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2013-01-01 | A new encoding scheme is presented for a fuzzy-based nonlinear system identification methodology, using the subtractive Fuzzy C-Mean clustering and a modified version of non-dominated sorting genetic algorithm. This method is able to automatically select the best inputs as well as the structure of the fuzzy model such as rules and membership functions. Moreover, three objective functions are considered to satisfy both accuracy and compactness of the model. The proposed method is then employed to identify the inverse model of a highly nonlinear structural control device, namely Magnetorheological (MR) damper. It is shown that the developed evolving Takagi–Sugeno-Kang (TSK) fuzzy model can identify and grasp the nonlinear dynamics of inverse systems very well, while a small number of inputs and fuzzy rules are required for this purpose. | A Multi-objective Subtractive FCM Based TSK Fuzzy System with Input Selection, and Its Application to Dynamic Inverse Modelling of MR Dampers | 10.1007/978-3-642-38658-9_20 |
2013-01-01 | Mag can be used not only as controllable damping devices but also to emulate a controllable positive or negative stiffness in combination with the dissipative force. However, the dissipative nature of MR dampers constrains the stiffness control. This work formulates the problem of combined stiffness and damping control with MR dampers if the damper is subjected to pure harmonic motion. A new method is presented that ends up in precise stiffness emulation with MR dampers, also when the sum of the stiffness and dissipative forces is constrained by the semi-active nature and residual force of MR dampers. The new control concept is applied to a semi-active tuned mass damper with an MR damper (MR-STMD). The numerical and experimental results demonstrate that the MR-STMD outperforms the passive TMD significantly. | Precise Stiffness Control with MR Dampers | 10.1007/978-1-4614-6555-3_8 |
2013-01-01 | A method for evaluating the economic efficiency of a semi-active Magneto-Rheological (MR) damper system for cable-stayed bridges under earthquake loadings is described and its evaluation results are investigated in this paper. The economic efficiency of semi-active MR damper system is addressed by introducing the concept of life-cycle cost. We simply define the life-cycle cost as the sum of the initial construction cost and the expected cost of the damage over the lifespan of the structure. To evaluate the expected damage cost, the probability of failure is estimated by use of the crossing theory in conjunction with the simulation methods. As a measure of economic efficiency, the cost-effectiveness index is defined as the ratio of life-cycle costs between a bridge structure with the MR damper system and a bridge structure with shock transmission units. In order to examine the cost-effectiveness of the MR damper system, the scale of damage cost and the scale of damper cost are adopted as two parametric variables. The evaluation results show that the scale of damper cost has little influence on the cost-effectiveness of the MR damper system, while the scale of damage cost has a significant influence on its cost-effectiveness. It is also found that the MR damper system is highly cost-effective especially for the ground motion in regions of moderate seismicity with soft soil conditions and strong seismicity with stiff soil conditions. | Cost-effectiveness evaluation of an MR damper system based on a life-cycle cost concept | 10.1007/s12205-013-1244-6 |
2013-01-01 | This paper proposes a real-time trajectory generation algorithm for both arms of a humanoid robot. Since it is hard to find a closed form of inverse kinematics for each arm of seven degrees of freedom, the damped least-squares method is employed to obtain the inverse kinematics. The trajectory is generated by the minimum-jerk method to maximize the position accuracy. Considering the performance in computation time, a software SD/FAST is used to find a Jacobian matrix of the arm. Computer simulation was performed to verify the effectiveness of the proposed algorithm using a Webot simulator for the upper body of Mybot developed in the RIT Lab., KAIST. The results show that the proposed algorithm generates trajectory in real-time and it is robust to singularity. | Real-Time Trajectory Generation for Both Arms of a Humanoid Robot | 10.1007/978-3-642-37374-9_37 |
2012-12-13 | In this paper, we are concerned with a system of nonlinear viscoelastic wave equations with initial and Dirichlet boundary conditions in R n ( n = 1 , 2 , 3 ). Under suitable assumptions, we establish a general decay result by multiplier techniques, which extends some existing results for a single equation to the case of a coupled system. MSC: 35L05, 35L55, 35L70. | General decay for a system of nonlinear viscoelastic wave equations with weak damping | 10.1186/1687-2770-2012-146 |
2012-12-01 | This paper addresses the dynamic properties of automotive shock absorber modules. Analyzing an equivalent linear system, a set of characteristic dimensionless numbers are introduced in order to qualify the dynamic performance of the damper and the damper module. The dependency of these numbers on the main parameters of the module like the damping constant, the spring stiffness of the damper, the top mount stiffness and the piston rod mass is shown. These numbers may also serve as similarity coefficients for quite different dampers regarding their dynamic behavior. Furthermore, they can be used to adjust the stiffness of the different force elements of the damper module to achieve an optimal damping quality. | Dynamic properties of automotive damper modules | 10.1007/s00419-012-0627-3 |
2012-12-01 | We have investigated a DW motion driven by AC external field with a variation of damping parameter α in Landau–Lifshitz–Gilbert equation as well as a variation of an oscillating force frequency by means of a micromagnetic simulation. Straight ferromagnetic wires having a DW at the wire center is considered, where the DW is assumed to behave like a free quasiparticle. With variation of strength and frequency of the external AC field, we have observed that relative phase delays between the forced DW motion and the AC field depends on the damping constant. The overall behavior is explainable with a single-degree-of-freedom model of a damped forced oscillation without a restoring force. | Micromagnetic Study of Forced Oscillation of Magnetic Domain Wall in Ferromagnetic Nanowires with Variation of Damping Constant | 10.1007/s10948-011-1268-4 |
2012-12-01 | Ferromagnetic resonance measurements were carried out for single crystalline Co_2MnAl thin films as a function of the angle between applied external magnetic field and normal of the film surface. In- and out-of-plane angular dependence of the resonance field and only out-of-plane angular dependence of the linewidth of FMR spectra were analyzed using the Landau–Lifshitz–Gilbert equation. The easy and hard axes were determined by analyzing the in-plane angular dependence of resonant field. The films annealed at various temperatures showed four-fold magnetic anisotropy symmetry and the damping factor was estimated from the analysis of the angular dependency of FMR spectra. | Magnetic Properties of Single Crystalline Co_2MnAl Heusler Alloy Thin Films | 10.1007/s10948-011-1238-x |
2012-12-01 | Polycrystalline quaternary Co_2MnAl_1− x Sn_ x films with x =0.25, 0.5, 0.75, 1 were prepared at room temperature using magnetron sputtering technique on SiO_2 substrates and post-annealed at various temperatures. We investigated the crystal structures, magnetic properties, and magnetic damping constants ( α ) of the prepared films. Out-of-plane angular dependences of the resonance field and the linewidth of the ferromagnetic resonance spectra were measured and analyzed using the Landau–Lifshitz–Gilbert equation to determine the magnetic properties and damping constant. Co_2MnAl_0.75Sn_0.25 and Co_2MnSn films had A2 ordered crystal structure while Co_2MnAl_0.25Sn_0.75 and Co_2MnAl_0.5Sn_0.5 films had A2 ordering up to 400 °C and 300 °C annealing temperature, respectively, and they had B2 ordering for the remaining temperatures. Also the crystal structure deteriorated at 600 °C for all of the film systems. The saturation magnetization, M _ S , of films increased with annealing temperature till 400 °C except Co_2MnAl_0.5Sn_0.5 in which M _ S increased till 500 °C, which is consistent with the structural analysis. The effective magnetization was obtained from the FMR spectra and it was found that it decreased with increasing Sn-concentration and reached a minimum value at Co_2MnAl_0.25Sn_0.75 composition. Lastly, Co_2MnAl_1− x Sn_ x films annealed at 500 °C showed the best crystal ordering. The lowest α value was 0.008 and obtained from Co_2MnAl_0.5Sn_0.5 films annealed at 500 °C. | Gilbert Damping Constant of Quaternary Co_2MnAl_1−x
Sn_
x
Heusler Alloy Thin Films | 10.1007/s10948-011-1272-8 |
2012-12-01 | Radiation damping of surface plasmon oscillations in metallic nanoparticles is proportional to their volume. For relatively large particles, this canal dominates the other mechanisms of relaxation and becomes the main limiting factor for spectral sensitivity of nanoparticles. In this communication, we consider metallic nanoshell with the dielectric core and calculate the radiation damping rate of surface plasmon oscillations, depending on the geometry and dielectric constants of the surrounding environment and the core. It is shown that surface plasmon radiation damping in nanoshell is suppressed by several orders of magnitude as compared to the solid particle of the same outer radius. This effect is conditioned by strong redshift of surface plasmon frequencies with the decrease of shell thickness. It is also demonstrated that the radiation damping rate of core–shell particle is highly sensitive with respect to the refractive index of surrounding media. | Strong Suppression of Surface Plasmon Radiation Damping Rate in Noble Metal Nanoshells | 10.1007/s11468-012-9368-y |
2012-12-01 | A necessary and sufficient condition is established for the equilibrium of the damped superlinear oscillator $$x^{\prime\prime} + a(t)\phi_q(x^{\prime}) + \omega^2x = 0$$ to be globally asymptotically stable. The obtained criterion is judged by whether the integral of a particular solution of the first-order nonlinear differential equation $$u^{\prime} + \omega^{q-2}a(t)\phi_q(u) + 1 = 0$$ is divergent or convergent. Since this nonlinear differential equation cannot be solved in general, it can be said that the presented result is expressed by an implicit condition. Explicit sufficient conditions and explicit necessary conditions are also given for the equilibrium of the damped superlinear oscillator to be globally attractive. Moreover, it is proved that a certain growth condition of a ( t ) guarantees the global asymptotic stability for the equilibrium of the damped superlinear oscillator. | Global Asymptotic Stability for Oscillators with Superlinear Damping | 10.1007/s10884-012-9256-3 |
2012-12-01 | This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear vibrations of sandwich plate with orthotropic laminated composite faces separated by a flexible core. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composites. The Golla–Hughes–McTavish method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. The first-order shear deformation theory and the Von Kármán type nonlinear strain displacement relations are used for analyzing this coupled electro-elastic problem. A three dimensional finite element model of smart laminated composite sandwich plate integrated with ACLD patches has been developed to investigate the performance of these patches for controlling the geometrically nonlinear vibrations of the plates. The numerical results indicate that the ACLD patches significantly improve the damping characteristics of the sandwich plates with laminated cross-ply and angle-ply facings for suppressing their geometrically nonlinear vibrations. Particular emphasis has been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD treatment. | Active constrained layer damping of geometrically nonlinear vibrations of smart laminated composite sandwich plates using 1–3 piezoelectric composites | 10.1007/s10999-012-9201-y |
2012-12-01 | In this study, the concept of Output Frequency Response Functions (OFRFs) is applied to represent the transmissibility of nonlinear isolators in frequency domain. With the OFRFs estimated from numerical simulation responses, an explicit analytical relationship between the transmissibility and the nonlinear characteristic parameters is derived for a wide class of nonlinear isolators that have nonlinear anti-symmetric damping characteristics and a comprehensive pattern about how the nonlinear damping characteristic parameters might affect the force and displacement transmissibility is built for the vibration isolators. The results reveal that it is reasonable to analyze the force and displacement transmissibility of the nonlinear isolators by simply investigating the fundamental harmonic components of the force and displacement outputs of the nonlinear isolators, and the introduction of a nonlinear anti-symmetric damping into vibration isolators can significantly suppress both the force and displacement transmissibility over the resonant frequency region, but has almost no effect on the transmissibility at non-resonant regions. These conclusions are of significant importance in the analysis and design of the nonlinear vibration isolators with nonlinear anti-symmetric damping. | Evaluation of transmissibility for a class of nonlinear passive vibration isolators | 10.1007/s11465-012-0349-9 |
2012-12-01 | The development of a two dimensional numerical wave tank (NWT) with a rocker or piston type wavemaker based on the high order boundary element method (BEM) and mixed Eulerian-Lagrangian (MEL) is examined. The cauchy principle value (CPV) integral is calculated by a special Gauss type quadrature and a change of variable. In addition the explicit truncated Taylor expansion formula is employed in the time-stepping process. A modified double nodes method is assumed to tackle the corner problem, as well as the damping zone technique is used to absorb the propagation of the free surface wave at the end of the tank. A variety of waves are generated by the NWT, for example; a monochromatic wave, solitary wave and irregular wave. The results confirm the NWT model is efficient and stable. | Two dimensional fully nonlinear numerical wave tank based on the BEM | 10.1007/s11804-012-1153-y |
