| The Deepwater Spar platform is a key tool for human to push forward the deep sea,it plays an important role in deepwater oil and gas field development.Due to the complicated and changeable loads in the deep sea environment,the aerodynamic performance of the Spar platform needs to be tested strictly under the combined action of wind load,wave load and ocean current load.The Spar platform is typically moored and kept in position by steel wires or polyester lines that are anchored at the seafloor.When one or more mooring line(s)/anchor(s)failure due to seafloor geotechnical hazards/instabilities or other reasons,it imposes great risks on the Spar.The paper herein checks the floater’s trajectory motions and the impact on mooring and riser strengths under the mooring line/anchor failure conditions.A case study considers a deepwater Spar platform installed in a water of 1507 m depth.(1)Research on hydrodynamic performance of Spar platform.With the help of SESAM software,based on the three-dimensional potential flow theory,establish the geometric model and hydrodynamic model of Spar platform,then calculate the hydrodynamic coefficients of the platform,including the added mass and damping coefficients,the first-order wave force and other aspects of the results.(2)Based on the overall response analysis of Spar platform,the coupling analysis of the Spar platform and its mooring system in time domain aims to obtain the time history curve of the platform motion,and its also an important basis for the coupled motion analysis of the mooring system and the platform body.(3)Various environmental conditions and load cases are also considered to assess the platform movement tracks and the maximum motions.The three important factors of environmental impact,mooring mode and mooring cable material are studied in this paper.Comparative studies are performed for steel wire mooring lines or polyester ropes,respectively,appreciating advantages or weaknesses of adoption of different mooring systems.(4)The fracture failure of the platform cable should be considered in the design and evaluation of the Spar platform,The transient response of tether tension at the moment of single cable breaking failure is calculated by means of ANSYS-Aqwa hydrodynamic analysis software,and its influence on mooring system and platform is analyzed.The results show that compliant hydrodynamic performance of the Spar Platform was verified.The maximum displacement of the platform in the time domain coupling analysis did not exceed 10% of the maximum water depth,which met the specification API RP 2SK requirements and environmental load requirements.In addition,the mooring performance of the platform can be improved by the taut mooring method and the polyester mooring line.When a single mooring line fails,the mooring system of the Spar platform shows obvious robustness.At the same time,attention should be paid to prevent tension cable fracture failure,to ensure the stability of the platform. |
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