ISSUE NO. 1,
10th Ippen Award Lecture, 27th IAHR Congress, San Francisco, 1997
FASCINATIONS OF HYDRAULIC RESEARCH
Willi H. Hager
Dear Mr. Iyler, Mr. President, Dear friends and colleagues Ladies and
gentlemen HYDRAULICIANS!
It is a particular pleasure to present the 10th Ippen Award Lecture.
I would like to acknowledge the support of my research group and the director
of Versuchsanstalt für Wasserbau, Hydrologie and Glaziologie (VAW),
Dr. Daniel Vischer, thank you to all colleagues for their interest in
our research results and providing data, and last but not least to thank
the IAHR Awards Committee for giving me the chance to present this lecture.
Before coming to the lecture, it is in order to review briefly the life
and impact of the late Prof. Ippen. His grandson Mr. Iyler will certainly
know the most important achievements of Ippen, but you, ladies and gentlemen,
are maybe not familiar with the life of a great hydraulician.
Arthur Thomas Ippen was born July 28, 1907 in London UK. His family moved
to Lake Constance in Germany before World War I and Arthur Thomas was
thus familiar with English and German. He obtained the degree of Civil
Engineer from the University of Aachen, Germany, in 1931, where he also
met Prof. von Karman. By chance, he received an exchange scholarship and
moved in 1932 to the State University of Iowa, USA. He continued his trip
to the west in 1934, and obtained a PhD at CalTech in 1936 for a study
of high-speed flow in open channel curves, under the guidance of Prof.
R.T. Knapp. Figure A shows Ippen together with two close friends.
After having been a faculty member of Lehigh University, Dr. Ippen became
Associate Professor at MIT in 1945, and became a full Professor for hydraulics
and fluid mechanics at MIT in 1948. It was there that he started to build
up a hydraulic lab of world-wide reputation. Fig.B shows the young professor
in 1951. He had then just received the Karl Emil Hilgard Prize from ASCE
for his paper Mechanics of supercritical flow.
Fig.C shows Prof. Ippen together with his former teacher at Aachen, Prof.
von Karman (left). Prof. Ippen retired in 1973 and died April 5, 1974
at his home in Belmont, Mass. He contributed significantly to environmental
and coastal hydraulics, and to engineering education. He received Honorary
Doctorates from the universities of Toulouse (F) in 1963, Karlsruhe (G)
in 1967 and Manchester (UK) in 1968. He was President of IAHR from 1959
to 1963, and it was in this period that the Journal of Hydraulic Research
was founded. Fig. D shows Art Ippen while in retirement.
MODELLING OF LMR FUEL PIN TEMPERATURE BEHAVIOUR USING WATER
P.A. Ushakov, A.P. Sorokin, G.P. Bogoslovskaya,
This paper describes the possibilities for modelling of non-uniform temperature
behaviour around the metal fuel pins in reactors cooled by liquid metal
using water. The temperature non-uniformities arise due to non-symmetric
heat removal from the pin.
The data on heat transfer to mercury, sodium-potassium alloy and water
in compact pin bundles found in the State Scientific Centre of Russian
Federation «Institute of Physics & Power Engineering»
are analysed here. The principles of thermal similarity of fuel pins form
the basis of the analysis mentioned.
ENERGY AND MOMENTUM IN ONE DIMENSIONAL OPEN CHANNEL FLOW
W. G. Field, M. F. Lambert, B. J. Williams,
The equations of continuity, momentum and energy are derived, incorporating
depth-dependent correction factors for velocity distributions over compound
cross sections. It is shown that the friction slope and the energy slope
are equivalent in steady uniform flow but not in unsteady flow. The difference
between the two forms is explained and reasons are given for the preferential
use of the momentum equation. Comparisons of backwater profiles are presented.
RELATION ENTRE COEFFICIENTS DE MÉLANGE LONGITUDINAL ET TRANSVERSAL
DANS DES COURS D¦EAU NATURELS
Samir Gharbi And Jean-Louis Verrette,
Dans cet article, nous proposons une nouvelle formule pour prédire
la valeur du coefficient de mélange transversal connaissant les
valeurs moyennes du coefficient de mélange longitudinal, du débit,
de la profondeur d¦écoulement et du rapport entre la largeur
et la profondeur. C¦est une formule développée à
partir de l¦expression suggérée par les auteurs en
1994 pour définir la relation entre les coefficients de mélange
longitudinal et transversal prenant en considération toutes les
valeurs des coefficients mesurés simultanément pour des
conditions hydrauliques similaires.
La formule proposée exprime le coefficient de mélange transversal
en fonction du coefficient de mélange longitudinal. Elle représente
plus fidèlement les résultats expérimentaux et va
dans le même sens que les études effectuées au cours
des dernières années qui favorisent l¦approche faisant
appel au produit des coefficients pour décrire l¦interaction
entre le mélange longitudinal et transversal.
EXPERIMENTAL INVESTIGATION OF FLUCTUATION UPLIFT ON ROCK BLOCKS AT
THE BOTTOM OF THE SCOUR POOL DOWNSTREAM OF THREE-GORGES SPILLWAY
P.Q. Liu, Ph.D, J.R. Dong, C. Yu,
This paper uses the model of transient flow to analyse the mechanism
of fluctuating pressure propagation within the cracks of bed rock and
the cause of fluctuating uplift generation in details. A predicting formula
for the maximum fluctuating uplift on rock blocks in a scour pool is deduced.
To confirm the theoretical results, fluctuating uplift on different sized
rock blocks at the bottom of scour pool downstream of the Three Gorges
spillway model are measured.
IMPINGING JET AND SURFACE FLOW REGIMES AT DROP
S. Wu, N. Rajaratnam,
This paper presents the results of a laboratory study on the flow regimes
at a rectangular drop with a sub-critical approach flow, when the tailwater
depth approaches the height of the drop or exceeds it. It was found that
the flow at the drop could be in either the impinging jet or surface flow
regime. An empirical scheme has been developed for predicting the occurrence
of either of these regimes, which was found to be affected by the direction
of change of the tailwater depth.
