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Department
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Technion, Israel Institute of Technology, |
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Dr.
(I)
Environmental fluid mechanics
As the head of the Flow Measurements Seidel Laboratory (Grand Water Research Institute), Dr. Shavit is looking for ways to apply techniques such as Particle Image Velocimetry (PIV) in water flow and environmental problems. The PIV abilities are used to study the micro-scale flow field. Improved macro-scale modeling is then achieved using the PIV results, mathematical techniques such as spatial and temporal averaging, analytical and numerical solutions, which provide new insights into a variety of environmental fluid mechanics problems.
The research projects that are currently underway in Dr. Shavit laboratory are:
The flow field at the vicinity of porous media interfaces.
The dispersion of tracers in complex environments.
The hydrodynamics
of coral reefs
Flow above
streambeds
(II)
Hydrology
Currently he is involved in the following projects:
Salinization of the Israeli Coastal Aquifer.
Water quality along the Lower Jordan River.
Flow and transport modeling of groundwater around the Sea of Galilee.
(III) Particle Image Velocimetry (PIV)
PIV is used to generate sets of instantaneous velocity vectors in studies such as interface flow and dispersion in wetlands. It is based on powerful pulsed dual laser system and a double shutter imaging system. Seeding particles which are being added to the flowing fluid are captured by the imaging system. Cross-correlation algorithm is used to calculate the mean local displacement from which velocity is being measured. PIV provides overwhelming information which is unavailable otherwise. Recently an enhancement technique called Intensity Capping was developed and is available here. By means of a very simple image enhancement technique, PIV results are greatly improved.
Intensity
Capping, Enhancement Tool
(IV) Nitrogen processes in streams and
sediments
Aquatic systems nitrogen is highly sensitive to
anthropogenic influences. Streams such as the
Courses
The following
courses are given during either the winter semester or spring semester and are
taken by both graduate and undergraduate students. The following links give access to lecture notes,
recitation notes, homework assignments, and exams of both the Introduction to
Fluid Mechanics course and the Physics of Porous Media course. All notes are in
Hebrew.
074133 Introduction
to Fluid Mechanics
014957 Introduction
to transport and pollution in soils
017012 Physics of Porous Media
014958 Irrigation
Engineering 1&2
014213 Introduction
to Hydraulics and Hydrology
Post Docs
Completed In
progress
Dr. Amir
Polak Dr.
Dr.
Graduate Students
Studies
completed
Merav
Reiss, Nutrient Controlled Release from Gel-Based Devices, MsC, Technion, 1996
(supervisor: Prof. A. Shaviv)
Zohar
Bachar, Device for Dynamic Monitoring of Ion Transport and Environmental
Systems, MsC, Technion, 1997 (supervisor: Prof. A. Shaviv)
Alex
Furman, Identification of Formation Process of Salinity Plumes in the Coastal
Plain Aquifer of Israel and Possible Solutions, MsC, Technion, 1998
(co-advisor: Prof. D. Zaslavsky)
Tuval
Brandon, Dispersion in Open Channel Flow with Vegetation, MsC, Technion,
2002.
Ran
Holtzman, Water
Quality and Quantities along the
Michal
Segal, Nitrogen
Pollutants, Sources and Processes along the Lower Jordan River MsC, Technion, 2003 (co-advisor: Prof. A. Shaviv).
Sharon
Maltshinov, Quantitative
Analysis of Resuspension Phenomena Using PIV Measurements, MsC, Technion, 2003 (co-advisor: Prof. Y. Agnon).
Shiri Kirshner, primary
supervisor: U. Shavit, The role of aquifer bottom slope on the Coastal Aquifer salinization
process, M.Sc., Technion.
Hila Abu,
Salinization
Mechanisms of the Tabgha Saline Springs,
PhD, Technion (co-advisor: Dr. A. Rimmer).
Guy
Bar-Yoseph, Velocity Field of Water Flow Over Soil Surfaces, MsC, Technion.
Yigal Master,
primary supervisor: Prof. A. Shaviv, Nitrogen Pollutants, Sources and Processes
in the
Dana Lorber, Investigation of the Flow Field in Coronary Arteries Model in the Presence of Stenosis Using PIV, PhD, Technion (supervisor: Prof. E. Kimmel).
