Improvement Of Liquid Cargo Handling Simulator Of LNG Carrier

In recent years,natural gas has gained increasing attention because of its clean and efficient combustion.National supply-side structural reform,reducing the share of coal and improving the share of natural gas in primary energy consumption and expanded cost-benefit ratio of natural gas due to the rebound of crude oil price,will directly or indirectly promote the consumption of natural gas in our country in the future.At present,the consumption of natural gas in our country is larger than the output,the gap needs to be made up through imports.A considerable portion of imported natural gas is transported by LNG carriers.In order to ensure the safe operation of LNG carriers,the crew should be trained through the professional simulators.This thesis aims to make improvement to the already developed liquid cargo handling simulator prototype of LNG carrier.There are two problems in the liquid cargo handling simulator prototype of LNG carrier.One is that the gas temperature and pressure response model of liquid cargo tank concentrates on the initial and end status,and it can't analyze the mechanism over time.The other is the gas pressure in the tank is easily deviated from the normal range.To solve the above problems,the analysis of membrane tank's thermal load is carried out from the point of heat transfer theory,and the rationality of thermal load's simplified calculation is verified by substituting the ship's parameters of DAPENG SUN.According to the relationship between the inflow,outflow energy and the variation of internal energy in the control volume of liquid cargo tank,the energy conservation equation is constructed considering the gas-liquid energy conversion and liquid cargo evaporation during the liquid cargo operation.Based on the way to calculating each energy,the relation of gas temperature and pressure changing over time can be derived.The inflow and outflow energy of gaseous working fluid in the control volume are not same under the different liquid cargo operation.The mechanism model of gas temperature and pressure changing over time is used to simulate the preloading,loading and unloading operations of the parent vessel DAPENG SUN.Meanwhile,the control strategies are designed to invoke the tank pressure control equipment automatically to stabilize the tank pressure in the appropriate zone.The precooling results between the simulation and experiment of DAPENG SUN show a small difference,which verifies the validity of the constructed model.During the loading and unloading conditions,the simulation results of constructed model are close to the measurement values of Kongsberg simulator in gas temperature,gas quality and LNG volume,and the trend of tank gas temperature during the unloading condition is consistent with the calculation results of the relevant literature,which further verify the accuracy of the constructed model.Meanwhile,the pressure difference control of insulation spaces is designed using the mirror mapping technique.Simulation results show that the proposed control law possesses good effect and certain robustness.Firstly,the gas temperature and pressure model of liquid cargo tank constructed in this thesis fully reflects the mechanism of gas temperature and pressure changing over time under the different liquid cargo operation.Secondly,the designed automatic control scheme of tank pressure can ensure the tank pressure stabilizing in the appropriate zone.The research of this thesis can help to enhance the realism of liquid cargo handling simulator prototype and make it more credible.