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2020-10-22 | In this paper, we consider the Cauchy problem for a generalized Boussinesq equation with double damping terms. By using improved convexity method combined with potential well method and Fourier transform, we show the finite time blow-up of the solution with arbitrarily high initial energy while many similar results require the corresponding energy to be less than some certain numbers. | Blow-up for Generalized Boussinesq Equation with Double Damping Terms | 10.1007/s00009-020-01604-5 |
2020-10-19 | We consider the initial boundary value problem in exterior domain for strongly damped wave equations with power-type nonlinearity $$|u|^p$$ | u | p . We will establish blow-up results under some conditions on the initial data and the exponent p , using the method of test function with an appropriate harmonic functions. We also study the existence of mild solution and its relation with the weak formulation. | Finite Time Blow-Up for Wave Equations with Strong Damping in an Exterior Domain | 10.1007/s00009-020-01607-2 |
2020-10-17 | The paper presents a case study of a small off-road vehicle and its response to ground excitations regarding the geometrical suspension properties and the variation of adjustable damping parameters, that can change restoring force in fast bump, slow bump and rebound zones. The shock absorber behaviour in force–velocity graphs is obtained from experimental data and introduced in the simulation by a lookup table strategy, without a mathematical model describing the damping behaviour. The analysis is done through a seven degrees-of-freedom model, describing the full vehicle, and assembled in a state space form. Ground excitations are inserted as wheel displacement from random road vibrations and a single road bump, with the use of a roller contact model. The acceleration transmitted to the driver is compared to comfort standards to verify possible discomfort or danger to health damages in long exposure. The outputs are validated with linear potentiometers, showing that the model can accurately predict the shock absorbers behaviour and, consequently, the accelerations transmitted to the driver. To the shock absorbers studied, low bump velocities do not affect significantly exposure risk to vibrations and present a small comfort improvement. Otherwise, through road bumps, a softer regulation ensures a better performance, reducing sprung mass displacement in 31% and accelerations transmitted in 33% at the shock absorber regulation range. | Assessment of adjustable damping in the ride comfort of a baja SAE vehicle | 10.1007/s40430-020-02660-4 |
2020-10-17 | A priori bounds constitute a crucial and powerful tool in the investigation of initial boundary value problems for linear and nonlinear fractional and integer order differential equations in bounded domains. We present herein a collection of a priori estimates of the solution for an initial boundary value problem for a singular fractional evolution equation (generalized time-fractional wave equation) with mass absorption. The Riemann–Liouville derivative is employed. Results of uniqueness and dependence of the solution upon the data were obtained in two cases, the damped and the undamped case. The uniqueness and continuous dependence (stability of solution) of the solution follows from the obtained a priori estimates in fractional Sobolev spaces. These spaces give what are called weak solutions to our partial differential equations (they are based on the notion of the weak derivatives). The method of energy inequalities is used to obtain different a priori estimates. | A priori bounds of the solution of a one point IBVP for a singular fractional evolution equation | 10.1186/s13662-020-03049-2 |
2020-10-06 | The aim of this work is to improve the oscillation results for second-order neutral differential equations with damping term. We consider the noncanonical case which always leads to two independent conditions for oscillation. We are working to improve related results by simplifying the conditions, based on taking a different approach that leads to one condition. Moreover, we obtain different forms of conditions to expand the application area. An example is also given to demonstrate the applicability and strength of the obtained conditions over known ones. | Amended oscillation criteria for second-order neutral differential equations with damping term | 10.1186/s13662-020-03013-0 |
2020-10-05 | Machine foundations are generally affected by the vibratory shocks from different machines. The behavior of these foundations is influenced by the properties of underlying soil and the excitation frequency of the applied dynamic load. The influence of material damping on the dynamic impedance functions of a circular disk embedded in homogeneous elastic half space is analyzed using one-dimensional wave propagation in cones (cone model) and the results are presented in the form of dimensionless plots to observe the more realistic response of machine foundations. Three different types of material damping models viz., Hysteretic, Voigt and Kelvin model are introduced in the above elastic solutions using correspondence principle. The spring and damping coefficients of the embedded foundation are then computed in a wide range of frequency of excitation under vertical and horizontal mode of vibration varying the influencing parameters namely dimensionless frequency ( a _0), Poisson’s ratio ( ν ), embedment ratio ( e / r _0) and damping ratio ( ξ ). The outcomes from the present analysis suggest that the spring coefficient is nonlinearly affected by the dimensionless frequency and embedment ratio, for both the modes of vibration. The effect of material damping on spring coefficient is only significant for a _0> 2, irrespective of the damping model used. | Effect of material damping on the impedance functions of an embedded circular foundation under vertical and horizontal excitation | 10.1007/s41062-020-00370-3 |
2020-10-01 | In this paper we prove that every compact invariant subset $$\mathscr{A}$$ associated with the semigroup S _ n,k ( t )_ t ≥0 generated by wave equations with variable damping, either in the interior or on the boundary of the domain where Ω ⊂ ℝ^3 is a smooth bounded domain, in H _0 ^1 (Ω) × L ^2(Ω) is in fact bounded in D ( B _0) × H _0 ^1 (Ω). As an application of our results, we obtain the upper-semicontinuity for global attractor of the weakly damped semilinear wave equation in the norm of H ^1(Ω) × L ^2(Ω) when the interior variable damping converges to the boundary damping in the sense of distributions. | Regularity of Invariant Sets in Variable Internal Damped Wave Equations | 10.1007/s10255-020-0978-4 |
2020-10-01 | Aiming at the problem of global climate change and energy crisis, wind power has become the focus of energy sustainable development in all countries. The wind turbines (WTs) power system is connected to the grid via the power electronic converter, causing the system inertia level to drop. In this paper, the direct-drive WT system is considered as the research object, and the whole-system frequency response model is established. The inertia and damping characteristics of the WT converter systems with virtual inertia control are analyzed. With the support of fan rotor kinetic energy and the energy saved in a capacitor, the simple control can also make the system exhibit different degrees of inertia and damping features. The results show that the equivalent inertia and the WT inertia time constant, capacitance parameters and virtual control parameters k _d are related; the equivalent damping parameter is related to the steady-state operating point parameters and the virtual control parameter k _p; the equivalent synchronization parameter is related to the steady-state operating point parameters and the virtual inertia control parameter k _i. Finally, the correctness of the inertial and damping characteristics of the WT grid-connected system is verified by simulation, which provides a theoretical reference for studying the inertial damping of power electronic dominant systems. | Modeling and mechanism analysis of inertia and damping issues for wind turbines PMSG grid-connected system | 10.1007/s00500-020-04897-6 |
2020-10-01 | Based on the Hamilton’s principle, a nonlinear mathematical model of the cantilever-type piezoelectric energy harvester with a tip mass is systematically derived under parametric and external excitations. The proposed model accounts for geometric and electro-mechanical coupling nonlinearities, damping nonlinearity and the inextensibility condition of beam. Using the Galerkin approach, the proposed model is converted into the electro-mechanical coupling Mathieu–Duffing equations. Analytical solutions of the frequency–response curves are presented by the multiple scales method. Nonlinear characteristics of the energy harvesters are explored under parametric excitation and hybrid parametric and external excitations. Analytical results provided new insights into the effects of tip mass and nonlinear damping on the performance of the energy harvester. The results show that with the tip mass increasing, the frequency–response curves of the energy harvester change from the nonlinear hardening type to the nonlinear softening type and the operating bandwidth and the output voltages of the energy harvester enlarge. For parametrical excitation, variation of the quadratic damping does not alter the initial threshold of the harvesters and the position of two transcritical bifurcation points of the frequency–response curves. The initiation threshold decreases with the tip mass increasing. Hybrid parametric and external excitations enhance the bandwidth and output voltage of the energy harvester, which will probably be used as an ideal way to improve the performance of the energy harvesting system. | Performance analysis of piezoelectric energy harvesters with a tip mass and nonlinearities of geometry and damping under parametric and external excitations | 10.1007/s00419-020-01721-3 |
2020-10-01 | Purpose A randomly excited spring–damper–mass system placed on a uniformly moving belt is investigated with the consideration of the Coulomb friction between the system and the belt. The system response is analytically studied. The physical essence of friction and the influences of the belt speed, the friction amplitude and the excitation intensity on the random responses are discussed in detail. Methods The random response of the system is studied through the equivalent nonlinear system method. The influence of the friction between the mass block and the belt on the random response is approximated by dissipative and conservative components. The dissipative component is expressed by a linear damping and an energy-dependent nonlinear damping with undetermined coefficients while the conservative component is represented by an undetermined constant force and a restoring force with undetermined linear and cubic nonlinear stiffness coefficients. The undetermined coefficients are derived by minimizing the mean-square difference between the original system and the equivalent nonlinear system. The approximate analytical solutions are compared with the results by the Monte-Carlo simulation to validate the proposed procedure. Results The proposed procedure gives the formally analytical expression of stationary response probability density of spring–damper–mass–belt system. It is found that the proposed procedure is valid for small values of friction amplitude and is effective for a large range of excitation intensity. Contrary to physical intuition, the friction between block and moving belt can exhibit dissipative and conservative mechanisms simultaneously. Moreover, the dissipative and conservative mechanisms of friction compete with each other regarding the variation of belt speed. The friction amplitude and the excitation intensity also have noticeable effects on the distribution of dissipation and conversation of friction. | Random Response of Spring–Damper–Mass–Belt System with Coulomb Friction | 10.1007/s42417-019-00168-3 |
2020-10-01 | Abstract The paper presents a generalization of the conventional analytical approach where the quasi-steady theory is utilised to evaluate the across-wind aerodynamic damping of slender single beam structures. This generalized theory considers the variation of structural and aerodynamic parameters along the structural height, together with the nature of the vertical wind profile and mode shapes. Closed-form solutions for typical uniform and tapered tall buildings are given. A numerical application on a prototype tall building shows that the conventional method may be oversimplified, which results in incorrect predictions of the aerodynamic damping. Graphic Abstract | Predicted aerodynamic damping of slender single beam structures in across-wind vibrations | 10.1007/s10409-020-00981-0 |
2020-10-01 | In this paper, the Discrete Sources Method has been extended to describe the influence of the geometry asymmetry of a core-shell particle accounting for the effect of spatial dispersion inside the plasmonic metal shell. We found that varying the plasmonic shell thickness has more influence on the near field intensity distribution then on the average enhancement factor. Besides, we demonstrates that the effect of spatial dispersion can decrease the near field intensity up to 60% of its value and it provides a small blue shift. | Discrete Sources Method for Investigation of the Influence of Geometry Asymmetry of Core-Shell Particles Accounting For Spatial Dispersion | 10.1007/s10598-021-09506-1 |
2020-10-01 | Abstract — The structural state of iodide titanium after deformation by drawing at 77 K, which is the final stage of severe plastic deformation (SPD), has been analyzed and estimated in this work. The SPD has been implemented by a sequential combination of deformation techniques (compression-squirting-extrusion-drawing) that provide different stress epures. The temperature dependence of the logarithmic damping decrement of torsional oscillations in the 77–250 K temperature range has been studied to give a physical interpretation of the nonmonotonic change in the strength of the iodide titanium after SPD and to compare the calculated strength with that obtained for low purity titanium. | Analysis of the Structural State Formed in Titanium at the Final Severe Plastic Deformation Stage | 10.1134/S0031918X20090100 |
2020-10-01 | In this study, we develop an analytical formula to approximate the damping coefficient as a function of the coefficient of restitution for a class of continuous contact models. The contact force is generated by a logical point-to-point force element consisting of a linear damper connected in parallel to a spring with Hertz force–penetration characteristic, while the exponent of deformation of the Hertz spring can vary between one and two. In this nonlinear model, it is assumed that the bodies start to separate when the contact force becomes zero. After separation, either the restitution continues or a permanent penetration is achieved. Therefore, this model is capable of addressing a wide range of impact problems. Herein, we apply an optimization strategy on the solution of the equations governing the dynamics of the penetration, ensuring that the desired restitution is reproduced at the time of separation. Furthermore, based on the results of the optimization process along with analytical investigations, the resulting optimal damping coefficient is analytically expressed at the time of impact in terms of system properties such as the effective mass, penetration velocity just before the impact, coefficient of restitution, and the characteristics of the Hertz spring model. | Optimal damping coefficient for a class of continuous contact models | 10.1007/s11044-020-09745-x |
