Vibration, Structural Engineering and Measurement II

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Authors: Hua Bing Wen, Yan Yan Zuo, Zi Long Peng, Hua Shen
Abstract: A ring-stiffened cylindrical shell of experimental model with four equipment support pedestals was designed. The effect of vibr-ation transmission characteristics of the ring-stiffened cylindri-cal shell by the internal base structural style and layout positi-on was researched. The original mechanical admittances of su-pport pedestals were analyzed. Taking mechanical vibration ve-locity mobility as evaluation index, the vibration transmission characteristics from pedestals to the surface of ring-stiffened cylindrical shell have been experimentally studied, the mecha-nical admittance distribution pattern of the cylindrical shell sur-face has been indicated. The difference of mechanical admitt-ances at different positions is large at low frequencies, which is influenced by the mode shape of vibration of the shell struc-ture. However, the difference of mechanical admittances of dif-ferent positions is little at high frequencies, and the vibration transmission characteristics from pedestals to cylindrical shell can be indicated by the concept of spatial equivalent mecha-nical mobility.
Authors: Xiang Bi An, Da Wei Li, Hu Wang, Long Wang
Abstract: The performance of the rotor of the electric eddy current dynamometer has a great influence on the capability of the dynamometer. The stiffness and damping of the rotor can be obtained by analyzing its motion equation. And the critical speed can be achieved by getting the natural frequency and the vibration through ADAMS based on the theory of flexibility. Based on the machine design handbook, some proofs were provided by the conclusion that the speed of the rotor should be the range of the different critical speed of the modal in order to assure the safety and high efficiency of the dynamometer. Focused on the need for the design of the rotor, this method which solves the difficulties of the intensive calculation in the design and optimization of the dynamometer’s rotor is exact and effective.
Authors: Wei Gao, Chun Li, Quan Liu, Yu Chen
Abstract: The blade is an important component of the wind turbine, which is essential to proper blade design. This paper summarizes the process of the blade design, the selection of the design parameters, and the design of megawatt-scale blades. The finite element method was applied on the model generated in 3D graphics software. After selecting the material parameters of the blade, the modal analyses under prestresses were conducted so as to determine the modal shapes, frequency, maximum deflection and maximum stress at different orders of vibration. Thus the results were compared with those of modal analysis under the non-prestressed condition. Thus the conclusion on the effect of gravity and rotation-prestress on the modal frequency, maximum deflection and maximum stress in modal analysis will be drawn.
Authors: Jie Wang, Dong Xu Li, Jian Ping Jiang
Abstract: This paper investigates the modal characteristics of a coilable mast for space mission applications. Finite element models are established for characterizing the coilable mast. The simplification of joints between longerons and batten frames and the pre-tension in cables are carefully considered. A parametric modal analysis is performed with considering the following factors, the joint model in the truss, the pre-tension in cables, elements selected for longerons and battens, the mass attached to the top of the mast. Research results show that the natural frequencies of the coilable mast are sensitive to the selected elements and the attached mass. The pre-tension level in cables and the precision degree of the joint model have little effect on natural frequencies. The regularity expressed in the parametric modal analysis is useful for designers and engineers.
Authors: Min Zheng, Fan Shen
Abstract: Modal identification methods based on the Hilbert Transform are applied to identify modal parameters of time-varying system using impulse response time histories. First, the response data are decomposed into modal responses through the empirical mode decomposition (EMD). Then, the Hilbert transform is applied to each modal response to obtain the instantaneous frequencies. The applications of the proposed methods are illustrated using a 3 degree-of-freedom (DOF) systems with time-varying dynamic characteristics. Numerical simulation results demonstrate that the proposed system identification methods yield good results.
Authors: Xiang Zheng, Jing Lin Yao, Jun Ling Wang
Abstract: High-speed press is pressure processing equipment that can form parts in high-speed operation conditions. In this paper, in order to improve machining accuracy, analyze ant-vibration performance using finite element method; analyze vibration effect of complete machine and combination machine with steel and cast iron material respectively. Observe vibration reduction in different screw pre-tightening force; Select the best body structure to do modal analysis. If the experimental results and the FEM results are the same, state the validity of the model. In dynamic characteristics simulation analysis, it’s more accurate when considering the effect of material and pre-tightening force.
Authors: Hai Dong Guo, Shun Ming Li, Yuan Yuan Zhang, Xing Xing Wang, Sai Ma
Abstract: For weak vibration signal with strong noise, a new kind of weak vibration signal detection method was proposed in this paper. Based on the redundancy reducing capability and the uncertain amplitude of independent component analysis, virtual noise was introduced to extend the dimension of original observed signal after we analyzed the prior features of noises in observed signal. Then extended signals were processed to get the independent source signals by applying to blind source separation (BSS). Thus, the noise embedded in observed signal was removed and characteristics of weak vibration signal were obtained successfully. Through the theoretical analysis and the simulation, the introduced method of this paper was checked to be available and then it was applied to faults analysis of rotor misalignment successfully. Finally, we made a conclusion that this method had great application value for the extraction of weak vibration signal.
Authors: Yong Fa Nie, Hai Chao Zhu, Rong Fu Mao
Abstract: To effectively reduce radiation noise of the structures, the information detailed of the acoustic field is required. An approach of acoustic field reconstruction based mono-poles array modes is developed. The acoustic source is expressed as the form of some mono-poles array superposition which is defined as mono-poles array radiation mode. The amplitudes of these mono-poles are equal and their phase angles are in phase or out of phase in each array form. The amplitudes of mono-poles array modes are obtained by means of the complex pressures measured in near field, and then the whole acoustic field can be reconstructed. Feasibility of this approach is verified through a numerical example of a single-point harmonic excited and simple supported plate and the error analysis shows that the near field reconstruction result is accurate and the far field reconstruction result is more accurate.
Authors: Dao Lin Wang
Abstract: Chatter occurring in cutting process is an unstable vibration phenomenon, which affects the machining accuracy and the production efficiency, studied by many researchers for dozens of years. By analyzing the relationship with energy feedback and energy consumption on the machine structure system, this paper revealed that the mechanism of vibration reduction by variable speed cutting, qualitatively analyzed the obvious effect in suppressing cutting chatter by the continuous change of spindle speed. According to the principle of vibration, it established mathematical model of vibration reduction by variable speed cutting. Calculate the spindle phase difference angle within a week and each vibration after a week, thus get variable amplitude values after the start of each cycle. And further example analyzed the advantage of variable speed in suppressing cutting chatter.
Authors: Gong Yu Pan, Ying Zhang
Abstract: The ride comfort is one of the most important performances of the ambulance. In order to avoid patients' illness or injury to deteriorate during the transportation, the ambulance is required to hold smooth motion and high speed. Therefore, it is necessary to develop stretcher vibration isolation system to improve ambulance ride comfort. In this paper, a mathematic model of six degree freedom ambulance-stretcher-occupant system is established. Based on the theory of linear quadratic optimal control, the linear quadratic regulator (LQR) controller of active ambulance stretcher is designed. The simulation results indicate that the active system equipped with the optimal controller has better vibration reduction perfomance on vertical acceleration and pitch angular acceleration of the ambulance stretcher.

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