate nonlinear dynamical behavior of a wire-rope isolator and an asymmetric Stockbridge damper. The experimental vibration signals were acquired through accelerometers placed along the sample. The wire-rope isolator system was excited using and electromechanical shaker with constant values of acceleration, and the Stockbridge damper was excited using a cam machine with different profiles. The numeric and experimental data were approximated using particle swarm optimization method. The agreement between numerical and experimental data show that the model of Bouc–Wen is well suited for dynamic analysis of such systems. | Nonlinear dynamic analysis of wire-rope isolator and Stockbridge damper | 10.1007/s11071-016-2903-1 |
2016-10-01 | Virtual simulation and optimization of the dynamic behavior of machine tools in the development phase is required to satisfy the increasing demands on machine tool performance. While mass and stiffness properties can be simulated with sufficient accuracy, often no suitable damping models are available for the components of machine tools. The commonly used linear damping models are predominantly linear hysteretic or viscous models. However, the linear damping models are often not appropriate to reflect the occurring nonlinear effects in machine tools with the required accuracy. The reason for these nonlinearities are predominantly the friction forces in feed drive components. To resolve these deficits, the friction in feed drive components is comprehensively investigated in this paper, models for friction forces are identified and coupled with a reduced, flexible multi-body system. With the identified friction models the measured friction curves can be reproduced very precisely. The coupled, reduced, flexible multi-body model allows to simulate the nonlinear effects and to predict the dynamic behavior of machine tools with high accuracy. Consequently, a further important step towards accurate virtual simulation of machine tools is made. | Friction in feed drives of machine tools: investigation, modeling and validation | 10.1007/s11740-016-0678-3 |
2016-10-01 | The present paper is devoted to an investigation on the asymptotic stability for the damped oscillators with multiple degrees of freedom, $$\begin{aligned} {\mathbf {x}}'' + h(t)\,{\mathbf {x}}' + A\,{\mathbf {x}} = {\mathbf {0}} \end{aligned}$$ x ′ ′ + h ( t ) x ′ + A x = 0 and its generalization $$\begin{aligned} M\,{\mathbf {x}}'' + C(t)\,{\mathbf {x}}' + K\,{\mathbf {x}} = {\mathbf {0}}, \end{aligned}$$ M x ′ ′ + C ( t ) x ′ + K x = 0 , where $$h: [0,\infty ) \rightarrow [0,\infty )$$ h : [ 0 , ∞ ) → [ 0 , ∞ ) is a function, A , M and K are $$n \times n$$ n × n real constant matrices. and C is an $$n \times n$$ n × n matrix whose elements are real-valued functions. The functions h and C correspond to the damping coefficient and the damping matrix, respectively. The origin $$({\mathbf {x}},{\mathbf {x}}') = ({\mathbf {0}},{\mathbf {0}})$$ ( x , x ′ ) = ( 0 , 0 ) is the only equilibrium of the above-mentioned damped oscillators. Necessary and sufficient conditions are presented for the equilibrium of these oscillators to be asymptotically stable. The obtained conditions are given by the forms of certain growth conditions concerning the damping h and C , respectively. | Asymptotic Stability of Coupled Oscillators with Time-Dependent Damping | 10.1007/s12346-015-0175-7 |
2016-10-01 | Machine tools are generally used with process parameters that are as productive as possible yet stable. One way to raise productivity is to increase the process parameters like cutting speed or depth of cut (DOC). However, this approach will lead to process instabilities sooner or later. An increased rotational speed of the spindle will excite higher eigenfrequencies depending on the tools teeth count. In combination with higher cutting forces resulting from a deeper DOC, the process can become instable because of chatter or other oscillations and vibrations of the machine tool. This paper describes the identification of a critical eigenfrequency and corresponding eigenmode. An active damper was then developed to mitigate the negative effect this critical eigenfrequency has including a robust controller which protects the process from instabilities through changing eigenfrequencies caused by changing machine positions. It will also enable increased process parameters for a higher productivity of the machine tool. A simulation environment of the active damping system with a classic control and a robust $$\mu$$ μ -control was developed. The damper was applied to the machine tool and tested. | Simulation and development of an active damper with robust μ-control for a machine tool with a gantry portal | 10.1007/s11740-016-0691-6 |
2016-10-01 | This study investigated the damping effects of a tuned mass damper (TMD) on a fixed-free 3D nonlinear beam resting on a nonlinear elastic foundation with existing internal resonances. The nonlinear elastic foundation below ( y -direction) and beside ( z -direction) the nonlinear beam was simulated using cubic nonlinear springs via the method of multiple scales for the analysis of this problem. We first examined this system to ensure if the internal resonance exists. The 1:3 internal resonance was found in the 1st and 2nd modes of the system. This prompted us to add a TMD on the elastic beam in order to suppress internal resonance and vibrations. We also examined the influence of the mass and location of the TMD as well as damping and spring coefficients on the damping effects. Analysis data is presented in graphs, including 3D maximum amplitude plots of the modes and 3D maximum amplitude contour plots. Our results show that placing the TMD in the y -direction also suppresses vibrations in the z -direction. The locations of the maximum amplitudes between node points in the mode shapes and near the free end of the beam indicate where the TMD should be placed with regard to damping. | Influence of tuned mass damper on fixed-free 3D nonlinear beam embedded in nonlinear elastic foundation | 10.1007/s11012-016-0372-8 |
2016-09-22 | In this paper, we are concerned with the general decay result of the quasi-linear wave equation for Kirchhoff type containing Balakrishnan-Taylor damping with a delay in the boundary feedback and acoustic boundary conditions. | General decay of solutions for Kirchhoff type containing Balakrishnan-Taylor damping with a delay and acoustic boundary conditions | 10.1186/s13661-016-0679-3 |
2016-09-01 | In this work, we present an analytical and numerical study of the Korteweg-de Vries (KdV) equation on a bounded domain in the presence of a dissipation mechanism. We present results on the existence and uniqueness of strong solutions using the Faedo–Galerkin method and studying a regularized version of the KdV equation. We also analyze the influence of this dissipation mechanism on the system energy. We introduce a numerical method based on a finite element discretization in space using Hermite polynomials as basis functions and the Crank–Nicolson finite difference scheme in time. Error estimates in Sobolev space for both the semi and fully-discrete problems are presented. Numerical simulations are also included in order to illustrate the applicability of the method. They also show the influence of the dissipative mechanism on the energy of the system. | Analysis and computation of a nonlinear Korteweg-de Vries system | 10.1007/s10543-015-0589-2 |
2016-09-01 | We report on a novel technique to measure quartz tuning forks, and possibly other vibrating objects, in a quantum fluid using a multifrequency lock-in amplifier. The multifrequency technique allows to measure the resonance curve of a vibrating object much faster than a conventional single frequency lock-in amplifier technique. Forks with resonance frequencies of 12 kHz and 16 kHz were excited and measured electro-mechanically either at a single frequency or at up to 40 different frequencies simultaneously around the same mechanical mode. The response of each fork was identical for both methods and validates the use of the multifrequency lock-in technique to probe properties of liquid helium at low fork velocities. Using both methods we measured the resonance frequency and drag of two 25- $$\upmu $$ μ m-wide quartz tuning forks immersed in liquid $$^4$$ 4 He in the temperature range from 4.2 K to 1.5 K at saturated vapour pressure. The damping and shift of resonance frequency experienced by both tuning forks at low velocities are well described by hydrodynamic contributions in the framework of the two-fluid model. The sensitivity of the 25- $$\upmu $$ μ m-wide tuning forks is larger compared to similar 75- $$\upmu $$ μ m-wide forks and in combination with the faster multifrequency lock-in technique could be used to improve thermometry in liquid $$^4$$ 4 He. The multifrequency technique could also be used for studies of the onset of non-linear phenomena such as quantum turbulence and cavitation in superfluids. | Probing Liquid
$$^4$$
4
He with Quartz Tuning Forks Using a Novel Multifrequency Lock-in Technique | 10.1007/s10909-016-1634-5 |
2016-09-01 | The viability of a complete structural characterization of civil structures is explored and discussed. In particular, the identification of modal (i.e. natural frequencies, damping ratios and modal shapes) and physical properties (i.e. mass and stiffness) using only the structure’s free decay response is studied. To accomplish this, modal analysis from free vibration response only (MAFVRO) and mass modification (MM) methodologies are engaged along with Wavelet based techniques for optimal signal processing and modal reconstruction. The methodologies are evaluated using simulated and experimental data. The simulated data are extracted from a simple elastic model of a 5 story shear building and from a more realistic nonlinear model of a RC frame structure. The experimental data are gathered from shake table test of a 2-story scaled shear building. Guidelines for the reconstruction procedure from the data are proposed as the quality of the identified properties is shown to be governed by adequate selection of the frequency bands and optimal modal shape reconstruction. Moreover, in cases where the structure has undergone damage, the proposed identification scheme can also be applied for preliminary assessment of structural health. | Output-only identification of the modal and physical properties of structures using free vibration response | 10.1007/s11803-016-0345-x |
2016-09-01 | This paper presents an experimental setup aiming at evaluating the magneto-mechanical and damping properties of the thermoplastic magnetorheological elastomer (MRE). The idea of the system is to create controllable conditions similar to those present in a vehicles and other mechanical constructions and to make it possible to determine parameters only relating to the MRE material itself. The test stand is based on four samples stimulated with highly effective Halbach arrays. The upper plate of the test stand is excited with use of a modal shaker to assure a constant impact force value during each test. This enables control of impact character and allows automation of the test stand. The last section of this paper presents preliminary test conducted to find the resonance frequency dependence on the impact force of the system for a constant value of magnetic field. The results indicate nonlinear behavior of the material and therefore exclude use of the simple Kelvin-Voight model based approach for damping properties determination, that is a commonly used model for description of different materials. | Test setup for examination of magneto-mechanical properties of magnetorheological elastomers with use of a novel approach | 10.1016/j.acme.2015.12.002 |
2016-09-01 | The present study evaluates the role of the microstructure in the static and dynamic mechanical behavior of as-cast Al7075 alloy promoted by ultrasonic treatment (US) during solidification. The characterization of samples revealed that US treatment promoted grain and intermetallics refinement, changed the shape of the intermetallic phases (equilibrium phases of soluble M and/or T (Al, Cu, Mg, Zn) and their insoluble Al-Cu-Fe compounds) and lead to their uniform distribution along the grain boundaries. Consequently, the mechanical properties and damping capacity above critical strain values were enhanced by comparison with values obtained for castings produced without US vibration. This results suggest that the grain and secondary phases refinement by US can be a promising solution to process materials to obtain high damping and high strength characteristics. | Effect of grain and secondary phase morphologies in the mechanical and damping behavior of Al7075 alloys | 10.1007/s12540-016-6073-y |
