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2018-09-21 | In power systems, increasing the renewable energy penetration with small signal stability is one of the demanding and critical tasks in recent days. This research work aims to develop a multistage optimization technique, namely particle swarm optimization (PSO), for improving both the energy penetration and small signal stability. Here, the wind and solar power sources are considered, and its penetration is maximized by satisfying the grid requirements such as the bus voltage, line flows, and real and reactive power generation within the limit. This work includes two stages: in the first stage, PSO algorithm is implemented for maximizing the renewable energy penetration to the test systems. Then, in the second stage, the small signal stability of the systems is improved with maximum renewable energy penetration in which the best locations for connecting the wind farm are identified by using the calculation of wind farm placement index and solar generation is fixed by considering voltage and bus load absorption capability. During simulation, the proposed method is tested and validated by using IEEE 14-bus standard system, and the 220 kV Kerala (India) grid practical system with the solar and wind power. Moreover, various measures such as power generation, load and bus voltage are evaluated for two different case studies. In this evaluation, it is proved that the renewable energy sources are safely integrated with the power system with increased energy penetration and improved small signal stability. | An enhanced particle swarm optimization algorithm for improving the renewable energy penetration and small signal stability in power system | 10.1186/s40807-018-0053-4 |
2018-09-15 | Background Dramatic progress has recently been made in cryo-electron microscopy technologies, which now make possible the reconstruction of a growing number of biomolecular structures to near-atomic resolution. However, the need persists for fitting and refinement approaches that address those cases that require modeling assistance. Methods In this paper, we describe algorithms to optimize the performance of such medium-resolution refinement methods. These algorithms aim to automatically optimize the parameters that define the density shape of the flexibly fitted model, as well as the time-dependent damper cutoff distance. Atomic distance constraints can be prescribed for cases where extra containment of parts of the structure is helpful, such as in regions where the density map is poorly defined. Also, we propose a simple stopping criterion that estimates the probable onset of overfitting during the simulation. Results The new set of algorithms produce more accurate fitting and refinement results, and yield a faster rate of convergence of the trajectory toward the fitted conformation. The latter is also more reliable due to the overfitting warning provided to the user. Conclusions The algorithms described here were implemented in the new Damped-Dynamics Flexible Fitting simulation tool “ DDforge ” in the Situs package. | Accurate flexible refinement of atomic models against medium-resolution cryo-EM maps using damped dynamics | 10.1186/s12900-018-0089-0 |
2018-09-05 | In this paper we investigate the existence and uniqueness of weighted pseudo almost automorphic mild solution for a class of strongly damped wave equations where the semilinear forcing term is a Stepanov weighted pseudo almost automorphic function. | Strongly damped wave equations with Stepanov type nonlinear forcing term | 10.1186/s13662-018-1770-0 |
2018-09-01 | A thick 400-micron amorphous carbon nitride (a-CN_X) coating material was synthesized by means of plasma-enhanced chemical vapor deposition process. High-power impulse magnetron sputtering technique was used to sputter a pure graphite target plate in reactive argon (Ar), nitrogen (N_2) and acetylene (C_2H_2) environment for depositing the composite coating. Structural and chemical/elemental composition of the a-CN_X composite material was investigated by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and micro-Raman spectroscopy. The root-mean-square surface roughness ( S _q) and structure were estimated by atomic force microscopy. Mechanical properties such as hardness and Young’s modulus (Oliver–Pharr method) at room temperature were characterized by Vickers micro-indentation test. Operational temperature test of the deposited a-CN_X coating reveals that it can withstand up to 400 °C without cracking. An inverted shaker test, based on central impedance method, was adopted to investigate the dynamic damping property of the coating material, and it was found that the first bending mode damping lossfactor of the reported a-CN_X coating is 0.015 ± 0.001 and corresponding loss modulus (Young’s modulus multiplied by lossfactor) is 0.234 ± 0.011 GPa. | Manufacturing and Characterization of a Carbon-Based Amorphous (a-CN_X) Coating Material | 10.1007/s41871-018-0014-y |
2018-09-01 | The technique of squeeze liquid film damping is adopted in precision boring. After finishing the static stimulating vibration experiments, dynamic experiments and real cutting experiments, the results show that squeeze liquid film damper (SLFD) can ameliorate the machining condition and improve the precise boring quality. At the same time, structure parameters of SLFD are confirmed through experiments and the important gist is provided for optimal design of the damper. | Research on Effect of Decreasing Vibration with Liquid Film Damping in Precision Boring | 10.1007/s11277-017-5141-z |
2018-09-01 | Behaviors of sandy soils under dry and saturated conditions significantly differ from each other, especially under cyclic loading conditions. This paper highlights the behavior of dry and saturated Brahmaputra sand (DBS and SBS) subjected to constant strain monotonic and cyclic triaxial tests. Monotonic tests were conducted on specimens prepared at 60% relative density at a constant deformation rate 1.2 mm/min and varying confining pressures (50, 100, and 150 kPa), while the cyclic tests were conducted with varying cyclic shear strain amplitudes (0.015–7%). Monotonic tests reveal a phase transformation for SBS from contractive to dilative, while DBS shows an ever dilative response. An progressive asymmetric hysteresis behavior was observed under higher cyclic strains, based on which a modified methodology is developed to evaluate the dynamic properties of soil. Beyond 1% shear strain, damping ratio for dry sand was found to follow an asymptotic trend, while the saturated sand exhibited a significant reduction in magnitude. Comparison of the present findings with the standard dynamic models exhibits the importance of conducting site-specific dynamic soil characterization. | High Strain Dynamic Properties of Perfectly Dry and Saturated Cohesionless Soil | 10.1007/s40098-017-0255-5 |
2018-09-01 | This paper is concerned with the development of mesh free model for the performance analysis of active constrained layered damping ( ACLD ) treatments on smart laminated composite beams. The overall structure is composed of a substrate laminated composite beam integrated with a viscoelastic layer and a piezoelectric layer attached partially or fully at the top surface of the substrate beam. The piezoelectric layer acts as the active constraining layer of the smart beam and the viscoelastic layer acts as the constrained layer. A layer wise displacement theory has been used to derive the models. Both symmetric cross-ply and antisymmetric angle-ply laminated beams are considered for the numerical analysis. It is observed that ACLD treatment significantly improves the active damping properties of the substrate beam. The numerical results also reveal that the triangular ACLD treatment is more effective than the rectangular ACLD treatment of same thickness and volume for active damping of smart composite beams. | Analysis of smart damping of laminated composite beams using mesh free method | 10.1007/s10999-017-9379-0 |
2018-09-01 | Abstract An analysis of the characteristics of the output filters of electromagnetic compatibility of a frequency converter, including their logarithmic amplitude-frequency characteristics, is carried out by mathematical modeling. The filters with the different parameters, are considered in the steady operation mode at the carrier frequency of pulse-duration modulation of 2.5 kHz and basic frequency of supply voltage of the asynchronous motor of 50 Hz, including with the different connection diagrams of the damping resistors—with parallel connection of inductance in the longitudinal filter branch and series connection of the capacity in the transverse filter branch. In addition, the filter is studied, not including the damping resistors. The losses in the filters are considered. A conclusion is drawn that it is necessary to consider the parasitic parameters of the capacitors: equivalent series inductance, equivalent series resistance, equivalent parallel resistance considering the leakage current through the capacitor, and voltage regulator diode simulating the behavior of the capacitor under the overvoltages. | Characteristics of Output Filters Providing Electromagnetic Compatibility of the Frequency Converter of an Electric Drive with Asynchronous Motors | 10.3103/S1068371218090080 |
2018-09-01 | Lightweight sand–EPS beads composite is a new artificial geo-material, which has been recently found applications in geotechnical engineering projects. A series of laboratory tests were carried out using a large-scale cyclic direct shear test apparatus to evaluate the monotonic, cyclic and post-cyclic behaviour of an interface between EPS-sand mixtures and a Polyfelt geogrid. EPS were added to sand at 0%, 0.5%, 1%, and 2% by weight. Tests were conducted under three different vertical stresses (30 kPa, 60 kPa and 90 kPa). The influences of cyclic shear semi-amplitude, number of cycles and normal stress on interface properties are investigated. The test results revealed that for a given strain level, interface shear stiffness decreases and damping ratio was shown to increase with increasing EPS content. Hardening behaviour was observed with the number of cycles under different normal stress levels and EPS contents. The EPS-sand-geogrid specimens did not develop clear peak shear stress at monotonic and post-cyclic direct shear tests. The EPS-sand-geogrid mixtures represent an overall contraction behaviour in monotonic, cyclic and post-cyclic stages. The apparent adhesion of interface was shown to increase and the friction angle of interface to decrease with EPS content. | Cyclic and Post-Cyclic Shear Behaviour of Interface between Geogrid and EPS Beads-Sand Backfill | 10.1007/s12205-018-0945-2 |
2018-09-01 | Since the power transmission line (PTL) passes through the high mountain and heavy snowfall region, it is necessary to keep the stability of the PTL. In this study, PTL is modeled as the mass-spring-damper system by using multi-body dynamics analysis program. In order to analyze the dynamic behavior of PTL, a damping coefficient for a multi-body model is derived by using the free vibration test and Rayleigh damping theory. The icing cross section of the transmission line is considered by ellipse and triangle shape. The aerodynamic coefficient for each cross sections are derived by using the commercial CFD program, ANSYS Fluent. The fluctuating wind velocity is regenerated with time history by using Kaimal spectrum. Galloping simulations are performed for the elliptical and triangular iced sections by using the generated fluctuating wind velocity. There is an attack angle which showed the maximum vertical displacement according to the icing section. As a results, the triangular icing shape on the fluctuating wind velocity is more dangerous for the galloping phenomenon. This results can be available to the tower design for the power transmission line. | Galloping Simulation of the Power Transmission Line under the Fluctuating Wind | 10.1007/s12541-018-0164-2 |
2018-09-01 | Slippage corresponds to the relative displacement of a bolted joint subjected to shear loads since the construction clearance between the bolt shank and the bolthole at assembly can cause joint slip. Deflections of towers with joint slippage effects is up to 1.9 times greater than the displacements obtained by linear analytical methods. In this study, 8 different types of joints are modelled and studied in the finite element program, and the results are verified by the experimental results which have been done in the laboratory. Moreover, several types of joints have been modelled and studied and load-deformation curves have also been presented. Finally, joint slip data for different types of angles, bolt diameter and bolt arrangements are generated. Thereupon, damping ratios (ζ) for different types of connections are reported. The study can be useful to help in designing of wind turbine towers with a higher level of accuracy and safety. | Joint slip investigation based on finite element modelling verified by experimental results on wind turbine lattice towers | 10.1007/s11709-017-0393-y |
2018-09-01 | To enhance the low-frequency vibration isolation performance of the high-static–low-dynamic stiffness (HSLDS) isolator, a novel design of the geometric nonlinear damping (GND) comprising semi-active electromagnetic shunt damping is proposed. The GND is dependent on the vibration displacement and velocity, which can make the HSLDS isolator attain different damping characteristics in different frequency bands. Firstly, the configuration of the HSLDS isolator assembled with GND is presented, and then the restoring force, stiffness, and damping are derived. The dynamics of the mount under both base and force excitations are investigated based on the harmonic balance method, which are then verified by numerical simulations. After that, the effects of GND on the displacement and force transmissibility are studied, and the excellent performance caused by GND is analyzed based on the equivalent viscous damping mechanism. Finally, the comparison between the GND and cubic nonlinear damping is performed. The results demonstrate that the HSLDS isolator assembled with GND can realize the requirements of an isolation system under both base and force excitations of broadband vibration isolation performance and a low resonance peak with the high-frequency attenuation unaffected. Moreover, the GND outperforms the linear damping no matter the base excitation or force excitation is applied. For base excitation, the GND exhibits some desirable properties that the cubic nonlinear damping does not have at high frequencies. | Enhanced isolation performance of a high-static–low-dynamic stiffness isolator with geometric nonlinear damping | 10.1007/s11071-018-4328-5 |
