Drillship Moonpool Design to Reduce Added Resistance for Fuel Saving

Abstract

During transit, a drillship moonpool creates added resistance that can be more than 50% of the total resistance and hence significantly increase the fuel consumption. This paper reports a real case study for reducing moonpool added resistance by model tests and Computational Fluid Dynamics (CFD) simulations. Model test data show that, unlike conventional ships that experience nearly constant resistance, a drillship resistance presents largely fluctuating behaviour. In CFD validation, the physics based CFD best practices are applied for resistance predictions. The largely fluctuating resistance is well captured in simulations. It is found from flow visualizations of the large amount of CFD simulation results that the high moonpool induced added resistance is mainly attributed to the vortices shed from the moonpool front wall, which enter into the moonpool and impinge on the rear wall. The CFD predicted mean resistance are in good agreement with the model test data, within 3% difference for a wide range of speeds. The well validated CFD tool is applied to study the effects of moonpool dimensions on the added resistance. The results of parametric study reveal a design principle that smaller moonpool dimension results in smaller added resistance. Through comprehensive CFD parametric study, a universal design principle and CFD best practice are established for industry applications.