Yuan Zifeng: Multi-scale method to solve the prediction problem

What is the material? Can you damage what extent? Answers can be found with the mechanical model. Use the model as much as possible to reflect the real material world, this is the fact that Beijing University Mechanics and Engineering Science Department, Yuan Zifeng, has been working hard. Providing high fidelity calculation models for composites, with a multi-scale multi-physical field coupling method to accurately describe the complex evolution of composite materials, which is his expectation for future. At the moment, his goal is to combine product engineering practice to get work more and more ground.

Yuan Zifeng took pictures in doctoral graduation ceremony in Columbia University

Yuan Zifeng introduced that, like other disciplines, macro classic mechanics also has a basic knowledge system. Just like Sun Wuki can’t escape, like a Buddhist palm, classic mechanics has not escaped the framework of Newton’s classic mechanics, and do not open various conservative laws. Although these conservative laws work in the description of the simple structure, it is difficult to make a clear analysis in complex structures, which requires calculation of mechanics, and Yuan Zifeng is engaged in calculating the research work of solid mechanics.

There is a goal of calculating solid mechanics – prediction. Prediction is a matter of concern, and people in all walks of life predict what will happen tomorrow in their respective fields. Yuan Zifeng’s work is to predict the mechanical performance of the product. "For example, a mug, falling down in how high the location will be broken? But you can get an answer through experiments. But you will take a cup every day to do experiments. It is not the best way. The general method is that the quality of product materials is used to use models. predict."

However, it is not a mechanical performance of all products to predict the model. In the computational mechanics framework, the material properties are characterized by the model model. However, in a conventional model system, the stress state of the material is not determined by a smaller scale state. Instead, the local model is obedient. Therefore, for composite materials, the complex mechanical properties of materials are difficult to describe existing modes of modes. In addition, the plasticity, breaking, damage, fatigue, etc. From the perspective of phenomena, a complex constitutive model that is fitted is not to explain the mechanism of failure of the material, thereby there is no mechanical properties from predicting materials.

The macro and median scale is coupled, and the multi-scale method is undoubtedly a way to solve the above problems. Macro material response comes from the averaging and homogenization of the mediative scale, and the understanding problem is solved by a photographed material component, a meta-geometry and a corresponding macro deformation state, the theory and actual calculation of multi-scale methods. The cost requires careful balance.

In general, the introduction of the median scale will greatly increase the calculation complexity. A complete macroscopically nonlinear finite element simulation coupled with a computational complexity of the nonlinear finite element solving, about the number of macro cells multiplied by a photographic unit, and therefore, the high resolution of the photographic scale calculation can cause the calculation amount. Big, not feasible. "Today, in order to achieve higher computing accuracy, the messenger of the median scale can reach millions of levels, which seriously reduces the possibility of introducing online calculations in macro scale. On this issue, the mechanics academic circles are calculated. There is no good solution to the actual industrial needs. "Yuan Zifeng introduced.

At the same time, with the booming of the materials discipline, the characterization of advanced functional materials in complex work environments put forward higher challenges. On the one hand, the functionality of advanced materials comes from a more deep understanding of the photographic scale of the material; on the other hand, objective material evolution also needs to consider the coupling effect of a variety of physics. This coupling analysis of this multi-scale multi-physics is both difficult to calculate the mechanics, but also a major opportunity for breaking through domestic computational mechanics software, which is more significant for the academic, industry, and calculating mechanics software industries. Therefore, developing advanced computational mechanics technology has become a very important thing.

In order to establish a feasible multi-scale analysis method system, the multi-scale method can be implemented in the macro-large scale structure calculation, but also to design a multi-scale multi-physical field computational mechanics software for user-friendly, strong versatility and high reliability, Yuan Zifeng It has accumulated for many years.

Yuanzifeng visited Cornell University when studying abroad

After graduating from the Department of Mechanics and Engineering Sciences, Peking University Institute of Engineering, Yuan Zifeng began in the 10 years of study in the United States. He completed a master’s degree in civil engineering and engineering mechanics at Columbia University. He continued to do a postdoctoral work after doctoral studies. Professor Jacob Fish engages in multi-scale calculation methods. "My request for myself is that the method doesn’t need to learn very much, but as long as you learn, you have to do it as possible. This is also the reason I have made a lot of years." Yuan Zifeng said.

