The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial load...The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial loading rate in coal and rock mechanics test.Therefore,uniaxial compression tests under various loading rates of 0.05,0.1,0.15,0.25,0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones.The results show that 1)the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing;2)with the loading rate increasing,the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover,the failure mode gradually transfers from type I to type III;3)With the loading rate increasing,the total input strain energy,elastic strain energy,and dissipated strain energy generally increase;4)the damage variable presents the evolution characteristics of inverted“S”shape with time,and with the loading rate increasing,the damage degree of the deep sandstone is aggravated.The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.展开更多
According to the characteristics of deep engineering surrounding rock main shaft of No.3 mining district in Jinchuan, electron microscope scanning and rock mechanics test were adopted to analyze the damage features of...According to the characteristics of deep engineering surrounding rock main shaft of No.3 mining district in Jinchuan, electron microscope scanning and rock mechanics test were adopted to analyze the damage features of rock. The software of FLAG3D and Burgers body （Kelvin-Maxwell model） were used to research on rheological theory, and rheological model was modified. The results indicate that the damage of rock mass is very serious, and the rheological characteristics also outstanding; rheological behavior of deep surrounding rocks of the shaft can be taken as superposition of transient and stable rheology; and there exist the most dangerous zone on 100 m higher than 1 063 m level, so it is necessity that works of monitor and corresponding reinforcement should strengthen.展开更多
Prostaglandin E_2 (PGE2) levels in gingival crevicular fluid (GCF) of 46 normal controls and 90 patients suffering from periodontitis with different periodontal pocket depths were measured by radioimmunoassay (RLA).Th...Prostaglandin E_2 (PGE2) levels in gingival crevicular fluid (GCF) of 46 normal controls and 90 patients suffering from periodontitis with different periodontal pocket depths were measured by radioimmunoassay (RLA).The results demonstrated that PGE2 levels in the GCF of the periodontal pockets are higher in patients with periodontitis.The PGE2 level rises as the periodontal pocket deepens, especially in cases where the periodontal pocket depth exceeds 6 mm. This study shows that the PGE2 level is significantly related to the severity of bone destruction in periodontitis.展开更多
Deformation and failure of deep clay samples are closely related to energy changes.Investigating the energy conversion and damage behavior of deep clay during loading and unloading tests has important significance for...Deformation and failure of deep clay samples are closely related to energy changes.Investigating the energy conversion and damage behavior of deep clay during loading and unloading tests has important significance for prevention-control of soil destabilization damage caused by mine shaft excavation.In the present work,triaxial tests of consolidated clay under different stress paths and stress rates were conducted.The results reveal that the mechanical properties of soils have strong stress rate effects and the samples mainly experience energy storage in the elastic stage,after that,the energy conversion mainly undergoes an increase of dissipative energy and release of elastic energy,which is also confirmed by the results of the analysis in the subsequent CT tests.Two damage indicators were compared,finding that the indicator based on dissipative energy has more obvious differences in two stress paths and can be used as a better indicator to describe the damage evolution of soils.Finally,in the triaxial shear test,due to the unloading effect of confining pressure,the damage of soils increased more rapidly near breaking than in the triaxial compression test,which indicates that the damage caused by unloading on deep soil is more abrupt than that caused by loading.展开更多
To improve the accuracy and anti-noise ability of the structural damage identification method,a bridge damage identification method is proposed based on a deep belief network(DBN).The output vector is used to establis...To improve the accuracy and anti-noise ability of the structural damage identification method,a bridge damage identification method is proposed based on a deep belief network(DBN).The output vector is used to establish the nonlinear mapping relationship between the mode shape and structural damage.The hidden layer of the DBN is trained through a layer-by-layer pre-training.Finally,the backpropagation algorithm is used to fine-tune the entire network.The method is validated using a numerical model of a steel truss bridge.The results show that under the influence of noise and modeling uncertainty,the damage identification method based on the DBN can identify the accurate damage location and degree identification compared with the traditional damage identification method based on an artificial neural network.展开更多
The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit dia...The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.展开更多
