| 1. |
- Camenen, Benoit, et al.
(författare)
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Accuracy of Equivalent Roughness Height Formulas in Practical Applications
- 2013
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Ingår i: Journal of Hydraulic Engineering. - 1943-7900. ; 139:3, s. 331-335
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a discussion on the application and accuracy of roughness height formulas from a practical point of view. Such formulas have been proposed to describe the equivalent roughness height for plane bed conditions on the basis of the Shields parameter. The application of these relationships requires an iterative solution technique. However, as this paper demonstrates, the roughness estimates are not always reliable because the application of the formulas yields large discrepancies in the results. DOI: 10.1061/(ASCE)HY.1943-7900.0000670. (C) 2013 American Society of Civil Engineers.
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| 2. |
- Borell Lövstedt, Charlotta, et al.
(författare)
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Wave Damping in Reed: Field Measurements and Mathematical Modeling
- 2010
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Ingår i: Journal of Hydraulic Engineering. - 1943-7900. ; 136:4, s. 222-233
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Tidskriftsartikel (refereegranskat)abstract
- Wave damping in vegetation in shallow lakes reduces resuspension and thereby improves the light climate and decreases nutrient recycling. In this study, wave transformation in reed (Phragmites australis) was measured in a shallow lake. Theoretical models of wave height decay, based on linear wave theory, and transformation of the probability density function (PDF), using a wave-by-wave approach, were developed and compared to the collected data. Field data showed an average decrease in wave height of 4–5% m/sup -1sup/ within the first 5–14 m of the vegetation. Incident root-mean-square wave height was 1–8 cm. A species-specific drag coefficient CD was found to be about 9 (most probable range: 3–25). CD showed little correlation with a Reynolds number or a Keulegan-Carpenter number. The PDF for the wave heights did not change significantly, but for longer distances into the vegetation and higher waves it tended to be more similar to the developed transformed distribution than to a Rayleigh distribution. Relationships developed in this study can be employed for management purposes to reduce resuspension and erosion.
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| 3. |
- Zhang, Jie, et al.
(författare)
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Simple Methods for Direct Computation of Bed Roughness due to Sediment Transport
- 2021
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Ingår i: Journal of Hydraulic Engineering. - 1943-7900. ; 147:8
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this technical note is to present methods that allow for direct computation of the bed roughness due to sediment transport based on a formula developed in the literature for cases involving current or waves separately. The methods result in approximate nondimensional expressions for the exact solutions in terms of polynomials determined by least-square fits, where the accuracy of the polynomials is high. Using the present methods may significantly reduce calculation times of roughness due to sediment transport in numerical models of morphological change.
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| 4. |
- Pitorac, Livia, et al.
(författare)
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Hydraulic Scale Modeling of Mass Oscillations in a Pumped Storage Plant with Multiple Surge Tanks
- 2022
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Ingår i: Journal of Hydraulic Engineering. - : American Society of Civil Engineers (ASCE). - 0733-9429 .- 1943-7900. ; 148:9
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Tidskriftsartikel (refereegranskat)abstract
- As power systems include more intermittent renewable energy sources, energy storage solutions are needed to support them. Pumped hydro is a reliable alternative for long-term energy storage. A solution for bringing more pumped hydro into the power system is to upgrade existing hydropower plants into pumped hydro. To investigate this possibility, a case study with a complex tunnel system and multiple surge tanks along both the headrace and the tailrace tunnels is selected. A hydraulic scale model and validation methods were developed. The challenges in developing and validating complex models involving multiple surge tanks, throttles, head loss, and limited prototype information are detailed.
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| 5. |
- Teng, Penghua, 1987-, et al.
(författare)
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Modeling and Prototype Testing of Flows over Flip-Bucket Aerators
- 2018
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Ingår i: Journal of Hydraulic Engineering. - : ASCE-AMER SOC CIVIL ENGINEERS. - 0733-9429 .- 1943-7900. ; 144:12
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Tidskriftsartikel (refereegranskat)abstract
- The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water-air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.
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| 6. |
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| 7. |
- Camenen, Benoit, et al.
