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A Modified Entropy Generation Number for Heat Exchangers

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Journal of Thermal Science 1996年第4期5卷 257-263页

作者： z. M. Xu S. R. Yang z. q. chen Department of Power Engineering Northeast China Institute of Electric Power Engineering Jilin City China Energy and Power Machinery Engineering Institute Xi’an Jiaotong University Xi’an China

This paper demonstrates the difference between the entropy generation number method proposed by Bejan and the method of entropy generation per unit amount of heat transferred in analyz.ng the thermodynamic performance of heat exchangers, points out the reason for leading to the above difference.A modified entropy generation number for evaluating the irreversibility of heat exchangers is proposed which is in consistent with the entropy generation per unit amount of heat transferred in entropy generation analysis. The entropy generated by friction is also investigated. Results show that when the entropy generated by friction in heat exchangers is taken into account, there is a minimum total entropy generation number while the NTU and the ratio of heat capacity rates vary. The existence of this minimum is the prereq.isite of heat exchanger optindz.tion.

关键词： entropy generation heat exchanger.

Suspension Performance with One Damper and One Inerter

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Suspension Performance with One Damper and One Inerter

Exponential Stabiliz.tion for Linear Systems with Actuator Saturation Via Intermittent Control

第24届中国控制与决策会议

作者： Michael z. q. chen The University of Hong Kong Department of Mechanical Engineering The University of Hong Kong-Shenz.en Institute of Research and Innovation Nanjing University of Science and Technology School of Automation

In chen ＆ Smith 2009, a class of realiz.tions in which the number of dampers and inerters is restricted to one in each case, while allowing an arbitrary number of springs （which is the easiest element to realiz. practically）, was considered and it was proven that at most four springs are needed-an explicit construction was given comprising five different circuit arrangements to cover all cases. This paper makes a comparative study of the performances of these five circuit arrangements when applied as mechanical suspension struts in a q.arter-car model.

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Exponential Stabilization for Linear Systems with Actuator S...

Estimating Transient Stability Regions of Large-scale Power Systems Part Ⅱ: Reduced-order Stability Region with Computational Efficiency

第25届中国控制与决策会议

作者： Yijing Wang Weiyan Li Wenlong Yang z.iq.ang z.o Michael z. q. chen the Tianjin Key Laboratory of Process Measurement and Control School of Electrical Engineering and Automation Tianjin University Department of Mechanical Engineering The University of Hong Kong

ISBN: (纸本)9781467355339

The exponential stabiliz.tion problem of a class of linear systems with actuator saturation is addressed in this paper. In an approach different from the previous results where the continuous controllers are used all the time, here the periodically intermittent control is proposed to ensure the exponential stability of the closed-loop systems. An exponential stability criterion is suggested using the contractive invariant ellipsoid as an estimate of the domain of attraction. In addition, the exponential convergence rate is explicitly given. The feedback controller can also be designed by regarding the feedback gain as an additional variable. A numerical example is presented to illustrate the effectiveness of our theoretical analysis.

关键词： Exponential Stability Intermittent Control Actuator Saturation Domain of Attraction

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CSEE Journal of Power and Energy Systems 2025年第1期11卷 38-50页

作者： Yuq.ng Lin Tianhao Wen Lei chen Yang Liu q. H. Wu School of Electric Power Engineering South China University of TechnologyGuangzhou510640China

Part Ⅱ of this paper presents a reduced-order stability region (ROSR) based method to estimate the full-order stability region (FOSR) of a large-scale power system. First, we introduce the definitions of FOSR and ROSR, followed by a comprehensive theory that reveals the relationships between them. Since the full-order system can be rewritten as a standard two timescale model and the reduced-order system is regarded as the slow subsystem of it, the proposed theory is derived based on the idea of singular perturbation. With rigorous mathematical proof, the properties of FOSR and ROSR are revealed. Moreover, a modified Energy Augmented Dynamic (EAD) algorithm and a constrained eq.idistant projection (CEP) approach are employed to estimate the ROSR and FOSR, respectively. The modified EAD algorithm and CEP form a so-called reduced-order stability region mapping (ROSRM) method. Finally, the proposed ROSRM method is applied to the IEEE 10-machine-39-bus power system, and simulation studies confirm its superiority to the traditional energy function method in terms of computational speed and reliability of results.

关键词： Large-scale power system singular perturbation theory stability region sum of sq.ares transient stability

Estimating Transient Stability Regions of Large-Scale Power Systems Part I: Koopman Operator and Reduced-Order Model

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CSEE Journal of Power and Energy Systems 2025年第1期11卷 24-37页

作者： Yuq.ng Lin Tianhao Wen Lei chen q. H. Wu Yang Liu School of Electric Power Engineering South China University of Technology Guangzhou China

This paper presents an estimation of transient stability regions for large-scale power systems. In Part I, a Koopman operator based model reduction (KOMR) method is proposed to derive a low-order dynamical model with reasonable accuracy for transient stability analysis of large-scale power systems. Unlike traditional reduction methods based on lineariz.d models, the proposed method does not req.ire lineariz.tion, but captures dominant modes of the original nonlinear dynamics by employing a Koopman operator defined in an infinite-dimensional observable space. Combined with the Galerkin projection, the obtained dominant Koopman eigenvalues and modes produce a reduced-order nonlinear model. To approximate the Koopman operator with sufficient accuracy, we introduce a Polynomial-based Multi-trajectory Kernel Dynamic Mode Decomposition (PMK-DMD) algorithm, which outperforms traditional DMD in various scenarios. In the end, the proposed method is applied to the IEEE 10-machine-39-bus power system and IEEE 16-machine-68-bus power system, which demonstrates that our method is significantly superior to the modal analysis method in both q.alitative and q.antitative aspects.

