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2017-01-09 | In this paper, we study a Timoshenko system with local Kelvin–Voigt damping, which models the dynamics of a beam. We prove that the energy of the system decays exponentially or polynomially and the decay rate depends on properties of material coefficient function. The method is based on the frequency analysis and inequalities of Poincaré’s and Hardy’s type. | Stability of a Timoshenko system with local Kelvin–Voigt damping | 10.1007/s00033-016-0765-5 |
2017-01-01 | This chapter discusses three typical topics of rotor dynamics problems: internal/external damping effects, vibration due to non-symmetrical shaft stiffness and thermal unbalance behavior. Though a rotor should rotate in a stable manner in a rotation test, problems are encountered in some cases. Most of the problems are related to unbalance, against which the countermeasure is balancing. However, more serious problems may occur that cannot be solved by balancing. In such cases other solutions must be sought. This chapter discusses the following three problems that may be encountered: (1) Internal damping: Loose fittings on the shaft cause damping due to sliding friction. It might seem that any damping is welcome, but this type of damping is rather a destabilizing factor at high speeds of rotation. (2) Asymmetric section of the rotor: Asymmetry in shaft stiffness, e.g. due to a key slot on the shaft often generates troublesome vibration. (3) Vibration due to thermal bow: The unbalance vibration vector of a rotor can be monitored during operation by a Nyquist plot. While the vector point normally remains unchanged during steady state operation, thermal deformation of the rotor, e.g., due to rubbing will move it. The mechanism of this phenomenon is described. For simplicity, a single-degree-of-freedom model is used in the following discussion. | Stability Problems in Rotor Systems | 10.1007/978-4-431-55456-1_11 |
2017-01-01 | We conduct a series of tensile analyses on metal-plate specimens to investigate the relation between the fatigue level and the material’s response to external loads. We use Electronic Speckle-Pattern Interferometery (ESPI) to measures the in-plane displacement, and an acoustic transducer to assess the elastic modulus of the specimen via acoustic velocity measurement at various stress levels. We apply a tensile load at a constant pulling rate up to a certain stress level substantially lower than the yield stress, and analyze the strain field obtained with the ESPI setup at each time step. At the same time, we measure the acoustic velocity at various tensile stress levels. We have found repeatedly in the experiment on an aluminum-alloy specimen that (a) the strain field changes over several seconds after the tensile machine stops pulling, and (b) the acoustic velocity at the same point of the specimen considerably varies from measurement to measurement at the same stress level. These observations indicate that the specimen is deformed even if the crosshead of the tensile machine is stationary. This mysterious phenomenon is consistent with the observation made by Pappalettera et al. in their fatigue analysis that the acoustic emissions, which normally stops when the fatigue reaches a certain level, resumes if the specimen is dismounted from the test machine and remounted for continuation of the test. | Dynamic Deformation with Static Load | 10.1007/978-3-319-41600-7_3 |
2017-01-01 | This paper deals with a class of elastic systems with structural damping subject to nonlocal conditions. By using a suitable measure of noncompactness on the space of continuous functions on the half-line, we establish the existence of mild solutions with explicit decay rate of exponential type. An example is given to illustrate the abstract results. | Decay mild solutions for elastic systems with structural damping involving nonlocal conditions | 10.3103/S1063454117010083 |
2017-01-01 | This work looks at the effectiveness of constant weight metastructures for vibration suppression. A metastructure is a structure with distributed vibration absorbers. The metastructures are compared to a baseline structure of equal mass. The equal mass constraint shows that any increase in performance is due to the addition of the vibration absorbers and not due to adding additional mass to the structure. In this paper, two different metastructure designs are compared. These structures are designed to suppress longitudinal vibrations traveling along the length of the bar. The metastructures have ten vibration absorbers distributed on the length of the bar and the ratio of mass of the absorbers to mass of the host structure is 0.26. One metastructure has all the absorbers tuned to the natural frequency of the host structure and the other metastructure uses absorbers that are tuned to frequencies that have linearly varying natural frequencies. These structures were modeled using two different methods, a one-dimensional (1D) finite element method with lumped mass vibration absorbers and a fully three-dimensional (3D) finite element model. The results show that the metastructure with linearly varying natural frequencies outperforms that metastructure with vibration absorbers tuned to a single natural frequency. | Constant Mass Metastructure with Vibration Absorbers of Linearly Varying Natural Frequencies | 10.1007/978-3-319-54810-4_16 |
2017-01-01 | True behaviour of an arbitrary structural system is dynamic and nonlinear. To analyze this behaviour in many real cases, e.g. structures in regions under high seismic risk, a versatile approach is to discretize the mathematical model in space, and use direct time integration to solve the resulting initial value problem. Besides versatility in application, simplicity of implementation is an advantage of direct time integration, while, inexactness of the response and the high computational cost are the weak points. Considering the sizes of the integration steps as the main parameters of time integration, and concentrating on transient analysis against ground acceleration, this chapter presents discussions on: (1) the role of integration step size in time integration analysis, specifically, from the points of view of accuracy and computational cost, (2) conventionally accepted comments, codes/standards’ regulations, and some modern methods for assigning adequate values to the integration step sizes in constant or adaptive time integration, and concludes with some challenges on time integration analysis and integration step size selection in structural dynamics and earthquake engineering. | Integration Step Size and Its Adequate Selection in Analysis of Structural Systems Against Earthquakes | 10.1007/978-3-319-47798-5_10 |
2017-01-01 | With regard to G.H. Bryan’s publication in 1890, we call the following Bryan’s law (or Bryan’s effect): “The vibration pattern of a revolving cylinder or bell revolves at a rate proportional to the inertial rotation rate of the cylinder or bell”. Bryan’s factor is the proportionality constant that can be theoretically calculated for an ideal vibratory gyroscope (VG). If a perfectly symmetric VG is not ideal, that is, if imperfections and damping are present, then the precession rate (pattern rotation rate) depends on a number of factors. Indeed it depends on the rotation rate of the vehicle it is attached to, mass-stiffness and symmetry imperfections as well as any anisotropic damping (linear or nonlinear) that may be present in the VG. Assuming perfect axissymmetry for the VG, we show how to negate the effects of manufacturing mass-stiffness imperfections as well as the effects of any type of tangentially anisotropic damping that might occur. We achieve this by showing exactly how to symmetrically arrange an electronic array about the symmetry axis. This array consists of curved capacitors under a mixture of a constant (fixed) charge and a small meander charge. We show exactly how the fixed voltage on the capacitor should be adjusted in order to eliminate the frequency split caused by the mass-stiffness imperfection. Furthermore, we show how the meander voltages of the capacitors should be adjusted in order to maintain principal vibration, eliminate quadrature vibration and restore spurious pattern drift in the VG so that it obeys Bryan’s law, restoring the precession rate to the ideal rate so that Bryan’s factor can be used for calibration purpose. Equations of motion are derived in the form of averaged ODEs that provide us insight into VG behaviour. | On Electronically Restoring an Imperfect Vibratory Gyroscope to an Ideal State | 10.1007/978-3-319-56050-2_12 |
2017-01-01 | This chapter specifies the definitions, calculation and measurement of basic vibration properties: natural frequency, modal damping, resonance and Q -value ( Q -factor) Q-value (Q-factor) . Basic properties featuring in a vibrating system, which are obtained from the free vibration waveform, are: Natural frequency Natural frequency f _ n [Hz], or natural angular (or, circular) frequency ω _ n =2 π f _ n [rad/s] Damping ratio ζ [–], or logarithmic decrement δ = 2 π ζ [–] Using these parameters, the resonance caused by forced excitation can be predicted with Resonance frequency Resonance frequency (critical speed in unbalanced vibration) = natural frequency f _ n [Hz] Resonance sensitivity Resonance sensitivity Q = 1/(2 ζ ) [–] Since separation of resonance or reduction of the Q -value are fundamental requirements in the vibration design of rotating machinery, the placements of a natural frequency and the damping ratio are very important design indices. | Basics for a Single-Degree-of-Freedom Rotor | 10.1007/978-4-431-55456-1_2 |
2017-01-01 | Mechanical vibrations represent one of the key issues in the development of direct drives with a complex mechanical structure, i.e., with non-stiff connections between motor and driven mechanisms and with variable moments of inertia. A solution for motion control in relation to a direct drive, with highly dynamic performance, coupled with multi-mass mechanical load is proposed in the chapter. Due to high resonance frequencies that are difficult to be actively damped by the control system, an original solution is proposed, which is based on damping the highest resonance frequencies with a specially selected and tuned filter, leaving the damping of the lowest frequencies to the control system. In the first part of this chapter, the identification method is presented, along with robust notch filters, which are tuned for the whole range of parameter variability. Due to variable moment of inertia, two robust control methods are proposed in the second and third parts of this chapter: one is based on an adaptive neural speed controller, while the other is based on a terminal sliding mode control (SMC). The online learning neural speed controller is based on the resilient back propagation (RPROP) algorithm. A modified terminal sliding control law is proposed for a system with delays and unmodelled dynamics. The advantages of both solutions are verified on the basis of experiment investigations. | Selected Methods for a Robust Control of Direct Drive with a Multi-mass Mechanical Load | 10.1007/978-3-319-45735-2_4 |
2017-01-01 | We analyze the deterministic and stochastic components of the realizations of longitudinal vibrations of a rod weakened by a crack determined with the help of numerical solutions of a nonlinear differential equation with stochastic driving force. It is shown that the damping coefficient strongly affects the structure of forced vibrations, which leads to changes in the diagnostic parameters. We present the results of the analysis of dependences of the characteristics of vibrations on the frequencies of the carrier stochastic driving force and on the rate of decay of correlations in its envelope. | Influence of the Parameters of Damping and Stochastic Loading on the Properties of Longitudinal Vibrations of a Rod with Crack | 10.1007/s11003-017-9993-x |
2017-01-01 | External damping devices For direct damping apparatuses Damping apparatus , base isolation Base isolation , hanging isolation Hanging isolation , dynamic absorber Dynamic absorber and lock-up and shock transmission devices, three types of techniques are available for vibration control: passive, semi-active and active, which are illustrated in Fig. 28.1. Moreover, hybrid technique takes the advantages of both passive and active control technique. | Control Techniques for External Damping Devices | 10.1007/978-3-642-31854-2_28 |
2017-01-01 | A study into the vibration characteristics of adhesively bonded single-lap joints has been carried out to investigate the effect of joint geometry and temperature variation on overall system damping. Concepts of vibration damping are introduced, and it is shown how to determine the damping of a system. The methodology of calculating the damping of even a simple bonded element in the form of a lap joint from material and geometric parameters is shown to be complex. The vibration damping of bonded joints has been extended into an experimental program using four different adhesives. These were AV119, a one-part epoxy; 9245, a structural bonding tape; 3532, a two-part polyurethane; and Hysol XEA 9359.3, a two-part structural adhesive. High-strength steel adherends were used to manufacture single-lap joints of varying overlap lengths. The specimens were vibrated flexurally and the damping values calculated using the free decay method. In this investigation, the damping of the adhesive layer dominates the damping of the specimens rather than the damping of the adherends. An optimum overlap ratio was found at approximately 0.25 in this study. The adhesives were tested under varying temperature conditions to illustrate the dominance of the glass transition temperature on the damping of the specimen. It has been shown that the damping of a structure is unlikely to be improved by using adhesive bonding as a joining method. | Vibration Damping of Adhesively Bonded Joints | 10.1007/978-3-319-42087-5_30-2 |
2017-01-01 | We propose a simulation model using viscous damping to predict the moving velocity (v) of a landslide before it reaches a strain limit. We call this model “Lumped mass damper model”, and it is based on a motion equation using a mass system model composed of a damper. The damper introduces a damping force in the opposite direction to the downward force (F) of the landslide, according to the landslide velocity. For slope-stability analysis, a simple model such as the Fellenius method is used. In the analysis, the resistance force (R) and driving force (D) are calculated in each individual slice and summed up for all slices. the safety factor (Fs) is indicated as Fs = R/D. Then, the equation of motion is shown as $$ {\text{m}}\upalpha = {\text{F}} - {\text{A}} \cdot {\text{Cd}} \cdot {\text{v}} $$ . In the equation m is mass and α is acceleration of the landslide. After solving this motion equation, the formula ‘ $$ {\text{v}}{ \approx }{\text{F}}/{\text{A}} \cdot {\text{Cd}} $$ ’ is obtained. ‘A’ is the area of the slip plane of the landslide. ‘Cd’ is the viscosity coefficient of the damper, which exerts its effect on the slip surface of the landslide. Analytical results using this technique on the Kostanjek landslide in Croatia show that this Lumped mass damper model was able to reproduce the variations in landslide motion in response to the variation of groundwater level. Also, the Takino landslide of 4th August 1986 which was induced by embankment construction for a Japanese highway was successfully analyzed using this technique. |