2012-12-01 | Floating unit, mooring lines and risers comprise an integrated dynamic system that responds to environmental loading due to wind, waves and currents in a complex way. The sea current forces acting on the moorings/risers and the resulting damping effects can be an important contribution for the floating unit response. For the integrity assessment of the riser system, one of the traditional methodologies employed is to consider wave frequency (WF) floater motion as dynamic excitation through the vessel Response Amplitude Operator (RAO), while low frequency (LF) floater motions are accounted for by an additional static offset. In deep waters, especially with a large number of slender structures supported by the vessel, it becomes increasingly important to consider the coupling effect between the floating unit, mooring lines and risers, since this can affect the motions of the platform and consequently the riser system response. In this paper, the coupled vs. de-coupled approaches for assessment of the riser system are evaluated by case studies of a deep water, spread-moored Floating, Production, Storage and Offloading unit (FPSO) operating in offshore Brazil. Analyses for floating unit response coupled with moorings/risers and the top connection response of the slender structures are presented and the two approaches are compared. | The effect of coupled dynamic analysis of floater motions on the mooring and riser system response of a FPSO | 10.1007/BF03449303 |
2012-12-01 | We discuss the unitary equivalence of generators G _ A , R associated with abstract damped wave equations of the type $${\ddot{u} + R \dot{u} + A^*A u = 0}$$ in some Hilbert space $${\mathcal{H}_1}$$ and certain non-self-adjoint Dirac-type operators Q _ A , R (away from the nullspace of the latter) in $${\mathcal{H}_1 \oplus \mathcal{H}_2}$$ . The operator Q _ A , R represents a non-self-adjoint perturbation of a supersymmetric self-adjoint Dirac-type operator. Special emphasis is devoted to the case where 0 belongs to the continuous spectrum of A * A . In addition to the unitary equivalence results concerning G _ A , R and Q _ A , R , we provide a detailed study of the domain of the generator G _ A , R , consider spectral properties of the underlying quadratic operator pencil $${M(z) = |A|^2 - iz R - z^2 I_{\mathcal{H}_1}, z\in\mathbb{C}}$$ , derive a family of conserved quantities for abstract wave equations in the absence of damping, and prove equipartition of energy for supersymmetric self-adjoint Dirac-type operators. The special example where R represents an appropriate function of | A | is treated in depth, and the semigroup growth bound for this example is explicitly computed and shown to coincide with the corresponding spectral bound for the underlying generator and also with that of the corresponding Dirac-type operator. The cases of undamped ( R = 0) and damped ( R ≠ 0) abstract wave equations as well as the cases $${A^* A \geq \varepsilon I_{\mathcal{H}_1}}$$ for some $${\varepsilon > 0}$$ and $${0 \in \sigma (A^* A)}$$ (but 0 not an eigenvalue of A * A ) are separately studied in detail. | Abstract wave equations and associated Dirac-type operators | 10.1007/s10231-011-0200-7 |
2012-12-01 | The stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative of Caputo’s definition is analyzed. First, the system state is approximately described by Itô equations through the stochastic averaging method based on the generalized harmonic function. Then, the associated expression for the largest Lyapunov exponent of the linearized averaged Itô is derived, and the necessary and sufficient condition for the asymptotic stability with probability one of the trivial solution of the original system is obtained approximately by letting the largest Lyapunov exponent be negative. The effects of fractional orders and random excitation intensities on the asymptotic stability with probability one determined by the largest Lyapunov exponent are shown graphically. | Stochastic stability of the harmonically and randomly excited Duffing oscillator with damping modeled by a fractional derivative | 10.1007/s11433-012-4888-1 |
2012-12-01 | The use of seismic hysteretic dampers for passive control is increasing exponentially in recent years for both new and existing buildings. In order to utilize hysteretic dampers within a structural system, it is of paramount importance to have simplified design procedures based upon knowledge gained from theoretical studies and validated with experimental results. Non-linear Static Procedures (NSPs) are presented as an alternative to the force-based methods more common nowadays. The application of NSPs to conventional structures has been well established; yet there is a lack of experimental information on how NSPs apply to systems with hysteretic dampers. In this research, several shaking table tests were conducted on two single bay and single story 1:2 scale structures with and without hysteretic dampers. The maximum response of the structure with dampers in terms of lateral displacement and base shear obtained from the tests was compared with the prediction provided by three well-known NSPs: (1) the improved version of the Capacity Spectrum Method (CSM) from FEMA 440; (2) the improved version of the Displacement Coefficient Method (DCM) from FEMA 440; and (3) the N2 Method implemented in Eurocode 8. In general, the improved version of the DCM and N2 methods are found to provide acceptable accuracy in prediction, but the CSM tends to underestimate the response. | Shaking table tests of structures with hysteretic dampers: experimental results versus prediction using non-linear static methods | 10.1007/s10518-012-9375-6 |
2012-12-01 | Shape memory alloys (SMAs) are very interesting smart materials not only for their shape memory and superelastic effects but also because of their significant intrinsic damping capacity. The latter is exhibited upon martensitic transformations and especially in martensitic state. The combination of these SMA properties with the mechanical and the lightweight of fiberglass-reinforced polymer (FGRP) is a promising solution for manufacturing of innovative composites for vibration suppression in structural applications. CuZnAl sheets, after laser patterning, were embedded in a laminated composite between a thick FGRP core and two thin outer layers with the aim of maximizing the damping capacity of the beam for passive vibration suppression. The selected SMA Cu_66Zn_24Al_10 at.% was prepared by vacuum induction melting; the ingot was subsequently hot-and-cold rolled down to 0.2 mm thickness tape. The choice of a copper alloy is related to some advantages in comparison with NiTiCu SMA alloys, which was tested for the similar presented application in a previous study: lower cost, higher storage modulus and consequently higher damping properties in martensitic state. The patterning of the SMA sheets was performed by means of a pulsed fiber laser. After the laser processing, the SMA sheets were heat treated to obtain the desired martensitic state at room temperature. The transformation temperatures were measured by differential scanning calorimetry (DSC). The damping properties were determined, at room temperature, on full-scale sheet, using a universal testing machine (MTS), with cyclic tensile tests at different deformation amplitudes. Damping properties were also determined as a function of the temperature on miniature samples with a dynamical mechanical analyzer (DMA). Numerical modeling of the laminated composite, done with finite element method analysis and modal strain energy approaches, was performed to estimate the corresponding total damping capacity and then compared to experimental results. | Numerical and Experimental Characterizations of Damping Properties of SMAs Composite for Vibration Control Systems | 10.1007/s11665-012-0293-1 |
2012-12-01 | In this study, the effectiveness of a tuned liquid column-gas damper, TLCGD, on the suppression of seismicinduced vibrations of steel jacket platforms is evaluated. TLCGD is an interesting choice in the case of jacket platforms because it is possible to use the structural elements as the horizontal column of the TLCGD. The objective here is to find the optimum geometric parameters, namely orientation and configuration of vertical columns, length ratio, and area ratio of the TLCGD, considering nonlinear damping of the TLCGD and water-structure interaction between the jacket platform and sea water. The effects of different characteristics of ground motion such as PGA and frequency content on the optimum geometry are also investigated and it is observed that these features have some influence on the optimum area ratio. Finally it is observed that pulse arrangement of ground acceleration is one of the most important parameters affecting the efficiency of a TLCGD. In other words, it is found that the TLCGD’s capability to reduce the RMS responses depends only on the frequency content of the ground acceleration, but its capability to reduce the maximum responses depends on both the frequency content and the pulse arrangement of the ground acceleration. | Optimum geometry of tuned liquid column-gas damper for control of offshore jacket platform vibrations under seismic excitation | 10.1007/s11803-012-0143-z |
2012-11-09 | Conflicts and discrepancies around nanoparticle (NP) size effect on the optical properties of metal NPs of sizes below the mean free path of electron can be traced to the internal damping effect of the hybrid resonance of the inner band (IB) and the conduction band (CB) electrons of the noble metals. We present a scheme to show how alternative mathematical formulation of the physics of interaction between the CB and the IB electrons of NP sizes <50 nm justifies this and resolves the conflicts. While a number of controversies exist between classical and quantum theories over the phenomenological factors to attribute to the NP size effect on the absorption bandwidth, this article shows that the bandwidth behavior can be well predicted from a different treatment of the IB damping effect, without invoking any of the controversial phenomenological factors. It finds that the IB damping effect is mainly frequency dependent and only partly size dependent and shows how its influence on the surface plasmon resonance can be modeled to show the influence of NP size on the absorption properties. Through the model, it is revealed that strong coupling of IB and CB electrons drastically alters the absorption spectra, splitting it into distinctive dipole and quadrupole modes and even introduce a behavioral switch. It finds a strong overlap between the IB and the CB absorptions for Au and Cu but not Ag, which is sensitive to the NP environment. The CB modes shift with the changing refractive index of the medium in a way that can allow their independent excitation, free of influence of the IB electrons. Through a hybrid of parameters, the model further finds that metal NP sizes can be established not only by their spectral absorption peak locations but also from a proper correlation of the peak location and the bandwidth (FWHM). | Damping effect of the inner band electrons on the optical absorption and bandwidth of metal nanoparticles | 10.1007/s11051-012-1261-2 |
2012-11-01 | A new method for measuring the contribution of the local viscous and dry friction forces on the micrometer scale is described. The velocity dependence of the local friction force is obtained using a dual-axis micromechanical probe with an electrostatic actuator. It is used to obtain the local damping coefficient and dry friction force of nm-thick lubricant films patterned on the micrometer scale. This method is useful for clarifying the mechanism of thin-film-based and boundary lubrications. | Measured Viscous and Dry Friction Forces in Nanometer-Thick Lubricant Film by Friction Force Microscopy with Micromechanical Probe | 10.1007/s11249-012-0013-x |
2012-11-01 | The reason for the decrease in the amplitude of longitudinal vibration combustion self-oscillations in the combustion chamber of a liquid-propellant rocket engine by means of antipulse partitions has been justified. A mathematical model of the development of combustion instability in such a chamber on attachment of a Helmholtz resonator to it has been obtained. The character of the damping of vibration combustion self-oscillations excited by the action of the Crocco mechanisms and negative thermal resistance, when varying the acoustic parameters of the resonator and of the pressure head characteristics of combustion chamber is established. | Concerning the problem of dynamic damping of the vibration combustion self-oscillations in a liquid-propellant rocket engine | 10.1007/s10891-012-0781-z |
2012-11-01 | Quantum Sturm–Liouville problems introduced in our paper (Büyükaşık et al. in J Math Phys 50:072102, 2009 ) provide a reach set of exactly solvable quantum damped parametric oscillator models. Based on these results, in the present paper we study a set of variable parametric nonlinear Madelung fluid models and corresponding complex Burgers equations, related to the classical orthogonal polynomials of Hermite, Laguerre and Jacobi types. We show that the nonlinear systems admit direct linearazation in the form of Schrödinger equation for a parametric harmonic oscillator, allowing us to solve exactly the initial value problems for these equations by the linear quantum Sturm–Liouville problem. For each type of equations, dynamics of the probability density and corresponding zeros, as well as the complex velocity field and related pole singularities are studied in details. | Exactly solvable Madelung fluid and complex Burgers equations: a quantum Sturm–Liouville connection | 10.1007/s10910-012-0060-4 |
