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Novel Models and Algorithms of Load Balancing for Variable-structured Collaborative Simulation under HLA/RTI

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Chinese Journal of Mechanical engineering 2013年第4期26卷 629-640页

作者： YUE Yingchao FAN Wenhui XIAO Tianyuan MA Cheng state cims engineering research center Tsinghua University

High level architecture(HLA) is the open standard in the collaborative simulation field. Scholars have been paying close attention to theoretical research on and engineering applications of collaborative simulation based on HLA/RTI, which extends HLA in various aspects like functionality and efficiency. However, related study on the load balancing problem of HLA collaborative simulation is insufficient. Without load balancing, collaborative simulation under HLA/RTI may encounter performance reduction or even fatal errors. In this paper, load balancing is further divided into static problems and dynamic problems. A multi-objective model is established and the randomness of model parameters is taken into consideration for static load balancing, which makes the model more credible. The Monte Carlo based optimization algorithm(MCOA) is excogitated to gain static load balance. For dynamic load balancing, a new type of dynamic load balancing problem is put forward with regards to the variable-structured collaborative simulation under HLA/RTI. In order to minimize the influence against the running collaborative simulation, the ordinal optimization based algorithm(OOA) is devised to shorten the optimization time. Furthermore, the two algorithms are adopted in simulation experiments of different scenarios, which demonstrate their effectiveness and efficiency. An engineering experiment about collaborative simulation under HLA/RTI of high speed electricity multiple units(EMU) is also conducted to indentify credibility of the proposed models and supportive utility of MCOA and OOA to practical engineering systems. The proposed research ensures compatibility of traditional HLA, enhances the ability for assigning simulation loads onto computing units both statically and dynamically, improves the performance of collaborative simulation system and makes full use of the hardware resources.

关键词： static load balancing dynamic load balancing variable-structure collaborative simulation under HLA/RTI multi-objective optimization ordinal optimization

Real-Time Control for CPS of Digital Airplane Assembly with Robust H-Infinity Theory

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tsinghua Science and Technology 2015年第4期20卷 376-384页

作者： Hui Li Linxuan Zhang Tianyuan Xiao Jietao Dong state cims engineering research Cente at tsinghua university

This study introduces a real-time controller design method under the effects of network time delay and external disturbance. The study first introduces the digital, virtual, intelligent trend of airplane assembly and reveals the status and problems of digital airplane assembly studies. The Cyber-Physical System （CPS） structure is then proposed for digital airplane assembly, and the real-time control issues are discussed. Then, the question of real- time control undertaken by a parallel robot is simplified to a control question with bounded time delay and complex interference, and a mathematical description is presented. Next, a robust Hoo controller with a disturbance degree of decay 7 is designed according to the mathematical description. Finally, a simulation is conducted. All of the experiment results show the feasibility of the above proposed methods.

关键词： cyber physical system network time delay robust H-infinity control linear matrix inequality

Data fusion and simulation-based planning and control in cyber physical system for digital assembly of aeroplane

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International Journal of Modeling, Simulation, and Scientific Computing 2015年第3期6卷 66-84页

作者： Hui Li Linxuan Zhang Tianyuan Xiao Jietao Dong State CIMS Engineering Research Center at Tsinghua University Main Building Room 604 Beijing 100084P.R.China State CIMS Engineering Research Center at Tsinghua University Main Building Room 601 Beijing 100084P.R.China State CIMS Engineering Research Center at Tsinghua University Main Building Room 619 Beijing 100084P.R.China

This paper introduces a CPS application for intelligent aeroplane assembly.At first,the CPS structure is presented,which acquires the characteristics of general CPS and enables“simulation-based planning and control”to achieve high level intelligent assembly.Then the paper puts forward data fusion estimation algorithm under synchronous and asynchronous sampling,respectively.The experiment shows that global optimal distributed fusion estimation under synchronized sampling proves to be closer to the actual value compared with ordinary weighted estimation,and multi-scale distributed fusion estimation algorithm of wavelet under asynchronous sampling does not need time registration,it can also directly link to data,and the error is smaller.This paper presents hybrid control strategy under the circumstance of joint action of the inner and outer loop to address the problems caused by the less controllable feature of the parallel mechanism when undertaking online process simulation and control.A robust adaptive sliding mode controller is designed based on disturbance observer to restrain inner interference and maintain robustness.At the same time,an outer collaborative trajectory planning is also designed.All the experiment results show the feasibility of above proposed methods.

