Estimating the hydrodynamic forces on a mini TLP with computational fluid dynamics and design-code techniques

This paper reports on the prediction of the hydrodynamic forces on a full-scale mini Tension Leg Platform (TLP) of the type typically deployed for deep-sea operation. Two alternative prediction techniques were used: Computational Fluid Dynamics (CFD), which is based on the solution of the fundamental equations that govern turbulent fluid flow; and 'engineering' calculations based on force coefficients derived from a design code that is in routine use in the Offshore Industry. The results from these two techniques were compared with each other and with experimental data obtained from wind-tunnel and towing-tank tests on a 1-70 scale model. It was found that the two techniques, while yielding very similar predictions for the front TLP members, give substantially different predictions for the aft members - a result that is consistent with the presence of significant interference effects that are captured only by the CFD. The design code yielded the highest value for the global drag coefficient, followed very closely by the towing-tank result. The wind-tunnel tests produced the lowest value for this parameter. The CFD predictions, which were the first to be obtained in this study, fall in the mid-range of the experimental values. These and other results are discussed in the context of the use of CFD in practical design applications. (C) 2000 Elsevier Science Ltd. All rights reserved.