Vibrational And Acoustical Sensor Placement Study For Structural Borne Sound Radiation Prediction

In the prediction of structural borne sound radiation, the vibration and sound information needs to be measured by using vibration and acoustic sensors. This brings the sensor placement problem. In this dissertation, the vibration velocity sampling for the sound pressure prediction, the vibration velocity sampling for the sound power prediction, and the mixed placement of vibration and acoustic sensors for sound radiation prediction are considered. Then, the method for sound power prediction of a submerged complex double-layer structure is proposed.For the vibration velocity sampling in the sound pressure prediction, baffled rectangular plates with simply supported and clamped boundary conditions are chosen as the models. This dissertation shows that the thumb rule of 1/6 acoustic wavelength cannot be used for all conditions. When vibration frequency is low, the sampling interval requirement is determined by the vibration velocity distribution while the interval requirement is proportional to the corresponding acoustic wavelength and the proportionality coefficient depends on the prediction precision requirement when the vibration frequency is high. The critical frequency dividing the low and high frequency domain, Fm , satisfies the rule km sinθ=const ( k m = 2πFmc,θis the elevation angle of the field point and c is the sound wave speed) for rectangular plates with zero velocity boundary condition.For the vibration velocity sampling in the sound power prediction, the simply supported rectangular plates with the point force excision are chosen as the models. This dissertation shows that the number requirement of the vibration velocity sensor is determined by two factors when mode decomposition methods (Radiation Mode Decomposition method and Vibration Mode Decompsotision method, abbreviated as RMD and VMD) are used for sound power prediction, the mode number requirement and the sampling point requirement for mode amplitude estimation. Employing RMD requires fewer vibration velocity sensors below the first resonance frequency than employing VMD, while employing VMD at structural resonance frequencies requires fewer vibration velocity sensors than that employing RMD. In addition, a numerical method based on the BEM is proposed for calculating the acoustic radiation modes of arbitrary structures, and the grouping characteristics of the radiation modes of a finite cylinder shell are presented.For the mixed placement of vibration and acoustic sensors in sound radiation prediction, a simply supported rectangular plate is chosen as the model. This dissertation shows that the employing the iterative regularization in the vibration velocity estimation can reduce the error of sound power prediction. It is assumed that the acoustic sensors are not less than the nodes where the vibration velocity needs to be estimated. When the traditional pseudo-inverse solution is adopted in the vibration velocity estimation, the precision improvement of sound power prediction can be achieved by increasing the vibration velocity sensors, and the increase of acoustic sensors can improve or depress the prediction precision with different conditions. When the iterative regularization is adopted in the vibration velocity estimation, the sound power prediction precision nearly has no relationship with the number of the acoustic sensors with the precondition that the acoustic sensors are not less than the nodes with unkown vibration velocity.For the sound power prediction of a submerged complex double-layer structure, the governing functions of the whole system are deduced by employing the mode decomposition method. In this dissertation, the effects of the radiation resistance in the water and the ring ribs on the vibro-acoustic characteristics of a cylindrical shell are investigated separately. The transmission paths between two concentric cylindrical shells, the ring water and the rib plates, are also analyzed. Based on the prediction model, it is shown that the sound radiation from the outer cylindrical shell can be predicted using the measured vibration velocity distribution of the inner shell and only the radial coupling effect of the rib plates needs to be considered at low frequencies when the given structure is only excited by the radial forces.