publicationDate stringlengths 10 10 | abstract stringlengths 0 37.3k | title stringlengths 1 5.74k | doi stringlengths 11 47 ⌀ |
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2013-07-01 | In this study, the effects of variable damping setting induced brake pressure oscillations on axle and wheel oscillations have been experimentally explored. For this, antilock brake system (ABS) tests are conducted on wet and slippery rough roads with hard, medium-hard and soft shock absorbers. In ABS tests, the axle height, the longitudinal and vertical axle accelerations have been measured. The results are discussed for time and frequency responses of axle vibrations in vertical and longitudinal direction. The time responses are separately considered for high and low piston velocities of damper. Also, in order to occur the effects of changes in ABS-brake pressure on axle vibrations, novel rules are designed. These rules are based on the integration of suspension dynamics into braking dynamics. The results show that the brake pressure is distinctly changed by variable damping settings. In time responses, these differences are determined by changes in time period and magnitude of brake pressure during build-up and reduction process. In frequency responses, the brake pressure differences are occurred by the different change frequencies of brake pressure causing resonance at axle vibrations. Also, the changes in magnitude of resonance peaks have determined the effects of brake pressure changes on axle vibrations. As a result, it is possible to damp the oscillations by changing the magnitude and frequency of brake pressure by means of the damper settings during ABS-braking. | Dynamical investigation of effects of variable damper settings induced brake pressure oscillations on axle and wheel oscillations during ABS-braking based on experimental study | 10.1007/s11012-012-9654-y |
2013-07-01 | Water-ligand observed via gradient spectroscopy (WaterLOGSY) is a widely used nuclear magnetic resonance method for ligand screening. The crucial procedure for the effectiveness of WaterLOGSY is selective excitation of the water resonance. The selective excitation is conventionally achieved by using long selective pulse, which causes partial saturation of the water magnetization leading to reduction of sensitivity, in addition to time consuming and error prone. Therefore, many improvements have been made to enhance the sensitivity and robustness of the method. Here we propose an alternative selective excitation scheme for WaterLOGSY by utilizing radiation damping effect. The pulse scheme starts simply with a hard inversion pulse, instead of selective pulse or pulse train, followed by a pulse field gradient to control the radiation damping effect. The rest parts of the pulse scheme are similar to conventional WaterLOGSY. When the gradient pulse is applied immediately after the inversion pulse, the radiation damping effect is suppressed, and all of the magnetization is inversed. When the gradient pulse and the inversion pulse are about 10–20 ms apart, the radiation damping effect remains active and drives the water magnetization toward +z-axis, resulting in selective non-inversion of the water magnetization. By taking the differences of the spectra obtained under these two conditions, one should get the result of WaterLOGSY. The method is demonstrated to be simple, robust and sensitive for ligand screening. | Biomolecular ligands screening using radiation damping difference WaterLOGSY spectroscopy | 10.1007/s10858-013-9748-4 |
2013-07-01 | The effect of stiffness of shock-absorbing pads of a real explosion chamber on the degree of vibration damping and maximum stresses in the body of the camera is experimentally and numerically investigated. The results are analyzed. A relation between the seismic effect on the foundation after a charge explosion inside the chamber and durability of its operation is revealed. | Effect of stiffness of shock-absorbing pads on the stresses in explosion chambers | 10.1134/S0021894413040196 |
2013-07-01 | In this article, a new two-stage hybrid optimization method based on the Particle Swarm Optimization and the Big Bang-Big Crunch algorithm (BB-BC) is introduced for identification of highly non-linear systems. In this hybrid algorithm, the term of the center of mass from the BB-BC algorithm is incorporated into the standard particle swarm optimizer to markedly improve its searching abilities. In order to investigate the effectiveness of the newly formed optimization algorithm in identification of non-linear and hysteretic systems, it is utilized to optimally find the Bouc-Wen model’s parameters for a sample MR damper in which the damper’s force is related to its piston’s motion through a non-linear differential equation. The obtained results indicate that the proposed optimization method is highly robust and accurate and can be utilized successfully in such intricate non-linear identification problems. | A new hybrid optimization algorithm for recognition of hysteretic non-linear systems | 10.1007/s12205-013-0341-x |
2013-06-01 | The operating range of aerodynamic compressors is usually limited by a phenomenon known as surge. Active surge control has showed the ability to extend the operating range significantly. This study presents a solution to this problem based on classical PID regulator and a new PI fuzzy logic approach with three lines of protection. The fuzzy controller is designed to avoid the surge instability on a given compressor model. Simulation studies show promising results at different operating points compared to the results obtained using PID controller. | PID and Novel Approach of PI Fuzzy Logic Controllers for Active Surge in Centrifugal Compressor | 10.1007/s13369-013-0601-6 |
2013-06-01 | This paper is concerned with a system of nonlinear wave equations with supercritical interior and boundary sources and subject to interior and boundary damping terms. It is well-known that the presence of a nonlinear boundary source causes significant difficulties since the linear Neumann problem for the single wave equation is not, in general, well-posed in the finite-energy space H ^1(Ω) × L ^2(∂Ω) with boundary data from L ^2(∂Ω) (due to the failure of the uniform Lopatinskii condition). Additional challenges stem from the fact that the sources considered in this article are non-dissipative and are not locally Lipschitz from H ^1(Ω) into L ^2(Ω) or L ^2(∂Ω). With some restrictions on the parameters in the system and with careful analysis involving the Nehari Manifold, we obtain global existence of a unique weak solution and establish (depending on the behavior of the dissipation in the system) exponential and algebraic uniform decay rates of energy . Moreover, we prove a blow-up result for weak solutions with nonnegative initial energy . | Global existence and decay of energy to systems of wave equations with damping and supercritical sources | 10.1007/s00033-012-0252-6 |
2013-06-01 | A general contact force law for arbitrarily shaped bodies is presented. At first an advanced contact force law is derived from the well know Hertz contact law. The obtained formulation of the Hertz contact law can be applied to the contact of arbitrarily shaped bodies. In a second step this contact model is applied to the contacts among polyhedral particles. The results are compared to finite element simulations. The model is extended by terms for damping and friction. The behaviour of the damping and friction model are demonstrated with simple examples. The force law is then implemented in the discrete element method (DEM). The application of this DEM is demonstrated by a simulation of the particle movement in a mixer. | Contact forces of polyhedral particles in discrete element method | 10.1007/s10035-013-0417-9 |
2013-06-01 | The heave motion of a floating structure is critical, as a favorable heave characteristic permits dry tree systems, amongst other benefits. The heave response can be suppressed by installing heave plates. However, the associated hydrodynamic effects, which include viscous damping and added mass, are very complicated. Moreover, there are limited experimental investigations to understand the heave plate effects on actual platform designs. This paper aims to study the abovementioned issue based on a novel deep draft multi-spar (DDMS) platform, for four different configurations (with/without upper and lower heave plates). A set of experiments (free decay, regular and irregular wave tests) are conducted, and compared with time domain and linearized frequency domain analyses. Amongst other things, the investigations and discussions include the added mass and damping coefficients for the platform and heave plates, comparison of experimental and numerical results, and the influence of the heave plates on the surge, heave and pitch motions. | Experimental and numerical study of the effects of heave plate on the motion of a new deep draft multi-spar platform | 10.1007/s00773-012-0203-0 |
2013-06-01 | The performance of a classical damping matrix, constructed either from the use of initial structural properties or current structural properties, in the step-by-step solution of a nonlinear multiple degree of freedom (MDOF) system is analytically evaluated. The analytical results are confirmed by numerical examples. Consequently, some conclusions are drawn from these analytical results that might be considered as rough guidelines for practical applications. It is found that a classical damping matrix constructed from initial structural properties is adequate for practical applications, since it has approximately the same damping effect as obtained by current structural properties and is more efficient in terms of computing. | Nonlinear performance of classical damping | 10.1007/s11803-013-0171-3 |
2013-06-01 | We consider the Cauchy problem for the semilinear wave equation $${u_{tt} - \Delta u + V(x)u_t = |u|^p}$$ .When $${V(x) = V_0(1 + |x|^2)^{-1/2}, V_0 \geq n}$$ , we prove that the critical exponent for the problem is $${p_c(n)=\left\{\begin{array}{ll} 1+\frac{2}{n-1},& n \geq 2,\\ +\infty,& n=1. \end{array}\right.}$$ | Critical exponent for semilinear wave equation with critical potential | 10.1007/s00030-012-0214-x |
2013-06-01 | In this paper, we investigate the Cauchy problem for the generalized improved Boussinesq equation with Stokes damped term in n -dimensional space. We observe that the dissipative structure of the linearized equation is of the regularity-loss type. This means that we have the optimal decay estimates of solutions under the additional regularity assumption on the initial data. Based on the decay estimates of solutions to the corresponding linear equation and smallness condition on the initial data, we prove the global existence and asymptotic of the small amplitude solution in the time-weighted Sobolev space by the contraction mapping principle. | On the asymptotic behavior of solution for the generalized IBq equation with Stokes damped term | 10.1007/s00033-012-0257-1 |
2013-06-01 | Many of the existing wave energy converters (WEC) are of oscillating water column (OWC) and point absorber (PA) types. Fewer references have been published in public on the pendulum type WEC. A series of experimental tests on a bottom-hinged pendulum WEC model are carried out and some results are revealed in the present study. The purpose of this paper is to present a detailed description of the tests. It is found that wave energy conversion efficiency varies with the applied damping and wave conditions. In addition, special attention is given to the effect of the water ballast on the efficiency of the wave energy converter. It is demonstrated that the ballast plays an important role in energy extraction. Better understanding on how the performance of the device is influenced by damping, wave height, wave period and ballast is shown. | Experimental study on a pendulum wave energy converter | 10.1007/s13344-013-0031-y |
2013-06-01 | In the paper the application of the polynomial chaos expansion in case of parametric vibrations problem is presented. Hitherto this innovative approach has not been applied to such a stochastic problem. The phenomenon is described by a nonlinear ordinary differential equation with periodic coefficients. It can be observed among others in cable-stayed bridges due to periodic excitation caused by a deck or a pylon. The analysis is focused on a real situation for which the problem of parametric resonance was observed (a cable of the Ben-Ahin bridge). The characteristic of the viscous damper is considered as a log-normal random variable. The results obtained by the use of the polynomial chaos approximations are compared with the ones based on the Monte Carlo simulation. The convergence of both methods is discussed. It is found that the polynomial chaos yields a better convergence then the Monte Carlo simulation, if resonant vibrations appear. | Application of the polynomial chaos approximation to a stochastic parametric vibrations problem | 10.1016/j.acme.2012.12.007 |
