Onde

Résumé

vignette|Propagation d'une onde. Une onde est la propagation d'une perturbation produisant sur son passage une variation réversible des propriétés physiques locales du milieu. Elle se déplace avec une vitesse déterminée qui dépend des caractéristiques du milieu de propagation. vignette|Une vague s'écrasant sur le rivage. Il existe trois principaux types d'ondes :

les ondes mécaniques se propagent à travers une matière physique dont la substance se déforme. Les forces de restauration inversent alors la déformation. Par exemple, les ondes sonores se propagent via des molécules d'air qui entrent en collision avec leurs voisines. Lorsque les molécules entrent en collision, elles rebondissent aussi l'une contre l'autre. Cela empêche alors les molécules de continuer à se déplacer dans la direction de la vague ;
les ondes électromagnétiques ne nécessitent pas de support physique. Au lieu de cela, elles consistent en des oscillations périodiques de champs électriques et magnétiques g

Source officielle

https://fr.wikipedia.org/wiki/Onde

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A design of a wave pool for surfing is defined in this work. The geometry is designed in order to optimize the relatively small area available for the project. The bathymetry is suited to the different levels of surfers. A wave generation system composed of aligned plungers is selected in view of minimizing energy consumption and not infringing the patents registered. A 3D model on the CFD software Flow-3D is produced in accordance with the theory to confirm the results obtained. A lateral energy dispersion effect is observed which leads to a non-uniform generated wave height. An estimate of the energy efficiency and cost per wave is calculated, and a study of the main environmental impacts is made.

2020

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Single-molecule imaging methods are of importance in structural biology, and specifically in the imaging of proteins, since they can elucidate conformational variability and structural changes that might be lost in imaging methods relying on averaging processes. Low-energy electron holography (LEEH) is a promising technique for imaging individual proteins with negligible radiation damage, which can be combined with a sample preparation process by native electrospray ion beam deposition (native ES-IBD) ensuring the creation of chemically pure samples suitable for holographic imaging.The central step in the analysis of data measured by LEEH is the numerical reconstruction of the object from the experimentally acquired holograms.Full information about the imaged object consists of both amplitude and phase information imprinted on the scattered wave during the interaction of the electron beam with the molecule and encoded in the hologram created by the interference of the scattered wave and the transmitted incident wave. A propagation-based algorithm with the goal of reconstructing the wave field in the plane of the object is presented and applied to holograms of individual proteins prepared by ES-IBD and measured with a low-energy electron holography microscope. The information retrieved from the reconstruction of the amplitude distribution in the object plane is discussed by analysing holograms of antibodies, demonstrating that the inherent conformational variability of these molecules can be mapped by LEEH. The influence of the sample preparation process on the surface conformations is tracked by tuning the landing energy of the proteins during deposition.To complement the amplitude data, an iterative phase retrieval algorithm is implemented to reconstruct the phase distribution in the object plane along with the amplitude distribution. The algorithm's performance and robustness is thoroughly evaluated and simulations regarding multiple scattering effects and element-dependent variations in scattering strength are carried out to provide a reference for the interpretation of phase data retrieved from experimentally acquired holograms. The iterative phase retrieval algorithm is then applied to protein data, indicating that both molecular density and charges can be related to features in the phase reconstructions, while the presence of metals does not correlate with specific phase signals at the current resolution obtainable from the experimental data.Since proteins are inherently three-dimensional, approaches towards three-dimensional reconstruction schemes are discussed, which will be the focus of future work.

EPFL2022

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Structural Response of ‘’La Jument’’ Lighthouse under Extreme Wave Loading – Analysis and Concept of Maintenance

Nizar Jaber

Ancient off-shore lighthouses have a phenomenal cultural significance. They were built as physical aid for navigation to guide mariners and to warn them from dangerous shallow rocky reefs. Understanding their structural response under waves loading is a challenging task. La Jument lighthouse, off the coast of Brittany, has sustained extreme environmental loading for more than 110 years. The main motivation of the present study is to characterize its structural response under extreme waves loading by 3D Finite Element Modeling using the commercial software DIANA. The model is calibrated based on the data collected from accelerometers and photographical documentations during a measurement campaign in winter 2018 in which the highest wave recorded with 19 meters height is considered for this study. The effect on the lighthouse’s structural response of slamming pressure magnitude, tide level, and slamming area is investigated in a parametric study. The predictions of the FE model were comparable to the actual measurements confirming the main hypothesis in this study. The tide level was proven to be an important factor contributing to the structural response parameters. The FE model suggested 230 kPa as the most likely pressure of the wave under consideration. Moreover, intervention methods using UHPFRC combined with a measurement campaign are proposed to preserve the outstanding cultural significance of La Jument lighthouse. Extending the life of off-shore lighthouses is essential to understand non-linear characteristics of extreme waves in future field measurements which helps validating numerical computations and removing uncertainties about their dynamic behavior.

2022

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EPFL2022