2020-10-01 | Abstract This study is a continuation of the article “Formulation and solution of a generalized Chebyshev problem: First Part,” in which a generalized Chebyshev problem was formulated and two theories of motion for nonholonomic systems with higher order constraints were presented for its solution. These theories were used to study the motion of the Earth’s satellite when fixing the magnitude of its acceleration (this was equivalent to imposing a third-order linear nonholonomic constraint). In this article, the second theory, based on the application of the generalized Gauss principle, is used to solve one of the most important problems of control theory: finding the optimal control force that translates a mechanical system with a finite number of degrees of freedom from one phase state to another in the specified time period. The application of the theory is demonstrated by solving the model problem of controlling the horizontal motion of a cart bearing the axes of s mathematical pendulums. Initially, the problem is solved by applying the Pontryagin maximum principle, which minimizes the functional of the square of the desired horizontal control force, which transfers the mechanical system from a motionless state to a new motionless state in the specified time period with the cart’s horizontal displacement S (the vibration damping problem is considered). This approach is called the first method for solving the control problem. It is shown that a (2 s + 4)-order linear nonholonomic constraint is continuously fulfilled. This suggests applying the second theory of motion for nonholonomic systems with higher order constraints to the same problem (see the previous article), the theory developed at the Department of Theoretical and Applied Mechanics of the Faculty of Mathematics and Mechanics of St. Petersburg State University. This approach is called the second method for solving the problem. Calculations are performed for the case s = 2 and show that the results of both methods are practically identical for a short motion of the system but they differ substantially for a long motion. This is due to fact that the control determined using the first method contains harmonics with the system’s natural frequencies, which tends to bring the system into resonance. For a short motion this is not noticeable, and for a long motion there are large fluctuations in the system. In contrast, when the second method is used, the control is polynomial in time, which provides a relatively smooth motion of the system. In addition, in order to eliminate the jumps in the control force at the beginning and end of the motion, it is proposed to solve the generalized boundary value problem. Some special cases occurring when using the second method for solving the boundary value problem are discussed. | Formulation and Solution of a Generalized Chebyshev Problem: Second Part | 10.1134/S1063454120040111 |
2020-10-01 | In this paper, it is proposed a quantization procedure for the one-dimensional harmonic oscillator with time-dependent frequency, time-dependent driven force, and time-dependent dissipative term. The method is based on the construction of dynamical invariants previously proposed by the authors, in which fundamental importance is given to the linear invariants of the oscillator. | Dynamical Invariants and Quantization of the One-Dimensional Time-Dependent, Damped, and Driven Harmonic Oscillator | 10.1007/s13538-020-00765-8 |
2020-10-01 | Damping ratio is an important and central parameter for the dynamic analysis of structures. The present study focuses on the estimation of the equivalent damping ratio in a post-yield region for RC frames, both with and without infills. One-story one-bay RC frames casted non-integrally with fly ash (FA) bricks and autoclaved aerated concrete (AAC) blocks infills are considered and are tested under monotonic lateral half-cycle loading. Post-yield behavior parameters, displacement ductility and maximum drift ratio, are used to estimate the equivalent damping ratio at each cycle of lateral loading, and empirical relationships are established. Secant stiffness and stiffness degradation for RC frames are also extracted to determine the contribution and effectiveness of type of infills. Free vibration tests on RC frame specimens are conducted subsequent to each cycle of monotonic lateral loading, and the damping ratio is evaluated. It is found that the equivalent damping ratio substantially increases for RC frames with the onset of damage in the post-yield region. The major advantage of the infilled RC frame is a drastic reduction in the maximum drift ratio. However, types of infill are found to yield equivalent damping ratio at par, suggesting similar energy dissipation capabilities. RC frame infilled with AAC block is recommended due to its higher initial as well as secant stiffness vis- $$\grave{a}$$ a ` -vis FA brick-infilled RC frames and higher stiffness degradation that allows it to behave similar to RC frame without infill. | Post-yield Damping Ratio Estimation Studies for Masonry-Infilled Reinforced Concrete Frames | 10.1007/s40996-019-00342-3 |
2020-10-01 | This study proposes a new method toward optimizing the design of non-conventional tuned mass dampers in multi-degree-of-freedom systems. An important application of the proposed method is in mega-sub-controlled structures in which the seismic vibration of the system is controlled by using isolated sub-structures. The method estimates the optimum parameters of the sub-structures including frequency ratio and damping ratio based on formulations derived for optimal design of SDOF systems with tuned mass dampers. The method is verified by comparing the results with a numerical method. It is shown that the proposed method returns the optimum parameters with acceptable accuracy (less than 5% difference from numerical results), and in some cases the results are identical to the numerical method. In the final part, the method is applied to three mega-structures with different control systems in order to examine its accuracy in predicting the optimum parameters of the non-conventional tuned mass dampers. It is concluded that the method is efficient and can be used for optimal design of such systems. | Toward Optimizing Dynamic Characteristics of Non-conventional TMDs in Multi-degree-of-Freedom Systems | 10.1007/s40996-019-00338-z |
2020-10-01 | In this paper we consider the situation that three identical two-level atoms resonantly interact with three distant single-mode optical cavities via a one-photon hopping separately, and there exist the phenomena of atom-decay and cavity-decay. Under Jaynes-Cummings model the time evolution of the system is given. The tripartite negativity is used to quantify the degree of tripartite entanglement. The tripartite entanglement dynamics among atoms and among cavities are studied. The influences of the atom-decay and the cavity-decay on tripartite entanglement are discussed. The results obtained using the numerical method show that the tripartite entanglement among atoms and that among cavities all display damping oscillation behavior. On the other hand, as the atomic decay rate increases, their decays are accelerated, and so do they with the increase of cavity decay rate. | Tripartite Entanglement Dynamics in the System Consisting of Three Damping Jaynes-Cummings Models | 10.1007/s10773-020-04574-2 |
2020-10-01 | A numerical model is proposed for analyzing the effects of added mass and damping on the dynamic behaviors of hydrofoils. Strongly coupled fluid-structure interactions (FSIs) of hydrofoils are analyzed by using the 3-D panel method for the fluid and the finite element method for the hydrofoils. The added mass and damping matrices due to the external fluid of the hydrofoil are asymmetric and computational inefficient. The computational inefficiencies associated with these asymmetric matrices are overcome by using a modal reduction technique, in which the first several wet mode vectors of the hydrofoil are employed in the analysis of the FSI problem. The discretized system of equations of motion for the hydrofoil are solved using the Wilson- θ method. The present methods are validated by comparing the computed results with those obtained from the finite element analysis. It is found that the stationary flow is sufficient for determining the wet modes of the hydrofoil under the condition of single-phase potential flow and without phase change. In the case of relatively large inflow velocity, the added damping of the fluid can significantly affect the structural responses of the hydrofoil. | Numerical analysis of added mass and damping of elastic hydrofoils | 10.1007/s42241-020-0066-5 |
2020-10-01 | Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing motor neuron degenerative disease that is without effective treatment. The receptor for advanced glycation end products (RAGE) is a major component of the innate immune system that has been implicated in ALS pathogenesis. However, the contribution of RAGE signalling to the neuroinflammation that underlies ALS neurodegeneration remains unknown. The present study therefore generated SOD1^G93A mice lacking RAGE and compared them with SOD1^G93A transgenic ALS mice in respect to disease progression (i.e. body weight, survival and muscle strength), neuroinflammation and denervation markers in the spinal cord and tibialis anterior muscle. We found that complete absence of RAGE signalling exerted a protective effect on SOD1^G93A pathology, slowing disease progression and significantly extending survival by ~ 3 weeks and improving motor function (rotarod and grip strength). This was associated with reduced microgliosis, cytokines, innate immune factors (complement, TLRs, inflammasomes), and oxidative stress in the spinal cord, and a reduction of denervation markers in the tibialis anterior muscle. We also documented that RAGE mRNA expression was significantly increased in the spinal cord and muscles of preclinical SOD1 and TDP43 models of ALS, supporting a widespread involvement for RAGE in ALS pathology. In summary, our results indicate that RAGE signalling drives neuroinflammation and contributes to neurodegeneration in ALS and highlights RAGE as a potential immune therapeutic target for ALS. | Absence of Receptor for Advanced Glycation End Product (RAGE) Reduces Inflammation and Extends Survival in the hSOD1^G93A Mouse Model of Amyotrophic Lateral Sclerosis | 10.1007/s12035-020-02019-9 |
2020-09-28 | In this paper, we consider large time behaviour of solutions to the 3D Navier–Stokes equations with damping term $$|u|^{\beta -1}u$$ | u | β - 1 u ( $$\beta \ge 1$$ β ≥ 1 ). For $$\beta >\frac{7}{3}$$ β > 7 3 , we derive decay rates of the $$L^2$$ L 2 -norm of the solutions. By using Fourier splitting method, we also prove that the solutions are asymptotically equivalent to the solutions of the classic 3D Navier–Stokes equations. | Large time behaviour of solutions to the 3D Navier–Stokes equations with damping | 10.1007/s00033-020-01404-7 |
2020-09-16 | We are interested in studying a system coupling the compressible Navier–Stokes equations with an elastic structure located at the boundary of the fluid domain. Initially the fluid domain is rectangular and the beam is located on the upper side of the rectangle. The elastic structure is modeled by an Euler–Bernoulli damped beam equation. We prove the local in time existence of strong solutions for that coupled system. | Local Existence of Strong Solutions of a Fluid–Structure Interaction Model | 10.1007/s00021-020-00520-8 |
2020-09-11 | In this study, power capture performance of a heaving wave energy converter has been optimized by investigating the effect of variation of power take-off damping. The wave energy converter model used in this study utilizes the sliding discrete Fourier transform technique to estimate the local wave frequency. The power take-off parameters are adjusted according to the estimated wave frequency. As a part of the study, two different cases are evaluated. In the first case, the conventional approach based on using power take-off damping equal to radiation damping which is a function of the estimated wave frequency is considered. In the second part of the study, as a proposed approach, the power take-off damping is calculated with a gain factor. This gain factor varies the hydrodynamic analysis-based frequency-dependent radiation damping by multiplying with it. The results show that the captured power results can be increased from 1.64 to 10.38%, while, in average, the power capture increase covering all datasets is 5.95%. | Power capture performance of a heaving wave energy converter for varying b_rad/b_pto ratio | 10.1007/s42452-020-03230-y |
2020-09-08 | The waste of olive pomace (OP) particle filler was incorporated with glass fiber-reinforced composites (GFRP)/epoxy resin to manufacture OP particles-modified GFRP composites. Different weight ratios (0.5, 1, 2, 5, 10, and 15 wt%) of OP particles were incorporated within the common matrix of epoxy resin to investigate the effects of OP particles on tensile, flexural, and vibration damping properties on GFRP composites. In the mechanical tests, addition of OP filler contributed the significantly enhancement in tensile and flexural modulus, and samples at 5 wt% of OP filler showed highest flexural and tensile strength, while further addition of OP filler resulted in reduction of maximum elongation value at breaking point. In dynamic tests, it was found that damping ratios of the OP particles included samples were improved by 70% at OP content of 10 wt%, while first-mode natural frequency was reached optimum value at 5 wt% of OP particles, indicating better chemical compatibility at this weight content, and further incorporation of OP particles into the epoxy resin resulted in reduction for both of mechanical and dynamic properties as a result of particle aggregation effects between OP particles–epoxy resin–fiber interfaces. | An experimental investigation on dynamic and mechanical characterization of olive pomace-filled glass/epoxy composite laminates | 10.1007/s40430-020-02592-z |
2020-09-02 | In this paper, we study the initial boundary value problem for a Petrovsky type equation with a memory term, a linear weak damping and superlinear source. Finite time blow-up results have been obtained for the case in which the initial energy $$E(0)\le M$$ E ( 0 ) ≤ M , where M is a positive constant. By utilizing Levine’s classical concavity method, we give a new blow-up criterion which includes the case of $$E(0)>M$$ E ( 0 ) > M and derive an explicit upper bound for the blow-up time. By using the Fountain Theorem, we show that the problem with arbitrary positive initial energy always admits weak solutions blowing up in finite time. | Finite time blow-up for a nonlinear viscoelastic Petrovsky equation with high initial energy | 10.1007/s42985-020-00031-1 |
2020-09-01 | The investigation of soil response to dynamic loads is necessary to predict site-specific seismic hazard. This paper presents the results of cyclic and dynamic laboratory tests carried out after the 2016–2017 Central Italy Earthquake sequence, within the framework of the seismic microzonation studies of the most damaged municipalities in the area. The database consists of 79 samples investigated by means of dynamic resonant column tests, cyclic torsional shear tests or cyclic direct simple shear tests. Results are firstly analysed in terms of field and laboratory values of small-strain shear wave velocity, highlighting the influence of the sample disturbance and of the mean effective consolidation pressure. The cyclic threshold shear strains as a function of plasticity index are then compared with findings from the published literature and the outliers are analysed. Subsequently, the dynamic soil behaviour is investigated with reference to the small-strain damping ratio. Differences between results from different tests are analysed in the light of the loading frequencies. Finally, the database is used to develop a predictive model for soil nonlinear curves according to plasticity index, mean effective confining stress, and loading frequency. The model represents a useful tool to predict the nonlinear stress–strain behaviour of Central Italy soils, necessary to perform site-specific ground response analyses. | Dynamic characterization of fine-grained soils in Central Italy by laboratory testing | 10.1007/s10518-019-00611-6 |
