Uncertainty estimation of mesh-free and mesh-based simulations of the dynamics of floaters

Abstract

Numerical simulations are increasing their importance as an alternative to physical tests in the field of hydrodynamics. To ensure the accuracy of numerical results, quantification of associated uncertainties is crucial. In this paper, comparisons are made between the uncertainty quantification methods and the accuracy of mesh-free and mesh-based simulations due to discretization. A constant CFL based approach is applied in the uncertainty analysis of CFD results, as an alternative to the ITTC recommendations of using independent grid and time-based discretization approaches. Two open-source tools DualSPHysics (mesh-free) and OpenFOAM (mesh-based) are used to investigate problems related to wave energy converters, such as Point Absorbers and Oscillating Water Columns. Two cases are studied: a sphere free-falling into the water and a heaving box subjected to regular waves. For each case, several spatial resolutions are analysed to obtain the convergence of the numerical methods using Taylor diagrams. Numerical uncertainties are quantified using the Factor of Safety method, Correction Factor method, and least square fit method. Numerical results obtained from the higher spatial resolution are compared with published experiments, showing that both numerical methods converge as the spatial resolution increases. The accuracy of the results obtained with DualSPHysics and OpenFOAM using high spatial resolutions are similar. The validation and verification analysis show that all three uncertainty estimation methods are reliable when a constant CFL number is used.