关键词： Intelligent aeroplane assembly cyber physical system multi-sensor data fusion simulation-based control disturbance observer robust adaptive sliding mode controller

100 km wear-free sliding achieved by microscale superlubric graphite/DLC heterojunctions under ambient conditions

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National Science Review 2022年第1期9卷 17-24页

作者： Deli Peng Jin Wang Haiyang Jiang Shuji Zhao Zhanghui Wu Kaiwen Tian Ming Ma Quanshui Zheng Department of engineering Mechanics Tsinghua University center for Nano and Micro Mechanics Tsinghua University Institute of Superlubricity Technology Research Institute of Tsinghua University in Shenzhen state Key Laboratory of Tribology Tsinghua University Department of Mechanical engineering Tsinghua University

Wear-free sliding between two contacted solid surfaces is the ultimate goal in the effort to extend the lifetime of mechanical devices,especially when it comes to inventing new types of micro-ele ctromechanical systems where wear is often a major obstacle.Here we report experimental observations of wear-free sliding for a micrometer-sized graphite flake on a diamond-like-carbon(DLC) surface under ambient conditions with speeds up to 2.5 m/s,and over a distance of 100 km.The coefficient of friction(COF) between the microscale graphite flake,a van der Waals(vdW) layered material and DLC,a non-vdW-layered material,is measured to be of the order of 10-3,which belongs to the superlubric regime.Such ultra-low COFs are also demonstrated for a microscale graphite flake sliding on six other kinds of non-vdW-layered materials with sub-nanometer roughness.With a synergistic analysis approach,we reve al the underlying mechanism to be the combination of interfacial vdW interaction,atomic-smooth interfaces and the low normal stiffness of the graphite flake.These features guarantee a persistent full contact of the interface with weak interaction,which contributes to the ultra-low COFs.Together with the extremely high in-plane strength of graphene,wear-free sliding is achieve d.Our results broaden the scope of superlubricity and promote its wider application in the future.

关键词： structural superlubricity wear-free microscale graphite DLC

Adaptive scheduling method for dynamic robotic cell based on pattern classification algorithm

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International Journal of Modeling, Simulation, and Scientific Computing 2018年第5期9卷 74-91页

作者： Chuyuan Wang Linxuan Zhang Chongdang Liu National cims engineering research center tsinghua university Beijing 100084P.R.China

In order to deal with the dynamic production environment with frequent fluctuation of processing time,robotic cell needs an efficient scheduling strategy which meets the real-time requirements.This paper proposes an adaptive scheduling method based on pattern classification algorithm to guide the online scheduling process.The method obtains the scheduling knowledge of manufacturing system from the production data and establishes an adaptive scheduler,which can adjust the scheduling rules according to the current production status.In the process of establishing scheduler,how to choose essential attributes is the main difficulty.In order to solve the low performance and low efficiency problem of embedded feature selection method,based on the application of Extreme Gradient Boosting model(XGBoost)to obtain the adaptive scheduler,an improved hybrid optimization algorithm which integrates Gini impurity of XGBoost model into Particle Swarm Optimization(PSO)is employed to acquire the optimal subset of features.The results based on simulated robotic cell system show that the proposed PSO-XGBoost algorithm outperforms existing pattern classification algorithms and the newly learned adaptive model can improve the basic dispatching rules.At the same time,it can meet the demand of real-time scheduling.

关键词： Robotic cell adaptive scheduling simulation particle swarm optimization extreme gradient boosting.

An extended HLA multilayer federation integration architecture for multidisciplinary collaborative simulation

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High Technology Letters 2009年第4期15卷 429-433页

作者：唐树才 National cims engineering research center Tsinghua University

The development of complex products is essentially concerned with multidisciplinary knowledge.Running on Internet, integration based on multilayer federation architecture and dynamic reuse of simulationresources are the major difficulties for complex product collaborative design and simulation. Since thetraditional Run-Time Infrastructure (RTI) is not good at supporting these new requirements, an extendedhigh level architecture (HLA) multilayer federation integration architecture (MLFIA), based on the resourcemanagement federation (RMF) and its supporting environment based Service-oriented architecture(SOA) and HLA (SOHLA) are proposed, The idea and realization of two key technologies, the dynamiccreation of simulation federation based on RMF, TH_RTT, an extensible HLA runtime infrastructure(RTI), used at Internet are emphasized. Finally, an industry case about multiple unit (MU) is given.