(författare)
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Equivalent roughness height for plane bed under steady flow
- 2006
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Ingår i: Journal of Hydraulic Engineering. - 1943-7900. ; 132:11, s. 1146-1158
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new relationship between the roughness height and the main hydrodynamic and sediment parameters for plane beds under steady current conditions. In order to derive such a formula, a large data base involving plane-bed experiments was compiled from previous investigations and analyzed. Comparisons between the data and different existing predictive formulas for the bed roughness obtained from the literature were also made. A relationship with the Shields parameter only, which is commonly proposed, appeared to be insufficient. The roughness was also found to be a function of a Froude number and a dimensionless settling velocity. A critical Shields parameter was identified up to which the equivalent roughness ratio is proportional to the Shields parameter. The new empirical equation that was developed yields the best results for all conditions investigated, and should improve the understanding of the total shear stress.
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| 8. |
- CASTELLARIN, A, et al.
(författare)
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Optimal Cross-Sectional Spacing in Preissmann Scheme 1D Hydrodynamic Models
- 2009
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Ingår i: Journal of Hydraulic Engineering. - 0733-9429 .- 1943-7900. ; 135:2, s. 96-105
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Tidskriftsartikel (refereegranskat)abstract
- Choosing a suitable set of cross sections for the representation of the natural geometry of a river is important for the efficiency of one-dimensional (1D) hydraulic models, but only few guidelines are available for the selection of the most suitable distance between cross sections, depending on the hydraulic problem at hand. This issue is investigated by examining models of a ∼55km reach of the River Po, Italy, and a ∼16km reach of the River Severn, United Kingdom, for both of which high quality laser scanning altimetry are available. The high-resolution digital terrain models of the two river reaches enabled the construction of a series of hypothetical topographical ground surveys with different spacing between cross sections, which could be used as input to a standard 1D model (UNET). Both historical and synthetic flood events for the two river reaches were simulated, and the results were then analyzed to quantify the accuracy associated with each resolution and to assess how survey resolution impacts the performance of standard 1D models. The study results agree with the available suggestions in the literature and provide useful guidelines for 1D hydrodynamic modeling.
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| 9. |
- Dargahi, Bijan, Assoc. Prof.
(författare)
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Controlling Mechanism of Local Scouring
- 1990
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Ingår i: Journal of Hydraulic Engineering. - : American Society of Civil Engineers (ASCE). - 0733-9429 .- 1943-7900. ; 116:10, s. 1197-1214
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Tidskriftsartikel (refereegranskat)abstract
- Experimental study of clear water scouring around a circular cylinder shows that the scour mechanism is coupled to the three‐dimensional separation of the upstream boundary layer and the periodic vortex shedding in the wake of the cylinder. The first scour appears in the wake of the cylinder. The main scouring agent in the upstream region is a system of horseshoe vortices. The vortices have a periodical character that causes a triple‐scour profile to develop in the upstream region. During scouring, the number and periods of horseshoe vortex shedding undergo no appreciable change. Despite the clear water stage, the transport phenomenon is periodical. Transport of sediment takes place through turbulent scales of comparable size to macro‐length scales. The size of the horseshoe vortices are representative for the macroscale. Wake scouring is caused by the primary wake vortices and the accelerated side flow. The process is characterized by a strong periodical transport and the formation of ripples. The periodicity is controlled by the shedding frequency of the wake vortices. Collars attached to the cylinder cannot prevent the formation of the vortices.
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| 10. |
- Dargahi, Bijan
(författare)
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Experimental study and 3D numerical simulations for a free-overflow spillway
- 2006
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Ingår i: Journal of Hydraulic Engineering. - : American Society of Civil Engineers (ASCE). - 0733-9429 .- 1943-7900. ; 132:9, s. 899-907
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Tidskriftsartikel (refereegranskat)abstract
- The main objectives of the present work were to investigate the flow field over a spillway and to simulate the flow by means of a three-dimensional (3D) numerical model. Depending on the wall curvature, the boundary layer parameters decreased or increased with increasing distance along the spillway. The growth of the boundary layer along the spillway is better described as a function of Reynolds number than the normalized streamwise length. A simplified form of the 3D momentum equation can be used to obtain a rough estimate of the skin friction. The velocity profile in the boundary layer along the spillway is described by a velocity-defect relationship. Numerical models provide a cost-effective means of simulating spillway flows. In this study, the water surface profiles and the discharge coefficients for a laboratory spillway were predicted within an accuracy range of 1.5-2.9%. The simulations were sensitive to the choice of the wall function, grid spacing, and Reynolds number. A nonequilibrium wall function with a grid spacing equal to a distance of 30 wall units gave good results.
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