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1
Hong, SeungHo. "Interaction of Bridge Contraction Scour and Pier Scour in a Laboratory River Model." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7533.
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The engineering design of a hydraulic structure such as a river bridge requires consideration of the factors that affect the safety of the structure. Among them, one of the most important variables is bridge foundation scour. However, engineering experience seems to indicate that computation of scour depth using current scour formulas tends to overpredict scour in comparison to field measurements. The result can be an overdesigned bridge foundation that increases the cost of the bridge. One possible reason for the overprediction is the current practice of adding separate estimates of contraction scour and pier scour when in fact these processes occur simultaneously and interact.
During the occurrence of a flood, velocities and depths increase but they are affected by changes in the distribution of discharge between the main channel and floodplain. In addition, the time history or time development of contraction scour and local pier scour is not the same. As a result, the influence of contraction scour on pier scour, for example, is time dependent.
Laboratory experiments are proposed using a 1:45 scale hydraulic model of the Ocmulgee River bridge at Macon, Georgia. Initially, the contraction scour will be measured without the bridge piers in place. In this experiment, the time history of the scour and the velocity distributions at the equilibrium state will be measured. Then the piers will be placed at the bridge cross-section in the flume, and the same measurements will be made. The sensitivity of the measurements to small changes in depth at the same discharge will also be determined, and comparisons will be made with field measurements of scour depth. The results will be used to assess the relative contribution of contraction scour and local pier scour to the final design of the bridge foundation depth.
2
Lavictoire, Alexandra. "Bore-Induced Local Scour around a Circular Structure." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/31950.
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Recent natural disasters, such as major tsunamis, have prompted researchers and practicing engineers to improve their understanding of the impacts of bore-like waves on structures and their foundations. The high velocity and the relatively short duration of hydraulic bores causes local scouring which is different from that generated by river flows and waves. The present study uses an experimental model to simulate the propagation of a hydraulic bore over a movable sediment bed placed around a circular pier-like structure. Measurements of water surface elevation, bore propagation velocity and scour distribution were taken. The linear relationship between reservoir depth and bore depth led to an increase in flow acceleration, and thus to an increase in flow velocity. Final scour bed elevations indicated that scour depth was highly dependent on the bore velocity. The scour depth ratios suggested in current design guidelines were significantly lower than those obtained in this study.
3
Li, Junhong Li. "Pier Streamlining as a Bridge Local Scour Countermeasure and the Underlying Scour Mechanism." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1518565785864439.
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4
Kabir, Alamgir. "Modelling local scour around bridge piers using TELEMAC." Thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/6683.
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Scour at bridge crossings is a major cause of bridge failure. There are several different types of scour such as general scour, constriction scour and local scour. One of the most serious types is local scour which occurs as a result of vortex formation around bridge piers and abutments (Hoffmans & Verheij, 1997; Raudkivi, 1998; Melville & Coleman, 2000; Richardson & Davis, 2001; Armitage & McGahey, 2003). Local scour is also one of the most difficult to predict accurately. If not adequately designed for, local scour of a riverbed at a bridge pier may become deep enough to undermine the pier foundation and eventually cause the bridge to collapse. Complete protection against scour is expensive and therefore not a favourable design option. It is generally cheaper to ensure that the foundation lies below the maximum expected scour depth. Traditionally, the maximum scour depth is predicted from empirical equations derived from simple laboratory tests without much regard for local conditions. Alternatively, smaIlscale hydraulic models, which are laborious and time intensive, are widely used. In view of the above, increasing attention is being paid to the use of Computational Fluid Dynamics (CFD) based modelling for the prediction of local scour and its opposite, local deposition. The ever-improving capabilities of computers and the increasing availability of powerful and flexible CFD codes have further assisted in this process. This study is a contribution in this direction.
5
Ozalp, Murat Can. "Experimental Investigation Of Local Scour Around Bridge Pier Groups." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615594/index.pdf.
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It is an important task that design engineers in practice predict the local scour around bridge piers as accurately as possible because excessive local scour around bridge piers unbalance and demolish the bridges. Many equations have been proposed previously by various researchers, based on their experimental findings, but no general method has been developed so far due to the complexity of the topic. In the present study two new bridge pier groups were employed to investigate the inclination effect of the most upstream and downstream piers on the local scours around all piers. Total of 72 experiments have been conducted with 3 inclination angles, one of which representing the vertical case, each experiment lasting 6 hours, under uniform flow and clear-water conditions for a range of water depths and flow velocities on the uniform bed material. It is clearly observed and measured that the amount of local scour reduces substantially by the effect of inclination in the group piers, especially the reduction in the scour around the most upstream pier is found notable. Based on the experimental data, regression analyses are made and an empirical scour depth equation is developed for each individual pier in the pier groups studied. Comparisons with the similar studies performed by other researchers have been made and the results discussed.
6
Lee, Seung Oh. "Physical modeling of local scour around complex bridge piers." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/29398.
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Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.<br>Committe Chair: Terry W. Sturm; Committe Members: Dr. Fotis Sotiropoulos; Committee Members: Dr. Philip J. Roberts; Committee Members: Dr. Donald R. Webster; Committee Members: Dr. Anthony Hayter. Part of the SMARTech Electronic Thesis and Dissertation Collection.
7
Daskin, Sueyla. "Effects Of Collars On Local Scour Around Semi-circularend Bridge Abutments." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613310/index.pdf.
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During severe floods, bed material around bridge piers and abutments are scoured by the flow and as a result, bridges are subject to damages. These damages are mostly unrepairable and can result in loss of lives and property. In this thesis study,
abutment scour under clear-water condition was investigated and collars were tested as scour countermeasures around the abutments. The experimental study was carried out in a rectangular channel with an almost uniform cohesionless bed material of d50=1.50 mm for a test period of 3-hours. The channel was 28.5 m long and 1.5 m wide. The erodible bed material was placed into the test section that was 5.8 m long
and 0.48 m deep.
For this thesis study, 60 experiments were carried out with and without various collars placed at different elevations around the abutments. The scour formation around the abutments with collars was observed and scour reduction efficiencies of the collars were studied. Experiment results were compared with the previous studies of Dogan (2008) and Kayatü<br>rk (2005) in terms of sediment size, abutment shape and flow depth, and the effects of these factors on collar'<br>s scour reduction efficiency were studied. Based on the results of the experimental studies, it was observed that scour
depths decreased as the collar width increased and the collar placed deeper into the sediment bed for a given abutment length. When the present study and the previous studies were compared, it was observed that sediment size and flow depth had no significant effect on the scour reduction performances of the collars.
8
Cesme, Murat. "Experimental Investigation Of Local Scour Around Inclined Dual Bridge Piers." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606597/index.pdf.
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For a bridge engineer, it is very important to estimate the maximum scour depth around the piers as accurately as possible, in order to design the footing safely. Many experimental studies have been performed by several investigators until now, in order to obtain information about scouring mechanism. The aim of this experimental study is to examine the effect of inclination of the dual bridge piers on scour depth. The experiments have been conducted with dual pier models under clear-water conditions, for various uniform flow depths. Scour depths had been measured at four different points around the piers<br>namely upstream and downstream faces of both piers. Dimensional and non-dimensional scour curves have been developed and presented to show the temporal variation of scour depth. The depths of local scour around inclined piers have been observed to be smaller than the scour depths around vertical piers.
9
Ghoma, Mohamed Ibrahem. "The effect of wall jet flow on local scour hole." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.
10
Cunninghame, Margaret. "Numerical modelling of local scour in rivers using fluent 6.2." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/5057.
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Includes bibliographical references.<br>Scour and deposition are natural processes which take place in a river as the stream profile adjusts to changing flow rates, sediment loads and other environmental conditions. Man-made obstacles to the stream flow such as bridge piers and abutments and other hydraulic structures alter flow patterns causing local scouring and deposition. Excessive scour undermines the foundations of bridges and other fluvial structures which may ultimately cause their collapse. Reliable methods are needed to model the complex flow features at bridge piers and abutments and hence predict the associated patterns of local scour. Empirical formulae are notoriously inconsistent in their predictions of local scour depth (Johnson, 1995) while physical modelling is time-consuming and therefore expensive.
11
Walker, Wayne O. "Field measurements of local pier scour in a tidal inlet." Thesis, (10.49 MB), 1995. http://handle.dtic.mil/100.2/ADA303503.
