scholarly journals Analysis of the Characteristics and Influencing Factors of Gas Explosion in Heading Face

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xue-bo Zhang ◽  
Jian-liang Gao ◽  
Jing-zhang Ren ◽  
Chun-xia Wang
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Influencing Factors ◽  
Geometric Model ◽  
Great Influence ◽  
Ignition Energy ◽  
Gas Explosion ◽  
Step Size ◽  
Time Step ◽  
Time Space

In order to accurately grasp the characteristics and influencing factors of gas explosion in heading face, the mathematical model of gas explosion was determined. According to the actual size of a heading face of a coal mine, a 3D geometric model with a length of 100 m was established, and the effects of ignition energy and gas explosion equivalent on the gas explosion characteristics of the heading face were analyzed. The results show the following. (1) The mathematical models for numerical simulation of gas explosion can accurately simulate the gas explosion and its propagation process. The time-space step size has a great influence on the simulation results. The grid spacing for numerical simulation of mine gas explosion is determined to be 0.1 m and the time step length is determined to be 0.001 s. (2) The ignition energy has a limited effect on gas explosion characteristics. It only has a certain influence on the gas explosion process, but has little influence on the overpressure of shock wave. The larger the ignition energy is, the faster the explosion reaction speed is, and the maximum overpressure increases slightly. When the ignition energy increases to a certain value, the time of peak shock wave and the maximum overpressure both tend to be stable. The ignition energy has little effect on gas explosion characteristics when an explosion accident occurs underground with a large amount of gas accumulation. (3) The gas explosion equivalent has a great influence on the overpressure of gas explosion shock wave. The higher the explosion equivalent is, the greater the pressure is, and the peak value of the shock wave overpressure increases with the explosion equivalent as a power function. The research results have important guiding significance for the research and development of new technology for prevention and control of gas explosion.

scholarly journals Local Discontinuous Galerkin Method for Nonlinear Time-Space Fractional Subdiffusion/Superdiffusion Equations

2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Meilan Qiu ◽  
Dewang Li ◽  
Yanyun Wu
Keyword(s):  
Convergence Rate ◽  
Fractional Derivative ◽  
Discontinuous Galerkin ◽  
Numerical Schemes ◽  
Step Size ◽  
Time Step ◽  
Local Discontinuous Galerkin ◽  
Time Space ◽  
Backward Euler ◽  
Heterogeneous Rocks

Fractional partial differential equations with time-space fractional derivatives describe some important physical phenomena. For example, the subdiffusion equation (time order 0<α<1) is more suitable to describe the phenomena of charge carrier transport in amorphous semiconductors, nuclear magnetic resonance (NMR) diffusometry in percolative, Rouse, or reptation dynamics in polymeric systems, the diffusion of a scalar tracer in an array of convection rolls, or the dynamics of a bead in a polymeric network, and so on. However, the superdiffusion case (1<α<2) is more accurate to depict the special domains of rotating flows, collective slip diffusion on solid surfaces, layered velocity fields, Richardson turbulent diffusion, bulk-surface exchange controlled dynamics in porous glasses, the transport in micelle systems and heterogeneous rocks, quantum optics, single molecule spectroscopy, the transport in turbulent plasma, bacterial motion, and even for the flight of an albatross (for more physical applications of fractional sub-super diffusion equations, one can see Metzler and Klafter in 2000). In this work, we establish two fully discrete numerical schemes for solving a class of nonlinear time-space fractional subdiffusion/superdiffusion equations by using backward Euler difference 1<α<2 or second-order central difference 1<α<2/local discontinuous Galerkin finite element mixed method. By introducing the mathematical induction method, we show the concrete analysis for the stability and the convergence rate under the L2 norm of the two LDG schemes. In the end, we adopt several numerical experiments to validate the proposed model and demonstrate the features of the two numerical schemes, such as the optimal convergence rate in space direction is close to Ohk+1. The convergence rate in time direction can arrive at Oτ2−α when the fractional derivative is 0<α<1. If the fractional derivative parameter is 1<α<2 and we choose the relationship as h=C′τ (h denotes the space step size, C′ is a constant, and τ is the time step size), then the time convergence rate can reach to Oτ3−α. The experiment results illustrate that the proposed method is effective in solving nonlinear time-space fractional subdiffusion/superdiffusion equations.

