Abstract
A method for the morphing of surface/volume meshes suitable to be used in hydrodynamic shape optimization is proposed. Built in the OpenFOAM environment, it relies on a Laplace equation that propagates the modifications of the surface boundaries, realized by applying a free-form deformation to a subdivision surface description of the geometry, into the computational volume mesh initially built through a combination of BlockMesh with cfMesh. The feasibility and robustness of this mesh morphing technique, used as a computationally efficient pre-processing tool, is demonstrated in the case of the resistance minimization of the DTC hull. All the hull variations generated within a relatively large design space are efficiently and successfully realized, i.e., without mesh inconsistencies and quality issues, only by deforming the initial mesh of the reference geometry. Coupled with a surrogate model approach, a significant reduction in the calm water resistance, in the extent of 10%, has been achieved in a reasonable computational time.
Highlights
Computational fluid dynamics (CFD) methods are nowadays widely used both to predict the ship resistance at all the design stages and to realize simulation-based design by optimization (SBDO) processes directly to design high-performance hull shapes by the systematic use of numerical calculations
Built in the OpenFOAM environment, it relies on a Laplace equation that propagates the modifications of the surface boundaries, realized by applying a freeform deformation to a subdivision surface description of the geometry, into the computational volume mesh initially built through a combination of BlockMesh with cfMesh
Successful examples of the application of such approaches for performance predictions of both displacing and planing hulls in calm waters and in waves can be found in [6,7,8]. These results encouraged the use of CFD analyses in the context of automatic SBDO solving single and multi-objective hydrodynamic shape optimization of conventional and unconventional vessels [9,10,11,12] similar to those applied to propellers [13], combining true CFD calculations with multi-fidelity and data-fusion optimization methods [14,15,16]
Summary
Computational fluid dynamics (CFD) methods are nowadays widely used both to predict the ship resistance at all the design stages and to realize simulation-based design by optimization (SBDO) processes directly to design high-performance hull shapes by the systematic use of numerical calculations. When using Eulerian, mesh-based, RANS calculations for the estimation of the ship resistance, one of the most expensive phases is the realization of a high-quality computational grid This issue is exacerbated when very deformed hull shapes, such as those generated by an optimization based design on a large design space, are considered. Morphing an initial high-quality mesh, represents an effective approach to address this problem in the pre-processing phase of an automatic design optimization method. This ensures a significant saving of resources, since the morphing process is usually more efficient than the crude re-gridding of each new candidate considered in the design procedure. The DTC hull is introduced and a new shape of its bulbous bow, capable of a reduction of resistance higher than 10%, is proposed as the results of an optimization based on the developed pre-processing tool combined with CFD calculations and surrogate models estimations of the ship resistance
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