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Concept

Pression dynamique

En mécanique des fluides la pression dynamique est une mesure de l'énergie cinétique d'un fluide par unité de volume. Elle joue un rôle fondamental dans la conservation de l'énergie et sert de référence pour la définition des coefficients aérodynamiques. Définition La pression dynamique P_{dyn} est l'énergie cinétique E_c par unité de volume au sein d'un fluide : ::E_{c}=\frac{1}{2},mv^2 = \frac{1}{2},(\rho V_{ol})v^2 où \rho est la masse volumique du fluide, V_{ol} son volume et v sa vitesse. L'énergie cinétique par unité de volume est donc, en divisant par V_{ol}: ::P_{dyn} = \frac{1}{2},\rho v^2 La pression dynamique a la dimension d'une pression, d'où son nom. Dans le cas d'un gaz parfait elle s'écrit : ::P_{dyn}=\frac{1}{2},\gamma ,p ,M^2 où p est la pression, \gamma l'indice adiabatique et M le nombre de

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Considering snow depositions and transport mechanisms in meteorological analysis of predicting snow loads on buildings

Michael Lehning, Borui Zhang, Qingwen Zhang

The meteorological conditions determine snow evolutions on and around buildings. Those climatic impacts have been independently considered in the current design codes of buildings, namely the wind pressure and the snow load. But snow load estimates are only based on precipitation assessments without considering the joint effect of wind and snow precipitation which lead to wind dominated deposition and snow transport. Thus, the statisticsbased data provided by those building codes seem practically inadequate or at least incomplete. Using the data provided by upper-air and ground meteorological stations in northern China, including snowfall, wind velocity, and temperature, as indicators, we propose a series of statistical relationships covering aspects of snow precipitation and snow drifting. For those meteorological indicators that can affect building snow evolutions, more detailed analyses on their spatial and temporal changes have been achieved. The regionalization of snow precipitation features in northern China has also been proposed based on the clustering analysis on meteorological joint effects. The result shows that the snowfall in most northern regions of China is generally not heavy and in the form of a uniform deposition. The wind dominated depositions around buildings are more likely to appear in the regions around the Bohai Sea.

ELSEVIER2022

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Electron flux and pressure dynamic in the LHC vacuum pilot sector as a function of beam parameters and beam pipe properties

Vincent Baglin, Elena Buratin, Ambrogio Fasoli

The Large Hadron Collider (LHC) is affected by the electron cloud (EC) phenomenon that can provoke beam instabilities, detrimental heat loads and pressure increases in the vacuum system. An innovative dedicated system called vacuum pilot sector (VPS) provides a continuous monitoring of the electron flux and of the pressure signals thanks to electron pickup and vacuum gauges. The VPS system is installed in a room temperature, field-free part of the LHC storage ring. Several technical surfaces, such as ex situ nonevaporable getter (NEG), amorphous carbon coating and copper, are simultaneously tested. The main outcomes of this study show that the EC signals have: (1) a linear dependence upon the number of bunches and upon the bunch population in the multipacting regime, (2) a multipacting threshold at a given bunch population, (3) a reduction under beam conditioning, (4) a strong dependence on the filling pattern and beam energy. The comparison between different surfaces shows that amorphous carbon coating reduces drastically the EC buildup, thanks to its low secondary electron yield (SEY) and photoelectron yield (PY), while copper and ex situ NEG coated surfaces suffer of EC multipacting, even after several months of operation. The multipacting rate coefficients are higher for copper than for ex situ NEG, as predicted from the SEY estimation. Other detailed experimental observations are discussed in this paper.

AMER PHYSICAL SOC2020

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Polarized Linear Motor Combined With Levitation Actuators Working in a Partial Vacuum Environment — Application to Swissmetro

Christophe Espanet, Pascal Hagmann, Marcel Jufer

Worldwide high speed Maglev (> 400km/h) developments refer to Maglev such as the Japanese JR-Maglev MLX, the German Transrapid and the USA Inductrack Maglev. Other world projects exist such as the Japan HSST (< 300km/h) and the China HTC. The JR-Maglev, the Transrapid and the HSST have reached industrial levels. The Swissmetro Project presents a unique aspect of Maglev: it is designed to work under partial vacuum (< 10kPa) in two tunnels and for high speeds (>400km/h). The authors investigate new possibilities to combine both the propulsion and the levitation. In order to minimize the heat due to the motor levitation and guidance losses, a polarized excitation is proposed. The use of permanent magnet NdFeB for the excitation is still not applied for high speed Maglev, requiring mechanical power greater than 6MW. Such a solution only appears in Urban Rapid Transit Maglev (

2006

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Nombre de Mach

Le nombre de Mach est un nombre sans dimension, noté Ma, qui exprime le rapport de la vitesse d'un objet dans un fluide à la vitesse du son dans ce même fluide. La vitesse du son dans un gaz variant

Dynamique des fluides

La dynamique des fluides (hydrodynamique ou aérodynamique), est l'étude des mouvements des fluides, qu'ils soient liquides ou gazeux. Elle fait partie de la mécanique des fluides avec l'hydrostatiqu

Pressure measurement

Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have

ME-341: Heat and mass transfer

This course covers fundamentals of heat transfer and applications to practical problems. Emphasis will be on developing a physical and analytical understanding of conductive, convective, and radiative heat transfer.

PHYS-201(d): General physics: electromagnetism

The topics covered by the course are concepts of fluid mechanics, waves, and electromagnetism.

PHYS-427: Relativity and cosmology I

Introduce the students to general relativity and its classical tests.