Several Problems About Analyses of Finite Element Method on Coalbed Gas Seepage Flow

Based on the govering equation of gas seepage flow,this paper an alyzes;the re-lationship of the underground pressure and permeability of coal seams,discusses the averagedly dis-crete metheds of small terms of time variable which is related to mining progress of coal seams,and set up the element property form ulation on the basis of the weak statement of Galerk in integral e-quation.     

Multi-field coupling effect on coalbed methane seepage characteristics and numerical simulation

This paper studies the seepage of coal samples under the influence of each single factor, the axial stress, confining pressure, gas pressure, and temperature by experiments. It uses Ansys12.0 to numerically simulate the law of coalbed methane seepage, coal deformation, pore pressure, the distribution of flow field under the influence of each single field and multi-field coupled. The numerical simulation show that the result of numerical simulation of gas seepage law in the coal under each single fields is basically the same as the experimental result. The curve of gas seepage and average effective stress under the condition of multi-field coupled is negative exponential relationship. Stress influenced the deformation of the specimen is greater than the seepage field. The axial stress on the deformation of the specimen is greater than confining presses The influence on the flow field by confining pressure is greater than axial stress, the influence of axial stress on the pore pressure is greater than confining pressure, pore-pressure under the action of multi-field is bigger than pro-pressure under each single field. To study the seepage law of coalbed methane, it should consider the influence of gas-solid-heat at the same time.     

Mathematical Model of Methane Transport in Coal Seam

This paper studies the effects of ground stress and ground electrical field onmethane transpont in coal seam. A gas seepage equation is set up based on the principles of seepagetheory,which takes the ground stress and ground electrical field into considerationz     

Analysis and numerical simulation of fluid-structure coupling of gas drainage from boreholes

Gas drainage from boreholes is main method of utilization and management of Chinese coal seam gas. As the exploitation depth increases, stress field and other factors on the impact of gas seepage are increasingly apparent. Based on the basis of a series of assumptions of coal seam gas, porosity and permeability equations are described by considering stress, coal seam gas pressure change on the coal produced by deformation of the skeleton. The fluid-structure coupling equations are derived by using the basic theorem of porous media flow and the fluid structure coupling theory. The gas seepage field is simulated and analyzed by using multi-physics coupling analysis software. The effect of gas pressure distribution, different burial depths and different drilling parameters (drainage negative pressure, drilling radius) on gas seepage field is obtained. Analysis of simulation results can provide theoretical guidance for on-site gas drainage.     

Experimental study of coalbed methane seepage in fuxin basin

Taking raw coal samples collected from the wangying colliery in Fuxin basin as the research object, the experiment of coalbed methane seepage law is conducted by the triaxial osmoscope and the relationship between effective stress and coal permeability is presented. The experiment results indicate that the coal permeability is of stress sensitivity and tended to decline in exponent with the increment of effective stress, which is consistent with the former research results. The seepage flow curves from experiments demonstrate the nonlinear characteristics under different confining pressures and moisture contents, and it accurately reflecte the effect of coal body deformation on the coalbed methane seepage flow in the experimental process. Therefore considering the influence of effective stress on the coal body deformation, a new motion equation for the nonlinear percolation characteristic of coalbed methane is established. Moreover, the motion equation is correlated well with the experimental data, and the fitting correlation coefficients are above 99.6%.     

The influence of initial internal structure of coal sample on gas flow characteristic

Three kinds of coal samples with different components are chosen as study objects.Density calculation and SEM are adopted to study their internal structures,and a self made triaxial gas seepage instrument is used to study their internal gas flow characteristics.The results show that internal structures of coal samples made of different particle size coal powders under identical external conditions are various,and nonlinearity is presented on the influence caused by fabric.Gas flow characteristic is complex in complete stress strain process,generally it firstly increases and then decreases,initial gas flow velocity is lower than the one after the failure of coal sample,and obvious hysteretic nature of gas flow characteristic is showed.The influence of gas flow characteristic caused by initial internal structure of coal sample is nonlinear and the stress sensitivity is high on the influence of gas flow characteristic caused by initial internal structure.The more complex the initial internal structure of the coal sample is,the lower the axial tress sensitivity is,and the higher the confining pressure sensitivity is.     

An Investigation of Electrochemical Properties of Gelled Polymer Electrolytes

According to the two kinds of expressions of the quadratic functions and the power functoin for describing the non_linear seepage flow,this paper advances that the two kinds of expressions should have identity,that is to say they can transform each other.And by means of least square method,the relational expression for the two kinds of functions to transform each other is derived.From the verification of the two kinds of particular seepage flow(laminal flow and adequate turbulent flow)and the hypothetic data,it has been shown that the relational expression can express the identity between them adequately,it can afford the references to the further research on the non_linear seepage flow.     