2020-09-01 | The purpose of this work is to investigate the stabilization of a system of weakly coupled wave equations with one or two locally internal Kelvin–Voigt damping and non-smooth coefficient at the interface. The main novelty in this paper is that the considered system is a coupled system and that the geometrical situations covered (see Remarks 5.6, 5.12) are richer than all previous results, even for simple wave equation with Kelvin–Voigt damping. Firstly, using a unique continuation result, we prove that the system is strongly stable. Secondly, we show that the system is not always exponentially stable, instead, we establish some polynomial energy decay estimates. Further, we prove that a polynomial energy decay rate of order $$t^{-1/2}$$ t - 1 / 2 is optimal in some sense. | A transmission problem of a system of weakly coupled wave equations with Kelvin–Voigt dampings and non-smooth coefficient at the interface | 10.1007/s40324-020-00218-x |
2020-09-01 | This paper is concerned with well-posedness and long-time dynamics for a class extensible beams with nonlocal Balakrishnan–Taylor and frictional damping. The related model describes vibrations in nonlinear extensible beams arising in connection with models of oscillation in pipes and supersonic panel flutter. Our main results feature the study of the nonlinear dynamical system generated by the problem. The main novelty is to explore the global $$L^q$$ L q -regularity ( $$q\ge 2$$ q ≥ 2 ) in time of the nonlocal Balakrishnan–Taylor term and show how it generates a dissipative term that plays an important role in the asymptotic behavior of solutions, mainly in what concerns to achieve the useful property of quasi-stability in the theory of infinite-dimensional dynamical systems. | Long-Time Dynamics of Balakrishnan–Taylor Extensible Beams | 10.1007/s10884-019-09766-x |
2020-09-01 | Deployable/retractable damped cantilever beams are a class of time-varying parametric structures which have attracted considerable research interest due to their many potential applications in the intelligent robot field and aerospace. In the present work, the dynamic characteristics of a deployable/retractable damped cantilever beam are investigated experimentally and theoretically. The time-varying damping, as a function of the beam length, is obtained by both the enveloped fitting method and the period decrement method. Furthermore, the governing equation of the deployable/retractable damped cantilever beam is derived by introducing the time-varying damping parameter, and the corresponding closed-form solution and vibration principles are investigated based on the averaged method. The theoretical predictions for transient dynamic responses are in good agreement with the experimental results. The dynamic mechanism analysis on time-varying damping offers flexible technology in mechanical and aerospace fields. | Dynamic analysis of a deployable/retractable damped cantilever beam | 10.1007/s10483-020-2650-6 |
2020-09-01 | Gyeongju bentonite is a Ca-bentonite and a highly compacted buffer material primarily considered in Korea, as a part of an engineered barrier system (EBS) of high-level radioactive waste (HLW) repository. During the repository lifetime, the buffer material should guarantee the safe disposal of HLW against any external mechanical impact, including seismic activity. Therefore, the dynamic deformation properties of buffer material is crucial to validate its lifetime effectiveness and performance. Even though there are some researches to investigate the dynamic properties of the bentonite buffer, there has been no researches for the Korean bentonite buffer. For this reason, the paper aims to evaluate the dynamic properties at small-strain of Gyeongju bentonite and correlate the small-strain deformation properties with unconfined compressive strength using seismic and static laboratory tests. Three sets of compacted cylindrical bentonite specimens with varying dry densities (1.50 g/cm^3 to 1.77 g/cm^3) were produced using a cold isostatic pressing technique under three different pressing loads. Free-free resonant column (FFRC) tests and unconfined compressive (UC) tests were performed. The FFRC tests measured deformation properties at small strain, including unconstrained and constrained compression velocities, Young’s modulus ( E _max), constrained modulus ( M _ax), material damping ratio ( D _min), and Poisson’s ratio. The UC tests evaluated the compressive strength and secant modulus ( E _50) at large-strain. In this study, it was found that the deformation properties ( E _max and M _max) and unconfined compressive strength increase with the increase in a design rage of dry density. Poisson’s ratio measured at constrained boundary yields relatively constant value close to 0.4 for specimens at a range of dry density higher than 1.5 g/cm^3. In addition, it was found that the elastic moduli have an almost linear relationship with the unconfined compressive strength. Finally, empirical equations between elastic moduli and unconfined compressive strength for Gyeongju compacted bentonite are proposed for a Koeran design guideline. | Experimental Investigation on Small-Strain Dynamic Properties and Unconfined Compressive Strength of Gyeongju Compacted Bentonite for Nuclear Waste Repository | 10.1007/s12205-020-0372-z |
2020-09-01 | Abstract— Axisymmetric and non-axisymmetric in-plane vibrations of thin radially growing disc are considered in the frame of the Kelvin–Voigt model of linear viscoelasticity. The main focus of the research is on asymptotic behavior of solutions to the model. Mixed boundary value problems are formulated and converted into standard form by means of time dependent coordinate transformation. The boundary value problems obtained are transformed into infinite systems of ordinary differential equations using the Galerkin-Kantorovich method. It is shown that both axisymmetric and non-axisymmetric problems can be considered in terms of the same mathematical model. The simplified single mode model of the growing disc vibration is formulated and analysed. In the frame of this model the exact solutions are obtained in some interesting special cases. In the general case, solutions are derived using the Wentzel–Kramers–Brillouin (WKB) method. Depending on the exponent of radial growth, the vibration amplitude of the disc demonstrates qualitatively different behavior: if the exponent is less than 0.5 the vibration amplitude decays, if it is more than 0.5 the amplitude increases without bound no matter what size of damping coefficient is assumed. If the exponent equals 0.5 the vibration behavior depends on damping, namely there exist the critical damping coefficient and if the damping coefficient of a particular mode is less than this coefficient, the vibration amplitude grows without bound. Otherwise, if the damping coefficient of the mode is larger than the critical damping coefficient the vibration amplitude decays to zero. In the case where damping coefficient equals to the critical damping one, the amplitude of vibration remains constant. All of the qualitative results obtained for the single mode model are numerically tested and verified using a truncated multimodal system. | Axisymmetric and Non-Axisymmetric Vibration of Thin Growing Viscoelastic Disc | 10.3103/S0025654420050179 |
2020-09-01 | Formulas for calculating the change of vibration of the support of a turbine-generator set with an attached dynamic vibration damper are given in the frequency band of its efficient operation. In calculation with the relative damping ratio of the dynamic vibration damper, the value of which is determined by the proposed method, taking account of the changes of the dynamic properties of a mechanical system, the best approximation to the measured values was obtained in conducting bench trials. | Influence of Damping on the Calculation Results of the Vibration Parameters of the Support of a Turbine-Generator Set with an Attached Dynamic Vibration Damper | 10.1007/s10749-020-01221-y |
2020-09-01 | In this work, planar free vibrations of a single physical pendulum are investigated both experimentally and numerically. The laboratory experiments are performed with pendula of different lengths, for a wide range of initial configurations, beyond the small angle regime. In order to approximate the air resistance, three models of damping are considered—involving the three components of the resistive force: linear (proportional to velocity), quadratic (velocity-squared) and acceleration-dependent (proportional to acceleration). A series of numerical experiments is discussed, in which the damping coefficients are estimated by means of several computational methods. Based on the observed efficiency, a gradient method for optimization is treated as the main tool for determination of a single set of damping parameters, independent of the system’s initial position. In the model of resistive force, the term proportional to acceleration, associated with the empirical Morison equation, seems to be indispensable for the successful approximation of the real pendulum motion. | Estimation of parameters of various damping models in planar motion of a pendulum | 10.1007/s11012-020-01197-z |
2020-09-01 | In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments, an impedance-based adaptive reference trajectory generation scheme is used. Secondly, in order to improve the robustness to environmental changes and reduce the contact force errors caused by trajectory tracking errors, the backstepping sliding mode controller is combined with the adaptive reference trajectory generator. Finally, a virtual damping control based on velocity and pressure feedback is proposed to solve the problem of contact force disappearance and stall caused by sudden environmental change. The simulation results show that the proposed scheme has higher contact force tracking accuracy when the environment is unchanged; the contact force error can always be guaranteed within an acceptable range when the environment is reasonably changed; when the environment suddenly changes, the drive unit can move slowly until the robot re-contacts the environment. 为了提高在不确定和非结构化环境下液压四足机器人的力跟踪性能, 采用了基于阻抗的自适应 参考轨迹生成方案。然后, 了提高对环境变化的鲁棒性并减少由轨迹跟踪误差引起的接触力误差, 将反步滑模控制器与自适应参考轨迹生成器结合使用。最后, 提出了一种基于速度和压力反馈的虚拟 阻尼控制, 以解决环境突然变化引起的接触力消失和失速的问题。仿真结果表明, 该方案在环境不变 的情况下具有较高的接触力跟踪精度。当环境发生合理变化时, 接触力误差始终可以保证在可接受的 范围内; 当环境突然改变时, 驱动单元可以缓慢移动, 直到机器人足端重新接触环境。 | Robust force tracking control via backstepping sliding mode control and virtual damping control for hydraulic quadruped robots | 10.1007/s11771-020-4490-z |
2020-09-01 | Polymeric composites exhibit load sensitive stiffness unlike the case of homogeneous metallic material. Composites are widely used in dynamic loading environment and hence it is necessary to study their response in terms of structural properties. Behavioural changes of glass epoxy composite laminate on exposure to cyclic loading has been assessed in terms of energy dissipation (E_d) and Damping factor (DF) by hysteresis loop. GFRP composite specimens (UD-0, 0/30/60/0, 0/45/0/-45, 0/90/90/0, and 0/90/0/90) are exposed to low velocity constant amplitude cyclic loading using a laboratory arrangement (by an eccentric disc) at 4.6 Hz and 8.6 Hz frequencies. In fibre-reinforced composites apart from the fibre volume fraction, the fibre interaction angle significantly influences their dynamic properties on loading. Unidirectional (UD-0) laminate exhibits low damping/energy dissipation, while 0/90/0/90 laminate with large fibre interaction angle shows highest damping/energy dissipation. Whereas, symmetric cross ply (0/90/90/0) laminate acts as a performance demarcation among the chosen laminates. Thus, optimum E_d/DF properties of GFRP laminate in dynamic environment is attributed to symmetric lay-up, smaller fibre orientation interaction angle in the lay-up sequence and 0 fibre layer at the boundary. | Assessment of Cyclic Load Induced Energy Dissipation and Damping on GFRP Composite Laminate | 10.1007/s12221-020-9813-z |
2020-09-01 | In this paper, the considered two-DOF system consists of a linear oscillator (LO) under external harmonic excitation and an attached lightweight nonlinear energy sink (NES) with local potential and geometrically nonlinear damping. With the application of complex-averaging method, the steady-state dynamical behavior of the system is investigated by the slow invariant manifold, folding singularities and equilibrium points. Different scenarios of strongly modulated responses are presented based on the geometry of SIM, and the numerical simulation results are in consistent with the analytical prediction. The incremental harmonic balance method is applied to detect the frequency response curves of the system around the fundamental resonance, and the accuracy of the theoretical analysis is fully verified by the numerical results obtained by direct integration of equations of motion of the system. It is demonstrated that the increase in external forcing amplitude, global nonlinear stiffness and local nonlinear stiffness can drive the frequency response curves move toward the right and widen the frequency bandwidth of the coexistence of multiple steady-state response regimes, while the increase in nonlinear damping the reverse. The numerical simulation results also show that the addition of geometrically nonlinear damping and local potential in the proposed NES can drastically enhance the capacity of the nonlinear vibration absorber to suppress the shock-induced response of the LO, and the proposed NES is effective for a comparatively broad range of applied impulsive energies, particularly for the high impulsive energies. | Dynamic analysis of the nonlinear energy sink with local and global potentials: geometrically nonlinear damping | 10.1007/s11071-020-05876-0 |
2020-09-01 | Nonlinear flexural vibrations of rectangular atomic force microscope cantilever have been investigated by both the theoretical model and experimental works. As for the theoretical model, the Timoshenko beam theory which takes the rotatory inertia and shear deformation effects into consideration has been adopted. To increase the accuracy of the theoretical model, all necessary details for cantilever and sample surface have been taken into account. Differential quadrature method as a simple and fast numerical method has been used for solving the differential equations. During the investigation, the softening behavior was observed for all cases. It was also seen that raising the amplitude of vibrations led to a decrease in the nonlinear resonant frequency to linear resonant frequency ratio. The effects of different parameters such as normal and lateral contact stiffness, cantilever thickness, the angle between cantilever and sample surface and tip height in the presence of air as environment on the softening behavior were also examined. It was also demonstrated that increasing the lateral and normal contact stiffness, but decreasing the Timoshenko beam parameter would lead to an increase in the amplitude of vibrations for the first and second modes. The vibrational behavior of cantilever immersed in different liquids including water, methanol, acetone and carbon tetrachloride has been studied. Results show that increasing the liquid density reduces the nonlinear frequency. Furthermore, experimental works were compared with theoretical model for water and air environments. Results show good agreement. | Experimental and theoretical investigations about the nonlinear vibrations of rectangular atomic force microscope cantilevers immersed in different liquids | 10.1007/s00419-020-01703-5 |
