A comparative study on state-of-the-art prediction tools for seakeeping

An accurate prediction of the seakeeping behavior of ships is important for both their design and operation. The following issues play a role:

• Wave induced (relative) motions and accelerations should be minimized for the well-being of the crew and passengers, and in the extreme; to minimize capsize risk and to avoid slamming.
• Internal loads should be kept at acceptable levels to ensure structural integrity during a ship’s lifetime.
• The added resistance in waves increases fuel consumption and should be minimized.

The Cooperative Research Ships (CRS) is a group of companies with a common interest in research in ship hydrodynamics. The research tasks carried out are aimed at fundamental research and at design and operation. Together they decide which research topics are investigated and carry out the research. CRS now has 23 members, which include shipyards, ship owners, classification societies, navies, consulting firms and research institutes/model basins. CRS has been working since 1969. Within CRS a vast amount of research knowledge is being accumulated. Moreover, the international cooperation in executing the work strongly broadens the knowledge of the members.

The CRS recognizes the importance of improving the accuracy of seakeeping tools and sought means to make a step forward. The CRS therefore organized a workshop in which a number of research groups were invited to carry out seakeeping predictions for a number of ships. For these ships model tests have been carried out in the past and results are made available to workshop participants. The ultimate goal of the workshop was to select a method as a basis for the next generation CRS seakeeping tool . This method should have enough accuracy, robustness and computational efficiency. The research groups were selected such that they covered a range of different methods:

• Approximate Forward Speed (AFS): Linear potential method linearising around the undisturbed flow, applying zero-speed Green Functions.
• Exact forward speed (EFS): Linear potential method linearising around the undisturbed flow applying forward-speed Green Functions.
• Double Body (DB): Linear potential method linearising around the double-body flow.
• Non Linear Steady (NLS): Linear potential methods linearising around the non-linear steady wave field.
• Computational Fluid Dynamics (CFD)

The test cases that were selected include a container ship and a ferry, for which experimental data was available. The comparison focused on motions, relative motions, added resistance and internal loads.