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Adaptive finite element-element-free Galerkin coupling method for bulk metal forming processes

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第3期10卷 353-360页

作者： Lei-chao liu Xiang-huai DONG Cong-xin LI National Die and Mould CAD Engineering Research Center Shanghai Jiao Tong University Shanghai 200030 China

An adaptive finite element-element-free Galerkin (FE-EFG) coupling method is proposed and developed for the numerical simulation of bulk metal forming processes. This approach is able to adaptively convert distorted FE elements to EFG domain in analysis. A new scheme to implement adaptive conversion and coupling is presented. The coupling method takes both advantages of finite element method (FEM) and meshless methods. It is capable of handling large deformations with no need of remeshing procedures, while it is computationally more efficient than those full meshless methods. The effectiveness of the proposed method is demonstrated with the numerical simulations of the bulk metal forming processes including forging and extrusion.

关键词： Meshless method Adaptive coupling method Bulk metal forming Numerical simulation

Control Strategies for Digital Twin Systems

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IEEE/CAA Journal of Automatica Sinica 2024年第1期11卷 170-180页

作者： guo-Ping liu IEEE the Center for Control Science and Technology Southern University of Science and TechnologyShenzhen 518055China

With the continuous breakthrough in information technology and its integration into practical applications, industrial digital twins are expected to accelerate their development in the near future. This paper studies various control strategies for digital twin systems from the viewpoint of practical *** make full use of advantages of digital twins for control systems, an architecture of digital twin control systems, adaptive model tracking scheme, performance prediction scheme, performance retention scheme, and fault tolerant control scheme are proposed. Those schemes are detailed to deal with different issues on model tracking, performance prediction, performance retention, and fault tolerant control of digital twin systems. Also, the stability of digital twin control systems is analysed. The proposed schemes for digital twin control systems are illustrated by examples.

关键词： Digital twin control systems fault tolerant control model tracking performance prediction performance retention

Coordination of Networked Nonlinear Multi-Agents Using a High-Order Fully Actuated Predictive Control Strategy

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IEEE/CAA Journal of Automatica Sinica 2022年第4期9卷 615-623页

作者： guo-Ping liu IEEE the Department of Electronic and Electrical Engineering Southern University of Science and Technology

This paper is concerned with the coordinative control problem of networked nonlinear multi-agents(NNM)with communication delays.A high-order fully actuated(HOFA)model is introduced to describe the nonlinear *** on this model,a HOFA predictive coordination method is proposed to compensate for the communication delays actively and achieve simultaneous stability and *** method largely simplifies the design of networked nonlinear multi-agents and makes the control performance be same for networked nonlinear multi-agents with and without communication *** analysis on the closed-loop systems derives the simultaneous stability and consensus criteria of networked nonlinear multiagents using the HOFA predictive coordination *** the presented way of designing HOFA predictive coordination controllers,a simulated example demonstrates the advantages of the proposed method.

关键词： method nonlinear coordination

Predictive Control of High-Order Fully Actuated Nonlinear Systems with Time-Varying Delays

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Journal of Systems Science & Complexity 2022年第2期35卷 457-470页

作者： liu guo-Ping Department of Electronic and Electrical Engineering Southern University of Science and TechnologyShenzhen 518055China

This paper investigates the control problem of high-order fully actuated nonlinear systems with time-varying delays in the discrete-time *** make the compensation for time-varying delays concise,active and universal,a novel nonlinear predictive control method is *** designed nonlinear predictive controller can achieve the same expected control performance as the nonlinear systems without *** the same time,the necessary and sufficient conditions for the stability of the closed-loop nonlinear predictive control systems are *** examples show that the proposed nonlinear predictive controller design method can completely compensate for the time-varying delays of nonlinear systems.

关键词： High-order fully actuated control systems nonlinear systems predictive control timevarying delays

Networked Learning Predictive Control of Nonlinear Cyber-Physical Systems

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Journal of Systems Science & Complexity 2020年第6期33卷 1719-1732页

作者： liu guo-Ping Department of Artificial Intelligence and Automation Wuhan UniversityWuhan 430072China

Cyber-physical systems integrate computing,network and physical environments to make the systems more efficient and cooperative,and have important and extensive application prospects,such as the Internet of *** paper studies the control problem of nonlinear cyber-physical systems with unknown dynamics and communication delays.A networked learning predictive control scheme is proposed for unknown nonlinear cyber-physical *** scheme recursively learns unknown system dynamics,actively compensates for communication delays and accurately tracks a desired *** multi-step predictors are presented to predict various step ahead outputs of the unknown nonlinear cyber-physical *** optimal design of controllers minimises a performance cost function which measures the tracking error predictions and control input increment *** system analysis leads to the stability criteria of closed-loop nonlinear cyber-physical systems employing the networked learning predictive control *** example illustrates the outcomes of the proposed scheme.

