The classic hydraulic resistance formulas, such as those in the Darcy–Weisbach methods, perform well in the hydraulic design with the characteristic roughness height ks smaller than the flow depth, which can be linke...The classic hydraulic resistance formulas, such as those in the Darcy–Weisbach methods, perform well in the hydraulic design with the characteristic roughness height ks smaller than the flow depth, which can be linked with the momentum roughness height based on the turbulent boundary-layer theory with the log-law formulation. However, when the roughness scale is of the same order as the flow depth, the traditional log-law formulation cannot provide satisfactory results because the flow structure is complicated and the vortices in different layers are dominated by various principles, such as the Karman streets near the channel bed, the mixing layer near the vegetation top, and a canonical turbulent boundary layer above the vegetation layer. Thus, the distribution of the streamwise velocity in the vegetated flow is a combination of the velocity profile linked with the dominant vortex and shows significant differences as compared with the traditional log-law distribution. This paper proposes a new characteristic roughness height of vegetation kv by linking vegetation attributes, especially the characteristics of the cross section in the flow within the vegetation. The power law resistance formula is derived based on a large amount of experimental data. Results show that the new formula is applicable to shallow flows with vegetation.展开更多
In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy （LIBS）. The emission intensity with the spatial confineme...In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy （LIBS）. The emission intensity with the spatial confinement is dependent on the height of the confinement cavity. It is found that, by selecting the appropriate height of cylindrical cavity, the signal enhancement can be significantly increased. At the cylindrical cavity （diameter = 2 mm） with a height of 6 mm, the enhancement ratio has the maximum value （approximately 8.3）, and the value of the relative standard deviation （RSD） （7.6%） is at a minimum, the repeatability of LIBS signal is best. The results indicate that the height of confinement cavity is very important for LIBS technique to reduce the limit of detection and improve the precision.展开更多
为了迅速获取森林资源调查的树高因子,以南宁树木园坛里管理区为研究对象,基于无人机影像数据,结合实地调查,采用PostFlight Terra 3D软件处理得到研究区的DOM、DEM和DSM,利用ArcGIS空间分析技术估测树高;比较分析实测样木树高与估测树...为了迅速获取森林资源调查的树高因子,以南宁树木园坛里管理区为研究对象,基于无人机影像数据,结合实地调查,采用PostFlight Terra 3D软件处理得到研究区的DOM、DEM和DSM,利用ArcGIS空间分析技术估测树高;比较分析实测样木树高与估测树高精度,建立实测样木树高与估测树高相关模型并估测林分平均高。结果表明:通过无人机影像提取的树高与实测树高比较,总体平均精度达90.9%;提取树高与实测树高存在较强相关性,模型树高的平均精度达93.2%;估测林分平均高准确率达97.2%。该树高参数自动化提取方法,能够达到相关实践要求,可以在一定程度上替代人工实测,在人工林中具有广阔的应用前景。展开更多
A new algorithm is proposed to solve the problems of shape-finding of suspension bridge with spatial cables what include tedious iteration,slow convergence speed and even no convergent under some circumstances.In this...A new algorithm is proposed to solve the problems of shape-finding of suspension bridge with spatial cables what include tedious iteration,slow convergence speed and even no convergent under some circumstances.In this paper,the stress analysis of the main cable is carried out,and the relationship between the slope change and the coordinate change is found.This paper also discussed how to find the minimum slope point of symmetrical or asymmetric main cable,and the deformation compatibility equation is established and solved to obtain the shape of main cable.The algorithm in this paper can ensure the convergence of the solution for the suspension bridge with spatial cables.The calculation accuracy is high through the demonstration of the calculation examples.展开更多
基金Project supported by the China Postdoctoral Science Foundation(Grant No.2017M610949)the National Natural Science Foundation of China(Grant No.51439007)
文摘The classic hydraulic resistance formulas, such as those in the Darcy–Weisbach methods, perform well in the hydraulic design with the characteristic roughness height ks smaller than the flow depth, which can be linked with the momentum roughness height based on the turbulent boundary-layer theory with the log-law formulation. However, when the roughness scale is of the same order as the flow depth, the traditional log-law formulation cannot provide satisfactory results because the flow structure is complicated and the vortices in different layers are dominated by various principles, such as the Karman streets near the channel bed, the mixing layer near the vegetation top, and a canonical turbulent boundary layer above the vegetation layer. Thus, the distribution of the streamwise velocity in the vegetated flow is a combination of the velocity profile linked with the dominant vortex and shows significant differences as compared with the traditional log-law distribution. This paper proposes a new characteristic roughness height of vegetation kv by linking vegetation attributes, especially the characteristics of the cross section in the flow within the vegetation. The power law resistance formula is derived based on a large amount of experimental data. Results show that the new formula is applicable to shallow flows with vegetation.
基金the support from the Fundamental Research Project of Chinese State Key Laboratory of Laser Interaction with Matter(Grant No.SKLLIM 1502)the National Natural Science Foundation of China(Grant Nos.11674128,11474129 and 11504129)the China Postdoctoral Science Foundation(Grant No.2014M551169)
文摘In this paper, we present a study on the spatial confinement effect of laser-induced plasma with a cylindrical cavity in laser-induced breakdown spectroscopy （LIBS）. The emission intensity with the spatial confinement is dependent on the height of the confinement cavity. It is found that, by selecting the appropriate height of cylindrical cavity, the signal enhancement can be significantly increased. At the cylindrical cavity （diameter = 2 mm） with a height of 6 mm, the enhancement ratio has the maximum value （approximately 8.3）, and the value of the relative standard deviation （RSD） （7.6%） is at a minimum, the repeatability of LIBS signal is best. The results indicate that the height of confinement cavity is very important for LIBS technique to reduce the limit of detection and improve the precision.
文摘为了迅速获取森林资源调查的树高因子,以南宁树木园坛里管理区为研究对象,基于无人机影像数据,结合实地调查,采用PostFlight Terra 3D软件处理得到研究区的DOM、DEM和DSM,利用ArcGIS空间分析技术估测树高;比较分析实测样木树高与估测树高精度,建立实测样木树高与估测树高相关模型并估测林分平均高。结果表明:通过无人机影像提取的树高与实测树高比较,总体平均精度达90.9%;提取树高与实测树高存在较强相关性,模型树高的平均精度达93.2%;估测林分平均高准确率达97.2%。该树高参数自动化提取方法,能够达到相关实践要求,可以在一定程度上替代人工实测,在人工林中具有广阔的应用前景。
文摘A new algorithm is proposed to solve the problems of shape-finding of suspension bridge with spatial cables what include tedious iteration,slow convergence speed and even no convergent under some circumstances.In this paper,the stress analysis of the main cable is carried out,and the relationship between the slope change and the coordinate change is found.This paper also discussed how to find the minimum slope point of symmetrical or asymmetric main cable,and the deformation compatibility equation is established and solved to obtain the shape of main cable.The algorithm in this paper can ensure the convergence of the solution for the suspension bridge with spatial cables.The calculation accuracy is high through the demonstration of the calculation examples.
