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2021-08-01 | Considering the complexity geometry and thin wall feature, the semiconical shell workpiece will induce complicated and intense vibration in the milling process leading to poor surface quality and large machining deformation. In order to suppress the vibration, this paper focused on the semiconical shell workpiece and proposed a multiple distribution tuned mass damper (MDTMD) vibration control technique by attaching a series of optimized tuned mass dampers (TMD) to each optimal position of workpiece. The vibration characteristics and modal shapes of workpiece were obtained with the use of spectro-geometric-Ritz method (SGM) and the dynamic model of workpiece with MDTMD was established. A novel design of TMD was proposed. The optimal parameters and positions of each TMD were determined simultaneously using numerical optimization algorithm based on the modal summation method. Theoretical studies and experiment results shown that the proposed MDTMD method can remarkably improve the dynamic stiffness of the workpiece. The performance of vibration suppression is further verified in the impact tests and milling experiments. | Milling vibration control of semiconical shell workpiece with multiple distribution tuned mass dampers | 10.1007/s00170-020-06427-y |
2021-08-01 | In this study, a new hybrid energy dissipation device is developed by combining two friction dampers (auxiliary and main fuse) in series to be used for the seismic control of two different earthquake intensities. Compared with the conventional friction dampers, the new hybrid damper has an advantage in that only the auxiliary fuse (with low sliding force) is activated for moderate earthquakes and both fuses work simultaneously for strong earthquakes. Cyclic loading tests of the combined hybrid dampers are carried out to evaluate their seismic energy dissipation capability. The obtained experimental force displacement indicates proper details of the new damper to create two performance levels. Finite element analyses of the test specimens are also carried out for comparison and have good agreement with the test results. Force–displacement characteristics, energy dissipation, and equivalent viscous damping are also derived and good agreement has been found. Moreover, it is demonstrated that by engaging the main fuse with non-loaded pretension bolts, the strength losses of the hybrid damper in the subsequent cycles are limited compared with the common friction dampers, which can be called the “resurrection-type” behavior of the main fuse in the main shocks. To evaluate the effects of the proposed damper, typical 3- and 9-story steel buildings are modeled and their seismic responses under 22 earthquake excitations are investigated using incremental dynamic nonlinear time-history. Comparison of incremental dynamic analysis (IDA) curves and their medians revealed that using a hybrid friction damper (HFD) reduces the probability of reaching all the defined damage states. Moreover, the reduction effect of HFD was recognizable in 9-story frames. | A New Hybrid Friction Damper (HFD) for Dual-Level Performance of Steel Structures | 10.1007/s13296-021-00507-9 |
2021-07-20 | Steel eccentrically braced frame systems (EBF) with buckling restraint braces are extensively used as a lateral load resisting system due to their high-energy dissipation characterized by the inelastic shear deformation of the short links. In performance-based seismic design of such structural systems using the direct displacement-based design procedure (DDBD), equivalent viscous damping (EVD) coefficient is used to represent the energy dissipation capacity which has not been developed particularly for this structural system yet even though expressions to calculate EVD coefficient have been already developed for other major lateral load systems supporting DDBD procedure. Therefore, in this study, a new EVD expression was developed incorporating 25 predetermined single degree of freedom (SDOF) eccentrically braced frame (EBF) systems which were selected by varying the length and the section geometry of the link considering them as the dominant parameters that affect the energy dissipation of the system. Firstly, EVD coefficients were calculated using Jacobsen’s area-based approach for quasi-static loading and they were corrected by considering the effects of earthquake characteristics using 13 spectrum compatible earthquake records. Finally, a new equation to calculate the equivalent viscous damping coefficient for eccentrically braced frame systems was formulated as a function of the ductility of equivalent SDOF system to the multi-degree of freedom (MDOF) systems. | Equivalent viscous damping for steel eccentrically braced frame structures with buckling restraint braces | 10.1007/s41062-021-00503-2 |
2021-07-19 | We consider a damped plate model with rotational forces in a bounded domain. The plate is either clamped or hinged. The rotational forces and damping involve the spectral fractional Laplacian with powers $$\theta $$ θ in [0, 1] and $$\delta $$ δ in [0, 2], respectively. Using the frequency domain approach, and appropriate interpolation inequalities, we show that the underlying semigroup is: (a) analytic for all $$\theta $$ θ in [0, 1] and $$\delta $$ δ in $$[(2+\theta )/2,2]$$ [ ( 2 + θ ) / 2 , 2 ] , (b) not analytic for all $$\theta $$ θ in [0, 1] and $$\delta $$ δ in $$(\theta ,(2+\theta )/2)$$ ( θ , ( 2 + θ ) / 2 ) , (c) of Gevrey class $$\alpha >(2-\theta )/2(\delta -\theta )$$ α > ( 2 - θ ) / 2 ( δ - θ ) for all $$\theta $$ θ in [0, 1] and $$\theta<\delta <(2+\theta )/2$$ θ < δ < ( 2 + θ ) / 2 . We also prove that for each admissible value of $$\theta $$ θ , the semigroup is exponentially stable for $$\delta \ge \theta $$ δ ≥ θ , and only polynomially stable, with rate $$O(t^{-{2-\theta \over 2(\theta -\delta )}})$$ O ( t - 2 - θ 2 ( θ - δ ) ) , for $$\delta <\theta $$ δ < θ , when $$\theta >0$$ θ > 0 . In particular, in the hinged plate case, we show that the polynomial decay rate is optimal. | Regularity and stability for a plate model involving fractional rotational forces and damping | 10.1007/s00033-021-01589-5 |
2021-07-13 | We estimate the ultimate bound of the energy of the solutions to the equation $$\begin{aligned}u''(t)+ Au(t)+g(u'(t))=f(t),\;\; t\ge 0, \end{aligned}$$ u ′ ′ ( t ) + A u ( t ) + g ( u ′ ( t ) ) = f ( t ) , t ≥ 0 , where A is a positive selfadjoint operator on a Hilbert space H , g is a nonlinear damping operator and f is a bounded forcing term with values in H . The paper concerns the asymptotic behavior of the solution. We prove that the bound of the solution is of the form $$\begin{aligned} C(1+\Vert f\Vert ^{2(a+2)/(a+1)}_{\infty }) \end{aligned}$$ C ( 1 + ‖ f ‖ ∞ 2 ( a + 2 ) / ( a + 1 ) ) where the constant $$a\ge 0$$ a ≥ 0 appears in the coercivity condition on the nonlinear damping operator g . and $$\Vert f\Vert $$ ‖ f ‖ stands for the $$L^{\infty }$$ L ∞ norm of f with values in H . Moreover, we investigate other cases, for instance, in the case of a special class of damping operator and the case of antiperiodic solutions. The last part of this paper is devoted to study the rate of decay for the solution of the equation as $$t\rightarrow +\infty $$ t → + ∞ . | Ultimate bound of solutions to second-order evolution equation with nonlinear damping term | 10.1007/s42985-021-00110-x |
2021-07-13 | This paper investigates the generalized Zakharov–Kuznetsov (GZK) equation and generalized modified Zakharov–Kuznetsov equation in the presence of external periodic forcing term together with damping. An approximate analytical solution is obtained by employing the direct assumption technique. The framework staged here reveals number of beautiful wave features such as positive amplitude soliton, rare effective soliton, periodic rational soliton, kink type soliton, etc. Moreover, two new parameters along with a control function is introduced to extend the study of traveling wave solution and to create new types of solitary wave solution that are depicted from a numerical standpoint. It is noticed that the generalized wave solution for GZK in presence of external periodic forcing with a damping, positive potential soliton may transform into a rare effective soliton due to an increase in the nonlinearity of the system. | Approximate Analytical Solutions of Generalized Zakharov–Kuznetsov and Generalized Modified Zakharov–Kuznetsov Equations | 10.1007/s40819-021-01034-1 |
2021-07-10 | The object of this paper is to study a sixth-order Boussinesq equation with dispersive, linear strong damping and nonlinear source by using potential well methods, including the following aspects: firstly, the local well-posedness of the solutions is studied; secondly, the global existence and the finite time blow-up conditions are studied at two different initial energy levels by using the relationship between the initial energy and the depth of the potential well; thirdly, a blow-up condition independent of the depth of the potential well is established and by using of this condition, the existence of blow-up solutions at arbitrary initial energy level is studied; finally, the upper bound estimation of blow-up time and some necessary and sufficient conditions for existing finite time blow-up solutions are established. | Well-Posedness of Solutions for the Sixth-Order Boussinesq Equation with Linear Strong Damping and Nonlinear Source | 10.1007/s00332-021-09730-4 |
2021-07-01 | A Langevin equation is suggested to describe a system driven by correlated Gaussian white noise as well as with positive and negative damping demarcated by a critical velocity. The equation can be transformed into the Fokker–Planck equation by the Kramers–Moyal expansion. The solution of this equation exhibits some non-equilibrium phenomena. In the beginning the distribution curve of velocity/energy takes on a random oscillation, and then a near-equilibrium distribution described by the Boltzmann distribution is gradually established. However, a spike appears on the distribution curve and breaks this stable distribution. The spike moves in the direction of velocity/energy decreasing and is nonlinearly enlarged so as to sustain. The final distribution is a sharp peak formed by a monotonically ascending segment and a monotonically descending one. The calculating results of the statistical quantities demonstrate that the process is a sub-diffusion, and the spike originates from the correlation between noise and space. Two basic definitions are suggested to map the observations in this physical system to a social system to understand the propagation of public opinion or message, i.e., the generalized displacement is defined as the quantity of information carried by the opinion particle, and the velocity is defined as the sensitivity of the opinion particle to an event. | Non-equilibrium diffusion in a particle system and the correspondence to understanding the propagation of public opinion | 10.1007/s11071-021-06597-8 |
2021-07-01 | Abstract— The problem of active suppression of vibrations of an elastic panel moving longitudinally in an ideal fluid flow is considered. The dynamics equation of the panel includes the fluid response and external mechanical action that serves to implement the damping process. The conditions of extremality of lateral vibration damping are derived and the efficiency of the optimal distribution of the forces applied to the panel and the optimal time program of the external influence functioning are estimated. | ON THE OPTIMAL METHODS OF DAMPING HYDROELASTIC VIBRATIONS | 10.3103/S0025654421040038 |
2021-07-01 | Background Nowadays, vibration control is one of the limitless and major operating parameters in science and technology. The most promising and adaptive dynamic vibration absorber (DVA) with an air spring–air damper assembly is designed with a facility to change the spring rate and damping in the system to control the vibration. Method To optimize and effectively controlling the resonant amplitude ratio efficiently, a Maxwell-type air damper mathematical model is formulated for an SDOF vibrating system subjected to sinusoidal base excitation for better performance of DVA. Insight into the physics of such systems was carried out by mathematical modeling, design, and development of an air spring–air damper system for the SDOF vibrating system. Result Experimental investigation of an air spring–air damper for the primary mass displacement amplitude to optimize and effectively control the vibration. It will provide a compact and right platform for DVA among the current potential market and provide the major attention of the control community as a platform for the development of low-frequency nonlinear devices. | Mathematical Modeling and Experimental Evaluation of an Air Spring–Air Damper Dynamic Vibration Absorber | 10.1007/s42417-020-00263-w |
2021-07-01 | Particle dampers show a huge potential to reduce undesired vibrations in technical applications even under harsh environmental conditions. However, their energy dissipation depends on many effects on the micro- and macroscopic scale, which are not fully understood yet. This paper aims toward the development of design rules for particle dampers by looking at both scales. This shall shorten the design process for future applications. The energy dissipation and loss factor of different configurations are analyzed via the complex power for a large excitation range. Comparisons to discrete element simulations show a good qualitative agreement. These simulations give an insight into the process in the damper. For monodisperse systems, a direct correlation of the loss factor to the motion modes of the rheology behavior is shown. For well-known excitation conditions, simple design rules are derived. First investigations into polydisperse settings are made, showing a potential for a more robust damping behavior. | Toward a design methodology for particle dampers by analyzing their energy dissipation | 10.1007/s40571-020-00363-0 |
2021-07-01 | Anecessary requirement for automatic excitation regulation systems is ensuring the stability of the electric energy systems (EES) and the required quality of the transients (TP) of changes in operating parameters under the effect of various disturbances. In order to improve the damping of TEES, various stabilization channels of the automatic excitation regulator (AER) are used, as a rule. In the microprocessor regulator (MR) of the AER are stabilization channels, both internal (from the derivatives of the rotor current and stator voltage) and external (from the deviation and derivative of the frequency of stator voltage). The article compares the quality of stabilization of the operating parameters when using the AER signal in the frequency stabilization channels of the voltage on the generator buses (regular signal), and the differences between the deviation of the frequency of rotation of the generator shaft and the frequency of voltage on the station buses in EES mode and in certification mode. The effect of the parameters of the synchronous generator and of the conditions of its operation on the areas of the stability of the regulation system and the quality of damping is examined. It is shown that changing the parameters of the stabilization channel filters can increase the regions of stability and enhance the quality of damping of transient fluctuations. | Analysis of the Functioning of Automatic Synchronous Generator Excitation Regulators with Various Input Signals of Frequency Stabilization Channels in the Certification Scheme^1 | 10.1007/s10749-021-01355-7 |