关键词：集成架构协同仿真多学科多层抗原高层体系结构产品协同设计资源再利用

A dynamic delivery strategy for material handling in mixed-model assembly lines using decentralized supermarkets

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International Journal of Modeling, Simulation, and Scientific Computing 2015年第4期6卷 73-91页

作者： Jietao Dong Linxuan Zhang Tianyuan Xiao Hui Li National cims engineering research center tsinghua university Beijing 100084 P.R.China

Material handling has become one of the major challenges in modern production management.Consequently,this paper intends to investigate the part delivery of mixedmodel assembly lines with decentralized supermarkets and tow trains.Besides,uncertain exception disturbances,including tow train failures and adjustments of the production sequence,are also considered.To solve this problem,a heuristic-based dynamic delivery strategy is proposed,which dynamically schedules the route,departure time,quantities and types of loaded parts for each tour.To evaluate the performance of this strategy,it is used to solve an instance in comparison with the periodic delivery strategy,experimental results are reported and their performances are compared under different metrics.Moreover,a multi-scenario analysis is employed to determinate the long-term decisions,including the number of tow trains and the route layout.Finally,the critical storage is suggested to be set for each station to avoid part starvation resulting from disturbances,and its effect on the delivery performance is investigated.

关键词： Mixed-model assembly lines dynamic part delivery supermarket tow train critical storage.

GREEDY NON-DOMINATED SORTING IN GENETIC ALGORITHM-ⅡFOR VEHICLE ROUTING PROBLEM IN DISTRIBUTION

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Chinese Journal of Mechanical engineering 2008年第6期21卷 18-24页

作者： WEI Tian FAN Wenhui XU Huayu National cims engineering research center Tsinghua University Beijing 100084 China

Vehicle routing problem in distribution （VRPD） is a widely used type of vehicle routing problem （VRP）, which has been proved as NP-Hard, and it is usually modeled as single objective optimization problem when modeling. For multi-objective optimization model, most researches consider two objectives. A multi-objective mathematical model for VRP is proposed, which considers the number of vehicles used, the length of route and the time arrived at each client. Genetic algorithm is one of the most widely used algorithms to solve VRP. As a type of genetic algorithm （GA）, non-dominated sorting in genetic algorithm-Ⅱ （NSGA-Ⅱ） also suffers from premature convergence and enclosure competition. In order to avoid these kinds of shortage, a greedy NSGA-Ⅱ （GNSGA-Ⅱ） is proposed for VRP problem. Greedy algorithm is implemented in generating the initial population, cross-over and mutation. All these procedures ensure that NSGA-Ⅱ is prevented from premature convergence and refine the performance of NSGA-Ⅱ at each step. In the distribution problem of a distribution center in Michigan, US, the GNSGA-Ⅱ is compared with NSGA-Ⅱ. As a result, the GNSGA-Ⅱ is the most efficient one and can get the most optimized solution to VRP problem. Also, in GNSGA-Ⅱ, premature convergence is better avoided and search efficiency has been improved sharply.

关键词： Greedy non-dominated sorting in genetic algorithm-Ⅱ （GNSGA-Ⅱ） Vehicle routing problem （VRP） Multi-objective optimization

Performance Improvement of Distributed Systems by Autotuning of the Configuration Parameters

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tsinghua Science and Technology 2011年第4期16卷 440-448页

作者：张帆曹军威刘连臣吴澄 National cims engineering and research center Tsinghua University research Institute of Information Technology Tsinghua University tsinghua National Laboratory for Information Science and Technology

The performance of distributed computing systems is partially dependent on configuration parameters recorded in configuration files. Evolutionary strategies, with their ability to have a global view of the structural information, have been shown to effectively improve performance. However, most of these methods consume too much measurement time. This paper introduces an ordinal optimization based strategy combined with a back propagation neural network for autotuning of the configuration parameters. The strat- egy was first proposed in the automation community for complex manufacturing system optimization and is customized here for improving distributed system performance. The method is compared with the covariance matrix algorithm. Tests using a real distributed system with three-tier servers show that the strategy reduces the testing time by 40% on average at a reasonable performance cost.

关键词： distributed systems performance evaluation autotune configuration parameters ordinal optimization covariance matrix algorithm