By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mech...By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mechanism of main roof first breaking is revealed, and the asymmetry breaking parameter is determined at all.展开更多
Using general multi-phase-field model,detailed microstructures corresponding to different initial lamellar sets were simulated in a binary eutectic alloy with an asymmetric phase diagram.The simulation results show th...Using general multi-phase-field model,detailed microstructures corresponding to different initial lamellar sets were simulated in a binary eutectic alloy with an asymmetric phase diagram.The simulation results show that regular or unstable oscillating lamellar structures depend on the initial lamellar widths of two solid phases.A lamellar morphology map associating with the initial widths has been derived,which is capable of showing the condition of forming various lamella structures.For instance,a regular lamella was formed with fast solidification while large lamella resulted from disorder growth with low interfacial velocity. The investigated interface velocities indicate that with fast solidification to form regular lamella,a disorder growth manner or a large lamellar spacing causes a low interface velocity.These results are in good agreement with those proposed by Jackson-Hunt model.展开更多
Shell-and-tube vaporizers are the most commonly used and dominated types of vaporizers in liquefied natural gas （LNG） realm. Due to efficient performance, shell-side flow in this type of vaporizers has received cons...Shell-and-tube vaporizers are the most commonly used and dominated types of vaporizers in liquefied natural gas （LNG） realm. Due to efficient performance, shell-side flow in this type of vaporizers has received considerable attention and has been investigated extensively. However, the detailed flow structure in the shell needs to be determined for reliable and effective design. Therefore, the objective of this study was to clarify the flow structure in shell by particle image velocimetry （PIV）. Experiments were conducted using two types of model; 15% baffle cut having inlet and outlet positions !n the direction of 90° to the cut and 30% baffle cut having inlet and outlet positions in the direction of 180° to the cut. Each test section is 169 mm in inner diameter and 344.6 mm in length. The flow features were characterized in different baffle cuts with regards to the velocity vector field and velocity distribution. The results show that the flow characteristics of 15% baffle cut type vaporizer are comparable to those of 30% baffle cut type vaporizer.展开更多
The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification...The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.展开更多
The mineral phases and structure of pincer for the freshwater lobster were analyzed and observed by using X-ray diffraction and field-emission scanning electronic microscope with energy dispersive spectroscopy, and th...The mineral phases and structure of pincer for the freshwater lobster were analyzed and observed by using X-ray diffraction and field-emission scanning electronic microscope with energy dispersive spectroscopy, and the mechanical properties of pincer were determined by using nano-indenter and micro-tribometer. The results showed that the pincers contained Ca, Mg, C, O, Na, etc. elements and there were many amorphous mineral phases in the lobster pincers. There were many concave hollows and convex domes with seta on the surface of pincer, and some spines were observed on the surface of seta, which exhibited non-smooth surface. The exoskeleton of pincer consisted of epicuticle, exocuticle and endocuticle, and the microstructure of exocuticle and endocuticle displayed the twisted plywood structure with chitin protein fibers. The mean hardness and elastic modulus on the surface of fresh pincers were 0.27 GPa and 5.28 GPa, respectively. With the increase in distance from the surface, the hardness and elastic modulus all decreased gradually. This indicated that the transition of hardness and elastic modulus occurred from exocuticle to endocuticle. When the heat treatment temperature was lower than 200°C, the values of hardness and elastic modulus fluctuated slightly, while they increased at the temperature beyond 200°C. As the pincers slid against Si3N4 balls in water and air, the friction coefficients in water were higher than those in air. The research could provide a bio-inspired basis for the structural design of composite materials and anti-friction surface.展开更多
文摘By field observation and simulating test in shallow seam longwall mining, the asymmetry breaking of main roof is discovered during the first weighting. Based on simulating model test and theoretical analysis, the mechanism of main roof first breaking is revealed, and the asymmetry breaking parameter is determined at all.
