| Oil & gas resources are the most concerned topics due to its heavy consumption. As is known that oil exploitation both on land and nearshore has been on for a certain history, more oil resources still hide in offshore deepwater even ultra deepwater areas.Offshore West Africa (WOA) is one of the hottest three spots for offshore oil and gas exploitation. China is one of the fastest developing countries, and she has a greater demand for oil and gas resources. It is one of the most significant strategies for China to participate in oil & gas exploitation overseas. In present paper, theoretic analyses, numerical calculations and model tests are conducted to investigate the hydrodynamic performances of multi-point moored FPSO (Floating Production Storage & Offloading), CALM buoy and shuttle tanker, which are the main floaters in typical pattern for oil and gas exploitation in WOA.One of the most concerned priorities is to figure out the environment conditions and motion characteristics of floating platforms offshore West Africa. Long period swell exists with short period wind-sea in different directions, which shares a great difference against other sea areas. Generally, sea loads in WOA seem relatively benign, but long swells have an indispensable and distinct effect on the motion response of floating units, which might cause some special problems.Investigation on FPSO hydrodynamics is conducted in bi-directional swell and wind-sea in WOA. The concerned topics mainly include FPSO vertical motions, i.e. heave, roll and pitch, and FPSO horizontal motions, i.e. surge and sway. Vertical motions are dominated mainly by swell. On the other hand, swell and wind-sea are both indispensable for low frequency drift loads and induced horizontal motions.Horizontal LF drift forces on FPSO can be decomposed into four parts in bi-directional waves, two parts separately from each directional contribution and other two from the coupling interaction between both incident waves. In WOA, it is found that the coupling interaction between different incident waves is relatively small due to the deviation of wind-sea and swell.FPSO motions are sensitive to the variation of swell incident angles, peak periods and peak factor. Roll and sway keep the response period as their own eigen periods, though heave and pitch follow the swell's characteristic period. Peak factor does not influence the motion response period, but it has a great effect on horizontal LF drift loads and motions.Focusing on the main pattern of oil & gas exploitation in WOA, investigations on Calm buoy and shuttle tanker are performed. Hydrodynamic performances of buoy have been obtained. Due to the small size of buoy, the coupling and viscous effect from slender structures become indispensable, and then the coupled solution in time domain can make a reasonable prediction on the motion response. Motions in different DOF are dominated by different wave components, i.e. swell and wind-sea.Hydrodynamic performances are investigated on the complete system consisting of buoy and shuttle tanker. Still due to the size difference, hydrodynamic interaction between each other is relatively small. Coupled analyses on the complete system are performed to find that vertical motions of shuttle tanker are dominated by swell, while on the other hand, horizontal motions are most influenced by low frequency wave drift force, current force and wind force, etc. Meanwhile, it is obvious to see the cycle phenomenon for horizontal trajectory of shuttle tanker.To satisfy the demand for oil exploitation overseas, hydrodynamic performances of floating platforms are investigated in bi-directional swell and wind-sea in WOA. Focusing on the main floaters, e.g. in typical pattern offshore West Africa, an effective calculation for LF drift loads and induced motions is established. Meanwhile, general rules are obtained for complicated horizontal motions of coupled system consisting of buoy and shuttle tanker. Advices are provided for further engineering practice. |
PDF Full Text Request