The Dynamical Modeling And Simulation Of Deepwater Hoisting Process

With the gradual metastasis of oil exploration from epicontinental sea to abysmalse, the importance in lifting of subsea equipment such as subsea manifold in deep-seaoil and gas exploration gradually emerge. In the process of deepwater lifting, thesystem consisted of cables, lifting objects and installation mothership suffer thecombined effects of wind and wave. Since the environment deepwater dipping systemworks in is complicated, and therefore it’s difficult and high-costing to obtain motionfeature of lifting objects and installation mothership in through experimental methods.Simulation method is widely used at the present stage to achieve the dynamicsanalysis of deepwater dipping system.Mothership and dipping system is taken as subject of the research to dodynamics analysis of installation process. In simulation of lifting process, thesimulation of environment mothership work in is indispensable, Jonswap spectrum isadopted to achieve the simulation of three-dimensional surface. Two-dimensionalslice method based on potential theory is used in this study to actualize dynamicsmodeling and analysis of installation mothership. This paper employs Simple GreenFunction method to solve two-dimension radiate potential function, superimposetwo-dimensional hydrodynamic parameters along the captain to obtainthree-dimensional hydrodynamic coefficients, and finally get the amplitude frequencyresponse curve of mothership’s longitudinal motion (consist of heave and pitchmotion)combined main parameters of mothership. The Interval of wave’s frequencyin which amplitude in heave and pitch motion of mothership change significantlycould be obtained through the analysis of amplitude frequency response curve. Themotion control system of lifting systems need the support of measurement technology,research of data processing of three-dimensional motion measurement system thatmothership equipped with needs to be done. Adaptive outlier monitoring method isadopted to achieve automatically removed and replaced of outliers in measured data,and then least-squares curve fitting is used to do filtering of measured data so as toprovide accurate input signal for the deepwater dipping heave compensation system.Establish the model of cable based on Ablow&Schechter model, use SDOFequation to describe underwater vehicle, and get the cable’s approximate analyticalexpressions tangential undamped natural frequency and tangential dynamic tensioncombined with the boundary conditions of cable’s ends. The wave frequency rangethat dipping operation should avoid as much as possible could be acquired combinedwith frequency spectrum of the seas in which mothership works. The tangentialdynamic tension curve of cable length release and node position could be got throughthe simulation of tangential dynamic tension so as to avoid tremendous impact loadwhen the cable tighten after slack.Amplitude of heave and pitch motion change significantly when wave frequencybelongs to0.4to0.9rad/s which could be got through kinetic analysis of mothership.When encounter angle is equal to90degree, impact of wave on heave motion ofmothership achieve maximum. When encounter angle is equal to45or0degree,impact of wave on pitch motion of mothership achieve maximum. Through theanalysis of cable and lifting objects, it could be got that tangential undamped naturalfrequency of cable increases with the length of the reduced release, the farther node isaway from the focus of lifting objects, the bigger tangential dynamic tension is. Whentangential dynamic tension is bigger than tangential static tension, laxity of cableappears.