The operational weather window of a jack-up barge is determined by its stability. Allowing more harsh weather conditions at increased water depth, enlarges its operating time. The question was raised under which condition of weather and leg height, resonance could occur. This resonance would endanger the safety of the barge.
To determine the conditions provoking vortex induced vibrations, fluid simulation of the flow along one leg was performed for different water velocities. Furthermore, the structure resonance was computed. The eigen-frequency of the structure approaches the frequency of the vortexes under some conditions of anchoring, height and water velocity, being the most dangerous conditions.
A safe operational window to avoid lock-in of the legs was identified and critical conditions have been determined.
Natural frequency of oscillation
Structure excitation and displacement
Vortex behind leg