| This paper based on the national "863Program" offshore oil and gas exploration anddevelopment technology, special projects-" Research on the key technologies of dockingand emplacement of the novel jack-up platform with double unitsâ€. General Performanceand docking dynamic characteristics of the novel offshore jack-up platform with doubleunits were thoroughly studied.By theoretical studies, numerical calculation and laboratoryphysical model calculations, this thesis is devoted to investigation on the overallstability of the upper and lower units, safe ups and downs posture of the lower unit, thecollision time course during docking and the influence factors and their sensitivities,overall performance of the platform under environment load after docking, indoorsphysical model tests and results analysis and so on were researched and some progresseswere made. The main findings are summarized as follows:1The Overall Stability and Safe Ups and Downs Posture of Jack-Up Platform withDouble UnitsBy theoretical analysis, numerical model were built for the upper and lower units,under the conditions of oil-field towing and ocean towing with the different wind direction,the wind wave current combined force moment were calculated by PANB software ofoffshore platform static stability analysis. The overall stability of the lower and upper unitsduring floating, the safe ups and downs posture of the lower unit, and the overallsupporting stability after docking were analyzed. The lower unit will sometimes submergebelow the sea level during the practical condition. Stowage planning numericalprogressivenumerical model was built and uniform ups and downs were chosen. Thevariance of the posture of the lower unit was studied and the safe critical point wasobtained.The anti-overturning and anti-sliding stabilities of the platform after docking wereanalyzed.With the different wind direction, the component force moment, global forcemoment, anti-overturning moment, anti-sliding moment and safe factor of sliding forcewere calculated under integrated conditions. Results showed that the stabilities met therequirements,the structure design of the lower unit met the floating stability requirements,the overall supporting stability of the platform met the requirements.2The Collision Time Course during Docking and the Influence Factors RegularityAnalysisUnder external loads and internal factors, the jack-up platform with double unitsinevitable collision during the docking process.The influence factors and their sensitivitiesof collision between the legs of the upper unit and the lower unit were analyzed during thecourse of docking. Numerical simulation of stress wave spreading progress and rules wasmade based on Lagrangian approach. The influence and sensitivities of the key influencefactors on collision was analyzed using dynamic analysis program.Studies showed that the collision process is a process of millimeter; wave and flow are the key influence factors forthe initial state of the collision. The higher stress appears at legs, radiant panelconnected to the leg, and the conjunction supporting the lower unit. The maximum stressand the global collision force increase nearly linearly with the increment of collisionvelocity and the weight of the upper unit. They will also increase obviously with theincrement of collision angle. The friction factor has little influence on the collision.Choosing appropriate shock-absorbing material will obviously reduce collision.3Dynamic Response Analysis of the Platform Overall Structure and Guiding CableThe docking process between the upper unit and lower unit was completedmechanically by the guide cable. The load response and displacement response propertiesof the guide cable under different environmental conditions and different platform weighthas important influence on finishing docking correctly. After positioning on the wellhead,due to the increment of the water depth and harsh environmental conditions, the dynamicsensitivity and nonlinear response of the overall structure of the platform and the pile legwas significantly enhanced. It is necessary to perform dynamic response analysis of theoverall structure to guarantee the safety of the platform. The motions of the platform inwaves were analyzed by using three-dimensional linear potential flow theory and Morisontheory. The water and power factor in the different impact conditions was calculatedbased on the frequency domain analysis. The stress distribution and displacementresponse of the guide cable were analyzed by time domain analysis method. Using FEMsoftware, static analysis was performed for the jack-up platform with double units, and byselecting a series of different impact parameters, the overall performance of the platformwas studied. Furthermore, modal analysis and transient dynamic analysis were alsocarried out for the platform. Studies showed that the plan of guide cable was feasible anddynamic response of the platform structure was safe.4Indoors Physical Model Tests and Results AnalysisBased on the numerical analysis, the overall performance and the dynamiccharacteristics of the platform were tested by indoors experiments with a certain scalephysical model. The accuracy of the conclusions of numerical simulation analysis wasverified by experiments results.By analyzing the bearing loads of the guide cable under the external environmentloads, the dynamic response characteristics were researched during the process of dockingprocess. By performing the ups and downs experiments of the lower unit, the ups anddowns stability and safety critical point of structure floating state were researched. Bydocking impact test, the docking techniques and the reliability of instruments werevalidated. Shock resistance reduction measures and docking course were researched.By vibrating and shocking experiments of the upper unit, the vibration influencing factorsand regularity of the upper units were analyzed. The experimental results indicated that overall performance and docking dynamic characteristics of the jack-up platform withdouble units met the requirements of engineering applications. The experimentsestablished the theoretical foundation for further engineering application of the platform. |
PDF Full Text Request