publicationDate stringlengths 10 10 | abstract stringlengths 0 37.3k | title stringlengths 1 5.74k | doi stringlengths 11 47 ⌀ |
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2017-08-01 | In the present study, the nature of dielectric layer above metal layer in surface plasmon resonance sensor is investigated. The performance-defining parameters, i.e., shift in resonance angle, half width at half maximum, and minimum reflection intensity, are investigated according to the variation of refractive index (real as well as imaginary) of dielectric layer. Moreover, these parameters are investigated according to the thickness variation of the dielectric layer at different purely real as well as complex refractive index of the dielectric layer. | Influence of Dielectric Coating on Performance of Surface Plasmon Resonance Sensor | 10.1007/s11468-016-0366-3 |
2017-08-01 | In this work, we investigate the dynamics of quantum correlation measured by measurement-induced nonlocality (MIN) and local quantum uncertainty (LQU) in correlated amplitude damping (CAD) channel. We find that the memory parameter brings different influences on MIN and LQU. In addition, we propose a scheme to protect quantum correlation by executing prior weak measurement (WM) and post-measurement reversal (MR). However, better protection of quantum correlation by the scheme implies a lower success probability (SP). | Protecting Quantum Correlation from Correlated Amplitude Damping Channel | 10.1007/s13538-017-0509-9 |
2017-08-01 | High dimensional quantum system plays a vital role in quantum information processing. However, decoherence induced by the coupling between quantum system and environment often destroys quantum resource. In this paper, we study the dynamics and protection of qutrit quantum coherence (QC) under amplitude damping (AD) decoherence. We propose two schemes to protect QC. We find that the first scheme can not always protect QC and the second scheme has prominent advantage over the first scheme. In addition, better protection requires lower success probability (SP). | Protecting Qutrit Quantum Coherence | 10.1007/s10773-017-3407-6 |
2017-08-01 | This paper investigates the low-velocity impact response of a shear deformable laminated beam which contains both carbon nanotube reinforced composite (CNTRC) layers and carbon fiber reinforced composite (CFRC) layers. The effect of matrix cracks is considered, and a refined self-consistent model is selected to describe the degraded stiffness caused by the damage. The beam including damping effects rests on a two-parameter elastic foundation in thermal environments. Based on a higher-order shear deformation theory and von Kármán nonlinear strain–displacement relationships, the motion equations of the beam and impactor are established and solved by means of a two-step perturbation approach. The material properties of both CFRC layers and CNTRC layers are assumed to be temperature-dependent. To assess engineering application of this hybrid structure, two conditions for outer CNTRC layers and outer CFRC layers are compared. Besides, the effects of the crack density, volume fraction of carbon nanotube, temperature variation, the foundation stiffness and damping on the nonlinear low-velocity impact behavior of hybrid laminated beams are also discussed in detail. | Nonlinear low-velocity impact on damped and matrix-cracked hybrid laminated beams containing carbon nanotube reinforced composite layers | 10.1007/s11071-017-3557-3 |
2017-08-01 | The major function of smoke control system is to prevent smoke from penetrating to vertical shaft or stairwell by pressurizing vestibule where is generally located between the vertical shaft and living room. Thus, it is important to calculate the required flow rate of air supply for remaining the pressure difference of 40 ~ 60 Pa between the shaft and vestibule. Heat and mass transfer from fire plume and leaking flows among building structures are representative influence factors on the flow rate. The previous studies, however, focused on calculation of the flow rate of air supply without considering the fire effect and damper leakage. In this study, the effect of damper leakage and fire size on the performance of smoke control system was investigated when considering various parameters, i.e., building size and pressurizing method. The effective damper leakage area was measured in a wind tunnel and used to numerical analysis for parameter study. As the results, in the case of whole floor pressurizing method, the increase rate of the flow rate is about two times than that of the parted floor pressurizing method. Also, the pressure difference steeply decreases at the fire floor whereas it slightly increases at the other floors as the fire size increases. | The effect of damper leakage and fire size on the performance of smoke control system in high-rise building | 10.1007/s12206-017-0750-8 |
2017-08-01 | The external squeeze film damping (SFD) of microelectromechanical systems (MEMS) resonators is a dominant factor to lower the quality factor (Q-factor) due to their large surface area to volume ratio and small spacing. To improve the Q-factor of MEMS resonators, the effect of gas rarefaction (low gas ambient pressure in thin gas film thickness) or operating in higher mode should be considered in SFD analysis. The modified molecular gas lubrication (MMGL) equation is applied for modeling the SFD with gas rarefaction effects taken into consideration. The effects of inverse Knudsen number, surface accommodation coefficients (ACs) and operating frequency on SFD are discussed. The combined effects of SFD, thermoelastic damping (TED) and anchor loss on the total Q-factors of MEMS resonators are considered. The contribution of SFD on the total Q-factor (weighting of SFD) is also discussed. The results show that weighting of SFD could be decrease at low inverse Knudsen number or low ACs or operating at high resonant frequencies. | Effect of gas rarefaction on the quality factors of micro-beam resonators | 10.1007/s00542-016-3068-z |
2017-08-01 | 目 的 针对典型高铁轨道结构, 对钢轨减振器的设计参数进行研究, 进一步揭示钢轨减振器的工作机理, 为合理设计和应用提供科学依据。 创新点 运用基于傅里叶变换的无限长周期结构动态特性的分析方法, 从轨道结构的频散特性、共振特性、振动衰减特性和振动能量(近似声辐射能力)等多个方面对钢轨减振器的参数进行研究; 提出荷载移动对振动衰减率的影响问题。 方 法 运用基于傅里叶变换的无限长周期结构动态特性的分析方法, 结合典型高铁轨道结构, 对钢轨减振器的设计参数对轨道结构动力学特性的影响进行研究。研究的动力学特性包括: 频散特性、共振特性、振动衰减特性和振动能量(近似声辐射能力)。 结 论 1. 加装钢轨减振器会引入新的阻带, 从而增加整个阻带的宽度; 2. 在移动和不移动的情况下, 荷载的振动衰减率是不同的; 荷载的高速移动会降低振动衰减率; 3. 从阻带尽量宽、振动衰减率尽量大和振动能量尽量小这三方面的要求来看, 钢轨减振器的设计频率应该接近原来轨道结构的Pinned-Pinned 频率, 并且质量越大越好; 4. 如果能够保证足够高的阻尼, 钢轨减振器的频率可以设计得比Pinned-Pinned 频率低。 Installation of rail vibration dampers (rail dampers for short) onto rails between sleepers is one of the measures to control rail noise generation and roughness growth. Amid the rapid expansion of high-speed and underground railway networks in China, many suppliers are actively marketing and promoting their products, often giving confusing information. In this paper, a parametric study is used to investigate the effect of rail dampers on the dynamical behavior of a Chinese high-speed railway track. The Fourier transform-based method developed for analyzing dynamics of a railway track as an infinitely long periodic structure, with or without rail dampers, is applied in the investigation. It is hoped that results in this paper can help develop the understanding of the working mechanism of rail dampers, and provide useful information for product design and application. | Theoretical investigation into the effect of rail vibration dampers on the dynamical behaviour of a high-speed railway track | 10.1631/jzus.A1600697 |
2017-08-01 | A magneto rheological (MR) fluid damper offers cost effective solution for semiactive vibration control in an automobile suspension. The performance of MR damper is significantly depends on the electromagnetic circuit incorporated into it. The force developed by MR fluid damper is highly influenced by the magnetic flux density induced in the fluid flow gap. In the present work, optimization of electromagnetic circuit of an MR damper is discussed in order to maximize the magnetic flux density. The optimization procedure was proposed by genetic algorithm and design of experiments techniques. The result shows that the fluid flow gap size less than 1.12 mm cause significant increase of magnetic flux density. | Optimization of Magneto-Rheological Damper for Maximizing Magnetic Flux Density in the Fluid Flow Gap Through FEA and GA Approaches | 10.1007/s40032-016-0251-z |
2017-08-01 | The dynamics of jacket supported offshore wind turbine (OWT) in earthquake environment is one of the progressing focuses in the renewable energy field. Soil–structure interaction (SSI) is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper (MTMD) in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology (RSM) has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions: fixed base (without SSI) and flexible base (with SSI). Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance. | Multiple tuned mass damper based vibration mitigation of offshore wind turbine considering soil–structure interaction | 10.1007/s13344-017-0054-x |
2017-07-29 | In this paper, we consider a hydroelastic model to examine the radiation of waves by a submerged sphere for both heave and sway motions in a single-layer fluid flowing over an infinitely extended elastic bottom surface in an ocean of finite depth. The elastic bottom is modeled as a thin elastic plate and is based on the Euler–Bernoulli beam equation. The effect of the presence of surface tension at the free-surface is neglected. In such situation, there exist two modes of time-harmonic waves: the one with a lower wavenumber (surface mode) propagates along the free-surface and the other with higher wavenumber (flexural mode) propagates along the elastic bottom surface. Based on the small amplitude wave theory and by using the multipole expansion method, we find the particular solution for the problem of wave radiation by a submerged sphere of finite depth. Furthermore, this method eliminates the need to use large and cumbersome numerical packages for the solution of such problem and leads to an infinite system of linear algebraic equations which are easily solved numerically by any standard technique. The added-mass and damping coefficients for both heave and sway motions are derived and plotted for different submersion depths of the sphere and flexural rigidity of the elastic bottom surface. It is observed that, whenever the sphere nearer to the elastic bed, the added-mass move toward to a constant value of 1, which is approximately twice of the value of added-mass of a moving sphere in a single-layer fluid flowing over a rigid and flat bottom surface. | Effects of elastic bed on hydrodynamic forces for a submerged sphere in an ocean of finite depth | 10.1007/s00033-017-0837-1 |
2017-07-01 | The viscous damping coefficient (VDC) of hydraulic actuators is crucial for system modeling, control and dynamic characteristic analysis. Currently, the researches on hydraulic actuators focus on behavior assessment, promotion of control performance and efficiency. However, the estimation of the VDC is difficult due to a lack of study. Firstly, using two types of hydraulic cylinders, behaviors of the VDC are experimentally examined with velocities and pressure variations. For the tested plunger type hydraulic cylinder, the exponential model $$B = \alpha \upsilon^{ - \beta } ,(\alpha > 0,\beta > 0)$$ B = α υ - β , ( α > 0 , β > 0 ) or $$B = \alpha_{1} e^{{ - \beta_{1} \upsilon }} + \alpha_{2} e^{{ - \beta_{2} \upsilon }} (\alpha_{1} ,\alpha_{2} > 0,\beta_{1} ,\beta_{2} > 0)$$ B = α 1 e - β 1 υ + α 2 e - β 2 υ ( α 1 , α 2 > 0 , β 1 , β 2 > 0 ) , fits the relation between the VDC and velocities for a given pressure of chamber with high precision. The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa. Furthermore, the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types. In order to investigate the VDC of a plunger type hydraulic actuator drastically, a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrication, back-up ring related friction behaviors and shear stress of fluid. It is shown that the simulated results of VDC agree with the measured results with a good accuracy. The proposed method provides an instruction to predict the VDC in system modeling and analysis. | Theoretical Investigation of the Viscous Damping Coefficient of Hydraulic Actuators | 10.1007/s10033-017-0153-x |
2017-07-01 | The consequences of emergencies of turbosets for different application are revealed, the cause of forced shutdown and even catastrophic destructions of which many researchers consider the rotor-to-stator rubbing and development—to a greater or lesser extent—of the phenomena of the rotor generation roll over the stator. The synchronous or asynchronous generation roll is determined by the rotor precession direction, coinciding or not coinciding with the self-rotation direction of the rotor. Asynchronous generation roll is the most dangerous form of the rotor-stator contact interaction with the vibrations with rubbing. The basic equations of rotor vibrations are presented: symmetric rotor fixed on two supports and that fixed on several supports after abrupt imbalance with and without rotor coming in contact with a flexible stator. The vibration process is considered as the rotor motion in a backlash with subsequent contact with the stator, loss of contact, or development of generation roll. The latter essentially depends on the properties of the “rotor–support–stator” dynamic system. The stator stiffness characteristic is specified in “force–deformation” coordinates that make it possible to take into account damping in the supports and power loss in the stator. The diagram of elastic-damping device was presented, which makes it possible to ensure a certain level of power loss at the stator displacements. The exciting forces promoting development of self-exciting vibrations of the rotor in the form of asynchronous generation roll were compared with the exciting forces of oil film of sliding bearings and forces of aerodynamic excitation in the turbine flow path and sealings. For the rotor systems of high and medium pressure of a 300 MW capacity turboset, the simulation results of the process of development of asynchronous generation roll at the vibrations with rubbing were revealed, and the basic characteristics of development of generation roll in a span between supports and time variation of casual coefficients of contact stiffness defining the forces exciting the generation roll at the contact interaction of the rotor with the stator were presented. The dependence of coefficients of contact stiffness on the rotor displacements submits to the hyperbolic law. The increase of damping decreases the probability of occurrence of dangerous consequences of emergencies, which are defined by many factors, including the rotor imbalance level. | Forces exciting generation roll at rotor vibrations when rotor-to-stator rubbing | 10.1134/S0040601517070072 |
