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Stochastic transient analysis of thermal stresses in solids by Explicit time-domain method

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Theoretical & Applied Mechanics Letters 2019年第5期9卷 293-296,I0004页

作者： Houzuo Guo Cheng Su Jianhua Xian School of Civil Engineering and Transportation South China University of TechnologyGuangzhou 510640China State Key Laboratory of Subtropical Building Science South China University of TechnologyGuangzhou 510640China

Stochastic heat conduction and thermal stress analysis of structures has received considerable attention in recent years.The propagation of uncertain thermal environments will lead to stochastic variations in temperature fields and thermal stresses.Therefore,it is reasonable to consider the variability of thermal environments while conducting thermal analysis.However,for ambient thermal excitations,only stationary random processes have been investigated thus far.In this study,the highly efficient Explicit time-domain method(ETDM)is proposed for the analysis of non-stationary stochastic transient heat conduction and thermal stress problems.The Explicit time-domain expressions of thermal responses are first constructed for a thermoelastic body.Then the statistical moments of thermal displacements and stresses can be directly obtained based on the Explicit expressions of thermal responses.A numerical example involving non-stationary stochastic internal heat generation rate is investigated.The accuracy and efficiency of the proposed method are validated by comparison with the Monte-Carlo simulation.

关键词： Stochastic Non-stationary Heat conduction Thermal stress Explicit time-domain method

General Explicit solutions of most economic sections and applications for trapezoidal and parabolic channels

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Journal of Hydrodynamics 2019年第5期31卷 1034-1042页

作者： Yan-cheng Han Said MEasa Xue-ping Gao School of Water Conservancy and Environment University of JinanJinan 250022China Department of Civil Engineering Ryerson UniversityTorontoOntarioCanada State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China

A channel section that has minimum construction cost is known as the most economic section.Such a section has important implications for economic efficiency.However,the most economic section is a complex optimization model with nonlinear objective function and constraints that is difficult to use by ordinary engineers.A general simple formula for the most economic section has not been attempted.In this paper,the general differential equation for the most economic section is derived using Lagrange multiplier optimization method.A simple method to solve the most economic section is proposed that converted the optimization model into a general equation for the most economic section of any shape.By solving this equation,the dimensions of the most economic section are directly obtained.To illustrate,the direct formula for trapezoidal section is derived.To aid application in practice,a simple Explicit iterative formula for trapezoidal sections is presented.The direct and Explicit iterative formulas were validated.The proposed method is superior to the classical optimization method and as such represent a valuable tool for open channel design.To illustrate the versatility of the presented method,a direct formula for the parabolic section was also derived.

关键词： Most economic section channel parabolic Explicit hydraulic section

New Explicit algebraic stress and flux model for active scalar and simulation of shear stratified cylinder wake flow

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Science China(Technological Sciences) 2009年第9期52卷 2536-2546页

作者： HUA ZuLin GU Li XING LingHang DAI WenHong Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes of Ministry of Education College of Environmental Science&EngineeringHohai UniversityNanjing 210098China Yangtze River Scientific Research Institute Wuhan 430010China Centre for Water and Environment Queen’s UniversityKingstonOntarioK7L3N6Canada

On the numerical simulation of active scalar,a new Explicit algebraic expression on active scalar flux was derived based on Wikstrm,Wallin and Johansson model (aWWJ model). Reynolds stress algebraic expressions were added by a term to account for the buoyancy effect. The new Explicit Reynolds stress and active scalar flux model was then established. Governing equations of this model were solved by finite volume method with unstructured grids. The thermal shear stratified cylinder wake flow was computed by this new model. The computational results are in good agreement with laboratorial measurements. This work is the development on modeling of Explicit algebraic Reynolds stress and scalar flux,and is also a further modification of the aWWJ model for complex situations such as a shear stratified flow.

