Theoretical Study On Wind Velocity Distribution In The Section Of Roadway And Real Time Diagnostics On Mine Ventilation Systems

The distribution and migration law on coal mine gas flow field has an important impact on mine production and safety. Coal mine gas flow must supply fresh air for the staff and exclude underground toxic gases and dust.Researches for the coal mine gas flow field are only on network solution for the entire ventilation system and the wind speed distribution of special place. There are no value calculations and researches for the gas flow field in entire coal mine and distribution of wind speed in general roadway. In this paper, the airflow velocity distribution in mine roadways was studied through the field measurements and laboratory experiments. The air flow velocity distribution law on section of roadway was obtained. Then the flow field on entire coal mine has been simulated using the pressure in the cross section as variable and real time fault diagnosis method for underground ventilation system has been proposeed. The following results are acquired:1) The field measurements were carried out on the wind speed distribution in four different supporting rectangular roadways(bolting with wire mesh supporting roadway, bolting and shotcreting supporting roadway, I-steelsupporting roadway and flat wall supporting roadway), some results are obtained as follows:① The low wind speed region increased with the roughness of the roadway wall. The bolting with wire mesh supporting roadway with the maximum roughness wall has the largest low airflow velocity region in the four roadways. The distance percentage at 80% highest wind speed along direction a(reflecting wind distribution in the wall) from the border to the center was up to61%. While the flat wall supporting roadway with the minimum roughness wall has the smallest low airflow velocity region in the four roadways. The distance percentage at 80% highest wind speed along direction a(reflecting wind distribution in the wall) from the border to the center was only 17%.② The coal mine roadway speed distribution study can provide a reference for accurately calculate the amount of wind and the average wind speed in the roadwy. Site measurement and analysis shows the average wind speed in the section of roadway could be measured at the d-line(reflecting roof wind speed distribution) suspending from the roof of 0.231, 1.290, 0.202 and0.217 meter in the bolting with wire mesh supporting roadway, bolting and shotcreting supporting roadway, I-steel supporting roadway and flat wall supporting roadway, respectively. If the wind speed sensor suspended in the middle of roadway 0.2 meter from the roof, correction factor 1.05, 1.45, 1.03 and 1.02 should be multiplied in the bolting with wire mesh supporting roadway,bolting and shotcreting supporting roadway, I-steel supporting roadway and flatwall supporting roadway, respectively. The average wind speed multiply equivalent cross-sectional area is equal to the air volume in the roadway.2) The underground tunnel engineering simulation wind speed distribution experiments showed the low wind speed region increased with the roughness of the roadway wall and decreased with the average velocity in the cross section of roadways. This rule can be used to reduce the low wind speed region in the roadways and prevent accidents caused by that region.3) Field and laboratory measurements in underground roadway can provide a reliable basis data for the numerical simulation. These basic data include the roadway characteristic coefficient, roadway area, equivalent cross-sectional area,support form, of cross-sectional shape, equivalent roughness, average wind speed and air volume.4) The field and laboratory measurements were carried out on the wind speed boundary and low speed boundary area in three different supporting rectangular roadways(I-steel supporting roadway, bolting and shotcreting supporting roadway and flat wall supporting roadway), some results are obtained as follows:① The field measurements showed the fitting curves of winds and distance in boundary layer in I-steel supporting roadway, bolting and shotcreting supporting roadway and flat wall supporting roadway were conform to logarithmic curve, its fitting correlation coefficients were greater than 0.96,goodness of fit were greater than 0.93. Its basic function is obtained in the formof y = k Ln(x) + b type, where k and b are constants.② The underground tunnel engineering simulation wind speed distribution experiments showed the low speed boundary area increased with the roughness of the roadway wall and decreased with the average velocity in the cross section of roadways. The fitting curves of winds and distance in boundary layer in I-steel supporting roadway, bolting and shotcreting supporting roadway and flat wall supporting roadway were conform to logarithmic curve. The unified basic form fit function was obtained containing the center wind speed of the roadway.③ The thickness of low speed boundary area not only affected by the roadway center wind speed and the roadway wall roughness, but also affected by the size of the roadway cross section. With the oadway wall roughness is reduced, the impact of the roadway cross-section geometry for low speed boundary area thickness decreased.The low speed boundary area thickness ratio is not equal to 1/4 when the geometric similarity ratio is 1/4 and the wind speed in underground tunnel engineering simulation experiments is equal to the field measurements. This low speed boundary area thickness ratio is decreases with the wall roughness. The low speed boundary area thickness ratios on field measurements and underground tunnel engineering simulation experiments are2.00, 1.85 and 1.49 in I-steel supporting roadway, bolting and shotcreting supporting roadway and flat wall supporting roadway, respectively.5) We proposed mathematical model and simulation modeling on underground ventilation system, and carried out a detailed numerical simulation,some results are obtained as follows:① Numerical simulation of underground ventilation system throughout the mine ventilation system as the research object, using the finite element analysis method to process mathematical model, the simulation method writed by Fortran for numerical calculations. The simulation can give wind speed and air volume on all units(less than 10 m of tunnel micro segment). The results can be mapped to the three-dimensional coordinates. The ventilation conditions’ change reflected by the change of section feature coefficient and boundary condition. The section feature coefficient can be defined in units(less than10 m of tunnel micro segment).② The normal, ventilation door abnormal, ventilator negative pressure decreasing, tunnel fall and mine car residence 5 state simulations showed that the numerical simulation method can stabilize and quickly compute the underground tunnel wind speed and air volume under different conditions. The numerical simulation on ventilation system airflow proposed by this article has higher precision, better availability of results and wider adaptability compared with traditional ventilation network solution algorithm.6) We proposed real time fault diagnosis method for underground ventilation system, and carried out a detailed numerical simulation, some results are obtained as follows:① Real time fault diagnosis method for underground ventilation system is based on numerical simulation of underground ventilation system. The basicdesign ideas of the method is compared the finite number of airflow values obtained by monitoring sites with normal values to get the overall error value.Then, constantly adjusting section features coefficient in each regional representative unit by a predetermined optimization methods to reduce the overall error value and comparing each region’s effect in reduce the errors and ultimately give the optimal solution in minimize errors, the optimal solution’s corresponding area is the area where the fault located. Finally, the area of the accident was further accurate calculation, and giving the distribution of the wind speed and air volume in entire underground ventilation system after the accident.② The ventilation door abnormal, ventilator negative pressure decreasing,tunnel fall and mine car residence 4 state simulations showed that the real time fault diagnosis method can accurately locate the area where has a accident. The distribution of the wind speed and air volume in entire underground ventilation system after the accident could also be obtained by this method. The real time fault diagnosis method could provide guidance for the rapid exclusion of ventilation accident.