Research On The Seismic Response Of The Reef-seawater System

Reef island is almost the only land type in the South China Sea.Once the artificial islands and the upper constructions get damaged due to the natural disasters such as earthquakes,it will adversely affect the economic development,scientific research and regional security in the South China Sea.The reef-seawater system is taken as the research object in this dissertation.A coupled dynamic interaction analysis model of the reef-seawater system is established,and the distribution laws and seismic response characteristics of the ground motion fields on the reef-bedrock sites and the reef-coral sand sites are studied.The concrete works and main achievements of this dissertation are as follows.(1)The fluid-solid interaction algorithm based on the acoustic fluid finite element method is adopted,and its concept and modelling method are introduced.Based on the potential theory of fluid and the series expansion of Bessel's equation,a theoretical solution for the hydrodynamic pressure of the annular water container is derived.By comparing the theoretical solutions with the numerical solutions,the accuracy of the fluid-solid interaction algorithm adopted in this dissertation is verified.(2)Based on the wave theory of fluid medium,a spatially decoupled stress-type artificial boundary for fluid domain is proposed,and the integration of this artificial boundary in general finite element program is implemented.This fluid artificial boundary is further applied on the cutoff boundaries of fluid domain in the near-field reef-seawater model,to absorb the outgoing scattered waves in the seawater medium.(3)A seismic wave input method for the reef-seawater system is developed in this dissertation.Firstly,the time-domain analytical solution of the free wave field in the ocean site under the oblique incidence of seismic waves is derived.The free field waves are converted into the equivalent seismic loads through the dynamic analysis of the substructure of artificial boundaries.Then the seismic wave input in the reef-seawater system can be accomplished by applying the equivalent loads on the artificial boundary nodes.(4)Based on the proposed fluid artificial boundary and the seismic wave input method for the reef-seawater system,as well as the fluid-solid interaction algorithm and the solid artificial boundary,a reef-seawater dynamic interaction model is established and the corresponding integral analysis method in time domain is proposed,through self-programming and the general finite element programs.(5)The two dimensional and three dimensional dynamic interaction finite element models of typical reef-seawater systems are established,and large-scale numerical simulations are performed.The distribution laws and dynamic response characteristics of the ground motion fields on the reef-bedrock sites are analyzed.The research results of key ground motion parameters such as the ground motion amplification factors and the acceleration response spectrums are obtained,and have been adopted by the relevant engineering design departments,providing theoretical supports for the evaluation of the ground motion field and the seismic design of constructions,on the reef islands in the South China Sea.(6)A non-linear dynamic constitutive model for the reef coral sand is developed.Based on the secondary development of general finite element program,the corresponding constitutive model subroutine is compiled.On that basis,the nonlinear seismic analysis of the reef-coral sand site is conducted,and the influences of the coral sand layer on the seismic response of the reef site are studied.The distributions of ground motion fields and dynamic response characteristics of typical reef-coral sand engineering sites under large earthquakes are obtained.