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boundary scheme for lattice Boltzmann modeling of micro-scale gas flow in organic-rich pores considering surface diffusion

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Chinese Physics B 2019年第3期28卷 84-96页

作者： Hong Zuo Shou-Chun Deng Hai-Bo Li State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China University of Chinese Academy of Sciences Beijing 100049China

We propose a boundary scheme for addressing multi-mechanism flow in a porous medium in slip and early transition flow regimes, which is frequently encountered in shale gas reservoirs. Micro-gaseous flow in organic-rich shale involves a complex flow mechanism. A self-developed boundary scheme that combines the non-equilibrium extrapolation scheme and the combined diffusive reflection and bounce-back scheme(half-way DBB) to embed the Langmuir slip boundary into the single-relaxation-time lattice Boltzmann method(SRT-LBM) enables us to describe this process, namely, the coupling effect of micro-gaseous flow and surface diffusion in organic-rich nanoscale pores. The present LBM model comes with the careful consideration of the local Knudsen number, local pressure gradient, viscosity correction model, and regularization procedure to account for the rarefied gas flows in irregular pores. Its validity and accuracy are verified by several benchmarking cases, and the calculated results by this boundary scheme accord well with our analytical *** boundary scheme shows a higher accuracy than the existing studies. Additionally, a subiteration strategy is presented to tackle the coupled micro-gaseous flow and surface diffusion, which necessitates the iteration process matching of these two mechanisms. The multi-mechanism flow in the self-developed irregular pores is also numerically investigated and analyzed over a wide range of parameters. The results indicate that the present model can effectively capture the coupling effect of micro-gaseous flow and surface diffusion in a tree-like porous medium.

关键词： lattice Boltzmann method(LBM) surface diffusion Langmuir slip model boundary scheme

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boundary-layer transition of advanced fighter wings at high-speed cruise conditions

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Chinese Journal of Aeronautics 2019年第4期32卷 799-814页

作者： Yiming DU Zhenghong GAO Chao WANG Qianhuan HUANG School of Aeronautics Northwestern Polytechnical University

The achievement of laminar flow in the boundary layer at high-speed cruise conditions may further, in addition to shock-wave control, reduce the drag and extend the range of military fighter aircraft. To this end, a further investigation on transitional boundary-layer flow of fighter wings is needed due to different configurations from the wings used on conventional transport aircraft. In this paper, wind tunnel experiments and numerical simulations were conducted on three-dimensional transition of thin diamond-shaped wings used on advanced fighter aircraft at tran/supersonic design points. A newly proposed correlation of crossflow transition which includes the effect of surface roughness was introduced into the c-Rehttransition model. Predicted results were in good agreement with flow visualizations. Results showed that the strength of the crossflow component grew rapidly around the leading edge because of the severe flow acceleration, just as the same as wings with a large aspect ratio. However, there seemed no regular pattern of instabilitydominance variation in span-wise for a diamond configuration. The dominance of different instability mechanisms strongly depended on the local pressure distribution. Hereby, the research recommended a ‘‘roof-like" shape of pressure distribution to suppress both crossflow and Tollmien-Schlichting(T-S) instabilities. Besides, a sharp suction peak with a serious pressure rise should be cut off to avoid stronger instabilities. Further discussions also revealed an independence of the unit Reynolds number when transition was triggered by T-S instabilities. Aerodynamic force comparisons indicated that further benefit on drag reduction could be expected by including the three-dimensional transition effect into a wing design process.