关键词： active scalar Explicit algebraic model scalar flux Reynolds stress thermal shear stratified cylinder wake flow numerical simulation

Explicit formula for the Liutex vector and physical meaning of vorticity based on the Liutex-Shear decomposition

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Journal of Hydrodynamics 2019年第3期31卷 464-474页

作者： Yi-qian Wang Yi-sheng Gao Jian-ming Liu Chaoqun Liu School of Aerospace Engineering Tsinghua University Beijing 100084 China Department of Mathematics University of Texas at Arlington Arlington 76019 Texas USA School of Mathematics and Statistics Jiangsu Normal University Xuzhou 221116 China

In the present study, the physical meaning of vorticity is revisited based on the Liutex-Shear (RS) decomposition proposed by Liu et al. in the framework of Liutex (previously called Rortex), a vortex vector field with information of both rotation axis and swirling strength (Liu et al. 2018). It is demonstrated that the vorticity in the direction of rotational axis is twice the spatial mean angular velocity in the small neighborhood around the considered point while the imaginary part of the complex eigenvalue (2c.) of the velocity gradient tensor (if exist) is the pseudo-time average angular velocity of a trajectory moving circularly or spirally around the axis. In addition, an Explicit expression of the Liutex vector in terms of the eigenvalues and eigenvectors of velocity gradient is obtained for the first time from above understanding, which can further, though mildly, accelerate the calculation and give more physical comprehension of the Liutex vector.

关键词： Vorticity Liutex Liutex-Shear(RS)decomposition Explicit formula of Liutex

Development and Application of a High-Performance Triangular Shell Element and an Explicit Algorithm in OpenSees for Strongly Nonlinear Analysis

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Computer Modeling in Engineering & Sciences 2019年第9期120卷 561-582页

作者： Xinzheng Lu Yuan Tian Chujin Sun Shuhao Zhang Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry Department of Civil EngineeringTsinghua UniversityBeijing100084China Beijing Engineering Research Center of Steel and Concrete Composite Structures Tsinghua UniversityBeijing100084China.

The open-source finite element software,OpenSees,is widely used in the earthquake engineering community.However,the shell elements and Explicit algorithm in OpenSees still require further improvements.Therefore,in this work,a triangular shell element,NLDKGT,and an Explicit algorithm are proposed and implemented in OpenSees.Specifically,based on the generalized conforming theory and the updated Lagrangian formulation,the proposed NLDKGT element is suitable for problems with complicated boundary conditions and strong nonlinearity.The accuracy and reliability of the NLDKGT element are validated through typical cases.Furthermore,by adopting the leapfrog integration method,an Explicit algorithm in OpenSees and a modal damping model are developed.Finally,the stability and efficiency of the proposed shell element and Explicit algorithm are validated through the nonlinear time-history analysis of a highrise building.

关键词： Triangular shell element Explicit algorithm OpenSees strong nonlinearity

Dynamic Explicit FE modeling of hot ring rolling process

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Transactions of Nonferrous Metals Society of China 2006年第6期7卷 1274-1280页

作者：王敏杨合孙志超郭良刚欧新哲 College of Materials Science and Engineering Northwestern Polytechnical University

A new FE modeling method of hot ring rolling was presented by solving key technologies such as contact and heat boundary conditions,motion control over guide rolls,and mass scaling.The method has the following features:1)the elastic-plastic dynamic Explicit approach instead of the static implicit approach is adopted to solve the process so as to greatly improve computational efficiency without sacrificing computational accuracy;2)the coupled thermal-mechanical effect is considered as opposed to the conventional isothermal assumption,which is more practical;3)in contrast to the simplified 2D or local 3D ring model,the full 3D ring is modeled to simulate the process.Based on the FE modeling method,two cases of hot plain ring rolling are simulated in the FEA software ABAQUS/Explicit.The simulation results are compared with the experimental measurements and the good agreement between them is observed regarding the material flow and the temperature distribution of the ring.

