[0001] The Government has rights in this invention pursuant to Contract N00039-83-C-0191
awarded by the Department of the Navy, United States of America.
[0002] This invention relates generally to a stable support for structures at or above the
surface of a fluid medium and in particular to a communications buoy for use in the
ocean.
[0003] Many types of flotation devices exist with differing characterisitcs.
[0004] Damper plates and toroid shaped flotation devices have been used to create buoys
which are wave followers. For example, see Buoy Engineering, H.O. Berteaux, John and
Sons, 1976 Pg. 212-213. These surface following buoys are subject to strong heave
and pitch due to the motion of the ocean.
[0005] A more stable buoy can be built by decreasing the cross section of the buoy at the
water level. Such devices experience less heave. The mass of the buoy can also be
distributed to create a righting moment. This will decrease the pitch.
[0006] Further stability can be obtained by surface decouplino. A buoyant cylinder with
a counterweight suspended from its bottom is a typical example, Berteaux, supra. Such
spar buoys cannot have much reserve buoyancy and usually have a large draft. These
factors mitigate the usefulness of these types of buoys in deep water.
[0007] It is an object of this invention to provide a communications buoy having an antenna
which uses the surface of the ocean as a ground plane; such buoy having structure
which limits the antenna's motion with respect to the surface of the ocean to within
4 in (10 cm.) heave and 25
0 pitch.
[0008] It is another object of this invention to provide a stable buoy that can withstand
ocean conditions up to and including state 5.
[0009] The buoy according to the invention may be used as part of a search and rescue system
for locating downed aircraft and ships in distress. Such buoys would be carried by
vehicles and be deployed when needed. Their distress signal could be received by satellites
and their position located.
[0010] The bouy according to the invention could carry various other types of payloads or
support various antenna structures as well. Other possible uses include oceanographic
monitoring buoys and satellite linked sonobuoys.
[0011] It is an object of this invention to provide an apparatus for the stable support
of a structure, such as an antenna, in a fluid medium, such as water.
[0012] It is a futher object of this invention to limit the motion of an antenna supported
above the surface of the ocean, within the operational limits of the transmitting
system.
[0013] It is a further object of this invention to support an electronics payload near the
surface of the ocean such that the power loss between the electronics payload and
an antenna supported on the surface is within operational limits and, specifically,
less than 3db.
[0014] The invention is an apparatus for the stable support of a structure, such as an antenna,
in a fluid medium, such as water. The apparatus comprises a bouyant first member and
first means for engaging the structure. The first means is associated with the member.
Second means are provided for channeling the fluid which encroaches upon the bouyant
member due to any motion of the member with respect to the surface of the fluid medium,
the encroaching fluid being channeled back into the fluid medium such that the kinetic
energy of the bouyant first member is dissipated as the fluid is channeled back into
the fluid medium.
[0015] Alternatively, the apparatus according to the invention may comprise a bouyant first
member for supporting the structure, a payload and decoupling means for supporting
the payload below the bouyant member such that any motion of the payload is decoupled
from the member and any motion of the member is decoupled from the payload.
[0016] Alternatively, the apparatus according to the invention may comprise a bouyant member
with an inwardly arched bottom portion, and means, associated with the bouyant member,
for engaging the structure.
[0017] Alternatively, an apparatus according to the invention may comprise an antenna, a
bouyant member, first means for generating an r.f. signal, second means interconnecting
the first means and the antenna, and decoupling means for supporting the first means
below the bouyant member such that any motion of the member is decoupled from the
first means and the motion of the first means is decoupled from the member.
[0018] Alternatively, the invention may comprise a communications bouys which is stable
in a fluid medium and includes structures for minimizing the heave and pitch of the
bouy. Specifically, a flotation bag with a concave bottom formed by pulling in the
center of the bottom of the bag with straps secured to the inside walls of the bag
supports an antenna. A semi-rigid damper skirt extending around the base of the bag
is submerged when the apparatus is floating in the fluid medium. The bag is provided
with a ribbon fence comprising containers which have an opening above the fluid level,
and an opening below the fluid level, when the apparatus is floating in the medium,
allowing the fluid to flow in and out of the containers. The payload is supported
in a cylindrical chamber connected to the flotation bag by a flexible cable, enabling
the payload to swing.
Figure 1 is a side view of a communications bouy according to the invention deployed
in water.
Figure 2 is a side view of the bouy of Figure 1 with parts broken away to illustrate
internal structure.
Figure 3 is a perspective view of a communications bouy according to the invention
in an undeployed state.
Figure 4 is a top view of a flotation bag according to the invention.
Figures 5a -5g are graphs illustrating the operational transmission requirements and the estimated
performance of an antenna system according to the invention under varying conditions
of heave and pitch.
