scattering of flexural wave in a thin plate with multiple circular inclusions by using the multipole method

the multipole method is presented to analytically solve the scattering of flexural wave by multiple circular inclusions in an infinite thin plate. the near-field dynamic moment concentration factor (dmcf) and the far-field scattering pattern are both investigated in this paper. the former has a connection with the fatigue failures and the defects in plate-like structures can be detected by the latter. owing to the addition theorem, the multipole expansion for the multiple scattering fields can be transformed into one coordinate system centered at one circle where continuity conditions are required. in this way, a coupled infinite linear algebraic system is derived as an analytical model for an infinite thin plate with multiple circular inclusions subject to an incident flexural wave. the convergence analysis is conducted to provide the guideline of usage for the proposed method. the effects of the size and thickness of the flexible inclusion, and the central distance between inclusions on the near-field dmcf and the far-field scattering pattern are investigated in the numerical experiments. it shows that the scattering pattern correlates closely with the size and thickness of weakness, indicating the importance of the scattering pattern to detect the various defects. in addition, the dmcf of two corrosion defects is larger than that of one. therefore, it is essential to evaluate structural safety when multiple circular defects are very close to each other. the effect of the space between the inclusions on the near-field dmcf is different from that on the far-field scattering pattern.