Simulation Model to Predict Landslide Speed Using Velocity-Dependent Viscous Damping | 10.1007/978-3-319-53498-5_67 |
2017-01-01 | The dynamic response characteristics of a one-mass-spring-damper system are outlined. The resonant vibration, damping, and natural periods of the dynamic system are explained. Multi-masses-springs-dampers systems for the dynamic response analysis of buildings and other structures, and three methods of solving the differential equations governing the motions of the system: the direct integration in the time domain, the integration in frequency domain (Fourier transformation), and the modal analysis method are explained. Furthermore, the basic concept of the Finite Element Method (FEM), which is frequently used for the dynamic response analysis of reactor buildings/facilities, and foundation ground/surrounding slopes is introduced. | Dynamic Response Analysis | 10.1007/978-981-10-2516-7_14 |
2017-01-01 | The following formulas and problems are restricted to vibrations of linear systems with one degree of freedom. | Vibrations | 10.1007/978-3-662-53437-3_7 |
2017-01-01 | In order to improve the comfort of passengers in electrical vehicles, it is increasingly important to consider the vibroacoustic behavior of electrical machines during the design phase. In this work, a weakly coupled multiphysical model for electrical machine vibration and noise prediction is presented and applied to a 75 kW railway traction motor. The main objectives of the model are to obtain firstly the vibrational level and secondly the acoustic pressure level predictions. The multiphysical model includes an electromagnetic 2D model, a 3D structural vibrational model and an acoustic model, all of them based on the finite element method. The work is focused on the validation of the modal analysis and vibrational models, using a bottom-up approach. Experimental modal analyses at different assembly stages are performed in order to update uncertain input parameters of the structural model at those levels. An anisotropic damping model is developed and updated in order to obtain adequate FRF amplitudes and the mean squared error (MSE) metric is employed to quantify the correlation between the experimental and numerical results. Finally, vibrational spectra under nominal operational conditions of the motor are used to demonstrate the adequacy of the vibrational model. | Vibrational Model Updating of Electric Motor Stator for Vibration and Noise Prediction | 10.1007/978-3-319-54858-6_28 |
2017-01-01 | Ionic polymer metal composites (IPMCs) are electro-active polymers with excellent electromechanical coupling properties. They are efficient candidates in many advanced technological applications such as actuators, artificial muscles, biomimetic sensors, etc. The manufacturing of electrodes for IPMCs is very critical in their electromechanical coupling. Force optimization, selection of cations and particle size distribution within the IPMC structure, etc. are the various factors, which determines their efficiency. In this chapter, we briefly discuss the structure, components and working mechanisms of IPMCs. The synthesis and characterizations of IPMCs are discussed in detail with the help of examples. A brief outlook on the modeling and potential applications of IPMCs is also included. | Ionic Polymer Metal Composites | 10.1007/978-3-662-49514-8_7 |
2017-01-01 | The paper presents analysis of vibration transferred on the car body under different damping properties of suspension. Vehicle must be considered as a multi-technical system in which non-linear phenomena occur. The springing elements in modern cars are coil springs with non-linear characteristics, and the damping elements are telescopic shock absorbers with asymmetrical, strongly non-linear damping characteristics. The scope of the research contains relation between liquid volume and damping properties in hydraulic dampers and analysis of vibration of vehicle forced to vibration by an exciter machine. For comprehensive analysis of the vibration signals their representation in time, frequency and joint time-frequency domains are computed. The paper investigates several different liquid volumes, i.e. from 0% to 100%. The methodology is based on advanced signal analysis designed to determine the influence of fluid volume on the damper characteristics. | Vibration Signal Processing for Identification of Relation Between Liquid Volume and Damping Properties in Hydraulic Dampers | 10.1007/978-3-319-51445-1_13 |
2017-01-01 | In 2001, Taylor Devices Inc. developed special Viscous Dampers for use on the Millennium Bridge in London, England. These dampers were specified and designed to be used for mitigating the dynamic response of the bridge due to pedestrian traffic. Prior to the integration of the dampers, the bridge had experienced unacceptable movements, especially during periods when larger crowds of people were on the bridge. The result was that the bridge had to be closed until a solution was found. Much research was done and several papers were published about the nature of that problem and the ensuing solution. After successful component level testing and the installation of 37 Taylor Viscous Dampers, the bridge was re-opened to the public in February, 2002. Tests with approximately 2000 people demonstrated a much improved dynamic response. Since that time, the dampers have been subjected to almost constant dynamic input, some more than others. Due to the location of the bridge in central London, there has been nearly constant pedestrian traffic on the bridge each day and even throughout the night. However, because of the specialized nature of the damper design, no degradation in damper performance or in the dynamic response of the bridge itself has been experienced. This paper will outline the specifics in quantifying the continued damper performance through an intermediate inspection after 7 years, followed by a successful comprehensive inspection after 11 years. This included the removal, dynamic testing, and re-installation of three selected dampers. | Long-Term Performance of Specialized Fluid Dampers Under Continuous Vibration on a Pedestrian Bridge | 10.1007/978-3-319-54777-0_2 |
2017-01-01 | Understanding of the dynamic properties of municipal solid waste (MSW) and the response of waste landfill for cyclic loads are important for safe seismic design and ensuring sustainability of landfills. This study presents estimation of the dynamic properties through field and laboratory tests of MSW landfill and dynamic response of Mavallipura landfill in Bangalore. Both field tests and laboratory tests are used to develop model to represent variation of shear modulus and damping ratio for different strain levels. Ten ground motions are selected based on regional seismicity of landfill site, and detailed site response analysis was carried out considering one-dimensional nonlinear analysis in DEEPSOIL programme. Surface response parameters have been estimated; the surface spectral response varied from 0.6 to 2 g and persisted only for a period of 1 s for most of the ground motions. The minimum and maximum amplifications are 1.35 and 4.05. This study shows that Indian MSW has less shear stiffness and loose filling, may be subject to more amplification for moderate earthquake ground motions, which need to be accounted for seismic design of landfills. | Dynamic Properties of Municipal Solid Waste and Amplification of Landfill Site | 10.1007/978-981-10-4077-1_5 |
2017-01-01 | The rapid growth of energy demand in the recent years mandated exploiting energy resources alternative to the conventional fossil fuel-based resources. Nowadays, the renewable energy resources became a fundamental component of the current power systems. Numerous challenges are induced by these recent bulk systems such as low-frequency inter-area oscillations. This paper investigates three methods to damp inter-area oscillation in power systems with deep penetration of wind energy, which are: incorporating power system stabilizers in the automatic voltage regulator controls of the conventional generator, implementing a static var compensator in one of the system busbars, and implementing a high voltage dc transmission system to connect weakly-tied areas within the system. These methods helped increase inter-area oscillation damping when implemented in a modified system based on the classical two-area system. | Inter-area Oscillation Damping in Power Systems with Deep Penetration of Wind Energy | 10.1007/978-981-10-1721-6_81 |
2017-01-01 | The purpose of this work is the study of the dynamic behavior of sandwich beams with shear damage. The linear vibration method is used in this study. The technique focuses on the response of the material’s resonance modes as a function of the driving amplitude by sweeping the frequency. The sandwich materials used in this study is constructed with glass fiber laminates as skins and with PVC closed-cell foams with density 60 and 100 kg m^−3 as core. The response excitation of the shaker was established and the resonant frequencies and damping have been deducted for each frequency mode and each shear damage density. | Characterization of Sandwich Beams with Shear Damage by Linear Vibration Method | 10.1007/978-3-319-41459-1_6 |
2017-01-01 | We rigorously discuss the infrared behavior of the uniform three-dimensional dipolar Bose systems. In particular, it is shown that low-temperature physics of the system is controlled by two parameters, namely isothermal compressibility and intensity of the dipole–dipole interaction. By using a hydrodynamic approach, we calculate the spectrum and damping of low-lying excitations and analyze the infrared behavior of the one-particle Green’s function. The low-temperature corrections to the anisotropic superfluid density as well as condensate depletion are found. Additionally, we derive equations of the two-fluid hydrodynamics for dipolar Bose systems and calculate velocities of first and second sound. | Infrared Behavior of Dipolar Bose Systems at Low Temperatures | 10.1007/s10909-016-1659-9 |
2017-01-01 | One of the more common forms of passive vibration isolation in mechanical systems has been the use of elastomeric or foam pads. Cellular silicone foam is one such example which has been used for vibration isolation and mitigating the effects of mechanical shock. There are many desirable properties of cellular silicone, including its resilience and relative insensitivity to environmental extremes. However, there is very little test data that is useful for understanding its dynamic characteristics or for the development of a predictive finite element model. The problem becomes increasingly difficult since foam materials typically exhibit nonlinear damping and stiffness characteristics. In this paper we present a test fixture design and method for extraction of a few dynamic properties of one type of cellular silicone foam pad. The nonlinear damping characteristics derived from the experimental testing are then used to attempt to improve the predictive capability of a linear finite element model of the system. Difficulties and lessons learned are also presented. | Empirically-Derived, Constitutive Damping Model for Cellular Silicone | 10.1007/978-3-319-54735-0_8 |
2017-01-01 | This chapter discusses an approximate evaluation Approximate evaluation method to consider the effects of the dynamic characteristics of a bearing on the complex eigenvalues Complex eigenvalues (damping characteristics as the real part and damped natural frequency as the imaginary part). The method consists basically of two steps: (1) System reduction down to a single-dof system is executed based on the orthogonality condition of modes in the conservative system, and the equation of motion of reduced system is expressed in the complex displacement form, and (2) Approximate analysis of the complex eigenvalues of the system is used to ascertain the effects of the bearing parameters on the natural frequencies and damping characteristics. This combination provides a simple model that helps understanding the phenomena of practical interest, such as the effects of the cross-stiffness of the bearing on the system instability or the stabilizing effect of anisotropy in the bearing stiffness. In addition, the shapes of resonance curves in unbalance vibration are discussed in relation to the dynamic characteristics of the bearing. | Approximate Evaluation for Eigenvalues of Rotor-Bearing Systems | 10.1007/978-4-431-55456-1_7 |
2017-01-01 | This chapter discusses the discovery of the attenuation peak Attenuation peak in copper Materials (studied) copper (monocrystal) and carbon steels Materials (studied) carbon steels subjected to cyclic tension load and also the nonlinear peaks in carbon steels subjected to rotating-bending fatigue Fatigue rotating bending Fatigue . These clear indications are caused by the dislocation mobility and restructuring due to cyclic loading and occur at the specific fractions to the fatigue life, being independent of the stress amplitude. Continuous observation with EMAR can only detect such precursors and tell the remaining lifetime of components being fatigued. | Remaining-Life Assessment of Fatigued Metals | 10.1007/978-4-431-56036-4_16 |
2017-01-01 | A simple yet reasonably accurate constitutive model of shape memory alloys (SMAs) has been developed. It can treat more than three phases or/and variants and duplicate their rate-dependent deformation behavior quantitatively. This model was applied to damping enhancement analysis. Damping oscillations of cantilever beams with various SMA foils bonded on their both surfaces were simulated numerically. It was seen that bonding SMA foils is effective for the damping enhancement in some cases. Furthermore, it was found that adequate mechanical or/and thermal treatment for SMA foils improves the damping performance. | One-Dimensional Phase Transformation Model and Its Application to Damping Enhancement Analysis | 10.1007/978-3-319-53306-3_2 |
