Excessive hull pressure pulses induced by a badly designed propeller are well-known as a dangerous excitation mechanism for ship hull vibrations. HSVA offers either experimental or numerical predictions of those pressure variations to avoid vibration problems onboard.
Experimental predictions are obtained from model tests carried out with complete ship models in HYKAT, one of the world's largest cavitation tunnels. This way the realistic three-dimensional propeller inflow is generated by the ship model itself. Unsatisfactory simulation by wire screens or dummies is not necessary. Typically 14 tiny pressure pick-ups are located in the model hull above the propeller. Hull pressure amplitudes are measured up to the 5th harmonic of propeller blade rate order under cavitating as well as non-cavitating conditions. Conversion to full scale values is based on more than 20 years of experience with model testing in this facility correlated to full scale measurements. Frequency spectra are obtained to give additional information on the behavior "between" the harmonics and to avoid broad band vibration excitation.
Whenever noise emission is of interest, the superior background noise behavior of HYKAT becomes important. The tunnel itself is extremely silent and is equipped with a hydro-acoustic measuring chamber below the test section. These features allow full scale cavitation noise predictions, e.g. for high comfort mega yachts, seismic or fishery research vessels or for the navy.
For numerical predictions of hull pressure pulses – well suited for propeller design reviewing, pre-optimisation purposes or quick variant studies – HSVA's in-house potential flow code QCM as well as the well-known MIT software HPUF-3AL are in use.