B. Yildiz
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1
Compound weirs have been used as adjustable structures to divert flow, for example, through river branches at the river bifurcations. For this purpose, a wide variety of weir configurations can be used including asymmetric configurations that have not been studied in the literature yet. A proper one-dimensional representation of flow over these structures is needed as the effect they have on the river are generally added as subgrid energy losses to the river hydrodynamic models. In this study, an experimental study was conducted to estimate the correct representation of compound weirs at varying weir configurations and flow conditions. In the experimental campaign, eight weir configurations were used with six discharge values. Upstream flow depths at each case were recorded and their relationship with the flow rate and weir configuration was analyzed. A 1D model was proposed to estimate flow rates when the upstream flow depths are known. The proposed correction to the well-known Kindsvater and Carter approach was applied to modify the discharge coefficient when nonuniform geometries are used that cause horizontal flow contraction. To estimate and validate the proposed correction, additional numerical simulations using computational fluid dynamics (CFD) were conducted to estimate the detailed flow field upstream of the nonuniform weirs. Surface particle image velocimetry (SPIV) measurements were also conducted to validate the CFD model. The corrected 1D model predicted the flow rates at 48 cases covering uniform to highly nonuniform weir geometries with a maximum of 9.7% and a mean of 2.45% deviation from the measurements. Additional tests on the performance of the proposed model validated its effectiveness in various nonuniform geometries at low flows. However, when substantial changes are made to the geometry, such as the removal of buttresses, the model may require calibration to maintain its accuracy.
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Compound weirs have been used as adjustable structures to divert flow, for example, through river branches at the river bifurcations. For this purpose, a wide variety of weir configurations can be used including asymmetric configurations that have not been studied in the literature yet. A proper one-dimensional representation of flow over these structures is needed as the effect they have on the river are generally added as subgrid energy losses to the river hydrodynamic models. In this study, an experimental study was conducted to estimate the correct representation of compound weirs at varying weir configurations and flow conditions. In the experimental campaign, eight weir configurations were used with six discharge values. Upstream flow depths at each case were recorded and their relationship with the flow rate and weir configuration was analyzed. A 1D model was proposed to estimate flow rates when the upstream flow depths are known. The proposed correction to the well-known Kindsvater and Carter approach was applied to modify the discharge coefficient when nonuniform geometries are used that cause horizontal flow contraction. To estimate and validate the proposed correction, additional numerical simulations using computational fluid dynamics (CFD) were conducted to estimate the detailed flow field upstream of the nonuniform weirs. Surface particle image velocimetry (SPIV) measurements were also conducted to validate the CFD model. The corrected 1D model predicted the flow rates at 48 cases covering uniform to highly nonuniform weir geometries with a maximum of 9.7% and a mean of 2.45% deviation from the measurements. Additional tests on the performance of the proposed model validated its effectiveness in various nonuniform geometries at low flows. However, when substantial changes are made to the geometry, such as the removal of buttresses, the model may require calibration to maintain its accuracy.
The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one- or two-dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two-dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds-averaged Navier-Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining.
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The hydraulic resistance of groynes is an important factor in the determination of design flood water levels on rivers and the assessment of how much these levels are lowered by modifying the groynes. In standard one- or two-dimensional numerical hydrodynamic models for flood risk management, groynes are commonly represented as subgrid features with a local energy loss according to a weir formula. We tested this representation by using a two-dimensional horizontal mesh at various groyne submergence degrees by comparing the results with those of flume experiments. We also compared the results with simulations using different 2D and 3D approaches on finer grids that incorporate groynes in the bed topography. In one of the two tested 3D models, complete Reynolds-averaged Navier-Stokes equations were solved. The second tested 3D model was constructed simpler by assuming hydrostatic pressure distribution in the vertical direction. We employed Delft3D software in construction and execution of all models. One of the 3D models did predict the hydraulic resistance at low submergence better than the standard model, but it slightly underestimated the resistance at higher submergences. Despite differences in flow characteristics, weirs and groynes were found to produce similar flow resistances for the same height and boundary conditions. Simulations of groyne modifications showed that hydraulic resistance decreased nonlinearly with groyne lowering and streamlining.
