Note: Descriptions are shown in the official language in which they were submitted.
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PROPULSION SYSTEM FOR AN AUTONOMOUS UNDERWATER VEHICLE
TECHNICAL FIELD:
[0001] The following relates generally to propulsions systems for marine
vehicles, and has
particular utility when applied to underwater vehicles.
DESCRIPTION OF THE RELATED ART
100021 In the field of marine vehicles, a vehicle may be propelled using one
or more fixed
rear thrusters and the vehicle's orientation and positioning may be controlled
using various
control surfaces mounted to the hull of the vehicle. The flow of water across
the control surfaces
generates a force depending on the orientation of the control surface, and
thus a force on the
vehicle itself. Such an arrangement may be suitable when the vehicle is moving
at sufficiently
high speeds, wherein a greater force is generated as more water flows over the
control surfaces.
[0003] At slower speeds, generally less water flows over the control surfaces,
thereby
reducing the force directed to control the vehicle. The reduced force
generated by the control
surfaces affects the performance of underwater vehicles when carrying out
hovering manoeuvres.
During a hovering manoeuvre, an underwater vehicle may maintain a generally
fixed position
and orientation of the vehicle's hull for some time period, while compensating
for the effects of
cross-currents. This manoeuvrability may be used in various underwater
operations, including
without limitation, inspections that may involve high-detail imaging equipment
and robotic
manipulations that may involve precise movements.
[0004] Differential thrust systems may be used to produce a hover in low-speed
underwater
conditions. Generally, a differential thrust system may comprise several
thrusters that are
mounted at strategic locations around a vehicle and these thrusters are aimed
in certain
directions, allowing the vehicle to have some percentage of its total
available thrust act in any
direction. By varying the magnitude of thrust from each of the thrusters, a
vehicle may be able to
manoeuvre in various dimensions. Many remotely operated underwater vehicles
(ROVs) may
make use of differential thrust systems.
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[0005] The differential thrust system for propulsion allows for hovering for
inspection and
intervention in low speed applications and environments. The differential
thrusters also suitably
compensate for cross-current conditions while maintaining an absolute heading.
[0006] There are many configurations that strive to optimize the positioning
of differential
thrusters for increased control, such as positioning each of the differential
thrusters away from
vehicle's hull. However, many of such configurations may also reduce the
hydrodynamic
streamlining of the underwater vehicle, thereby leading to a loss in energy
efficiency.
100071 In many cases, the reduced operational and travel efficiency is
compensated by
tethering the underwater vehicle, wherein the tether provides some form of
energy to the vehicle.
As a result, an underwater vehicle's travel distance and path is limited to
the length of the tether.
Moreover, the above design considerations can add additional cost and
complexity to an
underwater vehicle.
100081 It is an object of the following to provide a propulsion system that is
configured to
address the above issues.
SUMMARY OF THE INVENTION
100091 In one aspect, there is provided an underwater propulsion system
comprising at least
one assembly comprising a rudder configured to be rotatably connected to the
hull of an
underwater vehicle to permit complete rotation of the rudder with respect to
the hull, an elevator
pivotally attached to the rudder to pitch about an axis perpendicular to the
axis of rotation of the
rudder, and a thrust generator extending from and attached to the elevator
such that the thrust
generator pitches with the elevator.
100101 In another aspect, there is provided an underwater vehicle comprising:
an upper and
lower body positioned vertically above one another and separated by at least
one propulsion
assembly; and the at least one propulsion assembly, each propulsion assembly
comprising: a
vertically oriented rudder configured to be rotatably connected between the
upper and lower
bodies and is fully rotatable about an axis of rotation; an elevator pivotally
attached to the rudder
to pitch about an axis perpendicular to the axis of rotation of the rudder;
and a thrust generator
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extending from and attached to the elevator such that the thrust generator
pitches with the
elevator.
BRIEF DESCRIPTION OF THE DRAWINGS
100111 Embodiments will now be described by way of example only with reference
to the
appended drawings wherein:
100121 Figure 1 a is a perspective view of an exemplary underwater vehicle.
[0013] Figure 1 b is a top planar view of the underwater vehicle shown in
Figure Ia.
100141 Figure 2 is a perspective view in isolation of the exemplary propulsion
system
shown in Figure 1 a.
[0015] Figure 3 is a block diagram of an exemplary embodiment of an underwater
vehicle
and propulsion system.
[0016] Figure 4 is a perspective view of the propulsion system similar to
Figure 2 and
showing various internal components shown schematically in Figure 3.
100171 Figure 5a is a top planar view of top and bottom cross sections of the
rudder, shown
in Figure 2.
