Hydro elastic Vibration Analyses

Hydroelastic vibrational aspects of fluid-structure interaction simulations

Vibration is a very important matter affecting people's comfort, equipments' operations and needs to be investigated through analyses at design stage.

The design of a ship construction without any excessive vibration is an important matter and needs to be investigated through analyses in the design stage. Three dimensional finite element method is a common procedure to obtain the ship's main vibration characteristics. Therefore, resonance frequencies can be obtained and through forced vibration analysis, the peak values of the displacements, velocities or accelerations can be checked with ISO standards.

The excitations induced by the propulsion system are the main source of the ship vibrations. These excitations from the propulsion system can be seen in can occur in several ways. Dynamic forces such as thrust and moment variations from the propeller are transmitted to the hull through shaft bearings. The propeller induced fluctuating pressures on the hull surface induces vibration on the ship structure. The main and auxiliary engines can excite the ship's natural frequencies through dynamic forces transmitted from the foundations and supports. These excitations can cause the vibration of the hull girder, deckhouses, local structures and equipment. The order of the excitation frequencies from the propulsion system can be shaft rotational frequency (RPM), blade frequency and their harmonics. The main engine induced unbalanced excitations for the slow speed diesel engines are the first and second order external forces and moments.

The hull structure will normally vibrate in the following modes;
  • Vertical Bending Modes
  • Horizontal Bending Modes
  • Torsional Modes
  • Longitudinal Modes
  • Coupling Modes between the Horizontal and Torsional Modes