2017-01-01 | After a brief overview of nanoplasmonics experiments that defy explanation with classical electrodynamics, we introduce nonlocal response as a main reason for non-classical effects. This concept is first introduced phenomenologically, and afterwards based on the semi-classical hydrodynamic Drude model (HDM) that indeed exhibits nonlocal response. In particular, we discuss recent generalizations and extensions of the HDM, to include both convection and diffusion dynamics of the induced charges. This generalized nonlocal optical response (GNOR) model allows for the first time unified semi-classical explanations of known experimental phenomena for both monomers and dimers that previously seemed to require microscopic theory. Finally, we turn to Landau damping and discuss the microscopic origin of the size-dependent damping captured by the classical diffusion mechanism in the GNOR model. | Nonlocal Response in Plasmonic Nanostructures | 10.1007/978-3-319-45820-5_12 |
2017-01-01 | Classical structural analysis techniques have proven time and time again to be remarkably accurate for systems consisting of a single, continuous piece of material. Unfortunately, nearly all real engineering structures are assembled from multiple parts, joined by bolts, rivets, or other fasteners, and these joints introduce nonlinearities and uncertainties into systems’ structural stiffness and damping. Nonlinear damping due to jointed connections in particular is critical to limiting the resonant response of a structure, yet it remains poorly understood. This work seeks to understand the degree to which joint properties are dependent on the rest of the structure. The testable hypothesis is that the boundary conditions and the far-field structure itself (i.e. distribution of the stiffness and mass) change the way in which the interface is loaded, thus altering the perceived or deduced nonlinear properties of the mechanical joint. This hypothesis is investigated using experimental impact hammer testing methods in order to understand the extent to which alteration in the boundary conditions and far-field structure change the interface properties as well as the underlying mechanics during loading. Numerical tools are also employed to investigate and complement the experimental results, focusing on two fronts: replicating the experimental results with discrete joint models, and investigating joint loading for different modes using numerical modal analysis. | Effect of Far-Field Structure on Joint Properties | 10.1007/978-3-319-54930-9_7 |
2017-01-01 | A new dynamic particle difference method (PDM) for the simulation of a proportionally damped system subjected to dynamic load and the fracture simulation of cracked concrete beam is presented. The dynamic PDM utilizes only node model without involving any mesh or grid structure to take advantage of the merits of strong formulation; it remarkably accelerates computational speed owing to the avoidance of numerical integration and also sophisticatedly handles awkward topological change due to the crack growth in node model. The proportional damping is successfully implemented in the dynamic PDM by adding both mass and stiffness proportional terms to the equation of motion and the constitutive equation, respectively. It provides extra stability in the dynamic fracture simulation by eliminating erroneous oscillations. Governing partial differential equation is straightforwardly discretized in time by using the central difference method. However, a novel modification is devised in the Newmark method implementation where the transient equations and update formulae for kinematic variables are newly formulated; this modification appropriately corrects the period and amplitude of kinematic variable responses. The stability and accuracy of the developed methods are verified by solving various dynamic problems involving transient loading. Furthermore, the fracture process of the cracked concrete beam under the impact loading is successfully simulated and the dynamic energy release rates are effectively evaluated during the simulation. | Dynamic particle difference method for the analysis of proportionally damped system and cracked concrete beam | 10.1007/s10704-016-0150-6 |
2017-01-01 | This chapter discusses an evaluation method for rotor vibration characteristics by utilizing the open-loop frequency response of the system, instead of conventional eigenvalue analysis. The vibration characteristics of a rotor system are represented by the (damped) natural frequency and damping ratio. They have been estimated in the previous chapters from the viewpoint of the eigenvalue solution, the impulse response waveform, and the resonance curve (FRA) under harmonic excitation. The open-loop characteristics are from a concept in control engineering. A rotor-bearing system can be conceived as a control system as shown in Fig. 8.1, of which the open-loop characteristics are related to the vibration characteristics: the gain cross-over frequency is an estimate of the natural frequency, and the phase margin is an indicator for the damping ratio. Details of estimation are described below. | Rotor System Evaluation Using Open-Loop Characteristics | 10.1007/978-4-431-55456-1_8 |
2017-01-01 | Aiming at the limitation of the traditional flexible robot’s single adjustment stiffness or damping, a magnetorheological (MR) actuator of which stiffness and damping can be adjusted simultaneously and independently is proposed for the robot joint. The principle of equivalent variable stiffness and damping is analyzed theoretically, and the adjustment range of stiffness and damping is deduced. As the first step, the performance of variable damping is evaluated with experiment by using a MR damper. The preliminary results show that the magnetorheological actuator is capable of changing the damping by controlling the current applied to the damper. | Research on Variable Stiffness and Damping Magnetorheological Actuator for Robot Joint | 10.1007/978-3-319-65298-6_11 |
2017-01-01 | This work describes an integrated method of 3D modelling algorithms with a modal approach in a multibody environment which provides a slimmer and more efficient simulation of flexible component contacts realistically reproducing system impacts and vibrations. A non-linear numerical model of the impulse contact forces based on the continuity approach of Lankarani and Nikravesh is developed. The model developed can evaluate deformation energy taking into account the material’s characteristics, surface geometries and the velocity variations of the bodies in contact. ADAMS®-type modelling is applied to the sliding contacts of the links of a chain and its mechanical tensioner (“blade”) in the timing of an internal combustion engine. The blade was discretized by subdividing it into smaller components inter-connected with corresponding centres of gravity through 3D General Forces. Static and dynamic tests were performed to evaluate the stiffness, damping and friction parameters for the multibody model and to validate the methodology. | An effective model for the sliding contact forces in a multibody environment | 10.1007/978-3-319-45781-9_68 |
2017-01-01 | The paper investigates the causes of failure of low pressure steam turbine blade of the last stage and suggests few techniques to overcome the failure causes is presented in this paper. The blade under investigation is made of chrome alloy steel. The fracture occurred at the airfoil region of the blade. The investigation included visual inspection, micro structural characterization, SEM-EDS microanalysis and spectroscopy test to identify the causes of failure. The paper also suggests the methods to reduce the blade fatigue subsequently through computation and to enhance the fatigue strength of the steam turbine blade. In order to reduce the blade fatigue susceptibility and to enhance the fatigue life of the steam turbine blade, the wedge shape friction damper is proposed. | Study of corrosive fatigue and life enhancement of low pressure steam turbine blade using friction dampers | 10.1007/s12206-016-1203-5 |
2017-01-01 | Positive Position Feedback (PPF) is a widely used control technique for damping the lightly damped resonant modes of various dynamic systems. Though PPF controller is easy to implement any rigorous mathematical optimization is not possible due to the controller structure. Therefore, almost all PPF designs reported in literature use a trial-and-error approach to push the closed-loop system poles adequately into the left-half plane to achieve adequate damping. In this paper, a full parametric study of the PPF controller based on the closed-loop DC gain vs achievable damping relationship is carried out. It is shown that the PPF controller best suited to only damp the resonance is not the best if both damping and tracking control is required (as is the case in most precision positioning systems). This leads to a more systematic and goal-oriented selection of appropriate PPF controller for specific applications, hitherto unreported in literature. Experiments performed on a piezoelectric-stack actuated nanopositioning platform are presented to support this conclusion. | Selection of Positive Position Feedback Controllers for Damping and Precision Positioning Applications | 10.1007/978-981-10-6463-0_25 |
2017-01-01 | This paper presents a new design of a Lyapunov-redesigned control system for large horizontal wind disturbance rejection on a small-scale unmanned autonomous helicopter (UAH). In this paper, the wind disturbance cannot be treated as small perturbations around the equilibrium state any more. Instead, wind disturbances are considered as force/moment disturbances in the state equation. The force/moment caused by the wind can be estimated by the experimental data obtained in the wind tunnel. The whole control system consists of a nominal system controller and a wind disturbance controller. The nominal system controller is designed with back-stepping algorithm while the wind disturbance controller is designed with nonlinear damping algorithm. The nonlinear damping is introduced to ensure that the whole system has a uniformly bounded solution under uncertain large horizontal wind disturbances. Both longitudinal and lateral wind disturbances are considered in the simulation. The simulation results show the wind disturbances are well rejected and the proposed method can be effective for the position control of UAH in windy environment. | Wind Disturbance Rejection in Position Control of Unmanned Helicopter by Nonlinear Damping | 10.1007/978-3-319-68345-4_52 |
2017-01-01 | Mitigation and analysis of very fast transient over voltages (VFTO) is very important in gas-insulated substations (GIS). In this paper a power transformer rating of 1500 MVA in 1000 kV GIS has been considered and different techniques for mitigation and analysis of VFTOs at the transformer are applied and the same results are analyzed by the application of discrete wavelet transform (DWT) as wavelet transform gives the accurate results. The proposed system has been designed with Mat Lab software platform and the system is simulated to evaluate the peak values of VFTOs generated at the both at transformer and open end of the transformer with and without RC filter, ferrite ring, and a nonocrystilline. The results show that the peak value of VFTOs can be considerably reduced by introducing RC filter ferrite ring and nano crystalline methods. The outcomes are explored to wavelet transform for transient information. By the application of wavelet transform it has concluded that an exact measurement VFTOs can be obtained and is shown in the results. | Mitigation and Analysis of Very Fast Transient over Voltages (VFTOs) of Transformer in 1000 KV Gas-Insulated Substation (GIS) Using Wavelet Transform | 10.1007/978-981-10-1708-7_8 |
2017-01-01 | In this chapter the dynamic problems for piezoelectric nanosized bodies with account for coupled damping and surface effects are considered. For these problems we propose new mathematical model which generalizes the models of the elastic medium with damping in sense of the Rayleigh approach and with surface effects for the cases of piezoelectric materials. Our model of attenuation and surface effects has coupling properties between mechanical and electric fields, both for the damping terms and constitutive equations for piezoelectric materials on the surface. For solving the problems stated the finite element approximations are discussed. A set of effective finite element schemes is examined for finding numerical solutions of week statements for nonstationary problems, steady-state oscillation problems, modal problems and static problems within the framework of modelling of piezoelectric nanosized materials with damping and surface effects. For transient and harmonic problems, we demonstrate that the proposed models allow the use of the mode superposition method. In addition, we note that for transient and static problems we can use efficient finite element algorithms for solving the systems of linear algebraic equations with symmetric quasi-definite matrices both in the case of uncoupled surface effects and in the case of coupled surface effects. | Mathematical Models and Finite Element Approaches for Nanosized Piezoelectric Bodies with Uncoulped and Coupled Surface Effects | 10.1007/978-981-10-3797-9_1 |
2017-01-01 | High damping rubber bearings have been used in the seismic isolation of buildings worldwide for almost 30 years now. After a brief introduction to the process leading to their manufacturing, a description is given of the main tests required by current seismic codes for the design of such devices. An extensive review is then presented of the models available in the literature for the simulation of the dynamic response of high damping rubber bearings under simultaneous shear and compression. Given the extremely complex and highly nonlinear behavior of these devices, no model is capable of capturing every single aspect of the dynamic response. Issues and uncertainties involved in the characterization of this complex behavior are pointed out. These include, among others, coupled bidirectional horizontal motion, coupling of vertical and horizontal motion, strength and stiffness degradation in cyclic loading, and variation in critical buckling load capacity due to lateral displacement. Finally, a novel 1D mechanical model for high damping rubber bearings is proposed, based on the combination of simple and well-known rheological models. The model is calibrated against a set of harmonic tests at strain amplitudes up to $$200\%$$ 200 % . Extension to bidirectional horizontal motion and to varying vertical load is subject of ongoing work. | Modeling of High Damping Rubber Bearings | 10.1007/978-3-319-56136-3_7 |
2017-01-01 | Structures of ancient Mediterranean cultures that have survived numerous earthquakes over the span of millennia relied on multifaceted rocking columns to dissipate seismic energy. Rocking columns are again emerging as an effective mechanism in modern structural systems; understanding the rocking behavior can provide insight into how to best design this type of system. This study examines the analytical and experimental rocking behavior of a rectangular column. Equations of motion that describe the rocking behavior of the polygonal columns are derived and analytical energy dissipation methods compared. A high-speed 3D motion capture system, providing noncontact measurement of the column motion, is used in a series of experiments on a uniaxial shake table to validate the analytical model. These experiments show variation indicating stochastic behavior during the excitation phase. The damping ratio and coefficient of restitution are calculated from the experimental results. The experimental results and analytical solution are compared. | Analytical and Experimental Analysis of Rocking Columns Subject to Seismic Excitation | 10.1007/978-3-319-54777-0_10 |