[0019] Referring to figures 1 and 2, flotation bag 1 is an inflated balloon-like structure
having a specific gravity less than the specific gravity of fluid medium W. Bag 1
encloses antenna 2 and supports a payload 3 below the surface of medium W.
[0020] Although this embodiment comprises flotation bag 1 which encloses antenna 2, the
invention includes flotation devices of any type which support structures.
[0021] Figures 5a-5g compare the estimated performance 102 of an antenna such as antenna
3 under varying conditions of heave and pitch with the operational performance requirement
101 for successful transmission. Antenna 3 uses the surface of the fluid W as a ground
plane. Heave and pitch disturb the relationship between the radiating antenna 3 and
the ground plane, changing the radiation pattern of antenna 3. As shown by graphs
5a, 5b, and 5f, the estimated performance 102 of antenna 3 crosses and falls below
the operational performance requirements for successful transmission between certain
points on the graphs. In summary, successful transmission is not achieved when antenna
3 undergoes more than 4 ins (10 cms) heave or 25° pitch. The apparatus according to
the invention limits the motion of the antenna relative to the ground plane to within
10 cms. heave and 250 pitch, under ocean conditions up to sea state 5.
[0022] A damper skirt 4 extends around the base of the flotation bag 1 and is made of a
semi-rigid material supported in a horizontal position by ribbon fence 5.
[0023] When the apparatus is afloat, damper skirt 4 is below the surface of the medium W.
The weight of the payload 3, the shape of the bottom of the flotation bag 1 and the
bouyancy of bag 1, which will be described in detail below, are configured so that
damper skirt 4 is below the water line when the apparatus is stable.
[0024] Damper skirt 4 increases the surface area in contact with the ocean, offering a surface
which resists motion V within medium W. In order to rise or tip in response to a wave,
damper skirt 4 must travel upwardly through the fluid. The resistance to upward movement
of skirt 4 is caused by the fluid above the skirt 4. The energy that would otherwise
cause heave and pitch of the flotation bag 1 is dissipated by this resistance and
any resulting movement of skirt 4 within the medium W.
[0025] As shown particularly in figure 4, ribbon fence 5 which supports the damper skirt
4 is a series of contiguous compartments, 5a-5g. Damper skirt 4 acts as the base of
the compartments-5a-5g of ribbon fence 5 and the side ls of the flotation bag 1 forms
the back wall of the compartments. The walls of the compartments in the embodiment
illustrated comprise a strip of semi-rigid material connected to the side of the flotation
bag 1 at spaced apart points P. The flotation bag 1, damper skirt 4 and the strip
form the contiguous compartments, the combination of which is referred to herein as
ribbon fence 5.
[0026] Each compartment 5a-5g has an opening 6 in the lower portion thereof, where the strip
joins to damper skirt 4. The compartments have an opened top 7. When stable in the
ocean, the bottom hole 6, which has a cross section less than the opening at the top
7, is beneath the level of the medium W. The water line on the flotation bag when
the apparatus is at rest in the ocean is approximately at the midpoint 8 of the height
of the ribbon fence 5.
[0027] Compartments 5a-5h act as containers for the fluid medium. Fluid encroaching upon
bag 1 can enter the compartments through hole 6 or the opened top 7 and can drain
from the compartments through the hole 6. When bag 1 rises due to the motion of the
ocean, sea water will drain out of the holes 6, dissipating the kinetic energy of
bag 1 created by the - rising motion of the ocean. Oscillating of the flotation bag
1 within the medium W are thereby damped. The compartments increase the resistance
to motion of damper skirt 4 by partially enclosing the fluid and by requiring the
damper skirt to lift the partially enclosed fluid in the compartments as the flotation
bag 1 rises in response to a wave. This acts to further decrease the heave and pitch
of the flotation bag.
[0028] The damper skirt 4 and ribbon fence 5 are described associated with each other, constructed
from semi-rigid materials for the purpose of stabilizing flotation bag 1. However,
the damper skirt 4 may be a submerged plate and the means for channeling fluid that
encroaches on the device. Such structures may be used separately or in combination
to decrease both the heave and pitch of the device.
[0029] Payload 3 comprises electronics 31 enclosed in a cylindrical housing 32. Housing
32 is connected to the bottom of the flotation bag 1 by nylon cord 8. One end of nylon
cord 8 connects to a point 8a within the housing, approximately one-quarter from the
top of the housing and the other end connects to the center of the bottom of the bag
8b, at bulkhead 9, which is a rigid portion. Electrical wires 311 also pass from the
electronics 31 into the bulkhead 9. Beneath the bulkhead 9 is microphonics bumper
91.