2021-07-01 | A longitudinal and transversal vibrations of the beam with nonlinear tension, a viscoelastic damping and distributed delay term is studied. Using the Faedo–Galerkin method, the well-posedness of the problem is established. A uniform decay result is proved by multiplier method. | Existence and energy decay of solution to a nonlinear viscoelastic two-dimensional beam with a delay | 10.1007/s11045-021-00766-z |
2021-07-01 | In this paper, the initial-boundary value problem of the original three-dimensional compressible Euler equations with (or without) time-dependent damping is considered. By considering a functional $$F(t,\alpha ,f)$$ F ( t , α , f ) weighted by a general time-dependent parameter function $$\alpha $$ α and a general radius-dependent parameter function f , we show that if the initial value $$F|_{t=0}$$ F | t = 0 is sufficiently large, then the lifespan of the system is finite. Here, f can be any $$C^1$$ C 1 strictly increasing function such that the sum of initial values of f and $$\alpha $$ α is non-negative. It follows that a class of conditions for non-existence of global classical solutions is established. Moreover, the conditions imply that a strong $$\alpha $$ α will lead to a more unrestrained necessary condition for classical solutions of the system to exist globally in time. | The Lifespan of Classical Solutions to the (Damped) Compressible Euler Equations | 10.1007/s40840-020-01036-0 |
2021-07-01 | A spring-damping contact force model considering the normal friction force is proposed and discussed in this paper. This model is an extension and development of Hertz theoretical model. The physical model of contact force in the contact process is established. The friction force during the elastic compression and restitution phases is represented using the product of tangential component of contact force and friction coefficient, which is a function of contact force and deformation. The friction dissipation coefficient is proposed to characterize the energy dissipation under different material properties and initial velocities. A velocity exponential model is proposed, and the expressions of damping coefficient and contact force are derived. Numerical analysis is carried out and the model in this paper is compared with classical models under two conditions, which proves the correctness and effectiveness of the model. The spring-damping model with normal friction force is applied to a simple spring contact system, and the energy dissipation process under the action of spring prestress is analyzed. | A spring-damping contact force model considering normal friction for impact analysis | 10.1007/s11071-021-06660-4 |
2021-07-01 | Most of the dynamic systems are inherently nonlinear either with stiffness nonlinearity or with damping nonlinearity. Presence of nonlinearity often leads to characteristic behaviours in response such as jump phenomenon, limit cycle and super-harmonic resonances. Such behviours can be accurately predicted only if the nonlinearity structure and related parameters are properly known. A majority of identification works is based on a-priori knowledge of nonlinearity structure and most of them consider only stiffness nonlinearities. Not much work has been reported on identification and parameter estimation in the area of damping nonlinearities. This paper presents a systematic classification of asymmetric damping nonlinearity and develops a parameter estimation algorithm using harmonic excitation and response amplitudes in terms of higher order Frequency Response Functions. The asymmetry in damping nonlinearity is modeled as a polynomial function containing square and cubic nonlinear terms and then Volterra series is employed to derive the response amplitude formulation for different harmonics using synthesied higher order Frequency Response Functions. Detailed numerical study is carried out with different combinations of square and cubic nonlinearity parameters to investigate appropriate excitation level and frequency so as to get measurable signal strength of second and third harmonics and at the same time keeping the Volterra series approximation error low. The estimation algorithm is first presented for nonlinear parameters and then it is extended for estimation of linear parameters including damping ratio. It is demonstrated through numerical simulation that nonlinear damping parameters can be accurately estimated with proper selection of excitation level and frequency. | Identification and Parameter Estimation of Asymmetric Nonlinear Damping in a Single-Degree-of-Freedom System Using Volterra Series | 10.1007/s42417-020-00266-7 |
2021-07-01 | A nonlinear vibration isolator with quasi-zero-stiffness (QZS) is designed inspired by the bi-stable Miura-origami tube. The isolator comprises a negative stiffness element with four rods and one horizontal spring, while a vertical linear spring is used to provide positive stiffness. The static characteristics of the negative stiffness element are studied and then the design procedure for the QZS isolation system with a lumped mass is provided. The static displacement is considered as an input parameter to illustrate the high-static-low-dynamicstiffness (HSLDS) property of the isolator. To further display the isolation ability of the present isolator, the dynamic model of the system under base excitation is established with the linear air damping and nonlinear damping caused by rotational joints. The nonlinear terms are then approximated by Taylor series and the averaging method is used to predict the dynamic performance. The present theory is verified by comparing the system’s free and forced responses under different frequencies of base excitation with those calculated by numerical simulation. The displacement transmissibility of the present nonlinear vibration isolator demonstrates the much improved vibration isolation performance as compared to its linear counterpart. | A nonlinear vibration isolator with quasi-zero-stiffness inspired by Miura-origami tube | 10.1007/s11071-021-06650-6 |
2021-07-01 | By using the reductive perturbation technique, the nonlinear dust ion-acoustic solitary wave models of the damped Korteweg–de Vries (D-KdV) and modified damped Korteweg–de Vries (D-mKdV) equations are formulated. We constructed the more general and new solitary wave solutions of nonlinear damped KdV and damped mKdV equations by using the modified mathematical technique. These obtained solutions are more useful in the development of quantum plasma, dynamics of solitons, dynamics of adiabatic parameters, dynamics of fluid and problems of biomedical, industrial phenomena. The new solutions are obtained in the shape of dark solitons, bright solitons, traveling wave and kink and anti-kink wave solitons. We show the physical structure of new solutions by two and three-dimensions graphical to know the physical interpretation of different structure of dust ion-acoustic solitary wave. The calculations show that this new technique is more powerful, effective, straightforward, and fruitfulness to study analytically other nonlinear complex physical models in plasma physics, mathematical physics, fluid mechanics, hydrodynamics, mathematical biology and many other physical sciences. | Ion-acoustic solitary wave solutions of nonlinear damped Korteweg–de Vries and damped modified Korteweg–de Vries dynamical equations | 10.1007/s12648-019-01645-x |
2021-07-01 | Anomalous diffusion is a widespread physical phenomenon, and numerical methods of fractional diffusion models are of important scientific significance and engineering application value. For time fractional diffusion-wave equation with damping, a difference (ASC-N, alternating segment Crank-Nicolson) scheme with intrinsic parallelism is proposed. Based on alternating technology, the ASC-N scheme is constructed with four kinds of Saul’yev asymmetric schemes and Crank-Nicolson (C-N) scheme. The unconditional stability and convergence are rigorously analyzed. The theoretical analysis and numerical experiments show that the ASC-N scheme is effective for solving time fractional diffusion-wave equation. | A Difference Scheme with Intrinsic Parallelism for Fractional Diffusion-wave Equation with Damping | 10.1007/s10255-021-1015-y |
2021-07-01 | Abstract— When two anisotropic rough surfaces contact, the interface is shown as the contact anisotropy or contact isotropy, which closely relates to the asperity contact azimuthal angles on the microscopic scale. The interfacial contact anisotropy/isotropy will influence the normal contact stiffness and damping of mechanical joints. A normal contact stiffness and damping model between two anisotropic rough surfaces is proposed, which includes the effects of the asperity shoulder-to-shoulder contact and adjacent asperity interaction. And the influence laws of the contacting match degree and the contact anisotropy on the normal contact stiffness and contact damping are revealed by a series of simulation experiments. Thereby, the normal contact stiffness and damping can be controlled by adjusting the surface topographic features and the contacting orientation between mechanical parts. | The Modeling for the Normal Contact Stiffness and Damping of Anisotropic Interface | 10.3103/S0025654421040063 |
2021-07-01 | A new system for damping longitudinal transport loads based on a special shock-absorbing dry-friction turnstiles is proposed. The aim of this work is to evaluate the efficiency of longitudinal shock absorbers during the rail transportation of heavy and oversized cargos. An extreme dynamic loading of a transport system with such a damping system is studied using methods of mathematical modeling. The equations of motion of the transport system are formulated and integrated numerically. During numerical experiments, the main characteristics of shock absorbers that affect the quality of their functioning are established. The efficiency of dry friction shock absorbers in reducing the dynamic impact on transported goods is assessed quantitatively. Shock absorbers can reduce the dynamic effects on transported goods by a factor of more than 6, compared with the existing traditional method of rail transportation. As a result of the numerical analysis of the dynamic behavior of the transport system, it was found that the longitudinal transport loads on the cargo can be reduced significantly by fixing them to the platform in a “movable-adjustable” way (as opposed to the traditional “rigid” fixation). | Dynamic Processes in a Mechanical System with Shock-Absorbing Cargo-Securing Devices with Dry Friction | 10.1007/s10778-021-01097-z |
2021-07-01 | Introduction Vibration suspension system is used in the automobiles to mitigate the excitations that can come from the travel over various road profiles. The conventionally used suspension systems are linear devices that are effective against high frequencies; however, they have limitations in isolation ability in the low-frequency ranges. Hence, nonlinear isolation system can be used to overcome such limitations. Methodology The quasi-zero stiffness (QZS) characteristics are efficient in the vibration isolation and can provide isolation efficiently against low-frequency excitations as well. This concept is taken into consideration and has designed a nonlinear vibration isolation system with QZS behaviour. The negative stiffness is achieved through the inclined spring arrangement, and the positive stiffness is obtained from the pneumatic system. The force–displacement model is used to develop the approximate dynamic modelling for small displacement. Results The performance is studied against various road profiles as per ISO 8608. The results showed that the isolation system effectively isolates the external excitations from the road profile and shows a high isolation capability in the higher velocities. The study shows the proposed system reduced on an average of 92% and 88% of external excitations in road class B–D and E–H, respectively. Conclusions Based on the computational study conducted in this work on the developed design, the isolation system is found to be effective in vibration isolation. The QZS system parameters highly influence the performance of the isolation system. The system developed in this work can be used to test for real-time automobile applications. | Nonlinear Vibration Control Device for a Vehicle Suspension Using Negative Stiffness Mechanism | 10.1007/s42417-020-00275-6 |
2021-07-01 | A new type of negative stiffness friction damping device (NSFDD) was developed in this study, which can solve the problem of poor energy dissipation of the existing passive negative stiffness damping device. The friction force is generated by squeezing the friction plate with the preloaded nitrogen spring vertically. When the NSFDD is working, the friction plate causes the nitrogen spring to rotate and negative stiffness force and friction force are generated. The results of the performance test show that the NSFDD can achieve negative stiffness in the hysteretic model. Comparing with the existing negative stiffness device, the NSFDD has larger stroke, more stable negative stiffness and better energy dissipation capacity. The finite element software has been used to simulate the low cycle reciprocation of a structure, and the results show that the NSFDD reduces the stiffness of the structure while increasing the damping of the structure. The results of the simulation and analysis of the shock absorption plan of the NSFDD show that the NSFDD reduces the stiffness of the floor, thereby effectively control on the shear force, displacement and acceleration response of the structure. | Development and Analysis of Negative Stiffness Friction Damping Device | 10.1007/s12205-021-1282-4 |
2021-07-01 | Background For the continuous operation of the power plant and to prevent any economic or fatal damages, the torsional vibration control of the large turbo-generator rotor is required. Compared to the flow mode dampers, the shear mode magnetorheological fluid dampers are less efficient in regulating the torsional vibrations of the large turbo-generator rotor because of the complicated configuration and low damping ability. Purpose This theoretical study explains how magnetorheological (MR) fluid dampers can be used to control torsional vibration of the turbo-generator rotor. A theoretical analysis is conducted to compare the damping efficiency of the MR damper under constant and variable magnetic fields. Methods The dq0 model is used to simulate the electromagnetic torque of the generator during multiple electrical failures. The turbo-generator rotor is simulated using the finite element method. MR fluid dampers are attached to the rotor's different coupling elements. For designing the dampers, the modified Bouc-Wen model is used. In MATLAB, the coupled finite element equations are solved using Newmark-beta integration method. Results The peak amplitude of torsional vibrations in element 35 reduce by 1–60 percent for various electrical faults using passive MR dampers and 10–46 percent using semiactive MR dampers. The peak amplitude of torsional vibrations in element No 74 reduces by 1–55 percent for various electrical faults using passive MR dampers and 7–50 percent using semiactive MR dampers. Conclusions During various electrical failures, the most severe torque evolved is three phase fault, followed by the line to ground, followed by mal-synchronization fault and line to line fault. The torsional vibrations produced on turbo-generator rotor due to this variation in electromagnetic torque of the generator and the numerical results show the significant reduction in the torsional vibration of the rotor when MR fluid dampers are used. | Numerical Investigation of Semi-active Torsional Vibration Control of Heavy Turbo-generator Rotor using Magnetorheological Fluid Dampers | 10.1007/s42417-020-00276-5 |