2012-11-01 | To investigate the nonlinear vibration behavior of a shrouded blade with friction dynamic contact interface, a friction contact stiffness model is proposed to describe the friction force at different rough interfaces and different normal loads. In the proposed model, the friction contact interface is discretized to a series of friction contact pairs and each of them can experience stick, slip, or separate states. Fractal geometry is used to simulate the topography of contact surfaces. The contact stiffness is calculated using the Hertz contact theory and fractal geometry, which is related to contact interfaces parameters including normal load, roughness, Young’s modulus, and Poisson’s ratio. The trajectory tracking method is used to predict the friction force and it is not necessary to judge the transition condition among stick, slip, and separate states. It is suitable for complicated periodic motion of the contact interfaces. The forced response of a real shrouded blade is predicted using the proposed model and the multi-harmonic balance method. The effect of surface roughness, initial normal load, and contact area on the forced response of a shrouded blade is studied. It is shown that contact stiffness increases with normal load and fractal dimension. The resonant amplitude is sensitive to the initial normal load and contact surface roughness. The response can be influenced by the contact area, which is an important parameter for blade designers. | A friction contact stiffness model of fractal geometry in forced response analysis of a shrouded blade | 10.1007/s11071-012-0615-8 |
2012-11-01 | In this study, ground vibrations due to dynamic loadings from trains moving in subway tunnels were investigated using a 2.5D finite element model of an underground tunnel and surrounding soil interactions. In our model, wave propagation in the infinitely extended ground is dealt with using a simple, yet efficient gradually damped artificial boundary. Based on the assumption of invariant geometry and material distribution in the tunnel’s direction, the Fourier transform of the spatial dimension in this direction is applied to represent the waves in terms of the wave-number. Finite element discretization is employed in the cross-section perpendicular to the tunnel direction and the governing equations are solved for every discrete wave-number. The 3D ground responses are calculated from the wave-number expansion by employing the inverse Fourier transform. The accuracy of the proposed analysis method is verified by a semi-analytical solution of a rectangular load moving inside a soil stratum. A case study of subway train induced ground vibration is presented and the dependency of wave attenuation at the ground surface on the vibration frequency of the moving load is discussed. | Ground-borne vibrations due to dynamic loadings from moving trains in subway tunnels | 10.1631/jzus.A12ISGT5 |
2012-11-01 | Traffic accidents are often caused by vibration of automotive steering because the vibration can make a vehicle run like a snake. A novel semi-active vibration control strategy of automotive steering with magneto-rheological (MR) damper is proposed in this paper. An adaptive RBF neural sliding mode controller is designed for the vibration system. It is showed that an equivalent dynamic model for the vibration system is established by using Lagrange method, and then treats it as actual system partially. A feedback control law is designed to make this nominal model stable. Uncertain part of system and outside disturbance are estimated using RBF neural network, and their upper boundary is obtained automatically. By constructing reasonable switch function, state variables can arrive at origin asymptotically along the sliding mode. Strong robust character of control system is proved by stability analysis and a numerical simulation example is performed to support this control scheme. | Nonlinear vibration semi-active control of automotive steering using magneto-rheological damper | 10.1007/s11012-012-9572-z |
2012-10-30 | The seismic response of linearly elastic, single-storey, one-way asymmetric building with linear and non-linear viscous dampers is investigated. The response is obtained by numerically solving the governing equations of motion. The effects of eccentricity ratio, uncoupled lateral time period, ratio of uncoupled torsional to lateral frequency and supplemental damping eccentricity ratio are investigated on peak responses which include lateral, torsional and edge displacements and their acceleration counter parts as well as control forces. To study the effectiveness of dampers, the controlled response of asymmetric system is compared with the corresponding uncontrolled response. Further, to study the effects of torsional coupling, the controlled response of asymmetric system is compared with the corresponding symmetric system. It is shown that the non-linear viscous dampers are quite effective in reducing the responses and the damper force depends on system asymmetry and supplemental damping. Also, the effectiveness of dampers significantly depends on structural and damping eccentricity ratio and torsional to lateral frequency ratio and the effects of torsional coupling are found to be more significant for torsionally flexible and strongly coupled systems. Further, effects of torsional coupling are less for asymmetric systems with non-linear dampers as compared to linear dampers. | Seismic response of asymmetric systems with linear and non-linear viscous dampers | 10.1186/2008-6695-4-5 |
2012-10-11 | A series of polyurethanes (PUs) based on poly (tetramethylene glycol) (PTMG), poly (ethylene adipate) (PEA) diol, polycaprolactone (PCL) diol and castor oil (CO) were synthesized. The tensile, damping and thermal properties were studied systematically in terms of the composition and isocyanate index ( R ). Results showed that when R is 2, the PUs exhibit a relatively high tensile strength more than 30 MPa. The PTMG-PU, PCL-PU and PEA-PU show high elongation at break compared to the cross-linked CO-PU. When R is 1.5, tensile strengths decrease compared to R is 2. But, the elongations of PTMG-PU, PCL-PU and CO-PU increase. DMA analysis showed that the glass transition temperature ( T _ g ) is increasing as the sequence of PTMG-PU, PCL-PU, PEA-PU and CO-PU. The T _ g of CO-PU is as high as 60.6 °C when R is 1.5 and 93.4 °C when R is 2. The T _ g ranges of the other linear PUs are between −50 and −12 °C. The damping temperature ranges of these PUs are relatively broad. Further, TG results showed the start degradation temperatures of them are approx 260 °C. These results show a good guidance to select a kind of PU when prepare the PU-polymer composites for given properties. | Preparation, tensile, damping and thermal properties of polyurethanes based on various structural polymer polyols: effects of composition and isocyanate index | 10.1007/s10965-012-9994-2 |
2012-10-01 | For forced radial oscillations of gas bubbles in liquids, a more rigorous expression of the acoustic damping constant based on Keller’s equation is developed. Comparison with those in published papers is also made. The expression offered in this paper will improve the predictions of total damping constant in particular for high frequencies and large bubbles, i.e., large ωR _0/ c _ l ( ω is the frequency of driving sound field, R _0 is the equilibrium bubble radius, c _ l is the sound speed in the liquid). Examples in ultrasound imaging and acoustical oceanography are demonstrated. | Effects of Liquid Compressibility on Radial Oscillations of Gas Bubbles In Liquids | 10.1016/S1001-6058(11)60301-6 |
2012-10-01 | The purpose of this study is to investigate analytically a single-degree-of-freedom (SDOF) building structure equipped with a friction damper for assessing its vibration control effect. Friction dampers are installed between stories to reduce inter-story displacements of building structures subjected to external loading. They are in general regarded to generate damping forces characterized by Coulomb damping, of which the directions are opposite to the inter-story velocities of building structures. Hence, the building structure model with friction dampers can be represented by a mass-spring-viscous-Coulomb damping system. The building response reduction as a result of damper installation can be provided by observing the damping ratio rather than the friction force contributed by the dampers. Since a large friction damper force is required to attenuate the response of the building due to strong excitation, friction force ratio is directly related to building response reduction, which is the friction force of the damper versus external force. Therefore, damping and friction force ratios are key parameters, playing a main role in selecting an optimal friction damper, which satisfies target response reduction. This study first identifies an SDOF building structure installed with a friction damper for free vibration with initial conditions. A closed-form expression of normalized displacement is derived in terms of friction force ratio in the time domain. Peak and valley of displacements are also found and then the time when the structure stops is derived with recursive interval number. This study is extended to identify steady-state vibration of the structure by deriving closed-form solution in case of resonance in terms of friction force ratio. Then, the dissipated energy balance is identified for both free and steady-state vibrations. Finally, equivalent viscous damping ratios are derived by using friction force ratio based on dissipated energy balance equation. The derived equations in terms of viscous damping ratio and friction force ratio can provide insight to design a friction damper for reducing structural displacement under external loadings. | Analytical investigation of an SDOF building structure equipped with a friction damper | 10.1007/s11071-012-0446-7 |
2012-10-01 | Cholinesterases (ChEs) display a hysteretic behavior with certain substrates and inhibitors. Kinetic cooperativity in hysteresis of ChE-catalyzed reactions is characterized by a lag or burst phase in the approach to steady state. With some substrates damped oscillations are shown to superimpose on hysteretic lags. These time dependent peculiarities are observed for both butyrylcholinesterase and acetylcholinesterase from different sources. Hysteresis in ChE-catalyzed reactions can be interpreted in terms of slow transitions between two enzyme conformers E and E′. Substrate can bind to E and/or E′, both Michaelian complexes ES and E’s can be catalytically competent, or only one of them can make products. The formal reaction pathway depends on both the chemical structure of the substrate and the type of enzyme. In particular, damped oscillations develop when substrate exists in different, slowly interconvertible, conformational, and/or micellar forms, of which only the minor form is capable of binding and reacting with the enzyme. Biphasic pseudo-first-order progressive inhibition of ChEs by certain carbamates and organophosphates also fits with a slow equilibrium between two reactive enzyme forms. Hysteresis can be modulated by medium parameters (pH, chaotropic and kosmotropic salts, organic solvents, temperature, osmotic pressure, and hydrostatic pressure). These studies showed that water structure plays a role in hysteretic behavior of ChEs. Attempts to provide a molecular mechanism for ChE hysteresis from mutagenesis studies or crystallographic studies failed so far. In fact, several lines of evidence suggest that hysteresis is controlled by the conformation of His438, a key residue in the catalytic triad of cholinesterases. Induction time may depend on the probability of His438 to adopt the operative conformation in the catalytic triad. The functional significance of ChE hysteresis is puzzling. However, the accepted view that proteins are in equilibrium between preexisting functional and non-functional conformers, and that binding of a ligand to the functional form shifts equilibrium towards the functional conformation, suggests that slow equilibrium between two conformational states of these enzymes may have a regulatory function in damping out the response to certain ligands and irreversible inhibitors. This is particularly true for immobilized (membrane bound) enzymes where the local substrate and/or inhibitor concentrations depend on influx in crowded organellar systems, e.g. cholinergic synaptic clefts. Therefore, physiological or toxicological relevance of the hysteretic behavior and damped oscillations in ChE-catalyzed reactions and inhibition cannot be ruled out. | Time-dependent kinetic complexities in cholinesterase-catalyzed reactions | 10.1134/S0006297912100070 |
2012-10-01 | In this paper vibration damping capacity of shape memory alloys (SMA) is studied which is based on two-dimensional Oberaigner, Fischer and Tanaka model. The thermodynamic based active and passive control paradigms in SMA are presented. The model solution is presented along with modification based on exact solution for the most general case of a set of conditions based upon general thermal regimes. For the particular cases, four examples of different thermal and mechanical loadings are given. This study incorporates the static thermal changes and dynamic thermal states. | Analytical technique for the two-dimensional stress wave model of memory alloy dampers | 10.1007/s12206-012-0814-8 |
2012-10-01 | In this paper, the occurrence of various types of bifurcation including symmetry breaking, period-doubling (flip) and secondary Hopf (Neimark) bifurcations in milling process with tool-wear and process damping effects are investigated. An extended dynamic model of the milling process with tool flank wear, process damping and nonlinearities in regenerative chatter terms is presented. Closed form expressions for the nonlinear cutting forces are derived through their Fourier series components. Non-autonomous parametrically excited equations of the system with time delay terms are developed. The multiple-scale approach is used to construct analytical approximate solutions under primary resonance. Periodic, quasi-periodic and chaotic behavior of the limit cycles is predicted in the presence of regenerative chatter. Detuning parameter (deviation of the tooth passing frequency from the chatter frequency), damping ratio (affected by process damping) and tool-wear width are the bifurcation parameters. Multiple period-doubling and Hopf bifurcations occur when the detuning parameter is varied. As the damping ratio changes, symmetry breaking bifurcation is observed whereas the variation of tool wear width causes both symmetry breaking and Hopf bifurcations. Also, under special damping specifications, chaotic behavior is seen following the Hopf bifurcation. | Bifurcation analysis of milling process with tool wear and process damping: regenerative chatter with primary resonance | 10.1007/s11071-012-0470-7 |
