Piano Key Weirs Research Articles

Hybrid meta-heuristics artificial intelligence models in simulating discharge passing the piano key weirs

Piano key weirs (PKWs) are acquired and developed for free surface control structures which improve their performance by increasing the storage capacity and flood evacuation. In this study, the potential combinations of two popular artificial intelligence data-driven models (AI-DDMs) of multi-layer perceptron neural network (MLPNN) and adaptive neuro-fuzzy inference system (ANFIS) with four meta-heuristic optimization algorithms (particle swarm optimization, genetic algorithm, firefly algorithm & moth-flame optimization) are assessed for predicting the PKW’s flow rate. Comparing the outcomes of the ten standard and hybrid AI-DDMs with three empirical relations based on several statistics and diagnostic analysis (such as the Taylor diagram) for estimating the flow rate shows that the AI-DDMs can predict the passing flow more accurately. In addition, the particle swarm optimization and firefly algorithm meta-heuristic algorithms improve the performance of ANFIS and MLPNN, respectively. The Mann-Whitney test for investigating the differences between two independent applied models indicates a significant difference between the AI-DDMs and two of the empirical relations at the 95% confidence level.

Discharge capacity evaluation and hydraulic design of a piano key weir

Abstract A piano key weir (PKW) is a new type of labyrinth weir that increases the unit discharge at the unregulated spillway inlet of the weir. It is considered to be an important structure in water supply and drainage systems. However, its complex geometry makes it difficult to achieve an optimal hydraulic design, and only a few design equations and criteria are available. This study investigates the discharge capacity of a PKW and evaluates the characteristics of its discharge using various sources of experimental data from a database. First, previously proposed discharge capacity formulas are summarized and analyzed. Then, a new formula that integrates the existing test data with the results of dimensional analysis and multiparameter optimization is proposed. The weir characteristics are evaluated using the proposed formula and a mathematical model. The results show that both the proposed formula and numerical model are promising approaches to evaluate the discharge capacity of an A-type PKW and can guide its design.

Numerical study of characteristics and discharge capacity of piano key weirs

A comprehensive numerical investigation was performed to better understand the flow patterns of Piano Key weirs (PKW) for different upstream heads, based on the volume-of-fluid model. The results of numerical simulation indicate that, the efficiency of side crests are limited by following factors: the change of side crest flow direction caused by the effect of the longitudinal flow velocity along the inlet keys, submerged flow regime in outlet keys, interference between nappes, and the head loss along the inlet keys, under the conditions of high upstream head, which eventually leads to the decrease in discharge efficiency with an increase in the upstream head. An orthogonal analysis revealed that, the weir height, inlet/outlet key width ratio, significantly affect the piano key weir discharge efficiency. New formulas with obvious physical significance and high accuracy for the piano key weir discharge were then derived and verified, which improve the accuracy of the design and structural optimization of the piano key weir.

Analysis of various parameters affecting weir design and fabrication of Weirs: An Overview

Several geometric parameters influence weir discharge and it is explained in our present study. The PK weir is more efficient than rectangular labyrinth weir due to reduction in entrance losses of PK weir inlet key geometry. PK weir is a type of labyrinth weir with variation in angle. Therefore, in this paper we also discuss about labyrinth weir. PKW are compatible for constructing on existing or new spillway with lesser space requirement and structural stability. PKW are installed in order to increase the discharge capacity for a given footprint area. PKW is used to increase the overflow capacity of existing dams such as, Hazelmare dam (South Africa), Dartmouth dam (Australia). Trapezoidal piano key weirs have higher discharge efficiency than rectangular weirs and it is due to interference wedge. Cd of TPKW is influenced by L/W but Wi/Wo has least effect.

Analysis of various parameters affecting weir design and fabrication of Weirs: An Overview

Several geometric parameters influence weir discharge and it is explained in our present study. The PK weir is more efficient than rectangular labyrinth weir due to reduction in entrance losses of PK weir inlet key geometry. PK weir is a type of labyrinth weir with variation in angle. Therefore, in this paper we also discuss about labyrinth weir. PKW are compatible for constructing on existing or new spillway with lesser space requirement and structural stability. PKW are installed in order to increase the discharge capacity for a given footprint area. PKW is used to increase the overflow capacity of existing dams such as, Hazelmare dam (South Africa), Dartmouth dam (Australia). Trapezoidal piano key weirs have higher discharge efficiency than rectangular weirs and it is due to interference wedge. Cd of TPKW is influenced by L/W but Wi/Wo has least effect.

