| 1. |
- Andersson, Anders G., et al.
(författare)
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CFD-modelling and validation of free surface flow during spilling of reservoir in down-scale model
- 2013
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 7:1, s. 159-167
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Tidskriftsartikel (refereegranskat)abstract
- Fully three dimensional modelling of the spilling from a reservoir with relatively complex geometry were performed and compared to experimental results from a physical scale model with the aim to advance the science of numerical modelling of free surface flow of real reservoirs. In the set-up in focus the water was spilled from the reservoir through three gates that could be manoeuvred separately. In the first case two of the gates were closed and the third gate was partly opened. In this experimental set-up the water surface in the reservoir was close to horizontal. Therefore it was here meaningful to compare a rigid lid modelling approximation to the more computational heavy method of Volume of Fluids. In the second case, all three gates were open, resulting in a nonhorizontal varied flow surface profile in the reservoir upstream critical sections at the spillway crests. This case was simulated with Volume of Fluids and the position of the air-water interface was derived for two turbulence models, the standard k-ε and SSG. Water levels, velocities and the shape of the water surface were compared to experiments. The simulation results capture qualitative features such as a vortex near the outlet and show good quantitative agreement with the experiments regardless of method used to simulate the free surface. In general, simulations with the standard k-ε and the more advanced SSG turbulence models give the same results with respect to the averaged quantities measured.
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| 2. |
- Andersson, Anders G., et al.
(författare)
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Effect of spatial resolution of rough surfaces on numerically computed flow fields with application to hydraulic engineering
- 2014
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 8:3, s. 373-381
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Tidskriftsartikel (refereegranskat)abstract
- In numerical simulations of flow over rough surfaces, the roughness is often not resolved but represented by a numerical model. The validity of such an assumption is investigated in this paper by Reynolds-Averaged Navier-Stokes simulations of flow over a surface with a large roughness. The surface was created from a high-resolution laser scanning of a real rock blasted tunnel. By reducing the geometrical resolution of the roughness in two steps, the importance of an appropriate surface description could be examined. The flow fields obtained were compared to a set-up with a geometrical flat surface where the roughness was represented by a modified form of the Launder and Spalding wall-function. The flow field over the surface with the lowest resolution was substantially different from those of the two finer resolutions and rather close to the results from the set-up with the wall-function. The results also yield that the finer the resolution is the more vorticity is formed close to the rough surface and more turbulence is generated.
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| 3. |
- Beyaztas, Ufuk, et al.
(författare)
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Construction of functional data analysis modeling strategy for global solar radiation prediction : application of cross-station paradigm
- 2019
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Taylor & Francis. - 1994-2060 .- 1997-003X. ; 13:1, s. 1165-1181
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Tidskriftsartikel (refereegranskat)abstract
- To support initiatives for global emissions targets set by the United Nations Framework Convention on climate change, sustainable extraction of usable power from freely-available global solar radia- tion as a renewable energy resource requires accurate estimation and forecasting models for solar energy. Understanding the Global Solar Radiation (GSR) pattern is highly significant for determin- ing the solar energy in any particular environment. The current study develops a new mathematical model based on the concept of Functional Data Analysis (FDA) to predict daily-scale GSR in the Burk- ina Faso region of West Africa. Eight meteorological stations are adopted to examine the proposed predictive model. The modeling procedure of the regression FDA is performed using two different internal parameter tuning approaches including Generalized Cross-Validation (GCV) and Generalized Bayesian Information Criteria (GBIC). The modeling procedure is established based on a cross-station paradigm wherein the climatological variables of six stations are used to predict GSR at two targeted meteorological stations. The performance of the proposed method is compared with the panel data regression model. Based on various statistical metrics, the applied FDA model attained convincing absolute error measures and best goodness of fit compared with the observed measured GSR. In quantitative evaluation, the predictions of GSR at the uahigouya and Dori stations attained corre- lation coefficients of R 0.84 and 0.90 using the FDA model, respectively. All in all, the FDA model introduced a reliable alternative modeling strategy for global solar radiation prediction over the Burkina Faso region with accurate line fit predictions.
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| 4. |
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| 5. |
- Diedrichs, Ben, et al.
(författare)
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On the aerodynamics of car body vibrations of high-speed trains crusing inside tunnels
- 2008
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Ingår i: ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 2:1, s. 51-75
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Tidskriftsartikel (refereegranskat)abstract
- Aerodynamically induced car body vibrations of high-speed trains inside tunnels have for approximately two decades been recognized as a problem in Japan, while other nations' high-speed rail services have not reported similar problems. In order to shed light on this contradiction the scope of the present paper is to primarily explore tail car vibrations of Deutsche Bahn AG's high-speed train ICE 2 and Japan Railways series 300 Shinkansen train. Despite similarities of these two trains the problems are reported only for the latter. Several large eddy simulations are carried out to predict the aerodynamics around simplified and smooth models of the above mentioned trains inside tunnels. The results focus on the ability to resolve PPD (propagating pressure disturbances) generated alongside the bodies, unsteady aerodynamic forces and their corresponding frequencies. Mesh refinement studies are undertaken for both train models, where mesh independence is quite a challenge for this type of application. Affordable meshes appropriate for LES could only be achieved for models confined to a typical car length. For smooth models and for a model with three generic inter-car gaps, the high spatial frequency of the resolved PPD does not make them sufficient to upset the ride quality of a car. A low frequency mode that strongly affects the forces of the tail of the Shinkansen models is described, which is caused by the confinement of the tunnel walls. A study of the implications of the lateral distance to the wall is further investigated. The findings reveal that the effects of the low frequency mode intensify with a narrow wall clearance, corresponding to the nominal lateral position of the train.