2017-07-01 | Active damped LCL-filter-based inverters have been widely used for grid-connected distributed generation (DG) systems. In weak grids, however, the phase-locked loop (PLL) dynamics may detrimentally affect the stability of grid-connected inverters due to interaction between the PLL and the controller. In order to solve the problem, the impact of PLL dynamics on small-signal stability is investigated for the active damped LCL-filtered grid-connected inverters with capacitor voltage feedback. The system closed-loop transfer function is established based on the Norton equivalent model by taking the PLL dynamics into account. Using an established model, the system stability boundary is identified from the viewpoint of PLL bandwidth and current regulator gain. The accuracy of the ranges of stability for the PLL bandwidth and current regulator gain is verified by both simulation and experimental results. | Impact of phase-locked loop on stability of active damped LCL-filter-based grid-connected inverters with capacitor voltage feedback | 10.1007/s40565-017-0302-3 |
2017-07-01 | In this paper, linear and nonlinear vibration absorbers are designed to suppress regenerative chatter in micro-milling process. Suppressing regenerative chatter leads to improve surface finish. Micro-milling process is considered as a two degree of freedom system, and the run-out effects of cutting tool are also taken into account. Linear and nonlinear absorbers in two directions are composed of mass, spring and dashpot elements. The optimum values of the absorber parameters are determined by means of an optimization algorithm in order to minimize the cutting tool vibration. The effectiveness of different types of the absorbers in micro-milling process is illustrated. The optimum parameters for each type of absorbers are presented. | Application of linear and nonlinear vibration absorbers in micro-milling process in order to suppress regenerative chatter | 10.1007/s11071-017-3488-z |
2017-07-01 | The air spring component with a damper inside is widely used in the commercial vehicle as a vibration isolator. The nonlinear dynamics of the air spring component is important for full vehicle ride comfort evaluation. This paper aims to develop a mechanical model of the air spring component which can reproduce the air spring characteristics correctly. The proposed model consists of three split force branches in parallel describing the nonlinear elastic characteristics based on thermodynamics, the asymmetrical hysteresis and amplitude dependence by variable Berg’s friction, and the frequency dependency with four-parameter fractional derivative model. The air spring component bench tests are conducted, and the procedure of model parameter identification and model verification is presented. The nonlinear dynamic responses of the proposed model are investigated under a large amplitude excitation and different pre-compressions/pre-elongations by comparing with the Berg’s model which uses a linear elastic force element. Additionally, the proposed model and the Berg’s model for the air spring component are separately integrated into a full vehicle multibody dynamic model to evaluate the ride comfort as application for further verification through the co-simulation method using MATLAB/Simulink and MSC.ADAMS. The proposed model is verified to be more accurate than the Berg’s model through comparison with the full vehicle ride comfort test results. | Nonlinear dynamic model of air spring with a damper for vehicle ride comfort | 10.1007/s11071-017-3535-9 |
2017-07-01 | Cable stayed Bridges are highly vulnerable to strong wind load induced vibrations which are responsible of generating aerodynamic instability and in a critical situation lead to structural failure. This paper focuses on buffeting response and flutter instability in a cable stayed Bridge. A strong fluctuating wind is assigned to a cable stayed Bridge model in ABAQUS FE program to onset optimization and global sensitivity analysis through considering three aerodynamic parameters (wind attack angle, deck streamlined length and stay cables viscous damping) by targeting the vertical and torsional vibrations of the deck. The numerical simulations results in conjunction with the frequency analysis results emphasized the existence of such vibrations. Model validation performed by comparing the results of lift and moment coefficients between the present FE model and two benchmarks from the literature (flat plate theory and flat plate by Xavier et al ., 2015), which resulted in good agreements between them. Optimum values of the adopted aerodynamic parameters have been identified and discussed. Global sensitivity analysis based on Monte Carlo sampling method was utilized to formulate the surrogate models and the sensitivity indices so that to identify rational effect and role of each parameter on the aerodynamic stability of the structure. | Aerodynamic stability parameters optimization and global sensitivity analysis for a cable stayed Bridge | 10.1007/s12205-016-0962-y |
2017-07-01 | A bistable nonlinear energy sink conceived to mitigate the vibrations of host structural systems is considered in this paper. The hosting structure consists of two coupled symmetric linear oscillators (LOs), and the nonlinear energy sink (NES) is connected to one of them. The peculiar nonlinear dynamics of the resulting three-degree-of-freedom system is analytically described by means of its slow invariant manifold derived from a suitable rescaling, coupled with a harmonic balance procedure, applied to the governing equations transformed in modal coordinates. On the basis of the first-order reduced model, the absorber is tuned and optimized to mitigate both modes for a broad range of impulsive load magnitudes applied to the LOs. On the one hand, for low-amplitude, in-well, oscillations, the parameters governing the bistable NES are tuned in order to make it functioning as a linear tuned mass damper (TMD); on the other, for high-amplitude, cross-well, oscillations, the absorber is optimized on the basis of the invariant manifolds features. The analytically predicted performance of the resulting tuned bistable nonlinear energy sink (TBNES) is numerically validated in terms of dissipation time; the absorption capabilities are eventually compared with either a TMD and a purely cubic NES. It is shown that, for a wide range of impulse amplitudes, the TBNES allows the most efficient absorption even for the detuned mode, where a single TMD cannot be effective. | The tuned bistable nonlinear energy sink | 10.1007/s11071-017-3444-y |
2017-07-01 | This study investigates the efficiency of two types of rehabilitation methods based on economic justification that can lead to logical decision making between the retrofitting schemes. Among various rehabilitation methods, concentric chevron bracing (CCB) and cylindrical friction damper (CFD) were selected. The performance assessment procedure of the frames is divided into two distinct phases. First, the limit state probabilities of the structures before and after rehabilitation are investigated. In the second phase, the seismic risk of structures in terms of life safety and financial losses (decision variables) using the recently published FEMA P58 methodology is evaluated. The results show that the proposed retrofitting methods improve the serviceability and life safety performance levels of steel and RC structures at different rates when subjected to earthquake loads. Moreover, these procedures reveal that financial losses are greatly decreased, and were more tangible by the application of CFD rather than using CCB. Although using both retrofitting methods reduced damage state probabilities, incorporation of a site-specific seismic hazard curve to evaluate mean annual occurrence frequency at the collapse prevention limit state caused unexpected results to be obtained. Contrary to CFD, the collapse probability of the structures retrofitted with CCB increased when compared with the primary structures. | Effectiveness of two conventional methods for seismic retrofit of steel and RC moment resisting frames based on damage control criteria | 10.1007/s11803-017-0404-y |
2017-06-29 | Beam lifetime of a synchrotron is dominated by Touschek scattering. In the beamline Phase II project of Shanghai synchrotron radiation facility, a passive third harmonic cavity is to be installed for bunch lengthening and instability suppressing. In this paper, the beam dynamics of the cavity is investigated. The parameters of passive operation are optimized to cancel the slope of RF voltage and lengthen the bunches. The Touschek lifetime increases are estimated for optimum and non-optimum voltage flattening. A tolerance of the operation is studied in case that there is a shift on detuning angle. The effect caused by reduction in harmonic voltage generated by lengthened bunch distribution is also estimated using iteration method. An increase in synchrotron frequency spread due to nonlinearity of the voltage giving to the bunch is found by using tracking simulation. This spread can help in damping coupled bunch instability through Landau damping. | Improving Touschek lifetime and synchrotron frequency spread by passive harmonic cavity in the storage ring of SSRF | 10.1007/s41365-017-0259-y |
2017-06-09 | Ni–Mn–Ga–Cu microwires, with diameter of 20–80 μm, length of 30–150 mm and fined columnar grains, were produced by melt-extraction technique. The damping capacity of the extracted microwires was investigated by stretching a microwire under a tensile stress using dynamic mechanical analyzer. The damping capacity of the martensite and austenite phases shows a weak frequency dependence but a strong strain amplitude dependence. The damping capacity (Tan δ ) of the martensite and austenite phases reaches 0.08 and 0.04, respectively, under strain amplitude of 0.5% and frequency of 1 Hz. The high damping capacity of the martensite phase is related to the high mobility of martensite twin boudaries, while that of austenite phase to the motion of dislocations. The ferromagnetic Ni–Mn–Ga–Cu microwires, with high ductility and damping capacity, may act as promising materials for microscale devices, systems and composite fillers for passive dissipation of undesired vibrations and noises. | High damping capacity of Ni–Mn–Ga–Cu microwires prepared by melt-extraction technique | 10.1007/s12598-017-0925-6 |
2017-06-01 | Under the condition of actual sea state, hydrodynamic characteristics of floating horizontal-axis turbine are related to wave characteristics and floating carrier motion responses. We recently published the hydrodynamic performance and axial damping coefficient of the horizontal-axis tidal current turbine influenced by surge motion in constant inflow using CFD simulation (Zhang et al. Renew Energy 74:796–802, 2015). Encouraged by this result, this paper uses sliding mesh to analyze the hydrodynamic characteristics in uniform stream when the turbine is forced to roll and studies influences of different roll frequency, roll amplitude, and tip speed ratio on turbine’s performance. Roll-damping coefficient and added mass coefficient can be derived by torque almanacs curve of rolling turbine by the least square method. Results show that the turbine axial load, roll moment, and energy utilization ratio will fluctuate in roll motion; the more roll frequency and roll amplitude, and the more load and moment wave amplitude of momentary value. The crest value occurs in the balance position of rolling, while the amplitude of oscillation depends on the angular speed of rolling and rotating speed of the turbine. The frequency and amplitude of the roll have little impact on damping coefficient, but rotational speed of the turbine has positive impact on this coefficient. Results of this study can provide data to study motion response of floating carrier for floating tidal current turbine system and check the structural design and control of the electric output. | The effects of roll motion of the floating platform on hydrodynamics performance of horizontal-axis tidal current turbine | 10.1007/s00773-016-0408-8 |
2017-06-01 | This paper deals with the speed response characteristic of the concentrated flux synchronous motor (CFSM) using ferrite magnets for the electric power steering (EPS) system. To analyze the response characteristic of the CFSM, an analytical method using the electromechanical undamped natural frequency and damping ratio based on the transfer function is proposed. By using the method, the speed response according to the variations of the shape of the permanent magnets (PMs) and rotor core is analyzed. It was analyzed under the conditions of the constant volume of the PMs as well as the constant diameter of the rotor. By using the proposed analysis method, the improved model is desgined based on the initial model fulfilling the required specifications. Finally, the torque and speed response characteristics of two motors are simulated through the finite element analysis (FEA) and MATLAB Simulink. | Design of ferrite magnet CFSM to improve speed response of EPS system | 10.1007/s12239-017-0049-x |
2017-06-01 | We present an ab initio theory of the Gilbert damping in ferromagnetic alloys with substitutional disorder. The theory is based on nonlocal torques that are represented by nonrandom, site-off-diagonal, and spin-independent matrices, which simplifies the configuration averaging. The formalism is developed for the relativistic tight-binding linear muffin-tin orbital (TB-LMTO) method and the coherent potential approximation (CPA). The CPA-vertex corrections play a crucial role for the internal consistency of the theory and for its exact equivalence to other first-principles approaches based on random local torques. The theory is illustrated by calculations for various random transition metal alloys: FeNi, FeCo, Heusler alloys, permalloy with impurities, Fe with vacancies, and stoichiometric FePt and CoPt alloys with a varying degree of L1 _0 atomic long-range order. Results are in a reasonable agreement with other calculations and accessible experimental data. | Ab Initio Theory of the Gilbert Damping in Random Ferromagnetic Alloys | 10.1007/s10948-016-3662-4 |