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Thesis (M.S. in Civil Engineering)--University of Florida, December 1995.<br>"December 1995." Description based on title screen as viewed on February 8, 2010. DTIC Identifier(s): Scouring, Wind Waves, Sieve Analysis, Seiching. Includes bibliographical references (p. 139). Also available in print.
12
Smyre, Elizabeth Anne. "Effect of suspended fine sediment on equilibrium local scour depths." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000612.
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13
Ghoma, Mohamed I. "The Effect of Wall Jet Flow on Local Scour Hole." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5501.
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This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study.
In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations.
The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.
14
Nazariha, Mehrdad. "Design relationships for maximum local scour depth for bridge pier groups." Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/9989.
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An investigation of local scour at pier groups has been conducted with the aim of developing design recommendations and scour depth prediction equations for the bridge pier groups. A comprehensive series of steady uniform flow experiments was performed on groups of 2, 3, 4, and 6 model piers. All tests were conducted under clear-water scour conditions. Parameters governing local scour depth around bridge piers include: flow characteristics, sediment properties, and pier size and shape. The effects of these parameters on the maximum local scour depth for a single pier (D$\sb{\rm s}$), have been thoroughly investigated in the past. However, when design criteria developed for single piers are applied directly to pier groups, this approach ignores the following important group effects: (1) sheltering, (2) reinforcement, and (3) horse-shoe vortex (HSV) compression. Furthermore, the group effects will alter with changes in pier spacing, S, and flow angle of attack, $\beta$. This study, which investigates the local scouring process for the aforementioned groups of model bridge piers, and presents design relationships for predicting the corresponding maximum local scour depths, is an attempt to address this limitation in current design practice. Initially the local scour was examined for five different single pier diameters (0.0127 m, 0.018 m, 0.025 m, 0.033 m and 0.05 m). Having established single pier relationships, groups of 2, 3, 4, and 6 equally spaced piers were examined, while altering alignment to the flow and separation distances. For piers in line with the flow direction, downstream piers are sheltered by the upstream ones resulting in reducing scour depth around downstream piers. This effect diminishes with the increasing $\beta$ if there is only one row of piers i.e., 2 and 3 pier groups. In the case of 2 rows of piers aligned to the flow direction (i.e., 4- and 6-pier groups), there is a specific range of $\beta$ in which downstream piers are exposed to the flow. As $\beta$ increases, depending on pier spacing, the piers of one row may shelter the downstream piers of the other row. The reinforcement effect is significant only for small ratios of pier spacing/ pier diameter (S/d) when $\beta \le$ 10$\sp0$. In these ranges of S/d and $\beta$, the front piers are scoured more than that of a single pier. Moreover, the score depth of downstream piers, which are less than that of a single pier, increases with increasing S/d. The compressed (HSV) arms affect the local scour depth significantly if piers are staggered and S/d $\le$ 5. In this range of S/d, the HSV arms are intensified, resulting in a deeper scour hole. However, this effect also becomes insignificant with increasing S/d. The data obtained for each pier group were analysed, using a multiple regression model, to develop local scour depth prediction equations for the front, middle, and rear piers. The regression model includes two important dimensionless parameters ($\beta$ and S/d) associated with group effects, as regressors. The proposed prediction equations estimated the observed data and similar-type published data reasonably well, within marginal errors. From a general practical view-point, the number of prediction equations was reduced to two equations for all pier groups: one for the front piers and the second one for the downstream piers (i.e. combined middle and rear piers).
15
Bennetts, Tony Andrew. "Local scour around bridge piers under steady and unsteady flow conditions." Thesis, University of Hertfordshire, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394076.
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Armitage, Neil Philip. "A unit stream power model for the prediction of local scour." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/52716.
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Thesis (PhD)--Stellenbosch University, 2002.<br>ENGLISH ABSTRACT: Local scour is the erosion of a riverbed resulting from the flow of the river around an
obstacle. It is a principal cause of failure of bridges and other hydraulic structures.
Current design practice relies on the use of empirical formulae that are often
extremely inaccurate, or on the use of physical models that are very expensive.
Recent advances in the power of microcomputers have however made numerical
simulation increasingly attractive. One obstacle to numerical simulation though is
that there is no general agreement on the concept of incipient motion, that critical
point at which motion - and hence scour - begins.
In this dissertation, the unit stream power model developed by Rooseboom (1992) is
extended to handle the complex three-dimensional flow conditions that pertain close
to the riverbed in the vicinity of an obstacle. The relationship between unit stream
power (the dissipation function) and the Movability Number (the ratio of the shear
velocity to the terminal settling velocity of the critical sediment particles) is clearly
indicated. Since incipient motion is probabilistic in nature, a relationship was
established between the Movability Number and the intensity of motion with
allowance for bed-slope and relative depth. An extension of this work resulted in a
new bed-load transportation equation that could be used to determine the rate of scour
development. Physical modelling in a laboratory flume aided the selection of suitable
critical conditions for the onset of scour.
The usefulness of the above-mentioned relationships was then demonstrated through
the construction of a simple mathematical model of scour and deposition around a
structure. This model was used in conjunction with commercially available
computational fluid dynamics (CFD) software to predict the scour potential around
typical engineering structures. Physical model data was obtained for four situations,
and the measured scour was compared with that predicted by the numerical model.
There was reasonable agreement between the different models and such differences as
there were could be readily attributed to constraints on the numerical model, in
particular the lack of a free-surface routine and the coarseness of the grid.
This dissertation has opened up a new method for the prediction of local scour that
could be readily extended to include all types of scour. With the advent of
increasingly fast computers, it could become a useful engineering tool that would
assist engineers in the design of safe and cost-effective foundations for hydraulic
structures.<br>AFRIKAANSE OPSOMMING: Plaaslike uitskuring is die erosie van 'n rivierbed as gevolg van vloei verby 'n
obstruksie. Dit is 'n belangrike oorsaak van die swigting van brfïe en ander
hidrouliese strukture. Bestaande ontwerppraktyk berus op empiriese vergelykings wat
dikwels hoogs onakkuraat is, of op fisiese modelle, wat baie duur is. Numeriese
simulasie het die afgelope tyd 'n al hoe meer aantreklike opsie geword danksy die
snelle toename in die kapasiteit van mikro-rekenaars. 'n Struikelblok met numeriese
simulasies is die gebrek aan konsensus oor die konsep van begin-van-beweging,
daardie kritieke toestand waarby beweging en derhalwe uitskuring begin.
In hierdie proefskrif is die eenheidstroomdrywing model, ontwikkel deur Rooseboom
(1992), uitgebrei om die komplekse drie-dimensionele vloeitoestande, wat teenaan die
rivierbodem verby 'n obstruksie heers,te hanteer. Die verwantskap tussen Eenheid
Stroomdrywing (Dissipasiefunksie) en die Beweeglikheidsgetal (verhouding tussen
sleursnelheid en die ewewigvalsnelheid van die kritieke sedimentpartikels ) is duidelik
uitgewys. Aangesien begin van beweging probabilisties van aard is, is die
verwantskap bepaal tussen die Beweeglikheidsgetal en die Intensiteit van Beweging,
met voorsiening vir bodernhelling en relatiewe diepte. Verdere uitbreiding het gelei
tot 'n nuwe bedvrag vervoervergelyking wat gebruik kan word om die tempo van
uitskuring te bepaal. Kritieke toestande, waarby uitskuring begin, is met fisiese
modelle in die laboratorium gekwantifiseer.
Die bruikbaarheid van bogenoemde verbande is gedemonstreer deur die ontwikkeling
van 'n eenvoudige wiskundige model van uitskuring en afsetting rondom 'n struktuur.
Hierdie model is saam met bestaande kommersiële sagteware vir vloeidinamika
berekenings (CFD) ingespan om uitskuringspotensiaal rondom tipiese
ingenieurstrukture te voorspel. Fisiese modelmetings van uitskuring vanaf vier
uitlegte is vergelyk met die numeries voorspelde waardes. Bevredigende ooreenkoms
is gevind en verskille kon geredelik gewyt word aan beperkings van die numeriese
model, veral die gebrek aan' n vryvlakroetine en die growwe maas.