Free-flow discharge estimation method for Piano Key weir geometries

Currently, many existing spillways located throughout the globe require rehabilitation due to dam safety issues. Consequently, there is an increasing need for design tools that facilitate better, more economical spillway designs. Piano Key weirs (PK weirs), the focus of this study, represent one option to address spillway deficiencies. Two design approaches used by practitioners for estimating PK weir discharge were examined: (1) empirical prediction methods ranging from simple to sophisticated and (2) computational fluid dynamics. This evaluation included five published empirical design methods and CFD simulations featuring two different turbulence models (i.e., LES and RNG k-ε). The results indicate that, depending on geometry, differences exceeding 30% can exist between predictive method and experimental results. Also, CFD discharge results were relatively independent of turbulence closure schemes and showed very good agreement with experimental data (mean relative errors of 3–4%). Finally, recommendations are presented to designers that include a new empirical equation for Type-A PK weir geometries and rectangular labyrinth weirs.

Assessment of Piano Key Weirs Cost-Effectiveness: a Moroccan Case Study

In a water scarcity context, dam reservoirs play a key role in the socio-economic development. Currently, these dams face two major problems: the siltation that reduces their storage capacity, and the risk of submersion during the extreme floods events, which is directly related to the hydraulic insufficiency of spillways. To overcome these potential deficits in terms of storage capacity and flood discharge, at the least cost, the Piano Key Weir can constitute an advantageous alternative solution. In this paper, an exhaustive methodology to assess the PKW cost-effectiveness with a Moroccan case study are presented. This study is carried out on 32 large Moroccan dams. Results show that the PKW allows increasing the total capacity of the studied reservoirs by 1150 Mm3 that is about 20% of their current capacity, at a total cost of 930 MMAD. This recovered volume exceeds by far the total volume lost through siltation. The best cost-effectiveness is observed in both hydraulic basins of Loukkos and Sebou and particularly within dams of low specific flow rates and moderate hydraulic heads. A PKW cost-effectiveness analysis for increasing the flood discharge capacity and a PKW comparison to other alternative solutions are presented as well.

Flow Characteristics of Triangular Plan Form Weir

Weirs are used for discharge measurement and flow diversion in the open channels. However, modified weirs such as plan form weirs, Labyrinth weir, oblique weir and piano key weir, etc. having larger crest length compared to normal weir having same lateral space assist in enhancing discharging capacity for a given upstream head, without creating much afflux. An experimental study was carried out to understand the effect of the geometry of a triangular plan form weir on discharge coefficient under free and submerged flow conditions. In this paper attempts are made to investigate working of triangular plan form weir of vertex angle 45° with three heights 10, 20 and 30 cm under free and submerged flow conditions. The discharge coefficients were calculated under free & submerged flow conditions and the results were compared with normal weirs as well. Further, triangular plan form weir is quite simple device/geometry and easy to install & quite useful for discharge measurement in open channels.

Modifying the downstream hydrograph with staged labyrinth weirs

Labyrinth and piano key weirs are hydraulically more efficient than linear weirs of common width. As the spillway discharge efficiency increases, the required reservoir detention volume reserved for flood routing reduces and the maximum base-flow operating reservoir pool elevation can subsequently be increased (additional water storage) without a reduction in dam safety. Increased spillway discharge efficiency also causes the reservoir outflow hydrograph to compress temporally and increases the peak outflow discharge, potentially increasing downstream flooding impacts. The influence of linear, labyrinth, and staged labyrinth weir (i.e. cycles with different crest elevations) head-discharge characteristics on the outflow hydrograph behavior were evaluated by numerically routing various flood discharges through a reservoir; peak outflow discharges, the maximum water surface elevation, and the required detention volumes were quantified for each weir alternative. In addition to the benefit of isolating base flows to a subset of the labyrinth weir, the staged labyrinth weir proved to be an effective alternative for modifying (decreasing) the spillway discharge efficiency to limit downstream flooding impact for higher-frequency return-period storm events.

