To improve the level of active traffic management,a short-term traffic flow prediction model is proposed by combining phase space reconstruction(PSR)and extreme gradient boosting(XGBoost)algorithms.Firstly,the traditi...To improve the level of active traffic management,a short-term traffic flow prediction model is proposed by combining phase space reconstruction(PSR)and extreme gradient boosting(XGBoost)algorithms.Firstly,the traditional data preprocessing method is improved.The new method uses hierarchical clustering to determine the traffic flow state and fills in missing and abnormal data according to different traffic flow states.Secondly,one-dimensional data are mapped into a multidimensional data matrix through PSR,and the time series complex network is used to verify the data reconstruction effect.Finally,the multidimensional data matrix is inputted into the XGBoost model to predict future traffic flow parameters.The experimental results show that the mean square error,average absolute error,and average absolute percentage error of the prediction results of the PSR-XGBoost model are 5.399%,1.632%,and 6.278%,respectively,and the required running time is 17.35 s.Compared with mathematical-statistical models and other machine learning models,the PSR-XGBoost model has clear advantages in multiple predictive indicators,proving its feasibility and superiority in short-term traffic flow prediction.展开更多
In this paper, we prove the existence in H＋^2, an incomplete metric subspace of H^2×H^2×H^2, of global solutions to the system for a one-dimensional non-monotone fluid in bounded domainΩ=（0,1）. The resul...In this paper, we prove the existence in H＋^2, an incomplete metric subspace of H^2×H^2×H^2, of global solutions to the system for a one-dimensional non-monotone fluid in bounded domainΩ=（0,1）. The results in this paper have improved those previously related results.展开更多
Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （...Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （ANSR） are analyzed to investigate the hydrographic responses to the topography in this region. The results show that the topography of ANSR can induce internal waves around the submarine ridge that have a maximum current velocity of 1 m s 1 The spatial struc- ture of the turbulent kinetic energy （TKE） and shear in this region during 2010 is investigated using the high-resolution Princeton Ocean Model （POM） forced by the satellite-based Advanced Scatterometer （ASCAT） winds including the tide, The results show that the model successfully simulates the internal waves around the ANSR. Numerical experiments further indicate that both the topography and tide play an important role in the gen- eration of the internal waves in this region.展开更多
In order to reduce the computation of complex problems, a new surrogate-assisted estimation of distribution algorithm with Gaussian process was proposed. Coevolution was used in dual populations which evolved in paral...In order to reduce the computation of complex problems, a new surrogate-assisted estimation of distribution algorithm with Gaussian process was proposed. Coevolution was used in dual populations which evolved in parallel. The search space was projected into multiple subspaces and searched by sub-populations. Also, the whole space was exploited by the other population which exchanges information with the sub-populations. In order to make the evolutionary course efficient, multivariate Gaussian model and Gaussian mixture model were used in both populations separately to estimate the distribution of individuals and reproduce new generations. For the surrogate model, Gaussian process was combined with the algorithm which predicted variance of the predictions. The results on six benchmark functions show that the new algorithm performs better than other surrogate-model based algorithms and the computation complexity is only 10% of the original estimation of distribution algorithm.展开更多
The paper deals with impulse switching function which are used as exciting functions of one- and multidimensional state-space models of power electronic converters. Obviously, these functions are harmonic but using po...The paper deals with impulse switching function which are used as exciting functions of one- and multidimensional state-space models of power electronic converters. Obviously, these functions are harmonic but using power converters they can be strongly non-harmonic, sometimes piecewise constants with zero spaces between them. Then, one deals with power series of time pulses. The impulse switching functions which are orthogonal ones can be derived from these series. The new impulse switching functions are created using Z-transform, inverse Z-transform and numerical series/sequences. The impulse switching functions created this way can be used for both steady- and transient state investigation of converters.展开更多
As a pivotal element within the modern service industry,tourism possesses the capacity to reconfigure regional economic dynamics,alter resource flow patterns,and notably influence urban green development.By establishi...As a pivotal element within the modern service industry,tourism possesses the capacity to reconfigure regional economic dynamics,alter resource flow patterns,and notably influence urban green development.By establishing an evaluation index system for urban green development across 60 prefecture-level cities within the Yellow River Basin from 2006 to 2021,this study employs the spatial Durbin model to delve into the nonlinear relationship between the tourism economy and urban green development.Furthermore,it investigates the heterogeneous impact of the tourism economy on green development across varying levels of urbanization.This study reveals several key findings:(1)Both tourism economy and urban green development exhibit significant spatial clustering,with tourism economy showing“midstream>downstream>upstream”and urban green development showing“downstream>midstream>upstream”.(2)The tourism economy exerts a non-linear positive influence on the green development of cities,characterized by a non-linear inverted“S”shape in its direct impact and a nonlinear“S”shape in its indirect impact.(3)As urbanization rate level escalate,the positive influence of the tourism economy on urban green development follows a non-linear trajectory,initially declining before ascending.Specifically,when the urbanization rate level is below the first threshold value,the tourism economy notably promotes urban green development.However,between the first and second threshold values,this positive impact diminishes,only to rebound beyond the second threshold value.展开更多