基金Projects(50771041,50801019)supported by the National Natural Science Foundation of ChinaProject(20080430909)supported by China Postdoctoral Science FoundationProject(HITQNJS.2008.018)supported by Development Program for Outstanding Young Teachers in Harbin Institute of Technology,China
文摘Using general multi-phase-field model,detailed microstructures corresponding to different initial lamellar sets were simulated in a binary eutectic alloy with an asymmetric phase diagram.The simulation results show that regular or unstable oscillating lamellar structures depend on the initial lamellar widths of two solid phases.A lamellar morphology map associating with the initial widths has been derived,which is capable of showing the condition of forming various lamella structures.For instance,a regular lamella was formed with fast solidification while large lamella resulted from disorder growth with low interfacial velocity. The investigated interface velocities indicate that with fast solidification to form regular lamella,a disorder growth manner or a large lamellar spacing causes a low interface velocity.These results are in good agreement with those proposed by Jackson-Hunt model.
基金supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2010-013-D00007)2010 Research Professor Fund of Gyeongsang National University,Korea
文摘Shell-and-tube vaporizers are the most commonly used and dominated types of vaporizers in liquefied natural gas （LNG） realm. Due to efficient performance, shell-side flow in this type of vaporizers has received considerable attention and has been investigated extensively. However, the detailed flow structure in the shell needs to be determined for reliable and effective design. Therefore, the objective of this study was to clarify the flow structure in shell by particle image velocimetry （PIV）. Experiments were conducted using two types of model; 15% baffle cut having inlet and outlet positions !n the direction of 90° to the cut and 30% baffle cut having inlet and outlet positions in the direction of 180° to the cut. Each test section is 169 mm in inner diameter and 344.6 mm in length. The flow features were characterized in different baffle cuts with regards to the velocity vector field and velocity distribution. The results show that the flow characteristics of 15% baffle cut type vaporizer are comparable to those of 30% baffle cut type vaporizer.
基金Project(2009CB724504)supported by the National Basic Research Program of China
文摘The oil-pressboard insulation is a typical composite insulation system widely used in the design and manufactory of large power apparatus. The implement of oil-pressboard insulation may lead to surface electrification and discharge at the interface under certain condition. It is of significant importance to take an insight into the phenomenon occurring at the interface. Through experiment, the pressboard is found as a porous material. The interface changes abruptly from bulk pressboard to the bulk oil as a result of the porous structure. A new model is proposed which divides the interface into bulk oil region, transition region, and bulk pressboard region. The width of the transition region is decided according to the microtome figure. The effective permittivity of the transition region is calculated using a new model based on fractal theory. The model is validated and compared with previous calculation model. The effect of the existence of transition region on the electric field distribution is discussed.
基金supported by the National Natural Science Foundation of China (Grant No. 50635030)
文摘The mineral phases and structure of pincer for the freshwater lobster were analyzed and observed by using X-ray diffraction and field-emission scanning electronic microscope with energy dispersive spectroscopy, and the mechanical properties of pincer were determined by using nano-indenter and micro-tribometer. The results showed that the pincers contained Ca, Mg, C, O, Na, etc. elements and there were many amorphous mineral phases in the lobster pincers. There were many concave hollows and convex domes with seta on the surface of pincer, and some spines were observed on the surface of seta, which exhibited non-smooth surface. The exoskeleton of pincer consisted of epicuticle, exocuticle and endocuticle, and the microstructure of exocuticle and endocuticle displayed the twisted plywood structure with chitin protein fibers. The mean hardness and elastic modulus on the surface of fresh pincers were 0.27 GPa and 5.28 GPa, respectively. With the increase in distance from the surface, the hardness and elastic modulus all decreased gradually. This indicated that the transition of hardness and elastic modulus occurred from exocuticle to endocuticle. When the heat treatment temperature was lower than 200°C, the values of hardness and elastic modulus fluctuated slightly, while they increased at the temperature beyond 200°C. As the pincers slid against Si3N4 balls in water and air, the friction coefficients in water were higher than those in air. The research could provide a bio-inspired basis for the structural design of composite materials and anti-friction surface.
