CFD Study of Decay Function of Wall Shear Stress with Scour Around Complex-shape Bridge Pier PDF Download
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Author: Chen Li
Publisher:
ISBN: 9781339824581
Category :
Languages : en
Pages : 189
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Book Description
With surveyed full-scale bathymetries of the Feather River Bridge, this hybrid approach and the decay function were applied to study the pier scour problem. The decay trend and the envelope decay function were verified with the results of CFD modeling for the full-scale models. Using the soil composition of each layer, the application of the decay function was preliminarily developed.
Author: Chen Li
Publisher:
ISBN: 9781339824581
Category :
Languages : en
Pages : 189
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Book Description
With surveyed full-scale bathymetries of the Feather River Bridge, this hybrid approach and the decay function were applied to study the pier scour problem. The decay trend and the envelope decay function were verified with the results of CFD modeling for the full-scale models. Using the soil composition of each layer, the application of the decay function was preliminarily developed.
Author: Md Nazmus Sakib
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Shaghayegh Pournazeri
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The prevention and control of bridge scour is a challenging element in bridge-pier foundation design. Sediment scour from around the piers has been a main cause of all bridge failures. For the cost-effective and reliable design of pier foundations, one needs accurate prediction of flow-inducing scour. Such prediction can be obtained from numerical modelling, as a good extension of experimental results. General CFD software packages are incapable to simulate sediment transport (bedload) and bed-level change (scour/deposition). Some numerical models have been developed for bedload and scour simulations, but there are two major limitations: (1) the bed sediments are assumed to have uniform grain size which is not true in natural river channels; (2) the modelling techniques are not computationally efficient for applications at the field scale. Thus, new modelling techniques for scour prediction are needed.The objectives of this research are: (1) to modify an existing shallow-water hydrodynamics model to allow for non-hydrostatic pressure corrections; (2) to improve the prediction of bed shear stress, a key parameter for bedload prediction; (3) to incorporate a new module for calculating bedload of mixed sediment-grain sizes; (4) to verify the model’s prediction with existing experimental data.For pressure corrections, a seven-diagonal linear system is added to the model, which is symmetric and positively defined. This system is numerically solved for non-hydrostatic pressure through preconditioned conjugate gradient iterations. Then, corrections to velocity and water surface elevation due to non-hydrostatic pressure are obtained. Fractional bedload calculations are based on a surface-based transport function, which depends on a particle-hiding factor, bed shear stress, and grain size distribution. Bed level change caused by bedload is calculated using the Exner equation added to the model.The new model successfully predicts 3-D velocities around a circular pier in a fixed scour-hole and scour development on a mobile bed with uniform and non-uniform sediments. We improve bed shear stress prediction by using near-bottom velocities, as opposed to the widely used bottom-layer velocity, in the wall function method. Velocity and scour depth predictions agree well with experimental data. We show that scour emerges from the lateral sides of a pier, and scour patterns move toward its upstream nose. On the upstream side, relative to the pier’s centre, scour depth increases until the bed slope reaches the angle of repose of sediments. On the downstream side, scour continues until equilibrium is reached. Scour is deeper on the upstream than downstream side. Non-uniformity in grain sizes tends to reduce the magnitude of scour. The presence of the pier causes a strong vortex at its foot on the upstream side, which effectively moves sediments toward downstream. On the upstream side, the scour-hole’s outer shape is almost half a cone, true for both uniform and non-uniform sediments. These findings have implications to foundation design. The modelling techniques presented in this study are computationally efficient and are practical for applications at the field scale, which have been difficult so far.
Author: Seung Oh Lee
Publisher:
ISBN:
Category : Geophysical prediction
Languages : en
Pages :
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Book Description
Local scour around bridge foundations has been recognized as one of the main causes of bridge failures. The objective of this study is to investigate the relationships among field, laboratory, and numerical data for the purpose of improving scour prediction methods for complex bridge piers. In this study, three field sites in Georgia were selected for continuous monitoring and associated laboratory models were fabricated with physical scale ratios that modeled the full river and bridge cross sections to consider the effect of river bathymetry and bridge geometry. Three different sizes of sediment and several geometric scales of the bridge pier models were used in this study to investigate the scaling effect of relative sediment size, which is defined as the ratio of the pier width to the median sediment size. The velocity field for each bridge model was measured by the acoustic Doppler velocimeter (ADV) to explain the complicated hydrodynamics of the flow field around bridge piers as guided by the results from a numerical model. In each physical model with river bathymetry, the comparison between the results of laboratory experiments and the measurements of prototype bridge pier scour showed good agreement for the maximum pier scour depth at the nose of the pier as well as for the velocity distribution upstream of each bridge pier bent. Accepted scour prediction formulae were evaluated by comparison with extensive laboratory and field data. The effect of relative sediment size on the local pier scour depth was examined and a modified relationship between the local pier scour depth and the relative sediment size was presented. A useful methodology for designing physical models was developed to reproduce and predict local scour depth around complex piers considering Froude number similarity, flow intensity, and relative sediment size.
