부산대학교 도서관

As ships have become faster and bigger, two stroke low speed diesel engines are being used as the core of a propulsion system of these ships. Also, this causes these engine's output to increase. For this, we should consider 1) the torsional vibration of propulsion shafting system as well as 2) its torsional forced vibration by a cyclical excitation torque (cylinder's explosion pressure and return-inertial force). Once frequency of the torque is in consonance with that of propulsion shafting system, the torsional vibration amplitude rapidly increases so that can seriously damages a crankshaft or a gear. This paper presents a propulsion shafting system which consolidates its safety and reliability. For this, we theoretically analyze a torsional vibration of the system and then measure it by applying damping coefficient values to each part of two-stroke low speed diesel engines (8K80MC-C) according to a standard of engine manufacturers. Damping coefficient values are important factor for our experimentation because they are considered from an initial design phase of this system. As a result, we obtain accuracy of the theoretical interpretation through comparative analysis of measured results and this system satisfies the criteria of classification societies. Using analysis and measurement of the system, we have come to the conclusion for the torsional vibration mode, natural frequency and comparative analysis of additional stress. Firstly, the major torsional vibration mode of Crankshaft is 2nd and 3rd mode generating Maximum Stresses, and that of intermediate shaft and propeller shaft is 1st mode generating Maximum Stresses. Secondly, the natural frequency meets within 2 rpm (criticality value) so that input values, the moment of inertia and stiffness coefficients for shafting system, are relevant to the frequency when an analysis is achieving. Thirdly, torsional stress is within criticality value, 10% or 2 and this value is significantly less than normal value of the Classification Society. This means the accuracy of the damping value. Therefore, K80MC-C engine is proved in the aspect of the safety of the propulsion shafting system. Finally, we apply the major coefficient, the damping coefficient when analyzing torsional vibration of propulsion shafting system, and analyzed and measured values in the vibration are compared with regulations of the Classification Society. As a result, we were able to get a satisfactory result. Therefore, the system's stability and the reliability about inaccurate damping value when interpreting of the torsional vibration was secure.