Compound weirs are used as flow diversion structures by adding additional flow resistance to the anticipated regions at the rivers. Furthermore, they are used for measuring and regulating flow rates accurately over a wide range of flow depths. When they are used for this purpose, the cross sections are generally selected as symmetrical having the lowest level of the weir at the middle to constrain large flow contractions. However, when used as a flow diversion structure, the cross sections should be adjusted for different degrees of flow contractions to satisfy the anticipated amount of flow resistance. The literature includes several studies in which compound weirs are modelled as flow measurement structures. Modelling them with the aim of flow diversion received little interest in literature. The adaptation of previously proposed analytical and experimental weir models has problems especially in cases with high flow contractions. In this study, the free flow over the compound weirs is modelled numerically with the application of flow diversion in mind. The results are validated by comparing them with the surface velocity measurements obtained using Surface Particle Image Velocimetry (SPIV). The study aims at understanding how far upstream flow redistribution takes place, how big the transverse mass fluxes are and how this affects the flow at the weir openings, at various degree of flow contractions. Three compound weir configurations were used: One with high flow contraction and the other two with moderate to low flow contractions. The numerical model is constructed by using a three-dimensional mesh using OpenFOAM CFD solver. A multiphase flow analysis was conducted by using Volume-of-Fluid (VOF) approach. We have applied RANS modelling with k-ω SST turbulence closure. SPIV experiments were conducted in a 3-meter-wide, 20-m-long rectangular horizontal flume at the Water Lab of Delft University of Technology. A camera was mounted over the flume to record the floating particle positions during flow. The results gave the possibility to quantify transverse distribution of mass transfer among the openings at various degrees of horizontal contractions. The initiation of streamline curvature locations at the upstream were labelled such that a comparison was achieved among the configurations. The numerical model results gave the possibility to complement experimental data regarding the effective flow sections at the weir openings. In summary, the numerical model validated by the SPIV measurements helped understanding the behaviour of flow under high horizontal contraction. However, to develop a correction methodology for high contraction for the simplified 1D weir discharge prediction models, the numerical runs should be extended for various configurations and covering the submerged weir flow as well.
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Compound weirs are used as flow diversion structures by adding additional flow resistance to the anticipated regions at the rivers. Furthermore, they are used for measuring and regulating flow rates accurately over a wide range of flow depths. When they are used for this purpose, the cross sections are generally selected as symmetrical having the lowest level of the weir at the middle to constrain large flow contractions. However, when used as a flow diversion structure, the cross sections should be adjusted for different degrees of flow contractions to satisfy the anticipated amount of flow resistance. The literature includes several studies in which compound weirs are modelled as flow measurement structures. Modelling them with the aim of flow diversion received little interest in literature. The adaptation of previously proposed analytical and experimental weir models has problems especially in cases with high flow contractions. In this study, the free flow over the compound weirs is modelled numerically with the application of flow diversion in mind. The results are validated by comparing them with the surface velocity measurements obtained using Surface Particle Image Velocimetry (SPIV). The study aims at understanding how far upstream flow redistribution takes place, how big the transverse mass fluxes are and how this affects the flow at the weir openings, at various degree of flow contractions. Three compound weir configurations were used: One with high flow contraction and the other two with moderate to low flow contractions. The numerical model is constructed by using a three-dimensional mesh using OpenFOAM CFD solver. A multiphase flow analysis was conducted by using Volume-of-Fluid (VOF) approach. We have applied RANS modelling with k-ω SST turbulence closure. SPIV experiments were conducted in a 3-meter-wide, 20-m-long rectangular horizontal flume at the Water Lab of Delft University of Technology. A camera was mounted over the flume to record the floating particle positions during flow. The results gave the possibility to quantify transverse distribution of mass transfer among the openings at various degrees of horizontal contractions. The initiation of streamline curvature locations at the upstream were labelled such that a comparison was achieved among the configurations. The numerical model results gave the possibility to complement experimental data regarding the effective flow sections at the weir openings. In summary, the numerical model validated by the SPIV measurements helped understanding the behaviour of flow under high horizontal contraction. However, to develop a correction methodology for high contraction for the simplified 1D weir discharge prediction models, the numerical runs should be extended for various configurations and covering the submerged weir flow as well.
