The Experts below are selected from a list of 10506 Experts worldwide ranked by ideXlab platform
Timothy G. Fisher - One of the best experts on this subject based on the ideXlab platform.
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abandonment chronology of glacial lake agassiz s northwestern outlet
Palaeogeography Palaeoclimatology Palaeoecology, 2007Co-Authors: Timothy G. FisherAbstract:Abstract Spillway scour lakes and basins in northwestern Saskatchewan were cored to determine when the Spillways were abandoned. The cores contained the target contact of organic muck (gyttja) overlying inorganic sand or silty-clay rhythmites. New AMS radiocarbon dates on terrestrial macrofossils, in conjunction with previously published and unpublished data from the area, indicate that the Spillways were abandoned between 9.07 and 9.59 14C kyr BP (10,220–10,810 cal yr BP). Of great interest is whether the channels are associated with northwestern drainage from glacial Lake Agassiz. The radiocarbon ages recording Spillway abandonment are consistent with previous work, which claims that overflow through the northwestern outlet ended ∼ 9.5 14C kyr BP (10,700 cal yr BP); this is consistent with shifting drainage to the southern outlet at this time. The scarcity of dates from the northwestern outlets and other outlets of Lake Agassiz underscores the need to establish a tighter chronological control on outlet switching before outburst flooding from Lake Agassiz can be assumed to be the trigger for abrupt climate change.
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river warren boulders minnesota usa catastrophic paleoflow indicators in the southern Spillway of glacial lake agassiz
Boreas, 2004Co-Authors: Timothy G. FisherAbstract:Boulders resting on meltwater-sculpted and striated-granite bedrock near the head of the southern outlet Spillway of glacial Lake Agassiz are used to generate paleodischarge calculations. The rounded nature of many boulders suggests fluvial transport and a corestone origin. The distribution of boulders in clusters and linear trains records the interaction of clasts during transport and deposition. The geomorphology of the Spillway with streamlined erosional remnant hills is characteristic of other large flood Spillways. Using the Manning equation and a variety of empirical equations to determine paleovelocity, preferred discharges between 0.364 and 0.102 Sv are calculated. These discharges agree well with flood discharges using modeling methodologies, and most likely represent ephemeral and catastrophic flood events linked to either episodic incision at the outlet or the result of rapid inputs of meltwater to Lake Agassiz.
Hubert Chanson - One of the best experts on this subject based on the ideXlab platform.
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optical flow estimations in aerated Spillway flows filtering and discussion on sampling parameters
Experimental Thermal and Fluid Science, 2019Co-Authors: Matthias Kramer, Hubert ChansonAbstract:Image-based velocimetry captured a great interest in physical modelling of highly-aerated flows, for example in stepped Spillways. The present study investigated the performance of a novel filtering technique based upon a detailed systematic comparison with intrusive phase-detection probe data. All measurements were conducted in a large-size stepped Spillway. A sensitivity analysis provided recommendations in terms of optimum sampling and processing parameters for optical flow measurements in high-velocity air-water flows.
