Centre of Pressure of 6 Degree of Freedom Loads, Applied to Impact Measurements on a Propeller Blade
Author J. Brouwer, G. Hagesteijn
Title Centre of Pressure of 6 Degree of Freedom Loads, Applied to Impact Measurements on a Propeller Blade
Conference/Journal OMAE ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering, San Francisco, USA, 2014
Year 2014

Abstract
Load measurements on various structures and objects are nowadays common in technical industries and research fields. The same applies to numerical computations where fluid forces
are integrated over surfaces to come to resultant forces and moments. When forces and moments on a rigid body in 3D are considered, the total load is a 6 degree of freedom system. These are often denoted as the force in x-, y- and z-direction and the moments around the x-, y- and z-axis. A question that often arises in case of these 6 degree of freedom loads, is to find the position of the centre of pressure. This is the position with zero resulting moment when the loads are translated to it. In 2D this is straightforward. However for 3D systems there is no straightforward solution. Extending the mathematics from 2D to 3D one might find a system of equations with a determinant that is zero. Which means there is no solution or there are an infinite number of solutions.

Studying this system of equations, a very convenient alternative can be posed. This alternative solution has been applied to find the centre of pressure on a propeller blade originating from open water loads, artificial ice impacts and combined ventilation and cavitation impacts. These measurements are all performed at model scale using 5 or 6 degree of freedom load sensors. The alternative method proved to deliver meaningful results which are backed up by high speed video footage of the impacting events.

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