2016-09-01 | An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current (HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance. | Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability | 10.1007/s11771-016-3283-x |
2016-09-01 | A method for identification of the elastic and damping properties of soft materials in tension–compression and shear in a composition with a rigid (base) material is proposed. The method is based on the analysis of the lowest free vibration frequencies and amplitude dependences of internal damping parameters of three-layer test specimens of an appropriate structure: the base material is placed in the middle of the specimens for tension–compression, but as outer layers for shear. Identification of the elastic properties in tension−compression and shear is based on a comparison of calculated and experimental frequencies of corresponding test specimens. It is shown that the elastic properties found for a technical rubber depends on vibration frequencies of the test specimen. A quadratic functional containing experimental and calculated parameters of internal damping of test specimens is employed to identify the damping properties of soft materials. A three-layer finite element developed for this purpose is proposed for a numerical evaluation of the design parameters of internal damping of a three-layer test specimen. Calculations were carried out to identify the damping characteristics of the technical rubber in tension–compression and shear from the parameters of internal damping of test specimens with a D16AT aluminum alloy as the base material. | Identification of the Elastic and Damping Characteristics of Soft Materials Based on the Analysis of Damped Flexural Vibrations of Test Specimens | 10.1007/s11029-016-9596-x |
2016-09-01 | Transport models allowing for cost damping are characterised by marginally decreasing cost sensitivities in demand. As a result, cost damping is a model extension of the simple linear-in-cost model requiring an appropriate non-linear link function between utility and cost. The link function may take different forms and be represented as a non-linear-in-parameter form such as the well-known Box–Cox function. However, it could also be specified as non-linear-in-cost but linear-in-parameter forms, which are easier to estimate and improve model fit without increasing the number of parameters. The specific contributions of the paper are as follows. Firstly, we discuss the phenomenon of cost damping in details and specifically why it occurs. Secondly, we provide a test of damping and an easy assessment of the (linear) damping rate for any variable by estimating two auxiliary linear models. This turns out to be an important guidance as the damping rate largely dictates which link functions are appropriate for the data. Thirdly, inspired by the Box–Cox function, we propose alternative linear-in-parameter link functions, some of which are based on interpolation of approximate Box–Cox end points, and others which are inspired by Taylor Expansions. The different functions are tested in simulation experiments and subsequently in a large-scale demand model based on more than 22,000 revealed preference observations. It is concluded that the use of properly specified linear-in-parameter functions gives good data fit and sometimes even outperforms the Box–Cox functions without increasing the number of parameters. | Cost damping and functional form in transport models | 10.1007/s11116-015-9628-8 |
2016-09-01 | Metal/polymer-combined macro-composite structures are representative of a unique combination to achieve improved quality of products. In this work, a non-traditional method for manufacturing metal/polymer-combined sandwich structure for vibration damping was generated from a traditional method, plastic injection molding, which is then called plastic injection forming (PIF). In the experimental study, aluminum plates with dimensions for the metal part of the macro-composite and three different types of polymeric material were used for the core of the sandwich structure: polypropylene, nano-titan dioxide-added polypropylene, and thermoplastic elastomer (TPE). For determining flexural strength of macro-composite structures, a 3-point bending test was applied. Finite element analysis by commercial ANSYS code was utilized to compare the bending results with finite element method (FEM). Force transmissibility test was performed in order to define damping characteristics of the macro-composite structures. The damping ratio of each structure was figured out by performing frequency analysis. Finally, damping characteristics of these composite structures were discussed by comparing their damping ratios. | Manufacturing polymer/metal macro-composite structure for vibration damping | 10.1007/s00170-015-8259-8 |
2016-09-01 | Vibrations are very prejudicial to machining as they directly affect the dimensional accuracy and surface roughness of the machined part. Excessive vibration must be avoided or at least reduced. This can be achieved in several ways, including the use of dampers and more rigid material for tool holders. Tool vibration is stimulated in internal turning by the cantilever shape of the tool and the large tool overhang used, impairing the quality of the turned part. This is a serious problem in the turning of hardened steel because internal turning is usually the last operation carried out on the surface, making tight tolerances and low surface roughness values necessary. Excessive vibrations would harm the surface finish and could lead to tool breakage because of the low toughness of the tool materials used for this kind of application. The main objective of this work was therefore to identify alternative approaches for finishing internal turning of long holes in hardened steel parts. Different tool holder materials (steel and cemented carbide) and a particle impact damped steel tool holder were tested to determine the longest overhang that could be achieved in each configuration. The results showed that carbide bars reduced vibrations and allowed longer overhangs to be used. Particle impact dampers may be a simple alternative to the more expensive carbide bars. | The use of carbide and particle-damped bars to increase tool overhang in the internal turning of hardened steel | 10.1007/s00170-015-8328-z |
2016-09-01 | Regenerative chatter in machining process is a root cause for tool wear and poor surface finish resulting in low production rate. Hence research has to be focused to identify an opportunity to suppress these chatters. This investigation is attempted to reduce the tool wear in boring process by incorporation of shape memory alloy (SMA) mass dampers in boring tool. The copper and Zinc based SMA mass dampers were placed at various position of boring bar and the effect of damper position and machining parameters on the tool wear was studied. Boring process was carried out on grey cast iron pipe by varying the damper position (54, 64 and 74 mm), cutting velocity (25, 50 and 75 m/min) and depth of cut (0.2, 0.4 and 0.6 mm). The prediction model was developed to correlate the relationship between machining parameters and tool wear. The optimum damper position and machining parameters to minimize the tool wear was determined using response surface methodology (RSM). The confirmation test on the optimized value has witnessed efficient prediction of the damper position and machining parameters for reduced tool wear in boring process. | Modeling and Optimization of Tool Wear in a Passively Damped Boring process using Response Surface Methodology | 10.1007/s12666-015-0707-5 |
2016-09-01 | The main intention of the present study is to reduce wind, wave, and seismic induced vibrations of jackettype offshore wind turbines (JOWTs) through a newly developed vibration absorber, called tuned liquid column gas damper (TLCGD). Using a Simulink-based model, an analytical model is developed to simulate global behavior of JOWTs under different dynamic excitations. The study is followed by a parametric study to explore efficiency of the TLCGD in terms of nacelle acceleration reduction under wind, wave, and earthquake loads. Study results indicate that optimum frequency of the TLCGD is rather insensitive to excitation type. In addition, while the gain in vibration control from TLCGDs with higher mass ratios is generally more pronounced, heavy TLCGDs are more sensitive to their tuned frequency such that ill-regulated TLCGD with high mass ratio can lead to destructive results. It is revealed that a well regulated TLCGD has noticeable contribution to the dynamic response of the JOWT under any excitation. | Contribution of tuned liquid column gas dampers to the performance of offshore wind turbines under wind, wave, and seismic excitations | 10.1007/s11803-016-0343-z |
2016-09-01 | A new response-spectrum mode superposition method, entirely in real value form, is developed to analyze the maximum structural response under earthquake ground motion for generally damped linear systems with repeated eigenvalues and defective eigenvectors. This algorithm has clear physical concepts and is similar to the complex complete quadratic combination (CCQC) method previously established. Since it can consider the effect of repeated eigenvalues, it is called the CCQC-R method, in which the correlation coefficients of high-order modal responses are enclosed in addition to the correlation coefficients in the normal CCQC method. As a result, the formulas for calculating the correlation coefficients of high-order modal responses are deduced in this study, including displacement, velocity and velocity-displacement correlation coefficients. Furthermore, the relationship between high-order displacement and velocity covariance is derived to make the CCQC-R algorithm only relevant to the high-order displacement response spectrum. Finally, a practical step-by-step integration procedure for calculating high-order displacement response spectrum is obtained by changing the earthquake ground motion input, which is evaluated by comparing it to the theory solution under the sine-wave input. The method derived here is suitable for generally linear systems with classical or non-classical damping. | Complex complete quadratic combination method for damped system with repeated eigenvalues | 10.1007/s11803-016-0342-0 |
2016-08-05 | We investigate the asymptotic behavior of solutions of the non-autonomous Navier-Stokes equation with nonlinear damping in three-dimensional bounded domain. When 3 < β ≤ 5 $3< \beta\leq5$ , the existence of pullback attractors is proved in V and H 2 ( Ω ) $\mathbf{H}^{2}(\Omega)$ , respectively. | Pullback
D
$\mathcal{D}$
-attractors for three-dimensional Navier-Stokes equations with nonlinear damping | 10.1186/s13661-016-0654-z |
2016-08-01 | To date, nonlinear dynamic analysis for seismic engineering predominantly employs the classical Rayleigh damping model and its variations. Though earlier studies have identified issues with the use of this model in nonlinear seismic analysis, it still remains the popular choice for engineers as well as for software providers. In this paper a new approach to modelling damping is initiated by formulating the damping matrix at an elemental level. To this regard, two new elemental level discrete damping models adapted from their global counterparts are proposed for its application in nonlinear dynamic analysis. Implementation schemes for these newly proposed models using Newmark incremental method and revised Newmark total equilibrium method is outlined. The performance of these proposed models, compared to existing models, is illustrated by conducting nonlinear dynamic analyses on a four story RC frame designed to Eurocodes. The incremental dynamic analysis study presented in the paper illustrates the fact that both the proposed models seem to produce more reliable results from an engineering perspective in comparison to the global models. It is also shown that the proposed elemental damping models lead to smaller and more realistic damping moments in the plastic hinges. Furthermore, these models could be easily included in existing software frameworks without adding noticeably to the computational effort. The computation time required for these models is approximately equivalent to the one required when using the tangent Rayleigh damping matrix with constant coefficients. | Elemental damping formulation: an alternative modelling of inherent damping in nonlinear dynamic analysis | 10.1007/s10518-016-9904-9 |
