Papers by Keyword: Random Vibration

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Authors: Jun Liao, Da Fu Xu, Bing Yan Jiang
Abstract: A numerical procedure to compute the mean and covariance matrix of the random response of stochastic structures modeled by FE models is presented. With the help of Gegenbauer polynomial approximation, the calculation of dynamic response of random parameter system is transformed into an equivalent certainty expansion order system's response calculation. Non-stationary, non-white, non-zero means, Gaussian distributed excitation is represented by the well-known Karhunen-Loeve (K-L) expansion. The Precise Integration Method is employed to obtain the K-L decomposition of the non-stationary filtered white noise random excitation. A very accurate result is obtained by a small amount of K-L vectors with the vector characteristic of energy concentration, especially for the small band-width excitation. Correctness of the method is verified by the simulations.
Authors: Mehrisadat Makki Alamdari, Jian Chun Li, Bijan Samali
Abstract: This paper presents a novel damage localization method based on the measured Frequency Response Functions (FRFs) without demanding any previous data records of the structure in its healthy state. The main innovation of this study starts with reconstruction of FRFs curvature to develop spatial shape functions. It is demonstrated that reconstructed data significantly magnifies the influence of low-frequency spectra in damage detection procedure which is considered the milestone of this approach as excitation of the higher frequencies is not easy to obtain in most practical applications. The modified curvature data in all measured frequencies and locations is interpreted as a two dimensional image and then processed by employing 2-D discrete wavelet transform to detect any abrupt variation at damage site. Level one wavelet decomposition is utilised to provide the finest detail coefficients. It is illustrated that this approach presents a more recognizable pattern at damage site in all measured frequencies. The pattern can be described by a horizontal line parallel to the frequency spectra in 2-D image. Hence, the horizontal detail coefficients are utilised to detect this pattern as they are more sensitive to perturbation with orientation parallel to horizontal axis in the image. The main contribution of this approach lies in the fact that the proposed technique is able to detect the structural damage in all measured frequencies and the effectiveness of the method is independent of the excitation location. Moreover, the results provide a better visualisation at damage site which other FRF-based damage detection methods could not obtain. Applying broadband FRF data in this approach and the fact that there is no need for data from the healthy state of the structure are other advantages accompanying this method. The robustness of the proposed damage identification method was examined with various damage conditions in both single and multiple states. Moreover, the feasibility of the method was verified in presence of practical uncertainties such as noise using extensive numerical simulations. It was demonstrated that the proposed method is particularly attractive for practical applications as it opens an opportunity for online monitoring of the structural integrity without demanding any previous data records of the structure.
Authors: Xin Min Guo, Wei Min Kang, Jie Zhao
Abstract: The random vibration will cause a severe decline of the dynamic imaging quality if the seeker’s optomechanical system has not been properly optimized. Firstly, based on the integrated optomechanical analyzing method and the requirement of the seeker, an optimization approach utilizing the numerical simulation is presented. Then an optimization design of the support position, in which the optical modulation transfer function is as the optimal target, was processed under the random vibration with high-accelerator in a wide frequency range (10 GRMS). The simulation result shows that the optimum structure has a better performance than the other available structures in dynamic imaging quality: the degradation of optical modulation transfer function is less than 0.5% in central field of view and about 8.25% in the full relative field of view.
Authors: Xiao Guang Yu, L. Yang
Abstract: Through the cracking failure analysis of dump truck frame with large electric wheel, the static and dynamic frame analysis of performance evaluation are conducted by the finite element analysis method. From the strength and stiffness analysis frame structure in the weak links, it is easy to find out crack the parts and the reasons with frame, and through the modal analysis and random vibration and fatigue strength analysis the danger frequency of the frame induced by road encourage is obtained, which can prevent the occurrence of frame cracks and provide a foundation for further optimization of the frame.
