Curet, Oscar M.

Navigation of unmanned underwater vehicles in coastal zones, tight spaces and close to structures such as ports, ship hulls and pipelines remains a difficult challenge. Currently Autonomous Underwater Vehicles (AUVs) use a variety of techniques for motion control, including single thrusters with diving planes or hydrofoils, robotic wrists, or a moving mass. However, these techniques provide limited maneuverability. The objective of this work was to understand the mechanics of elongated fin propulsion for swimming and motion control of underwater vehicles. This bio-inspired propulsion is used by several fishes that swim by undulating a thin and elongated median fin that allow them to perform forward and directional maneuvers. In the first chapter we present the literature review as well as the mathematical formulation using thrust vectoring approach to achieve forward and turning maneuvers. In the second chapter, we used a robotic vessel with elongated fin propulsion to determine the thrust scaling and efficiency. Using precise force and swimming kinematics measurements with the robotic vessel, the thrust generated by the undulating fin was found to scale with the square of the relative velocity between the free streaming flow and the wave speed. In addition, a hydrodynamic efficiency is presented based on propulsive force measurements and a model on the power required to oscillate the fin laterally.

Hydrodynamics interaction is a factor in the performance of fish schooling or underwater vessels in close formation. In this work, we visualized the wake structure of pitching hydrofoils using an inclined soap film. We considered one-, two-, three- and nine-foil configurations with different spacing and actuation parameters: amplitude (A), frequency (f), phase difference (), and flow speed (U). The wake structures were recorded with a high-speed camera and analyzed to measure the vortex angle created. The wake structure of two- and three-foil configurations were compared with the Strouhal number, St = fA/U, of a single foil. For the nine-foil configuration, the wake velocity and the standard deviation of the velocity were used to interpret the hydrodynamic interaction. It was found that both spacing and phase difference between foils are relevant in the hydrodynamic interaction. Qualitative observations are also made, and vortex street behavior characteristics are identified.

Shell-and-tube heat exchangers (STHXs) are a popular choice in the petroleum refining industry,
chemical industry, food processing industry and in power generation plants. This kind of heat
exchanger is made up of an array of baffles that redirects the working fluid to increase heat
transfer. The objective of this work is to understand the underlying physics of the heat transfer in a
shell-and-tube heat exchanger and its interconnection to the fluid structure associated with their
design. This research focuses on the steady state three dimensional analysis of the time averaged
turbulent flow and heat transfer characterization of the shell side of a small scale single segmented
baffle heat exchanger. The study is carried out using the computational fluid dynamics (CFD) software
package ANSYS: FLUENT 15.0 on a hybrid unstructured mesh. The CFD results are then compared
against experimental results. The Reynolds averaged-Navier-stokes (RANS) based turbulent model
realizable is used to model the turbulence inside the heat exchanger. The results obtained from CFD
and experiment from the shell side wall outlet temperature differ by 5 %. Based on the computational
results it is found that the regions of highest velocity at the inlet and in the core flow lead to a higher
local heat transfer enhancement. A better understanding of the complex flow and heat transfer regimes
inside a shell and tube heat exchanger given by this work would aid to further the development of more
cost efficient and effective heat exchanger designs.

Ribbon-fin-based propulsion has the potential to improve the maneuverability of underwater vehicles in
complex environments. In this type of propulsion a series of rays are used to send traveling waves
along an elongated fin, which is referred to as ribbon fin. In this work, in order to know the effect of
flexural rigidities and aspect ratios on undulating ribbon fin propulsion; we built a robotic ribbon fin, and
tested the physical model in a water flume. In a series of experiments we measured the propulsive
force, power consumption and the free-swimming speed of the robotic fin as a function of wave
frequency for fins with different ray stiffness and aspect ratios. The propulsive performance of the
robotic ribbon fin was based on the propulsive force generated and power consumption. A series of
kinematic experiments were performed using a high-speed camera. Based on the fin kinematics, the
natural frequencies of the ribbon fin with different stiffness were determined. We found that the flexible
rays would improve or worsen the propulsive performance compared to a rigid counterpart depending
on the actuation parameters. For the aspect ratios considered, the propulsive efficiency improves with
increase in the fin height. Our data suggest that, the ribbon fin can yield best propulsive behavior close
to its natural frequency.

