Prediction of global vibration levels

Purpose

The objective is to investigate whether the specified vibration levels onboard a vessel are expected to be met and prevent structure to be in resonance with main excitation sources. The analyses may avoid excessive vibration affecting comfort, safety and operability of a vessel.

Benefits

DNV has leading-edge competence and tools to analyse the vibration behaviour of ship structures. The results will serve as a basis for the evaluation of compliance to specified vibration levels of the vessel. Based on our extensive experience base, we may propose possible modifications to the design in order to avoid the risk of excessive vibration, which affects comfort, safety and operability of the vessel.

Features

The analyses are based on the following information:

Line and structural drawings of the vessel
The applied forces are taken from the propeller excitation analysis and possible engine excitation forces given by the manufacturer.

A 3-D global Finite Element Model (FEM) of the vessel will be used to analyse the vessel’s vibration modes and vibration levels. The results are documented in a report covering: -

Global natural frequencies and mode shapes
The natural frequencies and mode shapes of large substructures
The forced global vibration level
The forced vibration level of large substructures.

The results are presented as mode shapes and coloured plots showing the distribution of the vibration levels on each deck. If any of the specified vibration levels are likely to be exceeded, the problems and consequences will be documented and structural modifications will be proposed and discussed with the yard.