[0018] Figure 5b is a top planar view of a middle cross section of the rudder,
shown in
Figure 2.
[0019] Figure 6 is a top planar view in isolation of the propulsion system
shown in Figure 2.
[0020] Figure 7 is a perspective view of another embodiment of an exemplary
underwater
vehicle deployed in an underwater environment.
100211 Figure 8 is a perspective view of the underwater vehicle shown in
Figure 7 while
heaving, surging and pitching.
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100221 Figure 9a is a perspective view of the rotational axes of the
underwater vehicle
shown in Figure 8, relative to the underwater vehicle's reference frame axes.
100231 Figure 9b is a profile view of the rotational axes of the underwater
vehicle shown in
Figure 8, relative to the underwater vehicle's reference frame axes.
[0024] Figure 9c is a planar view of the rotational axes of the underwater
vehicle shown in
Figure 8, relative to the underwater vehicle's reference frame axes.
[0025] Figure 10 is a perspective view of the underwater vehicle shown in
Figure 7 while
heaving.
100261 Figure 11 a is a perspective view of the rotational axes of the
underwater vehicle
shown in Figure 10, relative to the underwater vehicle's reference frame axes.
[0027] Figure l lb is a profile view of the rotational axes of the underwater
vehicle shown in
Figure 10, relative to the underwater vehicle's reference frame axes.
100281 Figure 11 c is a planar view of the rotational axes of the underwater
vehicle shown in
Figure 10, relative to the underwater vehicle's reference frame axes.
[0029] Figure 12 is a perspective view of the underwater vehicle shown in
Figure 7 while
yawing.
[0030] Figure 13a is a perspective view of the rotational axes of the
underwater vehicle
shown in Figure 12, relative to the underwater vehicle's reference frame axes.
[0031] Figure 13b is a profile view of the rotational axes of the underwater
vehicle shown in
Figure 12, relative to the underwater vehicle's reference frame axes.
[0032] Figure 13c is a planar view of the rotational axes of the underwater
vehicle shown in
Figure 12, relative to the underwater vehicle's reference frame axes.
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DETAILED DESCRIPTION
100331 It will be appreciated that for simplicity and clarity of illustration,
where considered
appropriate, reference numerals may be repeated among the figures to indicate
corresponding or
analogous elements. In addition, numerous specific details are set forth in
order to provide a
thorough understanding of the embodiments described herein. However, it will
be understood by
those of ordinary skill in the art that the embodiments described herein may
be practiced without
these specific details. In other instances, well-known methods, procedures and
components have
not been described in detail so as not to obscure the embodiments described
herein. Also, the
description is not to be considered as limiting the scope of the embodiments
described herein.
[0034] Generally, underwater vehicles comprise a body or hull to transport
various loads
while protecting the loads from a submersed marine environment. Various loads
may include
without limitation, scientific equipment, people and components required to
operate the
underwater vehicle. The body or hull of a vehicle may protect the loads from
the effects of the
water, including wetting, and hydrostatic and hydrodynamic pressure. Typically
a propulsion
unit attached to the body is used to move the body in certain directions.
100351 Figure 1 a shows an underwater vehicle comprising two bodies or hulls,
an upper body
2 and a lower body 4. It is noted that the terms `body' and `hull' refer to
the same structure, as
described in more detail below. Both bodies 2, 4 comprise an oblong-shaped
geometry for
streamlining. In the particular embodiment shown in the Figure 1 a, both the
upper and lower
bodies 2, 4 comprise a cylindrical hull having the end portions rounded to
reduce hydrodynamic
resistance. It is noted that the front end, or nose, of each body 2, 4 may be
comprise a more
hemispherical geometry, while the rear end, or tail, may comprise a more
conical geometry.
This profiled geometry allows for reduced water drag. The purpose of each body
or hull 2, 4 is
to house various loads while streamlining the flow of water over the surface
of each body or hull
2, 4 and that any means of doing so are encompassed within the various
possible configurations
for the underwater vehicle.
100361 Turning to Figure 1 b, a top planar view of the underwater vehicle is
shown in context
with directional terminology. The front of the underwater vehicle is referred
to as the fore and
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the rear is referred to as the aft. From the perspective of a person on the
underwater vehicle
facing towards the fore, the left-hand side is referred to as the portside,
while the right-hand side
is referred to as the starboard.
100371 Returning to Figure 1 a, the upper body 2 is positioned directly above
the lower body
4 and extending vertically between the two bodies 2,4 are a pair of rudders 6.
In the embodiment
shown in Figure 1 a, a fore rudder 6a is positioned towards the front of the
underwater vehicle
and an aft rudder 6b is positioned towards the back of the underwater vehicle.
