oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Shear Stress Variation at Scour Hole of Circular Pier  [PDF]
Joongu Kang, Hongkoo Yeo
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.411105
Abstract: The causes of local scour are generally categorized into flow condition, structure, and riverbed material. A three-dimensional vortex flow generated with the influence of the structure is the main factors of the flow conditions, and the size of the particles is assumed to be the main factor of the riverbed case. Various studies about pier local scour have been carried out by researchers since the 1960s, and a large number of experimental formulas have been suggested. Difficulties were encountered by these past studies, however, in terms of considering the influence of various riverbed materials and scour changes (floods, etc.) on time, with the condition of maximum scour depth. In the case of Korea, especially, scour influenced by various riverbed materials and the frequency of floods have been determined to be very important factors. Therefore, the ultimate purpose of this study on pier scour is to suggest the scour examination method that could consider various riverbed materials and the frequency of floods. In this study, the periodic changes in local scour based on the differences in the diameters of four types of bed materials, and on the hydraulic condition of the initial scour, were determined and compared with those in former studies. Using the results of the comparison, this study aims to determine the changes in the shear-stress around piers for various bed materials through the effect of time on scour depth (S, Smax), the shear-stress around piers, and the particles’ critical shear stress (τc).
Experimental and Numerical Investigation of the Effect of Different Shapes of Collars on the Reduction of Scour around a Single Bridge Pier  [PDF]
Afshin Jahangirzadeh, Hossein Basser, Shatirah Akib, Hojat Karami, Sareh Naji, Shahaboddin Shamshirband
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0098592
Abstract: The scour phenomenon around bridge piers causes great quantities of damages annually all over the world. Collars are considered as one of the substantial methods for reducing the depth and volume of scour around bridge piers. In this study, the experimental and numerical methods are used to investigate two different shapes of collars, i.e, rectangular and circular, in terms of reducing scour around a single bridge pier. The experiments were conducted in hydraulic laboratory at university of Malaya. The scour around the bridge pier and collars was simulated numerically using a three-dimensional, CFD model namely SSIIM 2.0, to verify the application of the model. The results indicated that although, both types of collars provides a considerable decrease in the depth of the scour, the rectangular collar, decreases scour depth around the pier by 79 percent, and has better performance compared to the circular collar. Furthermore, it was observed that using collars under the stream’s bed, resulted in the most reduction in the scour depth around the pier. The results also show the SSIIM 2.0 model could simulate the scour phenomenon around a single bridge pier and collars with sufficient accuracy. Using the experimental and numerical results, two new equations were developed to predict the scour depth around a bridge pier exposed to circular and rectangular collars.
Reduction of Local Scour at a Bridge Pier using Collar in a 180 Degree Flume Bend  [PDF]
A. Masjedi,M.S. Bejestan,A. Esfandi
Journal of Applied Sciences , 2010,
Abstract: In this study, the use of collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The adoption of a collar is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of the scour for a pier fitted with a collar and a pier without a collar. The study was conducted using in a 180 degree laboratory flume bend with a relative radius of R/B = 4.67 operated under clear-water conditions. The median size and geometric standard deviation of bed material were equal to d50 = 2 mm and sg = 1.7, respectively. Tests were conducted using one pier with 60 mm diameter in positions of 60 degree under one flow conditions. In this study, the time development of the local scour around the abutment fitted with and without collar plates was studied. The effects of various sizes of collars fitted at different elevations on the temporal development of scour depth at the abutment were also studied. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the size of a collar plate increases, the scour decreases. The minimum depth of scour occurs for the collar at diameter of 3D placed at elevation of -0.1 D from the bed surface.
Prediction of the Local Scour at the Bridge Square Pier Using a 3D Numerical Model  [PDF]
Nguyen Viet Thanh, Dang Huu Chung, Tran Dinh Nghien
Open Journal of Applied Sciences (OJAppS) , 2014, DOI: 10.4236/ojapps.2014.42005
Abstract: In this paper, the problem on local scour around a single square pier was studied by using both the numerical and physical models. The numerical model for the study is FSUM based on a finite-difference method to solve the Reynolds averaged Navier-Stokes equations (RANS) and the equations for suspended sediment concentration and bed morphology. The computed result was verified through data measured in the experimental flume with a sand bed. In general, the typical features of local scour around the pier were successfully simulated by FSUM, such as stream flow, bow flow, down flow, horseshoe vortex. The comparison between the computation and experiment data shows a quite good fitness. Both numerical model and experiment results show that the maximum scour depth occurs at two front edges of the pier. Although the computed result shows a little bigger scour depth in comparison with the measurement in the physical model, it still confirms the reliability of numerical model in some measure.
Effects of Bridge Pier Position in a 180 Degree Flume Bend on Scour Hole Depth
A. Masjedi,M.S. Bejestan,H. Kazemi
Journal of Applied Sciences , 2010,
Abstract: Local scouring around the bridge pier occurs because of flow separation and developing several vortexes around the bridge pier. Such scour hole can cause failure of the bridge especially during the river floods. Because of this several researches, have been conducted during the past three decades in straight flumes. For the case when the bridge piers located in river bend, little information is available. In this study, a series of experimental tests have been conducted in a 180 degree laboratory flume bend with a relative curvature of bend of 4.67. One oblong model pier of width 60 mm and length 180 mm was used for the study in seven different positions of 0, 30, 60, 90, 120, 150 and 180 degree under three different flow conditions were tested. Natural sand with uniform graining of d50 = 2 mm and uniformity factor of 1.7 were used as bed materials. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. The depth of the scour hole increases as with increasing duration of flow. The extent of scour observed at the pier also increases as the duration of the tests increases. The results of this study showed that, while oblong pier is placed in the bend, the maximum scouring depth is occurs in position of 60 degrees. Also, it was observed that in all positions, increasing the Froude number increases the scouring depth. Measuring depth of scouring based on experimental observation, an empirical relation is developed with high regression coefficient 94%.