Die proefskrif stel 'n nuwe metode vir die voorspelling van uitskuring daar wat
geredelik uitgebrei kan word na ander vorms van uitskuring. Met die ontwikkeling
van al vinniger rekenaars kan dit 'n nuttige hulpmiddel vir ingenieurs word om veilige
en koste-doeltreffende fondamente in waterlope te ontwerp.
17
Tekin, Fatime. "Local Scour Characteristics Around Semi-circular End Bridge Abutments With And Without Collars." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614405/index.pdf.
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The major damage to bridges occurs due to scour of the bed materials around piers
and abutments during severe floods. This study involves the experimental
investigations of the various scour patterns forming around abutment models tested
with and without collars as scour countermeasures. The experiments were conducted
in a rectangular channel under clear-water scour conditions.
In the first part of this study, 34 experiments were conducted with semi-circular end
abutment models with and without a collar for a period of 3 hours. Collars of various
sizes were placed at different elevations on the abutment models, and the scour
reduction efficiencies of collars were investigated for the different flow depths.
Based on the results of the experimental studies, the optimum locations of collars on
the abutments, which result in minimum scour depth around the abutments, are
obtained at the bed level and below the bed level depending on the flow intensity
values.
In the second part of this study, the effects of flow depth and abutment length on the
temporal development of local scour at bridge abutments were studied. 20
experiments were performed without collars for a time period of 8 hours. It was
observed that at the upstream of the abutment, the depth of the local scour increases
rapidly within the first three hours of the experiment for the different flow depths.
18
Abban, Benjamin. "Using the movability number to model local clear-water scour in rivers." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/7459.
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Includes bibliographical references.<br>Local scour is associated with a considerable number of bridge failures worldwide. It occurs at bridge piers and abutments as a result of interactions between complex flow features and the channel bed. The number of factors involved in the interactions makes it difficult to predict. A lot of research has therefore been performed by several investigators to gain insight into the scouring process and scour prediction. Currently, local scour is estimated using physical models, empirical formulae or numerical models. Of these methods, the use of numerical models appears to be more economical and ideal as it permits flexibility in the choice of flow parameters and allows different scenarios to be easily studied. The aim of this research was thus to investigation into the use of the commercial CFD code FLUENT 6.2 for scour prediction based on the Movability Number. The research, which focused exclusively on local clear-water scour at bridge piers, stemmed from previous works performed by Armitage & McGahey (2003) and Cunninghame (2005) in which the Movability Number approach was developed and assessed. Results from these studies indicated that there was considerable potential in the Movability Number approach and, also, there was a need for a completely automated procedure for scour prediction based on the approach. For the current research therefore, an 'equilibrium model' was developed in which the river bed was successively modified in response to computed bed Movability Numbers until the final result reflected an equilibrium clear-water scour hole. Unstructured grids were generated in GAMBIT 2.2 and imported into FLUENT for the simulations. The symmetry condition was applied and the grids were fined up in regions where large velocity gradients or changes in other fluid properties were expected. Before the clear-water scour evolution simulations were carried out, the performance of the standard k-& model was compared with that of the Reynolds Stress model, and standard wall functions with non-equilibrium wall functions for a flat bed. Both turbulence models predicted similar scour patterns. Results of the numerical simulations were compared with data from a physical model and it was found that the non-equilibrium wall functions predicted scouring in regions on the bed where scour was not observed in the physical model. The standard wall functions, on the other hand, appeared to give realistic results. Since the standard k-&model involved the solution of two transport equations whilst the Reynolds stress model involved the solution of seven, the former was used with the standard wall functions for the scour hole evolution simulations. It was believed that this would result in shorter simulation times. A scour potential was defined as the difference between a computed bed Movability Number and the critical Movability Number required for sediment movement. Scour was considered to occur at those locations where the scour potential values were greater than zero and the grid nodes were displaced in response. User-defined functions were written to perform the bed modifications and ensure the integrity of the mesh as the bed geometry changed. Five physical scour experiments were simulated numerically. These physical experiments were performed as part of the research and were carried out in a 0.6lm wide tilting flume in the Hydraulics laboratory of the Civil Engineering Department at the University of Cape Town. Results from the numerical simulations were compared with those from the physical models. Using the Movability Number to model local clear-water scour in rivers. Although, the numerically estimated equilibrium scour depths were relatively close to those from the physical models, the shapes of the scour holes were not that similar. This was attributed to numerical difficulties in accurately predicting the flow field (and hence the Movability Numbers) at the bed. It was recommended that ways of improving the accuracy of the flow field prediction be found in order to accurately predict the bed Movability Numbers. In general, however, the Movability Number approach showed considerable potential for use in the prediction of local clear-water scour.
19
Kho, Kai Tze. "An experimental study of local scour around circular bridge piers in cohesive soils." Thesis, University of Newcastle Upon Tyne, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407586.
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20
Zhou, Lu. "Numerical modelling of scour in steady flows." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC015/document.
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Cette thèse porte sur le développement d’un modèle numérique de l’affouillement causée par des obstacles montes sur le lit, combinant les processus hydrodynamiques et morphologiques. Le modèle numérique est basé sur le solveur de champ d’écoulement polyphasique de l’outil CFD open-source OpenFOAMR qui est distribue par OpenCFD Ltd. Le module hydrodynamique du modèle résout les équations de Navier-Stokes avec moyennes de Reynolds (RANS) et les modèles des turbulences k-ε ou k-ω. Il existe deux interfaces dans le domaine de simulation: la surface libre entre l’eau et l’air, qui est suivi par la méthode de Volume de Fluide (VOF); et l’interface entre l’eau et le lit du sédiment, qui est représentée par un maillage de surface finie déformable construit à partir de la limite en bas du maillage de volume fini. En outre, un module morphologique qui a été développé dans le cadre du projet se compose de trois composantes: un modèle de transport de sédiments comprenant la charge suspendue et le charriage; l’équation d’Exner pour mesurer la déformation du lit; et un mécanisme de glissement du sable pour limiter la pente du lit à être plus petite que l’angle de repos du sédiment. Le changement morphologique est incorporé dans le modèle hydrodynamique par la déformation du maillage. Des conditions limites spéciales et des corrections nécessaires pour le calcul en parallèle sont également ajoutées au modèle. Chaque partie du modèle est validée séparément avec les tests préliminaires correspondants, y compris les fonctions de paroi rugueuse, les performances de la méthode VOF, le modèle de transport de charge suspendu et le mécanisme de glissement de sable. Le modèle numérique est ensuite appliqué pour étudier un affouillent bidimensionnelle cause par un jet immerge provenant d’une ouverture sous écluse. Comparaison des résultats de la simulation avec des données expérimentales prouve la capacité du modèle. Et les limites du modèle sont également discutées. Enfin, le modèle est appliqué à l’étude du champ d’écoulement tridimensionnel et de la formation d’affouillement autour d’un obstacle dans l’écoulement. Tout d’abord, la déformation du lit n’est pas activée. Le tourbillon en fer à cheval devant un obstacle et le champ d’écoulement turbulent autour d’un cylindre sur un lit lisse ou rugueux sont simulés. Deux types de simulation pour le module hydrodynamique sont effectués: une simulation qui utilise une surface fixe et rigide pour représenter l’interface air-eau, et une simulation incluant à la fois les domaines de l’eau et de l’air avec la surface libre suivie par la méthode VOF. Les influences de la surface libre sur le champ d’écoulement sont identifiées et discutées. La comparaison avec les données expérimentales confirme l’importance de la déformation de la surface libre sur le champ d’écoulement. Ensuite, le lit est autorisé à se déformer et le développement temporel de l’affouillement tridimensionnelle autour d’un cylindre sur le lit est simule. Le développement temporel d’affouillement et la profondeur maximale du trou calcule devant et derrière le cylindre conviennent assez bien avec les mesures expérimentales. Les influences de l’affouillement sur le champ d’écoulement sont aussi étudiées et la performance du modèle numérique développé est discutée<br>This thesis describes the development of a numerical model for local scour caused by bed-mounted obstacles, combining the hydrodynamic and morphological processes. The basis of the numerical model is the multiphase flow field solver in the open-source CFD toolbox OpenFOAMR which is released by OpenCFD Ltd. The hydrodynamic module of the model solves the Reynolds Averaged Navier-Stokes (RANS) equations with either a k-ε or a k-ω model. There are two interfaces in the simulation domain: the free surface between water and air, which is tracked using the Volume of Fluid (VOF) method, and the interface between the water and the sediment, which is represented by a finite area mesh constructed from the bottom boundary of the finite volume mesh. A morphological module which has been developed as part of the project consists of three components: a sediment transport model which includes suspended load and bed load transport; the Exner equation to compute the bed deformation, and a sand-sliding mechanism to restrict the bed slope angle to be smaller than the angle of repose. The morphological changes are incorporated into the hydrodynamic field through deformation of the computational mesh. Additional boundary conditions and parallel computing corrections are also added into the model. Each individual part of the model has been validated separately with corresponding preliminary test cases including the rough wall functions, the performance of the VOF method, the suspended load transport model and the sand-sliding mechanism. The numerical model is then applied to study two-dimensional scour caused by a submerged jet issuing from an opening under sluice gate. Comparison of the simulation results with the experimental measurements proves the ability of the model for conducting two-dimensional simulations and the limitations of the model are also discussed. Finally, the model is applied to study the three-dimensional flow field and scour formation around an obstacle in flow. Initially, the bed deformation is not activated in the model. The horseshoe vortex formed in front of an obstacle in water and the turbulent flow field around a cylinder on smooth and rough beds are simulated. Two types of simulations for the hydrodynamic module are used: a rigid lid simulation with a slip boundary condition to represent the air-water interface, and a free surface simulation including both the water and air domains with the free surface tracked by the VOF method. The influences of the variation of the water depth on the flow field are identified and discussed. Comparison with the experimental data also confirms the importance of the water surface variation on the flow field. Next, the bed is allowed to deform in the model. The temporal development of three-dimensional scour around a cylinder on live-bed in a steady current is simulated. The development of the scour with time and the computed maximum scour depths in front of and behind the cylinder agree quite well with the experimental measurements. The influences of the scour process on the flow field are also studied and the performance of the numerical model is discussed
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Apaydin, Meric. "A Study On Risk Assessment Of Scour Vulnerable Bridges." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612427/index.pdf.