For continued
clarity of the description, suffix `a' herein refers to the fore portion of
the underwater vehicle and
suffix `b' refers to the aft portion. Both the fore rudder 6a and aft rudder
6b comprise rigid
structures that position the upper body 2 at a fixed distance from the lower
body 4. It is
appreciated that a rudder 6 is a control surface that affects the yaw of the
underwater vehicle.
Both rudders 6a, 6b are able to yaw independently of each other, as indicated
by the movement
arrows 16a and 16b. The fore and aft positioning of the rudders 6a, 6b and the
independent
direction of yaw forces generated from the fore rudder 6a and aft rudder 6b
allow for
manoeuvres of various complexities as discussed further below.
100381 In this example, the purpose of each rudder 6 is to act as a control
surface affecting
the yaw, and any configuration capable of doing so is encompassed by the
embodiments
described herein.
100391 The two rudders 6a, 6b form a structural base for the underwater
vehicle's propulsion
system, which further comprises respective elevators 12 and thrusters 14. An
elevator 12
protrudes from both sides of a rudder 6 and comprises a rigid control surface
or plane that is
generally perpendicular to the rudder 6. The flow of fluid over the elevator
12 generates forces
that affect the pitch or inclination of the underwater vehicle. Each elevator
12 is able to rotate or
pitch, as indicated by the movement arrows 18a and 18b. In the embodiment
shown in Figure
1 a, both the fore elevator 12a and aft elevator 12b have a swept wing
geometry to reduce drag. It
is understood that elevators 12 comprising other geometries to control the
pitch while reducing
drag are equally applicable.
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100401 Similar to the rudders 6a, 6b, both the fore elevator 12a and aft
elevator 12b are able
to move independently from one another. In one example, the fore elevator 12a
may pitch
downwards, while the aft elevator 12b may pitch upwards to create a coupled
moment, thereby
pitching the underwater vehicle downwards. The fore and aft positioning of the
elevators 12a,
12b and the independent direction of pitch forces generated from the fore
elevator 12a and aft
elevator 12b allow for manoeuvres of various complexities as discussed further
below.
[0041] It is noted that all control planes (i.e. rudder 6 and elevator 12)
advantageously use
NACA OOxx airfoil profiles, an industry standard in naval architecture. The
NACA OOxx airfoil
profiles provide hydrodynamic efficiency and geometrical convenience. It will
be appreciated
that other airfoil profiles that allow for the same are equally applicable.
100421 Fixed to each elevator 12 is a thrust generator 14, such that the
thrust generator 14 is
oriented with the same pitch as the elevator moves. Since each elevator 12 is
fixed to a rudder 6,
the elevator 12 and, therefore the thrust generator 14, will also be oriented
to have the same yaw
as the rudder 6. The thrust generator 14 is located behind the trailing edge
of the rudder 6 so as
to allow for a larger range of pitch rotation, while avoiding interference
between the thrust
generator 14 and rudder 6. Other configurations between the thrust generator
14, elevator 12,
and rudder 6 that allow the thrust generator to move across a sufficient range
for pitch and yaw
are equally applicable.
[0043] The thrust generator 14 shown in Figure 1 a, comprises a single
propeller driven by a
motor. Other embodiments of a thrust generator 14 may include one more motors
driving one or
more propellers. Alternatively, a thrust generator 14 may comprise the release
of a pressurized
gas or liquid. It is appreciated that any mechanisms for generating thrust are
equally applicable.
[0044] The direction of the force generated by the thrust generator 14 is
indicated by the
direction arrows 20a and 20b. The coupling of a thrust generator 14 to the
elevator 12 and
rudder 6, allows the thrust generator 14 to direct the thrust at various pitch
and yaw angles. The
independent movement of the fore and aft thrust generators 14a, 14b, and the
positioning of the
tbrust generators 14a, 14b in relation to the upper and lower bodies 2, 4
allow the underwater
vehicle to carry out complex manoeuvres, discussed in further detail below.
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[0045] Turning to Figure 2, a perspective view of an isolated propulsion
system is shown in
greater detail. The thrust generator 14, in one embodiment shown in Figure 2,
comprises a
propeller 24 driven by a motor assembly 22. The motor 22 may be located
external to the rudder
6 and elevator 12 to allow the thrust generator 14 to rotate or pitch relative
to the rudder 6. In
addition to increased range of rotation, placing the motor 22 external to the
rudder 6 and elevator
12 reduces the complexity of transferring the motor's energy to the propeller
24. The motor
assembly 22 is fixed to a U-shaped bracket 26, and more particularly to the
portion that bridges
the two armatures of the bracket 26. Each armature on the bracket 26 is
situated between the
elevator 12 and rudder 6. The bracket 26 is fixed to the elevator 12, wherein
the pitch movement
of the elevator 12 and, therefore, the thrust generator 14 may be identical.
