Modelling And Simulation Of Ballast System Of A 50,000DWT Semi-submersible Vessel

Ballast system is in the process when operating the ship, we can discharged or injection the ships ballast water through the ballast tanks of ships to adjust the ship’s draft and hull stability(including hull longitudinal, transverse smooth and appropriate metacentric height) in order to reduce the hull deformation, hull vibration and improve the cabin air ship seaworthiness purposes, ballast system is a semi-submersible vessel ship design is an important part of the semi-submersible vessel design. Large semi-submersible vessels have larger ballast water and bigger changes in ballast draft condition than other types of ships. Most conventional algorithms which based on the steady-state are conservative. In compare with the real ballast time, the calculated results of most conventional algorithms are excessive. So it’s necessary for us to have a simulation system which can dynamically reflect the ballast system process. In this Thesis, the calculation principle computational method and deficiency of conventional algorithms widely applied now have been analyzed. Aiming at studying a semi-submersible vessel, mathematical models on the ballast process have been built. The modeling process has taken into account the interrelationship between ballast water filling and discharge and floating condition, and other factors such as the real pipe resistance and the air flow.Having taken Matlab/SIMULINK as the development platform, the principle of modular modeling has been adopted to make a ballast tank module base which has three ballast modes. Module base was used to make the semi-submersible vessel simulation system, analysis the ballast rate of three ballast modes, and draw conclusions of features about free loading, ballast pumps and compressed air ballast. We built dynamic model subjects in a 50,000 DWT semi-submersible vessel which has done an overall consideration of demands on ship’s structure, loading efficiency and stability, proposed the ballast scheme of semi-submersible vessel and conducted a simulation calculation which shown the accuracy of our dynamic model. Finally, the thesis has put forward reasonable suggestions on conventional algorithms.