In order to meet the requirements of high reliability,long-lifetime and lightweight in a new generation of aerospace,aviation,high-speed train,and energy power equipment,integrated components are urgently needed to re...In order to meet the requirements of high reliability,long-lifetime and lightweight in a new generation of aerospace,aviation,high-speed train,and energy power equipment,integrated components are urgently needed to replace traditional multi-piece,welded components.The applications of integrated components involve in a series of large-size,complex-shaped,highperformance components made of difficult-to-deform materials,which present a huge challenge for forming ultra-large size integrated components.In this paper,the developments and perspectives of several extreme forming technologies are reviewed,including the sheet hydroforming of ultra-large curved components,dieless hydroforming of ellipsoidal shells,radial-axial ring rolling of rings,in situ manufacturing process of flanges,and local isothermal forging of titanium alloy components.The principle and processes for controlling deformation are briefly illustrated.The forming of typical ultra-large size integrated components and industrial applications are introduced,such as the high strength aluminum alloy,3m in diameter,integrated tank dome first formed by using a sheet blank with a thickness the same as the final component,and a 16m diameter,integrated steel ring rolled by using a single billet.The trends for extreme forming of ultra-large size integrated components are discussed with a goal of providing ideas and fundamental guidance for the further development of new forming processes for extreme-size integrated components in the future.展开更多
In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD ...In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O^+) >S(He^+)>S(H^+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O^+) > η(He^+) > η(H^+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase,the observed decay rates for different RC ions meet the relationship: R(O^+) > R(He^+) > R(H^+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O^+ is shorter than those of H^+ and He^+.展开更多
A dynamic mechanical model is proposed to describe the complexing actions of all the rolls on the ring during the ultra-large radial-axial ring rolling(RARR)process with four guide rolls.Based on the model,the calcula...A dynamic mechanical model is proposed to describe the complexing actions of all the rolls on the ring during the ultra-large radial-axial ring rolling(RARR)process with four guide rolls.Based on the model,the calculation models for bending moment and normal stress at any section of the ring are deduced by force method.If the maximum section bending normal stress exceeds the yield stress of the ring materials,the ring will be distorted thus leading to the instability of the RARR process.According to this,a plastic instability criterion for the ultra-large RARR process with four guide rolls is developed,based on which a mathematical model to calculate the critical guide force for avoiding plastic instability of ring is obtained.The influence rule of the position of guide roll on the dangerous ring section of plastic instability is revealed,from which it is found the dangerous ring section mainly appears at the radial and axial deformation regions and the contact positions of the guide rolls and ring.The optimized layout of guide roll around the ring in favor of stability is determined to be about a1=61°and a2=119°.The plastic instability criterion is proven to be reliable from the aspects of the critical guide force,the section bending moment and normal stress and the dangerous ring section of plastic instability.Intelligent simulation case studies for the RARR process of ultra-large aluminum alloy ring indicate that the stable forming of the process can be effectively realized by regulating the guide force based on the plastic instability criterion.This work could provide a valuable guidance for the control of guide rolls and the optimization of the ultra-large RARR process with four guide rolls.展开更多
The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chr...The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chronology and climatic conditions based on tree-ring width samples from three sites on the northeast slopes of Yangming Mountain. This data is used to study the relationship between the tree-ring width of a young tree and climatic conditions in a moist hilly region of southern China and to understand the general pattern of climate variation and its effects on tree growth in the past in this region. The results indicate that changes in tree-ring widths in these sites are closely related to local climatic conditions. There is a significant positive correlation between the radial growth of Pinus massoniana and the mean temperature of the current year from January to May（coefficient of correlation, R, is 0.596, P〈0.01） and the mean temperature of the previous year from June to July（R is 0.639, P〈0.01）. The radial growth of Pinus massoniana is negatively correlated with the total precipitation of the previous year from January to March and November to December（R is-0.46, P〈0.05） and negatively correlated with the total precipitation of the previous year from June to July（R is-0.582, P〈0.05）. The effect of precipitation on the radial growth of Pinus massoniana is known as the ＂hysteresis effect＂.展开更多
Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the c...Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the continuity equation, a two-dimensional hydrodynamic model was established to describe the hydrodynamic behavior in the double-ring RFRs. The successive over-relaxation(SOR) method was applied to solve the two-dimensional hydrodynamic model. The flow assignment parameters(T_i) of mass flow in the inner channel to the outer catalyst bed and the inner catalyst bed were optimized by the Powell method. Simulations showed the trend of change in gas distribution uniformity along the axial direction and the weight hourly space velocity(WHSV) with the variation of reactor size. The model can be used to analyze the reasonability of dehydrogenation reactor design, and it can also provide quantitative reference for the design of new double-ring RFRs.展开更多
基金This work was funded in part by the National Key Research and Development Program of China(2017YFB0306304)the National Natural Science Foundation of China(51705102,U1637209).The authors wish to express their gratitude for the funding.