2018-09-01 | For any linear dynamical system coupled with one or more nonlinear dynamical attachments, the effect of nonlinear energy content on modal damping variations of the entire system has not been clearly addressed in the literature. Accordingly, a novel method is employed here to formulate the amplitude-dependent modal damping matrix for such nonlinear dynamical systems using an amplitude-dependent stiffness approach. The proposed method is directly applied into the equations of motion where numerical and analytical solutions are not required to be known a priori. This advantage is highly desirable to study the dynamical behavior of nonlinear dynamical systems by direct application of methods into equations of motion. Accordingly, the modal damping content variations under the effect of amplitude-dependent stiffness are investigated here. The method is based on linearizing the nonlinear coupling stiffness where a scaled amplitude-dependent stiffness has been obtained to replace the original nonlinear coupling stiffness in the system. Accordingly, the amplitude-dependent modal damping matrix in modal coordinates is obtained and investigated. Consequently, new significant findings regarding modal damping content variations under the effect of the change in nonlinear energy during oscillation are achieved through this study. Furthermore, the nonlinear amplitude-dependent modal damping matrix of the equivalent system is found to be satisfying all matrix similarity conditions with the linear amplitude-independent modal damping matrix of the original system. These findings are expected to be of significant impact on passive nonlinear targeted energy transfer for shock mitigation and energy-harvesting fields. | Modal damping variations in nonlinear dynamical systems | 10.1007/s11071-018-4342-7 |
2018-09-01 | Research on dynamics and stability of machining operations has attracted considerable attention. Currently, most studies focus on the forward solution of dynamics and stability in which material properties and the frequency response function at the tool tip are known to predict stable cutting conditions. However, the forward solution may fail to perform accurately in cases wherein the aforementioned information is partially known or varies based on the process conditions, or could involve several uncertainties in the dynamics. Under these circumstances, inverse stability solutions are immensely useful to identify the amount of variation in the effective damping or stiffness acting on the machining system. In this paper, the inverse stability solutions and their use for such purposes are discussed through relevant examples and case studies. Specific areas include identification of process damping at low cutting speeds and variations in spindle dynamics at high rotational speeds. | Use of inverse stability solutions for identification of uncertainties in the dynamics of machining processes | 10.1007/s40436-018-0233-x |
2018-09-01 | The damping capacity of Ni–Mn–Ga–Gd films annealed for different durations has been investigated by dynamic mechanical analysis (DMA) measurement. The DMA results show that the internal friction peaks are absent in the IF curves, due to very low transformation rate and low transformation strain in the films. With the increase of annealing time, the value of tan delta in martensite first increases then decreases due to the combined effect of grain size and martensite structure change. Owing to the occurrence of high-temperature creep behavior, an abrupt increase of tan delta takes place over 400 °C in the film annealed for 10 h. The film annealed for 5 h shows good thermal stability of phase transformation and keeps a high damping capacity in martensite after ten times of repeated DMA measurement. In terms of the high damping capacity (tan δ = 0.046) in martensite, high transformation temperature ( A _s = 292 °C), and good thermal stability, the film annealed for 5 h can be used as a damping material for MEMS devices in elevated temperature. | Damping Capacity of Ni–Mn–Ga–Gd High-Temperature Shape Memory Thin Film | 10.1007/s40830-018-0182-z |
2018-09-01 | The effect of intrinsic damping on the interaction between a two-level atom and a multi-photon cavity field in the presence of an external classical field is studied. Under certain conditions and use of a transformation, the system is transformed to a generalized Jaynes Cummings model, with the influence of classical field included in the detuning parameter. The temporal evolution of some statistical aspects such as, the atomic inversion, the squeezing phenomena and linear entropy are obtained. In addition, we present the effects of the intrinsic damping and detuning parameters on the above mentioned quantities, for one and two photons. The entropy is used as a measure of the degree of entanglement, and consequently discussed. | Influence of an External Classical Field on the Interaction Between a Field and an Atom in Presence of Intrinsic Damping | 10.1007/s10773-018-3799-y |
2018-09-01 | In this paper, we demonstrate a method for self-organization and leader following of nonholonomic robotic swarm based on spring damper mesh. By self-organization of swarm robots we mean the emergence of order in a swarm as the result of interactions among the single robots. In other words the self-organization of swarm robots mimics some natural behavior of social animals like ants among others. The dynamics of two-wheel robot is derived, and a relation between virtual forces and robot control inputs is defined in order to establish stable swarm formation. Two cases of swarm control are analyzed. In the first case the swarm cohesion is achieved by virtual spring damper mesh connecting nearest neighboring robots without designated leader. In the second case we introduce a swarm leader interacting with nearest and second neighbors allowing the swarm to follow the leader. The paper ends with numeric simulation for performance evaluation of the proposed control method. | Virtual spring damper method for nonholonomic robotic swarm self-organization and leader following | 10.1007/s00161-018-0664-4 |
2018-09-01 | This paper is concerned with the oscillatory behavior of the damped half-linear oscillator ( a ( t ) ϕ _ p ( x ′))′ + b ( t ) ϕ _ p ( x ′) + c ( t ) ϕ _ p ( x ) = 0, where ϕ p ( x ) = | x |^ p −1 sgn x for x ∈ ℝ and p > 1. A sufficient condition is established for oscillation of all nontrivial solutions of the damped half-linear oscillator under the integral averaging conditions. The main result can be given by using a generalized Young’s inequality and the Riccati type technique. Some examples are included to illustrate the result. Especially, an example which asserts that all nontrivial solutions are oscillatory if and only if p ≠ 2 is presented. | Integral averaging technique for oscillation of damped half-linear oscillators | 10.21136/CMJ.2018.0645-16 |
2018-09-01 | Presented in this paper is an experimental investigation of a passive auto-tuning mass damper with Pulley connections (PATPD). It is a passive vibration control device that consists of a box filled with silica sand on roller supports. The silica sand provides the mass of the damper. The PATPD is connected to the structure to be controlled by a group of inelastic ropes and pulleys; it is free to move in any translational direction. The pulleys and rope transfer a driving force, resulted from the movement of the structure under control, to the damper. The inertial force from the damper mass, via the connecting rope and pulley, acts on the structure in the direction opposite to any movement and thus providing the vibration control of the structure. Free and forced vibration tests are performed on six MDOF test structures with and without the PATPD as the natural frequencies of the test structures are varied by changing its mass or stiffness whilst keeping the PATPD constant. The test results reveal that the proposed damper, without any tuning or specific adjustment, produces effective control on translational, torsional and coupled vibration of the MDOF structure—even if the vibration frequencies or natural frequencies of the structure that is being controlled changes significantly. The PATPD is simple, effective, robust and adaptive which renders this proposed damper appealing for engineering applications. | Experimental investigation on a passive auto-tuning mass damper for vibration control | 10.1007/s40435-017-0381-z |
2018-09-01 | The fly ash cenosphere/AZ91D composites were successfully prepared and isothermally heat-treated at different temperatures for different time. The effects of semi-solid isothermal heat treatment on the microstructures and damping capacities of fly ash cenosphere/AZ91D composites were investigated. With the increase in isothermal temperature or holding time, the small liquid droplets within grains increased in size but decreased in quantity. The average size and shape factor of Mg_2Si particles increased with the rise of isothermal temperature. The damping capacities of the composites were improved by isothermal heat treatment. At room temperature, the composites after heat treatment at 520 and 550 °C had a higher damping capacity due to interface damping when the strain amplitude was lower than about 8.8 × 10^−5, and the composite after heat treatment at 580 °C had a better damping capacity because of the dislocation damping under the condition of high strain amplitude. The damping capacities of the composites increased with the rise of the test temperature, and the damping mechanisms varied depending on different test temperatures. The interface damping played an important role when the test temperature was below about 100 °C, and the dislocation damping and grain boundary damping took effect with the rise of test temperature. | Effects of Semi-solid Isothermal Heat Treatment on Microstructures and Damping Capacities of Fly Ash Cenosphere/AZ91D Composites | 10.1007/s40195-018-0722-8 |
2018-08-30 | The Newtonian gravitational constant, G , is one of the most fundamental constants of nature, but we still do not have an accurate value for it. Despite two centuries of experimental effort, the value of G remains the least precisely known of the fundamental constants. A discrepancy of up to 0.05 per cent in recent determinations of G suggests that there may be undiscovered systematic errors in the various existing methods. One way to resolve this issue is to measure G using a number of methods that are unlikely to involve the same systematic effects. Here we report two independent determinations of G using torsion pendulum experiments with the time-of-swing method and the angular-acceleration-feedback method. We obtain G values of 6.674184 × 10^−11 and 6.674484 × 10^−11 cubic metres per kilogram per second squared, with relative standard uncertainties of 11.64 and 11.61 parts per million, respectively. These values have the smallest uncertainties reported until now, and both agree with the latest recommended value within two standard deviations. The Newtonian gravitational constant is measured with two independent methods, yielding results with relative standard uncertainties of 11.6 parts per million—the lowest uncertainty reported until now. | Measurements of the gravitational constant using two independent methods | 10.1038/s41586-018-0431-5 |
2018-08-21 | This paper presents an analytical study on the effect of couple stress on static and dynamic characteristics of wide tapered land slider bearing in the presence of applied magnetic field. A non-dimensional modified Reynolds equation is derived for the bearing under consideration. Closed-form expressions for the steady fluid film pressure, steady load carrying capacity and dynamic characteristics, viz., dynamic stiffness and dynamic damping coefficients are obtained. Numerical computations of the results revealed that magnetohydrodynamics tapered land slider bearing lubricated with couple stress fluid provides higher steady load carrying capacity, dynamic stiffness coefficient and dynamic damping coefficient as compared with the corresponding Newtonian case. It is observed that the presence of applied magnetic field characterized by the Hartmann number in the couple stress lubrication of tapered land slider bearing provides the improved static and dynamic characteristics as compared with the non-magnetic case. | Effect of couple stresses on static and dynamic characteristics of MHD wide tapered land slider bearing | 10.1007/s12046-018-0940-9 |
2018-08-17 | A nonlinear transient model for the prediction of damper force based on the flow of magnetorheological (MR) fluid through the channel of a semi-active MR damper has been presented which has a potential for its application in the design of adaptive control policies for such dampers. In this work, a transient analytical fluid dynamics model is developed by using a combination of Laplace and Weber transform and Duhamel’s superposition of velocity boundary condition. The solution of the system of nonlinear simultaneous equations, obtained by applying conservation of volumetric flux with nonlinear effects of fluid compressibility and gas spring, zero velocity gradient across the plug and force equilibrium of Bingham plastic plug flow through the annular channel. This method is shown to generate direct and inverse model of an MR device. The temporal variation of yield shear stress corresponding to the change in field excitation has been taken into account by using Fourier series. The model has been validated by testing a commercial MR damper on a test rig for sinusoidal velocity signals for constant field excitation current and constant velocity signals with square wave field excitation current. A useful outcome of the damper tests with constant velocity driving signal and square wave field excitation is that it can be used to measure the sum of non-controllable components of the damper force. The model predictions agree with the experiments within 13.5% error. The benchmarking and comparison with phenomenological/hysteresis models shows that such models can predict response for low-frequency current excitation and in the limited range for damper velocity variations. The phenomenological models are not suitable for high-speed MR damper applications. | A nonlinear transient model for magnetorheological damper response for a time varying field controllable yield shear stress | 10.1007/s40430-018-1343-x |
2018-08-09 | In this paper, we consider the Cauchy problem in $$\mathbb {R}^n,$$ R n , $$n\ge 1,$$ n ≥ 1 , for semilinear damped wave equations with space–time dependent potential and nonlinear memory. A blow-up result under some positive data in any dimensional space is obtained. Moreover, the local existence in the energy space is also studied. | Finite time blow-up for damped wave equations with space–time dependent potential and nonlinear memory | 10.1007/s00030-018-0533-7 |
2018-08-01 | The reduction of vibration by acoustic black holes (ABHs) with damping treatments can be achieved in two stages: energy focalization and energy dissipation. The energy focalization is mainly due to changes of the local thickness by slowing down the flexural wave speed and energy dissipation can be achieved by using viscoelastic damping materials. In structures with embedded ABHs, the damping effectiveness can depend significantly on the types of damping treatments. In this paper, 4 different damping treatments according to the types of attached region are considered in order to estimate the effectiveness of damping treatments as 1) a fully-covered unconstrained damping treatment, 2) a fully-covered constrained damping treatment, 3) a partially-covered unconstrained damping treatment and 4) a partially- covered constrained damping treatment as well as no damping treatment as reference data. In this study, the performance of damping treatments is explored using numerical simulations of three-dimensional thin plate embedded truncated ABH(s). The wave energy in the ABH, the normalized total energy and the focalization ratio are introduced to compare the effectiveness of the damping treatments. The numerical results show that the fully-covered constrained damping treatment provides the most effective configuration in terms of the wave energy in ABH and the normalized total energy. | Numerical analysis of wave energy dissipation by damping treatments in a plate with acoustic black holes | 10.1007/s12206-018-0705-8 |
