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Transplantation and development of finite element analysis software on supercomputer

Abstract:

this paper first introduces the configuration and performance of the "Shenwei I" super parallel computer, and then discusses the idea and implementation scheme of the secondary development of the commercial large-scale finite element software NASTRAN on the "Shenwei I" system, According to the requirements of some specifications, the powerful finite element analysis ability of Tran and the high-performance computing ability of supercomputer are combined to expand the analysis scale and improve the analysis speed; Then an example is given to illustrate the correctness and efficiency of the development function; Finally, the application prospect of Shenwei machine is prospected

With the vigorous development of computers and computing methods, scientific computing has become the third pillar of human cognitive world after theory and experiment. High performance computing power and related technologies are the strategic commanding heights that the world competes for, and one of the important symbols to measure a country's comprehensive national strength. Various supercomputers at home and abroad came into being. The development and use of supercomputers such as "Shenwei", "Yinhe" and "dawn" shows that China has reached the international advanced level in supercomputer hardware technology. On the other hand, as an important part of numerical calculation, various finite element analysis software has been widely used in aerospace, automotive, machinery, construction, chemical and other fields. Technically, supercomputers are generally source code compatible. Domestic supercomputers cannot directly install commercial finite element software. What is more serious is that Western governments have strict control over China in terms of high-performance computing hardware and software. Therefore, the application of supercomputers independently developed by China in the field of engineering is greatly limiteddeveloping parallel finite element analysis software for "Shenwei I" from scratch requires great workload and the investment of technicians in all aspects, so it requires a long time and strong funds. From the theory and practice of finite element analysis, we can know that the main analysis time of finite element analysis is applied to scientific calculation (for structural analysis, it is mainly to solve linear equations and sparse matrix eigenvalues), and the parallel development of these calculations began earlier, which is relatively mature, and some software can have source code for free. This raises a question: can we combine the publicly available serial finite element analysis software with the scientific computing software library of supercomputer for secondary development and system integration, so as to form a large-scale finite element analysis software of supercomputer with independent intellectual property rights? With the strong support of the special fund for informatization of Shanghai informatization office, Shanghai Jiaotong University and Shanghai Supercomputing Center have successfully transplanted the commercial finite element analysis software NASTRAN on the "Shenwei I" supercomputer system and redeveloped the parallel computing function after more than a year of research and development, so as to explore a new way for the development of supercomputer application software, At the same time, it provides a platform for engineering applications of high-performance computing

II. Introduction to Shenwei I supercomputer system

"Shenwei I" computer is a scalable large-scale parallel processing supercomputer system. It absorbs and develops the advanced design ideas and technologies of supercomputers in the world, and adopts isomorphic, distributed and shared main memory and planar grid architecture. It is a parallel processing system with multiple instruction streams and multiple data streams. Its peak operation speed is as high as 384billion floating point results per second, with 48gb main memory capacity and 1.28tb disk capacity. The whole system is mainly composed of host system, front-end system, disk array system and software system. "Shenwei I" supercomputer is suitable for various computing fields that need high-speed and large-capacity parallel processing

"Shenwei I" computer software system mainly includes the following aspects: distributed parallel operating system, various parallel programming languages, parallel program development and supporting environment, scientific computing software library, peripheral local area system, distributed database management system, scientific computing visualization system, etc. Among them, parallel programming languages mainly include parallel C, high-performance FORTRAN (HPF), parallel FORTRAN, OpenMP and parallel java languages. Scientific computing software library mainly includes HPF language scientific computing library and scientific computing library based on pvm/mpi. Parallel program development and supporting environments mainly include ppme, PVM, MPI, etc

III. development ideas and implementation schemes

the existing commercial large-scale finite element analysis software, such as Tran and stran, is highly open, and these software allow users to carry out secondary development. Through development, we can give full play to the advantages of commercial finite element software in pre-processing and post-processing, human-computer interaction interface and so on. So far, the parallel processing function of NASTRAN software is also very limited. The overall development idea of this topic is to make full use of the speed advantage of large-scale parallel computer and transplant the most time-consuming equation solving and eigenvalue solving parts in finite element analysis to Shenwei machine. Using the secondary development tools PCL and DMAP programming technology, the seamless and visual integration of commercial finite element software and supercomputer parallel computing software is realized

among various finite element analysis software, including NASTRAN, static analysis, modal analysis, buckling analysis, dynamic response, etc. are the most basic and commonly used analysis functions. Therefore, the parallelization of these functions should be considered first when the finite element software is transplanted on "Shenwei I". The goal of this project is to develop the parallel computing function of the above four basic modules. For the static analysis module, the key calculation is to solve large-scale sparse matrix linear equations. Dynamic response analysis is also a similar problem, but its right-hand term changes with time (iteration steps) and is related to the previous solution results. As long as the step size is appropriate, this simplification can still achieve quite accurate results. For the modal analysis process, the key calculation is to solve the large-scale sparse matrix generalized eigenvalue problem. Buckling analysis is the synthesis of static analysis and modal analysis. From the above analysis, it can be seen that the core problem of parallelizing the calculation of the basic functions of finite element analysis software is the solution of large-scale sparse matrix equations and eigenvalue calculation