Engaged in multi-scale calculation methods, there is a need for computer programming capabilities. In the same age, Yuan Zifeng is an earlier contact programming. In junior high school, it has been programmed. He has a strong interest and has reached a high level, which can be used in work, and it is a pleasure for Yuan Zifeng.

Theory, algorithm, and program implementation are the three-driving carriages of solid mechanical research, Yuan Zifeng strives to break through three aspects. For this reason, he has received many opportunities to cooperate with foreign companies and participated in the research and development of many projects. He wrote completely independently designed nonlinear universal finite element Foof (full name Finite Element Solver Based On Object-Oriented Fortran), which is used by MultiScale Design System and subsequent MultiScale Designer as a non-linear finite element computing engine for software, There is no major mistake, and the commercialization is reflected in good. The FOOF software architecture is excellent, which has strong expansion and good maintenance.

At the same time, Yuan Zifeng also participated in the glass fiber of general automobiles – nylon composites in high temperature and high humidity, residual stress during carbon fiber-epoxy resin, initial injury simulation, silicon carbide / silicon carbide composite material Oxidation creep simulation, carbon fiber-epoxy resin super-high fatigue injury simulation and other engineering projects, have accumulated a large number of engineering composites, multi-physics simulation, not only multi-scale for advanced materials in complex environments There is a certain understanding of multi-physical field failure mechanism, and more understanding of the demand model of engineering software clients.

In cooperation, Yuan Zifeng feels that foreign simulation methods have attached great importance to the development of mechanics. In the development of commercial software, it has been taken for many years than China, and has accumulated a lot of experience and form a very good ecology. At the same time, it is more concerned that the European and American simulation software market has emerged in a large number of software or third-party plug-ins, based on multi-scale multi-physicological methods, including advanced materials industries including composites. Among them, Altair’s MultiScale.Sim (as a third-party plug-in), the third-party plug-in in Siemens, the multimechanics, composite analysis software, composite, composite curing simulation software Raven, etc. In particular, Abaqus has provided simple material homogenization function modules in the latest version.

In contrast to foreign "hundred flowers", China’s simulation software is another scene. It does not form a market. It is not validated, the software is scarce, the function is single, and the existence of software exists, the launch of many scientific research work has been set up. Passover obstacles. If you want to add some features, there are many restrictions to foreign purchases, and I have been developed and facing bottlenecks. However, to achieve the development of the vision theory, the new algorithm attempt, meet the needs of the industry, have a self-designed software is imminent.

Yuan Zifeng noted that there are many open source software abroad. Just take a platform, propose a versatile structure, code, let others use, the platform will continue to expand in the process of us, more and more improved. "Why don’t we do some open source software in China, provide some tools to the industry, academia, helping everyone solve some problems, slowly build ecology?" During the University of Columbia, Yuanzifeng I have been holding this idea. With the further deepening of the foreign simulation software market, the desire to achieve this idea is more urgent in Yuan Zifeng.

Moreover, according to him, there are many Chinese people who have a mechanics in foreign schools, but there are very few people engaged in this study. Since domestic computing mechanics is so mature, they will be more than they have more things, in order to calculate More Chinese voice made some contributions.

With a decade, with the ideal of the country, Yuan Zifeng returned to the alma mater to start a new journey.

Yuan Zifeng stood in the statue of Mr. Deng Jiaxiang.

"Select back to Peking University has many reasons. It is my alma mater, with China’s smartest student and teacher, and there is a tradition of calculating mechanical research. Many teachers hope that I will come back together, this is a good opportunity to me. Yuan Zifeng said.

After leaving 10 years, I returned to my alma mater. Yuan Zifeng felt that the atmosphere of Peking University is still as early as early as the beginning, and you can do everything you want to do. In the project, in the project, he will implement the direct homogeneous method and the anti-order homogeneous method of the independent nonlinear finite element software platform; in the autonomous nonlinear finite element software platform Writing a photographic library of photographic scale materials, including but not limited to linear elasticity, elasticity, viscoelasticity, viscosity, continuous injury, circulating loading fatigue damage, etc.; more physics is also implemented Field coupling method. The project will integrate existing mature multi-scale methods, combined with multi-physical field coupling theory, to establish a complete theory, simulation, and software system for characterization issues.

