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A numerical approach for pressure transient analysis of a vertical well with complex fractures

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Acta Mechanica Sinica 2016年第4期32卷 640-648页

作者： Yizhao Wan Yuewu Liu Wenchao Liu Guofeng Han Congcong Niu institute of mechanics Chinese Academy of Sciences

A new well test model for a vertical fractured well is developed based on a discrete-fracture model in which the fractures are discretized as one dimensional（1-D） *** model overcomes the weakness of complex meshing,a large number of grids, and instability in conventional stripe-fracture models. Then, the discrete-fracture model is implemented using a hybrid element finite-element *** elements are used for matrix and line elements for the fractures. The finite element formulation is validated by comparing with the semi-analytical solution of a single vertical fractured well. The accuracy of the approach is shown through several examples with different fracture apertures,fracture conductivity, and fracture amount. Results from the discrete-fracture model agree reasonably well with the stripefracture model and the analytic solutions. The advantages of the discrete-fracture model are presented in mesh generation, computational improvement, and abilities to handle complex fractures like wedge-shaped fractures and fractures with branches. Analytical results show that the number of grids in the discrete-fracture model is 10 % less than stripefracture model, and computational efficiency increases by about 50 %. The more fractures there are, the more the computational efficiency increases.

关键词： fractured permeability reservoir reasonably branches porosity instability weakness shale handle

Statistical Estimation of the Shannon Entropy

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Acta Mathematica Sinica,English Series 2019年第1期35卷 17-46页

作者： Alexander BULINSKI Denis DIMITROV Steklov Mathematical institute of russian academy of sciences and Department of mathematics and mechanics Lomonosov Moscow State UniversityMoscow 119234Russia

The behavior of the Kozachenko–Leonenko estimates for the(differential) Shannon entropy is studied when the number of i.i.d. vector-valued observations tends to infinity. The asymptotic unbiasedness and L^2-consistency of the estimates are established. The conditions employed involve the analogues of the Hardy–Littlewood maximal function. It is shown that the results are valid in particular for the entropy estimation of any nondegenerate Gaussian vector.

关键词： Shannon differential entropy Kozachenko-Leonenko estimates Hardy-Littlewood maxi-mal function analogues asymptotic unbiasedness and L^2-consistency Gaussian vectors

A two-scale contact model for collisions between blocks in CDEM

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Science China(Technological sciences) 2015年第9期58卷 1596-1603页

作者： LI ShiHai TANG DeHong WANG Jie institute of mechanics Chinese Academy of Sciences

Contact detection between interacting blocks is of great importance to discontinuity-based numerical methods, such as DDA, DEM, and NMM. A rigorous contact theory is a prerequisite to describing the interactions of multiple blocks. Currently, the penalty method, in which mathematical springs with high stiffness values are employed, is always used to calculate the contact forces. High stiffness values may cause numerical oscillations and limit the time step. Furthermore, their values are difficult to identify. The intention of this study is to present a two-scale contact model for the calculation of forces between colliding blocks. In this new model, a calculation step taken from the moment of contact will be divided into two time stages: the free motion time stage and the contact time stage. Actually, these two time stages correspond to two real physical processes. Based on this, we present a new numerical model that is intended to be more precise and useful in calculating the contact forces without mathematical springs. The propagation of the elastic wave during collision is of a characteristic length, which determines the volume of material involved in the contact force calculation. In conventional contact models, this range is always regarded as the length of one element, which may lead to an inaccurate calculation of contact forces. In fact, the real scale of this range is smaller than the length of a single element, and subdivided elements, which are refined according to the characteristic length and are presented in the new contact model.

关键词： two-scale contact model collision elastic wave element subdivision

Numerical investigation of a coupled moving boundary model of radial flow in low-permeable stress-sensitive reservoir with threshold pressure gradient

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Chinese Physics B 2016年第2期25卷 262-270页

作者：刘文超刘曰武牛丛丛韩国锋万义钊 institute of mechanics Chinese Academy of Sciences

The threshold pressure gradient and formation stress-sensitive effect as the two prominent physical phenomena in the development of a low-permeable reservoir are both considered here for building a new coupled moving boundary model of radial flow in porous medium. Moreover, the wellbore storage and skin effect are both incorporated into the inner boundary conditions in the model. It is known that the new coupled moving boundary model has strong nonlinearity. A coordinate transformation based fully implicit finite difference method is adopted to obtain its numerical solutions. The involved coordinate transformation can equivalently transform the dynamic flow region for the moving boundary model into a fixed region as a unit circle, which is very convenient for the model computation by the finite difference method on fixed spatial grids. By comparing the numerical solution obtained from other different numerical method in the existing literature, its validity can be verified. Eventually, the effects of permeability modulus, threshold pressure gradient, wellbore storage coefficient, and skin factor on the transient wellbore pressure, the derivative, and the formation pressure distribution are analyzed respectively.

