계류계 및 부유체 연성거동을 고려한 계류삭 피로해석

Abstract

This paper numerically investigates fatigue life of mooring lines of a FSRU (Floating Storage Re-gasification Unit) system based on coupled analysis of floating body and mooring system. Hydrodynamic coefficients & forces of floating body are calculated using HOBEM (Higher Order Boundary Element Method) and time domain equation is formulated using convolution. FEM (Finite Element Method) was applied to formulate nonlinear discrete equation of catenary mooring system and Newmark integration is used in time marching. Coupled solution is obtained by finding iteratively compatibility at fairleads. After solving coupled equation, mooring line tensions are obtained. Then, fatigue damage component can be calculated in a statistical manner using design rules such as API-RP-2SK with signal analysis such as FFT, filtering, zero-upcrossing, etc. By combining damage components, total damage is calculated and fatigue life is finally obtained. Three methods such as SS (Simple Summation), CS (Combined Spectrum) and CSDNV (Combined Spectrum with Dual Narrow Band) are applicable in combining damage components. A 315 meter long FSRU moored with nine catenary chains is analyzed for numerical example. Mooring line tensions are calculated by using developed coupled solver in given sea states. From the tension results, fatigue lifes are calculated based on SS, CS and CSDNV and their results are compared.