Influence of non-uniform flow conditions on riverbed stability: The case of smooth-to-rough transitions

2016 ◽  
pp. 504-504
Author(s):  
D Duma ◽  
S Erpicum ◽  
P Archambeau ◽  
M Pirotton ◽  
B Dewals
Keyword(s):  
Uniform Flow ◽  
Flow Conditions

Self-Aeration and Friction over Rock Chutes in Uniform Flow Conditions

2010 ◽  
Vol 136 (11) ◽  
pp. 959-964 ◽  
Author(s):  
Stefano Pagliara ◽  
Iacopo Carnacina ◽  
Thendiyath Roshni
Keyword(s):  
Uniform Flow ◽  
Flow Conditions

Dynamic Modeling of a Steerable Drifter

2020 ◽  
Author(s):  
Eric Gaskell ◽  
Xiaobo Tan
Keyword(s):  
Energy Efficient ◽  
Uniform Flow ◽  
Prior Work ◽  
Flow Conditions ◽  
Local Flow ◽  
Ambient Flow ◽  
Control Scheme ◽  
Parabolic Flow ◽  
And Control ◽  
Relative Flow

Abstract Drifters are energy-efficient platforms for monitoring rivers and oceans. Prior work largely focused on free-floating drifters that drift passively with flow and have little or no controllability. In this paper we propose steerable drifters that use multiple rudders for modulating the hydrodynamic forces and thus maneuvering. A dynamic model for drifters with multiple rudders is presented. Simulation is conducted to examine the behavior of the drifter in two different flow conditions, uniform flow and parabolic flow. When there is no difference in relative flow between the rudders, as in uniform flow, the drifter can only be controlled until its velocity approaches that of the water. However, when present, local flow differentials can be exploited to initiate motion lateral to the ambient flow and control the trajectory of the drifter to some degree. The motion of the drifter is further classified as belonging to one of three major modes, rotational, oscillatory, and stable. The behavior of the drifter in a simulated river was mapped for different rudder angles. Identifying the parameters that induce each mode lays the groundwork for developing a feedback control scheme for the drifter.

HistoFlex—a microfluidic device providing uniform flow conditions enabling highly sensitive, reproducible and quantitative in situ hybridizations

Lab on a Chip ◽  
2011 ◽  
Vol 11 (22) ◽  
pp. 3896 ◽  
Author(s):  
Martin Jensen Søe ◽  
Fridolin Okkels ◽  
David Sabourin ◽  
Massimo Alberti ◽  
Kim Holmstrøm ◽  
...  
Keyword(s):  
Microfluidic Device ◽  
Uniform Flow ◽  
Flow Conditions ◽  
Highly Sensitive ◽  
In Situ Hybridizations

scholarly journals Modeling the effect of vegetation on river floodplain hydraulics

2013 ◽  
Vol 14 (3) ◽  
pp. 371-377
Keyword(s):  
Free Surface ◽  
Uniform Flow ◽  
Low Flow ◽  
Grid Refinement ◽  
Flow Conditions ◽  
Mean Flow ◽  
River Floodplains ◽  
Tetrahedral Elements ◽  
The Mean ◽  
Grid Independence

Vegetation in river floodplains has significant influence on the flood hydraulics and fate of suspended sediments, nutrients and contaminants. In the present, work preliminary 3-D calculations were performed to examine the effect of vegetation on the mean flow in open channels using the CFD model CFX-12.1, employing the RANS k-epsilon turbulence model. Calculated flow velocity distributions were compared against an experiment of free surface uniform flow in a vegetated experimental channel, filled with cylindrical submerged elements representing vegetation; these elements were rigid and arranged in a staggered pattern. Four unstructured numerical grids were employed, ranging from approximately 9.5 to 27.5 millions of tetrahedral elements. The main characteristics of the flow were (a) the formation of small recirculation regions in the wakes of the cylinders and (b) the relative uniform flow conditions throughout the length of the channel. Low flow velocities were observed in the vegetated region, implying the resistance due to vegetation, and higher velocities close to the free surface. The best agreement with experimental data was achieved for the finest grid that also included grid refinement at the top of the cylinders. Grid independence behaviour using relatively very fine grids was rather surprising and requires further detailed investigation.