关键词： boundary layer transition Fighter aircraft design Supersonic aircraft wings Transonic wing aerodynamics Wind tunnel measurements

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The boundary Contour Method for Half-Plane Piezoelectric Media

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上海交通大学学报 2004年第Z2期38卷 176-181页

作者： WANG Guoqing WANG Qing LIU Zhengxing DING Haojiang Department of Engineering Mechanics Shanghai Jiaotong Univ. Shanghai200030 China Department of Engineering Mechanics Shanghai Jiaotong Univ. Shanghai200030 China Department of Engineering Mechanics Shanghai Jiaotong Univ. Shanghai200030 China Department of Civil Engineering Zhejiang Univ. Hangzhou310027 China

This paper presents a further development of the boundary Contour Method (BCM) for half-plane piezoelectric media. Firstly, the divergence free property of the integrand of the half-plane piezoelectric boundary element is proven. Secondly, the boundary contour method formulation is derived and potential functions are obtained by introducing linear shape functions and Green's functions[1] for half-plane piezoelectric media. Finally, numerical solutions for illustrative example are compared with exact ones and that of conventional boundary element method (BEM) ones. The numerical results of BCM coincide very well with exact solution, and the feasibility and efficiency of the method are verified.

关键词： boundary contour method piezoelectricity half-plane shape function

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boundary condition modelling and identification for cantilever-like structures using natural frequencies

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Chinese Journal of Aeronautics 2019年第6期32卷 1451-1464页

作者： Wei LIU Zhichun YANG Le WANG Ning GUO School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China Xi’an Aerospace Propulsion Institute Xi’an 710100China

The actual boundary conditions of cantilever-like structures might be non-ideally clamped in engineering practice, and they can also vary with time due to damage or aging. Precise modelling of boundary conditions, in which both the boundary stiffness and the boundary mass should be modelled correctly, might be one of the most significant aspects in dynamic analysis and testing for such structures. However, only the boundary stiffness was considered in the most existing methods. In this paper, a boundary condition modelling and identification method for cantilever-like structures is proposed to precisely model both the boundary stiffness and the boundary mass using sensitivity analysis of natural frequencies. The boundary conditions of a cantilever-like structure can be parameterized by constant mass, constant rotational inertia,constant translational stiffness, and constant rotational stiffness. The relationship between natural frequencies and boundary parameters is deduced according to the vibration equation for the lateral vibration of a non-uniform beam. Then, an iterative identification formulation is established using the sensitivity analysis of natural frequencies with respect to the boundary parameters. The regularization technique is also used to solve the potential ill-posed problem in the identification *** simulations and experiments are performed to validate the feasibility and accuracy of the proposed method. Results show that the proposed method can be utilized to precisely model the boundary parameters of a cantilever-like structure.

关键词： boundary condition identification boundary condition modelling Iterative method Natural frequency Sensitivity analysis

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boundary Diffraction Method for Aperture Near-Field Diffraction

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Chinese Physics Letters 1999年第11期16卷 811-813页

作者： XIE Jian-ping WU Wei-min FANG Hui SUN Xiao-hong WU Yun-xia MING Hai Department of Physics University of Science and Technology of ChinaHefei 230026

The boundary diffraction method is introduced to analyze the near-field diffraction of a subwavelength aperture. A self-consistent formula of boundary diffraction suitable to near field is derived. The near-field diffraction patterns of slits and circular apertures are obtained. The influence of incident light polarization on these diffraction patterns is also shown. These results are in good agreement with other theoretical and experimental results.

关键词： boundary circular boundary

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boundary element method (BEM) applied to the rough surface contact vs. BEM in computational mechanics

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Friction 2019年第4期7卷 359-371页

作者： Yang XU Robert L.JACKSON Mechanical Engineering Department Auburn University

In the numerical study of rough surfaces in contact problem, the flexible body beneath the roughness is commonly assumed as a half-space or a half-plane. The surface displacement on the boundary, the displacement components and state of stress inside the half-space can be determined through the convolution of the traction and the corresponding influence function in a closed-form. The influence function is often represented by the Boussinesq-Cerruti solution and the Flamant solution for three-dimensional elasticity and plane strain/stress, respectively. In this study, we rigorously show that any numerical model using the above mentioned half-space solution is a special form of the boundary element method(BEM). The boundary integral equations(BIEs) in the BEM is simplified to the Flamant solution when the domain is strictly a half-plane for the plane strain/stress condition. Similarly, the BIE is degraded to the Boussinesq-Cerruti solution if the domain is strictly a half-space. Therefore, the numerical models utilizing these closed-form influence functions are the special BEM where the domain is a half-space(or a half-plane). This analytical work sheds some light on how to accurately simulate the non-half-space contact problem using the BEM.

