Pondering their modeling and simulation techniques behind on the digital twin in recent years, the term (DigitalTwin) digital twin fame, become a hot concept. But with the industry and academia continue to interpretation of the digital twin, its meaning is more complicated and confusing, and a number of other related concepts boundaries are increasingly blurred. What is a digital twin in the end, what to do, where the border, and it is anything to do with modeling and simulation and so on to make a lot of people confused. This paper attempts to some of the doubts which were superficial analysis. 1, Digital Twin in the end mean? Because Digital Twin Chinese translation divergent (this issue will be mentioned later), DT represents the temporary use Digital Twin. In the field of information, a concept open to various interpretations already is a common occurrence. But mostly vague concept, although in the beginning emerge, ill-defined, but after a period of discussion and after the precipitation will gradually form a consensus, such as cloud computing. The DT is very interesting, when it is the beginning, the meaning is still relatively clear, but with further research, the definition and meaning is increasingly blurred. In addition, many of the concepts, although there are many different definitions and explanations, but the difference lies roughly either look at different angles and focus problems, different levels of detail or explanation or written expression in different ways, but the concept itself is pointing but the main thing is certain. Such as DT, different definitions point to a different subject, but rare. The word DT, the industry generally believed that the concept is a University of Michigan professor MichaelGrieves for Product Lifecycle Management (PLM) proposed in 2002, had not called Digital Twin, but called mirror-space model (Mirrored Space Model [ 123] , MSM), and later NASA’s John Vickers will be named Digital Twin . Attribute their model is very clear CONTROL ENGINEERING China Copyright , although did not cause too much concern, but there is no ambiguity, DT is a digital model. But with the introduction of its NASA “NASA Space Technology Roadmap”DT meaning undergone important changes. NASA explanation given is this: DT full use of physical models, sensor update, run the historical data, integrated multi-disciplinary, multi-physical, multi-scale, multi-probability simulation process, to complete the mapping in the virtual space, to reflect the relative entity corresponding to equipment life cycle process . DT’s body into a simulation. Or this report, very clear that, NASA’s Digital Twin is “Simulation-based systems engineering” (Simulation-Based Systems Engineering). DT’s body, it is a systems engineering. NASA DT interpretation of these is probably the root causes of subsequent DT definition and meaning of ambiguous. We might as well give some representative definitions. (1) DT is a real-time digital copy of the physical device . (2) DT is a digital copy of animate or inanimate physical entity. By connecting the physical and virtual worlds, seamless data transfer, so that the virtual entity and physical entities exist . (3) DT is constructed of digital artificial or natural environment asset, process or system is represented . (4) DT software assets and processes are represented, for understanding, forecasting and optimization to improve business performance . (5) DT is the actual virtual representation of a product or process, used to understand and predict the performance characteristics counterparts . (6) DT is coupled model of the real machine running on a cloud platform, and uses the integrated analysis algorithms and knowledge of other available physical knowledge from data-driven health status simulation . (7) DT is a dynamic system in a virtual or physical object throughout its life cycle, said real-time data to achieve understanding, learning and reasoning . (8) DT physical system performing real-time optimization digital copies . (9) DT is the real world and the virtual bridge to the world of digital communication . FIG 1 is a DT and related parts of the various definitions mentioned above. Physical object comprising ①, ② data, ③ model, ④ and ⑤ simulation simulation results. FIG 1 the various parts associated with DT
These definitions are directed to different portions of the DT 1 in FIG. First class: the definition of (1) to (5) will be given DTDefined as a digital copy, digital, said software representation or virtual representation, point ③, namely DT is with physical objects in real-time update of the model, because whether it is a digital copy, digital representation or software representation or virtual representation, belong to the scope of the model. The second category: definition (6) to (8) DT point ③ and ④, i.e., DT is the model plus the simulation. Third class: definitions (9) and DT point ② ⑤, i.e., DT is a bridge between physical objects and models. Then, as a rigorous academic term, which is more reasonable? You may wish to analyze. The second type of modeling and simulation together to define a new concept, on the one hand there is no need, on the other hand also unreasonable. Because although closely related to modeling and simulation, but they are two things. Model is a description of things, and the simulation model is based on a variety of activities, like