2017-06-01 | In this paper, the response behaviors of two parallel structures coupled by Lead Extrusion Dampers (LED) under various earthquake ground motion excitations are investigated. The equation of motion for the two parallel, multi-degree-of-freedom (MDOF) structures connected by LEDs is formulated. To explore the viability of LED to control the responses, namely displacement, acceleration and shear force of parallel coupled structures, the numerical study is done in two parts: (1) two parallel MDOF structures connected with LEDs having same damper damping in all the dampers and (2) two parallel MDOF structures connected with LEDs having different damper damping. A parametric study is conducted to investigate the optimum damping of the dampers. Moreover, to limit the cost of the dampers, the study is conducted with only 50% of total dampers at optimal locations, instead of placing the dampers at all the floor level. Results show that LEDs connecting the parallel structures of different fundamental frequencies, the earthquake-induced responses of either structure can be effectively reduced. Further, it is not necessary to connect the two structures at all floors; however, lesser damper at appropriate locations can significantly reduce the earthquake response of the coupled system, thus reducing the cost of the dampers significantly. | Seismic analysis of parallel structures coupled by lead extrusion dampers | 10.1007/s40091-017-0157-x |
2017-06-01 | This paper describes a test stand along with a model of a lance used in glass works. A prototype friction damper was used for vibration damping of the lance. Experimental tests were conducted, whose aim was to determine operating conditions under which the damper will be the most effective. Damping was evaluated based on the damping decrement determined using the resonance curve for the first form of vibration of the lance. It was found that a friction damper has optimal values of preload force from the point of view of damping of the lance’s resonant vibration. | Testing the vibration damping of a glass gatherer robot arm using a friction damper | 10.1016/j.acme.2016.10.004 |
2017-06-01 | Thin film bulk acoustic resonator (FBAR) higher quality factor ( Q ) provides steep skirt and low insertion losses in the pass band. In this paper, three different loss sources are identified and FBAR is design and simulated in order to reduce the losses. Firstly, the FBAR’s top electrode is simulated for the areas of 150 × 150, 300 × 300 and 400 × 400 μm^2 and the quality factor is improved as the area increased to 102, 432.6 and 743.7 respectively. The impedance of the FBAR is reduced as the area of the electrode is increased. Secondly, the anchor width is reduced from 60 to 45 μm and the quality factor is increased from 341 to 432.6 respectively. The losses through the anchor reduce as the anchor reduces. Electrode area and anchor area simulation are showing the notable effect and no other paper is reported for the comparison. Thirdly, the damping factor coefficient ( β ) is varied as 4.7e^−14, 3.84e^−14 and 2.5e^−14. The quality factor is increased as the damping factor reduces and reported as 283.2, 341.2 and 444.5 respectively. The damping reduction leads the FBAR structure to vibrate more freely at the resonance. The losses through damping are reduced and more energy has stored at the resonance so it increases the quality factor. | Design and Simulation of FBAR for Quality Factor Enhancement | 10.1007/s12647-016-0195-z |
2017-06-01 | This paper is concerned with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear vibrations of sandwich plates with facings composed of fuzzy fiber reinforced composite (FFRC). FFRC is a novel composite where the short carbon nanotubes (CNTs) which are either straight or wavy are radially grown on the periphery of the long continuous carbon fiber reinforcements. The plane of waviness of the CNTs is coplanar with the plane of carbon fiber. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1–3 piezoelectric composites (PZCs) while the constrained viscoelastic layer has been sandwiched between the substrate and the PZC layer. The Golla–Hughes–McTavish method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. A three dimensional nonlinear finite element model of smart FFRC sandwich plates integrated with ACLD patches has been developed to investigate the performance of these patches for controlling the geometrically nonlinear vibrations of these plates. This study reveals that the performance of the ACLD patches for controlling the geometrically nonlinear vibrations of the sandwich plates is better in the case of the facings composed of laminated FFRC than that in the case of the facings made of conventional orthotropic laminated composite. Particular emphasis has been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD treatment. The research carried out in this paper brings to light that even the wavy CNTs can be properly utilized for attaining structural benefits from the exceptional elastic properties of CNTs. | Active damping of geometrically nonlinear vibrations of sandwich plates with fuzzy fiber reinforced composite facings | 10.1007/s40435-015-0180-3 |
2017-06-01 | There is an inherent trade-off between stability and transparency in haptic interaction systems when interacting with virtual environments. Therefore, no perfect transparency can be displayed with absolute stability. For meaningful interactions, anyhow, some level of transparency is necessary for providing realistic feelings. On the other hand, robust stability must absolutely be guaranteed against any virtual environments because unstable behaviors disrupt contact realism completely and/or may also injure human operators. In order to increase magnitude transparency of the haptic interaction system, this paper proposes a way of systematic inclusion of Coulomb friction component in the previous force bounding approach. In the inclusion, two type of force bounding approach are derived. The less conservative condition can generate significantly higher magnitude transparency in terms of the initial contact crispness as well as the steady-state contact force for very stiff virtual objects. However, there occur some contact oscillations to diminish contact realism due to the energy accumulation during free motion. In order to avoid contact oscillations, a more conservative condition is proposed for systematically removing the past accumulated energy. The proposed algorithm is also compared with the other similar algorithm. Comprehensive experimental results are presented to show the effectiveness of the proposed approaches. | An enhanced force bounding approach for stable haptic interaction by including friction | 10.1007/s12541-017-0097-1 |
2017-06-01 | Structural dynamic characteristics are the most significant parameters that play a decisive role in structural damage assessment. The more sensitive parameter to the damage is the damping behavior of the structure. The complexity of structural damping mechanisms has made this parameter to be one of the ongoing research topics. Despite all the difficulties in the modeling of damping, there are some approaches like as linear and nonlinear models which are described as the energy dissipation throughout viscous, material or structural hysteretic and frictional damping mechanisms. In the presence of a mathematical model of the damping mechanisms, it is possible to estimate the damping ratio from the theoretical comparison of the damped and un-damped systems. On the other hand, solving the inverse problem of the input force estimation and its distribution to each SDOFs, from the measured structural responses plays an important role in structural identification process. In this paper model-based damping approximation method and a model-less structural input estimation are considered. The effectiveness of proposed methods has been carried out through analytical and numerical simulation of the lumped mass system and the results are compared with reference data. Consequently, high convergence of the comparison results illustrates the satisfactory of proposed approximation methods. | Approximation of structural damping and input excitation force | 10.1007/s11709-016-0371-9 |
2017-06-01 | In this paper, a novel structural modification approach has been adopted to eliminate the early coupling between the bending and torsional mode shapes of vibrations for a cable stayed bridge model generated using ABAQUS software. Two lateral steel beams are added to the middle span of the structure. Frequency analysis is dedicated to obtain the natural frequencies of the first eight mode shapes of vibrations before and after the structural modification approach. Numerical simulations of wind excitations are conducted for the 3D model of the cable stayed bridge with duration of 30 s supporting on real data of a strong wind from the literature. Both vertical and torsional displacements are calculated at the mid span of the deck to analyze both the bending and the torsional stiffness of the system before and after the structural modification. The results of the frequency analysis after applying lateral steel beams declared a safer structure against vertical and torsional vibrations and rarely expected flutter wind speed. Furthermore, the coupling between the vertical and torsional mode shapes has been removed to larger natural frequencies magnitudes with a high factor of safety. The novel structural approach manifested great efficiency in increasing vertical and torsional stiffness of the structure. | A novel structural modification to eliminate the early coupling between bending and torsional mode shapes in a cable stayed bridge | 10.1007/s11709-016-0376-4 |
2017-06-01 | Attention focuses on how plastic deformation and asymmetric loading affect the properties of Fe‒Al and Mn–Cu damping alloys. When the vibrational amplitude is small, the damping properties of Fe‒Al alloys are highly sensitive to external static loads; the sensitivity is much less for Mn–Cu alloys. With decrease in the grain size of Fe–Al alloys, the sensitivity to external static loads is much reduced. | Influence of plastic deformation and asymmetric loading on the properties of Fe–Al and Mn–Cu damping alloys | 10.3103/S0967091217060031 |
2017-06-01 | A design sensitivity analysis for the transient response of the non-viscously damped dynamic systems is presented. The non-viscously (viscoelastically) damped system is widely used in structural vibration control. The damping forces in the system depend on the past history of motion via convolution integrals. The non-viscos damping is modeled by the generalized Maxwell model. The transient response is calculated with the implicit Newmark time integration scheme. The design sensitivity analysis method of the history dependent system is developed using the adjoint variable method. The discretize-then-differentiate approach is adopted for deriving discrete adjoint equations. The accuracy and the consistency of the proposed method are demonstrated through a single dof system. The proposed method is also applied to a multi-dof system. The validity and accuracy of the sensitivities from the proposed method are confirmed by finite difference results. | Design sensitivity analysis for transient response of non-viscously damped dynamic systems | 10.1007/s00158-016-1636-6 |
2017-06-01 | Time-dependent problems modeled by hyperbolic partial differential equations can be reformulated in terms of boundary integral equations and solved via the boundary element method. In this context, the analysis of damping phenomena that occur in many physics and engineering problems is a novelty. Starting from a recently developed energetic space-time weak formulation for the coupling of boundary integral equations and hyperbolic partial differential equations related to wave propagation problems, we consider here an extension for the damped wave equation in layered media. A coupling algorithm is presented, which allows a flexible use of finite element method and boundary element method as local discretization techniques. Stability and convergence, proved by energy arguments, are crucial in guaranteeing accurate solutions for simulations on large time intervals. Several numerical benchmarks, whose numerical results confirm theoretical ones, are illustrated and discussed. | Energetic BEM-FEM coupling for the numerical solution of the damped wave equation | 10.1007/s10444-016-9500-1 |
2017-06-01 | The importance of robust feedback control for uncertain negative imaginary system lies in its practical relevance and engineering applications, for example, lightly damped flexible structures with collocated position sensors and force actuators. This article investigates an LMI based robust static state internally stabilizing feedback controller of the negative imaginary system in presence of strictly negative imaginary uncertainties. The paper first presents some basic theory of negative imaginary systems and then, a necessary and sufficient condition is established for the internal stability of the positive feedback interconnections of negative imaginary systems. The paper provides a systematic controller synthesis procedure based on negative imaginary lemma to achieve robustness in the feedback control of negative imaginary systems. To show the effectiveness of controller synthesis method, one design example is considered and a static state-feedback controller is constructed to force the plant to be stable. The simulation results of this article demonstrate the usefulness of the design method and we believe that feedback control of the negative imaginary system can benefit control engineering practitioners in a number of ways. | LMI based robust state feedback control of negative-imaginary systems | 10.1007/s40435-015-0188-8 |