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discussion of cavitation potential of flow on stepped Spillways by k warren frizell floriana m renna and jorge matos
Journal of Hydraulic Engineering, 2015Co-Authors: Hubert ChansonAbstract:The authors presented a very interesting contribution to the topic of stepped Spillway hydrodynamics. Based on a water-tunnel study, they presented some detailed flow features, for example, in terms of the strain rate, which are valuable to designers. The authors stated that “stepped Spillways have no documented damage.” It is partially correct. Indeed no cavitation damage and sign of cavitation pitting were reported on stepped Spillways after more than 3,000 years of operation, but there were documented damages and failures of stepped Spillway systems (Marsh 1957; Jansen 1983; Pravdivets 1993; Chanson 1995b, 2000, 2001a). In this discussion, a number of prototype stepped Spillway tests are reviewed and the operational experiences are discussed with a focus on the stepped chute performances. Several prototype stepped Spillway tests were conducted in China, Russia, Germany, the United Kingdom, and Africa. Some extensive tests were performed on the Dachaoshan rollercompacted concrete (RCC) Dam Spillway in 2002 with discharge per unit width up to 72 m=s (Lin and Han 2001; K. Lin, personal communication, 2002, 2012). Detailed inspections after each series of test indicated no damage or any sign of pitting. A series of tests conducted at the Dnieper hydroplant were performed with discharges per unit width up to 59.4 m=s, velocities up to 23 m=s, a step height of 0.405 m, and water depths between 0.5 and 3 m (Grinchuk et al. 1977). No damage was reported. Full-scale tests were undertaken in the Sorpe Dam Spillway in 2002–2003 to investigate some jump-wave instabilities (P. Kamrath, personal communication, 2003). Some field tests were conducted successfully on the Brushes Clough Dam Spillway in the United Kingdom up to 1 m=s, although for a short duration (Baker 1994). Some inspection of the M’Bali RCC Dam stepped Spillway after a wet season operation showed no sign of damage and pitting (Bindo et al. 1993). Further, a number of prototype overflow events were documented worldwide (Chanson 1995b, 2001b). In China, the
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effects of step pool porosity upon flow aeration and energy dissipation on pooled stepped Spillways
Journal of Hydraulic Engineering, 2014Co-Authors: Hubert ChansonAbstract:AbstractThe hydraulics of stepped Spillways with flat steps has been studied for the last three decades, including for embankment dam slopes, but studies of alternative stepped designs are limited. In this study, a pooled stepped Spillway was investigated in a relatively large-size facility, and three different pool wall porosities were tested. The flow patterns, the macro- and microscopic air-water flow properties, and the energy dissipation performances were recorded; the results were compared with the flat stepped Spillway design for the same chute slope (θ=26.6°). The investigations highlighted a close agreement between air-water flow properties on the configurations in terms of void fraction, turbulence levels, bubble count rate, and chord sizes. The interfacial velocity distributions showed larger interfacial velocity on the pooled step configurations of approximately 5–10% linked with a reduced flow depth. On the porous pooled stepped Spillways, the interfacial velocities within the cavity highligh...
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Embankment dam Spillways and energy dissipators
2014Co-Authors: Hubert ChansonAbstract:For the last fifty years, the design floods of a number of embankment dams were re-evaluated and the revised Spillway outflows are often larger than the original design discharges. Several embankment overtopping protection systems were developed for earthfill structures, and the applications range from river dykes to tsunami protections including embankment dams. Well- known designs include timber cribs, sheet-piles, riprap and gabions, reinforced earth, minimum energy loss (MEL) weirs, embankment overflow stepped Spillways and the precast concrete block protection systems. In this review, several design techniques are reviewed and discussed based upon prototype experiences. A critical analysis of their performances highlights that a safe operation of embankment dam Spillways and associated energy dissipators relies upon a sound design and a good quality of construction, suitable flow conditions, together with regular maintenance
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aeration flow instabilities and residual energy on pooled stepped Spillways of embankment dams
Journal of Irrigation and Drainage Engineering-asce, 2013Co-Authors: Stefan Felder, Hubert ChansonAbstract:AbstractAir-water flow experiments were conducted on some flat and pooled stepped Spillways with slopes of 8.9° and 26.6° in transition and skimming flows. The study comprised the observations of the flow patterns, characteristic air-water flow properties, and energy dissipation performances. The air-water flow properties showed some differences in terms of interfacial velocity, bubble count rate, and turbulence intensity between the stepped chutes for the two channel slopes. These differences were also reflected in the residual energy data, highlighting a better energy dissipation rate for the pooled stepped Spillway with slope of 8.9°. However, the aerated flows on the pooled stepped Spillways exhibited some hydrodynamic instabilities, and a safe operation must be tested in physical models. The flat stepped Spillway appeared to be the preferable design in terms of energy dissipation and flow stability.
Jorge Matos - One of the best experts on this subject based on the ideXlab platform.