the two dimensionless numbers are different, it can not be added up into a number. The third sounds very provocative, but most unreasonable. If the data from physical objects or simulation feedback data is called a “bridge” to blame, but two types of data can not be called Twin physical objects. Thus, the first class definition is still relatively most reasonable, i.e. DT is a digital model of the physical object. But this model can receive real-time data from physical objects, which can continue to evolve in order to be consistent with the physical object. Of course not to say that the previous model does not have the characteristics of evolution, just before the evolution of the model does not address real-time. In the understanding of DT’s, there is a troubling issue, namely whether DT should include a physical object, that is, in Figure 1 ①? It also makes a lot of people with information on the physical relationship DT system confused. The root cause of the problem is also related literature from NASA and the Air Force Office of Research [12-13], they think the concept DT consists of three distinct parts: the connection between the physical product, digital / virtual product and two products . I.e., even in FIG. 1 ①②③ ⑤. But clearly there is a problem on the logic of this explanation. If DT which contains physical system, then the Twin there is no reference. Because Twin must be another person (or object) relative. Of course, if the ① and ③ collectively referred Twins, namely twins comes in makes sense, but can not be called Digital Twins, because one is digital,Another is physical. It still should be put in DT concept in digital models of physical objects and distinguish these two parts. According to the above analysis, if a digital model of a physical object is defined as DT, DT and then the relationship between the information of a physical system (Cyber Physical System) it is easy to sort out, i.e. digital model based on the digital model of the various activities (simulation) connected (data and simulation results) between physical objects and digital objects forming a physical model and information of a physical system, as shown in FIG. Problem
The relationship between the DT and the information of the physical system 2 of FIG.
Further, there is a possibility ambiguous, i.e. whether DT should include data acquired from the physical system, i.e. in FIG. 1 ②? I think, DT concept does not require such data should not be included because the model here is based on the real-time evolution of these data, the information data will be reflected in the model. And there is data on a specific technology that Digital Thread technology, which can be used to process the data and Digital Twin-related issues. Then look at the Chinese translation questions about DT. At present, although the term used in digital twin is more common, but the numbers of twins and other titles or digitized twins are still often used. DT was first translated into digital or digital twins twins. Later confirmed by the experts, read digital twin. Probably mean, twins refers to two people, or twins, or twins, the corresponding English word should be the Twins, Twin refers to a twin, so it should be called twins. In fact, twins word in Chinese is also rare alone, and brothers and sisters in conjunction In most cases, such as twin brothers, twin sisters and so on. But just from the accuracy of the meaning of terms, digital twin correspond Digital Twin, indeed more reasonable than some digital twins. DT various explanations about the concept of the association mentioned earlier, the digital twin DT translated, means that the default model DT refers to the fact, and does not contain physical system. Because the twin refers to a twin, obviously it does not include the corresponding physical system itself. If neither part contains model also contains the physical part, called digital (technology) twins should be more appropriate, although not too serious, because as I said before, not a number of physical systems.In Chinese literature, there is a interpretation of DT, which is about to be construed as a method and process modeling, also called twin digital technology, the use of this model is called a digital technique constructed twin model, twin or digital body. This interpretation is clear and can not correspond to the basic meaning of DT. DT to obscure the understanding of the concept, it is also an important cause of Chinese translation has not unified. In summary, I believe, it would translate into a digital twin DT more in line with its original meaning. For digital twins can be understood: Digital twin digital model of the physical objects, the model in real time by receiving data from the evolution of a physical object, whereby the physical objects in consistent with the life cycle. Twins can be based on digital analysis, prediction, diagnosis, training, etc. (ie simulation), and the simulation results back to physical objects, thus helping to optimize the physical objects and decision-making. Physical objects, and digital simulation based on twin and twin digital feedback information, together constituting a physical system (cyberphysical systems). Technology for digital twin lifecycle (build, evolution, assessment, management, use) technology is called digital twin (DigitalTwin Technology). 