Study on Strengthening and Toughening Mechanism of Nb V Bearing High Strength Steels

It is an important subject to solve numerically the problems of anisotropic unsteady seepage flow.This paper presents a numerical method for computing the anisotropic_orthotropic unsteady seepage flow with BEM.The paper introduces the so_called boundary_only technique to solve time dependent problem.The Volume domain integral is voided by using the Green formula again.Several numerical examples are presented.     

Numerical simulation of seepage field of gas extraction drilling of single bedding of mining-coal bed

Aiming at the problem of reasonable decorate of coal gas extraction drilling, combining with the initial and boundary condition of borehole extraction, the solid and gas coupling mathematical model of gas seepage of borehole extraction is deduced based on established control equations of seepage field and deformation field. Taking gas extraction of stone coal slit as an example, according to the characteristics of coal seam in the research, the numerical simulation method is used to obtain the distribution rule of gas pressure, coalbed gas permeability, and coalbed gas seepage velocity as well as seam deformation. The effective radius of gas extraction drilling of single bedding about mining-coal bed is determined, which provides the basis for optimum arrangement of gas extraction drilling of single bedding. The results show that the effective radius of stone coal is about 4 m. If the prolonging drilling drainage time is less than 20%, the drilling quantities would reduce by about 50%.     

Analysis of Numerical Simulation of Seepage Failure and Seepage Feature of Seawall

In order to analyze seepage feature and seepage failure mechanisms of seawall under flood infiltration, a numerical model for saturated-unsaturated and unsteady seepage flow analysis considering soil permeability variation with seepage failure process was established. And the corresponding finite element computation program was made. Numerical simulation of flood seepage for typical section of real seawall was carried out by use of the program. The computed results were compared with the measured results of field test, which shows good agreement. Based on the numerical simulation results, it can be seen that flood seepage of seawall is a saturated-unsaturated and unsteady seepage flow process and seepage failure of seawall is caused by long time flood infiltration under large seepage gradient. Therefore, upon the flood infiltration, seepage failure of the seawall is a very complicated process, which involves soil permeability variation with seepage failure process and saturated-unsaturated/unsteady seepage flow. It is questionable to use the steady seepage analysis method to simulate seepage failure process of seawall.     

ANALYSIS OF STABILITY OF ZERO SOLUTION OF LAMINAR BOUNDARY LAYER EQUATION WITH SIMILAR FLOW

When having similar flow,a two-dimensional equationfor incompressible laminar boundary layer can be transformed into aFalkner-Skan equation.This paper has made transformation of F-Sequation into two-order non-autonomous system by variable permutationwith its stability around zero solution discussed and explained physi-cally.     

Stability Analysis for the Excavation Engineering Under Coupling Effect of Seepage from Heavy Rain and River Fluctuation

The seepage accident is very easily occurred, when the excavation engineering has been constructed in rainy season and it is very easily influenced by the coupling effect of seepage duo to heavy rain and water level fluctuation of neighboring river. So a coupling seepage equation that based on the theory of Dupuit has been established for the ground water in the layered foundation. And then, the water table surrounding the excavation engineering has been determined on the consideration of the coupling effect of seepage duo to heavy rain and water level fluctuation of river. In the meantime, by means of the theory of coupling analysis of stress and seepage and the software of Midas, a model of coupling analysis of stress and seepage has been built for the specific excavation engineering and the seepage destroy characteristics of this project has been researched.     

Elastic Buckling and Critical Load of an Pre- stressing Arch

According to the field theory of additional deformation on pre - stressed configuration , in the paper , the ordinary expression of the governing equation and variational equation of elastic buckling are brought forward . Under the theory system, through lowering dimensions, the governing equation and variational equation for the critical condition solution of elastic buckling of a plane arch are deduced, and the eigenvalues problem of the linear homogeneous differential equations corresponding to the equations are concluded While Abandoning the plane assumption and considering shearing deformation, the linear finite element method arithmetic of bending bar's cross section containing six degree of freedom is given. The process of derivation and calculational results show that, under this system info, the finite element equations of bending bar deduced are accurate and easy to be used to numeric calculations, and the conclusion achieved is more practical.     