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Many river bridges fail or are seriously damaged due to excessive local scouring around piers and abutments. To protect a bridge from scour-induced failure, it should be designed properly against excessive scouring and its scour criticality should be checked regularly throughout the service life to take prompt action. The Federal Highway Administration of United States (FHWA) developed a program, HYRISK, as a basis for evaluation of existing scour failure risk of a bridge. It provides implementation of a risk-based model, which is used to calculate the annual risk of scour failure of a bridge or series of bridges in monetary values. A case study is carried out for a bridge crossing Fol Creek in Black Sea Region (close to Vakfikebir), for the illustration of this software. Besides, hydraulic analysis and scour depth computations of the bridge are carried out via HEC-RAS program. Also, a study is carried out to recommend scour countermeasures that can be applied to the aforementioned bridge.
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Abida, Habib. "A laboratory investigation of local scour downstream of box culvert outlets and an alternative measure for its control." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5251.
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Suehiro, Atsushi. "Treatment of Acute Vocal Fold Scar with Local Injection of Basic Fibroblast Growth Factor: A Canine Study." Kyoto University, 2010. http://hdl.handle.net/2433/120922.
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McConnell, George Charles. "Chronic inflammation surrounding intra-cortical electrodes is correlated with a local, neurodegenerative state." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26615.
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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2009.<br>Committee Chair: Bellamkonda, Ravi; Committee Member: Babensee, Julia; Committee Member: Butera, Robert; Committee Member: DeWeerth, Steve; Committee Member: Lee, Robert; Committee Member: McKeon, Robert. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Rodríguez, Pérez Rubén Darío Jesús, and Manrique Geraldine Zuley Yataco. "Comparación de los modelos numéricos 1D y 2D en el análisis de socavación total en el puente Huallaga." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/654632.
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La socavación en las bases de los puentes es una de las principales causas de fallas de estas infraestructuras en el mundo, lo que conlleva a elevados gastos en reparación, aislamiento de poblaciones y pérdidas de vidas humanas. El presente trabajo de investigación tiene como principal objetivo calcular, analizar y comparar la socavación total que se produce en los pilares y estribos del puente Huallaga mediante un modelo unidimensional y un modelo bidimensional. Para lograr este objetivo se recopilaron las diferentes metodologías de cálculo de socavación y se escogieron las óptimas para el presente estudio. Luego, se identificaron los parámetros que tienen mayor influencia en la simulación del proceso de socavación. Después, se calculó la socavación total del puente Huallaga con el modelo 1D (HEC-RAS) y 2D (IBER). Finalmente, se realizó un análisis comparativo entre los resultados obtenidos en ambos programas. Adicionalmente, se obtuvieron como una de las principales conclusiones que los valores calculados de socavación obtenido a partir de los datos del modelo 2D son menores en comparación a los valores calculados de socavación obtenidos a partir de los datos del modelo 1D, haciendo al segundo modelo hasta un 49.8% más representativo para los cálculos de socavación.<br>The scour of the bases of the bridges is one of the main causes of failure of these infrastructures in the world, which leads to repair costs, isolation of populations and human losses. The main objective of this research work is to calculate, analyze and compare the total scour that occurs in the pillars and abutments of the Huallaga bridge using a one-dimensional model and a two-dimensional model. To achieve this objective, the different scouring calculation methodologies were compiled, and the optimal ones were chosen for the present study. Then, identify the parameters that have the greatest influence on the simulation of the scour process. Then, he calculated the total scour of the Huallaga bridge with model 1D (HEC-RAS) and 2D (IBER). Finally, a comparative analysis was performed between the results obtained in both programs. Furthermore, it was obtained that the calculated values of scour obtained from the data of the 2D model are lower compared to the calculated values of scour obtained from the data of the 1D model, making the second model up to 49.8 more representative for scour calculations.<br>Tesis
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Acharya, Anu. "EXPERIMENTAL STUDY AND NUMERICAL SIMULATION OF FLOW AND SEDIMENT TRANSPORT AROUND A SERIES OF SPUR DIKES." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145391.
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The intensive research on sediment transport indicates a need of an appropriate equation for predicting the total sediment load in rivers to manage reservoirs, operate dam and design in-stream hydraulic structures. None of the available equations in sediment transport has gained universal acceptance for predicting the total sediment transport rate. These facts indicate the need of a general formula to represent all these formula for predicting the sediment transport rate. The first goal of this dissertation is to find a unified total sediment transport equation for all rivers. On the other hand, scour around hydraulic structures such as spur dikes and bridge piers can be a serious problem that weakens structural stability. An investigation on the turbulent flow field and turbulence distribution around such hydraulic structures is essential to understand the mechanism of local scour and to determine which turbulence properties affect the local sediment transport. In addition, a universal turbulent model that is valid for all cases of turbulent flow in open channels does not exist. This dissertation thoroughly examined the turbulent flow field and turbulence distribution around a series of three dikes. The goal is to determine the significant turbulent properties for predicting the local sediment transport rate and to identify the appropriate turbulence model for simulating turbulent flow field around the dikes.To develop a general unified total load equation, this study evaluates 31 commonly used formulae for predicting the total sediment load. This study attributes the deviations of calculated results from different formulae to the stochastic properties of bed shear stresses and assumes that the bed shear stress satisfies the log- normal distribution. At any given bed shear stress, Monte Carlo simulation is applied to each equation, and a set of bed shear stresses are randomly generated. Total sediment load generated from each Monte Carlo realization of all the equations are assembled to represent the samples of total sediment load predicted from all the equations. The statistical properties of the resultant total sediment loads (e.g. standard deviation, mean) at each given bed shear stress are calculated. Then, a unified total sediment load equation is obtained based on the mean value from all the equations. The results showed the mean of all the equations is a power function of dimensionless bed shear stress. Reasonable agreements with measurements demonstrate that the unified equation is more accurate than any individual equation for predicting the total sediment load.An experimental study and numerical simulation of the flow field and local scour around a series of spur dikes is performed in a fixed flat bed and scoured bed condition. A micro-Acoustic Doppler Velocimeter (ADV) is used to measure the instantaneous velocity field in all the three spatial directions and the measured velocity profiles are used to calculate the turbulence properties. Results show that the local scour develops around the first dike. Turbulence intensity together with the mean velocity in the vertical direction measured at the flat bed closely correlates to the scour depth. In addition, the maximum bed shear stress, occurring at the tip of the second dike in the three-dike series, does not correspond to the maximum scour. Large bed load transport due to bed shear stress may not initiate bed scouring, but turbulence bursts (e.g. sweeps and ejections) will entrain sediment from bed surface and develop the local scour.A three-dimensional numerical model FLOW-3D is used to simulate the turbulent flow field around a series of spur dikes in flat and scoured bed. This study examines Prandtl's mixing length model, one equation model, standard two-equation model, Renormalization-Group (RNG) model, and Large Eddy Simulations (LES) turbulence model. The Prandtl's mixing length model and one equation model are not applicable to flow field around dikes. Results of mean flow field by using the standard two-equation model, and RNG turbulence model are close to the experimental data, however the simulated turbulence properties from different turbulent model deviate considerably. The calculated results from different turbulence models show that the RNG model best predicts the mean flow field for this series of spur dikes. None of the turbulence closure models can predict accurate results of turbulence properties, such as turbulence kinetic energy. Based on those results, this study recommends the use of RNG model for simulating mean flow field around dikes. Further improvements of FLOW-3D model is needed for predicting turbulence properties near this series of spur dikes under various flow conditions.
