Study Of Vibration Model For Large Scale Ship Shafting Subjected To Hull Deformations And Main Engine Excitations

The ship propulsion system mainly consists of main propulsion plant,supporting system,propeller,engine room automation system and related auxiliary machinery equipment system.It is responsible for energy supply,power transmission,ship propulsion,and to ensure the safety of the work and personnel lives on board,which is an important part of the ship.In the recent years,the development of large-scale ships effectively promotes the transportation of global ocean cargo.The breakthrough of upsizing technology is an important embodiment of the advanced ship design and building level.As a kind of soft structure,the large scaled ship hull is easily deformed by changing the relative stiffness and positions shaft supporting bearings,which leads to the frequently variation of propulsion system working environment.Especially for large cargo and other stern-engined ship,the short and thick size of shaft makes that the propulsion system has large stiffness.Therefore,the shaft would vibrate severely in transverse direction,even when its vertical location fluctuates within a narrow range.So the research on the effect of hull deformation on power performance of the propulsion system in different navigation and working conditions is very important.This paper mainly takes the large ship propulsion shaft as the research object.Considering the effects of the hull deformation and main engine to the propulsion shafting separately,the vibration model of ship propulsion shafting was built preliminary.Based on the shaft vibration models,the vibration characteristics of propulsion shafting taking the hull deformations and main engine excitations into account separately were analyzed.The theory results were verified by the vibration test of marine shafting in the laboratory environment,which could improve the engineering application value of the theory model,provide the methods and technical support for the optimization design,installation,performance monitoring and maintenance of large ship propulsion shafting.It also could provide the references for the maintenance and repair to prolong the service life of ship.Based on the large ship propulsion,the main works in this paper are as follows:1.Considering the hull deformation,the vibration modelling theory of ship propulsion shaft is built.The dynamic equations of the sub-structures such as hull,main engine,shaft,bearings are combined to build the whole hull-propulsion shaft system through the variation principle.Shaft relative motion factors and twist factors are introduced.Based on the 297000 DWT VLCC,it investigates the efforts of the key factors in the ship design stage.As a result,some suggestions are proposed to optimize the ship hull structure.2.The excitations of main engine to the shaft is discussed and the main engine-propulsion shaft model considering the main engine exciations is built to analyze the coupling effects of shaft torsional and transverse vibration.Taking the MAN B&W 12K98MC-C main engine in the 8530 TEU container as an example,it verifies the accuracy of the model.3.Based on the propulsion shaft dynamic characteristics experimental platform in laboratory environment,the model of shaft in the experimental platform is built by the proposed theory above and the accuracy is testified.Meanwhile,the effects of hull deformations and different rotating speeds are analyzed by testing the vibration of the shaft.4.Taking the 8530 TEU container as th e object of real ship test,the experimental research of its propulsion shaft system is made and the shaft vibration responses under the effects of hull deformations and main engine excitations in different navigation and working conditions are analyzed.By the research of ship hull-propulsion shaft vibration modeling theory and main engine-propulsion shaft vibration modeling theory,the reasonable optimization suggestion that the shaft frequency factor(The ratio of the shaft first bending natural frequency and the hull first bending natural frequency)should be far from 1 is proposed in the preliminary stage of ship design and building.Moreover,monitoring and adjusting some parameters such as rotate speeds could avoid the coupling effects of the torsional and transverse vibration of the main engine-propulsion shaft system during the operation,reduce the losses of power of shaft and guarantee the safety of reliable navigation.Meanwhile according to the experimental analysis in the laboratory and testing analysis in the real ship,the main influence factors leading to the shaft various virbations are verified which could provide technical support for the future shaft vibration research during the ship sailing in the sea conditions.