1,354 research outputs found
Thermo-mechanical coupling in fiber-reinforced continua: mixed finite element formulations and energy-momentum time integration
Our research activity is motivated by accurate dynamic simulations of fiber-
reinforced materials in light-weight structures. In order to accomplish this, we have to
take various steps. The material behavior is formulated with an anisotropic, polyconvex strain
energy function. We combine different mixed element formulations (e.g. see Ref- erence [2] or
[3]) with a Galerkin time integrator as shown in Reference [5]. This reduces the volumetric
locking effect of an incompressible matrix material as well as the locking effect due to stiff
fibers. In addition, we increase the accuracy by using Galerkin-based higher-order time
integrators. Since in long-term simulations a hugh energy error is a strong problem, we
apply the mixed finite element formulations to an energy-momentum time integration scheme (see
Reference [6]). In the next step, we extend the material formulation by adding a
thermo-mechanical coupling as shown in Reference [7]. Here we also describe the directional heat
conduction of the fiber. As numerical examples with multiple material domains and families of
fibers serve cooks cantilever beam as in Ref- erence [5]. The Dirichlet boundary conditions are
modelled by the Lagrange-multiplier method (see Reference [7]) and as Neumann boundary condition a
pressure distribution
is used
Energy and Charged Particle Flow in 10.8 A GeV/c Au+Au Collisions
Experimental results and a detailed analysis are presented of the transverse
energy and charged particle azimuthal distributions measured by the E877
collaboration for different centralities of Au+Au collisions at a beam momentum
of 10.8 A GeV/c. The anisotropy of these distributions is studied with respect
to the reaction plane reconstructed on an event-by-event basis using the
transverse energy distribution measured by calorimeters. Results are corrected
for the reaction plane resolution. For semicentral events we observe directed
flow signals of up to ten percent. We observe a stronger anisotropy for slow
charged particles. For both the charged particle and transverse energy
distributions we observe a small but non zero elliptic anisotropy with the
major axis pointing into the reaction plane. Combining the information on
transverse energy and charged particle flow we obtain information on the flow
of nucleons and pions. The data are compared to event generators and the need
to introduce a mean field or nucleon-nucleon potential is discussed.Comment: RevTex, 25 pages, 13 figures included as one Postscript file,
submitted to Phys. Rev.
Energy-Momentum Scheme with Drilling Degrees of Freedom for Composites with Curvature-Twist Stiffness
This paper is motivated by the increasing application of 3D fiber-reinforced composites in rotating systems [1]. In 2D fiber-reinforced composites, single fibers with a diameter in the range of micrometers are embedded in a matrix material. But, these composites are prone to delamination damage, wherefore the development of 3D composites has been undertaken. Here, fiber bundles are woven, knitted, braided or stitched, in order to fix the fibers before they are surrounded by a matrix material. From a material modelling point of view, these two kind of composites make a huge difference, because a fiber bundle has to be considered as a beam-like structure with curvature-twist (bending as well as twisting) stiffness, in addition to the usual stretching stiffness (cf. [2]). The former is then responsible for the increasing strength-to-weight ratio of 3D fiber-reinforced composites for thin-walled lightweight structures. Therefore, 3D fiber-reinforced composites demand for a bespoke simulation technique. We have to consider a representative volume element, in which secondary effects as a micro inertia and a curvature-twist stiffness must be taken into account. We introduce these secondary effects in a continuum formulation by means of independent drilling degrees of freedom (cf. [3]). The resulting nonisothermal constrained micropolar continuum is derived by a mixed principle of virtual power (cf. [4]). This variational principle simultaneously generates in the discrete setting a mixed B-bar method and a Galerkin-based energy-momentum scheme of higher order. We also take into account viscoelastic material behaviour, which arises from a mixture of organic and inorganic fibers in a polymeric matrix material. Representative numerical examples demonstrate the twisting and bending stiffness of the fiber bundles
