The paper deals with the modeling of slamming loads on subsea structures at the first step of their installation, i.e. when the structure is going through the free surface, the so-called splash zone. The actual engineering calculations methods seem quite conservative and reduce drastically the operability window which induces a direct cost impact on the installation vessel mobilization and on overall project planning. In the way to describe the physical phenomena and to propose new methodology, large scale experimental tests were performed with simplified porous structures in a wave tank. In parallel, CFD calculations were carried out to identify the expected level of accuracy of standard RaNS code including free surface modeling. Results are given for horizontal plates with skirt and with different rate of porosity and for a set of impact conditions both in still water and waves.
INTRODUCTION With rapid technological developments, new deep water oil field developments require subsea installation. When lowering such objects through the splash zone, strong vertical load may lead to slack events in the rigging process. The usual engineering calculation methods are based on simplified assumptions which are inaccurate for slamming load prediction. To overcome this problem, some empirical methods are often used such as the incidence of the object (to lower the peak of hydrodynamic pressure at the impact) or increasing the existing holes dimensions to involve porosity effects. Nevertheless no recommendations are available to improve these operations. Present study includes experimental and numerical investigations of mud mats (plate with skirts) slamming in calm water under the project French CITEPH program. Cushioning effects are in particular concern of present analysis. Experiments are conducted at OCEANIDE BGO First on a scale of 1/16. Numerical computations are carried out with in-house unsteady Reynolds average Navier Stokes based method (RaNS). Free surface is captured with volume of fluid technic (VOF).