Modeling And Simulation Of LNG Carrier Propulsion System

With the development and growth of China's LNG fleet, it is significant to train skilled marine engineers for LNG carrier through the marine engine room simulator. However, it is entirely dependent on foreign expensive engine simulators of LNG carrier for marine engineers' education and training at present stage in China. The situation has restricted the development of China's LNG carrier transportation to a certain extent. Therefore, in order to break the monopoly of foreign expensive products and save money, it is necessary to carry out mathematical modeling and simulation research for a typical LNG carriers'propulsion system, which lays the foundation of theory and practice for the developing of the LNG carrier engine simulator, which has independent intellectual property rights.In this thesis, the propulsion system of domestic LNG carrier is taken into study. Using the methods of modular modeling and lumped parameters modeling to establish the dual-fuel main boilers model, typical auxiliary systems model of main boilers, main propulsion steam turbine system model and simplified propeller model. The Matlab/Simulink software is the simulation tool. Simulation results are compared with designed experimental data and some sea-trials data; using the system dynamics theory to establish the dynamic characteristics analysis model of LNG propulsion system from the macro description perspective. The VENSIM software is the simulation tool. Simulation results are compared with the classical differential equation model simulation results; the main propulsion simulation system for LNG carrier is developed on the basis of verified model. Specifically, the main contribution of this thesis includes the following:According to the characteristics of the dual fuel main boiler system for domestic LNG carrier. reasonable boiler sub-modules are divided in detail. Mathematical model for each sub-module is established, including the furnace, drum. rising water wall tube, downcomer, water tube and header, superheater, economizer, air preheater and flue gas side heat transfer model. In the furnace dynamic model, the ratio of fuel oil and fuel gas is defined to establish the furnace flue gas oxygen content simulation model, which expands the simulation parameters. A simplified internal embedded superheater simulation model is given. which meets the requirements of accuracy and simulation speed in simulator. The whole boiler simulation model in Matlab/Simulink is established through linking sub-models and carrying out static and dynamic simulation. The static simulation data agrees well with the actual designed data, and the overall accuracy is less than5%, which can meet the requirements of steady-state accuracy of engine room simulator; dynamic simulation data" trend is reasonable, which is consistent with the dynamic corresponding characteristic of the real ship. Also the main boiler fuel oil system model, fuel gas system model and feed-water system model are analyzed and established through analyzing. An improved simulation model for fuel oil tank level computational is conducted.According to the characteristics of main steam turbine system and propulsion shaft system for domestic LNG carrier, the main steam turbine mathematical model, propulsion shaft model, simplified propeller and ship motion model are established. The whole simulation model in Matlab/Simulink is established through linking sub-models and carrying out static and dynamic simulation. Simulation results show that the steady-state simulation results are consistent with design data, which meet the requirements of the whole accuracy of the simulator; dynamic simulation results basically correspond to the sea-trial data.From a macro point of view of systems analysis, a dynamic characteristics analysis model of LNG carrier propulsion system is established based on system dynamics theory. In VENSIM platform, the causal loop diagram, stock and flow diagram, structure equations are established, and simulation studies are conducted. The simulation results show that the system dynamics model is easy to understand presentation, simplified and high accuracy, which is appropriate for the dynamic characteristics analysis and optimized control of LNG carrier steam turbine system. This modeling method can be extended to the optimization modeling and analysis of the whole marine system.Finally, on the foundation of established and validated models, the first set of domestic LNG carrier propulsion simulation system is developed through high-level computer programming language. This simulation system is the core of the LNG carrier engine room simulator. The overall planning and design of the LNG carrier engine room simulator is conducted, and a practical optimization method is put forward from the perspective of the simulation model and simulation program interface design. Using the Visual C#programming language, the simulation software is developed successfully. including the main boiler system, main steam turbine propulsion system, monitoring and alarm system, and coach management system software module. The developed software system has advantages such as nice interface, easy and flexible operation, real-time, high accuracy and profession. The successful development of the system will promote China's LNG carrier engineers'education and training.