This work focused on exploring a computational fluid dynamics(CFD)method to predict the macromixing characteristics including the mean flow field and impeller capacity for a 45° down-pumping pitched blade turbine...This work focused on exploring a computational fluid dynamics(CFD)method to predict the macromixing characteristics including the mean flow field and impeller capacity for a 45° down-pumping pitched blade turbine(PBT)in stirred tanks. Firstly, the three typical mean flow fields were investigated by virtue of three components of liquid velocity. Then the effects of impeller diameter(D)and off-bottom clearance(C)on both the mean flow field and three global macro-mixing parameters concerning impeller capacity were studied in detail. The changes of flow patterns with increasing C/D were predicted from these effects. The simulation results are consistent with the experimental results in published literature.展开更多
In this paper, we consider a class of submanifolds with parallel mean curvacture vector fields. We obitain the suffitient conditions that the above submanifolds is of tatall umbilical and that its codimension is decre...In this paper, we consider a class of submanifolds with parallel mean curvacture vector fields. We obitain the suffitient conditions that the above submanifolds is of tatall umbilical and that its codimension is decrease.展开更多
Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their impo...Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their importance in the quantification of the bedload rate,the collective influence of a boulder array on the approach timeaveraged and turbulent flow field has to date been overlooked.The overarching objective is,thus,to assess the collective effects of a boulder array on the time-averaged and turbulent flow fields surrounding an individual boulder within the array,placing particular emphasis on highlighting the bed shear stress spatial variability.The objective of this study is pursued by resolving and comparing the timeaveraged and turbulent flow fields developing around a boulder,with and without an array of isolated boulders being present.The results show that the effects of an individual boulder on the time-averaged streamwise velocity and turbulence intensity were limited to the boulder's immediate vicinity in the streamwise(x/d c < 2-3) and vertical(z/d c < 1) directions.Outside of the boulder's immediate vicinity,the time-averaged streamwise velocity was found to be globally decelerated.This global deceleration was attributed to the form drag generated collectively by the boulder array.More importantly,the boulder array reduced the applied shear stress exerted on theindividual boulders found within the array,by absorbing a portion of the total applied shear.Furthermore,the array was found to have a "homogenizing" effect on the near-bed turbulence thus significantly reducing the turbulence intensity in the near-bed region.The findings of this study suggest that the collective boulder array bears a portion of the total applied bed shear stress as form drag,hence reducing the available bed shear stress for transporting incoming mobile sediment.Thus,the effects of the boulder array should not be ignored in sediment transport predictions.These effects are encapsulated in this study by Equation(6).展开更多
The influence of the chiral mean field on the in-plane flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture...The influence of the chiral mean field on the in-plane flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the in-plane flow. The calculated results show that the new FOPI data can be reasonably described using the Brown & Rho parametrization, which partly takes into account the correction of higher order contributions in the chiral expansion. This indicates that one can abstract the information on the kaon potential in a nuclear medium from the analysis of the in-plane flow.展开更多
In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied...In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied in neutron stars. We calculate the energy gap of A hyperons and investigate the effects of the ^1S0 superfluidity （SF） of A hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data △ BAA ～ 1.01 ±0.20-0.11^＋0.18 MeV. The results indicate that the ^1S0 SF of A hyperons exists in most density ranges of happening the two reactions. The theoretical cooling curves are in agreement with observation data.展开更多
文摘This work focused on exploring a computational fluid dynamics(CFD)method to predict the macromixing characteristics including the mean flow field and impeller capacity for a 45° down-pumping pitched blade turbine(PBT)in stirred tanks. Firstly, the three typical mean flow fields were investigated by virtue of three components of liquid velocity. Then the effects of impeller diameter(D)and off-bottom clearance(C)on both the mean flow field and three global macro-mixing parameters concerning impeller capacity were studied in detail. The changes of flow patterns with increasing C/D were predicted from these effects. The simulation results are consistent with the experimental results in published literature.
文摘In this paper, we consider a class of submanifolds with parallel mean curvacture vector fields. We obitain the suffitient conditions that the above submanifolds is of tatall umbilical and that its codimension is decrease.
基金supported by the United States National Science Foundation (Grant No. CBET1033732)
文摘Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their importance in the quantification of the bedload rate,the collective influence of a boulder array on the approach timeaveraged and turbulent flow field has to date been overlooked.The overarching objective is,thus,to assess the collective effects of a boulder array on the time-averaged and turbulent flow fields surrounding an individual boulder within the array,placing particular emphasis on highlighting the bed shear stress spatial variability.The objective of this study is pursued by resolving and comparing the timeaveraged and turbulent flow fields developing around a boulder,with and without an array of isolated boulders being present.The results show that the effects of an individual boulder on the time-averaged streamwise velocity and turbulence intensity were limited to the boulder's immediate vicinity in the streamwise(x/d c < 2-3) and vertical(z/d c < 1) directions.Outside of the boulder's immediate vicinity,the time-averaged streamwise velocity was found to be globally decelerated.This global deceleration was attributed to the form drag generated collectively by the boulder array.More importantly,the boulder array reduced the applied shear stress exerted on theindividual boulders found within the array,by absorbing a portion of the total applied shear.Furthermore,the array was found to have a "homogenizing" effect on the near-bed turbulence thus significantly reducing the turbulence intensity in the near-bed region.The findings of this study suggest that the collective boulder array bears a portion of the total applied bed shear stress as form drag,hence reducing the available bed shear stress for transporting incoming mobile sediment.Thus,the effects of the boulder array should not be ignored in sediment transport predictions.These effects are encapsulated in this study by Equation(6).
文摘The influence of the chiral mean field on the in-plane flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the in-plane flow. The calculated results show that the new FOPI data can be reasonably described using the Brown & Rho parametrization, which partly takes into account the correction of higher order contributions in the chiral expansion. This indicates that one can abstract the information on the kaon potential in a nuclear medium from the analysis of the in-plane flow.
基金Supported by National Natural Science Foundation of China under Grant Nos. 10675024, 11075063the National Fundamental Fund project Subsidy Funds of Personnel Training J0730311
文摘In the framework of the relativistic mean field theory （RMFT）, the relativistic energy losses of the direct Urea processes with hyperons （Y-DURCA ） for reactions A → p ＋ e ＋ υe and ≡^-→ A＋e＋υe are studied in neutron stars. We calculate the energy gap of A hyperons and investigate the effects of the ^1S0 superfluidity （SF） of A hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data △ BAA ～ 1.01 ±0.20-0.11^＋0.18 MeV. The results indicate that the ^1S0 SF of A hyperons exists in most density ranges of happening the two reactions. The theoretical cooling curves are in agreement with observation data.