2017-01-01 | Spherical friction pendulums (FP) represent the common approach to isolate civil engineering structures against earthquake excitation. As these devices are passive and friction damping is nonlinear the optimal friction coefficient for minimum absolute acceleration of the building depends on the peak ground acceleration (PGA). Therefore, the common procedure is to optimize the friction coefficient for the PGA of the design basis earthquake (DBE) and to verify by simulations that the absolute structural acceleration for the maximum considered earthquake (MCE) is within a tolerable limit which is far from optimal. In order to overcome this drawback of passive FPs, a semi-active FP based on real-time controlled oil damper with the use of the collocated bearing displacement only is described in this paper. Four different semi-active control laws are presented that target to produce controlled dynamic stiffness depending on the actual bearing displacement amplitude in order to control the isolation period in real-time. The desired damping is formulated based on optimal viscous damping taking into account the passive lubricated friction of the spherical surface. The four control laws are compared in terms of absolute structural acceleration, bearing force, bearing displacement and residual bearing displacement. The results point out that the approach of zero dynamic stiffness at center position of the slider and nominal stiffness at design displacement of the FP improves the isolation of the structure within the entire PGA range significantly and at the same time minimize maximum bearing force, maximum bearing displacement and maximum residual bearing displacement. | Semi-Active Base Isolation of Civil Engineering Structures Based on Optimal Viscous Damping and Zero Dynamic Stiffness | 10.1007/978-3-319-54777-0_1 |
2017-01-01 | This paper presents ride comfort and road holding analysis of passive and semi-active suspension system using quarter car model. Semi-active suspension system with magnetorheological (MR) damper was modeled as non-parametric model-based magnetic flux density in the fluid flow gap. The skyhook control strategy was used to analyze semi-active control performance. The simulation of passive and semi-active suspension system was carried out under random road profile for different velocities. The result shows that semi-active suspension has significant improvement in terms of ride comfort and road holding of vehicle than passive suspension system. Experimental studies have been conducted to characterize MR damper and a good match is observed between results with simulation results obtained using non-parametric model. | Vertical dynamic analysis of a quarter car suspension system with MR damper | 10.1007/s40430-015-0481-7 |
2017-01-01 | In this paper, the feasibility of using the finite element analysis method to predict the shelf life of the tea moisture proof package is studied. The finite element software was used to construct the diffusion model, with the aid of the finite element software heat conduction module, and the suitable conductivity coefficient was input into the heat conduction module to simulate the moisture diffusion. And by using Henry’s second diffusion law, the guarantee period of the moisture proof package is calculated. It is found that the heat conduction module with the help of the finite element software can be used to predict the moisture proof package’s guarantee period and match with the result of the calculation. A convenient, fast and accurate forecasting method is put forward, which has important significance in the actual production. | Finite Element Analysis of Moisture Diffusion in Damp-Proof Packing | 10.1007/978-981-10-3530-2_76 |
2017-01-01 | In this study, simplified numerical models are developed to analyze the soil-structure interaction (SSI) effect on frame structures equipped with viscoelastic dampers (VEDs) based on pile group foundation. First, a single degree-of-freedom (SDOF) oscillator is successfully utilized to replace the SDOF energy dissipated structure considering the SSI effect. The equivalent period and damping ratio of the system are obtained through analogical analysis using the frequency transfer function with adoption of the modal strain energy (MSE) technique. A parametric analysis is carried out to study the SSI effect on the performance of VEDs. Then the equilibrium equations of the multi degree-of-freedom (MDOF) structure with VEDs considering SSI effect are established in the frequency domain. Based on the assumption that the superstructure of the coupled system possesses the classical normal mode, the MDOF superstructure is decoupled to a set of individual SDOF systems resting on a rigid foundation with adoption of the MSE technique through formula derivation. Numerical results demonstrate that the proposed methods have the advantage of reducing computational cost, however, retaining the satisfactory accuracy. The numerical method proposed herein can provide a fast evaluation of the efficiency of VEDs considering the SSI effect. | Simplified analysis of frame structures with viscoelastic dampers considering the effect of soil-structure interaction | 10.1007/s11803-017-0377-x |
2017-01-01 | The magneto-rheological (MR) dampers used in automotive suspension improve the energy dissipation capacity for the vertical oscillations of the car body and wheel of the vehicle by increasing the damping force developed by piston motion. The determining of the time constant of the magneto-rheological fluid is essential in order to build a realistic dynamic model of an actuator, needed for implementing a real time control system provided with a comfort feedback. In this paper the authors compare the information collected from the dedicated literature, which currently are relatively restricted, to the results obtained from their own experimental determinations. The final objective of the paper is to help the optimal design a control structure for the assembly of the car magneto-rheological dampers. | Experimental Researches on the Magneto-Rheological Dampers Response to the Control Parameters | 10.1007/978-3-319-45447-4_28 |
2017-01-01 | The paper fills the gap in studying acoustic manifestations of a gas inclusion near an interface and makes it possible to analytically describe the behavior of a bubble at a small (comparable with its size) distance from the boundary. It is shown that the use of a specific (bispherical) coordinate system allows separation of variables and leads to a modified Rayleigh equation. Explicit dependences of natural frequency and damping on distance to the boundary and on physical parameters of contacting media are obtained. | Oscillations of a gas inclusion near an interface | 10.1134/S1063771016060099 |
2017-01-01 | In order to study damping characteristic and its influencing factors of E glass fiber/polyurethane composite leaf spring, we use finite element simulation method. Give a detailed research method of it: According to the structure semesters of the spring, building 3D models of composite laminate and spring and carrying out the grid division by the finite element software HYPERMESH and the mechanical property parameters of the material were given to the model; making tests of composite laminate and spring and convert the results into simulation semesters of the model; we make analysis by finite element software ABAQUS and compare the simulation results with the experimental results to find out that the mainly influence factors of composite leaf spring damping characteristic are laying angle and longitudinal tensile modulus of materials. Analysis results show that 0 angel layer damping ratio is 0.0074 belongs to small damping system. Above all, our research provides theoretical basis and research methods for studying composite leaf spring damping characteristic. | Damping Analysis and Test Research of a Composite Leaf Spring in a Light Bus | 10.1007/978-981-10-3527-2_29 |
2017-01-01 | To reduce lateral vibrations of rotating machines, the damping devices are placed between the rotor and its frame. This is enabled by magnetorheological squeeze film dampers. To achieve their optimum performance their damping effect must be adaptable to the current working conditions. In this paper, modelling of the magnetorheological squeeze film damper is based on the assumptions of the classical theory of lubrication except that for the lubricant. The model is completed with the magnetic force acting between the damper rings. Therefore, the magnetostatic approaches to determining the magnetic field in the damper gap at different distinguishing levels were proposed and compared. The developed mathematical model was applied for analysis of a rotating machine with a flexible shaft. The carried out computational simulations confirmed that the developed magnetorheological damper arrives at significant suppression of the rotor vibration in a wide range of running speeds. | Multi-physical Analysis of the Forces in the Flexible Rotor Supported by the Magnetorheological Squeeze Film Dampers | 10.1007/978-3-319-44087-3_12 |
2017-01-01 | High cycle fatigue (HCF) caused by large resonant stresses is a common cause for turbine blades failure. Passive damping systems, such as friction dampers are often used by aero-engine manufacturers to reduce the resonant stresses and mitigate the risk of HCF. The presence of friction dampers makes the dynamics of the system highly nonlinear, due to the complex stick-slip and separation phenomena taking place at the contact interface. Due to this nonlinear behaviour, an accurate understanding of the operating deflection shapes is needed for an accurate stress prediction. In this study, digital image correlation (DIC) in combination with a high speed camera is used to provide insights into the kinematics of the damper in a recently developed test rig. The in-phase and out-of-phase first bending modes of the blades were investigated leading to a full field measurement of the global ODS of the blades, and the local motion of the damper against its platforms. A significant change in the blades operational deflection shape could be observed due to the damper, and the sliding and rolling motion of the damper during a vibration cycle was accurately visualised. | DIC Measurement of the Kinematics of a Friction Damper for Turbine Applications | 10.1007/978-3-319-54930-9_9 |
2017-01-01 | Vehicle suspension systems are usually based on passive actuators and control modes in which the damping and stiffness parameters are predefined and kept constant for all road profiles and vehicle response. A different approach is to use active systems to monitor and control the suspension motion in order to improve the vehicle handling and comfort. However, these systems have a complex design requiring a relatively high power source to operate. Semi-active systems are also capable to modify the properties of the vehicle suspension but with low power requirements making them a promising technology for demanding vibration control systems. This paper presents the findings of a numerical simulation involving a simplified model of a vehicle suspension system equipped with a MR actuator. The system is designed to improve the behavior (comfort and handling) of the vehicle compared with a traditional passive suspension system. A simple fuzzy logic controller is used to decide the control action in accordance with the measured system response. | Fuzzy Based Control of a Vehicle Suspension System Using a MR Damper | 10.1007/978-3-319-43671-5_48 |
2017-01-01 | Dampers are frequently used for vibration reduction and isolation. While passive dampers are still being used, semi-active dampers such as MR and ER dampers have found their ways to expensive commercial applications. They use magnetorheological (MR) or electrorheological (ER) fluids as the damper fluid, subjected to a controllable field to obtain variable damping. These dampers are more efficient; however, due to the high cost of MR and ER fluids, they are too expensive to be used in the suspension systems for passenger cars Nonlinear Displacement-Dependent (NDD) damper has been recently developed for vibration reduction and control in mechanical systems. The damping coefficient of the NDD damper increases as the velocity reduces which compensates for the reduced velocity. This low-cost damper results in a smoother and more consistent damping force and energy dissipation and resolves the major drawback of the linear dampers, which is their poor performance, and the semi-active ones, which is their high cost. It also causes smaller force transmission in vibration isolation applications. In this paper the performance of the NDD damper in suspension systems has been investigated. The suspension system equipped with the NDD damper is modeled and its performance is compared to that of the conventional models. | Application of Nonlinear Displacement-Dependent Dampers in Suspension Systems | 10.1007/978-3-319-54404-5_17 |
2017-01-01 | Random motions on the line and on the plane with space-varying velocities are considered and analyzed in this paper. On the line we investigate symmetric and asymmetric telegraph processes with space-dependent velocities and we are able to present the explicit distribution of the position $$\mathcal {T}(t)$$ T ( t ) , $$t>0$$ t > 0 , of the moving particle. Also the case of a nonhomogeneous Poisson process (with rate $$\lambda = \lambda (t)$$ λ = λ ( t ) ) governing the changes of direction is analyzed in three specific cases. For the special case $$\lambda (t)= \alpha /t$$ λ ( t ) = α / t , we obtain a random motion related to the Euler–Poisson–Darboux (EPD) equation which generalizes the well-known case treated, e.g., in (Foong, S.K., Van Kolck, U.: Poisson random walk for solving wave equations. Prog. Theor. Phys. 87 (2), 285–292, 1992, [ 6 ], Garra, R., Orsingher, E.: Random flights related to the Euler-Poisson-Darboux equation. Markov Process. Relat. Fields 22 , 87–110, 2016, [ 8 ], Rosencrans, S.I.: Diffusion transforms. J. Differ. Equ. 13 , 457–467, 1973, [ 16 ]). A EPD-type fractional equation is also considered and a parabolic solution (which in dimension $$d=1$$ d = 1 has the structure of a probability density) is obtained. Planar random motions with space-varying velocities and infinite directions are finally analyzed in Sect. 5 . We are able to present their explicit distributions, and for polynomial-type velocity structures we obtain the hyper- and hypoelliptic form of their support (of which we provide a picture). | Random Motions with Space-Varying Velocities | 10.1007/978-3-319-65313-6_2 |