2018-08-01 | This paper systematically illustrates the deformation and damping mechanism of magnetic shape memory alloy (MSMA) and builds a damping mathematical model by using a single-degree-of-freedom vibration system. The results indicate that absorbed damping is proportional to the quadratic of external force and inversely proportional to the overall mass, the natural frequency and the total damping of the system when the system is in resonance. At the same time, the paper calculates the relative power and draws the stress–strain curve of mechanical property. The relations among temperature, stress, intensity of magnetic induction, and deformation of MSMA are studied through a static experiment. Meanwhile, an analysis of the damping characteristic indicates that the external force is 25–30 N when the temperature ranges from 23 to 29 °C and that the deformation rate is the largest and the damping performance is the best at a magnetic induction strength of 0.55 T. | Research and Experimental Analysis of Damping Characteristics of Magnetic Shape Memory Alloy | 10.1007/s42341-018-0047-3 |
2018-08-01 | Decay of the energy for the Cauchy problem of the wave equation on Riemannian manifolds with a variable damping term $$V(x)u_{t}$$ V ( x ) u t is considered, where $$V(x) \ge V_{0}(1 + \rho ^{2})^{-\frac{1}{2}}$$ V ( x ) ≥ V 0 ( 1 + ρ 2 ) - 1 2 ( $$\rho $$ ρ being a distance function under the Riemannian metric). Some relations among the decay rates of energy, the size of the coefficients $$V_{0}$$ V 0 , and the radial curvatures of the Riemannian metric are presented. | Energy Decay Rate of the Wave Equations on Riemannian Manifolds with Critical Potential | 10.1007/s00245-017-9399-z |
2018-08-01 | Semi-submersible drilling rigs are offshore plants that perform function such as ocean exploration for oil and gas acquisition, drilling and production, storage and unloading of crude oil and gas. Semi-submersible drilling rigs use watertight dampers as emergency buoyancy holders. Since the watertight damper is an emergency shutoff device, it is mainly driven by a pneumatic driving system that can operate without power supply. Pneumatic driving system has highly non-linear characteristics due to compressibility of air and external disturbance such as static and coulomb friction. In this paper, a new control algorithm is proposed for the watertight damper driving system based on the sliding mode control. To evaluate control performance and robust stability of the designed controller, the control results were compared with the results using the state feedback controller. As a result, it was confirmed that rack & pinon type of pneumatic driving system for driving the watertight damper using the sliding mode controller that can obtain excellent control performance against the parameter changes and the disturbance. | Design of robust controller of a watertight damper driving system for offshore rigs | 10.1007/s12206-018-0740-5 |
2018-08-01 | When the power transmission line (PTL) passes through a region of high mountains and heavy snowfall, maintaining the stability of the PTL and avoiding sleet jump and galloping are necessary. In this study, PTL is modeled as the mass-spring-damper system by using the multi-body dynamics analysis program, RecurDyn. The lumped mass model is compared with the finite element model based on deflection. To analyze the dynamic behavior of the PTL under icing and wind conditions, we obtained a damping coefficient for a multibody model from the free vibration test and Rayleigh damping theory. The icing cross-section of the transmission line is assumed to have ellipse and triangle shapes. The aerodynamic coefficients for each cross-section are derived by using the commercial CFD program, ANSYS Fluent. The occurrence of galloping is simulated for each shape according to the attack angle. Results indicate that the dynamic behavior of the PTL and the galloping conditions such as the icing shape, thickness, and attack angle, can be analyzed. Furthermore, the effects of each factor are evaluated. In the elliptical icing section, the effect of icing thickness is high; whereas in the triangular icing section, the wind velocity highly affects galloping. | Multibody dynamics study on galloping of power transmission line | 10.1007/s12206-018-0710-y |
2018-08-01 | This study investigated the effects of Sc and Zr additions, friction stir processing (FSP), and subsequent solid solution and artificial aging (T6) treatment on the microstructure, damping capacity, and mechanical properties of 7075 Al alloy. The minor Sc and Zr additions promoted the grain refinement of this alloy during FSP and inhibited the growth of fine equiaxed grains in the FSP sample during subsequent T6 treatment. Thus, the fine equiaxed grain structure and high density of the η′ precipitated phase were simultaneously obtained in the 7075 Al alloy containing Sc and Zr after FSP and T6 treatment, and this sample exhibited superior mechanical properties and damping capacity to those of the 7075 Al alloy after T6 treatment. This work provides an effective strategy for preparing Al alloys with excellent damping capacity and mechanical properties. | Fabrication of 7075-0.25Sc-0.15Zr Alloy with Excellent Damping and Mechanical Properties by FSP and T6 Treatment | 10.1007/s11665-018-3451-2 |
2018-08-01 | Key message Cabling co-dominant stems at different heights and tensions altered neither frequency nor damping ratio, but the location and proportion of pruned crown mass significantly influenced both frequency and damping ratio. Abstract Amenity trees provide many benefits, but can damage property and injure persons. Arboricultural treatments like pruning and cabling intend to reduce the likelihood of tree failure, but the effect of such treatments on tree sways is not well known. We measured the sway response (frequency and damping ratio) of seven Quercus rubra L. before and after consecutive arboricultural treatments, including the addition a climber swaying freely or secured rigidly to the tree. We also quantified crown architecture and tree mass. Cabling two co-dominant stems did not influence sway response, but pruning increased frequency and decreased damping ratio. The effect of pruning depended on the proportion and location of pruned crown mass. Adding a climber predictably affected frequency and damping ratio in accordance with physical principles. This work adds novel insights to the understanding of tree sways, since previous studies have been limited by single trees, pruning types, or pruning severities. | The effect of simulated trunk splits, pruning, and cabling on sways of quercus rubra L. | 10.1007/s00468-018-1690-3 |
2018-08-01 | Machining-induced damage severely affects surface and subsurface integrity in grinding of brittle materials. In this paper, a predictive model of subsurface damage (SSD) is proposed that takes into account grinding parameters and spindle dynamics. Results show that the grinding depth affects SSD, and the model neglecting the effect of tool forced vibration underestimates damage. The subsurface quality can be improved by increasing the grinding wheel surface speed or lowering the workpiece speed. Increasing frequency ratio tends to improve subsurface quality. Nonmonotonic dependence of SSD on the damping ratio is found. When the frequency ratio is greater than 1, the depth of SSD first increases and then decreases as the damping ratio increases. Good correlations between predictions of SSD and experimental results are observed in grinding of optical glass BK7. | Subsurface damage in grinding of brittle materials considering machining parameters and spindle dynamics | 10.1007/s00170-018-2191-7 |
2018-08-01 | Parametric nonoscillation region is given for the Mathieu-type differential equation $$\begin{aligned} x'' + (-\;\alpha + \beta c(t))\,x = 0, \end{aligned}$$ x ′ ′ + ( - α + β c ( t ) ) x = 0 , where $$\alpha $$ α and $$\beta $$ β are real parameters. Oscillation problem about a kind of Meissner’s equation is also discussed. The obtained result is proved by using Sturm’s comparison theorem and phase plane analysis of the second-order differential equation $$\begin{aligned} y'' + a(t)y' + b(t)y = 0, \end{aligned}$$ y ′ ′ + a ( t ) y ′ + b ( t ) y = 0 , where a , $$b: [0,\infty ) \rightarrow \mathbb {R}$$ b : [ 0 , ∞ ) → R are continuous functions. The feature of the result is the ease of chequing whether the obtained condition is satisfied or not. Parametric nonoscilla- tion region about $$(\alpha ,\beta )$$ ( α , β ) and some solution orbits are drawn to help understand the result. | Nonoscillation of Mathieu’s equation whose coefficient is a finite Fourier series approximating a square wave | 10.1007/s00605-017-1049-7 |
2018-08-01 | Multi-objective optimization approach has been applied to find an optimum Tuned Mass Damper (TMD) to attenuate the earthquake induced vibrations of a ten-stored frame structure. In the optimization process, the Response Surface Methodology (RSM) with the experimental design of central Composite Design (CCD) and weighted desirability function (WDF) have been utilized for getting an optimum TMD. The properties of TMD such as frequency ratio and damping ratio have been considered as design variables where the top floor root mean square displacement and frequency responses were considered as objective functions. The optimization has been executed under the El Centro earthquake loads. To evaluate the efficiency of RSM and WDF based optimum TMD, the structure has been analyzed with the Den Hartog’s, Sadek et al.’s and Warburton’s designed TMD respectively for the El Centro, California and Northridge earthquakes load. The evaluated results have been found more satisfactory with the RSM and WDF based optimum TMD than with the others TMD. | Multi-Objective Optimization of TMD for Frame Structure Based on Response Surface Methodology and Weighted Desirability Function | 10.1007/s12205-017-0387-2 |
2018-08-01 | The present study has focused on the comparison of MR damper dynamic models for the purpose of hardware in the loop simulation. A vehicle dynamic model for large-sized bus and a control logic for MR damper was built. Two typical MR damper models, viz. Bouc-Wen and hyperbolic tangent model have been considered in this study and the advantages and disadvantages of each model on the aspect of HILS system is discussed. We discussed the limitations of each model based on the analysis of the vehicle dynamic simulation. The results showed that the existing models are not suitable for HILS system. We proposed the modified hyperbolic tangent model by adopting low-pass filters. The results from the simulation showed the advantages of the modified model which were validated through HILS system. | Comparison of Dynamic Models of Mr Damper for Hardware in the Loop Simulation of Large-Sized Buses | 10.1007/s12239-018-0065-5 |
2018-07-24 | Vibration control is one of the prominent factors, especially in lightweight structures in space technology. These structures, due to their low mass and thinness, frequently lose the stability under environmental disturbances. Piezoelectric materials as sensors/actuators have been widely used to control vibrations and mode shapes of such structures. Nowadays, piezoelectric and passive materials like viscoelastic materials have shown combined advantage of hybrid damping (active constrained layer damping) and with different parametric variations in them have shown remarkable property for control authority. This paper presents the details of parametric variations in smart structure using energy methods to demonstrate the utility for further structure design. Finite element model has been implemented using MATLAB software to analyze its effect of various parameters. Different environmental temperatures as thermal loads have been considered, and their effect on damping ratio is investigated. Parameters like percentage coverage of viscoelastic, piezoelectric material patches and the shape of patches on damping characteristics have been demonstrated. | Active vibration control of smart beam under parametric variations | 10.1007/s40430-018-1310-6 |
2018-07-16 | We are concerned with dynamical behaviors of solutions to nonlinear damped wave equations with nonlinear dampings and force terms, and subject to Wentzell boundary conditions which can be used to describe, for instance, the boundary behavior of a vibrating elastic body (resp. membrane) coated (resp. edged) with a thin layer (resp. coil) of high rigidity. Here the internal dampings are only assumed to be locally distributed and, especially, may disappear gradually over time. We find a new and effective method to overcome all the difficulties caused by the interplay of vanishing localized dampings, Wentzell boundary conditions, as well as nonlinear force terms. Ideal uniform decay rates of solution energies are obtained in terms of the exponents associated with the time-varying damping. Our result shows that the dynamical behavior of solutions is clearly stable without any bifurcation and chaos. To illustrate our theoretical results, we provide some numerical simulations. | Dynamical behaviors of solutions to nonlinear wave equations with vanishing local damping and Wentzell boundary conditions | 10.1007/s00033-018-0996-8 |
2018-07-11 | The intrinsic damping for the acoustic vibrations of single gold nanorods excited by ultrafast laser has been studied through the atomistic simulations. It is shown that the intrinsic damping for the breathing mode is strongly sensitive to the nanorod sizes, which is very likely due to the different energy redistributions between the vibrational modes of nanorods and could play a non-negligible role in the broad distribution of the experimentally measured breathing-mode quality factors. In comparison, the intrinsic damping for the extensional vibration of gold nanorods appears much less influenced by the variations of nanorod dimensions. Moreover, we also find that the intrinsic mechanism is a significant source for the vibrational damping of gold nanorods, particularly for the breathing mode. | Intrinsic damping for ultrafast laser-excited acoustic vibrations of single gold nanorods | 10.1007/s11051-018-4290-7 |
2018-07-05 | In this paper, we study the existence, multiplicity and stability of periodic solutions for a forced pendulum with time-dependent damping. The proof is based on the third order approximation method and a suitable version of the Poincaré–Birkhoff fixed point theorem. | Existence and stability of periodic solutions for a forced pendulum with time-dependent damping | 10.1186/s13661-018-1028-5 |
2018-07-05 | The objective of this paper is to offer sufficient conditions for the oscillation of all solutions of the third order nonlinear damped dynamic equation with mixed arguments of the form ( r 2 ( r 1 ( y Δ ) α ) Δ ) Δ ( t ) + p ( t ) ψ ( t , y Δ ( a ( t ) ) ) + q ( t ) f ( t , y ( g ( t ) ) ) = 0 $$\bigl(r_{2}\bigl(r_{1}\bigl(y^{\Delta}\bigr)^{\alpha}\bigr)^{\Delta}\bigr)^{\Delta}(t)+p(t)\psi \bigl(t,y^{\Delta}\bigl(a(t)\bigr)\bigr)+q(t)f\bigl(t,y\bigl(g(t)\bigr) \bigr)=0 $$ on time scales, where a ( t ) ≥ t $a(t)\geq t$ and g ( t ) ≤ t $g(t)\leq t$ . Using Riccati transformation, integral averaging technique, and comparison theorem, we give some new criteria for the oscillation of the studied equation. Our results essentially improve and complement the earlier ones. | Oscillation of third order nonlinear damped dynamic equation with mixed arguments on time scales | 10.1186/s13662-018-1654-3 |