In
progress
Sharon
Maltshinov, PhD, Technion
Tomer
Duman, MsC, Technion.
Shushanna
Kington, MsC, Technion
Hannah_Bardin,
MsC, Technion
Recent Publications
Shavit, U. and Furman, A., The Location of Deep Salinity Sources in the Israeli
Coastal Aquifer. J. of Hydrology, 250, 63-77, 2001 (pdf).
Frenkel, V., Gurka, R., Liberzon, A., Shavit,
U., Kimmel, E., Preliminary Investigation of Ultrasound Acoustic Streaming
Using Particle Image Velocimetry. Ultrasonics, 39, 153-156, 2001.
Shavit, U., Gas Liquid Interaction in the Liquid Breakup Region
of Twin Fluid Atomization. Experiments in Fluids, 31, 550-557, 2001 (pdf).
Shavit, U., and Brandon, T., Dispersion Within Emergent Vegetation Using PIV and
Concentration Measurements, 4th International Symposium on
Particle Image Velocimetry Gottingen, Germany, September 17-19, 2001 (pdf).
Shavit, U., Bar-Yosef,
G., Rosenzweig, R.,
and Assouline, S., Modified Brinkman Equation for a Free Flow Problem at the
Interface of Porous Surfaces: The Cantor- Taylor Brush Configuration Case.
Water Resources Research, 38(12), 1320-1334, 2002 (pdf).
Shavit, U., R.
Holtzman, M. Segal,
A. Vengosh, E. Farber, I. Gavrieli, T. Bullen, and ECO- Research Team, Water
Sources and Quality Along the Lower Jordan River, Regional Study. in Water
Resources Quality, Preserving the Quality of our Water Resources, Edited by H.
Rubin, H.P. Nachtnebel, J. Furst, and U. Shamir,
Shavit, U., Reiss,
M., and Shaviv, A., Wetting Mechanisms of Gel-Based Controlled -Release
Fertilizers. Journal of Controlled Release, 88(1), 71-83, 2003 (pdf).
Shavit, U., Moltchanov,
S., and Agnon, Y., Particles resuspension in waves using visualization and
PIV measurements - coherence and intermittency. International Journal of
Multiphase Flow, 29, 1183-1192, 2003 (pdf).
Master, Y., Laughlin, R. J., Shavit,
U., Stevens, R. J. and Shaviv A., The effect of secondary effluent
irrigation on gaseous nitrogen losses. Journal of Environmental Quality, 32(4),
1204-1211, 2003 (pdf).
Abbo, H.,
Shavit, U., Rosenzweig,
R., and Assouline, S., Free Flow at the Interface of Porous Surfaces:
Generalization of the Taylor Brush Configuration. Transport in Porous Media,
(54), 345–360, 2004 (pdf).
Farber, E., Vengosh, A.,
Gavrieli, I., Marie, A., Bullen, T.D., Mayer, B., Holtzman, R., Segal, M., and
Lahav O, Lu Y, Shavit U,
and Loewenthal RE. Modeling H2S(g) emission rates in gravity sewage collection
systems. Journal of Environmental Engineering- ASCE 130 (11): 1382-1389, 2004 (pdf).
Segal-Rozenhaimer, M., Shavit,
U., Holtzman, R., Vengosh, A., Farber, E., Gavrieli, I., Bullen, T., Mayer,
B., and Shaviv, A., Nitrogen Pollutants, Sources and Processes along the
Assouline S. and
Holtzman, R., Shavit, U., Segal-Rozenhaimer, M.,
Gavrieli, I., Marei, A., Farber, E., and Vengosh, A. Mixing Processes along the
Master, Y., Shavit, U.,
and Shaviv, A., Modified Isotope Pairing Technique to Study N Transformations
in Polluted Aquatic Systems: Theory, Environmental Science & Technology, 39
(6): 1749-1756, 2005 (pdf).
Kremen, A., Bear, J., Shavit,
U., and Shaviv, A., A model demonstrating the potential for coupled
nitrification denitrification in soil aggregates, Environmental Science &
Technology, 39 (11): 4180-4188, 2005 (pdf).