2017-06-01 | In modern technology, the protection of mechanical objects from vibrational effects is an important problem. The task of increasing the efficiency of a vibration–isolation system as applied to vehicles is discussed. Operator equations that describe the movement of a single-mass system for active vibration isolation with a controllable magnetorheological damper are presented. A mathematical model of a closed system with negative feedback with respect to the vibration acceleration of the protected object in the form of a block diagram is considered. A controller that provides a decrease in the vibration accelerations of the protected object within a certain frequency range to a preset level is created. The possibility of simplifying the controller without substantial losses in control quality is substantiated by comparing the dynamic characteristics of the system. On the basis of a computer simulation, the dynamic characteristics of the open- and closed-loop systems for a harmonic disturbance were investigated taking the mass of the vibroprotected object into account. The description of the developed experimental bench for investigating the dynamic characteristics of the vibration–isolation system is given. The frequency characteristics of the active vibration–isolation system were studied. Comparison of the calculated and experimental data testifies to the effectiveness of the developed models and the adopted assumptions. The possibility fundamentally improving the quality of a vibration–isolation system when using the created system is shown. | Investigations of the dynamic characteristics of an active vibration–isolation system of an object with varying parameters | 10.3103/S1068371217060025 |
2017-06-01 | Magnetorheological dampers (MR) are one of the semi active devices, which has the capability of providing variable damping force for the variable input current. Induced force is directly dependent on the amount of magnetic flux density developed in effective fluid flow gap of the MR damper. In the present work, influence of material properties on the magnetic flux is investigated by considering magnetic and nonmagnetic material for the outer cylinder of shear mode type MR damper. Magnetostatic analysis is carried out to obtain magnetic flux density for the initial configuration of the MR damper. From the analysis, it is found that usage of magnetic material cylinder which is insulated with nonmagnetic material provided higher value of magnetic flux and damping force. The geometric optimisation of MR damper is carried out to obtain the maximum flux density in the fluid flow gap. The objective function of the optimisation includes the maximum magnetic flux density and minimising fluid flow gap. Design variables considered are fluid flow gap, number of turns in the electromagnetic coil, length of the flange and DC current input. The optimisation is performed through response surface method using finite element analysis software (ANSYS). The best optimal design parameters are obtained by choosing the appropriate value of objective function. The best configuration of the design parameters, which induce the maximum magnetic flux density, is identified. The force induced in the MR damper is estimated analytically and a comparative study of the optimised and non-optimised results was carried out. | Optimisation of monotube magnetorheological damper under shear mode | 10.1007/s40430-017-0709-9 |
2017-06-01 | A three-storey half scale reinforced concrete (RC) building is fixed with X-shaped metallic damper at the ground floor level, is designed and fabricated to study its seismic response characteristics. Experimental studies are carried out using the (4 m × 4 m) tri-axial shake-table facility to evaluate the seismic response of a retrofitted RC building with open ground storey (OGS) structure using yielding type X-shaped metallic dampers (also called as Added Damping and Stiffness-ADAS elements) and repairing the damaged ground storey columns using geopolymer concrete composites. This elasto-plastic device is normally incorporated within the frame structure between adjacent floors through chevron bracing, so that they efficiently enhance the overall energy dissipation ability of the seismically deficient frame structure under earthquake loading. Free vibration tests on RC building without and with yielding type X-shaped metallic damper is carried out. The natural frequencies and mode shapes of RC building without and with yielding type X-shaped metallic damper are determined. The retrofitted reinforced concrete building is subjected to earthquake excitations and the response from the structure is recorded. This work discusses the preparation of test specimen, experimental set-up, instrumentation, method of testing of RC building and the response of the structure. The metallic damper reduces the time period of the structure and displacement demands on the OGS columns of the structure. Nonlinear time history analysis is performed using structural analysis package, SAP2000. | Earthquake Response of Reinforced Concrete Building Retrofitted with Geopolymer Concrete and X-shaped Metallic Damper | 10.1007/s40030-017-0209-z |
2017-05-12 | We consider a nonlinear Schrödinger equation with Dirac interaction defect. Moreover, non-standard boundary conditions are introduced in connection to the behavior of the solutions. First, we prove that this kind of Schrödinger equation can be characterized by an autonomous dynamical system. Then, based on this result, we show that such an equation possesses a maximal compact attractor in the weak topology of H 1 $\mathbf{H}^{\mathbf{1}}$ . | Existence of global attractor for one-dimensional weakly damped nonlinear Schrödinger equation with Dirac interaction and artificial boundary condition in half-line | 10.1186/s13662-017-1194-2 |
2017-05-05 | In this paper we consider a quasilinear viscoelastic wave equation with initial-boundary conditions, strong damping and source term. Under suitable assumptions on the initial data and the relaxation function, we establish a blow-up result of a solution for negative initial energy and some positive initial energy if the influence of the source term is greater than the dissipation. We show that the solution exists globally for any initial data if the influence of dissipation is greater than the source term. | Blow-up and global existence for solution of quasilinear viscoelastic wave equation with strong damping and source term | 10.1186/s13661-017-0796-7 |
2017-05-01 | In this paper, we study the well-posedness and exponential decay for the porous thermoelastic system with the heat conduction given by Cattaneo’s law and a time-varying delay term, the coefficient of which is not necessarily positive. Using the semigroup arguments and variable norm technique of Kato, we first prove that the system is well-posed under a certain condition on the weight of the delay term, the weight of the elastic damping term and the speed of the delay function. By introducing a suitable energy and an appropriate Lyapunov functional, we then establish an exponential decay rate result. | Well-posedness and exponential decay for a porous thermoelastic system with second sound and a time-varying delay term in the internal feedback | 10.1007/s00161-017-0556-z |
2017-05-01 | We investigate the Cauchy problem for the Vlasov–Poisson system with radiation damping. By virtue of energy estimate and a refined velocity average lemma, we establish the global existence of nonnegative weak solution and asymptotic behavior under the condition that initial data have finite mass and energy. Furthermore, by building a Gronwall inequality about the distance between the Lagrangian flows associated to the weak solutions, we can prove the uniqueness of weak solution when the initial data have a higher order velocity moment. | Existence, uniqueness and asymptotic behavior for the Vlasov–Poisson system with radiation damping | 10.1007/s10114-016-6310-9 |
2017-05-01 | In this paper, a study of the thermoelastic damping of a gold microbeam resonator in the context of the generalized thermoelasticity with one relaxation time has been improved. An explicit formula of thermoelastic damping has been derived in general form includes the speed of the beam in the direction of its principal axis and without any external body force. Influences of the speed, the rotation, and the magnetic field have been studied. We discussed the effect of the speed of the beam, the rotation, and the magnetic field on the thermoelastic damping (Q-factor). The moving and the rotation of the microbeam have significant effects on the thermoelastic damping and the energy dissipation. The external magnetic field with tiny induced magnetic field acts on the microbeam has a significant effect on the thermoelastic damping and the energy dissipation. The energy dissipation of the microbeam decreases when the speed of the microbeam, the rotation angular speed, and the external magnetic field acts on the microbeam decrease. | Effect of the speed, the rotation and the magnetic field on the Q-factor of an axially clamped gold micro-beam | 10.1007/s11012-016-0498-8 |
2017-05-01 | We propose a comprehensive numerical procedure to calculate the hydrodynamic coefficients of a moving body with NACA0012 hydrofoil by means of Computational fluid dynamics (CFD). To accomplish maneuverability study and dynamic analysis of an Autonomous underwater vehicle (AUV), these hydrodynamic coefficients were obtained by finding the body hydrodynamic responses to some specified time variant motions. Here, on the basis of linearized equations of motion in which the hydrodynamic coefficients appear explicitly, three distinct oscillating maneuvers are proposed. To obtain the hydrodynamic responses of the moving body, a CFD method based on Reynolds averaged Navier-Stokes (RANS) equations was used with dynamic mesh technique to simulate the specified maneuvers. To verify the numerical scheme, the computational results were then validated by comparison with experimental data. Hydrodynamic coefficients were calculated from resulting hydrodynamic loads. Finally, the effects of oscillating motions frequency and amplitude variations on the hydrodynamic coefficients were investigated. | Numerical investigation of oscillation frequency and amplitude effects on the hydrodynamic coefficients of a body with NACA0012 hydrofoil section | 10.1007/s12206-017-0422-8 |
2017-05-01 | The spin-orbit driven phenomena, such as the anisotropic magnetoresistance (AMR), the anomalous Hall conductivity (AHC), and the Gilbert damping in disordered fcc-PdCo alloys were studied from first principles using a unified electronic structure model. In PdCo alloys around equiconcentration composition partial order can exist and we investigate its effect on the transport properties and Gilbert damping. It was found that the partial order significantly improves agreement of the calculated AMR ratio and the experiment as compared to the random alloy case. The influence of ordering on the AHC and the Gilbert damping is much weaker. | Galvanomagnetic Transport Properties and Gilbert Damping in Ferromagnetic PdCo Alloys | 10.1007/s10948-016-3661-5 |
2017-05-01 | The damped harmonic oscillator is modeled as a local mode X with mass m and frequency $$\omega _{0}$$ ω 0 immersed in a phonon bath with spectral density function $$j_{0}(\omega $$ j 0 ( ω ). This function behaves as $$\omega ^{s}\, (s= 1,2,3,\ldots )$$ ω s ( s = 1 , 2 , 3 , … ) when $$\omega \rightarrow 0$$ ω → 0 . The limit $$\omega _{0} = 0$$ ω 0 = 0 represents translational (free) Brownian motion. The earlier work (Hakim and Ambegaokar in Phys Rev A 32:423, 1985 ) concluded that the so defined limit transition is prohibited for spectral densities with $$s<2$$ s < 2 . In the present study we demonstrate that a specially constructed preliminary excitation changing the original bath spectrum as $$j_{0}(\omega ) \rightarrow j(\omega )$$ j 0 ( ω ) → j ( ω ) allows for treating the free damped motion of X with no restriction for the initial spectrum dimensionality. This procedure validates the finite mass renormalization (i.e. $$m\rightarrow M$$ m → M when $$\omega _{0}\rightarrow 0)$$ ω 0 → 0 ) for the conventional bath spectra with $$s=1,2$$ s = 1 , 2 . We show that the new spectral density $$j(\omega )$$ j ( ω ) represents the momentum bilinear interaction between mode X and the environmental modes, whereas the conventional function $$j_{0}(\omega )$$ j 0 ( ω ) is inherent to the case of bilinear coordinate interaction in terms of the same variables. The translational damping kernel is derived based on the new spectral density. | The mass renormalization for the translational Brownian motion | 10.1007/s10910-017-0741-0 |
2017-05-01 | It is shown that explosive welding may be used to create bimetal material exhibiting simultaneously high strength and good damping capacity. Bimetal strength is provided due to a layer of high-strength high-quality steel 30KhGSA, and damping capacity is provided as a result of using a layer of damping steel 60G40D. A heat treatment regime is revealed with which bimetal damping capacity surpasses that of alloy 60G40D as a result of forming a tetragonal distorted lattice and twinned structure of manganese-copper alloy. |
Preparation of Bimetal with Good Damping Properties
| 10.1007/s11015-017-0455-3 |
2017-05-01 | We study the theory of bending of a layered stack. The theoretical model takes into account shear and normal strains and stresses. We perform the detailed analysis of the distribution of stresses in a three-layer beam for different frequencies of vibrations. We also estimate the shock-absorbing properties of the beam within the frequency range. The experimental data are presented for a steel beam with soft face layers. | Determination of Energy Dissipation in Layered Beams Under Vibratory Loads | 10.1007/s11003-017-0022-x |