The bracket 26 also
positions the propeller 24 further away from the trailing edge of the rudder
6, thereby allowing
the thrust generator 14, in this case the propeller 14, to achieve a larger
range of pitch rotation.
It is appreciated that alternate configurations of the propeller 14, motor 22
and bracket 26 that
allow for a sufficient range of rotation are equally applicable.
100461 Also shown in Figure 2 is an XYZ reference frame that in this example
is fixed
relative to the underwater vehicle body for the purpose of describing the
various configurations
below. The XYZ reference frame is oriented such that the X axis is oriented
along the length of
the vehicle and is directed toward the rear or aft of the vehicle. The Z axis
is oriented vertically
between the upper body 2 and lower body 4, such that the Z axis is aligned
with the vertical
length of the rudder 6, and is directed upwards toward the upper body 2. The Y
axis is oriented
perpendicular to both X and Z axes and, in accordance with chirality, is
directed towards the
starboard side of the underwater vehicle in this example. This reference may
be used to describe
the axes of rotation for the above components.
[0047] The propeller 24 rotates about the axis A. The axis A, in this case,
extends along the
length of the bracket 25 and motor assembly 22. The axis A and the elevator 12
both rotate, or
pitch, about axis B. It is appreciated that the A axis rotates with the
elevator 12 about axis B
since the bracket 25 and motor assembly 22 are fixed to the elevator 12. It is
further understood
that rotational axes A and B remain perpendicular to one another. Axes A and
B, and the rudder
6 rotate, or yaw, about axis C.
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[0048] The three rotational axes, A, B, and C, introduced above, may be
described relative to
the underwater vehicle's XYZ reference frame. In a neutral orientation, the
underwater vehicle's
control surfaces are oriented such that the underwater vehicle is directed in
a straight heading,
with no yawing or pitching movements. In this neutral orientation, the
rotational axis A is
parallel with the X axis. The A axis is oriented towards the back or aft of
the underwater vehicle
in the same direction with the X axis, which is also oriented towards the back
or aft of the
vehicle. In a neutral orientation, the rotational axis B is oriented parallel
to the Y axis.
However, according to the convention shown here, the positive B axis is
oriented towards the
portside of the underwater vehicle and the positive Y axis is oriented towards
the starboard side
of the underwater vehicle. The rotational axis C always remains oriented
parallel and in the
same direction as the vertical Z axis when using this reference frame.
[0049] It is noted that the A axis may pitch about the B axis by some angle +/-
alpha (a). It
is also understood that the thrust from the thrust generator 14 is directed
along the A axis. For
example, when the A axis inclines above the X axis by + alpha, the elevator 12
and direction of
thrust is pitched in a downward direction. Similarly in another example, when
the A declines
below the X axis by - alpha, the elevator 12 and the direction of thrust is
pitched in an upward
direction. It is further appreciated that when the thrust is directed in along
the X axis, then the
thrust is directed towards the aft of the underwater vehicle, thereby
propelling or pushing the
underwater vehicle forward.
[0050] With regard to the yaw movement, both A and B axes, as well as the
rudder 6, may
pivot about axis C by some angle +/- beta ((3). For example, when the
propulsion assembly yaws
by +beta, the rudder 6 and the A axis rotate from the X axis in a counter
clockwise direction.
Similarly, the B axis rotates from the -Y axis in a counter clockwise
direction by +beta. In yet
another example, when the propulsion assembly yaws by beta, the trailing edge
of the rudder 6
and the A axis rotate from the X axis in a clockwise direction, and the B axis
rotates from the -Y
axis in a clockwise direction. It can be appreciated that the propulsion
system may yaw about
the C axis by 360 degrees in either a clockwise or counter clockwise
direction. As will be
exemplified below, such freedom of rotation about the C axis enables complex
and controlled
movements that provides greater handli.ng and control of an underwater
vehicle.
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[0051] The combined movements of the pitch and yaw allows the axis A, and
therefore
thrust vector, to be oriented in various directions. The combination of the
two or more in-line
propulsion systems with the described underwater vehicle allow for various
manoeuvres with
five degrees of freedom, including pitch, yaw, heave (i.e. moving up and
down), surge (i.e.
moving forward and backward) and sway (i.e. moving left and right).
