The uniform design and response surface methodology (RSM) are applied to the multi-objective optimization of a 2-D mixed compression scramjet inlet. The set of experimental design points on the design space is selec...The uniform design and response surface methodology (RSM) are applied to the multi-objective optimization of a 2-D mixed compression scramjet inlet. The set of experimental design points on the design space is selected by the uniform design, and the inlet performance is analyzed by computational fluid dynamics (CFD). Then complete quadratic polynomial response surface approximation models are constructed based on the performance analysis results and then used to replace theoriginal complex inlet performance model. The optimization is conducted using a multi-objective genetic algorithm NSGA-Ⅱ, and the Pareto optimal solution set is obtained. Results show that the uniform design and RSM can reduce the computational complexity of numerical simulation and improve the optimization efficiency.展开更多
The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Resul...The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.展开更多
Measuring the internal velocity of debris flows is very important for debris flow dynamics research and designing debris flow control works. However, there is no appropriate method for measuring the internal velocity ...Measuring the internal velocity of debris flows is very important for debris flow dynamics research and designing debris flow control works. However, there is no appropriate method for measuring the internal velocity because of the destructive power of debris flow process. In this paper, we address this problem by using the relationship between velocity and kinetic pressure, as described by surface velocity and surface kinetic pressure data. Kinetic pressure is the difference of impact pressure and static pressure. The former is detected by force sensors installed in the flow direction at the sampling section. Observations show that static pressure can be computed using the formula for static water pressure by simply substituting water density for debris flow density. We describe the relationship between surface velocity and surface kinetic pressure using data from seven laboratory flume experiments. It is consistent with the relationship for single phase flow, which is the measurement principle of the Pitot tube.展开更多
The loads of shock wave effect on fabricated anti-blast wail and distribution law around the wall were investigated by using near surface explosion test method and FEM. The pressure-time histories and variety law on t...The loads of shock wave effect on fabricated anti-blast wail and distribution law around the wall were investigated by using near surface explosion test method and FEM. The pressure-time histories and variety law on the foreside and backside of the anti-blast wall were adopted in the tests of variety of different explosion distances and dynamites, as well as in the comparison between the test and numerical calculation. The test results show that the loads of shock wave effect on the anti-blast wall were es- sen-tially consistent with calculation results using criterion under surface explosion when explosion dis- tances exceed 2 m, the distribution of overpressure behind wall was gained according to variety law based on small-large-small. It is also demonstrated that the peak overpressure behind wall had com- monly appeared in wall height by 1.5--2.5 multiples, and the peak overpressures of protective building behind wall could be reduced effectively by using the fabricated anti-blast wall.展开更多
According to the movement and change rules of mechanical structure of surrounding rock coal mass system during coal excavation, the mechanism of sudden instability and damage was found out. The criterions that disting...According to the movement and change rules of mechanical structure of surrounding rock coal mass system during coal excavation, the mechanism of sudden instability and damage was found out. The criterions that distinguishing the occurring of the pressure bump were put forward. This criteria have been applied successfully in the comprehensive prevent of pressure bumps in Tangshan colliery.展开更多
Ground improvement has been used on many construction sites to densify granular materials, in other word, to improve soil properties and reduce potential settlement. This work presents a case study of ground improveme...Ground improvement has been used on many construction sites to densify granular materials, in other word, to improve soil properties and reduce potential settlement. This work presents a case study of ground improvement using rapid impact compaction (RIC). The research site comprises the construction of workshop and depots as part of railway development project at Batu Gajah-Ipoh, Malaysia. In-situ testing results show that the subsurface soil comprises mainly of sand and silty sand through the investigated depth extended to 10 m. Groundwater is approximately 0.5 m below the ground surface. Evaluation of improvement was based on the results of pre- and post-improvement cone penetration test (CPT). Interpretation software has been used to infer soil properties. Load test was conducted to estimate soil settlement. It is found that the technique succeeds in improving soil properties namely the relative density increases from 45% to 70%, the friction angle of soil is increased by an average of 3°, and the soil settlement is reduced by 50%: The technique succeeds in improving soil properties to approximately 5.0 m in depth depending on soil uniformity with depth.展开更多