2012-10-01 | This paper proposes a new finite element model for active constrained layer damped (CLD) rotating plate with self-sensing technique. Constrained layer damping can effectively reduce the vibration in rotating structures. Unfortunately, most existing research models the rotating structures as beams that are not the case many times. It is meaningful to model the rotating part as plates because of improvements on both the accuracy and the versatility. At the same time, existing research shows that the active constrained layer damping provides a more effective vibration control approach than the passive constrained layer damping. Thus, in this work, a single layer finite element is adopted to model a three-layer active constrained layer damped rotating plate. Unlike previous ones, this finite element model treats all three layers as having the both shear and extension strains, so all types of damping are taken into account. Also, the constraining layer is made of piezoelectric material to work as both the self-sensing sensor and actuator. Then, a proportional control strategy is implemented to effectively control the displacement of the tip end of the rotating plate. Additionally, a parametric study is conducted to explore the impact of some design parameters on structure’s modal characteristics. | Modeling and analysis of rotating plates by using self-sensing active constrained layer damping | 10.1007/s12206-012-0817-5 |
2012-10-01 | A piezoelectric plate with a damper and a matching layer is considered. Water was chosen as an acoustic load. On the basis of the use of the apparatus of circuits-analogues of piezoelectric transducers (PETs), the relationships were obtained that determine the frequency dependences of the modulus and phase of the input electric impedance of the considered transmitter. Numerical investigations of the aforementioned electric characteristics of the PET were performed within a wide band of relative frequencies and the interrelationships of these characteristics with the shape of the frequency characteristics of the PET-transmitted acoustic power were studied. | On the problem of the frequency dependences of the input electric impedance of a broadband immersion transducer | 10.1134/S1061830912100063 |
2012-10-01 | In the present study, the Volterra series theory is adopted to theoretically investigate the force transmissibility of multiple degrees of freedom (MDOF) structures, in which an isolator with nonlinear anti-symmetric viscous damping is assembled. The results reveal that the anti-symmetric nonlinear viscous damping can significantly reduce the force transmissibility over all resonance regions for MDOF structures with little effect on the transmissibility over non-resonant and isolation regions. The results indicate that the vibration isolators with an anti-symmetric damping characteristic have great potential to solve the dilemma occurring in the design of linear viscously damped vibration isolators where an increase of the damping level reduces the force transmissibility over resonant frequencies but increases the transmissibility over non-resonant frequency regions. This work is an extension of a previous study in which MDOF structures installed on the mount through an isolator with cubic nonlinear damping are considered. The theoretical analysis results are also verified by simulation studies. | Reducing force transmissibility in multiple degrees of freedom structures through anti-symmetric nonlinear viscous damping | 10.1007/s10409-012-0100-0 |
2012-10-01 | Methods of studies are based on solving a nonlinear system of equations of magnetically connected circuits. Determination of the currents in elements of damping windings of salient and nonsalient pole types of machines and series of linear transformations of MMF and flux density in a complex plane is carried out; MMF and flux density are represented in the form of complexes of symbolic method. Formulas for currents in elements of damping windings and complex amplitudes of currents are obtained. Practical examples are given. | Electromagnetic loads of synchronous machines in asynchronous modes (taking into consideration current distribution in the damping winding) | 10.3103/S1068371212100033 |
2012-10-01 | In this paper, a novel scheme for nonlinear displacement-dependent (NDD) damper is introduced. The damper is attached to a simple mass-spring-damper vibration system. The vibration system equipped with a NDD damper is mathematically modeled and the nonlinear governing differential equation of the system is derived. To obtain the displacement of the system, the approximate analytical solution of the governing equation is elaborated using the multiple scales method. The advised approximate analytical algorithm is performed for several case studies and is also verified by the numerical fourth-order Runge–Kutta method. In addition, the performance of the NDD damper is analyzed and compared with the performance of the traditional linear damper. It is found that the proposed NDD damper scheme along with the multiple scales method is not only feasible for vibration reduction but also yields satisfactory response performance rather than the existing traditional linear damper. | A novel scheme for nonlinear displacement-dependent dampers | 10.1007/s11071-012-0465-4 |
2012-10-01 | A stochastic fractional optimal control strategy for quasi-integrable Hamiltonian systems with fractional derivative damping is proposed. First, equations of the controlled system are reduced to a set of partially averaged It $\hat{o}$ stochastic differential equations for the energy processes by applying the stochastic averaging method for quasi-integrable Hamiltonian systems and a stochastic fractional optimal control problem (FOCP) of the partially averaged system for quasi-integrable Hamiltonian system with fractional derivative damping is formulated. Then the dynamical programming equation for the ergodic control of the partially averaged system is established by using the stochastic dynamical programming principle and solved to yield the fractional optimal control law. Finally, an example is given to illustrate the application and effectiveness of the proposed control design procedure. | Stochastic fractional optimal control of quasi-integrable Hamiltonian system with fractional derivative damping | 10.1007/s11071-012-0547-3 |
2012-10-01 | The equations governing wind-induced internal pressure responses for a two-compartment building with a dominant opening and background porosity were derived. The unsteady form of the Bernoulli equation, the law of mass conservation, and adiabatic equation were used for the derivation. The precision of the governing equations was verified by a wind tunnel test on a rigid model of a low-rise building. The results show that the governing equations can effectively analyze the wind-induced internal pressure responses. The internal pressure responses in both compartments are suppressed due to the additional damping provided by background porosity. The responses of internal pressure in both compartments, especially in the compartment without an external opening, decrease with increased lumped leakage area. | Responses of wind-induced internal pressure in a two-compartment building with a dominant opening and background porosity Part 1: Theoretical formulation and experimental verification | 10.1007/s11771-012-1362-1 |
2012-10-01 | The complex behaviors of Duffing equation with periodic damping and external excitations are investigated. The existence conditions and bifurcations of periodic orbits with three different frequencies resonant conditions are concerned by the second-order averaging method and the Melnikov method. The rich dynamical behaviors are so distinct when different periodic damping excitations are added, including more complicated averaged equations, bifurcation curves, bifurcation conditions, and even chaos. The numerical simulations show the consistence with the theoretical analysis and reveal new complex phenomena which cannot be given by theoretical analysis. | Bifurcations of periodic orbits in Duffing equation with periodic damping and external excitations | 10.1007/s11071-012-0467-2 |
2012-10-01 | In this paper, a new kind of combined lead extrusion magnetorheological (CLEMR) damper is proposed. First, tests on CLEMR damper at different currents, excitation amplitudes, and frequencies are carried out. Experimental results show that even when power fails, CLEMR damper can still absorb and dissipate vibration energy of the structure effectively, and its damping force can also be well adjusted in a large range of damping force. Then a mathematical model employing the current, excitation amplitude, and frequency as inputs is proposed and verified by comparing experimental and numerical results. Comparison results show that the proposed model can describe the effects of current, amplitude, and frequency on properties of CLEMR damper. Finally, elastic-plastic dynamic time-history analyses on frame structure with and without CLEMR damper are carried out to evaluate the effectiveness of CLEMR damper in reducing seismic responses of the structures; dynamic responses of the uncontrolled and the controlled structures are then compared. Comparison results show that the displacement responses of each floor of the controlled structure, as well as the number of the cracking point and yielding point of the member, reduce significantly, which implies that the proposed CLEMR damper holds promise in reducing and suppressing the vibration responses of the civil structures. | Testing and modeling of a CLEMR damper and its application in structural vibration reduction | 10.1007/s11071-012-0557-1 |
2012-10-01 | This work develops an analytical approach to optimally design electrorheological (ER) dampers, especially for vehicle suspension system. The optimal design considers both stability and ride comfort of vehicle application. After describing the schematic configuration and operating principle of the ER damper, a quasi-static model is derived on the basis of Bingham rheological laws of ER fluid. Based on the quasi-static model, the optimization problem for the ER damper is built. The optimization problem is to find optimal value of significant geometric dimensions of the ER damper, such as the ER duct length, ER duct radius, ER duct gap and the piston shaft radius, that maximize damping force of the ER damper. The two constrained conditions for the optimization problem are: the damping ratio of the damper in the absence of the electric field is small enough for ride comfort and the buckling condition of the piston shaft is satisfied. From the proposed optimal design, the optimal solution of the ER damper constrained in a specific volume is obtained. In order to evaluate performance of the optimized ER damper, simulation result of a quarter-car suspension system installed with the optimized ER damper is presented and compared with that of the non-optimized ER damper suspension system. Finally, the optimal results of the ER damper constrained in different volumes are obtained and presented in order to figure out the effect of constrained volume on the optimal design of ER damper. | An analytical approach to optimally design of electrorheological fluid damper for vehicle suspension system | 10.1007/s11012-012-9544-3 |
2012-09-01 | Correlating damage level and changes in dynamic characteristics of a structure forms the basis for damage detection techniques in structural health monitoring. In reinforced concrete building structures such correlation is not well established. A damage detection technique capable of identifying the structural condition of the system based on its small amplitude vibration response is desirable because such response is easier to obtain. It is a common practice in engineering applications to estimate dynamic parameters from small-amplitude vibrations assuming a linear behavior of the structure. This simplification causes inaccurate estimation of the dynamic properties in reinforced concrete structures due to the presence of nonlinear elastic behavior. In this study no such assumption is made and a linear model is only used for sets of data corresponding to the same displacement amplitude of a nonlinear elastic system. The trends found between small-amplitude vibration dynamic properties and past levels of maximum displacement in various reinforced concrete structures are reported. In addition to analytical and numerical studies, results from a series of laboratory tests are reported to demonstrate the use of the approach. One full-scale three-story reinforced concrete flat-plate building and six small-scale reinforced concrete beams were examined. In this study, small displacements are defined as displacements below an overall drift ratio of 0.03%. The displacement dependence of the dynamic properties is considered explicitly. It was found that while fundamental frequencies of the examined reinforced concrete specimens were found to decrease uniformly as past peak displacement level increased, the equivalent viscous damping ratio was found to increase until the past peak displacement reached the neighborhood of nominal yield displacement and then observed to decrease when the specimens are pushed beyond the nominal yield displacement level, which has not been reported in literature before. Recommendations are provided as to how small amplitude vibration tests should be set up to avoid misleading observations due to nonlinear response at small amplitude response, observations that could lead to erroneous conclusions regarding the damage state of a structure. | Variation of Small Amplitude Vibration Dynamic Properties with Displacement in Reinforced Concrete Structures | 10.1007/s11340-011-9590-0 |
