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Collar performance in bridge pier scour with debris accumulation

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International Journal of Sediment Research 2022年第3期37卷 328-334页

作者： Hossein Hamidifar Seyed Mohammad Bagher Shahabi-Haghighi yee meng chiew Water Engineering Department Shiraz University School of Civil and Environmental Engineering Nanyang Technological University

The mechanism of bridge pier scour becomes more complex in the presence of debris accumulation upstream of the pier. While using countermeasures may be effective in reducing scour, their efficacy could be undermined in such a situation. The current study investigates the effectiveness of using a collar in the presence of different types of floating debris accumulation in reducing scour around a cylindrical bridge pier with non-cohesive bed sediment. The experimental results reveal that using a collar can reduce the scour depth by up to 39% when compared to that without the collar in the absence of debris accumulation under the same flow conditions. Also, the collar’s efficiency is reduced by up to 25% when debris accumulation is present. However, depending on the relative size of the accumulated debris and collar, the effectiveness of collars may be increased as a pier-scour protection device. A new parameter,which is defined as the Debris Protrusion Ratio(DPR), is used to quantify the effect of debris layout size on scour depth. Moreover, a semi-empirical equation that may be used to predict the depth of the scour hole that forms around cylindrical collar-fitted piers with floating debris accumulation is proposed. The equation’s performance is evaluated using the available data in the literature. Based on the analysis, the current study shows that the accuracy of the proposed equation is satisfactory in predicting the maximum scour depth.

关键词： Bridge pier Scour Debris Collar Blockage

A comparison between artificial neural network algorithms and empirical equations applied to submerged weir scour evolution prediction

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International Journal of Sediment Research 2023年第1期38卷 105-114页

作者： Dawei Guan Jingang Liu yee-meng chiew Jian-Hao Hong Liang Cheng Key Laboratory of Ministry of Education for Coastal Disaster and Protection Hohai University School of Civil and Environment Engineering Nanyang Technological University Sustainability Center Nanhua University School of the Environment and Safety Engineering Jiangsu University

Estimating the time evolution of a local scour hole downstream of submerged weirs can help determine the maximum scour depth and length and is essential to designing submerged weir *** the current study, artificial neural networks with a backpropagation learning algorithm were used to estimate the temporal variation of scour profiles downstream of submerged weirs under clear water conditions. Physical factors, such as the flow condition, weir size, and sediment characteristics, are general scour considerations. Two sets of data combinations, namely original and non-dimensional data, were utilized in developing the backpropagation network(BPN) model. Using the data combinations and a trial-and-error method, the appropriate number of hidden neurons in the model architecture was determined. The results indicated that using non-dimensional variables as inputs in estimating the time evolution of scour holes downstream of a submerged weir is more suitable for the BPN model. Comparisons of the prediction results of the BPN model and an empirical regression formula revealed that the BPN model was more accurate and more direct in predicting the temporal variation of the local scour hole profile. In addition, sensitivity analysis showed that the dimensionless time exerted the most significant impact on the time evolution of the non-dimensional scour hole profile.

关键词： Submerged weir Scour profile Artificial neural networks (ANNs) Time evolution Backpropagation

Local scour at offshore windfarm monopile foundations: A review

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Water Science and Engineering 2022年第1期15卷 29-39页

作者： Da-wei Guan Yu-xuan Xie Zi-shun Yao yee-meng chiew Ji-sheng Zhang Jin-hai Zheng Key Laboratory of Ministry of Education for Coastal Disaster and Protection Hohai UniversityNanjing 210098China College of Harbour Coastal and Offshore EngineeringHohai UniversityNanjing 210098China Department of Civil and Environmental Engineering The University of AucklandAuckland 1142New Zealand School of Civil and Environmental Engineering Nanyang Technological UniversitySingapore 639798Singapore

In this article,current research findings of local scour at offshore windfarm monopile foundations are *** scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized,including the current-only condition,wave-only condition,combined wave-current condition,and complex dynamic ***,this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific *** weakness of existing researches and future prospects are also *** is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex *** computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.

