The role of different forms of natural riparian vegetation on turbulence and kinetic energy characteristics     

O. Yagci  U. Tschiesche  M.S. Kabdasli 《Advances in water resources》2010

Flow measurements were conducted by ADV Vectrino to investigate the role of different forms of single natural emergent vegetation elements on kinetic energy characteristics and the flow structure in open channel flow. Experiments were carried out for both forms of “erect” and “compressed” vegetation. The findings revealed that the form of “erect” has greater retaining influence on time-averaged mean velocity characteristics than “compressed” form. Furthermore, the turbulence and kinetic energy patterns behind the single vegetation were also examined. An empirical equation giving the relationship between the kinetic energy components of flow was derived based on the data. The ratio between turbulence kinetic energy and mean kinetic energy at a certain distance downstream of vegetation element was predicted by the empirical equation depending on the vegetation characteristics. These predictions were compared with a different experimental data set and produced satisfactory results. Also, the mean flow and turbulence characteristics behind an isolated natural plant and a volumetrically equivalent rigid cylinder were also compared.  相似文献   

Effect of submerged aquatic vegetation on turbulence induced by an oscillating grid   总被引：1，自引：0，他引：1  

Dolors Pujol  Jordi ColomerTeresa Serra  Xavier Casamitjana 《Continental Shelf Research》2010

In wetlands wind-induced turbulence significantly affects the bottom boundary, and the interaction between turbulence and plant canopies is therefore particularly important. The aim of this study is to advance understanding of the impact of this interaction in submerged aquatic vegetation (SAV)¹ on vertical mixing in a fluid dominated by turbulence. Wind-generated turbulence was simulated in the laboratory using an oscillating grid. We quantify the vertical distribution of turbulent kinetic energy (TKE)² above and within different types of vegetation, measured by an acoustic Doppler velocimeter. Experimental conditions are analysed in two canopy models (rigid and semi-rigid) with seven solid plant fractions (SPFs)³, three stem diameters (d)⁴ and three oscillation grid frequencies (f)⁵ and four natural SAVs (Cladium mariscus, Potamogeton nodosus, Myriophyllum verticillatum and Ruppia maritima).  相似文献   

湍流混合输运通量的数学物理描述基础——高确定性闭合的湍流二阶矩和基本特征量控制方程组     

袁业立  庄展鹏  杨光兵 《海洋与湖沼》2017,48(5):895-911

湍流,在海洋动力系统其他类运动的控制方程组中,主要以输运通量剩余项的形式出现,它是最重要的海洋混合运动主体。本文的主要研究目标是,在湍流最新研究成果及其子系统控制方程组基础上,提出高确定性的二阶矩闭合原理,导出闭合的二阶矩和基本特征量控制方程组,建立湍流输运通量的数学物理描述基础。现有的湍流基本特征量方程组,其右端项的闭合办法实际上是非独立的。因此要么在今后的研究中引入独立的闭合办法,要么回归到湍流的现场实验分析研究,给出独立的特征量实验关系,从而有可能得到湍流混合系数的解析估计。  相似文献   

一种采用图像特征匹配技术的RGB-D SLAM算法     

许晓东  陈国良  李晓园  周文振  杜珊珊 《测绘通报》2017,(10):48-51

针对复杂环境下运动机器人自主运行的任务要求,提出了一种采用图像特征匹配技术的视觉SlAM算法。相比于传统滤波器方法在机器人长时间运动过程中产生的误差积累,采用了基于图优化的SlAM方法,本文算法分为两个部分：前端和后端。前端负责处理图像数据提取机器人位姿几何关系,首先提取彩色RGB图像的特征点,创建特征点的高维特征描述子,建立特征点的位置对应关系;后端负责表达各时刻机器人的位姿并最大化地消除轨迹漂移问题,根据前端处理所产生的信息,构建一个代表机器人几何位置关系及其不确定性的关系图,通过对图的优化将测量轨迹最大化地逼近真实轨迹,最后生成稀疏点云地图和高精度的机器人运行轨迹。试验表明本文所提出的方法实用性强,具有较高的鲁棒性。  相似文献   

