Vibration, Structural Engineering and Measurement II

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Authors: Yan Huang, Song Lin He
Abstract: The cycle formula of undamped free vibration of odd power oscillators has been gotten by theoretical analysis. The formula shows that the cycle is related to the initial conditions. The numerical experiments reveal that there are three states such as damped oscillation, critical damped oscillation and overdamped oscillation while an odd power oscillator moves in linear damping force. These situations are same as that of a linear oscillator. Unlike the linear oscillator, the critical damping constant of an odd power oscillator is related to the initial conditions. The quantitative expression of the critical damping constant changing with system parameters and initial conditions has been obtained. By analyzing of numerical experimental data, the exponential decay law of the amplitude of an odd power oscillator which moves in damped state has been discovered.
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Authors: Zhong Jun Yin, Yan Shu Cao, Tian Han, Xiao Song Wang
Abstract: The main purpose of the numerical simulation that described in this paper is to investigate the damping influence on vortex-induced vibration (VIV) system. By considering different damping ratios, the 1-dof vortex-induced vibration of a rigid cylinder with low mass ratio is investigated numerically by the RANS solver combined with SST turbulence model. Comparing of the simulation results that obtained under low damping ratio by J.S. Wang and experimental results which carried out by Williamson and Govardhan, it indicates that the computing model in this paper is reliable. In addition, by using our model we analyze the vibration under the other two damping ratios, including the corresponding amplitude response and frequency response. We observed significant frequency locking phenomenon under different damping conditions, and locking region decreases with increasing damping.
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Authors: Hong Lin, Chang Li Zhou, Jun Shi, Zhi Hua Feng
Abstract: Axially moving fabric can be met in many textile devices. In most cases, the transverse vibrations of fabric can cause a series of negative influents to the product. In this paper, the transverse vibration of axially accelerating moving fabric, which is excited by velocity fluctuations, is investigated by experimental method. The harmonic varying velocity is achieved through a brushless DC motor controlled by PWM technology based on the embedded microcontroller LPC1768. An inductive non-contact displacement sensor is used to measure transversal vibration of fabric. The motor speed is measured by a photoelectric encoder. The experimental data is processed by measurement platform based on Labview and the analysis is given. Laboratory measurements demonstrate the effect of velocity fluctuations on transverse vibration of fabric, particularly near the parametric resonance region.
150
Authors: Jun Li, Chu Sheng Liu, Feng Li, Zhong Xian Wang
Abstract: Structural wave propagation in beam structures can lead to unwanted noise transmission and radiation. Dissipation effects of the multiple absorbers have been proved. This paper presents a model of flexible beam with complex boundary conditions and this model with multiple attaching absorbers which are used to dissipate energy of main structure. The beam model are formulated by linear Lagrange equation and discretized by the Ritz method and the model with multiple absorbers is introduced by substructure method. Consequently, the mass matrix and stiffness matrix are obtained and numerical simulation is processed. Natural frequencies with corresponding modal mode of are obtained. Comparing the results between two models, the absorbers can enhance the natural frequencies effectively and the quantities of absorbers agree with the orders of frequencies and corresponding modes.
154
Authors: Hui Xue Dang, Feng Li Yang, Xin Min Li, Jing Bo Yang
Abstract: Accounting for the disastrous phenomena of ice-accreted conductor galloping, wind tunnel tests of LGJ630/45 conductor accreted with crescent-shaped ice are conducted. Based on the test results, conductor galloping is simulated by employing the PCL language of ANSYS commercial software package and then the influences of span lengths as well as free-stream speeds on galloping characteristics are studied. The results indicate that, conductor galloping consists several different frequency components. With the increase of span length, galloping energy moves from low-frequency component to its high-frequency counterpart, and finally high-frequency component dominates the galloping phenomenon. And with the movement of energy, galloping traces transforms from ellipse to that similar to a butterfly. With the increase of span length, the maximum cable tension first increases, next decreases sharply, and then increases again.
158
Authors: Shi Liu, Cong Wang, Bing Li, Chang Chen, Dan Mei Xie
Abstract: To calculate a shaftings natural frequency of torsional vibration is one of the most important tasks in turbo-generators design, manufacture and frequency adjusting process. The sensitivity analysis of shafting structural parameters impact on the torsional vibration characteristics has important significance in reducing the amplitude of torsional vibration and ensuring the turbo-generators safe operation. In this paper, a 1000MW USC unit was taken as a research object to analyze the shaftings sensitivity to moment of inertia.
162
Authors: Ya Nan Zhang, Tadaatsu Satomi, Wen Si
Abstract: Aerostatic guideway is an essential sub-system for high-accuracy measurement. As compressible air is used for suspension, several problems arise aside of its other advantages. The most important aspect that should be taken into consideration is self-excited vibration activated by inner or/and outer environments. This paper discusses how the orifice layouts and the orifice diameter affect the self-excited vibration of the aerostatic guideway, or two-dimension x-y stage as a whole. Theoretical formulas for flow coefficient of orifices are obtained and experiment of differential pressure test is conducted. Both theoretical and experimental approaches of aerostatic guideway design and characteristics of vibration attenuation are proposed in this research. The results show that by optimizing orifice diameter and orifice layouts, good effect on reduction of self-excited vibration can be achieved, with the time of vibration attenuation reduced from 1.8s to 0.9s.
166
Authors: Pei Pei Ge, Gui Lan Yu
Abstract: By using the finite element method, the band structures of the periodic hollow cylinder sandwich panels are investigated, and the influences of the material and geometrical parameters on the band gap are discussed in detail. The results show that The Young's modulus of panel and the coated layer have the greatest influences on the band gap of binary periodic hollow steel cylinder sandwich panels. The smaller the Young's modulus, the lower the frequency band gap. The material and geometrical parameters of the core have important influences on the lower edges of the band gap. Thicker and higher hollow steel cylinder with large density is favorable to gain a wide low-frequency band gap. The work presented will provide a theoretical guidance in the vibration isolation research.
172
Authors: Jing Zhang, Bin Zhang, Ying Hua Liu, Long Qi Wang, Yu Bin Wu
Abstract: Field tests were carried out on Sihui metro depot of Beijing metro line 1 and its superstructure. The acceleration time history of sleepers and floors of the building was obtained, and the waves-propagation laws of building were studied through the tests. Test analysis shows that the structure vibrations show zigzag tendencies ascends with the height of the building. Based on current situation of Sihui metro depot, a metro-soil-building 3-dimensional finite element model is established on ANSYS. By using actual acceleration of sleepers as inputs, the dynamic responds rule of the superstructure is obtained. Compared calculation results with the experimental results, the given numerical model can predict the vibrations of the building induced by moving trains quite well. This method can provide guidance and technical support for future development of superstructure.
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Authors: Amir Reza Askari, Masoud Tahani
Abstract: In this paper, combination of the Galerkin decomposition procedure and homotopy analysis method (HAM) is utilized to derive analytical approximate solutions for nonlinear vibration of a fully clamped nanobeam used in the applications of nano-electromechanical systems (NEMS), under the effect of van der Waals (vdW) force. The model accounts for the inherent nonlinearity of distributed vdW force and geometrical nonlinearity of von Kármán mid-plane stretching as well as the influence of applied axial loading. The HAM is also optimized to accelerate the convergence of approximate solution. The present results are found to agree well with those obtained by the fourth-order Runge-Kutta method.
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