Comparison of the Californian Desert Dunes With the Mediterranean Coastal Dunes at the Sea Shores

2004 ◽  
Author(s):  
Levent Yilmaz
Keyword(s):  
Fluid Flow ◽  
Flow Structure ◽  
Sand Dunes ◽  
Computational Simulation ◽  
Coastal Dunes ◽  
Sand Transport ◽  
Fluid Properties ◽  
Dune Morphology ◽  
Desert Dunes ◽  
Mixed Fluid

The development of the dunes is governed by the effects of turbulence. Turbulence is a type of fluid flow that is strongly rotational and apparently chaotic. Turbulence separates nearby parcels of air and thus mixed fluid properties. The evolution of sand dunes is determined by the interactions between the atmosphere, the surface and the transport and deposition of sand. We are concerned with this physical process and its computational simulation from three perspectives; namely, (1) flow structure; (2) sand transport and deposition and (3) interactions between flow structure and sand transport-deposition, which determine the dune morphology.

The transversely isotropic poroelastic wave equation including the Biot and the squirt mechanisms: Theory and application

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 309-318 ◽  
Author(s):  
Jorge O. Parra
Keyword(s):  
Wave Equation ◽  
Fluid Flow ◽  
Analytical Solution ◽  
Seismic Waves ◽  
Transversely Isotropic ◽  
P Wave ◽  
Fluid Properties ◽  
Permeability Anisotropy ◽  
Attenuation And Dispersion ◽  
Maximum Permeability

The transversely isotropic poroelastic wave equation can be formulated to include the Biot and the squirt‐flow mechanisms to yield a new analytical solution in terms of the elements of the squirt‐flow tensor. The new model gives estimates of the vertical and the horizontal permeabilities, as well as other measurable rock and fluid properties. In particular, the model estimates phase velocity and attenuation of waves traveling at different angles of incidence with respect to the principal axis of anisotropy. The attenuation and dispersion of the fast quasi P‐wave and the quasi SV‐wave are related to the vertical and the horizontal permeabilities. Modeling suggests that the attenuation of both the quasi P‐wave and quasi SV‐wave depend on the direction of permeability. For frequencies from 500 to 4500 Hz, the quasi P‐wave attenuation will be of maximum permeability. To test the theory, interwell seismic waveforms, well logs, and hydraulic conductivity measurements (recorded in the fluvial Gypsy sandstone reservoir, Oklahoma) provide the material and fluid property parameters. For example, the analysis of petrophysical data suggests that the vertical permeability (1 md) is affected by the presence of mudstone and siltstone bodies, which are barriers to vertical fluid movement, and the horizontal permeability (1640 md) is controlled by cross‐bedded and planar‐laminated sandstones. The theoretical dispersion curves based on measurable rock and fluid properties, and the phase velocity curve obtained from seismic signatures, give the ingredients to evaluate the model. Theoretical predictions show the influence of the permeability anisotropy on the dispersion of seismic waves. These dispersion values derived from interwell seismic signatures are consistent with the theoretical model and with the direction of propagation of the seismic waves that travel parallel to the maximum permeability. This analysis with the new analytical solution is the first step toward a quantitative evaluation of the preferential directions of fluid flow in reservoir formation containing hydrocarbons. The results of the present work may lead to the development of algorithms to extract the permeability anisotropy from attenuation and dispersion data (derived from sonic logs and crosswell seismics) to map the fluid flow distribution in a reservoir.

Fluid Flow Structure in Arterial Bypass Anastomosis

2005 ◽  
Vol 127 (4) ◽  
pp. 611-618 ◽  
Author(s):  
C. M. Su ◽  
D. Lee ◽  
R. Tran-Son-Tay ◽  
W. Shyy
Keyword(s):  
Fluid Flow ◽  
Flow Structure ◽  
Bypass Graft ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Arterial Bypass ◽  
Flow Recirculation ◽  
Area Reduction ◽  
Complex Flow Structure

The fluid flow through a stenosed artery and its bypass graft in an anastomosis can substantially influence the outcome of bypass surgery. To help improve our understanding of this and related issues, the steady Navier-Stokes flows are computed in an idealized arterial bypass system with partially occluded host artery. Both the residual flow issued from the stenosis—which is potentially important at an earlier stage after grafting—and the complex flow structure induced by the bypass graft are investigated. Seven geometric models, including symmetric and asymmetric stenoses in the host artery, and two major aspects of the bypass system, namely, the effects of area reduction and stenosis asymmetry, are considered. By analyzing the flow characteristics in these configurations, it is found that (1) substantial area reduction leads to flow recirculation in both upstream and downstream of the stenosis and in the host artery near the toe, while diminishes the recirculation zone in the bypass graft near the bifurcation junction, (2) the asymmetry and position of the stenosis can affect the location and size of these recirculation zones, and (3) the curvature of the bypass graft can modify the fluid flow structure in the entire bypass system.

