Vibration Analysis And Optimization Design Of An Official Vessel

As a main vehicle for maritime law enforcement,special attentions are paid on the vibration performance of official ships.In this paper,vibration analysis was carried out for an official ship,and the dynamic optimization design was carried out for some local structures of the ship.Firstly,primary excitation sources of official ships were described in the paper.Except for the generally considered propeller and main engine excitations,the principals of wave excitation and thrust excitation were also demonstrated in brief.The empirical formulas to calculate the propeller induced pressure impulses,surface forces and axial forces were introduced.Secondly,free vibration analysis was carried out by finite element method in the paper.Vibration characteristics of the object vessel were obtained,including natural frequencies and natural modes.The selection of main engine specifications was carried out according to the object vessel's vibration characteristics.And at last,the main engine specifications considered both general performance and vibration performance were obtained.Thirdly,forced vibration analysis was carried out by finite element method in the paper.Global vibration level of hull girder and local vibration level of accommodation cabins were obtained under the excitation of propeller and main engine.The calculation results indicated that the vibration level of object vessel meet the criteria.Finally,dynamic optimization design model was established for a local structure of the subject vessel in the paper,and the corresponding mathematical formula was given out.By modifying the design variables,an optimized design was obtained.Compared with the initial design,the optimized one had less structure weight and its vibration level could satisfy the criteria.This research can provide a useful reference to predict the vibration performance and to carry out the dynamic optimization design of official ships.