2013-05-01 | Space launchers are submitted to complex vibration environments and this can impact the payload it is carrying. Ensuring the protection of the payload therefore requires the addition of a secondary system. In this paper, a rapid design method for the dimensioning of a friction damper is developed, based on the equivalent energy dissipation with that of a viscous damper. A friction damper is designed and a prototype is built. The friction damper is first characterised alone and it is then mounted inside a scale model of a launcher last stage. The friction damper is adequately modelled by a spring in series with a friction element. The damper prototype proves to efficiently damp the rocket engine vibrations, and the design method used for dimensioning the friction damper gives a good approximation for the optimal sliding force of the damper. | Design and test of a friction damper to reduce engine vibrations on a space launcher | 10.1007/s00419-012-0718-1 |
2013-05-01 | The authors study the Cauchy problem for the semi-linear damped wave equation $$u_{tt} - \Delta u + b\left( t \right)u_t = f\left( u \right), u\left( {0,x} \right) = u_0 \left( x \right), u_t \left( {0,x} \right) = u_1 \left( x \right)$$ in any space dimension n ≥ 1. It is assumed that the time-dependent damping term b ( t ) > 0 is effective, and in particular tb ( t ) → ∞ as t → ∞. The global existence of small energy data solutions for | f ( u )| ≈ | u |^ p in the supercritical case of $$p > \tfrac{2} {n}$$ and $$p \leqslant \tfrac{n} {{n - 2}}$$ for n ≥ 3 is proved. | Semi-linear wave equations with effective damping | 10.1007/s11401-013-0773-0 |
2013-05-01 | It is proven that linear oscillatory systems with hysteretic damping in the form of complex stiffness and/or complex elastic moduli satisfy the causality principle: the response of such a system to an arbitrary external force cannot appear earlier than the onset of the force. The proof, based on a rigorous solution to the problem of forced oscillations, is presented in detail for an oscillator with a complex stiffness, as well as in a brief explanation for a system with N mass. It is also shown that these systems are Lyapunov-unstable. A comparison is made to other linear hysteretic damping models. | Hysteretic damping and causality | 10.1134/S1063771013030032 |
2013-05-01 | Instrumented indentation is used to measure the complex modulus of highly plasticized polyvinyl chloride (HP-PVC) and four kinds of polyethylene over the frequency range of 1–50Hz. Over this range, the loss factor for the HP-PVC increases from 0.3 to 1, making this an ideal material for damping out noise and vibration. The storage moduli for the four polyethylene samples are ordered according to density, with the lowest-density material have the lowest storage modulus. Results for both storage modulus and loss factor compare well with published results obtained by dynamic mechanical analysis for nominally similar materials. | Measuring the complex modulus of polymers by instrumented indentation testing | 10.1111/j.1747-1567.2011.00732.x |
2013-05-01 | The current paper uses the Extended Kantorovich Method (EKM) to analytically solve the problem of squeezed film damping in micromirrors. First a one term Galerkin approximation is used and following the extended Kantorovich procedure, the solution of the Reynolds equation which governs the squeezed film damping in micromirrors is reduced to solution of two uncoupled ordinary differential equation which can be solved iteratively with a rapid convergence for finding the pressure distribution underneath the micromirror. It is shown that the EKM results are independent of the initial guess function. It is also shown that EKM is highly convergent and practically one iterate is sufficient for obtaining a precise response. Furthermore using the presented closed form solutions for the squeezed film damping torque, it is proved that when the tilting angle of the mirror is small, the damping is linear viscous one, while when the tilting angle is finite, the damping would be linearly proportional with the angular velocity of the mirror and at the same time it is a nonlinear function of the tilting angle of the mirror. Results of this paper can be used for accurate dynamical simulation of micromirrors with presence of the squeezed film damping. | Modeling squeezed film air damping in torsional micromirrors using extended Kantorovich method | 10.1007/s11012-012-9632-4 |
2013-05-01 | In this paper, we establish a set of sufficient conditions for the controllability of damped second-order impulsive neutral integrodifferential systems with nonlocal initial conditions in Banach spaces. The approach used is the Sadovskii fixed point theorem combined with a noncompact condition on the cosine family of operators. An example is presented to illustrate the result. | Controllability results for damped second-order impulsive neutral integrodifferential systems with nonlocal conditions | 10.1007/s11768-013-1084-4 |
2013-05-01 | The control study of vehicle semi-active suspension with magneto-rheological (MR) dampers has been attracted much attention internationally. However, a simple, real time and easy implementing semi-active controller has not been proposed for the MR full-vehicle suspension system, and a systematic analysis method has not been established for evaluating the multi-objective suspension performances of MR full-vehicle vertical, pitch and roll motions. For this purpose, according to the 7-degree of freedom (DOF) full-vehicle dynamic system, a generalized 7-DOF MR and passive full-vehicle dynamic model is set up by employing the modified Bouc-wen hysteretic force-velocity ( F-v ) model of the MR damper. A semi-active controller is synthesized to realize independent control of the four MR quarter-vehicle sub-suspension systems in the full-vehicle, which is on the basis of the proposed modified skyhook damping scheme of MR quarter-vehicle sub-suspension system. The proposed controller can greatly simplify the controller design complexity of MR full-vehicle suspension and has merits of easy implementation in real application, wherein only absolute velocities of sprung and unsprung masses with reference to the road surface are required to measure in real time when the vehicle is moving. Furthermore, a systematic analysis method is established for evaluating the vertical, pitch and roll motion properties of both MR and passive full-vehicle suspensions in a more realistic road excitation manner, in which the harmonic, rounded pulse and real road measured random signals with delay time are employed as different road excitations inserted on the front and rear two wheels, by considering the distance between front and rear wheels in full-vehicle. The above excitations with different amplitudes are further employed as the road excitations inserted on left and right two wheels for evaluating the roll motion property. The multi-objective suspension performances of ride comfort and handling safety of the proposed MR full-vehicle suspension are thus thoroughly evaluated by comparing with those of the passive full-vehicle suspension. The results show that the proposed controller can ideally improve multi-objective suspension performances of the ride comfort and handling safety. The proposed harmonic, rounded pulse and real road measured random signals with delay time and asymmetric amplitudes are suitable for accurately analyzing the vertical, pitch and roll motion properties of MR full-vehicle suspension system in a more realistic road excitation manner. This research has important theoretical significance for improving application study on the intelligent MR semi-active suspension. | Skyhook-based semi-active control of full-vehicle suspension with magneto-rheological dampers | 10.3901/CJME.2013.03.498 |
2013-05-01 | This paper deals with an input-based half car vehicle model moving with constant velocity over a terrain surface, where MR damper is fixed in both the wheels. The half car model fixed in a rolling dynamometer is operated with various input frequencies corresponding to various speeds. To design and develop control algorithms that will give optimum benefits of the unique features of the MR damper, models have been developed which adequately characterize the damper’s genuine, natural nonlinear behavior. The controller controls both the dampers according to variations in parameters of road surface, speed and load etc., with an advanced time with a particular time bound, through input (pre-programmed) based skyhook on/off control system. Comparison of experimental results of input based and ordinary skyhook on/off results indicates that the model is more functional and rewarding for vibration suppression over a wide range of operating conditions and is passable for control design and analysis. | Input advanced control of semi active half car heave model | 10.1007/s12206-013-0306-5 |
2013-04-10 | In this paper, the local fractional variational iteration method is given to handle the damped wave equation and dissipative wave equation in fractal strings. The approximation solutions show that the methodology of local fractional variational iteration method is an efficient and simple tool for solving mathematical problems arising in fractal wave motions. MSC: 74H10, 35L05, 28A80. | Damped wave equation and dissipative wave equation in fractal strings within the local fractional variational iteration method | 10.1186/1687-1812-2013-89 |
2013-04-01 | This paper is concerned with the dynamics of a spacecraft with multi-strut passive damper for large flexible appendage. The damper platform is connected to the spacecraft by a spheric hinge, multiple damping struts and a rigid strut. The damping struts provide damping forces while the rigid strut produces a motion constraint of the multibody system. The exact nonlinear dynamical equations in reducedorder form are firstly derived by using Kane’s equation in matrix form. Based on the assumptions of small velocity and small displacement, the nonlinear equations are reduced to a set of linear second-order differential equations in terms of independent generalized displacements with constant stiffness matrix and damping matrix related to the damping strut parameters. Numerical simulation results demonstrate the damping effectiveness of the damper for both the motion of the spacecraft and the vibration of the flexible appendage, and verify the accuracy of the linear equations against the exact nonlinear ones. | Dynamics of a spacecraft with large flexible appendage constrained by multi-strut passive damper | 10.1007/s10409-013-0005-6 |
2013-04-01 | Field data and two linear layered models were used to examine the baroclinic response to wind in a small elongated two-basin lake, Amisk Lake (Alberta, Canada). For the first vertical baroclinic mode, wind-forced horizontal modes were simulated using a dynamic two-layer variable cross-section (TVC) model. The first horizontal mode, H1, was found to dominate the exchange between the two basins of Amisk Lake. The highest velocities associated with H1 occurred in the constricted channel connecting the two basins. This high velocity led to strong damping which brought H1 in near-resonance with the diurnal wind despite a difference in periods. Along with H1, the second horizontal mode, H2, was detected at a thermistor mooring. The TVC showed that H2 resulted from the coupling between along-thalweg wind distribution and the bathymetry of Amisk Lake. The damping for H2 was found to be weaker than for H1, likely because of weaker bottom drag in the connecting channel. The evolution of vertical H1 modes were simulated using a multi-layered box model. In response to wind pulses, the first vertical mode V1H1 initially dominated over higher vertical modes causing two-layer exchange. Following the faster decay of V1H1, higher vertical modes shifted the exchange to three and more layers. Our study shows the importance of the coupling between wind stress distribution and lake bathymetry in exciting horizontal modes, reveals the effect of damping on resonance with wind, and explains the evolution of exchange associated with vertical modes. | The baroclinic response to wind in a small two-basin lake | 10.1007/s00027-012-0268-1 |
2013-04-01 | Hydrogels have gained wide usage in a range of biomedical applications because of their biocompatibility and the ability to finely tune their properties, including viscoelasticity. The use of hydrogels on the microscale is increasingly important for the development of drug delivery techniques and cellular microenvironments, though the ability to accurately characterize their micromechanical properties is limited. Here we demonstrate the use of microelectromechanical systems (MEMS) resonant sensors to estimate the properties of poly(ethylene glycol) diacrylate (PEGDA) microstructures over a range of concentrations. These microstructures are integrated on the sensors by deposition using electrohydrodynamic jet printing. Estimated properties agree well with independent measurements made using indentation with atomic force microscopy. | Micromechanical properties of hydrogels measured with MEMS resonant sensors | 10.1007/s10544-012-9730-z |
