Papers by Keyword: Damping Coefficient

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Authors: Wan Fu Xu, Xiu Hua Li, Gang Ma
Abstract: By using dual number, the dynamic property of gas-lubricated thrust bearings or non-contacting face seals is analyzed in the small perturbation approximation, then an essential conclude, that the perturbation dynamic Reynolds’ equations independently of its whirl frequency, is advanced. According to this, the calculation of the stiffness and damping coefficients independently of system motion equations of bearings and seals is expedited.
Authors: Yu Feng Luo, Yuan Shan Li, Xu Chen
Abstract: This papers deals with fast solving method of natural frequency and vibration isolation coefficient of multiple degrees of freedom vibration isolation system. In the foundation of a mathematical model of vibration motion differential equation, a new state space method is derived and presented. Through transforming the vibration isolation differential equations into the state space equations, it is convenient to facilitate the solution of vibration isolation coefficient of vibration isolation system of multiple degrees of freedom with damping, by using the state space method and the MATLAB/Simulink module. Simulation results showed the result is consistent with the theory result. Simulation results also showed that with the help of damping, the maximal vibration isolation coefficient of x direction is lowered from 90 to 3.2 in the 5.31Hz, which eliminate the resonance phenomenon. In y and z direction, the maximal vibration isolation coefficient is also decreased from 78 to 2.4 and from 210 to 2.35. The state space method can find further applications on the selection of vibration isolation system and the evaluation of vibration isolation efficiency.
Authors: Xiao Chuang Zhu, Wei Guo Gao, Teng Liu, Sheng Hui Zhao, Guan Wei Zhang, Da Wei Zhang
Abstract: Hydrostatic guideway is widely used in heavy and ultra-precision machine tools due to their high bearing capacity, low coefficient of friction and high capacity of precision-remaining. So it is necessary to carry on theoretical research on its dynamic characteristics. Firstly, the oil-film damping coefficient of closed hydrostatic guideway throttled by capillary is derived. Secondly, a new dynamic mathematical model, considering the oil damping effect, the extrusion effect and the volume effect, of the closed hydrostatic guideway is proposed. Thirdly, the frequency characteristics and step characteristics of it are simulated in Matlab Simulink through the transfer function. Finally, the paper investigates the influence of damping coefficient, the oil pressure, volume effect and the initial oil-film thickness on the dynamic characteristics of closed hydrostatic guideway throttled by capillary.
Authors: Jun Jie Chang, Xing Guo Wang, Ying Chun Shan, Jiu Jun Xu
Abstract: The capability of Rayleigh wave to be used as a tool for the evaluation of CVD DLC coating layer has been presented in this paper. One uncoated specimen and two CVD DLC coated specimen has been used. The dispersion curves of group velocity of leaky Rayleigh wave were measured. The dispersion curve of uncoated specimen shows that the group velocities were same at different frequencies, as there is no coating layer affecting the group velocities at different frequencies. There are distinct different between ‘sound’ specimen and ‘bad bonding’ specimen as the ‘bad bonding’ specimen show unevenness on its dispersion curve.
Authors: P. Gadaud, S. Pautrot
Abstract: Young’s modulus and damping coefficient measurements performed on various materials by means of dynamic resonant method in free bending mode, exhibit transient effects during first heating, while there is no obvious structural evolution. It has been more particularly observed on sintered and rolled bulk materials as well as coated materials. It can be indubitably related to the release of internal stresses introduced during elaboration. The measurement of the resonance frequency shift associated to this release and the development of a model of beam vibration integrating the presence of internal stresses allow the estimation of the initial level of internal stresses. The mechanical model comes from the application of Hamilton principle minimizing potential and kinetic energies described by the Lagrangian of the vibrating system. Then, the effect of internal stresses is introduced, based on a model of pre-stressed vibrating beam found in literature. Three experimental illustrations are given: a HIP (high isostatic pressure) sintered MAX phase with compression internal stresses, a 70 % rolled Co base steel with very high elastic limit and anisotropic plane tension stresses and a platinum aluminide coating deposited on AM1 superalloy.
Authors: I. Herrera, H. Su, Stefan Kaczmarczyk
Abstract: Modelling the dynamic performance of an elevator car system represents a complex task and forms an important step in the elevator system design procedure. The need to consider the behaviour of passengers travelling in the car complicates the procedure further. This paper presents an original approach to identify the stiffness and damping characteristics of an elevator car system. A simplified model is developed and the experimental rig with a rectangular elevator platform fixed on the top of four silent blocks attached to a shaker is setup. The transmissibility measurements are carried out with a harmonic excitation applied first to a platform with no passenger load and then to the platform with one passenger within the frequency range of 1 – 20 Hz. A single person standing on the platform is employed in order to assess the passenger’s contribution to the dynamic behaviour of the elevator car system. The curve fitting technique implemented in MATLAB is used to determine the damping and stiffness coefficients both for the empty car system and the car-passenger system. Investigation on the tolerances for both parameters is carried out. An approach to simplify the experimental procedure and to reduce the number of individual tests is proposed.
Authors: Hong Tan, Jian Gao, Shi Song Li, Zheng Kun Li
Abstract: Damping coefficient is an important parameter in the system of swinging balance. There are various factors, such as knife hysteresis and the air resistance around the swinging balance, which influence the damping coefficient during the swing process. The energy of the balance and the amplitude of the oscillation will decay with time. It will stop swinging in numerable period. This damping phenomenon prevents us from measuring the oscillation period. So we need to analyse and study the damping coefficient. In this paper, we firstly analyse the working principle of the swinging balance, and then we measure the damping coefficient in different driving frequencies using experimental method and spectrum analysis. In the end, we get the evolution of damping coefficient under different driving frequencies.
Authors: Tadashi Shioya, Toshikatsu Asahina
Abstract: Fracture toughness, stress-strain relation and the damping characteristics of bamboo are investigated. The fracture toughness of bamboo in tearing along the longitudinal direction is measured by the use of newly devised apparatus in which the crack opening displacement is controlled in a constant velocity and a quasi-steady extension of the crack is maintained. The stress-strain relation of bamboo is examined in a reversible elastic range using a conventional tensile test in the longitudinal direction. Repeated tensile loading tests show that the stress-strain relation has a strong non-linear hysteresis and that it converses to a steady loop. The damping of bamboo is measured by the use of inverted torsion pendulum apparatus. The specimen is taken so that damping of twisting longitudinal bar is measured. The damping coefficient of bamboo is much larger than that of metals. The mechanical properties of bamboo are examined in terms of water concentration and fiber density in the bamboo.
Authors: Shinji Shimizu, Yoshiaki Kabaya, Haruhisa Sakamoto, Kenichi Yamashita
Abstract: In this study, we examined influencing factors on the identification accuracy and improving method of the identification accuracy. As a result, the influence of the condition of the dynamic characteristic values is large and these values should correspond to the tangential and vertical directions. The influence of treating dynamic characteristic parameters of the same plural joints is also large, and then the parameters of the same plural joints should have the same value. In addition, the tangential dynamic characteristics should be identified from the vibration mode which has large tangential relative displacement between the joint interfaces. Similarly, the vertical one should be identified from the vibration mode which has large vertical relative displacement between the joint interfaces. Finally, the identification accuracy can be improved greatly by considering these influences.
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