2017-05-01 | Hydrogen bonding is considered to have significant effect on the interaction between polymeric chains and on the viscoelasticity of the polymeric materials. In this paper, we attempt to discuss the relationship between hydrogen bonding density and damping behavior and mechanical properties of polyethylene-based polymeric materials. For this reason, a series of pendant chain hydrogen bonding polymers ( PCHBP ) with different hydrogen bonding density (HBD) were prepared by quantitatively changing the content of pendent hydroxyl groups on the main chain of polyethylene. It was found that PCHBP with low HBD showed similar properties to polyethylene, indicating that the property of the materials was dependent mainly on the structure of the main chain. However, PCHBP with high HBD exhibited two tan δ peaks and a platform of loss modulus as well as a high storage modulus (about 400 MPa) at the second tan δ peak temperature, demonstrating that a polymeric material with high strength and damping properties was obtained. More importantly, the maximum of loss modulus showed a linear increase with the HBD, indicating that a higher HBD greatly improved the damping properties of the polymeric materials. | High damping and mechanical properties of hydrogen-bonded polyethylene materials with variable contents of hydroxyls: Effect of hydrogen bonding density | 10.1007/s10118-017-1918-5 |
2017-05-01 | Among the retrofitting techniques available, steel braces can be considered as one of the most efficient solution for seismic performance upgrading of RC frame structures. Added Damping and Stiffness (ADAS) elements are designed to dissipate energy thought the flexural yielding deformation of mild-steel plates. The current paper deals with the response ductility and the modification factors (R) of bare RC frames, RC frames with chevron steel braces, and RC frames with steel slit dampers (SSD). For this purpose three RC frames of 8, 12 and 20 stories were analyzed without considering the existence of dampers, then each frame equipped with a SSD was studied. A nonlinear pushover analysis was performed. The results show that the response modification factors of RC frames equipped with steel slit dampers is higher than the other systems. Also the effect of height of frame on the response modification factor was investigated. | Evaluating response modification factor (R) of reinforced concrete frames with chevron brace equipped with steel slit damper | 10.1007/s12205-016-1055-7 |
2017-05-01 | AZ31 alloy sheet fabricated by rolling was processed by friction stir processing (FSP) with different passes. The effect of FSP on the microstructure and damping capacity of AZ31 alloy sheet was discussed. The fine and equiaxed grains were obtained in the stirred zone (SZ) for FSPed samples from 1 pass to 3 passes with the average grain size of 10.6, 10.4 and 13.6 μm, respectively. The damping peak P_1 was presented on the curves of temperature-dependent damping capacity for FSPed samples. The damping peak P_2 was restrained after FSP and the damping peak P_1 was a relaxation process. The FSPed samples (2-pass FSP and 3-pass FSP) obtained high damping capacity. The best damping values Q _0 ^-1 ( ε =10^-4) and damping values Q _H ^-1 ( ε =10^-3) of the sample subjected to 3-pass FSP (0.0131 and 0.0496) increased by 33.7% and 157.0%, respectively. | Effect of friction stir processing on microstructure and damping capacity of AZ31 alloy | 10.1007/s11771-017-3506-9 |
2017-05-01 | The material removal rate and required workpiece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the system. Therefore, the suppression of vibration is an unavoidable problem during milling. A novel partial surface damping method is proposed to modify the mode of the thin walled cantilever plate and to suppress vibration during milling. Based on classical plate theory, the design criterion is analyzed and configuration of the partial surface damper is introduced, in which viscoelastic plate and constraining plate are attached to the surface of the plate to increase the system’s natural frequency and loss factor. In order to obtain the energy expression of the cutting system, the Ritz method is used to describe the unknown displacements. Then, with Lagrange’s equation, the natural frequency and loss factor are calculated. In addition, the plate is divided into a finite number of square elements, and the regulation of treated position is studied based on theoretic and experimental analysis. The milling tests are conducted to verify its damping performance and the experimental results show that with treatment of partial surface damper, the deformation of the bare plate is reduced from 0.27 mm to 0.1 mm, while the vibration amplitude of the bare plate is reduced from 0.08 mm to 0.01 mm. The proposed research provides the instruction to design partial surface damper. | Partial Surface Damper to Suppress Vibration for Thin Walled Plate Milling | 10.1007/s10033-017-0107-3 |
2017-05-01 | A phenomenological approach which we refer to as kinematic is proposed to describe hysteresis; according to this approach, the force and kinematic parameters of a mechanical system are related by a first-order ordinary differential equation. The right-hand side is chosen in the class of functions ensuring the asymptotic approach of the solution to the curves of the enveloping (limit) hysteresis cycle of steady-state vibrations. The coefficients of the equation are identified by experimental data for the enveloping cycle. The proposed approach permits describing the hysteresis trajectory under the conditions of unsteady vibrations with an arbitrary starting point inside the region of the enveloping cycle. As an example, we consider the problem on forced vibrations of a pendulum-type damper of low-frequency vibrations. | Vibrations of mechanical systems with energy dissipation hysteresis | 10.3103/S0025654417030037 |
2017-04-01 | This paper presents the implementation of fractional order PID (FO-PID) controller using hardwired modules of constant phase element (CPE). A new approach of phase shaping by slope cancellation of asymptotic phase plots for zeros and poles within the given bandwidth is realized. Analog circuits, which exhibit analog fractional-order integrator and fractional-order differentiator, are used for building the FO-PID controller. The design procedure is developed to obtain the optimal pole–zero pairs and respective “Fractance” components to realize for any value of fractional differ-integrator. These CPE elements give minimum error tolerance over the set phase value by using commercially available (R–C) components and Op-Amps. The pole–zero location in the root locus plot with constant asymptotic angle under various feed-forward gains is achieved with these analog integrodifferential circuits of the FO-PID. The iso-damping feature of the controller is practically demonstrated. A comparative performance is demonstrated under various settings of feed forward gains, which indicate the constant overshoot with FO-PID against the conventional PID. These circuits are developed and implemented with a DC motor emulator to confirm the designed performance of the controller. | Design of new practical phase shaping circuit using optimal pole–zero interlacing algorithm for fractional order PID controller | 10.1007/s10470-016-0920-0 |
2017-04-01 | This paper describes an efficient method to predict the nonlinear steady-state response of a complex structure with multi-scattered friction contacts. The contact friction force is equivalent to additional stiffness and damping based on optimal approximation theory, and as a consequence, the computation is simplified greatly by the linearization for a nonlinear system. In order to obtain accurate pressure distribution on the contact interfaces, the dynamic contact normal pressure is obtained by the equivalent static analysis which is validated for most engineering cases. Considering the complex procedure to determine the transformation between two different contact states, the differential forms of friction force are given to solve the tangential force accurately under the complex movement of interfaces. The approaches developed in this paper are particularly suitable to solve the dynamic response of large-scale structures with local contact nonlinearities. The entire procedure to calculate the steady-state response of a finite element model with a large number of degrees of freedom is demonstrated taking the blades with underplatform dampers as an example. The method is proved to be accurate and efficient; in particular, it does not suffer convergence problem in the allowable range of precision error, which exhibits remarkable potential engineering application values. | An effective numerical method for calculating nonlinear dynamics of structures with dry friction: application to predict the vibration response of blades with underplatform dampers | 10.1007/s11071-016-3239-6 |
2017-04-01 | In this paper, we analyze the dynamics of tuned mass dampers with inerters. In the beginning, we describe the influence of inertance value with respect to the overall mass of the damping device. For further analysis, we pick three practically significant cases—each corresponding to different composition of tuned mass damper inertia. Then, we focus on the effects caused by different types of inerters’ nonlinearities. Viscous damping, dry friction and play in the inerter gears influence the dynamics of the tuned mass damper and affect its damping efficiency. Finally, we examine the dynamics of the model that incorporates all of these factors and propose its simplification which is genuine but more convenient. Our results show how to adjust the inerter type and the parameters depending on our needs and intended application. The knowledge on how to model the behavior of tuned mass dampers with inerters will be of practical use to engineers working with mechanical dampers. | Effects of play and inerter nonlinearities on the performance of tuned mass damper | 10.1007/s11071-016-3292-1 |
2017-04-01 | We investigate the shape of the solution of the Cauchy problem for the damped wave equation. In particular, we study the existence, location and number of spatial maximizers of the solution. Studying the shape of the solution of the damped wave equation, we prepare a decomposed form of the solution into the heat part and the wave part. Moreover, as its another application, we give $$L^p$$ L p - $$L^q$$ L q estimates of the solution. | Movement of time-delayed hot spots in Euclidean space | 10.1007/s00209-016-1735-5 |
2017-04-01 | Machining is one of the important manufacturing processes used in industry. Dynamic interaction between the tool and the workpiece may lead to the occurrence of chatter vibrations, which are associated with problems of poor surface finish, reduced workpiece quality, and low productivity. In the past, researchers developed some important methods to investigate the dynamics of machining processes. Dynamic responses of cutting systems were firstly identified by means of sensors, followed by chatter stability analysis using stability lobe diagrams to determine the stable and unstable regions, and finally, chatters were suppressed by either active or passive damping techniques. Previous reviews emphasized on identification of the chatter vibration with less focus on control. This paper mainly reviews the state of the art on the control of machining chatter vibrations, including damping methods related to boring, turning, and milling processes. | Dynamic damping of machining vibration: a review | 10.1007/s00170-016-9862-z |
2017-04-01 | This paper investigates the stabilizing effect of process damping at low cutting speeds for regenerative machine tool vibrations of milling processes. The process damping is induced by a velocity-dependent cutting force model, which takes into account that the actual cutting velocity is different from the nominal one during machine tool vibrations. The chip thickness and the cutting force are calculated according to the direction of the actual cutting velocity. This results in an additional damping term in the governing delay-differential equation, which is time-periodic for milling and inversely proportional to the cutting speed. In the literature, this term is often assumed to be constant and is considered to improve stability properties at low spindle speeds. In this paper, it is shown that the velocity-dependent cutting force model captures the improvement in the low-speed stability only for turning operations and milling with large radial immersion, while it results in a negative process damping term for low-immersion milling. Consequently, an extended process damping model is needed to explain the low-speed stability improvement for low radial immersion milling. | Extension of process damping to milling with low radial immersion | 10.1007/s00170-016-9780-0 |
2017-04-01 | In this paper, we consider a viscoelastic flexible structure modeled as an Euler-Bernoulli beam. The beam is moving in the direction of its axis. This is one of the main features of this work. We will be dealing with variable intervals of integration and therefore the standard computation using differentiation under the integral sign is no longer valid. The boundary conditions are of ‘cantilever’ type: there is no displacement at one end and the other end is free. In fact, it is subject to a nonlinear force acting there. We prove that when the velocity of the beam is smaller than a critical value, the dissipation produced by the viscoelastic material is sufficient to suppress the transversal vibrations that occur during the axial motion of the beam. The rate of decay is shown to be exponential. | Stability of an Axially Moving Viscoelastic Beam | 10.1007/s10883-016-9317-8 |
2017-04-01 | Machining chatter often becomes a big hindrance to high productivity and surface quality in actual milling process, especially for the thin-walled workpiece made of titanium alloy due to poor structural stiffness. Aiming at this issue, the stability lobes are usually employed to predict if chatter may occur in advance. For obtaining the stability lobes in milling to avoid chatter, this article introduces an extended dynamic model of milling system considering regeneration, helix angle, and process damping into the high-order time domain algorithm which can guarantee both high computational efficiency and accuracy. Via stability lobes, the reasonability and accuracy of the proposed method are verified globally utilizing specific examples in literature. More convincingly, the time-domain numerical simulation is also implemented to predict vibration displacement for partial stability verification. In this extended model, process damping is well-known as an effective approach to improve the stability at low spindle speeds, and particularly, titanium alloy as typical difficult-to-machine material is generally machined at low spindle speeds as well due to its poor machinability. Therefore, the proposed method can be employed to obtain the 3D stability lobes in finish milling of the thin-walled workpiece made of titanium alloy, Ti-6Al-4V. Verification experiments are also conducted and the results show a close agreement between the stability lobes and experiments. | Chatter prediction utilizing stability lobes with process damping in finish milling of titanium alloy thin-walled workpiece | 10.1007/s00170-016-9834-3 |