关键词： hot ring rolling dynamic Explicit approach coupled thermal-mechanical FEM

Absolute band alignment at semiconductor-water interfaces using Explicit and implicit descriptions for liquid water

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npj Computational Materials 2019年第1期5卷 256-261页

作者： Nicolas G.Hörmann Zhendong Guo Francesco Ambrosio Oliviero Andreussi Alfredo Pasquarello Nicola Marzari Theory and Simulation of Materials(THEOS) and National Centre for Computational Design and Discovery of Novel Materials(MARVEL)École Polytechnique Fédérale de Lausanne1015 LausanneSwitzerland Chair of Theoretical Chemistry Technische Universität München85748 GarchingGermany Chaire de Simulationàl’Echelle Atomique(CSEA) École Polytechnique Fédérale de Lausanne1015 LausanneSwitzerland Department of Physics University of North TexasDentonTX 76207USA

Quantum mechanical simulations that include the effects of the liquid environment are highly relevant for the characterization of solid-liquid interfaces,which is crucial for the design of a wide range of devices.In this work we present a rigorous and systematic study of the band alignment of semiconductors in aqueous solutions by contrasting a range of hybrid Explicit/implicit models against Explicit atomistic simulations based on density-functional theory.We find that consistent results are obtained provided that the first solvation shell is treated Explicitly.Interestingly,the first molecular layer of Explicit water is only relevant for the pristine surfaces without dissociatively adsorbed water,hinting at the importance of saturating the surface with quantum mechanical bonds.By referencing the averaged electrostatic potentials of Explicit and implicit water against vacuum,we provide absolute alignments,finding maximal differences of only~0.1–0.2 V.Furthermore,the implicit reference potential is shown to exhibit an intrinsic offset of−0.33 V with respect to vacuum,which is traced back to the absence of an Explicit water surface in the implicit model.These results pave the way for accurate simulations of solid-liquid interfaces using minimalistic Explicit/implicit models.

关键词： theory implicit Explicit

Three-point Explicit compact difference scheme with arbitrary order of accuracy and its application in CFD

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Applied Mathematics and Mechanics(English Edition) 2007年第7期28卷 943-953页

作者：林建国谢志华周俊陶 College of Environmental Science and Engineering Dalian Maritime University

Based on the successive iteration in the Taylor series expansion method, a three-point Explicit compact difference scheme with arbitrary order of accuracy is derived in this paper. Numerical characteristics of the scheme are studied by the Fourier analysisl Unlike the conventional compact difference schemes which need to solve the equation to obtain the unknown derivatives in each node, the proposed scheme is Explicit and can achieve arbitrary order of accuracy in space. Application examples for the convectiondiffusion problem with a sharp front gradient and the typical lid-driven cavity flow are given. It is found that the proposed compact scheme is not only simple to implement and economical to use, but also is effective to simulate the convection-dominated problem and obtain high-order accurate solution in coarse grid systems.

关键词： arbitrary order of accuracy compact scheme three-point stencil Explicit lid-driven cavity flow

Energy Separation and Explicit Dynamic Analysis of Low Temperature Impact Toughness of Transmission Tower Material Q420B

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Journal of Shanghai Jiaotong university(Science) 2019年第3期24卷 381-387页

作者：余兴学张映华张晓敏蒋渝 College of Materials Science and Engineering Sichuan UniversityChengdu 610065China Sichuan Tongyuan Electric Power Technology Co. Ltd.Chengdu 610072China

To determine the physical significance of the impact toughness parameters and accurately characterize the low temperature impact toughness of transmission tower material Q420 B,the finite element model of Charpy impact test is established on the basis of experiment.The simulation and test results are verified,and the specimen fracture is analyzed by scanning electron microscope.The formation and growth mechanism of the crack are dynamically analyzed.On this basis,energy separation method is used to investigate the effect of low temperature on impact toughness.The results show that the simulation and test results are in good agreement,and the ductile-brittle transition temperature of Q420 B is about-50 ℃.The breaking process of the specimen is divided into the crack formation and propagation.When temperature drops from 20 to-60 ℃,the crack propagation energy decreases from 51.0 to 11.9 J,the crack formation energy reduces from 39.9 to 15.8 J,and the fracture time of the material drops from 1.8 to 0.6 ms.

关键词： Q420B low temperature impact toughness simulation Explicit dynamic energy separation