2018-07-01 | To predict the maximum earthquake response of an SDOF structure with a Maxwell fluid damper or supplemental brace-viscous damper system using the seismic design response spectrum technique, a new approach is presented to determine the first- and second-order equivalent viscous damping and stiffness, the peak responses, and the damper force of the above structure. Based on the fact that the dynamic characteristics of a general linear viscoelastically damped structure are fully determined by its free vibration properties and the relaxation time constants of a Maxwell fluid damper and supplemental brace-viscous damper system in engineering practice are all small, the method of improved multiple time scales and the equivalent criterion in which all free vibration properties are the same are used to obtain the first- and second-order equivalent viscous damping and stiffness of the above structure in closed form. The accuracy of the proposed method is higher and significantly better than that of the modal strain energy method. Furthermore, in the parametric range of the requirements of the Chinese "Code for Seismic Design of Buildings", the error of the proposed second-order equivalent system for the above-mentioned engineering structure is not more than 0.5%. | Equivalent damping of SDOF structure with Maxwell damper | 10.1007/s11803-018-0467-4 |
2018-07-01 | In this paper, a battery energy storage system (BESS) based control method is proposed to improve the damping ratio of a target oscillation mode to a desired level by charging or discharging the installed BESS using local measurements. The expected damping improvement by BESS is derived analytically for both a single-machine-infinite-bus system and a multi-machine system. This BESS-based approach is tested on a four-generator, two-area power system. Effects of the power converter limit, response time delay, power system stabilizers and battery state-of-charge on the control performance are also investigated. Simulation results validate the effectiveness of the proposed approach. | Damping control for a target oscillation mode using battery energy storage | 10.1007/s40565-017-0371-3 |
2018-07-01 | Causality in electrodynamics is reviewed in regard to the interrelations among the causal requirement, the analyticity of the dielectric permittivity, and the Kramers-Kronig relations. We show that the collisionless damping (Landau damping) of a plasma wave can be formally derived from the causal requirement imposed on the susceptibility of a Vlasov-Poisson plasma. Here, the causal requirement is that the susceptibility χ ( t ) be nil for t < 0, which means the future electric field has nothing to do with the response effected in the medium at the present time. We show that this single requirement provides the analyticity of χ ( ω ) in the upper half- ω plane, the Kramers- Kronig relations, and Landau damping. Cerenkov emission which is the inverse process of Landau damping is also discussed in the light of causality. We present an easy way to calculate the electric fluctuation in a magnetized plasma by regarding a plasma as an assembly of non-interacting cold beams. We investigate the case of a separable distribution function $$g(x,t,v) = \tilde g(v)f(x - {v_0}t)$$ g ( x , t , v ) = g ˜ ( v ) f ( x − v 0 t ) , which corresponds to a special type of Benstein-Greene-Kruskal wave and a slight generalization of Van Kampen’s distribution function. We review Van Kampen’s theory of a Vlasov-Poisson system, which corresponds to the Sturm-Liouville theory of differential equations, and show that the Vlasov- Poisson equations in this separable case are trivially solved in terms of the separation constant. It is philosophically interesting that the collisionless damping of a plasma wave can be attributed to causality, which defines the direction of time and is operative in general electrodynamics. | Causality in Plasma Electrodynamics | 10.3938/jkps.73.65 |
2018-07-01 | Experimental data clearly show a strong and nonlinear dependence of damping from the maximum vibration amplitude reached in a cycle for macro- and microstructural elements. This dependence takes a completely different level with respect to the frequency shift of resonances due to nonlinearity, which is commonly of 10–25% at most for shells, plates and beams. The experiments show that a damping value over six times larger than the linear one must be expected for vibration of thin plates when the vibration amplitude is about twice the thickness. This is a huge change! The present study derives accurately, for the first time, the nonlinear damping from a fractional viscoelastic standard solid model by introducing geometric nonlinearity in it. The damping model obtained is nonlinear, and its frequency dependence can be tuned by the fractional derivative to match the material behaviour. The solution is obtained for a nonlinear single-degree-of-freedom system by harmonic balance. Numerical results are compared to experimental forced vibration responses measured for large-amplitude vibrations of a rectangular plate (hardening system), a circular cylindrical panel (softening system) and a clamped rod made of zirconium alloy (weak hardening system). Sets of experiments have been obtained at different harmonic excitation forces. Experimental results present a very large damping increase with the peak vibration amplitude, and the model is capable of reproducing them with very good accuracy. | Nonlinear damping in large-amplitude vibrations: modelling and experiments | 10.1007/s11071-017-3889-z |
2018-07-01 | Oblique water wave damping by two fully submerged vertical parallel porous plates of different heights is investigated within the framework of linear water wave theory. A channel of infinite horizontal extent but of finite depth is divided into three regions in each of which three different velocity potentials are considered and subsequently the corresponding boundary value problems are formulated. By means of eigenfunction expansion and least square method, complete analytical solution in each of the regions is obtained. With the help of the matching conditions along the vertical boundaries between any two successive regions, the reflection and transmission coefficients, and hence the energy loss (in %), are obtained numerically by applying a matrix method. Numerical study is carried out for various relevant parameters and it is found that with an appropriate choice of the parameters and positioning of the porous plates, both of the reflection and transmission coefficients become significantly low and consequently the porous plates can be utilized as an effecting wave absorber. Comparison of this work with earlier available work is made, and the good agreement in the results suggests the applicability of this method in further engineering purposes. A particular case of two free surface piercing plates is also investigated on similar line and the results are presented in order to observe the difference with the earlier case. | Oblique water wave damping by two submerged thin vertical porous plates of different heights | 10.1007/s40314-017-0545-7 |
2018-07-01 | The article deals with an arbitrary elastic 3D-system (body) that performs a controlled finite rotation with respect to some fixed axis and small nonstationary oscillations. The system oscillations occur due to external load (power control) or inertial load of the rotational transportation of the carrying body (kinematic control). The linear equations of oscillations are used in normal coordinates, in which motion is represented by eigenmodes of vibrations for system that is free in the rotation angle (including system rotation as a solid body in the case of power control) and for system fixed in rotation angle in the case of kinematic control. It is assumed that the (power or inertial)load acting on the system is proportional to some controlling finite time function from a certain class. The purpose of this article is to solve the problem of system rotation for a certain time from one rest position to another at a given finite angle using the given control function and to eliminate the elastic oscillations on the several lowest eigenmodes at the stopping time. The relations between the time of the system rotation under the action of a given control function and the eigenmodes frequencies for oscillations being eliminated are obtained on the basis of the exact solutions of the equations in normal coordinates. These relations satisfy the zero initial and final conditions. They are “tuned” by minimizing the positive definite quadratic form written for them by varying the system parameters to fulfill these relations simultaneously for several eigenfrequencies. As an example, the calculations for a model of a symmetrical spacecraft with two identical elastic solar cell panels consisting of four planar non-deformable sections connected by elastic hinges are carried out for comparison and analysis of the results accuracy. The finite rolling motion of the system with the damping at the stopping time of rotation for several (from one to three) lowest eigenmodes of antisymmetric vibrations is considered. The comparisons of the initial equations of motion for the system in generalized coordinates using several simple control functions and the found parameters of the “tuned” system with numerical solutions are accomplished. | Elimination of Nonstationary Oscillations of an Elastic System at the Stopping Time after Finite Rotation by the Given Law via the Tuning of Eigenfrequencies | 10.3103/S0025654418040027 |
2018-07-01 | We study the following second-order differential system 0.1 $$\begin{aligned} -\ddot{u}(t)-M\dot{u}(t)+L(t)u(t)=H_u(t,u(t)),\quad t\in \mathbb {R}, \end{aligned}$$ - u ¨ ( t ) - M u ˙ ( t ) + L ( t ) u ( t ) = H u ( t , u ( t ) ) , t ∈ R , which can be regarded as a second-order Hamiltonian system with a damped term. Here, the nonlinearity H ( t , u ) is superquadratic as $$|u|\rightarrow \infty $$ | u | → ∞ . We do not need any periodic conditions, and we obtain infinitely many nontrivial homoclinic orbits of this system by variational methods. Our result improves and extends the corresponding results existed. | Multiple Homoclinics for Nonperiodic Damped Systems with Superlinear Terms | 10.1007/s40840-016-0396-1 |
2018-07-01 | Employing a critical point theorem (local minimum result) for differentiable functionals, we prove the existence of at least one non-trivial weak solution for a class of impulsive damped vibration systems under an asymptotical behavior of the nonlinear datum at zero. Two examples are presented to illustrate the feasibility and effectiveness of the results. | Existence Results for Impulsive Damped Vibration Systems | 10.1007/s40840-016-0400-9 |
2018-07-01 | We analyze eigenvalues emerging from thresholds of the essential spectrum of one-dimensional Dirac operators perturbed by complex and non-symmetric potentials. In the general non-self-adjoint setting, we establish the existence and asymptotics of weakly coupled eigenvalues and Lieb–Thirring inequalities. As physical applications, we investigate the damped wave equation and armchair graphene nanoribbons. | Eigenvalues of one-dimensional non-self-adjoint Dirac operators and applications | 10.1007/s11005-018-1051-6 |
2018-07-01 | The propagation of weak disturbances in a water–air bubble medium has been studied under the conditions when in addition to the gas (e.g., air) undissolved in water the bubbles contain steam that can convert into water in the process of mixture motion. The air contained in the bubbles will in this case exert diffusion resistance and influence the intensity of phase transitions in the steam–water system. The influence of the initial parameters of a two-phase water–bubble mixture (volume content of phases, dispersed phase size, water temperature) on the evolution of harmonic waves in a bubble liquid has been analyzed. | Characteristic Features of Sound Propagation in a Warm Bubble-Laden Water | 10.1007/s10891-018-1809-9 |
2018-07-01 | Chatter is a kind of self-excited vibrations which is related to regenerative effect, mode coupling effect, and process damping, etc. To predict milling chatter more accurately, a suitable dynamical model of milling process which can reflect the practical chatter mechanism should be obtained firstly. In this paper, a new milling dynamical model which simultaneously considers the regenerative effect, mode coupling effect, and process damping is established. Based on the new dynamical model and the updated full-discretization method (FDM), the coupling influences of regenerative effect, mode coupling effect, and process damping on the accurate of the stability lobe diagrams (SLDs) for up-milling and down-milling operations are investigated. A series of numerical simulation and experiments are carried out to verify the accuracy of the proposed milling dynamical model. The experiment results show that the mode coupling effect and process damping have great influences on the prediction of milling stability. The SLD which obtained by the new milling dynamical equation (considering the regenerative effect, mode coupling, and process damping) is more accurate than that which obtained by only considering the regenerative effect. | Milling stability prediction with simultaneously considering the multiple factors coupling effects—regenerative effect, mode coupling, and process damping | 10.1007/s00170-018-2017-7 |
2018-07-01 | This paper aims at designing an adaptive fractional order fuzzy proportional–integral-derivative controller for seismic control of smart base-isolated structure by means of variable friction dampers (VFD). One main challenge occurs when large displacement of the isolator happens due to near-field motions. To overcome this challenge, a solution is to use VFDs. However, the floor accelerations of the superstructure can increase because of sudden changes in the damper friction force of VFDs. Therefore, a suitable control strategy is desired to handle the displacement of isolator without any increase in superstructure acceleration responses during both far-field and near-field earthquakes. First, a sub-level fractional order fuzzy PID (FOFPID) controller is designed to reduce the isolator displacement without significant increase in roof acceleration based on a multi-objective optimization algorithm. Using an adaptive strategy, the fuzzy rule weights of the FOFPID controller are then tuned on-line based on information sensed from both the earthquake and the building responses. Considering nine important performance criteria and several real-data earthquakes, numerical studies are carried out for a benchmark base-isolated structure equipped with VFDs. Simulation results show the superior performance of the proposed controller in mitigation of seismic responses of base-isolated structure against various types of earthquakes in comparison with other controllers presented in previous researches. | Online tuning of fractional order fuzzy PID controller in smart seismic isolated structures | 10.1007/s10518-017-0294-4 |
