| Oil and gas resources in the South China Sea account for 1/3 of the country,and most of them were found in the deep water area at 500?3000m.With the national strategies of "Build Ocean Power","Made in China 2025" and "the 21st—Century Maritime Silk Road" have been implemented,leading to more and more ships or platforms working in deep water and requiring dynamic positioning(DP)system.Now marine industry has tightened the requirements of operation safety and reliability of the dynamically positioned ships or platforms.To meet these more stringent requirements,the control precision of dynamic positioning system in normal opertation and effective mitigation of failure must be ensured.This dissertation established a mathematical model of the dynamic positioning system ship.A scaled model ship(1:38 replica of a supply vessel)was designed,constructed to serve as the platform for marine environment disturbance simulation and control algorithm development.The model predictive control algorithm based on a state estimator is proposed.Based on the drift and drive curve of drilling platform,the software is developed to detect the loss of position of the dynamic positioning system,and verified on the "Hai Yang Shi You 981" platform.The main research tasks and contributions can be summarized in the following four aspects:1.The ship motion coordinate system is described,the mathematical model of the ship dynamic positioning system is established.The model captures both kinematics and kinetics of the ship motion for the offshore platform supply ship model(1:38 scale).Hydrodynamic parameters of the ship model were obtained from towing tank experiments.The mathematical model of the ship dynamic positioning system is built in Matlab and this model ship is used as the foundation for the subsequent simulation and ship model test.2.Environmental disturbance is a key issue for the research on the ship dynamic positioning control system.In order to effectively quantify the impact of the ocean environment on ship dynamic positioning,the mathematical models of wind,wave and current are established respectively.A simulation platform is established in Matlab/Simulink to investigate the characteristics of the disturbance force/moments of wind and wave,as well as their impact on the positions of the ship.Experiments are conducted in a pool using the supply ship model to verify that the disturbance simulation platform is effective and versatile.3.Aiming at solving control problem with unmeasured states for the dynamic positioning system,the model predictive control algorithm based on a state estimator is proposed under the constraints of control actuation.A comparative analysis through simulation of model predictive control with or without constraints was performed with a state estimator designed in Matlab/Simulink.The pool tests were conducted by using the supply ship model.Both simulations and model tests confirmed that state estimator-based model predictive control algorithm is effective and accurate.4.For the deepwater drilling ships or platforms,the time of emergency disconnect of the riser system in case of failure is very important.Data on the loss of position incidents of the DP systems of the drilling ships or platforms was collected and analyzed.The failure mode was analyzed.After the dynamic positioning system loss of position,the platform motion law is investigated.According to the marine environment disturbance simulation platform,the drilling platform drift curve was simulated and calculated.The algorithm of determining the threshold of emergency disconnection of riser system for deepwater drilling ships or platforms is developed.The software is developed to detect the loss of position of the dynamic positioning system,and verified on the "Hai Yang Shi You 981" platform.It ensures that the emergency disconnection of the riser system is in time,effective and accurate,thereby ensuring the operation safety of the deepwater dynamically positioned drilling platform. |
PDF Full Text Request