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Process, mechanism and impacts of scale formation in alkaline flooding by a variable porosity and permeability model

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Acta Mechanica Sinica 2016年第3期32卷 406-421页

作者： Zhen Zhang Jiachun li Key Laboratory of Mechanics in Fluid Solid Coupling Systems Institute of Mechanics Chinese Academy of Sciences

In spite of the role of alkali in enhancing oil recovery（EOR）, the formation of precipitation during alkaline-surfactant-polymer（ASP） flooding can severely do harm to the stratum of oil reservoirs, which has been observed in situ tests of oil fields such as scale deposits found in oil stratum and at the bottom of oil wells. On the other hand,remarkable variation of stratum parameters, e.g., pore radius,porosity, and permeability due to scale formation considerably affects seepage flow and alkaline flooding process in return. The objective of this study is to firstly examine these mutual influential phenomena and corresponding mechanisms along with EOR during alkaline flooding when the effects of precipitation are no longer negligible. The chemical kinetic theory is applied for the specific fundamental reactions to describe the process of rock dissolution in silicabased reservoirs. The solubility product principle is used to analyze the mechanism of alkali scale formation in *** a 3D alkaline flooding coupling model accounting for the variation of porosity and permeability is established to quantitatively estimate the impact of alkali scales on reservoir stratum. The reliability of the present model is verified in comparison with indoor experiments and field tests of the Daqing oil field. Then, the numerical simulations on a 1/4well group in a 5-spot pattern show that the precipitation grows with alkali concentration, temperature, and injection pressure and, thus, reduces reservoir permeability and oil recovery correspondingly. As a result, the selection of alkaliwith a weak base is preferable in ASP flooding by tradeoff strategy.

关键词： Alkali Precipitation Chemical flood Permeability Oil recovery

Numerical Simulation of Rotor-aerodynamic Surface Interaction in Hover Using Moving Chimera Grid

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Chinese Journal of Aeronautics 2012年第3期25卷 342-348页

作者： li Yibo MA Dongli School of Aeronautic Science and Engineering Beihang UniversityBeijing 100191China

Three-dimensional unsteady Navier-Stokes equations are numerically solved to simulate the aerodynamic interaction of rotor, canard and horizontal tail in hover based on moving chimera grid. The variations of unsteady aerodynamic forces and moments of the canard and horizontal tail with respect to the rotor azimuth are analyzed with the deflection angle set at 0° and 50°, respectively. The pressure map of aerodynamic surfaces and velocity vector distribution of flow field are investigated to get better understanding of the unsteady aerodynamic interaction. The result shows that the canard and horizontal tail present different characteristics under the downwash of the rotor. The canard produces much vertical force loss with low amplitude fluctuation. Contrarily, the horizontal tail, which is within the flow field induced by the down wash of the rotor, produces only less vertical force loss, but the amplitudes of the lift and pitching moment are larger, implying that a potential deflection angle scheme in hover is 50° for the canard and 0° for the horizontal tail.

关键词： unsteady flow chimera grid canard rotor/wing aerodynamic interaction numerical simulation

Concept and Research Framework for Coordinated Situation Awareness and Active Defense of Cyber-physical Power Systems Against Cyber-attacks

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Journal of Modern Power Systems and Clean Energy 2021年第3期9卷 477-484页

作者： Ming Ni Manli li Jun’e li Yingjun Wu Qi Wang the NARI Group Corporation(State Grid Electric Power Research Institute) NARI Technology Co.Ltd.and the State Key Laboratory of Smart Grid Protection and ControlNanjing 211106China the School of Cyber Science and Engineering Wuhan Universityand the Key Laboratory of Aerospace Information Security and Trusted Computing of the Ministry of EducationWuhan 430072China the College of Energy and Electrical Engineering Hohai UniversityNanjing 211100China the School of Electrical Engineering Southeast UniversityNanjing 210096China

Due to the tight coupling between the cyber and physical sides of a cyber-physical power system(CPPS),the safe and reliable operation of CPPSs is being increasingly impacted by cyber *** situation poses a challenge to traditional security defense systems,which considers the threat from only one side,i.e.,cyber or *** cope with cyberattacks,this paper reaches beyond the traditional one-side security defense systems and proposes the concept of cyber-physical coordinated situation awareness and active defense to improve the ability of *** example of a regional frequency control system is used to show the validness and potential of this ***,the research framework is presented for studying and implementing this ***,key technologies for cyber-physical coordinated situation awareness and active defense against cyber-attacks are introduced.