2021-06-30 | Brittleness is an inherent shortcoming of epoxy resin which results in the longitudinal fatigue cracking of mixtures during the long service time of orthotropic steel deck bridges. In this paper, this problem was addressed by introducing a reactive thermoplastic elastomer, epoxidized styrene–butadiene–styrene copolymer (ESBS) into epoxy asphalt binder (EAB). Epoxy ESBS modified asphalts (EESBAs) with various epoxidation degrees were prepared. Double phase separation occurred in the EESBAs. In the EESBAs with 18% and 31% epoxidation degrees, most of ESBS domains dispersed on the edge of the secondary asphalt phase and in the epoxy phase. Furthermore, the size and number of ESBS domains decreased in the epoxidation degree. However, un-epoxidized SBS domains completely dispersed the asphalt phase and all ESBS domains moved to the epoxy phase when the epoxidation degree increased to 39%. In EESBAs, the average diameters of asphalt domains increased in the epoxidation degree. The inclusion of ESBS increased the viscosity of the pure EAB and the viscosity of EESBAs increased in the epoxidation degree. Nevertheless, all EESBAs had at least a 150-min allowable construction time. By adding 2 wt% ESBS with 39% epoxidation degree, the glass transition temperature ( T _g) decreased. The T _g of EESBAs decreased in the epoxidation degree. The inclusion of ESBS greatly enhanced the damping properties of the pure EAB. The elongation at break and toughness of the pure EAB were remarkably increased by 263% and 93%, respectively, with the incorporation of 2 wt% ESBS with 39% epoxidation degree. Furthermore, the toughness of EESBAs increased in the epoxidation degree. | Improving toughness of epoxy asphalt binder with reactive epoxidized SBS | 10.1617/s11527-021-01744-4 |
2021-06-25 | The stabilization properties of dissipative Timoshenko systems have been attracted the attention and efforts of researchers over the years. In the past 20 years, the studies in this scenario distinguished primarily by the nature of the coupling and the type or strength of damping. Particularly, under the premise that the Timoshenko beam model is a two-by-two system of hyperbolic equations, a large number of papers have been devoted to the study of the so-called partially damped Timoshenko systems by assuming damping effects acting only on the angle rotation or vertical displacement (Almeida Júnior et al. in Math Methods Appl Sci 36:1965–1976, 2013; in Z Angew Math Phys 65:1233–1249, 2014; Alves et al. in SIAM J Math Anal 51(6):4520–4543, 2019; Ammar-Khodja et al. in J Differ Equ 194:82–115, 2003; Muñoz Rivera and Racke in Discrete Contin Dyn Syst Ser B 9:1625–1639, 2003; J Math Anal Appl 341:1068–1083, 2008; Santos et al. in J Differ Equ 253(9):2715–2733, 2012). In these cases, the desired exponential decay property of the energy solutions is achieved when the non-physical equal wave speed assumption plays the role to stabilization according since the pioneering Soufyane’s paper (C R Acad Sci Paris 328(8):731–734, 1999). Recent results due to Almeida Júnior et al. (Z Angew Math Phys 68(145):1–31, 2017; Z Angew Math Mech 98(8):1320–1333, 2018; IMA J Appl Math 84(4):763–796, 2019; Acta Mech 231:3565–3581, 2020) show that the second vibration mode or simply second spectrum of frequency and it’s damaging consequences appears as a lost element in analysis of stabilization and now it’s more clear that the damping importance into stabilization scenario of Timoshenko type systems. This paper considers a one-dimensional viscoelastic Timoshenko type system in the light of the second spectrum of frequency where the equal wave speed assumption is not needed for getting the exponential decay property. Precisely, we consider the so-called truncated version for the Timoshenko system according studies due to Elishakoff (Advances in mathematical modelling and experimental methods for materials and structures, solid mechanics and its applications, Springer, Berlin, pp 249–254, 2010; ASME Am Soc Mech Eng Appl Mech Rev 67(6):1–11, 2015; Int J Solids Struct 109:143–151, 2017; J Sound Vib 435:409–430, 2017; Int J Eng Sci 116:58–73, 2017; Acta Mech 229:1649–1686, 2018; Z Angew Math Mech 98(8):1334–1368, 2018; Math Mech Solids, 2019) and we added a viscoelastic damping acting on shear force. We firstly prove the global well-posedness of the system by Faedo–Galerkin approximation. By assuming minimal conditions on the relaxation function, we establish an optimal explicit and energy decay rate for which exponential and polynomial rates are special cases. This result is new and substantially improves earlier results in the literature where the equal wave speeds plays the role for getting the stability properties. It is likely to open more research areas to Timoshenko system and probably others. | The optimal decay rates for viscoelastic Timoshenko type system in the light of the second spectrum of frequency | 10.1007/s00033-021-01574-y |
2021-06-25 | The weight transfer is continuously excited by brake pressure changes during braking with activated ABS. For this reason, the wheel load oscillations become more severe with activated ABS, which makes difficult the manipulation of brake pressure due to wheel slip oscillations and wheel acceleration changes which are control variables for ABS. Thus, this study aims to reduce wheel load oscillations during braking with activated ABS (anti-lock brake system). For this aim, the integration between suspension system and ABS was developed by designing the control strategy based on the results of ABS road tests. ABS tests are conducted on wet and slippery road by using hard and medium-hard stages of same damper to determine the rules of control strategy. The control strategy sets the damper stages according to the build up and reduction rates of measured brake pressure via estimated dynamic wheel load information. Estimation of dynamic wheel load is performed with ANN (artificial neural network) using multilayer perceptron networks. This is a novel approach for determining wheel load changes during braking with activated ABS due to difficulties in measuring of dynamic wheel load. Therefore, the results show that the reductions in wheel load are the most influence method to suppress simultaneously both brake pressure and wheel acceleration. In addition, one of the most important results of this study is that the proposed control strategy shortens the braking distance. | A novel approach on improvement of the dynamic wheel load oscillations by integrating suspension system into ABS during braking with ABS | 10.1007/s40430-021-02961-2 |
2021-06-25 | Particle damping is a promising damping technique for a variety of technical applications. However, their non-linear behavior and multitude of influence parameters, hinder currently its wide practical use. So far, most researchers focus either on determining the energy dissipation inside the damper or on the overall damping behavior when coupled to a structure. Indeed, currently almost no knowledge exchange between both approaches occurs. Here, a bridge is build to combine both techniques for systems under forced vibrations by coupling the energy dissipation field and effective particle mass field of a particle damper with a reduced model of a vibrating structure. Thus, the overall damping of the structure is estimated very quickly. This combination of both techniques is essential for an overall efficient dimensioning process and also provides a deeper understanding of the dynamical processes. The accuracy of the proposed coupling method is demonstrated via a simple application example. Hereby, the energy dissipation and effective mass of the particle damper are analyzed for a large excitation range first using a shaker setup. The particle damper exhibits multiple areas of different efficiency. The underlying structure is modeled using FEM and modal reduction techniques. By coupling both parts it is shown that multiple eigenmodes of the structure are highly damped using the particle damper. The damping prediction using the developed coupling procedure is validated via experiments of the overall structure with particle damper. | Damping prediction of particle dampers for structures under forced vibration using effective fields | 10.1007/s10035-021-01128-z |
2021-06-08 | We investigate the longitudinal and transversal vibrations of the viscoelastic beam with nonlinear tension and nonlinear delay term under the general decay rate for relaxation function. The existence theorem is proved by the Faedo–Galerkin method and using suitable Lyapunov functional to establish the general decay result. | Existence and general decay of solution for nonlinear viscoelastic two-dimensional beam with a nonlinear delay | 10.1007/s11587-021-00598-w |
2021-06-02 | The dynamic performance of a high-speed machine tool spindle primarily depends on the rigidity between the spindle-holder couplings. The machining stability of such system is determined by the rigidity at the tapered portion of the coupled joints. This paper presents a methodology to evaluate tool-tip frequency response function (FRF) by considering the tool holder-spindle interface stiffness using finite element analysis. Furthermore, a comparative analysis is carried out on the spindle-tool system with constant contact spring stiffness and the variable structural damping factors. This approach is applied to identify the correct set of interface parameters of a practical spindle-tool unit using the experimental test data. An effective optimization strategy is used to update the finite element model with the various statistical sampling parameters to obtain the rigidity. Further, the optimal data set is identified by using single point simulated annealing (SA) and metaheuristic genetic algorithms (GA) schemes. The proposed methodology can help to standardize the tests with various spindle-holder interfaces by modeling the machine tool spindle. | Identification of practical spindle-tool interface parameters using an optimization based statistical approach | 10.1007/s12046-021-01635-y |
2021-06-01 | In this article we investigate the global existence as well as long-term dynamics for a wide class of lattice plate equations on the entire integer set with nonlinear damping driven by infinite-dimensional nonlinear noise. The well-posedness of the system is established for a class of nonlinear drift functions of polynomial growth of arbitrary order as well as locally Lipschitz continuous diffusion functions depending on time. Both existence and uniqueness of weak pullback mean random attractors are established for the non-autonomous system when the growth rate of the drift function is almost linear. In addition, the existence of invariant measures for the autonomous system is also established in $$\ell ^2\times \ell ^2$$ ℓ 2 × ℓ 2 when the growth rate of the drift function is superlinear . The main difficulty of deriving the tightness of a family of distribution laws of the solutions is surmounted in light of the idea of uniform tail-estimates on the solutions developed by Wang (Phys D 128:41–52, 1999). | Long-Time Dynamics of Stochastic Lattice Plate Equations with Nonlinear Noise and Damping | 10.1007/s10884-020-09830-x |
2021-06-01 | The nonlinear modes of a non-conservative nonlinear system are sometimes referred to as damped nonlinear normal modes (dNNMs). Because of the non-conservative characteristics, the dNNMs are no longer periodic. To compute non-periodic dNNMs using classic methods for periodic problems, two concepts have been developed in the last two decades: complex nonlinear mode (CNM) and extended periodic motion concept (EPMC). A critical assessment of these two concepts applied to different types of non-conservative nonlinearities and industrial full-scale structures has not been thoroughly investigated yet. Furthermore, there exist two emerging techniques which aim at predicting the resonant solutions of a nonlinear forced response using the dNNMs: extended energy balance method (E-EBM) and nonlinear modal synthesis (NMS). A detailed assessment between these two techniques has been rarely attempted in the literature. Therefore, in this work, a comprehensive comparison between CNM and EPMC is provided through two illustrative systems and one engineering application. The EPMC with an alternative damping assumption is also derived and compared with the original EPMC and CNM. The advantages and limitations of the CNM and EPMC are critically discussed. In addition, the resonant solutions are predicted based on the dNNMs using both E-EBM and NMS. The accuracies of the predicted resonances are also discussed in detail. | Comparison of different methodologies for the computation of damped nonlinear normal modes and resonance prediction of systems with non-conservative nonlinearities | 10.1007/s11071-021-06567-0 |
2021-06-01 | This paper is devoted to study the asymptotic behavior of a binary mixture problem of solids with fractional damping and sources terms. We prove the existence of global attractors with finite fractal dimension and the existence of exponential attractors. Moreover, we prove the upper-semicontinuity of global attractors as the fractional exponent tend to zero. | Existence and Upper-Semicontinuity of Global Attractors for Binary Mixtures Solids with Fractional Damping | 10.1007/s00245-019-09590-1 |
2021-06-01 | With the presence of internal interfaces such as the austenite–martensite interface and the internal twin boundaries in the martensite, shape memory alloys (SMAs) can be employed in passive/active damping applications. Due to the latent heat of transformation, a temperature rise/drop during a load/unload cycle is expected to dynamically couple with the mechanical response of the SMA and influence the stress levels of forward/reverse transformation and thus the hysteretic area (i.e. the dissipated energy). Additionally, the temperature change per cycle is a function of loading frequency due to momentary heat transfer effects. To this end, for the first time, we demonstrate a rate insensitive shape memory alloy system, Fe_43.5Mn_34Al_15Ni_7.5 which also exhibits near-zero temperature dependent stress–strain response. Contrastingly, we show that Ni_50.8Ti, which is widely used commercially, is highly rate sensitive. With straightforward in situ experiments, complemented with thermomechanical modelling, we pinpoint the key material parameter which dictates frequency sensitivity. The corresponding results are then discussed in the light of different mechanisms contributing to the damping capacity of SMAs. | Unraveling Frequency Effects in Shape Memory Alloys: NiTi and FeMnAlNi | 10.1007/s40830-021-00335-0 |