[0052] It may be noted that roll movements may also be achieved if the
elevators 12 are
controlled to pitch in opposite directions. For example, if the starboard
elevators were to pitch
upwards and the portside elevators were to pitch downwards, then the
underwater vehicle may
tend to roll towards the portside.
[0053] Turning to Figure 3, the various components in the propulsion system
are shown
schematically. The rudder 6 subassembly, elevator 12 subassembly and thrust
generator 14
subassembly each comprise a motor 30, 36, 42 motor controller 28, 34, 40 and
gearbox 32, 38,
44. In general, each motor controller 28, 34, 40 receives signals from a
vehicle control unit 48
through a network communication system 46. The motor controller 28, 34, 40
then actuates its
corresponding motor 30, 36, 42, which may be coupled to a gearbox 32, 38, 44,
to modify the
speed and power output of the motor 30, 36, 42.
[0054] The vehicle control unit 48 is preferably a computer, housed in the
upper body 2 of
the underwater vehicle, which contains the vehicle's control system software
(not shown but can
be appreciated as any computer instructions, data structures, memory and other
software
components stored on and/or accessible from a computer readable medium). Based
on
navigational sensor input (e.g. GPS, DVL, Altimeter, Attitude Sensor) and
using pre-
programmed mission criteria, the control system software may calculate the
desired vehicle
speed, pitch, roll, and heading. Then, based on the current speed, pitch,
roll, and heading, the
control system sends control information via a network communication system
46, such as a
controller-area network (i.e. CAN) bus (as shown in Figure 3), to the
respective motor
controllers 28, 34, 40 for each rudder 6, elevator 12 and thrust generator 14
to achieve the
desired orientation.
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[0055] The sub-assemblies in Figure 3 are indicated by the dashed lines, while
the outer solid
lines indicate the pressure housings. The rudder subassembly, comprising the
rudder's motor
controller 28, motor 30 and gearbox 32, is completely contained within its own
pressure housing,
located in the upper body 2 of the underwater vehicle. Components from the
elevator and thrust
generator subsystem share a pressure housing located in the rudder 6. The
elevator's motor
controller 34, motor 36 and gearbox 38, as well as the thrust generator's
motor controller 40 are
located within the pressurized portion of the rudder 6. The thrust generator's
motor 42 and
gearbox 44 are located external to the rudder 6 and elevator 12 in a separate
pressure housing 22
fixed to the end of the bracket 26. The purpose of placing the above
components in various
pressure housings is to protect the above components from the effects of the
water while
reducing mechanical complexity.
100561 Figure 4 shows various ones of the above components when housed in the
physical
structures. In this embodiment, the rudder 6 is divided into three logical and
physical sections;
the top 52, middle 54, and bottom 56 sections. The top 52 and bottom 56
sections are free-
flooding to allow for water to enter and exit freely through designated
drainage holes. The
drainage holes are positioned in certain areas along the airfoil of the rudder
6 to maintain
hydrodynamic efficiency. In one embodiment, the drainage holes may be placed
along the top
and bottom surfaces of the rudder 6, wherein the top surface is adjacent to
the underside of the
upper body 2 and the bottom surface is adjacent to the topside of the lower
body 4. The middle
section 54 of the rudder 6 is pressurized to house the elevator's motor
controller 34, motor 36
and gearbox 38, as well as the thrust generator's motor controller 40. It can
be appreciated that
the top 52 and bottom 56 sections of the rudder 6 are free-flooding to reduce
the effects of
dynamic shifting buoyancy forces on the underwater vehicle.
[0057] Cabling from the upper body 2 to the lower body 4 may also be routed
through the
hollow shaft 50 around which the rudder 6 rotates. Cabling from the upper body
2 to the
respective elevators 12 and thrust generators 14 on the rudder 6 is also
routed through this
hollow shaft 50 to the components in the pressure housings, which require
access to power and
the communication network 46.
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100581 In this embodiment, the rudder's top 52 and bottom 56 sections are
almost identical
or mirror images of each other except for one difference pertaining to the
joints. The joint from
the top section 52 to the upper body 6 contains the motor 30 for rotating the
rudder 6, whereas
the joint from the bottom section 56 to the lower body 4 contains a bearing to
allow for smooth
yaw movement.
[0059] The geometry and functionality of the rudder's middle section 54 differ
from the top
52 and bottom 56 sections, although it is mechanically attached to the other
two sections. The
profile of a top 52 or bottom 56 section, shown in Figure 5a, comprises a
rounded leading edge
and a pointed trailing edge. The front face of the middle section 54 is curved
to match the nose
radius of the airfoil-like profile of the rudder's top 52 and bottom 56
sections. However, as
shown in Figure 5b, the trailing edge portion of the rudder's middle section
54 has a different
rectangular profile instead of a pointed edge.
