The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low s...The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head(NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model(κ-ε). It is found that axial force of pump with radical reflux balance holes of5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.展开更多
Cantilever casting concrete arch bridge using form traveller has a broad application prospect.However,it is difficult to obtain reasonable initial cable force in construction stage.In this study,stress balance and inf...Cantilever casting concrete arch bridge using form traveller has a broad application prospect.However,it is difficult to obtain reasonable initial cable force in construction stage.In this study,stress balance and influence matrix methods were developed to determine the initial cable force of cantilever casting concrete arch bridge.The stress balance equation and influence matrix of arch rib critical section were established,and the buckle cable force range was determined by the allowable stress of arch rib critical section.Then a group of buckle cable forces were selected and substituted into the stress balance equation,and the reasonable initial buckle cable force was determined through iteration.Based on the principle of force balance,the initial anchor cable force was determined.In an engineering application example,it is shown that the stress balance and influence matrix methods for the determination of initial cable force are feasible and reliable.The initial cable forces of arch rib segments only need to be adjusted once in the corresponding construction process,which improves the working efficiency and reduces the construction risk.It is found that the methods have great advantages for determining initial cable force in cantilever casting construction process of concrete arch bridge.展开更多
针对现有平衡能力评估系统中存在的人机互动性差、交互系统反馈较单一等问题,文章提出一种平衡能力评估人机交互策略,研制平衡能力评估装置,设计开发出一套基于足底力的平衡评估人机交互系统。该系统以压力中心(center of pressure,CoP...针对现有平衡能力评估系统中存在的人机互动性差、交互系统反馈较单一等问题,文章提出一种平衡能力评估人机交互策略,研制平衡能力评估装置,设计开发出一套基于足底力的平衡评估人机交互系统。该系统以压力中心(center of pressure,CoP)变量和足底力分布信息为平衡评估特征参数,实现静态、主动性以及反应性平衡能力的评估;以足底压力信息为输入信号,通过CoP跟踪、CoP轨迹图的绘制以及平衡评估特征值进行平衡能力评估。平衡能力评估试验结果表明,系统传感器能准确实时地采集数据,绘制的CoP轨迹图能准确反映人体的重心偏移情况。该人机交互系统系统可以实现对人体平衡能力评估的量化。展开更多
微推力器是实现卫星姿态与轨道控制不可或缺的执行机构,精确测量其推力性能至关重要.针对传统微推力测量装置存在的推力力臂难以精确测定,羽流随扭摆转动而偏转以及装配调试复杂等问题,设计并研制了一种基于罗伯威尔平衡结构的新型微推...微推力器是实现卫星姿态与轨道控制不可或缺的执行机构,精确测量其推力性能至关重要.针对传统微推力测量装置存在的推力力臂难以精确测定,羽流随扭摆转动而偏转以及装配调试复杂等问题,设计并研制了一种基于罗伯威尔平衡结构的新型微推力测量装置.该装置的推力力臂长度固定,不受微推力器安装位置的干扰,有效消除了力臂测量引入的不确定度,同时降低了微推力器的装配与调试难度.此外,该装置确保了推力羽流在扭摆转动过程中不发生偏转,便于同步监测推力器羽流信息.本研究利用电磁标准力对其开环和闭环两种测量模式开展了性能测试与评估,并使用该装置对一套冷气微推力器进行了标定.性能测试结果显示,在开环模式下,该装置量程为2 m N,分辨力优于1μN,包含因子为3时的测量不确定度为2.33μN+0.99%T(其中T为实测力值).在闭环模式下,测量量程达到100 mN,分辨力优于5μN,测量不确定度则为18.00μN+0.31%T.该装置可满足多种微牛级至毫牛级微推力器的推力测量需求,为我国商业航天的快速发展提供助力.展开更多
基金Project(51179075)supported by the National Natural Science Foundation of ChinaProject(BK20131256)supported by the Natural Science Funds of Jiangsu Province,ChinaProject supported by the Priority Academic Program Development of Jiangsu High Education Institutions,China
文摘The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head(NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model(κ-ε). It is found that axial force of pump with radical reflux balance holes of5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.
基金Projects(51478049,51778068)supported by the National Natural Science Foundation of ChinaProject(14JJ2075,2019JJ40301)supported by the Hunan Natural Science Foundation of China+1 种基金Project(17A010)supported by the Scientific Research Fund of Hunan Provincial Education Department of ChinaProject(2017GK4034)supported by the Major Technological Achievements Transformation Program of Hunan Strategic Emerging Industries of China
文摘Cantilever casting concrete arch bridge using form traveller has a broad application prospect.However,it is difficult to obtain reasonable initial cable force in construction stage.In this study,stress balance and influence matrix methods were developed to determine the initial cable force of cantilever casting concrete arch bridge.The stress balance equation and influence matrix of arch rib critical section were established,and the buckle cable force range was determined by the allowable stress of arch rib critical section.Then a group of buckle cable forces were selected and substituted into the stress balance equation,and the reasonable initial buckle cable force was determined through iteration.Based on the principle of force balance,the initial anchor cable force was determined.In an engineering application example,it is shown that the stress balance and influence matrix methods for the determination of initial cable force are feasible and reliable.The initial cable forces of arch rib segments only need to be adjusted once in the corresponding construction process,which improves the working efficiency and reduces the construction risk.It is found that the methods have great advantages for determining initial cable force in cantilever casting construction process of concrete arch bridge.
文摘针对现有平衡能力评估系统中存在的人机互动性差、交互系统反馈较单一等问题,文章提出一种平衡能力评估人机交互策略,研制平衡能力评估装置,设计开发出一套基于足底力的平衡评估人机交互系统。该系统以压力中心(center of pressure,CoP)变量和足底力分布信息为平衡评估特征参数,实现静态、主动性以及反应性平衡能力的评估;以足底压力信息为输入信号,通过CoP跟踪、CoP轨迹图的绘制以及平衡评估特征值进行平衡能力评估。平衡能力评估试验结果表明,系统传感器能准确实时地采集数据,绘制的CoP轨迹图能准确反映人体的重心偏移情况。该人机交互系统系统可以实现对人体平衡能力评估的量化。
文摘微推力器是实现卫星姿态与轨道控制不可或缺的执行机构,精确测量其推力性能至关重要.针对传统微推力测量装置存在的推力力臂难以精确测定,羽流随扭摆转动而偏转以及装配调试复杂等问题,设计并研制了一种基于罗伯威尔平衡结构的新型微推力测量装置.该装置的推力力臂长度固定,不受微推力器安装位置的干扰,有效消除了力臂测量引入的不确定度,同时降低了微推力器的装配与调试难度.此外,该装置确保了推力羽流在扭摆转动过程中不发生偏转,便于同步监测推力器羽流信息.本研究利用电磁标准力对其开环和闭环两种测量模式开展了性能测试与评估,并使用该装置对一套冷气微推力器进行了标定.性能测试结果显示,在开环模式下,该装置量程为2 m N,分辨力优于1μN,包含因子为3时的测量不确定度为2.33μN+0.99%T(其中T为实测力值).在闭环模式下,测量量程达到100 mN,分辨力优于5μN,测量不确定度则为18.00μN+0.31%T.该装置可满足多种微牛级至毫牛级微推力器的推力测量需求,为我国商业航天的快速发展提供助力.
