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1
Sun, Yonggan. "Study on the Dynamic Performance of Locally Resonant Plates with Elastic Unit Cell Edges". Mathematical Problems in Engineering 2021 (4 de junio de 2021): 1–7. http://dx.doi.org/10.1155/2021/5541052.
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A Floquet–Bloch approach is employed to demonstrate the stop bands for an infinite locally resonant plate. In addition, the effects of the connection stiffness of the unit cells on the band gap and dynamic performance of a locally resonant plate are analysed. The results show that the degree of inhibition of elastic waves in the band gaps increases rapidly when the connection stiffness of the unit cells increases within the scope of the transition stage stiffness. However, outside of the range of transition stage stiffness, the degree of inhibition of elastic waves in the band gaps basically remains unchanged. This discovery widens the application scope for vibration and noise control using locally resonant plates.
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WANG, BAOSHENG, JIANMIN ZUO y MULAN WANG. "ANALYSIS AND COMPENSATION OF STIFFNESS IN CNC MACHINE TOOL FEED SYSTEM". Journal of Advanced Manufacturing Systems 10, n.º 01 (junio de 2011): 77–84. http://dx.doi.org/10.1142/s0219686711002004.
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Based on the elastic mechanics theory, the mathematical models of axial stiffness and torsion stiffness are constructed in accordance with single end thrust and two ends thrust. The effects of stiffness on dead band error are analyzed. With the analysis of displacement deviation induced by axial stiffness and angular displacement deflection caused by torsion stiffness, a formula to calculate the dead band error is presented. A model for Computer Numerical Control (CNC) machine tool feed system with stiffness is established. By applying computer simulation, dynamic performances, static performances and steady-state error of the system are analyzed. To reduce the effect of stiffness on the system, the feedforward control method is used to compensate stiffness. The simulation analysis shows the result that dynamic and static performances are improved, as well as steady-state error of the system is reduced by more than 58% with this approach.
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Xu, Qiang-Rong, Yang Zhu, Kang Lin, Cheng Shen y Tian-Jian Lu. "Low-frequency sound insulation performance of novel membrane acoustic metamaterial with dynamic negative stiffness". Acta Physica Sinica 71, n.º 21 (2022): 214301. http://dx.doi.org/10.7498/aps.71.20221058.
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For improving the low-frequency sound insulation properties of membrane/plate structures, a new quasi-zero stiffness membrane acoustic metamaterial with dynamic magnetic negative stiffness is proposed. When the equivalent magnetic charge theory is used to investigate the dynamic magnetic negative stiffness, a theoretical model of proposed metamaterial with finite dimension is established based on the Galerkin method. Through a combination of theoretical analysis, numerical simulation and experimental measurement, the low-frequency (1–1000 Hz) sound insulation performance of the metamaterial is investigated from several perspectives, including structural modality, vibration mode, average velocity, phase curve, equivalent mass density, and equivalent spring-mass dynamics model. The results show that at a certain initial membrane tension, the decreasing of the magnetic gap or the increasing of the residual flux density can increase the dynamic magnetic negative stiffness. This in turn leads the peak frequency to decrease and the bandwidth of sound insulation to increase, thus achieving effective low-frequency sound insulation over a wide frequency band. Further, when the magnetic gap is larger than the second critical magnetic gap and smaller than the first critical magnetic gap, the first-order modal resonance of the metamaterial disappears, and the corresponding value of sound insulation valley increases significantly, thus demonstrating superior sound insulation effect in a wide frequency band. The proposed method of using dynamic magnetic negative stiffness to improve low-frequency sound insulation valleys due to modal resonance provides useful theoretical guidance for designing membrane/plate type low-frequency sound insulation metamaterials.
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Sun, Ya Zhou, Xue Mei Yu, Hai Tao Liu y Ying Chun Liang. "Analysis of Dynamic Stiffness and Damping of Partial Porous Aerostatic Thrust Bearings". Applied Mechanics and Materials 16-19 (octubre de 2009): 596–600. http://dx.doi.org/10.4028/www.scientific.net/amm.16-19.596.
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Porous materials have been successfully used in an aerostatic bearing. In this paper, the dynamic stiffness and damping of partial porous aerostatic thrust bearings are analyzed by numerical calculation method. Firstly, the pressure distribution function of the bearing is divided into the static and dynamic pressure distribution functions through minor perturbation method. Then, the static and dynamic pressure distribution functions are calculated by FEM. Finally, the dynamic stiffness and damping coefficients of the bearing are solved. The result indicates that the dynamic stiffness increases obviously with the increment of supply pressure and first increases then decreases with the increment of frequency, and that there is negative damping in the low frequency band and the supply pressure has a great impact on the stability of the bearing.
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Ding, Lan, Zhi Ye y Qiao-Yun Wu. "Flexural vibration band gaps in periodic Timoshenko beams with oscillators in series resting on flexible supports". Advances in Structural Engineering 23, n.º 14 (16 de junio de 2020): 3117–27. http://dx.doi.org/10.1177/1369433220928529.
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The propagation properties of waves in Timoshenko beams resting on flexible supports and with periodically attached harmonic locally resonant oscillators are studied by the transfer matrix methodology. Through calculating the differential equations of the beam for the flexible vibration and the dynamic equations of the oscillators in series, the matrix of dynamic stiffness and the resulting transfer matrix are derived. Accordingly, the band gap in infinite system characterized by the propagation constant can be verified by comparing to the curve of transmission property, determined with the finite element method for the finite system. The mechanism of each band gap formation is further explored. Numerical results show that different from the single degree-of-freedom mass-spring model, one more locally resonant band gap is generated in the system of two oscillators in series. The introduction of flexible supports, allowing for variable internal coupling between the adjacent cells, produces an extra band gap with a minimum frequency of zero. It is also found that the starting frequencies of the locally resonant gaps are related to the spring stiffness and mass of the oscillator. Therefore, the positions and widths of the band gaps can be tuned by properly adjusting the four parameters of the oscillators and also the stiffness of the flexible supports.
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Esteva, Luis. "Nonlinear Seismic Response of Soft-First-Story Buildings Subjected to Narrow-Band Accelerograms". Earthquake Spectra 8, n.º 3 (agosto de 1992): 373–89. http://dx.doi.org/10.1193/1.1585686.
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The nonlinear dynamic response of shear systems representative of buildings with excess stiffness and strength at all stories above the first one is studied. Variables covered were number of stories, fundamental period, along-height form of variation of story stiffness, ratio of post-yield to initial stiffness, in addition to the variable of primary interest: the factor r, expressing the ratio of the average value of the safety factor for lateral shear at the upper stories to that at the bottom story. The lateral strength at the latter was taken as equal to the nominal value of the corresponding story shear computed by conventional modal dynamic analysis for the design spectrum specified by Mexico City seismic design regulations of 1987 for a seismic behavior (ductility) reduction coefficient of 4.0. The excitation was in some cases the EW component of the accelerogram recorded at the parking lot of the Ministry of Communications and Transport in the same city during the destructive earthquake of September 19, 1985, and in some other cases an ensemble of artificial accelerograms with similar statistical properties. It is concluded that the nonlinear seismic response of shear buildings whose upper stories have lateral strengths and stiffnesses which correspond to safety factors larger than those applied to the first story is very sensitive to the relation between the average of the over-strength factors at the upper stories and that at the first one, as well as to the ratio of post-yield to initial stiffnesses. The nature and magnitude of the influence of r on the maximum ductility demands at the first story depend on the low-strain fundamental natural period of the system. The ductility demands computed for elastoplastic systems may in some cases be extremely large. Accounting for P-delta effects leads to an enhancement of the sensitivity of the response with respect to r.