2017-04-01 | The Metal-Matrix Composites (MMCs) containing hollow spherical reinforcements are under active development for the applications such as space structures, submarine hulls etc. where weight is of critical importance. When these materials are subjected to a time varying strain field, energy is dissipated because of the thermoelastic effect (Elastothermodynamic Damping or ETD). The quasi-static ETD analysis for the MMCs containing hollow spherical particles has been reported in literature. The entropic approach, which is better suited for composite materials with perfect or imperfect interfaces, is used for the analysis. In the present work, the effect of inertia forces is carried out on ETD of hollow particle-reinforced MMCs. For given particle volume fractions ( V _ p ), the inertia forces are found to be more significant at higher value of thermal parameter (Ω_ T 1) (alternatively, frequency of vibration if reinforcement radius is fixed), large cavity volume fraction ( V _ h ) and low value of the parameter B_1. | Dynamic Effects in Elastothermodynamic Damping of Hollow Particle Reinforced Metal-Matrix Composites | 10.1007/s40032-016-0253-x |
2017-04-01 | In this article, we study the weak dissipative Kirchhoff equation $${u_{tt}} - M\left( {\left\| {\nabla u} \right\|_2^2} \right)\Delta u + b\left( x \right){u_t} + f\left( u \right) = 0$$ u t t − M ( ‖ ∇ u ‖ 2 2 ) Δ u + b ( x ) u t + f ( u ) = 0 , under nonlinear damping on the boundary $$\frac{{\partial u}}{{\partial v}} + \alpha \left( t \right)g\left( {{u_t}} \right) = 0$$ ∂ u ∂ v + α ( t ) g ( u t ) = 0 . We prove a general energy decay property for solutions in terms of coefficient of the frictional boundary damping. Our result extends and improves some results in the literature such as the work by Zhang and Miao (2010) in which only exponential energy decay is considered and the work by Zhang and Huang (2014) where the energy decay has been not considered. | General energy decay of solutions for a weakly dissipative Kirchhoff equation with nonlinear boundary damping | 10.1007/s10255-017-0669-y |
2017-04-01 | The paper studies different types of dampers for rotor supports of gas turbine engines (GTE). The advantages of hydrodynamic dampers are shown. Hydrodynamic dampers for GTE rotor supports are studied. A new design and technique of calculation are proposed for an adjustable hydrodynamic damper. | Trends in research of hydrodynamic damping in rotor supports of gas turbine engines | 10.3103/S1068799817020118 |
2017-04-01 | This paper presents a new damping boring bar with a variable stiffness dynamic vibration absorber (VSDVA) based on dynamic vibration absorber theory. The new designed VSDVA is installed in a cavity which is in the front of the damping boring bar. A new vibration reduction method is proposed by adjusting the stiffness of the VSDVA to adapt the different cutting parameters. The dynamic model of the damping boring bar system is established. The influences of the excitation frequency and the overhang length of the VSDVA on the amplitude ratio are discussed, and the optimal curves are obtained. The damping zone and non-damping zone are obtained as well. These analyses provide a theoretical basis for the design of the damping boring bar and the choice of cutting parameters. The proposed damping boring bar is tested with excitation experiments, impact tests, and boring experiments. The results show that the vibration is reduced, which verifies the feasibility of the proposed method. The accuracy of the dynamic model is substantiated by comparing the experimental data with the theoretical data. | Research on the performance of damping boring bar with a variable stiffness dynamic vibration absorber | 10.1007/s00170-016-9612-2 |
2017-04-01 | Attention focuses on reducing the vibration of energy-intensive electrical systems, such as the power units of autonomous vehicles. The amplitude–frequency spectra of input and output vibrational signals for hydraulic vibrational bearings and cable vibrational dampers are investigated. Cable vibrational dampers are more effective in quenching impact loads, while hydraulic vibrational bearings are better at suppressing long-term vibration. | Damping of vibrations at resonant frequencies of electrical systems | 10.3103/S1068798X17040049 |
2017-04-01 | Chatter usually occurs in cutting of thin-walled workpiece due to poor structural stiffness, which results in poor surface quality and damaged tool. Aiming at process damping caused by interference between a tool flank face and a machined surface of thin-walled part, the dynamic model and critical condition of stability are proposed by the relative transfer functions, when both the tool structure and the machined workpiece have similar dynamic behaviors in this paper. Using the frequency method to solve the stability of the cutting chatter, it can be seen that the process damping can significantly improve the stability of the low speed region. Moreover, the stability domain is different and more exact than the one that derives from the simple superposition of the tool and the workpiece lobe diagrams. The correctness of the model is validated by experiments. These conclusions provide a theoretical foundation and reference for the milling mechanism research. | Investigation on chatter stability of thin-walled parts in milling based on process damping with relative transfer functions | 10.1007/s00170-016-9431-5 |
2017-04-01 | A novel nonlinear structure with adjustable stiffness, damping and inertia is proposed and studied for vibration energy harvesting. The system consists of an adjustable-inertia system and X-shaped supporting structures. The novelty of the adjustable-inertia design is to enhance the mode coupling property between two orthogonal motion directions, i.e., the translational and rotational directions, which is very helpful for the improvement of the vibration energy harvesting performance. Weakly nonlinear stiffness and damping characteristics can be introduced by the X-shaped supporting structures. Combining the mode coupling effect above and the nonlinear stiffness and damping characteristics of the X-shaped structures, the vibration energy harvesting performance can be significantly enhanced, in both the low frequency range and broadband spectrum. The proposed 2-DOF nonlinear vibration energy harvesting structure can outperform the corresponding 2-DOF linear system and the existing nonlinear harvesting systems. The results in this study provide a novel and effective method for passive structure design of vibration energy harvesting systems to improve efficiency in the low frequency range. | Nonlinear vibration energy harvesting with adjustable stiffness, damping and inertia | 10.1007/s11071-016-3231-1 |
2017-04-01 | In this paper, we propose a method based on collocation of exponential B-splines to obtain numerical solution of a nonlinear second-order one-dimensional hyperbolic equation subject to appropriate initial and Dirichlet boundary conditions. The method is a combination of B-spline collocation method in space and two-stage, second-order strong-stability-preserving Runge–Kutta method in time. The proposed method is shown to be unconditionally stable. The efficiency and accuracy of the method are successfully described by applying the method to a few test problems. | Numerical solution of second-order one-dimensional hyperbolic equation by exponential B-spline collocation method | 10.1134/S1995423917020070 |
2017-03-22 | In this paper we study the initial value problem for the nonlinear wave equation with damping and source terms u t t − ρ ( x ) − 1 Δ u + u t + m 2 u = f ( u ) $$ u_{tt}-\rho(x)^{-1}\varDelta u+u_{t}+m^{2}u=f(u) $$ with some ρ ( x ) $\rho(x)$ and f ( u ) $f(u)$ on the whole space R n $\mathbb{R}^{n}$ ( n ≥ 3 $n\geq 3$ ). For the low initial energy case, which is the non-positive initial energy, based on a concavity argument we prove the blow-up result. As for the high initial energy case, we give sufficient conditions of the initial data such that the corresponding solution blows up in finite time. In other words, our results imply a complete blow-up theorem in the sense of the initial energy, − ∞ < E ( 0 ) < + ∞ $-\infty< E(0)<+\infty$ . | Global non-existence for some nonlinear wave equations with damping and source terms in an inhomogeneous medium | 10.1186/s13661-017-0762-4 |
2017-03-22 | In the present work we study the influence of both the fluctuation effects of the atom velocity and the atomic decay on the fidelity corresponding to a protocol for the quantum state transfer between two modes of a bimodal cavity QED. In our model the atom interacts separately with each mode, which is made possible by applying the Stark shift effect on the atomic-levels to tuning (detuning) properly modes A and B . | Comparing the effects of atomic damping and velocity fluctuations upon transfer of quantum state in a bimodal cavity QED | 10.1007/s11082-017-0989-4 |
2017-03-01 | Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P / D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range. | Experimental study on cross-flow induced vibrations in heat exchanger tube bundle | 10.1007/s13344-017-0011-8 |
2017-03-01 | This paper presents the propagation of thermoelastic waves along circumferential direction in homogeneous, transradially isotropic spherical curved plates. Mathematical modeling of the problem to obtain dispersion curves for transversely isotropic thermally conducting spherically curved elastic plates leads to coupled differential equations. The coupled differential equations of motion and heat conductions equation in conjunction with stress free, rigidly fixed thermal boundary conditions on the inner and outer surfaces of a spherical curved plate are solved with matrix Fröbenius method. In order to illustrate theoretical development, numerical solutions are obtained and presented graphically for a zinc, cobalt and silicon nitride plate. The graphical results are compared with the available literature. Thermal variations for the non-axially symmetric case of plane strain vibrations, these modes remain coupled and are affected by temperature change. Moreover, these vibration modes are found to be dispersive in nature. | Circumferential Waves in Transradially Isotropic Thermoelastic Spherical Curved Plates | 10.1007/s40010-016-0283-z |
2017-03-01 | A procedure for deriving the complete equations of motion to compute an isolator’s displacement due to strong ground motion is applied to structures isolated with friction pendulum systems. The resulting equations, which contain the vertical inertia forces, were studied to estimate the influence of these forces on the isolator’s behavior. The nonlinear equation is solved employing the technique of successive approximations. The results obtained showed that the influence of the vertical inertia forces on structural response is negligible for the case of a long-distance ground motion, while becoming significant for a near-source ground motion. On the other hand, very small values of the isolator’s radius R cause an increase of the aforementioned influence. | The influence of the vertical inertia forces on the behavior of friction pendulum bearings (FPB) | 10.1007/s00419-016-1201-1 |
2017-03-01 | This paper investigates the response of microcantilever and microbridge actuators, under alternating current (AC) and direct current (DC) excitations. The analysis is carried out by simulating the electrical equivalent circuit of the actuators. An analogous circuit model for evaluation of velocity and acceleration in the microstructure is incorporated to the basic circuit model. The influence of squeeze film on the vibrating structure is also investigated. The effect of DC bias voltage on displacement, capacitance and electrostatic force are investigated. The transient response predicts a minimal change due to the pressure variation in the damping medium owing to the geometrical dimensions of the elements in the actuator. The frequency dependence of velocity and acceleration are also evaluated in this study. | An analysis of electrostatically actuated micro vibrating structures incorporating squeezed film damping effect using an electrical equivalent circuit | 10.1007/s40430-016-0492-z |
2017-03-01 | In this paper, we study the time evolution of the geometric phase and nonlocal correlations for a three-level atom interacting with the quantum field emerged in a nonlinear Kerr medium. We discuss the dependence of the physical quantifiers on the phase damping effect. We examine the effects of the initial state and different system parameters on the evolution of the nonlocal correlation and geometric phase with and without the phase damping effect. Furthermore, we explore the link between the geometric phase and the nonlocal correlation during the time evolution. Finally, we show that the model proposed will be very useful to avoid the phase damping effect by a proper choice of the physical parameters in the field for both cases of the initial pure and mixed states of the three-level atom. | Quantum Phase and Nonlocal Correlations for a Three-Level System Interacting with Laser Light in a Nonlinear Kerr Medium Under Decoherence | 10.1007/s10946-017-9626-8 |