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Cavitation Potential of Flow on Stepped Spillways
Journal of Hydraulic Engineering, 2013Co-Authors: Kathleen H. Frizell, Floriana Maria Renna, Jorge MatosAbstract:AbstractCavitation on Spillways has proven to be an undesirable condition. The formation of vapor-filled bubbles and cavities and their eminent collapse has led to significant damage to major Spillway components and appurtenant structures worldwide. Although stepped Spillways are thought to be less prone to cavitation damage than smooth Spillways, designers continue conservative practices regarding specifying stepped Spillways at many sites. Using laboratory experiments in a specialized reduced ambient pressure chamber, cavitation was shown to form on stepped geometries that are representative of typical stepped Spillways currently in service. Experiments in a nonaerated closed conduit revealed the strength and extents of the highly intense shear layer that forms above the step tips, and the friction characteristics were determined and compared with results from previous researchers. Advanced techniques for detecting cavitation characteristics along with high-speed videography have given additional insigh...
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Laboratory measurements and multi-block numerical simulations of the mean flow and turbulence in the non-aerated skimming flow region of steep stepped Spillways
Environmental Fluid Mechanics, 2011Co-Authors: Fabián A. Bombardelli, Ines Meireles, Jorge MatosAbstract:We present and discuss the results of a comprehensive study addressing the non-aerated region of the skimming flow in steep stepped Spillways. Although flows in stepped Spillways are usually characterized by high air concentrations concomitant with high rates of energy dissipation, the non-aerated region becomes important in small dams and/or Spillways with high specific discharges. A relatively large physical model of such Spillway was used to acquire data on flow velocities and water levels and, then, well-resolved numerical simulations were performed with a commercial code to reproduce those experimental conditions. The numerical runs benefited from the ability of using multi-block grids in a Cartesian coordinate system, from capturing the free surface with the TruVOF method embedded in the code, and from the use of two turbulence models: the $${k{-}\varepsilon}$$ and the RNG $${k{-}\varepsilon}$$ models. Numerical results are in good agreement with the experimental data corresponding to three volumetric flow rates in terms of the time-averaged velocities measured at diverse steps in the Spillway, and they are in very satisfactory agreement for water levels along the Spillway. In addition, the numerical results provide information on the turbulence statistics of the flow. This work also discusses important aspects of the flow, such as the values of the exponents of the power-law velocity profiles, and the characteristics of the development of the boundary layer in the Spillway.
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skimming flow in the nonaerated region of stepped Spillways over embankment dams
Journal of Hydraulic Engineering, 2009Co-Authors: Ines Meireles, Jorge MatosAbstract:Traditionally, research on stepped Spillway hydraulics has been focused on the air-water flow region but for the hydraulic design of small embankment dams experiencing relatively large overtopping flows, the nonaerated region can be very important. Empirical formulas are presented for predicting skimming flow properties upstream of the point of inception of air entrainment for 1V:2H sloping stepped Spillways, and the location and flow depth at the point of inception. Particular emphasis is placed on the clear-water depth, velocity distribution, and the energy dissipation characteristics in the developing nonaerated flow region. The velocity distribution is well described by a power law. The normalized clear-water depth and the normalized specific energy varied with the relative distance along the Spillway and the effect of the normalized critical depth was negligible. Finally, the rate of energy dissipation was small, which has direct implications for the design of the downstream energy dissipator.
Mazen R Tabbara - One of the best experts on this subject based on the ideXlab platform.
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computational modeling of flow over an ogee Spillway
Computers & Structures, 2004Co-Authors: Jean G Chatila, Mazen R TabbaraAbstract:Abstract This paper presents an investigation into the hydraulics of regular ogee-profile Spillways. The free-surfaces of the fluid for several flow heads as measured in the hydraulics laboratory are used as benchmarks. The finite element computational fluid dynamics software, ADINA, was used to predict the free surface over an ogee Spillway and thus model the flow field. Since the actual flow is turbulent the k–e flow model was used. For the cases considered in this paper, ADINA predicted reasonable free surface results that are consistent with general flow characteristics over Spillways. The results are also in close agreement with measured free-surface profiles over the entire length of the Spillway.