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Gamboa, Melgarejo Jorge Luis, and Rios Valeria Sandra Quintanilla. "Modelamiento numérico hidrodinámico para reducir la socavación local en pilares cilíndricos y rectangulares de puentes de ríos." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/657642.
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En la presente investigación se evaluó la eficiencia de las pilas de sacrificio en la reducción de la socavación local de pilares cilíndricos y rectangulares de puentes de ríos. Para ello, se realizaron modelaciones numéricas hidrodinámicas, en el software Iber, y se aplicaron las ecuaciones de la Universidad Estatal de Colorado (CSU) y de Froechlich.
En esta investigación, se emplearon los resultados del ensayo físico del pilar cilíndrico aislado de 30mm de diámetro, ensayado en el artículo científico desarrollado por Vahdati et al. (2020). Asimismo, se emplearon los resultados del pilar rectangular de nariz semicircular de 30mm de ancho y 150mm de largo, ensayado en el artículo científico desarrollado por Vijayasree, Eldho, Mazumder y Ahmad (2019). Estos ensayos físicos fueron calibrados para, posteriormente, adicionar las pilas de sacrificio, en diferentes configuraciones, y analizar su eficiencia en la reducción de la socavación local. Las configuraciones propuestas para las pilas son: triangular 30°, triangular 180°, en tandem y en tridem. Para el pilar cilíndrico aislado y para el pilar rectangular de nariz semicircular se obtuvieron porcentajes de reducción de la socavación local de hasta 45.32% y 60.75%, respectivamente. De acuerdo a los resultados, las configuraciones en tridem y triangulares de 180° fueron las más eficientes. Además, se realizó un análisis dimensional para conocer la influencia de las variables que intervienen en el fenómeno de socavación local. A partir de los resultados, se observó que el número de Froude (Fr) es el numero adimensional más influyente.<br>In this research, the efficiency of sacrificial piles in reducing local scour of cylindrical and rectangular piers of river bridges was evaluated through hydrodynamic numerical modeling (in the Iber software) and the application of the equations of Froechlich and Colorado State University (CSU).
The results of the physical test of the 30 mm diameter single cylindrical pier, tested by Vahdati et al. (2020), and the results of the physical test of the rectangular pier with semi-circular nose of 30 mm wide and 150 mm long, tested by Vijayasree, Eldho, Mazumder and Ahmad (2019), were used. These physical tests were calibrated to add the sacrificial piles in different configurations and analyze their efficiency in reducing local scour. The proposed configurations for the piles were: triangular 30°, triangular 180°, tandem and tridem. The maximum percentages of reduction of local scour obtained were 45.32% and 60.75% for the single cylindrical pier and the rectangular semi-circular nose pier, respectively. According to the results, tridem and triangular 180° configurations were the most efficient. Likewise, a dimensional analysis was carried out to determine the influence of the variables involved in the phenomenon of local scour. From the results, the Froude number (Fr) was the most influential dimensionless number.<br>Tesis
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Bressan, Filippo. "Large Eddy Simulation of turbulence around a scoured Bridge Abutment." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3511.
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2008/2009<br>In this work the turbulent field developing in case of local erosion around a 45° wing-wall bridge abutment was investigated numerically. Three different scour conditions were considered: beginning of the process, logarithmic phase and equilibrium stage. The flow field was computed using a wall-resolving large eddy simulation (a simulation where the near-wall viscous sub-layer is directly resolved) and the bathymetric data were taken from physical experiments with an equivalent geometry. The dynamics of the coherent structures forming around the obstacle and inside the scour-hole was investigated and its influence on the modeling of the problem and on the erosion process was discussed. The analysis suggested that the full dynamics of the vortex system should be directly solved since simple eddy-viscosity models, as the k-ε model in RANS approach, were found to be not suited for this kind of problem and since high-order statistics were found to be important for the evolution of the local scour. The results of the present study may be helpful to formulate new physical-based local scour models to be used for practical evaluation of the scour depth around bridge abutments.<br>XXII Ciclo<br>1981
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Bazan, Ravines Mauricio Javier, and Vargas Jorge Daniel Coronado. "Control de erosión fluvial en la curva externa, haciendo uso de paletas sumergidas en los sectores La Perla-Florida y Cantagallo en el Rio Rímac aplicando modelamiento numérico." Bachelor's thesis, Universidad Peruana de Ciencias Aplicadas (UPC), 2021. http://hdl.handle.net/10757/654947.
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La presente tesis tiene como objetivo evaluar una propuesta para el control de erosión fluvial de la curva externa del rio Rimác ubicada entre los sectores Cantagallo y La Perla en Chosica, verificando su eficacia a través de un modelamiento con fines de calcular la socavación producida para diferentes periodos de retorno y proponer como estructura de control a las paletas sumergidas, comparando ambos resultados obtenidos para evaluar sus beneficios.
El tramo escogido presentó fallas en los muros de contención ubicados a lo largo del cauce según un estudio previo realizado por el INGEMMET, por lo que es necesario mejorar la infraestructura ya construida, por lo que la presencia de las paletas sumergidas podría actuar como tal. Por este motivo, el modelamiento hidráulico, realizado en el software Iber, nos permitirá conocer el comportamiento del río para obtener las variables de diseño y conocer los valores de velocidades y esfuerzos cortantes de fondo producidos en la curva externa.
Se realizó la simulación para dos escenarios, uno considerando las máximas avenidas producidas en años previos y el segundo despreciando dichos valores. Esto nos permite comparar las dimensiones y comportamiento de ambas estructuras para un futuro diseño.
Finalmente, en ambos escenarios se verificó que la presencia de las paletas sumergidas en la curva externa reduce los niveles de erosión local y general producido para los diferentes caudales simulados, por lo que resulta una estructura viable a ser aplicada como medida de control.<br>The objective of this thesis is to evaluate a proposal for the control of fluvial erosion of the external bend of the Rimac river located between the Cantagallo and La Perla sectors in Chosica, verifying its effectiveness through a modeling in order to calculate the undercut produced for different return periods and propose submerged vanes as a control structure, comparing both results obtained to evaluate their benefits.
The chosen section presented failures in the retaining walls located along the channel according to a previous study carried out by INGEMMET, so it is necessary to improve the infrastructure already built, so the presence of the submerged vanes could act as such. For this reason, the hydraulic modeling, carried out in the Iber software, will allow us to know the behavior of the river to obtain the design variables and to know the values of speeds and shear stresses produced in the external bend.
The simulation was performed for two scenarios, one considering the maximum avenues produced in previous years and the second disregarding these values. This allows us to compare the dimensions and behavior of both structures for a future design.
Finally, in both scenarios it was verified that the presence of the submerged vanes in the external curve reduces the levels of local and general scour produced for the different simulated flows, making it a viable structure to be applied as a control measure.<br>Tesis
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ARYA, ADITYA. "SCOUR AROUND DIFFERENT SHAPES OF PIERS AT DIFFERENT ORIENTATION WITH FLOW." Thesis, 2014. http://dspace.dtu.ac.in:8080/jspui/handle/repository/15500.