2020-09-01 | The efficacy of forty treatments of inorganic salts as possible alternatives to synthetic fungicides for suppressing damping-off of cotton seedlings was evaluated. Seed treatments at rates of 2, 4, 6, 8, and 10 g salt per kg seeds were applied. The results showed that potassium phosphate monobasic (2 g per kg seeds) was the least effective salt in controlling the disease, while ammonium phosphate dibasic (4 g per kg seeds) was the most effective one. The linear growth of Sclerotium rolfsii and Pythium sp. was wholly inhibited at concentrations as high as 40 and 50 mM, respectively. On the other hand, potassium bicarbonate was not able to completely inhibit the linear growth of any of the other fungi even at the highest concentrations. The tested fungi showed differential sensitivities to the applied concentrations of potassium bicarbonate, as their differential regression models demonstrated. The interaction between three randomly selected treatments of inorganic salts and seven fungi involved in the damping-off of cotton seedlings was evaluated under greenhouse conditions. ANOVA showed an insignificant interaction between treatments and fungi. These comparisons showed that all treatments were effective in controlling the disease. In conclusion, bicarbonate as anion and potassium and ammonium as cations were effective in reducing damping-off. Also, acidic treatments were more effective than alkaline ones in controlling the disease. It can be concluded that inorganic salts may have potential as environmentally compatible nontoxic seed-dressing fungicides for controlling damping-off of cotton seedlings. In der Studie wurde die Wirksamkeit von vierzig Behandlungen mit anorganischen Salzen als mögliche Alternativen zu synthetischen Fungiziden zur Unterdrückung der Umfallkrankheit von Baumwollsämlingen bewertet. Es wurden Saatgutbehandlungen mit Raten von 2, 4, 6, 8 und 10 g Salz pro kg Saatgut angewendet. Die Ergebnisse zeigten, dass monobasisches Kaliumphosphat (2 g pro kg Saatgut) das am wenigsten wirksame Salz zur Bekämpfung der Krankheit war, während dibasisches Ammoniumphosphat (4 g pro kg Saatgut) am wirksamsten war. Das lineare Wachstum von Sclerotium rolfsii und Pythium sp. war bei Konzentrationen bis zu 40 bzw. 50 mM vollständig gehemmt. Andererseits war Kaliumbicarbonat nicht in der Lage, das lineare Wachstum eines der anderen Pilze auch bei höchsten Konzentrationen vollständig zu hemmen. Die getesteten Pilze zeigten eine unterschiedliche Empfindlichkeit gegenüber den angewandten Konzentrationen von Kaliumhydrogencarbonat. Die Interaktion zwischen drei zufällig ausgewählten Behandlungen mit anorganischen Salzen und sieben Pilzen, die an der Umfallkrankheit von Baumwollsämlingen beteiligt sind, wurde unter Gewächshausbedingungen untersucht. Die Varianzanalyse ergab eine nicht signifikante Interaktion zwischen Behandlungen und Pilzen. Diese Vergleiche zeigten, dass alle Behandlungen zur Kontrolle der Krankheit wirksam waren. Zusammenfassend lässt sich sagen, dass Bikarbonat als Anion sowie Kalium und Ammonium als Kationen die Umfallkrankheit wirksam reduzieren. Auch säurehaltige Behandlungen waren bei der Kontrolle der Krankheit wirksamer als alkalische. Daraus kann geschlossen werden, dass anorganische Salze als umweltverträgliche, ungiftige Fungizide Potenzial zur Kontrolle der Umfallkrankheit von Baumwollsämlingen haben könnten. | Control of Cotton Seedling Damping-off by Treating Seed with Inorganic Salts | 10.1007/s10343-020-00510-w |
2020-09-01 | Carbonate soils are located in temperate and tropical regions of the earth. This kind of soil has special mechanical properties compared with siliceous sand due to special sedimentary environment. In this paper, resonant column device is used to investigate the shear modulus and damping ratio of carbonate sand in the South China Sea at small and moderate shear strain amplitudes. At the same time, the dynamic properties of siliceous sands with the same gradation are also studied for the comparison. The influence of isotropic effective confining pressure and relative density on the dynamic characteristics of the sands is studied. The shear modulus of tested carbonate and siliceous sands increases with the increase of effective confining pressure and relative density. The influence of relative density on the shear modulus and maximum shear modulus of carbonate sand is more obvious than that of siliceous sand under identical test conditions. The damping ratio of both two sands decreases significantly with the increase of effective confining pressure, but the influence of relative density on the damping ratio is not obvious. A comparison between the dynamic characteristics of the carbonate and siliceous sand shows that carbonate sand has higher shear modulus, higher damping ratio, and faster shear stiffness degradation. Based on this study and other existing dynamic and cyclic tests data of different carbonate soils, a database of normalized shear modulus and damping ratio for carbonate soils was created, and a modified hyperbolic model was proposed for calculating the normalized shear modulus and damping ratio of carbonate soils with different calcium carbonate contents. | The study of dynamic properties of carbonate sand through a laboratory database | 10.1007/s10064-020-01785-z |
2020-09-01 | We developed a novel magnetic resonance elastography (MRE) analysis method based on Fourier transform to assess the responsive characteristics for different tissue stiffness and degree of transmission of the vibration wave emanating from a passive driver during MRE. A phantom tissue study was conducted with an MRE sequence and vibration wave system using a clinical MR scanner. The phantom tissue consisted of two layers of agar: 0.75 wt% and 1.0 wt%. Phase-unwrapped images derived from acquired MRE phase images were used to generate a phase profile curve, with a line plotted for the phase-unwrapped images. Fourier transform was performed, and the peak value of the power spectrum was derived. The damping rate/ratio was calculated using the Hilbert transform of the phase profile. We found that the mean shear stiffness value of 1.0 wt% agar was higher than that of 0.75 wt% agar. The responsive frequency of the 0.75 wt% agar layer showed a wider range and the damping rate of the signal showed a higher value than the respective values of the 1.0 wt% agar layer. In conclusion, Fourier transform analysis of MRE enabled us to obtain more detailed information of the tissue characteristics and vibration-wave conditions. | Quantitative analysis of vibration waves based on Fourier transform in magnetic resonance elastography | 10.1007/s12194-020-00579-y |
2020-09-01 | Identifying the susceptible period when environmental factors affect disease risk is essential for understanding disease etiology. Most existing epidemiologic studies use oversimplified summaries of time-dependent exposures such as baseline or most current exposure, or the cumulative average of exposure over available follow-up periods. In this paper, we introduce a damped exponential weighting model for estimating optimal exposure weights for different time intervals. This model can accommodate flexible patterns of weights and can be fit using standard software. We applied the model to assess the latency of BMI and alcohol for post-menopausal breast cancer based on 30-year exposure history in the Nurses’ Health Study. We have also performed a simulation study to assess the validity of the proposed hypothesis testing and estimation procedures in realistic conditions. We found that the type I error is close to 0.05; the bias in our parameter estimates is low and the coverage probability of interval estimates is close to 0.95. For ER+/PR+ breast cancer we found that recent BMI was a more important predictor of risk than more distant BMI; for ER−/PR− breast cancer, no latency was found and risk was characterized by cumulative high levels of BMI over a long period of time. For alcohol intake, we saw a strong positive association with cumulative intake for ER+/PR+ breast cancer; no significant association was found for cumulative intake or for any latency measure of risk for ER−/PR− breast cancer. Our results underscore the value of an easy-to-implement approach to latency analysis of exposure profiles for chronic disease. | Latency estimation for chronic disease risk: a damped exponential weighting model | 10.1007/s10654-020-00658-9 |
2020-09-01 | Abstract The angular motion of a CubeSat-type nanosatellite with a passive magnetic attitude control system is mathematically modelled. The attitude control system consists of a permanent magnet and hysteresis dampers in the form of a plate or a set of rods. The parameters of the hysteresis dampers are studied using a laboratory facility. A comparative analysis of the damping time using the plate and the set of rods is presented. | Modeling a Nanosatellite’s Angular Motion Damping Using a Hysteresis Plate | 10.1134/S2070048220050075 |
2020-09-01 | Semi-active systems with variable stiffness and damping have demonstrated excellent performance. The aim of this study is to investigate the new configuration of a semi-active single-stage nonlinear vibration isolation system with a Magneto-Rheological (MR) damper to reduce the magnitude of force transmissibility over the both resonant and non-resonant regions. The magnitude of force transmissibility is widely used to performance measurement for the isolation system. In current study, to achieve this reduction, two horizontal springs and one MR damper were added to the isolator. Theoretical analysis reveals that the nonlinear system with MR damper can produce ideal vibration isolation. However, due to the nonlinear characteristics behavior of the MR damper, conventional control algorithms to reach the desired are cumbersome. To address this issue, an artificial intelligent strategy using wavelet network and fuzzy logic controller is considered to be constructed to copy the inverse dynamics of the MR damper and the nonlinear isolator. Accordingly, simulation results demonstrated that the intelligent algorithm has acceptable performance. | Modeling and controlling a semi-active nonlinear single-stage vibration isolator using intelligent inverse model of an MR damper | 10.1007/s12206-020-0804-1 |
2020-09-01 | Presently, earthquake-resistant design provisions are based on the assumption of inelastic behaviour of structures in major earthquake occurrences. It is generally possible to achieve ductile behaviour with significant damage in steel and reinforced concrete structures. The passive control system is generally used to protect a building from the damaging effect of an earthquake. In the present work, the study of building with Base Isolated top floor as a tuned mass damper (TMD) is considered. The top storey is used as TMD for this purpose, the isolation system is provided at the base of the top storey of a building. This TMD being made up of concrete has the same damping ratio as that of the main building. Effectiveness of Base Isolated TMD is ascertained by comparing the results of the considered building of analysis by using Time History Analysis. By comparing the results, it is observed that Base Isolated TMD is quite effective as compared to building without TMD. | Vibration control of structure by top base isolated storey as tuned mass damper | 10.1007/s40435-020-00614-1 |
2020-08-28 | This work underlines the importance of the application of fractional-order derivative damping model in the modelling of the viscoelastic foundation, by demonstrating the effect of various orders of the fractional derivative on the dynamic response of plates resting on the viscoelastic foundation, subjected to concentrated step load. The foundation of the plate is modelled as a fractionally-damped Kelvin–Voigt model. Modal superposition method and Triangular strip matrix approach are used to solve the partial fractional differential equations of motion. The influence of (a) fractional-order derivative, (b) foundation stiffness, and (c) foundation damping viscosity parameter on the dynamic response of the plate are investigated. Theoretical results show that with the increase in the order of derivative, the damping of the system increases, which leads to decreased dynamic response. The results obtained from the fractional-order damping model and integer-order damping model are compared. The results are verified with literature and numerical results (ANSYS). | On the transient response of plates on fractionally damped viscoelastic foundation | 10.1007/s40314-020-01285-6 |
2020-08-27 | We introduce a new model of the nonlocal wave equation with a logarithmic damping mechanism, which is rather weak as compared with frequently studied fractional damping cases. We consider the Cauchy problem for the new model in $$\mathbf{R}^{n}$$ R n and study the asymptotic profile and optimal decay rates of solutions as $$t \rightarrow \infty $$ t → ∞ in $$L^{2}$$ L 2 -sense. The damping terms considered in this paper is not studied so far, and in the low-frequency parameters, the damping is rather weakly effective than that of well-studied power type one such as $$(-\Delta )^{\theta }u_{t}$$ ( - Δ ) θ u t with $$\theta \in (0,1)$$ θ ∈ ( 0 , 1 ) . When getting the optimal rate of decay, we meet the so-called hypergeometric functions with special parameters, so the analysis seems to be more difficult and attractive. | Asymptotic profile and optimal decay of solutions of some wave equations with logarithmic damping | 10.1007/s00033-020-01373-x |
2020-08-24 | Damped vibration of a cracked Timoshenko beam with ends supported with damper, linear and rotational springs is investigated. Frequencies in complex forms have been obtained for both cracked Euler–Bernoulli and Timoshenko beams. Depending upon the crack-depth and crack-location, frequencies have been tabulated in each case. The results have also been compared in terms of the ratio of the beam depth to the beam length. Modal shapes for various conditions have also been plotted. | Damped vibration analysis of cracked Timoshenko beams with restrained end conditions | 10.1007/s40430-020-02558-1 |
2020-08-14 | This paper addresses the problem of determining the optimal parameters of a sky-hook damper type suspension in the control of the stationary random response of half car vehicle models traversing a rough road with constant velocity. The feedback control scheme is realized by approximating the sky-hook damper strategy, and the optimal parameters of the sky-hook damper are obtained by equating the sky-hook damper suspension force with that of a fully active suspension force using linear quadratic regulator with preview control (LQR with preview control). Results show that the overall performance of the sky-hook damper approximately 99% matches with performance of LQR with preview control (look ahead preview control) over a specified vehicle velocity range. | Optimal response of half car vehicle model with sky-hook damper using LQR with look ahead preview control | 10.1007/s40430-020-02552-7 |
2020-08-01 | Based on the similarity theory, two physical models of the double-arch tunnel with and without the damping layer are set. Through the shaking table test and numerical simulation, the damping effect of the foam concrete damping layer on the acceleration, stress, displacement and internal force of the shallow-buried bias double-arch tunnel is studied. Research indicates: (1) Foam concrete damping layer only affects the peak acceleration response and does not change the spectral characteristics of the acceleration time history curve. (2) Foam concrete damping layer reduces the principal stress peak and peak displacement of the vault and the spandrel of the double-arch tunnel to some extent. It shows that the foam concrete damping layer can improve the seismic performance of the double-arch tunnel. (3) The damping effect of foam concrete on different measuring points of double-arch tunnels is different, and the damping effects of internal forces of different properties of the same measuring point are different. In the damping design of foam concrete applied to underground projects such as double-arch tunnels, the damping effects of axial force, shear and moment should be considered separately. | Shaking Table Test and Numerical Simulation for Dynamic Response of Shallow-Buried Bias Double-Arch tunnel | 10.1007/s10706-020-01267-9 |