This paper suggested to reformulate cylindrical deep drawing parameters with dimensionless form. A diagram, in which a feasible zone is drawn to bound both the maximal allowable tension and compression stress during t...This paper suggested to reformulate cylindrical deep drawing parameters with dimensionless form. A diagram, in which a feasible zone is drawn to bound both the maximal allowable tension and compression stress during the deep drawing process, was established. Since it is presented in a dimensionless form, it may be applied for both conventional and micro deep drawing. Cylindrical cup deep drawing was taken as an example to show the dimensionless process design method. In addition, the size effects should be taken into account. Two kinds of size effects on micro deep drawing were investigated, which can be explained by surface layer model and strain gradient model. Numerical simulations were carried out to compare the strain distribution with or without consideration of size effect.展开更多
This paper is aimed at the streamers in natural esters (vegetable oils) in point--plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are invest...This paper is aimed at the streamers in natural esters (vegetable oils) in point--plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are investigated. Six untreated commercial oils extracted from grape seeds, sunflower and rape seeds, corn, rice and sesame that could constitute potential liquids for high voltage applications are tested. A naphthenic mineral oil is also tested for comparison. It's shown that the streamers are filamentary for both polarities. For a given voltage, the stopping lengths (Lf) of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf-are very close in all tested oils. The streamers' velocities are in the same range for all vegetable oils and they vary between 0.4 km/s and 1.2 km/s for positive polarity and 0.2 km/s and 0.8 km/s for negative polarity.展开更多
Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of j...Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of jet flow structures with impinging distance is characterized using the technique of particle image velocimetry (PIV). Correspondingly, the distributions of wall pressure and heat transfer on the plate are measured. At sufficiently large impinging distances, without swirling flow, the obtained flow and wall pressure/heat transfer data are consistent with the classical observation for a conventional annular impinging jet, showing the transition from annular impinging jet flow to single circular impinging jet-like flow. In contrast, no such transition occurs in the presence of flow turning by short guide vanes. At short and intermediate impinging distances, flow turning causes more non-uniform distributions of wall pressure and heat transfer on the target plate and the local heat transfer rates higher than those of the conventional annular jet. This is attributed to the vortical flow structures shed and convected downstream from the short guide vanes. In sharp contrast, at large impinging distances, the larger momentum loss due to flow turning results in lower heat transfer rates on the plate.展开更多
The hypersonic long-run scramjet test tunnel is one of the key ground facilities for the studies of ramjet/scramjet and hypersonic thermal management.Due to the significantly large heat loading,the nozzle of the tunne...The hypersonic long-run scramjet test tunnel is one of the key ground facilities for the studies of ramjet/scramjet and hypersonic thermal management.Due to the significantly large heat loading,the nozzle of the tunnel facility demands effective cooling protection.In this work,the two-dimensional,three-dimensional and axisymmetric Mach 6.5 nozzles at an inlet total temperature of 1840 K and a total pressure of 6.4 MPa were studied with main focuses on the properties of aerodynamic heating of nozzles.The present work aims to provide insights into the design of an effective cooling system for the nozzle and other components of the hypersonic long-run wind tunnel.展开更多
Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure...Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure effect the cooling effectiveness in the channel seriously. Numerical simulation to the flow field of scramjet cold panel with four different fuel injection island structures respectively has been carried out using the CFD commercial software-CFX in this research. The results reveal that flow dead area has been eliminated and flow field has been improved for the optimized structure. Furthermore, local resistance loss has been decreased and the mass flow rate non-uniform distribution in the channel has been reduced. Based on the optimized results, some suggestions about the local design of cooling panel have been proposed in this research.展开更多
文摘The uniform design and response surface methodology (RSM) are applied to the multi-objective optimization of a 2-D mixed compression scramjet inlet. The set of experimental design points on the design space is selected by the uniform design, and the inlet performance is analyzed by computational fluid dynamics (CFD). Then complete quadratic polynomial response surface approximation models are constructed based on the performance analysis results and then used to replace theoriginal complex inlet performance model. The optimization is conducted using a multi-objective genetic algorithm NSGA-Ⅱ, and the Pareto optimal solution set is obtained. Results show that the uniform design and RSM can reduce the computational complexity of numerical simulation and improve the optimization efficiency.
