Efcient and accurate monitoring and early warning of coal dynamic disaster and other disasters can provide guarantee for the efcient operation of mine transportation system.However,the traditional threshold early warn...Efcient and accurate monitoring and early warning of coal dynamic disaster and other disasters can provide guarantee for the efcient operation of mine transportation system.However,the traditional threshold early warning method often fails to warning some accidents.To address above issues,a new early warning method was proposed based on"quiet period"phenomenon of AE and EMR during fracture.It is found that,a"quiet period"of AE and EMR was present before the load reaches the peak stress,which could be used as one of the precursors to warn the imminent failure of coal and rock specimens.MS and AE signals increased abnormally followed by the phenomenon of"quiet period"before the occurrence of coal dynamic disaster on site,and the decrease of MS events in the"quiet period"is about 57%–88%compared with that in previous abnormal increase stage.During the damage evolution of coal and rock,"quiet period"phenomenon usually occurred at 85%–90%of the peak stress,where the slope of damage parameter curve is almost zero.The"quiet period"of the AE-EMR signals and the low change rate of damage parameter before failure provide a theoretical foundation for the coal dynamic disaster warning based on the"quiet period"precursor found in MS-AE-EMR monitoring system.These fndings will help reduce the number of under-reported events and improve early warning accuracy.展开更多
In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the e...In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.展开更多
This paper investigates the performance of the latest International Reference Ionosphere model to predict the critical frequency at low latitudes in the African region. The variability of the critical frequency of the...This paper investigates the performance of the latest International Reference Ionosphere model to predict the critical frequency at low latitudes in the African region. The variability of the critical frequency of the F2 layer of the ionosphere (foF2) is studied for the different seasons of the phase minimum of solar cycle 22 during quiet geomagnetic activity at the Ouagadougou station. The data used are those provided by the ionosonde and the predictions of the two subprograms: International Radio Consultative Committee (CCIR) and International Radio-Scientific Union (URSI) of the 2016 version of the International Reference Ionosphere model. This study shows that, in general, URSI and CCIR of the IRI-2016 model are able to reproduce fairly well the variability of the critical frequency of the F2 layer of the ionosphere at low latitudes during the phase minimum at the Ouagadougou station. However, the model shows an almost homogeneous overestimation of the foF2 during the four seasons studied. The good response is observed between 0700 TL and 1900 TL for the available data. The agreement between the subroutine responses and the observed results is between reasonable and poor. The best match state response is obtained in winter with the CCIR subroutine. These results show that there is a need to improve both CCIR and URSI subroutines of the IRI-2016 model in low latitudes in the African region.展开更多
基金supported by Grants from the National Natural Science Foundation of China(No.52004016)the Postdoctoral Research Foundation of China(No.2021M700371)+3 种基金the Major Science and Technology Innovation Project of Shandong Province(No.2019SDZY02)the Open Fund Project of Shaanxi Key Laboratory of Prevention and Control Technology for Coal Mine Water Hazard(No.2021SKMS05)Science and Technology Support Plan Project of Guizhou Province(No.[2021]515)The authors are grateful to the anonymous referees for their precious comments and suggestions.
文摘Efcient and accurate monitoring and early warning of coal dynamic disaster and other disasters can provide guarantee for the efcient operation of mine transportation system.However,the traditional threshold early warning method often fails to warning some accidents.To address above issues,a new early warning method was proposed based on"quiet period"phenomenon of AE and EMR during fracture.It is found that,a"quiet period"of AE and EMR was present before the load reaches the peak stress,which could be used as one of the precursors to warn the imminent failure of coal and rock specimens.MS and AE signals increased abnormally followed by the phenomenon of"quiet period"before the occurrence of coal dynamic disaster on site,and the decrease of MS events in the"quiet period"is about 57%–88%compared with that in previous abnormal increase stage.During the damage evolution of coal and rock,"quiet period"phenomenon usually occurred at 85%–90%of the peak stress,where the slope of damage parameter curve is almost zero.The"quiet period"of the AE-EMR signals and the low change rate of damage parameter before failure provide a theoretical foundation for the coal dynamic disaster warning based on the"quiet period"precursor found in MS-AE-EMR monitoring system.These fndings will help reduce the number of under-reported events and improve early warning accuracy.
文摘In this paper we simulate the repeated occurrence of strong earthquakes along a strike-slip fault by using a finite element model. The fault valve mechanism is included in the model in order to take into account the effeCt of POre fluid pressure variation. Five parameters are used to characterize the rheology of the fault, POre pressure variation, and fracture criteria. By Systematically varying these parameters and calculating a large number of models we carried out a preliminary investigation on the alternatively quiet and active periods of seismicity and their relation to model Parameters and loading conditions. Under the action of a constant-rate boundary movement, in the case of intermediate stress and pore pressure, the models display a regular quiescence-activity phenomenon with a cycle length of 1/3-1 of the recurrence pened. When the model is under high stress or high pore pressure, this phenomenon becomes irregular or inexplicit. When the model is subject to periedic boundary forces and the amplitude of force variation is not too small, it results in an alternatively quiet and active seismicity Pattern with the same Period Of the force variation.
文摘This paper investigates the performance of the latest International Reference Ionosphere model to predict the critical frequency at low latitudes in the African region. The variability of the critical frequency of the F2 layer of the ionosphere (foF2) is studied for the different seasons of the phase minimum of solar cycle 22 during quiet geomagnetic activity at the Ouagadougou station. The data used are those provided by the ionosonde and the predictions of the two subprograms: International Radio Consultative Committee (CCIR) and International Radio-Scientific Union (URSI) of the 2016 version of the International Reference Ionosphere model. This study shows that, in general, URSI and CCIR of the IRI-2016 model are able to reproduce fairly well the variability of the critical frequency of the F2 layer of the ionosphere at low latitudes during the phase minimum at the Ouagadougou station. However, the model shows an almost homogeneous overestimation of the foF2 during the four seasons studied. The good response is observed between 0700 TL and 1900 TL for the available data. The agreement between the subroutine responses and the observed results is between reasonable and poor. The best match state response is obtained in winter with the CCIR subroutine. These results show that there is a need to improve both CCIR and URSI subroutines of the IRI-2016 model in low latitudes in the African region.
基金Projects (2013BAB02B01, 2013BAB02B03) supported by the Key Projects in the National Science & Technoogy Pillar Program During the Twelfth Five-Year Plan PeriodProjects (51274055, 51204030, 51204031, 51109035) supported by the National Natural Science Foundation of ChinaProjects (N110301006, N110501001, N110401003) supportecd by the Fundamental Research Funds for the Central Unviersity, China