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Qin, Zhaoye, Delin Cui, Shaoze Yan y Fulei Chu. "Application of 2D finite element model for nonlinear dynamic analysis of clamp band joint". Journal of Vibration and Control 23, n.º 9 (3 de agosto de 2015): 1480–94. http://dx.doi.org/10.1177/1077546315594065.
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Due to frictional slippage between the joint components, clamp band joints may generate nonlinear stiffness and friction damping, which will affect the dynamics of the joint structures. Accurate modeling of the frictional behavior in clamp band joints is crucial for reliable estimation of the joint structure dynamics. While the finite element (FE) method is a powerful tool to analyze structures assembled with joints, it is computationally expensive and inefficient to perform transient analyses with three-dimensional (3D) FE models involving contact nonlinearity. In this paper, a two-dimensional (2D) FE model of much more efficiency is applied to investigate the dynamics of a clamp band jointed structure subjected to longitudinal base excitations. Prior to dynamic analyses, the sources of the model inaccuracy are determined, upon which a two-step model updating technique is proposed to improve the accuracy of the 2D model in accordance with the quasi-static test data. Then, based on the updated 2D model, the nonlinear influence of the clamp band joint on the dynamic response of the joint structure is investigated. Sine-sweep tests are carried out to validate the updated 2D FE model. The FE modeling and updating techniques proposed here can be applied to other types of structures of cyclic symmetry to develop accurate model with high computational efficiency.
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Wang, Yong, Shunming Li, Chun Cheng y Xingxing Jiang. "Dynamic Analysis of a High-Static-Low-Dynamic-Stiffness Vibration Isolator with Time-Delayed Feedback Control". Shock and Vibration 2015 (2015): 1–19. http://dx.doi.org/10.1155/2015/712851.
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This paper proposes the time-delayed cubic velocity feedback control strategy to improve the isolation performance of High-Static-Low-Dynamic-Stiffness (HSLDS) vibration isolator. Firstly, the primary resonance of the controlled HSLDS vibration isolator is obtained by using multiple scales method. The equivalent damping ratio and equivalent resonance frequency are defined to study the effects of feedback gain and time delay on the primary resonance. The jump phenomenon analysis of the controlled system without and with time delay is investigated by using Sylvester resultant method and optimization method, respectively. The stability analysis of the controlled system is also considered. Then, the 1/3 subharmonic resonance of the controlled system is studied by using multiple scales method. The effects of feedback gain and time delay on the 1/3 subharmonic resonance are also presented. Finally, force transmissibility is proposed to evaluate the performance of the controlled system and compared with an equivalent linear passive vibration isolator. The results show that the vibration amplitude of the controlled system around the resonance frequency region decreases and the isolation frequency band is larger compared to the equivalent one. A better isolation performance in the high frequency band can be achieved compared to the passive HSLDS vibration isolator.
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Solaroli, G., Z. Gu, A. Baz y M. Ruzzene. "Wave Propagation in Periodic Stiffened Shells: Spectral Finite Element Modeling and Experiments". Journal of Vibration and Control 9, n.º 9 (septiembre de 2003): 1057–81. http://dx.doi.org/10.1177/107754603030677.
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The capability of periodic structures to act as filters for propagating waves is used to control the propagation of waves in thin shells. The shells are stiffened by periodically placed rings in order to generate periodic discontinuities in the stiffness and inertial spatial distribution along the longitudinal axes of these shells. Such discontinuities result in attenuation of the wave propagation over certain frequency bands called stop bands. A distributed-parameter approach is used to derive a spectral finite element model of the periodically stiffened shell. The model accurately describes the dynamic behavior of the shell using a small number of elements. The stiffening rings, modeled using the curved beam theory, are considered as lumped elements whose mass and stiffness matrices are combined with those of the shell. The resulting dynamic stiffness matrix of the ring-stiffened shell element is used to predict the wave propagation dynamics in the structure. In particular, the shell propagation constants are determined by solving a polynomial eigenvalue problem, as a numerically robust alternative to the traditional transfer matrix formulation. The study of the propagation constants shows that the discontinuity introduced by the stiffeners generates the typical stop/pass band pattern of periodic structures. The location and width of the stop bands depend on the spacing and geometrical parameters of the rings. The existence of the stop bands, as predicted from the analysis of the propagation constants, is verified experimentally. Excellent agreement between theoretical predictions and experimental results is achieved. The presented theoretical and experimental techniques provide viable means for designing periodically stiffened shells with desired attenuation and filtering characteristics.
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Li, Jun Lan, Shao Ze Yan y Xue Feng Tan. "Modeling and Simulation of Clamp Band Dynamic Envelope in a LV/SC Separation System". Applied Mechanics and Materials 141 (noviembre de 2011): 359–63. http://dx.doi.org/10.4028/www.scientific.net/amm.141.359.
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The clamp band system is a typical locked and separated device of the launch vehicle (LV) / the spacecraft (SC), and its release-separation process is one of the important factors that affect the LV/SC separation movement. A nonlinear spring-damper model was employed to describe the contact-impact behavior between the V-segment of the clamp band and the LV/SC interface, and lumped mass method was used to depict the clamp band. By using ADAMS, a dynamic model of the clamp band system was established. The simulation results show that the impulse of the explosive bolts and the stiffness of lateral-restraining springs have significant effects on the clamp band dynamic envelope. The shock of the satellite-vehicle separation is very vulnerable to the clamp band pretension and the friction coefficient between the V-segment and the LV/SC interface.
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Ma, Qiang, Jie Jian Di, Xiao Wu Du y Quan Liang Zhao. "Research of a Dynamic Vibration Absorber with Tunable Resonant Frequency and its Vibration Attenuation Characteristics". Applied Mechanics and Materials 511-512 (febrero de 2014): 601–5. http://dx.doi.org/10.4028/www.scientific.net/amm.511-512.601.
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In order to improve working frequency band and damping effect of a dynamic vibration absorber, a new kind of dynamic vibration absorber is presented. Its resonant frequency could be real-time adjusted by adapting the stiffness of the spring. The vibration attenuation characteristics are analyzed theoretically and numerically. According to simulation analysis, effects of geometrical parameters are researched and optimum geometric parameters are determined. The damping effect was simulated in a flat structure, the results show that the working frequency band and damping effect of the DVA are both remarkable.
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Lund, Douglas y Robert Crawford. "Novel Guided Head Expander Design Uses Close Coupled Inertial Masses and Hydrostatic Bearings to Minimize Cross-Axis Motion". Journal of the IEST 53, n.º 1 (1 de abril de 2010): 69–82. http://dx.doi.org/10.17764/jiet.53.1.18m5h0u285845u84.
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When vertical vibration testing of large test articles is required, it is common to install a head expander on the armature of a shaker. Larger test articles often have a center of gravity relatively far above the mounting surface. When combined with the armature and head expander, these test articles may exhibit multiple structural resonances within the desired test band that do not exist in the intended application. These test configuration-driven characteristics are likely to create unwanted cross-axis excitation during a vibration test. The difficulty in controlling unwanted cross-axis motion usually increases when testing large items. Excessive cross-axis motion can "over-test" the test item, creating the risk of damaging the test item, or can limit the input in the test axis, thus jeopardizing a successful test. Orbital Sciences commissioned the design of a guided head expander system that greatly reduces the cross-axis motion at the test article mounting surface of the head expander. The design submitted by Team Corporation couples large inertial masses to the head expander through high-stiffness, hydrostatic, self-aligning bearings. Together, the guided head expander and inertial mass structures have a first resonance higher than the test band of interest and provide high dynamic stiffness. The head expander and inertial masses are supported by a suspension system with a low first resonance, below the test band of interest. It is noteworthy that this design approach exhibits high "dynamic" stiffness and low static stiffness. Conventional designs for this type of equipment may have relatively high cross-axis load ratings, which might suggest that such designs would provide good cross-axis motion control, but these designs often suffer from structural resonances within the test band of interest that produce unwanted cross-axis motion.