2017-03-01 | This paper focuses on the transient nonlinear dynamics and targeted energy transfer (TET) of a Bernoulli–Euler beam coupled to a continuous bistable nonlinear energy sink (NES). This NES comprises a cantilever beam with the partial constrained layer damping (PCLD) and an end mass controlled by a nonlinear magnetostatic interaction force. The theoretical model of the nonlinear system is built based on the Lagrange equations and assumed-modes expansion method. A new parameter system damping ratio is proposed to evaluate the TET efficiencies. Impact experiments are carried out to verify the theoretical model and mechanisms. The results show that the bistable NES can achieve high and strongly robust TET efficiencies under broad-range impacts. The shear modulus of the viscoelastic layer, the length of the PCLD and the end mass have significant influences on TET efficiencies. Analyses of the TET mechanisms in the bistable NES show the following: steady transition of the stable state is an important reason for maintaining high TET efficiencies; nonlinear beatings can occur in high-frequency, fundamental and long-period subharmonic branches; and resonance captures featuring fundamental and subharmonic also help achieve rapid energy dissipation. | Highly efficient continuous bistable nonlinear energy sink composed of a cantilever beam with partial constrained layer damping | 10.1007/s11071-016-3220-4 |
2017-03-01 | Due to their low intrinsic damping, stay cables in cable-stayed bridges are vulnerable to dynamic excitation. The cables have often been exhibiting undesirable and excessive vibrations, which result in increasing maintenance frequency and disruption to normal operations of the entire bridges. Mitigation of undesired cable vibration can be achieved by attaching a traditionally mechanical damper near the anchorage. Although utilizing this type of damper demonstrates vibrating diminishment in cables, the approach is not the most effective method due to geometric constraints. Tuned Mass Damper (TMD) has been used to overcome the deficiency of the traditional mechanical damper since it can be mounted anywhere along a cable. This paper proposes a new type of damper called the Tuned Mass - High Damping Rubber (TM-HDR) damper for increasing damping ratio of the cable. Oscillation parameters of cable with an attached TM-HDR damper are investigated in detail using an analytical formulation of the complex eigenvalue problem. As a result, optimal parameters of the damper can be evaluated and selected in order to reduce vibrations of cable. In addition, this paper demonstrates the effects of TM-HDR damper by using an example. | Tuned mass-high damping rubber damper on a taut cable | 10.1007/s12205-016-0857-y |
2017-03-01 | A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li_7- x La_3Zr_2- x Nb_ x O_12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment. | Enhanced micro-vibration sensitive high-damping capacity and mechanical strength achieved in Al matrix composites reinforced with garnet-like lithium electrolyte | 10.1007/s11706-017-0363-2 |
2017-03-01 | Carbonate sands comprise typical foundation soils for offshore engineering structures such as oil platforms, found in natural deposits. These sands have a high shear strength but also very high compressibility which characteristics are due to the shape and the low tensile strength of the grains. For the seismic design of offshore structures, two key properties comprise the stiffness and damping of the subsoil which depend on the porosity, the level of the confining pressure and the strain amplitude. In this article, the small-strain Young’s modulus (E_max), small-strain damping (D_f,min) and the strain-dependent Young’s modulus and damping of a carbonate sand were studied in the laboratory through resonant column tests in flexural mode of vibration. This mode applies a medium-frequency excitation to the sample, typically in the range of 30–80 Hz. The samples were prepared in a dry state and tested under isotropic conditions of the confining pressure with (p′) varying from about 25 to 800 kPa. The small-strain dynamic properties were analysed by means of power law type formulae and the sensitivity of E_max and D_f,min to pressure was quantified and discussed. The results indicated that the flexural damping values were much greater in comparison to corresponding results in the literature derived from torsional resonant column tests on sands. This observation is in alignment with a recent study on the flexural response of quartz sands. Overall, the sensitivity of stiffness to pressure was less pronounced than that of reported data in the literature. The medium-strain tests showed a similar trend with respect to the stiffness degradation and damping increase as in the case of torsional resonant column tests reported in the literature for granular soils with a slight dependency of the medium-strain properties to the confining pressure level. | The behavior of a carbonate sand subjected to a wide strain range of medium-frequency flexural excitation | 10.1007/s40948-016-0045-z |
2017-03-01 | A geometric nonlinear damping is proposed and applied to a quasi-zero stiffness (QZS) vibration isolator with the purpose of improving the performance of low-frequency vibration isolation. The force, stiffness and damping characteristics of the system are presented first. The steady-state solutions of the QZS system are obtained based on the averaging method for both force and base excitations and further verified by numerical simulation. The force and displacement transmissibility of the QZS vibration isolator are then analysed. The results indicate that increasing the nonlinear damping can effectively suppress the force transmissibility in resonant region with the isolation performance in higher frequencies unaffected. In addition, the application of the nonlinear damping in the QZS vibration isolator can essentially eliminate the unbounded response for the base excitation. Finally, the equivalent damping ratio is defined and discussed from the viewpoint of vibration control. | Force and displacement transmissibility of a quasi-zero stiffness vibration isolator with geometric nonlinear damping | 10.1007/s11071-016-3188-0 |
2017-03-01 | The deployment of a synchrophasor-based wide-area measurement system (WAMS) in a power grid largely improves the observability of power system dynamics and the operator’s real-time situational awareness for potential stability issues. The WAMS in many power grids has successfully captured system oscillation events, e.g. poorly damped natural oscillations and forced oscillations, from time to time. To identify the root cause of an observed oscillation event for further mitigation actions, many methods have been proposed to locate the source of oscillation based on different ideas and principles. However, most methods proposed so far for locating the oscillation source in a power grid are not reliable enough for practical applications. This paper presents a comprehensive review of existing location methods, which basically fall into four major categories, plus a few other methods. Their advantages and disadvantages are discussed in detail. Some trends and challenges on the problem of oscillation source location are pointed out along with potential future research directions. Finally, a practical, general scheme for oscillation source location using available location methods is suggested and analyzed. | Location methods of oscillation sources in power systems: a survey | 10.1007/s40565-016-0216-5 |
2017-03-01 | In this paper, the performance of multiple tuned liquid damper (MTLD) has been investigated in mitigating the response of a structure under dynamic loading, i.e., harmonic excitation. For comparative study, the responses of single-tuned liquid damper (STLD) have also been considered. A set of experiments are conducted on a scaled model of steel-structure-STLD and MTLD systems to evaluate the performance of the respective TLD models under harmonic excitation. Several excitation frequency ratios (0.5–2.0) and depth ratios (0.05–0.30) are considered for this study. The effect of resonance as well as tuned condition ( ω _ d / ω _ s = 1) on the structural response has also been noticed. The effectiveness of the STLD and MTLDs is evaluated based on the response reduction of the structure. It has been found that the structural responses of displacement and acceleration are reduced significantly due to the installation of STLD and MTLD to the structure, respectively. Therefore, from this experimental study, it can be concluded that a TLD can successfully mitigate the response of the structure, but MTLD is not significantly more effective than an STLD when the liquid sloshing in the TLD is large. | An experimental study on response control of structures using multiple tuned liquid dampers under dynamic loading | 10.1007/s40091-016-0146-5 |
2017-03-01 | Tuned mass dampers (TMDs) are one of the most widely used devices to mitigate vibrations in structures. Usually, in conventional TMDs, viscous dampers convert the energy of vibration into heat. A new type of TMDs, called regenerative TMDs, has been developed. Energy transducers either are coupled to traditional TMDs or replace the dampers. Instead of being dissipated as heat, energy of vibration is now converted into electricity. This paper describes a regenerative TMD using piezoelectricity regenerative components as energy transducers. This piezoelectric energy-harvesting TMD (PETMD) is designed to mitigate vertical vibration as with conventional TMDs, while harvesting energy as a power resource for immediate use or storage. The system design and general design strategy of the PETMD are described, outlining the manner in which the vibration control performs its functions efficiently. The piezoelectric regenerative component is then configured and optimized by finite element analysis to maximize the power generation capacity. Finally, a small prototype is constructed to confirm the results from analysis. An energy of 80 μW was harvested from the prototype when excited by harmonic forces of about 2 N at 5 Hz and coupled to a resistor of 9.9 kΩ. | Development of piezoelectric energy-harvesting tuned mass damper | 10.1007/s11431-016-0280-5 |
2017-03-01 | This paper presents a novel multifunctional magnetic actuator, which not only damp the vibration of machine tools but also measure the cutting force in real time. The actuator is composed of four identical electromagnetic units which are linearized with a novel design strategy. The magnetic force can be delivered in two radial directions for active damping of the flexible structures in the machine tools. Cutting force is estimated from the armature displacement and the control current of the actuator. The performance of both active damping and cutting force measurement are demonstrated on a boring bar which is clamped to the turret of a CNC lathe. Experimental results show that the boring bar vibration is damped significantly with a velocity feedback controller, resulting in a higher chatter-free depth of cut, while the measured cutting force from the actuator agrees with the reference force quite well. | Active damping of machine tool vibrations and cutting force measurement with a magnetic actuator | 10.1007/s00170-016-9118-y |
2017-03-01 | The concept introduced previously by the authors on the best sound absorber having the maximum allowable efficiency in absorbing the energy of an incident sound field has been extended to arbitrary linear elastic media and structures. Analytic relations have been found for the input impedance characteristics that the best vibrational energy absorber should have. The implementation of these relations is the basis of the proposed impedance method of designing efficient vibration and noise absorbers. We present the results of a laboratory experiment that confirms the validity of the obtained theoretical relations, and we construct the simplest best vibration absorber. We also calculate the parameters and demonstrate the efficiency of a dynamic vibration absorber as the best absorber. | Impedance approach to designing efficient vibration energy absorbers | 10.1134/S1063771017020014 |
2017-03-01 | A technique for determining the damping properties of a rigid isotropic material from the experimental data on the damping capacity of elongated cantilever-fixed test specimens due to the internal and external aerodynamic damping is proposed. The following two methods for eliminating the aerodynamic damping component are considered: the extrapolation of the data on the damping capacity of a series of test specimens of different widths to the point corresponding to the zero width and the theoretical-experimental approach. The damping properties of the material are determined by the vibration logarithmic decrement depending on the amplitude of the linear deformation. This dependence is represented by a power polynomial. The polynomial coefficients are determined from the minimum condition of the goal function for the positive logarithmic decrement of the material vibrations. These coefficients are sought at the reference point by repeatedly solving the direct problem of determining the damping capacity of the test specimen from the given damping properties of the material. An example is considered to illustrate the identification of the damping properties of steel St.3. | Identification of the damping properties of rigid isotropic materials by studying the damping flexural vibrations of test specimens | 10.3103/S0025654417020108 |
2017-03-01 | This paper is dedicated to exploit the same optimization mechanism of targeted energy transfer under different types of excitation. Specifically, a linear oscillator (LO) coupled with a vibro-impact nonlinear energy sink is analytically studied with an asymptotical method. The optimization mechanism under periodic excitation with a single frequency and under transient excitation is numerically obtained and experimentally validated for the first time. For periodic excitation, the boundary between the regime with two impacts per cycle and that of strongly modulated response (SMR) is proved to be optimal rather than SMR. The chaotic SMR is experimentally observed from the viewpoint of displacement of LO. The above-observed mechanism is further applied to explain the optimization mechanism under transient excitation and that under periodic excitation with a range of frequency. It is experimentally verified that the optimization of the latter can be simplified to the optimization under an excitation with a single resonance frequency. For transient excitation, the efficiency of different transient response regimes is experimentally compared, which agrees with the periodic results. Moreover, the efficiency comparison of different lengths of cavity is also experimentally validated. In short, the close relation of optimization under different excitations is clearly demonstrated. | Optimization mechanism of targeted energy transfer with vibro-impact energy sink under periodic and transient excitation | 10.1007/s11071-016-3200-8 |