Charged Particle Pseudorapidity Distributions in Au+Al, Cu, Au, and U Collisions at 10.8 AGeV/c
We present the results of an analysis of charged particle pseudorapidity
distributions in the central region in collisions of a Au projectile with Al,
Cu, Au, and U targets at an incident energy of 10.8~GeV/c per nucleon. The
pseudorapidity distributions are presented as a function of transverse energy
produced in the target or central pseudorapidity regions. The correlation
between charged multiplicity and transverse energy measured in the central
region, as well as the target and projectile regions is also presented. We give
results for transverse energy per charged particle as a function of
pseudorapidity and centrality.Comment: 31 pages + 12 figures (compressed and uuencoded by uufiles), LATEX,
Submitted to PR
Directed flow of antiprotons in Au+Au collisions at AGS
Directed flow of antiprotons is studied in Au+Au collisions at a beam
momentum of 11.5A GeV/c. It is shown that antiproton directed flow is
anti-correlated to proton flow. The measured transverse momentum dependence of
the antiproton flow is compared with predictions of the RQMD event generator.Comment: 16 pages, 6 figure
Proton and Pion Production in Au+Au Collisions at 10.8A GeV/c
We present proton and pion tranverse momentum spectra and rapidity
distributions for Au+Au collisions at 10.8A GeV/c. The proton spectra exhibit
collective transverse flow effects. Evidence of the influence of the Coulomb
interaction from the fireball is found in the pion transverse momentum spectra.
The data are compared with the predictions of the RQMD event generator.Comment: plain tex (revtex), 24 pages Submitted to Phys. Rev.
Two-pion correlations in Au+Au collisions at 10.8 GeV/c per nucleon
Two-particle correlation functions for positive and negative pions have been
measured in Au+Au collisions at 10.8~GeV/c per nucleon. The data were analyzed
using one- and three-dimensional correlation functions. From the results of the
three-dimensional fit the phase space density of pions was calculated. It is
consistent with local thermal equilibrium.Comment: 5 pages RevTeX (including 3 Figures
Measurement of Pion Enhancement at Low Transverse Momentum and of the Delta-Resonance Abundance in Si-Nucleus Collisions at AGS Energy
We present measurements of the pion transverse momentum (p_t) spectra in
central Si-nucleus collisions in the rapidity range 2.0<y<5.0 for p_t down to
and including p_t=0. The data exhibit an enhanced pion yield at low p_t
compared to what is expected for a purely thermal spectral shape. This
enhancement is used to determine the Delta-resonance abundance at freeze-out.
The results are consistent with a direct measurement of the Delta-resonance
yield by reconstruction of proton-pion pairs and imply a temperature of the
system at freeze-out close to 140 MeV.Comment: 12 pages + 4 figures (uuencoded at end-of-file
Proton and Pion Production Relative to the Reaction Plane in Au + Au Collisions at AGS Energies
Results are presented of an analysis of proton and charged pion azimuthal
distributions measured with respect to the reaction plane in Au + Au collisions
at a beam momentum of about 11 AGeV/c. The azimuthal anisotropy is studied as a
function of particle rapidity and transverse momentum for different
centralities of the collisions. The triple differential (in rapidity,
transverse momentum, and azimuthal angle) distributions are reconstructed. A
comparison of the results with a previous analysis of charged particle and
transverse energy flow as well as with model predictions is presented.Comment: 23 pages (LaTeX), 12 figure
Two-Proton Correlations from 14.6A GeV/c Si+Pb and 11.5A GeV/c Au+Au Central Collisions
Two-proton correlation functions have been measured in Si+Pb collisions at
14.6A GeV/c and Au+Au collisions at 11.5A GeV/c by the E814/E877 collaboration.
Data are compared with predictions of the transport model RQMD and the source
size is inferred from this comparison. Our analysis shows that, for both
reactions, the characteristic size of the system at freeze-out exceeds the size
of the projectile, suggesting that the fireball created in the collision has
expanded. For Au+Au reactions, the observed centrality dependence of the
two-proton correlation function implies that more central collisions lead to a
larger source sizes.Comment: RevTex, 12 pages, 5 figure
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