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Song, Weizhi, Zhien Liu, Chihua Lu, Yongchao Li y Bin Li. "Research on vibration reduction performance of dynamic vibration absorber based on damping characteristic of a new material". Advances in Mechanical Engineering 12, n.º 11 (noviembre de 2020): 168781402096159. http://dx.doi.org/10.1177/1687814020961596.
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The absorbing effect of traditional dynamic vibration absorber (TDVA) is satisfactory only when the natural frequency is close to the excitation frequency. For this defect, a semi-active vibration absorber is designed with magnetorheological elastomer (MRE) as a stiffness element, that its stiffness can be controlled by magnetic field, to widen the frequency band of the absorber. Theory and experiments show that reducing the damp of the absorber can improve the performance of the absorber at the anti-resonance point, but it will cause the vibration of the controlled system at the new resonance point, which caused by the addition of a DVA, to be more intense. For this problem, the compatibilizer: silane coupling agent KH570, is added to the preparation of MRE to reduce material damping, at the same time, the stiffness control strategy is used to eliminate the resonance of the controlled system caused by the addition of DVA. The final experimental results show that the frequency band of vibration reduction has been broadened effectively and the vibration reduction performance has been improved considerably. Moreover, the resonance has been eliminated very well.
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Powers, Joseph D., Pasquale Bianco, Irene Pertici, Massimo Reconditi, Vincenzo Lombardi y Gabriella Piazzesi. "Contracting striated muscle has a dynamic I‐band spring with an undamped stiffness 100 times larger than the passive stiffness". Journal of Physiology 598, n.º 2 (enero de 2020): 331–45. http://dx.doi.org/10.1113/jp278713.
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Fan, Rang-Lin, Yu-Fei Dou y Fu-Liang Ma. "Fixed Points on Active and Passive Dynamics of Active Hydraulic Mounts with Oscillating Coil Actuator". Actuators 10, n.º 9 (6 de septiembre de 2021): 225. http://dx.doi.org/10.3390/act10090225.
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Active hydraulic mounts with an inertia track, decoupler membrane, and oscillating coil actuator (AHM-IT-DM-OCAs) have been studied extensively due their compact structure and large damping in the low-frequency band. This paper focuses on a comprehensive analysis of the active and passive dynamics and their fixed points in mid-low-frequency bands, which will be helpful for parameter identification. A unified lumped parameter mechanical model with two degrees-of-freedom is established. The inertia and damping forces of the decoupler/actuator mover may be neglected, and a nonlinear mathematical model can be obtained for mid-low-frequency bands. Theoretical analysis of active and passive dynamics for fluid-filled state reveals the amplitude dependence and a fixed point in passive dynamic stiffness in-phase or active real-frequency characteristics. The amplitude dependence of local loss at the fluid channel entrance and outlet induces the amplitude-dependent dynamics. The amplitude-dependent dynamics constitute a precondition for fixed points. A single fixed point in passive dynamics is experimentally validated, and a pair of fixed points in active dynamics for an AHM-IT-DM-OCA is newly revealed in an experiment, which presents a new issue for further analysis.
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Man, Dawei, Gaozheng Xu, Huaiming Xu, Deheng Xu y Liping Tang. "Nonlinear Dynamic Analysis of Bistable Piezoelectric Energy Harvester with a New-Type Dynamic Amplifier". Computational Intelligence and Neuroscience 2022 (25 de junio de 2022): 1–14. http://dx.doi.org/10.1155/2022/7155628.
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A distributed parametric mathematical model of a new-type dynamic magnifier for a bistable cantilever piezoelectric energy harvester is proposed by using the generalized Hamilton principle. The new-type dynamic magnifier consists of a two-spring-mass system, one is placed between the fixed end of the piezoelectric beam and the L-shaped frame, and the other is placed between the L-shaped frame and the base structure. We used the harmonic balance method to obtain the analytical expressions for the steady-state displacement, steady-state output voltage, and power amplitude of the system. The effect of the distance between the magnets, the spring stiffness ratio and mass ratio of the two dynamic magnifiers, and the load resistance on the performance of the harvester is investigated. Analytical results show that compared with the bistable piezoelectric energy harvester with a typical spring-mass dynamic magnifier, the proposed new-type energy harvester system with a two-spring-mass dynamic magnifier can provide higher output power over a broader frequency band, and increasing the mass ratio of the magnifier tip mass to the tip magnet can significantly increase the output power of the BPEH + TDM system. Properly choosing the stiffness ratio of the two dynamic amplifiers can obviously improve the harvested power of the piezoelectric energy harvester at a low excitation level.
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Liu, Zhihao y Qinhe Gao. "In-plane vibration response of time and frequency domain with rigid-elastic coupled tire model with continuous sidewall". Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 232, n.º 4 (5 de diciembre de 2017): 429–45. http://dx.doi.org/10.1177/1464419317744681.
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The in-plane vibration characteristic of time and frequency domain for heavy-loaded radial tire with a larger flat ratio (close to 1) is researched by utilizing the rigid-elastic coupled tire model with continuous sidewall. The sidewall bending stiffness is considered and the flexible beam on the elastic continuous beam tire model is proposed and investigated analytically to simulate the in-plane vibration of the heavy-loaded radial tire within more wider frequency band. The rigid-elastic coupled tire model is derived with finite difference method and the analytical stiffness matrix; mass matrix is formed based on the geometrical and structural parameters of heavy-loaded radial tire. Structural parameters are identified utilizing genetic algorithm based on the error between the analytical and experimental modal frequency. In-plane frequency domain transfer function and time domain dynamics response of heavy-loaded radial tire is investigated and compared with the experimental result. Experimental and theoretical results show that in-plane rigid-elastic coupled tire model with sidewall bending stiffness can be used to precisely predict the transfer function and vibration feature within the frequency band of 300 Hz, compared with the tire model with the distributed independent sidewall element. The flexible beam on the elastic continuous beam tire model and rigid-elastic coupled tire model with continuous sidewall can be extended to the dynamic analysis of the tire with larger flat ratio or the tire under the impulsive loading conditions.
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Stickley, Christopher D., Melanie M. Presuto, Kara N. Radzak, Christina M. Bourbeau y Ronald K. Hetzler. "Dynamic Varus and the Development of Iliotibial Band Syndrome". Journal of Athletic Training 53, n.º 2 (1 de febrero de 2018): 128–34. http://dx.doi.org/10.4085/1062-6050-122-16.
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Context: Although the risk of osteoarthritis development after acute knee injury has been widely studied, the long-term consequences of knee overuse injury are not well understood. Objective: To identify the relationship between gait-related risk factors associated with osteoarthritis and the development of iliotibial band syndrome (ITBS) in members of a single University Army Reserve Officers' Training Corps unit. Design: Prospective cohort study. Setting: Biomechanics laboratory. Patients or Other Participants: Sixty-eight cadets undergoing standardized physical fitness training. Intervention(s): Three-dimensional lower extremity kinematics (240 Hz) and kinetics (960 Hz) were collected for 3 bilateral trials during shod running at 4.0 m/s ± 10%. Injury tracking was conducted for 7 months of training. Main Outcome Measure(s): Biomechanical variables, including varus thrust and knee-adduction moment, were compared between the injured and control groups. Results: Twenty-six cadets with no history of overuse injury served as the control group, whereas 6 cadets (7 limbs) who developed ITBS that required them to modify their training program or seek medical care (or both) served as the injured group. Maximum varus velocity was higher (P = .006) and occurred sooner during stance (P = .04) in the injured group than in the control group, indicating greater varus thrust. Maximum knee-varus angle and maximum knee-adduction moment were higher (P = .02 and P = .002, respectively) and vertical stiffness was lower (P = .03) in the injured group. Conclusions: Measures of dynamic varus stability appeared to be altered in individuals who developed ITBS. Biomechanical knee variables previously identified as increasing the risk for knee osteoarthritis were also associated with the development of ITBS in healthy adults.