Research into the characteristics of geothermal fields is important for the control of heat damage in mines. Based on measured geothermal data of boreholes from 200 m to 1200 m in a Jiahe Coal Mine, we demonstrate non...Research into the characteristics of geothermal fields is important for the control of heat damage in mines. Based on measured geothermal data of boreholes from 200 m to 1200 m in a Jiahe Coal Mine, we demonstrate non-linear but increasing relations of both geo-temperatures and geothermal gradients with increases depth. Numerically, we fitted the relationship between geo-temperatures and depth, a first-order exponential decay curve, formulated as: T(h) = 4.975 + 23.08 exp(h/1736.1).展开更多
Objective To observe the therapeutic effect of intensive and deep needling method of fire-needle for chronic gluteus medius impairment. Methods The tenderness of anterior superior iliac spine which was the starting po...Objective To observe the therapeutic effect of intensive and deep needling method of fire-needle for chronic gluteus medius impairment. Methods The tenderness of anterior superior iliac spine which was the starting point of gluteus medius was taken as the center, i cm around it, 4-8 needle insertion points were fixed. Fire-needle with intensive and deep needling method was applied deeply on the surface of the bone then immediately taken out. The treatment was given once every 3 days, 3 times as a course. Results After 2 courses, 22 cases were fully recovered, 22 cases with remarkable effect, 4 cases without effect, and the total effective rate was 92.5%. Conclusion Fire- needle with intensive and deep needling method has remarkable therapeutic effect.展开更多
A simplified empirical model for fatigue analysis of deepwater marine risers due to vortex-induced vibration (VIV) in non-uniform current is presented. A simplified modal vibration equation is employed according to th...A simplified empirical model for fatigue analysis of deepwater marine risers due to vortex-induced vibration (VIV) in non-uniform current is presented. A simplified modal vibration equation is employed according to the characteristics of deepwater top tensioned risers. The response amplitude of each mode is determined by a balance between the energy feeding into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainder based on the data from self-excited oscillation and forced oscillation experiments of rigid cylinders. Multi-modal VIV fatigue loading is obtained by the square root of the sum of squares approach. Compared with previous works, this model can take fully account of the main intrinsic natures of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping. In addition, a closed form solution of fatigue damage is presented for the case of a riser with uniform mass and cross-section oscillating in a uniform flow. Fatigue analysis of a typical deepwater riser operating in Gulf of Mexico and West Africa shows that the current velocity profiles affect the riser’s fatigue life significantly and the most dangerous locations of the riser are also pointed out.展开更多
基金Projects(52034009, 51974319) supported by the National Natural Science Foundation of ChinaProject(2020JCB01)supported by the Yue Qi Distinguished Scholar Project of China。
文摘The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial loading rate in coal and rock mechanics test.Therefore,uniaxial compression tests under various loading rates of 0.05,0.1,0.15,0.25,0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones.The results show that 1)the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing;2)with the loading rate increasing,the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover,the failure mode gradually transfers from type I to type III;3)With the loading rate increasing,the total input strain energy,elastic strain energy,and dissipated strain energy generally increase;4)the damage variable presents the evolution characteristics of inverted“S”shape with time,and with the loading rate increasing,the damage degree of the deep sandstone is aggravated.The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.
基金Supported by the National Natural Science Foundation of China(50874042)Key Projects in the National Science & Technology Pillar Program in the Eleventh Five-Year Plan Period(2008BAB32B01)
文摘According to the characteristics of deep engineering surrounding rock main shaft of No.3 mining district in Jinchuan, electron microscope scanning and rock mechanics test were adopted to analyze the damage features of rock. The software of FLAG3D and Burgers body （Kelvin-Maxwell model） were used to research on rheological theory, and rheological model was modified. The results indicate that the damage of rock mass is very serious, and the rheological characteristics also outstanding; rheological behavior of deep surrounding rocks of the shaft can be taken as superposition of transient and stable rheology; and there exist the most dangerous zone on 100 m higher than 1 063 m level, so it is necessity that works of monitor and corresponding reinforcement should strengthen.
文摘Prostaglandin E_2 (PGE2) levels in gingival crevicular fluid (GCF) of 46 normal controls and 90 patients suffering from periodontitis with different periodontal pocket depths were measured by radioimmunoassay (RLA).The results demonstrated that PGE2 levels in the GCF of the periodontal pockets are higher in patients with periodontitis.The PGE2 level rises as the periodontal pocket deepens, especially in cases where the periodontal pocket depth exceeds 6 mm. This study shows that the PGE2 level is significantly related to the severity of bone destruction in periodontitis.
