Horizontal Apron Research Articles

Apron and Cutoff Wall Scour Protection for Piano Key Weirs

Piano key (PK) weirs are used in a variety of flow control structure applications, including spillway crests and open channel diversion structures. However, to the best of authors’ knowledge, structure-specific design guidance for scour mitigation is still needed. To fill this gap of knowledge, a systematic experimental campaign was conducted by testing different configurations of horizontal aprons with a cutoff wall. Protection structures were located at the toe of the PK weir. Namely, experiments were performed at large-scale to assess the effect of three apron lengths on downstream scour hole geometry under different hydraulic conditions. It was observed that a horizontal apron deflects the plunging jets originating from the PK weir, thus significantly reducing scour. Experimental evidence allowed corroboration that significant scour depth reduction occurs for an apron length 1.5 times the weir height, with longer aprons found to provide marginal benefits. Finally, also provided herein are tools to estimate the main scour characteristics and help practitioners in optimizing apron design.

Entrainment and Transport Dynamics of Shipping Containers in Extreme Hydrodynamic Conditions

An experimental study was performed to examine multiple debris entrainment and transport in tsunami-like flow conditions. The study was performed in the Tsunami Wave Basin at Waseda University. The wave basin used a falling-head driven elongated solitary wave that broke at the edge of a horizontal apron to generate a tsunami-like surge. The debris, modeled as scaled-down (1:40 length scale) 20-foot standard shipping containers, was placed on the horizontal apron. The debris was tracked using a camera-based object tracking algorithm. The study examined the effect of the debris configuration, the number of debris, and orientation of debris on the entrainment and transport within the inundating surge. In examining the transport of multiple debris, the debris tended to be transported within the surge as an agglomeration. Using a previously derived model of debris transport, the study determined experimentally derived coefficients to explain the difference in debris transport between various configurations.

Experimental Investigations of Debris Dynamics over a Horizontal Plane

Abstract This study presents the results of an experimental research program dealing with spatial debris motion on a horizontal apron depicting a typical harbor wharf. Accordingly, scaled-down 6.1-m (20-ft) shipping containers were equipped with a novel yet nonintrusive real-time tracking system and motion sensors. The instrumentation allowed for the spatiotemporal tracking of debris specimens moving across the apron while entrained by an incoming tsunami-like broken bore. The system proved its capabilities and accuracy; this was particularly challenging since this was the first time the system was used in water. The experiments involved using various numbers of shipping containers that were either arranged in one layer or stacked in two layers. In addition, the effect of different numbers of container rows was also investigated to study the influence of the overall container count and placement with respect to their longitudinal displacement and dispersion (spreading) across the apron. Linear relationshi...

EVALUATION OF LOCAL SCOUR DEVELOPMENT DOWNSTREAM AN APRON OF DIFFERENT ANGLES FOR AN OGEE SPILLWAY

Local scour downstream of hydraulic structures, such as low head and high head structures, spillways, and culverts is an important research field due to its significant practical value. In this study laboratory experiments were conducted to compute the local scour downstream apron of an ogee spillway under different slopes of apron to study its effect on the characteristics of the scour. Developed physical models for spillway and aprons are installed into the water in the channel where conducted under subcritical flow and clear-water condition by using uniform cohesionless (soil) as bed material with a medium grain size (d50 = 0.65 mm). Four angles of an apron were used (0 ̊, 2.73 ̊, 5.19 ̊, and 7.43 ̊) to show the effect of the slope for apron on local scour. It is found that the slope of an apron is one of the important parameter to reduce the local scour depth and the extent of scour hole. The influence of slope for aprons angle showed a reduction of about (53, 46, and 35) % in the maximum scour depth and about (33, 49, and 33) % in the maximum scour length compared with horizontal apron for angles (2.73 ̊, 5.19 ̊, and 7.43 ̊), respectively.

Experimental analysis of debris motion due the obstruction from fixed obstacles in tsunami-like flow conditions

Experimental research was conducted focusing on debris motion over a horizontal apron featuring vertical obstacles in the path of the debris propagation. The apron was designed as a typical representation of a harbor threatened by an inundating tsunami. The experimental setup idealized often complex harbor settings. The debris was a scaled-down 20-foot shipping container modelled at a 1 in 40 Froude length scale. Offand onshore regions were separated by a vertical quay wall which allowed the incoming elongated solitary wave used to represent the first part of a tsunami to steepen, break and propagate over the initially dry surface as a tsunami-like bore. In the path of propagation, a varying number of debris were entrained within the inundating bore over the horizontal apron. The entrained debris interacted with regularly spaced vertical obstacles representing infrastructure and houses within the propagation path. Varying debris and obstacle arrangements were tested to evaluate the effects the obstacles would have on the debris' maximum longitudinal displacement and the spreading angle. The main conclusion is that the spreading angle of the debris is not as significantly altered by the presence of obstacles on the harbor apron whereas the maximum longitudinal displacement of the debris was significantly affected.