2018-06-21 | As the most important thermoplastic and thermosetting modifiers, styrene–butadiene–styrene triblock copolymer (SBS) and epoxy resin have been widely applied in asphalt modifications. In this paper, epoxy SBS-modified asphalts (ESBAs) were prepared with epoxy monomer, curing agent and SBS-modified asphalts (SBAs) with various styrene–butadiene structures, which in turn were subjected to laser scanning confocal microscopy (LSCM), viscous measurements, thermal analysis and tensile tests. The LSCM results revealed that both polymer-rich phase and fluorescent particle-rich phase were observed in the asphalt matrix. Moreover, the number of SBS particles in SBAs increased with the increase of styrene contents. The presence of SBS decreased the size of dispersed domains in the continuous epoxy phase of the neat epoxy asphalt binder (EAB). For ESBAs, a double phase separation occurred between SBA and epoxy in the continuous epoxy phase and between asphalt and SBS in the dispersed SBA phase. Both number and size of SBS domains in the dispersed SBA phase of ESBAs increased with the increase of styrene contents. The inclusion of styrenic polymers increased the viscosity of the neat EAB. The viscosity of ESBAs increased with the increase of average molecular weights of the styrenic polymers. The addition of styrenic polymers increased the glass transition temperature ( T _g) and storage modulus ( E ′) of the neat EAB. Meanwhile, the inclusion of styrenic polymers weakened the damping properties of the neat EAB. The styrene-butadiene structures had little effect on the T _g and damping properties of ESBAs. The E ′ of ESBAs decreased with the increase of styrene contents. The presence of SBS enhanced the thermal stability of the neat EAB. Tensile results showed that the addition of SBS increased the tensile strength of the neat EAB. | Microstructures, thermal and mechanical properties of epoxy asphalt binder modified by SBS containing various styrene-butadiene structures | 10.1617/s11527-018-1217-9 |
2018-06-11 | The liquid film damping is one of the main technology for the aerospace, navigation, and machine tool. However, the research on the fine boring is very limited. The paper set up the fine boring squeezed liquid film damped system of multi degree of freedom vibration simulation model and solve mathematical model by transfer matrix theory. The damping coefficient for the fine boring system can be obtained. The mechanical device of liquid film damping system is established. 20# machine oil, 40# machine oil, and cutting fluid are used to the system. The tests indicate that the effect of liquid film formed by cutting fluid is better than oil film formed by machine oil in the static test, but oil film formed by machine oil is better than liquid film formed by cutting fluid in the effect of dynamic test. The simulation model has high accuracy to reliability. The simulation model can directly obtain the optimal parameters, so as to provide effective way to guide field processing. | Research on fine boring simulation based on squeezed liquid film damper | 10.1186/s13638-018-1164-8 |
2018-06-07 | The appropriate use of energy dissipating devices improves the behavior of structures when subjected to external loads, defining the optimal location of the dampers; therefore, it is crucial to ensure their efficiency. In this work, the mathematical expressions of an efficient and systematic procedure proposed by Takewaki were adapted and detailed to find the optimum location of dampers when a structural damper is used. This procedure consists of minimizing the sum of the amplitudes of the transfer functions evaluated at the undamped fundamental frequency of a structural system subject to constraints on the sum of the damping coefficients of the added dampers. For instance, at the beginning and end of the calculation, the sum of the damping coefficients entered must be the same. A series of numerical examples on shear building models within a range of two to six stories are used to verify the efficiency of the systematic procedure. The results showed that the optimal placement method is efficient due to the amplitude reduction of the transfer function after the optimal distribution of the damping coefficients in the structure. | Optimal placement of damping devices in buildings | 10.1007/s40430-018-1238-x |
2018-06-01 | In design and certification of spacecraft, payload/launcher coupled load analyses are performed to simulate the satellite dynamic environment. To obtain accurate predictions, the system damping properties must be properly taken into account in the finite element model used for coupled load analysis. This is typically done using a structural damping characterization in the frequency domain, which is not applicable in the time domain. Therefore, the structural damping matrix of the system must be converted into an equivalent viscous damping matrix when a transient coupled load analysis is performed. This paper focuses on the validation of equivalent viscous damping methods for dynamically condensed finite element models via correlation with experimental data for a realistic structure representative of a slender launch vehicle with solid rocket motors. A second scope of the paper is to investigate how to conveniently choose a single combination of Young’s modulus and structural damping coefficient—complex Young’s modulus—to approximate the viscoelastic behavior of a solid propellant material in the frequency band of interest for coupled load analysis. A scaled-down test article inspired to the Z9-ignition Vega launcher configuration is designed, manufactured, and experimentally tested to obtain data for validation of the equivalent viscous damping methods. The Z9-like component of the test article is filled with a viscoelastic material representative of the Z9 solid propellant that is also preliminarily tested to investigate the dependency of the complex Young’s modulus on the excitation frequency and provide data for the test article finite element model. Experimental results from seismic and shock tests performed on the test configuration are correlated with numerical results from frequency and time domain analyses carried out on its dynamically condensed finite element model to assess the applicability of different equivalent viscous damping methods to describe damping properties of slender launch vehicles in payload/launcher coupled load analysis. | Experimental validation of solid rocket motor damping models | 10.1007/s12567-017-0191-3 |
2018-06-01 | We modeled a one-dimensional actuator including the Casimir and electrostatic forces perturbed by an external force with fractional damping. The movable electrode was assumed to oscillate by an anharmonic elastic force originated from Murrell–Mottram or Lippincott potential. The nonlinear equations have been solved via the Adomian decomposition method. The behavior of the displacement of the electrode from equilibrium position, its velocity and acceleration were described versus time. Also, the changes of the displacement have been investigated according to the frequency of the external force and the voltage of the electrostatic force. The convergence of the Adomian method and the effect of the orders of expansion on the displacement versus time, frequency, and voltage were discussed. The pull-in parameter was obtained and compared with the other models in the literature. This parameter was described versus the equilibrium position and anharmonicity constant. | Anharmonic 1D actuator model including electrostatic and Casimir forces with fractional damping perturbed by an external force | 10.1007/s10409-017-0746-8 |
2018-06-01 | In this paper, we are interested to prove the uniform exponential decay of the energy for the finite difference fully-discretization of 1-D wave equation with an interior damping at $$\xi $$ ξ . To this end, we decompose the fully discrete system into two subsystems: a conservative system, and a non conservative one. We show under a numerical hypothesis on $$\xi $$ ξ that a uniform observability inequality holds for a conservative system, when the mesh size tends to zero using Fourier series technique. Then, we use the observability inequality to prove the uniform exponential decay of the energy for the damped system. Finally, we describe some numerical experiments to illustrate the exponential decay of the energy. | Uniform interior stabilization for the finite difference fully-discretization of the 1-D wave equation | 10.1007/s13370-018-0559-3 |
2018-06-01 | In this paper the macroscopic damping model for dynamical behavior of the structures with random polycrystalline configurations at micro–nano scales is established. First, the global motion equation of a crystal is decomposed into a set of motion equations with independent single degree of freedom (SDOF) along normal discrete modes, and then damping behavior is introduced into each SDOF motion. Through the interpolation of discrete modes, the continuous representation of damping effects for the crystal is obtained. Second, from energy conservation law the expression of the damping coefficient is derived, and the approximate formula of damping coefficient is given. Next, the continuous damping coefficient for polycrystalline cluster is expressed, the continuous dynamical equation with damping term is obtained, and then the concrete damping coefficients for a polycrystalline Cu sample are shown. Finally, by using statistical two-scale homogenization method, the macroscopic homogenized dynamical equation containing damping term for the structures with random polycrystalline configurations at micro–nano scales is set up. | Macroscopic damping model for structural dynamics with random polycrystalline configurations | 10.1007/s10409-017-0733-0 |
2018-06-01 | This study considers the quasilinear elliptic equation with a damping term, $$\begin{aligned} \text {div}(D(u)\nabla u) + \frac{k(|{\mathbf {x}}|)}{|{\mathbf {x}}|}\,{\mathbf {x}}\cdot (D(u)\nabla u) + \omega ^2\big (|u|^{p-2}u + |u|^{q-2}u\big ) = 0, \end{aligned}$$ div ( D ( u ) ∇ u ) + k ( | x | ) | x | x · ( D ( u ) ∇ u ) + ω 2 ( | u | p - 2 u + | u | q - 2 u ) = 0 , where $${\mathbf {x}}$$ x is an N -dimensional vector in $$\big \{{\mathbf {x}} \in \mathbb {R}^N: |{\mathbf {x}}| \ge \alpha \big \}$$ { x ∈ R N : | x | ≥ α } for some $$\alpha > 0$$ α > 0 and $$N \in {\mathbb {N}}\setminus \{1\}$$ N ∈ N \ { 1 } ; $$D(u) = |\nabla u|^{p-2} + |\nabla u|^{q-2}$$ D ( u ) = | ∇ u | p - 2 + | ∇ u | q - 2 with $$1 < q \le p$$ 1 < q ≤ p ; k is a nonnegative and locally integrable function on $$[\alpha ,\infty )$$ [ α , ∞ ) ; and $$\omega $$ ω is a positive constant. A necessary and sufficient condition is given for all radially symmetric solutions to converge to zero as $$|{\mathbf {x}}|\rightarrow \infty $$ | x | → ∞ . Our necessary and sufficient condition is expressed by an improper integral related to the damping coefficient k . The case that k is a power function is explained in detail. | Convergence of Radially Symmetric Solutions for (p, q)-Laplacian Elliptic Equations with a Damping Term | 10.1007/s10884-016-9560-4 |
2018-06-01 | The high-damping elastic response spectra have several important applications in evaluating the design of earthquake resistant structures. They are derived from the reference spectrum for damping equal to 5% using the damping reduction factor (DRF). Most damping reduction factors currently used were derived from observing the effects of viscous damping on the maximum response elastic of SDOF systems subjected to earthquakes. This factor depends on the equivalent viscous damping of the structure, its vibration period, the epicentral distance, earthquake magnitude, and other parameters), and several different expressions of damping reduction factors were proposed and then adopted in a form somewhat different in seismic codes. The aim of this work is to propose a DRF formulation for the Algerian Seismic Regulations (RPA). First, four sets of natural records are selected from the world ground motion database PEER considering the soil classification of RPA. The selection is based on the shear wave velocity Vs30, which is the parameter used for the soil classification in RPA. These records are compatibles (on average) with RPA response spectra for soil classes. Afterward, those records have been used to estimate the response spectrums with different values of damping ratio (7.5, 10, 15, and 20%). Then, the DRF values are calculated for all records for the range of period of interest in structure seismic design. Those values of DRF are used on nonlinear regression to find a formula of the DRF values in a function of the structure dynamic characteristics (damping ratio and vibration period). A comparison between the proposed formulation and some formulations from the literature is presented, and the results were discussed in terms of the errors between the results from each formulation and the exact results. | Formulation of damping reduction factor for the Algerian seismic code | 10.1007/s42107-018-0023-6 |
2018-06-01 | The study of rotating machines is usually carried out taking into account linearized hydrodynamic forces, considering dynamic coefficients of stiffness and damping, although a high order of nonlinearity can be significantly present in the system. To solve the nonlinear problem, the solution of Reynolds equation is practically mandatory for each time step in the numerical integration procedure, leading to high computational costs that often can make its application unavailable. In this paper, the validity of linear approximation for the oil film forces is discussed when the system operates under specific conditions, pointing out the influence of critical phenomena and dynamic parameters in rotordynamic analysis. Experimental tests are compared to numerical simulations for linear and nonlinear models of bearings in laboratory test rig in order to validate the analysis. Afterward, several simulations were accomplished, in time domain, for a rotor configuration more susceptible to critical operation, comparing the results for linear and nonlinear models. The main focus is on the influence of internal damping, gyroscopic effects, journal eccentricities, and excitation forces. The results demonstrate that the excitation force plays a fundamental role in nonlinearity degree of response, namely in extreme operation conditions under high excitation forces, the linear approach fails in representing the hydrodynamic bearings. | Discussion about nonlinear boundaries for hydrodynamic forces in journal bearing | 10.1007/s11071-018-4177-2 |
2018-06-01 | Squeeze-film dampers (SFD) are used as indispensable bearings in many rotating machines to suppress lateral vibration and enhance stability. The kinetic energy of the damping fluid is sometimes greater than that of SFD’s journal. Therefore, the influence of the damping fluid must be considered in establishing a dynamic model of a rotor–bearing system. A concept that involves the added mass of the damping fluid is proposed in this work, and the calculation formula is derived based on laminar flow theory and the mean-square speed of the fluid. The unbalance responses of a rotor–bearing system are solved by numerical iteration and with the transfer matrix method. The results calculated with and without added mass are compared. Experimental results indicate that introducing the added mass of the damping fluid into a dynamic model is effective. | Study on the added mass effect in squeeze-film dampers | 10.1007/s12206-018-0544-7 |
