We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in p...We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in particular, its significance and importance in the approach of the algebraic Reynolds stress modelling, such as in a nonlinear K-ε model. To this end and for illustration of the effect of extended intrinsic spin tensor on turbulence modelling, we examine several recently developed nonlinear K-ε models and compare their performance in predicting the homogeneous turbulent shear flow in a rotating frame of reference with LES data. Our results and analysis indicate that, only if the deficiencies of these models and the like be well understood and properly corrected, may in the near future, more sophisticated nonlinear K-ε models be developed to better predict complex turbulent flows in a non-inertial frame of reference.展开更多
在弱交流系统下对于附带有STATCOM的电网换相换流器高压直流输电(Line Commutated Converter based High Voltage Direct Current, LCC-HVDC)系统,存在着LCC逆变站与STATCOM之间耦合导致LCC-HVDC系统的稳定裕度下降问题,这会减弱LCC-HVD...在弱交流系统下对于附带有STATCOM的电网换相换流器高压直流输电(Line Commutated Converter based High Voltage Direct Current, LCC-HVDC)系统,存在着LCC逆变站与STATCOM之间耦合导致LCC-HVDC系统的稳定裕度下降问题,这会减弱LCC-HVDC抑制换相失败的能力。此外,HVDC控制环节之中的电压指令电流控制(voltage dependent current order limiter, VDCOL)环节的输出电流指令大幅剧烈波动还有几率会导致HVDC系统在首次换相失败之后发生后续换相失败。针对上述问题提出了一种“改进参考电压”的思想,对STATCOM和VDCOL的参考电压与输入电压分别进行修正。首先在STATCOM原本的参考电压经过一个“虚拟电抗”之后得到一个新的参考电压,通过这个改进参考电压弱化了STATCOM电压外环控制模块与LCC逆变站的耦合,减小了交流系统等效阻抗的大小,提升了系统对干扰的抵抗能力。然后对VDCOL的输入电压进行改进,新的改进输入电压改善了故障后VDCOL输出电流指令的大幅剧烈波动情况。最后通过三个层次的对照试验,验证了所提方法的有效性。展开更多
This paper investigates the daily labor supply decisions of Hangzhou cabdrivers. We find that Hangzhou cabdrivers.wage elasticity is significantly positive, their working decisions are largely affected by shift time, ...This paper investigates the daily labor supply decisions of Hangzhou cabdrivers. We find that Hangzhou cabdrivers.wage elasticity is significantly positive, their working decisions are largely affected by shift time, and crude proxy variables for income;hours targets can hardly explain their working behavior. Nevertheless, Hangzhou cabdrivers are still affected by reference dependent preference. Using new empirical strategies, we show that cabdrivers are more likely to continue working when wage rates are unexpectedly low and more likely to quit when wage rates are unexpectedly high.展开更多
文摘We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in particular, its significance and importance in the approach of the algebraic Reynolds stress modelling, such as in a nonlinear K-ε model. To this end and for illustration of the effect of extended intrinsic spin tensor on turbulence modelling, we examine several recently developed nonlinear K-ε models and compare their performance in predicting the homogeneous turbulent shear flow in a rotating frame of reference with LES data. Our results and analysis indicate that, only if the deficiencies of these models and the like be well understood and properly corrected, may in the near future, more sophisticated nonlinear K-ε models be developed to better predict complex turbulent flows in a non-inertial frame of reference.
文摘在弱交流系统下对于附带有STATCOM的电网换相换流器高压直流输电(Line Commutated Converter based High Voltage Direct Current, LCC-HVDC)系统,存在着LCC逆变站与STATCOM之间耦合导致LCC-HVDC系统的稳定裕度下降问题,这会减弱LCC-HVDC抑制换相失败的能力。此外,HVDC控制环节之中的电压指令电流控制(voltage dependent current order limiter, VDCOL)环节的输出电流指令大幅剧烈波动还有几率会导致HVDC系统在首次换相失败之后发生后续换相失败。针对上述问题提出了一种“改进参考电压”的思想,对STATCOM和VDCOL的参考电压与输入电压分别进行修正。首先在STATCOM原本的参考电压经过一个“虚拟电抗”之后得到一个新的参考电压,通过这个改进参考电压弱化了STATCOM电压外环控制模块与LCC逆变站的耦合,减小了交流系统等效阻抗的大小,提升了系统对干扰的抵抗能力。然后对VDCOL的输入电压进行改进,新的改进输入电压改善了故障后VDCOL输出电流指令的大幅剧烈波动情况。最后通过三个层次的对照试验,验证了所提方法的有效性。
文摘This paper investigates the daily labor supply decisions of Hangzhou cabdrivers. We find that Hangzhou cabdrivers.wage elasticity is significantly positive, their working decisions are largely affected by shift time, and crude proxy variables for income;hours targets can hardly explain their working behavior. Nevertheless, Hangzhou cabdrivers are still affected by reference dependent preference. Using new empirical strategies, we show that cabdrivers are more likely to continue working when wage rates are unexpectedly low and more likely to quit when wage rates are unexpectedly high.