THE ARRESTED GRAVEL FRONT: STABLE GRAVEL-SAND TRANSITIONS IN RIVERS
PART 1: SIMPLIFIED ANALYTICAL SOLUTION
Gary Parker and Yantao Cui,
Most rivers exhibit a tendency for the characteristic size of the bed
material to become finer in the downstream direction. In addition, most
river sediments also exhibit a paucity of material in the pea gravel range.
Because of this paucity the transition in the downstream direction from
a gravel-bed stream to a sand-bed stream is usually rather abrupt, and
is often marked by a discontinuity in bed slope and stream morphology
as well. If the front marking the gravel-sand transition is not to prograde
continuously in the direction of the point at which base level is established,
e.g. the ocean, then some mechanism must operate to arrest it in place.
Here two such mechanisms are examined; abrasion of gravel and basin subsidence
(or alternatively base level rise). It is found that either one or a combination
of the two can act to stabilise the spatial location of the gravel-sand
transition. The present paper is devoted to a simplified analytical solution
to the problem that renders the structure of the formulation relatively
transparent. A complete numerical solution that more realistically describes
the field manifestation is presented in a companion paper.
ENVIRONMENTAL HYDRAULICS OF SANITARY LANDFILLS
Cajsa Berglund,
This paper analyses sanitary landfills as biochemical reactors and particularly
the significance of water balance and multi-phase flow in a landfill system.
Field studies reveal a strong coupling between water content and landfill
gas production. This study focuses on evaluation of field observations
on water content, temperature, gas and leachate production in specially
designed and operated landfills. Theoretical simulation of multi- phase
flow conditions water and gas transport has been carried out for different
components of the landfill system. Top cover as barrier to gas exchange,
1-D heat transport and heat source distribution and water percolation
reproducing mechanical dispersion due to presence of waste elements in
the sanitary landfill are modelled to improve insight into the overall
performance of sanitary landfills.
SIMULATION OF OIL SPILLS FROM UNDERWATER ACCIDENTS II: MODEL VERIFICATION
Poojitha D. Yapa And Li Zheng,
A companion paper presented the development of a three-dimensional numerical
model to simulate the behaviour of buoyant oil jets that result from underwater
accidents. The numerical model was developed based on a Lagrangian integral
technique.
The model can simulate the behaviour of oil in stratified or unstratified
ocean environments. The presence of a multi-directional ambient current
is considered. The fluid in the buoyant jet can be a liquid, gas, or liquid/gas
mixture, which is typical of many underwater oil-related accidents. The
model formulation includes the diffusion and dissolution of oil from the
jet to the ambient environment.
In this paper, the numerical model is tested against a variety of conditions.
First, the model results are compared with all available asymptotic results.
Second, the model is run for cases in which experimental data (both small
and large scale) are available, so that the numerical model results can
be compared with the observed data. The experimental data includes buoyant
jets in stratified and unstratified environments and relatively deep water
experiments. They include cases both with and without ambient current.
The cases compared include two-dimensional and three-dimensional oil jet
trajectories. All comparisons show that the numerical model results match
very well with the experimental data. In addition, the model is used to
simulate buoyant oil jets for several cases of practical interest.
NATO-WORKSHOP CONTROVERSIES BETWEEN WATER RESOURCES DEVELOPMENT AND
PROTECTION OF THE ENVIRONMENT
V. Yevjevich, . Starosolszky
Conflicts between development and environmental protection is often inevitable.
The paper, based upon the results of a NATO-workshop, defines the problems
and the sustainability criteria. With these sharpened definitions it can
be expected that conflicts can be easier discussed between the different
parties which eases optimal decisions: conflicts are reduced to disputes
and disputes are reduced to low-level issues.
ISSUE NO 2
THE VARIATION OF WATERSURFACE SLOPE AND ITS SIGNIFICANCE FOR BEDLOAD
TRANSPORT DURING FLOODS IN GRAVELBED STREAMS
L. Meirovich, J.B. Laronne, I. Reid,
Watersurface slope is usually assumed to be constant when predicting
bedload sediment transport in rivers despite its significance as a determinant
of shear stress and the impact that variability would have on calculated
sediment flux. This is pragmatic. It recognises that confirmatory data
are unlikely to be available, especially during flood flows, and it is
an appropriate assumption where discharge is steady. Where discharge is
unsteady, watersurface slope varies and an expected pattern of hysteresis
in the relation between watersurface slope and flow depth emerges from
datasets collected in four gravelbed streams, two ephemeral, one seasonal
and one perennial. When watersurface slope is treated as a variable in
applying a bedload equation, it is shown that flood bedload yields are
about 8 percent higher than those derived with the same equation but with
watersurface slope held constant and approximating the slope of the channel
bed. It is concluded that, in engineering design, accounting for the variation
in watersurface slope in aridzone ephemeral streams, where bedload yield
is high, is more significant than in perennial streams, where event frequency
may be high but transport rates are low and highly variable.
THE ARRESTED GRAVEL FRONT: STABLE GRAVELSAND TRANSITIONS IN RIVERS
- PART 2: GENERAL NUMERICAL SOLUTION
Y. Cui, G. Parker
Many rivers have an abrupt transition from gravelbed to sandbed morphology.
In many cases the point of transition is neither prograding nor retrograding,
but is rather arrested in place. Two mechanisms are hypothesized as responsible
for stabilizing the gravelsand transition, basin subsidence (or alternatively
base level rise) and abrasion of gravel. The companion paper offers a
simplified analytical solution for the long profile of a river with such
a transition. This treatment allows for direct insight into the relation
between the morphology and the controlling mechanisms at the expense of
several gross approximations. The present paper offers a rigorous complete
numerical solution which takes such facts as the streamwise sorting of
heterogeneous gravel into consideration.
