Numerous theoretical and experimental efforts have been made to explain the dependence of the static wrink^h~g morphology on the materials' physical properties, whereas the dy- namic wrinkling process remains elusive...Numerous theoretical and experimental efforts have been made to explain the dependence of the static wrink^h~g morphology on the materials' physical properties, whereas the dy- namic wrinkling process remains elusive. In the present work, we design a wrinkling model consisting of a soft substrate and a graphene-like rigid thin film to investigate this dynamic process. The simulation shows that the whole wrinkling process includes three stages. At the incubation and wrinkling stages, the stress along the horizon direction of the soft substrate transfers to the stiff film. However, at the equilibrium stage, the stress of the rigid film slowly transfers back to the substrate although the total energy still decreases. It is found that the stress of the substrate concentrates at the top surface, especially at the trough, whereas the stress distribution of the film depends on direction. In the perpendicular direc- tion, the stress at the wave's equilibrium position surpasses that at the crest and trough and, oppositely, the stress concentrates at the crest and trough in the horizon direction. Present model reproduces both wrinkling and delamination patterns and can be a powerful tool to deeply understand the structure deformation of material induced by stress release.展开更多
Based on the developed distributed model for calculating astronomical solar radiation (ASR), monthly ASR with a resolution of 1 km×1 km for the rugged terrains of Yellow River Basin was calculated, with DEM data ...Based on the developed distributed model for calculating astronomical solar radiation (ASR), monthly ASR with a resolution of 1 km×1 km for the rugged terrains of Yellow River Basin was calculated, with DEM data as the general characterization of terrain. This model gives an all-sided consideration on factors that influence the ASR. Results suggest that (1) Annual ASR has a progressive decrease trend from south to north; (2) the magnitude order of seasonal ASR is: summer>spring>autumn>winter; (3) topographical factors have robust effect on the spatial distribution of ASR, particularly in winter when a lower sun elevation angle exists; (4) the ASR of slopes with a sunny exposure is generally 2 or 3 times that of slopes with a shading exposure and the extreme difference of ASR for different terrains is over 10 times in January; (5) the spatial differences of ASR are relatively small in summer when a higher sun elevation angle exists and the extreme difference of ASR for different terrains is only 16% in July; and (6) the sequence of topographical influence strength is: winter>autumn>spring>summer.展开更多
It is very difficult to reasonably evaluate the loads acting on coal pillars in longwall panels during the planning of a new pillar system. The application of empirical equations is a common practice in calculating co...It is very difficult to reasonably evaluate the loads acting on coal pillars in longwall panels during the planning of a new pillar system. The application of empirical equations is a common practice in calculating coal pillar loads while designing a new pillar. This paper proposes numerical models for evaluating coal pillar loads. The key of building a successful numerical model for calculating coal pillar loads lies in the fact that the model should represent the redistribution of stress all over the longwall panels and the surrounding areas, and it is especially important to include the characteristics of the stress rebuilding process in the gob areas, which are crucial for the building process of coal pillar loads. Based on the geo-mechanical background of the Baoshan Coal Mine, this paper details the procedures of applying numerical models to the evaluation of coal pillar loads and their local practices. The study results show it is feasible and reasonable to use numerical models to evaluate coal pillar loads.展开更多
Based on statistical damage mechanics,the constitutive model of a rock underthree-dimensional stress was established by the law that the statistical strength of rockmicro-element obeys Weibull distribution.The acousti...Based on statistical damage mechanics,the constitutive model of a rock underthree-dimensional stress was established by the law that the statistical strength of rockmicro-element obeys Weibull distribution.The acoustic emission (AE) evolution model ofrock failure was put forward according to the view that rock damage and AE were consistent.Moreover,in the failure process of rock under three-dimensional stress,the change inrelationship between stress condition parameter and the characteristic parameters of AE,such as the event number and its change rate,were studied.Also,the rock AE characteristicunder uniaxial compression was analyzed in theory and verified with examples.Theresults indicate that the cumulative event number and change rate of AE in rock failure aredetermined by stress state parameter F.Along with the gradual increase of F,first the cumulativeevent number increases gradually,then rapidly,and then slowly after the stresspeak.The form of change rate of an event by increasing F is consistent with the distributionform of rock micro-element strength.The model explained the phenomenon that a relativelyquiet period of AE appears before rock rupture that is observed by many researchersin experiments.Verification examples indicate that the AE evolution model is consistentwith the test results,so the model is reasonable and correct.展开更多
A method based on solution of the inverse heat conduction problem was presented for online stress monitoring and fatigue life analysis of boiler drums. The mathematical model of the drum temperature distribution is ba...A method based on solution of the inverse heat conduction problem was presented for online stress monitoring and fatigue life analysis of boiler drums. The mathematical model of the drum temperature distribution is based on the assumptions that the difference of temperature along the longitudinal axis of the boiler drum is negligible with changes only in the radial direction and the circumferential direction, and that the outer surface of drum is thermaUy insulated. Combining this model with the control-volume method provides temperatures at different points on a cross-section of the drum. With the temperature data, the stresses and the life expectancy of the boiler drum are derived according to the ASME code. Applying this method to the cold start-up process of a 300 MW boiler demonstrated the absence of errors caused by the boundary condition assumptions on the inner surface of the drum and testified that the method is an applicable technique for the online stress monitoring and fatigue life analysis of boiler drums.展开更多
The purpose of this paper is to reveal the stress distribution characteristic along the full length anchor bolt. Based on the mechanic model set up, the author calculated the anchor mechanism of the full length resin ...The purpose of this paper is to reveal the stress distribution characteristic along the full length anchor bolt. Based on the mechanic model set up, the author calculated the anchor mechanism of the full length resin rock bolt. The stress distribution characteristic is different according to different type of surrounding rock. The conclusion is important to optimize the roadway bolt support design.展开更多
基金the High Performance Computing Center of Tianjin University, China and the National Natural Science Foundation of China (No.91127046, No.21274107, and No.21474075).