Authors: Hong Sen Xie, Peng Zhou, Jun Gan Wei, Ding Wang
Abstract: In order to provide precise guidance for the landing of carrier-based aircrafts, the phased array antenna and the principle of time reference scanning beam are used in the shipborne MLS. The phased array antenna is installed under the flight deck of the ship stern, so the vibration could change the relative position of antenna elements, which will cause the navigation error. In this paper, through the establishment of antenna array pattern and phased array antenna vibration error model, an error calibration algorithm is proposed after the simulation of phased array antenna’s random vibration effects on the guiding performance of shipborne MLS in three axes. Computer simulations show that the calibration algorithm could improve the guiding performance of shipborne MLS.
Authors: Qi Gong, Yan Li, Duo Su
Abstract: Aimed at fatigue damage in the antenna structure caused by large amplitude vibration with long time fluctuating wind loads, this paper use the harmonic synthesis method to transform power spectrum of Davenport fluctuating wind to fluctuating wind speed time series based on time domain. Then comprehensively considering the surface roughness coefficient, wind pressure coefficient of variation with height, wind vibration coefficient in Beijing area ,it transforms the fluctuating wind speed into the fluctuating wind pressure curve, takes the structural dynamics simulation and is obtained the dynamic response of the antenna structure in turbulent wind Loads; By the method of rain-flow counting , the fatigue life is analyzed with the statistics for the dangerous location of the antenna structure coursed of fatigue stress with time.
Authors: Xiao Jing Li
Abstract: The random vibration of simply-supported beam is simplified of the random vibration of the SDOF theory ,the paper analyse its random response. We get the displacement power spectral density function the velocity power spectral density and the acceleration power spectral density function of the maximum displacement point. The same example is calculated by ANSYS, it also get the same results.It proved that using the finite element analysis software ANSYS to anlaysis the random vibration of the simply-supported beam has advantages of fast speedhigh precisioneasy stepsthe small error and so on..
Authors: Xiang Yu Hao, Ming Li, Xue Feng Han, Hong Guang Jia
Abstract: In order to improve its precision in dynamic environment, a Kalman filter was designed. Firstly, two sets of random drift data of MEMS gyro were respectively analysed, and it was found that the variance of random drift under random vibration significantly increased and its mean also changed. Then calculation results show that attitude angle error under random vibration is 2.6°, while in the static test it is 0.25°. Analysis on the characteristics of random drift was carried out, and it is found that it can be treated as stable, normally distributed random signal. Finally, a corresponding Kalman filter was designed. The results indicated that after filtering the variance of random drift is reduced to 0.0282, 26.4% of pre-filtering and the attitude angle error is reduced to 1.5°, 57.7% of pre-filtering. The above method can effectively compensate for the attitude angle error of MEMS gyro caused by random vibration. This study can be a reference to the application of low-cost MEMS gyro in aircraft navigation.
Authors: C. Li, S. Hu, J. Li
Abstract: This paper presents the application of modal analysis and parameter identification using data of random vibration test to a cylinder structure. It is deduced that the impulse response function can be substituted by the cross-correlation function computed directly from the response-only data based on the white noise excitation or broadband input. So the modal parameter identification can be done by the least squares complex exponential (LSCE) method. And the modal parameters are obtained from the random vibration test data by the complex exponential method. Compared with the results of traditional modal test, the results of random vibration test are proved to be correct, and also the feasibility of this idea is proved well.
Authors: Yi Li, Yi Qiang Xiang, Bao Chun Chen
Abstract: For the reliable assessment of bridge health and safety conditions, it is crucial to identify fundamental frequencies of suspender real time and automatically from random vibration signal that is weak and interfered with noise when suspender tension is measured online by frequency method. According to the characteristics of vibration signal spectrum, auto-power spectrum combined with autocorrelation function method which result was periodic distribution of spectral information in frequency domain. Plus from the spectrum the resonant peak of suspender was highlighted to reduce the noise disturbance which helped identify fundamental frequency and improved identification effect and result precision. In addition a field experiment in a tied arch bridge was carried out to analyze the collected vibration data. The practical application shows that this kind of measurement method is feasible and useful.
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