2013-04-01 | Excessive vibration, such as chatter, is a common problem in machining processes. Meanwhile, numerous hard, brittle metals have been shown to form segmented chips, also known as sawtooth chips, during machining. In the literature, a cyclic cutting force has been demonstrated where segmented chips are formed, with the force cycle corresponding to the formation of segments. Segmented chip formation has been shown to be linked to high vibration levels in turning and milling processes. Additionally, it has been proposed that the amplitude of chatter vibrations can be limited by interference between the tool flank and wavy workpiece surface, a phenomenon known as tool-flank process damping. In this contribution, a model is proposed to predict the amplitude of forced vibration arising due to the formation of segmented chips during turning. The amplitude of vibration was calculated as a function of cutting parameters. It was demonstrated that the model can be extended to account for the effect of tool-flank process damping. For validation, titanium Ti6Al4V alloy was turned using a flexible toolholder, with surface speed ranging from 10 to 160 m/min, feed rate from 0.1 to 0.7 mm/rev and width of cut from 0.35 to 4 mm. In the experimental validation, 25 of 68 test cuts exhibited high-amplitude vibration. In 16 of these cases, the main cause was concluded to be chip segmentation, which can be predicted by the model. The model is thus considered of practical value to machinists. | Modelling of segmentation-driven vibration in machining | 10.1007/s00170-012-4319-5 |
2013-04-01 | Noise measurements are especially a problem when the object under investigation is largely dimensioned and can only be measured from the distance. To obtain information about the location of noise generation, a measurement technique which makes sound visible in order to introduce further specific technical measures is advantageous. The question is if the time dependence of the signal got from such a non touching and non destructive acoustic method has the potential to calculate the materials damping from. Using a small sound source localization system (Microflown™ probe), specimens of magnesium alloys with different grain sizes obtained by hydrostatic extrusion were investigated. It has been demonstrated that the fine grained microstructure led to a lower damping and its dependence on the strain was reduced. In this context, acoustic measurements by a sound source localisation system which makes materials characterization possible could be used as a quality tool to detect changes in highly stressed components. This approach allows to promote a selective substitution of conventional materials by more innovative ones. The offshore sector is considered to be a field of application: Wind turbines produce noise emission which stems mainly from turbulences at the tips of the rotor blades and vibrations of components inside the nacelle ( e.g. gearbox, generator, …). If the vibration amplitudes are too high, microcracks of components can lead to failure over the long term. The monitoring of microstructural changes using a larger type of a sound source localisation system is considered as an innovative technical approach with respect to maintenance activities. | Acoustic measurements for determination of the materials damping using a sound source localisation system | 10.1007/s40195-012-0155-8 |
2013-04-01 | This paper investigates the effects of desired damping matrix and desired Hamiltonian function in the matching equation for Port–Hamiltonian (PH) systems. Once the desired Hamiltonian function is chosen, if the desired damping matrix is large enough, the convergence speed of the control law asymptotically stabilizing the PH system works more quickly. On the other hand, the desired Hamiltonian function can be replaced by a new desired energy function, which is also effective in energy-shaping. Finally, a three-phase synchronous generator example is given to show the correctness of the above contents. | On the effects of desired damping matrix and desired Hamiltonian function in the matching equation for Port–Hamiltonian systems | 10.1007/s11071-012-0693-7 |
2013-04-01 | We explore characteristics of onset and damping in a thermoacoustic engine (TE) driven by cryogens instead of conventional heat sources above the ambient temperature by a comprehensive study of a self-made standing-wave thermoacoustic engine driven by liquid nitrogen. The experiments verify the feasibility of enhancing the thermoacoustic oscillation at cryogenic temperatures. The onset temperature difference along the stack of the TE significantly decreases, compared with that of a conventional TE driven by high-temperature heat sources. The resonance frequency of the cryogen-driven TE is smaller than that of the heat-source-driven TE, mainly due to the lower average temperature of the working gas. Experiments and calculations show that the temperature discrepancy between onset and damping is partly caused by the linear temperature distribution along the stack before damping, together with the nonlinear distribution before onset. These results will contribute to a better understanding of thermoacoustic oscillation and to the recovery of the cold energy of cryogens. | Characteristics of onset and damping in a standing-wave thermoacoustic engine driven by liquid nitrogen | 10.1007/s11434-012-5214-z |
2013-04-01 | This work focuses on applying fuzzy control embedded in microcontrollers in an experimental apparatus using magnetorheological fluid damper. The non-linear behavior of the magnetorheological dampers associated with the parametric variations on vehicle suspension models corroborate the use of the fuzzy controllers. The fundamental formulation of this controller is discussed and its performance is shown through numeric simulations. An experimental apparatus representing a two degree of freedom system containing a magnetorheological damper is used to identify the main parameters and to evaluate the performance of the closed-loop system with the embedded low-cost microcontroller-based fuzzy controller. | Fuzzy Control Embedded in Microcontroller and Applied to an Experimental Apparatus Using Magnetorheological Fluid Damper | 10.1007/s40313-013-0012-7 |
2013-04-01 | The article describes the original design of a slit flow rheometer. The behavioral problems of MR fluids and the main deviation from the commonly introduced Bingham model, which describes the MR fluid, are explained at the beginning of this article. Furthermore, the usual operating parameters of the MR fluids and devices are defined, such as: shear rate, viscosity in the off-state, yield stress, their dependence on temperature and the expected life of the filling. In the absence of a suitable rheometer a new design of rheometer was proposed, which allows long-term testing of MR fluids under real loading conditions. This article describes the important details of the construction. Particular attention is devoted to temperature measurement, calibration of the rheometer and data analysis, including mathematical tools and statistical evaluation of a set of measured points. | Load and rheometric unit for the test of magnetorheological fluid | 10.1007/s11012-012-9620-8 |
2013-04-01 | The moderately damped regime (MDR) in a Josephson junction (JJ) is quite distinct from the well-known case of underdamped systems and quite common in devices characterized by low critical currents. Measurements of switching current distribution (SCD) are a direct way of discriminating the phase dynamics and the transport also in nontrivial cases of moderate damping. MDR is going to be more and more common with advances in nanopatterning superconductors and in materials science finalized to build hybrid devices. We report on measurements of SCDs, both in the thermal and quantum regime, on moderately damped NbN/MgO/NbN JJs. A transition from the Thermal Activation (TA) regime to Macroscopic Quantum Tunnelling (MQT) occurs at about 90 mK, while above 1.6 K a phase diffusive dynamics is clearly observed. The combined analysis of these regimes through numerical simulations allowed us to extract the fundamental parameters, which completely characterize the phase dynamics of such moderately damped JJs. | Study of Phase Dynamics in Moderately Damped Josephson Junctions | 10.1007/s10948-012-1863-z |
2013-03-29 | Spin-transfer torque (STT) magnetization reversal in a magnetic tunneling junction (MTJ), Ta/CoFeB/MgO/CoFeB/Ta, built on the tip of a nanoprobe in a direct contact with a copper substrate is demonstrated in the previously unexplored sub-10-nm diameter range. With the contact resistance of the order of 185 kOhm, the measured magnetoresistance value was 29 %. The average STT reversal current of 95 nA indicated a switching current density of approximately 0.1 MAcm^−2 which is more than 30 times smaller than the smallest value reported for STT-MTJs of larger dimensions. An atomistic-scale theory confirmed the experimental result which indicates at least an order of magnitude reduction of the spin damping in the sub-10-nm diameter range. | Energy-efficient spin-transfer torque magnetization reversal in sub-10-nm magnetic tunneling junction point contacts | 10.1007/s11051-013-1599-0 |
2013-03-01 | Adhesives fulfil a damping function | 10.1365/s35784-013-0202-5 | |
2013-03-01 | In the present study, the effect of various soil–rock and rock–rock foundation systems on dynamic response of block foundations of different mass and equivalent radius under vertical mode of vibration is investigated. The frequency dependent stiffness and damping of foundation resting on homogeneous soil and rocks are determined using the half-space theory. The dynamic response characteristics of foundation resting on the layered system considering soil–rock and rock–rock combinations are evaluated using finite element program with transmitting boundaries. The procedure to determine the frequency amplitude response of soil–rock and weathered rock–rock systems is discussed in detail and the equations are proposed for the same. The variation of natural frequency and resonant amplitude with shear wave velocity are investigated for different top layer thickness. The dynamic behaviour of foundation is also determined for different rock–rock systems by considering sandstone, shale and limestone underlain by basalt rock. The variation of the stiffness, damping and amplitudes of foundation with frequency are shown in this study for various rock–rock combinations. It has been observed that the natural frequency increases and the peak displacement amplitude decreases with increase in shear wave velocity ratio. The variation of natural frequency and peak displacement amplitude are also studied for different top layer thickness and eccentric moments. Finally the parametric study is carried out to determine the natural frequency and resonant amplitude for block foundations of size 4 m × 3 m × 2 m and 8 m × 5 m × 2 m using generalized relations proposed in the present study. | Dynamic Response of Block Foundations Resting on Soil–Rock and Rock–Rock System Under Vertical Excitation | 10.1007/s40098-012-0036-0 |
2013-03-01 | The mechanisms of energy dissipation are discussed in this paper by reviewing the models and research in atomic-scale friction. The study is undertaken to answer a fundamental question in the study of friction: How is frictional work dissipated, particularly in cases where material damage and wear are not involved. The initiation of energy dissipation, the role of structural commensurability, and the estimation of the interfacial shear strength have been examined in detail by introducing the Tomlinson model, the Frenkel-Kontorova model, and the cobblestone model, respectively. The discussion is extended to energy dissipation progress described in terms of phononic and electronic damping. The contributions from other mechanisms of dissipation such as viscoelastic relaxation and material wear are also included. As an example, we analyzed a specific process of dissipation in multilayer graphene, on the basis of results of molecular dynamics (MD) simulations, which reveal a reversible part of energy that circulates between the system and the external driver. This leads us to emphasize that it is crucial in future studies to clearly define the coefficient of dissipation. | Energy dissipation in atomic-scale friction | 10.1007/s40544-013-0002-6 |
2013-03-01 | A third-order correction was recently suggested to improve the accuracy of the half-power bandwidth method in estimating the damping of single DOF systems. This paper analyzes the accuracy of the half-power bandwidth method with the third-order correction in damping estimation for multi-DOF linear systems. Damping ratios in a two-DOF linear system are estimated using its displacement and acceleration frequency response curves, respectively. A wide range of important parameters that characterize the shape of these response curves are taken into account. Results show that the third-order correction may greatly improve the accuracy of the half-power bandwidth method in estimating damping in a two-DOF system. In spite of this, the half-power bandwidth method may significantly overestimate the damping ratios of two-DOF systems in some cases. | Accuracy of the half-power bandwidth method with a third-order correction for estimating damping in multi-DOF systems | 10.1007/s11803-013-0149-1 |
2013-03-01 | The analysis of elastomeric coating influence on dynamic resonant stresses values in spring is presented in this paper. The appropriate equations determining the effectiveness of dynamic stress reduction in resonant conditions as a function of coating parameters were derived. It was proved that rubber coating will not perform in satisfactory manner due to its low modulus of elasticity in shear. It was also demonstrated that about-resonance areas of increased stresses are wider and wider along with the successive resonances and achieve significant values even at large distances from the resonance frequencies. | Analysis of the influence of elastomeric layer on helical spring stresses in longitudinal resonance vibration conditions | 10.1016/j.acme.2012.10.009 |
