Characteristics of a Hydraulic Jump Formed on Upstream Vegetation of Varying Density and Thickness

2020 ◽  
Vol 14 (03) ◽  
pp. 2050012
Author(s):  
Ghufran Ahmed Pasha ◽  
Norio Tanaka
Keyword(s):  
Energy Loss ◽  
Froude Number ◽  
Hydraulic Jump ◽  
Variable Density ◽  
Maximum Energy ◽  
Coastal Vegetation ◽  
Critical Flow ◽  
Vegetation Density ◽  
Sparse Vegetation ◽  
Upstream Flow

The effectiveness of coastal vegetation as a barrier to mitigate a tsunami greatly depends on the magnitude of tsunami and vegetation structure. This paper summarizes a series of laboratory experiments that investigated the upstream flow structure and energy loss due to a hydraulic jump in a steady super-critical flow. The characteristics of the jump were determined against vegetation of variable density ([Formula: see text], where [Formula: see text] of each cylinder in cross-stream direction, [Formula: see text] of cylinder), thickness (dn, where [Formula: see text] of cylinder, [Formula: see text] of cylinders in the stream-wise direction per unit of cross-stream width), and initial Froude number (Fro, where Froude number is obtained from a model without vegetation in the flume). In super-critical flow ([Formula: see text]–1.83), a weak hydraulic jump formed on upstream side of vegetation. The height of the jump, its location, and the resulting energy loss were increased by increasing both the vegetation density and thickness. Due to reduced reflection at vegetation front, the drag force against sparse vegetation ([Formula: see text]/[Formula: see text]) was higher compared to intermediate ([Formula: see text]/[Formula: see text]) and dense ([Formula: see text]/[Formula: see text]) vegetation. Under these conditions, the maximum energy reduction due to a weak hydraulic jump reached 9.4% for dense vegetation while it was 8.1% and 7.8% for intermediate and sparse vegetation, respectively.

Energy dissipation by vertically placed screens

2007 ◽  
Vol 34 (4) ◽  
pp. 557-564 ◽  
Author(s):  
Zafer Bozkus ◽  
Pinar Çakir ◽  
A Metin Ger
Keyword(s):  
Energy Dissipation ◽  
Froude Number ◽  
Hydraulic Jump ◽  
Large Range ◽  
Hydraulic Structure ◽  
Flow Depth ◽  
Supercritical Flow ◽  
Series Of Experiments ◽  
Upstream Flow

Screens can be utilized efficiently for dissipating energy of water. In this study, water flowing beneath a gate is used to simulate the flow downstream of a small hydraulic structure, and vertically placed screens are used as an alternative tool for energy dissipation. Investigations are conducted using a series of experiments. The porosity, thickness, and location of the screens are the major parameters together with the Froude number of the upstream flow. The experiments cover a range of supercritical Froude numbers between 5.0 and 18.0, porosities between 20% and 60%, and screen locations up to 100 times the undisturbed upstream flow depth. The thicknesses of the screens used are in the order of the undisturbed upstream flow depth. The results show the importance of each parameter in the energy-dissipating performance of the screens and the system. It is observed that screens dissipate significantly more energy than a conventional hydraulic jump within the large range of Froude numbers covered in the study. The results are also in agreement with the results of an earlier similar study.Key words: screen, energy dissipation, hydraulic jump, porosity, supercritical flow.

scholarly journals Experimental study of the hydraulic jump on reverse bed with porous screens

2019 ◽  
Vol 9 (7) ◽  
Author(s):  
A. Abbaspour ◽  
T. Taghavianpour ◽  
H. Arvanaghi
Keyword(s):  
Experimental Study ◽  
Energy Dissipation ◽  
Energy Loss ◽  
Froude Number ◽  
Hydraulic Jump ◽  
Open Channels ◽  
Supercritical State ◽  
Supercritical Flow ◽  
Study Results

Abstract Nowadays, the porous screens have been used extensively in open channels to prevent erosion in ditches as the water in supercritical state flows past the screen which forces the formation of a hydraulic jump upstream of the screen and produces significant energy loss. In this investigation, the operation of screens has been studied for supercritical flow and the Froude number in the range of 4.5 to 10.6 on two reverse slopes experimentally. In this study, the parameters included arrangements of screens in both the single and double types, and the angle and distance of screens from the hydraulic jump toe. The screens were studied with a porosity of about 50% with square holes. The study results showed that using of screens on the reverse slope of − 0.025 dissipates more energy compared to reverse slope of − 0.015. The screens with double arrangement have better performance and dissipate more energy than the screens with single arrangement, while the distance of screens from the toe of the hydraulic jump does not have a significant effect on the energy dissipation.

