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Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

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Journal of Iron and Steel Research International 2016年第9期23卷 940-948页

作者： Hong-bin LI yun-li FenG Tao YAN en-lin yu National engineering Research Center for Equipment and Technology of Cold Strip Rolling Yanshan University College of Metallurgy and energy North China University of Science and Technology Equipment Manufacturing College Hebei University of Engineering

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of tem- peratures and strain rates using a Gleeble-3500 thermo-simulation machine. The results show that the flow stress in- creased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was con- sidered, was established here. The stresses revised by the new method deviated from the measured stresses with in- creasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.

关键词： friction correction temperature correction deformation heating flow stress constitutive model

Performance of Polyaniline-coated Short Carbon Fibers in Electromagnetic Shielding Coating

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Journal of Materials Science & Technology 2007年第4期23卷 529-534页

作者： Dongxiu yu jiang CHenG Zhuoru YANG School of Chemical and energy engineering South China University of Technology Guangzhou 510640 China

Combined nitric acid oxidation method and polyaniline （PANI）-coated method were applied to modify the surface properties of short carbon fibers （SCF）. The electrical and mechanical properties of acrylic coatings with 50 wt pct PANI-coated carbon fiber were investigated by using scanning electron microscope （SEM）, UV-Vis spectrophotometer, four-probe method and the coaxial cable method. The results of the pH measurement and XPS （X-ray photoelectron spectroscopy） patterns showed that the oxygen functional groups, such as -OH and -COOH, were attached on the carbon fiber surfaces after oxidation treatment. The XPS analysis of PANl-coated oxidized SCF （PAOSCF） revealed that PANI may bond on the surface of oxidized SCF with chemical bonds. SEM images and surface roughness analyses showed that PANl-coated layer changed the surface morphology. Compared with SCF/acrylic coating, the surface resistivity of PAOSCF/acrylic coating decreased from17.1 to 5.3 Ω/sq and the shielding efficiency （SE） value increased from 1.54 to 23.3 dB.

关键词： Carbon fibers Polyaniline Surface treatment Dispersion stability Shielding effectiveness

New approach to eliminate structural redundancy in case resource pools using α mutual information

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Journal of Systems engineering and Electronics 2013年第4期24卷 625-633页

作者： Man Xu Haiyan yu jiang Shen Department of Industrial engineering Nankai University College of Management and Economics Tianjin University

Structural redundancy elimination in case resource pools （CRP） is critical for avoiding performance bottlenecks and maintaining robust decision capabilities in cloud computing services. For these purposes, this paper proposes a novel approach to ensure redundancy elimination of a reasoning system in CRP. By using α entropy and mutual information, functional measures to eliminate redundancy of a system are developed with respect to a set of outputs. These measures help to distinguish both the optimal feature and the relations among the nodes in reasoning networks from the redundant ones with the elimination criterion. Based on the optimal feature and its harmonic weight, a model for knowledge reasoning in CRP （CRPKR） is built to complete the task of query matching, and the missing values are estimated with Bayesian networks. Moreover, the robustness of decisions is verified through parameter analyses. This approach is validated by the simulation with benchmark data sets using cloud SQL. Compared with several state-of-the-art techniques, the results show that the proposed approach has a good performance and boosts the robustness of decisions.

关键词： case resource pool (CRP) knowledge reasoning redundancy elimination α mutual information robust decision.

An inverse problem to estimate an unknown order of a Riemann-Liouville fractional derivative for a fractional Stokes' first problem for a heated generalized second grade fluid

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Acta Mechanica Sinica 2015年第2期31卷 153-161页

作者： Bo yu Xiaoyun jiang Haitao Qi School of Mathematics Shandong University School of Mathematics and Statistics Shandong University

In this paper,we propose a numerical method to estimate the unknown order of a Riemann-Liouville fractional derivative for a fractional Stokes＇ first problem for a heated generalized second grade *** implicit numerical method is employed to solve the direct *** the inverse problem,we first obtain the fractional sensitivity equation by means of the digamma function,and then we propose an efficient numerical method,that is,the Levenberg-Marquardt algorithm based on a fractional derivative,to estimate the unknown order of a Riemann-Liouville fractional *** order to demonstrate the effectiveness of the proposed numerical method,two cases in which the measurement values contain random measurement error or not are *** computational results demonstrate that the proposed numerical method could efficiently obtain the optimal estimation of the unknown order of a RiemannLiouville fractional derivative for a fractional Stokes＇ first problem for a heated generalized second grade fluid.

