Analysis Of Response Variance And Research On Surrogate Models For Acoustic Radiation Of Underwater Structures

In the field of marine engineering, prediction and control of the structural vibration and noise is an especially important subject for both civil ships and naval vessels. Model fidelity and manufacturing variability has led to dynamic changes of the structure, In engineering practice, it is inevitable to consider the impact of parameter variation on the response of the structure. In the optimal design of underwater structural vibration and acoustic radiation, the relationship between design parameters and system response need complex and time-consuming numerical calculations, if the numerical model is used directly to design optimization, it can not be implemented as the huge computation. The surrogate model can be used instead of high-precision model to give the vibro-acoustic response results in real time.Therefore,it is important to perform the analysis of response variance and research on surrogate models for acoustic radiation of underwater structures, whith is of great significance for the prediction of vibration and noise and optimal design of engineering structures. This dissertation addresses a detailed study of numerical analysis of response variance and surrogate models of acoustic radiation from a structure underwater. The major work completed is as follows:Combining with the elasticity theory and structural dynamic theory, a four-node plate/shell element with rotational degrees of freedom considering transverse shear effects based on the Mindlin plate theory is presented for dynamic analysis of a plate. Some research on the finite element models has been done based on the Mindlin plate theory. A simply supported plate is involved to verify the effectiveness of the model. Natural frequencies of the plate in vacuo has been calculated and compared with analytical value.The fundamental theory and numerical method of vibro-acoustic coupling problem is introduced and the boundary element method for acoustic radiation in a three-dimensional full space is concerned.Finite element method and boundary element method are combined to calculate structural acoustic radiation of fluid-loaded plates. The boundary element model is based on the Rayleigh integral on the surface for a baffled plate. The effects of fluid medium, plate thickness, the location of point force, boundary condition and plate material on radiated sound power are studied.Modal models are developed for vibro-acoustic response computation of fluid-structure interaction problems on the basis of modal frequencies and modal damping ratios. The modal parameters are obtained using the modal reduction method. The uncoupled equations are built using fluid-loaded undamped real mode shapes and solved for the coupled response of the fluid-loaded structures. The accuracy and efficiency of the technique is demonstrated with an example of computing the mean-square normal velocity and radiated power response of a fluid-loaded plate.Single degree of freedom analysis method is employed for response variance calculation of acoustic radiation. The response variance of acoustic radiation from a plate with different thickness or different distribution of lumped masses is calculated and the envelope with known perturbation range of the natural frequencies is drawn. The numerical results based on single degree of freedom method are compared with finite element-boundary element coupling method.The surrogate model based on the Kriging model is applied to predict resonant frequency and corresponding sound power level of underwater structural vibration and acoustic radiation. The principal component decomposition is combined with the Kriging model to construct a surrogate model for predicting vibro-acoustic response in the frequency band of interest. These surrogate models give the vibro-acoustic response results in the whole design space in real time based on sample information. An underwater stiffened plate is involved to show the building and verification of the surrogate models. First, sample points in the design space are selected based on optimal symmetric Latin hypercube sampling method, then calculates the response of sample points using high-precision method for underwater structural vibration and acoustic radiation, finally the surrogate model based on the Kriging model and the principal component decomposition is constructed and verified.