Author: Junliang Tao
Publisher:
ISBN:
Category :
Languages : en
Pages : 256
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Book Description
Bridge scour is the erosion of sediments around bridge piers or abutments due to flowing water. It is the number one cause of bridge failures in the United States. However, the mechanism of bridge scour remains a mystery due to the complex interaction between structures, flow, and sediments; there is also an urgent demand to develop countermeasures reducing the risk caused by bridge scour. This dissertation work aims to provide innovative solutions to address such challenges through highly interdisciplinary efforts. A tremendous effort has also been placed to review and synthesize the existing literature. Computational Fluid Dynamics (CFD) technique is employed to simulate the flow and scour patterns around bridge piers with different geometries. The effects of pier shape, aspect ratio and attack angle on the flow and scour patterns are evaluated. The findings of this work not only further advance the understanding of scour, but also provide insightful practical implications. A numerical simulation framework integrating advanced CFD techniques and a novel sediment transport model is also developed, aiming to model the scour process. The uniqueness of this advanced model is that it incorporates the influence of turbulence, which plays a crucial role in the process of scouring but has been overlooked for decades. To facilitate the characterization of the turbulence at the interface of sediment and river flow, bio-inspired flow sensors are developed. The innovative sensors mimic the function and structure of the hair cells in fish, which is sensitive to turbulence in flow. Smart material (piezoelectric microfiber) is employed to construct the artificial hair cell and the unique patterning of electrodes enables the linear sensitivity as well as the directional sensitivity of the sensor. Three designs are proposed, modeled and optimized. The performance of the prototype sensors is evaluated through laboratory experiments. A field monitoring system is designed and deployed in the field to remotely monitor the evolution of the scour depth around real bridge piers. This system includes an innovative sensor based on Time Domain Reflectometry (TDR) technique and the sensor is proved to be sensitive, durable and cost effective. It also includes a field data acquisition system, which automatically collects the TDR data and transmits the data wirelessly. The scour depth data can be utilized to calibrate the various scour depth prediction equations. It can also be integrated into the bridge risk management system to assist in decision making.
Author: Erin M Dougherty
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Laura Christine Bolduc
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Scour at a bridge pier is the formation of a hole around the pier due to the erosion of soil by flowing water; this hole in the soil reduces the carrying capacity of the foundation and the pier. Excessive scour can cause a bridge pier to fail without warning. Current predictions of the depth of the scour hole around a bridge pier are based on deterministic models. This paper considers two alternative deterministic models to predict scour depth. For each deterministic model, a corresponding probabilistic model is constructed using a Bayesian statistical approach and available field and experimental data. The developed probabilistic models account for the estimate bias in the deterministic models and for the model uncertainty. Parameters from both prediction models are compared to determine their accuracy. The developed probabilistic models are used to estimate the probability of exceedance of scour depth around bridge piers. The method is demonstrated on an example bridge pier. The values of the model parameters suggest that the maximum sour depth predicted by the deterministic HEC-18 Sand and HEC-18 Clay models tend to be conservative. Evidence is also found that the applicability of the HEC-18 Clay method is not limited to clay but can also be used for other soil types. The main advantage of the HEC-18 Clay method with respect to the HEC-18 Sand method is that it predicts the depth of scour as a function of time and can be used to estimate the final scour at the end of the design life of a structure. The paper addresses model uncertainties for given hydrologic variables. Hydrologic uncertainties have been presented in a separate paper.
Author: Jorgen Fredsoe
Publisher: World Scientific
ISBN: 981449805X
Category :
Languages : en
Pages : 550
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Book Description
This book discusses the subject of wave/current flow around a cylinder, the forces induced on the cylinder by the flow, and the vibration pattern of slender structures in a marine environment.The primary aim of the book is to describe the flow pattern and the resulting load which develops when waves or current meet a cylinder. Attention is paid to the special case of a circular cylinder. The development in the forces is related to the various flow patterns and is discussed in detail. Regular as well as irregular waves are considered, and special cases like wall proximities (pipelines) are also investigated.The book is intended for MSc students with some experience in basic fluid mechanics and for PhD students.
Author: Hiroshi Okada
Publisher: Springer Nature
ISBN: 303027053X
Category : Technology & Engineering
Languages : en
Pages : 1278
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Book Description
This book gathers the latest advances, innovations, and applications in the field of computational engineering, as presented by leading international researchers and engineers at the 24th International Conference on Computational & Experimental Engineering and Sciences (ICCES), held in Tokyo, Japan on March 25-28, 2019. ICCES covers all aspects of applied sciences and engineering: theoretical, analytical, computational, and experimental studies and solutions of problems in the physical, chemical, biological, mechanical, electrical, and mathematical sciences. As such, the book discusses highly diverse topics, including composites; bioengineering & biomechanics; geotechnical engineering; offshore & arctic engineering; multi-scale & multi-physics fluid engineering; structural integrity & longevity; materials design & simulation; and computer modeling methods in engineering. The contributions, which were selected by means of a rigorous international peer-review process, highlight numerous exciting ideas that will spur novel research directions and foster multidisciplinary collaborations.
Author: David C. Wilcox
Publisher:
ISBN: 9781928729082
Category : Fluid dynamics
Languages : en
Pages : 522
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