The 12th International Conference on Hydrodynamics
18 – 23 september 2016, Egmond aan Zee, The Netherlands
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CFD SIMULATION OF WAVE IMPACT ON A SEMI-SUBMERSIBLE: A NUMERICAL CASE STUDY


Go-down ichd2016 Tracking Number 106

Presentation:
Session: Computational Fluid Dynamics III
Room: Room 2
Session start: 15:30 Mon 19 Sep 2016

Peter van der Plas   P.van.der.Plas@rug.nl
Affifliation: University of Groningen

Arthur Veldman   A.E.P.Veldman@rug.nl
Affifliation: University of Groningen


Topics: - Computational fluid dynamics

Abstract:

In offshore applications, extreme events of wave impact on rigid and floating structures are of high interest. In the past the CFD simulation tool ComFLOW [2] has been successfully used for these purposes. For accurate prediction of wave run-up and wave loading on offshore structures high resolution is required in the areas of interest. In order to reduce the number of grid points absorbing boundary conditions are used to limit the computational domain. The computational time is further reduced by application of local grid refinement and parallelization. This case study concerns the application of CFD to the simulation of wave impact on a semi-submersible [1,3]. Various regular waves are considered, of which the properties are only known within a given uncertainty range. Small variations in the incoming wave can cause large differences in the measured impact forces on the structure. This presents a complicating factor in interpreting the CFD results. In a similar fashion, small changes in the simulation setup can cause seemingly disproportionate differences in the solution if interpreted in a deterministic sense. The variation observed in the experimental measurement poses several challenges. Firstly, the experiment has to be reconstructed in the numerical simulation. A representative wave is constructed by means of averaging of the experiment data [1]. Secondly, given the variation of the flow conditions around the semi-submersible in the test basin, a deterministic interpretation of the numerical results is of limited value. In the current study the deterministic comparison is complemented by a statistical approach to assess the average and variation of the impact forces. The statistical approach is also applied to investigate grid convergence behaviour. [1] B. Iwanowski, M. Lefranc and R. Wemmenhove, “CFD Simulation of Wave Run-up on a Semi-Submersible and Comparison with Experiment”, ASME 2009 28th Int. Conf. on Ocean, Offshore and Arctic Eng. (2009). [2] A.E.P. Veldman, R. Luppes et al., “Turbulence Modelling, Local Grid Refinement and Absorbing Boundary Conditions for Free-Surface Flow Simulations in Offshore Applications”, ASME 2014 33rd Int. Conf. on Ocean, Offshore and Arctic Eng. (2014). [3] R. Wemmenhove, R. Luppes et al., “Numerical simulation of hydrodynamic wave loading by a compressible two-phase flow method”, Computers & Fluids, Vol. 114, pp. 218-231, (2015)