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Ren, Tao, Chunchuan Liu, Fengming Li y Chuanzeng Zhang. "Active tuning of the vibration band gap characteristics of periodic laminated composite metamaterial beams". Journal of Intelligent Material Systems and Structures 31, n.º 6 (21 de enero de 2020): 843–59. http://dx.doi.org/10.1177/1045389x19898757.
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A novel strategy is proposed to investigate the vibration band-gap and active tuning characteristics of the laminated composite metamaterial beams. The piezoelectric actuator/sensor pairs are periodically placed along the laminated composite beam axis so that the vibration frequency band-gap and active tuning characteristics can be induced. The dynamic equations of the laminated composite metamaterial beams bonded by the piezoelectric actuator/sensor pairs are established based on the Euler–Bernoulli beam theory. The negative proportional feedback control strategy is employed to provide the positive active control stiffness for the piezoelectric actuator/sensor patches. The spectral element method is used to calculate the dynamic responses of the laminated composite metamaterial beams with the periodically placed piezoelectric patches, and the calculation accuracy for the dynamic responses is validated by the finite element method. The results demonstrating the high-performance vibration band-gap properties in the low-frequency ranges can be achieved by properly designing the sizes and the number of the piezoelectric patches. Moreover, the vibration band-gap characteristics, especially the band-gap width and the normalized band-gap width with respect to the considered excitation frequency range, can be significantly changed by tuning the structural parameters of the piezoelectric actuators and sensors. In addition, the cross-ply angle of the laminated composite metamaterial beams has significant influences on the band-gap characteristics and the vibration reduction performance of the laminated composite beam structures.
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Wang, Mingze, Chengbiao Cai, Shengyang Zhu y Wanming Zhai. "Experimental study on dynamic performance of typical nonballasted track systems using a full-scale test rig". Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 231, n.º 4 (4 de marzo de 2016): 470–81. http://dx.doi.org/10.1177/0954409716634751.
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This paper presents an experimental study on dynamic performance of China Railway Track System (CRTS) series track systems using a full-scale test rig. The test rig has been constructed based on 55.17 m long full-scale nonballasted tracks composed of four typical CRTS track elements in high-speed railways. First, the dynamic characteristics of different nonballasted tracks are investigated by conducting wheel-drop tests, where a wheel-drop testing vehicle with a dropping wheelset is devised to provide the wheel-drop load. The vibration levels of different track systems are assessed by the root-mean-square acceleration per one-third octave band, and the vibration transmission characteristics of the CRTS series tracks are evaluated by transfer functions. Further, a mathematical track model is used to extract the dynamic stiffness and damping coefficient of the four types of nonballasted track systems based on the wheel–rail impact response. The vibration characteristics, the dynamic stiffness, and damping coefficient of different nonballasted track systems under various wheel-drop heights are compared and discussed in detail.
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Yan, Bo, Ning Yu y Chuanyu Wu. "A state-of-the-art review on low-frequency nonlinear vibration isolation with electromagnetic mechanisms". Applied Mathematics and Mechanics 43, n.º 7 (julio de 2022): 1045–62. http://dx.doi.org/10.1007/s10483-022-2868-5.
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AbstractVibration isolation is one of the most efficient approaches to protecting host structures from harmful vibrations, especially in aerospace, mechanical, and architectural engineering, etc. Traditional linear vibration isolation is hard to meet the requirements of the loading capacity and isolation band simultaneously, which limits further engineering application, especially in the low-frequency range. In recent twenty years, the nonlinear vibration isolation technology has been widely investigated to broaden the vibration isolation band by exploiting beneficial nonlinearities. One of the most widely studied objects is the “three-spring” configured quasi-zero-stiffness (QZS) vibration isolator, which can realize the negative stiffness and high-static-low-dynamic stiffness (HSLDS) characteristics. The nonlinear vibration isolation with QZS can overcome the drawbacks of the linear one to achieve a better broadband vibration isolation performance. Due to the characteristics of fast response, strong stroke, nonlinearities, easy control, and low-cost, the nonlinear vibration with electromagnetic mechanisms has attracted attention. In this review, we focus on the basic theory, design methodology, nonlinear damping mechanism, and active control of electromagnetic QZS vibration isolators. Furthermore, we provide perspectives for further studies with electromagnetic devices to realize high-efficiency vibration isolation.
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Sun, Jing, Ke Zhang, De Hong Zhao, Yu Hou Wu y Feng Lu. "The Design and Analysis of Saw-Milling Working Head for Special Shaped Stone". Applied Mechanics and Materials 577 (julio de 2014): 209–13. http://dx.doi.org/10.4028/www.scientific.net/amm.577.209.
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For a new type of saw-milling composite work-head, using the finite element method and modal analysis tests to get the dynamic characteristics analysis of the system. We have made dynamic parameters analyses which are mode shape, natural frequency and damping ratio of the whole machine and the piece structure of work-head, and identified the weak links of the machine. The research shows that: the composite work-head’ weaknesses are in the sliding saddle joint, and the vibration instability trend would drive the whole machine; the dynamic stiffness of spindle is lower in the low frequency band, and it causes a certain influence on the machining accuracy.
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Li, Ming, Wei Cheng y Ruili Xie. "Design and experiments of a quasi–zero-stiffness isolator with a noncircular cam-based negative-stiffness mechanism". Journal of Vibration and Control 26, n.º 21-22 (19 de febrero de 2020): 1935–47. http://dx.doi.org/10.1177/1077546320908689.
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This article presents a quasi–zero-stiffness isolator with a cam-based negative-stiffness mechanism, where the cam has a user-defined noncircular profile to generate negative stiffness to counterbalance the positive stiffness of the vertical spring and yield the quasi–zero-stiffness characteristic around the equilibrium position. Unlike previous studies, the proposed quasi–zero-stiffness isolator has the preferable feature that the desired cubic restoring force can be directly obtained through the well-designed profile of the cam in the negative-stiffness mechanism with the friction considered during the model design, rather than through the Taylor expansion and friction-ignoring assumption, which can avoid the approximation error between the theoretical design and the specific realization. The pure-cubic nonlinear differential equation of motion of the quasi–zero-stiffness isolator is derived and solved with the harmonic balance method, followed by the discussion of the relevant dynamic characteristics. Experimental studies are carried out based on the physical prototype of the quasi–zero-stiffness isolator. The results show that the quasi–zero-stiffness isolator can greatly extend the isolation frequency bandwidth and has a much lower resonance peak. In the low-frequency band, the quasi–zero-stiffness isolator greatly outperforms the corresponding linear system but is equivalent or even inferior in the high-frequency range with the increase of excitation force.
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Kang, Tae-Sik, Dong-Hoon Choi y Tae-Gun Jeong. "Optimal Design of HDD Air-Lubricated Slider Bearings for Improving Dynamic Characteristics and Operating Performance". Journal of Tribology 123, n.º 3 (6 de julio de 2000): 541–47. http://dx.doi.org/10.1115/1.1308031.
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Flying attitudes of the slider, which are flying height, pitch, and roll, are affected by air-flow velocity, skew angle, and manufacturing tolerances. In the traditional design process of air-bearing surfaces, we have considered only the steady state flying attitude over the recording band. To reduce the flying height variation during track seek as well as in steady state, we design a new shape for air-bearing surfaces. An optimization technique is used to improve the dynamic characteristics and operating performance of the new air-bearing surface shapes. The quasistatic approach is used in the numerical simulation of the track seek operation because the skew angle effect dominates the inertial effect even at high seek velocities. The perturbation method is applied to the lubrication equation to obtain the air-bearing stiffness. We employ the method of modified feasible directions and use the weighting method to solve the multicriteria optimization problem. The optimally designed sliders show enhanced flying and dynamic characteristics. The steady state flying heights are closer to the target values and the flying height variations during track seek operation are smaller than those for the original ones. The pitch and roll angles are kept within suitable ranges over the recording band during track seek operation as well as in steady state. The air-bearing stiffnesses of the optimally designed sliders are larger than those of the original ones.