The influence of asymmetries in overlying stratification on near-bed turbulence and sediment suspension in a partially mixed estuary   总被引：3，自引：1，他引：2  

Malcolm E.?ScullyEmail author  Carl T.?Friedrichs 《Ocean Dynamics》2003,53(3):208-219

Data collected from the York River estuary demonstrate the importance of asymmetries in stratification to the suspension and transport of fine sediment. Observations collected during two 24-h deployments reveal greater concentrations of total suspended solids during the flood phase of the tide despite nearly symmetric near-bed tidal current magnitude. In both cases, tidally averaged net up-estuary sediment transport near the bed was clearly observed despite the fact that tidally averaged residual near-bed currents were near zero. Tidal straining of the along-channel salinity gradient resulted in a stronger pycnocline lower in the water column during the ebb phase of the tide and appeared to limit sediment suspension. Indirect measurements suggest that the lower, more intense, pycnocline on the ebb acted as a barrier, limiting turbulent length scales and reducing eddy diffusivity well below the pycnocline, even though the lower water column was locally well mixed. In order to more conclusively link changes in stratification to properties of near-bed eddy viscosity and diffusivity, longer duration tripod and mooring data from an additional experiment are examined, that included direct measurement of turbulent velocities. These additional data demonstrate how slight increases in stratification can limit vertical mixing near the bed and impact the structure of the eddy viscosity below the pycnocline. We present evidence that the overlying pycnocline can remotely constrain the vertical turbulent length scale of the underlying flow, limiting sediment resuspension. As a result, the relatively small changes in stratification caused by tidal straining of the pycnocline allow sediment to be resuspended higher in the water column during the flood phase of the tide, resulting in preferential up-estuary transport of sediment.Responsible Editor: Iris Grabemann  相似文献   

Transport-Dissipation Analytical Solutions to the E-∈Turbulence Model and their Role in Predictions of the Neutral ABL     

A. Frank R. Freedman  B. Mark Z. Jacobson 《Boundary-Layer Meteorology》2002,102(1):117-138

E- turbulence model predictions of the neutralatmospheric boundary layer (NABL) are reinvestigated to determine thecause for turbulence overpredictions found in previous applications. Analytical solutions to the coupled E and equations for the case of steady balance between transport and dissipation terms, the dominant balance just below the NABL top, are derived. It is found that analytical turbulence profiles laminarizeat a finite height only for values of closure parameter ratio c ₂ /_e equal toor slightly greater than one, with laminarization as z for greater . The point = 2 is additionally foundthat where analytical turbulent length scale (l) profilesmade a transition from ones ofdecreasing ( < 2) to increasing ( > 2)values with height. Numerically predicted profiles near the NABL topare consistent with analytical findings. The height-increasingvalues of l predicted throughout the NABL with standard values ofclosure parameters thus appear a consequence of 2.5(> 2), implied by these values (c ₂ = 1.92, _{= 1.3}, _{e = 1}). Comparison of numericalpredictions with DNS data shows that turbulence overpredictions obtained with standard-valued parameters are rectifiedby resetting and _e to 1.1 and 1.6, respectively, giving, with c ₂ = 1.92, 1.3, and laminarization of the NABL's cappingtransport-dissipation region at a finite height.  相似文献   

Study On Development And Application Of A Regional Pbl Numerical Model   总被引：9，自引：0，他引：9  

Weimei Jiang  Mi Zhou  Min Xu  Weiguo Wang 《Boundary-Layer Meteorology》2002,104(3):491-503

A regional scale (a few km to a few hundred km, minutes to days)planetary boundary layer (PBL) numerical model (RPBLM) has been successfully developed to simulateprecisely the boundary-layer three-dimensional characteristics. The RPBLM model with a high-resolutionnon-hydrostatic E - turbulence closure scheme has been applied to diagnose and prognosticate the PBL characteristicsover a complex underlying surface in the Hong Kong area of 60 km × 48 km. It is shown that the RPBLMmodel can be used to simulate the PBL characteristics including wind, temperature, water vapour andturbulence over such a complex underlying surface and that the simulated result is reasonably in agreementwith observations.  相似文献   