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Scour is the process of local lowering of stream bed elevation which takes place in the vicinity or around a structure constructed in flowing water. Scour takes place around bridge piers, abutments, around spurs, jetties and breakwaters due to modification of flow pattern in such a way as to cause increase in local shear stress. Due to improper knowledge of scour around bridge pier, there were lots of bridges failure cases faces by our country which leads to economic loss and life loss. To understand the phenomenon of local scour around piers an attempt is done by experiment on different shape of bridge piers at different angle of attack of flow.
A series of experiments were performed to study the phenomenon of local scour that takes place beside a bridge pier of different shape on straight channel at different angle of attack, and to investigate the relation between the dimensions of the scour hole and between non-dimensional parameters describing the flow ratio, and angle of flow attack. All tests were held under clear-water condition, using a horizontal bed consisted of non-uniform sandy soil.
The experiments were conducted under different condition of flow parameters which helps to better understanding of local scour around different shapes of piers, and piers along the channel flow, across the channel flow and inclined to channel flow. The shape of scour hole, depth of scour, length of scour hole upstream and length of scour hole downstream helps in understanding geometry of scour hole and rate of scour in different cases of piers shape and orientation.
Under the different condition of flow, its helps to understanding the scour depth variation with time, with parts run of flow and with continuous flow run in a certain time. The others parameters like length of scour hole upstream and downstream to study the variation of geometry of scour hole.
With the different shape of piers, the pier having minimum scour is best for the design consideration for scour point of view, it also helps in designing of foundation as the increasing depth of foundation increase the cost of project with proper knowledge about scour phenomenon helps in designing cost effective piers.
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CONG, XING-LU, and 叢興魯. "Study of local scour for engineering structures." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/21344848755944823611.
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Huang, Cheng-Chang. "Local scour at isolated obstacles on river beds." Thesis, 1990. http://hdl.handle.net/1957/37321.
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Maximum equilibrium scour depths, equilibrium scour volumes,
and induced equilibrium movements at isolated obstacles on river
beds were investigated in clear-water scour. The research was
achieved by a systematic flume study based on the results of
dimensional analysis of local scour.
The main tested obstacles for local scour were cubes. Local
scour at a circular cylinder of aspect ratio 1 and a sphere were
also examined for comparison with scour at cubes. Each obstacle was
placed on a flat movable bed and oriented normal to the incident
flow. Non-cohesive uniform medium sand and very fine gravel were
used as movable beds. The tested flow conditions were controlled to
give many combinations of the relevant dimensionless parameters for
local scour: the flow Froude Number, relative obstacle size, and
relative roughness of bed material.
Water surface profiles and longitudinal velocity profiles along
the plane of symmetry, as well as the horizontal velocities near the
bed around isolated obstacles on a fixed bed were examined in
several runs. For a slightly submerged cube, the path of maximum
velocity downstream of the cube moves from the water surface into
the lower part of the flow. At a greater distance downstream, the
path of maximum velocity tends to move upward toward the water
surface. An increase of flow Froude Number leads to a hydraulic
jump behind the cube. The relative longitudinal velocity near the
bed is increased in this region. The decrease of relative water
depth or the increase of flow Froude Number can lead to increased
average relative horizontal velocity (V/u) near a cube. The cube
has the highest average V/u value, as compared to flow near a
circular cylinder and a sphere.
The local scour processes and equilibrium scour patterns at
isolated cubes on movable beds were also examined. There is not a
unique equilibrium scour pattern for clear-water scour at a cube on
a movable bed. Equations were developed to predict the maximum
equilibrium scour depth and scour volume and the critical condition
for incipient motion of bed material at a cube in clear-water scour.
As the water becomes relatively deep, the shape effect of the
circular cylinder and the sphere become negligible. The major
equilibrium movement of a cube on a movable bed due to scour
involves longitudinal displacement, vertical settlement, and
longitudinal inclination. Equations were developed to predict the
equilibrium movement and the critical condition for incipient
upstream movement of a cube in clear-water scour.<br>Graduation date: 1991
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Wang, Shin-Kuei, and 王新貴. "Local Scour around Non-uniform Piers and Collar." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/80702982838879313086.
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碩士<br>國立中央大學<br>土木工程研究所<br>90<br>This study uses experimental mobile channel to examine the characteristics of local scour around non-uniform piers and the piers with collar protection. The maximum scour depth and the range of the scour hole is analyzed. Furthermore, the change of scour at different exposure elevations is compared by performing a series of case studies.
When the collar is close to the bed, the scour depth decreases. When it’s top is flush with the bed, the scour depth decreases obviously, and both the downflow and horseshoe vortex are guided to the downstream successfully far away from the bridge pier structure. The scour depth doesn’t change obviously with the increase of the location of the collar, so the horseshoe vortex is the main factor for scouring. The experiments of non-uniform piers at different exposure elevations showed that the increase of exposure elevation causes the increase of obstruction area. So, the range of scour hole and the depth of scour will increase. When the top of the pier foundation is flush with the bed, the scour doesn’t occur in front of the pier foundation, the result is similar to that for using collar. While the scour depth is much deeper for those causes when the scour occurs in front of the pier.
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Wu, Jiun_Hong, and 吳俊鋐. "Abutment local scour and velocity distribution by an." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/97883830973258966680.
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碩士<br>國立成功大學<br>水利及海洋工程學系<br>88<br>ABSTRACT
Previous in-bank flow studies showed that a main channel transitional section in front of and behind a bridge abutment in a compound channel could reduce abutment local scour. This study is interested in that how this transition affects the topography of the channel during over-bank flow conditions. Three experimental sets with or without this transition were thus conducted in a 20x1.1x0.3m movable bed compound channel that was constituted of a trapezoidal main channel and two horizontal floodplains. At each experiment, equilibrium local scour, water level and velocity profiles at various points near the bridge region were measured.
Due to large velocity profile measurement work and limit of time, the present study could not give a strong conclusion that inclusion of the transitions can reduce local scour depth around the bridge abutment. However, the following evidences give the light that the argument may be true. If there is a transition section, then in the main channel:
(1) Water level in front of the bridge abutment rises by 0.19%~0.57%,
(2) Velocities upstream the bridge reduce by 12%~20%, and
(3) Discharge through main channel reduces by 6.8﹪ and the measured maximum local scour depths reduce by 47.4%~61.5%.
In addition to the above evidences this study provided, it is thought that present velocity profile measurement and bed topography data are accurate. They can be used for the verification of further numerical studies.
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CHANG, YI-HSIN, and 張藝馨. "Local Scour aroung Nonuniform Piers and Pile Foundations." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/44218843847065938388.
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碩士<br>國立中央大學<br>土木工程研究所<br>88<br>Most rivers in Taiwan are severely degrading during last two decades due to fast growing in-stream sand mining and construction of water supply or diversion works. Consequently, the exposure of bridge foundations, such as caissons and piles of bridge piers , is one of the most critical issue for the design and maintenance of river-crossing bridges. Inadequate design of countermeasures at bridge crossings may incur further local and contraction scours. The scouring process, such as maximum scour depth and scour dept and scour depth and scour range, around non-uniform piers and pile foundations are examined in this study by employing laboratory experiments . The suitable countermeasures for those foundations will is also investigated
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Chen, Feng-Kun, and 陳峰琨. "Investigation of Local Scour Effects in Alluvial Rivers." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/90198126109564963623.
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碩士<br>國立臺灣大學<br>土木工程學研究所<br>99<br>In this thesis, the flow field and physical mechanism of local scour problem around the bridge piers is mainly used by numerical simulation. Two different field cases are studied: they are the bridge scour effects surrounding the Hou-Feng Bridge and the gap scour effects about the stepped concrete block grade control structure in Ta-Jia river, respectively. It is an extremely difficult problem by using the numerical programming to solve these problems. Hence we seek the help from the commercial software, Flow-3D, to analyze the problem. The problem setting includes the rigid-bed and mobile-bed simulation and the laboratory experiments are aided in the meantime. The numerical results of the rigid-bed simulation are compared with the laboratory results in terms of the fluid depth in front of the first pier. The results from numerical studies and laboratory experiments match very well. In the mobile-bed simulation, the ultrasound device is added in the experiment and the scour depth and the variation of the whole flow field are interfered with the sensor. Hence after the ultrasound device is removed, the influence of the overfall flow in the bridge scour simulation can be clearly classified. The mainly scour hole is concentrated in front of the first pier in the numerical simulation with the overfall flow. In the meantime, the upstream of the first pier is borne by the current flow and the maximum flow velocity is measured close the bottom of the first pier. If the overfall flow is not considered in the simulation, the mainly scour hole is concentrated around the first pier. The reasons are attributed to the down flow and the horseshoe vortex. As for the rigid-bed simulation of the gap scour, the third step of the stepped concrete block grade control structure always existed the obvious velocity on the Z-axis and the strong vortex near the edge of the stepped concrete block grade control structure in the numerical simulation no matter how strength of the flow. In the gap scour simulation, it is difficult to observe the accurate physical phenomenon during the numerical simulation in light of its physical problem setting belongs to the discontinuous arrangement. Hence the applied numerical simulation still requires further development.
