Yee-Meng Chiew

Nanyang Technological University | ntu · School of Civil and Environmental Engineering

Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes...

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 foundations. In the current study, artificial neural networks with a backpropagation learning algorithm were used to estimate the temporal variation of scour profiles do...

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...

The interaction between a forced vibrating pipeline and an erodible seabed in unidirectional flows is experimentally investigated. The experiments were conducted under clear-water scour conditions with a water depth of 0.3m and averaged approach velocity of 0.261 m/s. The pipeline model with a diameter (D) of 3.5 cm, was subjected to a vertical sin...

By conducting a two-dimensional experimental study, this paper aims to enhance the understanding of the mechanism of sand convective motions in the vicinity of a wall subjected to long-term cyclic lateral loadings. The experimental tests were conducted in a rectangular sandbox with a transparent front-wall, through which the process of sand particl...

Past researchers have studied particle entrainment on a flat-bed and the flow fields in a rectangular cavity without considering particle entrainment. However, particle entrainment from a rectangular cavity, which hitherto had rarely been studied, is the focus of this study. The entrainment phenomenon is investigated by using a frequentist probabil...

In this article, current research findings of local scour at offshore windfarm monopile foundations are presented. The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized, including the current-only condition, wave-only condition, combined current-wave condition, and complex dynamic condition....

The bed-load transport rates predicted using Einstein’s formula in the low and high transport regimes deviate from experimental data. The deviation, which becomes significant when the transport rate is extremely low or high, may be solely attributed to the folded Gaussian distribution assumed by Einstein. The limiting trends of an Einstein-type for...

Local scour in a sediment bed varies depending on the type, size and shape of hydraulic structures, and the properties of approach flow and sediment particles. Published studies are hitherto confined primarily to empirical experiments based on one particular type of hydraulic structure and there is almost no comparison of scour amongst different ty...

This study presents an experimental study on bed‐load transport in the presence of emergent vegetation, which is simulated using uniformly sized circular cylinders arranged in a homogeneous distribution. The spatial variability of bed‐load fluxes in vegetated flows is first examined. Then a model is proposed for evaluating the bed‐load transport ra...

An open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study’s primary objective is to comp...

This paper presents an extensive review of the characteristics of a propeller jet-induced flow field and its impact on scour formation. As the driving force of scour, the jet flow behavior is first explored, including both the free and bounded jets under various boundary conditions. Accordingly, their resulting scour, namely, unconfined and confine...

This paper presents results obtained from a detailed analysis of the experimental data of three hydraulic jumps with low Froude numbers (1.5-1.9) in a narrow flume. With the increasing Froude number, the three generated jumps exhibit an initial increasing then decreasing undular behavior. The turbulent velocity fields are measured with a high spati...

Scour, which represents a fascinating and complex engineering problem involving a number of physical mechanisms and interactions, has motivated a vast amount of research following different but complementary methodological approaches such as experimental, numerical, and field methods. Far from being completely understood, scour remains one of the m...

This study evaluates sediment gradation effects on clear-water scour at bridge piers. By considering the average erosion and deposition rates in a pier-scour hole, the normalized equilibrium scour depth is theoretically shown to be a cubic function of the densimetric Froude number. Comparisons with experimental data demonstrate that the cubic law a...

This study evaluates sediment gradation effects on clear-water scour at bridge piers. By considering the average erosion and deposition rates in a pier scour hole, the normalized equilibrium scour depth is theoretically shown to be a cubic function of the densimetric Froude number. Comparisons with experimental data demonstrate that the cubic law a...

This study presents measurements of the bed shear stress associated with the three-dimensional boundary layer induced by a wall-bounded swirling jet. The velocity profile within the viscous sublayer was measured in detail using a high-resolution particle image velocimetry system that enables direct evaluation of the bed shear stress from the veloci...

Swirling jets induced by propellers have a significant impact on riverine and marine environments. Erosion around quay structures and contaminant dispersion in harbors or along navigation channels are examples of these effects. Simulating propeller-induced jet velocities that extend from near to far fields is the first step in elucidating this phen...

This paper aims to explore the combined main flow and turbulence influence on sediment pickup rates by investigating four purposely devised cases, namely, (1) unobstructed flow over a plane bed; (2) unobstructed flow over a rigid‐dune bed; (3) flow obstructed by a horizontal pipe; and (4) flow obstructed by a vertical pipe. The four cases were used...