Yuan Zifeng introduced that this system is a common multi-scale multi-physical field methodology that can reproduce the laboratory test data of different industries, and then generate a large number of virtual physics experiments based on direct multi-scale methods. The purpose of manpower, material, and financial resources can also solve the problem of virtual physics experiments in real world. Real additional virtual experimental data can train down-order multi-scale models such that different components of the scale of the scale in the actual large-scale structure simulation calculation can still be independently characterized. Structural simulation, verification, optimization and other work will be improved, this methodology will provide a new idea for material design of a variety of industries.

At the same time, since the multi-scale multi-physical field material model is essentially improved the constant relationship between strain-stress, it does not essentially change the nonlinear finite element simulation process of the macro structure, so the traditional computational solid mechanical system is not subject to the large frame. Very great influence, the industry can quickly use this friendly new system.

"Everyone thinks the multi-scale threshold is very high. I want to put the document, papers, and procedures. It is actually not so high. In order to make users easy to get started, the software is very high, this is not a half The problem of the child can solve, the time cost is very large, should not stop writing documents, I have to test it, there are many jobs to do. "Yuan Zifeng said.

Not only do you have to do good things, but also do some innovations academically, there is such a plan for future work. As the work slowly launched, Yuan Zifeng intends to do some new work in addition to the previous work.

Many years of study, work experience tells him that doing things to understand problems from the perspective of customers, especially simulation can’t do some old ways, can’t close the door, to understand what customers’ needs. "I listened to the lecture in Peking University. Please pack the governor, in the aerospace field, they ask many questions, there are many ways to do from calculating mechanics." Yuan Zifeng said that users and tool manufacturers are mutual Promote the relationship, multi-communication can understand each other. So he intends to visit some universities and enterprises that have better domestic composites to understand what needs, and then provide them with some calculation tools, do some interesting, meaningful things, but because the epidemic continues, these things have to be It has been pushed back.

When I returned to China, Yuan Zifeng’s work was going well, he said that this will not be able to drive everyone’s support. "Our hands are empty, there is no big results, the country, Beijing, schools are our support for us, we are very grateful. We can only return everyone’s support only."

Review the growth of all the way, Yuan Zifeng wants to thank people, he said: "Professor Jacob Fish gives me enough trust, not only giving me a lot of help, not only in thinking mode, with the company’s cooperation I have inspired. Professor Tang Shaoqiang, Northern University, can simply understand the complex mathematics issues, let me kill the mathematics of the difficulty since high school to university, and then I was filled with Mr. Tang The lesson, this is a lot of help, and I have slowly embarrassed the cause of the road. "

When many years of students, Yuan Zifeng will also usher in their own students. He said that you have to serve the students as much as possible, let them be happy, because a person’s luckiest thing is to enjoy their work.

Watch the game, play the ball, cooking, Yuan Zifeng is a person who fully enjoys life, but he has never relaxed. He plans to serve the academia, industry.

"Jobs said, the user’s demand is more horses before the car, because they don’t know this thing, what we do is to let everyone know that there is a car in addition to the horse." Yuan Zifeng said, "I I hope to introduce yourself as soon as possible, let everyone use our software, understanding the open source software. I can do a lot of things. I am looking forward to the platform you have made, everyone can collide some different sparks, producing one Add a greater effect. "

Professor of Assistant, Department of Mechanics and Engineering Science, Peking University Institute of Engineering, special researcher. In 2009, he became a bachelor’s degree in Engineering and Engineering Science, the University of Peking University. In 2012, the Department of Technologies and Engineering Mechanics in Columbia University was a Philosophy of Philosophy, 2016 Civil Engineering and Engineering Mechanics, Columbia University. . In the University of Columbia, the Ph.D. in the University of Columbia, and the research work that has been engaged in multi-scale calculation methods in the post-doctoral work. Published 11 papers related to multi-scale multi-physics, including 10 articles. The direction of scientific research involves theoretical and application mechanics, engineering mechanics, calculation mechanics, calculating mechanical software design, multi-scale calculation method and multi-physical field coupling method.