The shape of a pendant drop is studied by employing free energy minimization. This free energy includes the gravitational potential energy and the interfacial surface energy. We employed the Lagrange multipliers method to minimize free energy while maintaining drop volume as constant. The differential equation for the shape of any pendant drop was established as a function of one dimensionless parameter only. This novel dimensionless parameter is defined as the shape factor. Around the origin of the chosen coordinate axis, an analytical solution to the differential equation was found. For a general solution, a numerical approach was followed to estimate drop shape. Furthermore, we calculated the detached volume from the bulk pendant drop. Comparison of the results with the experimental findings shows good agreements. A new Axisymmetric Drop Shape Analysis method is suggested, which can help users estimate any unknown of the problem if one geometrical data of the drop is known.
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The shape of a pendant drop is studied by employing free energy minimization. This free energy includes the gravitational potential energy and the interfacial surface energy. We employed the Lagrange multipliers method to minimize free energy while maintaining drop volume as constant. The differential equation for the shape of any pendant drop was established as a function of one dimensionless parameter only. This novel dimensionless parameter is defined as the shape factor. Around the origin of the chosen coordinate axis, an analytical solution to the differential equation was found. For a general solution, a numerical approach was followed to estimate drop shape. Furthermore, we calculated the detached volume from the bulk pendant drop. Comparison of the results with the experimental findings shows good agreements. A new Axisymmetric Drop Shape Analysis method is suggested, which can help users estimate any unknown of the problem if one geometrical data of the drop is known.
This study aims to search for optimum design parameters for a slurry pipeline problem and optimum operation parameters for a multi-reservoir scheduling problem by using Bi-Attempted Base Optimization Algorithm (ABaOA), which has been recently developed as a numerical bidirectional search algorithm. The slurry pipeline problem is a constrained non-linear cost minimization problem with constraints on facility capacities. It has two separate cost terms that behave differently with changes in decision variables. The problem includes several decision variables in addition to the fact that the objective function is highly non-linear. On the other hand, the multi-reservoir problem is a well-known problem in Hydraulics that aims to maximize benefit by optimizing the releases of each reservoir. The problem has a known global optimum, which is used to test the abilities of the ABaOA. The ABaOA is developed from Base Optimization Algorithm (BaOA) by transforming its operators with the aim to diversify the search paths to reach the global optimum. Its applications in hydrosystems show that it converges to the optimum solutions in reasonable times. The results from the first application are compared to the ones obtained from Genetic Algorithms (GA) application. It is observed that ABaOA outperformed GA in terms of speed of convergence and finding a better alternative solution. The ABaOA reaches the global optimum in the second application. In addition, alternatives with better benefit functions, including some penalties have been determined.
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This study aims to search for optimum design parameters for a slurry pipeline problem and optimum operation parameters for a multi-reservoir scheduling problem by using Bi-Attempted Base Optimization Algorithm (ABaOA), which has been recently developed as a numerical bidirectional search algorithm. The slurry pipeline problem is a constrained non-linear cost minimization problem with constraints on facility capacities. It has two separate cost terms that behave differently with changes in decision variables. The problem includes several decision variables in addition to the fact that the objective function is highly non-linear. On the other hand, the multi-reservoir problem is a well-known problem in Hydraulics that aims to maximize benefit by optimizing the releases of each reservoir. The problem has a known global optimum, which is used to test the abilities of the ABaOA. The ABaOA is developed from Base Optimization Algorithm (BaOA) by transforming its operators with the aim to diversify the search paths to reach the global optimum. Its applications in hydrosystems show that it converges to the optimum solutions in reasonable times. The results from the first application are compared to the ones obtained from Genetic Algorithms (GA) application. It is observed that ABaOA outperformed GA in terms of speed of convergence and finding a better alternative solution. The ABaOA reaches the global optimum in the second application. In addition, alternatives with better benefit functions, including some penalties have been determined.