2013-03-01 | When simulating seismic wave propagation in free space, it is essential to introduce absorbing boundary conditions to eliminate reflections from artificially truncated boundaries. In this paper, a damping factor referred to as the Gaussian damping factor is proposed. The Gaussian damping factor is based on the idea of perfectly matched layers (PMLs). This work presents a detailed analysis of the theoretical foundations and advantages of the Gaussian damping factor. Additionally, numerical experiments for the simulation of seismic waves are presented based on two numerical models: a homogeneous model and a multi-layer model. The results show that the proposed factor works better. The Gaussian damping factor achieves a higher Signal-to-Noise Ratio (SNR) than previously used factors when using same number of PMLs, and requires less PMLs than other methods to achieve an identical SNR. | A study of damping factors in perfectly matched layers for the numerical simulation of seismic waves | 10.1007/s11770-013-0361-9 |
2013-03-01 | The effect of the presence of a shield on the stress state of the casing of a real explosion chamber and the rate of decay of its vibrations was studied experimentally. Considerable decrease in the stress was observed in the shielded part of the casing and at its pole at which the shield was not installed. It was shown that the use of a local shield in the form of a shell ring significantly increased the duration of vibrations of the casing, in particular at the pole. | Effect of shielding of a part of the casing of a technological explosion chamber on its stress state | 10.1134/S002189441302020X |
2013-03-01 | In this paper, an analysis for active constrained layer damping (ACLD) of rotating composite beams undergoing geometrically non linear vibrations has been carried out. Commercially available vertically/obliquely reinforced 1-3 piezoelectric composite (PZC) material has been used as the material of the constraining layer of the ACLD treatment. A finite element (FE) model has been derived to carry out the analysis. The substrate beam is considered thin and hence, first order shear deformation theory (FSDT) and von-Karman type nonlinear strain–displacement relations are used to derive the coupled electromechanical nonlinear FE model. The rotary effect has been suitably modelled by incorporating extensional strain energy due to centrifugal force. The Golla–Hughes–McTavish method has been employed to model the constrained viscoelastic layer of the ACLD treatment in the time domain. The numerical responses revealed that the ACLD treatment with 1-3 PZC constraining layer efficiently performs the task of active damping of geometrically nonlinear vibrations of the rotating composite beams. The effects of the fibre orientation angles of the angle-ply substrate beams and the 1-3 PZC constraining layer on the ACLD of the geometrically nonlinear vibrations have been investigated. Also, the effect of the thickness variations of the 1-3 PZC layer and the viscoelastic constrained layer on the damping characteristics of the overall rotating composite beams has been studied. | Active constrained layer damping of geometrically nonlinear vibration of rotating composite beams using 1-3 piezoelectric composite | 10.1007/s10999-012-9207-5 |
2013-03-01 | In the present survey, some progress in the stochastic dynamics and fractional optimal control of quasi integrable Hamiltonian systems with fractional derivative damping is reviewed. First, the stochastic averaging method for quasi integrable Hamiltonian systems with fractional derivative damping under various random excitations is briefly introduced. Then, the stochastic stability, stochastic bifurcation, first passage time and reliability, and stochastic fractional optimal control of the systems studied by using the stochastic averaging method are summarized. The focus is placed on the effects of fractional derivative order on the dynamics and control of the systems. Finally, some possible extensions are pointed out. | Stochastic dynamics and fractional optimal control of quasi integrable Hamiltonian systems with fractional derivative damping | 10.2478/s13540-013-0013-z |
2013-03-01 | Based on existing low-frequency water-filled impedance tube testing facilities, which is a part of the Low Frequency Facility of the Naval Undersea Warfare Center in Beijing, an improved water-filled pulse tube method is presented in this short paper. This proposed study is significantly different from the conventional pulse tube method because of the capability for a single plane damped sine pulse wave to generate in the water-filled pulse tube with a regular waveform and short duration time of about 1ms. During the generation process of the pulse, an inverse filter principle was adopted to compensate the transducer response. The effect of the characteristics of tube termination can be eliminated through the generation process of the pulse. Reflection coefficient from a water/air interface was measured to verify the proposed method. When compared with the expected theoretical values, a relatively good agreement can be obtained in the low frequency range of 500–2 000 Hz. | An improved water-filled pulse tube method using time domain pulse separation method | 10.1007/s11804-013-1173-x |
2013-03-01 | The seismic performance of “added stories isolation” (ASI) systems are investigated for 12-story moment resisting frames. The newly added and isolated upper stories on the top of the existing structure are rolled to act as a large tuned mass damper (TMD) to overcome the limitation of the size of tuned mass, resulting to “12 + 2” and “12 + 4” stories building configurations. The isolation layer, as a core design strategy, is optimally designed based on optimal TMD design principle, entailing the insertion of passive flexible laminated rubber bearings to segregate two or four upper stories from a conventionally constructed lower superstructure system. Statistical performance metrics are presented for 30 earthquake records from the 3 suites of the SAC project. Time history analyses are used to compute various response performances and reduction factors across a wide range of seismic hazard intensities. Results show that ASI systems can effectively manage seismic response for multi-degree-of freedom (MDOF) systems across a broader range of ground motions without requiring burdensome extra mass. Specific results include the identification of differences in the number of added story by which the suggested isolation systems remove energy. | Innovative seismic retrofitting strategy of added stories isolation system | 10.1007/s11709-013-0195-9 |
2013-02-01 | Record of damages and casualties caused by earthquakes in Thailand reveals that Chiang Mai, the second largest province of Thailand, has faced the great threat among other provinces. Triaxial tests, standard penetration tests, and multichannel analysis of surface wave have been recently performed to understand the dynamic response of Chiang Mai ground. However, the cyclic simple shear test, which could convincingly represent the real seismic ground shaking under repeated horizontal shear force, has not been conducted yet. Therefore, this paper aims to characterize the behaviors of Chiang Mai sand under monotonic and cyclic loadings using a direct simple shear apparatus. Sand specimens taken from the Ping River were prepared by dry deposition technique. The mobilized friction angle at the critical state measured by the direct simple shear test is equal to 37.3° which is 9 % less than that measured by direct shear box test. This paper also provides the appropriate dynamic properties of Chiang Mai sand with the shear strain level <2 % for any practical purpose. Test results showed that the normalized shear modulus agrees well with other investigators while the damping ratio is noticeably smaller than the lower-bound range for sand reported in the past studies. | Monotonic and Cyclic Behavior of Chiang Mai Sand Under Simple Shear Mode | 10.1007/s10706-012-9563-9 |
2013-02-01 | This study seeks to develop a scientific understanding of the effects of dynamic loading history on the low-yield-strength shear panel damper (LYSPD) mechanical properties and fatigue performance. The LYSPD model is supposed as perfect elastic-plastic without strength deterioration. By adjusting the damper strength with the above supposition in the DYMO software, the serial earthquake response waves of the LYSPD under different soil conditions are obtained firstly. Subsequently, several waves, the most prone to damage at each soil condition, are selected as dynamic loading waves to verify the LYSPD dynamic performances experimentally. The test results suggest that the dynamic loading histories have no influence on the LYSPD strength or the supposed model while they affect the fatigue performance. The applicability and accuracy of three fatigue evaluation methods, cumulative plastic shear strain, cumulative energy absorption and Miner rule, are also compared according to the test results. | Research on the dynamic performance of low-yield-strength shear panel damper for bridge application | 10.1007/s12204-013-1374-5 |
2013-02-01 | The chaotic behavior of the elastic forced oscillators with real-power exponents of damping and restoring force terms under bounded noise is investigated. By using random Melnikov method, a mean square criterion is used to detect the necessary conditions for chaotic motion of this stochastic system. The results show that the threshold of bounded noise amplitude for the onset of chaos in the system increases as the intensity of the random frequency increases, and decrease as the real-power exponent of damping term increase. The threshold of bounded noise amplitude for the onset of chaos is determined by the numerical calculation via the largest Lyapunov exponents. The effects of bounded noise and real-power exponent of damping term on bifurcation and Poincaré map are also investigated. Our results may provide a valuable guidance for understanding the effect of bounded noise on a class of generalized double well system. | Noise-induced chaos in the elastic forced oscillators with real-power damping force | 10.1007/s11071-012-0672-z |
2013-02-01 | An approach is presented to the construction of the acoustic path for the waveguide method of testing using multiple reflections during nondestructive testing of linearly extended objects. The results of the studies on the method’s sensitivity, which depend on the test parameters, are given. | The acoustic path in the method of multiple reflections during nondestructive testing of linearly extended objects | 10.1134/S1061830913020058 |
2013-02-01 | In this article, the closed form expressions for the transverse vibrations of a homogenous isotropic, thermally conducting, Kelvin–Voigt type viscothermoelastic thin beam, based on Euler– Bernoulli theory have been derived. The effects of relaxation times, thermomechanical coupling, surface conditions, and beam dimensions on energy dissipation induced by thermoelastic damping in MEMS (micro-electromechanical systems) resonators are investigated for beams under clamped and simply supported conditions. Analytical expressions for deflection, temperature change, frequency shifts, and thermoelastic damping in the beam have been derived. Some numerical results with the help of MATLAB programming software in case of Silicon Nitride have also been presented. The computer-simulated results in respect of damping factor and frequency shift have been presented graphically. | Transverse vibrations in micro-scale viscothermoelastic beam resonators | 10.1007/s00419-012-0656-y |
2013-02-01 | The article illustrates an approach to the passive vibration control of thin plates utilizing prestressed superelastic shape memory alloy (SMA) wires. The SMA wires can freely slide within protective sleeves that are either embedded within the structure or bonded to its surface. The vibration control mechanism combines an effective continuous elastic foundation representing the support provided by SMA wires to the structure with the energy dissipation as a result of the hysteresis occurring in the wires. The other approach to the vibration control employs superelastic wires attached to the structure at discrete points. The mathematical formulation of the problem presented in the article can be adopted for a rigorous computational analysis. In particular, a closed form expression is obtained for the loss factor in large aspect ratio plates supported at the midspan by a system of parallel SMA wires. As follows from numerical examples presented for such plates, the proposed method offers a significant damping, far exceeding that observed in conventional engineering structures. | Vibrations of plates with superelastic shape memory alloy wires | 10.1007/s10665-011-9483-3 |
2013-01-01 | Steering torque effects on vehicle handling quality is investigated by a driver model based evaluation method. A driving simulator with a precise steering torque generating device is used for this experimental study. It is found the steering reactive torque to steering angle composed of spring, damping and spring-friction is effective on good handling quality. | A Study on Steering Reactive Torque for Steer-by-Wire Vehicle Using Driving Simulator | 10.1007/978-3-642-33795-6_20 |
