Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inle...Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inlet is presented in the paper, which include the basic flow pattern, formation condition of the cavity spiral flow, discharge Q, cavity diameter d0, wall pressure coefficient Cpw, velocity distribution, total energy dissipation rate η etc. The results show that the basic flow patterns can be divided into three zones according to the variations in amount of ventilation Ф, cavity diameter d0 and gas pressure p0 within cavity spiral flow when the upstream and downstream water level changes and that the basic hydrodynamics characteristics change with the flow pattern and have the different behaviour.展开更多
From July 19 to 21,2021,Henan,a province in northern China(NC),was affected by severe flooding(referred to hereafter as“21·7”)caused by a prolonged record-breaking extreme precipitation(EP)event.Understanding t...From July 19 to 21,2021,Henan,a province in northern China(NC),was affected by severe flooding(referred to hereafter as“21·7”)caused by a prolonged record-breaking extreme precipitation(EP)event.Understanding the extremes of the large-scale circulation pattern during“21·7”is essential for predicting EP events and preventing future disasters.In this study,daily atmospheric large-scale circulations over NC in the summers from 1979 to 2021 were investigated using the circulation classification method of an obliquely rotated principal component analysis in T-mode(PCT).The geopotential heights at 500 hPa and 925 hPa were applied successively in classification.Among the nine summer circulation patterns found at 500 hPa,the three days of“21·7”belonged to the Type 8 pattern,which had the second highest probability of EP days among all patterns.It was characterized by a southeasterly wind toward North China Plain driven by a dipole geopotential height field,with the West Pacific subtropical high(WPSH)extending far north to 30°N and low pressure to the south near NC.Tropical cyclones(TCs)occurred on 72.5%of EP days,in which larger amounts of precipitation and a longer duration of EP days were found along the mountains in NC,as compared with other patterns.The distribution of EP events under this pattern was mainly influenced by the location of the low pressure at 925 hPa in the dipole.The subtype 8-3 circulation,with low pressure in the east of Taiwan Island,included“21·7”and accounted for 1.6%of all summer days.Typhoon In-fa,together with the WPSH,gave rise to intense column integrated moisture flux convergence(IMFC)via the southeasterly wind to Henan,which occurred continuously during the 3 days of“21·7”,resulting in the largest(second largest)mean IMFC among 3 consecutive EP days under type 8(all types)during the past 43 summers in NC.Further analysis revealed that the large-scale dynamic process could not completely explain the record-breaking EP during“21·7”,indicating possible contribut展开更多
Optical fiber coil winding model is used to guide proper and high precision coil winding for fiber optic gyroscope （FOG） application. Based on the large-deformation theory of elasticity, stress analysis of optical f...Optical fiber coil winding model is used to guide proper and high precision coil winding for fiber optic gyroscope （FOG） application. Based on the large-deformation theory of elasticity, stress analysis of optical fiber free end has been made and balance equation of infinitesimal fiber is deduced, then deformation equation is derived by substituting terminal conditions. On condition that only axial tensile force exists, approximate curve equation has been built in small angle deformation scope. The comparison of tangent point longitudinal coordinate result between theory and approximation gives constant of integration, and expression with tangent point as origin of coordinate is readjusted. Analyzing the winding parameters of an example, it is clear that the horizontal distance from the highest point of wheel to fiber tangent point has millimeter order of magnitude and significant difference with fiber tension variation, and maintains invariant when wheel radius changes. The height of tension and accurate position of tangent point are defined for proper fiber guide. For application to fiber optic gyroscope, spiral-disc winding method and nonideal deformation of straddle section are analyzed, and then spiral-disc quadrupole pattern winding method has been introduced and realized by winding system. The winding results approve that the winding model is applicable.展开更多
Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable...Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.展开更多
Recently,waterproof lighting and luminescent displays have been achieved in perovskite–polymer composite materials.However,practical large-area display applications are still limited to the strong electrostatic adhes...Recently,waterproof lighting and luminescent displays have been achieved in perovskite–polymer composite materials.However,practical large-area display applications are still limited to the strong electrostatic adhesion(EA)and high productivity.To overcome these deficiencies,large-area(~600 cm2)homogeneous perovskite–polymer fiber membranes(PPFMs)are synthesized by an electrospinning strategy in this work.Due to the microscopic cladding of the hydrophobic polymer fibers,the electrospun PPFMs exhibit ultrastable underwater luminescence for more than 90 days,and strong EA to diverse materials without pretreatments or additional adhesives.Moreover,by utilizing a proposed programmable laser lithography strategy,designed PPFM patterns are fabricated as the assembly blocks of large-area colorful or tridimensional displays.Interestingly,due to laser thermal ablation effects,the disengaged edges of these blocks are self-stitched with high mechanical stability and operability.This work provides a simple and effective strategy to realize waterproof,self-adhesive,and large-area display applications of perovskite nanomaterials in real world settings.展开更多
