FLOATING CRANE RESPONSE IN SEA WAVES

Many activities present in the offshore technology are affected by sea waves and their safety strongly depends on the sea state. The fundamental question in operation risk analysis is the limit sea state which enables the safe operation controlled in all phases: from the sea surface to the sea bottom. The safe limit sea state is especially important when some lifting operation is performed in sea waves. This paper presents a dynamical model of a floating crane in sea waves with a hanging load at a high altitude above sea level. The model is defined as a linearized coupled double pendulum where the usual 6 DOF of the floating crane oscillatory motions in waves are extended by additional 3 DOF of the swinging load. The numerical model of the floating crane is calibrated and tuned according to the measured model in a towing tank. The significant values of the crane boom top accelerations were estimated for the given design sea state with different vertical load positions. The problem is illustrated by the example of a floating crane consisting of a simple single pontoon with an ordinary land crane mounted on the deck. The reliability of the proposed method is evaluated on the basis of correlation between the calculated and measured data.