Torsion moment conversion methods in model test with u-shape backbone

Abstract

Backbone structure is widely used in model test to investigate ship elasticity such as springing and whipping because force measurement and stiffness similitude are both possible with backbone. Measured strains on backbone can be converted to vertical bending moment (VBM) or torsion moment (TM) using theoretical or FEM (Finite Element Method) relations. However, TM conversion has still technical issues because torsion induced strains are different with loading modes due to warping effect. This study investigates and compares various conversion modes in TM measurement. Test results of WILS-JIP (Wave Induced Loads on Ships-Joint Industry Project) by KRISO (Korea Research Institute of Ships & Ocean Engineering) are used in this study. In TM conversion, four loading modes such as section-by-section decoupled 2nd mode, section-by-section decoupled 1st mode, coupled mode and full span 1st mode are applied and the results are compared. Copyright ？ 2014 by the International Society of Offshore and Polar Engineers (ISOPE).