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Abbasi, Amirhassan, SE Khadem y Saeed Bab. "Vibration control of a continuous rotating shaft employing high-static low-dynamic stiffness isolators". Journal of Vibration and Control 24, n.º 4 (29 de mayo de 2016): 760–83. http://dx.doi.org/10.1177/1077546316651559.
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In this paper, the effects of high-static low-dynamic stiffness (HSLDS) isolators on the supports of a continuous rotating shaft for vibration control of a rotary system under mass eccentricity force are investigated. The rotating shaft is modeled using the Euler–Bernoulli beam theory. HSLDS isolators have a linear damping and linear and nonlinear (cubic) equivalent stiffness. Isolators are positioned on the supports of the rotating shaft, so that their forces are applied in radial directions. Equations of motion are extracted using the extended Hamilton principle and they are analyzed using the multiple scale method; then, the steady-state solutions and stability are studied. The effects of variations in linear and nonlinear parameters of the isolators on the static load bearing, resonant peak, frequency band of isolation and hardening nonlinearity are considered, in order to design an appropriate HSLDS isolator and to set its parameters in an optimal way. Investigating the effects of the cubic stiffness and damping values on bifurcations of the system, one may observe that inappropriate setting of these parameters causes strong or weak nonlinearity in the system and, consequently, HSLDS isolators perform less effectively than a linear one does. Then, the results are verified through analyzing the time history of the rotary system under study.
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Sun, Xiuting y Xingjian Jing. "A nonlinear vibration isolator achieving high-static-low-dynamic stiffness and tunable anti-resonance frequency band". Mechanical Systems and Signal Processing 80 (diciembre de 2016): 166–88. http://dx.doi.org/10.1016/j.ymssp.2016.04.011.
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Man, Dawei, Huaiming Xu, Gaozheng Xu, Deheng Xu, Liping Tang y Qinghu Xu. "Dynamic Characteristics Analysis of Tri-Stable Cantilever Piezoelectric Energy Harvester with a Novel-type Dynamic Amplifier". International Journal of Heat and Technology 40, n.º 2 (30 de abril de 2022): 619–26. http://dx.doi.org/10.18280/ijht.400232.
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In this paper, a non-linear tri-stable piezoelectric cantilever energy harvester with a novel-type dynamic magnifier was proposed to achieve more effective broadband energy harvesting under low-level ambient excitations. According to the generalized Hamilton principle, a mathematical distributed parameter model of the piezoelectric energy harvester was proposed. The novel-type dynamic magnifier is a system consisting of two spring masses, one placed between the fixed end of the piezoelectric beam and the L-shaped frame, and the other, between the L-shaped frame and the base. The harmonic balance method was adopted to work out the analytical expressions of the steady-state displacement, steady-state output voltage and power amplitude of the energy harvester system. The effects of the distance between the magnets, the spring stiffness of the dynamic magnifier, and the load resistance on the performance of the system were also investigated. The results show that different from that of the conventional tri-stable piezoelectric energy harvester, the frequency response curve of the proposed novel-type energy harvester system with a two-spring-mass dynamic magnifier exhibits two peaks as a result of the interactions of the coupled elastic system, where the left peak stands for the resonant value of the tri-stable piezoelectric energy harvester, while the right one the resonant value of the dynamic magnifier. It is able to achieve higher output power over a broader frequency band under low-level environmental excitations, and the harvested power can be significantly strengthened if the mass and stiffness of the dynamic magnifier are selected properly.
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Ramakrishnan, Vinod y Michael J. Frazier. "Acoustic metamaterials with independently tunable mass, damping, and stiffness". Journal of the Acoustical Society of America 151, n.º 4 (abril de 2022): A96. http://dx.doi.org/10.1121/10.0010771.
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Over the past decades, metamaterials—whose engineered internal architecture grants unusual or extraordinary macroscopic response—have garnered increasing attention from researchers as the desire to shape material behavior beyond natural limitations (e.g., chemistry) arises within several areas of materials science and engineering. The bulk of reported acoustic metamaterial architectures are passive such that their properties and functions are fixed at fabrication. Nevertheless, a tuning capacity is desirable to expand the range of response, in general, and to allow for adaptation in the face of changing service requirements. Despite the diversity of proposed tuning strategies, most target the stiffness parameter alone, leaving the inertial and dissipative properties unaffected. In this presentation, we present a novel implementation of (geometric) bi-stability and kinematic amplification to independently tune the value and distribution of the effective mass, stiffness, and viscous damping within acoustic metamaterials, which impacts the dynamic response. Through analytical and numerical investigations of a 1D system, we show that the corresponding frequency band structure depends on the specific configurations of bi-stable elements within the unit cell. As the number of bi-stable elements per unit cell increases, so to do the number of unique dynamic responses to which to tailor the system. The proposed strategy significantly expands the property set available for tuning acoustic metamaterial performance post-fabrication.
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Hwang, Myungwon, Yeongeun Ki y Andres F. Arrieta. "Dynamics of tunable multistable metastructures". Journal of the Acoustical Society of America 152, n.º 4 (octubre de 2022): A38. http://dx.doi.org/10.1121/10.0015461.
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Connectivity yields unconventional properties. However, the attainable dynamics are strongly dependent on the unit cell size, restricting the effective behavior to narrow, high-frequencies bands. This is due to the nature of band gaps from local resonance or scattering, both of which are strongly related to unit’s size (mass) and stiffness. We present multistable metastructures displaying strong nonlinear interactions between propagating transition waves and structural modes. We show how transition waves excite the same type of response in the metastructure’s units regardless of the input excitation. This invariant response allows for efficient electromechanical energy transduction as the mechanical response can be tuned to electrical conversion circuits robustly. We also present a new dynamic phenomenon—solitonic resonance—leveraging soliton-structural mode interactions that enable multistable metastructures to exhibit extreme input-output energy exchange. By tuning the topology of our multistable metastructures we can transform energy input frequencies into output responses orders of magnitude apart. The presented metastructures break the dependence of the attainable unconventional dynamical properties on the unit cell's size. The dynamics of multistable metastructure provide a route to accelerating metamaterials adoption in engineering applications addressing the structural bandwidth.
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Carta, G., M. Brun y A. B. Movchan. "Dynamic response and localization in strongly damaged waveguides". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, n.º 2167 (8 de julio de 2014): 20140136. http://dx.doi.org/10.1098/rspa.2014.0136.
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In this paper, we investigate the formation of band-gaps and localization phenomena in an elastic strip nearly disintegrated by an array of transverse cracks. We analyse the eigenfrequencies of finite, strongly damaged, elongated solids with reference to the propagation bands of an infinite strip with a periodic damage. Subsequently, we determine analytically the band-gaps of the infinite strip by using a lower-dimensional model, represented by a periodically damaged beam in which the small ligaments between cracks are modelled as ‘elastic junctions’. The effective rotational and translational stiffnesses of the elastic junctions are obtained from an ad hoc asymptotic analysis. We show that, for a finite frequency range, the dispersion curves for the reduced beam model agree with the dispersion data determined numerically for the two-dimensional elastic strip. Exponential localization, boundary layers and standing waves in strongly damaged systems are discussed in detail.
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Zuo, Zhiyuan, Linya Liu, Yunlai Zhou, Jialiang Qin y Weitao Cui. "Acoustic Radiation Study of a Box Girder Viaduct Considering the Frequency-Dependent Viscoelasticity of the Rail Pad". Buildings 12, n.º 8 (12 de agosto de 2022): 1226. http://dx.doi.org/10.3390/buildings12081226.
