A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and ...A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.展开更多
It has been evident that the theory and methods of dynamic derivatives are playing an increasingly important role in hybrid modeling and computations. Being constructed on various kinds of hybrid grids, that is, tim...It has been evident that the theory and methods of dynamic derivatives are playing an increasingly important role in hybrid modeling and computations. Being constructed on various kinds of hybrid grids, that is, time scales, dynamic derivatives offer superior accuracy and flexibility in approximating mathematically important natural processes with hard-to-predict singularities, such as the epidemic growth with unpredictable jump sizes and option market changes with high uncertainties, as compared with conventional derivatives. In this article, we shall review the novel new concepts, explore delicate relations between the most frequently used second-order dynamic derivatives and conventional derivatives. We shall investigate necessary conditions for guaranteeing the consistency between the two derivatives. We will show that such a consistency may never exist in general. This implies that the dynamic derivatives provide entirely different new tools for sensitive modeling and approximations on hybrid grids. Rigorous error analysis will be given via asymptotic expansions for further modeling and computational applications. Numerical experiments will also be given.展开更多
Accurately evaluating the aerodynamic performance of a battle-structure-damaged aircraft is essential to enable the pilot to optimize the flight control strategy. Based on CFD and rigid dynamic mesh techniques,a numer...Accurately evaluating the aerodynamic performance of a battle-structure-damaged aircraft is essential to enable the pilot to optimize the flight control strategy. Based on CFD and rigid dynamic mesh techniques,a numerical method is developed to calculate the longitudinal and longitudinal-lateral coupling forces and moments with small amplitude sinusoidal pitch oscillation, and the corresponding dynamic derivatives of two fragment-structure-damaged and two continuous-rod-damaged models modified from the SACCON UAV. The results indicate that, at the reference point set in this paper, additional positive damping is generated in fragment-damaged configurations;thus, the absolute values of the negative pitch dynamic derivative increase. The missing wingtip induces negative pitch damping on the aircraft and decreases the value of the pitch dynamic derivative. The missing middle wing causes a noticeable increase in the absolute value of the pitch dynamic derivative;the missing parts on the right wing cause the aircraft to roll to the right side in the dynamic process, and the pitch-roll coupling cross dynamic derivatives are positive. Moreover, the values of these derivatives increase as the damaged area on the right wing increases, and an optimal case with the smallest cross dynamic derivative can be found to help improve the survivability of damaged aircraft.展开更多
Based on quasipotential analysis, a plasma sheath is studied through the derivation of the Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features as to the...Based on quasipotential analysis, a plasma sheath is studied through the derivation of the Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features as to the existence of sheaths are shown by solving the Sagdeev potential equation through the Runge–Kutta method, with appropriate consideration of adiabatically heated electrons and ions in the dynamical system. It has been shown that adiabatic heating of plasma sets a limit to the critical dust speed depending on the densities and Mach number, and it is believed that its role is very important to the sheath. One present problem is the contraction of the sheath region whereby dust grains levitated into the sheath lead to a crystallization similar to the formation of nebulons and are compressed to a larger chunk of the dust cloud by shrinking of the sheath. Our overall observations advance knowledge of sheath formation and are expected to be of interest in astroplasmas.展开更多
Data-driven techniques could be used to enhance decision-making capacity of breeders and farmers.We used an RGB camera on an unmanned aerial vehicle(UAV)to collect time series data on sugar beet canopy coverage(CC)and...Data-driven techniques could be used to enhance decision-making capacity of breeders and farmers.We used an RGB camera on an unmanned aerial vehicle(UAV)to collect time series data on sugar beet canopy coverage(CC)and canopy height(CH)from small-plot breeding fields including 20 genotypes per season over 3 seasons.Digital orthomosaic and digital surface models were created from each flight and were converted to individual plot-level data.Plot-level data including CC and CH were calculated on a per-plot basis.A multiple regression model was fitted,which predicts root weight(RW)(r=0.89,0.89,and 0.92 in the 3 seasons,respectively)and sugar content(SC)(r=0.79,0.83,and 0.77 in the 3 seasons,respectively)using individual time point CC and CH data.Individual CC and CH values in late June tended to be strong predictors of RW and SC,suggesting that early season growth is critical for obtaining high RW and SC.Coefficient of parentage was not a strong factor influencing SC.Integrals of CC and CH time series data were calculated for genetic analysis purposes since they are more stable over multiple growing seasons.Calculations of general combining ability and specific combining ability in F1 offspring demonstrate how growth curve quantification can be used in diallel cross analysis and yield prediction.Our simple yet robust solution demonstrates how state-of-the-art remote sensing tools and basic analysis methods can be applied to small-plot breeder fields for selection purpose.展开更多
