Module and Vessel Interaction Analysis for Module Ocean Transportation

Bechtel has been contracted for and is in the process of executing multiple onshore Liquefied Natural Gas (LNG) Engineering, Procurement, and Construction (EPC) projects utilizing the modular construction strategy. Modules and associated pieces of equipment have to be shipped to the job site from various manufacturing and fabrication facilities across open oceans. Naval Architects play a key role to assure safe and effective module ocean transportation. Primary naval architectural work consists of a routing study, module design criteria definition, ballasting and stability analysis, grillage and seafastening design, transportation vessel selection and support for module load out and load in. The main challenge is to make the modules, which are originally designed for onshore assembly, sound for ocean transportation. Therefore, module design criteria related to ocean transportation become crucial. Among these criteria, the wave induced inertia loads and vessel deflection have great impact on designed module structure integrity. In order to define inertia loads and deflection appropriately, the interface between vessel and module becomes a main concern. It raises the question of whether the transport vessel and module should be fully integrated. It also increases complexity of the hydrodynamic interaction, which has been demonstrated by widely divergent methods used to address the interface issue in offshore industry. More importantly, whether or not the interface is thoroughly taken into account is critical to successful module design and fully meeting the Marine Warranty requirements. In order to achieve safe and economic module design, a direct method of integrating vessel and module is considered preferable in analysis and design when the inertia effects and structure hydrodynamic response are significant. This paper will provide an overview of integrated vessel and module interaction analysis for the module ocean transportation and focus on the method and procedure of how Bechtel performs analyses: i) spectral motion analysis with a fully coupled constitutive model and ii) vessel and module interaction analysis utilizing an integrated 3D model with fully hydrodynamic loads transferred. In order to determine realistic extreme load case, the equivalent design wave selection will be addressed as well.