Coastal sand dunes as biological systems

1989 ◽  
Vol 96 ◽  
pp. 17-36 ◽  
Author(s):  
A. J. Willis
Keyword(s):  
Sand Dunes ◽  
Coastal Dunes ◽  
Nutrient Status ◽  
Large Animal ◽  
Ammophila Arenaria ◽  
Physiological Level ◽  
Tyria Jacobaeae ◽  
Ecological Importance ◽  
Dune Plants ◽  
Stress Metabolites

SynopsisWith the gradation of intensities of environmental factors from the strand-line to stable inland areas, coastal dunes show many ecological phenomena especially clearly. These are reviewed broadly, with some emphasis on topics on which important advances are being made. The nutrient status of dune soil and changes with time are shown with reference to several dune systems. Changes in major nutrients are given for Braunton Burrows, north Devon, where the influence of nitrogen fixation by Lotus corniculatus is illustrated. The effects of sand burial on plants are considered, and details given of the root systems of vigorous and relict marram; factors which may affect its decline in vigour are reviewed. Also discussed is the likely significance of nematodes in the decline of Hippophaë rhamnoides. Reasons for the richness of the dune flora are considered and also some autecological studies. At the physiological level, reference is made to the water relations of plants and at the biochemical level to the occurrence and possible ecological importance of stress metabolites. Life strategies, phenology, survivorship, competition and the population ecology of dune plants are reviewed and also the interaction of ragwort (Senecio jacobaea) and cinnabar moth (Tyria jacobaeae). The population genetics of dune plants is illustrated by reference to Festuca rubra and Ammophila arenaria and of animals to Cepaea nemoralis.The abundance and ecological relationships of the invertebrate fauna are exemplified by surveys at Spurn Point, extensive investigations on spiders and the influence of marram on arthropod communities. The ecology of the natterjack load is considered in relation to conservation and the effects of large animal grazers in relation to the diversity of vegetation.

scholarly journals The Importance of Nanoparticles Addition in a Base Fluid Flow through a Porous Medium

2013 ◽  
Vol 8-9 ◽  
pp. 225-234
Author(s):  
Dalia Sabina Cimpean
Keyword(s):  
Porous Medium ◽  
Fluid Flow ◽  
Boundary Conditions ◽  
Mixed Convection ◽  
Mathematical Models ◽  
Base Fluid ◽  
Porous Matrix ◽  
Fluid Properties ◽  
Flow Through ◽  
Energy Equations

The present study is focused on the mixed convection fluid flow through a porous medium, when a different amount of nanoparticles is added in the base fluid. The nanofluid saturates the porous matrix and different situations of the flow between two walls are presented and discussed. Alternatively mathematical models are presented and discussed. A solution of a system which contains the momentum, Darcy and energy equations, together with the boundary conditions involved, is given. The behavior of different nanofluids, such thatAu-water, Ag-waterandFe-wateris graphically illustrated and compared with the previous results.The research target is to observe the substantial increase of the thermophysical fluid properties, when the porous medium issaturated by a nanofluid instead of a classical Newtonian fluid.

Pans in humus podzols (Humods and Aquods) in coastal southern Queensland

Soil Research ◽  
1996 ◽  
Vol 34 (1) ◽  
pp. 161 ◽  
Author(s):  
CH Thompson ◽  
EM Bridges ◽  
DA Jenkins
Keyword(s):  
Soil Depth ◽  
Sand Dunes ◽  
Coastal Dunes ◽  
Particle Packing ◽  
Sand Mining ◽  
Coastal Sand Dunes ◽  
Organic Complex ◽  
Coastal Sand ◽  
Coastal Lowlands

An exploratory examination has been made of three different kinds of hardpans found in humus podzols (Humods and Aquods) of the coastal lowlands of southern Queensland, by means of slaking tests, a reactive aluminium test, acid oxalate and pyrophosphate extractions and electron microscopy. Samples from three indurated layers exposed by erosion or sand-mining in large coastal dunes were included for comparison. The investigation confirmed that, a pan in a bleached A2 (albic E) horizon is most likely caused by particle packing and that a pan in a black B2h (spodic) horizon is cemented by an aluminium-organic complex. Yellow-brown pans underlying black organic pans (spodic horizons) were found to be cemented by both a proto-imogolite/allophane complex and an organic substance. An inorganic reactive Al complex differing from the proto-imogolite allophane recorded in the overlying giant podzols appeared to be main cement of three indurated layers in the nearby coastal sand dunes. Mechanical disturbance of the pans, e.g. ripping, is unlikely to improve drainage and effective soil depth in the long term, because the disturbed zones are expected to be re-sealed by packed particles or by the aluminium-organic complex cement.

Pulsatile flow in rigid tubes

1965 ◽  
Vol 20 (5) ◽  
pp. 1078-1082 ◽  
Author(s):  
Robert G. Linford ◽  
Norman W. Ryan
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Pulsatile Flow ◽  
Fluid Velocity ◽  
Fluid Flow Rate ◽  
Tube Radius ◽  
Low Frequencies ◽  
Time Relationship ◽  
Fluid Properties

The purpose of this study was to examine critically the theoretical equations derived for pulsatile laminar flow in rigid straight tubes. These equations, presented in their most useful form by J. R. Womersley in 1955, give the fluid flow rate as a function of the pressure gradient-time relationship, pulse frequency, fluid properties, and tube radius, and they give the fluid velocity as a function of the above quantities and the radial position in the tube. A pulsatile flow apparatus was constructed which would allow measurement of all the variables mentioned above, and a computer program based on Womersley's equations was used to calculate the fluid flow rate and velocity profile from the pressure gradient-time relationship, fluid properties, and tube radius. Thus a comparison between measured and calculated values of flow and velocity could be made. Calculations and data agree within the estimated experimental error, thus providing evidence of the applicability of the theoretical equations to actual flow with large pulse amplitudes. The analog computer “pressure gradient technique” of D. Fry and associates was compared with the exact solution for straight rigid tubes and found to deviate less than 20% in amplitude and phase except at very low frequencies. hydrodynamics, pulsatile flow; blood flow, arterial; hemodynamics, pulse characteristics Submitted on April 6, 1964

Sign in / Sign up

Export Citation Format

Share Document