144 research outputs found
Scaling the propulsive performance of heaving and pitching foils
Scaling laws for the propulsive performance of rigid foils undergoing
oscillatory heaving and pitching motions are presented. Water tunnel
experiments on a nominally two-dimensional flow validate the scaling laws, with
the scaled data for thrust, power, and efficiency all showing excellent
collapse. The analysis indicates that the behaviour of the foils depends on
both Strouhal number and reduced frequency, but for motions where the viscous
drag is small the thrust closely follows a linear dependence on reduced
frequency. The scaling laws are also shown to be consistent with biological
data on swimming aquatic animals.Comment: 11 page
Propulsive performance of oscillating plates with time-periodic flexibility
We use small-amplitude inviscid theory to study the swimming performance of a
flexible flapping plate with time-varying flexibility. The stiffness of the
plate oscillates at twice the frequency of the kinematics in order to maintain
a symmetric motion. Plates with constant and time-periodic stiffness are
compared over a range of mean plate stiffness, oscillating stiffness amplitude,
and oscillating stiffness phase for isolated heaving, isolated pitching, and
combined leading edge kinematics. We find that there is a profound impact of
oscillating stiffness on the thrust, with a lesser impact on propulsive
efficiency. Thrust improvements of up to 35% relative to a constant-stiffness
plate are observed. For large enough frequencies and amplitudes of the
stiffness oscillation, instabilities emerge. The unstable regions may confer
enhanced propulsive performance; this hypothesis must be verified via
experiments or nonlinear simulations.Comment: 31 pages, 12 figure
Building a Mach Zehnder Interferometer with Limited Resources
Interferometers are simple optical devices that function by splitting a coherent light beam. The beam is recombined using beam splitters and mirrors. The addition of the two light beams produces interference patterns in the forms of fringes which can be used to study the path taken by the two beams. This is old technology and we sought to construct an interferometer using rudimentary and cast-off equipment. The purpose is to show that modern physics concepts can be measured inexpensively and by undergraduate student design. Though we had no optics table and or optical mounts, by careful alignment and adjustments to the equipment, we were able to produce fringes whose intensity could measure phase changes of a light beam as it goes through various mediums. We were able to determine and learn more about the properties of light and produce successful results. This demonstrates a method of introducing modern physics lab applications at a low cost
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