Whipping response analysis by one way fluid structure interaction-A case study

Accurate prediction of whipping induced hull girder response is important for evaluation of hull girder stresses and fatigue life assessment of ships structure. Traditionally, strip theories and panel methods have been popularly used for seakeeping analyses of ships for evaluating the slamming loads. These loads are used for whipping response prediction by idealizing the ship's hull as a free-free beam. In the present work, numerical seakeeping computations have been performed assuming ship's hull as a rigid beam. Wave loads thus computed are applied on to the real flexible structure of the ship to obtain the bending moment response amidships. For this purpose, modal superposition technique is utilized. Interaction of fluid (water) with structure (ship) is accounted only once, i.e. while computing fluid forces the structure is considered as rigid. Whipping response is hence obtained considering one way Fluid Structure Interaction (FSI). The obtained peak values are quite close to the experimental values. It is concluded that added mass effect and damping due to the degree of coupling between fluid and structure plays a vital role in whipping response prediction. The present method being computationally efficient and reasonably accurate can be practically used for whipping response predictions at initial design stage.