AN ABSORBING BOUNDARY CONDITION FOR SH WAVE PROPAGATION IN VISCOELASTIC MULTILAYERED MEDIA

A high-accuracy absorbing boundary condition in the time domain is proposed, which can be coupled with the finite element method seamlessly to simulate the propagation of the transient scalar wave in the D'Alembert viscoelastic multilayered media. First, a semi-discrete displacement equation of the semi-infinite domain and the force-displacement relationship in the artificial boundary are obtained by semi-discretizing the semi-infinite domain along the vertical depth. Modal decomposition is utilized to convert the field of the semi-infinite domain in the physical space into the modal space. Then the dynamic stiffness of the semi-infinite domain in the frequency domain in the modal space is obtained according to both the displacement equation and the force-displacement relationship in the modal space. Second, a scalar continued fraction, which is convergent over the whole frequency domain, is proposed to describe the scalar dynamic stiffness in the modal space of the D'Alembert viscoelastic single-layered medium. The scalar continued fraction is extended to the matrix form to represent the dynamic stiffness in the modal space of the D'Alembert viscoelastic multilayered media. Last, by introducing auxiliary variables, a time-domain absorbing boundary condition in the modal space is constructed based on the proposed continued fraction. Subsequently, considering the relationship of the field in the modal space and in the physical space, a time-domain absorbing boundary condition in the physical space is obtained by converting the absorbing boundary condition in the modal space into the physical space. Two numerical examples of a single-layered medium and a five-layered media verify that the proposed method is accurate and stable for the D'Alembert viscoelastic single-layered medium, and for the D'Alembert viscoelastic multilayered media, in order to ensure the proposed method's property of high-accuracy, the distance from artificial boundary to the region of interest needs to be about 0.5 times of the total layer height of the infinite domain.