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| 2. |
- Andersson, L. Robin, 1987-, et al.
(författare)
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Estimating localized pressure fluctuations in Gävunda hydropower tunnel
- 2020
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Ingår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020. - : The University of Queensland.
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Konferensbidrag (refereegranskat)abstract
- A numerical investigation of a hydropower tunnel has been implemented in this project. The tunnel geometry data were taken from a laser scanning of a tunnel positioned in Gävunda, Sweden. While the average cross-section of the tunnel is even, in accordance with the pre-excavation schematics, the instantaneous deviations are significant. ANSYS-CFX was applied for the simulations using a RANS approach with k-ε model for turbulence closure. To evaluate the results, the pressure was area averaged in 30 planes evenly spaced perpendicular to the flow direction inside the tunnel. Additionally, the pressure was sampled along a line running from the inlet to the outlet of the tunnel. Results show that the area averaged pressure is similar to the pressure modelled along the center line. This means that the roughness has a dominating effect on the bulk flow inside of the tunnel. Hence, cross-sectional based methods of evaluation (e.g. Gauckler-Manning) could potentially be used to evaluate the localized pressure inside the tunnel. Further evaluation show that the Gauckler-Manning and Haaland equation both can be used as an estimate of the modelled pressure inside of the tunnel. Both equations are highly dependent on the hydraulic radius and cross-sectional area. These results have many implications, continuous pressure measurements can potentially be used to monitor the structural integrity of tunnels. Similarly, tunnel data could be used to estimate pressure effects within the tunnel, which would enable easier and reliable risk assessment studies.
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| 3. |
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| 4. |
- Andersson, Robin, et al.
(författare)
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Inlet Blockage Effects in a Free Surface Channel With Artificially Generated Rough Walls
- 2018
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Ingår i: Proceedings of the 7th IAHR International Symposium on Hydraulic Structures. - 9780692132777 ; , s. 723-732
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Konferensbidrag (refereegranskat)abstract
- When considering free surface flow in channels, it is essential to have in-depth knowledge about the inlet flow conditions and the effect of surface roughness on the overall flow field. Hence, we hereby investigate flow inside an 18m long channel by using Particle Tracking Velocimetry (PTV) and Acoustic Doppler Velocimetry (ADV). The roughness of the channel walls is generated using a diamond-square fractal algorithm and is designed to resemble the actual geometry of hydropower tunnels. Four different water levels ranging from 20 to 50cm are investigated. For each depth, the inlet is blocked by 25 and 50% at three positions each, at the centre, to the right and to the left in the flow-direction. The flow is altered for each depth to keep the flow velocity even throughout the measurements. PTV is applied to measure the velocity of the free water surface; four cameras are placed above the setup to capture the entirety of the channel. The results show a clear correlation between roughness-height and velocity distribution at depths 20-30 cm. The surface roughness proved effective in dispersing the subsequent perturbations following the inlet blockage. At 50cm, perturbations from the 50% blockage could be observed throughout the channel. However, at 20cm, most perturbations had subsided by a third of the channel length. The ADV was used to capture the velocity in a total of 375 points throughout the channel, at a depth of 50 cm with no inlet perturbations.
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| 5. |
- Babicheva, T., et al.
(författare)
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The matching problem of empty vehicle redistribution in autonomous taxi systems
- 2018
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Ingår i: The 9th International Conference on Ambient Systems, Networks and Technologies (ANT 2018) / The 8th International Conference on Sustainable Energy Information Technology (SEIT-2018) / Affiliated Workshops. - : Elsevier. ; , s. 119-125
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Konferensbidrag (refereegranskat)abstract
- This article discusses empty vehicle redistribution algorithms for PRT and autonomous taxi services from a passenger service perspective. In modern literature reactive methods such as nearest neighbours are commonly used. In this article we first formulate the general matching problem on a bipartite graph of available vehicles and stations. In addition, we propose a new index-based proactive redistribution (IBR) algorithm based on predicted near-future demand at stations. Test results of six variations of combined proactive and reactive strategies on a test case in Saclay, France with 20 stations and 100 vehicles are given. The combined Nearest Neighbour / IBR provides a promising solution for both peak and off-peak demand, significantly outperforming all other methods considered, in terms of passenger waiting time (both average and maximum) as well as in terms of station queue lengths.
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| 6. |
- Burghout, Wilco, et al.
(författare)
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Incident management and traffic information : Simulation-based traffic prediction
- 2009
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Ingår i: 16th ITS World Congress.