关键词： Cyber-physical systems learning control networked predictive control nonlinear systems

Tracking Control of Multi-Agent Systems Using a Networked Predictive PID Tracking Scheme

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IEEE/CAA Journal of Automatica Sinica 2023年第1期10卷 216-225页

作者： guo-Ping liu IEEE the Center for Control Science and Technology Southern University of Science and TechnologyShenzhen 518055China

With the rapid development of network technology and control technology,a networked multi-agent control system is a key direction of modern industrial control systems,such as industrial Internet *** paper studies the tracking control problem of networked multi-agent systems with communication constraints,where each agent has no information on the dynamics of other agents except their outputs.A networked predictive proportional integral derivative(PPID)tracking scheme is proposed to achieve the desired tracking performance,compensate actively for communication delays,and simplify implementation in a distributed *** scheme combines the past,present and predictive information of neighbour agents to form a tracking error signal for each agent,and applies the proportional,integral,and derivative of the agent tracking error signal to control each individual *** criteria of the stability and output tracking consensus of multi-agent systems with the networked PPID tracking scheme are derived through detailed analysis on the closed-loop *** effectiveness of the networked PPID tracking scheme is illustrated via an example.

关键词： Coordinative tracking control networked multiagent systems PID control predictive control

Experimental Study on the Viscosity of Soft Cohesive Sediments Around A Vibrating Pillar

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China Ocean Engineering 2022年第2期36卷 289-298页

作者： DONG Chuan-ming YU guo-liang ZHANG huai-xin ZHANG Min-xi SKLOE CISSESchool of Naval ArchitectureOcean&Civil EngineeringShanghai Jiao Tong UniversityShanghai 200240China Navigation College Dalian Maritime UniversityDalian 116026China

Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the *** cyclic vibration loadings may affect the rheological property of the sediments adjacent to the foundation and the stability of the *** is especially true when the structures are founded on cohesive sedimentary *** this study,the viscosity of soft cohesive sediments adjacent to a vibrating pillar was considered,and as a primary index of the rheological characteristics of the *** investigation was performed using the sinking ball *** experimental findings indicated that the viscosity of cohesive sediments decrease with increase of the liquidity index and vibration intensity.A simple semi-empirical formula was *** structures of the cohesive sediments were destroyed due to the mechanical vibration,and the sediments were fluidized during vibration *** shear strength of the cohesive sediments decreased with increased vibration intensity,not only because of the increased pore water pressure but also the decreased viscosity of cohesive sediments following sediment fluidization.

关键词： cohesive sediment vibration intensity viscosity coefficient fluidization liquidity index

Evolution of hypersurfaces by the mean curvature minus an external force field

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Science China Mathematics 2007年第2期50卷 231-239页

作者： Yan-nan liu huai-yu JIAN Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China

In this paper, we study the evolution of hypersurface moving by the mean curvature minus an external force field. It is shown that the flow will blow up in a finite time if the mean curvature of the initial surface is larger than some constant depending on the boundness of derivatives of the external force field. For a linear force, we prove that the convexity of the hypersurface is preserved during the evolution and the flow has a unique smooth solution in any finite time and expands to infinity as the time tends to infinity if the initial curvature is smaller than the slope of the force.

关键词： parabolic equation mean curvature flow maximum principle (for tensor) 35K45 53A05

High Temperature Phase Transitions in Na_xCoO_2 Materials

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Chinese Journal of Structural Chemistry 2006年第8期25卷 997-1003页

作者： NIE Chang-Jiang YANG huai-Xin SHI You-guo LI Jian-Qi Department of Physics Xiaogan University Xiaogan 432100 China Beijing National Laboratory for Condensed Matter Physics Institute of Physics The Chinese Academy of Sciences Beijing 100080 China

Structural and thermal transitions in the materials with nominal compositions of NaxCoO2 （0.5≤x≤0.75） have been investigated from room temperature to 800 K. In-situ heating transmission electron microscopy observations revealed certain distinctive structural phase transitions commonly existing in this system. A superstructure hexagonal phase, proposed arising from partial Na ordering, appears in this system in a high temperature range. The structural model for the superstructure phase has been given. Measurements of thermogravimetry （TG） and differential thermal analysis （DTA） demonstrated that certain structural phase transitions appear around 430 K. NaxCoO2 is decomposed at a temperature higher than 600 K.

关键词： NaxCoO2 phase transition superstructure