100601 Returni.ng to Figure 4, the rectangular profile towards the trailing
edge increases the
volume within the middle section 54 of the rudder 6 and, therefore, allows
room for components,
such as motor controllers 34, 40, to be stored within the pressure housing. At
least one shaft 58
extends horizontally through the middle section, via two waterproof shaft
seals, connecting the
elevator motor 36 and gearbox 38 to the elevator planes 12. The rotation of
the horizontal shaft
58 may cause the elevator planes 12 to pitch. It may be noted that the
horizontal shaft 58
corresponds to the rotational axis B. The elevator 12 may be composed of two
identical planes,
attached on either side of the rudder's middle section 54 via the horizontal
shaft 58, as well as
the attached bracket 26 used for mounting the motor assembly 22 and propeller
24 aft of the two
planes.
[0061] Figure 4 also illustrates where the elevator planes may be connected
and aligned
together, such that one motor 36 is required to actuate both planes of the
elevator 12. A single
motor configuration reduces power consumption, reduces complexity and reduces
the amount of
space required. Alternatively, in another embodiment, the starboard plane and
portside plane
may each be coupled to their own separate motor for independent control.
Therefore, the two
separate motors may facilitate rolling movement.
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[0062] It may be noted that both planes in the elevator 12 do not contain
pressure housings,
and are free-flooding. Similar to the rudder 6, drainage holes are provided to
allow water to
enter and exit the elevator 12, and the holes are placed along the elevator 12
to maintain
hydrodynamic efficiency. In one embodiment, the drainage holes are placed on
the face of the
elevator plane 12 attached to the bracket 26 and further, coincident with an
identical hole in the
bracket 26 itself. This embodiment allows water to enter and/or exit through
the drainage holes
in the elevator 12, through the coincident holes in the attached bracket 26.
The elevator 12 is
free-flooding to reduce the effects of shifting buoyancy forces on the
underwater vehicle. As the
elevator 12 extends away from the centerline of the underwater vehicle, and
pitches and yaws in
various directions, the effects of positioning a pressurised housing, or
buoyancy generator, may
be avoided by flooding the elevator 12 structure. It is noted that the effects
of positioning a
pressurised housing in the elevator 12 may comprise changes in resulting
moments and force
vectors acting on the underwater vehicle during various manoeuvres.
[0063] Figure 4 further shows the thrust generator 14, which, in one
embodiment, comprises
a motor 42 and planetary gearbox 44 mounted inside a hydrodynamic pressure
housing for the
motor assembly 22, with a sealed bearing connecting the output shaft to a
large diameter
propeller 24. A cable from the motor assembly housing 22 to the pressurised
rudder housing, or
middle section 54, connects the motor 42 to the motor controller 40. It can be
appreciated that
the motor controller 40 is housed in the rudder's pressurised middle section
54 in this example.
[0064] The motor assembly 22 and propeller 24 are mounted to the bracket 26,
which is
mechanically attached to the elevator planes and placed slightly aft of the
trailing edge of the
rudder 6. The angle of rotation of the elevator 12 is limited to prevent the
bracket 26 and
propeller 24 from impacting the trailing edge of the rudder 6. Both hard
stops, implemented
mechanically, and soft stops, implemented in the vehicle control unit 48, may
be added to
prevent impacts.
[0065] Figure 6 shows the propulsion assembly from a top planar view. Seen
more clearly,
the axis A pitches about axis B and yaws about axis C. It is also noted in
this embodiment, the
pitch axis B may be offset from the yaw axis C. This offset is also reflected
in the
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implementation, wherein the rudder 6 pivots about the vertical hollow shaft
50, which is located
towards the leading edge of the rudder 6. The elevator 12 is attachable to the
rudder 6 by the
horizontal shaft 58, which is located further back from the leading edge of
the rudder 6.
[0066] In Figure 6, the profile of the rudder's middle section 54, which
comprises a
rectangular-shaped trailing edge, is also shown relative to the profile of the
rudder's top section
52. In addition, the bracket 26 is shown attached to an inner portion of the
elevator 12.
100671 Turning to Figure 7, one embodiment of the underwater vehicle in an
underwater
enviromnent is shown relative to a seabed 64. In this embodiment, various
sensors 60, for
example sonar and imaging equipment, are located in the lower body 4 and may
be used to
collect data about the seabed 64. Some sensors 60 may be positioned in the
lower body 4 to
allow for better line-of-sight with the area below the underwater vehicle.
