Propeller Hydrodynamic Forces Induced by Shaft Vibrations

Abstract

Many ships have become to equip a new diesel engine, which has logs stroke and a lesser number of cylinders. Some of the ships have experienced vibration troubles due to the longitudinal vibration of the engine. The new engine causes large torque variation in the shafting which can generate variation of the angular at the propeller position. The propeller thrust variation due to the angular variation can be generated. The thrust excites the engine longitudinally as well as the longitudinal force of the engine crank. In this paper, the calculation method of the additional propeller hydyodynamic forces due to the shaft vibration is presented, which is based on the unsteady lifting surface theory. The full-scale vibration measurements have been carried out. The calculations of the hydrodynamic forces have been done for the MAU series propellers, too. The calculated results are very related to the reduced frequency. The calculated results has been examined indirectly by the experiments of shaft exciting forces due to the non-uniformity of the flow. The calculated thrust agrees well with the full-scale measurement result.