A Numerical Coning Model

1970 ◽  
Vol 10 (04) ◽  
pp. 418-424 ◽  
Author(s):  
J.P. Letkeman ◽  
R.L. Ridings
Keyword(s):  
Numerical Simulation ◽  
Finite Difference ◽  
Two Dimensions ◽  
Solution Technique ◽  
Production Rates ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Size Limitation ◽  
Single Well

Abstract The numerical simulation of coning behavior bas been one of the most difficult applications of numerical analysis techniques. Coning simulations have generally exhibited severe saturation instabilities in the vicinity of the well unless time-step sizes were severely restricted. The instabilities were a result of using mobilities based on saturations existing at the beginning of the time step. The time-step size limitation, usually the order of a few minutes, resulted in an excessive amount of computer time required to simulate coning behavior. This paper presents a numerical coning model that exhibits stable saturation and production behavior during cone formation and after breakthrough. Time-step sizes a factor of 100 to 1,000 times as large as those previously possible may be used in the simulation. To ensure stability, both production rates and mobilities are extrapolated production rates and mobilities are extrapolated implicitly to the new time level. The finite-difference equations used in the model are presented together with the technique for incorporating the updated mobilities and rates. Example calculations which indicate the magnitude of the time-truncation errors are included. Various factors which affect coning behavior are discussed. Introduction The usual formulation of numerical simulation models for multiphase flow involves the evaluation of flow coefficient terms at the beginning of a time step and assumes that these terms do not change over the time step. These assumptions are valid only if the values of pressure and saturation in the system do not change significantly over the time step. The design of a finite-difference model to evaluate coning behavior of gas or water in a single well usually results in a model which uses radial coordinates. A two-dimensional single-well model is illustrated in Fig. 1. This type of model will often produce finite-difference blocks with pore volumes less than 1 bbl near the wellbore while producing large blocks with pore volumes greater producing large blocks with pore volumes greater than 1 million bbl near the external radius. If one chooses to use a reasonable time-step size of, say, 1 to 10 days, then normal well rates would result in a flow of several hundred pore volumes per time step through blocks near the wellbore. Therefore the assumption that saturations remain constant, for the purpose of coefficient evaluation, is not valid. Welge and Weber presented a paper on water coning which recognized the limitation of using explicit coefficients and applied an arbitrary limitation on the maximum saturation change over a time step. While this method is workable for a certain class of problems, it is not rigorous and is not generally applicable. In 1968, Coats proposed a method to solve the gas percolation problem which is similar in that it also results from explicit mobilities. This proposal involved adjusting the relative permeability to gas at the beginning of the time step so that an individual block would not be over-depleted of gas during a time step. This method is not conveniently extended to two dimensions nor to coning problems where a block is voided many times during a time step. Blair and Weinaug explored the problems resulting from explicitly determined coefficients and formulated a coning model with implicit mobilities and a solution technique utilizing Newtonian iteration. While this method is rigorous, achieving convergence on certain problems is difficult and, in many cases, time-step size is still severely restricted. In addition to the problems resulting from explicit flow-equation coefficients in coning models, the specification of rates requires attention to ensure that the saturations remain stable in the vicinity of the producing block. SPEJ P. 418

Research on the Uncertainty Analysis in CFD Simulation of the Dredging Dustpan

2016 ◽  
Author(s):  
Yu Lu ◽  
Ankang Hu ◽  
Xin Chang
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Uncertainty Analysis ◽  
Velocity Ratio ◽  
Step Size ◽  
Time Step ◽  
Outlet Cross Section ◽  
Time Step Size ◽  
Grid Convergence ◽  
Benchmark Database

