Starting a wave structure interaction CFD simulation from an advance time: Hot-start

This paper details the reduction of an OpenFOAM CFD WSI simulation to its major event, by starting it at an advance time: a new procedure named hot-start, which is a first step towards a future coupling development. The investigations concern the fluid flow and a structure motion hot-start, taken separately, and are restricted to numerical comparison. Four design waves based upon the NewWave theory are simulated with increasing starting times - where the wave field is initialized as the sum of the linear components of the considered wave - and compare to conventional ones - which are initialized with still water. The structure motion hot-start is assessed using a heave decay test: a conventional heave decay simulation is compared against several ones where the motion, velocity and acceleration of the structure are assigned for several time-steps. An initial mesh-deformation library is specifically created to assign the structure at the hot-start position by incrementally deforming the mesh towards the right structure position. Independent to the non-linearity of the case, a start 4 s prior to the main event is found to be enough to accurately represent the wave field. The motion of the structure was found to require at least 5 time-steps in order to converge to the reference one. Those results aim to be usable for other CFD WSI applications.