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You searched for +publisher:"EPFL" +contributor:("De Cesare, Giovanni"). Showing records 1 – 3 of 3 total matches.

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EPFL

1. Jenzer Althaus, Jolanda Maria Isabella. Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow.

Degree: 2011, EPFL

Reservoir sedimentation is worldwide a significant long term problem and requires in view of the current mitigation measures an alternative and more sustainable solution. This challenge motivated the present study with the purpose to develop an alternative efficient method to release sediment out of a reservoir. The concept is based on the release of sediment through the headrace tunnel and turbines whereby a special focus was set on the fine sediment in the area in front of the power intakes. Specific jet arrangements should provide the energy and generate the optimum circulation needed to maintain the sediment in suspension and enhance its entrainment into the power intakes during turbining sequences. This new idea was experimentally tested in a rectangular laboratory tank with the following dimensions: 2 m wide, 1.5 m high and 4 m long. Two jet configurations were systematically investigated: a configuration of four jets arranged in a circle on a horizontal plane and a linear jet configuration located parallel to the front wall. The influence of the jet characteristics (nozzle diameter dj, jet velocity vj, jet discharge Qj, and jet angle θ) and the geometrical configuration parameters on the sediment release was investigated. As initial condition an almost homogeneous sediment concentration distribution was induced by air bubbles. This condition simulated a muddy layer like in front of the dam by the fading of a turbidity current. The water level during all the experiments was held constant by releasing the same discharge through the water intake as was introduced by the jets (experiments with jets) or through the back wall (experiments without jets), respectively. Turbidity measurements combined with flow velocity measurements gave information about the sediment release efficiency. The sediment release (evacuated sediment ratio, ESR) is defined as the evacuated sediment weight Pout divided by the sediment weight initially supplied Pin and represents the normalized temporal integral of the released sediment amount: ESR = Pout/Pin. Analogously, the settled sediment ratio is the settled sediment divided by the sediment weight initially supplied Pin. Experiments without jets as reference configuration showed an almost linear relation between the sediment release and the discharge within the tested range: the higher the discharge, the higher the evacuated sediment ratio. For a constant discharge the ultimate sediment release as well as the settled sediment ratio was easily estimated by a simple physical approach taking into account the settling velocity and the flow field generated by the discharge through the water intake and the back wall. For the tested discharge range the sediment release was between 0.09 and 0.37 for … Advisors/Committee Members: Schleiss, Anton, De Cesare, Giovanni.

Subjects/Keywords: reservoir sedimentation; suspended sediment; sediment release; resuspension; circular jet arrangement; UVP-measurements; turbidity measurements; axial mixer-like flow pattern; radial mixer-like flow pattern; jet mixing; numerical simulation; physical experiments; hydro-power plants; turbidity current; sédimentation des réservoirs; sédiments en suspension; évacuation des sédiments; re-suspension; arrangement circulaire de jets; mesures UVP; mesures de turbidité; champs de vitesse de type mélangeur axial; champs de vitesse de type mélangeur radial; mélanges de jets; simulation numérique; expériences physiques; aménagements hydrauliques; courants de turbidité

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Jenzer Althaus, J. M. I. (2011). Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow. (Thesis). EPFL. Retrieved from http://infoscience.epfl.ch/record/154766

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Jenzer Althaus, Jolanda Maria Isabella. “Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow.” 2011. Thesis, EPFL. Accessed October 22, 2018. http://infoscience.epfl.ch/record/154766.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Jenzer Althaus, Jolanda Maria Isabella. “Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow.” 2011. Web. 22 Oct 2018.

Vancouver:

Jenzer Althaus JMI. Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow. [Internet] [Thesis]. EPFL; 2011. [cited 2018 Oct 22]. Available from: http://infoscience.epfl.ch/record/154766.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Jenzer Althaus JMI. Sediment Evacuation from Reservoirs through Intakes by Jet Induced Flow. [Thesis]. EPFL; 2011. Available from: http://infoscience.epfl.ch/record/154766

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


EPFL

2. Müller, Michael. Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs.

Degree: 2012, EPFL

Reservoir sedimentation and the resulting storage losses impact reliability, efficiency, safety and thus the sustainability of the hydropower schemes. Beside traditional storage hydropower plants, also pumped-storage facilities are affected. Flexible turbine and pump operations between two reservoirs allow demand-depending electricity production and absorption. Thus, they play a dominant role in peak load energy production as well as grid regulation. The storage volumes are influenced by continuous in- and outflow cycles. Their impact on sediment settling processes has not been addressed in research yet. Inspired by the cyclic, bidirectional water exchange of pumped-storage plants, a novel method for sediment removal from reservoirs was investigated in the present study. After high sediment yield into the reservoir, fine sediment should remain in suspension in front of the water intake due to the pumped-storage induced turbulence. Thus, the settling process may be delayed and sediment be evacuated by the power or flushing tunnels. In prototype measurements and laboratory experiments the influence of pumped-storage operations on flow patterns as well as the settling rates and sediment balance in two interconnected reservoirs has been studied. The two approaches were completed by numerical simulations. In the lower reservoir of a pumped-storage hydropower plant in the Swiss Alps, flow velocities in front of the intake/outlet were measured by Acoustic Doppler Current Profilers (ADCP). The devices with independent energy supply were implemented on the reservoir bottom and sampled 2D flow velocity profiles over several weeks. The measurements showed only local influence of pumping (outflowing water) near the intake, whereas turbine operations (inflowing water) induce large eddy flow fields in the reservoir. Depending on lake topography, patterns with backflow can appear. A frequency analysis of the discharge and flow velocity series indicated a corresponding main period between the flow velocity profiles and the in- and outflow cycles of 1 day. The ANSYS-CFD simulated flow fields corresponded to the in situ flow patterns. The computed turbulent kinetic energy input due to turbine operation was some 25 times higher than the natural input by wind-forcing. In the upstream part of the power shaft of the same hydropower scheme, a turbidity probe was installed for monitoring reasons. Over a period of eight months, sediment concentration of the operated water was continuously measured. An autonomous remote data acquisition and transfer system may be helpful for real-time monitoring by the hydropower operators. The measurements showed seasonal change of sediment concentration in the power system. In winter, high reservoir levels and ice-cover reduced sediment content, whereas in spring, snowmelt and low reservoir levels increased sediment yield. Short-term variations of sediment concentration up to 16% correlated with the in- and outflow cycles, especially for low reservoir filling. During the sampling period, about 45’000 t of… Advisors/Committee Members: Schleiss, Anton, De Cesare, Giovanni.

