| 1. |
- Andersson, Anders G.
(author)
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Simulations and measurements of free surface flow in regulated rivers
- 2010
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Licentiate thesis (other academic/artistic)abstract
- Open channel flow near hydropower stations is of interest for both engineering and environmental applications. In this research project Computational Fluid Dynamics simulations of free surface flow in regulated rivers were applied with both fish migration and validation of numerical simulations in focus. In the first paper, numerical simulations has been used to evaluate the flow downstream a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed and the measurements were used to validate the simulations. In the second paper ,simulations on the spilling from a dam were performed and compared to experimental results from a physical scale model. The third paper deals with more in depth analysis of field measurements where the variations in the flow downstream a hydropower plant was examined.
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| 2. |
- Billstein, Mats, et al.
(author)
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A numerical evaluation of air bubbles as a potential explanation to the higher than expected pore pressures in the core of WAC Bennett Dam
- 2002
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In: Journal of Hydraulic Research. - : Informa UK Limited. - 0022-1686 .- 1814-2079. ; 40:5, s. 623-630
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Journal article (peer-reviewed)abstract
- The objective of this study is to numerically evaluate if the Air Hypothesis is a potential explanation of the unusual pressure behaviour of the core at WAC Bennett Dam. Up to now, the pore pressures have exceeded the expected normal steady state distribution for about 25 years. The Air Hypothesis describes the influence of air bubbles on the pressure distribution in the core. An increased water pressure will compress the air bubbles and increases the amount of air that can go into solution at the upstream side of the core. At the downstream side, the situation is reversed, i.e. the air volume will increase and cause a hydraulic blockage. A one-dimensional numerical model, that is based on relevant conservation laws, physical laws (Darcy's, Boyle's, and Henry's laws) and the relationships between the relative hydraulic conductivity and water saturation level, is able to predict the pressure evolution in both a qualitative and quantitative way. The model is applied to both a hypothetical core and the core of WAC Bennett Dam. Results from a plug flow analysis on the dissolution of the air in the hypothetical core are in fair agreement with the numerical results. Comparisons with pressure measurements from WAC Bennett Dam show that the Air Hypothesis is a potential explanation to the unusual pressure distribution in the core
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| 3. |
- Billstein, Mats, et al.
(author)
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Application and validation of a numerical model of flow through embankment dams with fractures : Comparisons with experimental data
- 1999
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In: Canadian geotechnical journal (Print). - : Canadian Science Publishing. - 0008-3674 .- 1208-6010. ; 36:4, s. 651-659
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Journal article (peer-reviewed)abstract
- The focus of this paper is on the development and validation of a numerical model of flow through simplified embankment dams with fractures. Two laboratory experiments were conducted to provide data for validation of the numerical model, one dealing with steady flow in a Hele-Shaw cell and one with steady flow through a bed of packed glass beads. A horizontal fracture, extending from the upstream boundary to a point within the embankment, was used in both experiments, and it was shown to have a significant influence on the discharge, pressure distribution, height of the seepage face, and free surface profile. Comparisons between numerically determined and experimentally measured results were carried out with respect to the discharge, pressure distribution, height of the seepage face, and free surface profile. In the experiments it is shown that a fracture increases the discharge and that the discharge increases more when a fracture is located far away from the free surface profile than when it is located close to the free surface profile. The height of the seepage face above the tailwater is strongly dependent upon the length of the fracture. The influence on the free surface profile is greater when a fracture is close to the free surface profile than when it is far away from the free surface profile. These effects are also found in the numerical simulations. It is thus concluded that the agreement is generally satisfactory between the experimental and numerical results
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| 4. |
- Billstein, Mats, et al.
(author)
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Development and Validation of a Numerical Model of Flow Through Embankment Dams – Comparisons with Experimental Data and Analytical Solutions
- 1999
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In: Transport in Porous Media. - 0169-3913 .- 1573-1634. ; 35:3, s. 395-406
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Journal article (peer-reviewed)abstract
- The development and validation of a numerical simulation model of the flow through embankment dams is described. The paper focuses on basic verification studies, that is, comparisons with analytical solutions and data from laboratory experiments. Two experimental studies, one dealing with the flow in a Hele-Shaw cell and the other with the flow through a bed of packed glass beads, are also described. Comparisons are carried out with respect to the phreatic surfaces, pressure profiles, seepage levels and discharges. It is concluded that the agreement between experimental, analytical and numerical results is generally satisfactory.
