Qinzhong Shi

Reduction of Noise Inside a Cavity by Piezoelectric Actuators

A new analytical model is developed for the reduction of noise inside a cavity using distributed piezoelectric actuators. A modal coupling method is used to establish the governing equations of motion of the fully coupled acoustics-structure-piezoelectric patch system. Two performance functions relating global and local optimal control of sound pressure levels (SPL) respectively are applied to obtain the control laws. The discussions on associated control mechanism show that both the mechanisms of modal amplitude suppression and modal rearrangement may sometimes coexist in the implementation of optimal noise control.

Optimal Estimation of Dynamic Loads for Multiple-Input System

An optimal method is developed to estimate the dynamic loads for systems subjected to multiple inputs. The method focuses on minimizing the ensemble mean square error of the estimation. First, the inverse system analysis technique is employed to establish the error estimation equation. Then, by applying the noncausal Wiener filtering theory, the optimal estimator of dynamic loads is derived out. Numerical simulation work demonstrates that the method is of a good ability in suppressing the influence of measurement noises on estimation accuracy. Meanwhile, the simulating calculation of load estimation by a conventional method is also performed and the comparison of both results shows that the method proposed in this paper is rather effective and practicable for dynamic load estimation.

STRUCTURAL OPTIMIZATION BASED ON HOLOGRAPHIC NEURAL NETWORK AND ITS EXTRAPOLATION

A great number of functional evaluations may be required until convergence in the process of optimization, especially for the multidisciplinary optimization. Although approximation models constructed by the response surface methodology, which may greatly save the function evaluation, is usually used to conduct a trade off model for optimal designs, it is thought that the design accuracy may be dependent on the type of activation functions and the design region of interest. In this paper, techniques to search the region of interest containing the global optimal design by random seeds, and techniques for finding more accurate approximation using Holographic Neural Network (HNN) is investigated. Furthermore, the mapping method of extrapolation is proposed to make the technique available to general application in structural optimization and the formula to estimate the necessary function evaluations for functions under certain condition is presented. Application examples show that HNN may be expected an potential activate and feasible surface functions in response surface methodology than the polynomials in function approximations. Finally, the real design example of a vehicle component crashworthiness is used to show the effectiveness of the proposed method.

Optimal design method to automobile problems using holographic neural network’s approximation

A great number of functional evaluations may be required until reaching the convergence in the process of optimization. Although the approximation models constructed by the response surface methodology are usually used to get the optimal designs, it is thought that the design accuracy is dependent on the type of activate functions and the design region of interest. In this paper, techniques to search all the local optimal designs within the feasible design region, and techniques for finding more accurate approximation using Holographic Neural Network (HNN) are investigated. Furthermore, the proposed method is applied to the problems frequently encountered in design of automobiles such as increasing of energy dissipation in crashworthiness and reducing of interior noise to illustrate the effectiveness of the proposed method.

Investigation of Spacecraft Vibration Subjected to Acoustic Sound Field of Fill Effect

Payloads are exposed to severe vibro-acoustic environments during rocket launches as shown in Figure 1-(a). At the same time, fill effect [1-3] occurs in the cavity, which is located in the clearance gap between the inner side of the fairing and the solar paddles of the spacecrafts (Figure 1-(b)). This phenomenon results in a maximum increase in sound pressure level (SPL) by approximately 10 dB [2] and causes the natural frequencies of the solar paddles to shift to the coupling modes as shown in Figure 2. These modes are derived from both the vibrational modes of acoustic sound in the cavity and the solar paddles of the spacecrafts. These coupling modes are different from each vibrational mode in vaco [4, 5]. At the same time, the accelerance level of the solar paddle on the structural vibration modes decreases by delta Hv due to the shifts in natural frequencies. The larger the size of the solar paddles, the lower the natural frequencies. It is important to consider this influence during the development of spacecrafts, because the shifts in natural frequencies can make the accelerance level decreased. However, recent researches on the fill effect focus on the increase of SPL by using FEM: Finite Element Method and BEM: Boundary Element Method. Despite the fact that the shifts in natural frequencies due to the fill effect cannot be neglected, more researches are being carried out on the problems of SPL than the problems of the shifts in natural frequencies.

Prediction of Upper Tolerance Limit of Acceleration Power Spectrum Density of Satellite Panel under Diffused Acoustic Field Excitation

Severe vibroacoustic random vibration is easily induced to satellite structure during the flight. Design specification of acoustically induced random vibration for satellite and equipment component is based on the acceleration power spectral density (PSD) at the mount interface. Ground acoustic test is conducted to verify the structural design and abnormal function of equipments. The response of a satellite structure under acoustic test can be predicted by Statistical Energy Analysis. In addition to the mean energy vibration level obtained by SEA, upper tolerance limit of vibration response in PSD needs to be predicted for conservative design purposes. This paper deals with the upper tolerance limit of PSD acceleration level of a satellite plate under high frequency diffused acoustic excitation. The upper tolerance limit is derived based on the statistical distribution of the vibroacoustic response together with the theoretical description of response variance. The upper tolerance limit for the acceleration PSD level obtained by Statistical Energy Analysis is compared with the experiment result. The result from the comparison shows that the upper tolerance limit presented in this paper yields good estimate of PSD upper tolerance level for conservative design. The effect of PSD estimation error in experiment on variance is also discussed.

Upper Bound of Vibration Response of Satellite Panel Under Diffused Acoustic Field Excitation

Severe random vibration is easily induced to satellite structure during the flight. Acoustic test at ground is applied to verify the structural design and abnormal function of equipment. An accurate prediction of acoustic induced vibration response of equipment, therefore, is critical for design purposes. Especially for a satellite exterior panel, it has been shown that two subsystem statistical energy analysis model composed of an acoustic chamber and a single panel will simplify the analyses approach and gives a satisfactory result. This paper derives two subsystem SEA model for the prediction of the exterior satellite panel and formulates the damping loss factor equation based on the experiment data. Moreover, the upper bound value of the two subsystem SEA model is presented for further simplification with which response is obtained without structural damping loss factor and radiation coupling loss factor. These two models were validated well by acoustic tests of eleven satellite honeycomb panels.

Sound Vibration Analysis at the Time of an Artificial Satellite Launch

In spacecraft system acoustic tests, one often sees local pressure increase in the narrow gap between spacecraft primal structures and components facing toward the fairing wall. This acoustical environment load to the components differs from that the components are tested alone and the flight acoustic environment may not be actually simulated in the ground testing. In this paper, in order to clarify the mechanism and evaluate this pressure increase, basic experiment including acoustic testing and vibration modal survey are employed. It is found that the main reason of the phenomenon is dominated by the acoustic cavity on the appropriate boundary condition rather than structure vibration. Boundary element method is used to analize the phenomenon and comparison of analysis and experiment results are carried out. The analytical and experimental results agree well. Furthermore, it is understood that the phenomenon of local sound pressure level increase is dominated by the acoustical standing wave mode (1, 1) which can be predicted by the presented methods.

Optimal Placement of Piezoelectric Actuators to Interior Noise Control

An important problem to systems such as automobiles, ships and aircrafls is the control of interior noise whkii is being generated by the vibration of an elastic structure. In the present study, active control of interior noise is of primary interest In the past decade, closely related to ‘sound quality’ and spectrum shaping, the research on noise control has been paid more and more attention in attenuating low frequencies and reshaping the acoustical modes to obtain a satisfactory acoustical environment [1]. Active control with smart material becomes a topic in the recent development of material science and has been gaining a rapid development in real application [2].