3D Hydrodynamics of Trapezoidal Piano Key Spillways

This paper compares the hydraulics and 3D flow features of the ordinary rectangular and trapezoidal plan view piano key weirs (PKWs) using two phase RANS numerical simulations. The main aim is to investigate effects of the inlet key area and angle of the side walls on discharge capacity of the PKW, while keeping the developing length of the crest intact. The numerical model has been used to carry out a sensitivity analysis for geometrical parameters and hydrodynamics of the rectangular and trapezoidal weirs (TPKWs) have been compared for wide range of the water head on the weir. Results show that the trapezoidal weir has higher efficiency than the ordinary rectangular PKW. This is partly related to the inlet key flow conditions. The trapezoidal geometry increases the inlet flow area resulting in reduction of the velocity along the key axis. Consequently, flow is distributed more uniformly over the side crests. The gradual transition of the inlet key limits the development of the recirculation zones along the side walls, and it also limits the formation of the critical section along the inlet key. These phenomena result in increase of the effective weir length and thus discharge capacity increases in trapezoidal weir compared with rectangular one. Discretization of the discharge along the crest of the tested weirs clearly confirms these findings.

Scale effects in physical piano key weirs models

ABSTRACTWith inertia and gravity representing the dominant forces for most open channel flow applications (e.g. weir flow), Froude similitude is commonly used for scaling hydraulic performance data from the model to prototype structures. With weir flow, as the upstream head decreases, however, the relevance of surface tension and viscosity forces can increase to the point when the model and prototype similitude is not fully achieved through Froude scaling. Such discrepancies are referred as size-scale effects, and among other things, can result in variations in the head–discharge relationship, nappe trajectory, and air entrainment. Published criteria for avoiding significant size-scale effects for free flow over linear weirs have suggested that minimal heads of ∼0.02 to 0.07 m be respected, independently of the model size. In this study, the size-scale effect, minimum upstream head, and Weber number limits are investigated for four piano key weirs with geometric model scales of 1:1, 1:7, 1:15, and 1:25.

Mobile Riverbed Scour Downstream of a Piano Key Weir

AbstractIn parallel to their most frequent application as an auxiliary dam spillway, piano key weirs (PKWs) are also installed on low-head barrages in combination with run-off-the-river power plants. Their efficient rating curve, advantageous behavior under driftwood blockage, and the absence of mechanical elements are optimal for the hydraulic conditions associated with these run-off-the-river projects. However, in the absence of technical protection measures, scouring of the riverbed can occur at the downstream foundation. The unhindered scour formation and corresponding ridge generation caused by a PKW are investigated in this paper. Physical model tests were conducted under various conditions, providing a general estimation of the equilibrium scour and ridge dimensions. The maximum scour-hole depth dominates the shape of the hole and of the ridge. It was further shown that the maximum scour slope corresponds to the angle of repose of the sediments on the riverbed. Finally, a comparison of the present ...

Experimental study of discharge coefficient for trapezoidal piano key weirs

Piano Key Weirs (PKW) have been invented in the last decade to increase discharge capacity of hydraulic structures. Despite extensive studies on this type of weir with a rectangular plan form (RPKW), there are only a few pieces of research addressing trapezoidal piano key weirs (TPKW). In this experimental study, geometrical parameters of TPKW models were varied under different flow conditions and effects on discharge coefficient (Cd) were investigated. The Cd values were found to be mostly influenced by L/W whereas Wi/Wo had the least effect. Results also showed that TPKW has higher discharge efficiency in comparison with RPKW. This was believed to be related to formation of an “interference wedge” over the TPKW. Finally, quantitative values for distinguishing three flow regimes (i.e. nappe, transition and submergence) as well as criteria for design of TPKW are proposed.

INVESTIGATION OF HYDRAULIC PERFORMANCE OF PIANO SHAPED WEIRS USING THREE DIMENSIONAL NUMERICAL MODELING

3 Dept. of Hydraulic and Structures, Parab Fars Consulting Engineers Company, Shiraz, I. R. of Iran Abstract- Throughout history dams have been important structures in water storage. To avoid overtopping, damage, and or failure of a dam, adequate spillway is needed to release excess water from upstream floods. Researchers found that spillways have to be made nonlinear in order to reach an economic structure with high performance. A piano key weir is one of the best solutions. Piano key weirs are the modified and developed labyrinth spillways which can discharge greater volume of water than the common spillways in limited width and can be used as economic structures with high efficiency. In this article, a calibrated Flow-3D modeling by laboratory results has been used to evaluate and analyze the discharge coefficient of piano key weirs as related to the variation in width at inlet and outlet keys. According to the researches, the geometrical and hydraulic parameters are the most important factors for evaluating the performance of piano shaped weirs. In this study, the analytical effects of these parameters on discharge coefficient, and also the capability of discharge in these models have been investigated. Moreover, the important hydraulic parameters including depth, velocity and pressure have been studied through 3D numerical simulation. From the numerical results, a practical formula is proposed to obtain the discharge coefficient for the release capacity of the piano key weirs.