2018-06-01 | In this work, a magnetorheological (MR) damper valve is designed with the primary objective of controlling swing-phase damping in an above-knee prosthesis. Initially, a swing phase model of the desired single axis knee incorporating MR damper was modelled. The control parameters that govern damping force and displacement of the damper were identified and optimized to enable the prosthetic knee to produce near normal swing phase trajectory for ground walking as obtained from experimental data. Then, the MR damper valve is optimally designed by selecting typical performance indices of the damper for the intended application. A multi-objective optimization problem is formulated where the MR damper valve is constrained in a desired cylindrical volume defined by its radius and height. Effects of the geometrical design variables of the valve are analytically investigated by mapping finite element analysis (FEA) numerical responses with response surface method (RSM). The results show that the MR damper with designed damper valve enables the prosthetic knee to achieve near to normal swing phase trajectory, and compare to the existed MR damper, up to 71 % reduction by weight has been achieved. | Optimal design of an MR damper valve for prosthetic knee application | 10.1007/s12206-018-0552-7 |
2018-06-01 | In order to analyze the stability of a landfill site, it should analyze some properties of waste introducing the main structural elements. Up to now, it has not been done much research on the properties of municipal solid waste. In addition, due to the differences in waste properties from one country to another and even from one to another landfill site, it is impossible to generalize the results. These conditions caused local research on the evaluation of static and dynamic parameters of municipal solid waste to be done. Because Iran is a seismic country, the short-term behavior of waste controls landfill sites stability during seismic loads; so it is necessary to know the dynamic behavior of these materials. In this paper, about 18 cyclic tests were performed, and in addition to determining the dynamic parameters of municipal solid waste of Tehran Kahrizak Disposal Site using cyclic triaxial test, the effect of confining stress and loading frequency on dynamic properties of these materials was evaluated. The results have shown that with increasing the confining stress and loading frequency, shear modulus and damping ratio was increased and decreased, respectively, and it is related to the composition of the municipal solid waste materials. | Effect of confining stress and loading frequency on dynamic behavior of municipal solid waste in Kahrizak landfill | 10.1007/s13762-017-1465-1 |
2018-06-01 | Consider a semilinear hyperbolic boundary value problem associated to the nonlinear generalized viscoelastic equations with Direchlet-Neumann boundary conditions. Then, the global existence of a weak solution is established. The uniqueness of the solution has been obtained by eliminating some hypotheses that have been imposed by other authors for different particular problems. | Semilinear Hyperbolic Boundary Value Problem Associated to the Nonlinear Generalized Viscoelastic Equations | 10.1007/s40306-017-0229-9 |
2018-06-01 | In this paper, the damping property of thermoplastic polyurethane (TPU) was firstly regulated by introducing the phenolic resin (PR) with more active hydroxyl group and larger molecular weight. The mechanism of enhanced damping property was systematically elucidated through the combination of molecular dynamic (MD) simulation and experimental methods. The MD simulation results showed the hydrogen bonds (H-bonds), binding energy, and fractional free volume (FFV) in the quantitative way. When the PR content increased to 40%, it had the largest number of H-bonds, highest binding energy, and relative small FFV. Meanwhile, the experimental results showed that there indeed existed H-bonds interaction between PR and TPU polymer chains. Furthermore, the glass transition temperature ( T _g) as well as the loss factor (tan δ ) was remarkably improved with increasing the PR content, the effective damping temperature range was broadened, the peak position was also moved to room temperature. This study can provide some reference for designing high-performance TPU-based damping materials. | The study of damping property and mechanism of thermoplastic polyurethane/phenolic resin through a combined experiment and molecular dynamics simulation | 10.1007/s10853-018-2218-3 |
2018-06-01 | Dynamic stiffness and damping of epoxy adhesives are critical for ensuring the safety, reliability, and comfort of structures subjected to vibrations and impact loads. This study conducts split Hopkinson pressure bar (SHPB) tests to investigate the synergistic effects of silica micro-nanoparticles on these critical properties. Micro-nanoparticle content and composition ratio purity are varied at 2, 5, and 10% by weight (wt%) and from 0% (pure microparticles) to 100% (pure nanoparticles), respectively. Positive simultaneous stiffening and energy absorption effects are observed at a silica content of 5 wt% owing to improved nanoparticle dispersion; this increases the interface area and induces cooperative matrix–filler interactions. At this silica content and a composition ratio of 50%, stiffness and damping are 45 and 40% larger than those of neat epoxy, respectively. Silica micro-nanoparticles are less effective in improving particle dispersion at more than 5 wt%. Conventional mechanical dispersion is limited to applications below a certain silica content; the results suggest a simple, low-cost dispersion technique as an alternative to the in-situ technique and provide options for designing epoxy stiffness and damping appropriate for specific applications. | Synergistic Effects of Mixed Silica Micro-nanoparticles on Compressive Dynamic Stiffness and Damping of Epoxy Adhesive | 10.1007/s40870-018-0148-4 |
2018-06-01 | 目的 液压自由活塞发动机性能受燃油喷射系统开关阀性能限制。本文旨在对开关阀内部结构进行优化,降低液动力,从而提高阀的开启速度。 创新点 1. 提出一种易于安装的带孔阻尼套结构,可以用于改变阀芯表面压力分布和油液射流角,从而降低液动力;2. 建立数值仿真模型,分析阻尼套不同结构和安装参数对液动力和空化的影响。 方法 1. 进行数值模拟,分析阀芯表面压力分布和内部流场分布,并通过实验验证方法有效性和模型准确性;2. 对不同阻尼孔宽度、深度和相对位置下的阀芯液动力和流量损失情况进行对比和分析;3. 对上述不同阻尼孔结构下阀内空化情况进行仿真和对比;4. 建立燃油喷射系统试验台,验证阻尼套对提高阀开启速度的作用。 结论 1. 提出的带孔阻尼套结构可以有效降低阀芯液动力。2. 随阻尼孔的减小,其对液动力的改变作用和节流作用逐渐增强;阻尼孔足够小时液动力反向并逐渐加强。3. 阻尼套对油液的阻碍作用也会改变流场内的空化情况,但空化强度不一定随节流孔的变大而单调变强,其还受相对安装位置影响。4. 带孔阻尼套可以有效降低阀的开启时间。 The power of hydraulic piston engines is much affected by the on-off valves which control the fuel injection of the piston assembly. Therefore, the opening time of the seat valve used as the on-off valve is optimized by minimizing the axial flow forces on the spool. A damping sleeve with orifices is proposed to change the valve internal geometry. Experimental and numerical investigations of the flow forces acting on the spool with and without the proposed damping sleeve are carried out to identify the differences in the flow field and to minimize the forces’ effect. The simulated results fit the experimental results well. Both results show that the proposed damping sleeve affects the pressure distribution along the spool cone surface and the jet stream direction significantly. The effects of the orifice’s width, height, and relative sleeve installation positions on the flow field and cavitation are assessed using simulation methods. As a result of the flow field changing, the damping sleeve can reduce the flow forces significantly and even reverse the forces’ direction at the cost of a little flow loss. The opening time of the seat valve can be reduced by 31% to 0.67 ms by using the proposed damping sleeve. | Experimental and numerical investigation of flow forces in a seat valve using a damping sleeve with orifices | 10.1631/jzus.A1700164 |
2018-06-01 | This paper presents a theoretical model for analyzing the damping effect of underplatform dampers for turbine blades. At first, tangential and normal contact stiffness of the friction damper were studied based on a flat-to-flat contact model. The analytic expressions of contact stiffness were presented. Then, a microslip model was developed, and the frictional hysteresis loops were obtained by the Masing hypothesis. The so-called “B–B” (Blade to Blade) model was studied in this paper, and both cylindrical and wedge-shaped dampers were calculated in the case studied. The inertia and rotating effect of the damper were ignored for simplicity. Thus, the damper’s motion between blade platform locations could be determined by iteration of force balance equations of the damper once the blades’ motions as inputs of the system were determined. The effect of normal load on the contact stiffness was ignored for simplicity. The friction force was linearized by harmonic balanced method, considering only the first-order harmonic terms. Finally, the relationship between damping ratio and the maximum vibration stress of the blades was calculated to assess the damping effect of the damper. | Modeling of Microslip Friction and Its Application in the Analysis of Underplatform Damper | 10.1007/s42405-018-0039-x |
2018-06-01 | A dynamic model of the starting current of an active damper based on a magnetorheological elastomer is described, Experimental data for the damper are derived. | Dynamic Modeling of an Active Damper | 10.3103/S1068798X18060138 |
2018-05-30 | In this paper, we deal with the uniform stabilization to the mixed problem for a nonlinear wave equation and acoustic boundary conditions on a non-locally reacting boundary. The main purpose is to study the stability when the internal damping acts only over a subset $$\omega $$ ω of the domain $$\Omega $$ Ω and the boundary damping is of the viscoelastic type. | Uniform stabilization of wave equation with localized internal damping and acoustic boundary condition with viscoelastic damping | 10.1007/s00033-018-0977-y |
2018-05-26 | To obtain a hydraulic damper thermodynamic model that is much more realistic than the thermodynamic model of literature, research is carried out by introducing the stochastic uncertainty theory. The geometric variables of the hydraulic damper are defined as uncertain variables. The stochastic variables are defined with the stochastic factor method, and the stochastic thermodynamic model is established with the algebraic synthesis method. The results of the experiment are considered as the standards for verifying the correctness and superiority of the stochastic thermodynamic model. The results of the stochastic thermodynamic model and the thermodynamic model of literature are compared with the experimental results, respectively. The oil temperature at the stable state of the stochastic thermodynamic model is close to that of the experiment, indicating that the stochastic thermodynamic model is correct. The oil temperature curve of the stochastic thermodynamic model is much closer to that of the experiment than that of the thermodynamic model of the literature, indicating that the stochastic thermodynamic model is superior to the thermodynamic model of literature. | Modeling dissipative heating of hydraulic dampers under consideration of stochastic uncertainties in their geometric parameters | 10.1007/s40430-018-1236-z |
2018-05-25 | Based on the kinetic theory, Landau damping of dust acoustic waves (DAWs) propagating in a dusty plasma composed of hybrid nonthermal nonextensive distributed electrons, Maxwellian distributed ions and negatively charged dust grains is investigated using Vlasov-Poisson’s equations. The characteristics of the DAWs Landau damping are discussed. It is found that the wave frequency increases by decreasing (increasing) the value of nonextensive (nonthermal) parameter, q $q$ ( α $\alpha $ ). It is recognized that α $\alpha $ plays a significant role in observing damping or growing DAW oscillations. For small values of α $\alpha $ , damping modes have been observed until reaching a certain value of α $\alpha $ at which ω i $\omega _{i}$ vanishes, then a growing mode appears in the case of superextensive electrons. However, only damping DAW modes are observed in case of subextensive electrons. The present study is useful in the space situations where such distribution exists. | Landau damping of dust acoustic waves in the presence of hybrid nonthermal nonextensive electrons | 10.1007/s10509-018-3348-4 |
2018-05-23 | The escalating disposal of end-life tires has led to an urgent need for efficient reuse. The positive environmental impact of the application of this material in large-scale civil engineer construction, such as soil-retaining structures, or as seismic isolation technique, stems not only from the reuse of the tires, but also from the effect this material inherits to the response of these structures. The soil material properties in the form of shear modulus and damping degradation curves, G – γ – D , are key parameters in the numerical analysis of site-specific seismic response and seismic design of structures. To this end, the effect of the dynamic shear strain, γ , on the shear modulus, G , and damping ratio, D , of granular soils mixed with granulated rubber is studied. An experimental approach is presented, employing resonant column and cyclic triaxial tests to obtain an insight on the response of these mixtures in a wide band of dynamic strain. A range of rubber content in the mixture up to 60% per weight is tested, and the influence of the mean grain size ratio of the mixed materials is investigated. | Dynamic behaviour of granular soil materials mixed with granulated rubber: influence of rubber content and mean grain size ratio on shear modulus and damping ratio for a wide strain range | 10.1007/s41062-018-0156-1 |
2018-05-15 | This paper presents a study of the asymptotic behavior of the solutions for the history value problem of a viscoelastic wave equation which features a fading memory term as well as a supercritical source term and a frictional damping term: $$\begin{aligned} {\left\{ \begin{array}{ll} u_{tt}- k(0) \Delta u - \int \limits _0^{\infty } k'(s) \Delta u(t-s) \hbox {d}s +|u_t|^{m-1}u_t =|u|^{p-1}u, \text { in } \Omega \times (0,T), \\ u(x,t)=u_0(x,t), \quad \text { in } \Omega \times (-\infty ,0], \end{array}\right. } \end{aligned}$$ u tt - k ( 0 ) Δ u - ∫ 0 ∞ k ′ ( s ) Δ u ( t - s ) d s + | u t | m - 1 u t = | u | p - 1 u , in Ω × ( 0 , T ) , u ( x , t ) = u 0 ( x , t ) , in Ω × ( - ∞ , 0 ] , where $$\Omega $$ Ω is a bounded domain in $$\mathbb R^3$$ R 3 with a Dirichlét boundary condition and $$u_0$$ u 0 represents the history value. A suitable notion of a potential well is introduced for the system, and global existence of solutions is justified, provided that the history value $$u_0$$ u 0 is taken from a subset of the potential well. Also, uniform energy decay rate is obtained which depends on the relaxation kernel $$-k'(s)$$ - k ′ ( s ) as well as the growth rate of the damping term. This manuscript complements our previous work (Guo et al. in J Differ Equ 257:3778–3812, 2014 , J Differ Equ 262:1956–1979, 2017 ) where Hadamard well-posedness and the singularity formulation have been studied for the system. It is worth stressing the special features of the model, namely the source term here has a supercritical growth rate and the memory term accounts to the full past history that goes back to $$-\infty $$ - ∞ . | Energy decay of a viscoelastic wave equation with supercritical nonlinearities | 10.1007/s00033-018-0961-6 |
2018-05-15 | Dynamic analysis of structures often considers the effects of soil–structure interaction which requires estimation of the shear modulus and damping ratio of the soil. While the in situ properties can be measured, the properties of the backfill soils that surround substructures are rarely available at the time of design and in many cases are never measured. This study provides a practical means of estimating properties for compacted coarse-grained soils based on relative density. The results of more than 400 tests gathered from the literature were used to develop correlations between the small strain shear modulus, G _max and relative density for compacted coarse-grained soils, which can be used when the mechanical properties are not available. The proposed relationships better distinguish between the behavior of sand and gravel compared to existing correlations. Best-fit hyperbolic curves are also presented for the variation of normalized shear modulus and damping ratio with shear strain for compacted coarse-grained soils to represent the nonlinear behavior of the backfill in the dynamic analysis. | Shear modulus and damping relationships for dynamic analysis of compacted backfill soils | 10.1007/s41062-018-0152-5 |