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| 5. |
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| 6. |
- Billstein, Mats
(author)
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Influence of fractures and air bubbles on the pressure distribution embankment dams
- 2000
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Doctoral thesis (other academic/artistic)abstract
- In some large embankment dams unexpected pore pressure distributions within the core have been observed. As an example, the piezometer pressures in WAC Bennett Dam, Canada, which rose for about four years after the reservoir was filled, were steady for two years and subsequently declined. One peak pressure head was as much as 60 m higher than the expected steady state pressure head of 40 m. However, the pressure head had dropped 55 m from the peak value 25 years later. Four hypotheses have already been proposed to explain the anomalous pore pressures within embankment dams. The objective of this study is to examine two of them, inhomogenities (e.g. fractures) in the core and trapped air bubbles, which can both be examined from a fluid mechanical point of view. The other two mechanisms, settlements and bleeding of fine material, must also be examined from a geotechnical aspect. This examination, based on results from two numerical models, is mainly theoretical. Results from numerical simulations of simplified homogeneous and inhomogeneous embankment dams are compared with analytical solutions and basic experiments. Results from numerical simulations, including the influence of air bubbles, are evaluated using a plug flow analysis and field measurements. A Hele-Shaw cell and a bed of packed glass beads, both a homogeneous and an inhomogeneous experimental set up, were used in the examination of how inhomogenities influence the pressure distribution. In the inhomogeneous case, a horizontal fracture extended from the upstream boundary to a point within the embankment. The fracture was shown to have a significant influence on the pressure distribution, discharge, seepage level, and free surface profile. The numerical model is based on a direct solution of the conservation equations (mass and momentum). In the numerical simulations, the flow resistance is determined from a laminar velocity profile in a slot with smooth walls (Hele-Shaw cell) and from the Forchheimer equation (bed of packed glass beads). The problem is considered to be two-dimensional. Since air bubbles are always initially present in the voids, that air is compressible, and that the amount of air that can go into solution increases with pressure, a mechanism that generates hydraulic blockage in the downstream part of the core can be anticipated. The blockage decreases the hydraulic conductivity in the flow direction resulting in a pressure increase. The numerical model for this case is based on a direct solution of the conservation equations (mass and momentum) and Darcy's, Boyle's, and Henry's law. It is a two-phase problem treated as one-dimensional. The main result of the study is the development of numerical models to simulate how inhomogenities and trapped air bubbles influence the pressure distribution. These models have a solid foundation, i.e. are based on conservation principles, physical laws, and the best available empirical relationships. The models have been validated through comparisons with analytical solutions, basic experiments, and field measurements and thus provide a good starting point in the development of tools that can be used in dam engineering.
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| 7. |
- Kadia, Subhojit, et al.
(author)
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Experimental and numerical investigations of the water surface profile and wave extrema of supercritical flows in a narrow channel bend
- 2024
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In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14:1
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Journal article (peer-reviewed)abstract
- Supercritical flows in channel bends, e.g., in steep streams, chute spillways, and flood and sediment bypass tunnels (SBTs), experience cross-waves, which undulate the free surface. The designs of these hydraulic structures and flood protection retaining structures in streams necessitate computing the locations and water depths of the wave extrema. This study numerically and experimentally investigates the water surface profiles along the sidewalls, the wave extrema flow depths, and their angular locations in a narrow channel bend model of the Solis SBT in Switzerland. The 0.2 m wide and 16.75 m long channel has a bend of 6.59 m radius and 46.5° angle of deviation. The tested flow conditions produced Froude numbers ≈ 2 and aspect ratios ranging from 1.14 to 1.83. Two-phase flow simulations were performed in OpenFOAM using the RNG k–ε turbulence closure model and the volume-of-fluid method. The simulated angular locations of the first wave extrema and the corresponding flow depths deviate marginally, within ± 6.3% and ± 2.1%, respectively, from the experimental observations, which signifies good predictions using the numerical model. Larger deviations, especially for the angular locations of the wave extrema, are observed for the existing analytical and empirical approaches. Therefore, the presented numerical approach is a suitable tool in designing the height of the hydraulic structures with bends and conveying supercritical flows. In the future, the model’s application shall be extended to the design of the height and location of retaining walls, embankments, and levees in steep natural streams with bends.
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| 8. |
- Kadia, Subhojit, et al.
(author)
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Supercritical Flow Characteristics in a Narrow Channel Bend
- 2023
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In: Proceedings of the 40th IAHR World Congress - 2023: Rivers - Connecting Mountains and Coasts. - : International Association for Hydro-Environment Engineering and Research. ; , s. 87-93
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Conference paper (peer-reviewed)
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| 9. |
- Lundin, Urban, et al.
(author)
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Adding discharge capacity and redundancy using existing turbines
- 2021
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In: International journal on hydropower and dams. - 1352-2523. ; 28:5, s. 78-82
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Journal article (peer-reviewed)abstract
- The ability to discharge water plays a vital role in hydropower dam safety. There are several different designs that provide discharge capacity, with the two main types being surface and bottom spillways. Here, an alternative concept is presented, whereby the regular waterway through the turbine is utilized. In the event of grid loss a local load is connected which enables the unit in question to operate isolated from the main grid. This dump-load concept has been tested at pilot scale in Sweden with positive results and therefore proposed to be applied in existing power plants. Additional discharge capacity via a dump-load has a number of benefits compared to conventional spillgates, the most obvious being its significantly lower investment cost, fast installation and provision of redundancy.
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| 10. |
- Strömme Mattsson, Adam, 1997-, et al.
(author)
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A concept to ensure spill discharge capacity during grid blackout and flooding
- 2023
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In: Symposium “Management for Safe Dams” - 91st Annual ICOLD Meeting. S3-B Hydrology & Hydraulics – Design..
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Conference paper (peer-reviewed)abstract
- The core of dam safety is to safely store and discharge water and thereby prevent uncontrolled release of water. Excess water, e.g. in a flooding situation, is commonly discharged via different types of spillways (gated, weirs, surface, bottom outlets etc.).The turbine discharge is typically not included in the capacity as flooding scenarios could cause a grid-blackout rendering the turbine incapable of operating.The paper will describe a project that has tested island operation of a hydropower unit equipped with a developed dump-load device. The dump-load device will allow the unit to operate even during a black-out without risk for failure of the unit and thus assure the discharge capacity via the waterways connected to the unit. Stable operation is verified in the tests and this opens up for the turbine discharge to be included in the total discharge capacity of a facility. A cost-benefit analysis of the suggested solution and a brief description of the past and planned development of the device will be given. In addition to the extra discharge capacity, the new system can also be used to reduce the risk for surge during start- and stop sequences.Implementation of the system in two different facilities, with different purpose, is planned and details on the coming installations and the technical solutions around them will be given.
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