关键词： threshold pressure gradient stress-sensitive effect wellbore storage skin effect

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

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Plasma Science and Technology 2011年第2期13卷 201-207页

作者：邓晶李要建徐永香盛宏至 institute of mechanics Chinese Academy of Sciences

In this work, a magnetic fluid dynamics （MHD） model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.

关键词： modeling arc plasma torch MHD arc root fluid-solid coupled method

The Three-Stage Model Based on Strain Strength Distribution for the Tensile Failure Process of Rock and Concrete Materials

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Acta Mechanica Solida Sinica 2016年第5期29卷 514-526页

作者： Rukun Guo Shihai Li Dong Zhou institute of mechanics Chinese Academy of Sciences

A three-stage model is introduced to describe the tensile failure process of rock and concrete *** of the material is defined to contain three stages in the model,which include elastic deformation stage,body damage stage and localization damage *** failure mode change from uniform body damage to localization damage is *** heterogeneity of material is described with strain strength *** fracture factor and intact factor,defined as the distribution function of strain strength,are used to express the fracture state in the failure *** the distributive parameters can be determined through the experimental stress-strain curve.

关键词： fractured heterogeneity rock tensile Strain localization intact granite softening macroscopic

Late Paleozoic alkaline magmatism in Western Transbaikalia,Russia:Implications for magma sources and tectonic settings

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Geoscience Frontiers 2020年第4期11卷 1289-1303页

作者： Ivan Izbrodin Anna Doroshkevich Mikhail Rampilov Alexey Elbaev German Ripp Geological institute Siberian Branch of the Russian Academy of SciencesRussia V.S.Sobolev institute of Geology and Mineralogy Siberian Branch of the Russian Academy of SciencesRussia

This paper presents the results of geochronological(40Ar-39Ar,U-Pb SHRIMP Ⅱ),petrological and geochemical studies of the Late Paleozoic complexes of alkaline rocks(Zimovechinsky,Tuchinsky and Koma) located within the Vitim Plateau(the western part of the Mongol-Okhotsk Orogenic Belt).The rocks were formed at 310-280 *** is coeval with Late Paleozoic magmatism within the Central Asian Orogenic *** εNd(T) values show large variations from-2.1 to +3.3 as well as the initial Sr(I) isotopic ratios from 0.7042 to 0.7138,that demonstrate strong isotopic heterogeneity of the magmatic *** geochemical characteristics of the rocks show pronounced positive Pb and negative Ti,Zr-Hf anomalies that can be explained by involvement of the subducted component in primary *** rocks intruded in a setting of extension at the active continental margin of the Siberian Craton during subduction of Mongol-Okhotsk oceanic crust under the Siberian Craton.

关键词： Nepheline-bearing and nepheline-free syenites Geochronological and isotope data Late paleozoic magmatism Sources Central Asian orogenic belt

Asymptotic Properties of Solutions of Parabolic Equations Arising from Transient Diffusions

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Acta Mathematicae Applicatae Sinica 2002年第3期18卷 353-364页

作者： A.M.Il’in R.Z.Khasminskii G.Yin institute of mathematics and mechanics of russian academy ural branch EkaterinburgRussiaDepartment of MathematicsWayne State UniversityDetroitMI 48202Department of Mathematics Wayne State UniversityDetroitMI 48202

This work is concerned with asymptotic properties of a class of parabolic systems arising from singularly perturbed diffusions. The underlying system has a fast varying component and a slowly changing component. One of the distinct features is that the fast varying diffusion is transient. Under such a setup, this paper presents an asymptotic analysis of the solutions of such parabolic equations. Asymptotic expansions of functional satisfying the parabolic system are obtained. Error bounds are derived.

关键词： Singular perturbation diffusion backward operator asymptotic expansion

A Method Based on Thermo-Vibrational Effects for Hydrogen Transportation and Storage

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Fluid Dynamics & Materials Processing 2024年第12期20卷 2775-2788页

作者： Tatyana P.Lyubimova Sergey A.Plotnikov Albert N.Sharifulin Vladimir Ya.Modorskii S.Neshev Stanislav L.Kalyulin institute of Continuous Media mechanics Ural Branch of Russian Academy of SciencesPerm614013Russia Aerospace Faculty Perm National Research Polytechnic UniversityPerm614990Russia

Transporting and storing hydrogen is a complex technological task.A typical problem relates to the need to minimize the strength of fluid motion and heat transfer near the walls of the *** this work this problem is tackled numerically assuming an infinite cavity of pipe square cross-section,located in a constant external temperature *** particular,a method based on the application of vibrations to suppress the gravitational convection mechanism is explored.A parametric investigation is conducted and the limits of applicability of the method for small Grashof numbers(10e4)are *** is shown that it is possible to minimize the intensity of the vibrogravitational flow for any values of the problem parameters if correction factors are *** results obtained can be applied in technological processes associated with the transportation,storage and use of hydrogen:pumping the working fluid through pipes,storage in tanks,as well as flow processes in the combustion chambers of power plants.

关键词： Thermal vibration convection vibrations vortex structures square pipe cavity hydrogen transportation and storage