2021-06-01 | In this paper, the possibility of using fine scrap tyre rubber to improve the mechanical properties of soil subjected to cyclic loading is addressed. Ground rubber (0.1–0.8 mm) in various proportions (0, 9, 33% and 100% by weight) was mixed with a uniform river sand and a lean clay. Cyclic triaxial tests with bender elements were executed to observe the behaviour of the materials and also to determine damping and shear stiffness parameters. The results have shown that the addition of rubber has significantly decreased the density and shear stiffness of both types of soils, which favours mitigation of vibrations. The shear stiffness degradation at shear strains higher than 10^−3 was lower in specimens containing more rubber. Within this strain range, addition of rubber decreased the damping ratio, but increased the normalized accumulated absolute strain energy absorbed by the material. Higher rubber content in sandy specimens resulted in more elastic behaviour, with lower strain accumulation in each loading cycle, eventually resulting in a higher number of loading cycles before failure. The positive effect of rubber presence was not observed in compacted clay–rubber mixture, which sustained less loading cycles than clay alone. The influence of rubber addition in the p′-q stress space was expressed in the form of lower pore pressure generation which shifted the stress path further from the failure envelope. | Cyclic and Dynamic Behavior of Sand–Rubber and Clay–Rubber Mixtures | 10.1007/s10706-021-01704-3 |
2021-06-01 | We study the asymptotic behavior of Timoshenko systems with a fractional operator in the memory term depending on a parameter $$\theta \in [0,1]$$ θ ∈ [ 0 , 1 ] and acting only on one equation of the system. Considering exponentially decreasing kernels, we find exact decay rates. To be precise, we show that for $$\theta \in [0,1)$$ θ ∈ [ 0 , 1 ) , the system decay polynomially with rates that depend on the value of the difference of the wave propagation speeds. We also prove that these decay rates are optimal. Moreover, when $$\theta =1$$ θ = 1 and the equations have the same propagation speeds we obtain the exponential decay of the solutions. | Stability Results for a Timoshenko System with a Fractional Operator in the Memory | 10.1007/s00245-019-09587-w |
2021-06-01 | In this article, we study the solutions of the damped Navier–Stokes equation with the Navier slip boundary condition in a bounded domain $$\Omega $$ Ω in $${\mathbb {R}}^3$$ R 3 with sufficiently smooth boundary. We employ the Galerkin method to approximate the solutions of the damped Navier–Stokes equations with the Navier-slip boundary conditions. The existence of the solutions is global for $$\beta \ge 1$$ β ≥ 1 . We also established the regularity of the solutions for $$\beta \ge 3$$ β ≥ 3 , and the uniqueness of the solutions for $$\beta \ge 1$$ β ≥ 1 . | Existence and uniqueness of solutions to the damped Navier–Stokes equations with Navier boundary conditions for three dimensional incompressible fluid | 10.1007/s12190-020-01437-1 |
2021-06-01 | A nonlinear mathematical model is developed in the time domain to simulate the behaviour of two identical flexibly mounted cylinders in tandem while undergoing vortex-induced vibration (VIV). Subsequently, the model is validated and modified against experimental results. Placing an array of bluff bodies in proximity frequently happens in different engineering fields. Chimney stacks, power transmission lines and oil production risers are few engineering structures that may be impacted by VIV. The coinciding of the vibration frequency with the structure natural frequency could have destructive consequences. The main objective of this study is to provide a symplectic and reliable model capable of capturing the wake interference phenomenon. This study shows the influence of the leading cylinder on the trailing body and attempts to capture the change in added mass and damping coefficients due to the upstream wake. The model is using two coupled equations to simulate the structural response and hydrodynamic force in each of cross-flow and stream-wise directions. Thus, four equations describe the fluid–structure interaction of each cylinder. A Duffing equation describes the structural motion, and the van der Pol wake oscillator defines the hydrodynamic force. The system of equations is solved analytically. Two modification terms are added to the excitation side of the Duffing equation to adjust the hydrodynamic force and incorporate the effect of upstream wake on the trailing cylinder. Both terms are functions of upstream shedding frequency (Strouhal number). Additionally, the added mass modification coefficient is a function of structural acceleration and the damping modification coefficient is a function of velocity. The modification coefficients values are determined by curve fitting to the difference between upstream and downstream wake forces, obtained from experiments. The damping modification coefficient is determined by optimizing the model against the same set of experiments. Values of the coefficients at seven different spacings are used to define a universal function of spacing for each modification coefficient so that they can be obtained for any given distance between two cylinders. The model is capable of capturing lock-in range and maximum amplitude. | On the development of a nonlinear time-domain numerical method for describing vortex-induced vibration and wake interference of two cylinders using experimental results | 10.1007/s11071-021-06527-8 |
2021-06-01 | In this paper, we consider the stabilization for the Kirchhoff plate and equations connected by transmission conditions. We show that the energy of the transmission system is stable with logarithmic decay rate when feedback control acts on the small part of the plate as a viscoelastic material with Kelvin–Voigt constitutive relation. The proof is based on a new resolvent estimate by using some careful analysis for Kirchhoff plate-wave transmission system. | Stabilization of transmission system of Kirchhoff plate and wave equations with a localized Kelvin–Voigt damping | 10.1007/s00028-021-00682-6 |
2021-06-01 | The aim of this paper is to study the theoretical and numerical stability of the Bresse system in one-dimensional bounded domain with viscoelastic Kelvin–Voigt damping. We first showed the well posedness of the system. Then stability is obtained by applying the multiplicative techniques. Later a numerical scheme is proposed and analyzed. Finally a priori error estimate is established. | On the Stabilization of the Bresse Beam with Kelvin–Voigt Damping | 10.1007/s00245-019-09611-z |
2021-06-01 | The present article attempts to study the propagation of surface seismic waves (Stoneley waves) in the layered structure composed of rock and ice medium. The interface between the two media (ice and rock) is considered to be frictional. Mathematical model of the present problem is formulated by adapting the Coulomb frictional boundary conditions. The frequency relation is obtained in the determinant form. The non-dispersive nature of the Stoneley wave is observed through the frequency relation. The non-dimensional phase velocity and damping parameter curves have been plotted against the non-dimensional angular frequency. Effect of different parameters (viscoelastic coefficient of the rock medium, frictional interface parameter, anisotropy parameter and initial stress of both the media) on the phase velocity and damping has been distinctly marked and shown graphically. | Modelling of Stoneley wave transference at the frictional interface between ice and rock medium | 10.1007/s00419-021-01894-5 |
2021-06-01 | Stochastic flexural vibrations of small-scale Bernoulli–Euler beams with external damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as micro- and nano-electro-mechanical-systems. | Random vibrations of stress-driven nonlocal beams with external damping | 10.1007/s11012-020-01181-7 |
2021-06-01 | Wide-area damping controllers (WADCs) are effective means of improving the damping of inter-area oscillations and thereby ensuring a secure operation of modern highly stressed interconnected power systems; however, their implementation costs are high. Therefore, the controller must be well configured and designed to ensure its cost-effectiveness. Several techniques have been proposed in the literature to design effective controllers and good results have been achieved. However, some important practical aspects that could potentially impact the performance of the designed controller have not been addressed or studied in sufficient detail in these previous works. One such aspect is assessing the performance of the designed controllers under major system upsets resulting in large deviations in the frequency and fluctuations in the power. These may lead to controller saturation which could negatively impact its damping performance or even cause instability. In this paper, the impact of such large upsets is investigated on several test systems via extensive small- and large-signal analyses and it is shown that, during severe transients, controller saturation may occur and persist over a long period of time, posing a potential threat to the power system stability. This paper presents a very effective solution to alleviate this problem and help design more robust WADCs. The simulation results show that the proposed solution works well and leads to improved power system stabilisers performance during transient upsets. | Performance of wide-area power system stabilizers during major system upsets: investigation and proposal of solutions | 10.1007/s00202-020-01168-3 |
2021-06-01 | Conventional tuned liquid column dampers (TLCDs) are deficient in multidirectionality. In contrast, toroidal TLCDs are designed to extend the application to multidirectional vibration control. This article employs real-time hybrid simulation (RTHS) to experimentally investigate the nonlinear damping effects of toroidal and conventional TLCDs in different directions. The RTHS framework consists of toroidal and conventional TLCD models as the physical substructure and a single-degree-of-freedom (SDOF) structure as the numerical substructure. The excitations cover seismic ground motions and harmonic signals. Different structural parameters and peak ground acceleration (PGA) of the ground motions are assigned to the numerical substructure. It is reported that the conventional TLCD has the most remarkable vibration control effect in its main control direction, while it has efficiency loss in other directions. The efficiencies of toroidal TLCD in arbitrary directions are found to be slightly lower to that of convention TLCD in its main control direction. The toroidal TLCD has advantages on omnidirectional damping effects than the conventional TLCD. Lastly, the satisfactory performance of toroidal TLCD under different structural parameters and PGA values confirms the certain robustness of toroidal TLCD. | Experimental comparison of nonlinear damping performance of toroidal and conventional tuned liquid column dampers | 10.1007/s11071-021-06552-7 |
2021-06-01 | Abstract In this study, the molecular dynamics method was used to study the damping mechanism in Mg alloys at the atomic scale. The energy dissipated by the nucleation and motion of dislocations and by defects friction, and the effect of defects, such as vacancies, cracks, and grain boundaries, on them were studied. The study shows that different kinds of defect have different effects on the dislocation damping and defect friction damping. And then, the effect of strain amplitude and temperature on damping capacity of Mg was studied. The result shows that the amplitude independent damping is caused by defect friction and the amplitude dependent damping is mainly caused by the nucleation and motion of dislocation; the damping of Mg increased exponentially with the temperature, and the damping peck appeared at 440 K is attributed to the appearance of dislocations at the grain boundaries which may be caused by boundaries self-diffusion. Graphic Abstract | Dislocation Damping and Defect Friction Damping in Magnesium: Molecular Dynamics Study | 10.1007/s12540-019-00566-y |
2021-06-01 | In the present work, the quality factor (and thermoelastic damping) of a microbeam resonator is analyzed by employing the three-phase-lag thermoelasticity theory with memory-dependent derivative. We compare our results with different heat conduction models. An explicit formula of thermoelastic damping has been derived, and effects of the normalized frequency and the beam height on thermoelastic damping of the microbeam resonator have been studied. We presented our work numerically by taking Silicon. The effects of normalized frequency, beam height, and different kernel of memory-dependent derivative on thermoelastic damping has been presented with the numerical data of Silicon. | Analysis of the quality factor of micromechanical resonators using memory-dependent derivative under different models | 10.1007/s00419-021-01920-6 |
2021-06-01 | The characterization of mechanical vibrations in a hammer forging process is a tremendously important parameter for machine design and production engineering. The dynamic response of a forging hammer to the reaction forces is affected by material behaviour, time, spring-damper system and foundation. In this research firstly, the effect of mass ratio and coefficient of restitution on the forging efficiency were theoretical characterized. The interesting influence of anvil initial velocity on the forging efficiency is also analytically presented. The mechanical vibrations of a LASCO HO U-315 hammer were experimentally investigated. Two steel grades a S355 and a 42CrMo4 were used to forge trial parts. The velocity of the ram and acceleration of the anvil during a hot die forging process were measured using a laser velocity meter type LSV-2000-45. The influences of forging time, coefficient of restitution, energy loss and time interval (delay) between blows on the efficiency of the forging process were examined. The energy loss before die contact was determined to be approximately 10%. The investigations also showed that a variation of the time interval between blows within the usual range has no effect on the intensity of the vibrations of the anvil nor on the energy loss of the hammer. The dependence of the free damped vibrations of the anvil on machine stiffness, damper coefficient and mass of machine has been confirmed. Additionally, the loss of energy due to hammer movement as well as the free damped mechanical vibrations of the anvil were theoretically analysed in order to verify the experimental findings. Theoretical analysis showed an anvil initial velocity of approximately 0.2 m/s results in a 4% increase of forging efficiency. A good agreement between the experimental and theoretical results was observed. | Theoretical and experimental investigations of mechanical vibrations of hot hammer forging | 10.1007/s00170-021-07061-y |
2021-06-01 | Hybrid materials combining steel or cast iron with fibre or particle composites have a good potential for lightweight machine tool structural design with high damping ratio. These materials are analyzed in the paper with a focus on damping improvement of structural components and machine tool assemblies. Fibre composites and particle composites were selected as the lightweight elements for the hybrid machine tool structure. The fibre composites were designed as low-density, high stiffness-oriented reinforcements, which were bonded to build metal structural parts conventionally. The particle composites were applied as filler materials into the hollows of the metal structural parts. Both composite structures presented a possibility to reduce the mass of the component due to the reduction of wall thickness (fibre composite) or removal of heavy ribbing (particle composites) and to influence the parts’ static and dynamic stiffness. Hybrid structures, combining the light-weight elements with cast iron or welded steel, were designed and tested in case studies using experimental modal analysis methods. Experimental modal analysis was used as the main approach for identification of the damping ratio on a basic coupon level, followed by testing of structural parts in a stand-alone configuration and ending with a structural part assemblies testing. Both particle composites and fibre composites were successful in improving the damping ratio of single structural parts. However, the damping ratio of the hybrid component mounted into an assembly configuration shows only less significant improvement. The presented results demonstrate importance of the damping caused in the connecting interfaces. | On passive damping in machine tool hybrid structural parts | 10.1007/s00170-021-06865-2 |