Farber, E., Vengosh, A.,
Gavrieli, I., Marie, A., Bullen, T.D., Mayer, B., Holtzman, R., Segal, M., and Shavit, U., Management
scenarios for the
Shavit, U., Lowe, R.J., and Steinbuck J.V., Intensity capping:
a simple method to improve cross-correlation PIV results, Experiments in
Fluids, in print (Article,
Matlab Script
for Intensity Capping ).
Farber, E., Vengosh, A.,
Gavrieli,
Rosenzweig, R. and Shavit, U.,
The laminar flow field at the interface of a Sierpinski carpet configuration,
Water Resources Research (pdf).
Lowe. R.J., Shavit, U.,
Falter, J.L., Koseff, J.R., and Monismith, S.G., Canopy and porous media
modeling of momentum balance in coral pavements under oscillatory and
unidirectional flows, Limnology and Oceanography (pdf)
Research
1.
The flow field at the vicinity of porous media
surfaces.
A solution to
the problem of shallow laminar water flow above a porous surface is essential
when modeling phenomena such as erosion, resuspension, and mass transfer
between the porous media and the flow above it. Previous studies proposed
theoretical, experimental, and numerical insight with no single general
solution to the problem. Many studies have used the Brinkman equation, while
others showed that it does not represent the actual interface flow conditions.
We show that the interface macroscopic velocity can be accurately modeled by
introducing a modification to the Brinkman equation. A moving average approach
was proved to be successful when choosing the correct representative elementary
volume and comparing the macroscopic solution with the average microscopic
flow. As the size of the representative elementary volume was found to be equal
to the product of the square root of the permeability and an exponential
function of the porosity, a general solution is now available for any brush
configuration. Given the properties of the porous media (porosity and
permeability), the flow height and its driving force, a complete macroscopic
solution of the interface flow is obtained
Shavit, U., Bar-Yosef, G., Rosenzweig, R., and
Assouline, S., Modified Brinkman Equation for a Free Flow Problem at the
Interface of Porous Surfaces: The Cantor- Taylor Brush Configuration Case.
Water Resources Research, 38(12), 1320-1334, 2002 (pdf).
Shavit, U., Rosenzweig, R., and
Assouline, S., Free Flow at the Interface of Porous Surfaces: Generalization of
the Taylor Brush Configuration. Transport in Porous Media, in press (pdf).
Rosenzweig, R. and Shavit, U.,
The laminar flow field at the interface of a Sierpinski carpet configuration,
Water Resources Research (pdf).
2.
Dispersion of tracers in a flume with emergent vegetation.
The mixing of pollutants in natural and constructed systems such as
wetlands and streams received in recent years a renewed attention. The flow in
such systems passes in-between solid obstacles such as stems and vegetation
branches. In such cases, local geometry variations play the most important role
in affecting both flow and transport. Accurate modeling of pollutant transport
in streams, wetlands and other regions of open water flow involving vegetation
is crucial for keeping these environments clean and healthy.
Dispersion is a macro-scale representation of local, micro-scale,
transport mechanisms. It is the most important spreading process but the most
difficult to model. The detailed micro-scale geometry and the subsequent
complex local velocity field are typically unavailable. Even when the detailed
geometry is known, modeling of the fluid mechanics is nearly impossible due to
the wide range of scales. In practice, flow rate, stem diameter, and vegetation
density can only be estimated.
Particle image velocimetry (PIV) is an ideal measuring tool for such
problems. Instantaneous two dimensional velocity fields can be measured
accurately and non- intrusively in laboratory models. As PIV is based on imaging,
concentration measurements can be obtained simultaneously with minor
modifications. Using the PIV capabilities, we have examined the dispersion in a
laboratory flume containing randomly distributed glass cylinders which
represent plant stems in natural systems. Two dimensional velocity and
concentration fields were measured simultaneously as a function of array
density and flow rate.
Three methods were tested for measuring and calculating the dispersion
coefficient. These methods include an analytical solution of Fickian
dispersion, an averaging representation of the Eulerian transport equation, and
a Lagrangian approach. The presented results include four different flow rates
in a cylinder array of 3.5% density. The results of all methods are similar but
not identical. The analytical solution have produced a nearly linear increase
of the dispersion with mean velocity. The other two methods show an increase
followed by a decrease.
