Abstract:
The lateral line system on fish has been found to aid in schooling behavior, courtship
communication, active and passive hydrodynamic imaging, and prey detection. The
most widely used artificial prey stimulus has been the vibrating sphere, which some
fish are able to detect even when the signal velocities to its lateral line are orders
of magnitude smaller than background current velocities. It is not clear how the
fish are able to extract this signal. This thesis uses a series of computational fluid
dynamic (CFD) simulations, matched with recent experiments, to quantify the effects
of 3D fish body parts on the received dipole signals, and to determine signal detection
abilities of the lateral line system in background flow conditions.
An approximation is developed for the dipole induced, oscillatory, boundary layer
velocity profile over the surface of a fish. An analytic solution is developed for the case
when the surface is a wall, and is accurate at points of maximal surface tangential
velocity. Results indicate that the flow outside a thin viscous layer remains potential
in nature, and that body parts, such as fins, do not significantly affect the received
dipole signal in still water conditions. In addition, the canal lateral line system of the
sculpin is shown to be over 100 times more sensitive than the superficial lateral line
system to high frequency dipole stimuli.
Analytical models were developed for the Mottled Sculpin canal and superficial
neuromast motions, in response to hydrodynamic signals. When the background flow
was laminar, the neuromast motions induced by the stimulus signal at threshold had
a spectral peak larger than spectral peaks resulting from the background flow induced
motions. When the turbulence level increased, the resulting induced neuromast motions
had dominant low frequency oscillations. For fish using the signal encoding
mechanisms of phase-locking or spike rate increasing, signal masking should occur.