the serial processing version of NASTRAN software is installed on the front-end computer (alpha workstation) of "Shenwei I", and the parallel calculation needs to be carried out on the host, so the file transmission from the front-end computer to the host takes time. Through actual calculation, in the static analysis and calculation of NASTRAN, the time to solve the equation accounts for about 30% - 50% of the whole analysis process. In modal analysis and dynamic response analysis, the time of numerical calculation accounts for 90% or more of the analysis time. It can be seen that the key to the development is that the solver on Shenwei machine has high efficiency, which is enough to compensate for the additional time loss caused by matrix input and output

ease of use is also an important factor to be considered in this topic. Since the end user of the system may not know much about Shenwei machine, the relevant options and settings should be completed under the familiar Patran interface

Figure 1 shows the flow chart of running NASTRAN on the "Shenwei I" supercomputer platform after the completion of the project

we have completed the transplantation and development of NASTRAN software on "Shenwei I", including static analysis, dynamic response analysis, modal analysis and buckling analysis modules (the code of each analysis module in NASTRAN is 101109103105 respectively). Among them, the parallel equations of 101 and 109 modules are solved by direct method and iterative method, and the parallel programs are designed respectively. The equation solving part of 103 and 105 only adopts the direct method, and compiles the parallel solving program based on the famous software package parpack. Based on the NASTRAN solution results, the host parallel solver has high accuracy. The iterative method is generally accurate to 5~6 significant figures, and the direct method has higher accuracy. The example verification shows that the analysis time of the analysis program after parallel development is significantly shortened. The solution sequence of NASTRAN is reorganized. After determining the whole solution sequence and verifying its correctness, this sequence is recompiled and connected, and new S101, S103, S105, S109 sequences are established. This can simplify the generation of future task files (.Bdf) and improve the execution speed

in terms of visual integration, in order to better integrate with Patran program, the development program is written in Patran's own PCL language to ensure (2) aluminum alloy profile stretching must be moved to the stretching frame for stretching operation after the aluminum alloy profile is cooled to below 50 degrees (bare hands can hold it tightly), which proves the convenience of programming and the consistency of interface style. All parameter setting operations of the system are completed in Patran interface, so a drop-down menu "supercomputer" is added under Patran main window. Click the corresponding items in the menu to pop up an interface, in which you can set the name of the front-end machine, the number of CPUs used, and the partition name that can be fed back to us if the customer encounters any problems in use. The specific parameters of the parallel solver can be set in the next level interface. Figure 2 shows the user interface of parallel analysis

Figure 2: user interface of parallel analysis

through a large number of examples, we found that different finite element element element types and different element numbers have great differences in parallel computing acceleration ratio; For the same unit type, there is a certain number of units, and there is a number of CPUs with the highest speedup ratio; Among the four modules developed at present, the static analysis module has the worst acceleration ratio and the dynamic response analysis module has the highest acceleration ratio

IV. example

using the parallel analysis function of NASTRAN developed in this topic, the mechanical properties of a new type of compressed natural gas urban bus are analyzed

a plate and shell element model including body frame beam elements and inner and outer skins is established. Considering the influence of inner and outer skins, and considering the coordination of calculation accuracy and computer capacity and operation speed, the element division is not too detailed, with a total of 8166 shell elements, 2589 beam elements and 8738 nodes. The calculation conditions include: static analysis (static bending, torsion, emergency braking, sharp turning), modal analysis, transient response analysis (a wheel passes the boss), etc. Figure 4 shows the local deformation of the transient response of the vehicle body. Compared with microcomputer computing, the parallel computing analysis based on "Shenwei I" developed in this topic has obvious acceleration effect, which greatly saves the analysis time, and the analysis result is reliable

Figure 3: local deformation diagram of body transient response

v. conclusion and outlook

the system developed in this subject has passed the appraisal organized by Shanghai Science and Technology Commission. The appraisal conclusion is that "this project fills the domestic gap in the field of finite element parallel computing, the scheme design is innovative, and the system has reached the international advanced level. It has a good application prospect and good social and economic benefits"

the successful parallel development of commercial large-scale finite element analysis software NASTRAN on the "Shenwei I" supercomputer has explored a new way for the development of supercomputer application software, and provided a platform for the application of high-performance computing in the engineering community. It has broad application prospects in the following aspects: (1) the strength and stiffness analysis of large-scale complex structures, such as satellites, rockets and other extremely complex structures, in ensuring sufficient strength How to realize lightweight design under stiffness? Large structures like the Three Gorges Dam

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