2016-08-01 | Characteristics of El Niño-Southern Oscillation (ENSO) have changed since the late 1970s as it synchronized with the Pacific Decadal Oscillation (PDO). In order to investigate the primary feedback process responsible for the interdecadal change in ENSO characteristics according to the PDO, using the ocean assimilation data (SODA) and the reanalysis data (NCEP/NCAR), we performed Bjerknes linear stability index (BJ index) analysis of two decadal periods: one before the late 1970s (the nPDO period) and the other after the late 1970s (the pPDO period). The BJ index for the pPDO period (−0.07 year^−1 for the growth rate of the eastern Pacific SST anomaly) is significantly larger than that for the nPDO period (−0.25 year^−1). The larger BJ index value is primarily due to the enhanced zonal advection feedback (ZA; +0.44 year^−1), thermocline feedback (TH; +0.33 year^−1), and the reduced damping by the mean meridional current (MD; +0.16 year^−1). The increases in ZA and TH are mainly attributed to the shoaling of the mean thermocline depth, which increased the sensitivity of the ocean dynamic fields to the wind forcing; and the reduced MD is related to the reduced mean meridional current associated with the weakened trade wind. The enhanced positive feedback is partly compensated by the enhanced thermodynamic damping including the shortwave, sensible heat flux and latent heat flux (collectively, −0.88 year^−1). Interestingly, the change in air–sea coupling strength from the nPDO to the pPDO period was small. Without the two extreme El Niño events (1982–1983 and 1997–1998) in the pPDO period (pPDO_noBIG), the difference in BJ index between nPDO and pPDO_noBIG periods became smaller (~0.07 year^−1), indicating that the two extreme El Niño events largely contribute to the larger ENSO variability of the pPDO period, possibly due to nonlinear feedback processes. Nevertheless, qualitative similarity in each of the feedback and damping components of BJ index exists between the pPDO and pPDO_noBIG periods, which suggests that the tropical climate states of the pPDO period provided more favorable conditions for the emergence of extreme El Niño events by intensifying the linear feedback processes. | Inter-decadal change in El Niño-Southern Oscillation examined with Bjerknes stability index analysis | 10.1007/s00382-015-2883-8 |
2016-08-01 | Linear prediction methods, based on a Hankel data matrix, suffer from subspace leakage and degraded resolution when applied to data models that do not result in a mode matrix with Vandermonde structure, such as the constant- Q model. In the absence of noise, the Vandermonde structure ensures the equivalence between the number of backscattered signals and the rank of the data matrix. This paper first identifies the origin of subspace leakage residing in subspace-based and linear prediction methods when applied to data of the constant- Q model. Second, it proposes a frequency-distortion technique, based on the extension theorems, for suppressing the leakage and preserving the time resolution performance of these methods. The effectiveness of the distortion technique is then demonstrated on GPR simulated data by extending the damped MUSIC algorithm to the joint parameter estimation of the constant- Q model. | Subspace Leakage Suppression for Joint Parameter Estimation of Quality Factors and Time Delays in Dispersive Media | 10.1007/s00034-015-0180-8 |
2016-08-01 | In the article, the application of the electrical spike, instead of the tone-burst, to the ultrasonic pulsed-Doppler velocity profiling the first time is presented. To generate ultrasound, the ultrasonic sensor is excited by the spike. For the Doppler method, the spike excitation was not used previously. It has been used with wideband signal processing methods. In our study, first, the fluid-velocity profile measurement using spike excitation has been carried out for single-phase pipe flow. The received data have been validated by the logarithmic law of the wall, for turbulent flow regime. The flow rate calculated by using the mean velocity profile well coincides with the flow-meter data. Furthermore, the spike signal and the Doppler method are used in the multiwave ultrasonic velocity profile (UVP) method, for the bubbly flow measurement. The experiments show that, if the spike signal is slowly damped, the generated ultrasonic wave is similar to the tone-burst that is required for the Doppler method, but in this case, usually the pulse length is smaller and depends on the damping and sensor characteristics. The autocorrelation technique is used for echo signal processing. The derived UVP systems inherit the advantages from both the spike excitation and Doppler method. | Ultrasonic Doppler Velocity Profile Measurement of Single-and Two-Phase Flows Using Spike Excitation | 10.1007/s40799-016-0123-8 |
2016-08-01 | This paper presents a new direct modeling approach to analyze 3D dynamic SSI systems including building structures resting on shallow spread foundations. The direct method consists of modeling the superstructure and the underlying soil domain. Using a reduced shear modulus and an increased damping ratio resulted from an equivalent linear free-field analysis is a traditional approach for simulating behavior of the soil medium. However, this method is not accurate enough in the vicinity of foundation, or the near-field domain, where the soil experiences large strains and the behavior is highly nonlinear. This research proposes new modulus degradation and damping augmentation curves for using in the near-field zone in order to obtain more accurate results with the equivalent linear method. The mentioned values are presented as functions of dimensionless parameters controlling nonlinear behavior in the near-field zone. This paper summarizes the semi-analytical methodology of the proposed modified equivalent linear procedure. The numerical implementation and examples are given in a companion paper. | The near-field method: a modified equivalent linear method for dynamic soil–structure interaction analysis. Part I: Theory and methodology | 10.1007/s10518-016-9935-2 |
2016-08-01 | Improvements in the National Primary Standard for the Units of the Propagation Velocities of Longitudinal, Shear, and Surface Ultrasonic Waves in Solids are discussed. A new standard apparatus for reproduction of the unit of the damping coefficient for longitudinal ultrasonic waves is described. It is based on contactless capacitive methods for generating ultrasonic waves and pulse-echo and resonance measurement techniques for receiving them. The metrological characteristics of the National Primary Standard for the Units of the Propagation Velocities and Damping Coefficient of Ultrasonic Waves in Solids, GET 189-2014, are given. | National Primary Standard for the Units of the Propagation Velocities and Damping Coefficient of Ultrasonic Waves in Solids Get 189-2014 | 10.1007/s11018-016-0990-5 |
2016-08-01 | The parametric rolling (PR) in the head or following waves has been considered as one of the main stability failure modes in the development of the 2nd generation Intact Stability criterion by the International Maritime Organization (IMO). According to previous studies, the estimation methods of the roll damping affect the prediction of the PR significantly, and most of them are based on experiment data or Ikeda’s empirical formula. The accuracy of the estimation method for the roll damping could be a key aspect for the validity of its prediction for the full scale ship. In this research, a hybrid prediction method is developed for the numerical prediction of the parametric rolling when experiment data are not available for the roll damping. Comparison study is also carried out between the hybrid method and a nonlinear dynamics method, where the roll damping is estimated by the simplified Ikeda’s method and the direct CFD prediction method in a direct non-linear simulation based on the 3-D CFD approach in the model scale. It is shown that the results of the hybrid method are in satisfactory agreements with the model experiment results, and the method can be used for analysis especially at the early design stage where experiment data are often not available. | A study of hybrid prediction method for ship parametric rolling | 10.1016/S1001-6058(16)60666-2 |
2016-08-01 | This paper aims to investigate the strongly nonlinear vibro-impact dynamic system with fractional derivative damping under Gaussian white noise excitation, and this system considers both nonlinear factors and non-smooth factors. With the help of non-smooth transformation, the original system is rewritten as a smooth system, which is an easier handled form. For the altered function, we obtain the approximate stationary solutions analytically by generalized stochastic averaging method. To prove the validity of the approximate analytical methods, an efficient scheme with high accuracy is adopt to simulate the fractional derivative, then the fourth-order Runge–Kutta approach is used to obtain the numerically response statistics. Meanwhile the analytical solutions are verified by the numerical simulation solutions. At last, we research the responses of this system. In this context, we can consider the influences to this system caused by the fractional order, the restitution coefficient and the noise intensity through changing the values of corresponding parameters. The observation and investigation state that fractional derivative term, impact conditions and stochastic excitation can influence the responses of the fractional vibro-impact dynamic system. | Response of strongly nonlinear vibro-impact system with fractional derivative damping under Gaussian white noise excitation | 10.1007/s11071-016-2808-z |
2016-08-01 | The dynamic shear modulus G of soil was determined using a dynamic triaxial test system (DTTS) together with a fitting method. First, a novel linear relationship between G and damping ratio λ was proposed, which was used to select the appropriate G . Then, a hyperbolic model was constructed using the optimized parameters a and b representing the intercept and slope, respectively, from the linear regression of 1/ G and dynamic shear strain γ _d. Finally, the differences between the tested and predicted results for G were analyzed for different soil types. The experimental results show that this linear relationship can overcome the shortcomings of the nonlinear relationship found in the large deformation stage and can predict λ in the hysteresis loop that is not closed case. In addition to Baoji loess, G was slightly larger (10%) than the experimental curve in the elasto-plastic stage; however, the experimental results show that the attenuation curve of G for Baoji loess is greater than the calculated value in the elasto-plastic stage. The test and analysis results will improve the knowledge of the dynamic properties of soils and also provide reliable values of G for further evaluation of seismic safety at engineering sites. | A novel linear relationship for calculating dynamic shear modulus of geomaterials | 10.1007/s11595-016-1456-y |
2016-08-01 | To reduce vibration and impact loads, a gas–hydraulic damper is proposed. Its working element is a magnetic rheological liquid. | Impact-load damping by integral hydraulic bearings | 10.3103/S1068798X16080098 |
2016-07-05 | A method to model and minimize resonant structural oscillations using magnetorheological dampers is presented. The response of the magnetorheological fluid flowing in a circular tube under a pressure gradient to the applied variable magnetic field is tailored to determine the optimum stress field in the fluid to mitigate resonance effects. | Resonance modeling and control via magnetorheological dampers | 10.1007/s00033-016-0674-7 |
2016-07-01 | The study is concerned with isolation performance of a velocity-displacement-dependent (VDD) nonlinear damping, which has arbitrary nonnegative velocity exponent and displacement exponent. Displacement transmissibility of a single-degree-of-freedom (SDOF) vibration system with proposed damping under base excitation is investigated. The implicit amplitude-frequency equation is derived by using the averaging perturbation method. The stability analysis for both integer power law damping and rational powers less than unity in the nonlinearities is performed. The relative and absolute displacement transmissibility is obtained to evaluate the isolation performance. Parametric analysis is carried out to study the influence of damping parameters on the transmissibility. It shows that the proposed damping can not only suppress the response at resonance but also improve isolation performance at high frequencies if the velocity and displacement exponent as well as damping coefficient satisfy some conditions. The condition of a VDD damping that is independent on the excitation amplitude is obtained. Experimental investigation is performed by using a SDOF base excited vibration isolation system possessing a simple velocity feedback control active damper to reproduce the proposed nonlinear damping. The measured results are shown to be in good agreement with theoretical predictions thereby verifying the effects of VDD damping undergoing base excitation. The investigation is capable to enhance understanding of the effects of VDD damping, which will set a foundation for the design and exploitation on beneficial effects of this damping for vibration isolation in engineering systems. | The isolation performance of vibration systems with general velocity-displacement-dependent nonlinear damping under base excitation: numerical and experimental study | 10.1007/s11071-016-2722-4 |