The main focus of this paper is on the uncertainty analysis methodology and procedure in CFD recommended by 22nd ITTC and the benchmark database for the verification and validation of the results of dredging dustpan’s inlet and outlet cross-section velocity ratio coefficient viur. Compared with the previous uncertainty analysis of CFD focused on the fluid grid-convergence in the steady flow, which is less to consider other factors that may affect the accuracy of the results of numerical simulation, this study compensates for this deficiency and implements the grid-convergence and time-step-size-convergence studies respectively by using three types of grids and time step sizes with refinement ratio under the condition of unsteady flow. Through confirming the validity of CFD uncertainty analysis, the agreement between the numerical simulation correction values from the grid-convergence and time-step-size-convergence and the benchmark test data is found to be quite satisfactory. The results obtained in this study have shown that it is indispensable to carry out the time-step-size-convergence studies for CFD uncertainty analysis during the unsteady flow calculation because the numerical simulation errors respectively caused by the grid and time-step-size in the convergence study have the same order of magnitude. In further the present study of simultaneously conducting both grid-convergence and time-step-size-convergence is demonstrated efficient and effective in the CFD uncertainty analysis.

scholarly journals Effect of Computational Parameters on Output Properties of Underwater Explosion by Intelligent Numerical Simulation

2021 ◽  
Vol 2083 (3) ◽  
pp. 032086
Author(s):  
Yonghui Zheng ◽  
Jifeng Wei ◽  
Rui Xiao
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Near Field ◽  
Great Influence ◽  
Underwater Explosion ◽  
Propagation Distance ◽  
Rigid Boundary ◽  
Simple Method ◽  
Mesh Density ◽  
Explosion Load

Abstract The computational parameters are of great influence on underwater explosion load. A one-dimensional wedge model is established to analyze the influence of boundary condition (BC), water domain and mesh density on the numerical simulation results. The results show that flowout BC is rigid boundary and transmit BC is not suitable for simulating the collapses phase of bubble pulsation. According to propagation distance of shock wave and its reflected wave, a simple method to calculate appropriate water domain is proposed. A positive correlation between mesh density (λ) and calculated peak pressure of shock wave (P m) is found. When λ tends to infinity, simulated Pm in near field is quite reliable, but the values in relatively far field are lower than empirical results.

scholarly journals Influence of Roadway Cross-Section Shape on Gas Explosion Shock Wave Law in U-Type Ventilation Working Faces

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Jiajia Liu ◽  
Mengqi Shen ◽  
Shouqi Chen ◽  
Ming Yang
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Simulation Study ◽  
Simulation Software ◽  
Effective Length ◽  
Shaanxi Province ◽  
Gas Explosion ◽  
Cross Sectional ◽  
Working Face ◽  
Tunnel Section

In U-shaped ventilation working face, different tunnel section shapes are one of the important factors affecting the propagation of gas explosion shock wave. In order to study the propagation law of gas explosion shock wave in working face, the numerical simulation study was carried out by using Fluent simulation software combined with the actual situation of gas explosion in #415 working face of Chenjiashan Coal Mine in Shaanxi Province. By constructing a three-dimensional mathematical and physical model, a simulation study of the upper-corner gas explosion was carried out. The results are described as follows. (1) After the gas explosion shock wave propagates 40 m, the overpressure peak equidistant difference tends to be stable and attenuates and propagates in the form of a single shock wave. The study determines that the effective length of the U-shaped ventilation inlet/return tunnel is 40 m. (2) When the tunnel section is trapezoidal, the initial overpressure of the gas explosion shock wave propagating to the inlet/return airway is the highest, followed by rectangular and semicircular arches, but the internal overpressure attenuation trend of different cross-sectional shapes is the same. (3) The gas explosion shock wave propagates radially along the working face section during the working face propagation. The farther away the location is from the upper corner of the tunnel during a gas explosion with different cross-sectional shapes, the closer the cutoff overpressure peak is. The attenuation trend of overpressure with the propagation distance conforms to the power function law. The research results provide an important theoretical direction for the numerical simulation of gas explosions in coal mining faces.