3D Numerical Modelling of Energy Dissipation in Flexible Apron of Barrages

The 3D volume of fluid (VOF) realizable k–e model is used to predict the turbulence kinetic energy in the flexible apron placed downstream of the stilling basin of the barrage. Barrages form an important component of hydraulic structures constructed to intercept and divert part of the available flow of a river and use it for purposes like irrigation, hydropower, domestic or industrial water supply and Flexible Apron is the protection works provided in the barrage in order to safeguard the possibility of the scour hole traveling close to stilling basin. There is a close trend between experimental and numerical model result and attempt has been made to find out the turbulence kinetic energy for all possible flow conditions. The turbulence kinetic energy at the downstream end of inclined flexible apron is comparably less with respect to horizontal flexible apron for all the cases.

Measuring the Weathertight Performance of Flashings

Residential buildings are now better engineered to manage rainwater following the leaking building problem in New Zealand. The next challenge is to improve the weathertightness of medium-rise buildings which often use joint details widely applied on low-rise buildings but are subject to higher wind pressures and surface runoff rates. This study begins to address this challenge by measuring the water leakage performance limits of the following common flashings with static and dynamic rain and wind loads to see how their performance might be improved: (a) Horizontal H and Z jointers between direct fixed sheet claddings; (b) The window head flashing in a cavity wall; (c) A horizontal apron flashing at the junction between a roof and wall. At this stage, water penetration resistances have been measured but the data has not yet been discussed in the context of wind pressures and rain loads on mid-rise buildings. All of the joints were found to resist water leakage to pressures equivalent to the hydrostatic head of the upstand, so long as there were no air leakage paths through the joint. When vents were added, or openings were present that might arise due to construction tolerances, then the onset pressure for leakage was found to fall by as much as 50%. Vents, of course, are essential for ventilation drying in rainscreen walls and even with vents present, the onset of leakage was at generally at least twice the 50 Pa wet wall test pressure applied in New Zealand. Opportunities were found to improve the way vented joints deal with runoff by enlarging the gap between the cladding and flashing. This prevented the outer joint volume from filling with water and occluding the vents. The apron flashing was found to cope better than a window head joint with runoff, because of the larger 35 mm vertical gap between the cladding and apron.

Apron design for protecting double‐skin façade fires

SummaryAlthough double‐skin façade (DSF) is an environmental‐friendly architectural feature, its fire behaviour is a deep concern. The interior glass system including the glass pane, metal frame and associated accessories will be hotter than the exterior glass system as demonstrated by earlier studies. The glass pane above the fire room will be broken to spread flame into the upper compartment. Aprons are proposed to protect the air cavity of DSF in a way similar to those outside a single‐skin façade. In this paper, the effect of aprons in protecting against fire spread from an underlying compartment to the compartments above by preventing glass breakage of the inner glass pane was studied. Fire and smoke from a post‐flashover room fire adjacent to the DSF would be trapped in the air cavity between the two glass panes. Spreading of hot gases with different apron widths was studied by numerical simulations with CFD first. Fire environment with and without breaking the apron immediately above the fire room was studied. Full‐scale burning tests on part of an experimental DSF rig were then carried out to demonstrate the performance of horizontal apron in the DSF rig of 6 m tall and air cavity depth of 2 m with different apron widths. All demonstrated that providing apron is appropriate in protecting DSF fires. Copyright © 2014 John Wiley & Sons, Ltd.

Comparison of numerical, experimental and empirical results for flows over vertical drops

The complex flow over three vertical drops (horizontal apron, adverse apron, horizontal apron with an end sill) were studied numerically and compared to experiments and empirical functions. In addition to flow depth, energy loss, and free-surface profiles, detailed velocity, pressure and shear stress distribution, which are hard to be measured experimentally, were investigated. The 2D numerical results on a 57,512-node grid, using standard k-e turbulence model and standard wall function showed the best agreement with experimental results. The energy loss in the drop with an end sill was higher than the adverse apron drop and the latter more than the horizontal apron drop. The numerical length and velocity scales confirmed the experimental similarity profiles. However, due to dissipative nature of the turbulence model, the velocity gradient in the shear layer was numerically dispersed particularly near the pool end. The stagnation pressure and shear stress were computed numerically for the drops. The maximum stagnation pressure and shear stress occurred in the horizontal apron drop.

