This paper delivers a preliminary comparative study on the computation of wave resistance via a commercial CFD solver (STAR-CCM+®) versus an in-house developed IGA-BEM solver for a pair of hulls, namely the parabolic Wigley hull and the KRISO container ship (KCS). The CFD solver combines a VOF (Volume Of Fluid) free-surface modelling technique with alternative turbulence models, while the IGA-BEM solver adopts an inviscid flow model that combines the Boundary Element approach (BEM) with Isogeometric Analysis (IGA) using T-splines or NURBS. IGA is a novel and expanding concept, introduced by Hughes and his collaborators (Hughes et al, 2005), aiming to intrinsically integrate CAD with Analysis by communicating the CAD model of the geometry (the wetted ship hull in our case) to the solver without any approximation.
The prediction of wave resistance in naval architecture plays an important role in hull optimisation, especially for higher Froude numbers when wave-resistance's share in total resistance becomes higher. It is well known that the total resistance of a ship can be roughly decomposed into the sum of frictional, viscous-pressure and wave resistance. Model testing is commonly used to predict the resistance components for new ships (ITTC, 1987). With the recent improvements in CFD (Computational Fluid Dynamics) tools, CFD is likely to provide a decent alternative for saving time and money for the prediction of resistance for modern ship hulls. This is not, however, the case for ship-hull optimisation when the geometry is unknown, which increases drastically the overall computational cost and the significance of deviation between the accurate CAD model of a ship hull and its discrete approximation usually adopted by the CFD solvers.
An alternative lower-cost path for the wave-resistance estimation can be employed by appealing to the Boundary Element Method (BEM) for solving the Boundary Integral Equation (BIE), which results from adopting the so-called Neumann-Kelvin model for the flow around an object moving on the otherwise undisturbed free-surface of an inviscid and irrotational liquid; see, e.g., (Brard, 1972) and (Baar and Price 1988). Our purpose is to initiate a systematic comparative study between a CFD solver (STAR-CCM+) and an in-house BEM solver enhanced with the IGA concept, which permits to tightly integrate the CAD model of a ship hull and its IGA-BEM solver; see, e.g. (Belibassakis et al 2013). Under the condition that this study will secure that the discrepancy between the results provided by the two solvers are acceptable within the operational range of Froude numbers, one can proceed to develop a hybrid mid-cost optimisation framework that combines appropriately the low-cost IGA- BEM solver (Kostas et al, 2015) with the high-cost CFD one. In the present paper our comparison will involve two hulls, namely the Wigley and the KCS hull, which have been extensively used in pertinent literature for experimental and computational purposes.