Conservation of global biodiversity requires scalable tools to monitor species richness patterns,and satellite remote sensing offers a promising avenue.However,a great challenge lies in identifying how best to transla...Conservation of global biodiversity requires scalable tools to monitor species richness patterns,and satellite remote sensing offers a promising avenue.However,a great challenge lies in identifying how best to translate satellite data into ecologically meaningful biodiversity metrics.This study examines the effectiveness of dynamic habitat indices(DHIs)derived from satellite vegetation products,including gross primary productivity(GPP),fraction of absorbed photosynthetically active radiation,leaf area index,normalized difference vegetation index,enhanced vegetation index,and solar-induced chlorophyll fluorescence,in capturing global species richness across amphibians,birds,mammals,and reptiles.The DHIs consist of 3 subindices,with each representing an important productivity-species richness hypothesis,namely,annual cumulative productivity(DHI Cum,available energy hypothesis),annual minimum productivity(DHI Min,environmental stress hypothesis),and coefficient of variation of productivity(DHI CV,environmental stability hypothesis).Results showed that DHIs derived from satellite GPP data explain a large proportion of the variance in species richness globally(R^(2)=0.70 for amphibians,R^(2)=0.78 for birds,R^(2)=0.77 for mammals,R^(2)=0.77 for reptiles,and R^(2)=0.82 when all taxa combined),outperforming other satellite vegetation products.Validation with in situ DHIs calculated from tower-measured GPP at 124 globally FLUXNET sites demonstrated strong agreement with satellite DHIs,supporting the reliability of the satellite GPP-based DHIs.Furthermore,the relatively higher uncertainty of satellite DHIs at low-productivity sites also urges further development of satellite GPP algorithms.Globally,protected areas showed significantly higher DHI Cum and Min and lower DHI CV(P<0.0001),underscoring their superior habitat quality for biodiversity conservation.These findings highlight the potential of DHIs as a powerful and scalable tool for linking satellite observations to global biodiversity patterns,thus bridging the gap between remote sensing and biodiversity conservation community.展开更多
基金supported by the National Science Foundation for Distinguished Young Scholars of China (No.11622220)the Programme of Introducing Talents of Discipline to Universities (No.B17037)
文摘A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.
文摘It has been evident that the theory and methods of dynamic derivatives are playing an increasingly important role in hybrid modeling and computations. Being constructed on various kinds of hybrid grids, that is, time scales, dynamic derivatives offer superior accuracy and flexibility in approximating mathematically important natural processes with hard-to-predict singularities, such as the epidemic growth with unpredictable jump sizes and option market changes with high uncertainties, as compared with conventional derivatives. In this article, we shall review the novel new concepts, explore delicate relations between the most frequently used second-order dynamic derivatives and conventional derivatives. We shall investigate necessary conditions for guaranteeing the consistency between the two derivatives. We will show that such a consistency may never exist in general. This implies that the dynamic derivatives provide entirely different new tools for sensitive modeling and approximations on hybrid grids. Rigorous error analysis will be given via asymptotic expansions for further modeling and computational applications. Numerical experiments will also be given.
基金support of National Natural Science Foundation of China (Grant No. 11672236)Project funded by China Postdoctoral Science Foundation (Grant No. 2018M641381)。
文摘Accurately evaluating the aerodynamic performance of a battle-structure-damaged aircraft is essential to enable the pilot to optimize the flight control strategy. Based on CFD and rigid dynamic mesh techniques,a numerical method is developed to calculate the longitudinal and longitudinal-lateral coupling forces and moments with small amplitude sinusoidal pitch oscillation, and the corresponding dynamic derivatives of two fragment-structure-damaged and two continuous-rod-damaged models modified from the SACCON UAV. The results indicate that, at the reference point set in this paper, additional positive damping is generated in fragment-damaged configurations;thus, the absolute values of the negative pitch dynamic derivative increase. The missing wingtip induces negative pitch damping on the aircraft and decreases the value of the pitch dynamic derivative. The missing middle wing causes a noticeable increase in the absolute value of the pitch dynamic derivative;the missing parts on the right wing cause the aircraft to roll to the right side in the dynamic process, and the pitch-roll coupling cross dynamic derivatives are positive. Moreover, the values of these derivatives increase as the damaged area on the right wing increases, and an optimal case with the smallest cross dynamic derivative can be found to help improve the survivability of damaged aircraft.
