Estimate of the fatigue life of the propulsion shaft from torsional vibration measurement and the linear damage summation law in ships

Abstract

Most ships use a diesel engine for the propulsion system. Since a diesel engine is operated by the force of the cylinder from the explosion of the gas, the torsional vibration from the fluctuation torque is bigger than that of other types of engines, such as gas-turbine and electrical propulsion motors. Therefore, the propulsion shafts in ships frequently fail due to the extreme torsional vibration from diesel engines. Ships that require high power and revolution speed usually have V-type, 4-stroke diesel engines and reduction gears to increase the output torque. Therefore, a robust design of the shaft is required for this type of vessel. In this research, the fatigue stability and life cycles of the shaft are estimated with Soderberg׳s safety evaluation method and the linear damage summation law based on the torsional vibration data. When estimating them, non-standard sailing conditions such as starting the engine and zigzag maneuvers are included in addition to normal sailing conditions such as straight maneuvers.