ИСТИНА

The prospective use of floating structures for offshore oil and gas field developments in areas with harsh ice regime demands finding ways for ice loads decreasing. Among possible approaches, Floating Production Units (FPU) of ship-shape type are considered, including variants with non-disconnectable internal turret. The concept suggests the ability of the FPU to perform rather quick turning on the spot in close ice in order to take a position against current or anticipated ice drift direction. The problem involves a number of parameters of high indefiniteness. In the paper, the process of FPU turning on spot is analyzed within relatively simple engineering models based on consideration of mass, momentum and energy balances. Within the model, an assessment is performed of the mechanical work that is required for ice breaking and further ice piling up near moving FPU hull. Certain conclusions about the total thruster power on the ship can be derived on this basis. Conservative estimates demonstrate that the active turn of an FPU on 90 degrees at reasonable angular velocity in medium first-year level ice would require the total power being well above values now available. Another model considers an FPU turning on the spot in broken compact ice. Comparison with the case of passive turning of FPU under the action of drifting ice demonstrates that the overall design of the FPU mooring system can be inadequate when the design ice loads are addressed only for the case of FPU heading against ice drift direction.