2017-01-01 | Carrier tracking phase lock loop (PLL) applied extensively in GNSS receivers and high-precision time transfer systems. The PLL is one of the important structures for carrier phase tracking in receivers. Generally, carrier phase noise can be degraded by local frequency references. However, this modification induces phase jitter, so that the accuracy of carrier phase in PLL will be reduced. On this basis, the characteristic of phase noise in carrier tracking is analyzed under the classic power law model and the variance of carrier phase jitter is calculated in the conventional second-order carrier PLL. Optimization is analyzed to obtain the optimal design of loop bandwidth, damping factor and coherent integration time (CIT) under the influence of phase noise in GNSS receivers. As a result, it is useful for carrier tracking to improve the performance of carrier PLL in the presence of phase noise and to reduce the variance of carrier phase jitter. | Optimal Carrier Tracking PLL in the Presence of Phase Noise in GNSS Receiver | 10.1007/978-981-10-4588-2_80 |
2017-01-01 | The paper presents an approach to dumping of the pendulum during dynamic stabilization in an arbitrary angle. The rapid oscillations of the pendulum’s suspension point cause that created effective potential has a local minimum which guarantees the stability of the pendulum. The external disturbances bring an additional energy into the system and the pendulum increases the amplitude of oscillations around its equilibrium position. The aim of this paper is to describe the damping method of this excess oscillations during dynamic stabilization of the pendulum. | Damping of the pendulum during dynamic stabilization in arbitrary angle position | 10.1007/978-3-319-60699-6_6 |
2017-01-01 | The Bergsøysund Bridge is currently being extensively monitored with accelerometers, anemometers, wave radars and GNSS sensors. By applying Covariance-driven Stochastic Subspace Identification (Cov-SSI), the modal parameters of the bridge are estimated. The results are interpreted in the context of the environment, represented by significant wave heights. The problem is characterized by the fact that modes are closely spaced in frequency and have high damping. Two weighting algorithms for the Cov-SSI are applied, to assess their performance for application on structures with these characteristics. | Covariance-Driven Stochastic Subspace Identification of an End-Supported Pontoon Bridge Under Varying Environmental Conditions | 10.1007/978-3-319-54777-0_14 |
2017-01-01 | This work describes a novel method for measuring the damping, the elastic modulus and the non-linear behavior of high strength low damping fiber materials such as para-aramids, silicon carbide (SiC) and carbon. The method is based on resonant response characterization of a spring-mass system excited by a sine-wave forcing term which is applied as a vertical force to the suspended mass. The damping is obtained from the measured resonance quality factor Q , the elasticity modulus is calculated from the resonance frequency, and the non-linear coefficient is obtained with the backbone approach from resonance profile variations as a function of the forcing term amplitude. It is argued that the method is very sensitive, to the point that a maximum excitation amplitude of the order of a few percent of resistance is sufficient to obtain an estimate of the non-linear coefficient. This claim is supported by experimental results. A testing machine is also discussed, which provides the necessary sensitivity at such small excitation amplitudes and the capability of evaluating very small damping values, as expected in high strength low damping fiber materials. The sensitivity is guaranteed by an optical position sensor with sub-micron resolution. To evaluate small damping values, particular care has been taken to ensure that energy dispersions in the generator are much smaller than energy dispersions in the fibers themselves. Examples of dynamic characterization are shown for para-aramid, silicon carbide, and carbon fibers. | A New Testing Machine for the Dynamic Characterization of High Strength Low Damping Fiber Materials | 10.1007/s11340-016-0208-4 |
2017-01-01 | This study proposes to use the non-linear properties of the support bearing viscoelastic material for damping of resonance oscillations of a vertical unbalanced gyroscopic rotor. To this end, it analyzes in detail the impact of non-linear damping and non-linear elastic characteristics of the support bearing material on the resonance curve and vibration stability. The options of nonlinear quadratic and cubic stiffness of the material are considered. If a cubic nonlinear stiffness influences the transmissibility to much higher resonance regions, on the contrary a quadratic nonlinear stiffness influences the transmissibility to much lesser resonance regions. Under the influence of the nonlinear damping and nonlinear elastic characteristics of support bearing not only the resonance amplitude of oscillations greatly decreases, but also the boundaries of the instability region are moved down, and its width reduces significantly. The results are of significant importance in the analysis and design of nonlinear passive vibration isolators. | Dynamics of a Vertical Unbalanced Gyroscopic Rotor with Nonlinear Characteristics | 10.1007/978-3-319-45450-4_11 |
2017-01-01 | In this paper, a damped harmonic oscillator with multiple delays is investigated. The existence conditions under which the origin of the system is a Bogdanov–Takens (B–T) singularity are derived. By utilizing the center manifold reduction and choosing suitable bifurcation parameters, the second- and the third-order normal forms of the B–T bifurcation for the system are obtained. Finally, numerical simulations are presented to illustrate the theoretical criteria. | Bogdanov–Takens bifurcation in an oscillator with positive damping and multiple delays | 10.1007/s11071-016-3040-6 |
2017-01-01 | This research compares spatial damping identification methods, both theoretically and experimentally. In contrast to the commonly used damping methods (modal, proportional) the spatial damping information improves structural models with a known location of the damping sources. The real case robustness of full FRF matrix and local equation of motion methods were tested against: modal and spatial incompleteness, differences in viscous and hysteretic damping models and the effect of damping treatments. To obtain accurate results, a careful analysis of measurements in terms of reciprocity in the raw measurements, and in terms of how to preserve symmetry has to be done. It was found that full FRF matrix needs to be symmetrisized due to small deviations in reciprocity before the damping identification. Full frequency response function (FRF) matrix methods (e.g.: Lee-Kim) can identify the spatial damping if spatial and modal incompleteness are carefully evaluated, but the measurement effort increases with second order and, consequently, the size of the FRF matrix. | Frequency Based Spatial Damping Identification—Theoretical and Experimental Comparison | 10.1007/978-3-319-54735-0_3 |
2017-01-01 | Machining vibrations and dynamic instability of machine tools is an important consideration in machining systems. Common approaches for improving their dynamic performance target either the process, or intelligent, yet complex control systems with actuators. Given that machine tools’ dynamic characteristics are largely defined by the characteristics of the joints, this article proposes a novel concept, attempting to create a new paradigm for improving the dynamic behaviour of machine tools—introducing modular machine tools components (Joint Interface Modules—JIMs) with joints deliberately designed for increasing dynamic stiffness and enhancing damping with the use of viscoelastic materials. Through a systematic model-based design process, a prototype replicating a reference tool holder was constructed exploiting viscoelastic materials and the dynamic response of the machining system was improved as a result of its introduction; in machining experiments, the stability limit was increased from around 2 mm depth of cut to 4 mm depth of cut, without compromising the rigidity of the system or changing the process parameters. The article also includes the results of investigations regarding the introduction of such prototypes in a machine tool and discusses the shortcomings of the stability lobe diagrams as a method for evaluating the performance of machine tool components with viscoelastically treated joints. | Development and analysis of a consciously designed Joint Interface Module for improvement of a machining system’s dynamic performance | 10.1007/s00170-016-8781-3 |
2017-01-01 | Energy dissipation devices are widely utilized to improve the response of structures subjected to dynamic loadings (e.g. earthquakes, winds). In particular, viscous dampers are hydraulic devices widely employed in structural engineering that dissipate the kinetic energy by producing a damping force against the motion. Despite the uncertainty present in the loads (seismic input) and in the structural models, simplified approaches for the design of the damper properties often neglect the response dispersion due to these uncertainties, or treat them in a simplified way by focusing on the mean response only. In this study, a novel reliability-based methodology for the optimal design of nonlinear viscous dampers is proposed. The methodology involves a reliability analysis nested in an outer optimization loop, which seeks the minimization of an optimal function related to the damper cost subjected to the reliability constraint on the structural performance. In particular, subset simulation is used in the inner loop, while the optimization problem is solved via the COBYLA algorithm. The application of the Subset Simulation and of the proposed design approach is illustrated by considering a realistic case study consisting of a three-storey building equipped with nonlinear viscous dampers, for different levels of the damper nonlinearity. | Reliability-Based Methodology for the Optimal Design of Viscous Dampers | 10.1007/978-3-319-47886-9_29 |
2017-01-01 | Tail Drive Shaft of a helicopter transmits torque from the main gear box to the tail rotor and in most of the helicopter designs, tail shafts are designed to work in supercritical speeds. In order to limit resonance vibrations of the tail drive shaft, dry friction dampers can be used. Therefore, in order to study the effect of dry friction damping on the response of tail drive shaft, a mathematical model is developed. The tail drive shaft is modeled as a beam by using Euler-Bernoulli beam theory. Bearings supporting the shaft structure and couplings used are represented by linear and torsional springs, respectively. The dry friction damper is located at the middle section of the shaft which is modeled by using a one-dimensional macroslip friction model with constant normal load. The partial differential equation of motion obtained is discretized by using Galerkin’s Method with multiple trial functions. The resulting nonlinear ordinary differential equations are converted into a set of nonlinear algebraic equations by using harmonic balance method utilizing single harmonic. Finally, the solution of the resulting set of nonlinear algebraic equations are obtained by using Newton’s method. Using the model developed effects of parameters of the friction damper on the response of the tail drive shaft are studied. | Effect of Dry Friction Damping on the Dynamic Response of Helicopter Tail Shaft | 10.1007/978-3-319-54648-3_3 |
2017-01-01 | This paper describes the application of a Brain Emotional Learning (BEL) controller to improve the response of a SDOF structural system under an earthquake excitation using a magnetorheological (MR) damper. The main goal is to study the performance of a BEL based semi-active control system to generate the control signal for a MR damper. The proposed approach consists of a two controllers: a primary controller based on a BEL algorithm that determines the desired damping force from the system response and a secondary controller that modifies the input current to the MR damper to generate a reference damping force. A parametric model of the damper is used to predict the damping force based on the piston motion and also the current input. A Simulink model of the structural system is developed to analyze the effectiveness of the semi-active controller. Finally, the numerical results are presented and discussed. | Brain Emotional Learning Based Control of a SDOF Structural System with a MR Damper | 10.1007/978-3-319-43671-5_46 |
2017-01-01 | In this paper we investigate the implementation of the so-called freezing method for second order wave equations in one and several space dimensions. The method converts the given PDE into a partial differential algebraic equation which is then solved numerically. The reformulation aims at separating the motion of a solution into a co-moving frame and a profile which varies as little as possible. Numerical examples demonstrate the feasability of this approach for semilinear wave equations with sufficient damping. We treat the case of a traveling wave in one space dimension and of a rotating wave in two space dimensions. In addition, we investigate in arbitrary space dimensions the point spectrum and the essential spectrum of operators obtained by linearizing about the profile, and we indicate the consequences for the nonlinear stability of the wave. | Freezing Traveling and Rotating Waves in Second Order Evolution Equations | 10.1007/978-3-319-64173-7_14 |
2017-01-01 | In this chapter, seismic vulnerability of smart structures is assessed using fragility analysis framework. The fragility analysis framework is effective to evaluate the performance and the vulnerability of structures under a variety of earthquake loads. To demonstrate the effectiveness of the seismic fragility analysis framework, a three-story steel frame building employing the nonlinear smart damping system is selected as a case study structure. To investigate the impact of sensor failures, various sensor damage case scenarios are considered. The seismic capacity of the smart building is determined based on the typical structural performance levels used in the literature. The unknown parameters for the seismic demand models are estimated using a Bayesian updating algorithm. Finally, the fragility curves of the smart structures under a variety of sensor damage cases are compared. It is proved from the extensive simulations that the proposed seismic fragility analysis framework is very effective in estimating the control performance of smart structures with sensor faults. | Seismic Fragility Analysis of Faulty Smart Structures | 10.1007/978-3-319-47798-5_11 |
