Investigation on Long and Short Period Responses of Spread and Turret Systems in Ship-Mooring Coupled Behavior

Abstract

Yaw angle is usually small in spread ship because mooring lines are attached at multi-points. So, linear analysis without coordinate transform is applicable in motion analysis. While, yaw angle will be large in weathervaned turret ship if environmental load is applied in unwanted direction. In that case, coordinate transform due to large yaw angle is needed in motion analysis and the governing equation will take a nonlinear form. If the effect of mooring lines is included inthe analysis, the differences of two systems will be more complicated. The objective of this study is to compare ship-mooring coupled behaviors for spread and turret systems. A 300m long ship with twelve catenary mooring chains is analyzedin the comparison study. HOBEM (Higher Order Boundary Element Method) and convolution is applied for ship motion analysis. FEM (Finite Element Method) is applied for mooring line analysis. Coupled responses such as ship motions and mooringline tensions are calculated and the long & short period responses are compared for spread and turret systems. Results of linear and nonlinear analyses were also discussed.