Hydraulic jump in sloping channels: roller length and energy loss

2010 ◽  
Vol 37 (4) ◽  
pp. 535-543 ◽  
Author(s):  
M. K. Beirami ◽  
M. R. Chamani
Keyword(s):  
Energy Loss ◽  
Hydraulic Jump ◽  
Empirical Method ◽  
Hydraulic Jumps ◽  
Energy Principle ◽  
Stilling Basin ◽  
Semi Empirical ◽  
Upstream Flow

This paper deals with the roller length and energy loss of a large variety of hydraulic jumps in horizontal and sloping channels. The supercritical upstream flow originated from a standard ogee weir. A stilling basin with bottom slopes of 0.0, −0.025, −0.050, −0.075, and −0.100 was used to generate the jumps. Based on the energy principle, a semi-empirical method to predict the roller length is presented. Predictions based on the proposed method agree well with the results reported by the authors and other researchers. It is shown that the energy loss in the classical jump is greater than that in any jump forming on negative or positive slopes.

scholarly journals Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 90
Author(s):  
Md Abedur Rahman ◽  
Norio Tanaka ◽  
A. H. M. Rashedunnabi
Keyword(s):  
Laboratory Experiments ◽  
Flow Analysis ◽  
Maximum Energy ◽  
Energy Reduction ◽  
Coastal Vegetation ◽  
Vegetation Density ◽  
Flow Conditions ◽  
Flume Experiments ◽  
Tsunami Inundation ◽  
Tsunami Mitigation

As a countermeasure against tsunami inundation, the present study conducted a series of laboratory experiments using a compound mitigation system in which a seaward embankment (E) followed by landward coastal vegetation (V) over a mound (M) (EMV) was investigated in supercritical flow conditions. The changes of flow around the mitigation system and energy reduction were clarified under varying conditions of mound height and vegetation density. Cases of an embankment followed by only a mound (EMNV) were also considered for comparison. Experimental results showed that three basic types of flow structures were observed within the mitigation system in EMV cases. A water cushion was created within the mitigation system mainly due to the combined effects of the mound and vegetation. It significantly reduced the maximum total energy in EMV cases by approximately 41–66%, whereas in EMNV cases, the maximum energy reduction was found to be 23–65%. Increments in both mound height and vegetation density increased the intensity of the water cushion within the mitigation system by offering more drag and reflecting the flow, and hence, significantly reduced the energy of the flow.

Parallel Detection of Electron Energy Loss Spectra in Direct Mode

1990 ◽  
Vol 48 (2) ◽  
pp. 82-83
Author(s):  
Eckhard Quandt ◽  
Stephan laBarré ◽  
Andreas Hartmann ◽  
Heinz Niedrig
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Energy Resolution ◽  
Large Angle ◽  
Maximum Energy ◽  
Semiconductor Detectors ◽  
Parallel Detection ◽  
Photodiode Arrays ◽  
Electron Energy Loss ◽  
Electron Energy Loss Spectra

Due to the development of semiconductor detectors with high spatial resolution -- e.g. charge coupled devices (CCDs) or photodiode arrays (PDAs) -- the parallel detection of electron energy loss spectra (EELS) has become an important alternative to serial registration. Using parallel detection for recording of energy spectroscopic large angle convergent beam patterns (LACBPs) special selected scattering vectors and small detection apertures lead to very low intensities. Therefore the very sensitive direct irradiation of a cooled linear PDA instead of the common combination of scintillator, fibre optic, and semiconductor has been investigated. In order to obtain a sufficient energy resolution the spectra are optionally magnified by a quadrupole-lens system.The detector used is a Hamamatsu S2304-512Q linear PDA with 512 diodes and removed quartz-glas window. The sensor size is 13 μm ∗ 2.5 mm with an element spacing of 25 μm. Along with the dispersion of 3.5 μm/eV at 40 keV the maximum energy resolution is limited to about 7 eV, so that a magnification system should be attached for experiments requiring a better resolution.

scholarly journals The conditions for occurrence of critical flow regime of water in the open stream

2019 ◽  
Vol 97 ◽  
pp. 05006
Author(s):  
Yuliya Bryanskaya ◽  
Aleksandra Ostiakova
Keyword(s):  
Froude Number ◽  
Flow Regime ◽  
Water Flow ◽  
Practical Interest ◽  
Open Water ◽  
Critical Regime ◽  
Critical Flow ◽  
Channel Processes ◽  
Channel Deformations ◽  
Critical Flow Regime

For the solution of engineering problems require increasingly accurate estimates of the hydraulic characteristics of the water streams. To date, it is impossible to consider sufficiently complete theoretical and experimental justification of the main provisions of the theory of turbulence, hydraulic resistance, channel processes. The composition of tasks related to flows in wide channels, turbulence problems are of scientific and practical interest. Various interpretations of the determination of the critical Froude number in wide open water flows based on observations and theoretical transformations are considered. The conditions for the emergence of a critical regime of water flow in an open wide channel are analyzed in order to estimate the critical Froude number and critical depth. Estimates of the critical Froude number for laboratory and field conditions are given. The estimations allow us to consider the proposed approach acceptable for determining the conditions of occurrence of the critical flow regime. The General, physical interpretation of conditions of occurrence of the critical regime of water flow on the basis of phenomenological approach is specified. The results take into account the values of the components of the total specific energy of the section. This shows the estimated calculation. The results obtained theoretically make it possible to compare the above interpretations and determine their applicability, and the results of the analysis can be useful for the estimated calculations of flows in channels and river flows in rigid, undeformable boundaries and with minor channel deformations.

scholarly journals Comments on “Is the Faroe Bank Channel Overflow Hydraulically Controlled?”

