Vibration Analysisi Of The Full-revolving Propulsion Ship Stern

With the increasing demand for high speed and multifunction,high-power propulsion systems are used in steel ships, leading to more andmore vibration problems on ship structure. Ship vibration problems notonly have bad impacts on the use of ship, but also affect the normal workand health of board staffs. Ship stern is the main working area of powermachinery and propulsion systems, where vibration problems occur morefrequently. In order to meet with the demand for ocean engineering tasks,ships with full-revolving propulsion system are widely used in21st century.Although the full-revolving propulsion system improves themaneuverability and dynamic positioning ability of the ocean engineeringships, it makes vibration at ship stern more complex. For this reason,structure vibration characteristics of full-revolving propulsion ship sternare studied in this thesis. And the results in the research would provide areference for the acoustic design of ship stern structure.Theoretical, numerical and experimental methods are used to studythe structure vibration characteristics of full-revolving propulsion shipstern in this thesis. Firstly, a composite beam model of the ship stern isestablished and the theoretical solutions are deduced throughEuler-Bernoulli beam theory. Then three different finite element models ofthe ship holds are established for modal analysis of the ship stern. Effectsof added mass on the modes of ship stern are also studied. The results ofthe modal analysis are validated by ship modal tests. At last, a finiteelement model consisting of the stern holds and shaft structures isestablished and vibration responses caused by the propeller and mainengine at several important positions of ship stern are computed to get the transfer functions.Case study of a full-revolving propulsion ship stern vibration iscarried out through the combination of numerical and experimentalmethods. The process of vibration diagnosis and analysis in the case isintroduced in detail. A modification scheme of the structure at ship stern isput forward and validated. Finally the severe vibration problem issuccessfully solved.The research in this thesis reveals the main form of vibration at thefull-revolving propulsion ship stern and provides a new finite elementmodel which is more accurate for modal analysis of the ship stern. Besides,main reason and solution for stern vibration of full-revolving propulsionship are summarized at last, which provide a reference for acoustic design.