A POWER FLOW IN INFINITE VISCOELASTIC CYLINDRICAL SHELLS

In this paper, a solution of propagation wave in an. unconstrained damping viscoelastic cylindrical shells of infinte length under forced vibration is derived by Fourier integral transform techniques. The power flow transmitted along it is analysed. The power flow in an elastic cylindrical shell and that in a viscoelastic shell are compared. The effects of vibration reduction in two viscoelastic shells with different thickness are compared. The results provide a reference for designer in structural vibration reduction.     

Deformation of Soft Ground with Consideration of the Concomitant Damage

On the basis of continuum damage mechanics theory, the effective stress theory of damaged porous media was presented and its modified self contained seepage differential equation was deduced. The traditional Drucker Prager yield criterion subsequently was modified, and a coupled seepage and damage finite element computer program compiled that was combined with the modified Biot consolidation equation. A simple roadbed foundation model then was analyzed and calculated using the computer program we compiled, and the typical node settlement, pore pressure, and damage variables were discussed and compared with those from the analytic solution. The results show that the damage finite element program we compiled is reasonable and effective.     

Study on Methane Flow Regularity and Secondary Stress and Deformation of Coal Bady around Penetration Boreholes in Coal Seam

A new mathematical model for the coefficient of variable permeability affected by coal body, secondary stress & pressure in coalseam & a constitutive equation for gas migration are improved on the basis of the secondary stress & deformation of coal body around boreholes in coalseam. Using this model and equation,the gas flow field belongs to the 20102 experimental zone in BaiJiao coal Mine is computed & this verifies that the model & constitutive equation are both agreeable to practical results. Simultaneously, a comparison between the variable and constant permeabilities is carried out.     

Mechanism analysis of permeability based on promoting coal matrix shrinkage by water jet

High pressure pulsed water jet (HPWJ) is a new technology of effectively improving coal seam permeability. However, the mechanism of increased permeability is not yet clear, which restricts the application of HPWJ in different coal seams. From the perspective of improving permeability by coal matrix shrinkage, the impelled dynamic equations is established based on analysis of coal dynamic effects by water jet. According to theoretical analysis of the stress state of coal matrix, it is concluded that HPWJ can promote coal matrix shrinkage, and the relationship equation between jet impact-coal matrix is derived. Besides, the gas seepage function in the coal slotted by the HPWJ is gained by using PM model, which provides theoretical support for generalizing the technology in the coal mine.     

Analysis on Mechanism of Drain and Consolidation of Super Soft Soil

The ground treatment method for very soft soil do not satisfy the enineering needs presently. This paper studies the drain and consolidation mechanism for ground treatment method improvement of the super soft soil. It aims to obtain some varying laws of engineering properties during the super soft soil consolidated. By quantities of test data, the varying laws of the porosity, permeability, compressibility, consolidation properties and pore pressure, and their varying micro_mechanism during the seepage and consolidation of super soft soil are initially studied. Some mechanism of permeation and consolidation of super soft soil are ascertained. It concludes that the varying laws of above engineering properties is related each other, and the governing mechanism are the varying laws of the porosity and the pore pressure.     

热流固耦合作用下页岩渗透特性实验

为探讨地温对页岩渗流特性的影响规律,按照温度对页岩作用部位的不同,从流体动能、骨架应变、吸附解吸三个方面,分析甲烷内摩擦力对动能的影响、页岩热应力及热膨胀导致应变、甲烷解吸引起基质收缩随温度变化的规律,得出热流固耦合作用下页岩渗流特性。以渝东南酉阳龙马溪组页岩样品为分析对象,进行页岩型岩的温度渗流实验,提出三方面五因素的分析方法：温度增加,流体内摩擦力增大减小了流动速度;粘土矿物与有机质的差异性膨胀产生热应力,压缩了页岩骨架,加之基质热膨胀减小了基质间隙,双重作用使渗流通道减小;基质收缩效应对孔隙裂隙双重结构介质渗透量影响很小。温度升高对页岩渗流特性的主要影响体现为,内摩擦力的减速作用及热应力和热膨胀对渗流通道的压缩作用。     

Theoretical Analysis on 13-Bit Lattice Gas Automata Model with Poly-velocity and its Simulation

An 13 bit lattice gas automata model has been investigated from fluid discrete dynamics. By gaining the moment equations from lattice Boltzmann equation and using Chapman Enskog expansion, the fluid dynamics equation and energy equation of 13 bit lattice gas automata model with polyvelocity have been deduced. The validity of the model using for non isothermal fluid dynamics has been proved . Finally, simulation results for non isothermal flow pass plate have been shown