关键词： Riemann-Liouville fractional derivative Generalized second grade fluid Inverse problem Implicit numerical method Fractional sensitivity equation

Pressure and velocity cross-spectrum of normal modes in low-frequency acoustic vector field of shallow water and its application

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Journal of Systems engineering and Electronics 2015年第2期26卷 241-249页

作者： yun yu Qing Ling jiang Xu Naval Academy of Armament

The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especially the active component of the pressure and horizontal particle velocity cross-spectrum, also called ho- rizontal complex cross acoustic intensity, when only two normal modes are trapped in the waveguide. Both the approximate theo- retic analysis and the numerical results show that the sign of the horizontal complex cross acoustic intensity active component is independent of the range when vertically deployed receiving dual sensors are placed in appropriate depths, the sum of which is equal to the waveguide effective depth, so it can be used to tell whether the sound source is near the surface or underwater; while the range rate is expected to be measured by utilizing the sign distribution characteristic of the reactive component. The further robustness analysis of the depth classification algorithm shows that the existence of shear waves in semi infinite basement and the change of acoustic velocity profiles have few effects on the application of this method, and the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range.

关键词： low frequency acoustic vector field effective depth complex cross acoustic intensity active component target depth classificatio

An approach for machining distortion measurements and evaluation of thin-walled blades with small datum

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Chinese Journal of Aeronautics 2016年第6期29卷 1806-1814页

作者： yu Jianhua Chen Zhitong jiang Zepeng School of Mechanical engineering and Automation Beihang UniversityBeijing 100083China AVIC Commercial Aircraft engine Manufacturing Co. Ltd.Shanghai 201306China Co-Innovation Center for Advanced Aero-engine Beijing 100083China

Inspection techniques for aero-engine blades are a hot topic in industry. Since these blades have a sculptured surface and a small datum, measurement results may deviate from an actual position. There are few proper approaches compensating for non-uniform distribution errors that are within specified tolerance ranges. This study aimed to develop a meshing structure measuring approach for the distortion of blades via non-contact optical 3D scanning. A rough measurement and a registration procedure are initially adopted to rectify the coordinate system of a blade, which avoids the initial coordinate system errors caused by the small datum. A measurement path with meshing structure is then unfolded on the blade surface. For non-uniform distribution errors, the meshing structure measurement is more visual and clear than the traditional constant height curves method. All measuring points take only 7 min to complete, and the distribution of error is directly and accurately presented by the meshing structure. This study provides a basis for future research on distortion control and error compensation.

关键词： Free surface Machining distortion Optical testing Thin-walled workpiece Turbine blades

Effects of UV-B radiation on the growth interaction of Ulva pertusa and Alexandrium tamarense

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Journal of environmental Sciences 2005年第4期17卷 605-610页

作者： CAIHeng-jiang TANGXue-xi ZHANGPei-yu MarineEcologyLaboratory OceanUniversityofChinaQingdao266003China MarineEcologyLaboratory OceanUniversityofChinaQingdao266003China／／DepartmentofEnvironmentalScienceandEngineeringQingdaoUniversityQingdao266071China

