Experimental Design
The design
of the experimental apparatus, as well as the data
collection methods were developed in order to allow for the measurement of material
lines at unique time intervals. Initially, the experiment was designed to use
to fluids with different viscosities, generally water and another fluid such as
glycerin in order to investigate the development of flow related structures and
degree of mixing. However, this did not lend itself to easy measurement and
quantification. The use of flubber was successful in modeling glacial flow and
is easily photographed, therefore it makes an excellent analog experiment for
the mixing via shear mechanism.
The design of the experiment
is simple; the flubber will be arranged in the chute and allowed to flow
downward under the force of gravity (Sterns and Osterberg, 2003). Data collection
will be done by photographing the flubber at intervals, in map view and cross
sectional view. The photos will then be analyzed in “Image J” (the PC version
of NIH Image). This program allows the measurement of lines on the pictures so
that the changes of length and striation thickness can be quantified.
Additionally, particles in the form of small beads will be tracked. This will
give velocity and vorticity data.
Measurement of the changes
in length across a series of striations (the blue flubber) would show the
increase in surface area (in 3 dimensions) as the fluid flows. Initially, the material lines are more or less parallel. With time, due to shear stress along the margins of the flow,
the velocity in the center of the fluid increases, while that on the margins
stays somewhat constant. This leads to stretching of the parallel mineral lines
to form parabolic shapes. Below is an illustration of these measurements.
Additionally, velocity,
strain, and vorticity fields will be calculated by measuring the movement of
tracer particles through time. This will be accomplished by digitizing a series
of images using Golden Software’s Surfer program. This data will then be used
to calculate the derived measurements.
Initial time (note the particles used to trace the
movement of the flubber. (back)
At a later time (back)