Study on Hazard Effects of Gas Explosion in Coal Laneways

2011 ◽  
Vol 402 ◽  
pp. 846-849
Author(s):  
Lei Pang ◽  
Tong Wang ◽  
Yu Shu Xie ◽  
Wei Yao ◽  
Qi Zhang
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Temperature Field ◽  
High Temperature ◽  
Flame Front ◽  
Axial Distance ◽  
Distribution Characteristics ◽  
Gas Explosion ◽  
Flame Region ◽  
Air Explosion

Methane-air explosion is one of the main accidents in coal mines. In this paper, the hazard effects of the gas explosion in a long straight coal laneway were studied by virtue of numerical simulation. Distribution characteristics of the shock wave overpressure, the flame speed and the temperature field were obtained. Along the increasing axial distance, shock wave overpressure increases in original methane-air area and decreases beyond the original methane-air area. Range of flame exceeds original methane-air area. Flame accelerates continually in original methane-air area and decelerates beyond the original methane-air area. The temperature attenuates slowly along the increasing distance in the flame area by virtue of flame front, and attenuates quickly along the increasing distance beyond the flame region. High temperature hazard involves farther area beyond original methane-air area.

A Modification of Pragmatical Generalized Synchronization of Chaotic Systems with Uncertain Parameters by Adaptive Control

2012 ◽  
Vol 442 ◽  
pp. 375-378 ◽  
Author(s):  
Wen Guang Zhang ◽  
Jun Wei Lei ◽  
Guo Qiang Liang
Keyword(s):  
Numerical Simulation ◽  
Adaptive Control ◽  
Chaotic Systems ◽  
Uncertain Parameters ◽  
Generalized Synchronization ◽  
Kutta Method ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Runge Kutta Method

A modification to the synchronization law in [Zheng-Ming Ge, Pragmatical generalized synchronization of chaotic systems with uncertain parameters by adaptive control, Physica D (2007) 87-94] is proposed. To verify and demonstrate the effectiveness of the proposed method, a numerical simulation is done and the fourth-order Runge-Kutta method is used to solve the system with time step size 0.001.

Research on Influencing Factors for Stirring Effect of Blender Truck

2011 ◽  
Vol 308-310 ◽  
pp. 1454-1458 ◽  
Author(s):  
Tian Cheng Huang ◽  
Si Zhu Zhou ◽  
Xin Mei Yuan
Keyword(s):  
Numerical Simulation ◽  
Influencing Factors ◽  
Great Influence ◽  
Orthogonal Test ◽  
Test Method ◽  
Test Scheme ◽  
Range Analysis ◽  
Stirring Effect ◽  
Orthogonal Test Method ◽  
Influence Degree

Stirring system of blender truck as an important equipment of fracturing unit, its stirring effect has great influence on performance of fracturing fluid and fracturing operation of fracturing unit, so it is necessary to study the influencing factors for stirring effect of blender truck. On the basis of the theory of the orthogonal test method and the requirement of the design on the stirring system, the factors and their levels of numerical simulation experiment are confirmed and the orthogonal test scheme is established in this paper. Also the numerical simulation for mixing process of stirring system of the blender truck is carried out with CFD software. The influence degree of the factors on stirring effect is obtained with the range analysis method, the optimal structure size of stirring system is achieved according to this result.

scholarly journals Numerical Simulation of Shock Wave Structure in Gas Explosion

2011 ◽  
Vol 26 ◽  
pp. 1322-1329 ◽  
Author(s):  
Zhang Licong ◽  
Zhang Yulong ◽  
Xu Jingde ◽  
Yang Gengyu ◽  
Hou Shiqiang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Wave Structure ◽  
Gas Explosion ◽  
Shock Wave Structure
Sign in / Sign up

Export Citation Format

Share Document