Hull form optimisation
Many parameters like resistance and trim can be evaluated quite accurately by Computational Fluid Dynamics (CFD) and the hull optimisation can be guided by detailed insight in the flow features.
Hull line optimisation improves the flow around the hull, by changing the flow or wake properties in order to improve the inflow conditions to the propeller or by reducing the wave making and consequently lowering the required power.
The CFD code is conducted as a numerical towing tank test, similar to the test conducted in FORCE Technology’s physical towing tank. Computations are done in model scale and full scale results are made based on traditional scaling laws as if data came from the towing tank.
We use the CFD tool StarCCM+ as the standard tool in lines review and optimisation scopes. Through continuous development backed by validation against results from our physical towing tank, the computations have a more than 95% accuracy in predicted hull resistance – i.e. a very realistic estimate of the hull resistance.
Typically, one of two optimisation methods are applied: one being manual, iterative optimisation; the other being parametric optimisation utilising the FRIENDSHIP Framework.
Manual, iterative optimisation
In the manual, iterative optimisation, the hull form is optimised for a limited range of speeds and conditions, e.g. one condition, two speeds or vice versa. The optimisation is performed as a number of cycles.
The cycle is repeated 2-4 times depending on the scope of the optimisation and will typically lead to significant reductions in resistance and a well behaved flow around the ship.
Parametric optimisation using the FRIENDSHIP Framework
Many ships are operating at a large range of conditions and speeds making a one-speed, one-condition optimisation less useful as the ship will operate off-design a lot of the time and thus use disproportionally large amounts of fuel. Keeping an overview of the performance at several loading conditions and speeds in a traditional optimisation as described above, however, is troublesome especially when simultaneously having to take into consideration design constraints.
In order to overcome this, we have acquired the FRIENDSHIP Framework (FFW) which offers a good book-keeping ability to be able to rank a large number of hull forms over a range of conditions and speeds while checking that any constraints are not broken.
In addition to this, the FFW can apply hull form changes governed by a number of design parameters defined by our naval architects combined with sophisticated optimisation algorithms; this allows for automation of the optimisation process and the ability to test a very large number of hull forms within given limits. The result of this is a hull form which is fine tuned to operate at the exact operational profile given by the ship owner.
The actual CFD calculations are done outside the FFW by interfacing with StarCCM+ letting the FFW take care of hull changes and ranking of designs.