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| 6. |
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| 7. |
- Hemida, Hassan, 1972, et al.
(författare)
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Exploring Flow Structures Around a Simplified ICE2 Train Subjected to a 30 Degree Side Wind Using LES
- 2009
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 3:1, s. 28-41
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Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulation (LES) is conducted to investigate the flow around a simplified ICE2 trainunder side wind conditions at 30° yaw angle. The Reynolds number based on the height of the train and the freestream velocity is 200000. Two computations on two different meshes with different numbers of nodes are made tocheck the effect of the mesh resolution on the results. The fine and the coarse meshes give similar results meaningthat the results are mesh independent. The results are also verified against available experimental data. Goodagreement is obtained between the LES results and the experimental data. The LES results show that two flowregimes exist in the wake. The first flow regime consists of steady vortex lines in the upper part of the wake flow. Itchanges into unsteady shedding after a distance of about five train heights from their onset on the surface of thetrain. The second flow regime is the unsteady movement of the lower part of the wake vortices. They attach anddetach from the surface of the train in a regular fashion. The time-averaged flow and the instantaneous flow aroundthe ICE2 train at 30° yaw angle are explored.
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| 8. |
- Homsi, Rajab, et al.
(författare)
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Precipitation projection using a CMIP5 GCM ensemble model : a regional investigation of Syria
- 2020
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - UK : Taylor & Francis. - 1994-2060 .- 1997-003X. ; 14:1, s. 90-106
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Tidskriftsartikel (refereegranskat)abstract
- The possible changes in precipitation of Syrian due to climate change are projected in this study. The symmetrical uncertainty (SU) and multi-criteria decision-analysis (MCDA) methods are used to identify the best general circulation models (GCMs) for precipitation projections. The effectiveness of four bias correction methods, linear scaling (LS), power transformation (PT), general quantile mapping (GEQM), and gamma quantile mapping (GAQM) is assessed in downscaling GCM simulated precipitation. A random forest (RF) model is performed to generate the multi model ensemble (MME) of precipitation projections for four representative concentration pathways (RCPs) 2.6, 4.5, 6.0, and 8.5. The results showed that the best suited GCMs for climate projection of Syria are HadGEM2-AO, CSIRO-Mk3-6-0, NorESM1-M, and CESM1-CAM5. The LS demonstrated the highest capability for precipitation downscaling. Annual changes in precipitation is projected to decrease by −30 to −85.2% for RCPs 4.5, 6.0, and 8.5, while by < 0.0 to −30% for RCP 2.6. The precipitation is projected to decrease in the entire country for RCP 6.0, while increase in some parts for other RCPs during wet season. The dry season of precipitation is simulated to decrease by −12 to −93%, which indicated a drier climate for the country in the future.
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| 9. |
- Javadi, Ardalan, 1984, et al.
(författare)
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Active flow control of the vortex rope and pressure pulsations in a swirl generator
- 2017
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 11:1, s. 30-41
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Tidskriftsartikel (refereegranskat)abstract
- The vortex rope and pressure pulsations caused by a radial pressure gradient in the conical diffuser of a swirl generator is controlled using continuous slot jets with different momentum fluxes and angles injected from the runner crown. The swirl apparatus is designed to generate flows similar to those in the different operating conditions of a Francis turbine. The study is done with numerical modelling using the hybrid URANS-LES (Unsteady Reynolds-Averaged Navier–Stokes–Large Eddy Simulation) method with the rotor–stator interaction. The comprehensive studies of Javadi and Nilsson [Time-accurate numerical simulations of swirling flow with rotor–stator interaction. Flow, Turbulence and Combustion, Vol. 95, pp. 755–774], and Javadi, Bosioc, Nilsson, Muntean and Susan-Resiga [Experimental and numerical investigation of the precessing helical vortex in a conical diffuser, with rotor–stator interaction. ASME Journal of Fluids Engineering, doi:10.1115/1.4033416] are considered as the bench mark, and the capabilities of the technique is studied in the present work with the validated numerical results presented in those studies. The pressure pulsations caused by the pressure gradient generated by the swirl, present at off-design conditions, are cumbersome for hydropower structures. The investigation shows that the pressure pulsation, velocity fluctuations and the size of the vortex rope decrease when the jet is injected from the runner crown. The flow rate of the jet is less than 3% of the flow rate of the swirl generator. The momentum flux, angle of injection of the jet and the position of the slot are important factors for the effectiveness of the flow control technique.
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| 10. |
- Jianfeng, Lin, 1994, et al.
(författare)
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Hydrodynamic performance of a rim-driven thruster improved with gap geometry adjustment
- 2023
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- The hubless rim-driven thruster (RDT) has become increasingly interesting for ship propulsion. Gap flow has been proven as the main feature of RDT that cannot be simply neglected. In this study, based on a classical hubless RDT, the effects of the gap geometry are studied by adjusting its axial passage length, and inlet and outlet oblique angles. The hydrodynamic characteristics of the RDT were simulated with OpenFOAM based on the k – ω shear stress transport turbulence model. Due to the pressure increase after the main flow passes through the rotating blades, the flow inside gap is driven upstream, which is opposite to the main flow direction. It is found that the hydrodynamic efficiency is increased as the gap axial passage length is shortened, which is realized by increasing the oblique angle with the fixed inlet and outlet positions. Moving the inlet and outlet to further downstream and upstream positions has negligible effects on the hydrodynamic efficiency and leads to recirculating flow within the gap near its inlet. These findings shed light on the design of the gap geometry to improve the RDT hydrodynamic performance.
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