An experimental method to identify a component of wave orbital motion in propeller effective inflow velocity and its effects on load fluctuations of a ship main engine in waves

Improvements of estimation accuracy on propeller torque fluctuations in waves will contribute assessments on safe operation of a ship main engine as in adverse sea condition. The propeller torque and thrust in waves can be estimated by propeller effective inflow velocity in waves, using the propeller open-water characteristics. Fluctuation components in the mathematical model of the propeller effective inflow velocity in waves can be composed of two components, respectively caused by ship surge motion and wave orbital motion at propeller position. In this study, an experimental method by the model test to directly identify the characteristics of the component by the wave orbital motion is newly proposed. Furthermore, the free-running model test in regular waves, using a simulator of the marine diesel engine which manages the shaft speed of the motor on a ship model as behaving the actual diesel engine, is carried out to obtain realistic torque fluctuations for comparisons of the estimated results applying the proposed identification method. Through comparisons of estimated fluctuations with the measured results, the proposed approach for the component of the inflow velocity due to wave orbital motion is successfully validated.