Calculation And Analysis Of Non-linear Dynamics Of Propulsion System

In the dynamic investigation of propulsion shaft system formerly, main engine andshaft is analyzed separately. As a result the interaction of main engine, shaft and propellercould not be considered. In this thesis the propulsion shaft system is investigated. Amulti-body dynamic model of propulsion shaft system including diesel engine, shaft,propeller and simple bearing block is established based on FE-Models and substructuretechnique, where different bodies are coupled by several non-linear coupling elements. Thecalculation is performed when combustion pressure and propeller exciting force is loaded oncorresponding bodies at the state of power rating. The dynamic behavior of crankshaft, shaftand propeller is investigated within a complete engine cycle, as well as the influence ofpropeller exciting force to the system.The results indicate that, as the affects of propeller exciting force, at drive end ofcrankshaft, the oscillation of axial displacement is intensified obviously, the relative angulardisplacement is increased66%. Under different conditions, the trend and the maximumvalue of force and displacement of journals are consistent, but that is fluctuating tiny. So itis better to consider exterior load when analyzing the lubrication of crankshaft, for themodel being more realizable. The force and displacement of shaft is analyzed, and that ofpropeller and shaft at rear stern bearing location is mainly analyzed. At rear stern bearinglocation, as influence of propeller load, the force and displacement is changed periodicallyalong with the periodicity of exciting moment, and the value in vertical direction is bigger.The value of force at two ends is much bigger than that in middle, and the force close topropeller is about5times of that at the other end. The gravity and inertial moment ofpropeller affects dynamics obviously, the maximum value of inertial moment is almostequal to that of exciting torque, as a result the displacement in vertical direction is minusmost time within an engine cycle, in horizontal direction the value alternate between plusand minus. For propeller, the maximum value of displacement in vertical direction is2.86mm, and1.18mm in axial direction to the engine, the maximum relative angulardisplacement value is0.087radian. That provides an important reference for analyzing andimproving the reliability of propulsion system and implementing its optimization.