1,572 research outputs found
Numerical simulation of moving rigid body in rarefied gases
In this paper we present a numerical scheme to simulate a moving rigid body
with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated
by solving the Boltzmann equation using a DSMC particle method. The motion of
the rigid body is governed by the Newton-Euler equations, where the force and
the torque on the rigid body is computed from the momentum transfer of the gas
molecules colliding with the body. On the other hand, the motion of the rigid
body influences the gas flow in its surroundings. We validate the numerical
results by testing the Einstein relation for Brownian motion of the suspended
particle. The translational as well as the rotational degrees of freedom are
taken into account. It is shown that the numerically computed translational and
rotational diffusion coefficients converge to the theoretical values.Comment: 16 pages, 8 figure
Brownian dynamics of rigid particles in an incompressible fluctuating fluid by a meshfree method
A meshfree Lagrangian method for the fluctuating hydrodynamic equations
(FHEs) with fluid-structure interactions is presented. Brownian motion of the
particle is investigated by direct numerical simulation of the fluctuating
hydrodynamic equations. In this framework a bidirectional coupling has been
introduced between the fluctuating fluid and the solid object. The force
governing the motion of the solid object is solely due to the surrounding fluid
particles. Since a meshfree formulation is used, the method can be extended to
many real applications involving complex fluid flows. A three-dimensional
implementation is presented. In particular, we observe the short and long-time
behaviour of the velocity autocorrelation function (VACF) of Brownian particles
and compare it with the analytical expression. Moreover, the Stokes-Einstein
relation is reproduced to ensure the correct long-time behaviour of Brownian
dynamics.Comment: 24 pages, 2 figure
Momentum and Mass Fluxes in a Gas Confined between Periodically Structured Surfaces at Different Temperatures
It is well known that in a gas-filled duct or channel along which a
temperature gradient is applied, a thermal creep flow is created. Here we show
that a mass and momentum flux can also be induced in a gas confined between two
parallel structured surfaces at different temperatures, i.e.
\textit{orthogonal} to the temperature gradient. We use both analytical and
numerical methods to compute the resulting fluxes. The momentum flux assumes
its maximum value in the free-molecular flow regime, the (normalized) mass flux
in the transition flow regime. The discovered phenomena could find applications
in novel methods for energy-conversion and thermal pumping of gases.Comment: 6 pages, 5 figures, updated fig.5, updated text for the numerical
metho
Design and construction of a scintillating fibre tracker for measuring hard exclusive reactions at HERMES
This thesis describes design and construction of the SFT. The first section gives a comprehensive overview of the experimental set-up of HERMES and its components relevant for DVCS analysis. The second section introduces the Recoil Detector and Monte Carlo (MC) studies performed to evaluate the requirements for the individual detector parts. In the third section a detailed description of the design parameters and constraints is given and the chosen materials and assembling methods are discussed. This section is complemented by reporting results of the performance of SFT prototype modules from a test experiment conducted at GSI.
Finally, an introduction into the GPD formalism and its application to nuclei is given in the fourth section and pioneering results of DVCS off nuclei are presented in the fifth section.Im Rahmen dieser Arbeit wird die Planung und der Bau eines Spurrekonstruktionsdetektors aus szintillierenden Fasern (SFT) für den HERMES Recoil-Detektor beschrieben. Dies umfaßt die Festlegung der Entwurfsziele, Entwicklung von Herstellungverfahren, Auswahl der Detektorbestandteile sowie die Durchführung und Auswertung von Komponententests. Abschließend wird eine Einführung in den Generalised Parton Distribution-Formalismus (GPD) zur Beschreibung der nicht-perturbativen Nukleonstruktur gegeben. Dieser Formalismus kann auch auf Atomkerne angewendet werden und zu neuen Einsichten in die Kernstruktur und partonische Freiheitsgrade im Kern führen. Anschließend wird die Analyse tief-virtueller Compton-Streuereignisse an verschiedenen Kernen beschrieben
A COMPARISON OF TWO BODY SEGMENT PARAMETER MODELS VIA ANGULAR MOMENTUM AT TAKEOFF IN DIVING
The angular momentum production during the takeoff phase in diving was computed in two ways: The first approach used the Hanavan model based on 15 landmarks. The second one was an image-based individual model. The remote angular momenta of the body segments were computed and compared. It turned out that both methods yield almost the same angular momenta of the total body. Depending on the body mass the arm segments amount to 52 ± 6 % to the total angular momentum for the individual model and 57 ± 9 % for the Hanavan model. The leg contribution was 33 ± 6 % and 33 ± 7 %, the head contribution was 19.1 ± 4 % and 14.2 ± 4 % for the individual model resp. for the Hanavan model
- …