International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp.36-43, Article ID: IJCIET_10_04_005
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJCIET&VType=10&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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APPLICATION OF METHODS OF MINE
AEROGASDYNAMICS FOR SIMULATION OF
PROPAGATION OF BLAST WAVE IN JOINT
JUNCTIONS OF MINE WORKINGS
Vladimir Alekseevich Rodionov
Ph.D., Associate Professor, Department of Industrial Safety,
Saint Petersburg Mining University
Russian Federation, 199106, Saint Petersburg, Vasilievski Ostrov, 21 line, 2
Evgeniy Olegovich Sharavin
Ph.D. Student at the Department of Mine-Rescue Business and Explosion Safety, Saint
Petersburg University of State Fire Service of EMERCOM of Russia
Russian Federation, 196105, Saint Petersburg, Moskovskiy Prospect 149
Ekaterina Andreevna Kochetkova
Ph.D., Associate Professor, Department of Industrial Safety,
Saint Petersburg Mining University
Russian Federation, 199106, Saint Petersburg, Vasilievski Ostrov, 21 line, 2
ABSTRACT
This paper reviews the processes of blast wave propagation in joint junctions of
capital and preparatory mine workings, the blast wave is formed in blast of air-coal
mixture in the seams of horizontal and inclined occurrence. Methods of mine
aerogasdynamics applicable to various geometrical combinations of joints, were used
for simulation and calculations. At the initial stag of doing the research work, simplified
variants of rectangular types of joints were selected for studying aerogasdynamic and
thermophysical processes emerging in blast of aerosols of coal dust. The source data
for building a model in ANSYS FLUENT software were adopted based on the
experimental studies conducted by the authors on identifying the damaging factors of
blast in the laboratory device for conducting blasts of air-coal mixture in confined
space. The maximal pressure of the blast and the speed of pressure build-up in blast
was identified in a 20-litre spherical blast chamber. It was identified that the maximal
blast pressure emerges in the laboratory device in forced blast in the volume of coal
dust of 63-94 micrometers. As a result of constructing the model, according to the
obtained experimental data, the probability of emergence of reflected waves is
established. Emergence of reflected waves, according to the model built by means of
ANSYS FLUENT, causes formation of local zones of increased pressure. It was
established that the highest pressure develops in the front of blast waves in their mutual
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Application of Methods of Mine Aerogasdynamics for Simulation of Propagation of Blast Wave
in Joint Junctions of Mine Workings
encounter incident wave+ reflected wave and reflected +reflected blast waves. In this
respect, the biggest hazard in blast pressure build-up in the blast wave front is formed
in mine workings of rectangular T-shaped intersection. As a result of calculation and
modelling, the fact of the consistency of the obtained experimental results with the
actual process of blast wave propagation in elastic media, was identified. In addition,
the obtained experimental results in computer simulation, with use of ANSYS FLUENT
software, mine aerogasdynamic processes of blast wave propagation, enable to
calculate promptly and efficiently fairly complex joint junctures of mine workings. Work
in this area will be continued.
Key words: mine aerogasdynamics, mine workings, blast wave, ANSYS FLUENT,
explosive coal dust, maximal blast pressure, air-coal mixtures.
Cite this Article: Vladimir Alekseevich Rodionov, Evgeniy Olegovich Sharavin,
Ekaterina Andreevna Kochetkova, Application of Methods of Mine Aerogasdynamics
for Simulation of Propagation of Blast Wave in Joint Junctions of Mine Workings,
International Journal of Civil Engineering and Technology 10(4), 2019, pp. 36-43.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=4
1. INTRODUCTION
This work is of relevance due to the complexity of forecasting the implications of one of the
most hazardous manifestations of undreground blast – blast wave.
The magnitude of destruction depends on many factors which are difficult to identify
theoretically, including change in the intestity and direction of blast wave propagation [1-3].
Complexity of simulation of such dynamic processes is related to network of mine workings
constant variation and increasing sophistication, which requires constant monitoring and
creation of new mathematical models [2, 4-10].
Emergence of up-to-date means of computer simulation enables to study multiple hub
connections and take into account many factors which accompany blast war manifestation [9,
11-13]. In so doing, high degree of vizualization of various forms of the dynamic process of
pressure manifestation is achieved, which enables to estimate the blast parameters qualitatively
and quantitatively. [3, 5, 13-15].
