Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend an...Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.展开更多
Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams,shear deformation of steel beams and interface slip between steel beams and concrete slabs...Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams,shear deformation of steel beams and interface slip between steel beams and concrete slabs,the governing differential equations and boundary conditions of the steel-concrete composite box beams under lateral loading were derived using energy-variational method.The closed-form solutions for stress,deflection and slip of box beams under lateral loading were obtained,and the comparison of the analytical results and the experimental results for steel-concrete composite box beams under concentrated loading or uniform loading verifies the closed-form solution.The investigation of the parameters of load effects on composite box beams shows that:1) Slip stiffness has considerable impact on mid-span deflection and end slip when it is comparatively small;the mid-span deflection and end slip decrease significantly with the increase of slip stiffness,but when the slip stiffness reaches a certain value,its impact on mid-span deflection and end slip decreases to be negligible.2) The shear deformation has certain influence on mid-span deflection,and the larger the load is,the greater the influence is.3) The impact of shear deformation on end slip can be neglected.4) The strain of bottom plate of steel beam decreases with the increase of slip stiffness,while the shear lag effect becomes more significant.展开更多
In order to resolve the traffic congestion problem, many cable-stayed bridges are designed with a large width to span ratio. This results in significant shear lag effect to cause nonuniform stress distribution along t...In order to resolve the traffic congestion problem, many cable-stayed bridges are designed with a large width to span ratio. This results in significant shear lag effect to cause nonuniform stress distribution along the flanges of the beam of bridge. This paper reports study on the shear lag effect of the Lanzhou Xiaoxihu Yellow River Bridge. A 3D finite element model of the bridge was developed and finite element analysis (FEA) was done to obtain the theoretical results. To evaluate the theoretical results, a scaled model was made to conduct static test in laboratory. The experiment results accorded with the results obtained by FEA. It is proved that FEA is an effective method to predict shear lag effect of bridges of this type.展开更多
This paper studies a kind of non-autonomous respiratory disease model with a lag effect.First of all,the permanence and extinction of the system are discussed by using the comparison principle and some differential in...This paper studies a kind of non-autonomous respiratory disease model with a lag effect.First of all,the permanence and extinction of the system are discussed by using the comparison principle and some differential inequality techniques.Second,it assumes that all coefficients of the system are periodic.The existence of positive periodic solutions of the system is proven,based on the continuation theorem in coincidence with the degree theory of Mawhin and Gaines.In the meantime,the global attractivity of positive periodic solutions of the system is obtained by constructing an appropriate Lyapunov functional and using the Razumikin theorem.In addition,the existence and uniform asymptotic stability of almost periodic solutions of the system are analyzed by assuming that all parameters in the model are almost periodic in time.Finally,the theoretical derivation is verified by a numerical simulation.展开更多
The project of Xiaoxihu Yellow River Bridge in Lanzhou is chosen as partial cable-stayed bridge. To get the shear lag effect and anti-earthquake performance of the actual bridge under various loading conditions, organ...The project of Xiaoxihu Yellow River Bridge in Lanzhou is chosen as partial cable-stayed bridge. To get the shear lag effect and anti-earthquake performance of the actual bridge under various loading conditions, organic glass scaled model was adopted to have an experiment and a theory research at one time. The experiment result is the basically same as the theory calculation which proves the FEA method can well calculate shear lag effect and dynamical performance. As a result, because the bridge is located in a seismic area of 8 degree, an elasto-plastic seismic checking is performed by customized FEA program in this paper.展开更多
Intra-annual climatic variability plays a critical role in regulating wood formation dynamics during the growing season,particularly in seasonally arid regions—such as the Qinling Mountains,China,and Mediterranean fo...Intra-annual climatic variability plays a critical role in regulating wood formation dynamics during the growing season,particularly in seasonally arid regions—such as the Qinling Mountains,China,and Mediterranean forests—where trees exhibit bimodal radial growth patterns as an adaptive response to water stress.While these growth patterns reflect immediate climatic conditions,the role of ecological memory,specifically vegetation growth carryover(VGC)and lagged climate effects(LCEs),remains poorly quantified.We employed the Vaganov–Shashkin(VS)model to analyze intra-annual bimodal growth patterns in two regions and used a vector autoregressive model with impulse response functions to assess the duration and intensity of VGC and LCE on tree-ring growth and remote sensing vegetation indices(leaf area index(LAI)and gross primary productivity(GPP)).Our