2017-01-01 | The problem of improving driving safety for vehicles equipped with magnetorheological (MR) dampers is considered. It is proposed to control the MR dampers using the clipped LQ (Linear Quadratic) control which can be regarded as the two-dimensional Skyhook algorithm. The strategy is applied to a half-car model with four degrees of freedom, oriented on roll dynamics. Here, control algorithm optimised with respect to minimisation of roll vibrations is considered. Simulation experiments were performed assuming the model is subjected to impulse excitation generated as a torque applied in the centre of gravity, that is equivalent to a manoeuvre in the form of a sudden turning. The quality of the algorithm was validated using the RMS-based performance index and the results confirm the effectiveness of the proposed solution for the semi-active suspension. | The clipped LQ control oriented on driving safety of a half-car model with magnetorheological dampers | 10.1007/978-3-319-60699-6_21 |
2017-01-01 | The number of electronic components in modern vehicle chassis systems has been increasing, and energy harvesting systems are one of the main parts. Energy harvesting dampers have been developed to improve the energy efficiency, and in this paper, a ball-screw type energy harvesting damper system is modeled, and the dynamic characteristics of the system are analyzed. A quarter-car model is used to simulate the energy harvesting damper system. A comparison of the experimental and simulation results reveals that the ball-screw energy harvesting damper system modeling is adequate to develop a ball-screw energy harvesting damper system based on 48 V power system. | Vehicle Dynamic Analysis for the Ball-Screw Type Energy Harvesting Damper System | 10.1007/978-3-319-50904-4_86 |
2017-01-01 | Tuned mass dampers (TMDs) used in seismic vibration control are positioned on the top of the structures and it is the optimum position for regular structures. For structure with different stiffness values for each story, the optimum place of a TMD may be different. In this study, the story position of TMD is also included as a design variable. In methodology, harmony search algorithm is employed. The stroke capacity of the TMD is also considered in the methodology. As a numerical example, a six story structure is investigated. The stiffness of the first two stories are lower than the following two stories. The last two stories have higher stiffness than the other ones. In that case, the optimum position is not the top story. For that reason, the position of TMD is an important design variable for irregular structures in rigidity. | Tuning and Position Optimization of Mass Dampers for Seismic Structures | 10.1007/978-981-10-3728-3_23 |
2017-01-01 | In this study, a new approach is proposed for optimization of tuned mass damper positioned on the top of seismic structures. The usage of metaheuristic algorithms is a well-known and effective technique for optimum tuning of parameters such as mass, period and damping ratio. The aim of the study is to generate a new methodology in order to improve the computation capacity and precision of the final results. For that reason, harmony search (HS) and flower pollination algorithm (FPA) are hybridized by proposing a probability based approach. In the methodology, global and local search processes of HS are used together with global and local pollination stages of FPA. In that case, four different types of generation are used. In the methodology, these four types of generation have the same chance at the start of the optimization process and probabilities are reduced when the corresponding type of the generation is chosen. If an improvement is provided for the objective of the optimization, the probability of the effective type is increased. The proposed method has an effective convergence by providing improvement of the optimization objective comparing to classical FPA. | Optimum Tuning of Mass Dampers by Using a Hybrid Method Using Harmony Search and Flower Pollination Algorithm | 10.1007/978-981-10-3728-3_22 |
2016-12-08 | We study the asymptotic properties of the solutions of a class of even-order damped differential equations with p -Laplacian like operators, delayed and advanced arguments. We present new theorems that improve and complement related contributions reported in the literature. Several examples are provided to illustrate the practicability, maneuverability, and efficiency of the results obtained. An open problem is proposed. | Asymptotic behavior of even-order damped differential equations with p-Laplacian like operators and deviating arguments | 10.1186/s13660-016-1246-2 |
2016-12-01 | The approach of the phenomenological universalities of growth is considered to describe the behaviour of a system showing an oscillatory growth. Two phenomenological classes are proposed to consider the oscillatory behaviour of a system. One of them is showing oscillatory nature with constant amplitude and the other represents oscillatory nature with a change in amplitude. The term responsible for decay (or growth) in amplitude in the proposed class is also been identified. The variations in the nature of oscillation with the dependent parameters are studied in this communication. In this connection, the variation of a specific growth rate is also been considered. The significance of the presence and the absence of each term involved in the phenomenological description are also taken into consideration. These proposed classes might be useful for the experimentalists to extract a characteristic feature from the data set and to develop a suitable model consistent with their data set. | Phenomenological approach to describe oscillatory growth or decay in different dynamical systems | 10.1007/s12648-016-0884-z |
2016-12-01 | Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structural characteristics under normal environmental loadings and their behavior under dynamic loadings. In this research, a typical Tibetan wooden wall-frame building is selected to study its dynamic characteristics. Field measurements of the structure were conducted under environmental excitation to collect acceleration responses. The stochastic subspace identification (SSI) method was adopted to calculate the structural modal parameters and obtain the out-of-plane vibration characteristics of the slab and frames. The results indicated that the wall-frame structure had a lower out-of-plane stiffness and greater in-plane stiffness due to the presence of stone walls. Due to poor identified damping ratio estimates from the SSI method, a method based on the variance upper bound was proposed to complement the existing variance lower bound method for estimating the modal damping ratio to address the significant damping variability obtained from different points and measurements. The feasibility of the proposed method was illustrated with the measured data from the floor slab of the structure. The variance lower and upper bound methods both provided consistent results compared to those from the traditional SSI method. | Modal parameter identification and damping ratio estimation from the full-scale measurements of a typical Tibetan wooden structure | 10.1007/s11803-016-0358-5 |
2016-12-01 | We have observed and quantified the adiabatic and transient chirp in a directly modulated laser. The wavelength excursion for both chirp terms is well characterized by the phase rate equation model that describes the chirp behavior. In this study, the effect of gain compression and linewidth enhancement factor, below and above threshold, on the chirp characteristics is investigated by simulation. We have observed the trade-off between the two chirp terms i.e., transient part of the chirp is reduced by the strong damping introduced by gain compression, while as the adiabatic part increases with gain compression. We have observed that above threshold the α-factor increases with bias current, which is attributed to the enhancement of gain compression coefficient. It is shown that the higher the maximum gain, the lower the effects of gain compression and lower the α-factor. Finally, the effects of gain compression on the transmission characteristics are investigated. | Effect of gain compression above and below threshold on the chirp characteristics of 1.55 µm distributed feedback laser | 10.1007/s10043-016-0268-9 |
2016-12-01 | In recent years, a number of researches into dynamic characteristics of the noise and vibration in the railway have been performed. Since the high frequency vibration, which occurs in the irregularity(roughness) of the wheel and rail running surfaces, causes the track noise in railway system, analytic study with measurement of the vibration for the wheel and rail is needed. So, the algorithm and program for the vibration analysis in the track system were developed as a part of the analytic study. In this study, evaluation for the effect of the linearized contact spring in track dynamic system was studied with the developed program. In addition, analytical study for the comparison between hysteretic and viscous damping in this system was performed. The result shows that both the linearized contact spring stiffness and damping of track system are important factors in track dynamic analysis model. | Effect of linearized contact spring in track dynamic system | 10.1007/s13296-016-0077-9 |
2016-12-01 | The best known model for numerically simulating the hysteretic behavior of various structural components is the bilinear hysteretic system. There are two possible mechanical formulations that correspond to the same bilinear model from a mathematical viewpoint. The first one consists of a linear elastic spring connected in series with a parallel system comprising a plastic slider and a linear elastic spring, while the second one comprises a linear elastic spring connected in parallel with an elastic-perfectly plastic system. However, the bilinear hysteretic model is unable to describe either softening or hardening effects in these components. In order to account for this, the bilinear model is extended to a trilinear one. Thus, two trilinear hysteretic models are developed and numerically tested, and the analysis shows that both exhibit three plastic phases. More specifically, the first system exhibits one elastic phase, while the second one exhibits two elastic phases according to the level of strain amplitude. Next, the change of slope between the plastic phases in unloading does not occur at the same displacement level in the two models. Furthermore, the dissipated energy per cycle in the first trilinear model, as proven mathematically and explained physically, decreases in the case of hardening and increases in the case of softening, while in the second trilinear model the dissipated energy per cycle remains unchanged, as is the case with the bilinear model. Numerical examples are presented to quantify the aforementioned observations made in reference to the mechanical behavior of the two trilinear hysteretic models. Finally, a set of cyclic shear tests over a wide range of strain amplitudes on a high damping rubber bearing is used in the parameter identification of the two different systems, namely (a) trilinear hysteretic models of the first type connected in parallel, and (b) trilinear hysteretic models of the second type also connected in parallel. The results show that the complex nonlinear shear behavior of high damping rubber bearings can be correctly simulated by a parallel system which consists of only one component, namely the trilinear hysteretic system of the first type. The second parallel system was not able to describe the enlargement of the dissipated hysteresis area for large strain amplitudes. | Mechanical formulations for bilinear and trilinear hysteretic models used in base isolators | 10.1007/s10518-016-0014-5 |
2016-12-01 | Dampers are used to control response of structure in recent years. Seismic response is reduced by adding energy dissipation capacity to the building. Dampers are provided to dissipate energy to reduce the damages on buildings. Relative displacement of two floors are opposed by damper elements. Dampers dissipate energy with no or little degradation in strength and stiffness. This work presents the response of structure with energy dissipation device i.e. friction damper built on soft soil when the structure is subjected to a ground motion. Parameters that influence strength and stiffness of structure and energy dissipating device are studied. Response of structure with energy dissipating device is analyzed and it is shown that building with damper shows better performance during earthquake. Building structures are designed using results from elastic analysis, though inelastic behavior well observed during the earthquake. Actual response of the structure can be estimated in the inelastic range by using nonlinear structural analysis programs. Inelastic Damage indices of structural component, overall building are computed by formulating Modified Park and Ang model. Nonlinear analysis program IDARC 2D is used for modeling and analysis. Modeling of friction damper is done using a Wen–Bouc model without stiffness and strength or strength degradation. These devices are modeled with an axial diagonal element. Pseudo force approach is introduced to consider the forces in damper elements, that is, forces in damper elements are subtracted from external load vector. Smooth hysteretic model is used to model response of friction dampers. Nonlinear dynamic analysis is carried out using Newmark-Beta integration method and the pseudo-force method. Damaged state of structure is obtained to observe whether elements are cracked, yielded or failed during analysis. Response parameters such as lateral floor displacement, storey drift, base shear are also computed. | Inelastic Seismic Response of Building with Friction Damper | 10.1007/s40030-016-0184-9 |
2016-12-01 | Wave propagation in damped elbow pipes is investigated with the Fourier–Legendre spectral element method. The damped steady-state dispersion relationship is constructed by the frequency–wavenumber spectral decomposition of the governing wave equation, based on the strain–displacement relation of the ring coordinate. Then, the discretization formulation is obtained via the Legendre spectral element method where high-order spectral elements of polar coordinates are introduced to keep this finite element model consistent with the structures geometry. Finally, we give some dispersion curves of energy velocity and attenuation on damped elbow pipes with different curvatures in the ring wavenumber–frequency space. | Numerical modeling of wave propagation for damped elbow pipes using Fourier–Legendre spectral element method in polar coordinates | 10.1007/s00419-016-1164-2 |
