During the design of a Gravity-Base Structure (GBS) for harsh environments, it is essential to account for the maximum wave run-up in operational and extreme weather conditions. Linear diffraction theory and empirical correction factors are typically used in the early design phase of a project in which wave run-up is a concern. As the project nears final design, model tests are usually used to assess wave run-up and air gap requirements. This paper addresses the use of alternative methods for prediction of run-up around a GBS in approximately 100 m water depth. Results from a second-order diffraction code (WAMIT) and a fully nonlinear CFD program (ComFLOW) are compared to assess the importance of nonlinearities, which are shown to depend on incident wave steepness and wavelength. Extending diffraction theory to second-order significantly improves linear predictions and produces more realistic spatial patterns of maximum run-up. However CFD simulations are required to accurately predict run-up associated with very steep incident waves and highly nonlinear characteristics. In addition to regular wave computations, linear and second-order potential flow calculations are also compared against model test results for an irregular sea.

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