Planar Motion Mechanism with CFD
Over the years, FORCE Technology has performed captive model tests for shipowners to assess the manoeuvring capabilities of ships in the late design stage.
The benefits of simulating manoeuvres
By performing numerical captive model tests in the early design stage, we get an understanding of the vessel’s manoeuvrability and are thus able to improve it. This helps shipowners embody the improvements early in the design stage and thereby avoid costly and time-consuming last-minute changes to the design.
The advantage of CFD is a better understanding of the flow around the vessel because the calculations may be paused and the pressures, velocities etc. can be studied thoroughly. This provides the naval architect with a unique opportunity to improve details based on information that cannot be obtained through physical model testing solely focusing on force measurements.
Finally, the numerical setup is not limited by physical boundaries; the manoeuvring can be predicted in both deep and shallow water and in terms of larger dynamic manoeuvres such as turning circles.
A number of commercial projects have been performed successfully for various clients. The results from the simulated manoeuvring tests were applied as input to the mathematical ship model used in our in-house ship bridge simulator.
The numerical tests are typically used in three levels of increasing accuracy:
Development of the method
We continuously developed and validated the numerical PMM (Planar Motion Mechanism) setup against towing tank data from both our own and other facilities. The latest addition to the setup is the modelling of the actual propeller geometry in-place on the vessel. This means that the flow around the aft ship and the forces generated by the propeller are simulated more accurately than by means of the previously used momentum source models.
Compared to towing tank tests, the forces and moments found are usually within ~10%, which is acceptable in most applications. Apart from validating against towing tank tests on commercial, and thus confidential, vessels, a larger study has been performed on the MOERI Container Ship (KCS), which is a “public” ship used for research.
Captive model tests
Over the years, FORCE Technology has performed captive model tests for shipowners to assess the manoeuvring capabilities of ships in the late design stage. The result is a solid knowledge database of manoeuvring results for a large range of ship types and sizes. We still carry out captive model tests in our towing tank. As a new service, we provide the tests as numerical CFD tests in the early design stage.