关键词： boundary element method rough surface contact half-space half-plane Flamant solution Boussinesq-Cerruti solution

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boundary Conditions for NHEK through Effective Action Approach

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Chinese Physics Letters 2012年第4期29卷 23-26页

作者： CHEN Bin NING Bo ZHANG Jia-Ju Department of Physics and State Key Laboratory of Nuclear Physics and TechnologyPeking UniversityBeijing 100871

We study the asymptotic symmetry group (ASG) of the near horizon geometry of extreme Kerr black hole through the effective action approach developed by Porfyriadis and Wilczek (arXiv:1007.1031v1[gr qc]).By requiring a finite boundary effective action,we derive a new set of asymptotic Killing vectors and boundary conditions,which are much more relaxed than the ones proposed by Matsuo Y et al.[***.B 825 (2010) 231],and still allow a copy of a conformal group as its *** the covariant formalism,the asymptotic charges are finite,with the corresponding central charge *** using the quasi-local charge and introducing a plausible cut-off,we find that the higher order terms of the asymptotic Killing vectors,which could not be determined through the effective action approach,contribute to the central charge as *** also show that the boundary conditions suggested by Guica et al.[***.D 80 (2009)124008] lead to a divergent first-order boundary effective action.

关键词： asymptotic boundary charge

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boundary feedback stabilization of Timoshenko beam with boundary dissipation

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Science China Mathematics 1998年第5期41卷 483-490页

作者：冯德兴史东华张维弢 Institute of Systems Science Chinese Academy of Sciences Beijing

Nonlinear boundary feedback control to a Timoshenko beam is studied. Under some nonlinear boundary feedback controls, the nonlinear semi group theory is used to show the well posedness for the correspnding closed loop system. Then by using the energy perturbed method, it is proved that the vibration of the beam under the proposed control actions decays asymptotically or exponentially as t →∞.

关键词： Timoshenko beam boundary feedback control nonlinear semigroup energy perturbed method.

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boundary Poisson Structure and Quantization

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Communications in Theoretical Physics 2002年第10期38卷 429-432页

作者： ZHAO Liu HE Wen-Li Institute of Modern Physics Northwest University Xi''an 710069 China Institute of Modern Physics Northwest University Xi''an 710069 China

A new approach for treating boundary Poisson structures based on causality and locality analysis isproposed for a single scalar field with boundary interaction. For the case of linear boundarv condition, it is shown t... 详细信息

关键词： Poisson structure, boundary condition

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boundary element-free method for elastodynamics

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Science China(Physics,Mechanics & Astronomy) 2005年第6期48卷 641-657页

作者： CHENG Yumin1 & PENG Miaojuan2 1. Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China 2. Department of Civil Engineering, Shanghai University, Shanghai 200072, China Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai China Department of Civil Engineering Shanghai University Shanghai China

The moving least-square approximation is discussed first. Sometimes the method can form an ill-conditioned equation system, and thus the solution cannot be obtained correctly. A Hilbert space is presented on which an orthogonal function system mixed a weight function is defined. Next the improved moving least-square approximation is discussed in detail. The improved method has higher computational efficiency and precision than the old method, and cannot form an ill-conditioned equation system. A boundary element-free method (BEFM) for elastodynamics problems is presented by combining the boundary integral equation method for elastodynamics and the improved moving least-square approximation. The boundary element-free method is a meshless method of boundary integral equation and is a direct numerical method compared with others, in which the basic unknowns are the real solutions of the nodal variables and the boundary conditions can be applied easily. The boundary element-free method has a higher computational efficiency and precision. In addition, the numerical procedure of the boundary element-free method for elastodynamics problems is presented in this paper. Finally, some numerical examples are given.

关键词： moving least-square approximation, improved moving least-square approximation, elastodynamics, boundary integral equation, meshless method, boundary element-free method, Fourier eigen transform.

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