2016-07-01 | A theoretical and experimental method for determining the elastic and damping characteristics of materials is proposed based on analysis of vibrograms of damping flexural vibrations of test specimens with different structures. It is shown that during tension–compression and shear of a carbon fiber-reinforced plastic made of Porcher 3692 carbon fabric and EDT-69NM polymer binder, its dynamic elastic modulus decreases considerably with increasing frequency of deformation in the range of 0–120 Hz. The amplitude dependences of the logarithmic vibration decrements of the carbon fiber-reinforced plastic are determined by minimizing the discrepancy between the experimental and calculated internal-damping parameters of the test specimens in tension–compression and shear. | Identification of the elastic and damping characteristics of carbon fiber-reinforced plastic based on a study of damping flexural vibrations of test specimens | 10.1134/S0021894416040179 |
2016-07-01 | A new method to suppress conductor galloping with a roller damper as a component of a vibration isolation system is proposed. The dynamic behavior of the system is mathematically modeled taking into account the turn of the system together with damper due to the vertical deviation of the insulator set. The frequency response equation of the system is derived using a linear problem statement. A combined numerical/graphical method to tune the roller damper in frequency and amplitude is proposed. The roller damper provides a good damping effect by reducing the angle of deviation of the insulator chain by 80% | Effectiveness of a Roller Damper in Suppressing Conductor Galloping | 10.1007/s10778-016-0767-1 |
2016-07-01 | In machining titanium alloy as difficult-to-cut or hard materials, productivity is limited because of low heat conductivity at high spindle speed. Process damping is a damping mechanism during the machining process that can be exploited to improve the limited productivity in machining titanium alloy at low cutting speed. In the present study, experiments are performed to evaluate the wavelength performance of process-damped milling under irregular tool geometries such as uniform, variable helix, variable pitch, and variable helix/variable pitch. The effects of radial immersion, feed rate, depth of cut, and surface velocity as process parameters are also studied. By using flexible workpiece conditions, all tools are tested in machining titanium alloy at low speed to encourage the process damping phenomena. The wavelength performances are calculated on the basis of the chatter frequency domain analysis extracted from the acceleration signal in the time domain during the cutting process. The effect of irregular tool geometries shows that variable helix and variable pitch tools have the best wavelength performance compared with regular and other irregular tools. The effect of process parameters reveals that the radial depth of cut can also improve the process damping wavelength compared with regular tools. Irregular milling tool geometries with spindle speed and feed rate parameters can be used to suppress the chatter by exploiting the process damping behavior, thus improving machining productivity. | Effects of irregular tool geometry and machining process parameters on the wavelength performance of process damping in machining titanium alloy at low cutting speed | 10.1007/s00170-015-7906-4 |
2016-07-01 | Both the seat and cab system of truck play a vital role in ride comfort. The damping matching methods of the two systems are studied separately at present. However, the driver, seat, and cab system are one inseparable whole. In order to further improve ride comfort, the seat suspension is regarded as the fifth suspension of the cab, a new idea of “Five-suspensions” is proposed. Based on this idea, a 4 degree-of-freedom driver-seat-cab coupled system model is presented. Using the tested cab suspensions excitations as inputs and seat acceleration response as compared output, the simulation model is built. Taking optimal ride comfort as target, a new method of damping collaborative optimization for Five-suspensions is proposed. With a practical example of seat and cab system, the damping parameters are optimized and validated by simulation and bench test. The results show the seat vertical frequency-weighted RMS acceleration values tested for the un-optimized and optimized Five-suspensions are 0.50 m/s^2 and 0.39 m/s^2, respectively, with a decrease by 22.0%, which proves the model and method proposed are correct and reliable. The idea of “Five-suspensions” and the method proposed provide a reference for achieving global optimal damping matching of seat suspension and cab suspensions. | Damping collaborative optimization of five-suspensions for driver-seat-cab coupled system | 10.3901/CJME.2016.0201.018 |
2016-07-01 | We propose a new optical field named Laguerre-polynomial-weighted two-mode squeezed state. We find that such a state can be generated by passing the l -photon excited two-mode squeezed vacuum state C _ l a ^† l S _2|00〉 through an single-mode amplitude damping channel. Physically, this paper actually is concerned what happens when both excitation and damping of photons co-exist for a two-mode squeezed state, e.g., dessipation of photon-added two-mode squeezed vacuum state. We employ the summation method within ordered product of operators and a new generating function formula about two-variable Hermite polynomials to proceed our discussion. | Laguerre-Polynomial-Weighted Two-Mode Squeezed State | 10.1007/s10773-016-2962-6 |
2016-07-01 | Coupled vibrations may occur between ship lift structure and the ship chamber during seismic process due to the ship chamber being hung at the roof of the ship lift. An investigation is carried out to explore the possibility of using different devices to connect the ship lift towers and the ship chamber to prevent the coupled vibrations. A three-dimensional shell finite element model is established, and then simplified into a three-dimensional truss finite element model through dynamic equivalent principle. And the numerical model of coupled vibration analysis is formed through static condensation, calculating the coupled vibration response between the ship lift structure and the ship chamber under five connection conditions: no connection, rigid connection, spring, viscous liquid damper and magneto-rheological fluid damper. The result shows that no connection and rigid connection between them are both inadvisable; the magneto-rheological fluid damper provides better vibration damping effect if suitable semi-active control strategy is applied, in comparison with passive control devices. | Analysis and Control of the Coupled Vibration Between the Ship Lift and Ship Chamber | 10.1007/s40999-016-0041-2 |
2016-07-01 | The interaction of the ride and handling systems is one of the challenging topics in vehicle dynamics and control. In this study the dynamic behavior of a passenger car considering coupling among all the fourteen degrees of freedom is modeled using Boltzmann Hamel equations. In order to improve the ride quality and stability of the vehicle, a Magnetorheological damper and a differential braking system are used as control devices. Based on the nonlinear integrated ride and handling vehicle model, a nonlinear H-infinity controller is designed for an intermediate passenger car. The dynamic behavior of the controlled vehicle is simulated for single lane change and bump input, considering three different road conditions: Dry, rainy and snowy. The robustness of the designed controller is investigated when the vehicle is under these road conditions. The simulation results confirm the interactive nature of the ride and handling systems and the robustness of the designed control strategy. | Robust control of nonlinear integrated ride and handling model using magnetorheological damper and differential braking system | 10.1007/s12206-016-0601-z |
2016-07-01 | In recent years, ground vibration has become a popular research topic due to the growing construction close to vibration sources and the attentiveness of people about living conditions. Thus, vibrations caused by the passage of the train near buildings play an important role. In prediction of train-induced vibrations, many experimental and theoretical methods have been proposed. In order to study the vibration near the railway at Qaemshahr, a 2D finite element analysis employed for modeling of the train movement and its effect on the adjacent building. The validation of the numerical model was done by the high-speed train running measurements. The results show that the vibration level decreases by increasing the track centerline to building distance and decreasing train speed. The frequency of vibration up to 12 Hz was present in the incident wave field and the dominating part of the frequency content was between 2.5 and 5.5 Hz. The building foundation bending moment variations caused by train-induced vibrations was negligible. The track centerline to building edge distance of 18 m was seemed to be an acceptable value to reduce the annoyance and environmental effects caused by train-induced vibrations. | Numerical modeling of train-induced vibration of nearby multi-story building: A case study | 10.1007/s12205-015-0264-9 |
2016-07-01 | In combination of the advantages of both parallel mechanisms and compliant mechanisms, a compliant parallel mechanism with two rotational degrees of freedom is designed to meet the requirement of a lightweight and compact pan-tilt platform. Firstly, two commonly-used design methods i.e. direct substitution and Freedom and Constraint Topology are applied to design the configuration of the pan-tilt system, and similarities and differences of the two design alternatives are compared. Then inverse kinematic analysis of the candidate mechanism is implemented by using the pseudo-rigid-body model, and the Jacobian related to its differential kinematics is further derived to help designer realize dynamic analysis of the 8R compliant mechanism. In addition, the mechanism’s maximum stress existing within its workspace is tested by finite element analysis. Finally, a method to determine joint damping of the flexure hinge is presented, which aims at exploring the effect of joint damping on actuator selection and real-time control. To the authors’ knowledge, almost no existing literature concerns with this issue. | Design and analysis of a compliant parallel pan-tilt platform | 10.1007/s11012-015-0116-1 |
2016-07-01 | The Vectorial-wave method (VWM) is developed to study free and forced vibrations of cylindrical shells in the presence of dampers at supports. In modeling the issue, a circular cylindrical shell is considered with two ended supports, including separate springs and viscous dampers in the possible directions. Accordingly, based on Flügge thin shell theory and by considering the wave vectors going in the opposite direction along with the shell axis, reflection and transmission matrices are determined to satisfy the shell continuity as well as the boundary conditions. The proposed method is verified through comparing its results with the available literature and the numerical results calculated by Finite element method (FEM). Employing VWM, the viscous characteristics of the applied supports on natural frequencies of the shell are investigated. Furthermore, frequency responses of the shell, which are affected by point-load excitation, are obtained. Finally, the results show that several tandem resonance picks can be eliminated via accurate setting of the support damping. | A Vectorial-Wave Method for free and forced vibration analysis of extra thin cylindrical shells with boundary discrete damping | 10.1007/s12206-016-0610-y |
