A physics-based seakeeping and wave load numerical simulation system is being used for design and operation studies on the Mobile Offshore Base (MOB). This ship and platform simulation system solves three-dimensional time-domain large-amplitude nonlinear motion and load problems using a potential-flow boundary-element method including body-nonlinear effects and a linear or nonlinear solution of the local free surface. Under the MOB Program, the simulation system has been used to compute detailed local free surface elevations for air-gap evaluation and for predictions of motions and loads for a MOB geometry in both operating and transient conditions. A description of the simulation system, computational results for a "generic" MOB geometry including nonlinear effects, and comparisons between computational results and experimental air-gap measurements are presented.
The feasibility of using a Mobile Offshore Base (MOB) for military purposes has been studied intensively in recent years. A MOB consists of multiple (3–5) mobile modules and can be assembled to form a floating base up to 2 kilometers long. A MOB can operate in fairly high sea states and can survive extreme seas. Because of its enormous size and unique mission requirements, there are design considerations that may be very different from conventional floating platforms. One of the very important design considerations for a MOB is the air gap between the wave surface and the upper deck. The prediction of air gap involves several components including the incident waves, the diffraction waves, the radiation waves, and the motion of the platform itself. The results of using both linear and non-linear hydrodynamic methods for the air gap study of a generic MOB design are presented. The method solves the three-dimensional time-domain hydrodynamics problems using a potential-flow boundary-element method.