2018-05-01 | This study is concerned with the nonlinear dynamic characteristics of a micro-vibration fluid viscous damper used in a satellite. When a control moment gyroscope is working, it produces micro-vibrations, which is a disadvantage for imaging equipment. Taking a single-tube micro-vibration fluid viscous damper as our research subject, a nonlinear dynamic model of the micro-vibration fluid viscous damper under harmonic excitation is proposed. Then, the analytical form of the pressure gradient force is derived. Considering the entrance effect in the orifice, the nonlinear elastic force and nonlinear damping force are analyzed. The results reveal that if the entrance effect is not considered, the elastic force and damping force are linear forces. When the entrance effect is considered, the damper has a nonlinear elastic force and a nonlinear damping force. These nonlinear forces are related to the orifice length, diameter, fluid viscosity, excitation amplitude and frequency. In the low-frequency domain, the differences between the two cases are small, while in the high-frequency domain, they are considerable. | Nonlinear dynamic characteristics of a micro-vibration fluid viscous damper | 10.1007/s11071-018-4116-2 |
2018-05-01 | Owing to growing environmental awareness in green technology, the whole gamut of engineering sector has started shifting towards natural fibre-oriented materials from synthetic materials. The adequate dynamic stability and damping property are important design necessities in a polymer composite structure. Given this perspective, this paper discusses the formulation of distinct hybrid laminates with various weight ratios of jute- and linen-incorporated epoxy polymer and the influence of their weight ratios on the dynamic attributes. Dynamic mechanical thermal analysis is employed to quantify the viscoelastic attributes of the hybrid laminates. The natural frequency of cantilevered laminate beam is determined experimentally by free vibration analysis and the damping factor of the laminate beam is computed analytically by half power bandwidth technique. The cole–cole mapping analysis is made to understand the interfacial adhesion of the different laminates with hybrid configurations. The hybrid laminate with equal weight proportion of jute and linen is found to be optimal as it has exhibited maximum stiffness property and load bearing capability with high glass transition temperature. The influences of frequency on storage modulus and loss factor of the optimal hybrid laminate with respect to temperature are analysed. Several vibratory responses of the optimal hybrid laminate beam for different natural frequencies and damping factors are elicited and studied. | Investigation of viscoelastic attributes and vibrational characteristics of natural fabrics-incorporated hybrid laminate beams | 10.1007/s00289-017-2139-3 |
2018-05-01 | Cutting forces are critically important in cutting operations because they correlate strongly with cutting performance such as surface accuracy, tool wear, tool breakage, cutting temperature, self-excited, and forced vibrations. The drilling operation of titanium alloys is considered by manufactures as complex and difficult in view of the mechanical and thermal properties of this material. In fact, titanium has a very small coefficient of conduction which leaves a high temperature at the area of contact between the tool and the workpiece, which decreases the cutting forces and increases the wear of the tool. For this, more research has focused on the prediction of cutting forces during the drilling of titanium in order to improve the machinability of this material as well as the wear of the tool. Many efforts have been made by researchers to better understand the drilling process and to formulate theoretical cutting forces models to predict and to simulate the phenomenon. This paper presents a numerical model for prediction of cutting forces and torque during a drilling operation including the effect of the regenerative chatter and of the cutting process damping. The corresponding algorithm allows understanding the interaction between the tool and the workpiece and identifying numerically the three-dimensional evolution of the cutting force components and cutting torque generated by the drilling process of a titanium alloy. Verification tests are conducted on a vertical machine for titanium alloy Ti6Al4V and the effectiveness of the model and the algorithm is verified by the good agreement of simulation result with that of cutting tests under different cutting conditions. | Numerical modeling and experimental analysis of thrust cutting force and torque in drilling process of titanium alloy Ti6Al4V | 10.1007/s00170-018-1758-7 |
2018-05-01 | The adoption of a reliable shear model for predicting brittle failure modes of a reinforced concrete (r.c.) beam-column joint, beyond ductile flexural mechanisms at member level, is essential to retrofit r.c. framed buildings properly. The retrofitting of existing structures by means of the insertion of hysteretic damped braces (HYDBs) turns out to be a highly effective means of improving seismic response. In the present work, a Displacement-Based Design (DBD) procedure to proportion the HYDBs to attain, for a specific level of seismic intensity, a designated performance level has been revisited in order to take into account the effects of the nonlinear shear response of beam-column joints. To this end, two-, four- and eight-storey r.c. framed structures, representative of low-, mid- and high-rise r.c. framed buildings, are designed in line with a former Italian seismic code for a medium-risk seismic zone. These are then to be retrofitted by inserting HYDBs to attain performance levels imposed by the current Italian code in a high-risk seismic zone. A computer code for the nonlinear static analysis of r.c. framed structures has been developed, involving local shear response of beam-column joints. A path-following analysis based on the arc-length method has been adopted to obtain the pushover curves of primary and retrofitted test structures, with and without nonlinear shear modelling of the beam-column joints, and the HYDB response is idealized by a bilinear law on the assumption that buckling of the steel braces is prevented. | Shear modelling of the beam-column joint in the nonlinear static analysis of r.c. framed structures retrofitted with damped braces | 10.1007/s10518-017-0269-5 |
2018-05-01 | The Matsuno–Gill model for the atmospheric steady-state response to an imposed equatorial heat source is perhaps the most successful set of reduced equations in the theory of tropical dynamics. While it was originally designed to explain some key features of the tropical climatology such as the Walker and Hadley circulations, it is increasingly used for other transient tropical disturbances such as the Madden–Julian oscillation (MJO). Here, we provide a semi-analytic solution to the time dependent Matsuno–Gill equations, with periodic boundary conditions and without the long-wave approximation, based on a meridional expansion using the parabolic cylinder functions combined with the method of characteristics and Fourier series in the zonal direction. Our method of solution leads to an ODE system which is solved numerically. We use this transient solution to investigate the conditions under which the transient response convergences to the steady state and study the effect of a moving heat source on the structure of the response and speculate about its resemblance or not to the MJO structure. In particular, we look at the sensitivity of the long time behavior of the solution with respect to the model parameters, namely, the imposed dissipation rate and the speed of the moving heat source as well as the form of the heating itself. | The transient response to an equatorial heat source and its convergence to steady state: implications for MJO theory | 10.1007/s00382-017-3807-6 |
2018-05-01 | The effect of anisotropy and shear strains on the performance of piezoelectric sensors and actuators in active damping of the resonance vibrations of a hinged rectangular plate is studied. To model the vibrations of the plate, Timoshenko’s hypotheses are used. The analytical solution of the problem is obtained by Fourier’s method. Formulas for the voltage that should be applied to the actuators to balance the mechanical load are derived. Similar formulas are obtained for the sensor voltage. Formulas for the damping coefficient for the case of using both sensors and actuators for active damping of the resonant vibrations of the plate are presented. | Influence of Anisotropy and Transverse-Shear Strains on the Performance of Piezoelectric Sensors and Actuators | 10.1007/s10778-018-0884-0 |
2018-05-01 | Mechanical joints have considerable effects on dynamic behaviour of machine tools; thus, joint damping identification is important in studying the dynamics of mechanical structures. Due to the difficulties in analysis of microslip friction, the experimental prediction of microslip joint dynamics is of great importance. In this study, a new experimental approach is proposed to determine the damping of bolted lap joints. Because of the complex nature of the mechanical joints, the lap joint is isolated through the addition of a mechanical resonator, which consists of a lumped mass and spring, to the bolted structure. The frequency response function (FRF) of this system is used for joint damping identification. This approach is used for bolted structures under both translational and torsional excitations and overcomes difficulties associated with slip boundaries identification in the joint interface. The method is verified by comparing the obtained results with those of the hysteresis loop approach. | Development of a new method for joint damping identification in a bolted lap joint | 10.1007/s12206-018-0405-4 |
2018-04-25 | In this work, the effect of the damping component with/without individual grooved surface features on the friction-induced vibration and noise (FIVN) and surface wear performance is studied experimentally and numerically. The experimental results show that introducing a grooved damping component in the system has a significantly improved capability in suppressing the generation of FIVN. In addition, it is observed that the friction system with a grooved damping component suffers slighter wear. Numerical results show good agreement with the FIVN events observed in the experimental test. Through analysing the deformation behaviour of damping component and the contact behaviour of the friction system during friction process, it is speculated that the deformation behaviour of damping component plays a significant role in affecting the contact pressure and FIVN behaviour. In addition, linking the vibration performance and wear evolution, the connection between damping, and vibration and wear behaviour is discovered, which can further explain why the friction system with a grooved damping component shows improved capability in suppressing the FIVN of friction system. | Improving Dynamic and Tribological Behaviours by Means of a Mn–Cu Damping Alloy with Grooved Surface Features | 10.1007/s11249-018-1019-9 |
2018-04-16 | A fundamental understanding of frictional sliding at rock surfaces is of practical importance for nucleation and propagation of earthquakes and rock slope stability. We investigate numerically the effect of different physical parameters such as inertia, viscous damping, temperature and normal stress on the chaotic behaviour of the two state variables rate and state friction (2sRSF) model. In general, a slight variation in any of inertia, viscous damping, temperature and effective normal stress reduces the chaotic behaviour of the sliding system. However, the present study has shown the appearance of chaos for the specific values of normal stress before it disappears again as the normal stress varies further. It is also observed that magnitude of system stiffness at which chaotic motion occurs, is less than the corresponding value of critical stiffness determined by using the linear stability analysis. These results explain the practical observation why chaotic nucleation of an earthquake is a rare phenomenon as reported in literature. | The effect of inertia, viscous damping, temperature and normal stress on chaotic behaviour of the rate and state friction model | 10.1007/s12040-018-0935-2 |
2018-04-11 | We prove the global non-linear stability, without symmetry assumptions, of slowly rotating charged black holes in de Sitter spacetimes in the context of the initial value problem for the Einstein–Maxwell equations: if one perturbs the initial data of a slowly rotating Kerr–Newman–de Sitter (KNdS) black hole, then in a neighborhood of the exterior region of the black hole, the metric and the electromagnetic field decay exponentially fast to their values for a possibly different member of the KNdS family. This is a continuation of recent work of the author with Vasy on the stability of the Kerr–de Sitter family for the Einstein vacuum equations. Our non-linear iteration scheme automatically finds the final black hole parameters as well as the gauge in which the global solution exists; we work in a generalized wave coordinate/Lorenz gauge, with gauge source functions lying in a suitable finite-dimensional space. We include a self-contained proof of the linear mode stability of Reissner–Nordström–de Sitter black holes, building on work by Kodama–Ishibashi. In the course of our non-linear stability argument, we also obtain the first proof of the linear (mode) stability of slowly rotating KNdS black holes using robust perturbative techniques. | Non-linear Stability of the Kerr–Newman–de Sitter Family of Charged Black Holes | 10.1007/s40818-018-0047-y |
2018-04-03 | In this research, the application of active mass damper (AMD) has been experimentally tested using electromagnetic uniaxial shake table. The characteristic of an active damper has been presented. A state-feedback controller has been introduced for single flood active mass damper (AMD) using numerical modeling. The model was built and experiment was performed in laboratory having AMD to discuss the effect of model parameters and the development of parameters by inputting the data obtained from most severe earthquake on Oct 8 2005 in Pakistan. The system model, control design and observer were tested on shake table having 46 cm × 46 cm dimensions in real time vibrations. The shake table used has capability of running with powerful actuator having scaled accelerograms of real time earthquakes. The setup to operate the controller on real experimental work was discussed. It was observed that about 40% reduction in vibration can be achieved using active mass damper. | Structural health monitoring of single degree of freedom flexible structure having active mass damper under seismic load | 10.1007/s41062-018-0139-2 |
