| Periodic barriers exit band gaps(attenuation domain)for specific frequency range,and have drawn much attention as a new method to isolate earthquake and environmental vibration.Among them,barriers for surface wave can reduce vibration at ground surface,and protect the target buildings effectively.To pertinently and precisely control the target attenuation domain,this thesis carries out the reverse design and performance study of periodic surface wave barriers by topology optimization based on genetic algorithm and finite element method.This thesis mainly studies three types of periodic barriers,including embedded wave barrier,non-embedded wave barrier and open trench wave barrier.The overall process of topology optimization is realized through the joint simulation of COMSOL multiphysics 5.2a and MATLAB.According to the characteristics of the surface wave band gap,the fitness evaluation standard based on the energy distribution is proposed,which mainly solves the problem of "from scratch" of band gap in optimization.Taking the maximum width of surface wave band gaps as objectives,optimization problems with different barrier materials,design domain size,filling fractions and specific frequency range etc.are concerned.Based on the optimization results,the mechanism of surface wave band gap and configuration characteristics of barriers are investigated,and the performance of optimized barriers are analyzed through frequency domain and time domain response,respectively.The results show that:1.The fitness evaluation standard proposed in this paper can guide evolution to quickly search for structures with surface wave band gaps,especially showing strong applicability when surface wave modes are not rich or the objective is high-order band gaps.2.The frame of topology optimization based on genetic algorithm and finite element method in this thesis can effectively deal with the optimization problem for surface wave band gap,and the convergence of optimization results is stable.For different barrier types and optimization objectives,the optimized barriers can attenuate surface wave in a wide frequency range.3.The surface wave band gaps of embedded periodic barriers are based on Bragg scattering mechanism.The optimization results of the same order band gap with different barrier materials,design area heights,filling fractions and symmetry have similar topological characteristics.In the optimized structure of the first-order band gap,the main scatterer at the center can determines the lower edge of the band gap,and the subsidiary scatterers near the surface is used to adjust the upper edge.The optimized structures of high-order band gaps consist of two scatterers,whose relative position has a great influence on the band gaps.The width of the same order band gap increases with the increasing of the height and density of the barriers.The symmetry of unit cell has little effect.4.The non-embedded and open trench periodic barriers for surface wave have local resonance band gaps,and can effectively attenuate the vibration at low frequency.The optimized single scatterer only has three kinds of vibration modes(from low order to high order): bending vibration,longitudinal vibration and vibration at the junction of barrier and soil.The generation of higher-order surface wave band gaps requires that there are multiple scatterers in the unit cell,and the number of scatterers increases with the increasing of band gap order.The main scatterer of the optimized barrier is composed of a large mass and a slim connector,which can reduce the frequency of the lower edge of the band gap;the subsidiary scatterers can restrain the vibration at the soil surface and regulate the upper edge of the band gap,so as to increase the width of the band gaps. |
