# Multi-Domain Modeling and Analysis of Marine Steam Power System Based on Digital Twin
## 3 Digital Modeling of Marine Steam Power System Based on Modelica
After the system warmed up for 650 s, the flow of steam through steam valve was gradually increased, and after 270 s, the load was increased to about 20% of the working condition, and then the system operated stably for 740 s. Subsequently, the steam flow was increased again. After 190 s, the system rose to about 40% of the working condition and ran stably for 270 s under the 40% working condition. Then, an additional increase of the steam flow followed. After 180 s, the system rose to about 60% of the working condition. When the system had operated for 450 s under the 60% working condition, the steam flow was increased. After 300 s, the system rose to about 80% of the working condition, and then the system operated stably for 320 s. A final increase of the steam flow followed. After 200 s, the system rose to a 100% working condition. Under the condition that the main steam temperature, pressure and cooling water flow are kept under full working condition parameters, the load of the steam turbine unit can be increased by adjusting the main steam flow. The main steam temperature and pressure fluctuate due to various factors during operation. However, the state of fluctuation is controllable and safe. The measured boundary parameters of the turbine inlet are substituted into the established digital model of the marine steam power system, and a simulation curve for the turbine under 100% load rise conditions after start-up is obtained. The operation state parameters for key pieces of thermal equipment are compared with the digital simulation model for verification. The comparison diagram for steam turbine output power and the dynamic characteristic curve for the increasing temperature of the cooling water are shown in Figures 11-13. Figure 2:0 Comparison between experimental and simulation data of main steam flow. Figure 2:1 Cooling water outlet temperature. It can be seen from Figure 13 that the simulation data for the cooling water outlet temperature are consistent with the experimental data, but that, with the increase of the steam flow, the parameters fluctuate greatly as the load increases. Therefore, four operating points from the experimental and simulation data are selected for error analysis, as shown in Figure 2:2  
It can be seen from Table 3 that, among the four selected operating points, the one with the largest error, 1.5%, is T = 1800 s, and that the error of other operating points does not exceed \(\pm\)5%. Through the comparison and error analysis of the simulation curve and the experimental curve, it can be concluded that the main steam flow, the steam turbine output power and the cooling water outlet temperatures, etc. calculated by the digital model are close to the experimental curve, the dynamic operation trend is consistent, and the maximum error does not exceed \(\pm\)5%, which indicates a good simulation of the dynamic change process of the steam turbine. The digital model established in this paper has high accuracy and can realize virtual reality mapping between the model and the actual equipment. It can be used for the dynamic analysis of marine steam power systems and is conducive to promoting the further application of digital twin technology.