An experimental study was conducted to better understand the settling velocity of porous spherical particles. Tests of the settlement of porous particles with porosity, ε, ranging from 0.53 to 0.86 in glycerol-water mixtures in a range of Reynolds number from 1.9 to 24,470 were conducted. The study utilized particle tracking and image velocimetry (...

Although local scour around submarine pipelines has been extensively studied in the last few decades, understanding of the mechanism of local scour around pipelines is still in its infancy stage due to the complex nature of flow-pipeline-seabed interactions, especially when the pipeline is subjected to vibrations. This experimental study aims to ob...

A new numerical model is developed to simulate and investigate scour beneath a vibrating pipe during the tunnel erosion stage. This study is motivated by the fact that existing numerical models are not able to properly simulate scour under a vibrating pipeline, and the underlying physical mechanisms are not well understood due to the complex fluid-...

An experimental method is presented in this paper to facilitate visualization of the detailed flow fields and determination of the near-boundary shear and normal stresses within an equilibrium scour hole induced by a vibrating pipeline. This method involves the implementation of a pipeline vibration system in a straight flume, a time-resolved parti...

Although weirs or dikes in the riverine and coastal environments are frequently overtopped, few studies have hitherto examined the evolution of the scour process downstream of these structures under the submerged condition. This paper presents an experimental investigation on time evolution of the scour process downstream of submerged weirs with a...

This paper presents an experimental study on the characteristics of the propeller-induced flow field and its associated scour hole around a closed type quay (with a vertical quay wall). An “oblique particle image velocimetry” (OPIV) technique, which allows a concurrent measurement of the velocity field and scour profile, was employed in measuring t...

This study experimentally investigates the mean and turbulent flow fields of a propeller jet impinging on a vertical quay wall. Four impingement distances, namely, wall clearances (= longitudinal distance between the propeller and vertical wall), were used to examine their influence on the flow behaviors. In order to investigate the characteristics...

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 engineers. Although numerous studies that focus on scour-depth prediction have been done and published, understanding of the flow and turbulence characteristics of...

Submarine pipelines are widely used for the conveyance of hydrocarbons, oil or other fluids in the offshore industry. Although much progress has been made on pipeline-seabed interactions in the past decades, an experimental study solely devoted to investigating interactions between the flow fields, scour and forced vibrating pipelines in a quiescen...

Monopile foundations are the most common foundation type of offshore wind turbines. In the ocean environment, in addition to threats related to scour of the foundation, offshore monopiles of wind turbines also are subjected to lateral vibrations induced by waves and winds. Over the past decades, the scour process induced by flow and pile-soil inter...

This study presents results of the temporal development of propeller scour around a sloping bank. During the scouring process, the centerline scour profile along the propeller axis comprises a toe scour hole, a primary scour hole, or a combination of both. Their formation is dependent on the length of the toe clearances, which is defined as the lon...

By using the particle image velocimetry (PIV) technique, experimental results of the propeller jet flow field within a developing scour hole around an open quay are presented. The experiments were conducted with four toe clearances (defined as the longitudinal distance between the propeller face and toe of the quay slope), which account for three d...

Wei, M.X.; Chiew, Y.M., and Guan, D.W., 2018. Flow behavior of Propeller Jet around an Open-Type Quay. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 956–960. Coconut Creek (Florida), ISSN 0749-0208. T...

By using particle image velocimetry techniques, this paper presents new insights on the turbulence structure and time-averaged flows in a rectangular cavity with large aspect ratios. The three cavity aspect ratios (L/D, where L = cavity length, D = cavity depth) used in this study are 9.9, 13.0, and 18.9. The time-averaged velocity fields and Reyno...

Scour under a submarine pipeline can lead to structural failure; hence, a good understanding of the scour mechanism is paramount. Various numerical methods have been proposed to simulate scour, such as potential flow theory and single-phase and two-phase turbulent models. However, these numerical methods have limitations such as their reliance on c...

The flow properties of a propeller jet in the presence of a plane bed boundary were investigated using the particle image velocimetry technique. Three clearance heights, Zb = 2Dp, Dp, and 0.5Dp, where Dp = propeller diameter, were used to examine boundary effects on the development of the jet. In each case, the mean flow properties and turbulence c...

