Modeling ship energy flow with multi-domain simulation

Ship energy efficiency is becoming more and more attractive to ship owners, builders and researchers due to the increasingly high fuel cost and the accumulatively strict international maritime rules. It is especially evident for modern ships with complex power plants including mechanical, electrical and thermohydraulic systems. Marine engines, as the heart of ship power plant, play a key role in the fuel energy utilization. But, even for a very efficient marine engine, only less than 50% fuel energy can be converted to useful work. The other over 50% of fuel energy is mainly taken away in a form of heat energy by engine cooling water system and exhaust gas system during the combustion process. Practically, quite a many methods, such as waste heat recovery, have been already developed to enhance the total efficiency of ship power plants. However, there still is not a clear and thorough understanding of the operating efficiency of different processes due to their complexities, which is specifically true for the steam powered systems. In this paper, a new method is introduced to model the ship energy flow for thoroughly understanding the dynamic energy distribution of the marine energy systems. Due to the involvement of different physical domains in the energy processes, the multi-domain simulation method is employed to model the energy flow within Matlab/Simscape environment. The energy processes are described as multi-domain energy flow as function of time. All the main energy processes are to be modeled as subsystems only at a general and system level, and to be built as simple but comprehensive as possible to facilitate the simulation interaction among different main subsystems. For each subsystem, the developed model contains rather simple description of the energy processes involved. The operation and load profiles from real operation data can be given as inputs to examine the dynamic energy balance during the operation. The validation results have positively shown the feasibility and reliability of the energy flow simulation method. The developed energy flow simulation method could further help people better monitor the ship energy flow and understand ship energy systems. More importantly, it could give some valuable insights into how to design an energy-efficient ship power plant and how to operate the vessel efficiently. Furthermore, it could be easily utilized to test and verify new technologies, and hence to find possible ways to improve the energy efficiency of both the existing and new-building ships.
©CIMAC