MAXIMUM LOCAL SCOUR DEPTH AT BRIDGE PIERS AND ABUTMENTS
J.K. Kandasamy, B.W. Melville,
Results of recent laboratory investigations of local scour at bridge
piers and abutments are presented. Similarities between the principal
vortex occurring in local scour holes at abutments and the horseshoe vortex
and downflow at piers are highlighted. Pier and abutment laboratory data,
collected near the threshold conditions for sediment movement, display
similar trends in the variation of scour depth with length and flow depth.
This variation is best described in a three dimensional plot. A simple
equation, that can be used to predict the maximum local scour depth at
either piers or abutments aligned perpendicular to the flow, is presented
and compared with field data.
IN SITU FLUIDISATION BY A SINGLE INTERNAL VERTICAL JET
R.K. Niven, N. Khalili
Investigations have been conducted of in situ (unbounded) fluidisation
produced by a vertical jet acting internally within saturated sands. This
produces a sharply defined in situ fluidised zone, which changes with
increasing jet depth from an open, axi-symmetric, approximately ellipsoidal
form to an asymmetric, spouted profile, and thence to a submerged fluidised
cavity. Measurement and dimensional analysis of fluidised zone geometries
indicate in situ fluidisation to be controlled by two mechanisms: (i)
scour below the jet tip, which follows the linear velocity decrease of
a submerged jet; and (ii) the ability of the flow to maintain fluidisation,
which controls the zone diameter. The depth of fluidised cavity formation
is shown to be a function of the ratio of the flow rate to that required
for minimum (turbulent) fluidisation. The observations are justified in
terms of jet diffusion, sediment transport, fluidisation and slope stability
theory.
OSCILLATING VERTICAL PLANE TURBULENT JET IN SHALLOW WATER
S. Wu, N. Rajaratnam, C. Katopodis
The results of a laboratory investigation on the behaviour of plane turbulent
jets discharging vertically upwards into a stagnant shallow water body
have shown that for any depth H in terms of the half width b0 of the nozzle,
the jet could be in an oscillating mode if the velocity at the nozzle
U0 is greater than a critical value of [0.009(H/b0) + 0.357](g/H) where
g is the acceleration due to gravity. When the jet is oscillating, the
frequency of oscillation f is equal to 0.18(g/H). An earlier study on
vertical circular jets in shallow water did not find such an oscillating
flow pattern.
SOME ASPECTS OF TURBULENT FLOW STRUCTURE IN LARGE ALLUVIAL RIVERS
D.K. Barua, K. H. Rahman,
This paper reports different aspects of turbulent flow structure using
the shipboard timeseries velocity data collected by an Acoustic Doppler
Current Profiler (ADCP) in the large multithread Jamuna River in Bangladesh.
The measurements were made during different river stages in various bedform
environments ranging from megaripples to dunes. Based on the analysis
of the downstream flow velocity obtained from the three subdivisions of
the water column, different turbulence parameters such as frequency spectra
and intensities were found. Spectral analysis indicates a mixed picture
of random turbulent motion and periodicity. The maximum period observed
was about 18 min and the minimum was about 11.5 s. Analysis of the frequency
of occurrence of all the grouped events shows that about 70% of the turbulence
have their origins in the riverbed, the rest are horizontal eddies. It
is shown that a 15 min averaging time is required to estimate the higher
order moments such as the turbulence intensity. The vertical distribution
of the ratio of turbulence intensity and bed friction velocity indicates
the presence of two segments separated by a peak: a growing segment limited
within a height of 5 to 10% above the bed and an exponentially decaying
segment above. The turbulence intensity is 7 to 10% of the local downstream
velocity in the freestream region but increases to about 11 to 23% in
the wall region.
ENTRAINMENT ACROSS A DENSITY INTERFACE INSIDE A CYLINDRICAL TANK
WITH A CONCENTRIC BASE OPENING
E.B. Shuy, P.C. Chui, H.C. Chua, C.N. Chen,
The entrainment rate across a density interface formed inside a cylindrical
tank by a fresh water layer floating on top of sea water is investigated.
The tank has a concentric opening at its base, and floats in a body of
sea water. Mixing across the interface is induced by a unidirectional
current flow below the tank. The study was carried out to investigate
the feasibility of storing freshwater in a bottomless tank in the sea.
From dimensional and regression analyses of laboratory measurements over
a range of current speeds and sizes of the tank and base opening, empirical
equations for estimating the mixing rate in such a tank system are derived.
The results are compared with those for a rectangular compartment from
a previous study by Foo (1995). An approximate unified equation for estimating
the mixing rate in both circular and rectangular tanks is derived. Preliminary
field measurements in a pilot storage tank show much higher mixing rates
than the laboratory results. This is attributed to the different dynamic
conditions experienced by the freely floating field tank, as it is subjected
to constant impacts of wind, tides, currents and waves.
EXPERIMENTAL AND NUMERICAL VALIDATION OF THE DEADZONE MODEL FOR LONGITUDINAL
DISPERSION IN RIVERS
W. Czernuszenko, P. M. Rowinski, A. Sukhodolov,
Experimental results of longitudinal dispersion in rivers are discussed
in the light of new findings with respect to the “deadzone”
theory. Both the experiments made by authors as well as some literature
results are taken into consideration. The deadzone model parameters, namely
the relative deadzone volume, penetration time of the tracer into deadzones,
constant mean flow velocit and dispersion coefficient, are obtained with
the use of the nonlinear least square technique applied to the image functions
of concentration timedistributions. The statistical moments of the concentration
time distributions as functions of distance are also analyzed. Expressions
for statistical moments, recently obtained by authors, are found to agree
well with both experimental and computational results.
Issue No. 3
Experiments to dambreak wave: Horizontal channel
G. Lauber, W.H. Hager,
Dambreak waves in a smooth rectangular and horizontal channel are described.
Based on a literature review, the conditions required for Froude similarity
are first derived. Then, the positive and negative wave fronts are analytically
determined, based on the characteristic equations. Further, the effect
of the relative reservoir length on the wave maximum is specified and
a novel dimensionless co-ordinate X is introduced, that accounts for both
relative reservoir length and non-dimensional tailwater location.
