Vibration calculations in marine

Vibration phenomena on board ships may affect the comfort of the crew and passengers, the endurance of the hull steel-work, and the behaviour of engines and equipment. The importance of vibration phenomena is not only due to excitation sources like propeller, main engine, auxiliaries, etc. but also to the vibration response of the different elastic systems constituting the propulsive plant and the ship steel-work (possible resonant response of sub-assemblies).

A ship vibration analysis should be performed having in mind that the static contact conditions between interdependent parts - machinery and steel-work- will influence key parameters involved in vibration phenomena. These contact conditions may even modify the concerned elastic systems (ex: unloaded bearing) and change the values of their respective natural frequencies. There is really a need of a simultaneous integrated treatment of static and dynamic interaction between machinery and hull and. In particular, it's important to determine the most optimum alignment conditions by using an accurate method, such as elastic alignement when ship steelwork is quite flexible and/or when mean values of propeller forces and moments are big. 

Tecnitas can propose services related to ships vibrations at different stages:

  • at early design stage: vibration preliminary risk analysis,
  • at design stage: 3D Finite Element analysis (calculations of natural frequencies and vibrations modes, calculations of vibrations levels),
  • on a ship in service: Finite Element calculations, together with measurements for defining and validating solutions to decrease vibrations levels.

Calculations are performed on a finite element model of the whole ship, including the line shafting connected to the ship steelwork by equivalent elements representing lubricant film stiffnesses issued from elastic alignment calculations.