2017-03-01 | This paper is focused on the dynamic characteristics of a flexible rotor with squeeze film damper excited by two frequencies. The multiple harmonic balance method and Runge–Kutta method are combined to analyze the periodic solution and quasi-periodic solution of the system. The nonlinear characteristics discussed are fastened on the resonance region corresponding, respectively, to the rigid body translation mode and first bending mode. In the former region, the motion of disk center shows the ‘hard spring’ characteristic, and the combination frequencies are dominated by the difference between double low excitation frequency and high excitation frequency and the difference between double high excitation frequency and low excitation frequency. In the latter region, however, the combination frequencies are dominated by the difference between high excitation frequency and double low excitation frequency and the difference between triple low excitation frequency and double high excitation frequency. Moreover, the motion of disk center shows a kind of ‘cross’, ‘soft spring’ or ‘hard spring’ characteristics with the variation of the ratio of the two excitation frequencies. Besides, the independent quasi-periodic solution coexists with the periodic solution in these cases. The system is sensitive to the ratio of excitation frequencies, and it could have two independent quasi-periodic solutions in some conditions. The results in this paper provide a reveal of nonlinear characteristics in this type of double excitation nonlinear rotor system. | Dynamic characteristics of flexible rotor with squeeze film damper excited by two frequencies | 10.1007/s11071-016-3204-4 |
2017-03-01 | Tuned mass dampers are common solutions for passive control of bridge responses against dynamic loads. The present work concerns multiple-support seismic excitation as the source of dynamic loading and studies TMD performance in controlling consequent vertical response of simply supported steel bridges. TMD parameter optimization is treated as the first issue, utilizing the well-known charged system search where the dynamic structural constraints are evaluated via rigorous time-history finite element analyses. As another issue, superiority of multiple TMD over single TMD is investigated for the present problem after unifying their parameters via optimization. Treating a bridge model as the case study under a number of real-world recorded earthquakes, the error of uniform support excitation under such a non-uniform case is also evaluated. Superior efficiency of the utilized charged system search over popular genetic algorithm is shown for this problem. The results also revealed that how advantageous is optimally designed multiple TMD in controlling vibration modes of such a distributed-mass structural system. | Optimal Seismic Control of Steel Bridges by Single and Multiple Tuned Mass Dampers Using Charged System Search | 10.1007/s40999-016-0102-6 |
2017-02-15 | We consider the damped wave equation with Dirichlet boundary conditions on the unit square parametrized by Cartesian coordinates x and y . We assume the damping a to be strictly positive and constant for $$x<\sigma $$ x < σ and zero for $$x>\sigma $$ x > σ . We prove the exact $$t^{-4/3}$$ t - 4 / 3 -decay rate for the energy of classical solutions. Our main result (Theorem 1) answers question (1) of Anantharaman and Léautaud (Anal PDE 7(1):159–214, 2014 , Section 2C). | Optimal decay rate for the wave equation on a square with constant damping on a strip | 10.1007/s00033-017-0781-0 |
2017-02-08 | We study the Cauchy problem for the nonlinear damped wave equation and establish the large data local well-posedness and small data global well-posedness with slowly decaying initial data. We also prove that the asymptotic profile of the global solution is given by a solution of the corresponding parabolic problem, which shows that the solution of the damped wave equation has the diffusion phenomena. Moreover, we show blow-up of solution and give the estimate of the lifespan for a subcritical nonlinearity. In particular, we determine the critical exponent for any space dimension. | The Cauchy problem for the nonlinear damped wave equation with slowly decaying data | 10.1007/s00030-017-0434-1 |
2017-02-01 | Squeezed air film between two closely spaced vibrating microstructures is the important source of energy dissipation and has profound effects on the dynamics of microelectromechanical systems (MEMS). Perforations in the design are one of the methods to model these damping effects. The literature reveals that the analytical modeling of squeeze film damping of perforated circular microplates is less explored; however, these microplates are also an imperative part of the numerous MEMS devices. Here, we derive an analytical model of transverse and rocking motions of a perforated circular microplate. A modified Reynolds equation that incorporates compressibility and rarefaction effects is utilized in the analysis. Pressure distribution under the vibrating microplate is derived by using Green’s function and also derived by finite element method (FEM) to visualize the pressure distribution under perforated and non-perforated areas of the microplate. The analytical damping results are validated with previous renowned analytical models and also with the FEM results. The outcomes confirm the potential of the present analytical model to accurately predict the squeeze film damping parameters. | Analytical solution for squeeze film damping of MEMS perforated circular plates using Green’s function | 10.1007/s11071-016-3136-z |
2017-02-01 | In this paper, the solitary waves of a viscous plasma confined in a cylindrical pipe is investigated under two types of boundary condition. By using the reductive perturbation theory, a quasi-KdV equation is derived and a damping solitary wave is obtained. It is found that the damping rate increases with the viscosity coefficient of the plasma $$\nu '$$ ν ′ increasing and the radius of the cylindrical pipe R decreasing for second and third boundary condition. The magnitude of the damping rate is also dominated by boundary condition type. From the fact that the amplitude reduces rapidly when R approaches zero or $$\nu '$$ ν ′ approaches infinite, we confirm the existence of a damping solitary wave. | Damping solitary wave under the second and third boundary condition of a viscous plasma | 10.1007/s12648-016-0897-7 |
2017-02-01 | In this work a practical demonstration for simultaneous levitation and rotation for a ferromagnetic cylindrical object is presented. A hollow steel cylinder has been arranged to remain suspended stably under I-core electromagnet utilizing dc attraction type levitation principle and then arranged to rotate the levitated object around 1000 rpm speed based on eddy current based energy meter principle. Since the object is to be rotating during levitated condition the device will be frictionless, energy-efficient and robust. This technology may be applied to frictionless energy meter, wind turbine, machine tool applications, precision instruments and many other devices where easy energy-efficient stable rotation will be required. The cascade lead compensation control scheme has been applied for stabilization of unstable levitation system. The proposed device is successfully tested in the laboratory and experimental results have been produced. | System and Method for Obtaining Simultaneous Levitation and Rotation of a Ferromagnetic Object | 10.1007/s40031-016-0215-y |
2017-02-01 | In the process of designing a machine tool virtual models are required to predict the dynamic behavior and optimize the machine tool performance. For this purpose, the different influencing factors mass, stiffness and damping properties as well as friction forces, feed drive controls and movements have to be considered in the simulation. However, usually no suitable models and modeling approaches are available for all of these various influencing factors. In this paper, models are provided for the mentioned influencing factors. Subsequently, a modeling approach is proposed, which allows to predict the dynamic behavior with high accuracy. By using this modeling approach, the influencing factors are investigated and evaluated with regard to their effects on the vibration behavior of a machine tool. The nonlinear friction forces and the linear dissipation sources have the greatest impact on the damping behavior. In comparison, the impact of the feed drive control on the vibration behavior is low. Movements can greatly influence the vibration behavior. Their effects are mainly restricted to the axial modes of the feed drives. At these modes, the damping ratios can vary under motion by up to ±35% compared to a standstill. With these insights and the proposed models and modeling approaches new possibilities arise to predict and optimize the dynamic behavior of a machine tool and thus to enhance the machine tool performance. | Modeling of the dynamic behavior of machine tools: influences of damping, friction, control and motion | 10.1007/s11740-016-0704-5 |
2017-02-01 | Magnetorheological dampers are used for semi-active control of the vehicles vibration because of their useful features such as reducing the dynamic tire forces, improvement the ride quality of the passengers and protection of the vehicle from rollover. The dynamic model of these dampers is nonlinear. Therefore, their nonlinear characteristics can lead to make the chaotic behaviour of the vehicle system if a suitable controller is not used. This paper focuses on the active control of the chaotic behaviour generated by the nonlinear model characteristics of the MR dampers in a typical heavy articulated vehicle. The vehicle nonlinear dynamic study is conducted by detecting the irregular regions using the bifurcation diagrams and Poincaré maps. Then, the active controller is proposed to control the chaotic behaviours. The control law was derived based on the backstepping method, and the stability analysis is performed by Lyapunov theorem. Then, optimal backstepping control is designed for controlling the chaos in the vehicle. The simulation results show the vehicle displacements can track a periodic desired motion. The robustness of the proposed controller is studied by inserting external disturbance force. The simulation results show that the vehicle body displacements converge to periodic desired path in spite of the existing external disturbance. | Active chaos control of a heavy articulated vehicle equipped with magnetorheological dampers | 10.1007/s11071-016-3163-9 |
2017-02-01 | The distributed formation control of fractional-order multi-agent systems is mainly studied under directed communication graphs in this paper. Firstly, a control law with relative damping and communication delay are proposed. Then, some sufficient conditions for achieving formation control are derived using matrix theory, graph theory and the frequency domain analysis method. Finally, based on the numerical method of predictor-corrector, several simulations are presented to illustrate the effectiveness of the obtained results. | Distributed formation control of fractional-order multi-agent systems with relative damping and communication delay | 10.1007/s12555-015-0132-x |
2017-02-01 | This paper makes qualitative analysis to the bounded traveling wave solutions for a kind of nonlinear dispersive-dissipative equation, and considers its solving problem. The relation is investigated between behavior of its solution and the dissipation coefficient. Further, all approximate damped oscillatory solutions when dissipation coefficient is small are presented by utilizing the method of undetermined coefficients according to the theory of rotated vector field in planar dynamical systems. Finally, error estimate is given by establishing the integral equation which reflects the relation between approximate and exact damped oscillatory solutions applying the idea of homogenization principle. | Qualitative analysis and approximate damped oscillatory solutions for a kind of nonlinear dispersive-dissipative equation | 10.1007/s10255-017-0632-y |
2017-02-01 | An analytical description of a qubit interacting non-linearly and non-resonantly with a lossy cavity via intensity-dependent coupling has been obtained. With the amplitude cavity damping as a particular type of the thermal amplitude reservoir damping, Wehrl entropy and Wehrl density are used to investigate the dynamics of the loss of both qubit coherence and information. We show that the Q -function Wehrl entropy and its density are very sensitive not only to the amplitude cavity damping and the intensity of the coherent state but also to the frequency detuning. The information of the phase space and the coherence are quickly lost due to the coupling to the environment. When the qubit interacting non-linearly with the lossy cavity, we observe: (1) The mixedness of the atomic state can be decreased by increasing the coupling to the environment. (2) For the off-resonance case, if the cavity damping is increased, the information of the mixed evolved state can be protected. | Stationary phase-space information in a qubit interacting non-linearly with a lossy single-mode field in the off-resonant case | 10.1007/s11082-017-0917-7 |
2017-01-19 | In this paper, we extend the finite propagation speed property for the compressible Euler equations with damping from the three -dimensional case to the general N -dimensional case. Subsequently, blowup results of the N -dimensional compressible Euler equations with damping are obtained. More precisely, we show that if the initial data $$\displaystyle \int \limits _0^\infty f(r)V(0,r)\text {d}r$$ ∫ 0 ∞ f ( r ) V ( 0 , r ) d r are sufficiently large, then blowup phenomena occurs and the finite blowup time can be estimated, where f is a general test function with mild conditions and V represents the speed of the fluid in radial symmetry. | Blowup phenomena for the
$$\varvec{N}$$
N
-dimensional compressible Euler equations with damping | 10.1007/s00033-017-0770-3 |
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