Seakeeping Tests

The seakeeping of ships and offshore structures is determined by model tests and numerical simulations. Model tests in a seaway are carried out in the towing tank. For this purpose, a hydraulic wave generator is available with which various wave spectra as well as regular waves and transient wave packets can be generated. Significant wave heights are possible in model scale to 0.23 m and at modal periods up to 2.5 s. For a model scale of about 1:40, wave conditions can be simulated up to gale force with about 10 m significant wave height at 18 s modal period in ship scale. To avoid unwanted wave reflections there is a beach with a natural inclination and an additional lateral wave damper to absorb diagonal waves. Sea state testing done with free-running, self-propelled models is used for detecting movements and accelerations, the shipping of water, relative motion, propeller ventilation and slamming phenomena. The effectiveness of controlled, zero speed, fin stabilisers, regarding their roll damping is tested with models having no forward motion. The determination of force coefficients is done in experiments with a tethered model.

Seakeeping tests can be carried out in countering and following seas as well as quartering seas at an angle of up to 35° off course. The latter takes the form of zigzag driving, which is recognised by the classification societies as an experimental technique. The motion behaviour of tested objects is detected with a high resolution optical tracking system. This system allows contactless measurement of the coupled motions of two-body systems in all 6 degrees of freedom as well as speed and acceleration at defined positions.

For numerical simulations of sea keeping the UTHLANDE program system is available. Based on linear and non-linear strip method, this system allows the calculation of the motions and loads of mono hull ships and catamarans for all 6 degrees of freedom. The program provides the statistical characteristics (short and long term statistics) for long and short crested seas represented in Cartesian or polar diagrams and a video animation based on a “ship motion viewer”. The process provides valuable insights by varying different sea state specific parameters in the optimisation process and serves as a valuable support of model experiments.