2020-08-01 | Demand of higher speeds in rotor systems has elevated the possibility of numerous instabilities. Internal damping is one of the key parameters for instability in such machinery. Its studies are generally conducted for a possible range of chosen internal damping values. Hence, experimental estimation of internal damping along with external damping is very vital for an accurate prediction of rotor stability, which is scarcely addressed in the literature. To fill this gap, current paper presents an experimental identification methodology for estimation of the internal and external damping in a cracked rotor system. Other crucial unknown fault parameters of rotor system, like additive crack stiffness and unbalance, have also been identified. In present work, internal damping due to rub between transverse fatigue crack faces has been envisioned for the first time. Hence, internal damping has been considered due to combined effect of material hysteretic, i.e. the rub between transverse fatigue crack faces, and the rub between disc and shaft during shaft rotation. Measurements much below critical speeds ensures the main contribution of crack in internal damping due to weight dominance effect as compared to shaft material damping. In experimental setup, a hairline fatigue crack was artificially developed by three-point bending procedure in a shaft at a notch location. The opening and closure behavior of crack faces during rotation of the shaft leads to the forward and backward whirls of the rotor at multiple frequencies, which are apparent in the full spectrum. Mathematical modeling of the rotor system for development of identification algorithm is based on these behaviors of cracked rotor system. Experimentally measured responses have been converted into the full spectrum (both amplitude and phase) based on regression analysis and fast Fourier transform (FFT). Earlier, amplitudes of full spectrum have been used for qualitative indication of crack. But in the present work, corresponding phase has also been considered in quantitative estimation of crack parameter along with other system fault parameters. With the help of a multi-frequency reference signal, phase anomalies have been removed during processing of full spectrum. The bow effect of shaft has been removed from full spectrum responses with the help of a slow roll measurement. Estimated parameters are consistent for different sets of rotor speeds and for different frequency ranges of excitation forces due to fatigue crack. Validations of identified parameters have been done by comparing experimental responses with numerically generated system responses. The latter was generated using experimentally identified parameters in the mathematical model of cracked rotor system. | Experimental Identification of Internal and External Damping in a Rotor System with a Fatigue-Crack Using Full Spectrum | 10.1007/s40799-020-00368-7 |
2020-08-01 | Here we consider a string composed by three different materials: thermo elastic, viscoelastic and elastic. Our main result is that the exponential stability depends on the position of each material. That is, we prove that the model is exponentially stable if and only if the viscoelastic material is not in the center of the string. Otherwise, there is not exponential stability and the corresponding semigroup also goes to zero, but now polynomially. | Stability in Thermoviscoelasticity with Second Sound | 10.1007/s00245-018-9495-8 |
2020-08-01 | In this paper, we investigate the large time behavior of one dimensional coupled vibrating systems with fractionnal control applied at the coupled point. We prove well-posedness by using the semigroup theory. Also we establish an optimal decay result by frequency domain method and Borichev–Tomilov theorem. | On the asymptotic behaviour of two coupled strings through a fractional joint damper | 10.1007/s12215-019-00423-2 |
2020-08-01 | This paper investigates the dynamic response of a coated half-plane subjected to a harmonic Hertz load on the coating surface. The complex modulus is used to describe the hysteretic damping of the elastic homogeneous coating and half-plane. Using the Helmholtz decomposition and Fourier integral transform technique, we derive the stresses and displacements of the coating and half-plane from Navier’s elasticdynamic equations in the form of complex integrals. Then, the global adaptive quadrature algorithm is exploited to solve the complex integrals numerically. The effects of Young’s modulus ratio, density ratio, coating thickness, loss factor and external excitation frequency are discussed. It is found that the dynamic response of displacements and stresses becomes increasingly oscillatory with the increase in excitation frequency. | Dynamic Response of a Coated Half-Plane with Hysteretic Damping Under a Harmonic Hertz Load | 10.1007/s10338-019-00150-2 |
2020-08-01 | For a pulsating free surface source in a three-dimensional finite depth fluid domain, the Green function of the source presented by John [Communs. Pure Appl. Math. 3:45–101, 1950] is superposed as the Rankine source potential, an image source potential and a wave integral in the infinite domain $$(0, \infty )$$ ( 0 , ∞ ) . When the source point together with a field point is on the free surface, John’s integral and its gradient are not convergent since the integration $$\int ^\infty _\kappa $$ ∫ κ ∞ of the corresponding integrands does not tend to zero in a uniform manner as $$\kappa $$ κ tends to $$\infty $$ ∞ . Thus evaluation of the Green function is not based on direct integration of the wave integral but is obtained by approximation expansions in earlier investigations. In the present study, five images of the source with respect to the free surface mirror and the water bed mirror in relation to the image method are employed to reformulate the wave integral. Therefore the free surface Green function of the source is decomposed into the Rankine potential, the five image source potentials and a new wave integral, of which the integrand is approximated by a smooth and rapidly decaying function. The gradient of the Green function is further formulated so that the same integration stability with the wave integral is demonstrated. The significance of the present research is that the improved wave integration of the Green function and its gradient becomes convergent. Therefore evaluation of the Green function is obtained through the integration of the integrand in a straightforward manner. The application of the scheme to a floating body or a submerged body motion in regular waves shows that the approximation is sufficiently accurate to compute linear wave loads in practice. | New formulation of the finite depth free surface Green function | 10.1007/s10665-020-10058-3 |
2020-08-01 | This paper presents an integrated, new, and generic framework for layout optimization of viscoelastic damping for noise control of mid-frequency vibro-acoustic systems. The method is developed based on the concept of power balance among different modal energies between coupled structural and acoustic subsystems and is formulated within the framework of a statistical modal energy distribution analysis (SmEdA). In the novel optimization formulation, the total energy of the acoustic subsystem is chosen as the objective function for minimizing the internal acoustic response in the vibro-acoustic system; and the relative material volume densities for viscoelastic element groups are selected as design variables using a volume-preserving Heaviside function. A new sensitivity analysis formulation is developed in a semi-analytical form via a SmEdA for solving the vibro-acoustic optimization problem. Two numerical examples are presented to demonstrate the efficiency and effectiveness of the present method. The present numerical results reveal two important findings: (a) the total acoustic energy of the chosen vibro-acoustic system can be significantly reduced; and (b) the optimum viscoelastic material layouts not only decrease the peak values of the modal coupling strengths between structural and acoustic subsystems but also create relatively more uniform acoustic modal energy distribution. | Layout optimization of viscoelastic damping for noise control of mid-frequency vibro-acoustic systems | 10.1007/s00158-020-02524-4 |
2020-08-01 | The dynamic varied elastic modulus and damping coefficient of underground goaf are most important factors which describes the goaf absorption ability on seismic wave energy. This numerical simulation study have focused on the effect of goaf area on earthquake-wave propagation and seismic response on the ground surface in a coal mine area. The laboratory measurements were carried out by 135 porous samples cases consisting rocks and coal particles 0.12–0.25 mm in size to estimate the dynamic elastic modulus and damping coefficient of the fragmented rock masses. In this simulation, a new model on damping coefficient of longitudinal and transverse waves has been presented in considering rock size ( D ), effective stress ( σ _ e ), porosity ( φ ) and compaction time ( t ). The empirical correlation between the damping coefficient and effective stress (depth) as well as the compaction time of the goaf area has been derived and used for each goaf and strata grid blocks in the simulation. The results showed that the peak ground acceleration (PGA) above the goaf area exhibits 9–20% reduction compared to that of unexcavated condition (original coal seam), and around 10–35% seismic energy is trapped in the goaf area as goaf varied from 100 to 700 m. In the meantime, the peak ground displacement (PGD) is amplified up to seven times for the goaf depth ranging from 100 to 700 m compared to that of the unexcavated condition. Both PGA and PGD above goaf area are smaller than those above the undisturbed coal seam. | Simulation Study on Seismic Response of Ground Surface Above an Underground Longwall Goaf | 10.1007/s00024-020-02493-1 |
2020-08-01 | Thermoelastic damping (TED) is one of the main internal energy dissipation mechanisms in micro-/nano-resonators. Accurate evaluation of TED is important in the design of micro-electromechanical systems and nano-electromechanical systems. In this paper, a theoretical analysis on the TED in functionally graded material (FGM) micro-beam resonators is presented. Equations of motion and the heat conduction equation governing the thermodynamic coupling free vibration of non-homogenous micro-beams are established based on the Euler–Bernoulli beam theory associated with the modified couple stress theory. Material properties of the FGM micro-beam are assumed to change in the depth direction as power-law functions. The layer-wise homogenization method is used for solving the heat conduction equation. By using the mathematical similarity of eigenvalue problem between the FGM beam and the reference homogeneous one, the complex natural frequency including TED is expressed in terms of the natural frequency of the isothermal homogenous beam. In the presented numerical results, influences of various characteristic parameters, such as beam thickness, material gradient index, structure size, vibration mode and boundary conditions, on TED are examined in detail. It shows that TED decreases with the increases in the values of length scale parameters because the latter lead to the increase in structural stiffness. | Thermoelastic Damping of Functionally Graded Material Micro-Beam Resonators Based on the Modified Couple Stress Theory | 10.1007/s10338-019-00155-x |
2020-08-01 | In this paper, it is considered a quasi-linear strongly-damped wave equation defined by a non-linear partial differential equation of third order. The equation describes motions of viscoelastic solids. We study the conservation laws of this equation. By applying the multiplier method of Anco and Bluman to the equation, we find the multipliers. Consequently, we obtain a complete classification of conservation laws. Moreover, we use the Lie-group theory to analyse the symmetries of the equation. From the Lie symmetries, all the reductions are determined. Afterwards, we construct exact solutions with physical interest: travelling wave solutions. | Conservation laws and symmetry analysis for a quasi-linear strongly-damped wave equation | 10.1007/s10910-020-01146-x |
2020-08-01 | The paper highlights the importance of using site-specific shear modulus reduction ( G / G _max versus shear strain, γ ) curves and damping ratio ( D versus shear strain, γ ) curves for ground response analysis. In order to develop comprehensive G / G _max–γ and D – γ curves (i.e. over a wide range of strain level), two types of apparatus, viz. resonant column and cyclic simple shear, have been used. The case study considered the geological deposits from the river beds of Yamuna River originating from the Himalayan seismic zone of North India. The tests results have been analysed to develop G / G _max– γ and D – γ curves and compared with standard curves. It has been observed that upper and lower boundaries for the standard curves are remarkably different for the geological deposit under consideration. In order to assess the impact of using standard curves rather than site-specific curves, ground response analysis has been carried out at five sites along the Yamuna River using two types of curves (standard and site-specific developed in this study). The study showed that the amplification of shear waves at these sites based on the experimentally derived curves is much higher as compared to the standard curves. The proposed curves better represent dynamic behaviour of the soil deposits of the region and will provide a realistic response as far as practically possible, for the structures constructed in the states of Haryana and Delhi and nearby areas. It is anticipated that the data presented in this paper will have wide application and usage. | Dynamic soil properties and seismic ground response analysis for North Indian seismic belt subjected to the great Himalayan earthquakes | 10.1007/s11069-020-03995-w |
2020-08-01 | In this paper, a control system is proposed for the vibration suppression of a semi-submersible offshore wind turbine equipped with a tuned liquid multi-column damper (TLMCD). The TLMCD consists of three columns of liquid integrated into the superstructure of the semi-submersible platform. To improve the vibration suppression performance of the TLMCD, unlike previous works, the TLMCD is operated in a semi-active mode by introducing three flow control valves that allow liquid to transfer between columns. Since the rotor dynamics may greatly affect the platform vibrations, it has been included in the derived nonlinear dynamic model. In the proposed control loop, the closed-loop performance objectives of platform stabilization and rotor speed regulation are accomplished by two distinct controllers. For the platform stabilization purpose, three controller design methods of displacement-based ground-hook, velocity-based ground-hook, and bang–bang are investigated. Meanwhile, to achieve the rated rotor speed, two methods of the H _∞ and gain-scheduling control schemes are attempted. The closed-loop performance is investigated through numerical simulations. Realistic wind profiles along with a wave disturbance are implemented in the numerical simulations. The results show that the gain-scheduling control scheme for the rotor speed regulation and the velocity-based ground-hook method for the platform stabilization outperform other methods. Furthermore, to study the effect of the design parameters of the TLMCD on the closed-loop performance, several cases with different values of the design parameters are examined and compared. | Semi-active vibration control of a semi-submersible offshore wind turbine using a tuned liquid multi-column damper | 10.1007/s40722-020-00171-x |