关键词： Offshore windfarm Monopile foundation Scour mechanisms Scour depth prediction Numerical modeling Field observation Artificial intelligence Literature review

Protection of bridge piers against scouring with tetrahedral frames

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International Journal of Sediment Research 2009年第4期24卷 385-399页

作者： yee-meng chiew School of Civil and Environmental Engineering Nanyang Technological University

Armoring countermeasures, such as riprap stones, are the primary method used to protect bridge piers against scouring; however, these methods have not had definitive success. Recently, flow-altering countermeasures, such as sacrificial piles, have been tested as an alternative to armoring countermeasures. This study investigated the mechanics of an innovative flow-altering countermeasure device, frames in the shape of tetrahedrons that act as a pier-scour countermeasure. Results of measured characteristics for turbulence flow showed that the flow around the tetrahedral frames can be divided into three regions: (1) a deceleration region near the sediment bed; (2) an acceleration region in the middle of water depth region; and (3) a restoration region near the water surface. The velocity magnitudes, turbulent intensities and vorticities decreased in the deceleration region, increased in the acceleration region and reverted to that of the unprotected condition in the restoration region. This pier-scour countermeasure is innovative because of its ability to dissipate energy associated with the downflow and the horseshoes vortex generated around the bridge pier. The scour tests revealed that the frames protected the foundation of bridge piers against scour. The experimental results showed that the percentage reduction of scour depth decreased as the velocity ratio, U/U c , decreased, reaching a value of 50% for the range of parameters tested in this study. Moreover, its efficiency was dependent on the placement density of the frames. The data showed that the frames were more effective when η was larger. However, their influence becomes less significant when η≥ 0.16.

关键词： Bridge-pier scour Scour protection Tetrahedral frames protection Flow altering countermeasure

Effect of upward seepage on bedload transport rate

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Water Science and Engineering 2014年第2期7卷 208-217页

作者： Xiao-xie LIU yee-meng chiew State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University School of Civil and Environmental Engineering Nanyang Technological University

The paper presents an investigation of injection effects on the bedload transport rate. According to dimensional analysis, two dimensionless groups, an Einstein＇s parameter group and a modified densimetric Froude number group, were chosen to examine how injection affects the bedload transport rate. Experimental studies were conducted in an open-channel flume with an upward seepage zone. The sediment particles used for the test were 0.9 mm in diameter. The experimental results show that an increase in the injection velocity causes a reduction in the shear velocity excess, which is defined as the difference between the shear and critical shear velocities, leading to a reduction in the bedload transport rate. The equation for predicting the bedload transport rate in the presence of upward seepage was derived empirically. The proposed prediction method is suitable for engineering practice, since it only requires the undisturbed flow condition, properties of sediment particles, and the injection velocity.

关键词： upward seepage bedload transport rate shear velocity shear stress open-channel flow

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Incipient motion of cohesionless sediments on riverbanks with ground water injection

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International Journal of Sediment Research 2012年第1期27卷 111-119页

作者： Yan LU Yong-jun LU yee-meng chiew Nanjing Hydraulic Research Institute State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering School of Civil and Environmental Engineering Nanyang Technological Univ.

This study investigates the influence of ground water injection on the initial movement of non-cohesive sediment particles on a riverbank slope analytically and *** including the hydraulic gradient in the force analysis,the critical condition was derived to account for the effect of seepage flow, showing that the seepage hydraulic gradient and the riverbank slope are governing parameters in modifying the incipient motion of sediments on a riverbank *** investigations were performed in an open-channel flume for various riverbank slopes and hydraulic gradients of injection, showing that the critical shear stress increases with decreasing riverbank slopes and vise-versa,while injection reduces the critical *** experimental data agree well with the theoretical derived expression of the critical condition in the case of injection.

