Effect of model-structural dynamics on propeller-induced hull pressure measurements

Propellers are important sources of ship vibrations. Experimental model tests in tow-tank facilities are established methods to assess the design of propellers and ship hulls. However, during these tests, the ship model structural dynamics may affect the results when measuring the propeller-induced hull pressure pulses. This paper presents the results of towing tests on a scaled model of a bulk carrier at the atmospheric towing tank at NRC-OCRE combined with Operational Deflection Shape Analysis (ODS) of the model’s structures. The model was equipped with a four-blade fixed-pitch propeller. Twelve pressure sensors and two sets of eight accelerometers measured propeller-induced pressures and vibrations during the tests. Further, an Experimental Modal Analysis (EMA) identified the model’s natural frequencies and mode shapes. The towing tests were performed at different model hull speeds (Vm) and propeller speeds. The signals acquired were post-processed in MATLAB® to find the pressure amplitudes, perform an ODS, assess the structural dynamics, and check possible resonances. The results indicate that although the local plating does not resonate with the exciting pressure pulsations, the model structure has global modes in the frequency range of interest.