Numerical Motion Analysis For The Lifting Of Spar Upper Module

As one of the most commonly used offshore operation, whether the lifting operation canbe enforced successfully has a great influence on the schedule of an offshore project. Thus, awell established analysis model to assess the safety of lifting operation and to give a report onthe operation limits is essential for a time-saving and lower cost operation.In order to get the safety operation environmental conditions, it is necessary to performnumerical motion computation for the multi-body systems including transportation ship, craneship and spar upper module under different environmental conditions and then according tothe industry rules and requirements, motion states of multi-body systems must be verified.The main content of this paper can be described as follows:Based on the3-D radiation and diffraction theory, the RAOs of multi floating systems inwhich crane ship and transportation ship are arranged in T shape and crane ship are analyzedto evaluate their motion risk. After that, time domain analysis for three different stages(pre-lifting stage, lift-off stage and pendulum stage) are performed in actual operation order.In the pre-lifting stage, the significant wave height sensitive analysis and period sensitiveanalysis for13wave angles between0degree and180degree with equal space are performedto get the safe operational environmental conditions of this stage; In the lift-off stage, throughsimulating lift-off operations at different time in different velocity under the safe environmentconditions got from pre-lifting stage, it can be concluded that within permission range, a highlift-off velocity and good sea state will provide safer operations; In the pendulum stage, onlythe safe environment conditions are considered. In the last stage, through analyzing theinfluence on the motion safety when the upper module is at different height, it can beconcluded that the head sea state is more suitable for improving the safety of pendulum stage.Through all these computation analysis, the key points and operation strategy of liftingoperations are settled, which has a great influence on feasibility study of big size heavy liftingoperations.