Other sensors 60 may
also be located in the upper body 2. The upper body 2, for example, may house
a wireless
communications receiver and transceiver 62 to communicate with other marine
vessels or a base
station. The communications system 62 may relay various information including
for example,
control commands and sensor data. The communications system 62 may relay
command signals
to the vehicle control unit 48 to carry out various manoeuvres by orienting
the propulsion system
in particular configurations.
[0068] It has also been found that various ones of these components can be
housed in the
lower body 4 in order to lower the center of gravity, which assists in the
various movements of
the vehicle. By way of background, when a marine vessel is tilted the center
of buoyancy of the
vessel moves laterally. The point at which a vertical line through the tilted
center of buoyancy
crosses the line through the original, non-tilted center of buoyancy is the
metacenter. Lowering
of the center of gravity increases the metacentric height, that is the
distance between the
metacentre and center of buoyancy. A larger metacentric height increases the
natural stability of
the vehicle in pitch and roll.
[0069] It is appreciated that various manoeuvres, many of which utilize the
natural stability
of the underwater, may be achieved with the described propulsion system as
described below.
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[0070] Figure 8 shows the underwater vehicle ascending with the length of the
bodies 2, 4
being generally parallel with the flat seabed 64, and having a slight pitch.
This manoeuvre
involves the fore elevator 12a and thrust generator 14a pitching upwards,
which causes the nose
or front end of the underwater vehicle to move in an upwardly direction.
Simultaneously, the aft
elevator 12b and thrust generator 14b pitch upwards as well, which also causes
the tail or back
end of the underwater vehicle to move in an upwardly direction as well. This
combined
movement of both the fore and aft propulsion systems allows the underwater
vehicle to move
both forward and upward simultaneously. Alternatively, this manoeuvre may be
characterised
by pitch, heave and surge.
100711 Figures 9a to 9c show the perspective view, profile view and planar
view of the
rotational axes A, B, and C relative to the underwater vehicle's XYZ reference
frame during an
upward and forward ascending manoeuvre, according to Figure 8. From Figure 9a,
the fore
rotational axis Al rotates below the X axis by some angle -al degrees, thereby
directing the thrust
downwards. The aft rotational axis A2 also rotates below the X axis by some
angle -a2 degrees,
such a2 is slightly less than al. Therefore, more thrust is generally directed
downwards towards
the fore of the underwater vehicle compared to the aft, which may cause the
overall underwater
vehicle to pitch slightly upwards. The profile view in Figure 9b also shows
that the A axis has a
horizontal component direct along the X axis and, thus, the some of the force
or thrust from the
thrust generators 14a, 14b is acting along the X axis to propel the underwater
vehicle forward.
100721 Figure 9c also shows that no yawing action is involved in this
manoeuvre, since the
planar view shows that A1 and A2 are still aligned with X axis, and Bl and B2
are still aligned
with the -Y axis. Therefore, rotational angles (31 and (32 both equal0 .
10073] Turning now to Figure 10, the underwater vehicle is shown carrying out
another
manoeuvre, such that the underwater vehicle is vertically translating upwards,
or heaving, only.
There are no yaw, pitch, roll, surge and sway movements. This heave manoeuvre
may be useful
in various situations. For example, when the underwater vehicle wants to
inspect or navigate
with respect to the vertical face of an underwater cliff, the underwater
vehicle may move
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upwards and downwards along the height of the cliff while maintaining a fixed
horizontal
distance from the cliff face.
[0074] Figures 11 a to 11 c show different views of the orientations of the
rotational axes
relative to the XYZ reference frame for the heave-only manoeuvre. First, the
fore propulsion
system yaws 180 about the C axis, such that the leading edge of the fore
rudder 6a is directly
facing the leading edge of the aft rudder 6b. This yaw rotation is represented
by the angle (31,
which equals 180 . As shown in Figures 11 a and 11 c, after the rotation of
(31, the rotational axis
Bl is aligned and pointed in the same direction as the +Y axis. It is noted
that the aft propulsion
system does not yaw and, thus, (32 equals 00.
100751 After the first Bl rotation, Figures 11a and 11 b show that the
elevator 12 and thrust
generator both pitch upwards. Therefore, the A1 axis rotates below the -X axis
in a counter
clockwise direction by some angle +al, and the A2 axis rotates below by the X
axis in a
clockwise direction by some angle -a2. Assuming the magnitude of thrust is the
same from both
thrust generators 14a and 14b, the pitch angles a1 and a2 are equal in order
to cancel out the
horizontal forces along the X axis. The horizontal forces cancel each other
out since the thrust
generators 14a and 14b are directed in opposite directions along the X axis,
resulting in only
vertical forces. This allows the underwater vehicle to translate vertically
upwards.