2013-01-01 | This paper shows an investigation on optimal damping constant performed in the frequency domain. The optimal damping constant is meant as that value that minimizes the acceleration of all connected bodies characterizing a two degree of freedom system sketching a quarter car. The connected bodies are sprung and unsprung mass respectively for quarter of chassis and tire, this last keeps the contact with the ground and it is connected with the sprung mass through a shock absorber characterized by spring and fluid damper. Optimal damping constant was determined by imposing analytical conditions on the expression of acceleration of two masses. Afterwards, the variation of acceleration and position in function of frequency for the obtained value of damping constant is plotted numerically in two ways using Wolfram Mathematica and MSC Adams software. | Optimal Damping Constant Investigation on a Quarter-Car | 10.1007/978-94-007-6558-0_55 |
2013-01-01 | The cosmic microwave background (CMB) radiation, the relic of the early phases of the expanding universe, is bright, full of information, and difficult to measure. Along with the recession of galaxies and the primordial nucleosynthesis, it is one of the strongest signs that the Hot Big Bang Model of the universe is correct. It is brightest around 2 mm wavelength, has a temperature of $$T_{\mathrm{cmb}} = 2.72548 \pm 0.00057$$ K, and has a blackbody spectrum within 50 parts per million. Its spatial fluctuations (around 0.01% on 1 $${}^{\circ }$$ scales) are possibly the relics of quantum mechanical processes in the early universe, modified by processes up to the decoupling at a redshift of about 1,000 (when the primordial plasma became mostly transparent). In the cold dark matter (DM) model with cosmic acceleration ( $$\Lambda $$ CDM), the fluctuation statistics are consistent with the model of inflation and can be used to determine other parameters within a few percent, including the Hubble constant, the $$\Lambda $$ constant, the densities of baryonic and dark matter, and the primordial fluctuation amplitude and power spectrum slope. In addition, the polarization of the fluctuations reveals the epoch of reionization at a redshift approximately twice that determined from the Gunn-Peterson trough due to optically thick Lyman $$\alpha$$ absorption in QSO spectra. It is of historic importance, and a testament to the unity of theory and experiment, that we now have a standard model of cosmology that is consistent with all of the observations.Current observational challenges include (1) improvement of the spectrum distortion measurements, especially at long wavelengths, where the measured background is unexpectedly bright; (2) the search for the B-mode polarization (the divergence-free part of the polarization map), arising from propagating gravitational waves; and (3) the extension of fluctuation measurements to smaller angular scales. Much more precise spectrum observations near 2 mm are likely and would test some very interesting theories. Current theoretical challenges include explanation of the dark matter and dark energy; understanding, estimating, and removing the interference of foreground sources that limit the measurements of the CMB; detailed understanding of the influence of nonequilibrium processes on the decoupling and reionization phases; and searches for signs of the second order or exotic processes (e.g., isocurvature fluctuations, cosmic strings, non-Gaussian fluctuations). At this writing, we await the cosmological results of the Planck mission. | Cosmic Microwave Background | 10.1007/978-94-007-5609-0_13 |
2013-01-01 | A recently proposed two degrees-of-freedom model for axial and torsional vibrations of drill string elsewhere is here revisited. The model involves state-dependent time delay, with discontinuous cutting and friction force nonlinearities. The original model is, here, enhanced by introducing axial and torsional damping, and axial stiffness. Stability analysis, which is relatively recent for systems with state-dependent delays, is conducted on the enhanced model. For representative parameter values, it is concluded from the analysis that the original model (with no damping) had no stable operating regime, while the enhanced model possesses some practically relevant stable operating regime. The steady drilling state corresponding to the enhanced model is, however, still unstable for a major portion of the operating regime leading to stick-slip and bit-bounce situations. | Bit-Bounce and Stick-Slip in Drill-String Dynamics | 10.1007/978-94-007-5742-4_25 |
2013-01-01 | The goal of this paper is to derive L ^ p − L ^ q estimates away from the conjugate line for structural damped wave models. The damping term interpolates between exterior damping and viscoelastic damping. The crucial point is to derive at first L ^1 − L ^1 estimates. Depending on the behavior of the characteristic roots of the operator, one has to take into consideration oscillations in one part of the extended phase space. The radial symmetric behavior of the roots allows to apply the theory of modified Bessel functions. Oscillations may produce unbounded time-dependent constants (either for small times close to 0 or for large times close to infinity) in the L ^1 − L ^1 estimates. Some interpolation techniques imply the desired L ^ p − L ^ q estimates away from the conjugate line. |
L
^1 Estimates for Oscillating Integrals Related to Structural Damped Wave Models | 10.1007/978-1-4614-6348-1_11 |
2013-01-01 | A driving point dynamic load non destructive test can be used to determine the modal stiffness, damping and mass of a structure. If the constitutive equations of viscoelasticity consist of a combination of time independent elastic behavior and time dependent viscous behavior and can be modeled as a collection of spring-dashpot arrangements then the modal stiffness can be used to determine the time independent elastic behavior and the modal damping to determine the time dependent viscous behavior. Using a simple spring and dashpot in parallel model (Kelvin-Voigt), solutions for the material properties of uniform beams in axial deformation, torsion and bending will be given. For non-uniform beams, the elastic properties can be identified by the finite element method which is used to derive the equilibrium equations. The modal stiffness is used to get the zero frequency response (equivalent static response) which determines a single point in the global system flexibility matrix. The identification becomes a problem in minimizing the error norm of the equilibrium equations. Several numerical examples are presented, one of varying geometry and one of varying rigidity. | An Identification Method for the Viscoelastic Characterization of Materials | 10.1007/978-1-4614-4241-7_7 |
2013-01-01 | This contribution deals with the optimization of a tractor’s cab’s vertical acceleration. The mathematical model of the simplified system is derived. The acceleration of the chassis is considered as the actuating variable. In the optimization the acceleration of the tractor’s cab is minimized under the constraint of a maximum displacement between the cab and the chassis. The optimization result is used to get a smallest limit for the maximum of acceleration in case of active damping and acausal damping control. So the optimization result is a lower bound. | Vibration Attenuation by Semi-active Dampers | 10.1007/978-3-642-53862-9_35 |
2013-01-01 | This chapter is about time and transient responses of first-order systems. These systems are made of a combination of a mass, a damper, and a spring. Transient response refers to any excitation which will disappear after a while. In this chapter we also review the free response of the system because of non-zero initial conditions, and not because of excitation. | One Degree of Freedom, Time Response | 10.1007/978-1-4614-4160-1_7 |
2013-01-01 | Solving systems of linear equations (or linear systems or, also, simultaneous equations ) is a common situation in many scientific and technological problems. Many methods, either analytical or numerical, have been developed to solve them. A general method most used in Linear Algebra is the Gaussian Elimination, or variations of this. Sometimes they are referred to as “direct methods”. Basically, it is an algorithm that transforms the system into an equivalent one but with a triangular matrix, thus allowing a simpler resolution. In many cases, though, whenever the matrix of the system has a specific structure or is sparse and the like, other methods can be more effective. | Solution of Systems of Linear Equations | 10.1007/978-1-4614-5912-5_2 |
2013-01-01 | The use of Finite Element and Finite Difference methods of spatial and temporal discretization for solving structural dynamics problems gives rise to purely numerical errors. Among the many numerical methods used to damp out the spurious oscillations occurring in the high frequency domain, it is proposed here to analyse and compare the Bulk Viscosity method, which involves calculating the stresses, and a method recently presented by Tchamwa and Wielgosz, which is based on an explicit time integration algorithm. The 1-D study and the 2-D axisymmetric study on a bar subjected to compression and impact loads presented here show that the former method is insensitive to meshing irregularities, whereas the latter method is not. The Bulk Viscosity method was found to be sensitive, however, to the behavior of the material, contrary to the Tchamwa–Wielgosz method. Since comparisons of this kind are rather complex, a specific method of analysis was developed. | Numerical damping of spurious oscillations: a comparison between the bulk viscosity method and the explicit dissipative Tchamwa–Wielgosz scheme | 10.1007/s00466-012-0708-8 |
2013-01-01 | Numerous structures exhibit rocking behavior during earthquakes and there is a continuing need to retrofit these structures to prevent collapse. The behavior of stand-alone rocking structures has been thoroughly investigated, but there are relatively few theoretical studies on the response of retrofitted rocking structures. In practice, despite the benefits of allowing rocking motion, rocking behavior is typically prevented instead of optimized. This study characterizes the fundamental behavior of damped rocking motion through analytical modeling. A single rocking block analytical model is utilized to determine the optimal viscous damping characteristics which exploit the beneficial aspects of rocking motion while dissipating energy and preventing overturning collapse. To clarify the benefits of damping, overturning envelopes for the damped rocking block are presented and compared with the pertinent envelopes of the free rocking block. Preliminary experimental work to verify analytical modeling is also presented. Finally, the same principles of controlling rocking behavior with damping are extended to a particular class of rocking problems, the dynamics of masonry arches. A pilot application of the proposed approach to masonry arches is presented. | Seismic Overturning of Rocking Structures with External Viscous Dampers | 10.1007/978-94-007-6573-3_12 |
2013-01-01 | Studying the influence of temperature and loading frequency on the behavior of syntactic foams is important because of its diverse set of applications. Dynamic mechanical analysis (DMA) is a widely used technique for measuring viscoelastic properties of materials over a range of temperatures and loading frequencies. The storage modulus and loss modulus determined in a DMA experiment measure the capacity of a material to store and dissipate energy, respectively. In general, the storage modulus of syntactic foams decreases with increasing temperature. This response was consistent between plain and reinforced syntactic foams. Study of storage modulus of vinyl ester/glass hollow particle syntactic foams at three different temperatures concluded that the neat resin has higher storage modulus than the syntactic foams below glass transition temperature ( T _g) but this trend is reversed above T _g. Also, the room temperature (30 °C) storage modulus of syntactic foams increases with the increase in the wall thickness of hollow particles. The addition of nanoclay increased the storage modulus of epoxy matrix syntactic foams. The effect was attributed to the toughening of matrix resin by nanoclay particles. However, increased stiffness of nanoclay reinforced syntactic foams resulted in decreased loss modulus. Cyanate ester matrix syntactic foam with 4 vol. % of nanoclay showed higher storage modulus than the plain syntactic foams, owing to the restricted movement of the polymer chains which can be attributed to the good interaction between the nanoclay and the matrix resin. | Dynamic Mechanical Properties | 10.1007/978-3-319-01243-8_9 |
2013-01-01 | This chapter analyzes the differential equations governing the behavior of linear discrete multi degree-of-freedom systems with viscous damping. The free response of undamped systems is analyzed first, leading to the eigenvalue problem, the resonance frequencies and the mode shapes, and the orthogonality relationships. Next, this chapter analyzes the modal decomposition of the stationary response with the assumption of modal damping. The modal expansion of the dynamic flexibility matrix is established and its modal truncation is examined. The structures with rigid body modes have peculiar features which are discussed carefully. This chapter gives a special attention to the collocated systems in which the actuator and the sensor operate on the same degree of freedom; for this special type of system, the anti-resonances are defined, and the essential property of interlacing of the resonance and the anti-resonance frequencies is established; the relationship between the anti-resonance frequencies and the resonance frequencies of the constrained system are established. Finally, the eigenvalue problem of a building made of n identical floors is expressed as a difference equation and solved analytically. The chapter ends with a set of problems. | Multiple Degree-of-Freedom Systems | 10.1007/978-94-007-6383-8_2 |
