"Innovative Digital Twin" aims the creation of digital twin technology based on developing and validating complex event models after clarifying their basic principles by integrating various fundamental technologies. This strategic proposal offers a strategy for conducting R&D on the digitization of manufacturing, which has shown remarkable progress of late, and the fundamental technologies that support this digitization.

Digital twins have been gaining attention in recent years as a core technology for driving the digitization of manufacturing. A digital twin is an innovative simulation technology that virtually replicates a physical product in cyberspace based on digital data and that predicts events that will occur in the future in this virtual, digital world (Figure E-1). This technology is expected to provide high added value throughout the entire value chain of a product or service. The essence of the digital twin is in the development and validation od complex event models. R&D on related technologies and fundamental technologies for advanced design and manufacturing supporting these technologies must be conducted strategically and with the cooperation of industry, academia, and government. Moreover, the outcomes of this research must be used to preserve and strengthen Japan's mid-to long-term competitiveness in innovation, as well as to implement new manufacturing systems and to realize a future low-carbon economy society described as Society 5.0.

With the decreasing numbers of engineering specialists in Japan that are in charge of the fundamental technologies for manufacturing, including production, materials, structure and strength, machinery, combustion, heat transfer, fluids, vibrations, chemistry, and electricity, Japan has allowed other nations to close the gap in some of these areas in terms of individual research capabilities. In order to overcome this situation and lay the groundwork for Japan to once again lead the world in many engineering fields, Japan, as a nation, should implement R&D in a concerted manner.

While efforts necessary for constructing an innovative digital twin for manufacturing are wide-ranging, the following are three specific measures considered necessary in this proposal in view of the importance of developing and validating complex event models.

• (1) Developing and validating complex event models after clarifying their basic principles by integrating various fundamental technologies, developing efficient techniques for model calculations, and developing and standardizing methods of assessing constructed models.
• (2) Constructing a knowledge base from basic scientific research that is instrumental in (1) [identifying and understanding physical/chemical phenomena, establishing the underlying constitutive equations, acquiring and accumulating evaluation data, etc.]
• (3) Utilizing (2) to develop human resources that understand the basic principles of engineering, which supports the manufacturing industry, and human resources capable of manufacturing based on scientific rationale

The selection of equipment or service areas related to transportation, energy, and the environment as environment as target product categories or areas is effective, owing to their highly challenging manufacturing technologies, long development periods, and high costs (figure E-2). The use of digital twins is expected to have a great effect in these areas and to play a role in future international market gains and Japan's contribution toward a low-carbon society. Digital twins are anticipated to be required output for the design and manufacture or maintenance (life prediction) of environment/energy equipment and transportation equipment such as wind, gas, and steam turbines; automobiles; machine tools; and shipping.

Figure E-3 shows an organization of R&D issues aimed at achieving a unified implementation of measures (1) through (3) described above. These R&D issues are thought to be bottlenecks common to products of different types. The objectives od addressing these issues are to elucidate the related physical and chemical mechanisms, establish constitutive model equations, develop and experimentally validate complex event models, develop and standardize methods of evaluating models, and establish digital twin technology through these efforts. Naturally, R&D for developing these technologies to be used with the individual products mentioned above will be necessary after addressing these common issues. The following are key elements in the issues common to many products.

a) Construct and validate process models for mechanical damage

• Elucidate damage mechanisms and crack propagation in mechanical elements including composite materials, etc.

b) Construct and validate coupled models for fluids, structures, and vibrations

• Elucidate interaction mechanisms among lubricant film flow and surface deformation for sliding surfaces of rotating machinery, etc.

c) Construct and validate

• Elucidate interaction mechanisms among fluids, structures, and acoustics in rotating machinery and transportation equipment, etc.

d) Construct and validate

• Elucidate interaction mechanisms among elementary combustion reactions and turbulence in rapid transient phenomena and eat transfer, etc.

e) Construct and validate

• Expand research to the target products mentioned above, develop and validate high-speed coupled analytical models for governing equations of complex events related to the motion, structural deformation, vibration, lubrication, fluids, heat transfer, combustion, chemistry, and electromagnetism of mechanical elements, etc.

Lastly, a system based on a network approach to promoting collaboration among industry, government, and academia (a consortium) must be appropriately constructed in order to effectively implement the three measures described above and to outshine the rest of the world in R&D on digital twin technology, and the fundamental technologies for advanced design and manufacturing that support this technology. This will require comprehensive R&D covering everything from basic research to social implementation. At the same time, it will be crucial to work steadily at creating a collaborative platform for data sharing, as well as human resources development and exit strategies for international standardization and deregulation, for example.