results revealed bimodal growth patterns with spring and autumn peaks,but the autumn peak occurred earlier in the Qinling Mountains(August–October)than in Mediterranean forests(late September–October).VGC exerted the strongest influence on tree-ring growth in the first year,diminishing significantly after eight years in both regions(p<0.01).Tree-ring growth exhibited positive LCE responses to precipitation and soil moisture but negative responses to temperature(p<0.05).Remote sensing indices(LAI and GPP)displayed stronger VGC effects in the Qinling Mountains than in Mediterranean forests.While both LAI and GPP responded positively to soil moisture,temperature-induced LCE was positive in the Qinling Mountains but negative in the Mediterranean forests(p<0.05).Overall,VGC was the dominant ecological memory effect in both regions.Our results suggest that coupling the VGC and LCE of multiple vegetation growth indicators at multiple scales has the potential to improve the accuracy of global dynamic vegetation models.展开更多
Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient me...Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.展开更多
In order to study the effect of time lag and stress loading rates on rock deformation,the conventional stepped stress loading mode was changed into a continuous mode to investigate the effect of effective pressure on ...In order to study the effect of time lag and stress loading rates on rock deformation,the conventional stepped stress loading mode was changed into a continuous mode to investigate the effect of effective pressure on permeability and porosity.The time lag effect of rock deformation illustrating the relationship between changes in permeability and steady time was studied.Permeability reduction ratios were measured under different stress loading rates which were achieved by different pump rate settings.The results show that permeability and porosity gradually decrease with increases in effective pressure.Permeability at high effective pressure attains stability quickly.Steady times at low effective pressure are very long.Reduction in permeability at lower stress loading rates is small,while,in contrast,it is large at high stress loading rates.展开更多
The objective of this paper is to identify time lag effect in the relationship between supply chain management and financial performance.We hypothesize that firms with higher supply chain management capability are ass...The objective of this paper is to identify time lag effect in the relationship between supply chain management and financial performance.We hypothesize that firms with higher supply chain management capability are associated with higher financial performance and the impact would last longer.In addition,we introduce two contextual variables,ownership and market orientation,to detect the moderating effect of ownership structure and organizational culture,respectively.We use firm-level empirical data from 1,131 public Chinese manufacturing firms for the 2010–2019 period to investigate the effect and the result shows that there is a two-year time lag effect in the relationship,which means the positive impact of current supply chain management would last for three years.Furthermore,we find evidence that supply chain management in non-state-owned firms is more efficient and its positive financial impact would last longer than that in state-owned enterprises.Finally,we indicate that market-orientation can’t moderate the relationship between supply chain management and financial performance.展开更多
Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated st...Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51709021)the Open Foundation of the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering(Grant No.2016491111)
文摘Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.
基金Projects(51078355,50938008) supported by the National Natural Science Foundation of ChinaProject(094801020) supported by the Academic Scholarship for Doctoral Candidates of the Ministry of Education,China+1 种基金Project(CX2011B093) supported by the Doctoral Candidate Research Innovation Project of Hunan Province, ChinaProject(20117Q008) supported by the Central University Basic Scientific Research Business Expenses Special Fund of China
文摘Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams,shear deformation of steel beams and interface slip between steel beams and concrete slabs,the governing differential equations and boundary conditions of the steel-concrete composite box beams under lateral loading were derived using energy-variational method.The closed-form solutions for stress,deflection and slip of box beams under lateral loading were obtained,and the comparison of the analytical results and the experimental results for steel-concrete composite box beams under concentrated loading or uniform loading verifies the closed-form solution.The investigation of the parameters of load effects on composite box beams shows that:1) Slip stiffness has considerable impact on mid-span deflection and end slip when it is comparatively small;the mid-span deflection and end slip decrease significantly with the increase of slip stiffness,but when the slip stiffness reaches a certain value,its impact on mid-span deflection and end slip decreases to be negligible.2) The shear deformation has certain influence on mid-span deflection,and the larger the load is,the greater the influence is.3) The impact of shear deformation on end slip can be neglected.4) The strain of bottom plate of steel beam decreases with the increase of slip stiffness,while the shear lag effect becomes more significant.
