Towards a General-Purpose Open Boundary Condition for Wave Simulations

Abstract

For the design of FPSO’s in harsh environments an accurate assessment of the ability of the platform to survive in extreme sea conditions is of prime importance. Next to scaled model tests on the FPSO in waves also CFD capabilities are at the disposal of the designer. However even with the fastest computers available it is still a challenge to use CFD in the design stage because of the large computational resources they require. In that respect to use a small computational domain will improve the turn around time of the computations, however at the expense of various numerical artifacts, like reflection on artificial boundaries in the computational domain. In order to mitigate the reflection properties new absorbing boundary conditions have been developed. The work in this paper is constructed on the previous study about the generating and absorbing boundary condition (GABC) in the ComFLOW project. We present a method to apply the GABC on all the boundaries in a three dimensional domain. The implementation of the GABC in ComFLOW is explained in detail.

Force and water jet impact reduction on adjacent structures by means of free surface breakwaters

“…The method is comparatively fast because of the use of local generating and absorbing boundary conditions [7,8] that take care of sending irregular waves into the domain while at the same time preventing re-reflection of reflected and transmitted waves. Local boundary conditions in this approach replace wave dissipation zones that require a significantly larger domain.…”

Multi-fidelity Kriging extrapolation together with CFD for the design of the cross-section of a falling lifeboat

“…Examples of extreme FSI are found when waves impact with structures [2,29,42,44,45]. Note that when waves are concerned, simulations benefit from Generating Absorbing Boundary Conditions [5,6], both in terms of accuracy and of computing time. Slamming of an object onto a free water surface constitutes another type of impact simulation, demonstrated by means of a falling cylinder on water in van der Eijk and Wellens [40].…”

An Absorbing Boundary Condition for Regular and Irregular Wave Simulations

“…All flow variables can be calculated by taking derivatives of (10). At this point a question crosses one's mind: Is it possible to develop a boundary condition which has the feature of allowing reflection only to an acceptable threshold for all the wave components which all together form an irregular wave?…”

“…In this paper we present the derivation of an absorbing boundary condition (ABC) [9,10] along with the numerical implementation of the analytical operator. The ABC is applied in three dimensional computational domains where a regular Stokes wave and an irregular JONSWAP spectrum wave are traveling under an angle of incidence.…”