Mécanique (technique) | EPFL Graph Search

La mécanique en tant que technique ou activité industrielle, est l'ensemble des activités, méthodes et techniques liées à la conception de structures (charpentes, coques, bâtis), machines ou de mécanismes. Ces activités regroupent l'étude, la conception, la fabrication, la maintenance et la déconstruction de toute structure ou dispositif (moteurs, véhicules) produisant ou transmettant un mouvement, une force, ou une déformation. On parle ainsi de génie mécanique, de mécanique automobile, de mécanique navale Historique Histoire de la mécanique Si la préhistoire de la construction mécanique se confond avec l’histoire de l’humanité son essor ne débute qu'à l'ère moderne. Il importe de distinguer la mécanique en tant que science de la mécanique en tant que technique. La première apparaît dès l'Antiquité, chez les Grecs, Archimède et Aristote pouvant être considérés comme les premiers grands mécaniciens de l'histoire. Lors de la Renaissance apparaissent les premiers ingéni

Fluid mechanics of intrathecal drug delivery

Radboud Michael Nelissen

The aim of this principally experimental study is to understand from fluid mechanic principles why an insignificant anesthetic dose administered as a short bolus into the cerebrospinal fluid inside the subarachnoid space provides greater pain relief than a larger dose continuously injected over a longer period. The subarachnoid space is modeled as an annular gap of constant or slowly varying cross section into which a catheter is introduced. The cerebrospinal fluid is replaced by water of 37°C which has very similar properties. This fluid in the annular gap is subjected to oscillations of amplitude and frequency (heart frequency) typically found in the subarachnoid space. The anesthetic is replaced by a fluorescent dye injected through the catheter. To study its dispersion, we have developed a 400 Hz laser scanning setup with which we perform quasi-instantaneous, quantitative 3D laser induced fluorescence (LIF) as well as 2D particle image velocimetry (PIV). The experiments are supplemented by an analytical axi-symmetric model as well as an exploratory numerical model to help interpret the results. The study has identified steady streaming (a nonlinear effect associated with the fluid oscillation) and enhanced diffusion (an effect associated with oscillating shear flow) as the principal agents of dye (anesthetic) dispersion. Besides the slowly varying cross section, the catheter tip has been identified as an important cause for steady streaming. In an attempt to identify optimal injection parameters of use for clinicians, a rough parametric model of the primary factors influencing drug spread (fluid oscillation frequency and amplitude, geometry, and injection rate) has been constructed.

EPFL2008

Mechanical characteristics of Swiss molassic formations

Mustapha Gencer, Jean-François Mathier

The Molasse is a geologic formation which covers most part of the Swiss plateau. This sedimentary formation is constituted by various types of rock such as sandstones, marls (claystones) and siltstones. The Rock Mechanics Laboratory (LMR) of the EPFL has a great number of test results (uniaxial, triaxial and Brazilian tensile strength) on various types of Molasse. The obtained results related to the lithological characteristics of this formation were statistically analyzed in order to define correlations between the different mechanical properties of these rocks. The parameters of the failure strength criteria according to Hoek-Brown and Mohr-Coulomb have been estimated for different components of Swiss Molasse.

CRC Press2013

Mass transport of water vapor and ions from Å-scale graphene nanopores

Wan-Chi Lee

Hydrodynamics at the nanoscale involves both fundamental study and application of fluid and mass transport phenomena in nanometer-sized confinements. Nanopores in single-layer graphene can be highly attractive for exploring the molecular transport of gas and water molecules and hydrated ions at the ultimate scales of pore size and pore length. However, the experimental data is limited, and the state-of-the-art artificial nanopores still underperform compared to biological channels in cellular membranes. This dissertation focuses on developing ultimate graphene nanopore devices to study mass transport phenomena under controlled spatial confinement. We first investigated the kinetics of liquidâvapor transport from nanoscale confinements which is attractive for novel evaporation and separation applications; however, it is not explored at the ultimate confinement limit, i.e., at the atomic-thick and Ã-scale nanopore placed at the liquidâvapor interface. We show that the evaporation flux from such nanopores increases with decreasing pore size by up to one order of magnitude relative to the bare liquidâvapor interface. Molecular dynamics simulations reveal that oxygen-functionalized nanopores render rapid rotational and translational dynamics to water molecules by reducing and shortening the lifetime of waterâwater hydrogen bonds. Graphene nanopores also enable the study of ion transport across sub-nanometer-scale 2D confinements. We produce tailor-made nanopores approaching the size of hydrated ions by decoupling the pore nucleation and expansion. Monovalent metal ions are efficiently sieved from divalent ions, with K+/Mg2+ selectivity up to 70 and Li+/Mg2+ selectivity up to 50, corresponding to a sieving resolution of 1 Ã. Mitigating the non-selective pore formation further enhance the ion-sieving performance, reaching K+/Mg2+ selectivity up to 350 and Li+/Mg2+ selectivity up to 260. The pore size and structure allow adjusting the diffusion of ions across the nanopores, suggesting that the sterically induced partial dehydration process may play an important role in the observed cation selectivities. These selectivities were realized from centimeter-scale suspended graphene membranes, prepared in crack-free fashion by using dual layer reinforcement strategy where the first layer is 200-nm-thick nanoporous carbon (NPC) film hosting 20 nm pores which ensures a conformal contact and reinforcement of the graphene film and the second (top) layer is Nafion.Finally, a dual layer reinforcement is also demonstrated for preparing crack-free centimeter-scale gas separation membranes to utilize the full potential of graphene nanopores for energy-efficient applications. The bottom layer of the composite film is NPC film while the top layer is made of a 500-nm thick multi-walled carbon nanotube (MWNT) film with a pore size ranging from 200 to 300 nm. The obtained selectivities from crack-free centimeter-scale graphene membranes for H2/CH4 and H2/CO2 are 11â23 and 5â8, respectively, which is significantly higher than the corresponding Knudsen selectivities. Overall, this dissertation presents a graphene nanopore toolkit for studying fluid mechanics at the ultimate scales. The findings of enhanced water evaporation rate and ion selectivity using the nanopore platform could enrich our understanding of mass transport under extreme confinement and open new opportunities for a range of separation applications.

EPFL2022

Mass transport of water vapor and ions from Å-scale graphene nanopores

Wan-Chi Lee

EPFL2022