2021-06-01 | We establish the global well-posedness of a strong solution to the 3D tropical climate model with damping. We prove that there exists the global and unique solution for α, β, γ satisfying one of the following three conditions: (1) α, β ⩾ 4; (2) 7/2 ⩽ α < 4, β ⩾ (5 α + 7)/(2 α ), γ ⩾ 7/(2 α − 5); (3) 3 < α ⩽ 7/2, β, γ ⩾ 7/(2 α − 5). | Global strong solution of 3D tropical climate model with damping | 10.1007/s11464-021-0933-6 |
2021-06-01 | This paper investigates the application of the robust control strategy for reducing structural vibrations using the hybrid protective system in the presence of network abnormalities. It focuses on the design of sliding mode control using a novel sliding variable and modified reaching law approach in the presence of time-varying transmission delay and matched uncertainties. The novel sliding variable is designed using compensated state information which nullifies the effect of time-varying or deterministic transmission delay and ensures finite-time convergence of state variables in the presence of system uncertainties. Further, the stability analysis of the proposed control algorithm with the closed-loop system in the presence of system uncertainties is also presented using the Lyapunov approach. The compound equation of motion of the hybrid protective structural system is formulated and solved in the time domain by the state-space approach. The simulation results are obtained for a typical massive storage structure equipped with a hybrid protective system under seismic excitation. To prove the efficacy of the proposed control algorithm, the results are compared with the power-rate reaching law and conventional delayed system. It is observed that the proposed control strategy is quite effective and robust in the presence of system uncertainties. | Design of sliding mode control for structural vibration system with time-varying transmission delays | 10.1007/s40435-020-00697-w |
2021-05-31 | The clutch is an important component of the vehicle driveline system. One of its major functions is to attenuate or eliminate the torsional vibration and noise of the driveline system caused by the engine. Based on experiments of vibration damping under different vehicle conditions, the structure and functional principle of a clutch-driven disc assembly for a wide-angle, large-hysteresis, multistage damper is investigated in this study using an innovative combined approach. Furthermore, a systematic integration of key technologies, including wide-angle low-stiffness damping technology, large-hysteresis clutch technology, a novel split pre-damping structure technology, damping structure technology for component cushioning, and multistage damping structure technology, is proposed. The results show that the total torsional angle of the wide-angle large-hysteresis, multistage damper is more than twice that of the traditional clutch damper. The multistage damping design allows a better consideration of various damping requirements under different vehicle conditions, which can effectively address problems of severe idle vibrations and torsional resonance that occur under idled and accelerated conditions. Meanwhile, the use of a large-hysteresis structure and wear-resistant materials not only improves the vibration damping performance, but also prolongs the product service life, consequently resulting in multi-faceted optimization and innovative products. | Design and Performance Study of Clutch Disc Assembly of Wide-Angle, Large-Hysteresis, Multistage Damper | 10.1186/s10033-021-00572-5 |
2021-05-24 | In this paper, we investigate the stabilization of a linear Bresse system with one discontinuous local internal viscoelastic damping of Kelvin–Voigt type acting on the axial force, under fully Dirichlet boundary conditions. First, using a general criteria of Arendt–Batty, we prove the strong stability of our system. Finally, using a frequency domain approach combined with the multiplier method, we prove that the energy of our system decays polynomially with different rates. | On the stability of Bresse system with one discontinuous local internal Kelvin–Voigt damping on the axial force | 10.1007/s00033-021-01558-y |
2021-05-22 | This paper studies the damped Schrödinger equation $$\begin{aligned} i\dot{u} +\Delta u+(I_\alpha *|u|^p)|u|^{p-2}u+ia(t)u+ib|u|^{2(q-1)}u+ic\frac{u}{|u|^\beta }+id (-\Delta )^su=0. \end{aligned}$$ i u ˙ + Δ u + ( I α ∗ | u | p ) | u | p - 2 u + i a ( t ) u + i b | u | 2 ( q - 1 ) u + i c u | u | β + i d ( - Δ ) s u = 0 . Indeed, in the energy sub-critical regime, global well-posedness and scattering versus finite time blow-up of solutions are discussed under some suitable conditions on the damping and the source term. | On damped non-linear Choquard equations | 10.1007/s40590-021-00359-7 |
2021-05-06 | In engineering applications, composite structures supported by elastic foundations are being vastly utilized in various operating environmental conditions. The nonlinear hygrothermal effect on vibration analysis of a magnetostrictive viscoelastic laminated composite sandwich plate rested on two-parameter Pasternak’s foundations is studied in the present article. The material properties of the viscoelastic plate’s layers are considered based on the Kelvin–Voigt model. The governing equation system is derived according to Hamilton’s principle. The analytical solution is obtained to study influences of the hygrothermal change, half wave number, magnitude of the feedback control gain, aspect ratios, thickness ratio, and structural viscoelastic damping coefficients on vibration damping characteristics of the plate including the frequencies, the damping rate, and the deflection. The obtained results indicate that the natural frequency and deflection reduce with increasing the structural viscoelastic damping value. The plate takes a long time for suppressing its vibration due to increasing the hygrothermal factor. | Nonlinear hygrothermal effects on the vibrations of a magnetostrictive viscoelastic laminated sandwich plate resting on an elastic medium | 10.1007/s43452-021-00230-6 |
2021-05-04 | In this paper, we show the global existence of classical solutions to the incompressible elastodynamics equations with a damping mechanism on the stress tensor in dimension three for sufficiently small initial data on periodic boxes, that is, with periodic boundary conditions. The approach is based on a time-weighted energy estimate, under the assumptions that the initial deformation tensor is a small perturbation around an equilibrium state and the initial data have some symmetry. | Global classical solutions to the elastodynamic equations with damping | 10.1186/s13660-021-02608-9 |
2021-05-01 | The stiffness and damping modeling of joint surfaces are important for analyzing the dynamic characteristics of bolted joints, which has a great influence on the working precision of the machine tool. In this paper, a damping model is presented to predict the tangential damping of the joint accurately. The fractal theory is introduced to characterize the rough contact surface by using fractal dimension D and fractal roughness parameter G. For each micro-contact, the contact region can be divided into stick section and slip one. The energy dissipation of the micro-contact, which can be described as the tangential damping of bolted joint, emerges in the slip section. The physics-based friction coefficient is introduced to define the energy dissipation function based on the relationship between the deformation of micro-contact and the normal pressure. The energy dissipation factor and the proportional damping of the micro-contact can be obtained. The total tangential damping of bolted joint can be obtained by integrating the whole contact surfaces. Experimental set-up is designed to verify the proposed model. Compared with the constant friction coefficient damping model, the results show that the proposed model can more accurately describe the tangential damping of bolted joint. | Tangential Damping Model of Bolted Joint with the Physics-Based Friction Coefficient | 10.1007/s12541-021-00485-2 |
2021-05-01 | For a real polynomial p ( s ) = a _ n s ^ n + ⋯ + a _1 s + a _0, its characteristic ratios are defined by $${\alpha _i}: = {{a_i^2} \mathord{\left/{\vphantom {{a_i^2} {{a_{i - 1}}{a_{i + 1}}}}} \right.\kern-\nulldelimiterspace} {{a_{i - 1}}{a_{i + 1}}}}$$ α i : = a i 2 / a i − 1 a i + 1 for i = 1, 2, ⋯, n −1, and the generalized time constant is defined by τ ≔ a _1/ a _0. In contrast, every coefficient of the polynomial p ( s ) can be represented in terms of α _ i and τ . We present a novel family of polynomials named characteristic ratio symmetric (CRS), where a polynomial p ( s ) is said to be CRS if α _ i = α _ n − i for 1 ≤ i ≤ n − 1 with any τ . This paper deals with the relationships between the roots and { α _ i , τ } of a CRS polynomial. It is shown that some of the roots of the CRS polynomial are on the circle of a specific radius ω _ c while the rest appear in four-tuples $$\left\{{{\lambda _i},{{\omega _c^2} \mathord{\left/ {\vphantom {{\omega _c^2} {{\lambda _i},}}} \right. \kern-\nulldelimiterspace} {{\lambda _i},}}\lambda _i^*,{{\omega _c^2} \mathord{\left/ {\vphantom {{\omega _c^2} {\lambda _i^*}}} \right. \kern-\nulldelimiterspace} {\lambda _i^ *}}} \right\}.$$ { λ i , ω c 2 / λ i , λ i ∗ , ω c 2 / λ i ∗ } . . For CRS polynomials of the fifth or lower order, we derive that the damping ratio and natural frequency of every root of these polynomials can be uniquely represented in terms of only { α _1, α _2, τ } or { α _1, τ } for less than third order. It is also shown that a special polynomial named K-polynomial is a CRS polynomial and the damping of an n th-order K-polynomial can be adjusted by just choosing a single parameter α _1. | Characteristic Ratio Symmetric Polynomials and Their Root Characteristics | 10.1007/s12555-019-1086-1 |
2021-05-01 | This paper is concerned with the Boussinesq system with a damping term and the homogeneous Dirichlet boundary conditions in 3D bounded domains. For a certain range of parameters, we prove that the weak solution is unique if the temperature belongs to $$L^{\infty }(0,T;L^{3}(\Omega ))$$ L ∞ ( 0 , T ; L 3 ( Ω ) ) . Also, the global existence of strong solutions to the problem is proved. | Uniqueness and regularity for the 3D Boussinesq system with damping | 10.1007/s11565-020-00351-5 |
2021-05-01 | We propose the application of a resonant shunt to wheels to reduce the high-frequency wheel noise generated by railway vehicles. High-frequency wheel noise is caused by the resonance of wheels owing to contact between rails and wheels. A resonant shunt is applied at specific frequencies to reduce wheel resonance. In this work, the high-frequency noise generated by a wheel moving on a curved railway track was analyzed and compared with the dynamic characteristics of the wheel. Further, to reproduce the high-frequency noise of the wheel, an external electric signal was input to a piezoelectric patch connected to the wheel to generate noise and vibration at the natural frequency of the wheel. The optimum mounting position of the piezoelectric patch was determined by numerically analyzing the strain energy of the wheel. Piezoelectric patches were connected to their respective resonant shunts to form a vibration reduction array. A synthetic inductor was tuned to effectively reduce the high-frequency vibration and noise of the wheel generated at its natural frequency. In the wheel excited at its natural frequency, vibration and noise were reduced by approximately 4–10 dB and 8–12 dB(A), respectively. In the wheels that were simultaneously excited at two natural frequencies, vibration and noise were reduced by 5 dB and 5 dB(A), respectively. The results showed that the resonant shunt could effectively reduce the noise and vibration generated by the wheel. Therefore, the resonant shunt is an effective circuit system for reducing noise and vibration even in large structures. | Reduction in High-Frequency Wheel Noise/Vibration of Railway Vehicles Using Piezoelectric Shunt | 10.1007/s40684-020-00294-4 |
2021-05-01 | Aiming at the reduction of low-frequency noise for large equipment, a damping optimization method based on the Operational Mode Analysis (OMA) is proposed. Due to the stability of the mode frequencies and shapes, damping application could make efficient noise reduction without bringing new problems compared with structural optimizations, which makes it one of the most important means for finalized products. Taking the engine compartment of an excavator as the study object, a damping optimization method based on the OMA test is proposed in this article, which makes a more efficient optimization for large equipment by its feasible modal test. Through simulation and experimental verification, the method is effective. The test results show that based on the OMA damping application method, the low-frequency sound power level has been significantly reduced, and after the damping application, the sound radiation power level defined by the national standard has also been reduced. | A Damping Optimization Method Based on the Operational Mode Analysis for Low-Frequency Noise Reduction | 10.1007/s11182-021-02306-5 |
2021-05-01 | In order to avoid the complexity of obtaining the sensitivity in the usual optimal flow with small signal stability, which is easily result from the mere consideration of active power output optimization or the change of element model, a new model is proposed to improve the small-signal stability of the system by constraining the perturbation trajectory curve. Based on the time-domain simulation method, a power flow optimization model with small-signal trajectory constraint is established by extracting the damping ratio of the perturbation trajectory and forming constraints. The optimization calculation results of Western Systems Coordinating Council 3-generator 9-node system and China Electric Power Research Institute 6-generator 22-node system prove that the corresponding minimum damping ratio of the system increases with the increase of the constraint value of approximate damping ratio, which demonstrates the effectiveness of the model. | OPF Calculation with Small-Signal Trajectory Constraints | 10.1007/s42835-021-00689-6 |
2021-05-01 | In this work, near fully dense NiTi components have been fabricated using a 55.2Ni-Ti (wt.%) powder through selective laser beam melting. The effect of the manufacturing process on mechanical and functional properties of the selected NiTi alloy has been systematically investigated by tuning the hatching distance, h , and the scanning speed, v , in order to define a set of 12 NiTi families. The as-built NiTi parts present phase transformation temperatures higher than those of the feedstock, ascribed to the depletion of Ni during the process. Pseudoelasticity and shape memory responses have been evaluated through uniaxial compression and bending measurements, respectively. Both quasi-static and dynamic analyses have been considered. It is shown that the resulting material may exhibit distinct damping and strain recovery responses depending on the used process parameters. | Towards an understanding of the functional properties of NiTi produced by powder bed fusion | 10.1007/s40964-020-00155-1 |
