The authors performed a computational fluid dynamics (CFD) analysis of a self-elevating mobile offshore drilling unit (SE MODU) as a replacement for wind tunnel testing. The authors utilized an unsteady RANS method to model wind forces on an SE MODU for a variety of wind headings. The simulation produced force and moment data for individual structural components of the SE MODU. The final data set presented sufficient information to calculate overturning moments of the SE MODU in a range of wind conditions.
This paper discusses several techniques developed for the SE MODU analysis: meshing of disparate structural scales, accurate simulation of large intricate structures, and accurate description of dynamic effects. The paper presents methodology for calculation of a center of effort that correctly relates vector force to vector moment in all three dimensions. The authors demonstrate that center of effort was not appropriate to dynamic flow situations; direct moment coefficients were more suitable.
As part of the validation process, CFD analysis was performed on a similar SE MODU design and compared to existing wind tunnel results. This paper compared forces and moments in all three axes for multiple wind headings. The CFD analysis compared very well with wind tunnel results, showing only a 10% difference from the experiment.
The project revealed several advantages of CFD over traditional wind tunnels in this application. The insights from CFD showed the contribution of each structural component to overturning moment, and results revealed significant elements of overturning moment not considered by the current industry standards. CFD analysis required a similar level of effort as a wind tunnel test but produced far more detailed knowledge.