文摘In order to resolve the traffic congestion problem, many cable-stayed bridges are designed with a large width to span ratio. This results in significant shear lag effect to cause nonuniform stress distribution along the flanges of the beam of bridge. This paper reports study on the shear lag effect of the Lanzhou Xiaoxihu Yellow River Bridge. A 3D finite element model of the bridge was developed and finite element analysis (FEA) was done to obtain the theoretical results. To evaluate the theoretical results, a scaled model was made to conduct static test in laboratory. The experiment results accorded with the results obtained by FEA. It is proved that FEA is an effective method to predict shear lag effect of bridges of this type.
基金supported by the National Natural ScienceFoundation of China(11401002,11771001)the Natural Science Foundation of Anhui Province(2008085MA02)+3 种基金the Natural Science Fund for Colleges and Universities in Anhui Province(KJ2018A0029)the Teaching Research Project of Anhui University(ZLTS2016065)the Quality engineering project of colleges and universities in Anhui Province(2020jyxm0103)the Science Foundation of Anhui Province Universities(KJ2019A005)。
文摘This paper studies a kind of non-autonomous respiratory disease model with a lag effect.First of all,the permanence and extinction of the system are discussed by using the comparison principle and some differential inequality techniques.Second,it assumes that all coefficients of the system are periodic.The existence of positive periodic solutions of the system is proven,based on the continuation theorem in coincidence with the degree theory of Mawhin and Gaines.In the meantime,the global attractivity of positive periodic solutions of the system is obtained by constructing an appropriate Lyapunov functional and using the Razumikin theorem.In addition,the existence and uniform asymptotic stability of almost periodic solutions of the system are analyzed by assuming that all parameters in the model are almost periodic in time.Finally,the theoretical derivation is verified by a numerical simulation.
文摘The project of Xiaoxihu Yellow River Bridge in Lanzhou is chosen as partial cable-stayed bridge. To get the shear lag effect and anti-earthquake performance of the actual bridge under various loading conditions, organic glass scaled model was adopted to have an experiment and a theory research at one time. The experiment result is the basically same as the theory calculation which proves the FEA method can well calculate shear lag effect and dynamical performance. As a result, because the bridge is located in a seismic area of 8 degree, an elasto-plastic seismic checking is performed by customized FEA program in this paper.
基金supported by the National Natural Science Foundation of China(Nos.42277448,42330501,41971104,and 41807431)。
文摘Intra-annual climatic variability plays a critical role in regulating wood formation dynamics during the growing season,particularly in seasonally arid regions—such as the Qinling Mountains,China,and Mediterranean forests—where trees exhibit bimodal radial growth patterns as an adaptive response to water stress.While these growth patterns reflect immediate climatic conditions,the role of ecological memory,specifically vegetation growth carryover(VGC)and lagged climate effects(LCEs),remains poorly quantified.We employed the Vaganov–Shashkin(VS)model to analyze intra-annual bimodal growth patterns in two regions and used a vector autoregressive model with impulse response functions to assess the duration and intensity of VGC and LCE on tree-ring growth and remote sensing vegetation indices(leaf area index(LAI)and gross primary productivity(GPP)).Our results revealed bimodal growth patterns with spring and autumn peaks,but the autumn peak occurred earlier in the Qinling Mountains(August–October)than in Mediterranean forests(late September–October).VGC exerted the strongest influence on tree-ring growth in the first year,diminishing significantly after eight years in both regions(p<0.01).Tree-ring growth exhibited positive LCE responses to precipitation and soil moisture but negative responses to temperature(p<0.05).Remote sensing indices(LAI and GPP)displayed stronger VGC effects in the Qinling Mountains than in Mediterranean forests.While both LAI and GPP responded positively to soil moisture,temperature-induced LCE was positive in the Qinling Mountains but negative in the Mediterranean forests(p<0.05).Overall,VGC was the dominant ecological memory effect in both regions.Our results suggest that coupling the VGC and LCE of multiple vegetation growth indicators at multiple scales has the potential to improve the accuracy of global dynamic vegetation models.