2012-09-01 | In this study, through novel drift-based equations of motion in the frequency domain, optimum placement and characteristics of linear velocity-dependent dampers are investigated. In this study, the sum of the square of the absolute values of transfer matrix elements for interstory drifts is considered as the optimization index. Optimum placement and characteristics of dampers are simultaneously obtained by minimizing the optimization index through an incremental procedure. In each step of the procedure, a predefined value is considered as the damper characteristic. The optimum story for this increment is selected such that it leads to a minimum value for the optimization index. The procedure is repeated for the next increments until the optimization index meets its target value, which is obtained according to the desired damping ratio for the overall structure. In other words, the desired overall damping ratio is the input to the proposed procedure, and the optimal placement and characteristics of the dampers are its output. It is observed that the optimal placement of a velocitydependent damper depends on the damping coefficient of the added damper, frequency of the excitation, and distribution of the mass, stiffness, and inherent damping of the main structure. | Optimum placement and characteristics of velocity-dependent dampers under seismic excitation | 10.1007/s11803-012-0130-4 |
2012-09-01 | This study proposes a modified eccentric circle model to simulate the rolling resistance of circle particles through the distinct element method (DEM) simulation. The proposed model contains two major concepts: eccentric circle and local rotational damping. The mass center of a circular particle is first adjusted slightly for eccentricity to provide rotational stiffness. Local rotational damping is adopted to dissipate energy in the rotational direction. These associated material parameters can be obtained easily from the rolling behavior of one rod. This study verifies the proposed model with the repose angle tests of chalk rod assemblies, and the simulated results were satisfactory. Simulations using other existing models were also conducted for comparison, showing that the proposed model achieved better results. A landslide model test was further simulated, and this simulation agreed with both the failure pattern and the sliding process. In conclusion, particle rolling simulation using the proposed model appears to approach the actual particle trajectory, making it useful for various applications. | Modeling Particle Rolling Behavior by the Modified Eccentric Circle Model of DEM | 10.1007/s00603-012-0227-0 |
2012-09-01 | This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy (SMA) link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitic SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%–12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly. | Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars | 10.1007/s11803-012-0128-y |
2012-09-01 | This paper deals with the analysis of active constrained layer damping (ACLD) of sandwich plate with laminated composite faces. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composites. Several honeycomb core materials like HEREX honeycomb and honeycomb with foam fill separated by different facing materials have been studied and a three-dimensional finite element model has been developed considering first order shear deformation theory individually for each layer of the sandwich plate. The effect of the ratio between the face sheet thickness and the core thickness of the sandwich plate on the frequency response has been studied. Particular emphasis has been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD treatment. | Active constrained layer damping of smart laminated composite sandwich plates using 1–3 piezoelectric composites | 10.1007/s10999-012-9186-6 |
2012-09-01 | Hollow-core composite post insulators, used in high voltage electrical equipment, are important parts of the power substation systems. In many applications the composite insulators are considered as slender cantilever columns, fixed at one end and connecting to a conductor at the other end. During earthquakes the post insulators are damaged and sometimes fail near their base connection. When the post is pulled laterally, the tube dislocates from the walls in the end flange, and slips in and out the flange. Subsequently the composite tube sticks in the flange and slips again if the load is reversed, as it is occurring during earthquakes. In this study, an analytical model is developed using a combination of linear and nonlinear springs, viscous and frictional dampers and inertial masses. The developed macroscopic model is governed by a third-order differential equation which is derived in a state-space and solved by using Runge–Kutta integration in MATLAB. Several prototype insulators have been tested at the University at Buffalo’s Structural Engineering and Earthquake Simulation Laboratory (SEESL). Through a methodical identification of the stiffness, mass, friction, and damping properties, the analytical model is verified to produce reliable estimates of strength, damping and global behavior. | Experimental test and modeling of hollow-core composite insulators | 10.1007/s11071-012-0376-4 |
2012-09-01 | The use of chamfered tools is widely spread in cutting processes. Prior investigation show, that a chamfer on the rake face of a milling tool can increase the stability of cutting processes significantly due to a contact between the chamfer surface and the workpiece and the resulting damping forces. In addition to higher process stability, it is possible that the chamfer shows positive effects on the machined surface as well. A sufficient chamfer length can cut off the feed marks on the machined surface, but also damping effects on the process vibrations can lead to a better flank surface when milling compliant parts or tools as well. This paper describes an approach of simulation of machining of the flank surface with consideration of the chamfer geometry. In the experimental and simulative investigations it was found that by the reduction of extensive workpiece vibrations, the chamfer does have positive effect on the flank surface quality due to a contact between the chamfer and the workpiece. Furthermore, this contact does apparently occur earlier than a theoretical consideration would predict from the kinematics of the process. With increase of the chamfer length on the other hand, also augmented appearance of smearing effects on the surface, which decrease the surface quality, was observed. | Flank milling of compliant workpieces with chamfered tools | 10.1007/s11740-012-0399-1 |
2012-09-01 | Response surface methodology (RSM) is a technique used to determine and represent the cause and effect of relationship between true mean responses and input control variables influencing the responses as an n-dimensional hyper surface. Welded joints are used extensively in many modern industries to fabricate jointed structures that contribute significantly to the inherent slip damping. The main problem faced in the manufacture of such structures is the selection of optimum combination of input variables for achieving the required damping. This problem can be solved by developing the mathematical models through effective and strategic planning and executing experiments by RSM. This investigation highlights the use of RSM by designing a four-factor three-level central composite rotatable design matrix with full replication of planning, conducting, executing and developing the mathematical models. This is useful for predicting the mechanism of interfacial slip damping in layered and welded structures. The design utilizes the initial amplitude of excitation, number of tack welded joints and surface roughness at the interfaces as well as the material property to develop a model for the logarithmic damping decrement of layered and welded structures with different end conditions. Experimental results indicate that the proposed mathematical models adequately predict the logarithmic damping decrement within the limits of the factors that are being investigated. | Slip Damping Mechanism in Welded Structures Using Response Surface Methodology | 10.1007/s11340-011-9563-3 |
2012-09-01 | The contributions of compressive load and support damping are included into the formulation of flexural wave motion in beams lying on elastic (Winkler) foundation. The beam is modeled by both Euler–Bernoulli’s and Timoshenko’s theories. First, dispersion analysis is performed, which reveals that, for a fixed wavenumber, phase velocity decreases as the intensity of the compressive force or the value of the support damping is increased. Secondly, the transverse displacement of a semi-infinite beam excited by a velocity step pulse at its finite end is examined in the transient regime by adopting Laplace transform approach. This latter study sustains the validity of the dispersion analysis outcomes and shows that compressive load and support damping cause an amplification and a diminution, respectively, of the displacement amplitudes at the various positions of the beam. | Effects of compressive load and support damping on the propagation of flexural waves in beams resting on elastic foundation | 10.1007/s00419-012-0611-y |
2012-09-01 | The Inner Formation Flying System (IFFS) consisting of an outer satellite and an inner satellite which is a sphere proof mass freely flying in the shield cavity can construct a pure gravity orbit to precisely detect the earth gravity field. The residual gas in the cavity is a significant disturbance source due to the temperature in-homogeneity and relative motion of the inner satellite. The expressions of the disturbance forces were derived based on the property of rarefied gas, including the radiometer effect and the damping force. According to the current design of IFFS, heat transfer analysis of the cavity and the inner satellite was carried out, and the surface temperature distribution of the cavity and the inner satellite was given. The relative motion of the inner satellite was obtained from the formation control simulation of IFFS. Then the residual gas disturbance was calculated. The disturbance acceleration acting on the inner satellite due to the radiometer effect was on the order of 10^−11 m s^−2 and the damping acceleration was on the order of 10^−15 m s^−2. | Analysis of residual gas disturbance on the inner satellite of Inner Formation Flying System | 10.1007/s11431-012-4962-y |
2012-09-01 | We study the distribution of eigenvalues for non-selfadjoint perturbations of selfadjoint semiclassical analytic pseudodifferential operators in dimension two, assuming that the classical flow of the unperturbed part is completely integrable. An asymptotic formula of Weyl type for the number of eigenvalues in a spectral band, bounded from above and from below by levels corresponding to Diophantine invariant Lagrangian tori, is established. The Weyl law is given in terms of the long time averages of the leading non-selfadjoint perturbation along the classical flow of the unperturbed part. | Diophantine Tori and Weyl Laws for Non-selfadjoint Operators in Dimension Two | 10.1007/s00220-012-1530-z |
2012-09-01 | The problem of the forced axisymmetric vibrations and self-heating of a clamped flexible circular plate with piezoelectric actuators is solved. The aspects of mechanical and electric excitation of vibrations and damping of mechanical vibrations with actuators are discussed. The effect of geometrical nonlinearity on the frequency dependence of deflections and self-heating temperature under electromechanical harmonic loading at the principal resonance of bending vibrations of the plate is studied | Forced resonant vibrations and self-heating of a flexible circular plate with piezoactuators | 10.1007/s10778-012-0540-z |
2012-09-01 | In this study we utilize the self-sensing capabilities of piezoelectric micro-actuators in hard disk drives (HDD) to actively suppress in-plane resonance modes of the suspension in an HDD. The self-sensing circuit is based on a tunable capacitance bridge that decouples the control signal from the sensing signal in the micro-actuator. A hybrid modeling technique based on a realization algorithm and least-squares optimization for continuous-time systems is used to model the single-input dual-output system. An analog controller was computed using standard $$H_{\infty}$$ -controller design tools and reduced in order using model reduction routines. Experimental implementation using analog filter design shows the effectiveness of the proposed method in reducing the main sway modes of the suspension. | Suppression of cross-track vibrations using a self-sensing micro-actuator in hard disk drives | 10.1007/s00542-012-1533-x |
2012-09-01 | An environmental vibration problem occurred at a house near a highway bridge on soft ground. Vibration experiments with a test truck were performed to investigate the cause of the problem and the vibration characteristics of the bridge and house. Experimental results showed that the house was resonating with the bridge. As a measure to reduce vibration, viscoelastic dampers were installed at the ends of the bridge girders. The effectiveness of this measure was evaluated by comparing the data gathered before and after the installation of the dampers using ordinary trucks running over the bridge. Moreover, a dynamic response analysis was carried out to investigate the vibration reduction as a function of the number of installed dampers as well as the various analytical conditions employed. Simulation results showed that the vibration reduction depends on the boundary condition, running position, and torsion modes that have a coupling vibration between the superstructure and the piers. | Effectiveness of dampers in controlling a vibration problem near a highway bridge | 10.1007/s13349-012-0022-3 |
2012-09-01 | In this paper, a control strategy is applied to a nonlinear ideal and nonideal vibrating system coupled to a magneto-rheological damping structure, exhibiting chaotic behavior. In order to suppress the chaotic oscillations and to improve the transient response, a combination of passive (energy pumping) and active (state feedback) control strategies. The chaotic vibrations are suppressed, bringing the system to a desired periodic orbit. Additionally, the control damping force is transformed into the electrical control signal variable. | On energy transfer phenomena, in a nonlinear ideal and nonideal essential vibrating systems, coupled to a (MR) magneto-rheological damper | 10.1007/s11071-012-0391-5 |