Flow hydrodynamics near inlet key of Piano Key Weir (PKW)

This paper presents fundamental outcomes from an experimental study on the hydrodynamic performance near inlet key of Piano Key Weir (PKW). Hydrodynamic performance was tested in a circulated open channel that comprised of PKW and sand bed (d50 = 0.25 mm). Instantaneous velocities were measured at 20 cross sections using Laser Doppler Velocimeter (LDV) with constant discharge and depth. Average velocity and turbulence intensities in both directions were investigated. Average longitudinal velocities are found very much consistent at every point and maximum around the midway of inlet key. In transverse direction, flow is bifurcating in two directions which are also confirmed by average transverse velocity estimation. Variation of turbulence intensity presents average 10 times higher transverse turbulence than longitudinal turbulence near inlet key of PKW.

Discussion of “Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow” by Michael Pfister, Damiano Capobianco, Blake Tullis and Anton J. Schleiss

Discussion of “Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow” by Michael Pfister, Damiano Capobianco, Blake Tullis and Anton J. Schleiss

Closure to “Debris-Blocking Sensitivity of Piano Key Weirs under Reservoir-Type Approach Flow” by Michael Pfister, Damiano Capobianco, Blake Tullis, and Anton J. Schleiss

Note: [1046] Reference EPFL-ARTICLE-213125doi:10.1061/(ASCE)HY.1943-7900.0000780View record in Web of Science Record created on 2015-10-21, modified on 2016-08-09

Closure to “Experimental parametric study and design of Piano Key Weirs” by O. MACHIELS, M. PIROTTON, P. ARCHAMBEAU, B. DEWALS and S. ERPICUM, J. Hydraulic Res. 52(3), 2014, 326–335

"Closure to “Experimental parametric study and design of Piano Key Weirs” by O. MACHIELS, M. PIROTTON, P. ARCHAMBEAU, B. DEWALS and S. ERPICUM, J. Hydraulic Res. 52(3), 2014, 326–335." Journal of Hydraulic Research, 53(4), p. 545

Developments to Improve Hydraulic Competence of Spillways

Dams whose collapse could cause loss of life or huge assets damage are considered to survive a probable maximum flood (PMF), but the PMF in various locations has been amplified at regular intervals, resulting in spillways that no longer convene the proposed norms. Spillway rehabilitation is required for lots of dams in India; in order to get better hydraulic competence. Catastrophe in Uttarakhand (June 2013) necessitates the research aspect of spillway rehabilitation. Increasing specific flow form hydraulic structures is one of the thought of spillway rehabilitation. Labyrinth weir may be used for amplifying specific flows of existing spillway. Sediment trapping behind Labyrinth weir might be one of the disadvantages for river with high sediment flow. The Piano Key Weir (PKW), ramped type Labyrinth weir is a hydraulically attractive alternative to linear overflow weirs, increasing the unit discharge for similar heads and spillway widths. This advantage allows operating dam reservoirs on an increased level and provides thereby an enhanced retention volume. It is a result of the non-linear nature of PKW being folded back and forth to make repeated cycles or keys. This type of weir is particularly suitable for sites where topographic conditions limit the extent of its width. Together with its high discharge capacity for low heads, this geometry makes these weirs interesting in spillway rehabilitation. This paper investigates the recent developments to improve hydraulic competence of spillways. Head reduction over crest can improve efficiency as well as reduce submergence. This study shows that for increasing discharge, head reduction with respect to conventional rectangular weir is reducing but reduction was found above seventy percent for all the experiments

Determination of Coefficient of Discharge for Piano Key Weirs of Varying Geometry

Determination of Coefficient of Discharge for Piano Key Weirs of Varying Geometry