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Chen, Jui-Chang, and 陳瑞昌. "The Local Scour Behavior Downstream of Aprons and Sills." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/50984262958758422572.
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碩士<br>國立中央大學<br>土木工程研究所<br>90<br>Aprons and sills are the common countermeasures for protecting the downstream riverbed. In this study the local scour behavior downstream of aprons and sills are examined by employing laboratory experiments. The scour characteristics of two homogeneous sand beds caused by the wall jet, the wall jet with apron, and the wall jet with end sill, are compared. By using theory and experimental data, a prediction model is developed, and is used to explore the characteristics of local scour near those structures.
Keywords：local scour、aprons 、sills、scour hole
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Cheng, Ko-Yu, and 鄭可佑. "The effect of aprons and sills local scour reduction." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/74698602964634365419.
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碩士<br>國立中央大學<br>土木工程研究所<br>92<br>In order to protect downstream riverbed of sluice gates, many energy dissipaters such as aprons and sills are installed on the channel bed. This study examines the effect of length of aprons and types of double sills on the local scour behaviors.
The variation of head cutting length and cyclic scouring are observed and measured in the experiments. The characteristics of scouring holes caused by the wall jets with aprons and the wall jets with double sills are compared. The characteristics of local scour near structures is explored by analyzing the experimental data.
According to experimental data, The protection of downstream riverbed is better when the length of aprons is longer ,. Double sills with long length of apron provide excellent protection for riverbed.
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Tsai, Kun-lin, and 蔡坤霖. "Local Scour around Eccentric Circular Piers with Steady Flow." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/74167331488813937712.
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碩士<br>逢甲大學<br>水利工程所<br>94<br>The research utilize hydraulic models to simulate local scour depth and scour depth change with time for non-uniform pier diameter ratio D/D* of 0.4 and 0.7, and different type pier and initial bed level relative under the foundation top elevation under steady flow. (V/Vc=0.95)
The research results show that the different scour depth with different initial bed level relative and different type pier, and accompany different type pier will make maximum scour depth to different position. The maximum scour depth of un-exposed bridge foundation (Y=+10 mm) is less than exposed bridge foundation (Y=-10 mm) whatever type piers are.
In the same flow condition, when the bridge foundation is un-exposed (Y=+10mm) and the diameter ratio is D/D* of 0.4 with type pier (A1), (B1), (C1), the non-uniform plane of foundation can retard downflow scouring effectively and make scour depth reduced. Opposite results are found for the exposed (Y=-10 mm) bridge foundation.
Local scour depth of the diameter ratio D/D* of 0.4 with type pier (A1), (B1), (C1) is less than that diameter ratio D/D* of 0.7 with type pier (A2), (B2), (C2); when the diameter ratio is D/D* of 0.4 with type pier (B1) of an un-exposed bridge foundation (Y=+10 mm), non-uniform plane can retard scour more effectively. Considering the safety of bridge structure, an eccentric non-uniform circular pier with D/D* which equals to 0.4 with type pier B is an ideal pier style.
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Lai, Wen-Jenq, and 賴文正. "Study on Local Scour Bridge Pier in Steep Channel." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/23494781754028921838.
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Castiblanco, Mário Enrique Moreno. "Experimental study of local scour around complex bridge piers." Doctoral thesis, 2016. https://repositorio-aberto.up.pt/handle/10216/85290.
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Cheng, Wei Shi, and 鄭暐曦. "Local Scour around Nonuniform Circular Piers under Unsteady Flow." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/70487305212544156755.
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碩士<br>國立中興大學<br>土木工程學系<br>93<br>One of the major problems relating to the bridge damage in Taiwan is the exposure of the bridge foundations. General scour may occur in a river due to either the man-induced or natural causes. Local scour is attributable to the existence of the bridge. Both general and local scours may affect the safety of a bridge.
In this study, different types of unsteady flow hydrographs, including the advanced, symmetrical, and delayed hydrographs, with non-uniform piers were used to conduct the laboratory bridge scouring experiments. The variation of local scour depth with exposure elevation (i.e. the relative elevation between the channel bed elevation and the discontinuous surface of non-uniform pier) was also investigated.
The experimental results revealed that the scour depth for the case with the soil surface above the discontinuous surface (foundation not exposed) was smaller than the case with the foundation exposed. The results implied that the discontinuous surface of the non-uniform pier can effectively reduce the local scour depth. In addition, it was found that among three kinds of hydrographs, maximum amount of reduction on the local scour occurred for the symmetrical flow hydrograph.
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Lin, Jiing Hwel, and 林景輝. "Study on the Local Scour around Cylindrical Bridge Piers." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/28934330597838009934.
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Castiblanco, Mário Enrique Moreno. "Experimental study of local scour around complex bridge piers." Tese, 2016. https://repositorio-aberto.up.pt/handle/10216/85290.
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Tafarojnoruz, Ali, Roberto Gaudio, and Sergio Rizzuti. "Flow-altering countermeasures against local scour at bridge piers." Thesis, 2014. http://hdl.handle.net/10955/596.
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Scuola di Dottorato "Pitagora" in Scienzae Ingegneristiche, Ciclo I, a.a.2007-2010<br>The ability to protect bridge piers and abutments against scour is critical to bridge safety.
Excessive pier scour can cause high maintenance costs or even bridge collapse resulting in the
interruption of traffic and possibly death.
Up to now, various types of countermeasures have been recommended to reduce scouring
around pier foundations. The countermeasures against pier scour can be broadly classified into
two categories: (1) flow-altering and (2) bed-armouring countermeasures.
This thesis focuses on the first category of countermeasures. Based on a comprehensive
review of the up-to-date studies on various types of flow-altering countermeasures, these can be
classified into four main groups based on their shapes and performances: (1) openings through
piers, (2) pier attachments, (3) bed attachments and (4) other devices. After evaluation and
considering all the countermeasures, a few countermeasures were recommended for further
investigations. Among them, five countermeasures were selected for analysis in the present
thesis. They are transverse sacrificial piles, collar, threading, pier slot and bed-sill.
The first part of the experiments, were performed in clear-water scour condition, near
threshold condition of sediment movement. In this part, countermeasures were tested
individually. Afterwards, countermeasures that showed appropriate efficiency in scour depth
reduction were combined one by one. Results of this part showed that a collar, pier slot and
sacrificial piles may show efficiency of about 30% in scour depth reduction; however, threading
cannot be assumed as a reliable pier scour countermeasure. Results show that the blockage ratio
of sacrificial piles is an important parameter, since by increasing the number of piles from three
to five, the efficiency reduces. In this part also optimum size and location of a pier slot were
criticised and best configuration based on previous and present studies was proposed. In fact, the
best configuration can be suggested as a pier slot half as long as the flow depth plus maximum
scour depth. In this case, the pier slot near the water surface may not significantly increase the
efficiency. A combination of sacrificial piles with a collar and sacrificial piles with a slot showed
that they cannot reduce the scour depth significantly with respect to each individual
countermeasure. In particular, a combination of a collar and sacrificial piles increases the rate of scouring with respect to a single collar. At the end of this part, a combination of a bed-sill and
cut-collar was selected as the best configuration. Two forms of this countermeasure were
proposed for further studies. In the first proposed countermeasure, the use of a sill as wide as the
channel width was recommended. This form, although reliable to prevent souring at the upstream
part of the bed-sill, may not be applicable for some practical purposes. Therefore, in another
attempt, a shorter bed-sill was also proposed, protected with two side-walls, in order to reduce the
risk of scour intrusion in front of the bed-sill. These two proposed countermeasures showed
efficiencies of 68.5% and 64.5% in scour depth reduction, however owing to the use of a border
around the collar rim, the scour did not reach the pier body.