关键词： Cyber-physical power system(CPPS) cyber security cyber-attack situation awareness active defense

Ant colony optimization algorithm and its application to Neuro-Fuzzy controller design

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Journal of Systems Engineering and Electronics 2007年第3期18卷 603-610页

作者： Zhao Baojiang li Shiyong Dept. of Control Science and Engineering Harbin Inst. of Technology Harbin 150001 P.R.China Dept. of Mathematics Mudanjiang Teachers Coll. Mudanjiang 157012 P.R. China

An adaptive ant colony algorithm is proposed based on dynamically adjusting the strategy of updating trail information. The algorithm can keep good balance between accelerating convergence and averting precocity and stagnation. The results of function optimization show that the algorithm has good searching ability and high convergence speed. The algorithm is employed to design a neuro-fuzzy controller for real-time control of an inverted pendulum. In order to avoid the combinatorial explosion of fuzzy rules due tσ multivariable inputs, a state variable synthesis scheme is employed to reduce the number of fuzzy rules greatly. The simulation results show that the designed controller can control the inverted pendulum successfully.

关键词： neuro-fuzzy controller ant colony algorithm function optimization genetic algorithm inverted pen-dulum system.

Effect of Exogenous Carboxyl and Hydroxyl Groups on Pyrolysis Reaction of High Molecular Weight Poly(L-Lactide)under the Catalysis of Tin

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Chinese Journal of Polymer Science 2021年第8期39卷 966-974,I0005页

作者： li-Dong Feng Xin-Chao Bian Gao li Xue-Si Chen Key Laboratory of Polymer Ecomaterials Changchun Institute of Applied ChemistryChinese Academy of SciencesChangchun 130022China Jilin Biomedical Polymers Engineering Laboratory Changchun 130022China

The effect of exogenous hydroxyl,carboxyl groups and/or Sn^(2+) on pyrolysis reactions of poly(L-lactide)(PLLA)was investigated by thermogravimetric analysis(TGA).The activation energy(fa)of pyrolysis reactions was estimated by the Kissinger-Akahira-Sunose *** kinetic models were also explored by the Malek method,and the random degradation behavior was determined by comparing the plots of ln{-ln[1-(1-w)05]}versus 1/7for experimental data from TGA with model *** pyrolysis reaction rate of PLLA was affected slightly by exogenous hydroxyl and carboxyl groups at lower levels of Sn with 65-70 mg·kg^(-1)but increased appreciably in the presence of extraneous Sn^(2+),-COOH/Sn^(2+),or-OH/Sn^(2+).The Ea values for the pyrolysis reactions of the PLLAs that provided lactide were different under the catalysis of Sn2+in different chemical environments because Sn^(2+) can form the new Sn-carboxylate and Sn-alkoxide with exogenous carboxyl and hydroxyl groups,which were different in steric hindrance for the formation of activated complex between Sn^(2+) and *** the catalysis of Sn^(2+),a lactide molecule can be directly eliminated selectively at a random position of PLLA molecular chains,and the molecular chain of PLLA cannot change two PLLA fragments at the elimination site of ***,it was regenerated into a new PLLA molecule with the molecular weight reduced by 144 g·mol^(-1).

关键词： Poly(L-lactide) Pyrolysis mechanism Carboxyl group Hydroxyl group Tin

Disordered packing density of binary and polydisperse mixtures of curved spherocylinders

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Particuology 2017年第3期15卷 73-81页

作者： lingyi Meng Shuixiang li Department of Mechanics Engineering School of Civil Engineering and Transportation South China University of Technology Guangzhou 510641 China Department of Mechanics &Aerospace Engineering College of Engineering Peking University Beijing 100871 China

Particle elongation is an important factor affecting the packing properties of rod-like particles. However, rod-like particles can be easily bent into non-convex shapes, in which the effect of bending should also be of concerned, To explore the shape effects of elongation and bending, together with the size and volume fraction effects on the disordered packing density of mixtures of non-convex particles, binary and polydisperse mixtures of curved spherocylinders are simulated employing sphere assembly models and the relaxation algorithm in the present work. For binary packings with the same volume, curves of the packing density versus volume fraction have good linearity, while densities are plotted as a series of equidistant curves under the condition of the same shape. The independence of size and shape effects on the packing density is verified for mixtures of curved spherocylinders. The explicit formula used to predict the density of binary mixtures, by superposing the two independent functions of the size and shape parameters, is extended to include a non-convex shape factor. A polydisperse packing with the shape factor following a uniform distribution under the condition of the same volume is equivalent to a binary mixture with certain components. The packing density is thus predicted as the mean of maximum and minimum densities employing a weighing method.

