On Numerical Treatments of the Infinite Condition in the Frequency-Domain Rankine Panel Method

Abstract

The frequency-domain Rankine panel method is one of the practical tool to estimate ship seakeeping. Although several numerical infinite conditions which are essential in the method have been proposed by many researchers around 1990, there still remains an unsettled problem on how to satisfy the infinite condition accurately in low-speed and/or low-frequency range where τ = Uωe/g takes small values. Recently Das et al.10)and Yuan et al.11) proposed a Sommerfeld-type radiation condition for that problem from a concept of the Doppler shift on ring waves. In this paper, we originally derive a general form of the Sommerfeld-type radiation condition applying the asymptotic wave theory. The result indicates irrational points of their method and leads us to a more accurate method. The proposed method is validated by solving the wave field generated by a point source and by comparing with other methods with different numerical infinite conditions. Then we confirm that the present method is the most accurate and also effective for the actual ship seakeeping problem.