2, modeling and simulation technology behind digital twin as academic research, we need to adopt the concept of a fair and unambiguous, and do not tangle at NASA explanation for DT. But for the real purpose of NASA NASA Digital Twin mentioned but can not be ignored. In fact a lot of people for the enthusiasm and motivation of DT research came from NASA Digital Twin brings infinite vision for the future of manufacturing. While we do not agree on the interpretation of NASA DT concept, but think about it from another angle, NASA did not actually DT will as a serious academic term to be defined. Its really want to say, it is to emphasize the value of simulation, that NASA research aircraft need to follow the “Simulation-based systems engineering” concept. Simulation technology is almost With the birth of computer technology arising from the 1950’s to now, has gone through sixty years of development. Since the simulation is to model-based, so in order to highlight the importance of modeling and simulation modeling often appear together, that is, Modeling & Simulation, often shrinkWritten as M & S. From this we can see the text below the US understanding of the modeling and simulation of the height reached. This text excerpt from the US Congress resolution No. 487 on July 16, 2007 by . United States of America is a great and prosperous nation, and modeling and simulation greatly contributed to this great and prosperous. In the United States, modeling and simulation is a unique application of computer science and mathematics, it is the validity of the model or simulation accuracy and repeatability, as well as thousands of Americans develop these models in modeling and simulation-based career Ability. Members of the government, industry and academia in the field of modeling and simulation for the United States to make outstanding contributions to the overall well-being, the following examples may be part of modeling and simulation to reflect the contribution made by the United States, even though these contributions too numerous to mention : (1) during the Manhattan Project, the first simulation to reproduce nuclear chain reaction, expanding the understanding of nuclear fission, and ultimately led to the end of World War II; (2) as “Stockpile Stewardship Program,” the basic elements that allow the US president can not be true in the case of nuclear testing, to ensure that more than a decade of stockpiles of nuclear weapons security and reliability, and to demonstrate the country’s commitment to nuclear non-proliferation. Only two contributions above, we can see the enormous power of modeling and simulation. And in this resolution, such cases were lists 11. In the same resolution, it made it clear that modeling and simulation is a “national core technology (National Critical Technology)”. The following content is more shocking. 1965 promulgated the “Higher Education Act” is a higher education legislation in US history, it is by expanding the role of the federal government in the fiscal area of higher education, the federal government involved in the development of American higher education, popularization of higher education lay the foundation for the United States the foundation. The law is a milestone in the reform of higher education in the United States . The December 2018 amendments to the new Higher Education Act came into force, the specialized modeling and simulation as an important content (20 US Code § 1161v – Modeling andsimulation) included among , and use a lot of space shows that the Government and society how should promote the popularization of modeling and simulation techniques at the University of Education. Throughout the bill, we have not seen any other of a technology able to enjoy such a high treatment, even in recent years,Artificial intelligence technology in full swing, it has not. As can be seen from these two documents, fundamental and long-term value of modeling and simulation technology has far exceeded the scope of its technology in the field, will have a significant impact on the national interest and national security. In manufacturing, modeling and simulation has been playing an irreplaceable role. In 2000, the US DARPA, Department of Commerce, Department of Energy, NSF jointly issued a National Development Strategy of Manufacturing Research and Promotion Program “Integrated Manufacturing Technology Roadmap (IntegratedManufacturing Technology Roadmapping, IMTR)”. IMTR proposed six “major challenges” facing the future of manufacturing, it becomes sophisticated and efficient business, improve response to customer businesses, the Internet has become a comprehensive enterprise, environmental sustainability, knowledge management, good application of new technologies. Easy to see that these six challenges into today still holds. IMTR then put forward four types of technical measures to meet the challenge of these six, that information systems for manufacturing, modeling and simulation technology, manufacturing technology and equipment, enterprise integration. This shows the importance of modeling and simulation techniques for manufacturing. In 1997, before the publication of this report, the US Department of Defense weapons procurement reform, the most important reform is that “Simulation Based Acquisition” (Simulation Based Acquisition, SBA), will soon be applied to modeling and simulation of weapons from needs analysis the whole life cycle eventually scrapped. And Lockheed Martin’s F35 is the first comprehensive introduction of the concept and the development of SBA products. November 2017, there were reports that Lockheed Martin as twin digital future first six leading technology of defense and aerospace industries. Behind Loma digital twin is actually SBA, which is based on simulation of the acquisition, which is exactly the same with NASA simulation-based systems engineering. Modeling and simulation techniques born sixty years ago in the United States, and has been in play an invaluable role in the national interest of the United States, but the Americans never put out the modeling and simulation of speculation. The reason is worth considering. 