The Hull Girder Vibration Analysis Of42m Trawler

In recent years, fish resources are reducing gradully at offshore with the increasingfishing intensity, so fishermen must leave offshore for fishing in order to get more fish, italso improves requirements of some indexes of fishing vessel, the vibration is an importantindicator. In the previous fishing work, because the inshore fishing lasts a relatively shorttime, the vibration of the ship will be ignored. The ship lasts long time when it fish in thedistant sea, the vibration problem is more prominent because the harmful vibration effectsship equipment and crew all time. This paper analyses the whole ship vibration for a42mtrawler by finite element software MSC.PATRAN/NASTRAN. Two working condition offull-loaded back and no-load to port will be analysised.Firstly, the hull inherent characteristics is calculated. The effective mass participatingin ship vibration will be considered when we analyze the hull vibration. In this paper, themass of the hull is simulated by plate elements and beam elements of three-dimensionalmodel. The mass of equipment on board is applied to corresponding position of device bymass point. The mass of goods on board is obtained by “hull calculations” and applied tothe model according to actual distribution. The mass of attached water is calculated byformula in CCS standard “boat Vibration Control Guide” and applied to the modelaccording to actual distribution. Then the model is analyzed by modal analysis, the inherentcharacteristics of hull is got. In addition, we analyze the change of the natural frequency ofhull without attached water.Secondly, the response of forced vibration of hull is calculated. The exciting forces arecalculated and the damping and boundary conditions is determined when we analyze thehull forced vibration response. The exciting force is divided into host exciting force,pulsating pressure and bearing force, the host force is calculated by formula in “ShipVibration Basic and Practical Calculation”, fluctuating pressure and bearing force arecalculated by formula in “Ship Vibration Control Guide”, the exciting forces are applied tothe model according to the actual situation. The damping is0.03. Spring constraint is usedboundary conditions. Then we analyze the model by transient response and obtain the threeresults of acceleration, velocity and displacement of hull vibration, the points at differentlocation are analyzed. Finally, the analysis results are compared with the vibration criterion,then we draw conclusions. Also we analyze the impact of attached water for forcedvibration response.Thirdly, local vibration attenuation is analyzed. The local structure of modal are modified when the forced vibration calculation is completed. In this paper, the modifiedmeasures mainly includes two parts of hull structure and engine base: the hull structuremodification measures includes setting the column in cabin and increasing quality in thestern; the modifications which a reference mentioned are used to engine base. We analyzethe modified hull by transient response and obtain modified results. Finally we compare theresults and get the best measure of vibration damping effect.