基金Project(2009ZX04014-074)supported by the National Science and Technology Major Project of ChinaProject(P2014-15)supported by the State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology,ChinaProject(20120006110017)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.
基金supported by the National Natural Science Foundation of China (Grant No. 40771026)the NSFC-RFBR project (Grant No. 40911120089, 08-05-92206 NSFCa)
文摘Measuring the internal velocity of debris flows is very important for debris flow dynamics research and designing debris flow control works. However, there is no appropriate method for measuring the internal velocity because of the destructive power of debris flow process. In this paper, we address this problem by using the relationship between velocity and kinetic pressure, as described by surface velocity and surface kinetic pressure data. Kinetic pressure is the difference of impact pressure and static pressure. The former is detected by force sensors installed in the flow direction at the sampling section. Observations show that static pressure can be computed using the formula for static water pressure by simply substituting water density for debris flow density. We describe the relationship between surface velocity and surface kinetic pressure using data from seven laboratory flume experiments. It is consistent with the relationship for single phase flow, which is the measurement principle of the Pitot tube.
基金Supported by National Natural Science Foundation of China(No.50578082,No.50678094)
文摘The loads of shock wave effect on fabricated anti-blast wail and distribution law around the wall were investigated by using near surface explosion test method and FEM. The pressure-time histories and variety law on the foreside and backside of the anti-blast wall were adopted in the tests of variety of different explosion distances and dynamites, as well as in the comparison between the test and numerical calculation. The test results show that the loads of shock wave effect on the anti-blast wall were es- sen-tially consistent with calculation results using criterion under surface explosion when explosion dis- tances exceed 2 m, the distribution of overpressure behind wall was gained according to variety law based on small-large-small. It is also demonstrated that the peak overpressure behind wall had com- monly appeared in wall height by 1.5--2.5 multiples, and the peak overpressures of protective building behind wall could be reduced effectively by using the fabricated anti-blast wall.
文摘According to the movement and change rules of mechanical structure of surrounding rock coal mass system during coal excavation, the mechanism of sudden instability and damage was found out. The criterions that distinguishing the occurring of the pressure bump were put forward. This criteria have been applied successfully in the comprehensive prevent of pressure bumps in Tangshan colliery.
基金Projects(RG148/12AET,RG086/10AET) supported by the UMRG,MalaysiaProject(PS05812010B) supported by the Post Graduate Research Fund,Malaysia
文摘Ground improvement has been used on many construction sites to densify granular materials, in other word, to improve soil properties and reduce potential settlement. This work presents a case study of ground improvement using rapid impact compaction (RIC). The research site comprises the construction of workshop and depots as part of railway development project at Batu Gajah-Ipoh, Malaysia. In-situ testing results show that the subsurface soil comprises mainly of sand and silty sand through the investigated depth extended to 10 m. Groundwater is approximately 0.5 m below the ground surface. Evaluation of improvement was based on the results of pre- and post-improvement cone penetration test (CPT). Interpretation software has been used to infer soil properties. Load test was conducted to estimate soil settlement. It is found that the technique succeeds in improving soil properties namely the relative density increases from 45% to 70%, the friction angle of soil is increased by an average of 3°, and the soil settlement is reduced by 50%: The technique succeeds in improving soil properties to approximately 5.0 m in depth depending on soil uniformity with depth.