2012-09-01 | In this study, the structural control strategy utilizing a passive tuned mass damper (TMD) system as a seismic damping device is outlined, highlighting the parametric optimization approach for displacement and acceleration control. The theory of stationary random processes and complex frequency response functions are explained and adopted. For the vibration control of an undamped structure, the optimal parameters of a TMD, such as the optimal tuning frequency and optimal damping ratio, to stationary Gaussian white noise acceleration are investigated by using a parametric optimization procedure. For damped structures, a numerical searching technique is used to obtain the optimal parameters of the TMD, and then the explicit formulae for these optimal parameters are derived through a sequence of curve-fitting schemes. Using these specified optimal parameters, several different controlled responses are examined, and then the displacement and acceleration based control effectiveness indices of the TMD are examined from the view point of RMS values. From the viewpoint of the RMS values of displacement and acceleration, the optimal TMDs adopted in this study shows clear performance improvements for the simplified model examined, and this means that the effective optimization of the TMD has a good potential as a customized target response-based structural strategy. | Parametric control of structural responses using an optimal passive tuned mass damper under stationary Gaussian white noise excitations | 10.1007/s11709-012-0170-x |
2012-08-30 | We investigate the degenerate Kirchhoff equations with strong damping and source terms of the form ε u t t − ∥ ∇ u ∥ 2 2 γ Δ u − Δ u t = f ( u ) , in a bounded domain. We obtain the optimal decay rate for ∥ ∇ u t ∥ 2 2 by deriving its decay estimate from below, provided that either ε is suitably small or the initial data satisfy the proper smallness assumption. The key ingredient in the proof is based on the work of Ono (J. Math. Anal. Appl. 381(1):229-239, 2011), with necessary modification imposed by our problem. MSC: 35L70, 35L80. | On decay properties of solutions for degenerate Kirchhoff equations with strong damping and source terms | 10.1186/1687-2770-2012-93 |
2012-08-08 | In this paper, we study the strongly damped quasilinear wave equation. By using spatial sequence techniques and energy estimate methods, we obtain the existence theorem of the solution to abstract a strongly damped wave equation and to a class of strongly damped quasilinear wave equations. MSC: 35L05, 35L20, 35D30, 35D35. | Existence of solutions to strongly damped quasilinear wave equations | 10.1186/1687-1847-2012-139 |
2012-08-01 | The goal of this work is to study a model of the strongly damped wave equation with dynamic boundary conditions and nonlinear boundary/interior sources and nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. In addition, we show that in the strongly damped case solutions gain additional regularity for positive times t >0. Second, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution grows as an exponential function. Moreover, in the absence of the strong damping term, we prove that the solution ceases to exists and blows up in finite time. | Existence and Asymptotic Behavior of the Wave Equation with Dynamic Boundary Conditions | 10.1007/s00245-012-9165-1 |
2012-08-01 | We present a quantized model of a harmonically confined dot atom with inherent damping in the presence of a transverse magnetic field. The model leads to a non-Hermitian Hamiltonian in coordinate space. We have analytically studied the effects of damping on Rabi type oscillations of the system. The model explains the decoherence of Rabi oscillations in a Josephson Junction. | Rabi type oscillations in damped two-dimensional single electron quantum dots | 10.2478/s11534-012-0064-5 |
2012-08-01 | An inorganically template metaphosphate of Co(II) complex has been synthesized and thermal properties have been studied at a low temperature up to 173 K from 298 K by the Differential Scanning Calorimeter (DSC). The specific heat capacity is measured in atmospheric O_2 at a heating rate of 283 K min^−1 from 298 K and kept constant at 173 K for 4 minutes then reversed to 298 K again. The bulk critical temperature of superconductivity of metaphosphatecobalt(II) salt was found at 173 K. | Superconductivity of Metaphosphatecobalt(II) Salt at 173 K | 10.1007/s10948-012-1589-y |
2012-08-01 | In this paper, we consider an n-dimensional thermoelastic system of second sound with a viscoelastic damping localized on a part of the boundary. We establish an explicit and general decay rate result that allows a wider class of relaxation functions and generalizes previous results existing in the literature. | Boundary stabilization of memory-type thermoelasticity with second sound | 10.1007/s00033-011-0190-8 |
2012-08-01 | The present experimental investigations study the effect of layering over rigid base on the dynamic behavior of foundation under vertical mode of vibration. Model block vibration tests were conducted on a rigid surface footing resting on different layered soil systems underlain by rigid base. The rigid base was used to simulate the presence of bedrock. The tests were carried out in a pit of size 2.0 m × 2.0 m × 1.9 m (deep) using a concrete footing of size 0.4 m × 0.4 m × 0.1 m. A rotating mass type mechanical oscillator was used for inducing vibration in vertical direction. Different layered soil systems were prepared within the total depth of 1,200 mm over the rigid base. Locally available gravel and fly ash were used to form different layered soil systems. In total, 132 nos. model block vibration tests in vertical mode were conducted for different layering and loading combinations. The experimentally obtained results are also compared with the results obtained from the analysis by mass-spring-dashpot and equivalent half-space theory. | Dynamic Response of the Foundations Resting on a Two-layered Soil Underlain by a Rigid Layer | 10.1007/s10706-012-9497-2 |
2012-08-01 | The stability of a kind of one-dimensional thermo-elastic system of type II is considered. This system consists of two strongly coupled wave equations. Suppose that there exists an viscoelastic damping at one end of the 1-d domain. If without coupling, this damping always makes one of these two wave equations (the corresponding pure elastic system) achieve exponential stability and the other wave system (heat equation of type II) be conservative. Whether the coupling can pass the damping effect from the dissipative elastic system to the conservative heat system of type II is discussed. However, by a detailed spectral analysis, it is proved that this thermo-elastic system is at most asymptotically stable but not exponentially stable. A numerical simulation is given to support these results obtained in this paper. | Stability analysis of a thermo-elastic system of type II with boundary viscoelastic damping | 10.1007/s00033-011-0184-6 |
2012-08-01 | Objective To investigate a method for quantitative differential diagnosis of damp-heat and cold-damp impeding syndrome of rheumatoid arthritis (RA) in Chinese medicine (CM). Methods Laboratory parameters were collected from 306 patients with RA. The clinical symptoms and laboratory parameters were compared between patients with these two syndromes (158 with RA of damp-heat impeding syndrome, and 148 with RA of cold-damp impeding syndrome), and a regression equation was established to facilitate discrimination of the two RA syndromes. Results There were significant differences in disease activity score in 28 joints [DAS28 (4)], erythrocyte sedimentation rate (ESR), white blood cell count (WBC), C-reactive protein (CRP), platelet count (PLT), albumin (ALB) and globulin (GLB) between the two syndrome of RA ( P <0.05). Logistic regression analysis showed that the parameters ESR, WBC, CRP, joint pyrexia, joint cold, thirst, sweating, aversion to wind and cold, and cold extremities were statistically useful to discriminate damp-heat from cold-damp impeding syndrome. The regression equation was as follows: P =1/{1+exp[-(3.0-0.021 X _1-0.196 X _2-0.163 X _3-1.559 X _4+1.504 X _5-0.927 X _6-1.039 X _7+1.070 X _8+1.330 X _9)]}. The independent variables X _1- X _9 were ESR, WBC, CRP, hot joint, cold joint, thirst, sweating, aversion to wind and cold, and cold limbs. A P value > 0.5 signified cold-damp impeding syndrome, and a P value < 0.5 signified damp-heat impeding syndrome. The accuracy was 90.2%. Conclusion The regression equation may be useful for discriminating damp-heat from cold-damp impeding syndrome of RA. | Logistic regression analysis of damp-heat and cold-damp impeding syndrome of rheumatoid arthritis: A perspective in Chinese medicine | 10.1007/s11655-012-1172-1 |
2012-08-01 | A self-consistent linear model is proposed for the transformation of the average intensity of the mode spectrum I ( z ) of the waveguide field in a multimode optical fiber with a stepped refractive index profile and the core having a rough surface. The model is based on the concept of the intermodal dispersion matrix of an elementary segment of the fiber, ∆, whose elements characterize the mutual transfer of energy between the waveguide modes, as well as their conversion to radiation modes on the specified interval. On this basis, the features of the transformation of the mode spectrum I ( z ) in a multimode optical fiber with a stepped refractive index profile are considered that is due to the effects of multiple dispersion of the signal by the stochastic irregularities of the duct. The effect of self-filtering of I ( z ) is described that results in the formation of a stable (normalized) distribution I *. The features of the normalization of the radiative damping of a group of modes I _ i ( z ) in an optical fiber are considered. | Interaction and dispersion of waveguide modes in an optical fiber with microirregularities of the core surface | 10.1007/s11182-012-9809-2 |
2012-08-01 | Methods of investigation of currents in elements of closed chain schemes, each link of which contains an EMF, having the same amplitude and following the harmonic law from link number N are stated. This scheme is a mathematical regime of damper windings of modern synchronous machines (salient-pole generators and motors, turbomotors, and high-power turbogenerators). Calculated expressions for currents in longitudinal and transverse elements of the scheme are obtained. | A study of currents in elements of a closed regular chain scheme (with reference to damper windings of synchronous machines) | 10.3103/S1068371212080056 |
2012-08-01 | In this article, the charged system search (CSS) optimization method is improved to identify the parameters of a non-linear hysteretic Bouc-Wen differential model. The CSS is suitable for those optimization problems involving non-smooth or non-convex domains. Bouc-Wen is a well-established non-linear model which has been used to portray the hysteretic and high non-linear real behavior of numerous physical and mechanical systems. To improve the effectiveness and adaptability of the CSS algorithm, it is combined with sub-optimization mechanism. The obtained results show that the adaptive CSS embodies great robustness and accuracy to be successfully employed in such highly non-linear identification problems. | Parameter identification of Bouc-Wen model for MR fluid dampers using adaptive charged system search optimization | 10.1007/s12206-012-0625-y |
2012-07-20 | In this paper, we study a strongly damped plate or beam equation. By using spatial sequence techniques and energy estimate methods, we obtain an existence theorem of the solution to abstract strongly damped plate or beam equation and to a nonlinear plate or beam equation. MSC: 35L05, 35L20, 35D30, 35D35. | Existence of solutions to strongly damped plate or beam equations | 10.1186/1687-2770-2012-76 |
2012-07-05 | In this article, we establish the new result on homoclinic orbits for a class of damped vibration systems. Some recent results in the literature are generalized and significantly improved. MSC: 49J40, 70H05. | On homoclinic orbits for a class of damped vibration systems | 10.1186/1687-1847-2012-102 |
2012-07-01 | This article deals with the question, to what extent damping due to nonsmooth Coulomb friction may affect the stability and bifurcation behavior of vibrational systems with self-excitation due to negative effective damping which—for the smooth case—is related to a Hopf bifurcation of the steady state. Without damping due to Coulomb friction, the stability of the trivial solution is controlled by the effective viscous damping of the system: as the damping becomes negative, the steady state loses stability at a Hopf point. Adding Coulomb friction changes the trivial solution into a set of equilibria, which—for oscillatory systems—is asymptotically stable for all values of effective viscous damping. The Hopf point vanishes and an unstable limit cycle appears which borders the basin of attraction of the equilibrium set. Moreover, the influence of nonlinear damping terms is discussed. The effect of Coulomb frictional damping may be seen as adding an imperfection to the classical smooth Hopf scenario: as the imperfection vanishes, the behavior of the smooth problem is recovered. | On the effect of nonsmooth Coulomb friction on Hopf bifurcations in a 1-DoF oscillator with self-excitation due to negative damping | 10.1007/s11071-011-0290-1 |
