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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

An experimental study on models of overtopping rockfill dams with rock armour protection

Al-Areeki, Mohamed Abdulwadood Saif January 2002 (has links)
No description available.
2

Extreme wave impinging and overtopping

Ryu, Yong Uk 02 June 2009 (has links)
This investigates the velocity fields of a plunging breaking wave impinging on a structure through measurements in a two-dimensional wave tank. As the wave breaks and overtops the structure, so-called green water is generated. The flow becomes multi-phased and chaotic as a highly aerated region is formed in the flow in the vicinity of the structure while water runs up onto the structure. In this study, particle image velocimetry (PIV) was employed to measure the velocity field of the water dominant region. For measurements of an aerated region that cannot be measured by PIV, a new measurement method called bubble image velocimetry (BIV) was developed. The principle and setup of the BIV method were introduced and validated. Mean and turbulence properties were obtained through ensemble averaging repeated tests measured by both methods. The dominant and maximum velocity of the breaking wave and associated green water are discussed for the three distinct phases of the impingement-runup-overtopping sequence. The distribution of the green water velocity along the top of the structure has a nonlinear profile and the maximum velocity occurs near the front of the fast moving water. Using the measured data and applying dimensional analysis, a similarity profile for the green water flow on top of the structure was obtained, and a prediction equation was formulated. The dam breaking solution used for the green water prediction was examined with determining initial water depth based on the experiment conditions. Comparison between measurements, the prediction equation, and the dam breaking flow was made. The prediction equation and the dam break flow with appropriate initial water depth may be used to predict the green water velocity caused by extreme waves in a hurricane. To demonstrate the aeration of the breaking wave and overtopping water, void fraction was also investigated. There is strong aeration in the region of overtopping water front generated by a plunging breaker. Void fraction of overtopping water was measured using a fiber optic reflectometer (FOR). The measured velocity and void fraction were also used to estimate flow rate and water volume of overtopping water.
3

Probabilistic assessment of the safety of coastal structures

Reis, Maria Teresa Leal Gonsalves Veloso dos January 1998 (has links)
No description available.
4

Evaluation of the Structure of Levee Transitions on Wave Runup and Overtopping by Physical Modeling

Oaks, Drake Benjamin 2010 May 1900 (has links)
Coastal regions are continually plagued by high water levels induced by river flooding or hurricane induced storm surges. As with any protective structure, it is essential to understand potential problematic regions which could result in a devastating loss for the regions nations value most. Coastal protective systems are primarily comprised of floodwalls and levees, each of which has practiced methodologies utilized for estimating their performance under design conditions. Methodologies concerning spatial variability are limited however, and transitions where earthen levees merge with floodwalls are considered vulnerable areas to erosion and possible breaching. Physical modeling of a specified levee transition is undergone in a three-dimensional wave basin to evaluate this hypothesis, and the detailed results of this assessment are presented within this thesis. From the physical model testing, analysis of the data reveals that the overtopping rates of the levee transition tend to be larger than traditional overtopping techniques have predicted. The runup values and floodwall wave heights tend to show potential problematic areas and mimic the variation of overtopping along the levee transition. Under the design conditions tested, extreme overtopping conditions and associated water level values propose that in order for the structure to sustain the hydraulic conditions, it must be well protected. It is shown that the variation of the still water level plays the largest role in the magnitude of the measured values, and increasing the peak wave period and wave heights also yields greater overtopping and water levels at the structure. Overall these extreme overtopping rates and water levels experienced at the structure irrefutably expose a greater risk of erosion and breaching of the protective structure than initially predicted. This study highlights the need to understand specific spatial variability along coastal protective systems, and provides a better understanding of the mechanisms affecting overtopping for the specific structure tested.
5

Overtopping Converter Prototype for Electrical Generation from Wave Energy : Laboratory Test

De Marichalar Alegre, Alexandra January 2011 (has links)
It is not a coincidence that over half the world‟s population live in coastal areas using the sea as a mean to develop its industry, thus the sea is present in most aspects of daily life. Because of the vital relationship with the marine environment, for many years mankind is aware of the high energy potential contained in waves. During the last hundred years, thousands patents of devices for the extraction of the energy from waves have been published. However, the researching still faces the challenge of develop the optimal wave energy converter that matches robustness, to withstand extreme marine conditions, and sensitivity, to respond the different sea states. In this thesis a scale model of a wave overtopping converter has been designed, built and tested. In this type of wave electricity converter the waves ascend a ramp, filling a reservoir located at a certain height above sea level. The stored water in the reservoir is discharged back into the sea, powering a turbine, thus generating electricity. The system is composed of a wave energy converter, at a scale of 1:100 without turbine, a test channel and a plunger type wave maker. Different sea conditions have been simulated, to assess how the different configurations of the device influence the obtained hydraulic power and flow. It has been concluded that there is an appropriate configuration of the wave electricity converter for each wave period and height. The simulated sea conditions were composed of wave periods of around a second and wave heights of about two centimeters. Finally by applying scale transformations, an estimation of the hydraulic power that the wave electricity converter would extract with this configuration in the deep waters of Tenerife South has been calculated. Summarizing, in this thesis the methodology of testing and the comparison with real conditions has been developed.
6