For reasons of simplicity, the most commonly used hydrological models are based on the Soil Conservation Service Curve Number （SCS-CN） model, which is probably a good choice for the estimation of runoff on the Loess...For reasons of simplicity, the most commonly used hydrological models are based on the Soil Conservation Service Curve Number （SCS-CN） model, which is probably a good choice for the estimation of runoff on the Loess Plateau of China; however, the high spatial heterogeneity, mainly caused by a fragmented landform and variations in soil type, may limit its applicability to this region. Therefore, applicability of the SCS-CN model to a small watershed, Liudaogou on the plateau, was evaluated and the most appropriate initial abstraction ratio （I~/S） value in the model was quantified by the inverse method. The results showed that the standard SCS-CN model was applicable to the estimation of runoff in the Liudaogou watershed and the model performance was acceptable according to the values of relative error and Nash-Sutcliffe efficiency. The most appropriate Ia/S value for the watershed was 0.22 because with this modified Ia/S value, the model performance was slightly improved. The model performance was not sensitive to the modification of the Ia/S value when one heavy rainfall event （50.1 mm） was not considered, which implied that the model, using a standard Ia/S value, can be recommended for the Liudaogou watershed because single rainfall events exceeding 50 mm seldom occurred in that region. The runoff amount predicted for the Liudaogou watershed by the SCS-CN model, using the modified Ia/S value, increased gradually with increasing rainfall when rainfall values were lower than 50 mm, whereas the predicted amount increased rapidly when the rainfall exceeded 50 mm. These findings may be helpful in solving the problem of serious soil and water loss on the Loess Plateau of China.展开更多
Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria： numerical qualities （preci...Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria： numerical qualities （precision and spectral characteristics）, and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and ＂low-cost＂ shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.展开更多
A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale v...A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.展开更多
Gust alleviation is very important to a large flexible aircraft.A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust.Based on the proper orthogonal d...Gust alleviation is very important to a large flexible aircraft.A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust.Based on the proper orthogonal decomposition method,a reduced order modeling of gust loads was proposed.And then the open-loop and closed-loop reduced order state space model for the transonic aeroelastic system was developed.The static output feed back control scheme was used to design a simple multiple-in multiple-out(MIMO)gust alleviation control law.The control law was demonstrated with the Goland+wing model with four control surfaces.The simulation results of different discrete gusts show the capability and good performance of the designed MIMO controller in transonic gust alleviation.展开更多
Abstract Instead of the invariant theory approach employed by Beloshapka and Mamai for constructing the moduli spaces of Beloshapka＇s universal Cauchy-Riemann （CR） models, we consider two alternative approaches bor...Abstract Instead of the invariant theory approach employed by Beloshapka and Mamai for constructing the moduli spaces of Beloshapka＇s universal Cauchy-Riemann （CR） models, we consider two alternative approaches borrowed from the theories of equivalence problem and Lie symmetries, each of which having its own advan- tages. Also the moduli space M（1, 4） associated to the class of universal CR models of CR dimension 1 and codimension 4 is computed by means of the presented methods.展开更多
基金The National Natural Science Foundation of China (No.71771019, 71871130, 71971125)the Science and Technology Special Project of Shandong Provincial Public Security Department (No. 37000000015900920210010001,37000000015900920210012001)。
文摘To improve the level of active traffic management,a short-term traffic flow prediction model is proposed by combining phase space reconstruction(PSR)and extreme gradient boosting(XGBoost)algorithms.Firstly,the traditional data preprocessing method is improved.The new method uses hierarchical clustering to determine the traffic flow state and fills in missing and abnormal data according to different traffic flow states.Secondly,one-dimensional data are mapped into a multidimensional data matrix through PSR,and the time series complex network is used to verify the data reconstruction effect.Finally,the multidimensional data matrix is inputted into the XGBoost model to predict future traffic flow parameters.The experimental results show that the mean square error,average absolute error,and average absolute percentage error of the prediction results of the PSR-XGBoost model are 5.399%,1.632%,and 6.278%,respectively,and the required running time is 17.35 s.Compared with mathematical-statistical models and other machine learning models,the PSR-XGBoost model has clear advantages in multiple predictive indicators,proving its feasibility and superiority in short-term traffic flow prediction.
