The main objective of the motion control of the semi-submersible equipped with mooring-assisted dynamic positioning system is to keep the vessel within a small radius from a target position while preventing the mooring lines from failure. The optimal setpoint chasing algorithm is applied to the semi-submersible equipped with thruster assisted mooring system to ensure the reliability of the mooring lines. The energy consumption equation of the mooring line tension is built according to the structural reliability indexes and dynamic weight coefficients. The optimal setpoint is calculated online by solving the energy consumption equation. The controller is then designed based on the proposed optimal setpoint chasing algorithm, which is verified and compared through time-domain simulations. The results show that with the same control parameters the presented setpoint chasing algorithm can keep the reliability index of the mooring lines at a relatively high level and improve the positioning accuracy while lower the dynamic response amplitude of the mooring line tension. It can promote further engineering applications of the mooring-assisted dynamic positioning system to semi-submersibles.

Deep-sea mining is the advanced deepwater and ultra-deepwater mining technology with high difficulty. In previous studies, the analysis of the coupling of the dynamic positioning process with the riser and equipment was insufficient. The hydrodynamic performance of the mining vessel is analyzed by the potential flow theory, and the dynamic modeling of the riser and the relay cabin is established by the lumped mass method and Morison equations. The PID controller with Kalman filtering is employed to model the ship dynamic positioning system and simulate the thrust allocation unit, fully considering the influence of the dynamic positioning on the coupled motion system. The time-domain coupling numerical analysis of the deep-sea mining system during the dynamic positioning of the mining vessel is carried out to obtain the movement of the mining vessel and relay cabin under specified sea state, the riser tension and the propeller thrust. The influence of the dynamic positioning system is the also analyzed. The simulation can provide reference for the design and analysis of the deep-sea mining.

The exhaust gas cleaning (EGC) system has been installed on more and more ships to reduce the sulfide emission from the ship exhaust gas, aiming at reducing the environment pollution generated by the ship exhaust gas and meeting the relevant regulations of the MARPOL 73/78 ANNEX VI amendment. The SCHEME A certification plan of the EGC system of a ship is researched from the system design, testing requirements and requirements of standard achievement. The research results show that the scheme design and verification results can meet the requirements of the rule, the EGC system can be used on ships of the same design without testing.

In order to meet the latest sulphur limit requirements of the international maritime organization(IMO), the retrofitting of the exhaust gas cleaning system for a very large crude carrier(VLCC) are examined based on the original system and its characteristics, such as the equipment selection, power load analysis, pipeline system design and general arrangement. The sea trial results show that this retrofitting plan can meet the code requirements and the operation requirements of shipowers.

A semi-submersible drilling platform adopts the evaporative fresh water generator using the waste heat of the diesel engine jacket water. However, the fresh water generating quantity decreases significantly when the operation area of the platform changes. It analyzes the causation of the insufficient fresh water generating quantity in view of both design principle and field-measurement data, and proposes the corresponding solutions.