Detailed results refer to the definition of wave profiles and distributions
of velocity and discharge in the wave body. A similarity plot defines
a single wave profile. The results so obtained are discussed and allow
a deeper insight into the mechanics of dambreak waves. The results are
readily available for applications, and a significant modification regarding
the initial flow conditions is described.
A simple model for turbulence induced flocculation of cohesive sediment
J.C. Winterwerp,
The transport and fate of fine grained cohesive sediments in estuarine
and coastal waters is influenced by the settling velocity of the sediment,
which in turn is affected by flocculation effects. The flocculation processes
depend on the physico-chemical properties of the sediment and the water,
and on several physical mechanisms, of which turbulence is a major one.
In the present paper the effects of turbulence are further analysed.
The flocs are treated as self- similar fractal entities. As a result,
the settling velocity is shown not to scale with the diameter D squared,
as predicted by Stokes’ law, but with Dnf – 1, where nf is the
fractal dimension. Based on a collision frequency function and a floc
break-up formulation, a simple flocculation model is proposed that can
be solved analytically for uniform conditions. The flocculation and floc
break-up coefficients were obtained from experiments described in literature.
It is shown that the maximal attainable floc size and settling velocity
are determined to a large extent, especially at low turbulence levels,
by the available residence time, i.e. water depth.
Response time analysis for suspended sediment transport
P.K. Stansby, M.A. Omar Awang
The way in which sediment characteristics and water depth determine the
time taken for suspended sediment concentration profiles to approach a
steady state has been investigated. The idealised situation of a bed of
sediment in a steady current with initially clear water is considered.
Analytical solutions are inferred from previous work and a numerical scheme
with a particular vertical mesh transformation has been found to be effective.
Response time, tr, however non-dimensionalised, is generally dependent
on the Rouse parameter ,g, and the particle size to depth ratio, d/h.
For g > 1 however, tru*/d depends only on g, where u* is the friction
velocity. It is also shown that trws/h, where ws is the fall velocity,
is always less than about 2.4, at least for d/h ³ 10–6 , the
smallest value investigated. The numerical scheme is used to compare with
some experimental measurements of non-equilibrium sediment transport in
a steady current to confirm some of the physical modelling assumptions.
Layer-averaged modelling of two-dimensional turbidity currents with
a dissipative-Galerkin finite element method. Part I: Formulation and
application example
S-U. Choi
A finite element technique has been applied to the layer-averaged equations
describing a turbidity current which propagates two-dimensionally in deep
ambient water. The governing equations form a hyperbolic system of partial
differential equations, namely continuity and x- and y-momentum equations
for the flow and mass conservation equation for sediment. The two-dimensional
modelling of the layer-averaged equations with a finite element method
has two important aspects; the dissipative algorithm and the front tracking
technique. Since the standard Galerkin method yields spurious oscillations
when applied to convection-dominated flows, the dissipative-Galerkin technique
having a selective dissipation property is used. Also, in order to track
the moving front accurately, a deforming grid generation technique based
on the arbitrary Lagrangian-Eulerian approach is employed for the two-dimensional
problem. The developed numerical procedure is applied to a decelerating-
turbidity current generated in the laboratory experiment by Luthi (1981).
Time-dependent profiles for the current thickness and layer-averaged velocity
field and volumetric concentration are obtained. The relevant depositional
structure by this underflow event is estimated by incorporating the double
grid finite element method into the flow algorithm.
TVD scheme for the shallow water equations
M. Louaked, L. Hanich,
A high-resolution algorithm is proposed for the solution of the two-dimensional
shallow-water equations by adopting the numerical flux for the generalised
formulation of the TVD Lax-Wendroff scheme developed by Sweby and Davis.
To obtain high resolution near the discontinuities, we apply the ACM (artificial
compression method) technique to the proposed scheme. Comparison of corresponding
results is exposed. A variety of hydraulic test cases show that the coupled
method (TVD-ACM) is quite robust and accurate.
Downstream characteristic Lagrangian hybrid method for flows in open
channels
G. Cui, B. Williams,
In this paper, we present a one step downstream characteristic Lagrangian
hybrid method (DSCLH) for solution of the time-dependent open channel
flow equations. It is a fixed-grid hybrid method, in which a numerically
stable Lagrangian method is used to compute the non-linear or linear convection
process by convecting the grid downstream one step along the trajectory
of a fluid particle. It significantly reduces numerical smoothing and
simplifies Lagrangian advection since there is no need to determine the
upstream interpolation points. It works well for both steady and unsteady
state calculations where discontinuities are present. Solutions are found
for the open channel flow equations using different initial and boundary
conditions. Comparison with known results shows that the DSCLH method
is both convergent and L• stable. It can be applied to a wide range
of shock problems and run for long times without oscillation. Certain
fundamental conditions which are necessary for the successful application
of the method in one and two dimensions are discussed.
Large-scale particle image velocimetry for flow analyses in hydraulic
engineering applications
I. Fujita, M. Muste, A. Kruger,
Large-Scale Particle Image Velocimetry (LSPIV), as presented herein,
is an extension of particle image velocimetry (PIV), which aims at providing
velocity fields spanning large flow areas in laboratory or field conditions.
Additional data, such as mappings of large-scale flow structures and discharges
are readily obtainable using LSPIV. While the image- and data-processing
algorithms are similar to conventional PIV, adjustments are required for
illumination, seeding procedures, and pre-processing of the recorded images.
This paper describes the implementation of video-based LSPIV in three
hydraulic engineering applications covering surfaces from 4 m2 to 45,000
m2. These applications are: gas-transfer processes downstream a model
spillway, ice conveyance through a model river confluence, and flood plain
flow in a full-scale river. The special problems encountered in each of
these experiments, as well as the selection and adjustments of the parameters
to properly solve them, are examined. LSPIV has proven to be a reliable,
flexible, and economically efficient flow diagnostic tool which can be
employed successfully in the surveillance planning, design, hazard warning,
operation, and management in water-related activities.