Compound weirs can be used as flexibly adjustable structures to regulate the flow and the flow distribution over the cross-section. Examples are found in rivers to create additional resistance in one side of the river bifurcations. It is done to distribute the discharge among the branches properly. They are placed at the flood plains and become active only during flooding. Therefore, the expected flow type over the weirs is generally submerged, unlike the modular weir flow which has been studied a lot in the literature. In this study, an experimental campaign was conducted to understand how flow over compound weirs consisting of 12 sections, differs from the flow over uniform weirs. The analyses were conducted under modular and submerged weir conditions to gain a comparative understanding. Configurations of the compound weirs are important as they may lead to horizontal and vertical contraction of flow at various degrees. In this study, nine compound weir configurations were used to include flow variety and a wide range of applications. The experiments were conducted in a 3-meter-wide, 20-m-long rectangular horizontal flume at the Water Lab of Delft University of Technology. Flow depths at the upstream and downstream sides of the weirs were recorded along with the flow rates. Six discharge values were used to include the effect of discharge variations in the results. The measurement results were compared with the standard formulas from the literature to estimate flow rates over uniform rectangular sharp-crested weirs. Experimental data showed strong deviations from the model in submerged cases and moderate to slight deviations in modular cases. The observed deviations showed dependence on weir configurations and discharge. This indicates that discharge coefficients and head losses cannot be treated per weir section, but should be considered in interaction with neighboring sections.
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Compound weirs can be used as flexibly adjustable structures to regulate the flow and the flow distribution over the cross-section. Examples are found in rivers to create additional resistance in one side of the river bifurcations. It is done to distribute the discharge among the branches properly. They are placed at the flood plains and become active only during flooding. Therefore, the expected flow type over the weirs is generally submerged, unlike the modular weir flow which has been studied a lot in the literature. In this study, an experimental campaign was conducted to understand how flow over compound weirs consisting of 12 sections, differs from the flow over uniform weirs. The analyses were conducted under modular and submerged weir conditions to gain a comparative understanding. Configurations of the compound weirs are important as they may lead to horizontal and vertical contraction of flow at various degrees. In this study, nine compound weir configurations were used to include flow variety and a wide range of applications. The experiments were conducted in a 3-meter-wide, 20-m-long rectangular horizontal flume at the Water Lab of Delft University of Technology. Flow depths at the upstream and downstream sides of the weirs were recorded along with the flow rates. Six discharge values were used to include the effect of discharge variations in the results. The measurement results were compared with the standard formulas from the literature to estimate flow rates over uniform rectangular sharp-crested weirs. Experimental data showed strong deviations from the model in submerged cases and moderate to slight deviations in modular cases. The observed deviations showed dependence on weir configurations and discharge. This indicates that discharge coefficients and head losses cannot be treated per weir section, but should be considered in interaction with neighboring sections.
Poster
(2021)
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Johan Harms, Víctor Chavarrías, Mohamed Yossef, Jeremy Bricker, Wim Uijttewaal, Burhan Yildiz
Weirs are flow control structures that can be used for flow diversion purposes. They are classified according to section geometry or their length in the flow direction. For sharp-crested rectangular weirs, Rehbock [1] derived stage-discharge equations. In contracted geometries, streamlines curve at the approach flow leading to variations in flow structures. For this case, [2] proposed an equation for discharge as a function of the opening rate at the section (ratio of opening width to total width, b/B). We developed CFD models to test their accuracy in modelling weir flow. For the contracted weir cases, flow structures were visualised upstream of the weir.
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Weirs are flow control structures that can be used for flow diversion purposes. They are classified according to section geometry or their length in the flow direction. For sharp-crested rectangular weirs, Rehbock [1] derived stage-discharge equations. In contracted geometries, streamlines curve at the approach flow leading to variations in flow structures. For this case, [2] proposed an equation for discharge as a function of the opening rate at the section (ratio of opening width to total width, b/B). We developed CFD models to test their accuracy in modelling weir flow. For the contracted weir cases, flow structures were visualised upstream of the weir.