Purpose of work
Creation of physical and mathematical two-dimensional model in ANSYS FLUENT software
for simulation of the pattern of blast wave formed in air-coal mixture blast, in various junction
junctures of mine workings.
2. METHODOLOGICAL FRAMEWORK
In order to describe the blast wave propagation in this model, we will use the elementary theory
of shock tube [3, 9, 14-17]. According to this theory, we use two constants for mathematical
simulation: molecular weight - 𝜇 and adiabatic index - 𝑘.
Constants 𝑘1 and 𝜇1 are related to the low-pressure area, and constants 𝑘2 and 𝜇2 are related
to the high-pressure area, respectively, 𝑝1 and 𝑝2 are initial pressures, and 𝑝2 ≫ 𝑝1 (Fig.1).
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Vladimir Alekseevich Rodionov, Evgeniy Olegovich Sharavin, Ekaterina Andreevna Kochetkova
Figure 1. General scheme of setting the conditions of blast wave propagation in ANSYS FLUENT
software: 1 – Boundary condition of pressure inlet; 2- high pressure area; 3- border between areas; 4 –
boundary conditions of walls; 5 – low pressure area.
In addition, for calculation simplification, we consider the shock tube as heat-insulated, and
movement of gas as adiabatic.
According to this theory, we have the following equation, which we
will subsequently use for simulation:
2𝑘2
𝑝2
2𝑘1
𝑘 −1
𝑘2 − 1
1 𝑎1 −𝑘2+1
2 1
=(
𝑀
) [1 −
(𝑀 − ) ]
𝑝1
𝑘1 + 1 1 𝑘1 + 1
𝑘1 + 1 1 𝑀1 𝑎2
(1)
where 𝑝2 ⁄𝑝1 is the set initial ratio of the pressures in different areas of the pipe; 𝑘1 𝑎𝑛𝑑 𝑘2
are the indicators of adiabat for the area of low and high pressure; 𝜇1 𝑎𝑛𝑑 𝜇2 is the molecular
weight for the area of low and high pressure; 𝑀1 is Mach number of blast wave:
𝑀1 =
𝜃
𝑎1
(2)
where 𝜃 is the flow rate; 𝑎1 is the local sound velocity.
𝑎1
𝑘1 ∗ 𝜇2
=√
𝑎2
𝑘2 ∗ 𝜇1
(3)
The key stages of mathematical simulation in ANSYS FLUENT for setting the blast wave:
1. Creation of required geometrical model;
2. Breaking the model down into elements (generation of calculation grid);
3. Setting the boundary conditions, material and pressure;
4. Selecting a necessary equation for solving and optimizing the parameters corresponding to
the equation;
5. Defining the blast wave parameters for building a reliable model of blast wave propagation
with using reference data;
6. Output and visualization of calculation data.
To study the issues of the possibility to the mathematical tools implemented by means of
applied software ANSYS FLUENT designated for studying the mine aerogasdynamics,
namely, the processes of blast wave propagation in joint junctions of mine workings, we have
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Application of Methods of Mine Aerogasdynamics for Simulation of Propagation of Blast Wave
in Joint Junctions of Mine Workings
made several assumptions. Taking into account the fact that we are at the beginning stage, we
have selected rectangular joints from all possible multitude of joints.
In our view, this approach will enable us to model the processes of the emergence and
propagation of the blast wave along the mine workings’ space. In addition, it will enable us to
identify in more detail and with higher reliability the areas of blast build-up and fading,
manifestation of reflected blast war, and also to identify the counter areas of blast wave fronts,
which have higher blast pressure than the initial maximal blast pressure [15-20].
One of the conditions for the model validity and evaluating the possibility of applying the
results in practice, is the need of identifying the characteristics of detonation combustion of coal
dust taken from the active workings of coal mines [7-10, 15, 18-21]. For this reason, in order
to enhance the practical component, we did research on identifying the damaging blast factors
of air-coal mixtures of mines. Using the obtained experimental data, we determined the
transformation coefficient. By means of this coefficient, it is possible to compare the calculation
parameters of the process of blast wave propagation with the data obtained by using during
constructing the model [18, 22-24].
In performing our research, we relied on the recommendations and data of other authors
studying similar issues, these recommendations are described in several studies [2, 3, 14, 17].
Scientifically proven selection of stone dust fraction was performed in line with the data of
studies [5, 13, 18], and is confirmed by the results we obtained.