文摘In this paper, we prove the existence in H＋^2, an incomplete metric subspace of H^2×H^2×H^2, of global solutions to the system for a one-dimensional non-monotone fluid in bounded domainΩ=（0,1）. The results in this paper have improved those previously related results.
基金supported by the Ministry of Science and Technology of the People's Republic of China(MOST)(Grant No.2011CB403504)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant Nos. KZCX2-EW-208 and KZCX2-YW-Q11-02)+1 种基金the National Natural Science Foundation of China(Grant No.41076009)100 Talent Program of the Chinese Academy of Sciences
文摘Using data collected by an Acoustic Doppler Current Profiler （ADCP） on a research cruise in April 2010 in the eastern Indian Ocean, the vertical cun＇ent structures surrounding the Andaman-Nicobar Submarine Ridge （ANSR） are analyzed to investigate the hydrographic responses to the topography in this region. The results show that the topography of ANSR can induce internal waves around the submarine ridge that have a maximum current velocity of 1 m s 1 The spatial struc- ture of the turbulent kinetic energy （TKE） and shear in this region during 2010 is investigated using the high-resolution Princeton Ocean Model （POM） forced by the satellite-based Advanced Scatterometer （ASCAT） winds including the tide, The results show that the model successfully simulates the internal waves around the ANSR. Numerical experiments further indicate that both the topography and tide play an important role in the gen- eration of the internal waves in this region.
基金Project(2009CB320603)supported by the National Basic Research Program of ChinaProject(IRT0712)supported by Program for Changjiang Scholars and Innovative Research Team in University+1 种基金Project(B504)supported by the Shanghai Leading Academic Discipline ProgramProject(61174118)supported by the National Natural Science Foundation of China
文摘In order to reduce the computation of complex problems, a new surrogate-assisted estimation of distribution algorithm with Gaussian process was proposed. Coevolution was used in dual populations which evolved in parallel. The search space was projected into multiple subspaces and searched by sub-populations. Also, the whole space was exploited by the other population which exchanges information with the sub-populations. In order to make the evolutionary course efficient, multivariate Gaussian model and Gaussian mixture model were used in both populations separately to estimate the distribution of individuals and reproduce new generations. For the surrogate model, Gaussian process was combined with the algorithm which predicted variance of the predictions. The results on six benchmark functions show that the new algorithm performs better than other surrogate-model based algorithms and the computation complexity is only 10% of the original estimation of distribution algorithm.
文摘The paper deals with impulse switching function which are used as exciting functions of one- and multidimensional state-space models of power electronic converters. Obviously, these functions are harmonic but using power converters they can be strongly non-harmonic, sometimes piecewise constants with zero spaces between them. Then, one deals with power series of time pulses. The impulse switching functions which are orthogonal ones can be derived from these series. The new impulse switching functions are created using Z-transform, inverse Z-transform and numerical series/sequences. The impulse switching functions created this way can be used for both steady- and transient state investigation of converters.
基金The National Social Science Foundation of China(20BJL103,23BTJ001)The National Natural Science Foundation of China(71934001)+1 种基金The Philosophy and Social Science Foundation of Anhui Province(AHSKZ2022D16)The Project of Graduate Student Research InnovationFund of Anhui University of Finance and Economics(ACYC2022155).