Shavit, U., and Brandon, T., Dispersion
Within Emergent Vegetation Using PIV and Concentration Measurements, 4th
International Symposium on Particle Image Velocimetry Gottingen, Germany,
September 17-19, 2001 (pdf).
3.
Quantitative analysis of re-suspension phenomena
using PIV measurements.
The objectives of the
research are to study the interaction of the flow field in lakes, reservoirs
and water treatment plants with bottom sediments. We observe the underling
physical processes, which control sediment settling and resuspension in order
to identify, understand and evaluate the relative importance of various
resuspension mechanisms in typical flow regimes.
Preliminary results were obtained through the use of special
combinations of fluids and particles that are transparent even at high
concentrations (by matching the refraction index). These indicate that particle
image velocimetry (PIV) can be applied successfully to visualize and measure
dense suspensions which occupy the near-bottom region.
Shavit, U., Moltchanov, S., and
Agnon, Y., Particles resuspension in waves using visualization and PIV
measurements - coherence and intermittency. International Journal of Multiphase
Flow, 29, 1183-1192, 2003 (pdf).
4.
Salinization of the Israeli Coastal Aquifer.
The salinization processes
of the Israeli Coastal aquifer led to an average concentration of about 200
mgCl/L with a significant number of salinity plumes in the middle and southern
regions. The salinity of these plumes is high (500-1000 mgCl/L) and increases
rapidly. Geochemical evidences have suggested that the salinity source in the
Be’er Tuvia plume (in the south part of the aquifer) is at the bottom of the
aquifer. This paper describes a solution of the source inverse problem and its
application in the Be’er Tuvia plume. A transient two dimensional finite
element model was solved and the source terms were computed at each node in a
The reconstruction of the chloride source term representing an average value during 1970–1990.
Shavit, U. and Furman, A., The Location
of Deep Salinity Sources in the Israeli Coastal Aquifer. J. of Hydrology, 250,
63-77, 2001 (pdf).
Assouline S. and
5.
Water quality along the
The
The Lower Jordan River received in the past a large volume of freshwater
from Lake Tiberias, the
The objective of the study is to evaluate the different components that presently control the quality of water in the
river. In particular, the study is looking for ways to assess the role played
by the subsurface contribution. We report here
on ongoing research which involves researchers from
Shavit, U., R.
Holtzman, M. Segal,
A. Vengosh, E. Farber, I. Gavrieli, T. Bullen, and ECO- Research Team, Water
Sources and Quality Along the Lower Jordan River, Regional Study. in Water
Resources Quality, Preserving the Quality of our Water Resources, Edited by H.
Rubin, H.P. Nachtnebel, J. Furst, and U. Shamir,
Farber, E., Vengosh, A.,
Gavrieli, I., Marie, A., Bullen, T.D., Mayer, B., Holtzman, R., Segal, M., and
Segal-Rozenhaimer, M., Shavit,
U., Holtzman, R., Vengosh, A., Farber, E., Gavrieli, I., Bullen, T., Mayer,
B., and Shaviv, A., Nitrogen Pollutants, Sources and Processes along the
Holtzman, R., Shavit, U., Segal-Rozenhaimer, M.,
Gavrieli, I., Marei, A., Farber, E., and Vengosh, A. Mixing Processes along the
Farber, E., Vengosh, A.,
Gavrieli, I., Marie, A., Bullen, T.D., Mayer, B., Holtzman, R., Segal, M., and Shavit, U., Management
scenarios for the
Farber, E., Vengosh, A.,
Gavrieli,
6.
Flow and transport modeling of groundwater around
the
Since the foundation of the Israeli National Carrier in 1964, water is
being pumped from
The risk in supplying high salinity water is in
the overall salinization of soil and groundwater resources. The salinity of
waste water is always higher than the salinity of supplied drinking water.
Similarly, the salinity of agricultural return flows is always higher than the
salinity of irrigation water. As a result, aquifers are facing a sever
salinization process. The Israeli Coastal Aquifer, for example, suffers from a constant
average salinization trend of about 2-3 mgCl/l per year. A concentration of 400 mgCl/l is considered to be the upper limit of allowable salinity for many
agricultural crops.
The source of the lake salinity is saline springs
from which saline water flows either directly from inner lake springs or
through shore springs located near Tabgha, Fulya and Tiberias. Where most of
the shore springs were captured and their waters are diverted through the
Saline Carrier, the lake springs could not be captured and they continue to
provide more than 90% of the lake salinity.
