Dynamic Analysis And Drive Control Method Study On Subsea Flex-Lay System

Subsea pipelines are generally applied to offshore oil and gas transportation throughout the world in this decade.Unlike laying pipe on land,the subsea laying operation of pipeline under complex marine environment depends extremely on dedicated equipments.As the worldwide accelerating exploitation of offshore oil and gas resource,high-tech pipe laying equipments play an increasingly important role in exploitation engineering.European and North American countries take the leading place in subsea pipe laying technique and operational equipment,while there are visible gaps on both theoretical study and engineering practice between western world and China.The study on key technique of subsea Flex-Lay system contributes greatly to the break of foreign technological block as well as the promotion of domestic technological level.The dynamic performance,the driving and controlling properties of subsea Flex-Lay system are studied in this theses to solve the problem of pipe kinetic state and tension control under marine operation environment.The main study contents include:Overview of subsea pipe laying technique and equipments are introduced,especially the highlight on subsea Flex-Lay system and relevant key techniques.These key techniques include:gross dynamic performance of laying system;dynamic braking driving technique under damping pipelay operation;compensation control technique under marine environment.Detailed study statuses,insufficient and referential achievements on related area are viewed.Directing at the integral laying system,discretization and transformation of both flexible pipe and rigid laying equipments are performed with the Rigid Finite Element Method,and simplified model of the rigid-flexible coupling multi-body kinematic chain is established.Joint coordinate system is built to describe the topological structure of the multi-body chain,and both local and global homogeneous transformation matrixes are provided.The position and orientation parameters of local body frame are selected as generalized coordinates.Lagrange operator,derivative of gravitational potential energy,and generalized force of ordinary part are defined,consequently the general form Lagrange equation can be deduced.Vector expression of generalized coordinates,Lagrange operator,derivative of gravitational potential energy and generalized force are defined and block matrix are constructed,thus the Lagrange equation set namely the dynamic model of integrated laying system can be established.Program to solve the dynamic equation set is developed in MATLAB.Elementary modeling parameter,material property parameter of flexible pipe and motion parameters of laying vessel are provided as the necessary initial conditions for solving the equation.Initial laying analysis and static equilibrium analysis are performed,and the driving effect and the influence of laying parameter and pipe material parameter on pipe tension and bending torque are studied.Pipe laying analysis under ideal operation condition is conducted,so stable values of pipe tension and bending torque are acquired.Pipe laying analysis under practical operation condition is also performed in terms of the six degrees of freedom vessel motion respectively,therefore crucial influences on laying speed,pipe tension and bending torque are confirmed.In order to acknowledge the effect of disturbance on the system,the key parameters,such as disturbance peak and frequency,are analyzed in different values conditions by the same method.Operation processes of subsea Flex-Lay system are introduced and structural scheme of main device are presented.Main items include the laying tower and the inclination angle adjusting system,the rotational drive system of storage reel and the vertical,lateral,longitudinal position adjusting device.The longitudinal walking device is studied intensively.Walking principle based on inchworm squirm and alternant drag is promoted,and corresponding mechanical structure together with hydraulic drive system are designed.The intermittently creeping and continuously dragging movement process is analyzed and the velocities of all moving parts are calculated.Maximization of frame walking velocity is set as optimization objective,and flow limitations of hydraulic system are chosen as optimization constraints.Mathematical optimization model is built with design variables of vertical and lateral motion time.Based on the dynamic analysis,principle of drive and control system is proposed according to different operating requirements of subsea Flex-Lay system.Hydraulic drive system with dynamic braking function is designed,which can also convert and consume gravity power of flexible pipe.Simulation model of the rotational drive system is built considering mechanical transmission system and hydraulic power system with MATLAB.Fuzzy control system is applied to achieve a tension compensation goal in this simulation model.Pipe tension resulting curves obtained in dynamic analyses are introduced in simulation to verify the compensation capacity of system.Design and manufacture of main equipment prototype are conducted and testing system is built to simulate gravity of pipe and motion of laying vessel.Constant damping laying test and tension compensation laying test of the rotational drive system is perform in the following three conditions:initial laying,ideal laying and realistic laying with disturbance applied.Dynamic analysis results,driving property,dynamic braking property and tension compensation property of the rotational drive system are verified through test.Hydraulic flow parameter of the longitudinal walking device is set according to the optimization result,and experiments are performed to examine the motion processes and maximum velocity.Dynamic model of subsea Flex-Lay system is built by Rigid Finite Element method and Lagrange equation.Hydraulic drive system with the function of dynamic braking and load power consuming is designed.Meanwhile drive control system with the function of tension compensation is devised.The first main device prototype is developed and simulation test on land is conducted.The study of this thesis can provide some valuable reference to subsea pipelay technology and equipment.