CALCULATIONS OF VIBRATIONS

Calculating the natural frequencies of a component or structure, is a key aspect of its design to avoid possible resonance problems. It is important to calculate these frequencies in the initial phases of the design with the intention of being able to act in time. This calculation must be made alongside to the identification of the acting forces, in order to maintain suitable margins in the working conditions.

In the propulsive installation of the ships, the calculation of the natural frequencies for lateral vibrations is made to guarantee that they are sufficiently far enough from the working frequencies of the installation. This type of vibration can be activated by the hydrodynamic loads from the propeller (forces and moments), as well as by unbalanced masses in the installation.

Another type of calculation which is usually made in ships, is the calculation of axial vibration modes. This type of vibrations is activated mainly by the fluctuations of the propeller thrust.