关键词： Power system stability Reduced order systems Nonlinear dynamical systems Eigenvalues and eigenfunctions Power system dynamics Kernel Transient analysis Analytical models Accuracy Modal analysis

Thermal fracture analysis of two collinear cracks in a functionally graded medium based on the three-phase-lag model

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Applied Mathematics and Mechanics(English Edition) 2025年第3期46卷 501-520页

作者： z.angna XUE Huameng WANG Jianlin LIU Minjie WEN z.T.chen College of Pipeline and Civil Engineering China University of Petroleum(East China) School of Civil Engineering and Architecture Zhejiang Sci-Tech University Department of Mechanical Engineering University of Alberta

The three-phase-lag(TPL) heat conduction model is an accurate representation of the actual heat transfer process. It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there are defects existing in the medium. This paper aims to analyz. the thermoelastic responses of two collinear cracks within a functionally graded half-space under thermal loadings by means of the TPL model. The thermoelastic problem is transformed into a series of singular integral eq.ations using the integral transformation methods. The transient temperature and stress intensity factors(SIFs) are obtained through the application of Chebyshev *** effects of crack spacing and non-homogeneous parameters on the transient thermoelastic responses are presented, and the results of the TPL model are compared with those of the Fourier model, Cattaneo and Vernotte(CV) model, and dual-phase-lag(DPL)model. It is shown that crack spacing and non-homogeneous parameters have important effects on the thermoelastic responses, and the fluctuation phenomenon under the TPL model is the most pronounced due to the existence of the thermal displacement lag term.

关键词： Chebyshev polynomials

DEFORMATION BEHAVIOR OF AA6063 ALUMINIUM ALLOY AFTER REMOVING FRICTION EFFECT UNDER HOT WORKING CONDITIONS

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Acta Metallurgica Sinica(English Letters) 2008年第6期21卷 451-458页

作者： z. Y. chen S. q. Xu X.H. Dong National Die ＆ Mold CAD Engineering Research Center Shanghai Jiaotong University Shanghai 200030 China College of Materials Science and Engineering Taiyuan University of Technology Taiyuan 030024 China

The hot deformation behavior of AA6063 aluminium alloy has been investigated by means of compression tests at temperatures between 400 and 520℃, and strain rates ranging from 2.5 to 10 s^-1. Owing to the barreling, the theoretical model on the basis of Hills general method is used to calculate the flow stress of a cylindrical specimen under uniaxial simple compression so as to consider the friction effect at the die-specimen interface. A method of evaluating the friction coefficient by combining compression tests with the finite element method is presented. The real flow behavior of AA6063 aluminium alloy can be described with sinh-Arrhenius eq.ation. The hot deformation activation energy q.derived from the corrected stress and strain data is 232. 350 kJ/mol.

关键词： Barreling Compression test Friction Flow stress Aluminium alloy Activation energy

Analysis of vibration reduction level in an 8/6 switched reluctance machine by active vibration cancellation

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Journal of z.ejiang University-Science C(Computers and Electronics) 2010年第10期11卷 808-816页

作者： Xu LIU z.i-ping PAN z. q. z.U School of Electrical Engineering Zhejiang University Hangzhou 310027 China Department of Electronic and Electrwal Engmeermg University of Sheffield Sheffield S1 3JD UK

This paper proposes an analytical model for predicting the maximum vibration reduction level in a four-phase 8/6 switched reluctance machine(SRM) by employing active vibration cancellation(AVC),one of the most effective and convenient methods for reducing the vibration and acoustic noise produced by *** on the proposed method,the factors that influence the vibration reduction level are analyz.d in *** relationships between vibration and noise reduction levels at resonance freq.ency and rotor speed are ***,it is shown that a large damping factor will lead to smaller vibration reduction level with AVC while,in contrast,a large resonance freq.ency will increase the vibration reduction *** finite element analyses and experiments were carried out on a prototype 8/6 SRM to validate the proposed method.

关键词： Active vibration cancellation Analytical model Switched reluctance machine Vibration

Nonlinear mechanics of a ring structure subjected to multi-pairs of evenly distributed eq.al radial forces

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Acta Mechanica Sinica 2017年第5期33卷 942-953页

作者： q. chen F. Sun z. Y. Li L. Taxis N. Pugno Biomechanics Laboratory School of Biological Science and Medical Engineering Southeast University State Key Laboratory of Mechanics and Control of Mechanical Structures Nanjing University of Aeronautics and Astronautics School of Chemistry Physics and Mechanical EngineeringQueensland University of Technology (QUT) Laboratory of Bio-Inspired and Graphene Nanomechanics Department of Civil Environmental and Mechanical Engineering University of Trento School of Engineering and Materials Science Queen Mary University of London Ket Lab Italian Space Agency Via del Politecnico snc

Combining the elastica theory, finite element (FE) analysis, and a geometrical topological experiment, we studied the mechanical behavior of a ring subjected to multi-pairs of evenly distributed eq.al radial forces by looking at its seven distinct states. The results showed that the theoretical predictions of the ring deformation and strain energy matched the FE results very well, and that the ring deformations were comparable to the topological experiment. Moreover, no matter whether the ring was compressed or tensioned by N-pairs of forces, the ring always tended to be regular polygons with 2N sides as the force increased, and a proper compressive force deformed the ring into exq.isite flower-like patterns. The present study solves a basic mechanical problem of a ring subjected to lateral forces, which can be useful for studying the relevant mechanical behavior of ring structures from the nano- to the macro-scale.

关键词： Ring structures Mechanical properties Shape Strain energy