Turbulent open-channel flow with upward seepage
N.S. Cheng, Y.M. Chiew
Measurements of turbulent open-channel flow subjected to an upward bed
seepage were performed in a laboratory flume using a two-dimensional Acoustic
Doppler Velocimeter and a minipropeller. The experimental results show
that the boundary seepage affects the time-mean streamwise velocity, the
rms values of the velocity fluctuations, the Reynolds shear stress and
the bed shear stress in open-channel flow. Along the seepage zone, the
mean streamwise velocity increases much more in the surface layer than
that in the near-bed region, whereas the turbulent intensities and Reynolds
shear stress increase significantly in the near-bed region. The bed shear
stress that was computed using the momentum integral equation shows a
steady reduction with increasing upward seepage velocity.
Issue No. 4
Three-dimensional numerical flow modeling for estimation of maximum
local scour depth
N.R.B. Olsen, H.M. Kjellesvig
Water flow is modeled numerically in three dimensions around a circular
cylinder placed vertically in a flume. The numerical model solves the
Navier-Stokes equations with the k-e turbulence model. This gives the
shear stress on the bed. A formula for concentration at the bed as a function
of the shear stress is used. The bed concentrations are used to solve
the convection-diffusion equation for the sediments. Continuity for the
cells close to the bed gives the bed changes. The water flow field is
solved simultaneously with the sediment calculation. The models include
time-dependency with transient terms, and calculation of the free surface
is also done. An adaptive grid is used, which follows the changes in bed
and water surface elevations. The model gives the development of the three-dimensional
scour hole around the cylinder. The resulting scour hole has a maximum
depth which compares well with empirical formulas for local scour.
Rheology of cohesive sediments: comparison between a natural and
an artificial mud
T. van Kessel, C. Blom
Concentrated cohesive sediment suspensions exhibit strongly non-Newtonian
and time-dependent behaviour caused by particle interactions, which complicates
the prediction of their strain or shear rate response to applied forces.
In this paper the rheological properties of both China clay, an artificial
mud, and Caland channel mud, a natural mud, are investigated. Four types
of experiments are involved: equilibrium flow curves, stepwise changes
in shear rate to investigate the time-scale of structural changes, experiments
in which the increase in yield stress with recovery time after structural
destruction was measured, and harmonic oscillation experiments to investigate
the visco-elastic behaviour of mud at low strains. For these measurements
both shear rate and shear stress controlled instruments were used. Equilibrium
flow curves revealed strong shear-thinning behaviour for China clay, which
was much less observed for Caland channel mud. Experimental results are
described in terms of a thixotropic model including two structural parameters
to account for structural changes within the material, one to describe
short-term changes when the material is flowing, another to describe long-term
changes when the material is at rest. From experiments with stepwise changes
in shear rate it followed that the time-scale of structural changes is
in the order of seconds. Both materials showed a yield stress, Caland
channel mud being the more cohesive mud. Yield stress measurements as
a function of rest time after pre-shearing showed that the time-scale
for the build-up of an interconnected aggregate structure is in the order
of 104–105 s. From harmonic oscillation experiments it can be concluded
that the range within which muds exhibit linear visco-elastic behaviour
is limited to strains smaller than approximately 1%.
Generalized study of erosion by circular horizontal turbulent jets
O. Aderibigbe, N. Rajaratnam
Experimental data on erosion by circular wall jets from thirteen sources
including the present experimental study were compiled and analyzed. The
present experimental study consisted of circular air jets on a bed of
canola seeds and circular water jets on sand and gravel beds. The compiled
data, consisting of over 350 experiments, cover wide ranges of flow submergence,
jet sizes and velocities, bed material size, relative channel width and
relative density difference. Similarity of the scour hole was examined
both in the unsteady and asymptotic states by determining the ratios between
the characteristic dimensions of the scour hole. The effect of jet submergence
on the asymptotic characteristic dimensions of the scour hole was found
to be pronounced when the densimetric particle Froude number Fo is greater
than 10. The effect of elevating the jet outlet on scour depth was also
investigated. Equations relating the asymptotic characteristic dimensions
of the eroded bed to Fo have been proposed. The effects of the relative
density difference on the characteristic dimensions of scour were addressed.
Experiments on flow around a cylinder; the velocity and vorticity
fields
W.H. Graf And B. Yulistiyanto
The flow field around a cylinder positioned normal to the flow in an
open channel has been investigated experimentally for two types of flow.
An Acoustic Doppler Velocity Profiler was used to obtain instantaneously
the three directions of the velocity in the flow. Subsequently the vorticity
of the flow field was calculated. Results of the experiments show that
a horseshoe-vortex system is established, existing of a measurable vortex
with underneath a return flow of negative vorticity. The system develops
itself in the upstream corner at the nose of the cylinder and stretches
around the cylinder towards the downstream.
Application of advanced data assimilation methods for the initialisation
of storm surge models
R. Canizares, A.W. Heemink, H.J. Vested
A sequential data assimilation technique (utilising a reduced-rank square-root
filter) has been incorporated into the complete non-linear equations of
a hydrodynamical module of a standard two dimensional hydrodynamic modelling
tool. The deterministic model output is corrected using the available
data and the best model initial conditions are generated. The deterministic
model is then used to generate the water level forecast. A description
of the general technique that is applied and its adaptation to this particular
problem are provided. The application to a real storm that occurred during
February 1993 in the North sea is presented.
Choking in water supply structures and natural channels
A. Molinas, K.B. Marcus
Techniques are presented to predict the choking phenomenon which occurs
in natural and man made waterways with constriction features. The techniques
use the energy equation, the momentum principle, and the continuity equation
in one dimensional flow derivation; both the form and the friction losses
are considered in the study. The different loss coefficients assumed and
introduced in the governing equations are extracted and grouped in functional
relationships to predict the choking occurrences. Governing equations
are transformed to relate a threshold value of Froude number, termed as
the limiting Froude number, to the geometry of the constriction feature
and to the discharge coefficient for different flow regimes including
subcritical and supercritical approach flow conditions. Governing flow
equations in constricted channels result in a Froude number termed as
the working Froude number. By comparing the limiting and the working Froude
numbers, occurrences of choking phenomenon can be predicted. Theoretical
derivations are used in conjunction with laboratory data for horizontal
board constrictions to develop a more general coefficient of discharge
applicable to severe contractions and to estimate the subcritical upstream
flow conditions.
