The Depressurised Wave Basin is a unique research facility for the testing of ships and offshore structures in most realistic (scaled) operational conditions. Due to the capability to reduce the ambient air pressure, it allows investigations in three important areas:
• Cavitation (in waves)
• Air chambers
• Wave impacts with air entrapment
In more detail:
Cavitation of the propeller(s) operating behind the complete ship model either in still water or waves or manoeuvring is possible. Cavitation and hull pressure tests are carried out in depressurised conditions, with the propeller(s) in Froude-scaled condition and the model in free surface conditions (free to trim and thus creating the proper propeller inflow).
Seakeeping tests at scaled ambient pressure to model the correct behaviour of wave impacts and slamming using the wave makers along the short and long side of the basin. The same wave makers can also be used for testing offshore structures and wave energy devices.
The facility can also be used as a multi-purpose model basin for hydrodynamic research related to the resistance and propulsion of ships and current loads and dynamics on offshore structures.
Tank dimensions are 240 x 18 x 8 m. The harbour (preparation) area is 26 m long and 4.2 m wide. The instrumentation allows for measuring up 100 channels at 20 kHz. The noise measurement system is able to test frequencies of 2 – 100 kHz.
According to the laws of similarity which apply to cavitation, the ambient air pressure in the tank must be reduced to the inverse of model scale. Through three vacuum pumps it can be lowered to a
minimum of 2500 Pa.
Wave generators are positioned at two adjacent sides of the basin and consist of hinged flaps. The wave generators are able to simulate various wave types, such as short-crested wave patterns. The system is equipped with compensation of wave reflection from the model and the wave absorbers. Opposite this wave generator, passive wave absorbers are installed. The short side wave maker has a capacity of 0.75 m waves at 4 s wave period and the long side wave maker 0.45 m waves, 3 s wave period.
Model size range
Models range from 2 – 12 m in length, up to 4 m beam and a maximum draught of 1 m. Maximum propeller diameter is 0.4 m.
The observation systems (both inside and outside the model) offer much operational flexibility through the remote control of camera position, camera settings (zoom and focus), lighting and stroboscope positions and intensity. Normal and high speed cameras are available.
• Cavitation observation and inception
• Pressure fluctuation measurements
• Radiated noise, flow noise measurements
• Wakefield measurements
• Resistance and propulsion tests
• Offshore structures, fixed, moored or controlled by dynamic positioning to determine motions and/or loads due to waves
• Seakeeping tests in waves from arbitrary directions
• Forced oscillation tests using an hexapod
• Flooding tests (still water, waves, scaled ambient pressure)
• VIM (Vortex Induced Motions)