Validation of Hydro-Structure Analysis Using Partial Structural Model

Nowadays direct Finite Element Method (FEM) calculation using partial or full length model is necessary for checking the structural integrity of ship and offshore structures under given environmental conditions. The main advantage of using hydro-structure analysis on partial model is to obtain better accuracy than usual computation based on rule loads and also a consistent decrease of the time necessary to build a complete ship model. The comparison of different three cargo hold models with the complete ship model and the improvement of our partial FEM models are the main objectives of the work. Unlike the classical partial FEM models approach, our hydro-structure analysis is based on creating an equivalent full FEM model from the partial model. The equivalent full FEM model is built by adding to the partial model two concentrated masses in the center of gravity of missing aft and fore parts. The mass and inertia properties of the equivalent full FEM model are the same as full ship FEM model. By using an equivalent full FEM model the problem of balancing the partial model transforms into the same problem for the corresponding full model. Instead of using the traditional method for interpolating the pressure from hydrodynamic mesh to structural mesh, the pressure components are recalculated over structural mesh. The inertial loads are then determined by motion equations integrating all pressure loads. In this way, the structural model is fully balanced. The balancing of the 3D FEM structural models represents one important issue to avoid unphysical structural response induced by an unbalanced structural model. This paper is focused on the validation of hydro-structure analysis methodology by comparing the results on a FSO unit using an equivalent full FEM model and a complete ship model.