关键词： Disordered packing Packing density Mixture Curved spherocylinder Non-convex particle

Joint sparsity and fidelity regularization for segmentation-driven CT image preprocessing

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Science China(Information Sciences) 2016年第3期59卷 146-152页

作者： Feng liU Huibin li School of Mathematics and Statistics Xi'an Jiaotong University

In this paper, we propose a novel segmentation-driven computed tomography(CT) image preprocessing approach. The proposed approach, namely, joint sparsity and fidelity regularization(JSFR) model can be regarded as a generalized total variation(TV) denoising model or a generalized sparse representation denoising model by adding an additional gradient fidelity regularizer and a stronger gradient sparsity ***, JSFR model consists of three terms: intensity fidelity term, gradient fidelity term, and gradient sparsity term. The interactions and counterbalance of these terms make JSFR model has the ability to reduce intensity inhomogeneities and improve edge ambiguities of a given image. Experimental results carried out on the real dental cone-beam CT data demonstrate the effectiveness and usefulness of JSFR model for CT image intensity homogenization, edge enhancement, as well as tissue segmentation.

关键词： CT image homogenization enhancement tissue segmentation gradient fidelity gradient sparsity

Analysis of Mixed Model in Gear Transmission Based on ADAMS

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Chinese Journal of Mechanical Engineering 2012年第5期25卷 968-973页

作者： li Xiufeng WANG Yabin National Key Laboratory on Electromechanical Dynamic Control Beijing Institute of TechnologyBeijing 100081China

The traditional method of mechanical gear driving simulation includes gear pair method and solid to solid contact method. The former has higher solving efficiency but lower results accuracy; the latter usually obtains higher precision of results while the calculation process is complex, also it is not easy to converge. Currently, most of the researches are focused on the description of geometric models and the definition of boundary conditions. However, none of them can solve the problems fundamentally. To improve the simulation efficiency while ensure the results with high accuracy, a mixed model method which uses gear tooth profiles to take the place of the solid gear to simulate gear movement is presented under these circumstances. In the process of modeling, build the solid models of the mechanism in the SolidWorks firstly; Then collect the point coordinates of outline curves of the gear using SolidWorks API and create fit curves in Adams based on the point coordinates; Next, adjust the position of those fitting curves according to the position of the contact area; Finally, define the loading conditions, boundary conditions and simulation parameters. The method provides gear shape information by tooth profile curves; simulates the mesh process through tooth profile curve to curve contact and offer mass as well as inertia data via solid gear models. This simulation process combines the two models to complete the gear driving analysis. In order to verify the validity of the method presented, both theoretical derivation and numerical simulation on a runaway escapement are conducted. The results show that the computational efficiency of the mixed model method is 1.4 times over the traditional method which contains solid to solid contact. Meanwhile, the simulation results are more closely to theoretical calculations. Consequently, mixed model method has a high application value regarding to the study of the dynamics of gear mechanism.

关键词： mixed model contact gear transmission runaway escapement

Effect of glow discharge on hypersonic flat plate boundary layer

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Applied Mathematics and Mechanics(English Edition) 2019年第2期40卷 249-260页

作者： Chi li Yunchi ZHANG State Key Laboratory for Turbulence and Complex Systems Peking University Department of Aeronautics and Astronautics College of EngineeringPeking University

Glow discharge is introduced as an artificial disturbance to investigate the evolution of first-and second-mode instabilities in a hypersonic flat plate boundary *** are conducted in a Mach 6.5 quiet wind tunnel using Rayleigh scattering visualization and particle image velocimetry(PIV). Detailed analysis of the experimental observations is provided. It is found that the artificially introduced 17 kHz disturbance,which belongs to the first-mode frequency band, can effectively enhance first-mode ***, it can enhance second-mode waves even more intensely. Possible mechanisms to explain this phenomenon are discussed.

关键词： glow discharge hypersonic particle image velocimetry(PIV)