Propeller-induced hull pressure measurement accuracy in tow-tank tests: a methodology for mitigating structural dynamics effects

Ship design has to include a comprehensive consideration of onboard vibrations, which is crucial for ensuring passenger comfort and safeguarding machinery and structural integrity. Marine propellers are significant sources of these vibrations, and studying propeller-induced hull pressures (PIHPs) is important in early design phases to mitigate excessive hull and shaft vibrations. Full-scale measurements of propeller-induced pressures (PIPs) are expensive and can only happen once a ship is built and operating, leading to the use of model-scale towing tests as the most effective methodology to assess PIHP in ship design. PIHPs are measured during model tests by a set of flush-mounted pressure transducers at the model stern. While performing the tests, PIHPs excite the model's structures, whose resulting vibrations can affect the accuracy of the measured data. Concerns about the impact of these vibrations on pressure measurements have been raised by ITTC cavitation committees across several conferences. This research aims to address the ITTC concerns by presenting a novel methodology to enhance the precision of PIP measurements and address the model structural dynamics. The presented methodology is based on a combination of experimental tests and numerical simulations. Self-Propulsion (SP), Bollard Pull (BP), and resistance tests were performed at the tow tank of the Ocean, Coastal, and River Engineering Research Centre of the National Research Council of Canada. These tests were combined with the Operational Deflection Shape (ODS) analysis of the ship model. A simplified Finite Element (FE) model of the scaled ship's complex structure was developed and updated using Latin Hypercube Sampling (LHS) and Response Surface Methodology (RSM) against results from Experimental Modal Analysis (EMA) tests. The added mass effect of the surrounding water was taken into account by employing a fully coupled Fluid-Structural Interaction (FSI) approach, combining Finite Element and Boundary Element methods (FE-BE). The validated FE model was used to evaluate the model's structural Vibration-Induced Pressures (VIP) using harmonic acoustic analysis. These results were then used to evaluate the impact of the model's structural dynamics on the measured PIHPs. Finally, the implementation of the proposed methodology to develop a simplified tool to predict PIHPs for different propellers' design parameters is discussed. This thesis presents a novel methodology to quantify and mitigate the effect of model structural vibrations on the accuracy of model scale propeller-induced pressures.