2013-01-01 | Treating rising damp in the walls of historical buildings is a very complex procedure. Moisture transfer in the walls of old buildings in direct contact with the ground leads to the migration of soluble salts, which are responsible for many building pathologies. This work follows two main lines of research: one theoretical (analytical and numerical) and one experimental. The theoretical part describes an extensive analysis of the phenomenon of rising damp using an analytical equation based on the concepts and methods of unsaturated flow theory, and a numerical validation study. The results show that the simple analytical model clearly describes the rising damp front when compared with the numerical simulations. The influence of wall thickness, boundary conditions, wall composition and material properties such as porosity and sorptivity are analyzed in detail. The experimental part presents the results of the work developed by the Building Physics Laboratory (LFC) to treat rising damp in a historical church, locate in Northern Portugal. The main purpose is to validate the technology of wall base ventilation, for treating rising damp in walls of historic buildings. The analytical model used and the numerical results obtained describe well the observed features of rising damp in walls, verified by in-field tests, who contributed for a simple sizing of the HUMIVENT device to be implement in historic buildings. | Degradation Control of Historical Walls with Rising Damp Problems | 10.1007/978-3-642-31158-1_6 |
2013-01-01 | This chapter first discusses physical causes of damping in buildings and dynamic properties of buildings, especially amplitude dependency of damping. It is emphasized that there is no evidence of increasing damping ratio in the very high amplitude range within the elastic range of main frames, unless there is damage to secondary members or cladding. Then, damping predictors are introduced based on the Japanese Damping Database, and design values for damping ratio are recommended. Next, damping estimation techniques are introduced and some points to note in damping estimation are discussed. The feasibility and efficiency of two simple and user-friendly but accurate damping estimation techniques are discussed. One is the Frequency Domain Decomposition technique, which uses Singular Value Decomposition of the Power Spectral Density matrix of multiple outputs, and the other is the Multi-mode Random Decrement technique. Both can be applied to ambient excitations such as micro-tremors, enabling easy handling of closely-spaced and even repeated modes. Some full-scale examples demonstrating the damping estimation efficiency of both techniques are also shown. | Damping in Buildings and Estimation Techniques | 10.1007/978-4-431-54337-4_13 |
2013-01-01 | Many studies have shown the importance of automotive suspension systems in vehicle dynamics, see for instance [10], [26], [33] and references therein. Except for passive suspensions whose characteristics are invariant, the semi-active and active suspensions can change their properties by using controlled external signals (voltage, current...). This is why the latter suspensions have been studied intensively in recent years. However, up to now, only the semi-active suspensions are used widely in automotive industry. Indeed, compared with fully active suspensions, semi-active ones can achieve the main performance objectives (see [17], [27]) while they are smaller in weight and volume, cheaper in price, more robust and less energy consuming (see also [9], [10], [16], [19]). So far, the control problem for semi-active suspensions has been tackled with many approaches during the last three decades. One of the first comfort-oriented control methods, successfully applied in commercial vehicles, is the Skyhook control proposed by Karnopp et al. [18]. Then, optimal control [12], [34], clipped optimal control [24], [36], [11], H _ ∞ control [30], [31] or Model Predictive Control [4], [28] have been considered. Recently, two new control design methods for semiactive suspensions using the LPV techniques have been presented. The first one, proposed in [29], can be applied for all kinds of semi-active dampers where only the bounds on damping coefficients and on the damper forces are necessary for the controller design. In the other one, proposed in [7], the nonlinearities of the semi-active damper (the bi-viscosity and the hysteresis) are taken into consideration. The comparison of these two recent LPV-based techniques on a nonlinear Magneto-Rheological (MR) damper model is proposed this chapter. The chapter is organized as follows: In section I, a brief bibliography concerning the modelling of semi-active dampers is given and two specific control-oriented models are detailed and will be used for the synthesis of the LPV controllers. In section II, the control problem of automotive suspension control is formulated in a common way so that the methods proposed in [29] (section III) and [7] (section IV) can be applied. Section V is devoted to numerical simulations on a nonlinear quarter car model. Some remarks and conclusions end this chapter. | LPV Control Approaches in View of Comfort Improvement of Automotive Suspensions Equipped with MR Dampers | 10.1007/978-3-642-36110-4_7 |
2013-01-01 | In this paper, we present a coupled finite element/boundary element method (FE/BE) for control of noise radiation and sound transmission of vibrating structure by active piezoelectric techniques. The system consists of an elastic structure (with surface mounted piezoelectric patches) coupled to external/internal acoustic domains. The passive shunt damping strategy is employed for vibration attenuation in the low frequency range. | Coupled Finite Element-Boundary Element Formulation for Noise and Vibration Attenuation Using Shunt Piezoelectric Materials | 10.1007/978-3-642-37143-1_16 |
2013-01-01 | This paper presents ride comfort and driving stability performances of electronic control suspension (ECS) equipped with controllable electrorheological (ER) damper and appropriate control strategy. In order to achieve this goal, a cylindrical type ER damper which is applicable to Macpherson strut type suspension of a mid-sized passenger vehicle is designed and manufactured on the basis of the required damping force level of an existing passenger vehicle. After experimentally evaluating the field-dependent damping force and dynamic characteristics of the controllable ER damper, ECS consisting of sprung mass, spring, tire and controller is established in order to investigate the ride comfort and driving stability performances. On the basis of the governing equation of motion of the suspension system, five control strategies (soft, hard, comfort, sports and optimal mode) are formulated. The proposed control strategies are then experimentally realized with the quarter-vehicle ECS system. Control performances such as vertical acceleration of the car body and tire deflection are evaluated in both time and frequency domains under various road conditions. In addition, a comparative work is undertaken to investigate inherent control characteristics of each control strategy. | Performance evaluation of electronic control suspension featuring vehicle ER dampers | 10.1007/s11012-012-9588-4 |
2013-01-01 | In order to develop a simple PD controlled autopilot system with rudder roll damping, the course-keeping controller and rudder roll damping controller are designed and adaptively optimized based on GA-PD method. The parameters of controllers are to be optimized by generic algorithm when the detected standard deviation of the course error or roll angle exceeds the set threshold values. The simulation tests are done on a nonlinear ship motion model, and results show that the controllers achieved good disturbance rejection near the ship’s natural roll frequency band, and stable performance of course-keeping and changing, with strong adaptivity to sea states. | Course-keeping Autopilot with RRD Based on GA-PD Adaptive Optimization | 10.1007/978-3-642-34528-9_73 |
2013-01-01 | The objective of this chapter is to introduce the topic of damping in the context of both its modeling and its effects in phononic crystals and acoustic metamaterials. First, we provide a brief discussion on the modeling of damping in structural dynamic systems in general with a focus on viscous and viscoelastic types of damping (Sect. 6.2) and follow with a non-exhaustive literature review of prior work that examined periodic phononic materials with damping (Sect. 6.3). In Sect. 6.4, we consider damped 1D diatomic phononic crystals and acoustic metamaterials as example problems (keeping our attention on 1D systems for ease of exposition as in previous chapters). We introduce the generalized form of Bloch’s theorem, which is needed to account for both temporal and spatial attenuation of the elastic waves resulting from the presence of damping. We also describe the transformation of the governing equations of motion to a state-space representation to facilitate the treatment of the damping term that arises in the emerging eigenvalue problem. Finally, the effects of dissipation (based on the two types of damping models considered) on the frequency and damping ratio band structures are demonstrated by solving the equations developed for a particular choice of material parameters. | Damped Phononic Crystals and Acoustic Metamaterials | 10.1007/978-3-642-31232-8_6 |
2013-01-01 | The mathematical basis for the physical modelling of mass and thermal flow systems is the set of three conservation equations of mass, energy and momentum. These equations are coupled through their common process variables and working fluid properties. Since most physical processes have both time and spatial dependencies, the conservation equations describing their unsteady behaviour are partial differential equations in both time and the three space coordinates. In this work attention will be restricted, in the main, to the axial coordinate only, that is, spatial effects will be considered only in the direction of flow. | Conservation Equations for Flow Systems | 10.1007/978-1-4614-4256-1_5 |
2013-01-01 | This chapter analyzes various ways of reducing vibration passively . Two main categories are examined: the first category consists of reducing the amplification of the resonance peak by dissipating the vibration energy; the second, known as isolation , consists of preventing the propagation of the disturbances to the sensitive part of the structure. The first part of this chapter is devoted to the Dynamic Vibration Absorber which may be used either for narrow band disturbances or for wide band disturbances (with a different tuning); its efficacy is illustrated on a n-storey building excited seismically. The second part of this chapter is devoted to isolation; first, the weaknesses of the single axis linear isolator are examined and the benefit of the relaxation isolator are pointed out. Next, the equations governing a six-axis isolator are formulated. The chapter ends with a few interesting specific problems: the isolation by kinematic coupling (used in helicopters), the centrifugal pendulum vibration isolator (used in car transmissions) and a quarter-car model of a car suspension. A set of problems is proposed at the end of the chapter. | Vibration Alleviation | 10.1007/978-94-007-6383-8_11 |
2013-01-01 | Structural seismic vulnerability assessment is one of the key steps in a seismic risk management process. Structural vulnerability can be assessed using the concept of fragility. Structural fragility is the probability for a structure to sustain a given damage level for a given input ground motion intensity, which is represented by so-called fragility curves or surfaces. In this work, we consider a moment-resisting reinforced concrete frame structure in the area of the Cascadia subduction zone, that is in the South-West of Canada and the North-West of the USA. According to shaking table tests, we first validate the capability of an inelastic fiber beam/column element, using a recently developed concrete constitutive law, for representing the seismic behavior of the tested frame coupled to either a commonly used Rayleigh damping model or a proposed new model. Then, for each of these two damping models, we proceed to a structural fragility analysis and investigate the amount of uncertainty to be induced by damping models. | Structural Seismic Fragility Analysis of RC Frame with a New Family of Rayleigh Damping Models | 10.1007/978-94-007-5134-7_16 |
2013-01-01 | In previous sections, we discussed the DC transport phenomena in nearly AF metals, and found that various non-Fermi-liquid-like behaviors originate from the same CVC. In principle, the AC transport phenomena can yield further useful and decisive information about the electronic status. Unfortunately, the measurements of the AC transport coefficients are not common because of the difficulty in their observations, except for the optical conductivity $${\sigma }_{xx}({\omega })$$ σ xx ( ω ) measurements. | AC Transport Phenomena in HTSCs | 10.1007/978-3-642-35365-9_7 |