A bio-inspired robotic underwater vessel was developed to test the effect of
fin morphology on the propulsive performance of caudal fin. The robotic vessel, called The
Bullet Fish, features a cylindrical body with a hemisphere at the forward section and a
conical body at the stern. The vessel uses an oscillating caudal fin for thrust generation.
The robotic vessel was tested in a recirculating flume for seven different caudal fins that
range different bio-inspired forms and aspect ratios. The experiments were performed at
four different flow velocities and two flapping frequencies: 0.5 and 1.0 Hz. We found that
for 1 Hz flapping frequency that in general as the aspect-ratio decreases both thrust
production tends and power decrease resulting in a better propulsive efficiency for aspect
ratios between 0.9 and 1.0. A less uniform trend was found for 0.5 Hz, where our data
suggest multiple efficiency peaks. Additional experiments on the robotic model could help
understand the propulsion aquatic locomotion and help the design of bio-inspired
underwater vehicles.

Mangrove trees play a prominent role in coastal tropic and subtropical regions, providing habitat for many organisms and protecting shorelines against storm surges, high winds, erosion, and tsunamis. The motivation of this proposal is to understand the complex interaction of mangrove roots during tidal flow conditions using simplified physical models. In this dissertation, the mangrove roots were modeled with a circular array of cylinders with different porosities and spacing ratios. In addition, we modeled the flexibility of the roots by attaching rigid cylinders to hinge connectors. The models were tested in a water tunnel for a range of Reynolds number from 2200 to 11000. Additionally, we performed 2D flow visualization for different root models in a flowing soap film setup. We measured drag force and the instantanous streamwise velocity downstream of the models. Furthermore, we investigated the fluid dynamics downstream of the models using a 2-D time-resolved particle image velocimetry (PIV), and flow visualization. The result was analyzed to present time-averaged and time-resolved flow parameters including the velocity distribution, vorticity, streamline, Reynolds shear stress and turbulent kinetic energy. We found that the frequency of the vortex shedding increases as the diameter of the small cylinders decreases while the patch diameter is constant, therefore increasing the Strouhal number, St=fD/U By comparing the change of Strouhal numbers with a single solid cylinder, we introduced a new length scale, the “effective diameter”. In addition, the effective diameter of the patch decreases as the porosity increases. In addition, patch drag decreases linearly as the spacing ratio increases. For flexible cylinders, we found that a decrease in stiffness increases both patch drag and the wake deficit behind the patch in a similar fashion as increasing the blockage of the patch. The average drag coefficient decreased with increasing Reynolds number and with increasing porosity. We found that the Reynolds stress (−u′v′) peak is not only shifted in the vortex structure because of shear layer interference, but also the intensity was weakened by increasing the porosity, which causes a weakening of the buckling of vorticity layers leading to a decline in vortex strength as well as increase in wake elongation.

Undulatory ribbon- n-based propulsion is an appealing propulsion mechanism
due to its rich locomotor capabilities that can improve the propulsive performance
and maneuverability of underwater vehicles. For instance, the swimming mechanics
of weakly electric black ghost knife sh (Apteronotus albifrons) is of great interest
to study because of their high swimming e ciency at low speeds and extraordinary
agility such as rapid reversal swimming, hovering in presence of water disturbance,
rolling and vertical swimming. In this thesis work, to facilitate our understanding on
the
exible undulatory ribbon n propulsion, we have four research motivations. The
rst objective is to study how the use of
exible rays and di erent n morphology
can in
uence the propulsive performance of ribbon- n propulsion. It is possible that
natural swimmers using this locomotion method could take advantage of passive n
motion based on the coupling of
uid-structure interaction and the elasto-mechanical
responses of the undulating n. Therefore, the second objective is to understand
how an under-actuated undulating n can take advantage of natural dynamics of
the
uid-structure interaction for the propulsive force generation. In addition to the
impressive propulsive performance of the undulatory n propulsion, the exceptional maneuverability of knife sh is also a key motivation that drives this thesis work.
Thus, we dedicate to investigate how traveling wave shapes and actuation parameters
(frequency, wavelength) can manipulate the maneuvering behaviors of a swimmer
propelled by an undulating ribbon n. Lastly, we aim to uncover the e ect of varying
traveling wave amplitudes and pectoral ns on its maneuvering performances. Two
robotic devices were developed to study the propulsive performance of both fullyactuated
and under-actuated ribbon n propulsion and investigate the maneuver
control of a free-swimming underwater robot propelled by an undulatory n.
For the rst research aim, we study the e ect of
exible rays and di erent
n morphology on the propulsive performance of ribbon- n propulsion. A physical
model composed of fteen rays interconnected with an elastic membrane was used to
test four di erent ray
exural sti ness and four aspect ratios. Our results show that