2012-07-01 | This paper investigates the optimal distribution of damping material in vibrating structures subject to harmonic excitations by using topology optimization method. Therein, the design objective is to minimize the structural vibration level at specified positions by distributing a given amount of damping material. An artificial damping material model that has a similar form as in the SIMP approach is suggested and the relative densities of the damping material are taken as design variables. The vibration equation of the structure has a non-proportional damping matrix. A system reduction procedure is first performed by using the eigenmodes of the undamped system. The complex mode superposition method in the state space, which can deal with the non-proportional damping, is then employed to calculate the steady-state response of the vibrating structure. In this context, an adjoint variable scheme for the response sensitivity analysis is developed. Numerical examples are presented for illustrating validity and efficiency of this approach. Impacts of the excitation frequency as well as the damping coefficients on topology optimization results are also discussed. | On topology optimization of damping layer in shell structures under harmonic excitations | 10.1007/s00158-011-0746-4 |
2012-07-01 | This paper proposes a simple methodology to analyse numerically the effects of air damping on the oscillatory motion of heated micro-cantilevers. The proposed methodology is fully solved by the fluid solver, because the solid domain is embedded into a subroutine executed at the end of each time step. The methodology is first validated against numerical and experimental data yielding acceptable results. Next, it is applied to predict the quality factor of a micro-cantilever heated by an electric resistance inserted inside it. The transferred heat flow and the evolution in time of temperature are analysed and the quality factors of both heated and isothermal micro-cantilevers are compared. | A simple numerical methodology for thermal-fluid-structural interactions of air damping over heated micro-cantilevers | 10.1007/s10404-012-0951-5 |
2012-07-01 | A mathematical model of wave propagation and instability on a charged surface of an infinite cylindrical column of a conducting fluid, surrounding a coaxial infinite porous core, is formulated and studied. The conditions are found under which the disturbances of the liquid column become unstable and result in its fragmentation into a chain of connected droplets. It is shown that the length of the droplets decreases with increase in the electric field. | Wave propagation on a charged surface of a cylindrical liquid column surrounding a long porous core | 10.1134/S0015462812040114 |
2012-07-01 | We investigate an analytical solution for a two-qubit field system in the dispersive regime with a reservoir. We analyze the influence of the phase damping on the Wigner function and the phase properties. We found that the phase damping destroys the phase probability of the global system for the coherent state and even coherent state. The phase damping leads to decay of the Wigner function for the coherent state. | Wigner function and phase properties for a two-qubit field system under pure phase noise | 10.1007/s10946-012-9292-9 |
2012-07-01 | The addition by vacuum infiltration of small quantities of a polymer has been found to increase significantly the ability of a plasma-sprayed coating to dissipate vibratory energy at temperatures in the glassy-rubbery transition range of the polymer. As vitreous enamels and glasses undergo a glassy transition, but at much higher temperatures, the addition of a small amount of glass to a ceramic has the potential of providing high damping at such temperatures. Mixtures of yttria-stabilized zirconia (YSZ) and a glass frit were plasma sprayed on specimens with bond coats. Measures of system response (resonant frequencies and loss factors) were extracted from frequency responses to excitations of cantilever beam specimens over a range of excitation amplitudes. Comparisons of values determined before and after coating were used to determine the damping properties of the coatings alone as functions of strain, at temperatures of special interest. Emphasis was given to identifying the lowest level of glass giving significantly more damping than that of the plasma-sprayed ceramic alone. Coatings with weight fractions of 5, 2, 1, ½, and 0% glass were tested. The inclusion of glass at all weight fractions considered was found to yield significant increases in both the stiffness and dissipation of the coatings. | Influence of Glass Content on Damping Properties of Plasma-Sprayed Mixtures of Zirconia and Glass | 10.1007/s11665-011-0011-4 |
2012-07-01 | We establish new Kamenev-type oscillation criteria for the half-linear partial differential equation with damping (E) $div(A(x)\left\| {\nabla u} \right\|^{p - 2} \nabla u) + \left\langle {b(x),\left\| {\nabla u} \right\|^{p - 2} \nabla u} \right\rangle + c(x)\left| u \right|^{p - 2} u = 0$ under quite general conditions. These results are extensions of the recent results developed by Sun [Y.G. Sun, New Kamenev-type oscillation criteria of second order nonlinear differential equations with damping, J. Math. Anal. Appl. 291 (2004) 341–351] for second order ordinary differential equations in a natural way, and improve some existing results in the literature. As applications, we illustrate our main results using two different types of half-linear partial differential equations. | New Kamenev-type oscillation criteria for half-linear partial differential equations | 10.1007/s10255-012-0168-0 |
2012-07-01 | After central nervous system (CNS) trauma, axons have a low capacity for regeneration. Regeneration failure is associated with a muted regenerative response of the neuron itself, combined with a growth-inhibitory and cytotoxic post-injury environment. After spinal cord injury (SCI), resident and infiltrating immune cells (especially microglia/macrophages) contribute significantly to the growth-refractory milieu near the lesion. By targeting both the regenerative potential of the axon and the cytotoxic phenotype of microglia/macrophages, we may be able to improve CNS repair after SCI. In this review, we discuss molecules shown to impact CNS repair by affecting both immune cells and neurons. Specifically, we provide examples of pattern recognition receptors, integrins, cytokines/chemokines, nuclear receptors and galectins that could improve CNS repair. In many cases, signaling by these molecules is complex and may have contradictory effects on recovery depending on the cell types involved or the model studied. Despite this caveat, deciphering convergent signaling pathways on immune cells (which affect axon growth indirectly) and neurons (direct effects on axon growth) could improve repair and recovery after SCI. Future studies must continue to consider how regenerative therapies targeting neurons impact other cells in the pathological CNS. By identifying molecules that simultaneously improve axon regenerative capacity and drive the protective, growth-promoting phenotype of immune cells, we may discover SCI therapies that act synergistically to improve CNS repair and functional recovery. | Achieving CNS axon regeneration by manipulating convergent neuro-immune signaling | 10.1007/s00441-012-1425-5 |
2012-07-01 | A semi-active magneto-rheological (MR) damper was experimentally investigated and compared to an original equipment manufacturer (OEM) damper for a passenger vehicle, by using a quarter car models. A full-scale two-degree-of-freedom quarter car experimental set-up was constructed to study the vehicle suspension. On-off skyhook controller and Fuzzy-Lyapunov skyhook controller (FLSC) were employed to control the input current for MR damper so as to achieve the desired damping force. Tests were done to evaluate the ability of MR damper for controlling vehicle vibration. Test results show that the semi-active MR vehicle suspension vibration control system is feasible. In comparison with OEM damper, on-off and FLSC controlled MR dampers can effectively reduce the acceleration of vehicle sprung mass by about 15% and 24%, respectively. | Semi-active control of a vehicle suspension using magneto-rheological damper | 10.1007/s11771-012-1217-9 |
2012-07-01 | In this paper, ongoing studies to solve nonlinear differential equations are extended by combining the Newmark-beta integration method and the piecewise linearization approach. The discussed method is illustrated with a practical example. In doing so, the coupled nonlinear differential equations of an impact oscillator, which incorporates the Hertzian contact, are derived. To investigate this problem, an object-oriented computer code, based on the presented method, is written in MATLAB. Furthermore, the discussed problem is solved numerically using the Runge–Kutta commercial code. To verify the calculated results, the contact durations, which are obtained using the discussed methods, are compared with the previous analytical results. In this study, accuracy of solution and the process time (cost) are selected as two main parameters of the solution method. The so-called adequacy factor is presented to combine the two main parameters of solution. Finally, it is shown that in the case of Hertzian contact, the presented method can be more adequate than the Runge–Kutta method. | An efficient method to solve the strongly coupled nonlinear differential equations of impact dampers | 10.1007/s00419-011-0605-1 |
2012-07-01 | In this paper we analyze the importance of initial conditions in exponential smoothing models on forecast errors and prediction intervals. We work with certain exponential smoothing models, namely Holt’s additive linear and Gardner’s damped trend. We study some probability properties of those models, showing the influence of the initial conditions on the forecast, which highlights the importance of obtaining accurate estimates of initial conditions. Using the linear heteroscedastic modeling approach, we show how to obtain the joint estimation of initial conditions and smoothing parameters through maximum likelihood via box-constrained nonlinear optimization. Point-wise forecasts of future values and prediction intervals are computed under normality assumptions on the stochastic component. We also propose an alternative formulation of prediction intervals in order to obtain an empirical coverage closer to their nominal values; that formulation adds an additional term to the standard formulas for the estimation of the error variance. We illustrate the proposed approach by using the yearly data time-series from the M3-Competition. | Initial conditions estimation for improving forecast accuracy in exponential smoothing | 10.1007/s11750-011-0221-9 |
2012-07-01 | Most of the currently employed vibration-based identification approaches for structural damage detection are based on eigenvalues and/or eigenvectors extracted from dynamic response measurements, and strictly speaking, are only suitable for linear system. However, the inception and growth of damage in engineering structures under severe dynamic loadings are typical nonlinear procedures. Consequently, it is crucial to develop general structural restoring force and excitation identification approaches for nonlinear dynamic systems because the restoring force rather than equivalent stiffness can act as a direct indicator of the extent of the nonlinearity and be used to quantitatively evaluate the absorbed energy during vibration, and the dynamic loading is an important factor for structural remaining life forecast. In this study, based on the instantaneous state vectors and partially unknown excitation, a power series polynomial model (PSPM) was utilized to model the nonlinear restoring force (NRF) of a chain-like nonlinear multi-degree-of-freedom (MDOF) structure. To improve the efficiency and accuracy of the proposed approach, an iterative approach, namely weighted adaptive iterative least-squares estimation with incomplete measured excitations (WAILSE-IME), where a weight coefficient and a learning coefficient were involved, was proposed to identify the restoring force of the structure as well as the unknown dynamic loadings simultaneously. The response measurements of the structure, i.e., the acceleration, velocity, and displacement, and partially known excitations were utilized for identification. The feasibility and robustness of the proposed approach was verified by numerical simulation with a 4 degree-of-freedom (DOF) numerical model incorporating a nonlinear structural member, and by experimental measurements with a four-story frame model equipped with two magneto-rheological (MR) dampers mimicking nonlinear behavior. The results show the proposed approach by combining the PSPM and WAILSE-IME algorithm is capable of effectively representing and identifying the NRF of the chain-like MDOF nonlinear system with partially unknown external excitations, and provide a potential way for damage prognosis and condition evaluation of engineering structures under dynamic loadings which should be regarded as a nonlinear system. | Restoring force and dynamic loadings identification for a nonlinear chain-like structure with partially unknown excitations | 10.1007/s11071-011-0260-7 |
2012-06-01 | Metal cutting processes involve interaction of the machining forces with the work piece. In this processes the vibrations are induced in machine tools which have adverse effect on tool life, surface integrity and occurrence of undesirable chatter phenomenon. In order to enhance the quality of surface of the work piece after machining and avoid chatter marks and breakage of tool, this paper gives a unique method to detect and suppress the chatter effect on the work piece finis. This method incorporates the features of Magneto-Rheological fluid which utilizes the input current as source to modify the magnetic field to enhance the variable stiffness and produce damping effect to control the end mill cutter vibration and suppress the chatter. The variables stiffness and damping can be maintained by the damper input current to attain desired magnetic field in the MR damper. In this work the chatter detection is observed by means of a remarkable Bingham number. The different machining parameters are considered in the experimental work and the results are compared with and without the magneto rheological damping effect and the results shows the enhancement of surface quality and reduced the chatter marks on the work piece by producing Magneto-Rheological damping to the end mill cutter during machining. | Experimental investigation of magneto rheological damping effect on surface roughness of work piece during end milling process | 10.1007/s12541-012-0109-0 |