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In order to investigate the mechanism of the frequency-dependent viscoelasticity of the rail pad on the acoustic radiation characteristics of a box girder viaduct, this study establishes a high-order model of its dynamic parameters to reveal the frequency-varying viscoelasticity of the rail pad, and establishes a vehicle–track–viaduct vertical coupling model. Finally, the acoustic radiation characteristics of a box girder viaduct are analyzed by combining the finite element method and the boundary element theory. The results show that the S-stiffness and D-stiffness of the rail pad increase with the increase in frequency, and the frequency sensitivity of the S-stiffness is greater than that of the D-stiffness. The high-order characterization model of the dynamic parameters of the rail pad has a good fitting effect. The main influence frequency band of the frequency variable viscoelasticity of the rail pad on the wheel–rail force and the equivalent discrete spring force of the sliding layer is 30–90 Hz, resulting in the shift of the dominant frequency to a high frequency by 4 Hz. We consider that the frequency-varying viscoelasticity of the rail pad will cause the dominant frequency of the acoustic pressure level of the field point to shift to a high frequency of 4–6 Hz, which has the greatest influence on the sound pressure level of each field point at the Peak Frequency Point of Insertion Loss (PFPIL), and the influence degree is consistent, resulting in the maximum value of the total sound pressure level of the surface field increasing by 4.1 dB. Without considering the frequency-varying viscoelasticity of the rail pad, the sound pressure level of each field point at 20–53 Hz will be overestimated and the sound pressure level of each field point in the 53–100 Hz frequency band will be underestimated. The panel sound power level contribution coefficient of the box girder is obviously different at different frequency points.
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Zhou, Jiaxi, Kai Wang, Daolin Xu y Huajiang Ouyang. "Local resonator with high-static-low-dynamic stiffness for lowering band gaps of flexural wave in beams". Journal of Applied Physics 121, n.º 4 (28 de enero de 2017): 044902. http://dx.doi.org/10.1063/1.4974299.
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Jin, Guoyong, Chunyu Zhang, Tiangui Ye y Jialiang Zhou. "Band gap property analysis of periodic plate structures under general boundary conditions using spectral-dynamic stiffness method". Applied Acoustics 121 (junio de 2017): 1–13. http://dx.doi.org/10.1016/j.apacoust.2017.01.024.
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Erden Gulebaglan, Sinem y Emel Kilit Dogan. "A comparison study of the structural electronic, elastic and lattice dynamic properties of ZrInAu and ZrSnPt". Zeitschrift für Naturforschung A 76, n.º 6 (12 de abril de 2021): 559–67. http://dx.doi.org/10.1515/zna-2021-0014.
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Abstract To estimate the structural, electronic, elastic and dynamic properties of ZrInAu and ZrSnPt compounds, the density functional theory within the general gradient approximation was used. The computed lattice parameters, bulk modulus and the derivation of bulk modulus with respect to pressure were displayed and compared with the theoretical result. The indirect band gap for ZrInAu was found to be 0.48 eV, and for ZrSnPt the indirect band gap was found as 1.01 eV. Elastic stiffness constants, bulk, shear and Young’s module, Poisson’s coefficients and Zener anisotropy factor are calculated. Elastic properties showed that the ZrSnPt compound is more durable than the ZrInAu compound. Phonon distribution curves and density of states were investigated using a density functional perturbation theory. Both ZrInAu and ZrSnPt compounds were demonstrated to be dynamically stable. The results of this study were obtained for the first time in the literature. These results will make an important contribution to the literature.
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Schmiedeke, Hannes, Michael Sinapius y Nontavut Prechavut. "Experimental Investigation of the Leaf Type Bearing Structure with Undersprings Under Dynamic Excitation". Machines 9, n.º 1 (15 de enero de 2021): 15. http://dx.doi.org/10.3390/machines9010015.
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With foil bearings, rotors achieve high rotational speeds with less friction and wear. In addition, here the required space is small and no peripheral components like liquid tanks or pumps are needed. The drawback is a more complex prediction of the real behavior in rotordynamic systems. Impedance test rigs are suitable for investigating the structural-dynamic bearing properties and for validating the theoretical models. This article presents and discusses the measurement of dynamic behavior, i.e., stiffness and damping coefficients, of the structure of a leaf type bearing with undersprings. These measurements include variations in static load due to the relative displacement of the bearing and shaft as well as an attempt to explain the noticed anisotropic behavior of the bearing. This article also shows how much a controlled excitation improves the comparability across the frequency band. For this purpose, a test rig is presented that has been further developed in comparison to known literature approaches. The results show, that the loss factors of the examined bearing structure are up to 4 times bigger below lift-off compared to the operation at 60,000 rpm. Furthermore, the movement amplitudes and the static loads have a great influence on the stiffness and the damping.
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Zhang, Ming y Qing-Guang Chen. "Numerical Model on the Dynamic Behavior of a Prototype Kaplan Turbine Runner". Mathematical Problems in Engineering 2021 (8 de septiembre de 2021): 1–12. http://dx.doi.org/10.1155/2021/4421340.
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Experimental and numerical investigations of the modal behavior of a prototype Kaplan turbine runner in air have been conducted in this paper. The widely used roving accelerometer method was used in the experimental modal analysis. A systematic approach from a single blade model to the whole runner has been used in the simulation to get a thorough understanding. The experimental results show that all the detected modes concentrate their displacements on the impacted blade. The numerical results show that the modes of the single blade form different mode families of the runner, and each mode family corresponds to a narrow frequency band. Harmonic response analysis shows that, at the response peak point, the single blade excitation can only get mode shapes with concentrations on the exciting blade due to the superposition of the close modes in each mode family, which explains the experimental results well, while the mode superposition can be avoided by the order excitation method. With the reduction of the connection stiffness between the blades and hub/control system, the frequencies of most modes change from insensitive to more and more sensitive to the connection stiffness change, which results in a sensitive area and an insensitive area. Through comparison with the experimental results, it is indicated that the natural frequencies of the runner can probably be predicted by merging the runner into a whole body.
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Xie, Yingjiang, Fu Niu, Jinggong Sun y Lingshuai Meng. "Design and Analysis of a Novel Quasi-Zero Stiffness Isolator under Variable Loads". Mathematical Problems in Engineering 2022 (31 de enero de 2022): 1–17. http://dx.doi.org/10.1155/2022/9082752.
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The designed load of most quasi-zero stiffness (QZS) isolators is constant. The isolation performance will drop sharply once the load changes. A novel QZS isolator that can adapt to variable loads is proposed in this paper to improve the range of application of the isolator. The isolator is designed by paralleling the electromagnetic spring (ES), which provides negative stiffness, and the pneumatic spring (PS), which provides positive stiffness. The positive and negative stiffness can be adjusted by changing the pressure and coil current, which provides the possibility for the isolator to adapt to variable loads. This paper derived the conditions for the isolation system to obtain QZS characteristics, proposed the dynamic model of the isolation system, derived and verified the analytical expressions of the amplitude-frequency response and force transmissibility (FT), and discussed the change of FT and displacement transmissibility(DT) under different loads. Theoretical analysis shows that changing the pressure and coil current in the same proportion can maintain the superior low-frequency isolation performance when the load changes, thanks to the preservation of the QZS characteristics of the system after adjusting the pressure and coil current. Finally, the simulation results fg and isolation frequency band over the linear isolation system and PS isolation system. Furthermore, the proposed isolator can be adjusted online.
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Hewson, P. "Method for estimating tyre cornering stiffness from basic tyre information". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 219, n.º 12 (1 de diciembre de 2005): 1407–12. http://dx.doi.org/10.1243/095440705x35071.
