Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegeta...Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter （ADV）. We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions： inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents （a relatively minor flow superimposed on the primary flow, with significantly different speed and direction）, generated by the anisotropy of the turbulence.展开更多
为了探究胶合板在室内开放环境下VOCs(挥发性有机化合物)释放的规律,选取18 mm厚的三聚氰胺浸渍纸饰面胶合板(MI)、PVC饰面胶合板(PVC)、水性漆饰面胶合板(WP)以及胶合板素板(UP)作为实验材料进行换气率为1次/h的循环试验,利用15 L VOC...为了探究胶合板在室内开放环境下VOCs(挥发性有机化合物)释放的规律,选取18 mm厚的三聚氰胺浸渍纸饰面胶合板(MI)、PVC饰面胶合板(PVC)、水性漆饰面胶合板(WP)以及胶合板素板(UP)作为实验材料进行换气率为1次/h的循环试验,利用15 L VOCs动态采样舱和气相色谱-质谱联用仪,对4种胶合板在实验的第1、3、7、14、21、28 d进行采样分析,进而得到VOCs的释放浓度与组分特征。结果表明:4种胶合板的VOCs浓度在释放平衡期受到装载率的影响要小于释放初期;MI释放初期在4种装载率条件下VOCs浓度差最大;装载率对于WP释放的VOCs浓度影响最小。饰面材料可以有效地阻隔板材内部芳香烃等VOCs向外散发。4种胶合板释放的VOCs浓度随装载率的增大呈现非线性上升趋势。占比大、浓度高的芳香烃类化合物随着装载率的变化呈现不同的增长趋势,醛类物质浓度较低,但总体上也随着装载率的增大而增大。实验测得4种胶合板释放的VOCs浓度以及醛类化合物的浓度均不超过优等品释放限值规定,本次研究为进一步探索胶合板优等品的最大装载率限量提供理论基础,也为室内装修胶合板的科学选材用材提供参考。展开更多
基金supported by the National Basic Research Program of China (973 Program, 2008CB418203)the National Natural Science Foundation of China (Grant No. 50709009)the Elitist Support Project of Ministry of Education (Grant No. NCET-07-0254)
文摘Aquatic vegetation can influence the transport of sediment and contaminants by changing the mean velocity and turbulent flow structure in channels. It is important to understand the hydraulics of the flows over vegetation in order to manage fluvial processes. Experiments in an open-channel flume with natural vegetation were carried out to study the influence of vegetation on the flows. In a half channel with two different densities of vegetation, the flow velocity, Reynolds stresses, and turbulence intensities were measured using an Acoustic Doppler Velocimeter （ADV）. We obtained velocity profiles in the lateral direction, Reynolds stresses in the vertical direction, and the flow transition between the vegetated and non-vegetated zones in different flow regimes. The results show that the streamwise velocity in the vegetated zone with higher density is almost entirely blocked. Reynolds stress distribution distinguishes with two different regions： inside and above the vegetation canopies. The turbulence intensities increase with increasing Reynolds number. The coherent vortices dominate the vertical transport of momentum and are advected clockwise between the vegetated zone and non-vegetated zone by secondary currents （a relatively minor flow superimposed on the primary flow, with significantly different speed and direction）, generated by the anisotropy of the turbulence.
文摘为了探究胶合板在室内开放环境下VOCs(挥发性有机化合物)释放的规律,选取18 mm厚的三聚氰胺浸渍纸饰面胶合板(MI)、PVC饰面胶合板(PVC)、水性漆饰面胶合板(WP)以及胶合板素板(UP)作为实验材料进行换气率为1次/h的循环试验,利用15 L VOCs动态采样舱和气相色谱-质谱联用仪,对4种胶合板在实验的第1、3、7、14、21、28 d进行采样分析,进而得到VOCs的释放浓度与组分特征。结果表明:4种胶合板的VOCs浓度在释放平衡期受到装载率的影响要小于释放初期;MI释放初期在4种装载率条件下VOCs浓度差最大;装载率对于WP释放的VOCs浓度影响最小。饰面材料可以有效地阻隔板材内部芳香烃等VOCs向外散发。4种胶合板释放的VOCs浓度随装载率的增大呈现非线性上升趋势。占比大、浓度高的芳香烃类化合物随着装载率的变化呈现不同的增长趋势,醛类物质浓度较低,但总体上也随着装载率的增大而增大。实验测得4种胶合板释放的VOCs浓度以及醛类化合物的浓度均不超过优等品释放限值规定,本次研究为进一步探索胶合板优等品的最大装载率限量提供理论基础,也为室内装修胶合板的科学选材用材提供参考。