2020-07-31 | This paper proposes a novel, simple and high-efficient submerged structural stabilization system for a self-stabilizing buoy that provides a stable platform for oceanographic and meteorological sensors. The proposed stabilization system is a Seesaw-like Tuned Mass Damper (STMD) combined with a foil and is designed in a way to harvest the activation energy from incoming waves. A fixed rudder in the rear underside of the buoy, as well as physical properties of the buoy, help to keep its balance in yaw and roll directions while encountering lateral waves. Therefore, the orientational stabilization of the whole structure is achieved by controlling only the pitch deviation. The proposed model is then simulated in a marine dynamic analysis software. Two different shapes of a thin rod and a foil were proposed for the sliding mass (slider) of the STMD and their performances are investigated and compared to each other in two different modes of passive and active control. In the passive mode, different mass ratios were conducted for the thin rod-shaped slider (i.e., a ratio of the effective mass of the stabilizing system to that of the whole structure) and a mass ratio of 8% could suppress the pitch deviation up to 81.3% in the resonance condition. The same STMD system with a mass ratio of 2% suppresses the pitch deviation by only 7%. In the active mode, the STMD with a thin rod-shaped slider and a mass ratio of 8% exhibits only 49.1% suppression effect in a multiwave condition. However, by changing the shape of the slider to a foil while controlling its angle of attack (AOA) mechanically, the system with the mass ratios of 2% and 8% could suppress the pitch deviation of the buoy up to 69.4% and 79.1%, respectively. | Design, assessment and evaluation of structural stabilization system for weather buoys using a moving foil | 10.1186/s40648-020-00178-x |
2020-07-16 | The dynamic properties of lime-solidified soft soil affect the safety and function of buildings. In this study, lime was used to solidify soft soil from the Binhai New District of Tianjin, China. A dynamic triaxial testing system was used to measure the dynamic stress-strain curves of solidified soft soil samples for different lime mixing ratios and confining pressures. The relationship between the dynamic strength and the static strength, the influence of the lime mixing ratio on the dynamic strength, and the variation of the dynamic shear modulus G and the damping ratio λ were analyzed. The results show that under static and dynamic loads, the internal friction angles of the lime-solidified soft soil are almost the same and range between 21.72° and 24.42°. Different cohesion values are obtained under static and dynamic loads, and these two values increase and approach each other with increasing lime mixing ratios. G and λ depend on the shear strain, the lime mixing ratio, and the confining pressure. These results serve as a reference for the formulation of a solidification scheme for soft soil. | Experimental study on the dynamic properties of lime-solidified soft soil under cyclic loading | 10.1007/s12517-020-05721-z |
2020-07-06 | In this work, the exponential growth of solutions for a coupled nonlinear Klein–Gordon system with distributed delay, strong damping, and source terms is proved. Take into consideration some suitable assumptions. | Growth of solutions for a coupled nonlinear Klein–Gordon system with strong damping, source, and distributed delay terms | 10.1186/s13662-020-02801-y |
2020-07-05 | The stress–strain characteristics of soil under monotonic loading conditions and the dynamic properties of soils under cyclic loading are necessary for foundation engineering, ground response analysis and soil structure interaction studies. In the absence of site/region-specific properties, it is a common practice to use representative parameters based on the index properties of soil and available standard correlations. Such correlations might be inadequate for regional soils of varying index properties. Based on monotonic and cyclic triaxial tests, this study reports the monotonic and dynamic soil properties of the prevalent soils from the northeastern region of India, namely the cohesionless, cohesive and silty-sandy soils. It is observed that monotonic response of cohesionless soil is mostly influenced by the initial relative density, while the response of cohesive and silty-sands are primarily influenced by the effective confining pressure and degree of saturation. The cyclic triaxial tests revealed that, irrespective of the soil type, the strain-dependent modulus reduction and especially the damping ratio curves are noticeably different from available standards. The study highlights the importance of identifying the site/region specific soil properties for their usage in GRA and SSI applications. | Monotonic and dynamic properties of riverbed sand and hill-slope soils of seismically active North-east India for ground engineering applications | 10.1186/s40703-020-00116-1 |
2020-07-03 | In this paper, we consider the spectral problem for a Stieltjes string with both ends fixed and with one-dimensional damping at an interior point. We solve an inverse problem of recovering parameters of the Stieltjes string using partial information on the string and partial information on the spectrum. First we prove uniqueness and give an algorithm of recovering the unknown parameters of the string by virtue of a finite number of distinct not pure imaginary complex eigenvalues and a certain even number of real eigenvalues. For the case where only complex eigenvalues are used we solve the existence problem, i.e. propose conditions on a set of complex numbers necessary and sufficient for these numbers to be a subset of the spectrum of the problem. | Inverse Problem for a Stieltjes String Damped at an Interior Point | 10.1007/s00020-020-02587-4 |
2020-07-01 | Abstract The damping composites from the materials with different elastic hysteresis properties have been studied at dynamic loads and temperatures of +23°C and –40°C. A sandwich shock absorber for a rail damping element that is 14 mm in thickness from fiber-reinforced rubber composite and thermoplastic elastomer, which combines the advantages of each material, has been developed. A procedure for the choice of elastic hysteresis characteristics of sandwich shock absorbers and a mathematical model of a wagon–track multiple-mass vibration system making it possible to evaluate the applicability and performance of such shock absorbers have been proposed. | Damping Composites from Materials with Different Elastic Hysteresis Properties for Sandwich Shock Absorbers of Railroad Transport | 10.1134/S2075113320040218 |
2020-07-01 | A hybrid type magneto-rheological (MR) fluid damper based on electromagnet and two permanent magnets apart from electromagnet was designed and its characteristics were analyzed numerically. In the proposed MR damper, the magnetic field is generated by the permanent magnet and raised by the additional electromagnet. This combination provides a larger amount of damping force with lower consumption of electric energy. The proposed model has an additional advantage of providing a moderate damping force in case of electromagnet failure. The magnetic circuit of a hybrid MR valve was analyzed by applying Kirchhoff’s law and magnetic flux conservation rule. A 2D axisymmetric model of the proposed hybrid MR damper was developed in commercial software where magnetic field properties are analyzed by finite element method. The optimization process was developed to optimize the geometric parameters and generated damping force using design of experiment (DoE) technique. The damping force of the MR damper was selected as an objective function. The optimal solution to the optimization problem of the hybrid MR valve structure was evaluated and compared with the solution obtained from the initial parameters. It is demonstrated that the novel hybrid type provides higher damping force than the previous model. | Design and geometric parameter optimization of hybrid magnetorheological fluid damper | 10.1007/s12206-020-0627-0 |
2020-07-01 | In view of the problem that large-scale and high-penetration wind power access may weaken the stability of small interference in the power grid, this study proposes a novel additional damping controllers for the doubly-fed induction generator (DFIG) based on the genetic algorithm. A DFIG model and its control system is built, and the parameters of the controller are tuned using the genetic algorithm to optimize the control effect. Based on Western System Coordinating Council (WSCC) 3-machine 9-node system, multi-scenario simulation results verifies that the additional damping controller proposed in this study performs better to suppress the low-frequency oscillation than the power system stabilizer (PSS) installed on the synchronous generators which are farther to the disturbance point. Meanwhile, the proposed strategy is compared with the reactive power modulation control, which can provide a reference for engineering applications of an added DFIG damping controller. | Genetic Algorithm-Based Analysis of the Effects of an Additional Damping Controller for a Doubly Fed Induction Generator | 10.1007/s42835-020-00440-7 |
2020-07-01 | Abstract This paper considers the classical methods of surface damping of bending vibrations of thin-walled structures and a promising integral version of a damping coating consisting of two layers of a material with pronounced viscoelastic properties separated by a thin reinforcing layer of a high modulus material. A finite element with 14 degrees of freedom for modeling an elongated plate with the specified damping coating has been developed with consideration of the transverse compression of damping layers under high-frequency vibrations of the plate. The generalized problem of complex eigenvalues in the lower part of the spectrum of complex modes and frequencies of free vibrations of a damped plate is solved by the subspace iteration method taking into account the frequency dependence of the dynamic elastic moduli of the material. The damping properties of the plate are determined from the imaginary parts of the complex eigenfrequencies and the relative energy dissipation at resonance. | COMPLEX EIGENFREQUENCIES AND DAMPING PROPERTIES OF AN ELONGATED PLATE WITH AN INTEGRAL DAMPING COATING | 10.1134/S0021894420040148 |
2020-07-01 | Nanomaterials with their extremely high free surfaces can effectively augment damping in nanocomposites via frictional sliding along the interface of nanomaterials and a matrix. Despite this potential, existing state of knowledge about the damping behavior of graphene reinforced nanocomposites is at an embryonic stage. In particular, it is not clear how various morphological parameters of graphene contribute to damping. We aim to reveal the mechanical damping behavior of graphene-reinforced polymer nanocomposites as a function of the surface morphology of graphene nanoplatelets through combined experiments and continuum modeling. The vibrational damping behavior of graphene nanocomposites was studied via dynamic mechanical analysis via cycling tension-compression tests. Two graphene types, “single-layer graphene” (SLG) and “graphene nanoplatelets” (GNP), with different aspect ratios in polystyrene (PS) matrix were used. We developed a micromechanical model which relates damping in nanocomposites to filler-matrix frictional sliding. The experimental work demonstrated that the addition of GNP will increase the damping properties of the nanocomposites by up to ~70%. The model predictions for PS-GNP were in good agreement with experimental data. However, contrary to the model predictions, the damping coefficient of nanocomposites with lower aspect ratio particles (PS-SLG) was lower than PS-GNP. Further experimental studies showed that the surface roughness of the SLG (owed to their small thickness) has a negative effect on damping properties as they delay interfacial debonding and frictional sliding. Flat (less rough) graphene triggers intrinsic friction mechanism earlier and may be more beneficial to enhance damping. Surface undulation of the nanoparticles, which can happen for atomically thin particles, will delay damping. | Graphene Size and Morphology: Peculiar Effects on Damping Properties of Polymer Nanocomposites | 10.1007/s11340-020-00592-7 |
2020-07-01 | We present a unified model of electrostatic sensors comprising cantilever microbeam resonators in fluid media. The model couples Euler–Bernoulli beam equation to the nonlinear Reynolds equation. Static, damped eigenvalue, and dynamic reduced-order models were developed and validated by comparing a nonlinear frequency response of a gas sensor to its experimentally measured counterpart. Experiments were conducted to verify the capability of the developed model to predict the out-of-plane and in-plane natural frequencies of the sensor. The models were also used to investigate the potential operation of electrostatic chemical sensors based on different sensing mechanisms. While in-plane and out-of-plane vibration modes were found to be viable alternatives for resonant gas sensors, only in-plane modes were suitable to implement resonant chemical sensors due to the added mass and damping of liquid media. Similarly, higher-order modes were found more sensitive than lower order modes. Further, evidence was found for elastic interaction between out-of-plane modes and liquids in the channel underneath them but none for in-plane modes. Finally, the model predicts that in-plane modes provide the multi-valuedness necessary to implement bifurcation chemical sensors in liquid media. | A unified model for electrostatic sensors in fluid media | 10.1007/s11071-020-05780-7 |
2020-07-01 | An improved version of the direct displacement-based design (DDBD) method for the seismic design of plane moment resisting frames in the framework of performance-based design approach is presented. The method employs a multi-degree-of-freedom equivalent system instead of the single-degree-of-freedom equivalent system used by the conventional DDBD method. Thus, the proposed method can take more rationally and with higher accuracy into account the higher mode and P-Δ effects than the conventional one. This is accomplished with the aid of the concept of deformation dependent equivalent modal damping ratios previously developed by the present authors for other purposes and the concept of the design modal displacements developed herein. These design modal displacements are determined on the basis of target inter-storey drift ratios for every performance level and the first few modes significantly contributing to the structural response. Thus, one can determine from the displacement spectrum with high amounts of viscous damping the required modal periods for known values of the design modal displacements. From those modal periods, the corresponding required modal stiffness and hence the modal base shear forces can be obtained. The final required design base shear can be obtained by a combination rule, like the SRSS rule. Numerical examples involving the seismic design of two moment resisting reinforced concrete plane frames are presented in detail for illustrating the proposed approach and demonstrating its merits over the conventional DDBD method and the force-based design method of Eurocode 8. | A direct displacement-based seismic design method using a MDOF equivalent system: application to R/C framed structures | 10.1007/s10518-020-00857-5 |