In next part, the later form of proposed countermeasure that consists of a shorter bed-sill
and seems to be more practical, was evaluated in unsteady flow tests with the peak flow intensity
slightly greater than the threshold for the inception of sediment movement. In this section of the
thesis, circular and round nose and tail rectangular piers were tested in both configurations of
single and two in-line piers. The results of unsteady flow tests also show that the proposed
combined countermeasure can protect pier foundation during a flood event. Specifically, it seems
that the proposed countermeasure is more effective when it is applied to round nose and tail
rectangular piers than circular ones<br>Università degli Studi della Calabria
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Lee, Jun-Ying, and 李俊穎. "Local Scour around Concentric Circular Piers with Various Flow Hydrographs." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/03694785815647009079.
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碩士<br>逢甲大學<br>水利工程所<br>93<br>This study uses hydraulic models to measure the variation of local scour depth with time for non-uniform pier diameter ratios of 0.4 and 0.7, and different initial bed level relative to the foundation top elevation under unsteady flows with advanced, central and delayed peaks.
The research results show that the scour depth increases with an increase of flow intensity under different types of unsteady flow hydrographs. The scour depth reaches a maximum value within the rising phase of the unsteady flow. The scour variation for the central peak hydrograph is similar to that for the delayed peak hydrograph, and both of their scour depths are greater than that for the advanced peak hydrograph. The only discrepancy for the first two curves is the time lag.
Because of the scouring retardation by the top of foundation, the scour depth is reduced for the un-exposed bridge foundation ( ) under any unsteady flow. Opposite results are found for the exposed bridge foundation ( ). When the distance between the top of foundation and the initial bed level is greater than the scour depth ( ), the foundation top cannot retard scouring efficiently which leads scour depth to increase. However, the scour depth is still less than the condition with the bridge foundation exposed initially.
As regards to the effect of non-uniform pier diameter ratio ( ), local scour depth for a ratio of 0.4 is less than that for a ratio of 0.7. Also the former is more effective in scour hole volume retardation than the latter. The most effective scour hole volume retardation occurs when equals 0.6. Considering the safety of bridge structure, a non-uniform pier with equals to 0.4 is an ideal pier style.
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Cheng, Jen-hao, and 鄭人豪. "Local Scour around Eccentric Circular Piers under Unsteady Flow Conditions." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/97836784867224776711.
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碩士<br>逢甲大學<br>水利工程所<br>95<br>This study uses hydraulic models to measure the variation of local scour depth with time for eccentric pier diameter ratios D/D*of 0.4 ~ 0.7, and different initial bed level relative to the foundation top elevation under unsteady flows with advanced, central and delayed peaks.
The research results show that the scour depth increases with an increase of flow intensity under different types of unsteady flow hydrographs. The scour depth reaches a maximum value within the rising phase of the unsteady flow. The scour variation for the central peak hydrograph is similar to that for the delayed peak hydrograph, and both of their scour depths are greater than that for the advanced peak hydrograph. The only discrepancy for the first two curves is the time lag.
Because of the scouring retardation by the top of foundation, the scour depth is reduced for the un-exposed bridge foundation (0≦Y/D*≦0.6) under any unsteady flow. Opposite results are found for the exposed bridge foundation (Y/D*<0). As regards to the effect of eccentric pier diameter ratio (D/D*), when D/D* is equal to 0.4, because pier oncoming flow area is the smallest one so that downflow intensity is less; as non-uniform area is bigger and decrease more downflow energy so that bring smaller scour depth and effect area. Therefore, local scour depth for a ratio of 0.4 is less than that pier of other forms.
Scour hole volume retardation increases with an increase of different initial bed level relative to the foundation top elevation, when Y/D*=0.6 has the most effective retardation. As regards to the effect of eccentric pier diameter ratios (D/D*), the most effective scour hole volume retardation occurs when D/D* equals 0.4. Considering the safety of bridge structure, a eccentric pier with D/D* equals to 0.4 is an ideal pier style.
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Huang, Ren-Xiao, and 黃任孝. "Study on Local Scour around Bridge Pier with Diversion Device." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/77549548467684227447.
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碩士<br>逢甲大學<br>土木及水利工程研究所<br>88<br>The local scour around the bridge pier can be effectively mitigated or controlled, and in turn, the safety of the bridge may be enhanced if the bridge pier is equipped with a diversion device to lessen the impinging downflow. This study used part of the Kikkawa theory and the innovative diversion device which has nine types of models to conduct various clear-water hydraulic tests under the conditions of fixed channel slop (s=0.01), water depth (h=9.3) and bed material (d50=0.75mm). It is found that the diversion device which is attached to the round-nose pier with tapered body is the most effective design to mitigate the maximum scour depth, the scour hole volume and the range of scour around the bridge pier.
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Jhong, Ren-Kai, and 鍾仁凱. "Study on Local Scour and Sediment Exchange around Spur Dikes." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/vj36cf.
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博士<br>國立交通大學<br>土木工程系所<br>105<br>Spur dikes are hydraulic structures that extend from a river bank into the river channel, and in on-site applications, they are present in groups. In river engineering, spur dikes have diverse functions. When applied to erodible banks, spur dikes can deflect near-bank currents to the river center. In addition, the recirculation zones behind spur dikes have a slow flow velocity, which increases sedimentation at the riverbank footing and reduces riverbank erosion. Although spur dikes serve multiple river management functions, their inherent structure hampers water flow from upstream to downstream. Thus, when water flows approach a group of spur dikes, the potential energy of the flows is increased to overcome the resistance engendered by the spur dikes. This increase in potential energy indicates that water flows passing through spur dikes demonstrate increasing turbulence intensity of flow, resulting in complex bed change near spur dikes. The local scour issue of a single spur dike has been studied by many researches, but fewer studies analyzed local scour of spur dikes. In addition, less study discussed the relationship between local scour mechanism and sediment exchange around spur dike field. Based on the field investigation, numerical simulation and flume experiment, this study explained the mechanism of spur dike scour and sediment loss in the spur dike fields. In the submerged case, the sediment loss in the spur dike fields caused by upward vortex and the scour zone development of first spur dike. The thickness of sediment loss in the spur dike fields can be calculated by local scour depth of first spur dike, the distances from upstream and overtopping rate. In the emerged case, the sediment loss in spur dike field is less than the submerged case. Moreover, an empirical formula was developed to estimate the maximum scour depth around the on-site spur dike group.
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Wen-Yi, Chang, and 張文鎰. "Simulation and experimental verification for local scour around circular piers." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/43126751296736166460.
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博士<br>國立臺灣大學<br>土木工程學研究所<br>91<br>Steep riverbed slopes and rapidly varying discharges with relatively short duration are common characteristics in Taiwan’s rivers. During such a flood, severe scour around the bridge pier always occurs near the peak-flow discharge. These unsteady flow characteristics increase the difficulties of estimating the scour depth at pier nose under unsteady flow for design purposes. In addition, bed materials are generally composed of non-uniform sediment in alluvial river. Under the hydraulic sorting of surface bed materials, the coarser sediment tends to be left on bed surface to form an armor layer protecting the beneath bed materials. The armoring effects of non-uniform sediment have important influences on scour depth around the pier.
The present study is devoted to investigate the effects of sediment non-uniformity and unsteady flow characteristics on scouring processes. For experimental studies, experiments with uniform/non-uniform sediments have been carried out under unsteady flow conditions to obtain data for scour evolution. By analyzing the measured results, the effects of sediment non-uniformity and unsteady flow characteristics on scour depth are studied. For numerical simulation, the scour model developed by Chang (1998) is further improved. The bed-sediment transport rate is modified by considering the hiding/exposure effects of non-uniform sediment and gravitational effects of sediment on the sloping bed. In addition, the suspended load due to the downflow scour is also included in the model. Then the scour simulations under unsteady flow with non-uniform sediment are conducted by employing the quasi-steady approach and the mixing layer concept to compute the evolution of scour depth and sediment size. Experimental results obtained by Ettema (1980)、Kothyari (1989) and the present study are employed for calibration and verification of the scour model. Besides, a simplified unsteady scour model is developed in accordance with the superposition characteristic of scour evolution under unsteady flow, which can quickly simulate the scour evolution at pier nose. Finally, a systematic study has been carried out to investigate the influences of the unsteady flow scour parameter, dimensionless sediment size and sediment size gradation on scour depth.