100761 Turning to Figure 12, the underwater vehicle is shown in the middle of
a turn
manoeuvre towards the left or starboard side. The two separate propulsion
systems located at the
fore and aft of the underwater vehicle create a coupled moment about the
center of the
underwater vehicle, which allow for a smaller turning radius. In effect, the
underwater vehicle
could yaw about a central point with little forward or lateral movement. For
example, if the fore
rudder 6a directs its leading edge to the face the portside and the aft rudder
6b directs its leading
edge to face the starboard side, then the underwater vehicle may rotate or yaw
in a counter
clockwise direction about a point. This manoeuvrability may be used, for
example, to face a
forward mounted sensor on the vehicle in an opposite direction while in an
environment with
constrained space.
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100771 Figures 13a to 13c show the different views of the rotational axes A, B
and C relative
to the underwater vehicle's XYZ reference frame for a the starboard turn,
according to Figure 12.
It is appreciated that this manoeuvre does not require any pitching motion
and, thus, both fore
and aft elevators 12a, 12b do not rotate about the B axis. As a result al and
a2 are equal to 0 , as
shown most clearly in Figure 13b.
100781 Figures 13a and 13c show the fore propulsion system yawing by some
angle -(31 in
counter clockwise direction about the Cl axis. The rotational axis Al rotates
away from the X
axis by -(31, and the rotational axis Bl rotates away from the -Y axis by -
(31. It is noted that in
this embodiment, the rotational axes A and B remain perpendicular to one
another. With this
clockwise rotation, the leading edge of the fore rudder 6a is directed towards
the starboard side
and the thrust is directed towards the portside. This causes the nose of the
vehicle to turn
towards the right or starboard.
100791 Similarly, the aft propulsion system yaws by some angle (32 in a
clockwise direction
about the C2 axis. The rotational axis A2 rotates away from the X axis by (32,
and the rotational
axis B2 rotates away from the -Y axis by (32. It is noted that in this
embodiment, the rotational
axes A and B remain perpendicular to one another. With this counter clockwise
rotation, the
leading edge of the aft rudder 6b is directed towards the portside and the
thrust is directed
towards the starboard. This causes the tail end of the vehicle to turn towards
the left or portside.
In this example manoeuvre, the angle (32 is less than the angle (31 and, thus,
the nose of the
underwater vehicle turns more quickly to the starboard than the tail end turns
to the portside.
100801 There may be various combinations of pitch and yaw that allow for
different
movements. For example, if both rudders 6a, 6b direct their leading edges to
the left or portside,
then the entire underwater vehicle will sway, or laterally translate, towards
the portside. This
sway movement does not require any yawing rotations. Other movements may
include, for
example, pitching and yawing simultaneously, or heaving and yawing
simultaneously, or moving
backwards and pitching simultaneously. In a more specific example, the
underwater vehicle may
maintain a constant downwards pitch, while moving backwards and side-to-side.
Various
combinations of pitch, yaw, heave, surge and sway may be accomplished with the
propulsion
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system described herein. Furthermore, with independent starboard and portside
elevators, roll
may also be achieved. Therefore, the underwater vehicle may move in all six
degrees of
freedom.
[0081] Another advantage in movement is the underwater vehicle's ability to
hover, or stay
in a fixed position, while maintaining an absolute heading. The propulsion
system also allows
the underwater vehicle to hover in the presence of currents in any direction
and of reasonable
speed.
[00821 Different manoeuvres may also be achieved by varying the force produced
by the
thrust generators 14. In one manoeuvre, for example, the fore thrust generator
14 may produce
more force during a turn than the aft thrust generator 14b, thereby causing
the nose of the
underwater vehicle to move at a faster speed. This variable thrust may be
generated by
increasing or decreasing the speed at which the propeller 24 rotates about the
axis A. In
addition, the thrust may be varied by controlling the pitch, or angle of
attack, or the propeller's
blades.
[0083] Having two or more of the propulsion systems positioned towards the
fore and aft of
the underwater vehicle also allows for high manoeuvrability. This
configuration encompasses
the advantages of both thrust vectoring and differential thrusters.
Furthermore, by positioning
the two propulsion systems in-line with one another and situated between the
upper body 2 and
lower body 4, the drag is reduced and hydrodynamic efficiency is maintained.
100841 The configuration of the upper body 2 and lower body 4 also provides
the advantage
of increased stability with respect to pitch and roll. Separating and placing
the lower body 4
below the upper body 2, lowers the center of gravity and provides a higher
center of buoyancy.
100851 Although the above has been described with reference to certain
specific
embodiments, various modifications thereof will be apparent to those skilled
in the art as
outlined in the appended claims.
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