2020-07-01 | Abstract Theoretical explanation of the experimentally discovered effect of a decrease in the excitation energy of surface and volume plasma oscillations of valence Si (111) electrons during the implantation of Ba and alkaline-element ions with a large dose of D > 10^16 cm^–2 is presented in this paper. On the basis of a two-fluid model of the electron gas, the observed effect of a decrease in the Si(111) plasmon energy is explained by the strong damping of valence electron oscillations because of disordering of the Si(111) crystal structure up to full amorphization. | Theoretical Explanation of the Effect of a Decrease in the Si(111) Plasmon Energy during the Implantation of Ions with a Large Dose | 10.1134/S102745102004031X |
2020-07-01 | Subjected to dynamic excitations, bolted joint interfaces exhibit nonlinear characteristics that significantly affect the dynamic response of assembled structures. In this paper, a novel modeling method is developed to improve the prediction accuracy of the tangential contact behavior of bolted joint interfaces. This method is based on the framework of the Iwan model and builds the relationship between the Iwan density function and the distribution of the contact pressure. It is the first time to give an explicit physical significance of the Iwan density function. The effectiveness of the proposed model is validated well by comparing with published experiments. Then the proposed model is integrated into a numerical model of a bolted joint structure and combined with the alternating frequency/time method to study its applicability in dynamics analysis. The model is fully compatible with the current state-of-the-art numerical analysis tools. The results show that the simulated interface responses are in good agreement with the experiment. | Modeling tangential friction based on contact pressure distribution for predicting dynamic responses of bolted joint structures | 10.1007/s11071-020-05765-6 |
2020-07-01 | Abstract Basic approaches are outlined to solving complex engineering problems arising in the design and operation of power units at nuclear power stations (NPS) and based on large-scale physical simulation of dynamic conditions and parameters of dynamics and structural strength of modern power facilities. A procedure for physical simulation of specific dynamic processes in hydroelastic systems has been developed. Taking into account the identified distributions of pressure pulsations and flow rates on the surfaces of the structures of the investigated reactor plants (RU), hydrodynamic loads in various structures and facilities of modern power-machine buildings were determined considering the found distribution of fluctuations in flow pressure and velocity acting on the structure surfaces. The dynamic response parameters of the main structural members, such as dynamic strains and stresses, were obtained and analyzed. The effect of added masses of liquid, damping, and other factors on the dynamic processes in hydroelastic systems and ways for its reduction to increase the durability and service life of structures, first of all the critical elements of the studied power systems for each commissioned reactor, are determined. This approach is based on a comprehensive investigation of the interaction of a turbulent flow with the multicomponent structure of a reactor unit. The results of investigation confirmed the structure serviceability as to the relative error. The fitness for service of a structure during a specified operation time of the power unit was assessed. The implementation of the proposed approach involving large-scale physical simulation and, in many cases, numerical modeling, confirmed its effectiveness and the validity of the results obtained by the authors. | Physical Simulation of Dynamic Processes in Hydroeleastic Systems at Nuclear Power Stations | 10.1134/S0040601520070034 |
2020-07-01 | Abstract We study natural vibrations of the fluid column in a vertical oil well that occur during sudden shutdown or start-up of the well (water hammer). In this case, the period of vibration and the intensity of vibration damping are determined not only by the length and diameter of the fluid column in the well and the rheological properties of the fluid, but also by the reservoir characteristics of the bottomhole zone (in particular, permeability, the quality of well perforation, and the properties of the hydraulic fractures formed). Solutions to the problem of damped natural vibrations of the fluid column in the well are found using a mathematical model describing the movement of the fluid column in the well and filtration in the bottomhole zone. Characteristic equations for determining complex frequencies (frequency of vibration and the damping coefficient) are obtained. The dependences of the vibration frequency, damping coefficient, and damping decrement on reservoir permeability are studied, and the amplitudes of vibrations at different points of the well are obtained. | DAMPED NATURAL VIBRATIONS OF FLUID IN A WELL INTERFACED WITH A RESERVOIR | 10.1134/S002189442004001X |
2020-07-01 | This paper investigates the axial vibration of single-walled carbon nanotubes (SWCNTs) with fractional damping based on doublet mechanics. The Kelvin–Vigot model is used to incorporate damping effect for CNTs. By solving the equation of motion, the relation between natural frequency with scale parameter and fractional order is derived in the axial mode of vibration. It is shown that fractional order and scale parameter play significant roles in the axial vibration behavior of SWCNTs. Such effects decrease the natural frequency compared to the predictions of the classical continuum mechanics models and also ignores the damping effects. These effects on the natural frequency are more apparent in higher mode numbers and lower tube lengths and radii. Results for complex roots of characteristic equation obtained for a SWCNT without viscoelastic foundation, where imaginary parts represent damped frequencies, were compared with the results found from molecular mechanics simulations and a good agreement was achieved. | Axial vibration of single-walled carbon nanotubes with fractional damping using doublet mechanics | 10.1007/s12648-019-01547-y |
2020-07-01 | Microbeam resonators are widely used due to their scientific and engineering applications. The accurate prediction of thermoelastic damping (TED) is necessary to evaluate the performance of resonators at micro- and nanoscales with less energy dissipation. This article aims to present an analytical method for analyzing TED and dynamic behavior of microbeam resonators based on the Moore–Gibson–Thompson (MGT) generalized thermoelasticity theory. The finite Fourier sine transform and Laplace transform methods are used to solve the coupled thermoelastic equations. The analytical solutions are obtained for deflection and thermal moment of beams. The vibration responses of deflection and thermal moment are established in microbeams with simply supported and isothermal boundary conditions. The responses of deflection and thermal moment in beams are analyzed by comparing the results obtained under the MGT model with the corresponding results under the Lord–Shulman (LS) and Green–Naghdi (GN-III) models. The obtained results show that the amplitudes of deflection and thermal moment are attenuated, and the vibration frequency is increased due to the effect of thermoelastic coupling. It has been observed that the amplitudes of deflection under these three models are approximately the same, while the amplitude of thermal moment under the MGT model is higher than under the GN-III model and agrees with the LS model. It has been further noticed that TED depends on the size of the beams when the thermoelastic coupling effect is considered. | Thermoelastic damping analysis in microbeam resonators based on Moore–Gibson–Thompson generalized thermoelasticity theory | 10.1007/s00707-020-02688-6 |
2020-07-01 | A nonlinear vibration isolation system is promising to provide a high-efficient broadband isolation performance. In this paper, a generalized vibration isolation system is established with nonlinear stiffness, nonlinear viscous damping, and Bouc-Wen (BW) hysteretic damping. An approximate analytical analysis is performed based on a harmonic balance method (HBM) and an alternating frequency/time (AFT) domain technique. To evaluate the damping effect, a generalized equivalent damping ratio is defined with the stiffness-varying characteristics. A comprehensive comparison of different kinds of damping is made through numerical simulations. It is found that the damping ratio of the linear damping is related to the stiffness-varying characteristics while the damping ratios of two kinds of nonlinear damping are related to the responding amplitudes. The linear damping, hysteretic damping, and nonlinear viscous damping are suitable for the small-amplitude, medium-amplitude, and large-amplitude conditions, respectively. The hysteretic damping has an extra advantage of broadband isolation. | Research on linear/nonlinear viscous damping and hysteretic damping in nonlinear vibration isolation systems | 10.1007/s10483-020-2630-6 |
2020-07-01 | A damped Newton’s method to find a singularity of a vector field in Riemannian setting is presented with global convergence study. It is ensured that the sequence generated by the proposed method reduces to a sequence generated by the Riemannian version of the classical Newton’s method after a finite number of iterations, consequently its convergence rate is superlinear/quadratic. Even at an early stage of development, we can observe from numerical experiments that DNM presented promising results when compared with the well known BFGS and Trust Regions methods. Moreover, damped Newton’s method present better performance than the Newton’s method in number of iteration and computational time. | Damped Newton’s method on Riemannian manifolds | 10.1007/s10898-020-00885-0 |
2020-06-22 | In this paper, we prove that the existence of global attractors for a Kirchhoff wave equation with nonlinear damping and memory. | Global attractors for Kirchhoff wave equation with nonlinear damping and memory | 10.1186/s13661-020-01413-5 |
2020-06-19 | In this paper, we study the initial-boundary value problem for a system of nonlinear viscoelastic equations with Balakrishnan–Taylor damping terms and nonlinear source of polynomial type. We demonstrate that the nonlinear source of polynomial type is able to force solutions to blow up infinite time even in presence of stronger damping with non positive initial energy combined with a positive initial energy. | Blow-Up of Solutions for a System Viscoelastic Equation with Balakrishnan–Taylor Damping and Nonlinear Source of Polynomial Type | 10.1007/s40819-020-00858-7 |
2020-06-10 | A new semi-active mass damper, included active joint to control Lock/Unlock between the mass of damper and structure, is proposed to avoid “de-tuning effect” in this study. A ten-floor shear building with Tuned Mass Damper (TMD) and Semi-Active Mass Damper (SAMD) under excitation of 26 earthquake records is simulated by numerical analysis to compare the shock absorption effects. Analysis results show that: (1) Shock absorption of roof displacement and root mean square (RMS) roof displacement is 9.9%, 15.8% and 67.9%, 70.9% for structure with TMD and SAMD under excitation of Kobe 1995 earthquake respectively. Shock absorption of roof displacement and RMS roof displacement 52.7%, 62.1% and 55.7%, 66.3% for structure with TMD and SAMD under excitation of Sumatra 2007 earthquake respectively. (2) Structural response of building with SAMD controlled is very low sensitivity to frequency ratio. SAMD control effect is better than that of TMD on near fault earthquakes and suitable for far-field earthquakes. Otherwise, SAMD is almost without “de-tuning effect”. (3) Shock absorption ratio of the roof displacement responses and RMS displacement responses for structure with SAMD under excitation of far-field earthquake is above 38% and 62%, respectively. The frequency ratio of SAMD controlled should be limited to less than 4.0 to avoid enlarging the maximum acceleration responses. The practicability of this proposed SAMD has been verified by numerical analysis. | Development of semi-active mass damper with impulsive reaction | 10.1007/s12046-020-01395-1 |
2020-06-02 | In the present study, it was attempted to investigate the cyclic resistance of equi-proportionate silt–sand range pond ash (with 50% fines) at relatively high shear strains using the strain-controlled cyclic triaxial test. The cyclic triaxial tests have been performed considering the effect of relative compaction (97–99%), cyclic shear strain (0.6–1.35%), frequency of loading (0.3–1 Hz) and effective confining pressure (50–100 kPa) on cyclic resistance of pond ash. Dynamic characteristics such as dynamic shear modulus and damping ratio of equi-proportionate silt–sand range pond ash was evaluated for all the parameters considered at high shear strain. The maximum value of the dynamic shear modulus and damping ratio of pond ash observed in this study was 6534.8 kPa and 23.64%, respectively. The dynamic shear modulus and damping ratio of pond ash was decreased from 6534.8 to 5023.87 kPa and 23.64 to 14.17% with the increase in shear strain amplitude from 0.6 to 1.35%. Besides, few relationships were established between the amount of energy dissipated until liquefaction and parameters influencing liquefaction using an energy concept. | Experimental Investigation on Dynamic Characterization of Equi-Proportionate Silt–Sand Range Pond Ash at High Strain | 10.1007/s40891-020-00211-4 |
2020-06-01 | This paper considers a spherical particle damper that is subjected to impact loading. An experiment using a viscoanalyser machine was performed to obtain the viscoelastic properties (Young’s modulus and loss factor) at any temperature and any frequency. This procedure extracts the master curve for the viscoelastic material. A suitable Prony series/parameters (Generalised Maxwell equation) model to represent viscoelastic behaviour is fitted to the master curve data. These Prony series are used to define the material properties of the particle in the finite element (FE) analysis. To validate the FE model, the stiffness contact property for particle is compared with Hertz contact theory. A study of the impact response of viscoelastic particles was carried out to test the ability of the Prony series in conjunction with the FE model to replicate real behaviour. The FE model was also validated using an impact/rebound experiment. The comparison between FE model and experiment shows fairly good agreement. | Viscoelastic Behaviour of Element of Particle Damper: Experimental and Numerical Study | 10.1007/s40997-018-0277-3 |
2020-06-01 | This paper presents a theoretical investigation on the response of free vibration of functionally graded material (FGM) micro-plates with thermoelastic damping (TED). Continuous through thickness variation of the mechanical and thermal properties of the FGM plate is considered. By employing the simplified one-way coupled heat conduction equation and Kirchhoff’s plate theory, governing equations for the free vibration of the FGM micro-plates with thermoelastic coupling effect are established, in which stretching-bending coupling produced by the material inhomogeneity in the thickness direction is also considered. The heat conduction equation with variable coefficients is solved effectively by a layer-wise homogenization approach. Harmonic responses of the FGM micro-plates with complex frequency are obtained from the mathematical similarity between the eigenvalue problems of the FGM micro-plate with TED and that of the homogenous one without TED. The presented analytical solutions are suitable for evaluating TED in FGM micro-plates with arbitrary through-thickness material gradient, geometry and boundary conditions. Numerical results of TED for a ceramic-metal composite FGM micro-plate with power-law material gradient profile are illustrated to quantitatively show the effects of the material gradient index, the plate thickness, and the boundary conditions on the TED. The results indicate that by adjusting the physical and geometrical parameters of the FGM micro- plate, one can get the minimum of the TED which is even smaller than that of the pure ceramic resonator. | Analysis of free vibration of functionally graded material micro-plates with thermoelastic damping | 10.1007/s00419-020-01664-9 |
