Multi-objective optimisation of a semi-planing hull using CFD RANSE simulations with low number of cells

ABSTRACT: An integrated use of a CFD software with an algorithm for multi-objective optimization is proposed in this paper. Currently, optimisations regarding hydrodynamic performance for a given ship or marine vehicle design (eg. choice of best shape for the minimization of wave resistance) can be carried out interfacing multiobjective algorithms with parametric 3D modelers and suitable hydrodynamic solvers. Having to manipulate a great number of alternatives, the requirement for the computing chain is to rely on fast and tested methodologies especially for the flow solvers. The use of RANS viscous CFD simulations offers more complete and detailed information to evaluate the resistance and the flow around ships hulls and is now well established. These methods, however generally require to represent the flow domain by a high number of cells with consequent substantial increase of hardware and computing time requirements. A research has been carried out to define and standardize operating modes to carry out viscous simulations with a number of cells as low as possible. It has allowed to obtain adequate results within a reasonable short time and without the necessity of requiring high computing resources. In this way it is possible to achieve adequate RANS simulations in a short time so as to make them competitive as far as computational costs with panel methods also in optimization problems, especially in the evaluation phase of many different design alternatives. The optimization of a hard-chine semi-planing hull, based on the reduction of the total resistance at two different speeds through the integration of software optimisation with the RANS simulations with low number of cells has been performed and is presented and discussed. The results obtained are validated by experimental tests in towing tank.