Study On Measuring And Adjusting Pivotal Techniques Of Bearing Loads For Propulsion Shafting Of Large Ships

With the ongoing increase of cargo ship size, the size of marine propulsion shaft has been rising, leading to the bearing load increase. In order to ensure the normal operation of the marine propulsion shafting system, the shipping group puts forward higher requirement for shaft alignment. Many shipyards commonly check the quality of shaft alignment by the method of measuring bearing reactions. However, the technical methods of measuring bearing reactions are still traditional, which cannot meet engineering demands. For that reason, this paper researches the techniques for measuring and adjusting bearing load of marine propulsion system.Firstly, the paper analyses the bearing load measurement technique based on jack-up method in theory. The meaning of common jack-up curve and the calculation method of bearing reaction are presented in the paper. The bearing reaction measurement system based jack-up method is established by the integration of sensor technology, data acquisition technology and visual programming software VB.NET. This system includes the jack-up data acquisition hardware system and operation software.Its reliability and accuracy are verified by actual measures in ships.Secondly, in this paper the other bearing load measurement technique based on strain gauge method is theoretically researched. A vessel is likely to have stern tube forward bearing or not. In both cases, the calculation methods of load distribution between the forward end and after end of stern tube after bearing are proposed in the paper. Through the analysis of measuring and computational errors, a principle for distribution of strain gauges and a method of selecting strain gauges for calculating bearing loads are introduced. Beyond that, the calculating software of bearing load based on strain gauge method is developed, and the measured process is optimized, which simplifies the flow of pasting resistance strain gauges on the surface of shaft and increasing measuring accuracy. Through the actual measurement, the comparison between the measuring results based on jack-up method and the measuring results by strain gauge method suggests that the bearing reaction measurement system based strain gauge method is accurate.Lastly, the methods to optimize bearing offsets are studied to solve the problem that the actual measuring bearing loads cannot comply with the theoretical values of bearing loads provided by calculation of shaft alignment. An inference algorithm of bearing stiff based on jack-up method is introduced and a calculation method of bearing load influence number considering bearing stiff based on finite element method is proposed in the paper. The methods to optimize bearing offsets based on nonlinear programming and bearing load influence number are presented. Through the study on the adjustment technology of main engine main bearing, the bearing offset constraints of main engine are set in the paper. Based on this, the calculating software of bearing offsets is developed and the comparison between calculation results and measurement results show that the algorithm and the software are feasible and reliable.