Local scouring downstream of a spillway with an apron

Local scour downstream of stilling basins constitutes an important field of research in the context of the stability of hydraulic structures. This paper deals with the temporal and spatial evolution of local scour downstream of low-head spillways with a horizontal apron. Experiments were carried out in a 1 m wide and 20 m long rectangular channel. Three different, nearly uniform, sediments were used for the mobile bed. Tests were of long duration from 48 up to 196 h, but a few runs of short duration (1 or 3 h) were also carried out to better analyse the earlier scour stages. It was found that the main dimensionless parameters governing the scouring process are the tailwater densimetric Froude number, the relative time, and the relative distance of the toe of the hydraulic jump from the apron edge. Based on the experimental data, the salient features of the local bed morphology evolution are described through simple power-type equations. No experimental evidence was found in support of the similarity of scour profiles.

Hydraulic Design and Analysis of Labyrinth Weirs. II: Nappe Aeration, Instability, and Vibration

AbstractNappe behavior should be considered in the design of labyrinth weirs to ensure hydraulic optimization and to account for potential vibrations, pressure fluctuations, noise, and flow surging. Information regarding nappe aeration conditions (clinging, aerated, partially aerated, and drowned), nappe instability, and nappe vibrations for trapezoidal labyrinth weirs on a horizontal apron with quarter- and half-round crests (6°≤ sidewall angle ≤35°) is presented. Corresponding headwater ratio ranges and hydraulic behaviors associated with nappe aeration conditions are documented and discussed to aid in labyrinth weirs design, including design options directly related to nappe behavior (e.g., crest shape, crest roughness, vents, nappe breakers, notches, and staged cycles). The effects of artificial nappe aeration (a vented nappe) on nappe behavior and discharge capacity are also discussed, including recommended placements of nappe breakers.

INVESTIGATING THE FLOW CHARACTRISTICS DUE TO CHUTE AND BAFFLE BLOCKS (Case Study: New Assiut Barrage Spillway)

sluiceway with baffles using a 2-D flume model. Head losses between the upstream and downstream of the sluiceway gate, pressure along the inclined drop and on the horizontal apron were measure and calculated. Local head losses due to sill and flow velocities were measured. Ten tests for fully opened gate (flood evacuation)were carried out. Two tests were conducted to test the cases before and after implementing of chute-blocks on the inclined drop together with baffled apron. During these tests, the velocity was varied between 4.0 m/s to 4.5 m/s by varying the discharges from 5000 m3/s to 7000 m3/s. The results showed that, the maximum calculated head loss after installing the chute and baffle blocks were 0.02 m and 0.27 m when the flow discharge was increased from 5000 to 7000 m3/s, respectively (i.e. the losses increased by 92.6 % when the discharge increased by 28.5 %). The maximum measured head losses after installing the chute and baffle blocks were 0.03 m and 0.23 m when the discharge was increased from 5000 m3/s to 7000 m3/s, respectively (i.e. the losses increased by 87 % when the discharge increased by 28.5 %). On the other hand, the maximum pressure values before and after installing the chute and baffle blocks were 13.9 m and 13.93 m at a discharge of 5000 m3/s. These values were 15.44 m and 16.14 m at a discharge of 7000 m3/s. The study concluded that adding the chute and baffle blocks has no sensible effect on the pressure and the head losses values.

Determination of the length of hydraulic jumps using artificial neural networks

Hydraulic jumps have many uses such as dissipation of energy while water is flowing over spillways, increasing the water surface channels for distribution, chlorinating of wastewater, and many other cases. The length of hydraulic jumps is one of the most important parameters in designing the stilling basin, however, it cannot be calculated by mathematical analyses only - experimental and laboratorial results should also be used. In this study, an artificial neural network (ANN) technique was developed to determine the length of the hydraulic jumps in a rectangular section with a horizontal apron. Two algorithms, namely Levenberg-Marquardt (LM) and gradient descent with momentum and adaptive learning rule back propagation (BP) are employed to reach optimum model. From the different model structures that were examined, an LM algorithm with a 3-4-1 structure was adapted as the final model. The selected model can predict the length of jumps with high accuracy and satisfy the evaluation criteria, with root mean square error RMSE=0.01224, mean absolute percentage error MAPE=2.59%, and coefficient of determination R^2=0.9962. A comparison between the selected ANN model and empirical Silvester equation was also done and the results showed that the ANN method is more precise.

