simulation of the natural frequency of the jacket legs of Oil platform under water wave force with various boundary conditions on the legs

The offshore structures are always under water wave force. One of the effects of waves on the jacketsis is deformed and collapse phenomena. We know if the natural frequency of structure was near the frequency of the applied wave force, the resonance phenomenon will take place intensified. To prevent this phenomenon can with changes in the structure prevent from resonance phenomenon. In the paper we modify the boundary conditions of the jacket legs attached to the bed of the sea floor, it is shown which boundary conditions the natural frequency of the structure will be more distance from forced frequency of the wave. Finally,appropriate boundary condition is applied.