CFD Investigation Into the Flow Field in a Four Row Staggered Plate Fin-and-Tube Heat Exchanger Experiencing Gross Fin-Side Flow Maldistribution Using the K-ω Turbulence Model

2009 ◽  
Author(s):  
J. Hoffmann-Vocke ◽  
J. Neale ◽  
M. Walmsley
Keyword(s):  
Heat Exchanger ◽  
Flow Field ◽  
Flow Regime ◽  
Turbulence Model ◽  
Uniform Flow ◽  
Flow Conditions ◽  
Cfd Modelling ◽  
Tube Heat Exchanger ◽  
Flow Maldistribution ◽  
Side Flow

The flow field in a section of a four-row staggered plate fin-and-tube heat exchanger with gross inlet flow maldistribution has been investigated using CFD modelling. The commercial CFD code Fluent 6.3 has been used to carry out 3D unsteady flow modelling using the low Reynolds number variation of the standard k-ω turbulence model. A significant amount of flow dispersion is shown to occur upstream of the heat exchanger inlet resulting in a 37% reduction in inlet velocity before the flow enters the heat exchanger. Flow dispersion as the fluid passes through the heat exchanger results in a further 28% reduction in the average flow velocity. Significant sections of the heat exchanger experience angled flow resulting in a flow pattern commonly seen in inline tube arrangements. The lower friction factor of the inline flow regime results in a higher mass flux when compared to areas exhibiting the staggered flow regime. This variation results in off-centre velocity peaks entering and leaving the heat exchanger. On average the non-uniform flow cases resulted in a 29.4% increase in pressure drop across the heat exchanger system when compared to uniform flow conditions. Average heat transfer coefficients for the non-uniform flow conditions showed a 20.3% increase over uniform flow conditions of equal mass flow.

Thrombus formation on artificial surfaces: Correlative microscopy

1990 ◽  
Vol 48 (3) ◽  
pp. 840-841
Author(s):  
Quintin J. Lai ◽  
Stuart L. Cooper ◽  
Ralph M. Albrecht
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Low Voltage ◽  
Thrombus Formation ◽  
Blood Platelets ◽  
Polymer Surfaces ◽  
Flow Conditions ◽  
Transmission Electron ◽  
Adhesion Of Platelets ◽  
Microscopic Techniques

Thrombus formation and embolization are significant problems for blood-contacting biomedical devices. Two major components of thrombi are blood platelets and the plasma protein, fibrinogen. Previous studies have examined interactions of platelets with polymer surfaces, fibrinogen with platelets, and platelets in suspension with spreading platelets attached to surfaces. Correlative microscopic techniques permit light microscopic observations of labeled living platelets, under static or flow conditions, followed by the observation of identical platelets by electron microscopy. Videoenhanced, differential interference contrast (DIC) light microscopy permits high-resolution, real-time imaging of live platelets and their interactions with surfaces. Interference reflection microscopy (IRM) provides information on the focal adhesion of platelets on surfaces. High voltage, transmission electron microscopy (HVEM) allows observation of platelet cytoskeletal structure of whole mount preparations. Low-voltage, high resolution, scanning electron microscopy allows observation of fine surface detail of platelets. Colloidal gold-labeled fibrinogen, used to identify the Gp Ilb/IIIa membrane receptor for fibrinogen, can be detected in all the above microscopies.

Hydrodynamic flow conditions through permeable walls

1992 ◽  
Vol 2 (8) ◽  
pp. 1565-1569
Author(s):  
S. Vollmar ◽  
J. A. M. S. Duarte
Keyword(s):  
Hydrodynamic Flow ◽  
Flow Conditions ◽  
Permeable Walls

Platelet and Shear Rate Promote Tumor Cell Adhesion to Human Endothelial Extracellular Matrix - Absence of a Role for Platelet Cyclooxygenase

1989 ◽  
Vol 61 (03) ◽  
pp. 485-489 ◽  
Author(s):  
Eva Bastida ◽  
Lourdes Almirall ◽  
Antonio Ordinas
Keyword(s):  
Cell Adhesion ◽  
Shear Rate ◽  
Tumor Cell ◽  
Umbilical Vein ◽  
Blood Platelets ◽  
Flow Conditions ◽  
Tumor Cell Adhesion ◽  
Rate Dependent ◽  
Static Conditions

SummaryBlood platelets are thought to be involved in certain aspects of malignant dissemination. To study the role of platelets in tumor cell adherence to vascular endothelium we performed studies under static and flow conditions, measuring tumor cell adhesion in the absence or presence of platelets. We used highly metastatic human adenocarcinoma cells of the lung, cultured human umbilical vein endothelial cells (ECs) and extracellular matrices (ECM) prepared from confluent EC monolayers. Our results indicated that under static conditions platelets do not significantly increase tumor cell adhesion to either intact ECs or to exposed ECM. Conversely, the studies performed under flow conditions using the flat chamber perfusion system indicated that the presence of 2 × 105 pl/μl in the perfusate significantly increased the number of tumor cells adhered to ECM, and that this effect was shear rate dependent. The maximal values of tumor cell adhesion were obtained, in presence of platelets, at a shear rate of 1,300 sec-1. Furthermore, our results with ASA-treated platelets suggest that the role of platelets in enhancing tumor cell adhesion to ECM is independent of the activation of the platelet cyclooxygenase pathway.

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