文摘As a pivotal element within the modern service industry,tourism possesses the capacity to reconfigure regional economic dynamics,alter resource flow patterns,and notably influence urban green development.By establishing an evaluation index system for urban green development across 60 prefecture-level cities within the Yellow River Basin from 2006 to 2021,this study employs the spatial Durbin model to delve into the nonlinear relationship between the tourism economy and urban green development.Furthermore,it investigates the heterogeneous impact of the tourism economy on green development across varying levels of urbanization.This study reveals several key findings:(1)Both tourism economy and urban green development exhibit significant spatial clustering,with tourism economy showing“midstream>downstream>upstream”and urban green development showing“downstream>midstream>upstream”.(2)The tourism economy exerts a non-linear positive influence on the green development of cities,characterized by a non-linear inverted“S”shape in its direct impact and a nonlinear“S”shape in its indirect impact.(3)As urbanization rate level escalate,the positive influence of the tourism economy on urban green development follows a non-linear trajectory,initially declining before ascending.Specifically,when the urbanization rate level is below the first threshold value,the tourism economy notably promotes urban green development.However,between the first and second threshold values,this positive impact diminishes,only to rebound beyond the second threshold value.
基金Supported by the National Natural Science Foundation of China (No.41001156)the Beijing Novel Program, China (No.2009B25)+1 种基金the Beijing Municipal Natural Science Foundation, China (No.8102015)the Open Fund of the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau of China (No.10501-295)
文摘For reasons of simplicity, the most commonly used hydrological models are based on the Soil Conservation Service Curve Number （SCS-CN） model, which is probably a good choice for the estimation of runoff on the Loess Plateau of China; however, the high spatial heterogeneity, mainly caused by a fragmented landform and variations in soil type, may limit its applicability to this region. Therefore, applicability of the SCS-CN model to a small watershed, Liudaogou on the plateau, was evaluated and the most appropriate initial abstraction ratio （I~/S） value in the model was quantified by the inverse method. The results showed that the standard SCS-CN model was applicable to the estimation of runoff in the Liudaogou watershed and the model performance was acceptable according to the values of relative error and Nash-Sutcliffe efficiency. The most appropriate Ia/S value for the watershed was 0.22 because with this modified Ia/S value, the model performance was slightly improved. The model performance was not sensitive to the modification of the Ia/S value when one heavy rainfall event （50.1 mm） was not considered, which implied that the model, using a standard Ia/S value, can be recommended for the Liudaogou watershed because single rainfall events exceeding 50 mm seldom occurred in that region. The runoff amount predicted for the Liudaogou watershed by the SCS-CN model, using the modified Ia/S value, increased gradually with increasing rainfall when rainfall values were lower than 50 mm, whereas the predicted amount increased rapidly when the rainfall exceeded 50 mm. These findings may be helpful in solving the problem of serious soil and water loss on the Loess Plateau of China.
文摘Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria： numerical qualities （precision and spectral characteristics）, and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and ＂low-cost＂ shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50176027 and 50706021)a grant from the Research Committee of The Hong Kong Polytechnic University (Grant No.G-U294)
文摘A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.
基金supported by the National Natural Science Foundation of China(Grant Nos.11272005,10902082,91016008)
文摘Gust alleviation is very important to a large flexible aircraft.A nonlinear low-order aerodynamic state space model is required to model the nonlinear aeroelastic responses due to gust.Based on the proper orthogonal decomposition method,a reduced order modeling of gust loads was proposed.And then the open-loop and closed-loop reduced order state space model for the transonic aeroelastic system was developed.The static output feed back control scheme was used to design a simple multiple-in multiple-out(MIMO)gust alleviation control law.The control law was demonstrated with the Goland+wing model with four control surfaces.The simulation results of different discrete gusts show the capability and good performance of the designed MIMO controller in transonic gust alleviation.
文摘Abstract Instead of the invariant theory approach employed by Beloshapka and Mamai for constructing the moduli spaces of Beloshapka＇s universal Cauchy-Riemann （CR） models, we consider two alternative approaches borrowed from the theories of equivalence problem and Lie symmetries, each of which having its own advan- tages. Also the moduli space M（1, 4） associated to the class of universal CR models of CR dimension 1 and codimension 4 is computed by means of the presented methods.