Generalised design of single profile (self basing) weirs
K.K. Murthy, C. Rangaraj
This paper presents a generalised theory and design of a new class of
self basing weirs of constant indication accuracy giving a discharge a(head)n
for ½ £ n £ ³/2. Unlike in the earlier designed
compound weirs for n < ³/2, (eg., Sutro weir) the weir is defined
by a single profile throughout and a portion of the weir above the crest
acts as a base. Single profile weirs eliminate the source of error associated
with compound weirs arising from the assumption of single value of coefficient
of discharge (Cd) for both the base weir and the complementary weir above
whereas two separate Cds' should be used.
The depth of the base weir can be reduced by altering certain parameters
to suit the practical considerations. The discharge through this weir
for all flows above a threshold depth "d" and depth of flow
"h", is proportional to hn; ½ £ n £ ³/2;
within a prefixed allowable error of ±1%. The problem is approached
by using a hyperbolic function as the discharge generating function. The
generalised design presented in this paper allows balancing between the
contradictory requirements of accuracy and reduction of afflux in the
field.
Experiments with three weirs for n = 2/3, n = 3/4 & n = 5/4 confirm
the theory by giving a constant average coefficient of discharge for each
weir.
A capacitance tomographic system for the measurement of void fraction
in transient cavitation
M.S. Adam, W.Q. Yang, R. Watson
Transient cavitation, which may be caused by "water hammer",
has been extensively investigated by mathematical modelling. In order
to verify the mathematical models, various experimental methods have been
developed using different transducers. This paper describes a novel instrument
– electrical capacitance tomography (ECT) system – for transient
cavitation investigation, including void fraction measurement. By interrogating
the process using a multi-electrode capacitance sensor, the cross sectional
images can be reconstructed. Experimental results obtained from the ECT
system are compared with pressure, photograph and calculation results,
showing that the ECT technique is promising for investigating transient
cavitation processes.
Issue No. 5
Design and management of hyperintensive aquaculture tanks
F. Cioffi F. Gallerano
In order to identify the optimum design and management criteria for hyperintensive
aquaculture rectangular tanks, a hydrodynamic model and a water quality
model have been developed. The models allow the simulation of the velocity
fields in the tanks and of the concentration evolution, in space and time,
of the significant species: dissolved oxygen, phytoplankton and nitrogen
compounds. These models can be used to identify both the critical conditions
for the survival of the reared aquatic organisms and the pollutant load
discharged in the environment from the tanks.
The hydrodynamic fields are obtained by solving numerically, on a symmetric
vertical plane of the tank, the two-dimensional turbulent motion equations
expressed in terms of vorticity and stream function; the eddy viscosity
which appears in the motion equations is obtained by solving a standard
k-$ model. The concentration fields of each chemical and biological species
are obtained by solving their mass balance equations, in which the physical,
chemical and biological phenomena are represented.
The models have been validated by means of laboratory and field measurements
taken in hyperintensive aquaculture units in use. A number of simulations,
reproducing possible critical conditions, have allowed the identification
of the optimum design criteria and have functioned as a guide for the
management of the hyperintensive aquaculture tanks.
Flood Inundation Analysis Resulting from Levee-Break
K-Y. Han, J-T. Lee, J-H. Park
A combined, one- and two-dimensional hydrodynamic model for flood wave
propagation from a breached levee is studied. The one-dimensional model
solves the Saint-Venant equations by the Preissmann method, and the two-dimensional
model solves a diffusion wave equation by the integrated finite difference
method. The overflow through the broken levee is treated as an internal
boundary condition in a channel. The model is applied to an actual levee-break
case, which occurred on September 12-13, 1990 on the Han River, Korea.
Two-dimensional velocity distributions and inundation maps are presented.
The computed results agree with observations in terms of inundated depth,
flood arrival time, and flooded area.
Experiments To Dambreak Wave: Sloping Channel
G. Lauber, W.H. Hager
Dambreak flows in a smooth, rectangular channel are considered. In all
experiments, the abrupt rupture on an absolutely dry tailwater channel
was modelled. The effect of bottom slope up to 50% is analyzed, and the
results are compared with those pertaining for the horizontal channel.
The positive and negative wave fronts are determined based on the characteristic
equations. Also, the drying front is computed and the effect of viscosity
is analyzed. The experiments are in agreement with the observations collected
with a specially designed Video system. The positive wave front is found
to tend towards a pseudo-uniform flow for large locations downstream of
the dam section.
The characteristics of the dambreak waves are then described, including
the maximum wave height, and a generalized wave profile. The decay of
maximum wave height is related to a combined parameter that includes the
position, the bottom slope and the initial water depth. Further, the velocities
in the wave body are determined and the velocity distribution is discussed.
The discharge as the product of depth times velocity is demonstrated to
be nearly independent of the bottom slope. With these results, a rather
complete description of the dam-break wave can be furnished.
Three-dimensional numerical flow modelling for estimation of spillway
capacity
N.R.B. Olsen, H.M. Kjellesvig
Water flow over a spillway was modelled numerically in two and three
dimensions for various geometries. The model solved the Navier-Stokes
equations with the k-e turbulence model on a structured non-orthogonal
grid. A method based on water continuity was used to calculate the movement
of the water surface. Using an adaptive grid in the vertical direction,
the location of the water surface was recalculated from an initially horizontal
profile. After several iterations a steady solution emerged. The location
of the water surface was used to calculate the capacity and the coefficient
of discharge for the spillway.
Physical model studies were carried out to determine the accuracy of
the numerical model. The coefficient of discharge was also compared with
empirical formulas. The deviation of the calculated coefficient of discharge
was 1 % for the two-dimensional cases, and 0.5 % for the three-dimensional
case. Reasonable agreement was also found for the pressure at the spillway
bed, which was measured in one of the physical model studies. In another
physical model study the water surface was measured, and this also compared
well with the results from the numerical model.