Subjects/Keywords: Reservoir sedimentation; suspended sediment; settling behavior; flow patterns; inand outflow cycles; prototype investigations; Acoustic Doppler Current Profilers; turbidity monitoring; laboratory experiments; cycle magnitude; cycle frequency; kinetic energy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Müller, M. (2012). Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs. (Thesis). EPFL. Retrieved from http://infoscience.epfl.ch/record/180650

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Müller, Michael. “Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs.” 2012. Thesis, EPFL. Accessed October 22, 2018. http://infoscience.epfl.ch/record/180650.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Müller, Michael. “Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs.” 2012. Web. 22 Oct 2018.

Vancouver:

Müller M. Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs. [Internet] [Thesis]. EPFL; 2012. [cited 2018 Oct 22]. Available from: http://infoscience.epfl.ch/record/180650.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Müller M. Influence of in- and outflow sequences on flow patterns and suspended sediment behavior in reservoirs. [Thesis]. EPFL; 2012. Available from: http://infoscience.epfl.ch/record/180650

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


EPFL

3. Adam, Nicolas Jean François Pascal Ghislain. Characterization of hydraulic behavior of orifices in conduits.

Degree: 2017, EPFL

High-head power plants are the main pillar of Swiss peak electricity production. With the 2050 Energy Strategy approved by Swiss voters, the annual production of hydroelectricity should increase by 4%, while 90% of the technically feasible potential is already used. The flexibility of high-head storage power plants may be improved by increasing the installed capacity or heightening existing dams in order to concentrate the electricity production during peak demand periods and for the critical winter supply,. These upgrades of existing hydropower plants can lead to more critical mass oscillations between the upstream reservoir and the surge tank, which is a hydraulic device allowing dampening of the fast change of discharge and reducing the consequences of water hammer in the pressure tunnel of high-head power plants. A simple way to reduce the amplitudes of the mass oscillations is to place an orifice at the entrance of the surge tank. Three different orifice geometries, chamfered, rounded orifices with a sharp side or two chamfered orifices, were systematically studied in conduits with laboratory experiments and numerical simulations in order to gain deeper knowledge of the behavior of orifices such as the steady and transient head losses, influence and reattachment length and the incipient cavitation number. Steady head losses were evaluated with both approaches. A catalog summarizes the produced head loss coefficients in the two different flow directions as a function of all the geometries. Furthermore, three different empirical relationships were developed in order to predict the head loss coefficient for a sharp, chamfer or rounded approach flows and to design orifices as throttle. On the one hand, the length of the zone disturbed by the orifice has been experimentally evaluated and increases with the orifice opening area. On the other hand, reattachment length has been numerically estimated and does not depend on the presence of a chamfer. Empirical formulas were derived to predict the two characterizing lengths. Transient experiments were performed on chamfered orifices and revealed a clear transient behavior that could account for up to 20% of the steady head losses. The global head losses were higher for accelerate flow and less for decelerate flow than the corresponding steady head losses. The incipient cavitation number was evaluated for chamfered orifices with single-phase computational fluid dynamics (CFD) simulations in order to develop predictive empirical relationships. This allowed for the assessment of the risk of cavitation. A cavitation number predicting the cavitation of the vena-contracta was also determined. A graphical view of the cavitation risk is suggested to evaluate the cavitation risk for surge throttles during mass oscillations. Finally, one-dimensional (1-D) numerical simulations were conducted with the numerical software Hydraulic System on an existing high-head power plant to determine the throttling effects on the whole waterway. Advisors/Committee Members: Schleiss, Anton, De Cesare, Giovanni.

Subjects/Keywords: High-head power plant; surge tank; throttle; orifice; steady head loss; influence length; reattachment length; transient head loss; incipient cavitation

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Adam, N. J. F. P. G. (2017). Characterization of hydraulic behavior of orifices in conduits. (Thesis). EPFL. Retrieved from http://infoscience.epfl.ch/record/232496

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Adam, Nicolas Jean François Pascal Ghislain. “Characterization of hydraulic behavior of orifices in conduits.” 2017. Thesis, EPFL. Accessed October 22, 2018. http://infoscience.epfl.ch/record/232496.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Adam, Nicolas Jean François Pascal Ghislain. “Characterization of hydraulic behavior of orifices in conduits.” 2017. Web. 22 Oct 2018.

Vancouver:

Adam NJFPG. Characterization of hydraulic behavior of orifices in conduits. [Internet] [Thesis]. EPFL; 2017. [cited 2018 Oct 22]. Available from: http://infoscience.epfl.ch/record/232496.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Adam NJFPG. Characterization of hydraulic behavior of orifices in conduits. [Thesis]. EPFL; 2017. Available from: http://infoscience.epfl.ch/record/232496

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.