Papers by Keyword: Power Spectral Density (PSD)

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.

Abstract: Understanding the characteristics of stochastic loading is the premise and foundation for structure analysis. Traditional amplitude spectrum and power spectral density (PSD) method based on Fourier transform (FT) has limitation, that is, it loses any information with time and can not reflect the non-stationary characteristics of stochastic loading. Wavelet transform possesses assembling ability in both time and frequency domain,and it possess stronger ability of analyzing non-stationary signal. In this paper, the method of estimating PSD and time-dependent PSD of stochastic loading using wavelet transform is researched. The calculating process is programmed and the method is validated by a numerical example. The analysis result of example indicates that the method presented in this paper is feasible.

Abstract: In this paper, in order to study the effect of nonlinear suspension system, a nonlinear dynamic model considering nonlinearity of suspension is built and another model with the respective of linear suspension system is developed which is for comparison. Then the dynamic equation of the model is set up. The simulation is accomplished through MATLAB/SIMULINK. It is found that the band-limited white noise module can simulate the power spectral density of road surface well. Finally, numerical simulation results indicates that an appropriate nonlinear suspension model fits reality better than a linear one and using relative control can provide the best ride comfort.

Abstract: A significant source of noise and vibration in high speed machine tool spindle is bearing induced vibration, which is caused by geometrical characteristics and interactions between rolling members with surface irregularities. In this paper, analytical approach was proposed to calculate the bearing internal load distribution of spindle, with consideration of the operating conditions. The influences of operating conditions to internal load distribution, contact angles were analyzed. Furthermore, the estimation of power spectral density (PSD) method was used to analyze determination of bearing frequencies. The bearing preload of machine tool spindle was estimated according to the change of ball bearing frequencies. Experiments were carried out in a spindle bearing test rig to verify the validity of the presented analytical method. The method described in this paper can achieve the estimation for bearing preload of machine tool spindle.

Abstract: To get the certain response of vehicle during the driving process, it’s necessary to measure the road irregularities. Existing method of gauging the roughness is based on physical measurements and the instrument is installed under the vehicle, which is expensive and will affect the vehicle dynamic responses. This paper shows an easier method to estimate the road roughness by measuring and calculating the power spectral density (PSD) of unsprung mass accelerations. This approach is possible due to the relationship between these two via a transfer function. By comparing the power spectral densities of estimated road and the standard classes, we can classify the current road classes easily. Besides, this paper also shows that it’s feasible to estimate the road profile by calculating the PSD of unsprung mass accelerations directly.

Abstract: It’s important to identify structural modal parameters, especially, accurate modal shapes in time domain for accurate damage identification and health monitoring of structures. The natural excitation vibration is used to identify the structural modal parameters. The power spectral density curve has obtained according to the measuring point vibration time domain curve, and then natural frequencies and vibration value are determined by the curve peak. The reference point is taken for the vibration unit values to normalize other modal shapes. The modal shapes are calculated using the phase measuring point relative to a reference point. After the finite element analysis and calculation, and the measured modal is compared with it. The results show that the dynamic performance of the bridge is reliable because the measurement method and the finite element method are basically consistent. The damping ratio of the bridge is larger dispersion but the average damping ratio is in line with the rules and scope of the cable-stayed bridge.

Abstract: Program critical, high cost and delicate space hardware like satellite built with pressurized tanks, sensitive optics, delicate electronics and hazardous chemicals need protection from various environmental hazards during transportation. These environmental hazards include shock, vibration and handling loads and climatic hazards such as temperature, humidity, rain, dust due to harsh ambient atmospheric conditions etc. The Satellite Transportation System (STS) is equipped with adequate protection and monitoring system. The environmental data acquisition system is used to monitor the environmental conditions of satellite during transportation. This paper describes the data acquisition system used for quantitative validation of shock and vibration attenuation system and temperature and humidity control system. The acquired data are processed and interpreted to express the environmental conditions during various phases of development such as road survey analysis, performance validation and refinement of design for the shock and vibration isolation system of trucks and STS. Further, these data are used for the post-transportation health assessment of satellite that are vital to minimize post transportation tests on satellite.

Abstract: The signal can be divided into a number of intrinsic mode components (IMF) through local wave decomposition. The decomposition process is equivalent to the adaptive filter for signal. The frequencies of each IMF have reduced with the decomposition order. This paper established judgment criteria of signal, noise and pseudo component based on the local wave decomposition, used the characteristics of cross-correlation coefficient and autocorrelation sequence, combined with the power spectral density. The dominant mode function was extracted effectively and the final effects are used gear reducer in the JZQ250 of fault rolling bearing inner ring. It provides a new method for non-stationary signal adaptive noise reduction and fault diagnosis of rotating machinery.

Abstract: Due to the precision of MEMS gyroscope is currently low level, even in low precision dynamic attitude measurement system, its error is also need to be estimated and compensated. Random drift is the one of the most important factor affects MEMS Gyro’s precision. At the same time, it is a non-stationary, weak non-linear and time-variant random signal. For improving precision of gyro and reducing effects of random drift, this paper used gray GM(1, 1) model to extract established tendency signal, and used power spectral density (PSD) to identify and extract the hidden periodic weak signal, then used ARMA method to model gyro’s random drift. As the example of LCG50 MEMS gyro, the simulation experimental results show that using this method can reduce the random drift and enhance precision of gyro.

Abstract: 9 models of tall buildings with different rectangular cross-sections are tested in a wind tunnel. After processing and analyzing the measured data of fluctuating pressure on the models, the effects of models’height, aspect ratio, side ratio on the power spectra of torsional wind loads are studied. New formulas of power spectral density of torsional wind loads are proposed by curve fitting method. The applicability of the formulas has been verified by the results from the wind tunnel test.