Numerical Modelling of Spillway Flow with Free Drop and Initially
Unknown Discharge
Y. Guo, X. Wen, C. Wu, D. Fang
The difficulties in solving the spillway flow arise not only from the
determination of the critical point, which has been used to divide the
subcritical and supercritical flows, but also from the fact that either
the boundary or the discharge is not known a priori. It is much more difficult
to deal with such flow pattern with free drop. In this paper, by using
the analytic functional boundary-value theory and the substitution of
variables, the non-singular boundary integral equations in the physical
plane are derived. A synchronous iterative method for the discharge and
the flow pattern is presented according to the consistency between the
discharge and the uniform velocity at far upstream. Flows over different
spillway profiles are treated. The discharge, the profiles of the free
drop and the pressure distributions on the walls are calculated. The numerical
results are in good agreement with the measured ones.
Reducing the siltation of a river harbour
S.A.H. van Schijndel, C. Kranenburg
Harbours often suffer from siltation of their basins, which may bring
about high costs of maintenance dredging and disposal of spoil, which
is contaminated in many cases. Therefore a need exists of methods by which
the sediment transport into harbours can be reduced. Of the mechanisms
causing such transport, the turbulent exchange of river-water containing
suspended sediment and clear water from a river harbour was examined in
a physical scale model. The water level was constant and there was no
net flow through the entrance of the harbour. A procedure has been developed
by which the siltation process can be simulated using slightly heated
water. The objective of this study was to devise modifications of the
harbour entrance so as to reduce siltation. It was found that a sill in
the entrance, a dam narrowing the entrance, and a permeable pile-groyne
placed upstream of the entrance all can reduce the exchange substantially.
The sill and the dam can be designed such that the exchange is minimized
while keeping allowance for navigation. Combining the pile groyne with
the sill thus optimized suppressed the exchange for the most part.
Linear Stability Analysis of Turbulent Mixing Layers and Jets in
Shallow Water Layers
D. Chen, G.H. Jirka
Free turbulent shear flows, such as mixing layers or jets, can exist
in a shallow fluid layer. Flows of these types have many hydraulic, environmental
or geophysical applications. The instability characteristics of these
laterally sheared flow types have been studied by means of a modified
depth-averaged Orr-Sommerfeld equation that describes spatial and temporal
growth of disturbances in the nominally parallel flow. Two major parameters,
a bed-friction parameter and a Reynolds number control the flow behavior.
In addition, the width of the flow domain relative to the sheared zone
width can have secondary influences. Results are presented as stability
diagrams for the separate and joint effects of viscosity and bed-friction,
respectively. Comparisons with available experimental evidence are given.
Laboratory Experiments of Buoyancy-Influenced Flow in Clarifiers
P. Krebs, M. Armbruster, W. Rodi
A hydraulic laboratory experiment is described that was designed to verify
numerical simulations of buoyancy-affected flow in clarifiers. Through
variations of the flow rate, the water depth and the inflow suspension
concentration, a typical range of density influences prevailing in secondary
clarifiers is covered. Since glass spheres serve as settling suspension,
the flocculation process is not considered. Therefore, the study concentrates
on the investigation of the flow features and the interaction with the
settling process. In order to provide well-defined test cases for numerical
simulations, i.e. to introduce boundary conditions that can be formulated
exactly in the numerical model, a new approach is introduced for setting
the bottom boundary conditions, that is a perfect sediment removal while
being a rough wall for the flow. The density effect turns out to stabilise
the flow pattern and to improve the removal efficiency of the tank. When
the density effect through high suspended-solids concentrations becomes
a dominating factor, the overflow-rate concept known from settling tanks
with discrete-type settling process will not apply any more, and the depth
of the tank becomes a determining parameter with regard to the performance
of the tank.
ISSUE NO.6,
Calculation and mesh generation of a three-dimensional matrix-fracture-system
C. König, B. Rosen
In solid rock aquifers low matrix permeability is often accompanied with
fractures and faults of different scales. Therefore, numerical modelling
of such coupled systems is very complex. Flow of groundwater and mass
transport processes in fractured systems have to be modelled along discrete
surfaces joined to the common matrix representation. This leads to high
demands on the quality of finite element mesh generation. Another difficulty
is the evaluation of field parameters needed in the design of realistic
models to simulate natural systems. This paper presents a strategy to
generate three dimensional finite element meshes, which allows the modelling
of groundwater flow and contaminant transport in a coupled matrix fracture
aquifer system. Software development and data evaluation for the discussed
application example comes from the research project "Development
and Application of Analytical Methods on Investigations of the Reliability
of Disposals in Open Mines" sponsored by the German Ministry of Education
and Research. The scope of this project is to determine the influence
of a rising groundwater level in closed coal mines on the transport of
contaminants from waste material deposits in cut coal seams.
Stochastic macrodispersion models for gravel aquifers
F. Stauffer, M. Rauber
Statistical information on sedimentary structures determined from natural
gravel deposits in north-eastern Switzerland is used to characterise transport
phenomena of aquifers. These aquifers essentially consist of a background
gravel matrix with embedded lenses of different hydraulic properties and
internal structure. One of the embedded materials is highly conductive
open framework gravel which leads to a bimodal probability density function
of the hydraulic conductivity of the overall gravel material. Based on
an analysis of this information three approaches to modelling macrodispersion
are suggested. In the first one distinct unconditioned realisations of
synthetic block shaped facies type aquifers are generated numerically
such that they exhibit the same statistical properties with respect to
facies geometry and hydraulic properties as the deposits themselves. Numerical
experiments simulating saturated flow and transport were subsequently
performed with the help of a three-dimensional finite element flow model
and a corresponding random walk transport model. A total of 100 experiments
allowed estimates of apparent, time dependent macrodispersivity values.
