École Nationale Supérieure de
Techniques Avancées

Abstract

At STX France, the calculation team uses the finite element software Ansys to model the behaviour of the hull structure of the ship, in response to realistic load cases. The ship is divided in working zones, each assigned to a team member who is allowed to modify it in his or her own copy of the model. The modifications are put together by a grouping process. The global mesh is coarse, therefore the geometric details that are of importance are analysed using the submodeling method: a specific zone is modelled with a fine mesh and the boundary conditions are extrapolated from the computation of the global model behaviour. The aim of this study is to determine how to make the grouping of models more flexible and how to integrate the results of submodeling in the global model, in order to get a model as up-to-date and exact as possible. Comparative tests between various potential solutions have been carried out to this purpose. The superelements method has been studied to this end. It consists in generating a macro-element from a substructure of the whole, and integrating it into the model as a single element with a specific type, whose detailed behaviour can be computed later on. This method is fairly complex since it includes of several steps involving a significant number of files; however it can help decrease the computation time and permit to integrate elaborated models into the global one. Connections between non matching meshes, that have different numbers of nodes at the junction, are usually modelled with constraint equations (CE) establishing linear links between intermediate nodes and shared nodes. However, this method cannot be used with superelements, therefore the MPC (multipoint constraints) method has been tested. The results have been compared with those obtained with the CE method on a ship model. This work made it possible to complete the integration of a fine mesh model of a cofferdam as a superelement into the ship model in a simplified load case, with satisfactory results. The topic of integrating modifications made by different users at the same time has been tackled by first studying the existing grouping process. This process has been made more flexible toward boundaries as well as more automated. The resulting program has been successfully tested on simple cases.