exible rays can improve the propulsive e ciency compared to a rigid counterpart.
In addition, the morphology of the ribbon n a ects its propulsive performance as
well, and there could exist an optimal n morphology. To understand how an underactuated
undulating n can modify its active and passive n motion to e ectively
control the hydrodynamic force and propulsive e ciency. We did a series of experiments
using the same robotic n model but with some structural modi cations and
we measured n kinematics, net surge force and power consumption. We nd that the
under-actuated n can keep the equivalent propulsive e ciency as the fully-actuated
counterpart within our experimental parameter range. Moreover, our results demonstrate
that the thrust force and power consumption of an under-actuated n follow
the same scaling laws as the fully-actuated n.
To conduct the free-swimming maneuver study, we developed a self-contained,
free-swimming robot propelled by an undulatory n, which is able to perform the
following maneuvers: forward, reversed swimming and hovering motion. We also
performed V3V PIV experiments to capture the
ow structures generated by the robotic device. Our results show that the robot can reach higher swimming e ciency
at low frequencies. As the number of traveling waves increases, the robot swims
more stably in roll, pitch and yaw motions. For cases with varying wave amplitudes,
traveling wave with incremental wave amplitude can achieve free-swimming velocity
higher than that of decremental wave amplitude. However, the latter case can generate
higher pitch angles. For the robot with slightly negative-pitched pectoral ns,
it can perform slow diving maneuvers. These ndings demonstrate that we can take
advantage of the undulating ribbon n propulsion to achieve high maneuverability
for the future underwater vehicles in complex environment.

A robotic ribbon fin with twelve independent fin rays, elastic fin membrane, and a body
of adjustable height was developed for this thesis specifically to test the 1990 theory put forth
by Lighthill and Blake that a multiplicative propulsive enhancement exists for Gymnotiform and
Balisiform swimmers based on the ratio of body and fin heights. Until now, the theory has not
been experimentally tested. Proof of such a momentum enhancement could have a profound effect
on unmanned underwater vehicle design and shed light on the evolutionary advantage to body-fin
ratios found in nature, shown as optimal for momentum enhancement in Lighthill and Blake’s theory.
Thrust tests for various body heights were conducted in a recirculating flow tank at different flow
speeds and fin flapping frequencies. When comparing different body heights at different frequencies
to a ’no-body’ thrust test case at each frequency no momentum enhancement factor was found. Data
in this thesis indicate there is no momentum enhancement factor due to the presence of a body on
top of an undulating fin.

In this work a bio-inspired flapping actuator based on varied magnetic fields is
developed, controlled and characterized. The actuator is sought to contribute to the
toolbox of options for bio-mimetics research. The design is that of a neodymium bar
magnet on one end of an armature which is moved by two air core electromagnetic coils
in the same manner as agonist and antagonist muscle pairs function in biological systems.
The other end of the armature is fitted to a rigid fin extending beyond the streamline
enclosure body to produce propulsion. A series of tests in still water were performed to
measure the kinematics and propulsive force for different control schemes including the
effect of adding antagonistic resistance to the control schemes. Control methods based on
armature position and based on setpoint error were tested and antagonist force was found
to increase consistency of control of the systems in certain cases.

Flow Structure and fluid transport via advection around pectoral fin of larval ZebraFish
are studied numerically using Immersed Boundary Method, Lagrangian Coherent
Structure, passive particle tracing, vortex core evolution and four statistically defined
mixing numbers. Experimental fish kinematics for nominal swimming case are obtained
from previous researchers and numerically manipulated to analyze the role of different
body motion kinematics, Reynolds number and fin morphology on flow structure and
transport. Hyperbolic strain field and vortex cores are found to be effective particle
transporter and their relative strength are driving force of varying flow structure and fluid
transport. Translation and lateral undulation of fish; as a combination or individual entity,
has coherent advantages and drawbacks significant enough to alter the nature of fluid
advection. Reynolds number increase enhances overall fluid transport and mixing in varying order for different kinematics and nominal bending position of fin has average
transport capability of other artificially induced fin morphology.