ADVANCED SEAKEEPING VALIDATION AND SELF-PROPULSION MODELLING USING HELYX-ECOMARINE

Hull performance in calm water conditions is a primary concern for ship design. Whilst this approach proves to be key to optimise the hull-form for the target operational speed, an optimal hull for calm water is will not necessarily perform well in waves. Although the ocean may be calm, most of the life of a ship is spent travelling through waves. In this context, the current regulations imposed by the IMO (International Maritime Organisation) foster active research work to optimize the EEDI (Energy Efficiency Design Index) with a special focus on reducing the installed power on board and fuel consumption when the ship travels in adverse weather condition while operating is safe conditions. In this regard, the effect played by the drift forces when the ship travelling in waves is fundamental to characterize the performance of the ship itself, especially when considering the added resistance which results in an increased engine power and related fuel consumption. For this purpose, unsteady RANS methods represent an accurate solution for seakeeping cases where second-order drift forces are present to accurately predict ship performance. Another important criterion to correctly predict engine power and propulsion system requirements is the prediction of the ship operating point in self-propulsion conditions. In this regard, the determination of the characteristics of the propeller, including the correct estimate of the revolution rate is key to assess the performance of the ship and the requirements of the propulsion system. In the work detailed here an innovative unsteady RANS solver for seakeeping simulations was developed based on the OpenFOAM library and made available to the HELYX-Ecomarine advanced package for marine applications. In terms of self-propulsion modelling, the rigid body motion library developed for seakeeping simulations was extended to account for self-propulsion by allowing both a fixed revolution speed applied to the propeller, and modelling of the ship operating point by using an RPM controller which was implemented via a PID control system. The initial part of this work was focussed on the validation of the KCS KRISO container ship for a series of sea states based on the Tokyo 2015 Case 2.10 specifications. In this context, calm-water and five regular wave conditions were considered and added resistance and hull motions were measured and validated against the experimental data available. The final part of the work discussed here focussed on the modelling of the ship in self-propulsion mode by the development of an innovative self-propulsion library for OpenFOAM. The same KCS hull model used for the seakeeping study was employed and the ship was simulated in calm water conditions in self propulsion mode with even keel and no rudder. The results achieved in propeller characteristics, measured hull resistance and velocity contours are presented in this work.