## 2 Literature Review
### Application of Digital Twin Technology in Product Design, Manufacturing and O&M
Digital twin technology can be applied at each stage of the product and can carry out feedback from the O&M service stage to the life cycle concept or design stage to optimize the whole life cycle system [48]. [PERSON] et al. [49] developed the design and manufacturing integration framework of complex product based on digital twin, which explores the key technology of design and manufacturing integration of complex products from the perspective of demand analysis, concept design, individualized design, multidisciplinary integration design, virtual prototype and product data management. [PERSON] et al. [50] proposed the design, manufacturing and service integration framework of complex product based on the digital twin technology, discussed the implementation process of design-manufacturing-service integrated optimization from the perspective of PLC, and analyzed the solution of process integration, data flow, modeling simulation and information fusion. [PERSON] et al. [51] raised the overall framework of manufacturing and O&M integration of complex product and the system integration mode of virtuality and reality combination for the independent manufacturing and O&M process of digital twin with the help of digital twin technology and analyzed the key technologies such as manufacturing and O&M integration, data fusion, modeling simulation, etc. to provide the foundation for the deep integration of manufacturing and O&M. Currently, there is relatively less study on the design-manufacturing- O&M integration of the complex product in the digital twin technology. Most of these researches aim at one or two aspects among design, manufacturing and O&M. As a result, the design information is low in reusability, the manufacturing information cannot be effectively conveyed to the O&M stage for comprehensive decision and cannot be efficiently fed back to the design stage to provide information support for product optimization. The useful information cannot be obtained in real-time at the O&M stage to improve the fault diagnosis efficiency and evaluation efficiency, and cannot be fed back to the manufacturing stage and design stage in real time for optimization and decision. Additionally, the existing results cannot meet the integration demands of complex products. Therefore, we raise a design-manufacturing-O&M integration framework based on digital twin, and the \"bridge\" established between the physical entity and virtual model through digital twin technology can guarantee the synchronization between the product's virtual design and the product's actual manufacturing and O&M process, and resolve the integration problem of comprehensive information of complex product in design, manufacturing and O&M. Such framework contents are described in Section 3. Construction of Design-manufacturing-O&M Integration Model for Complex Product Based on Digital Twin  
To achieve the data integration and sharing of complex products in the design, manufacturing and O&M process, this paper proposes an integrated model of complex product design-manufacturing-O&M based on digital twin, as shown in Figure 1. Such model mainly comprises a physical layer, a virtual model layer and a twin data platform. The design-manufacturing-O&M integration model of the design-manufacturing-O&M complex product driven by digital twin achieves the simulation model of the virtual world and the physical-entity mapping feedback of the real world mainly by constructing the whole life cycle and full-feature model of complex products. Such a model achieves the whole cycle multisource heterogeneous data integration of complex products from demand design, model design, simulation experiment, processing assembly to O&M via the acquisition and reconstruction of repair data, fault prediction data, processing process data, assembly data, etc., in O&M and manufacturing.