2012-06-01 | In this paper, numerical modeling and model testing of a complex-shaped remotely-operated vehicle (ROV) were shown. The paper emphasized the systematic modeling of hydrodynamic damping using the computational fluid dynamic software ANSYS-CFX™ on the complex-shaped ROV, a practice that is not commonly applied. For initial design and prototype testing during the developmental stage, small-scale testing using a free-decaying experiment was used to verify the theoretical models obtained from ANSYS-CFX™, Simulation results are shown to coincide with the experimental tests. The proposed method could determine the hydrodynamic damping coefficients of the ROV. | Modeling and testing of hydrodynamic damping model for a complex-shaped remotely-operated vehicle for control | 10.1007/s11804-012-1117-2 |
2012-06-01 | An integral equation approach is utilized to investigate the added mass and damping of floating production, storage and offloading system (FPSO system). Finite water depth Green function and higher-order boundary element method are used to solve integral equation. Numerical results about added mass and damping are presented for odd and even mode motions of FPSO. The results show robust convergence in high frequency range and can be used in wave load analysis for FPSO designing and operation. | Numerical analysis of added mass and damping of floating production, storage and offloading system | 10.1007/s10409-012-0075-x |
2012-06-01 | Pb(Zr $_{\mathbf{0\boldsymbol{\cdot}53}}$ Ti $_{\mathbf{0\boldsymbol{\cdot}47}})$ O_ 3 (PZT) thin films were prepared on Pt/Ti/SiO_ 2 /Si substrate by sol–gel method. The effect of film thickness on microstructure, ferroelectric and dielectric properties was investigated. The single-phase PZT films were obtained with different thicknesses. PZT films with a thickness of 190–440 nm had better dielectric and ferroelectric properties. The epoxy/PZT film/epoxy sandwiched composites were prepared. The thickness of PZT films influenced their damping properties of the composites, and the epoxy-based composites embedded with 310 nm-thick PZT films had the largest damping loss factor of 0 $\boldsymbol{\cdot} $ 915. | Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr_
0.53
Ti_
0.47
)O_
3
thin film with different thicknesses | 10.1007/s12034-012-0288-4 |
2012-06-01 | Currently, as well as in the past, researchers have shown great interest in developing suspension systems for vehicles and especially in the design and optimization of the suspension parameters, such as the stiffness and the damping coefficient. These parameters are considered to be important factors that have an influence on safety and improve the comfort of the passengers in the vehicle. This paper describes a simplified methodology to determine, in a quick manner, the suspension parameters for different types of passenger cars equipped with passive suspension systems. Currently, different types of passenger cars are produced with different types of suspension systems. Finding a simplified methodology to determine these parameters with sufficient accuracy would contribute a simplified and quick method to the inspection of the working conditions of a suspension system. Therefore, a simple system to determine these parameters is needed. An analysis of the suspension parameters is performed using mathematical modeling and numerical analysis conducted using the Working Model software. The result derived from the developed methodology shows small errors when compared with the generic values, and it can be concluded that the design of the suspension parameter measurement device using the developed methodology is useful, simple, and has sufficient accuracy. | Possible experimental method to determine the suspension parameters in a simplified model of a passenger car | 10.1007/s12239-012-0059-7 |
2012-06-01 | Biopolymers are vital structures for many living organisms; for a variety of bacteria, adhesion polymers play a crucial role for the initiation of colonization. Some bacteria express, on their surface, attachment organelles (pili) that comprise subunits formed into stiff helix-like structures that possess unique biomechanical properties. These helix-like structures possess a high degree of flexibility that gives the biopolymers a unique extendibility. This has been considered beneficial for piliated bacteria adhering to host surfaces in the presence of a fluid flow. We show in this work that helix-like pili have the ability to act as efficient dampers of force that can, for a limited time, lower the load on the force-mediating adhesin-receptor bond on the tip of an individual pilus. The model presented is applied to bacteria adhering with a single pilus of either of the two most common types expressed by uropathogenic Escherichia coli , P or type 1 pili, subjected to realistic flows. The results indicate that for moderate flows (~25 mm/s) the force experienced by the adhesin-receptor interaction at the tip of the pilus can be reduced by a factor of ~6 and ~4, respectively. The uncoiling ability provides a bacterium with a “go with the flow” possibility that acts as a damping. It is surmised that this can be an important factor for the initial part of the adhesion process, in particular in turbulent flows, and thereby be of use for bacteria in their striving to survive a natural defense such as fluid rinsing actions. | Helix-like biopolymers can act as dampers of force for bacteria in flows | 10.1007/s00249-012-0814-8 |
2012-06-01 | A synchronous control system for dual parallel stages is proposed in order that the synchronous error owing to the skew disturbances can be quickly and stably eliminated. The control system is composed of two disturbance observers and a synchronous controller. The two disturbance observers are designed to decrease the mismatched dynamics between a nominal model and a real plant with nonlinear properties and to reject instantly disturbances for each stage. The synchronous controller is designed from the view point of accurate synchronization and improvement of damping characteristics for the synchronous control system. The proposed synchronous control system is evaluated and compared experimentally with a normal cross-coupling control system without disturbance observer. The experiment results show that the new control system considerably reduces the synchronous error against skew disturbances. In addition, the synchronous error can be quickly and more stably eliminated through the improvement of the damping characteristics of the synchronous control system using a PD compensator. | A method of synchronous control system for dual parallel motion stages | 10.1007/s12541-012-0115-2 |
2012-06-01 | This article studies the Cauchy problem for the coupled nonlinear Klein-Gordon equations with damping terms. By introducing a family of potential wells, we derive the invariant sets and the vacuum isolating of solutions. Furthermore, we show the global existence, finite time blow-up, as well as the asymptotic behavior of solutions. In particular, we establish a sharp criterion for global existence and blow-up of solutions when E (0)< d . Finally, a blow-up result of solutions with E (0)= d is also proved. | Global Existence, Blow-up and Asymptotic Behavior of Solutions for a Class of Coupled Nonlinear Klein-Gordon Equations with Damping Terms | 10.1007/s10440-011-9662-2 |
2012-06-01 | Optimal problems are investigated in the present work in order to control the natural frequencies of a torsional shaft system including the total weight constraint and effects of tuned mass dampers. Maier objective functional is used. Pontryagin’s Maximum Principle is employed to derive necessary optimality conditions of the optimal problems. Numerical simulations are performed to study effects of tuned mass dampers on controlling natural frequencies as well as minimizing the system’s weight. Advantages of the proposed method are also discussed. | Optimal design of a torsional shaft system using Pontryagin’s Maximum Principle | 10.1007/s11012-011-9504-3 |
2012-06-01 | This paper proposes a base isolating system to reduce the seismic demands of low- or medium-rise structures and experimentally investigates its seismic response using shake-table tests. The base isolating system considered in this study consists of laminated-rubber bearings and U-shaped hysteretic (UH) dampers which are made of high toughness steel (HTS) and are machined with slotted holes to increase their deformation capacities. A base isolated 2-story specimen for shake-table tests was first designed and cyclic tests of laminated-rubber bearings and UH dampers implemented in the base isolating systems were then carried out. The component test for the laminated-rubber bearings shows typically low lateral stiffness with enough vertical stiffness to carry gravity loads. The test results for the UH dampers demonstrate that the use of HTS material and the introduction of the slotted holes details increase deformation capacities by inducing uniform stress distribution along a UH damper. Finally, shake-table tests were performed using specimens shaken with increasing ground acceleration records. The shake-table tests show that the proposed base isolating system with UH dampers limits the seismic demands of a base isolated structure by lengthening its structural period, concentrating displacement demands on the base isolating floor and adding seismic energy dissipation from the UH dampers. | Seismic response of base isolating systems with U-shaped hysteretic dampers | 10.1007/s13296-012-2011-0 |
2012-06-01 | An accurate and efficient differential quadrature time element method (DQTEM) is proposed for solving ordinary differential equations (ODEs), the numerical dissipation and dispersion of DQTEM is much smaller than that of the direct integration method of single/multi steps. Two methods of imposing initial conditions are given, which avoids the tediousness when derivative initial conditions are imposed, and the numerical comparisons indicate that the first method, in which the analog equations of initial displacements and velocities are used to directly replace the differential quadrature (DQ) analog equations of ODEs at the first and the last sampling points, respectively, is much more accurate than the second method, in which the DQ analog equations of initial conditions are used to directly replace the DQ analog equations of ODEs at the first two sampling points. On the contrary to the conventional step-by-step direct integration schemes, the solutions at all sampling points can be obtained simultaneously by DQTEM, and generally, one differential quadrature time element may be enough for the whole time domain. Extensive numerical comparisons validate the efficiency and accuracy of the proposed method. | Differential quadrature time element method for structural dynamics | 10.1007/s10409-012-0081-z |
2012-06-01 | First arrival travel time tomography has achieved wide application. However, tomographic resolution is insufficient because geometry constraints cause rays to be unevenly distributed in the velocity model. The variable damping constraint method adopts uneven priori information to match uneven data distribution which can lessen the correlation between velocity correction values and ray coverage density. In this paper, we combine the variable damping constraint with a smoothness constraint which is added into the regularization equations in velocity inversion to avoid instability caused by only using the variable damping constraint method. The alpha-trimmed-mean filter is used to smooth and denoise intermediate results in the velocity inversion process. We use the LSQR algorithm to enhance the convergence rate and suppress error propagation in solving linear equations. In this paper, we apply the proposed tomographic method to perform velocity inversion using VSP data. The application in recovery test of the checkerboard model and velocity inversion of real VSP data show that the variable damping constraint method can improve tomographic quality because it can solve the effects of uneven ray coverage. In addition, the examples show that the tomographic result near geophones is much more reliable than other areas in the velocity model. | Variable damping constraint tomography and its application in VSP Data | 10.1007/s11770-012-0328-2 |
2012-06-01 | The rotating chamber is expected to significantly benefit mid-caliber automatic guns with the high firepower-to-armament space ratio. However, the parallel index, which is a core component of the chamber system, tends to be flexible in rapid operation. This may cause the chamber prone to torsional vibration so that serious misalignment problems arise during ammunition loading as well as firing processes. In this context, an active control algorithm is proposed incorporating a reaction wheel as the actuator, suppressing only the residual vibration and optionally self-adapting the shooting rate to the actuator condition. For assessment of the idea, the entire system is mathematically modeled and then simulated in several cases. The comparative simulation results support that by the proposed method the chamber vibration can be reduced even to 6.5 percent at the expense of relatively small amount of actuator energy. | Torsional vibration control of the rotating chamber using a reaction wheel | 10.1007/s12541-012-0116-1 |
2012-06-01 | This paper presents an original approach to the problem of controlling a magnetorheological suspension of a driver’s seat for optimal reduction of whole-body vibration. The concept consists in taking into consideration the individual personal features (biomechanical parameters) of the driver in the control process of a MR damper by using human generated signals. The proposed algorithm enables the adaptation of the suspension for an individual driver and specific road conditions. The actual research has focused on numerical simulations with a complex model of the human-seat-vehicle system. The human model representing a specific driver has been described by several biomechanical parameters such as masses of body structures, moments of inertia, and stiffness and damping of the spine, intervertebral discs, spinal muscles and ligaments. | Controlling the magnetorheological suspension of a vehicle seat including the biomechanics of the driver | 10.2478/s13531-011-0061-2 |
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