Strongly coupled fluid―structure interaction method for structural loads on surface ships

A method to compute structural loads on surface ships coupling a CFD solver with rigid or elastic representations of the ship hull is presented. One-way and two-way coupling approaches were used for the cases when the ship was considered elastic, in which the forces obtained from the CFD solver were used to compute the structural loads. In the two-way coupling method the hull deformation influenced the CFD solution, while in the one-way coupling method this feedback was not needed. The flow field around the ship was calculated with the URANS/DES overset solver CFDShip-Iowa version 4, with the structural response obtained using modal superposition. Predictions of ship motions and structural loads were compared with available experimental data for the S175 containership, obtained from a segmented elastic model. Predicted heave and pitch transfer functions in regular waves matched well with the experimental values. The computations showed that slamming events greatly affected the vertical bending moment amplitude, showing sharp peaks for the rigid model. The elastic models predicted well the ringing of the structure and showed that the ringing was mainly triggered by bow flare slamming. The one-way coupled approach with a virtual mass correction provided a solution that in some aspects had almost the same quality as the two-way coupled solution, at a fraction of the cost.