Part B | 11
298 Part B Autonomous Ocean Vehicles, Subsystems and Control
11.7 Concluding Remarks
UUVs have wide-ranging naval utility. They are the
main work horse for unmanned missions, and their
long range, versatile payload capacity, and operational
envelope offer advantage and value in many naval applications. However, our studies have documented that
a large gap in turning ability exists between fish and
tactical scale UUVs [11.50]. Advances in digital control have not been able to close this gap. As a result, the
gap has been attributed to differences in the hydrodynamic mechanism of lift production – lift production in
steady fins versus that in flapping fins – that is, attached
fin flow versus pinned-LEV type modified dynamic
stall. At NUWC, we have proceeded to implement the
high-lift mechanism of flapping fins to naval utility
in hovering and low-speed maneuvering, while others
have proceeded to mimic swimming animals. These approaches to the development of biology-inspired UUVs
have been reviewed by filtering those that we believe
have matured the most.
The low-aspect-ratio, rigid flapping fin has been
found to be the most successful actuator in the biology-inspired UUVs. We have also been able to mate
the flapping fins to rigid cylinders – the most widely
used underwater hull form, and also to noncylindrical
sections.
Maneuverability and controllability have been
demonstrated in both bio-inspired and bio-mimicry
UUVs. Mission concepts, duration, payload capabilities, and sensor integration have been demonstrated,
and the former type of UUV appears to be somewhat
more advanced than the latter. A six-finned cylindrical
UUV has demonstrated long-duration reliability, performing incessant swimming for nearly 3 weeks with
low power consumption (Fig. 11.7).
While conventional PID controllers have been successfully developed for use with flapping fins, which
produce oscillatory forces, control of the instantaneous unsteady forces due to flapping fins using olivocerebellar dynamics should make the UUVs more
animal-like [11.24–26, 33, 51, 52]. This would give
a more logical foundation to the integration of nonlinear sensors and would also make the UUV controller
robust and most responsive to unsteady environmental disturbances. Autonomy is theoretically described as
a consequence of the self-regulating property of nonlinear oscillators.
To date, significant progress has been lacking in
the development of strong artificial muscles [11.44,
47, 48, 53, 54] and nonlinear sensing [11.35] for underwater application. When these developments move
forward, their integration with flapping fins controlled by olivo-cerebellar dynamics would lead to
radically new naval precision and other capabilities.
11.8 Nomenclature
A
Amplitude of fin oscillation
C x;wing
Coefficient of axial thrust in a single flapping fin [11.15]
F
Cubic polynomial function
F
0
x , F
0
xo
Instantaneous fluctuating force and force
amplitude, respectively
f , !, ! s
Frequency of fin oscillation
G, T
Constants
I Ca , I Na
Factors driving depolarization level of
inferior-olive neuron
I exti .t/
External stimulus
k
Factor that sets a relative time scale between the uv- and zw-subsystems
p iu , p iz
Nonlinear functions of u i and z i , respectively
R avg
Average fin radius
Re c
Fin chord (c) Reynolds number Uc==
St
Strouhal number of a flapping fin, St D
2f 0 R avg
U
U, U wing , U t Cruise speed, wing speed, and total forward speed
u i , v i , z i , w i States of oscillator i
˛
Effective fin angle of attack considering
fin–wake coupling
˛ g
Geometric fin angle of attack (excluding
fin–wake coupling)
i
Limit cycle orbit
" Ca , " Na
Factors controlling oscillator time scale
of oscillation of inferior-olive neuron
Â.t/, Â o , Â Bias Pitch at time t, pitch amplitude, and pitch
bias angle, respectively
.t/
Combined roll and pitch angle
w .t/
Temporal local wall-shear stress on the
flapping fin surface
.t/, o
Roll angle at time t and roll amplitude,
respectively
Phase difference between roll and pitch
oscillations
298 Part B Autonomous Ocean Vehicles, Subsystems and Control
11.7 Concluding Remarks
UUVs have wide-ranging naval utility. They are the
main work horse for unmanned missions, and their
long range, versatile payload capacity, and operational
envelope offer advantage and value in many naval applications. However, our studies have documented that
a large gap in turning ability exists between fish and
tactical scale UUVs [11.50]. Advances in digital control have not been able to close this gap. As a result, the
gap has been attributed to differences in the hydrodynamic mechanism of lift production – lift production in
steady fins versus that in flapping fins – that is, attached
fin flow versus pinned-LEV type modified dynamic
stall. At NUWC, we have proceeded to implement the
high-lift mechanism of flapping fins to naval utility
in hovering and low-speed maneuvering, while others
have proceeded to mimic swimming animals. These approaches to the development of biology-inspired UUVs
have been reviewed by filtering those that we believe
have matured the most.
The low-aspect-ratio, rigid flapping fin has been
found to be the most successful actuator in the biology-inspired UUVs. We have also been able to mate
the flapping fins to rigid cylinders – the most widely
used underwater hull form, and also to noncylindrical
sections.
Maneuverability and controllability have been
demonstrated in both bio-inspired and bio-mimicry
UUVs. Mission concepts, duration, payload capabilities, and sensor integration have been demonstrated,
and the former type of UUV appears to be somewhat
more advanced than the latter. A six-finned cylindrical
UUV has demonstrated long-duration reliability, performing incessant swimming for nearly 3 weeks with
low power consumption (Fig. 11.7).
While conventional PID controllers have been successfully developed for use with flapping fins, which
produce oscillatory forces, control of the instantaneous unsteady forces due to flapping fins using olivocerebellar dynamics should make the UUVs more
animal-like [11.24–26, 33, 51, 52]. This would give
a more logical foundation to the integration of nonlinear sensors and would also make the UUV controller
robust and most responsive to unsteady environmental disturbances. Autonomy is theoretically described as
a consequence of the self-regulating property of nonlinear oscillators.
To date, significant progress has been lacking in
the development of strong artificial muscles [11.44,
47, 48, 53, 54] and nonlinear sensing [11.35] for underwater application. When these developments move
forward, their integration with flapping fins controlled by olivo-cerebellar dynamics would lead to
radically new naval precision and other capabilities.
11.8 Nomenclature
A
Amplitude of fin oscillation
C x;wing
Coefficient of axial thrust in a single flapping fin [11.15]
F
Cubic polynomial function
F
0
x , F
0
xo
Instantaneous fluctuating force and force
amplitude, respectively
f , !, ! s
Frequency of fin oscillation
G, T
Constants
I Ca , I Na
Factors driving depolarization level of
inferior-olive neuron
I exti .t/
External stimulus
k
Factor that sets a relative time scale between the uv- and zw-subsystems
p iu , p iz
Nonlinear functions of u i and z i , respectively
R avg
Average fin radius
Re c
Fin chord (c) Reynolds number Uc==
St
Strouhal number of a flapping fin, St D
2f 0 R avg
U
U, U wing , U t Cruise speed, wing speed, and total forward speed
u i , v i , z i , w i States of oscillator i
˛
Effective fin angle of attack considering
fin–wake coupling
˛ g
Geometric fin angle of attack (excluding
fin–wake coupling)
i
Limit cycle orbit
" Ca , " Na
Factors controlling oscillator time scale
of oscillation of inferior-olive neuron
Â.t/, Â o , Â Bias Pitch at time t, pitch amplitude, and pitch
bias angle, respectively
.t/
Combined roll and pitch angle
w .t/
Temporal local wall-shear stress on the
flapping fin surface
.t/, o
Roll angle at time t and roll amplitude,
respectively
Phase difference between roll and pitch
oscillations