High-order adjustable boundary condition for absorbing evanescent modes of waveguides and its application in coupled fluid–structure analysis

The high-order local transmitting boundary conditions are one of the most efficient techniques for including the effect of unbounded media in a mathematical model. In spite of the previous developments in this field, the behavior of this sort of boundary condition needs to be improved in particular type of practical problems. In this paper, certain capabilities have been added to the multidirectional boundary condition to enhance its application in the dam–reservoir interaction problem. In this problem, the infinite reservoir’s bottom should be able to radiate and absorb pressure waves during the analysis procedure. Besides, the boundary condition should be able to absorb evanescent waves below the cutoff frequency. By including these competencies into the high-order boundary condition, this approach is implemented in the finite element method. The numerical experiments carried out on this technique show significant improvements compared to the previous studies.

► We improve the behavior of Higdon boundary condition by transmitting the evanescent waves. ► We include the ability of far-field boundary excitation in the formulation of the boundary condition. ► We analyze a dam–reservoir system and compare the results with previous exact solutions. ► We find that the proposed improvements can effectively enhance the behavior of the NRBC.