Thermal interaction between main engine body and ship hull

Abstract

The paper presents analysis of displacement of a propulsion system shaft line and a crankshaft axis caused by temperature of marine, slow-speed main engine. Detailed information of thermal displacement of a power transmission system axis is significant during a shaft line alignment and a crankshaft springing analysis and during designing of structural health monitoring (SHM) system. A warmed-up main engine is a source of deformations of an engine body as well as a ship hull in the area of an engine room and hence axis of a crankshaft and a shaft line. Engines' producers recommend the model of parallel displacement of the crankshaft axis under the influence of an engine heat. This model may be too simple in some cases (especially for SHM systems).The paper presents computations of MAN B&W K98MC type engine mounted on 3000 TEU container ship. The engine body is much stiffer than its foundation pads and ship hull (double bottom) - boundary conditions of the engine. Especially for the high power marine engines correct model of the boundary conditions plays a key role during the analyses. Presented numerical analyses are based on temperature measurements of the main engine body and the ship hull during a sea voyage. Numerical analyses were performed using Nastran software based on Finite Element Method. The FEM model of the engine body comprised over 800 thousand degree of freedom (dof); the model of the ship hull contains over 200 thousand dof. Both models are analysed separately; the mutually interaction between them is taken into account by heat transfer and special model of boundary conditions. The specialized SHM system dedicated to marine propulsion systems working in very bad environmental conditions is the future aim of the research.