enhanced UV-B(280-320 nm) radiation resulting from ozone depletion is one of global environmental problems. Not only marine organisms but also marine ecosystems can be affected by enhanced UV-B radiation. The effects of UV-B radiation on interaction of macro-algae and micro-algae were investigated using Ulva pertusa Kjellman and Alexandrium tamarense as the materials in this study. The results demonstrated that UV-B radiation could inhibit the growth of Ulva pertusa and Alexandrium tamarense when they were both mono-cultured, and the growth inhibition of algae was more significant with increasing doses of UV-B radiation. Alexandrium tamarense could inhibit the growth of Ulva pertusa in mixed culture, and the growth inhibition was more significant when increasing the initial cell density. However, Ulva pertusa could inhibit the growth of Alexandrium tamarense in early phase and stimulate the growth in latter phase when they were grown in mixed culture. Lower initial cell density(10~2 cell/ml) of Alexandrium tamarense could inhibit the growth of Ulva pertusa under UV-B radiation treatment,however, with the initial cell density increasing(10~3 and 10~4 cell/ml), the growth of Ulva pertusa was stimulated under lower dose of UV-B radiation and inhibited under higher dose of UV-B radiation by Alexandrium tamarense. Compared with that in mixed culture, Ulva pertusa showed more positive inhibition to the growth of Alexandrium tamarense under UV-B radiation treatment.

关键词： UV-B radiation mono-culture mixed culture Ulva pertusa Alexandrium tamarense growth

High-order implicit discontinuous Galerkin schemes for unsteady compressible Navier–Stokes equations

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Chinese Journal of Aeronautics 2014年第6期27卷 1384-1389页

作者： jiang Zhenhua Yan Chao yu Jian School of Aeronautic Science and engineering Beihang University

Efficient solution techniques for high-order temporal and spatial discontinuous Galerkin（DG） discretizations of the unsteady Navier–Stokes equations are developed. A fourth-order implicit Runge–Kutta（IRK） scheme is applied for the time integration and a multigrid preconditioned GMRES solver is extended to solve the nonlinear system arising from each IRK stage. Several modifications to the implicit solver have been considered to achieve the efficiency enhancement and meantime to reduce the memory requirement. A variety of time-accurate viscous flow simulations are performed to assess the resulting high-order implicit DG methods. The designed order of accuracy for temporal discretization scheme is validate and the present implicit solver shows the superior performance by allowing quite large time step to be used in solving time-implicit systems. Numerical results are in good agreement with the published data and demonstrate the potential advantages of the high-order scheme in gaining both the high accuracy and the high efficiency.

关键词： Discontinuous Galerkin scheme GMRES solver High order Implicit Runge–Kutta method Unsteady flows

Suitability of artificial viscosity discontinuous Galerkin method for compressible turbulence

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Science China(Technological Sciences) 2017年第7期60卷 1032-1049页

作者： yu Jian YAN Chao jiang ZhenHua School of Aeronautic Science and engineering Beijing University of Aeronautics and AstronauticsBeijing 100191China

A discontinuous Galerkin method based on an artificial viscosity model is investigated in the context of the simulation of compressible turbulence. The effects of artificial viscosity on shock capturing ability, broadband accuracy and under-resolved instability are examined combined with various orders and mesh resolutions. For shock-dominated flows, the superior accuracy of high order methods in terms of discontinuity resolution are well retained compared with lower ones. For under-resolved simulations, the artificial viscosity model is able to enhance stability of the eighth order discontinuous Galerkin method despite of detrimental influence for accuracy. For multi-scale flows, the artificial viscosity model demonstrates biased numerical dissipation towards higher wavenumbers. Capability in terms of boundary layer flows and hybrid meshes is also *** is concluded that the fourth order artificial viscosity discontinuous Galerkin method is comparable to typical high order finite difference methods in the literature in terms of accuracy for identical number of degrees of freedom, while the eighth order is significantly better unless the under-resolved instability issue is raised. Furthermore, the artificial viscosity discontinuous Galerkin method is shown to provide appropriate numerical dissipation as compensation for turbulent kinetic energy decaying on moderately coarse meshes, indicating good potentiality for implicit large eddy simulation.

关键词： discontinuous Galerkin method artificial viscosity compressible turbulence implicit large eddy simulation