文摘In order to meet the requirements of high reliability,long-lifetime and lightweight in a new generation of aerospace,aviation,high-speed train,and energy power equipment,integrated components are urgently needed to replace traditional multi-piece,welded components.The applications of integrated components involve in a series of large-size,complex-shaped,highperformance components made of difficult-to-deform materials,which present a huge challenge for forming ultra-large size integrated components.In this paper,the developments and perspectives of several extreme forming technologies are reviewed,including the sheet hydroforming of ultra-large curved components,dieless hydroforming of ellipsoidal shells,radial-axial ring rolling of rings,in situ manufacturing process of flanges,and local isothermal forging of titanium alloy components.The principle and processes for controlling deformation are briefly illustrated.The forming of typical ultra-large size integrated components and industrial applications are introduced,such as the high strength aluminum alloy,3m in diameter,integrated tank dome first formed by using a sheet blank with a thickness the same as the final component,and a 16m diameter,integrated steel ring rolled by using a single billet.The trends for extreme forming of ultra-large size integrated components are discussed with a goal of providing ideas and fundamental guidance for the further development of new forming processes for extreme-size integrated components in the future.
基金supported by the National Natural Science Foundation of China (41925018, 41874194)
文摘In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O^+) >S(He^+)>S(H^+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O^+) > η(He^+) > η(H^+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase,the observed decay rates for different RC ions meet the relationship: R(O^+) > R(He^+) > R(H^+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O^+ is shorter than those of H^+ and He^+.
基金supported by the National Natural Science Foundation of China (No. 51875468, 51575448)the Research & Development Institute of Northwestern Polytechnical University in Shenzhen (JCYJ20170815162709770)
文摘A dynamic mechanical model is proposed to describe the complexing actions of all the rolls on the ring during the ultra-large radial-axial ring rolling(RARR)process with four guide rolls.Based on the model,the calculation models for bending moment and normal stress at any section of the ring are deduced by force method.If the maximum section bending normal stress exceeds the yield stress of the ring materials,the ring will be distorted thus leading to the instability of the RARR process.According to this,a plastic instability criterion for the ultra-large RARR process with four guide rolls is developed,based on which a mathematical model to calculate the critical guide force for avoiding plastic instability of ring is obtained.The influence rule of the position of guide roll on the dangerous ring section of plastic instability is revealed,from which it is found the dangerous ring section mainly appears at the radial and axial deformation regions and the contact positions of the guide rolls and ring.The optimized layout of guide roll around the ring in favor of stability is determined to be about a1=61°and a2=119°.The plastic instability criterion is proven to be reliable from the aspects of the critical guide force,the section bending moment and normal stress and the dangerous ring section of plastic instability.Intelligent simulation case studies for the RARR process of ultra-large aluminum alloy ring indicate that the stable forming of the process can be effectively realized by regulating the guide force based on the plastic instability criterion.This work could provide a valuable guidance for the control of guide rolls and the optimization of the ultra-large RARR process with four guide rolls.
基金National Natural Science Foundation of China(41571509)
文摘The formation of tree-rings is closely related to climate variation. This paper establishes the tree-ring chronology of Pinus massoniana for a period of 36 years and examines the relationship between the tree-ring chronology and climatic conditions based on tree-ring width samples from three sites on the northeast slopes of Yangming Mountain. This data is used to study the relationship between the tree-ring width of a young tree and climatic conditions in a moist hilly region of southern China and to understand the general pattern of climate variation and its effects on tree growth in the past in this region. The results indicate that changes in tree-ring widths in these sites are closely related to local climatic conditions. There is a significant positive correlation between the radial growth of Pinus massoniana and the mean temperature of the current year from January to May（coefficient of correlation, R, is 0.596, P〈0.01） and the mean temperature of the previous year from June to July（R is 0.639, P〈0.01）. The radial growth of Pinus massoniana is negatively correlated with the total precipitation of the previous year from January to March and November to December（R is-0.46, P〈0.05） and negatively correlated with the total precipitation of the previous year from June to July（R is-0.582, P〈0.05）. The effect of precipitation on the radial growth of Pinus massoniana is known as the ＂hysteresis effect＂.
文摘Compared with the traditional radial flow reactors(RFRs), the double-ring RFRs possess advantages including lower pressure drop, shorter flow path and greater flow area. According to the Ergun's equation and the continuity equation, a two-dimensional hydrodynamic model was established to describe the hydrodynamic behavior in the double-ring RFRs. The successive over-relaxation(SOR) method was applied to solve the two-dimensional hydrodynamic model. The flow assignment parameters(T_i) of mass flow in the inner channel to the outer catalyst bed and the inner catalyst bed were optimized by the Powell method. Simulations showed the trend of change in gas distribution uniformity along the axial direction and the weight hourly space velocity(WHSV) with the variation of reactor size. The model can be used to analyze the reasonability of dehydrogenation reactor design, and it can also provide quantitative reference for the design of new double-ring RFRs.