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This paper proposes a simple mathematical tyre model that estimates tyre cornering stiffness. The model is derived by considering the tyre to be a combination of two independent systems. The sidewalls are assumed to be negligibly stiff in the lateral direction, and hence their influence on the lateral dynamics of the tyre will be ignored. The belt and tread area of the tyre will be considered to be an homogeneous uniform band, and its stiffness will be estimated with reference to measured tyre data. The resulting model is estimated to yield cornering stiffness values within about 30 per cent of the actual measured values.
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Hvazdouski, D. C. "First-principles study of stability and electronic properties of single-element 2D materials". Doklady BGUIR 19, n.º 8 (4 de enero de 2022): 92–98. http://dx.doi.org/10.35596/1729-7648-2021-19-8-92-98.
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We have estimated stability of single-element 2D materials (C2, N2, Si2, P2, Ge2, As2, Sn2, Sb2, Pb2, and Bi2) by ab initio calculations. The calculations of structural and mechanical properties of 2D materials were performed using the VASP software package. The results of calculations of stiffness tensors, Young's modulus, and Poisson's ratios show that all studied single-element 2D materials are mechanically stable. Dynamic stability was investigated by calculating the phonon dispersion of the materials using the finite displacement method. Only Pb2 has imaginary modes in the phonon dispersion curves and therefore it has dynamic unstable structure at low temperatures. The analysis of the band structures indicates the presence of insulators (N2), semiconductors (P2, As2, Bi2, Sb2), semimetals, and metals among the studied group of single-element 2D materials.
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Hu, Yong, Zipeng Guo, Andrew Ragonese, Taishan Zhu, Saurabh Khuje, Changning Li, Jeffrey C. Grossman, Chi Zhou, Mostafa Nouh y Shenqiang Ren. "A 3D-printed molecular ferroelectric metamaterial". Proceedings of the National Academy of Sciences 117, n.º 44 (19 de octubre de 2020): 27204–10. http://dx.doi.org/10.1073/pnas.2013934117.
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Molecular ferroelectrics combine electromechanical coupling and electric polarizabilities, offering immense promise in stimuli-dependent metamaterials. Despite such promise, current physical realizations of mechanical metamaterials remain hindered by the lack of rapid-prototyping ferroelectric metamaterial structures. Here, we present a continuous rapid printing strategy for the volumetric deposition of water-soluble molecular ferroelectric metamaterials with precise spatial control in virtually any three-dimensional (3D) geometry by means of an electric-field–assisted additive manufacturing. We demonstrate a scaffold-supported ferroelectric crystalline lattice that enables self-healing and a reprogrammable stiffness for dynamic tuning of mechanical metamaterials with a long lifetime and sustainability. A molecular ferroelectric architecture with resonant inclusions then exhibits adaptive mitigation of incident vibroacoustic dynamic loads via an electrically tunable subwavelength-frequency band gap. The findings shown here pave the way for the versatile additive manufacturing of molecular ferroelectric metamaterials.
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Zhou, Xiaojie, Qinghua Liang, Zhongxian Liu y Ying He. "IBIEM Analysis of Dynamic Response of a Shallowly Buried Lined Tunnel Based on Viscous-Slip Interface Model". Advances in Civil Engineering 2019 (6 de marzo de 2019): 1–14. http://dx.doi.org/10.1155/2019/1025483.
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A viscous-slip interface model is proposed to simulate the contact state between a tunnel lining structure and the surrounding rock. The boundary integral equation method is adopted to solve the scattering of the plane SV wave by a tunnel lining in an elastic half-space. We place special emphasis on the dynamic stress concentration of the lining and the amplification effect on the surface displacement near the tunnel. Scattered waves in the lining and half-space are constructed using the fictitious wave sources close to the lining surfaces based on Green’s functions of cylindrical expansion and the shear wave source. The magnitudes of the fictitious wave sources are determined by viscous-slip boundary conditions, and then the total response is obtained by superposition of the free and scattered fields. The slip stiffness and viscosity coefficients at the lining-surrounding rock interface have a significant influence on the dynamic stress distribution and the nearby surface displacement response in the tunnel lining. Their influence is controlled by the incident wave frequency and angle. The hoop stress increases gradually in the inner wall of the lining as sliding stiffness increases under a low-frequency incident wave. In the high-frequency resonance frequency band, where incident wave frequency is consistent with the natural frequency of the soil column above the tunnel, the dynamic stress concentration effect is more significant when it is smaller. The dynamic stress concentration factor inside the lining decreases gradually as the viscosity coefficient increases. The spatial distribution and the displacement amplitudes of surface displacement near the tunnel change as incident wave frequency and angle increase. The effective dynamic analysis of the underground structure under an actual strong dynamic load should consider the slip effect at the lining-surrounding rock interface.
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Hu, Zheng, Shiping Sun, Oleksii Vambol y Kun Tan. "Topology optimization of laminated composite structures under harmonic force excitations". Journal of Composite Materials 56, n.º 3 (12 de noviembre de 2021): 409–20. http://dx.doi.org/10.1177/00219983211052605.
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In this paper, a topology optimization approach for the design of laminated composite structures under harmonic force excitations is proposed. A novel method is developed to calculate the harmonic response for composite laminates, which consists of two steps: firstly, based on the strain energy approach, the damping matrix model of composite laminates is established with the proportional damping assumption; then, the displacement response is calculated by the mode acceleration method The design objective of topology optimization is to minimize the displacement amplitude at the concerning point with an excitation frequency or a frequency band. An extended polynomial interpolation scheme is introduced to penalize the stiffness, damped stiffness and mass of elements. The analytical sensitivities of the objective and constraint functions to the density variables are derived in detail, and the globally convergent method of moving asymptotes is used to solve the optimization problem. Numerical examples are performed to demonstrate the effectiveness and feasibility of the proposed topology optimization method in improving the dynamic performance of laminated composite structures. The influence rules of excitation frequency and layer sequence on topologic shape are also discussed.
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Ozmutlu, Aydin. "Wave Propagation in Shear Beams Comprising Finite Periodic Lumped Masses and Resting on Elastic Foundation". Symmetry 15, n.º 1 (21 de diciembre de 2022): 17. http://dx.doi.org/10.3390/sym15010017.
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In this study, the dispersion of an infinite shear beam with a lumped mass connected at periodic distances and resting on an elastic foundation was examined. The effect of periodicity in the finite region of the lumped masses on wave propagation was investigated through a one-dimensional model. The dispersion relationship for Bragg scattering, which consists of one-dimensional periodic lumped masses, was derived using the transfer matrix method. Subsequently, to evaluate the effect of parameters such as the magnitude of the lumped mass and foundation stiffness on the dynamic response of the shear beam, several simulations were performed. The band frequency characteristics of the shear beam are demonstrated with respect to the variations in stiffness and mass. Using the wave-based approach, the effect of periodic masses on wave propagation in a finite region of an infinite beam was revealed. Periodic masses have been shown to have a positive effect on the displacement amplitude; in other words, a lumped mass barrier is effective in providing wave attenuation.
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Sonekar, Parikshit y Mira Mitra. "A wavelet-based model of one-dimensional periodic structure for wave-propagation analysis". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, n.º 2113 (14 de octubre de 2009): 263–81. http://dx.doi.org/10.1098/rspa.2009.0369.
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In this paper, a wavelet-based method is developed for wave-propagation analysis of a generic multi-coupled one-dimensional periodic structure (PS). The formulation is based on the periodicity condition and uses the dynamic stiffness matrix of the periodic cell obtained from finite-element (FE) or other numerical methods. Here, unlike its conventional definition, the dynamic stiffness matrix is obtained in the wavelet domain through a Daubechies wavelet transform. The proposed numerical scheme enables both time- and frequency-domain analysis of PSs under arbitrary loading conditions. This is in contrast to the existing Fourier-transform-based analysis that is restricted to frequency-domain study. Here, the dispersion characteristics of PSs, especially the band-gap features, are studied. In addition, the method is implemented to simulate time-domain wave response under impulse loading conditions. The two examples considered are periodically simply supported beam and periodic frame structures. In all cases, the responses obtained using the present periodic formulation are compared with the response simulated using the FE model without the periodicity assumption, and they show an exact match. This validates the accuracy of the periodic assumption to obtain the time- and frequency-domain wave responses up to a high-frequency range. Apart from this, the proposed method drastically reduces the computational cost and can be implemented for homogenization of PSs.