2016-07-01 | In this paper, we consider the interval oscillation criteria for second-order damped differential equations with mixed nonlinearities $$\begin{aligned} \left( r(t)(x'(t))^\gamma \right) '+p(t)(x'(t))^\gamma +\sum ^n_{i=0}q_i(t)\left| x(g_i(t))\right| ^{\alpha _i}\text {sgn}\ x(g_i(t))=e(t), \end{aligned}$$ r ( t ) ( x ′ ( t ) ) γ ′ + p ( t ) ( x ′ ( t ) ) γ + ∑ i = 0 n q i ( t ) x ( g i ( t ) ) α i sgn x ( g i ( t ) ) = e ( t ) , where $$\gamma $$ γ is a quotient of odd positive integers, $$\alpha _0=\gamma , \alpha _i>0, i=1,\ 2,\ldots ,n$$ α 0 = γ , α i > 0 , i = 1 , 2 , … , n with $$r,\ p,\ e$$ r , p , e , and $$q_i\in C([t_0,\infty ),\mathbb {R}), r(t)>0, g_i:\ \mathbb {R}\rightarrow \mathbb {R}$$ q i ∈ C ( [ t 0 , ∞ ) , R ) , r ( t ) > 0 , g i : R → R are nondecreasing continuous functions on $$\mathbb {R}$$ R and $$\lim _{t\rightarrow \infty }g_i(t)=\infty , i=0,\ 1,\ 2,\ldots ,n.$$ lim t → ∞ g i ( t ) = ∞ , i = 0 , 1 , 2 , … , n . Our results in this paper extend and improve some known results. Some examples are given here to illustrate our main results. | Interval Oscillation Criteria for Second-Order Damped Differential Equations with Mixed Nonlinearities | 10.1007/s40840-015-0193-2 |
2016-07-01 | We investigate the asymptotic behavior of solutions to damped hyperbolic equations involving strongly degenerate differential operators. First we establish the existence of a global attractor for the damped hyperbolic equation under consideration. Then we prove the finite dimensionality of the global attractor. | Large-time behavior of solutions to degenerate damped hyperbolic equations | 10.1134/S0037446616040078 |
2016-07-01 | A solution to the problem of damper gain with a porous ring and compressible film of lubricant has been given. A feature of the solution is the combined assumption of a set of variable factors, which were previously only considered for particular cases. | Dаmреr with а pоrоus element fоr bearing arrangements | 10.3103/S1068366616040024 |
2016-07-01 | This paper investigates scaling a modified limited-memory algorithm to solve unconstrained optimization problems. The basic idea was to combine the damped techniques for the limited-memory update and the technique of equilibrating the inverse Hessian matrix. Enhanced curvature information about the objective function is stored in the form of a diagonal matrix and plays the dual roles of providing an initial matrix and equilibrating for damped limited-memory iterations. Numerical experiments indicated that the new algorithm is very effective. | Scaling Damped Limited-Memory Updates for Unconstrained Optimization | 10.1007/s10957-016-0940-z |
2016-07-01 | The design and characterisation of a magnetic vibration absorber (MVA), completely relying on magnetic forces, is addressed. A distinctive feature of the absorber is the ability of tuning the linear stiffness together with the nonlinear cubic and quintic stiffnesses by means of repulsive magnets located in the axis of the main vibrating magnetic mass, together with a set of corrective magnets located off the main axis. The tuning methodology is passive and relies only on three geometrical parameters. Consequently, the MVA can be adjusted to design either a nonlinear tuned vibration absorber, a nonlinear energy sink or a bi-stable absorber with negative linear stiffness. The expressions of the stiffnesses are given from a multipole expansion of the magnetic fields of repulsive and corrective magnets. A complete static and dynamic characterisation is performed, showing the robustness of the modelling together with the ability of the MVA to work properly in different vibratory regimes, thus making it a suitable candidate for passive vibration mitigation in a wide variety of contexts. | Design of a magnetic vibration absorber with tunable stiffnesses | 10.1007/s11071-016-2731-3 |
2016-06-08 | Amphiphilic triblock copolymer Poly(ε-caprolactone)-block-polydimethylsiloxane-block-poly(ε-caprolactone) (PCL-b-PDMS-b-PCL, LDL) was synthesized via the ring-opening polymerization of ε-caprolactone in the presence of hydroxyl-terminated polydimethylsiloxane (HTPDMS) and was utilized to modify epoxy. The tensile strength and elongation at break were simultaneously enhanced when the triblock copolymer was incorporated. With increasing the concentration of the triblock copolymer, the damping temperature range (tanδ >0.25) was broadened from 21 °C to 34.5 °C. Meanwhile, the storage modulus of the composites and the values of tanδ had no significant decrease. When the concentration of the triblock copolymer was 20 wt%, the value of K_IC attained 1.68 MN/m^3/2, which was 1.56 times that of the neat epoxy (1.08 MN/m^3/2). Besides, the characterization of hydrophobic and hydrophilic performance indicated that the incorporation of the triblock copolymer made epoxy resins transformed from hydrophilic to hydrophobic. It is expected that damping composites obtained by this method may be used as damping structural integration materials in future. | Preparation of damping structural integration materials via the formation of nanostructure in triblock copolymer modified epoxy resins | 10.1007/s10965-016-1019-0 |
2016-06-01 | We consider Kirchhoff equations with strong damping, namely with a friction term which depends on a power of the “elastic” operator. We address local and global existence of solutions in two different regimes depending on the exponent in the friction term. When the exponent is greater than 1/2, the dissipation prevails, and we obtain global existence in the energy space, assuming only degenerate hyperbolicity and continuity of the nonlinear term. When the exponent is less than 1/2, we assume strict hyperbolicity and we consider a phase space depending on the continuity modulus of the nonlinear term and on the exponent in the damping. In this phase space, we prove local existence and global existence if initial data are small enough. The regularity we assume both on initial data and on the nonlinear term is weaker than in the classical results for Kirchhoff equations with standard damping. Proofs exploit some recent sharp results for the linearized equation and suitably defined interpolation spaces. | Kirchhoff equations with strong damping | 10.1007/s00028-015-0308-0 |
2016-06-01 | The performance of piezoelectric energy harvesters (PEHs) operating in the anticipated vibration environments depends upon various nonlinearities existing in electromechanical dynamic system. In this paper, the influence of geometric, material and damping nonlinearities on the dynamic response of PEH is investigated. So far, the nonlinear geometric finite element analysis has not been used for analyzing PEHs. Moreover, the criterion for inclusion/exclusion of geometric nonlinearity in analyzing PEHs is not studied in detail. In this paper, firstly, the finite element modeling is used for analyzing the effect of geometric nonlinearity for low-frequency vibration sources. Simulations are carried out using ANSYS for different PEH configurations to assess the influence of geometric nonlinearity on harvester’s performance, and a parameter is proposed to determine the inclusion/exclusion of geometric nonlinearity in the analyzing PEHs. Subsequently, a nonlinear electromechanical model considering material and damping nonlinearities is derived for a cantilever-type PEH which uses macro-fiber composite (MFC) for power generation. In the earlier works on PZT-5A and PZT-5H, the nonlinear elastic and damping coefficients were identified by matching the analytical responses (e.g., voltage or displacement) with a set of experimental responses, which is an indirect method and might result in erroneous estimation of unknown coefficients as pointed out in the present work. In this study, the material behavior of MFC is directly obtained from tensile tests. The observed nonlinear stress–strain behavior of MFC is included in the nonlinear model to study the dynamics of the harvester. Energy harvesting experiments are conducted, and the harvester’s response is compared with the predictions from the proposed nonlinear model. The comparison shows very good agreement between the experimental and predicted responses. Moreover, the damping parameters are identified using the energy balance method, and it is shown that nonlinear damping is essential in accurate modeling of PEHs. | Modeling of geometric, material and damping nonlinearities in piezoelectric energy harvesters | 10.1007/s11071-016-2660-1 |
2016-06-01 | The damping modification factor (DMF) has been extensively used in earthquake engineering to describe the variation of structural responses due to varied damping ratios. It is known that DMFs are dependent not only on structural dynamic properties but also on characteristics of ground motions. DMFs regulated in current seismic codes are generally developed based on far-fault ground motions and are inappropriately used in structural design where pulse-like near-fault ground motions are involved. In this paper, statistical investigation of the DMF is performed based on 50 carefully selected pulse-like near-fault ground motions. It is observed that DMFs for pulse-like ground motions exhibit significant dependence on the pulse period T _ p in a specific period range. If the period of the structure in response is close to the pulse period, the DMF attains the same level as that derived from far-fault ground motions; as the period of the structure is considerably larger or smaller than the pulse period T _ p , the response reduction effect by the increased damping ratio is generally small, except for large earthquakes with long pulse periods, which exhibit significant reduction of response for structures with periods smaller than T _ p . Based on the statistical results of DMFs, the empirical formulas for estimating DMFs for displacement, velocity and acceleration spectra are proposed, the effect of structural period, pulse period and damping ratio are considered in the formulas, and the formulas are designed to satisfy the specific reliability requirement in the period range of 0.1 < T / T _ p < 1, which is of engineering interest. | Evaluation of the damping modification factor for structures subjected to near-fault ground motions | 10.1007/s10518-016-9885-8 |
2016-06-01 | In this paper, we consider the weak viscoelastic wave equations with dynamic boundary conditions related to the Kelvin Voigt damping and delay term acting on the boundary in a bounded domain. Under appropriate conditions on $$\mu _{1}$$ μ 1 and $$\mu _{2}$$ μ 2 , we prove the asymptotic behavior by making use an appropriate Lyapunov functional. | Asymptotic behavior for a weak viscoelastic wave equations with a dynamic boundary and time varying delay term | 10.1007/s12190-015-0917-3 |
2016-06-01 | Realistic representation of the frequency dependence of dielectric function of noble metals has a significant impact on the accuracy of description of their optical properties and farther applications in plasmonics, nanoscience, and nanotechnology. Drude-type models successfully used in describing material properties of silver, for gold are known to be not perfect above the threshold energy at 1.8 eV. We give the improved, simple dielectric function for gold which accounts for the frequency dependence of the interband transitions over 1.8 eV and, in addition, for the finite size effects in gold nanoparticles. On that basis, we provide the improved characterization of the spectral performance of gold nanoparticles. Furthermore, we give the direct size dependence of the resonance frequencies and total damping rates of localized surface plasmons of gold nanoparticles (retardation effects are taken into full account) in diverse dielectric environments. The results are compared to the data obtained experimentally for gold monodisperse colloidal nanospheres, as well with the experimental results of other authors. | Dielectric Function for Gold in Plasmonics Applications: Size Dependence of Plasmon Resonance Frequencies and Damping Rates for Nanospheres | 10.1007/s11468-015-0128-7 |
2016-06-01 | In this paper, a mathematical model is presented for studying thin film damping of the surrounding fluid in an in-plane oscillating micro-beam resonator. The proposed model for this study is made up of a clamped-clamped micro-beam bound between two fixed layers. The micro-gap between the micro-beam and fixed layers is filled with air. As classical theories are not properly capable of predicting the size dependence behaviors of the micro-beam, and also behavior of micro-scale fluid media, hence in the presented model, equation of motion governing longitudinal displacement of the micro-beam has been extracted based on non-local elasticity theory. Furthermore, the fluid field has been modeled based on micro-polar theory. These coupled equations have been simplified using Newton-Laplace and continuity equations. After transforming to non-dimensional form and linearizing, the equations have been discretized and solved simultaneously using a Galerkin-based reduced order model. Considering slip boundary conditions and applying a complex frequency approach, the equivalent damping ratio and quality factor of the micro-beam resonator have been obtained. The obtained values for the quality factor have been compared to those based on classical theories. We have shown that applying non-classical theories underestimate the values of the quality factor obtained based on classical theories. The effects of geometrical parameters of the micro-beam and micro-scale fluid field on the quality factor of the resonator have also been investigated. | Studying thin film damping in a micro-beam resonator based on non-classical theories | 10.1007/s10409-015-0482-x |