Simulation of wave overtopping by an incompressible SPH model

Shao, Songdong, Graham, D.I., Ji, C., Reeve, D.E., James, P.W., Chadwick, A.J. January 2006 (has links)
No / The paper presents an incompressible Smoothed Particle Hydrodynamics (SPH) model to investigate the wave overtopping of coastal structures. The SPH method is a grid-less Lagrangian approach which is capable of tracking the large deformations of the free surface with good accuracy. The incompressible algorithm of the model is implemented by enforcing the constant particle density in the pressure projection. The SPH model is employed to reproduce a transient wave overtopping over a fixed horizontal deck and the regular/irregular waves overtopping of a sloping seawall. The computations are validated against the experimental and numerical data and a good agreement is observed. The SPH modelling is shown to provide a promising tool to predict the overtopping characteristics of different waves. The present model is expected to be of practical purpose if further improvement in the spatial resolution and CPU time can be adequately made.
7

Converged stepped spillway models in OpenFOAM

Sweeney, Brian P. January 1900 (has links)
Master of Science / Department of Computing and Information Sciences / Mitchell L. Neilsen / The United States Department of Agriculture (USDA) is currently researching the effectiveness of various earth dam designs and their ability to prevent erosion. This report utilizes experimental results from the USDA experimental hydraulic engineering research unit to develop computational fluid dynamics models using OpenFOAM. Several variations of smooth and stepped dam models are created and analyzed with OpenFOAM on multiple cores using Message Passing Interface. In this report, seven dam designs are analyzed to extract flow velocities and pressures and animations. This data and OpenFOAM models are helpful for determining potential erosion conditions.
8

Computational modelling of combined storm surge and wave overtopping of embankments

Jones, David K. January 2012 (has links)
The primary function of seawalls and embankments is to protect against damage and injury caused by flooding. Coastal flooding is caused by combinations of high tides, waves, wind set-up and storm surges driven by low-pressure systems. However with global warming causing sea levels to rise and with increased storminess causing more extreme waves and storm surges, the likelihood of overtopping of seawalls with zero or negative freeboard may well be expected to increase. Researchers using physical and numerical models to develop design formulae have widely investigated wave overtopping of seawalls with positive freeboard. However the design of seawalls with zero or negative freeboard has attracted much less attention, and some variation exists between overtopping discharge calculated with current design formulae. The focus of this thesis is the extreme situation when overtopping caused by storm waves is combined with surge levels above the embankment crest. The local highly accelerative flow over the embankment crest caused by the high surge level will significantly alter the flow at the crest. This is likely to have a highly non-linear effect upon the overtopping waves. In this thesis, the flow is investigated with a 2DV numerical model based on the Reynolds averaged Navier-Stokes (RANS) equations developed by Lin and Liu (1998a). The model describes the flow characteristics of a breaking wave such as the velocities within the wave as well as the turbulence at the seabed boundary layer. As an example of the model’s ability to describe complex hydrodynamic flows, this study investigates its ability to represent the second order mass transport under progressive and standing waves. The model results are compared with available theory and experimental results. This shows that mass transport is successfully predicted, although there is some variation in the magnitude compared to the experimental and theoretical results. To consider the model’s ability to simulate storm surge wave overtopping of embankments, the RANS model has been used to simulate an experimental study conducted by Hughes and Nadal (2009). To examine the success of the model at reproducing the wave generation, transformation and overtopping processes the model results have been compared with the experimental laboratory data. This makes possible a wave-by-wave comparison of overtopping parameters such as discharge, depth and velocity for a storm surge event. Additionally the overtopping discharge predicted by the model is compared with design formulae and the differences in the overtopping discharge calculated with current design formulae are investigated and explained. Finally, the RANS model is used to determine the effect of embankment crest width on the magnitude of the overtopping discharge. Results from RANS model tests are used to provide design guidance in the form of an equation that allows the effect of crest width to be included when evaluating combined discharge at embankments.
9

Modélisation physique et numérique des écoulements générés par la formation de brèche dans les digues fluviales soumises aux surverses / Physical and numerical modeling of dike-breach induced flows due to overtopping

