# Multi-Domain Modeling and Analysis of Marine Steam Power System Based on Digital Twin
## 5 Fault Simulation Analysis of Marine Steam Power System Based on Digital Model  
A large number of data signals, such as flow, temperature, pressure, power and speed, are generated during the operation of the marine steam power system. These data signals reflect the operating characteristics and performance degradation laws of the thermal equipment. Nonetheless, it is still difficult to obtain data for each fault sample in the whole life cycle of the equipment. Especially for the multi-domain coupled marine system, due to the lack of fault sample data, it is not possible to accurately analyze the degradation law of equipment performance, nor to accurately achieve fault diagnosis and prediction. However, fault simulation and prediction under the framework of digital twin technology can overcome the problem of obtaining fault sample data. It builds a high-precision digital simulation model of physical entities, optimizes and solves the simulation model by relying on online monitoring, data analysis, fault prediction, life-cycle management, etc., and feeds back the simulation results to physical objects, so as to optimize and make decisions for physical objects. Relying on digital twin technology, fault simulation and prediction based on high-precision digital models can effectively realize the reverse mapping of digital models to physical equipment. The digital model can train the model using the fault sample data to lay the foundation for subsequent fault diagnoses. It can also inject fault points, and, through the dynamic analysis of fault behavior, grasp the law of performance degradation. The fault diagnosis process is shown in Figure 24.  
As can be seen from Figure 24, which shows the fault diagnosis process for the marine steam power system based on a digital model, using the digital model to simulate equipment faults and extract fault data is the most important step in establishing a fault database and is also the basis for realizing fault diagnoses. Therefore, this section takes the marine condensate feed water system as an example, and, making full use of the advantages of its digital model, inserts fault points on the basis of the digital model, conducts a quantitative analysis of the main fault types of the thermal equipment in the condensate feed water system, and uses the model to accurately describe the actual fault status, so as to realize the monitoring and early warning of faults by the digital model. On the one hand, this provides targeted measures to guide the safe and stable operation of marine vessel; on the other hand, it realizes the reverse mapping of digital models to physical equipment, which is also one of the important components of digital twin technology. As an important auxiliary system in the marine steam power system, the condensate feed water system and its operational reliability directly affect the whole power system. Influenced by complexity, randomness, dynamics and other factors, the condensate feed water system will also encounter various abnormal conditions in its operation. For each type of thermal equipment failure, accurate and effective measures need to be taken to regulate it. If this is not handled properly, frequent accidents will occur, causing equipment damage or unit shutdown. According to thermal calculations and on-site operating experience, the main causes of the failure of the condensate feed water system are water level regulation failure, the vacuum system not being tight, abnormal operation of the steam jet ejector, failure of the circulating water pump, reduction of the circulating water flow, a rise in the temperature of the cooling water, blockage of a cooling pipe, excessive steam exhaust in the steam turbine, etc. [18]. The main faults of the condensate feed water system are systematically analyzed below.