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Results
ABSTRACT The interaction between a vertical circular cylinder and regular waves is studied on a numerical basis under conditions defined in the EXPROCFD European Project. Computed data are obtained from either a coupled method between a Reynolds-averaged Navier-Stokes solver and a non-linear inviscid solver or an improved multi-fluid approach developed in the Navier-Stokes solver. First comparisons to experiments conducted by ECN and Sirehna (Borleteau et al., 2003) are also presented. INTRODUCTION The interaction between a vertical circular cylinder and regular waves is studied on a numerical basis. Conditions of simulations are those defined by the EXPRO-CFD European Project and concerns low and high steep waves ranging from L/2a= 20 to 10 and L/D= 2.5 to 10, where L is the incident wave length, a the wave amplitude and D= 0.508m the diameter of the cylinder. Numerical simulations are performed using the Navier-Stokes solver ISIS developed by DMN (Division Mod´elisation Num´erique) and the non-linear inviscid solver XWAVE from the DHN (Division Hydrodynamique Navale), both belonging to the CNRS-UMR research unit n_6598 at Ecole Centrale de Nantes. Computed data are obtained from either a coupled method between ISIS and XWAVE or an improved multi-fluid approach developed in ISIS. THE NON-LINEAR INVISCID SOLVER: XWAVE XWAVE (Ferrant, 1998) is a potential flow solver for fully nonlinear free surface flows. The numerical solution of the fully nonlinear initial-boundary-value problem is based on the so-called mixed-Eulerian- Lagrangian (MEL) approach. Starting from initial conditions, a two-step procedure is followed: first, a mixed Dirichlet-Neumann boundary value problem is solved for the normal velocity and for the velocity potential on the free surface; then, free surface elevation and the potential on the free surface are advanced in time using the kinematic and dynamic free surface conditions as O.D.E's.
- North America > United States (0.47)
- Europe > France > Pays de la Loire > Loire-Atlantique > Nantes (0.25)
ABSTRACT The flow dynamics in a moonpool is evaluated through analysis of experimental and numerical time series of surface elevations. Experimental results are obtained in the context of the interaction of irregular waves with the barge. The excitation of natural sloshing and piston modes is investigated as well as wave transmission in the bay. Dedicated numerical simulations of extinction tests of piston and sloshing modes are also performed, using a time domain potential flow solver. Three-dimensional effects are pointed out and a good agreement is found between experimental, numerical and analytical estimations of the moonpool natural frequencies. INTRODUCTION Recent studies on flow dynamics in moonpools of FPSOs or barges showed that 3D effects cannot be neglected, (Maisondieu & Le Boulluec 2001), and are to be investigated, especially when the bay is large compared to the size of the floating unit itself. Natural sloshing and vertical modes in the bay, which can be considered as a bottomless tank, may be excited by pressure fluctuations along the hull induced by the travelling waves or by the motions of the barge. Such water motions in the moonpool can alter the response of the floating structure and possible coupling, mostly with heave, roll and pitch motions are likely to occur. Evaluation of the flow in the bay and below is also of major interest for the design and the distribution of the aircans fixed to the upper part of the risers as tensionning floats. Decay tests of the piston and sloshing modes in the moonpool are performed and natural periods are compared to analytical solutions and experimental results. EXPERIMENTS Tests were carried out on a model of the Wellhead Barge (WHB®), which is designed with an unusually large moonpool. The experimental set-up is described in Maisondieu & Le Boulluec, 2001.
- Europe > France (0.29)
- North America > United States (0.28)
- South America > Brazil (0.28)