2021-05-01 | We deal with the Cauchy problem of three-dimensional incompressible magneto-micropolar fluid equations with a nonlinear damping term $$\alpha |{\mathbf {u}}|^{\beta -1}{\mathbf {u}}\ (\alpha >0\ \text {and}\ \beta \ge 1)$$ α | u | β - 1 u ( α > 0 and β ≥ 1 ) in the momentum equations. By cancelation properties of the system under study, we show that there exists a unique global strong solution for any $$\beta \ge 4$$ β ≥ 4 . Our work extends previous results. | Global Regularity of Three-Dimensional Incompressible Magneto-Micropolar Fluid Equations with Damping | 10.1007/s40840-020-01021-7 |
2021-05-01 | A new tuned vibration absorber (TVA) based on one degree-of-freedom (1DOF) of translational motion is proposed. The absorber mass takes the shape of a tank filled with fluid. This device is attached to the fluid circulating system which plays a role in changing the absorber mass. It fills the tank or drains it depending on the data received from the frequency force sensor. The type of TVA used is similar to the simple damped TVA. A numerical procedure is used to test the TVA and compare the performance with the other TVAs. This method is simple to carry out the performance of the TVA as it is adequate for real-life problems. | A New Tuned Vibration Absorber Based on One-Degree-of-Freedom of Translational Motion | 10.1007/s10778-021-01088-0 |
2021-05-01 | Rectangular flat-bottom liquid tanks known as tuned liquid dampers (TLDs) are often used as passive mechanical dampers. Sloped- and triangular-bottom TLDs have been reported to be more effective than flat-bottom TLDs, but optimum tuning and damping of sloped- and triangular-bottom TLDs have not yet been proposed, and nonlinear analysis of such TLDs has not been performed. This study aims to establish a practical analytical model for nonlinear sloshing in a triangular-bottom TLD and a method for designing a TLD using a triangular-bottom tank. We modify the concentrated mass model proposed in our previous paper to simulate nonlinear shallow water wave phenomena in a triangular-bottom tank. To confirm the validity of the modified model, its results are compared with the natural frequencies in a triangular-bottom tank obtained from FEM and experimental results for a triangular-bottom tank. All the model results agree well with the FEM and experimental results. Furthermore, optimum tuning and damping based on the concentrated mass model are derived in the case of a triangular-bottom TLD, and the physical reason why a triangular-bottom TLD is more effective than a flat-bottom TLD is investigated. | Modeling and design of a tuned liquid damper using triangular-bottom tank by a concentrated mass model | 10.1007/s11071-021-06433-z |
2021-05-01 | Structural materials and their properties in different applications with next-generation composite production techniques are quite promising areas. In this study, new composite blocks were produced with the addition of industrial and recycled steel fibers to high strength cementitious composites (HSCCs). The vibrational damping capabilities of the blocks produced in standard dimensions (16 cm × 4 cm × 4 cm) were tested by using the modal analysis method. In many different applications, structural materials are expected to absorb vibrations such as earthquakes or artificial vibrations from machine systems operating in industrial areas. In this study, the vibration damping capability of HSCCs was investigated and improved by adding steel fiber to HSCCs. The experimental study shows that adding steel fibers improves the bending stress by up to 127% and damping ratio over 200%. The fiber size and distribution play a significant role in this improvement. This effect was also achieved to a certain extent in the samples produced using recycled steel fibers obtained from waste tires. In this way, the vibration damping ability of the HSCCs is increased with an environmentally friendly approach. | Influence of Steel Fiber Addition on the Vibrational Characteristic of High Strength Cementitious Composites | 10.1007/s13369-020-05096-z |
2021-05-01 | This current research dealing the effect of adding high stiffness carbon fibre along with E-glass fibre and addition of nano-silica particles as a toughening agent in epoxy resin. The main aim of this research is to improve the damping, storage modulus and fatigue behaviour of glass-epoxy composite by using carbon fibre and nano-silica particles. The intra-ply glass and carbon fibre were prepared using handloom method with uniform weft and warp. The proposed composites were prepared using hand layup method followed by post-curing at 120^οC. The low-velocity impact test results revealed that the composites made with intra-ply carbon glass fibre along with 2 vol% of nano-silica offered maximum resistance against penetration. Similarly, the fatigue behaviour revealed that the presence of 1 vol% nano-silica and carbon fibre provides the highest life cycle of 30150 counts. The visco-elastic properties of glass-carbon intra-ply fibre with 2 vol% of nano-silica composite possess storage modulus of 9.5 GPa. The scanning electron microscope images revealed more shear cups in the fractured matrix, which indicates improved toughness of the epoxy matrix. | Low Velocity Impact, Fatigue and Visco-elastic Behaviour of Carbon/E-glass Intra-ply fibre-Reinforced Nano-silica Toughened Epoxy Composite | 10.1007/s12633-020-00566-3 |
2021-05-01 | We discuss the possibility of connecting Bateman’s approach to the concept of maximal acceleration in quantum theory. We show that if such a correlation exists, for very large acceleration or for very large time, waves propagate in atemporal space. This suggests that string theory is a limiting case of an underlying theory. | String propagation in space without time through an association between damping and maximal acceleration | 10.1007/s40509-021-00242-0 |
2021-05-01 | The article describes for the first time a method for determining the logarithmic decrements of damping of natural frequency oscillations of the arch-gravity dam of the Sayano-Shushenskaya Hydropower Plant based on engineering seismometric observations. The experimental and calculated results of damping decrements are compared. A number of factors that influence the change of the logarithmic decrement are identified. | Determination of the Logarithmic Decrement of Damping of Natural Frequency Oscillations of the Sayano-Shushenskaya Hydropower Plant Dam Based on Engineering Seismometric Observations | 10.1007/s10749-021-01318-y |
2021-05-01 | A series of silica mesoporous molecular sieves SBA-15 with a 7.7 ± 0.8 nm pore diameter, the surface of which is hydrophobized with methylsilyl groups, and polymethylsiloxane derivatives with a 1.6 ± 0.8 nm pore diameter were obtained. These sieves are characterized by X-ray phase analysis, adsorption of nitrogen at 77 K and water at 293 K, as well as IR spectroscopy. It is established that there is a significant resistance to water intrusion (absorption) only in the case of substances characterized by the nitrogen adsorption potential value ∆μ_0 ≤ 6.4 kJ/mol. The studied systems can be used as “molecular springs” in shock load damping devices due to their functional properties. | Influence of the Structure of Hydrophobic Porous Silica Materials of SBA-15 Type and Polymethylsiloxane Derivatives on the Value of Water Intrusion Pressure | 10.1007/s11237-021-09682-6 |
2021-04-13 | Measuring viscoelastic properties of soft tissues becomes a new biomarker in the medical diagnosis field. It can help in early diagnosis and related fields, such as minimally-invasive-surgery (MIS) applications and cell mechanics. The current work presents a tactile sensor for measuring the damping coefficient of the soft tissues. The proposed sensor can be miniaturized easily and used in MIS applications. Besides the proposed sensor, a mathematical model, based on Jacobsen’s approach, is built to calculate the damping coefficient of the specimens and the surrounding. These damping sources significantly influence the proposed sensor, such as air damping and hysteretic damping. The sensor system principally depends on a piezoelectric transducer, which is cheap, commonly available, and easily integrated into MEMS. To conceptually prove the sensor feasibility, silicon rubber samples with different stiffnesses have been fabricated and tested by the new sensor. The obtained results prove the newly proposed sensor’s capability to differentiate the damping coefficients for soft materials effectively. | Determination of damping coefficient of soft tissues using piezoelectric transducer | 10.1007/s10544-021-00558-z |
2021-04-07 | Exponential integrators based on discrete gradient methods are applied to non-canonical Hamiltonian systems with added linear forcing/damping terms, which may be time-dependent. Changes in the dynamics, such as conservation of energy or Casimirs, which result from inclusion of the linear forcing/damping terms, are not exactly preserved by standard discrete gradient methods. However, those changes are shown to be exactly preserved by the exponential integrators in special circumstances. The methods are also symmetric, second order, and linearly stable. To demonstrate advantages in both accuracy and efficiency over other standard methods, the exponential integrators are applied to a three dimensional Lotka-Volterra system and a damped/driven Ablowitz-Ladik system. | Exponential Integrators Based on Discrete Gradients for Linearly Damped/Driven Poisson Systems | 10.1007/s10915-021-01468-1 |
2021-04-01 | Abstract— The critical functional part of any high performance resonance based sensor is a mechanical resonator. The performance is measured by resonator quality factor ( Q -factor). Damping mechanisms such as thermoelastic damping (TED), anchor loss, surface loss, material internal friction, fluid damping and electronics damping are covered in this review with more focus on gyroscope resonators. Dissipations can be reduced by different means. Hence, the effects of various design to operational parameters on the Q -factor for different configurations, sizes and materials are reviewed in detail. Micro scale ring resonators can achieve a Q -factor of the order of hundreds of thousands. Macro scale hemispherical resonators are suitable for ultrahigh Q- factors. High temperature sensor operation is not preferred because of TED, while sub-zero operation is limited by material internal friction. Few orders of dissipation increase are seen with thin film metallic coating due to TED and coating material internal friction. High precision fabrication is mandatory to achieve the designed minimum anchor loss as it is highly sensitive to fabrication imperfections. Q -factor sensitivity to operating pressure is different for different resonator configurations. This review study helps to build a comprehensive mechanical resonator design, realization and operation strategy to achieve high sensor performance. A roadmap on future research requirements for developing compact mass producible CVG type sensors with ultrahigh Q -factor is also highlighted. | Design to Operational Parameters Dependency on Quality Factor of Sensor Mechanical Resonators | 10.1134/S207510872102005X |
2021-04-01 | The vortex-induced vibration may lead to a premature failure of hydraulic mechanical systems, especially under the resonance condition in the torsional mode. To predict the structural fatigue life, a careful consideration of the dynamic response to the hydraulic excitations is essential in the design phase. This study focuses on the numerical investigation of the relationship between the flow velocity, the added mass and the hydrodynamic damping, particularly, with respect to a Donaldson-type hydrofoil, vibrating in the first torsional mode. A two-way fluid-structure interaction (FSI) method is used to predict above two parameters. The flow velocity is in the range of 0 m/s–20m/s. To evaluate the hydrodynamic damping ratio, an identification method is proposed, based on a modified version of the logarithmic decay method. The relative deviations of the simulated natural frequencies and hydrodynamic damping ratios as compared with the experimental data for the first torsional modes, are within 8.1% and 16.6%, respectively. The analysis results show that the added mass coefficient for the first torsional mode is in the range of 1.59–1.86, and is around 44% of that for the first bending mode. The trends of the boundary layer thickness and the wake width against the reduced velocity are found to be opposite to that of the hydrodynamic damping ratio. The theoretical equation for predicting the hydrodynamic damping ratio is modified, which is shown to be more reliable due to its consideration of the velocity independent hydrodynamic damping phase. | Numerical studies of the hydrodynamic damping of a vibrating hydrofoil in torsional mode | 10.1007/s42241-021-0019-7 |
2021-04-01 | This paper presents a novel method for determination of location and tuning of parameters of electronic static synchronous compensator (E-STATCOM) for oscillation control in Wide area monitored power systems. The effect of active and reactive power injection by E-STATCOM, on the damping performance of a two-area interconnected system has been studied and analyzed. Dynamic non-linear simulations of the test system with appropriate modeling were carried out for evaluation of performance of the proposed controller design, and to take forward the previous works done on wide area control of power systems. Novel attempt has been made for optimal selection of nodes for positioning E-STATCOMs in multi-machine power system, by considering the participation factor of angular variation of voltage vector in modal analysis. Many operating conditions have been considered for the proposed study under both normal states and contingencies. Results of the simulation indicate that the proposed method is highly effective in suppressing the low frequency oscillations of the targeted modes and performs better than the flexible alternating current transmission system devices without the support of energy storage. This method is also used for cloud application. | Improvement of Oscillatory Stability in Wide Area Controlled Systems Using Power Injection | 10.1007/s11277-020-07800-6 |
2021-04-01 | The upper bound on the degrees of irreducible Darboux polynomials associated to the ordinary differential equations x t t + ε x t 2 + η x t + f ( x ) = 0 $ x_{tt}+\varepsilon {x_{t}}^{2}+\eta x_{t}+f(x)=0 $ with f ( x ) ∈ ℂ [ x ] ∖ ℂ $ f(x)\in \mathbb {C}[x]\setminus \mathbb {C} $ and ε ≠ 0 is derived. The availability of this bound provides the solution of the Poincaré problem. Results on uniqueness and existence of Darboux polynomials are presented. The problem of Liouvillian integrability for related dynamical systems is solved completely. It is proved that Liouvillian first integrals exist if and only if η = 0. | Liouvillian Integrability and the Poincaré Problem for Nonlinear Oscillators with Quadratic Damping and Polynomial Forces | 10.1007/s10883-020-09513-2 |
