小波变换具有时空双局部性特点,恰好适应了湍流特性。本文主要阐述了小波在湍流数值计算中的两大研究进展:一个是利用连续小波(高斯小波)可使L ap lace算子降阶的特性来求解N-S方程;另一个是正交小波与有限元法相结合的方法——相干涡...小波变换具有时空双局部性特点,恰好适应了湍流特性。本文主要阐述了小波在湍流数值计算中的两大研究进展:一个是利用连续小波(高斯小波)可使L ap lace算子降阶的特性来求解N-S方程;另一个是正交小波与有限元法相结合的方法——相干涡模拟。指出它们的优缺点及其存在的问题,并对小波在湍流计算中的应用前景作了展望。展开更多
The ecosystem apparent quantum yield(α),maximum rate of gross CO_(2) assimilation(Pmax)and daytime ecosystem respiration rate(R.),reflecting the physiological functioning of ecosystem,are vital photosynthetic paramet...The ecosystem apparent quantum yield(α),maximum rate of gross CO_(2) assimilation(Pmax)and daytime ecosystem respiration rate(R.),reflecting the physiological functioning of ecosystem,are vital photosynthetic parameters for the estimation of ecosystem carbon budget.Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation.However,the relative contribution and regulation pathway of environmental and physiological controls remain unclear,especially in semi-arid grasslands.We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia,Northern China,over 12 years from 2006 to 2017.Regression analyses and a structural equation model(SEM)were adopted to separate the contributions of environmental and physiological effects.The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations.Variations of air temperature(T,)and soil water content(SWC)drove the seasonal patterns of photosynthetic parameters,while SWC predominated their interannual variations.Moreover,contrasting with the predominant roles of T,onαand Ra,SWC explained more variance of Pmax than T,Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level.Moreover,leaf area index(LAl)directly affectedα,Pmax and R,and dominated the variation of Pmax.On the other hand,SWC influenced photosynthetic parameters indirectly through LAl and canopy surface conductance(gc).Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity,especially in water-limitedgrassland ecosystems.展开更多
Time sequence signals of streamwise and normal velocity components,as well as velocity strain rate,at different vertical locations in the turbulent boundary layer over a smooth flat plate in a wind tunnel have been fi...Time sequence signals of streamwise and normal velocity components,as well as velocity strain rate,at different vertical locations in the turbulent boundary layer over a smooth flat plate in a wind tunnel have been finely examined by the use of double-sensor hot-wire anemometry.The local module maximum for wavelet coefficient of longitudinal velocity component,as a detecting index,is employed to educe the ejection and sweep process of the coherent structure burst in the turbulent boundary layer from the random fluctuating background.The coherent waveforms of Reynolds stress residual contribution term for random fluctuations to coherent structure,as well as the velocity strain rate of coherent structure,are extracted by the conditional phase average technique.Based on the theoretical analysis of eddy viscosity coefficient in complex eddy viscosity model for coherent structure,the macro-relaxation effect between Reynolds stress residual contribution term of random fluctuations to coherent structure and the velocity strain rate of coherent structure is studied and the variations of the phase difference between them across the turbulent boundary layer are investigated experimentally.The rationality of complex eddy viscosity model for coherent structure is confirmed through the investigation.展开更多
文摘小波变换具有时空双局部性特点,恰好适应了湍流特性。本文主要阐述了小波在湍流数值计算中的两大研究进展:一个是利用连续小波(高斯小波)可使L ap lace算子降阶的特性来求解N-S方程;另一个是正交小波与有限元法相结合的方法——相干涡模拟。指出它们的优缺点及其存在的问题,并对小波在湍流计算中的应用前景作了展望。
基金the National Key Research and Development Program of China(2017YFA0604801)the National Natural Science Foundation of China(32071565 and 41773084)。
文摘The ecosystem apparent quantum yield(α),maximum rate of gross CO_(2) assimilation(Pmax)and daytime ecosystem respiration rate(R.),reflecting the physiological functioning of ecosystem,are vital photosynthetic parameters for the estimation of ecosystem carbon budget.Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation.However,the relative contribution and regulation pathway of environmental and physiological controls remain unclear,especially in semi-arid grasslands.We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia,Northern China,over 12 years from 2006 to 2017.Regression analyses and a structural equation model(SEM)were adopted to separate the contributions of environmental and physiological effects.The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations.Variations of air temperature(T,)and soil water content(SWC)drove the seasonal patterns of photosynthetic parameters,while SWC predominated their interannual variations.Moreover,contrasting with the predominant roles of T,onαand Ra,SWC explained more variance of Pmax than T,Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level.Moreover,leaf area index(LAl)directly affectedα,Pmax and R,and dominated the variation of Pmax.On the other hand,SWC influenced photosynthetic parameters indirectly through LAl and canopy surface conductance(gc).Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity,especially in water-limitedgrassland ecosystems.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10832001 and 10872145)Opening Subject of State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences
文摘Time sequence signals of streamwise and normal velocity components,as well as velocity strain rate,at different vertical locations in the turbulent boundary layer over a smooth flat plate in a wind tunnel have been finely examined by the use of double-sensor hot-wire anemometry.The local module maximum for wavelet coefficient of longitudinal velocity component,as a detecting index,is employed to educe the ejection and sweep process of the coherent structure burst in the turbulent boundary layer from the random fluctuating background.The coherent waveforms of Reynolds stress residual contribution term for random fluctuations to coherent structure,as well as the velocity strain rate of coherent structure,are extracted by the conditional phase average technique.Based on the theoretical analysis of eddy viscosity coefficient in complex eddy viscosity model for coherent structure,the macro-relaxation effect between Reynolds stress residual contribution term of random fluctuations to coherent structure and the velocity strain rate of coherent structure is studied and the variations of the phase difference between them across the turbulent boundary layer are investigated experimentally.The rationality of complex eddy viscosity model for coherent structure is confirmed through the investigation.
