Davide Wüthrich

Experimental Study of Tsunami-Like Waves Generated with a Vertical Release Technique on Dry and Wet Beds

Tsunamis, impulse waves, and dam failures are disasters that challenge humanity, often leading to massive casualties and extreme economic losses. The highly unsteady flow conditions generated by such events are often in the form of turbulent bores. The purpose of this study was to investigate and validate a new generation system for bores propagating over dry and wet bed conditions. There are multiple techniques to generate such waves experimentally, and the study focused on the generation of tsunami-like inundation conditions through the vertical release of a water volume. A detailed methodology to characterize the generated waves hydraulically, in terms of their wave heights and flow velocities, is presented, and good agreement with the classical dam-break case for both dry bed surges and wet bed bores was demonstrated. Because of the importance of estimating the impact forces induced by such waves, particular attention was given to the wavefront celerity and the velocity profiles measured behind the wavefront; these were found in agreement with Prandtls power law for open channel flows, and in-depth measurements allowed for the definition of an expression to estimate flow deceleration behind the wavefront. Along with considerations of the Froude number and momentum, this paper provides relevant information to assist engineers in designing safer infrastructures in areas prone to such extreme loading.

Experimental generation of tsunami-like waves

In the context of a comprehensive research project investigating the hydrodynamic loading on structures with openings, this paper focuses on the wave generation techniques currently used and the test results associated with it, proposing a particular tsunami-like wave using a vertical water volume release mechanism. The latter allowed a certain volume of water to flow gravitationally from an upper reservoir into a lower basin through a set of pipes. The propagation of the resulting wave took place in a horizontal channel where wave height and velocities were measured. Both dry bed surges and wet bed bores were investigated, however the present paper mostly focuses on dry bed surges. The study indicated that the surges generated with this mechanism had similar behavior to those resulting from a dam-break technique and a good agreement between the experimental points and the theoretical solutions of Ritter (1892) and Whitham (1955) was found. Lastly some differences between wet bed bores and dry bed surges are presented and briefly discussed herein.

Experimental study on the hydrodynamic impact of tsunami-like waves against impervious free-standing buildings

ABSTRACT Tsunamis, landslide-generated waves, and dam failures are rare, but highly destructive phenomena, associated with extreme loading on infrastructure. Recent events showed that specific measures must be taken to guarantee safety of both people and the built environment. This experimental study investigates the forces and moments exerted on free-standing buildings that are induced by both surges and bores. The hydrodynamic impact was characterized by high splash, subsequently followed by a quasi-steady flow around the structure. For dry bed surges, the time history of the horizontal force was proportional to the momentum flux per unit width. For wet bed bores, an attenuation of the peak force due to the presence of an aerated front was observed and the introduction of a reduction coefficient was necessary to achieve a realistic force estimation. Additional force analysis in terms of peak time, wave height at maximum force and impulse also pointed out some key differences between forces exerted by dry bed surges and wet bed bores. The occurrence of the maximum tilting moment on the building coincided with the maximum horizontal force and an evaluation of the cantilever arm was possible. These findings provide engineers with practical information for the design of safer coastal structures.

Hybrid Modelling Approach to Study Scour Potential at Chancy-Pougny Dam Stilling Basin

Chancy-Pougny is a run-of-river dam on the Swiss-French border constructed in the early 1920s. Since its inauguration, the operation of the four spillway gates was responsible for a progressive erosion of the stilling basin. Thus, a hybrid modelling was performed to study the scour potential and to determine adequate solutions to maintain future scour within acceptable levels. Visual observations on the physical model identified a strong recirculation in the non-symmetrical basin, that combined with the outflow from the spillway gate, lead to an enhanced specific discharge and to the formation of a turbulent vortex impacting the rocky foundation. Some measures to limit the recirculation, including a free-standing wall and various configurations of concrete prisms for scour protection, were tested on both the physical and numerical model. The pressure and water depth measurements resulting from the physical model were used within the numerical model to determine the corresponding scour potential for each of the tested mitigation measures. A solution containing a layer of randomly distributed concrete prisms laid on the basin’s current bottom was identified through this study, proving the importance of both numerical and physical approaches in hydraulic engineering

Protection de la fosse de dissipation du barrage de Chancy-Pougny avec prismes en béton

Davide WÜTHRICH, Sabine CHAMOUN, Giovanni DE CESARE, Anton J. SCHLEISS 1 Laboratoire de Constructions Hydrauliques (LCH), Ecole Polytechnique Fédérale de Lausanne, Suisse Station 18, 1015 Lausanne, Switzerland – davide.wuthrich@epfl.ch 2 Laboratoire de Constructions Hydrauliques (LCH), Ecole Polytechnique Fédérale de Lausanne, Suisse Station 18, 1015 Lausanne, Switzerland – sabine.chamoun@epfl.ch 3 Laboratoire de Constructions Hydrauliques (LCH), Ecole Polytechnique Fédérale de Lausanne, Suisse Station 18, 1015 Lausanne, Switzerland – giovanni.decesare@epfl.ch 4 Laboratoire de Constructions Hydrauliques (LCH), Ecole Polytechnique Fédérale de Lausanne, Suisse Station 18, 1015 Lausanne, Switzerland – anton.schleiss@epfl.ch