2021-04-01 | A modification of the homotopy perturbation method is suggested with three effective expansions to solve a nonlinear oscillator with damping terms to expand the solution, the frequency and the amplitude. The Duffing equation with linear damping is used as an example to illustrate the simple solution process and effective results. The analysis exhibits that the amplitude behaves as an exponential decay with the damping parameter. This scheme yields a more effective result for the nonlinear oscillators and overcomes the shortcoming in some problems. | Homotopy perturbation method with three expansions | 10.1007/s10910-021-01237-3 |
2021-04-01 | In this study, a nanoscale beam of transversely isotropic thermoelastic (TIT) medium with two temperature and with Green–Naghdi (GN) III theory of thermoelasticity for free vibrations with simply supported boundaries have been examined. Euler–Bernoulli (EB) beam theory is used to formulate a mathematical model of the nanoscale beam in a closed form. The lateral deflection, frequency shift, thermal moment and thermoelastic damping have been solved. A program in MATLAB software is developed to find the numerical values for different physical quantities. The lateral deflection, frequency shift, thermal moment and thermoelastic damping for the varying two temperature, different modes, frequency of time harmonic sources, thickness of nano-beam, and material medium of nano-beam has been represented graphically and discussed. The results for some particular cases have also been compared to some earlier work done. | Study of frequency shift and thermoelastic damping in transversely isotropic nano-beam with GN III theory and two temperature | 10.1007/s00419-020-01848-3 |
2021-04-01 | The parametric instability of a rotor system with electromechanically coupled boundary conditions under periodic axial loads is studied. Based on the current flowing piezoelectric shunt damping technique, the detailed rotor model is established by the finite element (FE) method. In the matrix assembly procedure, a novel simple process is proposed to make the equations of shunt circuits more conveniently to be introduced into the global FE equations. The discrete state transition matrix method which is used for determining the influence of circuit parameters on instability regions in this paper has also been presented. The numerical simulation shows that only the combination instability regions exist when the shaft is rotating. The mechanical damping has different effect on the simple and combined instability regions. These two points are consistent with the previous references, which verifies the obtained FE model. In addition, the simulated results also reveal that the introduction of shunt circuits has little influence on the rotor’s original whirling frequencies. It gives rise to the appearance of new synchronous whirl modes. The new whirling frequencies are combined with the original ones to form the new combination instability regions. Furthermore, the resistance of shunt circuits has the same performance as the mechanical damping has. That is, moving up the start points of instability regions and expanding its width. | Stability analysis of a rotor system with electromechanically coupled boundary conditions under periodic axial load | 10.1007/s11071-021-06339-w |
2021-04-01 | In this article, the damping forced harmonic vibration characteristics of magneto-electro-viscoelastic (MEV) nanobeam embedded in viscoelastic foundation is evaluated based on nonlocal strain gradient elasticity theory. The viscoelastic foundation consists of Winkler–Pasternak layer. The governing equations of nonlocal strain gradient viscoelastic nanobeam in the framework of refined shear deformable beam theory are obtained using Hamilton’s principle and solved implementing an analytical solution. In addition, a parametric study is presented to examine the effect of the nonlocal strain gradient parameter, magneto-electro-mechanical loadings, and aspect ratio on the vibration characteristics of nanobeam. From the numerical evaluation, it is revealed that the effect of electric and magnetic loading on the natural frequency has a predominant influence. | Chaotic dynamics and forced harmonic vibration analysis of magneto-electro-viscoelastic multiscale composite nanobeam | 10.1007/s00366-019-00865-3 |
2021-04-01 | Owing to limited rigidity and wall thickness, the machining of thin-walled components leads to chatter, poor surface quality, and low productivity. It is well-acknowledged that end-mill geometry and cutting conditions have a significant influence on the process stability of thin-walled parts. In order to reduce the milling chatter, an anti-vibration milling tool with an anti-vibration edge (60, 90, 120μm) on the flank face is proposed based on the analysis of the process damping effect. The dynamic modeling, numerical computation, and confirmatory experimental analysis are carried out to investigate the effect of anti-vibration edge length on the milling stability of thin-walled titanium-alloy components. The computation results have shown a stable and gradual increase in stable depth-of-cut with the increase of anti-vibration edge length at constant spindle speed. The ultimate stable axial depth increases with the increase of the anti-vibration edge. Besides, the increase of spindle speed reduced the interference between the flank surface of the milling tool and the workpiece due to the decrease of curvature of the vibration mark on the workpiece surface. At higher cutting speed, the relationship between the stability axial depth and anti-vibration edge length reduced. The comparison of computational and experimental results indicate that the anti-vibration edge improved the process damping effect at low cutting speeds, and 120μm anti-vibration edge is optimum to manufacture the flank face of the tools. | Study the effect of anti-vibration edge length on process stability of milling thin-walled Ti-6Al-4V alloy | 10.1007/s00170-021-06781-5 |
2021-04-01 | A novel boring bar was developed for chatter reduction of machining processes. By proposing an internal frictional damping structure, additional energy dissipation during bending vibrations was imposed to the boring bar. The structure consisted of some pins longitudinally press-fitted inside the boring bar. This structure resisted against bending of the boring bar during machining processes. After introducing the structure, an analytical model was presented to determine the amount of energy dissipated by the damper. Using the analytical model and finite element modeling (FEM), the most effective configuration was obtained for the proposed frictional damper structure. After determining the best configuration, a damped boring bar specimen was fabricated for experimental comparison with a regular boring bar. The modal and cutting tests were performed on the specimens. The modal test revealed a significant increase in the structural damping of the boring bar. The cutting tests were performed at different depths of cut and different spindle speeds, and the process was investigated through sound analysis and surface finish observation. Experimental comparisons indicated the higher performance of the proposed tool. | Development of a frictionally damped boring bar for chatter suppression in boring process | 10.1007/s00170-021-06791-3 |
2021-04-01 | Species specific hydrodynamic characterization is essential for assessing the suitability of various types of mangroves in coastal protection as the dissipation of wave energy within the mangroves is governed primarily by various aspects which are specific to the species to which they belong. In the present study a specific mangrove species was selected and its wave attenuation characteristics were studied with the help of scaled physical models under controlled wave and vegetation conditions in a laboratory wave flume. The plant was initially identified as Rhizophora Mucronata and the scaled models prepared had the same biomechanical properties as that of the parent plant. Effect of root soil was incorporated in scaled models as bottom friction. Wave heights were measured after the forest models to evaluate the wave attenuation. It was found that wave heights were following the exponential decay equation of Kobayashi et al. (1993) except for the cases which have incorporated bottom friction. For such cases exponential decay equation was modified by incorporating a new parameter ‘d/D_50’. Drag coefficients (C_D), characteristic of the species were also determined without incorporating and with incorporating the effect of bottom friction of root soil. It is seen that drag coefficients are following an inverse relation with non-dimensional numbers (R_e and KC). Empirical relations were developed between C_D and a modified Keulegan Carpenter number (modified considering mangrove root submergence and mean particle size) for predicting the drag coefficients specific to Rhizophora Mucronata species for a variety of wave and water level conditions. | Laboratory investigations on wave attenuation characteristics of Rhizophora Mucronata poir using physical models with bottom friction | 10.1007/s10652-020-09777-z |
2021-04-01 | The Xihoumen Bridge, with a main span of 1650 m and two side spans of 578 m and 485 m, respectively, is a long-span suspension bridge spanning the Jintang and Cezi islands in Zhejiang Province, China. In order to establish a reference baseline for vibration mitigation and condition assessment of the bridge under typhoons, the wind field properties, vibration energy distribution, and modal parameters of the bridge are identified through in-situ monitoring. Dynamic responses at different locations on main span and wind speeds at 1/2 main span of the bridge under 10 typhoons and under normal wind were collected for this study. Vibration energy distribution is estimated using wavelet packet transform. Modal parameters are identified by the peak-picking (PP) and data-driven stochastic subspace identification (SSI-DATA) methods. The results indicate that in the low-frequency range, the fluctuating wind energy of typhoons changes more significantly than that of normal wind. More than 80% of the vibration energy is concentrated in the frequency band (0–1.5625 Hz) under typhoons, while nearly 90% of the vibration energy under normal winds is evenly distributed in three frequency bands (0–1.5625 Hz, 1.5625–3.125 Hz, and 3.125–4.6875 Hz). When using typhoon-induced dynamic responses as input, the SSI-DATA method performs better than the PP method in the identification of modal parameters. The results obtained in this study can be used as a baseline for future structural condition assessment of the bridge after typhoon events. | Monitoring-based evaluation of dynamic characteristics of a long span suspension bridge under typhoons | 10.1007/s13349-020-00458-5 |
2021-04-01 | This paper focuses on the performance-based seismic design (PBSD) methodology of multi-story concentrically braced frames (CBFs) equipped with a novel brace, i.e., the shape memory alloy (SMA)-friction damping brace (SMAFDB). The fundamental response characteristics of the framing structure are first understood through nonlinear response history analysis on the equivalent single-degree-of-freedom (SDOF) systems. The parameters varied in the SDOF analyses are the period of vibration ( T ), the strength reduction factor ( R ), and the normalized friction slip displacement ( μ _ f ). The seismic response indexes of interest are the peak displacement, the ductility, the residual displacement and the peak acceleration. Relationships are built between the seismic response indexes and parameters of T , R and μ _ f . Then, the SDOF-based results are explored to develop the PBSD methodology, which defines the peak interstory drift, the peak floor acceleration and the residual interstory drift as the performance targets. To demonstrate and validate the proposed design methodology, the six-story prototype CBFs equipped with SMAFDBs are designed and then subjected to ground motions associated with hazard levels of design basis earthquakes (DBE) and maximum considered earthquakes (MCE). The performance evaluation results indicate that the frames can be effectively designed to meet the targeted performance objectives at the DBE level. It also indicates that the frames maintain seismic-resisting capacity at the MCE level. | Performance-based seismic design of multi-story CBFs equipped with SMA-friction damping braces | 10.1007/s10518-021-01060-w |
2021-04-01 | Suspension bridges due to their long span are susceptible against dynamic events, like air flow which can cause considerable problems for them. Flutter, as an aerodynamic phenomenon, makes bridges vibrate, whereas their amplitude gradually diverges, needed the vibration control strategies. Tuned mass damper or in brief TMD, as the simplest passive device, can be used for this purpose. The performance of it can be enhanced when it’s parameters are adjusted to their optimum values. In this paper, the TMD was optimized by meta-heuristic optimization algorithms to control the flutter of long span suspension bridges. In this regard, the Golden Gate suspension bridge and Car tracking algorithm were selected for case study and optimization process, respectively. Firstly, the flutter analysis of bridge was done by multi-mode method in the time domain, and at second part, the TMD’s parameters were simultaneously optimized for maximum increase of flutter velocity of all the vulnerable modes. The results indicated that TMD was perfectly suitable device to control the flutter of long span bridges. | Flutter Control of Long Span Suspension Bridges in Time Domain Using Optimized TMD | 10.1007/s13296-021-00469-y |
2021-04-01 | This article explores that the study on bending of magneto-electric-elastic nanobeams relies on nonlocal elasticity theory. The Vlasov’s model foundation utilizes the silica aerogel foundation. The guiding expressions of nonlocal nanobeams in the considered framework are used extensively and where parabolic third-order beam theory is achieved after using Hamilton’s principle. Parametric work is introduced to scrutinize the influence of the magneto-electro-mechanical loadings, nonlocal parameter, and aspect ratio on the deflection characteristics of nanobeams. It is noticed that the boundary conditions, nonlocal parameter, and beam geometrical parameters have significant effects on dimensionless deflection of nanoscale beams. | Magneto-electro-elastic analysis of piezoelectric–flexoelectric nanobeams rested on silica aerogel foundation | 10.1007/s00366-019-00869-z |
2021-04-01 | Untreated and treated jute fiber and nano-clay in various ratios were used to fabricate jute/nano-clay/epoxy hybrid composites through compression molding method. The dynamic mechanical and free vibration behaviours were evaluated by varying the concentration of NaOH (2.5%, 5% and 7.5%) and wt.% of nano-clay (1, 3, 5 and 7 wt.%). Experimental outcomes disclosed that the storage and loss modulus, damping factor and natural frequency are influenced by concentration of NaOH solution and nano-clay content. A positive shift (towards higher temperature) in glass transition temperature and enhanced natural frequency of the composites after NaOH treatment and nano-clay addition confirmed that superior interfacial bonding exists between the jute fibers and epoxy matrix. Finally, the composites incorporated with 5% treated fiber and 5 wt.% of nano-clay is suggested for low strength structural applications in construction and automobile industries. | Dynamic Mechanical Properties and Free Vibration Characteristics of Surface Modified Jute Fiber/Nano-Clay Reinforced Epoxy Composites | 10.1007/s10924-020-01945-y |