2016-06-01 | A hydraulic damper with self-adjustment of the damping force is developed for the executive mechanisms of mechatronic systems with cyclic control. Equations of motion of an executive mechanism with the damper are proposed, taking account of the external forces. Analytical formulas are derived for the basic structural parameters of the damper. | Self-adjusting hydraulic damper for a pneumatic robot | 10.3103/S1068798X16060137 |
2016-06-01 | It is well known that nonlinearity may lead to localization effects and coupling of internally resonant modes. However, research focused primarily on conservative systems commonly assumes that the near-resonant forced response closely follows the autonomous dynamics. Our results for even a simple system of two coupled oscillators with a cubic spring clearly contradict this common belief. We demonstrate analytically and numerically global effects of a weak local damping source in a harmonically forced nonlinear system under condition of 1:3 internal resonance: the global motion becomes asynchronous, i.e., mode complexity is introduced with a non-trivial phase difference between the modal oscillations. In particular, we show that a maximum mode complexity with a phase difference of $$90^{\circ }$$ 90 ∘ is attained in a multi-harmonic sense. This corresponds to a transition from generalized standing to traveling waves in the system’s modal space. We further demonstrate that the localization is crucially affected by the system’s damping. Finally, we propose an extension of the definition of mode complexity and mode localization to nonlinear quasi-periodic motions and illustrate their application to a quasi-periodic regime in the forced response. | Global complexity effects due to local damping in a nonlinear system in 1:3 internal resonance | 10.1007/s00419-015-1080-x |
2016-06-01 | Viscous damping is a dominant source of energy dissipation in laterally oscillating micro-structures. In micro-resonators in which the characteristic dimensions are comparable to the dimensions of the fluid molecules, the assumption of the continuum fluid theory is no longer justified and the use of micro-polar fluid theory is indispensable. In this paper a mathematical model was presented in order to predict the viscous fluid damping in a laterally oscillating finger of a micro-resonator considering micro-polar fluid theory. The coupled governing partial differential equations of motion for the vibration of the finger and the micro-polar fluid field have been derived. Considering spin and no-spin boundary conditions, the related shape functions for the fluid field were presented. The obtained governing differential equations with time varying boundary conditions have been transformed to an enhanced form with homogenous boundary conditions and have been discretized using a Galerkin-based reduced order model. The effects of physical properties of the micro-polar fluid and geometrical parameters of the oscillating structure on the damping ratio of the system have been investigated. | Viscous fluid damping in a laterally oscillating finger of a comb-drive micro-resonator based on micro-polar fluid theory | 10.1007/s10409-015-0550-2 |
2016-06-01 | Topology optimization of passive constrained layer damping (PCLD) treatment patched on thin plates with respect to sound radiation at low frequency resonance is investigated. An extended solid isotropic material with penalization (SIMP) model is described using an interface finite element model for viscoelastic layer. Then the given FE mesh for base structure can remain the same during the optimization process. The objective function, radiated sound power, is simplified by using sound radiation mode and modal strain energy method, the merit of which is the complex dynamic equations of the composite plate need not to be solved and only modal analyses for the associated undamped modal equations are required. Numerical and experimental results show that significant reductions of the sound power are achieved. Two optimal topologies of the PCLD patches are analyzed. It’s shown that to minimize the sound radiation power at low frequency, not only the structural damping but also the volume velocity should be concerned. | Topology optimization of PCLD on plates for minimizing sound radiation at low frequency resonance | 10.1007/s00158-015-1371-4 |
2016-06-01 | In this paper, a new method is presented for prediction of cutting forces, surface texture and stability lobes in end milling operation based on time series analysis. In the approach, an equivalent damping ratio is defined for the cutting zone while the damping ratio of non-cutting zone is determined by experimental modal analysis. Using correlation dimension criterion, the simulation and experimental force signals are compared to anticipate the value of process damping by assessing the variation of correlation dimension for both signals. The effect of cutter deflections and run out are taken into account. Moreover, the stability lobes are predicted by considering the variation of process damping with cutting conditions. The feasibility of the proposed algorithm is verified experimentally for machining of Aluminum 7075-T6. Comparison of experiment results against simulation results indicates that the improved model can accurately predict cutting forces, surface texture and stability lobes for low radial immersion. | Improved prediction of stability lobes in milling process using time series analysis | 10.1007/s10845-014-0904-9 |
2016-06-01 | This work addresses the problem of self-excited vibration, which degrades the stability of the levitation control, decreases the ride comfort, and restricts the construction cost of maglev system. Firstly, a minimum model containing a flexible bridge and a single levitation unit is presented. Based on the simplified model, the principle underlying the self-excited vibration is explored. After investigations about the energy transmission between the levitation system and bridge, it is concluded that the increment of modal damping can dissipate the accumulated energy by the bridge and the self-excited vibration may be avoided. To enlarge the equivalent modal damping of bridge, the sky-hooked damper is adopted. Furthermore, to avoid the hardware addition of real sky-hooked damper, considering the fact that the electromagnet itself is an excellent actuator that is capable of providing sufficiently fast and large force acting on the bridge to emulate the influence of the real sky-hooked damper, the technique of the virtual sky-hooked damper is proposed. The principle underlying the virtual sky-hooked damper by electromagnet is explored and the vertical velocity of bridge is estimated. Finally, numerical and experimental results illustrating the stability improvement of the vehicle-bridge interaction system are provided. | Maglev self-excited vibration suppression with a virtual sky-hooked damper | 10.1007/s11771-016-3188-8 |
2016-05-13 | The effect of damping on the re-stabilization of statically unstable linear Hamiltonian systems, performed via parametric excitation, is studied. A general multi-degree-of-freedom mechanical system is considered, close to a divergence point, at which a mode is incipiently stable and n − 1 modes are (marginally) stable. The asymptotic dynamics of system is studied via the Multiple Scale Method, which supplies amplitude modulation equations ruling the slow flow. Several resonances between the excitation and the natural frequencies, of direct 1:1, 1:2, 2:1, or sum and difference combination types, are studied. The algorithm calls for using integer or fractional asymptotic power expansions and performing nonstandard steps. It is found that a slight damping is able to increase the performances of the control system, but only far from resonance. Results relevant to a sample system are compared with numerical findings based on the Floquet theory. | On the effect of damping on the stabilization of mechanical systems via parametric excitation | 10.1007/s00033-016-0659-6 |
2016-05-04 | In this paper, we present some sufficient conditions for the oscillation of all solutions of a second order forced impulsive delay differential equation with damping term. Three factors-impulse, delay and damping that affect the interval qualitative properties of solutions of equations are taken into account together. The results obtained in this paper extend and generalize some of the the known results for forced impulsive differential equations. An example is provided to illustrate the main result. | Interval oscillation criteria for second-order forced impulsive delay differential equations with damping term | 10.1186/s40064-016-2117-5 |
2016-05-01 | In this article, an alternative to the classical dynamic equation formulation is presented. To achieve this goal, we need to derive the reciprocal theorem in rates and the principle of virtual work in rates, in a small deformation regime, with which we will be able to obtain an expression for damping force. In this new formulation, some terms that are not commonly considered in the classical formulation appear, e.g., the term that is function of jerk (the rate of change of acceleration). Moreover, in this formulation the term that characterizes material nonlinearity, in dynamic analysis, appears naturally. | Dynamic analysis: a new point of view | 10.1007/s00161-015-0419-4 |
2016-05-01 | We study how Unruh effect and quantum noise affect the payoffs of a quantum conflicting interest Bayesian game. Three types of noisy channels, i.e., the amplitude damping channel, the depolarizing channel and the phase damping channel, are employed to model the decoherence processes. We find that Unruh effect weakens the payoffs in the quantum game and the quantum payoffs are lower than the classical payoffs when the acceleration parameter is large enough. However, the variation of the payoffs with the decoherence parameter is not always monotonic. Sometimes more decoherence may lead to higher payoffs. | Relativistic Quantum Bayesian Game Under Decoherence | 10.1007/s10773-015-2873-y |
2016-05-01 | Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit (HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this paper has positive compensation effects on the load characteristics variation, i.e., this method decreases the effects of the load characteristics variation on the force control performance and enhances the force control system robustness with the constant PID parameters, thereby, the online PID parameters tuning control method which is complex needs not be adopted. All the above research provides theoretical and experimental foundation for the force control method of the quadruped robot joints with high robustness. | Force control compensation method with variable load stiffness and damping of the hydraulic drive unit force control system | 10.3901/CJME.2016.0311.030 |
2016-05-01 | The paper presents the esults of measuring the elastic parameters of an oscillatory system (coefficient of pondermotive elasticity, damping factor, and oscillation frequency) whose viscous inertial element is represented by a magnetic fluid confined in a tube by magnetic levitation in a strong magnetic field. The role of elasticity is played by the pondermotive force acting on thin layers at the upper and lower ends of the fluid column. It is shown that, by measuring the elastic oscillation frequencies of the magnetic fluid column, it is possible to develop a fundamentally new absolute method for determining the saturation magnetization of a magnetic colloid. | Free oscillations of magnetic fluid in strong magnetic field | 10.1134/S1063771016030131 |
2016-05-01 | We consider Vlasov fluctuations from a spatially uniform, infinitely extended plasma equilibrium and derive the appropriate Braun–Hepp evolution equations (with regularized potential). Assuming a Gaussian initial fluctuation field (of the form associated with the relevant central limit theorem), we show that at long times the fluctuating force field converges in law to a stationary Gaussian process. We also illustrate how the time-asymptotic fluctuating force field is formally associated with the diffusion matrix and drift vector for the Balescu–Guernsey–Lenard kinetic equation. | Time-Asymptotic Evolution of Spatially Uniform Gaussian Vlasov Fluctuation Fields | 10.1007/s10955-016-1504-1 |
