In connection with retrofit solutions, the hull form is mainly optimized locally, but for design of new ships, it is beneficial to follow a more global approach and use a fully parametric model in order to optimize several regions of the hull.

Global hull optimization can help the shipowner save fuel by considering specific aspects in the hull design process. These aspects could be the overall shape of the hull that influences the wave making and base drag and consequently the resistance of the ship as well as the local stern flow properties, both of which influence the propulsive performance.

Resistance reduction and propulsion improvement

To include the effect of hull form changes on the stern flow properties and the propulsive performance, FORCE Technology has developed a simplified approach that allows the optimization to use propulsive power as objective. By using this method, it is possible to work with both reduction of the resistance and improvement of the propulsive efficiency based on CFD results, propeller open-water data and information from our large database with model test results. During recent years FORCE Technology has been involved in a large number of optimization projects with good results. We carry out more and more projects concerning global hull form optimization where both bow and stern are modified.

The FRIENDSHIP-Framework

To handle the optimization process, FORCE Technology utilizes the FRIENDSHIP-Framework which is able to modify fully parametric geometries by varying design variables with a direct relevance to the flow characteristics. Coupled with internal optimization algorithms, the optimum design can be found, considering the operational profile and design constraints provided by the client. The hydrodynamic information needed by the optimization software is calculated by means of CFD. At FORCE Technology, the RANS code STAR-CCM+ is used for this purpose. Using advanced CFD tools for evaluation of the flow field is important in order to capture the hydrodynamic performance of each design variant; particularly in the stern region where complex turbulent and sometimes separating flows occur. As the numerical models become increasingly complex the requirement for computational power is also increasing, but with a continuous expansion of cluster capacity, FORCE Technology is aiming to meet this demand.

AT FORCE Technology, optimization plays an important role in order for us to provide good and fuel-efficient designs for our clients. Therefore, we are continuously working on improving the techniques. Today much focus is placed on single objective optimization which provides good results, but to include more details of the flow in the optimization, future effort will also be put into investigations of possible applications of multi-objective optimization.

Example of fully parametric model
Local wake flow before (left) and after (right) optimization of aftbody.