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Numerical Simulation of Wave Loading on Static Offshore Structures

Numeric estimation of loads on static offshore structures were of primary interest in this paper. Computational Fluid Dynamics (CFD) simulation with Finite Volume (FV) method is used and the accuracy of the numerical predictions is assessed. Simulations regarding 3D dam break and waves were considered, since they both have dominant free surface effects. When calculating loads on static structures, theoretical methods based on potential ow theory are often used. Nevertheless, they have certain drawbacks. For example, wave forces can be underpredicted in some cases [2]. In this paper, a FV approach is evaluated in order to test its applicability to wave loads problems. test it's applicability. Main advantage of this approach is that it implicitly accounts for viscosity and vorticity, as well as the violent free surface effect. The incompressible uid ow is described by Navier-Stokes equations. The pressure- velocity coupling is obtained by the PIMPLE algorithm, a combination of SIMPLE and PISO. Tight pressure-velocity coupling allows simulations with higher Courant numbers, leading to reduced computational expense. Volume of Fluid (VOF) [4] method is used for interface capturing. Waves are generated and absorbed with relaxation zones [3]. The complete algorithm is implemented into the OpenFOAM software package. The accuracy of simulation results is assessed through validation with two cases for which experimental data are available in literature [1] [2]. One case is a 3D dam break on a square column that was studied experimentally in [1]. The peak force in direction of water impact shows good agreement with experimental data. The second case describes a truncated vertical cylinder (model of Tension Leg Platform). The cylinder is immersed in water and exposed to incoming waves. Harmonic waves with different frequencies and heights are studied. Maximum forces in the direction of wave propagation are compared with experimental results from [2]. A mesh refinement study was performed and the dependency of the results with respect to mesh resolution is presented. Final test case describes the simulation of a harmonic wave breaking on a complex cylindrical shape with enlarged diameter near the free surface.

CFD, Volume of Fluid, Two Phase Flows, Wave Loads, OpenFOAM

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