文摘Based on quasipotential analysis, a plasma sheath is studied through the derivation of the Sagdeev potential equation in dusty plasma coexisting with adiabatically heated electrons and ions. Salient features as to the existence of sheaths are shown by solving the Sagdeev potential equation through the Runge–Kutta method, with appropriate consideration of adiabatically heated electrons and ions in the dynamical system. It has been shown that adiabatic heating of plasma sets a limit to the critical dust speed depending on the densities and Mach number, and it is believed that its role is very important to the sheath. One present problem is the contraction of the sheath region whereby dust grains levitated into the sheath lead to a crystallization similar to the formation of nebulons and are compressed to a larger chunk of the dust cloud by shrinking of the sheath. Our overall observations advance knowledge of sheath formation and are expected to be of interest in astroplasmas.
基金partially supported by CREST(JPMJCR1512)and the AIPAccelerationResearch(JPMJCR21U3)of JST.
文摘Data-driven techniques could be used to enhance decision-making capacity of breeders and farmers.We used an RGB camera on an unmanned aerial vehicle(UAV)to collect time series data on sugar beet canopy coverage(CC)and canopy height(CH)from small-plot breeding fields including 20 genotypes per season over 3 seasons.Digital orthomosaic and digital surface models were created from each flight and were converted to individual plot-level data.Plot-level data including CC and CH were calculated on a per-plot basis.A multiple regression model was fitted,which predicts root weight(RW)(r=0.89,0.89,and 0.92 in the 3 seasons,respectively)and sugar content(SC)(r=0.79,0.83,and 0.77 in the 3 seasons,respectively)using individual time point CC and CH data.Individual CC and CH values in late June tended to be strong predictors of RW and SC,suggesting that early season growth is critical for obtaining high RW and SC.Coefficient of parentage was not a strong factor influencing SC.Integrals of CC and CH time series data were calculated for genetic analysis purposes since they are more stable over multiple growing seasons.Calculations of general combining ability and specific combining ability in F1 offspring demonstrate how growth curve quantification can be used in diallel cross analysis and yield prediction.Our simple yet robust solution demonstrates how state-of-the-art remote sensing tools and basic analysis methods can be applied to small-plot breeder fields for selection purpose.
基金supported by the Director Fund of the International Research Center of Big Data for Sustainable Development Goals(grant number CBAS2022DF006)the Open Fund of the Key Laboratory of Land Satellite Remote Sensing Applications,Ministry of Natural Resources of the People’s Republic of China(grant number KLSMNR-202308)+2 种基金the Key Program of the Natural Science Foundation of Gansu Province,China(grant number 25JRRA646)the Fengyun Application Pioneering Project(grant number FY-APP-2024.0302)the National Natural Science Foundation of China(grant numbers 42171305 and 42311540014).
文摘Conservation of global biodiversity requires scalable tools to monitor species richness patterns,and satellite remote sensing offers a promising avenue.However,a great challenge lies in identifying how best to translate satellite data into ecologically meaningful biodiversity metrics.This study examines the effectiveness of dynamic habitat indices(DHIs)derived from satellite vegetation products,including gross primary productivity(GPP),fraction of absorbed photosynthetically active radiation,leaf area index,normalized difference vegetation index,enhanced vegetation index,and solar-induced chlorophyll fluorescence,in capturing global species richness across amphibians,birds,mammals,and reptiles.The DHIs consist of 3 subindices,with each representing an important productivity-species richness hypothesis,namely,annual cumulative productivity(DHI Cum,available energy hypothesis),annual minimum productivity(DHI Min,environmental stress hypothesis),and coefficient of variation of productivity(DHI CV,environmental stability hypothesis).Results showed that DHIs derived from satellite GPP data explain a large proportion of the variance in species richness globally(R^(2)=0.70 for amphibians,R^(2)=0.78 for birds,R^(2)=0.77 for mammals,R^(2)=0.77 for reptiles,and R^(2)=0.82 when all taxa combined),outperforming other satellite vegetation products.Validation with in situ DHIs calculated from tower-measured GPP at 124 globally FLUXNET sites demonstrated strong agreement with satellite DHIs,supporting the reliability of the satellite GPP-based DHIs.Furthermore,the relatively higher uncertainty of satellite DHIs at low-productivity sites also urges further development of satellite GPP algorithms.Globally,protected areas showed significantly higher DHI Cum and Min and lower DHI CV(P<0.0001),underscoring their superior habitat quality for biodiversity conservation.These findings highlight the potential of DHIs as a powerful and scalable tool for linking satellite observations to global biodiversity patterns,thus bridging the gap between remote sensing and biodiversity conservation community.
