Highly Maneuverable Biorobotic Underwater Vehicles 11.1 Biorobotics 283
Part B | 11.1
mals shown use flapping caudal and/or pectoral fins for
propulsion/maneuvering. Since the propulsive mechanism of these flapping lifting surfaces makes use of
transitional vortex shedding, it must be that larger and
larger biorobotic vehicles can also be built with flapping fin propulsion as long as the fin Reynolds number
is within the critical range. From the graph in Fig. 11.1,
this is a limit of displacement volume of the order of
1 m
3 (of the size of a large shark). (We have not been
able to find animal data between 2 and 100 m
3 , and
a higher limit is not ruled out.) The tuna white muscle
data shows that power required for maneuvering is 10
times greater than that required for cruising. Below, we
review our biorobotic vehicles of displacement volume
of the order of 0:05 m
3 .
Let us begin with several important definitions.
A mature platform based on bio-inspiration or biomimicry is one for which:
1. A user mission has been identified.
2. An instrumented version has been built and demonstrated both in the laboratory and in open/saltwaters.
3. Integration with mission sensors has been demonstrated.
4. Documentation or knowledge about improvements
over conventional engineering solutions and mechanisms have been experimentally verified and theoretically backed.
5. The biology principle, mechanism, and design laws
have been determined, are mathematically founded,
and have been peer reviewed, and
6. Long-duration performance has been demonstrated.
Bio-inspiration is described as an undertaking in
which the science has been distilled and implemented in
a framework that is useful to a user where a bio-inspired
platform does not necessarily resemble any animal. In
contrast, bio-mimicry is an effort in which, first and
foremost, biology is mimicked and whereby the resulting platform resembles the chosen animal. The latter,
which tends to draw popular interest, may have value in
camouflaging.
The subject of unmanned biorobotic underwater vehicles has been reviewed in the past [11.7, 8]. The
underlying science and technology have been reviewed
by several authors [11.2–4, 7–17]. From the larger
biorobotic point of view ( 1 m scale), we separate
the propulsive surfaces of animal swimmers in two
categories as follows: smaller swimmers with highly
flexible caudal and pectoral fins and with main bodies that are more on the flexible side (they have lower
Reynolds number); generally larger swimmers whose
fins are rather rigid (but not fully rigid) with bodies that are more on the rigid side (they have higher
Reynolds number) [11.13]. An example of the former
is sunfish (the kind of fish extensively studied in the
laboratory [11.18]), and the examples of the latter are
penguins, dolphins and whales (the fins are studied
mostly biorobotically [11.3, 11, 14, 15, 19]). (Box fish
with its rigid body and flexible fins straddles the two
categories [11.20].)
Biorobotics received an early boost with the biomimicry of caudal fin swimming of tuna fish [11.21–23]
in a similar flexible hull. This was followed by departure from bio-mimicry of form – by the application
of flapping fin propulsion technology to rigid cylinders – the common engineering underwater hull forms
of choice [11.19]. This chapter focuses mainly on flapping fin propulsion and control technology, and the fins
are large and fairly stiff (or only slightly flexible).
In relation to swimming animals and from a practical point of view, the primary interest is in the hovering
and maneuvering of flow-aligned cylinders or other
platforms of about 1 m in length and 30 cm in diameter or depth. Hovering and other maneuverings such
as yawing include station-keeping in sea states and in
currents. Ideally, such platforms should have high efficiency, with minimal input of momentum into the water
and very little acoustic radiation. It is also desirable to
have novel requirements such as a built-in disturbance
rejection capability (robustness) and rational integration of controllers, actuators, and sensors. Concepts
that have a rigorous mathematical formulation are preferred, and a synthesis of bio-physical advances shows
that this formulation needs to be nonlinear in character to achieve self-regulation and disturbance rejection
properties. (Theoretical definition of self-regulation and
why this is a nonlinear process is given in [11.15];
theory showing why the motion of animals is determined by olivo-cerebellar dynamics which is a nonlinear self-regulating process is given in [11.24–29]; and
the theory of why sensing, control, and actuator hydrodynamics in swimming and flying animals are likely
described by similar self-regulating equations, is given
in [11.28].
Below, the flapping fin and the transitional vortices produced are treated as coupled nonlinear oscillators. The transitional (reverse Karman) vortex production process, which is the key to thrust, is shown
schematically in Fig. 11.2 for a pectoral fin [11.15, 28].