Experiment of near surface layer parameters in ice camp over Arctic Ocean     

卞林根  张占海  马永锋  陆龙骅  程斌 《极地研究(英文版)》2007,18(2):91-99

Estimates of near surface layer parameters over 78°N drifting ice in ice camp over the Arctic ocean are made using bulk transfer methods with the data from the experiments operated by the Chinese Arctic Scientific Expedition in August 22-September 3,2003.The results show that the net radiation received by the snow surface is only 3.6 W/m2,among which the main part transported into atmosphere in term of sensible heat and latent heat,which account for 52% and 31% respectively,and less part being transported to deep ice in the conductive process.The bulk transfer coefficient of momentum is about 1.16×10-3 in the near neutral layer,which is a little smaller than that obtained over 75°N drifting ice.However,to compare with the results observed over 75°N drifting ice over the Arctic Ocean in 1999,it can be found that the thermodynamic and momentum of interactions between sea and air are significant different with latitudes,concentration and the scale of sea ice.It is very important on considering the effect of sea-air-ice interaction over the Arctic Ocean when studying climate modeling.  相似文献   

Numerical modelling of the turbulent flow developing within and over a 3-d building array,part ii: a mathematical foundation for a distributed drag force approach   总被引：1，自引：1，他引：0  

Fue-sang Lien  Eugene Yee  John D. Wilson 《Boundary-Layer Meteorology》2005,114(2):245-285

In this paper, we lay the foundations of a systematic mathematical formulation for the governing equations for flow through an urban canopy (e.g., coarse-scaled building array) where the effects of the unresolved obstacles on the flow are represented through a distributed mean-momentum sink. This, in turn, implies additional corresponding terms in the transport equations for the turbulence quantities. More specifically, a modified k-- model is derived for the simulation of the mean wind speed and turbulence for a neutrally stratified flow through and over a building array, where groups of buildings in the array are aggregated and treated as a porous medium. This model is based on time averaging the spatially averaged Navier--Stokes equations, in which the effects of the obstacle--atmosphere interaction are included through the introduction of a volumetric momentum sink (representing drag on the unresolved buildings in the array).The k-- turbulence closure model requires two additional prognostic equations, namely one for the time-averaged resolved-scale kinetic energy of turbulence,, and another for the dissipation rate, , of . The transport equation for is derived directly from the transport equation for the spatially averaged velocity, and explicitly includes additional sources and sinks that arise from time averaging the product of the spatially averaged velocity fluctuations and the distributed drag force fluctuations. We show how these additional source/sink terms in the transport equation for can be obtained in a self-consistent manner from a parameterization of the sink term in the spatially averaged momentum equation. Towards this objective, the time-averaged product of the spatially averaged velocity fluctuations and the distributed drag force fluctuations can be approximated systematically using a Taylor series expansion. A high-order approximation is derived to represent this source/sink term in the transport equation for . The dissipation rate () equation is simply obtained as a dimensionally consistent analogue of the equation. The relationship between the proposed mathematical formulation of the equations for turbulent flow within an urban canopy (where the latter is treated as a porous medium) and an earlier heuristic two-band spectral decomposition for parameterizing turbulence in a plant canopy is explored in detail.  相似文献   

An Assessment of Turbulence Profiles in Rural and Urban Environments Using Local Measurements and Numerical Weather Prediction Results   总被引：1，自引：1，他引：0  

N.?L.?Morrison  H.?N.?WebsterEmail author 《Boundary-Layer Meteorology》2005,115(2):223-239

Profiles of velocity variances based on observations in flat rural areas are well established, and are used for modelling turbulent dispersion in all types of regions including those of complex terrain and urban areas. Surface-based and balloon observations are used to assess the profiles in both rural and urban areas. It is shown that, with good meteorological inputs for the locality of friction velocity and surface sensible heat flux, the profiles are equally well suited to urban areas. The sensitivity of the profiles to the input meteorological data, in particular using numerical weather prediction (NWP) data, is discussed. This highlights the limitations of NWP data for dispersion modelling and stresses the importance of schemes for modelling urban meteorology.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.  相似文献