Optimization Design Of Asymmetric Acoustic Transmission

In today's daily life,one-way traffic is required.For example,the one-way revolving door at the exit or entrance of the railway station can only revolve in one direction and one-way street will be utilized when there are any traffic restrictions,which can improve the work efficiency greatly.Similarly,acoustic waves can only propagate in one specific direction in some periodic composite structures,namely,asymmetric propagation characteristics of acoustic waves.It is one of the bandgap property and is called directional bandgap in the band diagram.This characteristic has broad application in many fields,such as acoustic diodes and medical ultrasound devices,which has became a hot topic.Thus,optimizing the transmission spectra of asymmetric propagation of phononic crystals and obtaining the high transmittance in a wide frequency range show significant effect for transmission of energy and information.Selecting the fluid-solid phononic crystals as the research object,the asymmetric acoustic transmission properties are studied based on the existing basic theory,research methods,status and progress of phononic crystals.Finite element method is used to obtain the transmission spectrum of the phononic crystals.Multi-objective optimization of the structure parameters is used by combining the response surface surrogate models and genetic algorithms.At last,the optimized solutions are verified and analyzed in detail.The main research content is as follows:(1)Fluid-solid phononic crystal model is established.We use finite element method and finite difference time domain method to calculate the transmission spectrum and show the accuracy of the two methods.Based on the methods,water-brass phononic crystals model is built.By changing the geometric parameters of the structure,the effect of parameter variation on effective pass band frequency,transmittance peak and peak frequency is studied with finite element method.(2)The method of optimal Latin hypercube design is employed to obtain the initial samples of geometric parameters.Then the sampling points are solved by finite element method to obtain the objective values.These design variables and output response values are used to establish the radial basis function surrogate model.Finally the fitting accuracy test is used to verify the accuracy of the response surface model.(3)A mathematical model for multi-objective optimization of asymmetric acoustic propagation in fluid-solid phononic crystals is formulated.Taking the structure parameters as design variables,multi-objective optimization of effective operating frequency and transmittance peak for asymmetric propagation properties is implemented.A set of Pareto-solutions is obtained with optimization and some special points on the optimization curve are discussed in detail.And then,the optimal solutions are verified and discussed.Also,the transmission spectra before and after optimization is compared.