2020-06-01 | Reynolds equation for aerostatic bearing is numerically solved to obtain the stiffness, damping and critical frequency characteristics. The inertia and critical frequency are simulated as a function of bearing number and nozzle restriction number. The Reynolds equation is resolved for given dynamic properties of vibration. The numerical modeling is obtained using finite volume method. Numerical stability analysis for aerostatic bearing system is used to obtain the optimized design parameters. The variation in bearing stiffness, damping and critical frequency parameters with frequency of rotation is obtained numerically. The stability analysis depicts the variation in critical inertia parameters increases with frequency of rotation. Further, the eccentricity, which determines the shift of journal location from the bearing center, also influences the stability characteristics. It is further required to establish more detailed relation with observed frequency of vibration and design parameters. | Numerical Simulation of Aerostatic Bearing Stiffness, Damping and Critical Frequency Properties Using Linear Stability Analysis | 10.1007/s40032-020-00566-7 |
2020-06-01 | In this study, we focus on the controllability of fractional-order damped systems in linear and nonlinear cases with multiple time-varying delays in control. For the linear system based on the Mittag-Leffler matrix function, we define a controllability Gramian matrix, which is useful in judging whether the system is controllable or not. Furthermore, in two special cases, we present serval equivalent controllable conditions which are easy to verify. For the nonlinear system, under the controllability of its corresponding linear system, we obtain a sufficient condition on the nonlinear term to ensure that the system is controllable. Finally, two examples are given to illustrate the theory. | Controllability of fractional-order damped systems with time-varying delays in control | 10.1631/FITEE.1900736 |
2020-06-01 | In this article, we deal with the existence of mild L -quasi-solutions for damped elastic systems in Banach spaces. The results improve and extend some relevant results in ordinary differential equations and partial differential equations. Under monotone condition and the noncompactness measure condition on nonlinearity, we obtain the existence of extremal mild solutions. In addition, two examples are given to illustrate our results. | Mixed monotone iterative technique for damped elastic systems in Banach spaces | 10.1007/s11868-019-00296-0 |
2020-06-01 | An efficient global optimization algorithm has been developed by combining GA (genetic algorithm) and SA (simulated annealing). It is observed that the coupled optimization algorithm can converge faster than each single algorithm. It is applied for the design optimization of damper coil springs that absorb the torsional impact and vibration imposed on the clutch of an automatic transmission. Additionally, an user friendly computer program is developed in order to design various types of torque converter damper springs automatically. Dynamic characteristics and torque capacity of damper springs varies according to a spring constant that depends on a wire diameter, a coil diameter, the number of turns, a coil length, etc. The torque variation according to the spring constant characteristics of a curved compressive coil spring is calculated and compared with that of a straight one using the coupled simulated annealing and genetic algorithm. | Coupled GA-SA Optimization Algorithm and Application for Compressive Curved Damper Springs of Automotive Lockup Clutches | 10.1007/s12239-020-0061-4 |
2020-06-01 | Dealing with the physical interaction between humans and robots, Series Elastic Actuators (SEAs) are identified as one solution to overcome many limits, such as reducing contact forces or detect collisions. Nevertheless, the low-damping dynamic of a SEA can lead to undesired behaviours, especially during particular applications where a high level of precision is required. In this paper, a linear control architecture to enhance the damping performance of a SEA is presented. The proposed structure consists in a cascade control where loops are regulated using three types of controllers: PI, PD and a generalized controller specifically designed to damp oscillations. A frequency-domain approach with related constraints could not satisfy the time-domain goal in term of oscillation damping, for this reason an optimization problem able to consider them both is taken into account. A robust design is mandatory to the model mismatch introduced by neglecting coupling between motor. Therefore, robustness constraints are introduced in the optimization procedure. Indeed, the effectiveness of the control architecture is tested on a real compliant robot with six degrees of freedom equipped with as many SEAs. Each test aims to highlight the damping performance of the controlled system while the robot performs various tasks or it is subject to external disturbances. | A Robust Linear Control Strategy to Enhance Damping of a Series Elastic Actuator on a Collaborative Robot | 10.1007/s10846-019-01071-5 |
2020-06-01 | The aim of this work is to compare two different joining technologies for steel and carbon fibre reinforced polymer materials in a hybrid gear in order to improve the dynamic behaviour in terms of natural frequencies and damping properties. A comprehensive approach for the design and prototyping of hybrid metal-composite gears with interference fitting and adhesive bonding is provided. In a following phase, an accurate description of the experimental impact tests is shown in order to investigate modal performances. Successively, in a finite element environment, modal analyses are conducted and frequency response functions of the gear model are analysed by means of complex stiffness matrix that accounts for structural damping. Impact tests and simulations indicate that the solution with interference fitting is stiffer than the one with adhesive, even if the damping capacity is lower. The results for both technologies show that it is possible to enhance noise and vibrations behaviour of gears through the application of composite materials in place of conventional full-metal solutions. | A comparative analysis of adhesive bonding and interference fitting as joining technologies for hybrid metal-composite gear manufacturing | 10.1007/s12008-020-00647-y |
2020-06-01 | The studies on acoustical behaviour of composite boards made from five different types of natural fibres (bagasse, bamboo, banana, coir and corn husk) have been carried out for their utilization as sound-absorbing materials. The composite boards of all five types of fibres were prepared in three different density range (low, medium and high). The ranges of low, medium and high density boards varied from 280 to 300 kg/m^3, 320 to 350 kg/m^3 and 400 to 450 kg/m^3, respectively. The porosity, which was calculated based on bulk board density and fibre density, was found to vary from 50 to 79% depending upon the types of fibres and density of board. The damping coefficient (tan δ ) was determined using dynamic mechanical analyzer and found maximum (0.09) in banana and corn husk fibre boards having density 280–297 kg/m^3). The variation of sound absorption coefficient of fibre boards with frequency (up to 4 kHz) was measured. The noise reduction coefficient (NRC), which was calculated as an average of sound absorption coefficient values at 250, 500, 1000 and 2000 Hz, was found to decrease with the increase in board densities for all the five types of boards. The maximum NRC value of 0.40 was found for banana fibre boards having density of 280 kg/m^3 and therefore found comparatively more suitable as sound absorbing material. | Acoustical behaviour of natural fibres-based composite boards as sound-absorbing materials | 10.1007/s13196-020-00255-z |
2020-06-01 | In this paper, stability investigations of a novel roughing-finishing end mill are carried out. This tool possesses two sharp finishing teeth and two radially recessed, chamfered roughing teeth. By applying the same tool for roughing and finishing operations, tool changes and process time can be reduced. For the stability investigations, the semi-discretization method for calculating stability charts was extended and made applicable for the novel tool concept by taking into account the radial recession of the chamfered cutting teeth. This is necessary because the radial recession leads to varying time-delays during the tooth engagement. Stability charts were then calculated for roughing-finishing tools with different radial recession as well as for conventional finishing and roughing tools. Furthermore, experimental stability charts were created. The results show a good agreement between calculated and experimental stability charts for the finishing tool. However, the calculated stability limits of the roughing-finishing tool and the roughing tool do not met with the experimental stability limits, which is attributed to inaccuracies in the modelling of process damping. Nevertheless, calculated as well as experimental stability charts indicate a significant increase of the stability limit of the roughing-finishing tool compared to the finishing tool. | Process stability of a novel roughing-finishing end mill | 10.1007/s11740-020-00963-y |
2020-06-01 | The equation governing the dynamics of a heat-exchanger tube is a delay differential equation (DDE). In all the earlier studies, only the stability boundaries in the parametric space of mass-damping parameter and reduced flow-velocity were reported. The contour plots showing the damping in different regions of the stability chart has never been reported, due to the complexity in solving the infinite-dimensional nonlinear eigenvalue problem associated with characteristic roots of the governing DDE. In this work using Galerkin approximations, the spectrum (characteristic roots) of the DDE is obtained. The rightmost characteristic root, whose real part represents the damping in the heat-exchanger tube is included in the stability chart. Interestingly, it is found that the highest damping is present in localized areas of the stability charts, which are close to the stability boundaries. These stability charts can be used to determine the optimal cross-flow velocities for operating the heat-exchanger tube for achieving maximum damping. Explicit evaluation of the characteristic roots allows us to show that the roots cross the stability boundary with a non-zero velocity, clearly indicating the existence of Hopf bifurcation at the stability boundary. | A note on damping in heat-exchanger tubes subjected to cross-flow | 10.1007/s40435-019-00590-1 |
2020-06-01 | This study presents an advanced algorithm for controlling the web longitude and tension of nonlinear roll-to-roll systems in the form of a cascade structure. Parameter variation and disturbance attenuation problems are addressed systematically. The features of this article are divided into two parts. First, active damping terms are injected to stabilize the system nonlinear dynamics so that the first-order closed-loop transfer functions are obtained for each loop via pole-zero cancelation. Second, disturbance observers are introduced to ensure the performance recovery property by attenuating the disturbances from the model-plant mismatches. The closed-loop system is numerically emulated using MATLAB/Simulink to show the effectiveness of the proposed technique. | Active damping injection controller for web longitude and tensions of nonlinear roll-to-roll systems | 10.1007/s11071-020-05711-6 |
2020-06-01 | We prove $$L^r$$ L r -estimates on periodic solutions of periodically forced, linearly damped mechanical systems with polynomially bounded potentials. The estimates are applied to obtain a nonexistence result of periodic solutions in bounded domains, depending on an upper bound on the gradient of the potential. The results are illustrated on examples. | Nonexistence of Periodic Orbits for Forced–Damped Potential Systems in Bounded Domains | 10.1007/s00332-020-09607-y |
2020-06-01 | A new metal foam magneto-rheological (MR) fluid damper is optimized, and the mechanical performance is investigated experimentally. With a magnetic field, MR fluid is extracted from the metal foam and fills up the shear gap to produce the MR effect. The magnetic field density in the shear gap and the structural parameters are taken as the optimization object, and the optimal parameters of the metal foam MR fluid damper are updated. A testing system, including a DC motor with a speed controller, a force sensor with an amplifier and a power supply, is built to investigate the shear force of the metal foam MR fluid damper. The test signals are gathered and processed by a DAQ and a PC with LabVIEW software. A timer is designed to synchronize the start of the magnetic field. The experimental results show that the shear force decreases as the shear rate increases, and for the same shear rate, when the current ranges from 0.5 to 1.0 A, the difference of the shear force in the metal foam MR fluid damper is the most obvious. Additionally, the shear force after optimization clearly increases. When the current increases gradually, the shear force also increases. When the excited current increases from 0.5 to 1.5 A, as the current increases, the shear force increases obviously; however, once the current is above 1.5 A, the increase of the shear force is no longer obvious. In addition, for a shear rate of 2 s^−1 and a current of 1.0 A, the shear force of the metal foam MR fluid damper is improved by a factor of 1.46 compared to the value before optimization. | Parameter optimization of a metal foam magneto-rheological damper | 10.1007/s10999-019-09463-z |
2020-06-01 | Purpose An experimental–numerical study of an inverted pendulum system to control a reduced model of a main system is developed in this work. Method Initially, a dynamic system model with one degree of freedom (1DoF) translational in the horizontal direction is analyzed. To this system is coupled a passive control device in the geometry of a tuned mass damper inverted pendulum (TMD-IP). Different TMD-IP configurations are analyzed. The theoretical formulation adopted for free and forced vibration analysis is presented. Subsequently, an experimental bench composed of a reduced model with 1DoF, an TMD-IP and a dynamic exciter is designed and constructed. The data acquisition is performed via video techniques. A sensitivity analysis is performed, as well as an optimization, with the intention of finding the optimal parameters for the TMD-IP. Results Experimental and numerical analyses are performed on free vibration as well as forced vibration. Comparison of the results obtained showed a good agreement. Conclusions The TMD-IP showed to be a good solution reducing the main system horizontal vibrations. | Experimental Analysis of One-Degree-of-Freedom (1DoF) Dynamic System Controlled by Optimized Inverted Pendulum | 10.1007/s42417-020-00198-2 |
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