In this paper, we focus on the modeling of a fully-nonlinear, steep, irregular wave field of three-hour duration without structures in it. The fully-nonlinear effects are considered in the wave simulations using computational fluid dynamics (CFD), as well as potential theory. The overall approach for the numerical modeling is described in the paper. The Euler Overlay Method (EOM) is used to incorporate incoming waves, nonlinear effects, and CFD simulations in the numerical modeling. For computational efficiency, we also use potential theory to model the fully-nonlinear waves. Numerical damping was applied locally around the breaking region to enable simulations for large breaking waves. To compensate for energy loss in the numerical simulations, energy compensation factors of wave spectral frequency components are applied to the input wave spectrum. Results of convergence study, validation against high-order Stokes waves and fully-nonlinear irregular wave with prescribed target spectrum, as well as comparison between numerical wave crest distributions and those from multiple realizations of wave calibration tests are presented.

As Computational Fluid Dynamics (CFD) and High Performance Computing (HPC) technologies matured in many other industries, the offshore industry has begun to recognize CFD-based Numerical Wave Basin (NWB) as a design tool to evaluate offshore floater design more efficiently and with less uncertainty than the conventional ways relying on empirical methods. The recent NWB technology development has focused on the customization of CFD software for offshore design practices and validation of the developed analysis tools/procedures against physical model tests. Development has now extended to simulation of fully coupled hull-mooring-riser systems.Technology readiness of the NWB for field application is demonstrated for two benchmark problems: 1. Vortex-induced motion of a multi-column floater 2. Global performance of a multi-column floater in extreme wave environment The results indicates that the CFD-based numerical wave basin, although still computationally expensive, is technically ready to be a complementary tool to physical wave basin for offshore platform global performance design.

Several recent benchmark studies have demonstrated that Computational Fluid Dynamics (CFD) is capable of capturing both nonlinear and viscous effects in offshore marine hydrodynamics and predicting well certain wave- and current-induced offshore platform motion. In order to apply CFD for practical global performance analysis of a complete hull-mooring-riser coupled floating system, we develop an advanced numerical wave basin that combines CFD, nonlinear irregular wave modeling, and finite-element mooring modeling. Specifically, CFD is used to simulate the violent free-surface flow with hull motions; nonlinear wave modeling is applied to generate a realistic wavefield and provide initial and far-field conditions to CFD for efficient long-duration simulation; and mooring modeling is two-way coupled with CFD to account for dynamic mooring response and its effects on hull motion. In this study, to demonstrate the capability of such tool, the global performance of a semi-submersible with 4 mooring lines in a 3-hour extreme sea state is simulated for both head and quartering sea. The simulation results are compared to model test data of hull motion, mooring line tension, and relative wave elevation around the hull for validation. It is shown with spectrum and statistics that the simulations predict well the platform’s global performance in all frequency ranges, including low frequency where the mooring lines have the greatest influence on the motion response. Compared to the predictions from a conventional global performance design tool that is based on diffraction analysis and empirical coefficients, the CFD results show significant improvements. The encouraging results from this study indicate that a CFD-based numerical wave basin, although still computationally expensive, is technically ready to be a complementary tool to physical wave basin for offshore platform global performance design.

Following the successful application of CFD-based Numerical Wave Basin (NWB) to GBS, TLP and Semisubmersible platforms [1–4], the same methodology has been applied to simulate FPSO hull motion responses to irregular waves. It has been found that the NWB modeling practices developed for the other floater types must be modified for application to an FPSO. This paper describes how the NWB modeling practices have been improved, and then compares results from NWB simulations with those from physical model testing.

Technip recently has developed new cost-effective and riser-friendly Semi-submersible hull forms adapted to various operation sites, with considerable saves in design cost and time. This achievement is greatly in debt to Technip's numerical wave basin, which has been developed and validated through previous projects and collaborative R&D efforts with clients. Validation of the numerical wave basin against the model test and full-scale measurement data has proven that the numerical wave basin can provide more realistic and reliable prediction of the wave-and vortex-induced motion than the physical model test. The validated numerical wave basin has been applied to develop a new semi-submersible hull design for a given design environment, partially replacing the role of the physical model test in the traditional design spiral. The new design spiral based on numerical wave basin provides optimized hull design more expeditiously and efficiently than the traditional design spiral based on physical model test. Review of the development, current status and future prospects of numerical wave basin for offshore platform design is presented in this paper.re-calibrated to provide more accurate design parameter for the next phase of the project, which is the typical case for the design of conventional hull forms. There have been a few occasions, however, the discrepancy between prediction and model test results being beyond the adjustment of empirical formula and result into major modification of the hull design, and some cases even change of the design concepts, which lead to considerable delay and increase of project schedule and cost. This worst scenario occurs when unexpected physical phenomena that could not be modeled by the analytic model are observed in the model test. These unexpected physical phenomena are mostly related to nonlinear fluid force and viscous effects.Along with the efforts to improve conventional global performance tools, Technip has been investing in CFD capability for the analysis of viscous dominant problems such as drag coefficients of hull parts and vortex induced motion of Spars (Halkyard et al., 2006, Atluri et al, 2009, Lefevre et al., 2013. Recently, the utilization of CFD for offshore floater design extends to free-surface flow problems for Spars and multi-column floaters with the aides of the advances of CFD codes in free-surface capturing and moving mesh techniques, together with the computing power of modern high-performance parallel computers that has been growing exponentially year by year. Technip is developing numerical wave basin to provide design parameters of run up, air gap, green water and nonlinear wave load on the hull at the early stage of floater design. The numerical wave basin provides wave-induced loads and motion on fixed and floating structures correlating with the model test measurements within engineering tolerance for the design purpose , Wu et al., 2014. Numerical wave basin will gradually substitute the role of scaled model test in the design spiral, as depicted in ...