The Force Acting on a Horizontal Cylinder Passing Through the Water Surface

Abstract

The load fluctuation acting on a propeller blade in the condition that the propeller blade exposes partially over the water surface had been investigated experimentally. The experiment has made clear the interesting phenomenon that the negative torque acts on the blade at the moment when it passes through the water surface from water to air. And the former report proposed the hypothesis that the negative torque is due to the force caused by the change of the added mass of the blade along the rotational direction. In order to confirm the above hypothesis, the forces acting on a horizontal cylinder passing throught the water surface are experimentally investigated in this report. The experimental results are compared with the calculated results. The calculation is carried out according to the theory that the test cylinder is acted by a force system of 5 component, that is, the inertial force of real mass, the inertial force of added mass, the drag, the buoyancy and the force caused by the change of added mass. The last component acts in the same direction with the cylinder motion from water to air. It is called here a negative force. The calculated results are in approximate agreement with experimental results. The existence of the negative force component is confirmed.