Comparison of Three Commonly Used Equations for Calculating Local Scour Depth around Bridge Pier under Ice Covered Flow Condition  [PDF]
Mohammad Reza Namaee, Yuquan Li, Jueyi Sui, Todd Whitcombe
World Journal of Engineering and Technology (WJET) , 2018, DOI: 10.4236/wjet.2018.62B006
Abstract:
A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.
Investigation into Effect of Collar in Controling Scour around Circular Bridge Pier at a 180 Degree Bend  [cached]
A. Masjedi,M. Gholamzadeh Mahmoodi
Journal of Science and Technology of Agriculture and Natural Resources , 2011,
Abstract: Every year river flooding causes serious damage to the bridges at the time needed most. One of the most effective factors causing bridge failure is scouring around the piers in a river bend. One of the methods to decrease scouring around the bridge piers is fitting them with a coller on the piers. The collars protect the river bed against vortex flow in the vicinity of the pier base. An experiment was conducted to study lab flumes made of Plaxiglass with a 180 degree bend and 2.8 m central radius and a 0.6 m width. In this study, a 6cm diameter pier was placed with a circular collar with four different collar sizes in one position in bend with constant discharge and depth under clear-water conditions. The collar was placed at four different elevations. The soil material had a diameter of d50 = 2mm and geometric standard deviation of σg = 1.3. The results of the model study indicated that the maximum depth scouring was highly dependent on the experimental duration. It was observed that as the size of a collar plate increases, the scour decreases. So, minimum depth of scour is dependent on the 3D coller and -0.1D elevation. Circular collar results in maximum reduction in scour depth (93%) compared with no circular collar.
Bridge pier scour measurement by means of Bragg grating arrays  [cached]
Ballio F.,Cigada A.,Crotti G.,Inzoli F.
EPJ Web of Conferences , 2010, DOI: 10.1051/epjconf/20100634004
Abstract: This paper deals with a new method to measure scour level at bridge piers. The proposed technique is based on an array of Bragg grating temperature sensors, heated by an electrical circuit. The Bragg gratings in water sense a lower temperature than those buried in the river bed, because of the different heat scattering principles in the two situations. Furthermore the response of each sensor is slower if it is buried in the bed, with respect to the case it is in water. The paper presents laboratory tests, showing the method effectiveness and reliability, and it explains the advantages with respect to other more traditional methodologies to measure scour level.
Assessment of Turbulence Models on Bridge-Pier Scour Using Flow-3D  [PDF]
Chandara Man, Genguang Zhang, Vouchleang Hong, Shuang Zhou, Yulin Feng
World Journal of Engineering and Technology (WJET) , 2019, DOI: 10.4236/wjet.2019.72016
Abstract: The main purpose of this paper is to analyze the influence of different turbulence flow models on scouring pit of bridge-pier. Flow-3D software is applied in line with the purpose. The key motivation for this study is to contribute to the Flow-3D software by means of some modification and adjustment in the sediment scour model and shallow water model. An assessment of turbulence model adopted with the parameters of the Melville experiment to estimate the maximum scour-depth was performed. In the simulation results, the alternate eddy formation and shedding were repeated while the Karman vortex street formed behind the pier for the large eddy simulation LES turbulence model is more realistic in the flow phenomenon. The results of the scour development of large eddy simulation (LES) turbulence model were found to be more satisfied than the Renormalized group (RNG) turbulence model and close to the prior experiment results. The simulated scour results were significantly different with the observed data collected from previous literature in the reason of some unsuitability of meshing method in Flow-3D software.
Experimental study about scour protection at circular piers
Moncada M,Alix T; Aguirre Pe,Julián; Bolívar P,Juan C; Flores N,Edgar J;
Revista Técnica de la Facultad de Ingeniería Universidad del Zulia , 2007,
Abstract: in this paper an experimental study of scour around a pier is carried out. the effect produced by a collar around a circular pier and by the perforation of a slot as devices for controlling the depth of scour was analyzed. uniform sand with mean diameter of 1.4 mm and a circular pier of 7.3 cm diameter were used. firstly, two collars of 14.6 and 21.9 cm diameter were employed. the collar was placed around the pier at different positions with regard to the bed level. subsequently, a slot of 1.8 cm thickness and variable length was perforated at the pier. finally, experiments were carried out to study the effect produced by the combination of a collar and a slot. it is found that when the collar is placed at the bed level the minimum depth of scour is produced. it is obtained that the scour depth is reduced when the diameter of the collar is increased. for the case of the slot, it is found that the most favorable location to decrease the local scour is obtained by placing the slot near the bed. on the other hand, it is obtained that when the length of the slot increases, the scour depth decreases. for the combination of collar and slot, the scour depth was reduced altogether
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.