The application of particle image velocimetry for the analysis of high-speed craft hydrodynamics

As soon a ship operates at high forward speeds its weight is pre-dominantly supported by hydrodynamic, rather than hydrostatic forces. Small changes in the dynamic pressure distribution on the ship hull can have a significant influence on the ship’s running attitude in calm water, but also on its seakeeping performance. In order to further improve these vessels it is important to experimentally and numerically investigate the flow in the vicinity of the ship hull and to accurately determine global as well as local pressure distributions. In contrast to traditional experimental techniques, which often lack spatial resolution, this thesis presents an alternative experimentalmethod for the analysis of the flow field and the reconstruction of hydrodynamic pressures from particle image velocimetry (PIV). This is a non-intrusive, laser-optical measurement technique where the velocity field of an entire region within the flow is measured simultaneously. The thesis discusses to what extend the PIV technique can be used to analyse the hydrodynamics of high-speed ships during model tests in towing tanks. The research particularly focusses on the influence of high towing tank carriage velocities, that can result in structural vibrations and high out-of-plane velocities, on the quality of the measured velocity fields. Furthermore it is focussed on the reconstruction of hydrodynamic pressures from these, and the propagation of measurement uncertainties towards the final hydrodynamic pressure fields. Hereby, the spatial variation of uncertaintieswithin the measurement region is taken into account. The analysis is done by means of two practical applications with a towed underwater stereo-PIV system. A first test-case analyses the flow in the transom region of a generic planning hull and the influence of an interceptor on the local pressure distribution. A second test-case focusses on the analysis of the flow field in the bow region of a semi displacement hull. Results from both cases show, thatmeasurements can be obtained in regions, where high-spatial resolution is necessary, but cannot be provided by traditional techniques. Being interested in time- or phase-averaged results,multi-plane PIV measurements are used to extend the observed region to capture the three-dimensional velocity and pressure fields. The obtained experimental results are in good agreement with results from numerical simulations.