Hydrodynamic Response Analysis Of S-spar In Deep Water

With the development of deepwater oil exploitation technology, a lot of novelstructures suitable for deep water are being evolved concomitantly, such as FPSO,Semi-Submersible Platform, TLP and Spar. Spar platform attracts great attention ofengineering and academic domain because of its good performance. At the same time,all kinds of research field of Spar platform are being developed, especially about thedynamic response of Spar platform. The dynamic response of S-Spar platform withhelical strakes is investigated in the thesis and the thesis strives to obtain results whichcan take helical strakes into account. The main contents and conclusions aresummarized as follows：1. The evolvement as well as the structure characteristics, strengths andweaknesses, economy and the future of Spar platform is elaborated systematically.The notion, structure characteristics and strengths of S-Spar platform are introducedsystematically. The parameters of hull and mooring system for S-Spar platform aregiven in the thesis.2. The ANSYS/AQWA FE models of S-Spar platform with different helicalstrakes and heave plates are set up and the theories of potential flow anddiffraction/radiation are used to calculate dynamic response of S-Spar in the unit waveamplitude to obtain the hydrodynamic parameters in the frequency domain such asadded mass, radiation damping and motion RAO. The calculation results show thatadded mass and radiation damping of S-Spar platform have reached good level, andS-Spar platform is considered to have good motion characteristics. As the thickness ofheave plates gets bigger, the added mass and damping of surge, sway, roll and pitchtend to increase, and the added mass and damping of heave tend to decrease. Theadded mass of yaw for S-Spar platform with heave plate thickness of1m is thesmallest one among that of the three kinds of heave plate thickness. The radiationdamping of yaw tends to be stable as the thickness of heave plates varies.As the lead of helical strakes gets bigger, the added mass of surge, sway, roll and pitch tends to increase, and the radiation damping of the four motions does not varyapparently. Some values of radiation damping of heave and yaw for S-Spar with thehelical strake lead of90m and60m are negative, and it may aggravate the motions ofS-Spar platform. As the lead of helical strakes varies, the frequencies in which theamplitudes of RAO of surge, heave and pitch lie tend to be stable, and the amplitudesare also well controlled.3. The coupling analysis model of S-Spar platform with helical strakes andmooring system is set up using the software module AQWA-DRIFT based on resultsin the frequency domain. The dynamic response analysis of S-Spar platform withhelical strakes is performed through coupled method taking wave, wind, current andnonlinear effects into account. The wave force time history, motion time history,tension time history of mooring lines and maximum tension of S-Spar platform withhelical strakes are obtained. Then the results are compared with those of S-Sparplatform without helical strakes. The analytical results show that the motion responseof S-Spar platform and the safety factor of mooring lines satisfy the requirement ofrules when the mooring system is integral or one of mooring lines is broken. Thethesis compares dynamic response of S-Spar with helical strakes and without helicalstrakes. The results show that helical strakes may increase the amplitude of yawmotion and decrease the tension of mooring lines of S-Spar. The performance of yawmotion and extreme tension of mooring lines may be overestimated without taking theinfluence of helical strakes into account. At last, the dynamic response analysis ofS-Spar platform with helical strakes in extreme sea environment is performed whenone of tanks is broken. The calculation results satisfy the requirement of rules andshow that S-Spar platform has excellent motion performance.