关键词： Incipient motion Riverbank Injection Sediment Seepage

Characterization of horseshoe vortex in a developing scour hole at a cylindrical bridge pier

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International Journal of Sediment Research 2019年第2期34卷 118-124页

作者： Dawei Guan yee-meng chiew Maoxing Wei Shih-Chun Hsieh College of Harbour Coastal and Offshore EngineeringHohai University School of Civil and Environmental Engineering Nanyang Technological University

Since local scour at bridge piers in rivers and estuaries is a major cause of bridge failure,estimation of the maximum local scour depth is of great importance to hydraulic and coastal *** numerous studies that focus on scour-depth prediction have been done and published,understanding of the flow and turbulence characteristics of the horseshoe vortex that drives the scour mechanism in a developing scour hole still is *** study aims to quantify the detailed turbulent flow field in a developing clear-water scour hole at a circular pier using Particle Image Velocimetry(PIV).The distributions of velocity fields,turbulence intensities,and Reynolds shear stresses of the horseshoe vortex that form in front of the pier at different scour stages(t = 0,0.5,1,12,24,and 48 h)are presented in this *** scour development,the horseshoe vortex system was found to evolve from one initially small vortex to three *** strength and size of the main vortex are found to increase with increasing scour *** regions of both the maximum turbulence intensity and Reynolds shear stress are found to form at a location upstream of the main vortex,where the large turbulent eddies have the highest possibility of *** from this study not only provide new insight into the complex flow-sediment interaction at bridge piers,but also provide valuable experimental databases for advanced numerical simulations.

关键词： Sediment transport Scour Bridge pier PIV Horseshoe vortex Turbulence Scour hole

EFFECT OF DUNE MIGRATION ON SCOUR AT BRIDGE PIERS

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International Journal of Sediment Research 1992年第1期 77-92页

作者： yee meng chiew (Senior Lect., School of Civ. and Struct. Engrg., Nanyang Tech. Univ., Nanyang Avenue, Singapore 2263)

This paper examines the effect of dune migration on local scour around bridge piers. Experiments show that local scour depths fluctuate in response to the translation of dunes past the scour hole. The scour depths measured in a model study conducted in live-bed conditions contain both scour due to the pier and that due to dunes. The con’ tribution from scour due to the dunes may form a significant fraction of the total scour depth measured in model investigations. Therefore, it is imperative to separate these two components of scour for analysis and comparison. The study proposes that an equilibrium or time-average scour depth normalized using pier diameter be used for analysis, and the contribution from dunes to the total scour depth be added independently. Dune size, in the absence of field or measured data, may be estimated using published predictive curves. Comparisons between computed and measured scour depths show a good correlation, and 90% of all the data tested fall within a scatter of 15%.

关键词： Local scour Scour depth fluctuation Dune migration.

Local scour at submarine pipelines

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水道港口 2010年第5期31卷 322-322页

作者： yee-meng chiew School of Civil and Environmental Engineering Nanyang Technological University

The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore *** between the pipeline and an erodible bed under the influence of current and waves often lead to local scouring around the *** this occurs, the pipeline may be suspended on the seabed resulting in the formation of a *** the free span is long enough, the pipe may experience resonant flow-induced oscillations,leading to structural *** study examines the complex flow-structure-sediment interaction leading to the development of local scour holes around submarine *** reviews published literature in this area,which primarily is confined to the development of 2- dimensional scour *** the abundance of such research studies,pipeline-scour in the field essentially is 3-dimensional in ***,most of these studies have overlooked the importance of the transverse dimension of the scour hole,while emphasizing on its vertical *** clearly is an issue that must be re-examined in light of the potential hazard and environmental disaster that one faces in the event of a pipeline *** studies have begun to recognize this shortcoming,and attempts have been made to overcome the *** study presents the state-of-the-art knowledge on local scour at submarine pipelines,both from a 2-dimensional as well as the 3-dimensional perspective.

关键词： scour sediment transport submarine pipeline offshore pipelines

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