Bend scour protection using riprap

This paper presents laboratory tests using riprap as a countermeasure for river bend scouring. The bank is a vertical wall in a sharp bend. The riprap is a horizontal apron extended at the toe of this wall. The aims of the tests are to describe the behaviour of riprap in sharp bend flow and to examine how the main flow characteristics are affected by the riprap behaviour. The experimental results show that flexible riprap is able to adapt to bed deformation in river bends by tilting, spreading and paving a transverse slope which ensures that the bank remains protected. Even a blanket located at the initial bed elevation provides efficient protection if it is thick enough. The tests also show that the mainstream velocity and shear stress above the riprap increase after riprap adaptation.

Tungsten erosion in the outer divertor of JET

Erosion of tungsten in the outer JET divertor was determined with a set of tungsten coated divertor tiles during the 2001–2004 discharge campaign. The tungsten marker was strongly eroded, with the largest erosion at the outer strike point position, where more than 75% of the initial W disappeared. Strong erosion is also observed at the outer baffle and horizontal apron of tile 8, where about half of the tungsten has been removed. These numbers are lower boundaries, because the W was locally completely eroded. The tungsten erosion is inhomogeneous on a microscopic level and depends on the micro-topography of the rough surface: large erosion with complete disappearance of the W layer is observed on plasma-facing areas of microscopic ridges, while a smaller erosion and sometimes even deposition of carbon is found on the far side of ridges and in pores.

Energy Dissipation in Culverts by Forced Hydraulic Jump within a Barrel

Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel without the aid of tailwater. This research examines the jump geometry and the effectiveness of each jump type and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.

Energy Dissipation in Culverts by Forced Hydraulic Jump Within a Barrel

Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel without the aid of tailwater. This research examines the jump geometry and the effectiveness of each jump type and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.

Characteristics of Supercritical Flow below Sluice Gate

Supercritical flow below a sluice gate in a horizontal smooth rectangular channel is investigated to explain the effect of the inflow condition on the characteristics of the hydraulic jump. The movement of jump location to variations of tailwater level is also examined so the position of the jump in a horizontal apron can be stabilized. The distributions of mean velocities and turbulence intensities were obtained with a laser Doppler velocitymeter for a wide range of supercritical Froude numbers. The development of the turbulent boundary layer, the water‐surface profile, and the location of the critical point (the point where the limit of the boundary layer crosses the water surface) are predicted by an approach to the boundary‐layer analysis, and the agreement of those observations with the experimental data is presented. Using the analyzed water‐surface profiles, the movement of jump location to variations of tailwater level is predicted accurately and verified by laboratory experiments.

Cobble Lined Drop Structures

This paper describes the concept and the experimental study made to determine the design criteria for a drop structure comprised entirely of loose dumped rock. The three principal components of the design were: (1) the weir at the top of the slope, (2) the sloping portion downstream from the weir, and (3) the horizontal apron at the bottom. The rock weir was intended to prevent excessive drawdown and control upstream velocities. The sloping portion was a hydraulically steep reach, on which supercritical velocity occurred. The apron was intended to accommodate the transition back to subcritical flow at the end of the drop structure.The initial investigation involved study of the structure in two-dimensional flow. It was determined that the critical area for stability was in the terminal velocity region of the steeply sloping portion of the structure. The stone size and layer thickness required for channel stabilization was found to be a function of the channel slope and flow depth at terminal velocity. Eight combinations of variables were tested and included four different slopes, three different stone sizes, and two different layer thicknesses. Each combination was tested to failure.The failure process was unique in that there was an initial failure and an ultimate failure. Initial failure occurred when some stone at the lower end of the slope was displaced, exposing the subgrade. The exposed area was rapidly filled in by downstream migration of stones from further up the slope. The migration process continued until it was arrested at the top of the slope by the rock weir, and the structure became stable once again. A further large increase in discharge was required to precipitate a second or ultimate failure.Design criteria were formulated, including a recommended factor of safety based on initial failure, and the design was verified on a three-dimensional model.