基金Projects(51078355,50938008) supported by the National Natural Science Foundation of ChinaProject(CX2011B093) supported by the Doctoral Candidate Research Innovation Program of Hunan Province, ChinaProject(20117Q008) supported by the Basic Scientific Research Funds for Central Universities of China
文摘Considering three longitudinal displacement functions and uniform axial displacement functions for shear lag effect and uniform axial deformation of thin-walled box girder with varying depths,a simple and efficient method with high precision to analyze the shear lag effect of thin-walled box girders was proposed.The governing differential equations and boundary conditions of the box girder under lateral loading were derived based on the energy-variational method,and closed-form solutions to stress and deflection corresponding to lateral loading were obtained.Analysis and calculations were carried out with respect to a trapezoidal box girder under concentrated loading or uniform loading and a rectangular box girder under concentrated loading.The analytical results were compared with numerical solutions derived according to the high order finite strip element method and the experimental results.The investigation shows that the closed-form solution is in good agreement with the numerical solutions derived according to the high order finite strip method and the experimental results,and has good stability.Because of the shear lag effect,the stress in cross-section centroid is no longer zero,thus it is not reasonable enough to assume that the strain in cross-section centroid is zero without considering uniform axial deformation.
基金Projects 2008ZX05009-004 supported by the National Key Sci-Tech Major Special Item2006CB705805 by the National Basic Research Program of Chinasupported by the National Basic Research Program of China and "enhanced oil recovery basic theory for low permeability reservoirs" under grant 2002CCA00700
文摘In order to study the effect of time lag and stress loading rates on rock deformation,the conventional stepped stress loading mode was changed into a continuous mode to investigate the effect of effective pressure on permeability and porosity.The time lag effect of rock deformation illustrating the relationship between changes in permeability and steady time was studied.Permeability reduction ratios were measured under different stress loading rates which were achieved by different pump rate settings.The results show that permeability and porosity gradually decrease with increases in effective pressure.Permeability at high effective pressure attains stability quickly.Steady times at low effective pressure are very long.Reduction in permeability at lower stress loading rates is small,while,in contrast,it is large at high stress loading rates.
基金This work was supported by the National Natural Science Foundation of China(NSFC),under Grant 71871114.
文摘The objective of this paper is to identify time lag effect in the relationship between supply chain management and financial performance.We hypothesize that firms with higher supply chain management capability are associated with higher financial performance and the impact would last longer.In addition,we introduce two contextual variables,ownership and market orientation,to detect the moderating effect of ownership structure and organizational culture,respectively.We use firm-level empirical data from 1,131 public Chinese manufacturing firms for the 2010–2019 period to investigate the effect and the result shows that there is a two-year time lag effect in the relationship,which means the positive impact of current supply chain management would last for three years.Furthermore,we find evidence that supply chain management in non-state-owned firms is more efficient and its positive financial impact would last longer than that in state-owned enterprises.Finally,we indicate that market-orientation can’t moderate the relationship between supply chain management and financial performance.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences[grant numbers XDA23090102]the National Natural Science Foundation of China[grant numbers 42175078 and 42075040]+1 种基金the Health Meteorological Project of Hebei Province[grant number FW202150]the National Key Research and Development Program of China[grant number 2018YFA0606203].
基金Projects(51078355,50938008)supported by the National Natural Science Foundation of ChinaProject(094801020)supported by the Academic Scholarship for Doctoral Candidates of the Ministry of Education,China+1 种基金Project(CX2011B093)supported by the Doctoral Candidate Research Innovation Project of Hunan Province,ChinaProject(20117Q008)supported by the Central University Basic Scientific Research Business Expenses Special Fund of China
文摘Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.
