Realization Of Artificial Boundary Condition Of COMSOL Damping Layer

The impact of rail transit operations on building structures has always been a concern of residents and researchers along the route.When analyzing the dynamic response of structures caused by rail transit operations,the diffusion behavior of wave energy in an infinite foundation is critical,but solving such problems usually requires a very large amount of calculation,and also needs to consider different site conditions,such as Single-phase soil,saturated soil,and layered soil.In order to ensure the correctness and accuracy of the calculation results,it is necessary to adopt efficient numerical analysis methods and apply correct artificial boundaries.Among them,in the finite element analysis,the local artificial boundary conditions have attracted extensive attention from researchers because of the characteristics of space-time decoupling.Regrettably,the artificial boundaries that can currently be used for localization are not satisfactory.In particular,the artificial boundary that can be used to analyze the timedomain response of the wave barrier damping effect in saturated soil is even scarcer.In order to solve the problem of artificial boundary application in time domain analysis of vibration damping effect in saturated soil,this paper proposes a new artificial boundary condition and named it as “damping layer artificial boundary condition”.Studies have shown that this boundary can be used for both time domain analysis of single-phase media and time domain analysis of dual-phase media.The specific research content of this paper is as follows:(1)A new artificial boundary application method is proposed.First consider the boundary layer as a damping material and describe its material properties through constitutive relations.Assuming that the damping parameter is a continuous function of coordinates.To avoid changes in the wave propagation characteristics caused by the interface,the damping parameter is required to be continuously smooth at the interface between the calculation area and the artificial boundary.This boundary condition is named as the damping layer artificial boundary condition.(2)Based on the viscoelastic constitutive equation,the wave equations of singlephase medium and two-phase medium considering variable damping are established respectively,and then the artificial boundary control equation of damping layer for single-phase medium and two-phase medium is obtained.The boundary control equation is written into the COMSOL PDE module,and the correctness of the boundary condition is verified by the lamb problem.The effect of the parameters of artificial boundary on the absorption behavior is analyzed.(3)The artificial boundary of the damping layer is applied to the single-phase soil and the saturated soil,and the vibration isolation and vibration analysis is carried out by using the periodic structure to obtain the time domain response.By comparing with other boundary application methods,the effectiveness of the artificial boundary application method proposed in this paper is verified,and their advantages and disadvantages are pointed out.The work in this paper shows that the physical meaning of the artificial boundary conditions of the damping layer is very clear and the implementation method is simple.Whether it is for single-phase media or dual-phase media,the artificial boundary conditions can absorb the outgoing wave energy well without causing reflection,which has a good localization effect.