A stochastic optimization model for urban drainage design (SODD) was proposed in this study to help analyze the trade-off between investment and acceptable flood damage in urban drainage designs considering effects of both uncertainty and climate change. The simulation model [i.e., Storm Water Management Model (SWMM)], driven by designed rainfall e...

This laboratory study investigates the void fraction (or local air concentration), flow filed and bubble velocity in a simple hydraulic jump. The experimental data were obtained by using a dual-tip optical fiber probe in conjunction with the particle and bubble image velocimetry techniques. This paper aims to provide a full picture of the turbulent...

A hydraulic jump may occur in a closed conduit such as shaft spillways, culverts, etc. when the upstream super-critical flow meets a downstream sub-critical flow. If the sub-critical conjugate depth is less than the height of the conduit, a free surface will be present, causing the formation of a hydraulic jump, similar to those formed in open-chan...

This study experimentally investigates the temporal and spatial development of the scour hole induced by a confined propeller jet in the presence of an open type quay. The longitudinal distance between the propeller face and toe of the quay slope, i.e., toe clearance, was systematically varied to examine its influence on the scour hole development...

Vortex-induced vibration (VIV) has been studied extensively and much attention has been devoted to the “lock-in” phenomenon, which is primarily responsible for fatigue damage to structures. Nevertheless, the behavior of the surrounding flow can also be important. This paper investigates the flow characteristics of the wake in the initial branch for...

Bridge-pier scour in alluvial rivers often occurs in live-bed conditions with dune migration. The scour depth attains its deepest value when the dune trough reaches the pier, followed by depth reduction when the crest arrives. Therefore, the instantaneous scour depth may be larger than its time-average counterpart. Consequently, accurate prediction...

Although vortex-induced vibration (VIV) has been extensively studied, much of existing literature deals with uniform flow in the absence of a boundary. The VIV flow field of a structure close to a boundary generally remains unexplored, but it can have important engineering implications, such as pipeline scour if the boundary is an erodible seabed....

Particle-settling velocity is a fundamental variable in many aspects of sediment transport in the fluvial and coastal environments. Due to permeation, a different drag will be exerted on a porous object compared to a non-porous object with the same size and therefore settlement of porous particles needs special consideration. In this study the effe...

The evolution of bridge pier scour is very important for bridge safety warning and assessment. During typhoon seasons in Taiwan, the torrential river flow often causes scour monitoring instruments to fail in their attempt to measure the temporal variations of pier scour depths. To better understand the scouring phenomenon during a large flood event...

Sediment transport is fundamentally a two-phase phenomenon involving fluid and sediments; however, many existing numerical models are one-phase approaches, which are unable to capture the complex fluid-particle and inter-particle interactions. In the last decade, two-phase models have gained traction; however, there are still many limitations in th...

This study presents a scaling analysis of the time development of clear-water scour depth at bridge piers. It shows that the widely-used exponential formula can be theoretically derived with scaling arguments. The derivation provides connections between the physical pier-scouring process and two empirical constants used in the formula. The dependen...

When subjected to a strong swirling jet flow induced by a rotating ship's propeller, the bed of a waterway may undergo significant changes. These changes will not only cause instability to quay structures and damage the protection work of the beds/banks of rivers and canals, but also resuspend the bed sediment. The latter likely will pollute the wa...

This work extends a one-dimensional continuum model for granular flows down inclined planes [C. H. Lee and C. J. Huang, “Kinetic-theory-based model of dense granular flows down inclined planes,” Phys. Fluids 24, 073303 (2012)] to solve three-dimensional problems involving both static and flow states. The new model decomposes the shear stress and pr...

Suction effects on the flow characteristics of closed-conduit flow are experimentally investigated by using the particle image velocimetry technique in this study. The results show that as suction intensity, Is, increases, (1) the streamwise velocity becomes more uniformly distributed, (2) the vertical velocity becomes more negative, and (3) the tu...

Turbulent dispersion causes sediment particles to be transported from high concentration regions to low concentration regions and determines the concentration distribution of suspended sediment. In this study, a new turbulent dispersion model is proposed for large-scale flows with suspended sediment. Two Stokes numbers are used to describe the turb...

Experiments were conducted to investigate injection effects on sediment transport in closed-conduit flows. The results show that the sediment transport rate essentially remains unchanged when the ratio of the injection velocity and that at boiling, Vi/Vcr < 10. However, significant sediment transport rate is observed when Vi/Vcr increases beyond th...

