| Popis: |
As the offshore oil and gas industry seeks to reduce costs, a semi-submersible floatel, which provides the space for crew accommodation and open deck space for the necessary equipment, is used to perform maintenance instead of returning the FPSO to a shipyard. One of the unavoidable challenge we have to cope with is the large amount of shielding effects due to the FPSO in the vicinity. The objective of this study is to understand the hydrodynamic interactions and flow interference between them, which will help to develop a comprehensive numerical tool to predict the motion behavior and help designers increase the operability window. Firstly, the second-order diffraction program is used to evaluate hydrodynamic coefficients for a system composed of a floatel operating close to a turret moored FPSO. The calculation is carried out according to different relative positions and yaw angles between the vessels to assess the second-order nonlinear effects and the shielding effects due to waves. Secondly, CFD (computational fluid dynamics) software is used to determine the drag force coefficients due to current and the shielding effects for the two bodies. Numerical studies of thrusterthruster and thruster-hull interactions on unsteady loads are also conducted based on CFD numerical tools. Thirdly, a PID control scheme is used to control low-frequency relative position and orientation between the two bodies. Finally, using the wave, wind and current force coefficients and feedback of DP control system, the global motions of the two vessels in non-parallel environmental conditions are numerically simulated. By using this numerical tool, the shielding effect between a floatel and a FPSO is studied in detail, and all the nonlinearities of the problem can be assessed. New understanding is created through the parametric study, by which useful physics-based information can be provided to optimize the length requirement of gangway and help the operator to decide on the safe working operational scenario. The number of aging FPSO installations worldwide is increasing every year. These FPSOs are connected with massive permanent riser systems and mooring system and it is very costly to bring them to the dry dock for maintenance. By accurately estimating the interactions and shielding effects, improved predictions models are being developed which can increase the up-time of the floatel by up to 20%. This opens up new opportunities for on-site FPSO maintenance with reduced costs. |