In the second approach the statistical parameters characterising the overall
gravel deposit were directly applied to an analytical unimodal stochastic
model of apparent macrodispersivity according to Dagan (1988). For the
modelling of the bimodal nature of the hydraulic conductivity an analytical
anisotropic stochastic model was developed based on the isotropic model
of Rubin (1995). This third approach was again applied using the appropriate
statistical parameters. Differences in the results of the three models
are discussed. They can be attributed mainly to uncertainty in the input
parameters, and to the complex sedimentary structure predominant in the
natural gravel deposits which were investigated.
High performance computing as a tool for groundwater cleanup
J.F. Peters, S.E. Howington, J.P. Holland, F.T. Tracy, R. S. Maier
High Performance Computing (HPC) is a key enabling tool to interconnect
the many, varied simulation capabilities required to advance the science
of groundwater remediation. The US Army Engineer Waterways Experiment
Station is engaged in research and development that will provide a seamless
link to tools that combine diverse field data into accurate site characterisations,
and perform computer simulations of remediation processes. However, the
simulation models on which this capability is founded are still not adequate
to simulate real, heterogeneous media that make up the natural groundwater
environment. The inadequacy stems from the multi-scale structure of natural
media that is masked by the continuum formulations upon which numerical
models are based. The range of scales is simply too great to be spanned
by any present, or foreseeable, HPC resource. To advance the science of
multi-scale simulation, HPC may be viewed as an extension of the laboratory.
By stretching present resources to perform scale-spanning simulations,
stochastic models are created from data that could not be obtained previously
from physical experiments. A detailed description of this process is presented
for non-reactive, dispersive transport.
Quantifying the exchange rate between groundwater and small streams
V. Kaleris
The reliability of quantification (measurement and calculation) of the
exchange rate between groundwater and small streams is discussed. Concerning
measurements, two measuring techniques (discharge difference measurements
and seepage meter measurements) are investigated. Discharge difference
measurements can give reliable results if the length of the reach, at
the ends of which the discharge is measured, is appropriate. Infiltrometer
measurements are of questionable value when influenced by difficult to
detect installation errors. Concerning calculations the following issues
are addressed:
(a) The sensitivity of the calculated values of the exchange rate to
errors in various parameters. This problem is discussed by means of analytical
solutions. The analysis shows that, in case of stream beds with relatively
small hydraulic resistance, errors in the hydraulic conductivity of the
aquifer are important for the exchange rate. In case of stream beds with
high hydraulic resistance, exchange rate is strongly influenced by the
errors in the hydraulic resistance. In such cases, errors in the parameters
characterising the capillary forces in the porous media can increase the
resulting errors considerably.
(b) The reliability of estimations of the hydraulic resistance of the
stream bed by means of piezometric head measurements near the stream.
Investigations in a small stream show that, if the hydraulic resistance
of the stream bed is high, its estimation from measurements of the piezometric
heads is uncertain.
(c) The forecasting of the exchange rate by means of depth integrated
models under a hydrologic regime other than the one used for calibration.
By means of analytical solutions it is shown that in case of stream beds
with high hydraulic resistance and for porous materials in which the capillary
forces are negligible, the exchange coefficient used to describe the exchange
flow includes only the influence of the clogging layer. In such cases
the value of the exchange coefficient estimated from the calibration can
be used to forecast the exchange rate under changed hydrological conditions.
In cases where the hydraulic resistance of the stream bed is small and
for materials with non-negligible capillary forces, such forecasting can
be erroneous.
Heat transport in the unsaturated zone – comparison of experimental
results and numerical simulations
R. Helmig, H. Class, A. Faerber, M. Emmert
This paper presents the theoretical basis as well as the experimental
and numerical process research work for non-isothermal multiphase flow
and transport processes in porous media. Heat transfer occurs due to conduction
and multiphase convection, and includes latent heat effects. The heatpipe
verification problem describes the influence of a heat flux on a two-phase
system (aqueous phase, gas phase), which leads to the so-called heatpipe
effect. The second example shows the comparison of experimental and numerical
results from a steam injection process in wet coarse sand, in wet fine
sand and a cold air injection in wet coarse sand. In both cases, the numerical
results are in good quantitative agreement with the experimental data.
The numerical modelling of the non-isothermal multiphase processes is
a central element in the range of methods, which helps for a better understanding
of the complex flow and transport processes and allows for predictional
computations, e.g. with respect to possible remediation strategies.
Recent advancement of groundwater hydraulics in underground space
technology
K. Sato, K. Adachi, Y. Ito
Various types of underground space have been developed to support human
activities and civilisation. The knowledge of groundwater hydraulics is
indispensable in keeping excavation processes within safety limits and
mitigating impacts on the groundwater environment. This review paper summarises
history, categories, hydraulic problems and management in underground
space technology. Some topics of mathematical modelling and characteristics
in and around underground space structures are demonstrated to illuminate
recent advancement in groundwater hydraulics. Attractive themes involving
both hydraulics and underground space technology are suggested to boost
a future progress.
Travel time analysis of tracers and reactive solutes in the unsaturated
zone
A. Sun, Y. Rubin
This paper presents a Lagrangian stochastic approach for modelling field
scale contaminant transport in the heterogeneous unsaturated geological
environments. We derive the probability distribution function of the travel
times of tracers and reactive solutes, without limiting it to be either
normal or log-normal, and show how it can be used for computing the moments
of solute fluxes and breakthrough curves. We also provide closed-form
expressions for the travel time moments of tracers and reactive solutes
characterised by linear equilibrium and non-equilibrium sorption kinetics.
These expressions are useful for prediction and for interpretation of
field experiments. In our derivation we account for soil heterogeneity
by modelling the soil parameters, such as the saturated hydraulic conductivity
and the pore size distribution parameter, as weakly stationary random
space functions. Unlike previous studies, we account for the effect of
the spatial variability of the water content and refrain from assuming
that the saturation is practically constant in the unit gradient flow
zone. The derivation is done using a first-order perturbative expansion
of the flow equation, and is thus limited to small variability of the
input parameters. The effects of spatial variability on the displacement
and travel time statistics are discussed and demonstrated.
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