Two important issues need to be addressed when using lattice Boltzmann methods to simulate particulate flows: complex moving boundaries and near contact of two solid objects. This study introduces a new boundary treatment method for using lattice Boltzmann methods to study fluid-particle interaction problems in which solid objects are close to a wa...

Pier scour is considerably far more complex under unsteady flow conditions than under steady flow conditions. In recent years, numerous studies have investigated the temporal variations of pier-scour depth under steady flow conditions. However, only a few studies have examined the temporal development of pierscour hole under unsteady flow condition...

Scouring around a vibrating steel catenary riser (SCR) on a sandy seabed was modeled in the laboratory. Different vibration amplitudes and frequencies were tested to investigate the impact of these parameters on the development of the scour hole. Experiments of vortex induced vibrations (VIV) by using a two-dimensional circular cylinder mounted ela...

Although many papers have reported suction influence on sediment transport, only few of them considered effects of suction zone length on sediment transport rate. In this study, experiments were conducted to investigate suction effects on sediment transport rate in a horizontal conduit with a suction zone with variable lengths. The results show tha...

In most instances, local scour at bridge foundations is subjected to live-bed conditions during floods. However, most of the research regarding pier scouring is focused on clear-water scour especially for the investigation of the time variations of pier-scour depth. Considering the primary vortex in front of the pier, the migration rate of dunes an...

This paper presents the results of an experimental study on the mechanics of pipeline scour propagation in the spanwise direction. The experiments were conducted with uniform sediment under a unidirectional steady current in clear-water conditions. The study aims to provide a better understanding of how the differential pressure between the upstrea...

Laboratory experiments were conducted to investigate the influence of suction on sediment transport in closed-conduit flows in this study. The results show that the bed load transport rate essentially remains unchanged for small values of suction rates before abruptly increasing beyond a certain threshold. Theoretical analyses of the forces acting...

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-cha...

Experiments were conducted using cohesionless sand particles with median diameter of 0.48 mm to investigate the time variation of sediment transport rate under the influence of local downward seepage. The experimental results show that the bedload transport rate in terms of volumetric sediment transport rate per unit width increased rapidly with ti...

Laboratory experiments were conducted to investigate the influence of suction on sediment transport in closed-conduit flows in this study. The results show that the bed load transport rate essentially remains unchanged for small values of suction rates before abruptly increasing beyond a certain threshold. Theoretical analyses of the forces acting...

The swirling jet induced by a ship propeller has attracted the attention of many researchers. This is because the high velocity generated by a ship propeller not only can damage the ferry/quay structure but also induce sediment suspension from the seabed. In order to improve the understanding of the swirling jet induced by a ship-propeller, particl...

The scour hole induced by a propeller wash is experimentally investigated with noncohesive sediments. The associated scour profile at the asymptotic condition, which can be expressed by a combination of three polynomials, comprises (1)a small scour hole beneath the propeller, (2)a primary scour hole downstream of the small scour hole, and (3)a depo...

The experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear-water conditions. The results show that suction has a profound effect on pier-scour development, and the extent of the influence is related to the location of the suction source. When t...

It is common for engineers to use countermeasures to protect hydraulic structures against scour. This study aims to explore the effect of jet injection through the pier body as a pier-scour countermeasure. Laboratory experiments were conducted in two different flow depths (10.5 and 28 cm) using 1-jet and 3-jet injections, different jet locations, a...

The potential applicability of subsurface cooling in Singapore's condition was investigated. Three operation modes with different heat rejection methods were proposed. Mode 1 is an open-loop groundwater cooling system combined with cooling towers; Mode 2 is a pure groundwater cooling system without cooling towers; and Mode 3 is a surface water cool...

The three-dimensional flow velocity components at the span shoulder, which is located at the junction of a submarine pipeline and the associated scour hole, are measured in unidirectional steady current in order to investigate the flow structure and mechanics of the lateral propagation of a three-dimensional pipeline-scour hole. A naturally formed...

A green roof test bed, established at the Nanyang Technological Universityin Singapore, was used to investigate its benefit for storm water management and urban heat island effect mitigation. The system comprised 3 units, 2 in the form of vegetated roofs and the other a bare roof.The system was equipped with automatic monitoring devicesfor measurin...