文摘Numerous theoretical and experimental efforts have been made to explain the dependence of the static wrink^h~g morphology on the materials' physical properties, whereas the dy- namic wrinkling process remains elusive. In the present work, we design a wrinkling model consisting of a soft substrate and a graphene-like rigid thin film to investigate this dynamic process. The simulation shows that the whole wrinkling process includes three stages. At the incubation and wrinkling stages, the stress along the horizon direction of the soft substrate transfers to the stiff film. However, at the equilibrium stage, the stress of the rigid film slowly transfers back to the substrate although the total energy still decreases. It is found that the stress of the substrate concentrates at the top surface, especially at the trough, whereas the stress distribution of the film depends on direction. In the perpendicular direc- tion, the stress at the wave's equilibrium position surpasses that at the crest and trough and, oppositely, the stress concentrates at the crest and trough in the horizon direction. Present model reproduces both wrinkling and delamination patterns and can be a powerful tool to deeply understand the structure deformation of material induced by stress release.
基金Major State Basic Research Development Program of ChinaNo.G19990436-01 No.G20000779
文摘Based on the developed distributed model for calculating astronomical solar radiation (ASR), monthly ASR with a resolution of 1 km×1 km for the rugged terrains of Yellow River Basin was calculated, with DEM data as the general characterization of terrain. This model gives an all-sided consideration on factors that influence the ASR. Results suggest that (1) Annual ASR has a progressive decrease trend from south to north; (2) the magnitude order of seasonal ASR is: summer>spring>autumn>winter; (3) topographical factors have robust effect on the spatial distribution of ASR, particularly in winter when a lower sun elevation angle exists; (4) the ASR of slopes with a sunny exposure is generally 2 or 3 times that of slopes with a shading exposure and the extreme difference of ASR for different terrains is over 10 times in January; (5) the spatial differences of ASR are relatively small in summer when a higher sun elevation angle exists and the extreme difference of ASR for different terrains is only 16% in July; and (6) the sequence of topographical influence strength is: winter>autumn>spring>summer.
文摘It is very difficult to reasonably evaluate the loads acting on coal pillars in longwall panels during the planning of a new pillar system. The application of empirical equations is a common practice in calculating coal pillar loads while designing a new pillar. This paper proposes numerical models for evaluating coal pillar loads. The key of building a successful numerical model for calculating coal pillar loads lies in the fact that the model should represent the redistribution of stress all over the longwall panels and the surrounding areas, and it is especially important to include the characteristics of the stress rebuilding process in the gob areas, which are crucial for the building process of coal pillar loads. Based on the geo-mechanical background of the Baoshan Coal Mine, this paper details the procedures of applying numerical models to the evaluation of coal pillar loads and their local practices. The study results show it is feasible and reasonable to use numerical models to evaluate coal pillar loads.
基金Supported by the Key Program of National Basic Research Program(973)of China(2005CB221505)the National Natural Science Foundation of China(2005E041503)
文摘Based on statistical damage mechanics,the constitutive model of a rock underthree-dimensional stress was established by the law that the statistical strength of rockmicro-element obeys Weibull distribution.The acoustic emission (AE) evolution model ofrock failure was put forward according to the view that rock damage and AE were consistent.Moreover,in the failure process of rock under three-dimensional stress,the change inrelationship between stress condition parameter and the characteristic parameters of AE,such as the event number and its change rate,were studied.Also,the rock AE characteristicunder uniaxial compression was analyzed in theory and verified with examples.Theresults indicate that the cumulative event number and change rate of AE in rock failure aredetermined by stress state parameter F.Along with the gradual increase of F,first the cumulativeevent number increases gradually,then rapidly,and then slowly after the stresspeak.The form of change rate of an event by increasing F is consistent with the distributionform of rock micro-element strength.The model explained the phenomenon that a relativelyquiet period of AE appears before rock rupture that is observed by many researchersin experiments.Verification examples indicate that the AE evolution model is consistentwith the test results,so the model is reasonable and correct.
基金Funded by the National Science and Technology Support Project of China (No. 2006BAA03B02-03)
文摘A method based on solution of the inverse heat conduction problem was presented for online stress monitoring and fatigue life analysis of boiler drums. The mathematical model of the drum temperature distribution is based on the assumptions that the difference of temperature along the longitudinal axis of the boiler drum is negligible with changes only in the radial direction and the circumferential direction, and that the outer surface of drum is thermaUy insulated. Combining this model with the control-volume method provides temperatures at different points on a cross-section of the drum. With the temperature data, the stresses and the life expectancy of the boiler drum are derived according to the ASME code. Applying this method to the cold start-up process of a 300 MW boiler demonstrated the absence of errors caused by the boundary condition assumptions on the inner surface of the drum and testified that the method is an applicable technique for the online stress monitoring and fatigue life analysis of boiler drums.
文摘The purpose of this paper is to reveal the stress distribution characteristic along the full length anchor bolt. Based on the mechanic model set up, the author calculated the anchor mechanism of the full length resin rock bolt. The stress distribution characteristic is different according to different type of surrounding rock. The conclusion is important to optimize the roadway bolt support design.