2021-04-01 | This paper aims to improve the use of continuous wavelet transform (CWT) to identify the damping parameters from the free decay responses of structures. Numerical response functions (impulse response functions) were simulated with lower frequencies and higher damping parameters using the Hilbert Transform, and the damping parameters were estimated by extracting wavelet coefficients that corresponded to the frequency components of these numerical response functions. Numerical simulations were also performed on single-, separated- and closed-mode systems to analyze the effect of the center frequency of the mother wavelet on the estimation of system damping parameters. Experiments were performed on a two-span H-Beam. This study focuses on the damping parameter estimation errors for the center frequency setting of the mother wavelet function. The reliability of the estimated damping parameters can be improved by selecting the center frequencies of the mother wavelet function so that each corresponding scale is localized at half of the total scale. | Analysis of Center Frequency Effect on Damping Parameters Estimation Using Continuous Wavelet Transform | 10.1007/s12205-021-1255-7 |
2021-04-01 | Among the different functional properties provided by shape memory alloys (SMA), the damping attracted increasing interest in the last decades. Particularly, the exploitation of pseudo-elastic properties to damp or prevent the oscillations of physical systems has received wide attention in civil engineering. In this context and in other practical applications, intrinsic damping properties at low strains are not yet well explored. To fill this gap, in this work, a systematic approach was taken to study the internal friction (IF) coefficient of several NiTi and NiTiCu SMA by tuning the microstructural condition through different thermal treatments. The changing of IF with respect to temperature in tensile, flexural and torsional configurations has been considered; tests have been accomplished at a solicitation strain in the order of 10^−4 and at four frequencies (0.5, 1, 10 and 50 Hz). Results allow a broad overview of the intrinsic properties of the considered alloys with encouraging prospect for future applications. A reference scheme was reported in order to individuate the best SMA candidate in the light of the requirements in a wide range of possible applications, being a helpful guideline for the ideation and the design of novel devices. | Internal Friction Parameter in Shape Memory Alloys: Correlation Between Thermomechanical Conditions and Damping Properties in NiTi and NiTiCu at Different Temperatures | 10.1007/s11665-021-05609-3 |
2021-04-01 | Seismic modeling of massive structures requires special caution, as wave propagation effects significantly affect the responses. This becomes more crucial when the path-dependent behavior of the material is considered. The coexistence of these conditions renders numerical earthquake analysis of concrete dams challenging. Herein, a finite element model for a comprehensive nonlinear seismic simulation of concrete gravity dams, including realistic soil-structure interactions, is introduced. A semi-infinite medium is formulated based on the domain reduction method in conjunction with standard viscous boundaries. Accurate representation of radiation damping in a half-space medium and wave propagation effects in a massed foundation are verified using an analytical solution of vertically propagating shear waves in a viscoelastic half-space domain. A rigorous nonlinear finite element model requires a precise description of the material response. Hence, a microplane-based anisotropic damage-plastic model of concrete is formulated to reproduce irreversible deformations and tensorial degeneration of concrete in a coupled and rate-dependent manner. Finally, the Koyna concrete gravity dam is analyzed based on different assumptions of foundation, concrete response, and reservoir conditions. Comparison between responses obtained based on conventional assumptions with the results of the presented comprehensive model indicates the significance of considering radiation damping and employing a rigorous constitutive material model, which is pursued for the presented model. | Effect of seismic wave propagation in massed medium on rate-dependent anisotropic damage growth in concrete gravity dams | 10.1007/s11709-021-0694-z |
2021-04-01 | In order to study the mechanical property degradation rule of Q690 high-strength steel in the ocean wave splash area, the rusted specimen is obtained by indoor damp heat surrounding soaking environment corrosion test. The scanning electron microscopy, uniaxial tensile and cyclic loading tests of corroded steel are performed. This paper analyzes the steel from elastic modulus, yield strength, ductility and law of hysteresis degradation under different corrosion cycles and establishes the constitutive model of HSS. The results show that the appearance of HSS is obviously affected by the corrosion cycle. With the increase of the corrosion cycle, reddish-brown flaky corrosion products are formed on the surface of the steel and there are obvious corrosion pits. After 100 days of corrosion, the corrosion rate of steel reached 7.21%; the elastic modulus and yield strength under uniaxial tension load decreased by 10.2% and 4.9%. Under the effect of cyclic reciprocating load, the hysteretic energy is reduced by 15.3%; at the same time, the test curve is fitted by the secondary plastic flow model and the Ramberg–Osgood model and it is found that the shape parameter S_1 and the cyclic strengthening coefficient K' are reduced by 20.1% and 10.2%, While the shape parameter S_2 and the cycle strengthening index n' have no obvious changes. | Experimental Study on Mechanical Properties of Q690 High Strength Steel in Marine Corrosive Environment | 10.1007/s13296-021-00468-z |
2021-04-01 | Retrofitting buildings in densely populated areas with a soft story configuration on the first floor can pose a daunting challenge to the community. Against this backdrop, this study set out to evaluate the seismic retrofit strategy's adequacy in enhancing the seismic performance of buildings with a soft story. The proposed strategy utilizes an earthquake energy dissipation device consisting of a combination of a diagonal brace and a metallic-yielding damper at the ground story level. Two prototype buildings, one with five and the other with ten floors, were chosen to assess the proposed retrofit strategy's seismic response through nonlinear static and dynamic analyses. The seismic capacity, lateral displacement response, maximum inter-story drift ratio, energy dissipation, and collapse fragility are the major response parameters used to compare original and retrofitted buildings. The nonlinear static analysis results revealed that the seismic capacity for buildings equipped with a yielding damper was higher than that of the original buildings. It was also found that retrofitted frame buildings had a desirable structural behavior with a higher value of dissipated energy and a lower value of residual displacements and inter-story drift ratio, in turn reducing the likelihood of soft-story failure. | Numerical Investigation of Energy Dissipation Device to Improve Seismic Response of Existing Steel Buildings with Soft-First-Story | 10.1007/s13296-021-00466-1 |
2021-04-01 | We studied a new implicit method of order three based on two off-step points for the numerical solution of second-order nonlinear initial-value problems $$y^{\prime\prime} = f(t,y,y^{\prime}),\;y(t_{0} ) = \gamma_{0}$$ y ″ = f ( t , y , y ′ ) , y ( t 0 ) = γ 0 , $$y^{\prime}(t_{0} ) = \gamma_{1}$$ y ′ ( t 0 ) = γ 1 on a graded mesh. In practice, only a monotonically decreasing mesh will be employed. We applied the proposed method to a test equation $$y^{\prime\prime} + 2\alpha y^{\prime} + \beta^{2} y = g(t), \quad \alpha > \beta \ge 0,$$ y ″ + 2 α y ′ + β 2 y = g ( t ) , α > β ≥ 0 , and analyse the stability which is absolutely stable for a graded mesh and superstable for a uniform mesh. The proposed method is applicable to solve singular problems. Seven benchmark problems including three boundary layer problems are solved to demonstrate the stability and utility of the method discussed. Numerical results are given to confirm the usefulness of the developed method. | Absolute stability of an implicit method based on third-order off-step discretization for the initial-value problem on a graded mesh | 10.1007/s00366-019-00857-3 |
2021-03-28 | During an earthquake, adjacent buildings with insufficient separations often collide into each imposing unexpected impact loading on buildings causing severe damage and even collapse of many buildings. In the present study, the passive control of closely spaced fixed base structures is investigated under the effects of earthquakes and blast-induced vibrations. The study analyzes two closely spaced dynamically dissimilar fixed base buildings connected using linear and nonlinear fluid viscous dampers when subjected to blast and seismic excitations. A parametric study on the damping coefficient of fluid dampers is conducted to obtain an optimum damping coefficient for linear and nonlinear fluid viscous dampers. The present study investigates the comparative performance behavior of the linear and nonlinear dampers in response reduction of adjacent buildings under blast and earthquake motions. The placement of dampers in the response mitigation due to the selected excitations is also reviewed. Results exhibit the efficiency of viscous dampers in reducing the structural responses of flexible buildings. It is also concluded that the placement of dampers at the top floor alone yields significant reduction in the structural responses when compared with the placement of dampers at all floors. | Performance of Linear and Nonlinear damper connected buildings under blast and seismic excitations | 10.1007/s41062-021-00502-3 |
2021-03-26 | The paper deals with the numerical solution of 2D wave propagation exterior problems including viscous and material damping coefficients and equipped by Neumann boundary condition, hence modeling the hard scattering of damped waves. The differential problem, which includes, besides diffusion, advection and reaction terms, is written as a space–time boundary integral equation (BIE) whose kernel is given by the hypersingular fundamental solution of the 2D damped waves operator. The resulting BIE is solved by a modified Energetic Boundary Element Method, where a suitable kernel treatment is introduced for the evaluation of the discretization linear system matrix entries represented by space–time quadruple integrals with hypersingular kernel in space variables. A wide variety of numerical results, obtained varying both damping coefficients and discretization parameters, is presented and shows accuracy and stability of the proposed technique, confirming what was theoretically proved for the simpler undamped case. Post-processing phase is also taken into account, giving the approximate solution of the exterior differential problem involving damped waves propagation around disconnected obstacles and bounded domains. | Energetic boundary element method for accurate solution of damped waves hard scattering problems | 10.1007/s10665-021-10100-y |
2021-03-23 | This work considers a mathematical model describing a dynamic frictional contact between a viscoelastic body and an adhesive foundation. The contact is modeled with normal damped response condition associated with a new version of Coulomb’s law of dry friction with adhesion introducing a new term which gives a better transition from adhesion to friction. We present a variational formulation of the problem which is given as a system coupling an evolution inequality of the second order for the displacement and a differential equation of the first order for the bonding field. We establish the existence and uniqueness of the weak solution. The proof is based on parabolic variational inequalities of the second kind, differential equations and fixed point theorem. | Dynamic Contact Problem with Normal Damped Response, Friction and Adhesion | 10.1007/s00009-021-01740-6 |
2021-03-22 | This paper presents a general methodology for the analysis and synthesis of a positive semi-definite system described by mass, damping and stiffness matrices that is often encountered in impedance control in robotics research. This general methodology utilizes the fundamental kinematic concept of rigid-body and non-rigid-body motions of which all motions consist. The rigid-body mode results in no net change in the potential energy from the stiffness matrix of the multiple degree-of-freedom (DoF) discrete mechanical system. Example of an unconstrained discrete mechanical system is presented to illustrate the theoretical principle as applied in obtaining the free and forced vibration responses, as well as the dynamic characteristics of the system in natural frequency, $$\omega_n$$ ω n and damping ratio, $$\zeta$$ ζ . In addition, the methodology is applied to the impedance control of redundant robots. The rigid-body mode is equivalent to the motions of a redundant robot which result in no net change in potential energy, also called the zero-potential or ZP mode, of impedance control. Example of a redundant robot is used to demonstrate the application of the methodology in robotics. The dynamic characteristics of $$\omega _n$$ ω n and $$\zeta$$ ζ in the modal space are analyzed, which can be synthesized to modulate the damping of the system analytically. | Analytical methodology for the analysis of vibration for unconstrained discrete systems and applications to impedance control of redundant robots | 10.1186/s40648-021-00199-0 |
2021-03-20 | The present work is aimed at deriving a finite element model for active constraining layer damping treatment (ACLD) of layered skew plates by incorporating zig-zag behaviour using a Murakami zig-zag function (MZZF). The ACLD in skew patch form comprises of 1–3 PZC material and viscoelastic material in the layer form placed on substrate skew plate. The overall skew substrate ACLD system deformation kinematics are derived using MZZF and the equations of motion for the same are derived by virtual work method. A MATLAB subroutine for the overall skew plate ACLD system has been developed to present the closed loop frequency responses by successful implementation of closed-loop feedback system. The substrate skew plates with different lamination schemes namely symmetric/antisymmetric cross-ply and antisymmetric angle-ply are considered to assess the damping behavior of the skew plates undergoing ACLD. Also, the piezo-fiber angle (obliquely reinforced) variation of the PZC layer on the damping responses of the skew plates have been thoroughly examined. | Smart damping of skew composite plates using Murakami zig-zag function | 10.1007/s42452-021-04426-6 |
2021-03-18 | In this paper, we consider a variable coefficient thermo-viscoelastic-coupled system of second sound with acoustic boundary conditions, where the heat conduction is given by Cattaneo’s law. We establish a general decay of energy-associated solutions under a class of generality of the relaxation function. Our result extends the various decay results obtained for problems with or without thermo-viscoelasticity. | New general stability for a variable coefficient thermo-viscoelastic-coupled system of second sound with acoustic boundary conditions | 10.1007/s40314-021-01459-w |
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