2018-04-01 | We consider a Navier–Stokes–Voigt fluid model where the instantaneous kinematic viscosity has been completely replaced by a memory term incorporating hereditary effects, in presence of Ekman damping. Unlike the classical Navier–Stokes–Voigt system, the energy balance involves the spatial gradient of the past history of the velocity rather than providing an instantaneous control on the high modes. In spite of this difficulty, we show that our system is dissipative in the dynamical systems sense and even possesses regular global and exponential attractors of finite fractal dimension. Such features of asymptotic well-posedness in absence of instantaneous high modes dissipation appear to be unique within the realm of dynamical systems arising from fluid models. | Navier–Stokes–Voigt Equations with Memory in 3D Lacking Instantaneous Kinematic Viscosity | 10.1007/s00332-017-9422-1 |
2018-04-01 | In this paper, the empirical models for predicting the modal damping ratio ( $$\xi )$$ ξ ) of impact-damped flexible beams (IDFB) via gene expression programming (GEP) are proposed. The experimental data used in training and testing phases of the GEP are obtained from the literature. The training and testing sets of the empirical models for the GEP are chosen from the database. The empirical models are developed for predicting the $$\xi $$ ξ of IDFB as functions of gap between vibrating mechanical system and impact damper ( c ), mass of particle ( m ), modal amplitude at the location of the damper ( $${\varPhi }_\mathrm{d} )$$ Φ d ) , frequency of excitation ( f ), and peak value of the imaginary part of the frequency response functions ( $$F_\mathrm{I} )$$ F I ) . The results of empirical models are compared with the results of experimental study and equation given in the literature. The results of empirical models for the $$\xi $$ ξ are in good agreement with the experimental results according to the results of equation given in the literature. The results of empirical models also reveal that GEP technique exhibits better performance to predict the $$\xi $$ ξ of IDFB. | Empirical Modeling of Modal Damping Ratio of Impact-Damped Flexible Beams by GEP | 10.1007/s13369-017-2715-8 |
2018-04-01 | The present study examines the possibility of attenuating blood pulses by means of introducing prosthetic viscoelastic materials able to absorb energy and damp such pulses. Vascular prostheses made of polymeric materials modify the mechanical properties of blood vessels. The effect of these materials on the blood pulse propagation remains to be fully understood. Several materials for medical applications, such as medical polydimethylsiloxane or polytetrafluoroethylene, show viscoelastic behavior, modifying the original vessel stiffness and affecting the propagation of blood pulses. This study focuses on the propagation of pressure waves along a pipe with viscoelastic materials using the Maxwell and the Zener models. An expression of exponential decay has been obtained for the Maxwell material model and also for low viscous coefficient values in the Zener model. For relatively high values of the viscous term in the Zener model, the steepest part of the pulse can be damped quickly, leaving a smooth, slowly decaying wave. These mathematical models are critical to tailor those materials used in cardiovascular implants to the mechanical environment they are confronted with to repair or improve blood vessel function. | Arterial pulse attenuation prediction using the decaying rate of a pressure wave in a viscoelastic material model | 10.1007/s10237-017-0980-9 |
2018-04-01 | This paper presents an integrated passive damping approach in hybrid metal-CFRP parts for structural applications. In this concept a viscoelastic material is embedded in the joint zone of the hybrid component. To examine the connection strength single-lap-joint specimens were produced and tested and the influence of the used material combinations, different surface structures, and different process parameters i.e. the moment of cross-linking were evaluated. Afterwards, the metal-CFRP hybrids were tested in quasi-static tests to assess their connection strength and failure behaviour. Dynamic cyclic tensile tests with step-wise increased loading conditions were performed to determine the specimens damping behaviour and to estimate their fatigue performance. Finally, these results are compared to a state of the art metal-CFRP hybrid with rivets connecting both materials. | Intrinsic CFRP-metal-hybrids with rubber interface for the improvement of the damping behaviour | 10.1007/s11740-018-0792-5 |
2018-04-01 | During the last 2 decades experimental and theoretical studies have striven to evaluate the use of granulated rubber as a construction material in civil engineering applications. Several geotechnical structures using soil/rubber mixtures or clean granulated rubber proved the efficiency of this solution. In the framework of site seismic response analysis and seismic design of structures, the soil material properties in the form of G/G_o-γ-D/D_o curves are one of the main constituents in numerical analysis methods. To this end, an experimental approach is presented on the dynamic properties of granular soils mixed with granulated rubber, in terms of small-strain shear modulus, G_o, and damping ratio, D_o. The G_o and D_o values are obtained by combination of resonant column and cyclic triaxial tests’ results, for wide rubber content in the mixtures. The significant influence of the mean grain size ratio of the mixed materials is considered and finally, analytical expressions appropriate for the engineering practice for G_o and D_o, are proposed. | Dynamic Behaviour of Granular Soil Materials Mixed with Granulated Rubber: Effect of Rubber Content and Granularity on the Small-Strain Shear Modulus and Damping Ratio | 10.1007/s10706-017-0391-9 |
2018-04-01 | In our increasingly unstable and unpredictable world, population dynamics rarely settle uniformly to long-term behaviour. However, projecting period-by-period through the preceding fluctuations is more data-intensive and analytically involved than evaluating at equilibrium. To efficiently model populations and best inform policy, we require pragmatic suggestions as to when it is necessary to incorporate short-term transient dynamics and their effect on eventual projected population size. To estimate this need for matrix population modelling, we adopt a linear algebraic quantity known as non-normality. Matrix non-normality is distinct from normality in the Gaussian sense, and indicates the amplificatory potential of the population projection matrix given a particular population vector. In this paper, we compare and contrast three well-regarded metrics of non-normality, which were calculated for over 1000 age-structured human population projection matrices from 42 European countries in the period 1960 to 2014. Non-normality increased over time, mirroring the indices of transient dynamics that peaked around the millennium. By standardising the matrices to focus on transient dynamics and not changes in the asymptotic growth rate, we show that the damping ratio is an uninformative predictor of whether a population is prone to transient booms or busts in its size. These analyses suggest that population ecology approaches to inferring transient dynamics have too often relied on suboptimal analytical tools focussed on an initial population vector rather than the capacity of the life cycle to amplify or dampen transient fluctuations. Finally, we introduce the engineering technique of pseudospectra analysis to population ecology, which, like matrix non-normality, provides a more complete description of the transient fluctuations than the damping ratio. Pseudospectra analysis could further support non-normality assessment to enable a greater understanding of when we might expect transient phases to impact eventual population dynamics. | Inferring transient dynamics of human populations from matrix non-normality | 10.1007/s10144-018-0620-y |
2018-04-01 | Tuned Liquid Column Damper (TLCD) relies on the motion of a liquid mass in an open tube counteract the external motion, while a built-in orifice plate induces turbulent damping forces that dissipate kinetic energy. Although both the construction and working principle of TLCD differ from Tuned Mass Damper (TMD), the analogies between TLCD-structure and TMD-structure system for symmetric and asymmetric structures are given. The mass ratio, the optimal frequency ratio, the natural frequency and damping of the main structure, etc are achieved. Modal tuning of the TLCD, frequency ratio and damping, is classically done by applying the Den Hartog optimization criterion. The analysis of structural vibration control using finite element software is presented. Numerical simulations of the four-storey asymmetric structure and 20-storey benchmark model with single TLCD or TLCDs with the parameters using Den Hartog formula and structural analysis by SAP 2000 software show that the method of transforming TLCD-structure to TMD-structure system is reasonable and feasible. | Transforming Method of TLCD-structure to TMD-structure for Vibration Control | 10.1007/s12205-017-0287-5 |
2018-04-01 | In this article, a new magneto rheological (MR) sponge damper is proposed for suppression of vibrations in a washing machine. The article presents design optimization of geometric parameters of MR sponge damper (MRSD) using the finite element analysis (FEA) and first order derivative techniques for a washing machine. The article explains the hysteresis behavior and the relationship of damping force with input current for the proposed MRSD. Moreover, the characteristics of the MRSD such as energy dissipation and equivalent damping coefficient are investigated experimentally in terms of input current and excitation amplitude. The passive dampers installed in washing machine are ineffective in reducing unwanted vibrations at resonant frequencies due to real time unbalanced mass. For this purpose, a test setup is established in order to compare the performance of passive dampers with the proposed MRSDs in a washing machine. It is noticed that MRSDs reduce average vibrations of 75.61 % in a low frequency band, whereas in a high frequency band, the MRSDs lessen average vibrations of 30.57 % in a washing machine. In order to determine the performance of proposed design MRSD, a detailed comparison of the performance parameters, such as total damping force, passive force, maximum average vibrations after suppression by MR dampers, maximum current and power ratings is provided with the existing designs of MR damper for washing machine from the literature. | Design and analysis of a new magneto rheological damper for washing machine | 10.1007/s12206-018-0308-4 |
2018-04-01 | The railway bogie, the most important running component, has direct association with the dynamic performance of the whole vehicle system. The bifurcation type of the bogie that is affected by vehicle parameters will decide the behavior of the vehicle hunting stability. This paper mainly analyzes the effect of the yaw damper and wheel tread shape on the stability and bifurcation type of the railway bogie. The center manifold theorem is adopted to reduce the dimension of the bogie dynamical model, and the symbolic expression for determining the bifurcation type at the critical speed is obtained by the method of normal form. As a result, the influence of yaw damper on the bifurcation type of the bogie is given qualitatively in contrast to typical wheel profiles with high and low wheel tread effective conicities. Besides, the discriminant of bifurcation type for the wheel tread parameter variation is given which depicts the variation tendency of dynamics characteristics. Finally, numerical analysis is given to exhibit corresponding bifurcation diagrams. | Hopf bifurcation analysis of railway bogie | 10.1007/s11071-017-3634-7 |
2018-03-13 | In this paper, we are interested in the following damped vibration system: where B is an antisymmetric $$N\times N$$ N × N constant matrix, $$q:{\mathbb {R}}\longrightarrow {\mathbb {R}}$$ q : R ⟶ R is a continuous function, $$L(t)\in C({\mathbb {R}},{\mathbb {R}}^{N^{2}})$$ L ( t ) ∈ C ( R , R N 2 ) is a symmetric matrix, and $$W(t,x)\in C^{1}({\mathbb {R}}\times {\mathbb {R}}^{N},{\mathbb {R}})$$ W ( t , x ) ∈ C 1 ( R × R N , R ) are neither autonomous nor periodic in t . The novelty of this paper is that, supposing that $$Q(t)=\int ^{t}_{0}q(s)\mathrm{d}s$$ Q ( t ) = ∫ 0 t q ( s ) d s is bounded from below and L ( t ) is coercive unnecessarily uniformly positively definite for all $$t\in {\mathbb {R}}$$ t ∈ R , we establish the existence of ground-state homoclinic solutions for (1) when the potential W ( t , x ) satisfies a kind of superquadratic conditions due to Ding and Luan for Schr $${\ddot{o}}$$ o ¨ dinger equation. The main idea here lies in an application of a variant generalized weak linking theorem for strongly indefinite problem developed by Schechter and Zou. Some recent results in the literature are generalized and significantly improved. | On Ground-State Homoclinic Orbits of a Class of Superquadratic Damped Vibration Systems | 10.1007/s00009-018-1097-9 |
2018-03-12 | This work is concerned with the Dirichlet initial boundary problem for a semilinear viscoelastic wave system with nonlinear weak damping and source terms. For nonincreasing positive functions g and h, we show the finite time blow-up of some solutions whose initial data have arbitrarily high initial energy. | Blow-up of arbitrarily positive initial energy solutions for a viscoelastic wave system with nonlinear damping and source terms | 10.1186/s13661-018-0951-9 |
2018-03-01 | In the framework of discrete element method, a new damping model is introduced. Unlike the global mass-damping, the new model applies an approximately equal damping ratio to all particles in a granular assembly. This model does not require exact stiffness calculations, hence not involved in the unnecessary cost. The new and global damping models were compared based on overall equilibrium of samples during quasi-static simulations. The equilibrium status was quantified by the unbalanced force ratio (UFR) and moment index. Moment index, proposed herein, was designed to indicate the relative magnitude of unbalanced moments. Larger unbalanced forces and moments, measured by UFR and moment index respectively, indicate larger inertial effects, and being further away from quasi-static conditions. Two samples with different particle size distributions (PSD) were tested in triaxial compression simulations under drained conditions using both damping models and various damping ratios at different strain rates. The damping ratios that resulted in the best equilibrium, so-called optimum damping ratios, were determined and typical values were suggested for each model. Applying damping ratios greater than the optimum values reduced the kinetic energy however worsened the equilibrium of particles by adding to unbalanced forces and moments. With the optimum damping ratios and at an equal loading rate, the new damping model proved superiority over global mass-damping by establishing better force and moment equilibriums while providing the same mechanical response. The new damping model allows application of higher strain rates for quasi-static simulations, consequently leads to shorter runtimes, especially for samples with wide PSDs. | Size-dependent damping model for DEM: improved equilibrium compared with mass-damping at no extra computational cost | 10.1007/s10035-018-0794-1 |
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