Two conceptual models were suggested in the past
to explain the salinization mechanism. According to the first model, high
salinity brines lying underneath the lake are driven into the lake by a local
potential gradient (‘the self-potential brine model’). According to this model,
reducing the lake water level beyond a critical value might result in a fast
and irreversible salinization process. According to the second model,
salinization of the lake is a result of an interaction between meteoric water
flowing from the Galil aquifers and high salinity brines which mix together to
form high salinity springs (‘the leaching model’). Recent studies found good
correlation between rain events, water level fluctuations, discharge rates and
chloride concentrations. The conclusion of these studies was that the
salinization process is related to the Galil aquifers water cycle and that
either the ‘leaching model’ alone or a combination of the two models are needed
to explain the region hydrology
The objective of our study is to develop a
three-dimensional, time dependent, model that will compute the water flow and
solutes transport in the region. The model will serve as a computation tool and
predict the variations of discharge and solute concentration in the saline
springs. We have established the framework and were able to develop a schematic
model of the Tabgha springs.
Both the steady state and transient simulations of
flow and transport resulted in a good correlation between the calculated and
the measured discharge and salinity regimes of the onshore springs.
Abbo, H.,
7.
Particle Image Velocimetry (PIV).
PIV is used to generate sets of instantaneous velocity
vectors in studies such as interface flow and dispersion in wetlands. It is
based on powerful pulsed dual laser system and a double shutter imaging system.
Seeding particles which are being added to the flowing fluid are captured by
the imaging system. Cross-correlation algorithm is used to calculate the mean
local displacement from which velocity is being measured. PIV provides
overwhelming information which is unavailable otherwise. Recently an
enhancement technique called Intensity Capping was developed and is available
here. By means of a very simple image enhancement technique, PIV results are
greatly improved.
Laboratory Facilities
Our PIV system consists of a 160 mJ per pulse
Nd:YAG double laser system (2 Brilliant lasers, Quantel), a cross correlation
8-bit 1Kx1K CCD camera (Kodak, MegaplusES1.0) and a PCO Pixelfly qe, Double
shutter, 1360 x 1024, 12 bit camera, an articulated arm, an image acquisition
system, Digital Delay Pulse Generator Model 565 (Berkeley Nucleonics
Corporation, BNC), and a open source PIV analysis software packages (UraPIV and
MatPIV). In addition, the lab operates several glass flumes, and uses Acoustic
Doppler Velocimeters, Turner Designs CYCLOPS-7 Submersible Fluorometer for
Rhodamine-WT, Pumps. Flow meters (e.g., Micro-Motion, Elite CMF025, Coriolis
acceleration flow meter), and more.
PIV codes
URAPIV (Developed by Alex Liberzon, Roi Gurka, and Uri
Shavit)
Intensity Capping, Enhancement Tool
Any PIV realization consists of outliers (false velocity vectors). The cause for these outliers is often the presence of bright spots within the images. These bright spots are characterized by grayscale intensities much greater than the mean intensity of the image and are typically generated by intense scattering from seed particles. The displacement of bright spots can dominate the cross-correlation calculation within an interrogation window, and may thereby bias the resulting velocity vector. Intensity Capping is an efficient and easy-to-implement image-enhancement procedure that improves PIV results when bright spots are present. The procedure imposes a user-specified upper limit to the grayscale intensity of the images. The displacement calculation then better represents the displacement of all particles in an interrogation window and the bias due to bright spots is reduced. Capping offers competitive performance, low computational cost, ease of implementation, and minimal modification to the images.
Here is a link
to a Matlab
Script that applies Intensity Capping . It is used before the cross
correlation is applied and thus suitable for both commercial and in-house
codes.
Here is our Intensity Capping article published in Experiments in Fluids (Shavit, U., Lowe, R.J., and Steinbuck J.V., Intensity capping: a simple method to improve cross-correlation PIV results, Experiments in Fluids).
Contact
Civil and Environmental Engineering, Technion, Haifa, 32000, Israel
Tel: +972-4-829-3568, Fax:
+972-4-822-5696, e_Fax: +1-208-248-8091