3, the digital twin should not be over interpreted, the need to keep a cool head digital twin (digital twin) The word has been able to popularity, largely due to the propagation characteristics of the word itself, which formLike, catchy, easy to understand, even if outsiders but also from literally know about, but also lead to unlimited imagination. For the promotion of science or business, really is a good word. But as an academic term, they lack of rigor, at least so far still the case. There are currently two trends worth noting, first, in the connotation of the concept of the digital twin continued to enlarge, giving more and more content, resulting in even overlap with other concepts cross; second is to affix a digital twin in a conventional technique on the application s Mark. These two tendencies is not good for the development of digital technology twins. As previously said, speaking behind digital twin is modeling and simulation technology. Digital twin of the most attractive places, is a combination of digital models and things, and the ultimate goal of this combination is to be polished model closer to the true system. The networking technology for the new model provides a powerful tool
, and the lack of adequate understanding of the complex mechanism of the system, the acquired data may be based on artificial intelligent technology to model the system. This is a modeling technology developments and additions. And based on the analysis, forecasting, training and other activities model has always been to do the simulation. So the digital twin is essentially the application of information technology in a new generation of modeling and simulation. After half a century of development, modeling and simulation has become a well-established systems and technology system. In fact, in the field of simulation, dynamic real-time data modeling and simulation methods and techniques have been studied for many years, such as dynamic data-driven simulation (Dynamic Data Driven Simulations, DDDS), embedded simulation, hardware-in-loop simulation and so on. Of course, as an important part of the twin digital simulation technology through integration with the new generation of information technology, will further promote the development of modeling and simulation techniques. In addition, system modeling and simulation techniques can be used directly in a lot of research and application of digital twin, including theory, methods, standards, tools and platforms, without the need to repeat in the name of development of the digital twin. This is also in spite of the NASA Digital Twin achieve the target of 2027, but no follow-up and re-establish itself on the Digital Twin reason a new technology system. Because the technology, standards, tools and platforms required, in its modeling and simulation technology system where most of them are already in existence. ChangeLabel, and then engage in a set of something like that is a waste of resources, a waste of time. Digital twin hot, from a good name is important, but more important still benefit from Siemens, GE and other industry giants fueled. Sober profession are clear , the digital twin related core technology is mostly in the hands of foreigners, such as sensor technology, CAD technology, CAE technology, PLM technology, VR / AR technology . Siemens, Predix, Dassault, PTC, SAP, Ansys and other enterprises are exaggerating charming prospects and value of digital twins, because they really grasp the core technology of digital twin necessary, and along with twin digital upgrade of heat, these companies are selling real products. Industry enthusiasm for the new concept, has its own purpose Control Engineering Copyright , insiders are well aware. However, these core technologies and products mentioned above, it is the most lacking in our country. But interestingly, in the country, the study of digital twins often evasive, is more and more concerned about the periphery of the non-core stuff, and their enthusiasm is much higher than the concept put forward the concept of the United States and other industrial development country. Most of the time we are keen to hype the concept, say more, do less, do the virtual thing more, do less practical children. In fact, I do not know yet, we round a cry, are cheering for others. For the serious lack of core technology support us in the hot words are emerging today, we should keep a clear head. Buried strangle hold key technology research and development is the last word. Otherwise, we are not only a waste of resources, but also a waste of time, eventually lost a great opportunity and a strategic development initiative.