P. B. Deolalikar - One of the best experts on this subject based on the ideXlab platform.
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flow characteristics of orifice Spillway aerator numerical model studies
ISH Journal of Hydraulic Engineering, 2015Co-Authors: V. Jothiprakash, V. V. Bhosekar, P. B. DeolalikarAbstract:Orifice Spillways are provided in dams situated in hilly regions for carrying out dual function of passing the flood and flushing of sediments. Aerators are required on these Spillways for mitigating cavitation damage for head over Spillway exceeding 50 m. The available current literature describes mainly the investigations for aerators on overflow Spillways and no systematic work has been reported for aerators on orifice Spillways. Traditionally, physical model studies have been used for designing the aerators on overflow Spillways. However, extensive experimentation with sophisticated instrumentation is required to understand the flow field comprising pressure and velocity distribution and air entrainment characteristics. Numerical modelling using computational fluid dynamic techniques provides a complete picture on flow field in the vicinity of aerator. This study describes numerical simulation of flow over an aerator on deep-seated orifice Spillway. The two-phase three-dimensional (3D) numerical model...
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Orifice Spillway Aerator: Hydraulic Design
Journal of Hydraulic Engineering, 2012Co-Authors: V. V. Bhosekar, V. Jothiprakash, P. B. DeolalikarAbstract:AbstractOrifice Spillways are in vogue for the dams in the hilly regions where the Spillway has to serve the dual function of flood disposal and flushing of sediment through the reservoir. Deep-seated orifice Spillways are subjected to cavitation damage as the cavitation index drops below the critical cavitation index of 0.2 because of negative pressures on the profile and high flow velocities. Aerators are provided for mitigating cavitation damage. Design guidelines for aerator of orifice Spillways are scanty and not reported much in the literature so far; thus, there still remains gray area in the field of Spillway aerator design. The present study investigates the performance of an offset aerator with and without a ramp for deep-seated orifice Spillway on a physical and numerical model. Performance of the aerator for varying discharges, heads, and gate openings is studied for varying cavity subpressures. Results with respect to jet length, cavity subpressure and air entrainment coefficients are present...
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modeling hydrodynamic flow over Spillway using weakly compressible flow equations
Journal of Hydraulic Research, 2007Co-Authors: T I Eldho, M R Bhajantri, P. B. DeolalikarAbstract:Spillway hydrodynamics can be obtained through physical modeling or numerical modeling. Physical modeling of Spillway is expensive, cumbersome and time consuming. Numerical simulation of rapidly varied, supercritical, free surface turbulent flow over Spillway with all flow regimes is a challenging task. This paper explains the formulation and development of a numerical model based on weakly compressible flow equations for flow over Spillway. The developed model is used to investigate the hydraulic characteristics of flow over Spillway crest profile by simulating the velocity distribution, pressure distribution and discharge characteristics. The developed numerical model was applied to the two different types of Spillways. First Spillway studied is a surface Spillway with broad crested parabolic downstream crest profile. The second Spillway investigated is sluice Spillway, which is a submerged type of Spillway. The numerical results were compared with the respective physical model results. Good agreement i...
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hydrodynamic modelling of flow over a Spillway using a two dimensional finite volume based numerical model
Sadhana-academy Proceedings in Engineering Sciences, 2006Co-Authors: T I Eldho, M R Bhajantri, P. B. DeolalikarAbstract:Spillway flow, a classical problem of hydraulics, is generally a gravity-driven free surface flow. Spillway flows are essentially rapidly varying flows near the crest with pronounced curvature of the streamlines in the vertical direction. Two processes simultaneously occur in the flow over the crest, that is, formation and gradual thickening of the turbulent boundary layer along the profile, and gradual increase in the velocity and decrease in the depth of main flow. Spillway hydrodynamics can be obtained through physical modelling or numerical modelling. Physical modelling of Spillways is expensive, cumbersome and time-consuming. The main difficulties in solving the Spillway problem numerically are: rapidly varying flow, existence of both subcritical and supercritical flows, development of turbulent boundary layers, unknown free surface and air entrainment. Numerical simulation of such flows over Spillways in all flow regimes is a challenging task. This paper describes a numerical model and its application to a case study to investigate the hydraulic characteristics of flow over Spillway crest profiles by simulating the velocity distribution, pressure distribution and discharge characteristics. Results of the numerical modelling are compared with those from the physical modelling and found to be satisfactory.