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Sun, Min y Jianen Chen. "Dynamics of Nonlinear Primary Oscillator with Nonlinear Energy Sink under Harmonic Excitation: Effects of Nonlinear Stiffness". Mathematical Problems in Engineering 2018 (2 de septiembre de 2018): 1–13. http://dx.doi.org/10.1155/2018/5693618.
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The dynamics of a system consisting of a nonlinear primary oscillator, subjected to a harmonic external force, and a nonlinear energy sink (NES) are investigated. The analytical solutions for the steady-state responses are obtained by the complexification-averaging method and the analytical model is confirmed by numerical simulations. The results indicate that the introduction of the NES can effectively suppress the vibrations of the primary oscillator. However, as the excitation amplitude increased, the NES may lose its efficiency within certain frequency range due to the appearance of the high response branches. Following the results analysis, it is concluded that this failure can be eliminated by reducing the nonlinear stiffness of the NES properly. The effects of nonlinear stiffness of the primary oscillator on the corresponding responses are also studied. The increase in this nonlinear stiffness can reduce the response amplitude and alter the frequency band where the high branches exist.
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Huang, Dongmei, Wei Li, Guidong Yang, Meijuan He y Hong Dang. "Vibration Analysis of a Piecewise-Smooth System with Negative Stiffness under Delayed Feedback Control". Shock and Vibration 2017 (2017): 1–14. http://dx.doi.org/10.1155/2017/3502475.
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The principal resonance of a delayed piecewise-smooth (DPWS) system with negative stiffness under narrow-band random excitation is investigated in aspects of multiscale analysis, design methodology of the controller, and response properties. The amplitude-frequency response and steady-state moments together with the corresponding stability conditions of the controlled stochastic system are derived, in which the degradation case is also under consideration. Then, from the perspective of the equivalent damping, the comparisons of the response characteristics of the controlled system to the uncontrolled system, such as the phenomenon of frequency island, are fulfilled. Furthermore, sensitivity of the system response to feedback gain and time delay is studied and interesting dynamic properties are found. Meanwhile, the classification of the steady-state solution is also discussed. To control the maximum amplitude, the feedback parameters are determined by the frequency response together with stability boundaries which must be utilized to exclude the combinations of the unstable parameters. For the case with small noise intensity, mean-square responses present the similar characteristics to what is discussed in the deterministic case.
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Nieves, M. J. y M. Brun. "Dynamic characterization of a periodic microstructured flexural system with rotational inertia". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, n.º 2156 (2 de septiembre de 2019): 20190113. http://dx.doi.org/10.1098/rsta.2019.0113.
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We consider the propagation of waves in a flexural medium composed of massless beams joining a periodic array of elements, elastically supported and possessing mass and rotational inertia. The dispersion properties of the system are determined and the influence and interplay between the dynamic parameters on the structure of the pass and stop bands are analysed in detail. We highlight the existence of three special dynamic regimes corresponding to a low stiffness in the supports and/or low rotational inertia of the masses; to a high stiffness and/or high rotational inertia regime; and to a transition one where dispersion degeneracies are encountered. In the low-frequency regime, a rigorous asymptotic analysis shows that the structure approximates a continuous Rayleigh beam on an elastic foundation. This article is part of the theme issue ‘Modelling of dynamic phenomena and localization in structured media (part 1)’.
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Goto, Adriano Mitsuo, Victor Gustavo Ramos Costa Dos Santos y José Maria Campos Dos Santos. "Band structure and defect states in acoustic phononic crystals using expansion and micro-perforated chamber mufflers". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, n.º 5 (1 de agosto de 2021): 1194–205. http://dx.doi.org/10.3397/in-2021-1775.
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The expansion and the micro-perforated chamber mufflers are acoustic silencers designed to attenuate the sound propagation at duct systems. These silencers can show interesting phononic crystals behavior when set periodically. The concept of phononic crystals still is an emerging topic in vibration and sound control. The periodic arrangement of acoustic silencers can provide a significant enhancement of the sound absorption due to the "wave filtering" property where the wave cannot propagate at certain frequency ranges, called stopbands or bandgaps. However, these properties may be affected by defects, like the break of the periodicity due to manufacturing errors. For the present work, the influence of some defects on the acoustic efficiency is investigated numerically for expansion and micro-perforated chamber mufflers. A direct and efficient approach is used to obtain the transfer and dynamic stiffness matrices. Simulated examples are used to calculate the forced response, transmission loss, and dispersion diagram, which are verified by other methods.
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Yang, Haixu, Baolei Yang, Haibiao Wang, Maohua Zhang y Songyuan Ni. "Research on Dynamic Characteristics of Joint of RC Frame Structure with NES". Sustainability 14, n.º 18 (7 de septiembre de 2022): 11229. http://dx.doi.org/10.3390/su141811229.
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The NES (nonlinear energy sink) is a new type of nonlinear tuned mass damper that is connected to the shock-absorbing main structure through strong nonlinear stiffness and viscous damping. The vibrational energy in the main structure is transferred to the NES oscillator by means of target energy transfer. A shaking table test of a 1:4 scaled RC (Reinforced Concrete) frame structure model with a new type of NES shock absorber was conducted to study the damping effect of the NES shock absorber, especially for the influence of joint strength and deformation. The NES used in this experiment has a relatively large nonlinear stiffness and a wide vibration absorption frequency band. The variation of reinforcement strains, node failure mode, and structural natural frequency of 1 story and two-layer joints of the model frame structure with NES were studied. The test results showed that NES could effectively reduce the strains of longitudinal reinforcement and stirrup in beams and columns and delay the plastic hinge development at the bottom and the top of the column. The frame model with NES installed has failures at the beam ends and shear failures at the nodes, realizing the seismic mechanism of solid columns and weak beams. Compared with ordinary seismic structures, the NES can effectively reduce the shear stress of concrete at the joints and alleviate the shear failure of joints. The final failure of the NES shock absorbing structure was the yielding of the steel bars at the bottom of the column and the crushing of the concrete at the foot of the column, and the connection between the column foot and the backplane became loose simultaneously. The decreasing rate of the vibration frequency declined due to the NES with varied broadband absorbing capability. It can be seen that the NES shock absorber not only has a good effect on reducing the seismic response of the structure, but more importantly, the damage of the structural nodes is greatly reduced, and therefore, the seismic capacity of the structure improved.
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RAWES, M. L. y O. O. A. ONI. "Swan-Neck Deformity as a Complication of the Agee Technique". Journal of Hand Surgery 20, n.º 2 (abril de 1995): 255–57. http://dx.doi.org/10.1016/s0266-7681(05)80065-8.
Texto completoResumen
Unstable dorsal fracture dislocations of the PIP joint of a finger commonly result in joint stiffness following immobilization or open reduction and internal fixation (Green and Rowland, 1984). The Agee dynamic external fixator, or force couple splint (Agee, 1978Agee, 1987), was introduced in an attempt to avoid this complication and maintains a concentric reduction whilst allowing a full range of joint movement. The splint is constructed from three Kirschner wires and is activated by a single rubber band. A force couple is created across the proximal interphalangeal joint levering the base of the middle phalanx towards the palm whilst simultaneously lifting the distal end of the proximal phalanx dorsally to restore joint reduction. However, this technique is not without complications (Agee, 1987). We report a swan-neck deformity resulting from this treatment.