Acoustic Radiation Optimization For Stiffened Plates Based On The Evolutionary Strategy

The noise and vibration control is a major research subject in civil and military fields. It is of vital importance in acoustic stealth design for submarines. In naval structures, stiffened plates are widely adopted and their acoustic radiation behavior is significantly influenced by the locations of the stiffeners. Therefore, this thesis uses the stiffener locations as the design variables to optimize the acoustic radiation of the stiffened plates.Firstly, some preliminary knowledge about finite element method (FEM) is presented. Detailed deduction of stiffness matrices of beam and plate elements, coordinate transform of beam elements, the superposition method of stiffness matrix, and the FEM model update are also included in this part. Secondly, a method of computing the average acoustic radiation power of a baffled vibrating plate is introduced. The computation flow chart and the essence of the evolution strategy (ES) are also presented here. Thirdly, the thesis uses the stiffener locations as discrete variables to optimize the acoustic radiation of a baffled simply-supported plate under single point harmonic excitation. Optimization results are compared with those obtained by adding concentrated masses, distributed masses. It is demonstrated that the structure tailoring method by adding stiffeners is the lightest way to achieve the largest reduction in acoustic radiation power. Lots of simulation results reveal that the stiffeners have a trend to connect with the boundary. This phenomenon is explained qualitatively with the concept of impedance matching. Finally, the thesis summarizes the theoretical formulation for the acoustic radiation under the multiple-point white noise excitation and presents several numerical simulation results for a baffled simply-supported plate.