基金The National Natural Science Foundation of China (No50275059, 50005008)
文摘This paper suggested to reformulate cylindrical deep drawing parameters with dimensionless form. A diagram, in which a feasible zone is drawn to bound both the maximal allowable tension and compression stress during the deep drawing process, was established. Since it is presented in a dimensionless form, it may be applied for both conventional and micro deep drawing. Cylindrical cup deep drawing was taken as an example to show the dimensionless process design method. In addition, the size effects should be taken into account. Two kinds of size effects on micro deep drawing were investigated, which can be explained by surface layer model and strain gradient model. Numerical simulations were carried out to compare the strain distribution with or without consideration of size effect.
文摘This paper is aimed at the streamers in natural esters (vegetable oils) in point--plane electrode arrangement under lightning impulse voltage. The shape, stopping length, velocity and current of streamers are investigated. Six untreated commercial oils extracted from grape seeds, sunflower and rape seeds, corn, rice and sesame that could constitute potential liquids for high voltage applications are tested. A naphthenic mineral oil is also tested for comparison. It's shown that the streamers are filamentary for both polarities. For a given voltage, the stopping lengths (Lf) of streamers are longer when the point is positive than when it is negative; also, except mineral oil when the point is negative, the values of Lf-are very close in all tested oils. The streamers' velocities are in the same range for all vegetable oils and they vary between 0.4 km/s and 1.2 km/s for positive polarity and 0.2 km/s and 0.8 km/s for negative polarity.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2011CB610305)the National "111" Project of China (Grant No. B06024)the National Natural Science Foundation of China (Grant Nos. 10825210, 11072188)
文摘Annular jets impinging on a uniformly heated flat plate with or without swirling flow by short guide vanes are experimentally characterized. With the Reynolds number fixed at a relatively low value, the variation of jet flow structures with impinging distance is characterized using the technique of particle image velocimetry (PIV). Correspondingly, the distributions of wall pressure and heat transfer on the plate are measured. At sufficiently large impinging distances, without swirling flow, the obtained flow and wall pressure/heat transfer data are consistent with the classical observation for a conventional annular impinging jet, showing the transition from annular impinging jet flow to single circular impinging jet-like flow. In contrast, no such transition occurs in the presence of flow turning by short guide vanes. At short and intermediate impinging distances, flow turning causes more non-uniform distributions of wall pressure and heat transfer on the target plate and the local heat transfer rates higher than those of the conventional annular jet. This is attributed to the vortical flow structures shed and convected downstream from the short guide vanes. In sharp contrast, at large impinging distances, the larger momentum loss due to flow turning results in lower heat transfer rates on the plate.
基金supported by the National Natural Science Foundation of China(Grant Nos.11202218 and 11172309)
文摘The hypersonic long-run scramjet test tunnel is one of the key ground facilities for the studies of ramjet/scramjet and hypersonic thermal management.Due to the significantly large heat loading,the nozzle of the tunnel facility demands effective cooling protection.In this work,the two-dimensional,three-dimensional and axisymmetric Mach 6.5 nozzles at an inlet total temperature of 1840 K and a total pressure of 6.4 MPa were studied with main focuses on the properties of aerodynamic heating of nozzles.The present work aims to provide insights into the design of an effective cooling system for the nozzle and other components of the hypersonic long-run wind tunnel.
文摘Local structure of cooling panel has great effects on the heat transfer in the cooling channel for the scramjet. The problems of flow dead area and mass flow rate non-uniform distribution caused by the local structure effect the cooling effectiveness in the channel seriously. Numerical simulation to the flow field of scramjet cold panel with four different fuel injection island structures respectively has been carried out using the CFD commercial software-CFX in this research. The results reveal that flow dead area has been eliminated and flow field has been improved for the optimized structure. Furthermore, local resistance loss has been decreased and the mass flow rate non-uniform distribution in the channel has been reduced. Based on the optimized results, some suggestions about the local design of cooling panel have been proposed in this research.