“…11,12 By combining with quadtree/octree gridding techniques, the SBFE mesh generation becomes more efficient, and can even be directly conducted on the digital images of computing domains. 13,14 Due to these merits, such a kind of SBFEM has been used to deal with dynamic problems, 15,16 heat conduction problem, 17,18 uncertainty problem, 19,20 inverse problem. 21 Either in the appearance of BEM or FEM, however, a troublesome matter for SBFEM is the computational expense on solving a quadratic eigenvalue problem in generating stiffness matrix.…”