Practical Calculation Method of Rolling for Shallow Draft Ship

Abstract

Ordinary Strip Method (O.S.M.) is used to estmate motion and acceleration of a ship. But, for a shallow draft ship, the calculation accuracy by O.S.M. gets worse on rolling and transverse acceleration especially in short waves. This inaccuracy is mainly due to the inaccurate calulation of diffraction component of roll exciting moment. The authers present the following simplified calculation method of shallow draft ship motion. a) Diffraction forces are calculated by Strict Strip Method (S.S.M.) or Salvesen-Tuck-Faltinsen Method (S.T.F.M.), b) where hydrodynamic coefficients and diffraction forces are calculated by using rectangular form approximation, c) and Froude Krylov force is calculated strictly. This practical calculation method based on Rectangular Region Method (Ijima's method) has a short CPU time and good agreement with model test results and calculation results by close-fit S.T.F.M.