2013-01-01 | This chapter presents a simple performance-based design methodology of an analysis/redesign type for sizing and allocating friction dampers within existing 3D irregular framed structures in order to control seismic performance. The methodology allows the determination of brace stiffness of all added damping devices, under a constant predetermined slip displacement, using analysis tools only. The methodology allows the design of an irregular framed structure of any type and is nondependent of the type of irregularity. Using this methodology, fully stressed design solutions are obtained in an example of a linear 3D setback frame undergoing an ensemble of ground motions. | A Simple Methodology for the Seismic Passive Control of Irregular 3D Frames Using Friction Dampers | 10.1007/978-94-007-5377-8_19 |
2013-01-01 | Damping is a dynamic property that has not been fully understood. In particular, damping in bridges requires further study in order to gain a better understanding of the parameters that define its value and variation. In practice a constant ratio of 5 % of the critical damping is commonly used in seismic analysis and design. However, this may not be accurate for different levels of shaking. In addition, the experimental methods to estimate damping can provide different damping ratios for the same structure, which increases the uncertainties on the damping estimates. This paper presents a sensitivity analysis of the damping in bridges for different types of excitation and low levels of vibration. Data collected from different sources is used to conduct the assessment, namely, scaled model tests, ambient vibration tests, and seismic ground motions from instrumented bridges in California. A discussion of the results using several frequency and time domain methods for damping estimation is presented. | Sensitivity Analysis of the Lateral Damping of Bridges for Low Levels of Vibration | 10.1007/978-1-4614-6519-5_11 |
2013-01-01 | Pedestrian-induced footbridge vibrations are an issue that bridge designers often have to contend with. A plethora of research in recent years has led to the development of load models and procedures that allow for the determination of footbridge response. Nonetheless, measured footbridge responses often deviate from those predicted. One of the main deficiencies of the existing models and guidelines is the exclusion of the effect of changes in the footbridge’s dynamic properties due to the presence of pedestrians. More specifically, any change in mass and/or damping that a pedestrian might introduce to a bridge will affect the bridges overall dynamic response. This effect is an element of what is often referred to as human-structure interaction. In this paper, the results of an experimental study to determine the change in mass and damping of a vertically vibrating footbridge due to traversing pedestrians are presented. | Change in Mass and Damping on Vertically Vibrating Footbridges Due to Pedestrians | 10.1007/978-1-4614-6519-5_4 |
2013-01-01 | The structure of time-dependent Gaussian solutions for the Kostin equation in dissipative quantum mechanics is analyzed. Expanding the generic external potential near the center of mass of the wave packet, one conclude that: the center of mass follows the dynamics of a classical particle under the external potential and a damping proportional to the velocity; the width of the wave packet satisfy a non-conservative Pinney equation. An appropriate perturbation theory is developed for the free particle case, solving the long standing problem of finding analytic expressions for square integrable solutions of the free Kostin equation. The associated Wigner function is also studied. | Time-Dependent Gaussian Solution for the Kostin Equation Around Classical Trajectories | 10.1007/s10773-012-1302-8 |
2013-01-01 | In this paper, an investigation has been carried out on the passive vibration control of elevated water tank structures, subjected to earthquakes, by multiple tuned liquid dampers (MTLDs). An R.C.C. elevated water tank with shaft-type support has been considered. To account for the fluid-structure interaction, the sloshing of water in the water tank container has been modelled by the fundamental convective mode. The remaining water mass has been lumped with that of the container and supporting structure, resulting in a 2-DOF system model for the elevated water tank. The transfer function for the 2-DOF water tank model with MTLDs attached in a parallel configuration has been formulated. The input excitation has been characterized by a white noise power spectral density function (PSDF). The performance of the damper system has been examined on the basis of reduction in the root mean square (rms) value of the structural displacement. The frequencies of the TLDs have been fixed on the basis of tuning to the frequencies corresponding to the peaks of the transfer function curve of the 2-DOF system. This has been studied for three cases, namely, full, half-full and empty conditions of the water tank. The performance of the MTLD system for varying water level in the tank has been examined and has been found to be better in comparison with that for the single TLD case. The geometric parameters of the MTLDs have also been obtained and have been found to be feasible. | A Frequency Domain Study on the Seismic Response Mitigation of Elevated Water Tanks by Multiple Tuned Liquid Dampers | 10.1007/978-81-322-0757-3_38 |
2013-01-01 | A model to predict the dynamic response of space flight cables is developed. Despite the influence of cable harnesses on space structures’ dynamics, a predictive model for quantifying the damping effects is not available. To further this research, hysteretic and proportional viscous damping were incorporated in Euler-Bernoulli and Timoshenko beam models to predict the dynamic response of a typical space flight cable, using hysteretic dissipation functions to characterize the damping mechanism. The Euler-Bernoulli beam model was used to investigate the hysteresis functions specifically, and it was determined that including hysteretic dissipation functions in the equations of motion was not sufficient to model the additional modes arising in damped cables; additional damping coordinates in the method of Golla, Hughes and McTavish will be necessary to predict damping behavior when using dissipation functions for this case. A Timoshenko model that included viscous and time hysteresis damping was developed as well, and will ultimately be more appropriate for cable modeling due to the inclusion of shear and rotary inertia terms and damping coefficients. | Comparison of Damping Models for Space Flight Cables | 10.1007/978-1-4614-6555-3_21 |
2013-01-01 | In this paper the dynamics of the ideal and non-ideal Duffing oscillator with chaotic behavior is considered. In order to suppress the chaotic behavior and to control the system, a control signal is introduced in the system dynamics. The control strategy involves the application of two control signals, a nonlinear feedforward control to maintain the controlled system in a periodic orbit, obtained by the harmonic balance method, and a state feedback control, obtained by the state dependent Riccati equation, to bring the system trajectory into the desired periodic orbit. Additionally, the control strategy includes an active magnetorheological damper to actuate on the system. The control force of the damper is a function of the electric current applied in the coil of the damper, that is based on the force given by the controller and on the velocity of the damper piston displacement. Numerical simulations demonstrate the effectiveness of the control strategy in leading the system from any initial condition to a desired orbit, and considering the mathematical model of the damper (MR), it was possible to control the force of the shock absorber (MR), by controlling the applied electric current in the coils of the damper. | On the Chaotic Suppression of Both Ideal and Non-ideal Duffing Based Vibrating Systems, Using a Magnetorheological Damper | 10.1007/s12591-012-0128-4 |
2013-01-01 | In this chapter we show how to build uncertain system models using the functions of Robust Control Toolbox^®. Building such models is an important step in the design of control systems whose plants possess some type of uncertainty. The corresponding functions of Robust Control Toolbox^® allow to facilitate the process of building different uncertainty models and to analyze easily the properties of such models. First we describe how to build models of open-loop and closed-loop linear time-invariant systems (LTI models) and how to investigate their basic properties. Then we present various functions of Robust Control Toolbox^® that allow to create models of systems with structured (real) uncertainties. The usage of these functions is illustrated for the simple case of a second order mass–damper–spring system. It is shown how to investigate several properties of uncertain models in the time domain and frequency domain. Finally, we show how to build models of systems with unstructured (complex) uncertainty. Creation of models with additive or multiplicative uncertainty is considered in detail. | Building Uncertain Models | 10.1007/978-1-4471-4682-7_9 |
2013-01-01 | We are concerned with the global asymptotic stability of the equilibrium of the half-linear differential equation with a damped term $$\left(\phi_p(x')\right)' + h(t)\phi_p(x') + (p-1)\phi_p(x) = 0. $$ A necessary and sufficient growth condition on h ( t ) is obtained by using the generalized Prüfer transformation and the generalized Riccati transformation. Equivalent planar systems to the above-mentioned equation are also considered in the proof of our main result. | A necessary and sufficient condition for the global asymptotic stability of damped half-linear oscillators | 10.1007/s10474-012-0259-7 |
2013-01-01 | In this chapter we apply the abstract results of Chap. 5 in the study of three dynamic frictional contact problems. In the first two problems we model the material’s behavior with a nonlinear viscoelastic constitutive laws with short and long memory, respectively. In the third problem the body is supposed to be piezoelectric and, therefore, the process is mechanically dynamic and electrically static. In all problems under investigation we describe frictional contact with subdifferential boundary conditions. For each problem we deliver a variational formulation. For the first two problems it is in a form of a hemivariational inequality for the displacement field and, for the third one, it is in a form of a system of hemivariational inequalities in which the unknowns are the displacement and electric potential fields. Next, we use the abstract existence and uniqueness results presented in Chap. 5 to prove the weak solvability of the corresponding contact problems and, under additional assumptions, their unique weak solvability. Everywhere in this chapter we use the notation introduced in Chap. 6. | Analysis of Dynamic Contact Problems | 10.1007/978-1-4614-4232-5_8 |
2013-01-01 | In recent years, measures have been implemented to improve automotive environmental performance, such as increasing engine torque at low speeds and reducing idling speed. These measures tend to increase the engine’s torque fluctuation, which adversely affects the noise and vibration (NV) phenomena of the powertrain. Demand continues to increase for NV measures in powertrains. Gear rattle, which is a general NV problem of powertrains, strongly influences the torsional stiffness and the hysteresis torque of the clutch damper, which is an absorption element of a powertrain, and the inertia of the transmission or the flywheel. In this paper, we built a mechanism analysis model of a powertrain that can predict gear rattle and examined the relevance of the first stage hysteresis torque of a clutch damper and the gear rattle behavior. | The Effects of Clutch Damper in Idling Driveline Rattle | 10.1007/978-1-4614-6570-6_24 |
2013-01-01 | We study structural damping in a typical structural element of unidirectionally reinforced composites with insufficient adhesion on the interfaces. It is shown that the defects of gluing near the breaks of fibers increase damping and, in order to enhance the damping of composites reinforced with short fibers, it is necessary to remove friction in the central parts of the fibers. | Influence of structural defects on the structural damping of unidirectionally reinforced fibrous composites | 10.1007/s11003-013-9526-1 |
2013-01-01 | Parametric rolling has become an important design issue in the safe operation of large high-speed container ships. This interest is partly based upon the well-published large amplitude rolling incident of the APL China several years ago and numerous other incidents which have also since come to light. What we have found in our research is that a simple linear model of roll damping does not accurately predict the threshold nature of this phenomenon. However, when we accurately include nonlinear damping we are able to capture the qualitative nature of this phenomenon. Moreover the Mathieu Ince-Strutt stability diagram is limited to linear harmonic excitation. What we have done in this work is to extend the Mathieu Ince-Strutt stability diagram to include non-harmonic excitation and nonlinear damping. Analysis of ship parametric rolling has generally been restricted to simple analytical models and sophisticated time domain simulations. However, simple analytical models do not capture all the critical dynamics while time-domain simulations are time consuming to implement. Our model captures the essential dynamics of the system without over simplification. This work incorporates important aspects of the system and assesses the significance of including or ignoring these aspects. Many of the previous works on parametric rolling make the assumption of linearized and harmonic behaviour of the time-varying restoring arm or metacentric height. This assumption enables modelling the roll as a Mathieu equation. | Importance of Accurately Modeling Nonlinear Damping in Predicting Parametric Ship Rolling | 10.1007/978-94-007-5742-4_13 |
