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-s cale mini Tension Leg Platform (TLP) of the type typically deployed for dee p-sea operation. Two alternative prediction techniques were used: Computati onal Fluid Dynamics (CFD), which is based on the solution of the fundamenta l equations that govern turbulent fluid flow; and 'engineering' calculation s 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 c ompared with each other and with experimental data obtained from wind-tunne l and towing-tank tests on a 1-70 scale model. It was found that the two te chniques, while yielding very similar predictions for the front TLP members , give substantially different predictions for the aft members - a result t hat is consistent with the presence of significant interference effects tha t are captured only by the CFD. The design code yielded the highest value f or the global drag coefficient, followed very closely by the towing-tank re sult. The wind-tunnel tests produced the lowest value for this parameter. T he 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 d iscussed in the context of the use of CFD in practical design applications. (C) 2000 Elsevier Science Ltd. All rights reserved.