6,715 research outputs found
Estimating the charge size in explosive forming of sheet metal
A method is given for estimating the charge size for the explosive
forming of sheet metal components. The method is applied to a number of
relatively simple shapes and good agreement is shown with experimental
results
Crack formation in blanking and piercing
In recent experiments on blanking and piercing, it was found that
cracks occurred in the region of maximum hardness gradient and that
cracking could be eliminated by radiusing the punch and die edges. In
this paper, a simple stress analysis is made of the corresponding plane
strain deformation, account being taken of the strain-hardening property
of the work material. The above experimental observations are then
shown to be compatible with the predicted stress distributions
Dimensional changes resulting from the heat treatment of EN 30B and Nimar 125
Three components have been manufactured in both EN 30B and N1MAR 125.
Dimensional changes following heat treatment have been recorded and, while
the sample is only small, the report serves to illustrate the potential
benefits which arise from the use of a maraging steel. NIMAR 125 is
shown to have reasonably predictable dimensional characteristics and thus
indicates the feasibility of completing all machining operations prior
to heat treatment
Universality and properties of neutron star type I critical collapses
We study the neutron star axisymmetric critical solution previously found in
the numerical studies of neutron star mergers. Using neutron star-like initial
data and performing similar merger simulations, we demonstrate that the
solution is indeed a semi-attractor on the threshold plane separating the basin
of a neutron star and the basin of a black hole in the solution space of the
Einstein equations. In order to explore the extent of the attraction basin of
the neutron star semiattractor, we construct initial data phase spaces for
these neutron star-like initial data. From these phase spaces, we also observe
several interesting dynamical scenarios where the merged object is supported
from prompt collapse. The properties of the critical index of the solution, in
particular, its dependence on conserved quantities, are then studied. From the
study, it is found that a family of neutron star semi-attractors exist that can
be classified by both their rest masses and ADM masses.Comment: 13 pages, 12 figures, 1 new reference adde
Dependence of inner accretion disk stress on parameters: the Schwarzschild case
We explore the parameter dependence of inner disk stress in black hole
accretion by contrasting the results of a number of simulations, all employing
3-d general relativistic MHD in a Schwarzschild spacetime. Five of these
simulations were performed with the intrinsically conservative code HARM3D,
which allows careful regulation of the disk aspect ratio, H/R; our simulations
span a range in H/R from 0.06 to 0.17. We contrast these simulations with two
previously reported simulations in a Schwarzschild spacetime in order to
investigate possible dependence of the inner disk stress on magnetic topology.
In all cases, much care was devoted to technical issues: ensuring adequate
resolution and azimuthal extent, and averaging only over those time-periods
when the accretion flow is in approximate inflow equilibrium. We find that the
time-averaged radial-dependence of fluid-frame electromagnetic stress is almost
completely independent of both disk thickness and poloidal magnetic topology.
It rises smoothly inward at all radii (exhibiting no feature associated with
the ISCO) until just outside the event horizon, where the stress plummets to
zero. Reynolds stress can also be significant near the ISCO and in the plunging
region; the magnitude of this stress, however, depends on both disk thickness
and magnetic topology. The two stresses combine to make the net angular
momentum accreted per unit rest-mass 7-15% less than the angular momentum of
the ISCO.Comment: Accepted for publication in ApJ, 52 pages, 38 figures, AASTEX.
High-resolution versions can be found at the following links:
http://ccrg.rit.edu/~scn/papers/schwarzstress.ps,
http://ccrg.rit.edu/~scn/papers/schwarzstress.pd
Note: estimating the charge size in explosive forming of sheet metal
Note: Estimating the charge size in explosive forming of sheet metal
In the explosive forming of sheet metal some relatively easy method
of estimating the size of the charge is needed. This short note describes
a method in which the size of the charge is found by equating the work done
in forming the component to that part of the explosive energy available
for doing work on the component … [cont]
Primitive Variable Solvers for Conservative General Relativistic Magnetohydrodynamics
Conservative numerical schemes for general relativistic magnetohydrodynamics
(GRMHD) require a method for transforming between ``conserved'' variables such
as momentum and energy density and ``primitive'' variables such as rest-mass
density, internal energy, and components of the four-velocity. The forward
transformation (primitive to conserved) has a closed-form solution, but the
inverse transformation (conserved to primitive) requires the solution of a set
of five nonlinear equations. Here we discuss the mathematical properties of the
inverse transformation and present six numerical methods for performing the
inversion. The first method solves the full set of five nonlinear equations
directly using a Newton-Raphson scheme and a guess from the previous timestep.
The other methods reduce the five nonlinear equations to either one or two
nonlinear equations that are solved numerically. Comparisons between the
methods are made using a survey over phase space, a two-dimensional explosion
problem, and a general relativistic MHD accretion disk simulation. The run-time
of the methods is also examined. Code implementing the schemes is available for
download on the web.Comment: Accepted to ApJ, 33 pages, 8 figures (color and greyscale), 1
machine-readable table (tab2.txt), code available at
http://rainman.astro.uiuc.edu/codelib, a high-resolution and full-color PDF
version is located at
http://rainman.astro.uiuc.edu/codelib/codes/pvs_grmhd/ms.pd
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