文摘Based on the observation of a model test and in combination with some theoretical analysis, the researches of some basic hydrodynamics characteristics of cavity spiral flow in a large size level pipe with a shaft-inlet is presented in the paper, which include the basic flow pattern, formation condition of the cavity spiral flow, discharge Q, cavity diameter d0, wall pressure coefficient Cpw, velocity distribution, total energy dissipation rate η etc. The results show that the basic flow patterns can be divided into three zones according to the variations in amount of ventilation Ф, cavity diameter d0 and gas pressure p0 within cavity spiral flow when the upstream and downstream water level changes and that the basic hydrodynamics characteristics change with the flow pattern and have the different behaviour.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(Grant No.2019QZKK0105)the National Natural Science Foundation of China(Grant Nos.42030607&41975001)+1 种基金the 2018 Open Research Program of the State Key Laboratory of Severe Weather(Grant No.2018LASW-B17)Forecaster Research Project of China Meteorological Administration(Grant No.CMAYBY2019-137)。
文摘From July 19 to 21,2021,Henan,a province in northern China(NC),was affected by severe flooding(referred to hereafter as“21·7”)caused by a prolonged record-breaking extreme precipitation(EP)event.Understanding the extremes of the large-scale circulation pattern during“21·7”is essential for predicting EP events and preventing future disasters.In this study,daily atmospheric large-scale circulations over NC in the summers from 1979 to 2021 were investigated using the circulation classification method of an obliquely rotated principal component analysis in T-mode(PCT).The geopotential heights at 500 hPa and 925 hPa were applied successively in classification.Among the nine summer circulation patterns found at 500 hPa,the three days of“21·7”belonged to the Type 8 pattern,which had the second highest probability of EP days among all patterns.It was characterized by a southeasterly wind toward North China Plain driven by a dipole geopotential height field,with the West Pacific subtropical high(WPSH)extending far north to 30°N and low pressure to the south near NC.Tropical cyclones(TCs)occurred on 72.5%of EP days,in which larger amounts of precipitation and a longer duration of EP days were found along the mountains in NC,as compared with other patterns.The distribution of EP events under this pattern was mainly influenced by the location of the low pressure at 925 hPa in the dipole.The subtype 8-3 circulation,with low pressure in the east of Taiwan Island,included“21·7”and accounted for 1.6%of all summer days.Typhoon In-fa,together with the WPSH,gave rise to intense column integrated moisture flux convergence(IMFC)via the southeasterly wind to Henan,which occurred continuously during the 3 days of“21·7”,resulting in the largest(second largest)mean IMFC among 3 consecutive EP days under type 8(all types)during the past 43 summers in NC.Further analysis revealed that the large-scale dynamic process could not completely explain the record-breaking EP during“21·7”,indicating possible contribut
基金Fundamental Research Funds for the Central Universities (YWF-10-01-B30)
文摘Optical fiber coil winding model is used to guide proper and high precision coil winding for fiber optic gyroscope （FOG） application. Based on the large-deformation theory of elasticity, stress analysis of optical fiber free end has been made and balance equation of infinitesimal fiber is deduced, then deformation equation is derived by substituting terminal conditions. On condition that only axial tensile force exists, approximate curve equation has been built in small angle deformation scope. The comparison of tangent point longitudinal coordinate result between theory and approximation gives constant of integration, and expression with tangent point as origin of coordinate is readjusted. Analyzing the winding parameters of an example, it is clear that the horizontal distance from the highest point of wheel to fiber tangent point has millimeter order of magnitude and significant difference with fiber tension variation, and maintains invariant when wheel radius changes. The height of tension and accurate position of tangent point are defined for proper fiber guide. For application to fiber optic gyroscope, spiral-disc winding method and nonideal deformation of straddle section are analyzed, and then spiral-disc quadrupole pattern winding method has been introduced and realized by winding system. The winding results approve that the winding model is applicable.
基金supported by the National Natural Science Foundation of China(Grant Nos.52209108 and 52079034)Sichuan Science and Technology Program(Grant No.2023YFQ0021)+1 种基金the Natural Science Foundation of Heilongjiang Province,China(Grant No.LH2023E058)China Postdoctoral Science Foundation(Grant No.2022M720948)。
文摘Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.
基金supported by the Key Project of the National Key R&D program of China(Grant No.2022YFA1404500)the National Natural Science Foundation of China(NSFC)(Grant Nos.62005183 and 12074267)+2 种基金the Science and Technology Planning Project of Guangdong Province(2020B010190001)the Guangdong Natural Science Funds Grant(2021A1515012069)The authors would like to acknowledge the assistance with SEM and HRTEM observations received from the Electron Microscope Center of Shenzhen University.
文摘Recently,waterproof lighting and luminescent displays have been achieved in perovskite–polymer composite materials.However,practical large-area display applications are still limited to the strong electrostatic adhesion(EA)and high productivity.To overcome these deficiencies,large-area(~600 cm2)homogeneous perovskite–polymer fiber membranes(PPFMs)are synthesized by an electrospinning strategy in this work.Due to the microscopic cladding of the hydrophobic polymer fibers,the electrospun PPFMs exhibit ultrastable underwater luminescence for more than 90 days,and strong EA to diverse materials without pretreatments or additional adhesives.Moreover,by utilizing a proposed programmable laser lithography strategy,designed PPFM patterns are fabricated as the assembly blocks of large-area colorful or tridimensional displays.Interestingly,due to laser thermal ablation effects,the disengaged edges of these blocks are self-stitched with high mechanical stability and operability.This work provides a simple and effective strategy to realize waterproof,self-adhesive,and large-area display applications of perovskite nanomaterials in real world settings.
