A Theoretical Procedure for Calculating Propeller-Induced Hull Forces.

A method based on rational mechanics is presented for predicting hydrodynamic forces and moments on a hull of arbitrary geometry as a reaction to the propeller-induced velocity field. This method assumes that the hull surface can be represented by a distribution of sources. The numerical procedure is adapted to the CDC 7600 or Cyber 176 digital computer which furnishes the strength of the source distribution over the hull and the vertical component of the propeller-induced hull force at blade frequency. The program is executed for two widely different cases for which experimental measurements are available: a spheroidal head in the presence of a 3-bladed propeller operating in uniform inflow, and a Series 60 hull model (V-form stern) driven by a 4-bladed propeller. Theoretical predictions show agreement with corresponding experimental measurements within 11% for the body of revolution and 27% for the surface ship. A new method has lately been devised which replaces the sources by a distribution of doublets, thus replacing the three components of normal velocity by the negative of the velocity potential which has no directivity. Preliminary results show a substantial reduction in computing time and improvement in the accuracy of the results as well. The calculated theoretical predictions for the quadrilateral distribution now show an agreement with the measurements within 2% for the body of revolution and 10% for the surface ship.