2009 ◽  
Vol 39 (6) ◽  
pp. 1534-1538 ◽  
Author(s):  
Linda Enmar ◽  
Karin Borenäs ◽  
Iréne Lake ◽  
Peter Lundberg
Keyword(s):  
Froude Number ◽  
Water Transport ◽  
Cross Section ◽  
Deep Water ◽  
Flow Analysis ◽  
Critical Flow ◽  
Hydraulic Theory

Abstract In a recent paper Girton et al., due to what appears to be a misunderstanding, stated that a critical-flow analysis of the deep-water transport through the Faroe Bank Channel had been undertaken by Lake et al. on the basis of rotating hydraulic theory for a channel of parabolic cross section. In fact, this quoted investigation dealt with a rectangular passage. In the present comment it is demonstrated how the use of parabolic bathymetry leads to significant improvements of the Froude number results.

scholarly journals Modern vision for critical flow in an egg-shaped section

2021 ◽  
Author(s):  
Hachemi Rachedi Lamia ◽  
Lakehal Moussa ◽  
Achour Bachir
Keyword(s):  
Froude Number ◽  
Critical Regime ◽  
Critical Flow ◽  
New Approach ◽  
Smooth Channel ◽  
Critical Flow Regime ◽  
Modern Vision ◽  
The One ◽  
Definition Of ◽  
Steep Slopes

Abstract The critical regime plays a primordial role in the study of gradually varying flows by classifying flow regimes and slopes. Through this work, a new approach is proposed to analyze critical flow regime in an egg-shaped channel. Based on both the definition of Froude number and Achour and Bedjaoui general discharge relationship, a relation between critical and normal depths is derived and then graphically represented for the particular case of a smooth channel characterized by a generating diameter equal to one meter. The results show the influence of the slope on the frequency of occurrence of the critical regime. At the same time and independently of the flow rate, a very advantageous approach for the calculation of the Froude number has been proposed. The study shows that there are six zones to differentiate the various flow states, namely: on the one hand for steep slopes two subcritical zones interspersed by a supercritical zone and on the other hand for mild slopes a zone corresponding to uniform flow, an area where the flow is probably gradually varied and finally an area where the flow is abruptly varied. Based on the specific energy equation, a validation process concluded that the proposed relationships were reliable.

scholarly journals Энерговыделение при бомбардировке атомами дейтерия поверхности вольфрама

2019 ◽  
Vol 45 (11) ◽  
pp. 51
Author(s):  
Д.С. Мелузова ◽  
П.Ю. Бабенко ◽  
М.И. Миронов ◽  
В.С. Михайлов ◽  
А.П. Шергин ◽  
...  
Keyword(s):  
Energy Loss ◽  
Energy Range ◽  
Energy Release ◽  
Maximum Energy ◽  
Wide Energy Range ◽  
Tokamak Reactor ◽  
Tungsten Target ◽  
Wide Energy ◽  
Bragg Maximum ◽  
Maximum Energy Release

The distribution of energy release (linear energy loss) over depth was calculated when bombarded with deuterium atoms of a tungsten target in a wide energy range of incident particles of 100 eV - 10 MeV. It is shown that in the energy range up to 100 keV, the maximum energy release, contrary to the prevailing ideas, is near the surface of a solid. At energies above 100 keV, the nature of the distribution changes and the Bragg maximum appears near the point where the particle stops. The distribution of the energy release over depth in tungsten is obtained for conditions typical of the ITER tokamak reactor, which makes it possible to estimate the wall heating during bombardment by plasma atoms.

scholarly journals Wake behind a three-dimensional dry transom stern. Part 1. Flow structure and large-scale air entrainment

2019 ◽  
Vol 875 ◽  
pp. 854-883 ◽  
Author(s):  
Kelli Hendrickson ◽  
Gabriel D. Weymouth ◽  
Xiangming Yu ◽  
Dick K.-P. Yue
Keyword(s):  
Froude Number ◽  
Flow Structure ◽  
Large Scale ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Variable Density ◽  
Entrainment Rate ◽  
Two Phase ◽  
Density Spectrum

We present high-resolution implicit large eddy simulation (iLES) of the turbulent air-entraining flow in the wake of three-dimensional rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios $B/D$. We employ two-phase (air/water), time-dependent simulations utilizing conservative volume-of-fluid (cVOF) and boundary data immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent-corner-wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (rectangular) geometry of the ship. We show that the flow structure in the air–water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with $B/D$. We determine that the average surface entrainment rate initially peaks at a location that scales with draft Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the rectangular geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft Froude number and geometry. In Part 2 (Hendrikson & Yue, J. Fluid Mech., vol. 875, 2019, pp. 884–913) we examine the incompressible highly variable density turbulence characteristics and turbulence closure modelling.

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