VIBRATION ANALYSIS

Scope of this analysis is to assess the response of the structure to the several exciting forces acting on the ship.  The Main Engine operating speed affects the low frequency range, where significant hull girder normal modes usually occur. The hull girder resonance phenomenon can occur when the propeller blade frequency or the main engine unbalanced forces and moments frequencies approach or equate the natural frequency of one of the vibration modes of the ship. The comparison between exciting forces and hull girder natural frequencies should highlight critical frequency ranges.

The aim of the global analysis is to highlight any possible coincidence between the fundamental frequencies of the excitation of propeller and main diesel engine with the lower natural frequencies of the hull. Moreover, by plotting the fundamental modeshapes of the hull, the position of the main engine is going to be checked. Further analysis, based on the frequency response function, should be performed whenever dangerous operating condition would be observed.

 Two extreme loading conditions are considered:

-          Ballast Arrival;

 -        Full Load Homogeneous Departure.

Indications on the behavior of the structure in the intermediate loading conditions can be extrapolated once the results of these conditions are known.

 

FE model of a typical chemical carrier is reported here below.

Examples of the obtained results on a  25000 dwt Chemical Carrier:

  

 

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