High Performance Concrete is concrete designed to exceed the
performance of ordinary concrete.
Concrete is the most widely used building material. Any
improvement in the design of this material, for example, cost,
durablity, or strength, ripples through the economy.
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Images (Terence J. Griffin
)
The visualization was created using OpenDX. Each particle is an
idealized ellipsoid. We start with the OpenDX standard sphere
glyph. We stretch it based on a data file that
specifies the radii in X, Y and Z of each particle. A fin is added
to help the viewer see its orientation.
Another data file specifies the position and orientation of each
particle at each time step.
The stereo images are generated by adding a second camera to the
OpenDX scene that is pointed to the same "look-to" point as the
original, but from a slightly offset position. Left and right eye
images are captured and saved to a sequence of image files that can
be viewed on a computer display equipped with the necessary stereo
viewing hardware.
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VRML (Steven G. Satterfield
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Immersive Visualization (Steven G. Satterfield
) |
The visualization of our data plays an important role in the
validation of computer algorithms and the correctness of the physical
ideas used in modeling complex systems like suspensions.
Visualization plays an extremely important role from an educational
point of view. The images can stimulate ideas concerning new phenomena
that may be hard to deduce from the enormous data sets created during
a computer simulation. Also, visualization can help direct the
researcher in terms of what numerical tests or measures to apply to
evaluate the physical behavior of the systems. An example is the
strong ordering seen in the simulation of ellipsoids under shear at
high solid fractions. This was unexpected and led to improved ways of
quantifying such phenomena. Additionally, visualization assists in
communication of research results.
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| Observation of Jeffery's orbits |
We simulated a dilute suspension of 11 identical ellipsoids (axis
ratio 1:2:4) subject to shear to test our Quaternion-based
Dissipative Particle Dynamics (QDPD) algorithm. As can be seen in
the video, the ellipsoids undergo a rotational motion. This is a well
known phenomenon called Jeffery's orbits. The period of rotation was
derived by Jeffery, and our simulations were found to be consistent
with this theory, hence validating our numerical approach.
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| Suppression of Jeffery's orbits |
When the solid fraction (ratio of solid volume to total volume of
system) of ellipsoids was increased to about 15-20 percent, Jeffery's
orbits were suppressed. In this case, the ellipsoids have a tendency
to align. An interesting consequence of this alignment is that the
viscosity of the suspension is lower than that of an equivalent sphere
system (same number and volume of spheres). Note, in the dilute regime
(as in the previous movie) an equivalent suspension of spheres has a
lower viscosity. One way to think about it is that once the ellipsoids
align it is "easier" for them to get around each other. Hence the
viscosity decreases.
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| High density suspension of ellipsoids under shear |
This movie shows a dense suspension of ellipsoids similar in solid
fraction to that of the typical aggregate contribution in concrete.
Again, at this high solid fraction Jeffery's orbits are suppressed and
the alignment between ellipsoids is enhanced.
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| Flow around steel reinforcing bars (rebars) |
In the flow and placement of concrete, it is important that the
fluid concrete have the capability to move around barriers like
rebars. In this simulation, we show how spherical aggregates move
around stationary cylinders (z-axis is into the screen) which
represent steel rebars. We are currently carrying out a study
investigating the role of particle shape and size in the flow of
concrete around obstructions like rebars.
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| Model Rheometer |
This movie shows the motion of a suspension of spheres in a
coaxial geometry. The motion of the spheres is driven by the rotation
of the inner cylinder. The outer cylinder is not seen, but can be
inferred by the positions of the outer spheres. The viscosity of a
suspension is often determined in a coaxial rheometer where an inner
cylinder rotates as it is subject to an applied torque. Knowing the
torque and the subsequent rotation rate of the inner cylinder, one can
derive the viscosity of the fluid in this flow geometry. We are
currently investigating how the coupling of the inner cylinder to the
fluid suspension affects the measurement of viscosity.
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| Alternate View |
Ellipsoidal aggregate, in a shear flow, view from within the flow.
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| View with actual aggregate |
Image of actual aggregate, in a shear flow.
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| Immersive visualization simulation |
This demo is in OpenGL Performer binary format. It may be viewed with
perfly from SGI, or with
diversifly which is part of the DIVERSE package.
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| Quicktime movie of an Aggregate Flow Simulation. |
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