Rifai, Ismail 24 May 2018 (has links)
La surverse d’une digue fluviale (levée) peut conduire au développement d’une brèche par érosion externe, suivie d’une rupture brutale de la digue. Cela provoquerait une vague de submersion dans la plaine protégée, laquelle peut présenter des enjeux humains, économiques et financiers majeurs. La gestion et la prévention du risque d’inondation passe par une détermination précise de l’aléa. Pour ce faire, il est nécessaire d’avoir une estimation fiable du débit au travers de la brèche, donc du mécanisme de formation de la brèche et de sa dynamique d’expansion. Les approches existantes sont souvent adaptées pour les digues frontales (barrage et remblai en terre) soumises aux surverses. La transposition de ces approches pour les digues fluviales demeure peu fiable. Les processus qui régissent la formation des brèches dans les digues fluviales restent donc encore du domaine de la recherche. Un programme expérimental visant à améliorer notre compréhension des processus physiques qui régissent la rupture graduelle des digues fluviales par surverse a été mené conjointement par le Laboratoire National d’Hydraulique et Environnement (LNHE) de la division R&D d’EDF et le groupe de recherche Hydraulics in Environmental and Civil Engineering (HECE) de l’Université de Liège. Les travaux ont été conduits sur deux dispositifs expérimentaux distincts, chacun constitué d’un canal principal et d’une plaine d’inondation, séparés par une digue fluviale. Nous nous sommes focalisés sur les surverses localisées de digues homogènes non-cohésives. Une métrologie adaptée, incluant la mesure détaillée de l’évolution de la géométrie de la brèche en continu, par une technique non intrusive (profilométrie laser), a été développée et exploitée dans les travaux de cette thèse. Les tests, réalisés sous conditions contrôlées, ont permis d’investiguer l’évolution de la bèche et des débits sortants pour différentes conditions hydrauliques (débits d’entrée dansle canal principal, régulation du débit sortant en aval du canal principal, confinement de la plaine inondable). Les effets des dimensions du canal principal, de la taille des sédiments et de la cohésion apparente ou encore de la mobilité des fonds au pied de la digue ont fait également l’objet d’étude. En exploitant les mesures, l’évolution des écoulements au voisinage de la brèche a été simulée avec le code de calcul bidimensionnel TELEMAC-2D, permettant d’évaluer les performances de ce code pour des cas d’écoulements, en rupture de digue fluviale, hautement transitoires et complexes. Le couplage avec le code morpho dynamique 2-D SISYPHE a permis d’apprécier l’apport d’une modélisation hydro-morpho dynamique détaillée à l’étude des brèches dans les digues fluviales / Overtopping of fluvial dikes (dykes or embankment levees) can promote external erosion, leading to the initiation of breaching and potentially brutal dike failure and inundation of the protected area. This can generate major human, economic, and financial losses. Flood risk management and prevention require precise hazard quantification. Accurate estimate of the flow through the breach is paramount, for which a precise understanding of the breach formation and expansion is required. Existing methods are often the result of investigations conducted on overtopping of frontal dikes (embankment dams). The application of such approaches to fluvial dikes is not reliable and processes underpinning breach expansion are still under research. An innovative experimental program was conducted to fill this gap by investigating the physical processes involved in overtopping induced fluvial dike gradual breaching. Experiments were conducted in the framework of collaboration between the National Laboratory for Hydraulics and Environment (LNHE) of the R&D division of EDF and the research team Hydraulics in Environmental and Civil Engineering (HECE) of University of Liège. Experiments were conducted on two distinct experimental setups, each consisting of a main channel and floodplain area separated by an erodible fluvial dike. The focus was made on overtopping induced spatial erosion of homogenous, non-cohesive dikes. Measurements included continuous scanning of the dike geometry using a non-intrusive method (Laser Profilometry Technique), which was designed and developed specifically for the present works. Tests conducted under controlled flow and dike configurations allowed assessing the effects of channel inflow discharge, downstream channel regulation system, and floodplain confinement on the breach development and outflow. Effects of main channel size, dike material size, apparent cohesion, and bottom erodibility were studied as well. Using the experimental data, the flow features near the breach area was simulated using the two-dimensional depth-averaged hydrodynamic code TELEMAC-2D, which allowed assessing the performance of the code for highly transient and complex flows such as involved in dike breaching. Coupling TELEMAC-2D with the morphodynamic model SISYPHE enabled investigating the interest of a detailed hydro-morphodynamic modeling for fluvial dike breaching studies
10

A probabilistic approach to levee overtopping risk assessment

Flynn, Stefan G. 06 August 2021 (has links)
The most common mode of levee failure, breach due to overtopping, is generally considered as a function of a complex set of contributing factors. The goal of this research is to enhance the state of the art and practice for performing levee overtopping risk assessment. For this purpose, a dataset of levee overtopping event records within the portfolio of levee systems maintained by the U.S. Army Corps of Engineers (USACE) is presented. The dataset is utilized with logistic regression analysis to develop a probabilistic model to calculate system response probabilities and assess risk related to levee overtopping. The presented dataset can be used for identifying key factors controlling overtopping behavior, validation of model results, and providing new insight into the phenomenon of levee overtopping. The proposed model offers a practical yet robust tool for levee risk analysis and can be readily employed by engineers and other stakeholders.

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