2013-01-01 | This paper presents recent results in an ongoing effort to understand and develop techniques to process launch vehicle data, which is extremely challenging for modal parameter identification. The primary source of difficulty is due to the non-stationary nature of the situation. The system is changing, the environment is not steady, and there is an active control system operating. Hence, the primary tool for producing clean operational results (significant data lengths and data averaging) is not available to the user. This work reported herein uses a correlation-based two step operational modal analysis approach to process the relevant data sets for understanding and development of processes. A significant drawback for such processing of short time histories is a series of beating phenomena due to the inability to average out random modal excitations. A recursive correlation process coupled to a new convergence metric (designed to mitigate the beating phenomena) is the object of this study. It has been found in limited studies that this process creates clean modal frequency estimates but numerically alters the damping. | Progress in Operational Analysis of Launch Vehicles in Nonstationary Flight | 10.1007/978-1-4614-6546-1_6 |
2013-01-01 | Systems and techniques for fast damage detection based on vibration analysis are becoming very attractive in different engineering fields. Modal-based damage detection algorithms are well-known techniques for structural health assessment. However, the lack of automated modal identification and tracking procedures has been for long a relevant limit to their extensive use. The development of several automated output-only modal identification procedures in the last few years has led to a renewed interest in modal-based damage detection. However, robustness of automated modal identification algorithms, computational efforts and reliability of modal parameter estimates (in particular, damping) still represent open issues. In this paper, a novel algorithm for automated output-only modal parameter estimation is adopted to obtain reliable and very accurate modal parameter estimates. An extensive validation of the algorithm for continuous monitoring application is carried out based on simulated data. The obtained results point out that the algorithm provides fairly robust, accurate and precise estimates of the modal parameters, including damping ratios. This may potentially lead to a standardized, extensive characterization of modal damping ratios in structures, which is useful to gain knowledge about damping mechanisms in structures and to develop predictive models. | Accurate Damping Estimation by Automated OMA Procedures | 10.1007/978-1-4614-6555-3_1 |
2013-01-01 | The paper deals with the design of an auto-tuning fractional order proportional-integrative-derivative controllers and its implementation on hardware in the loop simulator for the real-time control of unknown plants. The proposed procedure can be applied to systems with delay and order greater than one, once specifications on cross-over frequency and phase margin are given. The auto-tuning procedure consists of two phases: the first one dedicated to the identification of the process at the desired cross-over frequency and the second one to determine all the parameters of the fractional order proportional-integrative-derivative controllers. The obtained controller ensures an iso-damping response of the plant. Experimental results are given to confirm the effectiveness of the proposed approach and show that the requirements are totally met for the system to be controlled. | Auto-Tuning and Fractional Order Controller Implementation on Hardware in the Loop System | 10.1007/s10957-012-0235-y |
2013-01-01 | The objective of this paper is to devise a scheme for generating arm gestures of humanoid robots. Inverse kinematics and the minimum-jerk trajectory method are used to generate trajectory of each gesture. To calculate the desired positions of arms, inverse kinematics is solved by the damped least-squares method. Human-like trajectory from initial position to desired position is generated by the minimum-jerk trajectory method. The effectiveness of the proposed method is demonstrated through a human robot interaction (HRI) experiment by using the humanoid robot Mybot-KSR, developed in KAIST RIT Laboratory. In the experiment, internal state of the robot is changed from the perceived environment. The internal state consists of emotion and homeostasis. Based on the emotion, the robot tries to interact with human by selecting proper gestures using the fuzzy integral and fuzzy measure. | Arm Gesture Generation of Humanoid Robot Mybot-KSR for Human Robot Interaction | 10.1007/978-3-642-40409-2_4 |
2013-01-01 | In this chapter we illustrate the use of linear second-order equations with constant coefficients in the analysis of mechanical oscillations and electrical vibrations. | Mathematical Models with Second-Order Equations | 10.1007/978-1-4614-7297-1_5 |
2013-01-01 | Increasing vibration serviceability problems of modern pedestrian structures have drawn researchers’ attention to detailed modelling and assessment of walking-induced vibration on floors and footbridges. Stochastic nature of human walking and unknown mechanisms of their interaction with the structure and surrounding environment, make it difficult to simulate. Ignoring these complexities has rendered the current design methods to a rough approximation of reality which often leads to considerable over or under-estimation of the structural response yielding unreliable assessment of vibration performance. Some aspects of human-structure interaction (HSI), such as synchronization, have been studied extensively, mostly in the lateral direction. But, despite of its much bigger significance, effects of walking pedestrians on dynamic properties of structures in the vertical direction are mostly ignored. This is mainly due to the lack of credible HSI experimental data in the vertical direction as well as models capable of simulating the interactions between the two dynamic systems. To address this gap, this paper tries to adapt a classic single degree of freedom mass-spring-damper (MSD) model of human body to illustrate the effects of walking pedestrians on dynamic properties of structures. Parametric studies were carried out to analyse effects of the human model dynamic properties on coupled system response. This MSD model can be seen as the basic building block of realistic human body models which are currently being developed to address both biomechanical specifics and HSI effects on structures occupied and excited by walking human. | Using MSD Model to Simulate Human-Structure Interaction During Walking | 10.1007/978-1-4614-6555-3_39 |
2013-01-01 | As part of the Canadian Seismic Research Network’s (CSRN) newly developed performance spectra-based design methodology for buildings with supplemental damping, this chapter proposes an index for quantifying the degree of vertical stiffness/strength irregularity based on elastic modal properties. Using this index, a damper distribution technique is developed to correct irregularities while adding damping to control the seismic response to meet a given set of performance targets. Nonlinear time-history analyses of simplified 4-, 9- and 15-storey irregular shear buildings with hysteretic and linear viscous and viscoelastic dampers are used to verify and to establish the limits of application of the proposed distribution technique. It is found that the procedure offers simplicity and sufficient accuracy for design purposes if the structure meets the criteria identified in this study. Retrofit examples using the proposed methodology are also presented for a 9-storey irregular steel moment frame in Canada. | Mitigation of the Seismic Response of Structures with Vertical Stiffness and Strength Irregularity Using Supplemental Dampers | 10.1007/978-94-007-5377-8_21 |
2013-01-01 | In this chapter, four examples of application of lotus metals are described. For heat sinks, penetrable pores are utilized to cool electronic devices. For artificial teeth, open pores are effective to let bone tissue intrude for fixation of the teeth into alveolar bones. For use of vibration–damping materials and golf putter, closed pores serve to damping effect. Thus, anisotropic pores in lotus metals contribute to such functions of products. | Various Applications of Lotus Metals | 10.1007/978-4-431-54017-5_10 |
2013-01-01 | Since the damped wave equation has the diffusion phenomenon, the critical exponent is expected to be the same as that for the corresponding diffusive equation with semilinear term. Therefore, we first remember the basic facts on the diffusion phenomenon. Then, from this point of view, we can conjecture the critical exponent for the damped wave equation and state several results. Finally, the small data global existence of solutions is shown in the supercritical exponent, while no global existence for some data is done in the critical and subcritical exponents. The latter part will be applied to the semilinear damped wave equation with quadratically decaying potential. | Critical Exponent for the Semilinear Wave Equation with Time or Space Dependent Damping | 10.1007/978-3-319-00125-8_11 |
2013-01-01 | The concept of performance-based design has recently been introduced and is well accepted in the current structural design practice of buildings. In earthquake-prone countries, the philosophy of earthquake-resistant design to resist ground shaking with sufficient stiffness and strength of a building itself has also been accepted as a relevant structural design concept for many years. On the other hand, a new strategy based on the concept of active and passive structural control has been introduced rather recently in order to provide structural designers with powerful tools for performance-based design. | Optimal Placement of Visco-Elastic Dampers and Supporting Members Under Variable Critical Excitations | 10.1007/978-1-4471-4144-0_12 |
2013-01-01 | A quarter car model with magnetorheological (MR) damper is studied in this paper. An adopted experimentally verified non – linear hysteretic mathematical model is used to represent the MR damper. Approaching road disturbances are measured by a sensor. Optimal preview control strategy for fully active suspension is derived with respect to road holding, suspension rattle space and ride comfort. Continuous inverse mathematical model of the MR damper for the use of control is derived. The effect of tire lift off is modeled using a continuous mathematical function. | Design of Semiactive Damper in Vehicle Suspension Considering the Tire Lift Off | 10.1007/978-3-642-34471-8_29 |
2013-01-01 | This chapter presents a methodology for the optimal design of multiple tuned mass dampers (TMDs) in 3D irregular buildings. The objective function minimizes the total mass of all added TMDs while constraints are added to limit the total accelerations experienced at the edges of the floors in the direction parallel to each edge. The formulation of the design methodology relies on optimality criteria conjectured herein; hence, a two-stage iterative analysis/redesign procedure, that is based on analysis tools only, is resulted. The methodology applies to all types of irregularity, which allows the application of the methodology in a practical design process. | Allocation and Sizing of Multiple Tuned Mass Dampers for Seismic Control of Irregular Structures | 10.1007/978-94-007-5377-8_22 |
2013-01-01 | The success of active vibration control in adaptronics decisively depends on the performance of the actuators used as multifunctional structural elements. DLR’s concept of impedance matched actuators proposes novel actuators in honeycomb design (Fig. 8.1 ). The partitions of their hexagonal cells are made of piezoceramic materials. The honeycomb geometry guarantees lightweight properties with nearly perfect load distributions in the plane perpendicular to the cell tubes. Furthermore there is a dynamic flexibility in this plane even when the static stiffness is very high. New fabrication methods are required to realize honeycomb actuators with very small cells, low wall thicknesses and perfect rounded corners. In order to fulfill the lightweight conditions self-organizing effects were used to guarantee optimal 3D geometries. In this context, a local thermal treatment of ceramic structures by employing lasers initiates self-organizing mechanisms via material flow. Experimental comparisons between piezoelectric honeycomb actuators and conventional monolithic actuators demonstrate a reduction of electrical power by a factor of 500. Honeycomb actuators seem to be the most promising candidate for technical applications that require low energy consumption. Fig. 8.1 Piezoceramic honeycomb actuator | Piezoceramic Honeycomb Actuators | 10.1007/978-3-642-29190-6_8 |
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