3. RESULTS AND DISCUSSION
According to studies [5, 13, 18], for solving the problem of determining he maximum blast
pressure, the velocity of blast pressure build-up and the transformation coefficient, and also of
the source data adjustment, we conducted tests in the laboratory unit which is a 20-litre
combustion chamber for studying the blast parameters of dust and gas mixtures of various
concentrations. The physical appearance of the main unit of the device which belongs to St.
Petersburg Mining University, are presented in Figure 2.
Figure 2. Physical appearance of 20-litre combustion chamber:
1 - base (stand); 2 – multiphase valve of dust/air inlet;
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Vladimir Alekseevich Rodionov, Evgeniy Olegovich Sharavin, Ekaterina Andreevna Kochetkova
3 – outlet of recirculation water; 4 – vacuum gauge; 5 – safety valve; 6 – handle of safety lock
of safety valve;
7 – twist handles of chamber lid; 8 – inlet for recirculation water;
9 – inspection hole; 10 – pressor sensor input; 11 – vessel for dust samples (pre-compression
vessel); 12 – ignition wire contacts in the removed position.
The authors of the studies [3, 5, 18] determined that fractions of 0-45 micrometers have the
highest blast pressure, but the formation of such fractions in the longwall space is not plausible.
This is explained by the fact that the smaller fractions are removed by air aerodynamic flow,
both by the application of irrigation systems to the face area by the surface miner working
elements, and by application of the dust suppression system. Obtaining the fractions by the
forced method when conducting dry granulometric sieving is complicated because of particle
adhesion and clogging sieve cells. For this reason, in the source data, during the construction
of the models, the dispersion of dust of 63-94 micrometer fraction was taken into account, with
which, the maximal damaging blast factors develop, which is confirmed by the authors of the
following studies [3, 5, 13, 18, 23, 24].
Conditions for conducting the experiment
•
Size distribution of coal dust sample: 63-94 μm;
•
Dispersion overpressure Pd = 2 MPa;
•
Initial pressure Pi = 0.1013 MPa (preevacuation of the explosion vessel down to 0.04 MPa);
•
Initial temperature Ti = 20°C0 (water cooling);
•
Ignition delay time tv = 60 ms;
•
Ignition source: chemical igniter of energy 10 kJ.
As a results of the performed research work, it was established that during blast of mine
coal dust fraction of 63-94 micrometers in dispersity: 1. The highest blast pressure is achieved
at the concentration of 250 g/m3; 2. The maximal blast pressure is Рm=0.76 MPа; 3. The pressure
build-up velocity during the explosion dP/dt=48.97 MPа/s.; 4. Transformation coefficient
Km=13.29 МPа*m/s.
Taking into account the abovementioned conditions and the obtained experimental data in
ANSYS FLUENT software for mine workings of rectangular and rectangular branch, a model
was constructed, its results are represented below in a graphical form.
Figure 3. Results of visualization of calculating pressure gradient of workings’ rectangular
intersection
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Application of Methods of Mine Aerogasdynamics for Simulation of Propagation of Blast Wave
in Joint Junctions of Mine Workings
Figure 4. Results of visualization of calculating pressure gradient of workings’ branch
As a result of constructing the models for rectangular intersection and rectangular branch
of mine workings, we identified the emergence of reflected waves. In case of rectangular
intersection, the pressure value at the encounter of incident blast wave and reflected blast wave,
are within the acceptable limits (blue area, see Figure 3). In a rectangular branch, we observe
pressure build-up in the front of blast wave formed by the incident and reflected blast waves
(see Figure 4), and the excessive pressure value is several times higher (up to 0.9 MPа) than in
the front of the incident blast wave.
6. CONCLUSIONS
The results obtained by us, suggest that in mine workings intersecting each other at an acute
angle, the emerged blast wave, under certain circumstances, will be extinguished by explosion
protection devices more effectively.
The results of simulation are in line with the pattern of the blast wave of the real experiments
presented in Album of Fluid Motion [9], hence, the used mathematical model, with a slight
adjustment, can also be used for two-dimensional simulation of the blast wave pattern for other
cross-sections of mine workings (trapezoidal, arched, round and others).
Thus, computer simulation with the use of ANSYS FLUENT for mathematical simulation
of blast waves, enables to calculate promptly and effectively fairly complex joint junctures of
mine workings.
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