Experimental evaluation of the hydrodynamic coefficients of a ROV through Morison's equation

The determination of hydrodynamic coefficients of full-scale ROV using system identification (SI) is an extremely powerful technique. The procedure is based on experimental runs and on the analysis of on-board sensors and thrusters signals. The technique is cost effective and it has high repeatability; however, it lacks accuracy due to the sensors noise and the poor modeling of thruster-hull and thruster-thruster interaction effects. In this work, forced oscillation tests using a planar motion mechanism (PMM) were undertaken with a full-scale open-frame ROV. These tests are unique in the sense that there are not many examples in the literature taking advantage of a PMM installation for testing a prototype and, consequently, allowing the comparison between the experimental results and the ones estimated by SI. The Morison equation inertia and drag coefficients were estimated with two parameter identification methods that are the weighted and the ordinary least-squares procedures. Error analysis showed that the ordinary least-squares provided better accuracy and, therefore, was used to evaluate the ratio between inertia and drag forces for a range of Keulegan-Carpenter and Reynolds numbers. The research provided a rich amount of reference data for comparison with reduced models as well as for ROV dynamic motion simulation. (C) 2011 Elsevier Ltd. All rights reserved.