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Konferensbidrag (refereegranskat)abstract
- Incident response and mitigation are the main tasks of operators at traffic control centres. Simulation models have a good chance of reproducing and predicting the effects of incident response by explicitly modelling drivers' responses to the incident and provided information. In the PREDIKT project, sponsored by the Swedish National Road Administration, a state-of-the-art mesoscopic simulation model (MEZZO) has been extended to provide decision support for incident management. In this paper we describe and test a number of essential modelling components such as modelling the incident response logic, a mixed-Logit model and a method for generation of alternative routes for drivers' route switching. In addition we present the results of a fast calibration method based on Simultaneous Perturbation Statistic Approximation (SPSA). The model components are tested in a small case study that investigates the impact of delay in information after incidents.
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| 7. |
- Hajkova, V., et al.
(författare)
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X-ray laser-induced ablation of lead compounds
- 2011
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Ingår i: DAMAGE TO VUV, EUV, AND X-RAY OPTICS III. - : SPIE.
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Konferensbidrag (refereegranskat)abstract
- The recent commissioning of a X-ray free-electron laser triggered an extensive research in the area of X-ray ablation of high-Z, high-density materials. Such compounds should be used to shorten an effective attenuation length for obtaining clean ablation imprints required for the focused beam analysis. Compounds of lead (Z=82) represent the materials of first choice. In this contribution, single-shot ablation thresholds are reported for PbWO(4) and PbI(2) exposed to ultra-short pulses of extreme ultraviolet radiation and X-rays at FLASH and LCLS facilities, respectively. Interestingly, the threshold reaches only 0.11 J/cm(2) at 1.55 nm in lead tungstate although a value of 0.4 J/cm(2) is expected according to the wavelength dependence of an attenuation length and the threshold value determined in the XUV spectral region, i.e., 79 mJ/cm(2) at a FEL wavelength of 13.5 nm. Mechanisms of ablation processes are discussed to explain this discrepancy. Lead iodide shows at 1.55 nm significantly lower ablation threshold than tungstate although an attenuation length of the radiation is in both materials quite the same. Lower thermal and radiation stability of PbI(2) is responsible for this finding.
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| 8. |
- Hedberg, P. A. Mikael, 1989-, et al.
(författare)
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Numerical modelling of flow in parallel spillways
- 2020
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Ingår i: Proceedings of the 8th IAHR International Symposium on Hydraulic Structures ISHS2020. - : The University of Queensland.
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Konferensbidrag (refereegranskat)abstract
- Mathematical modelling of single spillways is well documented in literature. For parallel spillways however, there is a lack of documented, verified, and validated cases. Here, in this article, ANSYS-CFX is used to simulate the flow over three parallel ogee-crested spillways. For mesh size verification, a grid convergence study is performed by Richardson extrapolation. The turbulence model chosen for this simulation is the k-ε model and the volume of fluid method is used to simulate the water-air interface. This article details the models ability to accurately predict flow distribution at the spillways, and the water levels. The mesh is kept relatively coarse at the channel inlet with increased mesh density at the spillways. The results are validated against experimental data from Vattenfall AB, R&Ds laboratories. The geometry and boundary conditions of the experiment are tailored for CFD. The flow rate of each spillway is measured separately with high accuracy, and for several different inlet volumetric flows. The simulation results lie within the error estimates of the measuring tools used in the experiments, within ±1%. The volume flow rate differences between the three outlets is very small, within ±1%.
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| 9. |
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| 10. |
- Jonsson, Patrick, et al.
(författare)
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Smoothed particle hydrodynamics modeling of hydraulic jumps
- 2011
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Ingår i: Particle-based Methods – Fundamentals and Applications. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 9788489925670 ; , s. 490-501
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study focus on Smoothed Particle Hydrodynamics (SPH) modeling of twodimensional hydraulic jumps in horizontal open channel flows. Insights to the complex dynamics of hydraulic jumps in a generalized test case serves as a knowledgebase for real world applications such as spillway channel flows in hydropower systems. In spillways, the strong energy dissipative mechanism associated with hydraulic jumps is a utilized feature to reduce negative effects of erosion to spillway channel banks and in the old river bed. The SPH-method with its mesh-free Lagrangian formulation and adaptive nature results in a method that handles extremely large deformations and numerous publications using the SPH-method for free-surface flow computations can be found in the literature. Hence, the main objectives with this work are to explore the SPH-methods capabilities to accurately capture the main features of a hydraulic jump and to investigate the influence of the number of particles that represent the system. The geometrical setup consists of an inlet which discharges to a horizontal plane with an attached weir close to the outlet. To investigate the influence of the number of particles that represents the system, three initial interparticle distances were studied, coarse, mid and fine. For all cases it is shown that the SPH-method accurately captures the main features of a hydraulic jump such as the transition between supercritical- and subcritical flow and the dynamics of the highly turbulent roller and the air entrapment process. The latter was captured even though a single phase was modeled only. Comparison of theoretically derived values and numerical results show good agreement for the coarse and mid cases. However, the fine case show oscillating tendencies which might be due to inherent numerical instabilities of the SPH-method or it might show a more physically correct solution. Further validation with experimental results is needed to clarify these issues.
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