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Rue, Switzerland

Mazzocchi E.,Ecole Polytechnique Federale de Lausanne | Pachoud A.J.,Ecole Polytechnique Federale de Lausanne | Farhat M.,Ecole Polytechnique Federale de Lausanne | Hachem F.E.,Stucky Ltd. | And 2 more authors.
Journal of Fluids and Structures | Year: 2016

Due to the increasing production of volatile new renewable energies as solar and wind, storage hydropower plants have to operate under harsh operation conditions in order to stabilize the electricity grid. As a result, highly transient water pressures occur in pressure tunnels and shafts more frequently. Non-intrusive monitoring techniques are therefore of special interest for these critical infrastructures. The propagation of a pressure wave generated actively by a cavitation bubble was experimentally investigated in a steel test pipe divided in several reaches. A local wall stiffness drop was simulated by replacing steel pipe reaches with less stiff materials as aluminum and PVC. Through the analysis of the pressure wave reflections due to the cavitation bubble explosion, recorded by two hydrophones placed at the extremities of the test pipe, the location of the weak reaches could be detected. An underwater spark generator was developed to produce cavitation bubbles in the pipe resulting in very steep shock waves. This allowed identifying very precisely the wave front and correspondingly the wave speed and the weak reach location. Compared to the wave analysis from water-hammer signals, the active cavitation bubble generation in the pipe is an innovative method that significantly increased the effectiveness of the detection of wall stiffness drops. © 2016 Elsevier Ltd. Source

Song J.-H.,University of South Carolina | Menouillard T.,Stucky Ltd. | Tabarraei A.,University of North Carolina at Charlotte
Mathematical Problems in Engineering | Year: 2013

A numerical method for dynamic failure analysis through the phantom node method is further developed. A distinct feature of this method is the use of the phantom nodes with a newly developed correction force scheme. Through this improved approach, fracture energy can be smoothly dissipated during dynamic failure processes without emanating noisy artifact stress waves. This method is implemented to the standard 4-node quadrilateral finite element; a single quadrature rule is employed with an hourglass control scheme in order to decrease computational cost and circumvent difficulties associated with the subdomain integration schemes for cracked elements. The effectiveness and robustness of this method are demonstrated with several numerical examples. In these examples, we showed the effectiveness of the described correction force scheme along with the applicability of this method to an interesting class of structural dynamic failure problems. © 2013 Jeong-Hoon Song et al. Source

Ribeiro M.L.,Stucky Ltd. | Pfister M.,Ecole Polytechnique Federale de Lausanne | Schleiss A.J.,Ecole Polytechnique Federale de Lausanne
Labyrinth and Piano Key Weirs II, PKW 2013 - Proceedings of the 2nd International Workshop on Labyrinth and Piano Key Weirs 2013 | Year: 2014

The interest in Piano Key weirs (PKW) was increasing over the past years, both in terms of application and hydraulic research. Several systematic model test series were performed and published so far, originating from different hydraulic laboratories around theworld. Therein, the key geometric parameters dominating the hydraulic capacity of PKWswere identified as developed crest length, transversal weir width, height of the walls and key widths. The present paper compares the available data-sets provided by several laboratories and as constructed on prototypes, partially including a systematic model testing of the relevant parameters. The present overview is based on the geometrical dimensions of the investigated and designed PKWs, without giving any hydraulic examination. ©2014 Taylor & Francis Group. Source

Tognola F.,Lombardi Engineering Ltd. | Balissat M.,Stucky Ltd.
Dams and Reservoirs under Changing Challenges - Proceedings of the International Symposium on Dams and Reservoirs under Changing Challenges - 79 Annual Meeting of ICOLD, Swiss Committee on Dams | Year: 2011

The new Muttsee Dam is part of the new pumped-storage power plant Limmern, presently under construction. With his 1000 MW installed capacity, this plant will be the largest pumped-storage power station in Switzerland. The plant includes a new underground powerhouse located close to the existing Limmern Arch Dam, at an altitude of about 1700 m a.s.l., and uses the about 600 m gross head between the Limmern reservoir (92 mio m 3) and the existing Muttsee natural lake. With the new dam at Muttsee the maximum water level of this natural lake will be raised up by 28 m. The live storage of the reservoir will be so increased from 9 mio to 24 mio m 3. The new dam is designed as a conventional gravity dam with 68 blocks of 15 m width each. The dam reaches a maximum height of 35 m, while the total concrete volume is 250'000 m 3. An ungated spillway extends over 5 dam blocks and is designed in order to release the maximal pumps discharge (160 m 3/s). The particular location of the dam in a high mountain area and the fact that the excavation material of the powerhouse shall be transported to the dam site by a cableway is particularly challenging from the logistic point of view. © 2011 Taylor & Francis Group. Source

Cekerevac C.,Stucky Ltd. | Laloui L.,Ecole Polytechnique Federale de Lausanne
Geotechnique | Year: 2010

This paper presents the results of an experimental study related to thermal effects on kaolin clay cyclic mobility. The thermal effects were identified by comparing the experimental results of cyclic triaxial tests performed at high temperature (90°C) with results of the same type of test carried out at ambient temperature (22°C). For the testing, a new temperature-controlled triaxial apparatus, developed by the authors, was employed. Experimental evidence shows that shear cycles on the heated samples induced smaller axial strain and pore-water pressure per cycle in comparison with the unheated samples. In addition, shear-induced pore-water pressure at large strains in the heated sample was slightly lower than in the unheated sample. In other words, the heated samples behaved as if they were denser, which is a result of thermal hardening. These results may be applied in geotechnical and earthquake engineering applications as a soil improvement technique. Source

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