基金Project(2016YFC0600904)supported by the National Key Research and Development Program of ChinaProject(BK20200653)supported by the Natural Science Foundation of Jiangsu,ChinaProject(2020M681768)supported by the China Postdoctoral Science Foundation。
文摘Deformation and failure of deep clay samples are closely related to energy changes.Investigating the energy conversion and damage behavior of deep clay during loading and unloading tests has important significance for prevention-control of soil destabilization damage caused by mine shaft excavation.In the present work,triaxial tests of consolidated clay under different stress paths and stress rates were conducted.The results reveal that the mechanical properties of soils have strong stress rate effects and the samples mainly experience energy storage in the elastic stage,after that,the energy conversion mainly undergoes an increase of dissipative energy and release of elastic energy,which is also confirmed by the results of the analysis in the subsequent CT tests.Two damage indicators were compared,finding that the indicator based on dissipative energy has more obvious differences in two stress paths and can be used as a better indicator to describe the damage evolution of soils.Finally,in the triaxial shear test,due to the unloading effect of confining pressure,the damage of soils increased more rapidly near breaking than in the triaxial compression test,which indicates that the damage caused by unloading on deep soil is more abrupt than that caused by loading.
基金The National Natural Science Foundation of China(No.51378104)。
文摘To improve the accuracy and anti-noise ability of the structural damage identification method,a bridge damage identification method is proposed based on a deep belief network(DBN).The output vector is used to establish the nonlinear mapping relationship between the mode shape and structural damage.The hidden layer of the DBN is trained through a layer-by-layer pre-training.Finally,the backpropagation algorithm is used to fine-tune the entire network.The method is validated using a numerical model of a steel truss bridge.The results show that under the influence of noise and modeling uncertainty,the damage identification method based on the DBN can identify the accurate damage location and degree identification compared with the traditional damage identification method based on an artificial neural network.
基金Science and Engineering Research Board,Government of India(ECR/2016/001402)BITS-Pilani,Hyderabad Campus。
文摘The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.
基金Financial support for this project,provided by the National Basic Research Program of China (No.2006CB202200)the Key Project of National Natural Science Foundation of China+1 种基金the Program for Changjiang Scholars,Innovative Research Team in University of China (No.IRT0656)the Fundamental Research Funds for the Central Universities (No.2010QL04)
文摘Research into the characteristics of geothermal fields is important for the control of heat damage in mines. Based on measured geothermal data of boreholes from 200 m to 1200 m in a Jiahe Coal Mine, we demonstrate non-linear but increasing relations of both geo-temperatures and geothermal gradients with increases depth. Numerically, we fitted the relationship between geo-temperatures and depth, a first-order exponential decay curve, formulated as: T(h) = 4.975 + 23.08 exp(h/1736.1).
文摘Objective To observe the therapeutic effect of intensive and deep needling method of fire-needle for chronic gluteus medius impairment. Methods The tenderness of anterior superior iliac spine which was the starting point of gluteus medius was taken as the center, i cm around it, 4-8 needle insertion points were fixed. Fire-needle with intensive and deep needling method was applied deeply on the surface of the bone then immediately taken out. The treatment was given once every 3 days, 3 times as a course. Results After 2 courses, 22 cases were fully recovered, 22 cases with remarkable effect, 4 cases without effect, and the total effective rate was 92.5%. Conclusion Fire- needle with intensive and deep needling method has remarkable therapeutic effect.
基金the National High Technology Research and Development Program (863) of China(No. 2006AA09A107)
文摘A simplified empirical model for fatigue analysis of deepwater marine risers due to vortex-induced vibration (VIV) in non-uniform current is presented. A simplified modal vibration equation is employed according to the characteristics of deepwater top tensioned risers. The response amplitude of each mode is determined by a balance between the energy feeding into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainder based on the data from self-excited oscillation and forced oscillation experiments of rigid cylinders. Multi-modal VIV fatigue loading is obtained by the square root of the sum of squares approach. Compared with previous works, this model can take fully account of the main intrinsic natures of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping. In addition, a closed form solution of fatigue damage is presented for the case of a riser with uniform mass and cross-section oscillating in a uniform flow. Fatigue analysis of a typical deepwater riser operating in Gulf of Mexico and West Africa shows that the current velocity profiles affect the riser’s fatigue life significantly and the most dangerous locations of the riser are also pointed out.