2016-05-01 | We present a model of interaction between a four-level atom and the cavity field initially prepared in the coherent state in the presence of the phase damping effect. We discuss the atom–field entanglement and statistical properties under the damping effect in view of numerical calculations. We use the Mandel parameter as a quantifier of the statistical properties of the field; moreover, we study the different effects of the collective parameters in the master equation on the dynamical behavior of the field statistical properties and the entanglement measured by the negativity. Finally, we explore the link between the entanglement and statistical properties in view of the numerical results during the time evolution. | Numerical Study of Some Statistical Quantities for Quantum Systems Under Damping Effects | 10.1007/s10946-016-9563-y |
2016-05-01 | The intersection between the two concepts of structural control and defectiveness is discussed. Two simple oscillators differently connected by serial spring-dashpot arrangement are used to simply simulate technically relevant cases: dissipatively coupled adjacent free-standing structures, structures equipped by TMD and base-isolated structures. Eigensolution loci of the two classes of systems are tracked against one or more significant parameters to determine the potential benefits realized by different combinations of stiffness and viscosity. In both studied cases, codimension-two manifolds in the four-parameter space corresponding to coalescing eigenvalues are determined by analytical expressions. Conditions to discern semi-simple eigenvalues from defective ones confirm that the latter is the generic case laying in a two-parameter space while the former span a one-parameter subspace. The knowledge of the location of the defective systems in the parameter space permits to determine regions with specific dynamical properties useful for control design purpose. | Structural control design and defective systems | 10.1007/s00161-014-0410-5 |
2016-04-30 | We establish the optimal $${L^{p}-L^{2}(1 \leq p < 6/5)}$$ L p - L 2 ( 1 ≤ p < 6 / 5 ) time decay rates of the solution to the Cauchy problem for the 3D inviscid liquid–gas two-phase flow model and analyze the influences of the damping on the qualitative behaviors of solution. Compared with the viscous liquid–gas two-phase flow model (Zhang and Zhu in J Differ Equ 258:2315–2338, 2015 ), our results imply that the friction effect of the damping is stronger than the dissipation effect of the viscosities and enhances the decay rate of the velocity. Our proof is based on Hodge decomposition technique, the $${L^{p}-L^{2}}$$ L p - L 2 estimates for the linearized equations and an elaborate energy method. | Decay of the 3D inviscid liquid–gas two-phase flow model | 10.1007/s00033-016-0658-7 |
2016-04-29 | By using the time-dependent mean-field approach based on the Popov approximation, the Landau damping in a Bose-Fermi superfluid mixture in the presence of a long-range $ 1/r$ interaction between bosons at finite temperature is studied. For a homogeneous three-dimension (3D) gas, we will show, since both Bose-Fermi and the $ 1/r$ interactions contributions are exponentially suppressed, the contact interaction has the dominant role to the low-temperature behavior of the Landau damping and the temperature behavior of the damping rate due to the $ 1/r$ and Bose-Fermi interactions similar to contact interaction is linear at high temperatures. In a two-dimension (2D) system, we will also show that the damping rate in a gas with the $ 1/r$ interaction has a minor role in comparison with contact and dipole-dipole interactions at all ranges of temperatures, and the low-temperatures behavior of the damping rate due to both the $ 1/r$ and dipole-dipole interactions scales as $ e^{-1/T}$ while the contact contribution changes as $T^{2}$ . Our results have important consequences for ongoing experiments and theoretical researches on ultracold gases with repulsive or attractive long-range $ 1/r$ interaction. | Effect of long-range 1/r interactions on the Landau damping in a Bose-Fermi mixture | 10.1140/epjp/i2016-16122-7 |
2016-04-21 | We give a new, simpler, but also and most importantly more general and robust, proof of nonlinear Landau damping on $${\mathbb {T}}^d$$ T d in Gevrey $$-\frac{1}{s}$$ - 1 s regularity ( $$s > 1/3$$ s > 1 / 3 ) which matches the regularity requirement predicted by the formal analysis of Mouhot and Villani [ 67 ]. Our proof combines in a novel way ideas from the original proof of Landau damping Mouhot and Villani [ 67 ] and the proof of inviscid damping in 2D Euler Bedrossian and Masmoudi [ 10 ]. As in Bedrossian and Masmoudi [ 10 ], we use paraproduct decompositions and controlled regularity loss along time to replace the Newton iteration scheme of Mouhot and Villani [ 67 ]. We perform time-response estimates adapted from Mouhot and Villani [ 67 ] to control the plasma echoes and couple them to energy estimates on the distribution function in the style of the work Bedrossian and Masmoudi [ 10 ]. We believe the work is an important step forward in developing a systematic theory of phase mixing in infinite dimensional Hamiltonian systems. | Landau Damping: Paraproducts and Gevrey Regularity | 10.1007/s40818-016-0008-2 |
2016-04-16 | The vibration control using the piezoelectric elements is an area interesting for many industrial sectors. Within this framework, we propose an improved control technique based in synchronized switch damping by energy transfer. It realizes the energy transfer using storage capacitances and switches synchronized with the structure modal coordinates or piezo-voltages. These switches produce either a voltage inversion on the piezoelements for damping or energy extraction purposes, or oscillating discharges between the piezoelements and the storage capacitances for energy transfer. This new method has an improvement in the modal damping technology SSDI-Max. Their performance is simulated with a model representative of a clamped plate with four piezoelectric elements coupled with the structural modes while taking into account realistic transfer losses. The damping effect is simulated in multi-modal with pulse or multi-sine excitation. | Multimodal vibration damping using energy transfer | 10.1007/s11082-016-0467-4 |
2016-04-07 | In this paper, we consider the viscoelastic wave equation with Balakrishnan–Taylor damping. This work is devoted to prove uniform decay rates of the energy without imposing any restrictive growth assumption on the damping term and weakening the usual assumptions on the relaxation function. Our estimate depends both on the behavior of the damping term near zero and on behavior of the relaxation function at infinity. | General decay rate estimates for viscoelastic wave equation with Balakrishnan–Taylor damping | 10.1007/s00033-016-0625-3 |
2016-04-01 | To study the damping capacity of BaTiO_3/Al composites, Al composites reinforced with BaTiO_3 powder (average grain sizes: 100 and 1000 nm) were fabricated by the hot-pressing sintering method. The damping properties of pure Al and BaTiO_3/Al composites were investigated and compared based on the dynamic mechanical analysis over a wide range of temperatures (50–285^∘C). Compared with pure Al matrix, 1000 nm BaTiO_3/Al composites with 5 and 10% mass fractions of BaTiO_3 exhibited better damping capacity. For 100 nm BaTiO_3/Al composite, its damping capacity is slightly higher than that of pure Al below 145^∘C, while it becomes lower above this degree. The damping capacity enhancement of BaTiO_3/Al composites can be explained by the ferroelastic domain damping. Furthermore, 5 and 10% BaTiO_3/Al composites have higher bending strength and hardness than pure Al sample. | A study on the damping capacity of BaTiO_3-reinforced Al-matrix composites | 10.1007/s12034-016-1171-5 |
2016-04-01 | We construct a damping term for general higher-order strictly hyperbolic homogeneous equations with constant coefficients. We derive long-time decay estimates for the solution to the Cauchy problem, and we show that no better dissipative effect can be obtained with a different damping term . | A damping term for higher-order hyperbolic equations | 10.1007/s10231-015-0477-z |
2016-04-01 | Plasmons are fundamental collective excitations in many particle charged systems like in free electron liquid in metals, high energy nuclear plasma in solar core or in fusion devices, in ion gas in ionosphere or in intra- and inter-galactic gas clouds. Plasmons play a central role also in small systems, in particular in metallic nanoparticles and in their arrays allowing for subdiffraction light manipulation. In analogy to metallic nanoparticles, we have developed description of the soft plasmonics in finite electrolyte systems confined in micrometer scale by insulating membranes. Plasmon-type excitations in such finite ionic systems are determined via originally formulated theoretical model allowing to describe surface and volume plasmons in confined geometry of the ion liquid. Size-effect for attenuation of surface plasmons in the finite electrolyte system is described and its various regimes are identified. The cross-over in the plasmon damping system-size-dependence is demonstrated including scattering of ions and their energy losses via irradiation. The plasmon resonances in ion systems replicate the metal cluster plasmon phenomena, though in distinct energy and size scale related to larger ion mass and lower ion concentration (in low energy plasma) in comparison to electrons in metals. The possibility for tuning plasmon resonances in finite ionic systems in a wide range by changing system size, ion, and electrolyte parameters is demonstrated. | Plasmons in Finite Spherical Electrolyte Systems: RPA Effective Jellium Model for Ionic Plasma Excitations | 10.1007/s11468-015-0064-6 |
2016-04-01 | Boring is one of the most common operations to enlarge or finish predrilled deep holes and is usually conducted in low spindle speed ranges. Due to low dynamic performances of conventional boring bar, boring operation is often hindered by drastic vibration. In this paper, a design and optimization method of a special boring cutter with constrained layer damping (CLD) bar is developed based on the CLD beam theory and finite element method (FEM). The boring cutter designed is composed of four modules: cutting head, substrate layer, damping layer, and constrained layer, which can greatly improve the dynamic performances in boring process. Meanwhile, the effectiveness and capability of boring cutter with CLD bar for forced- and chatter-vibration suppression are presented based on experimental and numerical methods. The results show that (1) the method for restraining forced vibration is different from that for chatter suppression. The former can be greatly avoided by shifting the natural frequency of boring system, e.g., changing dynamic stiffness. The latter, due to its complexity in low spindle speed range, on the other hand, cannot be entirely avoided and can only be eliminated by reducing the possibility of occurrence, e.g., increasing damping. (2) The boring cutter with CLD bar developed can change dynamic stiffness through constrained layer and improve damping performance through damping layer. So, it can avoid forced vibration and eliminate chatter to some extent. In the presented parameter domains, the capability of CLD bar for chatter suppression is improved five times corresponding to that of conventional bar. | Boring bar with constrained layer damper for improving process stability | 10.1007/s00170-015-7670-5 |
2016-04-01 | The squeal noise occurring from the disc brakes of passenger cars has been analyzed by using the complex eigenvalue method numerically. The contact between a disc and two pads was analytically modeled as many linear springs and dampers in an effort to develop the improved equation of motion derived on the basis of Lagrange’s equation and the assumed mode method. The finite element modal analysis results for disc brake components constitute an eigenvalue matrix in the analytical equation of motion. The complex eigenvalue analyses based on the equations of motion are able to examine the dynamic instability of a brake system, which is an onset of squeal, by considering the disc rotational effect. Numerical analyses showed that the modes unstable in an undamped analysis became stable in a damped case, which illustrates the important effect of damping on the squeal instability in a brake squeal simulation. Then several modified brake models were suggested and investigated how effectively they suppressed the occurrence of squeal noise. The brake parts such as a pad chamfer and a disc vane were modified and the influence of pad chamfer and vane shapes on squeal occurrence was proved to be significant. The numerical results showed that proper structural modification of a disc brake system can suppress the brake squeal to some extent. | Analysis of automotive disc brake squeal considering damping and design modifications for pads and a disc | 10.1007/s12239-016-0021-1 |