2016-12-01 | Raising the structural seismic-resistant capability by ductility design and structural control to alleviate the structural response to earthquake are two main concepts of modern structural design. Ductile designed building is subjected to nonlinear status to dissipate energy, thus eliminating the crisis caused by resonance amplification effect. Although it can avoid much base shear and survive an earthquake without collapse, the tremendous structural deformation will lead to much structural damages. To improve such shortcomings by altering the dynamic characters of a structure, the structural response of building subject to strong earthquake needs to be minimized to ensure building within the elastic region. A novel self-reliance control technology combined with the hydraulic interface is proposed in this research. This technology will provide autonomous controls similar to those achieved by using a semi-active control system but without the use of electronic sensors and controllers. Three-stage experimental tests are planned to test and verify the energy-dissipation ratio of this technology, connected to hydraulic jack of hydraulic dampers with various conditions and subject to different external force with various amplitude and frequency. Test results exhibit that (1) this proposed technology may exhibit the hysteretic phenomenon but still show a certain energy-dissipating effectiveness without using computer, and the reliability for using the structural deformation as sensor and also performing continuous control of these proposed controllers has been confirmed in this research, (2) the input energy from the external forces can be converted to produce control actions of this proposed technology, (3) the energy-dissipating efficiency of this technology increases with higher vibration amplitude. | Development and Laboratory Confirmation of Innovative Self-Reliance Controller | 10.1007/s13369-016-2219-y |
2016-12-01 | The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system (BAS). It becomes significant on reducing the weight of arresting system, improving the hindered efficiency, and guaranteeing the security of BAS. The hydraulic hindered device of impact load is currently used in BAS. There are some problems. For example, the system needs large power sources. However, once the power of active hydraulic control system is turned off, there arise unpredictable security risks. An arresting form of semi-active control based on magneto-rheological damper (MRD) is proposed, and the mechanical model of the BAS is established. Meanwhile, the state equation of impact load BAS is established according to the characteristics of impact load buffer arresting, and its sliding model buffer control is achieved. Due to the chattering characteristic of the output signal of sliding mode controller, the method to prevent chattering is designed based on short-term energy and zero-crossing rate detection. For the model and chattering suppression of sliding model buffer control algorithms, simulation results show that the proposed state equation and the arresting model are reasonable, and the design of semi-active control algorithm is effective. On the condition of the buffer control system requirement and the accuracy, the proposed algorithms effectively control the chattering of sliding mode control algorithms, and improve the security of the BAS. | Impact arresting process mechanical modeling and sliding model buffer control based on magneto-rheological fluid | 10.1007/s12204-016-1782-4 |
2016-12-01 | Mitochondria and mitochondrial debris are found in the brain’s extracellular space, and extracellular mitochondrial components can act as damage associated molecular pattern (DAMP) molecules. To characterize the effects of potential mitochondrial DAMP molecules on neuroinflammation, we injected either isolated mitochondria or mitochondrial DNA (mtDNA) into hippocampi of C57BL/6 mice and seven days later measured markers of inflammation. Brains injected with whole mitochondria showed increased Tnfα and decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation. Some of these effects were also observed in brains injected with mtDNA (decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation), and mtDNA injection also caused several unique changes including increased CSF1R protein and AKT phosphorylation. To further establish the potential relevance of this response to Alzheimer’s disease (AD), a brain disorder characterized by neurodegeneration, mitochondrial dysfunction, and neuroinflammation we also measured App mRNA, APP protein, and Aβ_1–42 levels. We found mitochondria (but not mtDNA) injections increased these parameters. Our data show that in the mouse brain extracellular mitochondria and its components can induce neuroinflammation, extracellular mtDNA or mtDNA-associated proteins can contribute to this effect, and mitochondria derived-DAMP molecules can influence AD-associated biomarkers. | Extracellular Mitochondria and Mitochondrial Components Act as Damage-Associated Molecular Pattern Molecules in the Mouse Brain | 10.1007/s11481-016-9704-7 |
2016-12-01 | Due to migration of people to urban area, high land costs and use of light weight materials modern buildings tend to be taller, lighter and flexible. These buildings possess low damping. This increases the possibility of failure during earthquake ground motion and also affect the serviceability during wind vibrations. Out of many available techniques today, to reduce the response of structure under dynamic loading, Tuned Liquid Damper (TLD) is a recent technique to mitigate seismic response. However TLD has been used to mitigate the wind induced structural vibrations. Flat bottom TLD gives energy back to the structure after event of dynamic loading and it is termed as beating. Beating affects the performance of TLD. Study attempts to analyze the effectiveness of sloped bottom TLD for reducing seismic vibrations of structure. Concept of equivalent flat bottom LD has been used to analyze sloped bottom TLD. Finite element method (EM) is used to model the structure and the liquid in the TLD. MATLAB code is developed to study the response of structure, the liquid sloshing in the tank and the coupled fluid-structure interaction. A ten storey two bay RC frame is analyzed for few inputs of ground motion. A sinusoidal ground motion corresponding to resonance condition with fundamental frequency of frame is analyzed. In the analysis the inherent damping of structure is not considered. Observations from the study shows that sloped bottom TLD uses less amount of liquid than flat bottom TLD. Also observed that efficiency of sloped bottom TLD can be improved if it is properly tuned. | Evaluation of Sloped Bottom Tuned Liquid Damper for Reduction of Seismic Response of Tall Buildings | 10.1007/s40030-016-0185-8 |
2016-12-01 | Semi-active control is based on the use of the emerging concept of active control and passive control. The developed accumulator semi-active hydraulic damper (ASHD) is converted to interaction element (IE) of active interaction control (AIC). Systemic equations of motion, control law and control rulers of this proposed new AIC are studied in this research. A full-scale multiple degrees of freedom shaking table is tested to verify the energy dissipation of this proposed AIC, including test building without control, with passive control added involving various stiffness ratios and also with synchronic control added involving various stiffness ratios. Shock absorption of displacement can be up to 74–81% of that of the test structure with stiffness ratio = 2.3387 and 1.790 at 1st and 2nd floor under control of synchronous switch of this proposed AIC, respectively. No matter what the test structure added with various stiffeners at 1st and 2nd floor under synchronous control, test results of shock absorption ratio of acceleration show good seismic proof capability. In addition, base shear control effects of this proposed AIC method are higher than those of the test structure with various stiffeners added under passive control. These results show that AIC with stiffeners for structural control provides the characteristics of a stabilized structure under excitation of near-fault earthquake with velocity impulse action. | Shaking table test and verification of development of an accumulated semi-active hydraulic damper as an active interaction control device | 10.1007/s12046-016-0570-z |
2016-12-01 | Magnetorheological (MR) dampers are devices that can be used for structural vibration reduction under seismic excitation. These devices are used in semi-active control which require less power compared to active devices and offer high reliability compared to passive devices. Despite the advantages of MR damper, use of these dampers in an effective way in a structure is highly challenging and a precise modelling is required as these dampers are highly non-linear. Among the parametric models available, Bouc–Wen model is widely used because of its effective modelling of the hysteretic force–velocity curve of MR damper. The parameters of Bouc–Wen model are damper dependent and hence need to be identified before utilising the damper for further simulation studies. In this work, the parametric identification of Bouc–Wen model for commercially available long stroke and short stroke MR damper (RD 8040-1 and RD 8041-1) is done. For this, experimental characterization of the dampers are carried out using hydraulic actuators mounted on a self-restraining frame. The damper is driven harmonically in the testing setup at various combinations of frequency, amplitude, current and displacement. Using the experimental characterization, parameters of Bouc–Wen model are identified by Levenberg–Marquardt optimization Algorithm (LMA). The identified parameters are validated by comparing with the experimental results. The identified parameters are believed to be worthwhile for the use of these MR dampers in further studies of real-time semi-active vibration control of structures. | Parameter Identification of Long Stroke and Short Stroke MR Damper for its Use in Semi-Active Vibration Control | 10.1007/s40030-016-0182-y |
2016-11-12 | A theoretical model is developed to analyze oil-film stiffness and damping coefficients of SGRSs using two different cavitation models, i.e., the Reynolds and JFO boundary conditions. By applying the small perturbation method, the steady and perturbed Reynolds equations could be obtained. The control volume method was used for the spiral grooves, and the upwind scheme was applied to improve the convergence of the solution. The performance of the computation algorithm was studied by analyzing the mesh dependencies and computing power. A new test setup was built to measure oil-film stiffness, to verify the theoretical models, and to study the validity of the Reynolds and JFO boundary conditions. A representative SGRS was analyzed at different operating speeds and inlet pressures to investigate the occurrence of cavitation and the dynamic characteristic. The effect of the spiral-groove parameters on the dynamic characteristics is also discussed. | Theoretical and Experimental Study of Cavitation Effects on the Dynamic Characteristic of Spiral-Groove Rotary Seals (SGRSs) | 10.1007/s11249-016-0784-6 |
2016-11-01 | The authors investigate the global existence and asymptotic behavior of classical solutions to the 3D non-isentropic compressible Euler equations with damping on a bounded domain with slip boundary condition. The global existence and uniqueness of classical solutions are obtained when the initial data are near an equilibrium. Furthermore, the exponential convergence rates of the pressure and velocity are also proved by delicate energy methods. | The 3D non-isentropic compressible Euler equations with damping in a bounded domain | 10.1007/s11401-016-1039-4 |
2016-11-01 | This is an exploration of dynamic tides on elastic bodies. The body is thought of as a dynamical system described by its modes of oscillation. The dynamics of these modes are governed by differential equations that depend on the rheology. The modes are damped by dissipation. Tidal friction occurs as exterior bodies excite the modes and the modes act back on the tide raising body. The whole process is governed by a closed set of differential equations. Standard results from tidal theory are recovered in a two-timescale approximation to the solution of these differential equations. | Dynamic Elastic Tides | 10.1007/s10569-016-9682-3 |
2016-11-01 | Internal damping process in a ribbon of NiTi shape memory alloy (NiTi SMA) during a reverse transformation, from low temperature phase (martensite) to high temperature phase (austenite), has been studied by dynamic mechanical analysis (DMA) and using fractional calculus for the experimental data analysis. A mechanical fractional model for the description of dynamic modulus, $$E^{*}$$ E ∗ , has been developed for this purpose. This fractional model takes into account the relaxation peak associated with internal damping, and its corresponding differential equation has derivatives of fractional order between 0 and 1. By applying Fourier transform to fractional differential equation and considering cooperative or noncooperative atomic mobility, the real and imaginary parts of $$E^{*}$$ E ∗ have been computed. An agreement between experimental data and theoretical results of fractional model has been achieved. The fractional order parameters of the model are related to atomic mobility associated with internal damping of NiTi SMA ribbon. | Application of fractional calculus to modeling the dynamic mechanical analysis of a NiTi SMA ribbon | 10.1007/s10973-016-5552-1 |
2016-11-01 | In this work, the thermoelastic damping of a nano-scale resonator is analyzed by the generalized thermoelasticity theory based on two-temperature model (2TLS). The effect of two-temperature parameter and relaxation time in nano-scale resonator are investigated for beams under clamped conditions. Analytical expressions for deflection, temperature change, frequency shifts, and thermoelastic damping in the beam have been derived. The theories of coupled termoelasticity and generalized thermoelasticity with one relaxation time can extracted as limited and special cases of the present model. The numerical results have been presented graphically in respect of thermoelastic damping and frequency shift. | A two-temperature model for evaluation of thermoelastic damping in the vibration of a nanoscale resonators | 10.1007/s11043-016-9309-9 |
2016-11-01 | The movement of a tubular manometric spring that experiences oscillations in the plane of curvature of the central axis in a viscous medium is investigated. The Manometr software package for automatic calculation of the damping parameters is developed. Experimental estimation of the reliability of the results obtained is performed. | Theoretical Foundations of the Design of Vibration-Resistant Manometers | 10.1007/s11018-016-1055-5 |