A leading-edge vortex (LEV) on the fin (Fig. 11.2c)
and a reverse Karman vortex train (Fig 11.2b) in the
wake are produced when the Strouhal number (St) and
pitch amplitude (and Reynolds number) are appropriate (Fig. 11.2f). Due to the motion of the stagnation
point [11.15], symmetry is broken [11.29]. As a result,
the lift force is enhanced and thrust is produced. This
vortex becomes uniform along the span when an appropriate twist is applied (Fig. 11.2d,e). Figure 11.2f shows
Part B | 11.1
mals shown use flapping caudal and/or pectoral fins for
propulsion/maneuvering. Since the propulsive mechanism of these flapping lifting surfaces makes use of
transitional vortex shedding, it must be that larger and
larger biorobotic vehicles can also be built with flapping fin propulsion as long as the fin Reynolds number
is within the critical range. From the graph in Fig. 11.1,
this is a limit of displacement volume of the order of
1 m
3 (of the size of a large shark). (We have not been
able to find animal data between 2 and 100 m
3 , and
a higher limit is not ruled out.) The tuna white muscle
data shows that power required for maneuvering is 10
times greater than that required for cruising. Below, we
review our biorobotic vehicles of displacement volume
of the order of 0:05 m
3 .
Let us begin with several important definitions.
A mature platform based on bio-inspiration or biomimicry is one for which:
1. A user mission has been identified.
2. An instrumented version has been built and demonstrated both in the laboratory and in open/saltwaters.
3. Integration with mission sensors has been demonstrated.
4. Documentation or knowledge about improvements
over conventional engineering solutions and mechanisms have been experimentally verified and theoretically backed.
5. The biology principle, mechanism, and design laws
have been determined, are mathematically founded,
and have been peer reviewed, and
6. Long-duration performance has been demonstrated.
Bio-inspiration is described as an undertaking in
which the science has been distilled and implemented in
a framework that is useful to a user where a bio-inspired
platform does not necessarily resemble any animal. In
contrast, bio-mimicry is an effort in which, first and
foremost, biology is mimicked and whereby the resulting platform resembles the chosen animal. The latter,
which tends to draw popular interest, may have value in
camouflaging.
The subject of unmanned biorobotic underwater vehicles has been reviewed in the past [11.7, 8]. The
underlying science and technology have been reviewed
by several authors [11.2–4, 7–17]. From the larger
biorobotic point of view ( 1 m scale), we separate
the propulsive surfaces of animal swimmers in two
categories as follows: smaller swimmers with highly
flexible caudal and pectoral fins and with main bodies that are more on the flexible side (they have lower
Reynolds number); generally larger swimmers whose
fins are rather rigid (but not fully rigid) with bodies that are more on the rigid side (they have higher
Reynolds number) [11.13]. An example of the former
is sunfish (the kind of fish extensively studied in the
laboratory [11.18]), and the examples of the latter are
penguins, dolphins and whales (the fins are studied
mostly biorobotically [11.3, 11, 14, 15, 19]). (Box fish
with its rigid body and flexible fins straddles the two
categories [11.20].)
Biorobotics received an early boost with the biomimicry of caudal fin swimming of tuna fish [11.21–23]
in a similar flexible hull. This was followed by departure from bio-mimicry of form – by the application
of flapping fin propulsion technology to rigid cylinders – the common engineering underwater hull forms
of choice [11.19]. This chapter focuses mainly on flapping fin propulsion and control technology, and the fins
are large and fairly stiff (or only slightly flexible).
In relation to swimming animals and from a practical point of view, the primary interest is in the hovering
and maneuvering of flow-aligned cylinders or other
platforms of about 1 m in length and 30 cm in diameter or depth. Hovering and other maneuverings such
as yawing include station-keeping in sea states and in
currents. Ideally, such platforms should have high efficiency, with minimal input of momentum into the water
and very little acoustic radiation. It is also desirable to
have novel requirements such as a built-in disturbance
rejection capability (robustness) and rational integration of controllers, actuators, and sensors. Concepts
that have a rigorous mathematical formulation are preferred, and a synthesis of bio-physical advances shows
that this formulation needs to be nonlinear in character to achieve self-regulation and disturbance rejection
properties. (Theoretical definition of self-regulation and
why this is a nonlinear process is given in [11.15];
theory showing why the motion of animals is determined by olivo-cerebellar dynamics which is a nonlinear self-regulating process is given in [11.24–29]; and
the theory of why sensing, control, and actuator hydrodynamics in swimming and flying animals are likely
described by similar self-regulating equations, is given
in [11.28].
Below, the flapping fin and the transitional vortices produced are treated as coupled nonlinear oscillators. The transitional (reverse Karman) vortex production process, which is the key to thrust, is shown
schematically in Fig. 11.2 for a pectoral fin [11.15, 28].
A leading-edge vortex (LEV) on the fin (Fig. 11.2c)
and a reverse Karman vortex train (Fig 11.2b) in the
wake are produced when the Strouhal number (St) and
pitch amplitude (and Reynolds number) are appropriate (Fig. 11.2f). Due to the motion of the stagnation
point [11.15], symmetry is broken [11.29]. As a result,
the lift force is enhanced and thrust is produced. This
vortex becomes uniform along the span when an appropriate twist is applied (Fig. 11.2d,e). Figure 11.2f shows