2016-04-01 | A displacement-based design procedure using hysteretic damped braces (HYDBs) is proposed for the seismic retrofitting of unsymmetric-plan structures. An expression of the viscous damping equivalent to the hysteretic energy dissipated by the damped braced frame is proposed under bidirectional seismic loads, where corrective factors are assumed as a function of design parameters of the HYDBs. To this end, the nonlinear dynamic analysis of an equivalent two degree of freedom system is firstly carried out on seven pairs of real ground motions whose displacement response spectra match, on average, the design spectrum proposed by the Italian seismic code for a high-risk seismic zone and a medium subsoil class. Then, the extended N2 method considered by the European seismic code, which combines the nonlinear static analysis along the in-plan principal directions of the structure with elastic modal analysis, is adopted to evaluate the higher mode torsional effects. The town hall of Spilinga (Italy), a reinforced concrete (r.c.) framed building with an L-shaped plan, is supposed to be retrofitted with HYDBs. Six structural solutions are compared considering two alternative in-plan distributions of the HYDBs, to eliminate (elastic) torsional effects, and three design values of the frame ductility combined with a constant design value of the damper ductility. To check the effectiveness and reliability of the DBD procedure, the nonlinear static analysis of the test structures is carried out, by evaluating the vulnerability index of r.c. frame members and the ductility demand of HYDBs for different in-plan directions of the seismic loads. | Nonlinear seismic analysis of unsymmetric-plan structures retrofitted by hysteretic damped braces | 10.1007/s10518-016-9873-z |
2016-04-01 | The resonant interaction of surface and internal waves produces a nonlinear mechanism for energy transfer among wave components in oceans, lakes, and estuaries. In many field situations, the stratification may be well approximated by a two-layer fluid with a diffuse interface. The growth and damping rates of sub-harmonic interfacial waves generated by a surface wave through a three-wave resonant interaction are measured in the laboratory. These measurements are compared with theoretical predictions. A diffuse interface reduces the damping rate and increases the growth rate. The predicted growth rate provides excellent comparison with the laboratory measurements. The inclusion of the effects of a diffuse interface significantly improve the comparison. | Growth and damping of interfacial waves on a diffuse interface | 10.1007/s10652-015-9429-9 |
2016-04-01 | This work evaluates the impact of added zirconia on the thermomechanical and thermoelastic fatigue properties of high-alumina refractory castables. Three testing scenarios are presented in the study: 1) Resonant Frequency Damping Analysis (RFDA) after cyclic temperature changes with and without mechanical load, 2) Refractoriness under Load (RuL) tests, and 3) results of abrupt temperature shifts between two high temperatures in a special thermal shock furnace. The tested refractory formulations were a reference castable based on tabular alumina and two castables each containing 13.75 mass-% of zirconia. The formulations of the zirconia castables had an addition of either fully-stabilized zirconia doped with 8 mol-% yttria (Y-FSZ) or partially-stabilized zirconia doped with 3 mol-% calcia (Ca-PSZ). The Y-FSZ castable displayed elastic and mechanical behaviour by means of RFDA and RuL similar to the reference sample and had good recovery after thermal shock testing. The Ca-PSZ formulation showed some beneficial toughening through energy dissipation of progressing cracks, but after cooling exhibited the matrix fracturing influence of the martensitic zirconia phase transformation which would negatively impact service life of the refractory. | Elastic and Mechanical Fatigue at High Temperatures of High-Alumina Castables with Addition of Partially Stabilized Zirconia | 10.1007/BF03401182 |
2016-04-01 | Recently, control approaches for a hydraulic robot in the field of robotics have attracted considerable attention owing to their high power-to-weight ratio. Many studies on behavior and control exploiting the advantages of hydraulic robots have been pursued. Application to hydraulically actuated systems, however, is not straightforward due to the nonlinear internal dynamics of the actuators. This paper presents a relatively simple method to improve the position precision of a hydraulic robot arm. We propose a simple control method concept based on a virtual spring–damper (VSD) controller, which enables the robot to realize a desired position. The main advantage of the VSD control is its simple calculation method, which eliminates the need to solve the Jacobian pseudo-inverse or ill-posed inverse kinematics. In this study, experiments were conducted to identify the problems in previous study results and evaluated the applicability of VSD control to the hydraulic robot arm. A relatively simple method was proposed to solve these problems and to verify improvements in the position precision. The proposed method is the dual VSD controller in which an additional VSD model is applied to the elbow, in addition to the conventional VSD model connected to the wrist. The effectiveness of the proposed control scheme is demonstrated in experimentation with the hydraulic robot arm. | Method for improving the position precision of a hydraulic robot arm: dual virtual spring–damper controller | 10.1007/s11370-015-0182-1 |
2016-04-01 | Purpose Danger-associated molecular patterns (DAMPs) released of trauma could contribute to an immune suppressed state that renders patients vulnerable towards nosocomial infections. We investigated DAMP release in trauma patients, starting in the prehospital phase, and assessed its relationship with immune suppression and nosocomial infections. Methods Blood was obtained from 166 adult trauma patients at the trauma scene, emergency room (ER), and serially afterwards. Circulating levels of DAMPs and cytokines were determined. Immune suppression was investigated by determination of HLA-DRA gene expression and ex vivo lipopolysaccharide-stimulated cytokine production. Results Compared with healthy controls, plasma levels of nuclear DNA (nDNA) and heat shock protein-70 (HSP70) but not mitochondrial DNA were profoundly increased immediately following trauma and remained elevated for 10 days. Plasma cytokines were increased at the ER, and levels of anti-inflammatory IL-10 but not of pro-inflammatory cytokines peaked at this early time-point. HLA-DRA expression was attenuated directly after trauma and did not recover during the follow-up period. Plasma nDNA ( r = −0.24, p = 0.006) and HSP70 ( r = −0.38, p < 0.0001) levels correlated negatively with HLA-DRA expression. Ex vivo cytokine production revealed an anti-inflammatory phenotype already at the trauma scene which persisted in the following days, characterized by attenuated TNF-α and IL-6, and increased IL-10 production. Finally, higher concentrations of nDNA and a further decrease of HLA-DRA expression were associated with infections. Conclusions Plasma levels of DAMPs are associated with immune suppression, which is apparent within minutes/hours following trauma. Furthermore, aggravated immune suppression during the initial phase following trauma is associated with increased susceptibility towards infections. | Plasma levels of danger-associated molecular patterns are associated with immune suppression in trauma patients | 10.1007/s00134-015-4205-3 |
2016-04-01 | The motivation of this work is to get an insight into the irreversible energy dissipation on the quantum level. The presented examination procedure is based on the Feynman path integral method that is applied and widened toward the calculation of the kernel of a quantum mechanical damped oscillator. Here, it is shown that the energy loss of the oscillator can be generated by the introduced harmonic complex potential. The related damped wave function, however, does not pertain to the probability as it is usual in the case of complex absorbing potentials. This decrease in the wave function is evaluated, by which the energy dissipation—the measure of the irreversibility—is also calculated. | Quantum particle motion in absorbing harmonic trap | 10.1007/s12648-015-0774-9 |
2016-04-01 | Instead of the L ^ p estimates, we study the modulation space estimates for the solution to the damped wave equation. Decay properties for both the linear and semilinear equations are obtained. The estimates in modulation space differ in many aspects from those in L ^ p space. | Modulation space estimates for damped fractional wave equation | 10.1007/s11425-015-5082-5 |
2016-03-16 | In this paper, we study a class of damped vibration systems, u ¨ ( t ) + B u ˙ ( t ) − L ( t ) u ( t ) + ∇ W ( t , u ( t ) ) = 0 , ∀ t ∈ R , $$ \ddot{u}(t)+B\dot{u}(t)-L(t)u(t)+\nabla W\bigl(t,u(t)\bigr)=0, \quad \forall t \in \mathbb{R}, $$ where W ( t , u ) $W(t,u)$ is of indefinite sign. By using a critical point theorem of Ding, we establish a new criterion to guarantee that the above system has infinitely many nontrivial homoclinic orbits under the assumption that W ( t , u ) $W(t,u)$ is asymptotically quadratic or subquadratic as | u | → ∞ $|u|\rightarrow\infty$ . Recent results in the literature are generalized and significantly improved. | Homoclinic orbits for damped vibration systems with asymptotically quadratic or subquadratic potentials | 10.1186/s13662-016-0805-7 |
2016-03-15 | Background Users of neuroprostheses employing electrical stimulation (ES) generally complete the stand-to-sit (STS) maneuver with high knee angular velocities, increased upper limb support forces, and high peak impact forces at initial contact with the chair. Controlling the knee during STS descent is challenging in individuals with spinal cord injury (SCI) due to the decreasing joint moment available with increased knee angle in response to ES. Methods The goal of this study was to investigate the effects of incorporating either (1) a coupling mechanism that coordinates hip and knee flexion or (2) a mechanism that damps knee motion to keep the knee angular velocity constant during the STS transition. The coupling and damping were achieved by hydraulic orthotic mechanisms. Two subjects with SCI were enrolled and each served as their own controls when characterizing the performance of each mechanism during STS as compared to stimulation alone. Outcome measures such as hip-knee angle, knee angular velocity, upper limb support force, and impact force were analyzed to determine the effectiveness of the two mechanisms in providing controlled STS. Results The coordination between the hip and knee joints improved with each orthotic mechanism. The damping and hip-knee coupling mechanisms caused the hip and knee joint ratios of 1:1.1 and 1:0.99, respectively, which approached the 1:1 coordination ratio observed in nondisabled individuals during STS maneuver. The knee damping mechanism provided lower ( p < 0.001) and a more constant knee angular velocity than the hip-knee coupling mechanism over the knee range of motion. Both the coupling and damping mechanisms were similarly effective at reducing upper limb support forces by 70 % ( p < 0.001) and impact force by half ( p ≤ 0.001) as compared to sitting down with stimulation alone. Conclusions Orthoses imposing simple kinematic constraints, such as 1:1 hip-knee coupling or knee damping, can normalize upper limb support forces, peak knee angular velocity, and peak impact force during the STS maneuvers. | Improving stand-to-sit maneuver for individuals with spinal cord injury | 10.1186/s12984-016-0137-6 |
2016-03-08 | In this paper, we establish two sufficient conditions for the oscillation of forced fractional difference equations with damping term of the form ( 1 + p ( t ) ) Δ ( Δ α x ( t ) ) + p ( t ) Δ α x ( t ) + f ( t , x ( t ) ) = g ( t ) , t ∈ N 0 , $$\bigl(1+p(t)\bigr)\Delta\bigl(\Delta^{\alpha}x(t)\bigr)+p(t) \Delta^{\alpha}x(t)+f\bigl(t,x(t)\bigr)=g(t),\quad t\in\mathbb{N}_{0}, $$ with initial condition Δ α − 1 x ( t ) | t = 0 = x 0 $\Delta^{\alpha-1}x(t)|_{t=0}=x_{0}$ , where 0 < α < 1 $0<\alpha<1 $ is a constant, Δ α x $\Delta^{\alpha}x$ is the Riemann-Liouville fractional difference operator of order α of x , and N 0 = { 0 , 1 , 2 , … } $\mathbb{N}_{0}=\{0,1,2,\ldots\}$ . | Oscillation results for certain forced fractional difference equations with damping term | 10.1186/s13662-016-0798-2 |
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