2016-11-01 | Aim of the paper is to propose a new approach for the determination of the so termed self-damping, or internal damping, of metallic cables. The formulation is developed starting from a recent mechanical model of a strand, from which the hysteretic bending behavior of stranded cables is derived. Each wire of the cable is individually modeled as an elastic curved thin rod. A kinematic model is defined to relate the axial strain and bending curvature of the strand to the generalized strains of the wire. The interaction among the wires belonging to adjacent layers is then studied by neglecting deformations of the contact surfaces and assuming a classic Amontons–Coulomb friction law. In the adopted strand mechanical model a function is derived, which defines the domain of admissible values of the wire axial force to prevent sliding. A simplified model of the cable hysteretic bending behavior is then derived from the cyclic response predicted with the adopted mechanical formulation of the strand, leading to a closed-form upper-bound estimate of the energy dissipated when the cable cross section is subjected to alternate bending. This expression is used as the starting block for the definition of an analytical equation giving an upper-bound estimate of the cable self-damping. The predictions of the proposed model are compared to available data resulting from experiments and empirical literature equations: the comparison is extended to a wide range of strands and parameters that characterize practically most of the configuration commonly used in overhead electrical lines. | A new approach to the definition of self-damping for stranded cables | 10.1007/s11012-016-0444-9 |
2016-11-01 | Many physical phenomena might be modeled with the well-known Mathieu equation. Engineering applications, such as wind turbine blade dynamics, and helicopter rotor dynamics, lead to equations of motions with frequency-dependent coefficients. In such applications, the rotations cause the periodic parametric excitations. In addition, (1) there is external excitation, (2) damping must be included in the model and (3) uncertainties must be taken into account. The aim of this article is to analyze the dimensionless form of the stochastic non-homogeneous damped Mathieu equation. Uncertainties are modeled using the probability theory and are propagated using the Monte Carlo method. The Floquet theory is employed to assess the deterministic and stochastic stability of the system. | Stochastic stability of the non-homogeneous damped Mathieu equation | 10.1007/s11071-016-2977-9 |
2016-11-01 | A hardware and software system for studying the damping and elastic properties of soft materials in a low-frequency range of deformation up to 100 Hz, which most fully corresponds to the range of dynamic actions in actual service conditions of structures, is proposed. A novel identification method for evaluating the elastic and damping properties of soft materials in shear is developed. It employs the frequency and amplitude characteristics of the resonance flexural vibrations of three-layer test specimens with a soft inner layer. Identification of the elastic shear properties is based on a comparison of calculated and experimental frequencies of resonance vibrations of test specimens. To evaluate the shear damping properties of soft materials, the condition of minimum of an objective function containing experimental and calculated amplitudes of vibrations of the free end of a test specimen is used. The possibility of evaluating the properties mentioned from the experimental and calculated internal damping parameters of test specimens, which significantly reduces the laboriousness of the problem considered, is shown. Numerical calculations are carried out for identifying the elastic and damping characteristics of a technical rubber in shear based on an analysis of resonance flexural vibrations of seven test specimens with outer layers made of a D16AT aluminum alloy. | Theoretical-Experimental Method for Evaluating the Elastic and Damping Characteristics of Soft Materials Based on Studying the Resonance Flexural Vibrations of Test Specimens | 10.1007/s11029-016-9608-x |
2016-11-01 | A subcritical or supercritical rotor is often employed to improve the energy storage efficiency of flywheel systems. Consequently, it is necessary to introduce Squeeze film dampers (SFD) in the rotor-bearing system to suppress the lateral vibration of the rotor. Although the dynamic behavior of the rotor-bearing system can be investigated in a timely manner with ANSYS software, it is difficult, if not impossible, to directly solve the unbalance responses by the Full method (FM) offered by ANSYS package. The reason is because the stiffness and the damping coefficients of the SFD, which are required in the computation, are in fact functions of eccentricity ratio determined by the unbalance responses. In this paper, the model of the flywheel system was firstly analyzed by QR damped method. Campbell diagram and critical speeds were then obtained from the results. Natural frequencies and their corresponding mode shapes at the rotational speed of 0.1rad·s^-1 were also calculated. Then, the unbalance responses of rotor-bearing system with SFD support were solved through iteration and through the FM with ANSYS Parametric design language routine. The comparison between the calculated unbalance responses and the experimental responses indicates that the dynamic model is valid. | Dynamic analysis for the energy storage flywheel system | 10.1007/s12206-016-1001-0 |
2016-11-01 | Extensive investigations were conducted in (Brameshuber et al., Standsicherheit horizontal belasteter Mauerwerkwände unter geringer Auflast, 2014 ) to analyse the load bearing and deformation behaviour especially of lightly loaded basement walls made of hollow clay units under out-of-plane shear load. Particular attention was paid to the bond between basement wall and the adjacent building members considering also the damp-proof courses. Therefore, an essential part of this work was the determination of the material laws of the bond at the bottom of the wall comprising the shear bond strength, the friction coefficient as well as the softening behaviour. For this purpose a test method was developed. The material laws were determined applying a two-dimensional numerical simulation of the shear tests by means of a best possible adjustment of the calculated curves to the test curves. Applying the material laws of the material components and the bond, two-dimensional numerical simulations of masonry walls under axial compression and out-of-plane shear load were performed. Simultaneously, experimental investigations with simplified horizontal load transfer were also conducted on floor-to-ceiling walls which served to calibrate the finite element (FE) model. Finally, a parameter study was performed with the calibrated FE model of the wall, selectively varying the distribution of the earth pressure as well as the value and eccentricity of the vertical load. From this study it becomes apparent that the earth pressure distribution exerts a decisive influence on the deformation and load bearing capacity of the basement wall. | Lightweight masonry basement walls under out-of-plane loading | 10.1617/s11527-016-0805-9 |
2016-11-01 | Entropic uncertainty relation (EUR) quantifies the precision of measurements for arbitrary two non-commuting observables within a specified system. Due to exposure in a noisy environment, a practical system unavoidably suffers from decay by interacting with the environment. Inthis paper, we investigate the dynamic behaviors of EUR for a pair of non-commuting observables under two typical dissipative environments. Specifically, we study the dynamics features of EUR in a single-qubit system under the degradation induced by amplitude damping (AD) and depolarizing noises, respectively. It has been found that AD and depolarizing noises do not always cause the increase of the uncertainty, and can reduce the amount in a relative long-time regime. Remarkably, it has been shown that there exists a critical phenomenon that AD noise can always lead to the reducing of the uncertainty when the ratio of ground state and excited state is beyond a threshold in the system. Furthermore, we propose a general and effective approach to steer EUR by means of a kind of non-unitary operations, namely, quantum weak measurements. It is verified that quantum weak measurements can effectively reduce the entropic uncertainty in the dissipative environment. | Entropic Uncertainty Relation Under Dissipative Environments and Its Steering by Local Non-unitary Operations | 10.1007/s10773-016-3085-9 |
2016-11-01 | Many works have been focused on the use of the base isolation to improve the dynamic response of the rigid blocks, avoiding the overturning of these systems. In this paper the effects of a mass damper on the rocking motion of a non-symmetric rigid block, subject to one-sine pulse type excitation, is investigated. The damper is modelled as a pendulum, hinged at the top of the block, with the mass lumped at the end. The equations of rocking motion, the uplift and the impact conditions are derived and the results are obtained by numerical integration of these equations. An extensive parametric analysis is performed, by taking as variable parameters the eccentricity of the centre of mass, the frequency and the amplitude of the excitation and the characteristics of the mass damper. Here the geometrical parameters characterizing the block are taken as fixed quantities, since the main objective of the study is understand if it is possible to find the optimal properties of the pendulum, capable to make more difficult the overturning of the body. The results show that the presence of the mass damper, if correctly designed, leads to a general improvement of the response of the system, since the overturning of the block occurs for values, of the amplitude of the base excitation, higher than those observed where no mass damper is used. Curves providing the optimum value of the characteristics of the mass damper versus the parameters characterizing the excitation, are finally obtained. | On the use of a pendulum as mass damper to control the rocking motion of a rigid block with fixed characteristics | 10.1007/s11012-016-0448-5 |
2016-11-01 | In this paper, a comprehensive review of the present literature on energy generated magnetorheological (MR) fluid based damper, modeling and applications of the MR damper are presented. The review starts with an introduction of the basic of MR fluid and their different modes, consequences with different types of MR fluids based devices, and their relevant applications. Besides, various forms of MR damper and its applications are presented. Following this, the modeling of the MR fluids and the modeling of the MR fluid based damper are deliberated according to arrangement and configurations. Finally, the review ends with the design and advancement issues, performance analysis matters, and analytical modeling of energy generated magnetorheological fluid damper systems. | Advancement in energy harvesting magneto-rheological fluid damper: A review | 10.1007/s13367-016-0035-2 |
2016-11-01 | This paper introduces a new type of tuned liquid damper (TLD) having a relatively simple, easy-to-model behavior and high effectiveness in controlling structural vibrations. It consists of a traditional TLD with addition of a floating roof. Since the roof is much stiffer than water, it prevents wave breaking, hence making the response linear even at large amplitudes. The roof also facilitates the incorporation of supplemental devices with which the level of damping of the liquid vibration can be substantially augmented. This newly proposed TLD, denoted as tuned liquid damper with floating roof (TLD-FR), maintains the traditional advantages of TLDs (low cost, easy installation and tuning), but its numerical characterization is much simpler because the floating roof suppresses higher sloshing vibration modes, resulting in a system that can be represented by a single-degree-of-freedom model. An efficient numerical scheme, where the dynamic behavior of the TLD-FR is expressed as a second-order lineal system of equations, is discussed and validated by scaled experimental tests. The equations of motion of a structure equipped with a TLD-FR are then derived and manipulated to offer a unifying representation dependent upon only four model characteristics of the TLD-FR: The first three (mass, frequency and damping ratios) are common for all type of mass dampers, whereas the final one, termed efficiency index, is related to a similar parameter used to characterize liquid column dampers. Through this approach, the behavior of the proposed TLD-FR can be easily correlated with the behavior of other well-known linear mass damper devices. The relationship between these parameters and the geometrical characteristics of the TLD-FR is also examined. Finally, the identification of the optimal characteristic of the TLD-FR (natural frequency and damping) under stationary stochastic excitation is discussed. | Modeling and experimental validation of a new type of tuned liquid damper | 10.1007/s00707-015-1536-7 |
2016-10-27 | Accurate determination of squeeze-film damping (SFD) plays an important role in the design of high- Q microresonators. Many analytical models for predicting SFD on the microplate vibrating in a tilting motion have been well established in the past. However, most of the previous works focused on the rectangular torsion microplates. There are few analytical models for the SFD on the circular microplate vibrating in the tilting motion. Only one model was developed by Xia et al. (Microfluid Nanofluid 19:585–593, 2015 ). However, the gas in the air gap was treated as an incompressible gas in their model, and the perforation effect was not considered. This paper first studies the SFD on a non-perforated circular microplate vibrating in the tilting motion. The effects of both gas compressibility and rarefaction are considered in a modified Reynolds equation. The air pressure under the circular microplate is approximated by using Bessel series. A more accurate analytical expression for the damping and spring constants has been developed. Then, the model for the non-perforated microplates is extended to include the perforation effect. The present models are validated by comparison of the numerical results obtained by finite element method over a wide range of frequency and perforation ratios. | Squeeze-film damping of circular microplates vibrating in a tilting motion | 10.1007/s10404-016-1816-0 |
2016-10-01 | The simple constant hysteretic damping model is known to be non-causal although it is used often in diverse branches of engineering. In this paper the response of a single degree of freedom oscillator having linear hysteretic damping under arbitrary force excitation has been studied after deriving the impulse response function of the system. Some shortcomings of the results available in literature have been pointed out. It has been shown that the damping model can be practically used for calculating the response of a physical system when the damping is small and the force has small duration. | On Response of a Single-Degree-of-Freedom Oscillator with Constant Hysteretic Damping Under Arbitrary Excitation | 10.1007/s40032-016-0249-6 |
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