## 2 Components of the Digital Twin System for Wind Turbines
### Five-Dimensional Digital Twin Model  
This paper employs a five-dimensional digital twin model framework, which includes the Digital Twin Service Layer (SL), Physical Entity Layer (PEL), Virtual Model Layer (VML), Visual Interface Layer (VII), and Data Center Layer (DCL), as illustrated in Equation (1).  
\[\text{DT}=\text{SL}+\text{PEL}+\text{VML}+\text{VIL}+\text{DCL} \tag{1}\]  
Based on the five-dimensional digital twin model framework, a digital twin model for the wind turbine has been developed, and the digital twin system has been established. The proposed intelligent monitoring system framework for wind turbines based on digital twin technology is shown in Figure 1, consisting of the five components mentioned above.  
The Digital Twin Physical Entity Layer represents the objective entities in the real world, including wind turbine equipment and various physical devices, such as sensors, installed on the turbines. It forms the foundation of the five-dimensional digital twin model. It perceives environmental information and various operational parameters of the wind turbine's physical devices in real time through sensing equipment and collects relevant data via sensors deployed on the turbine. The collected data primarily includes unit parameters, rotational speed, temperature, vibration, etc. The collaboration of different components ensures the stable operation and real-time status monitoring of the wind turbine.  
The role of the digital twin service layer is to analyze and support decision-making through algorithmic analysis, monitoring the wind turbine's health status, and triggering timely alarms in case of failures. It includes wind turbine management, fault diagnosis, and anomaly warning, utilizing diagnostic algorithms for relevant operations and ensuring the functionality and visual display of the entire system. A real-time data-driven model from the data center is used to monitor the wind turbine's operational state and visualize data such as vibration signals, temperature, and wind speed.  
The Digital Twin Virtual Model Layer is a three-dimensional model of wind turbines, accurately reflecting the physical entity of the turbine. It serves as a high-fidelity, high-confidence digital representation of the physical space, built using 3D modeling software (such as SolidWorks, CATIA, UG, etc.). The model must include part assembly constraints, motion simulation, and hierarchical information. Model construction forms the foundation and core of the digital twin. The model must be constructed considering aspects such as geometric structure, design parameters, design requirements, and transmission schemes. To reduce computational load and improve efficiency, the model can be optimized using 3D lightweight modeling technology. The virtual model layer supports the visual interface layer for monitoring and bearing fault diagnosis.  
The Digital Twin Visualization Interface Layer displays all functions within the application module. This layer monitors the wind turbine's operational state and real-time fault diagnosis results. For user convenience, the digital twin system is accessible via tablets, computers, mobile phones, and VR clients.  
The Digital Twin Data Center Layer contains twin data and algorithm models of the wind turbine's physical layer equipment. This layer is responsible for converting collected data into a consistent format. Additionally, the data layer processes and analyzes the collected data, including association analysis, cleaning, and handling abnormal data, which provides data sources for the service layer. When the data volume is small, it can be managed using file formats like.xlsx and.txt. For large data volumes, the data must be read and managed on the server using a database and TCP/IP protocol.