Hull form optimisation at the next level
We have taken hull form optimisation to the next level by incorporating the operational profile in the design.
Many hull forms are designed and optimized for operation at one speed and one draught. In reality, however, many ship types are not constantly operating at the design point since the speed and loading conditions vary during operation. This is important to take into account in the hull optimisation process since the hull form must perform well in all conditions. If this is neglected, the shipowner will pay a ‘penalty’ in terms of disproportionally high fuel consumption.
The challenge of optimization
Much optimisation work can be done manually based on experience, but keeping the overview of the performance of many design variants in several operational conditions and making the right hull form deformations while simultaneously satisfying design constraints on for instance LCB, displacement and tank and thruster tunnel arrangements is quite difficult without some sort of automation.
Therefore, in January 2012, FORCE Technology acquired the FRIENDSHIP Framework to automate the hull form optimisation process. FRIENDSHIP Framework is a tool which, based on parameterization of the hull form and automatic optimisation algorithms, can rank designs and find the optimum hull form within given design constraints using a given object function. FRIENDSHIP Framework is not a CFD tool, so the hydrodynamic design evaluation is done externally by external CFD software packages which are interfaced with FRIENDSHIP.
Large potential for cost reduction
At present, FORCE Technology has been involved in several optimisation assignments with good results. Looking at the ship’s performance, it is not unusual to see that the resistance, on average over the operational profile, has been reduced by 5 to 10% between initial and final designs. As the estimated saving is typically used as basis for evaluation of a business case which is used to judge if a design change is profitable, it is important that the accuracy of the estimated saving is reliable. To ensure this, FORCE Technology relies on its long-term experience within CFD applications using CFD tools and procedures that are well proven and continuously checked against towing tank tests every time projects involving both CFD and towing tank testing are executed. FRIENDSHIP Framework has been fully integrated in the optimisation work flow at FORCE Technology and is now offered as a ‘standard’ service to our clients. The applications cover optimisation of new ship designs as well as of ships that are in operation but need to be retrofitted with new bows.
In all cases, the optimisation process is done in close dialogue with the client in order to ensure that the right operational conditions and hull form constraints are taken into account and thereby make sure that the ship satisfies the client’s requirements and at the same time performs well.Currently, focus of the optimisation work has been to minimise the wave resistance, but in the near future, the applications will be extended to cover optimisation towards improved performance of the stern flows and improved seakeeping properties.