Study on the Mechanism of Rock Stress Sensitivity Using a Random Pore Network Simulation

Studies of rock stress sensitivity are mainly focused on experimental and data processing methods, and the mechanism cannot be adequately explained using specific pore shape models. This study, based on a random pore network simulation, explains the rock stress sensitivity mechanism for the first time. Based on the network model theory, the hydraulic conductivity equation, the dimensionless radius equation, and the effective stress equation for partially saturated rock are used to generate a three-dimensional random pore network model based on the QT platform. The simulation results show that the influence of the effective stress on the dimensionless radius becomes more significant as the aspect ratio decreases, and the relationship between dimensionless radius and effective stress can be effectively interpreted through different combinations of pore shapes. Moreover, the mechanism behind permeability stress sensitivity can be explained by establishing the relationship between permeability and effective stress.

Heat Transfer and Entropy Generation Analysis of Bingham Plastic Fluids in Circular Microchannels

The thermal characteristics of Bingham plastic fluid flows are analyzed in circular microchannels under uniform wall heat flux condition. The analytic approach presented here reveals that the governing parameters are Bingham number, dimensionless radius of the plug flow region, and Brinkman number. The results demonstrate that there is a strong influence of viscous dissipation on heat transfer and entropy generation for Brinkman numbers greater than a specific value. With increasing the Brinkman number and dimensionless radius of the plug flow region, entropy generation is increased, while the Nusselt number is decreased. The influence of these parameters on the entropy generation from heat transfer is strongly higher than the entropy generation from fluid friction. The average dimensionless total entropy shows that the Bingham plastic fluids generate entropy more than Newtonian fluids; also, an increase in the dimensionless radius of the plug flow region results in increasing the average dimensionless total entropy generation. By letting the dimensionless radius of the plug flow region equal to zero, the generalized expressions and results will be simplified to Newtonian fluids.

The Appropriate Blend Proportional Factor Value of Two Staggered Grids Used in the Free Energy Based LBM With Large Density Ratio

The effect of blend proportional factor α used in the free energy based two-phase flow LBM model with large density ratio on the shape description of a water droplet is investigated. The blend proportional factor α which combines the two kinds of staggered grids is adopted in the calculation process of the Poisson equation based fractional step method to satisfy the mass conservation in the LBM scheme, it is found to lead to varied degrees of shape deformation of a simulated liquid water droplet. The shape deformation degree of a liquid water droplet with certain dimensionless radius is measured by the radius lengths in 8 directions. The appropriate α which gives the better shape description accuracy of a water droplet with certain dimensionless radius is explored and its value change tendency with the dimensionless radius lengths is summarized. The α’s effect on the shape deformation is also presented.

Acoustic Emission at Wedge Indentation Fracture in Quasi-Brittle Materials

To improve the safety and automation of mechanical excavation methods used in tunnels, this present report studied the behavior of rock materials indented by a single cutter, based on the theory of indentation fracture mechanics. The development of microcracks during the indentation process and the correlation between microcracks and macrocracks was investigated using the nondestructive technique of acoustic emission. Microseismic activity of the microcracks received by the acoustic emission (AE) technique was used to interpret and represent the initiation and propagation of macrocracks. As the wedge angle increased, the maximum indentation force increased, but the nominal indentation pressure and the destructive indentation depth decreased. On the other hand, the direction of macrocrack propagation did not significantly change with the various wedge angles. Furthermore, the localization occurred earlier and the dimensionless radius of the elasto-plastic interface decreased with increased wedge angle. In addition, the dimensionless radius of the elasto-plastic interface obtained by the experiment was consistent with closed-form analytical solutions.

Focusing of a dark hollow Gaussian electromagnetic beam in a magnetoplasma

This paper presents an analysis and subsequent discussion of the self focusing of a dark hollow Gaussian electromagnetic beam (HGB) in a magnetoplasma, considering ponderomotive and collisional nonlinearities. A paraxial-like approach, in which the relevant parameters are expanded in terms of radial distance from the maximum of the irradiance rather than that from the axis, has been adopted to analyze the propagation of the HGB. The nature of self focusing is highlighted through the critical curves as a plot of dimensionless radius versus power of the beam. The effect of the magnetic field and the nature of the nonlinearity on self focusing of various order HGBs has also been explored.

Focusing of dark hollow Gaussian electromagnetic beams in a plasma

This paper presents an investigation of the focusing of dark hollow Gaussian electromagnetic beams (HGB) in plasma, considering collisional, ponderomotive, and relativistic nonlinearities. A paraxial like approach, in which the parameters are expanded, in terms of radial distance from the maximum of irradiance rather than that from the axis, has been adopted. To highlight the nature of focusing, both critical curves and the divider curves have been obtained as a plot of dimensionless radius vs. power of the beam. The effect of the order of HGB (n), and nature of nonlinearity on self focusing of the beam has also been explored.

Critical Load between Sea Ice and Sea Structure

The main objective of this paper is to propose the buckling equations of the sea sheets under concentrated forces. Two different cases of the acting forces are considered in this paper and the buckling equations of them are deprived, respectively. Then, the dimensionless forms of these equations are given. Furthermore, by adopting a numerical method, two cases of different thickness of the ice sheet and different distances between sea structures are explored. On the basis of the buckling equations, the expressions of the critical load between sea ice and sea structures are obtained. Finally, the relationship between the critical load factor and the dimensionless radius are presented

Pressure Behavior During Polymer Flow in Petroleum Reservoirs

This paper presents solutions of the nonlinear partial differential equation using the Douglas-Jones predictor-corrector method for the numerical solution of nonlinear partial differential equations. The results are presented in tabular form and as semilogarithmic and log-log type-curve graphs. Graphs of dimensionless pressure versus dimensionless radius also are presented. Compared to results from analytical solutions of the linear partial differential equation, the graphs have the same shape. The error introduced by the linearizing approximation is small for many values of the flow behavior index, n, and decreases as n tends to unity. Dimensionless pressure is a linear function of dimensionless radius to the power (1–n), near the well, as predicted by the steady-state equations. Also radius of investigation equation derived analytically agrees with results from numerical solutions.