[0030] Nylon cord 8 and the location of the connection between the housing 32 and the flotation
bag 1, at 8a and 8b, decouple the motion of flotation bag 1 from housing 32 such that,
over a certain range, the motion of bag 1 does not affect the motion of cylindrical
housing 32 and the motion of cylindrical housing 32 does not affect the housing motion
of bag 1. The range of motion depends on the demensions of the decoupling apparatus
including the diameter of housing 32 and the distance between the top of housing 32
and microphonic bumper 91.
[0031] Housing 32 is free to swing like a pendulum until the top of the housing 32a collides
with the microphonic bumper 91. Similarly, the flotation bag 1 can freely pitch until
the bumper 91 collides with the top of the housing 32a.
[0032] This allows for 10
0 - 1
50 of motion of the payload 3, measured from the vertical, before contact between housing
32a and microphonic bumper 91. Bumper 91 absorbs some of the energy of any impact
between bag 1 and payload 3, decreasing the effect such impact would have on the heave
and pitch of the flotation bag. Bumper 91 also protects the electrical wiring that
feed to the antenna, preventing interruption or interference with the transmission
of a message due to impacts between the housing 32a and the bulkhead 9 through which
wires 311 pass.
[0033] In the embodiment illustrated, electronics 31 is close to antenna 2 in order to minimize
the power loss due to transmission of a signal from electronics 31 to antenna 2 via
cable 311. Preferably, the power loss is less than 3db.
[0034] The upper portion 33, of housing 32, referred to herein as a collar, stores the entire
flotation apparatus before it is deployed, as shown in Figure 3. After deployment,
the upper portion 33 floods with water, through holes 14 in its sides, as shown in
Figures 1 and 2. The flooding reduces the buoyancy of the payload 3 which results
in payload 3 pulling the flotation bag 1 into the water, ensuring that the damper
skirt 4 and bottom hole 6 of ribbon fence 5 are submerged. This increases the stability
of flotation bag 1.
[0035] The flooding of upper portion 33 results in the center of mass of housing 32 being
lower in the medium W, increasing the period of oscillation of housing 32. This stabilizes
the entire structure and decreases the heave and pitch of flotation bag 1.
[0036] The center of the bottom of the flotation bag 1 is pulled upward by straps 13 secured
at 131, along the inside wall of flotation bag 1. This reduces the buoyancy of bag
1, aiding in maintaining the necessary waterline above damper skirt 4 and at the midpoint
of ribbon fence 5. The base of bag 16 is inwardly arched at its center 15 so that
the greatest bouyant forces are located at the outer portions of the bag 16. This
decreases the pitch of the flotation bag 1 by creating a longer torque arm which must
be overcome for the flotation bag to rotate. This righting moment further aids in
stabilizing the flotation bag. The adhesion caused by inwardly arched center 15 between
the surface of the bottom 16 of the bag and the fluid medium W also decreases the
heave of the flotation bag.
[0037] Although this particular embodiment describes a flotation bag with a concave bottom,
the invention is meant to cover flotation devices of any material with a bottom of
inwardly arched shape.
[0038] The apparatus and payload are ejected in the cylindrical housing 3, as shown in Figure
3. Antenna 4, flotation bag 1, ribbon fence 5 and damper skirt 4 are all stored in
upper chamber 33 of the housing 32. Housing 32, which is bouyant, floats to the surface
of the ocean after being ejected. The flotation bag and antenna are then deployed
and the preprogrammed messages are transmitted.
1. Apparatus for the substantially stable support of a device (2) in a fluid medium,
said apparatus including:
a buoyant member (1); and
support means associated with the buoyant member for supporting the device (2) to
be supported;
characterised by:
channel means (5) positioned to channel fluid which encroaches upon the buoyant member
due to any motion of the member relative to the surface of the fluid medium, said
encroaching fluid being channeled by said channel means (5) back into the body of
the fluid medium such that kinetic energy of the buoyant member associated with said
motion is dissipated as the fluid is channeled back into the body of the fluid medium.
2. Apparatus according to claim 1 characterised in that said channel means (5) comprises
at least one compartment (5a-5g) having an upper opening (7) and a lower opening (6),
the or each said compartment being connected to the buoyant member (1) with the upper
and lower openings (7,6) respectively above and below the mean surface level of the
fluid medium when the apparatus is floating therein, whereby encroaching fluid which
enters a said compartment (5a-5g) is channeled back through the lower opening (6).
3. Apparatus according to claim 2 characterised in that the or each said compartment
(5a-5g) is open at the top to provide said upper opening (7) and the or each lower
opening (6) has a cross-sectional area less than the cross-sectional area of the corresponding
upper opening (7).
4. Apparatus according to any one of claims 1 to 3 characterised by a damper member
(4) extending generally horizontally beneath the buoyant member (1) and below the
mean level of the fluid medium when the apparatus is afloat, whereby to impede vertical
motion of the apparatus relative to the fluid medium.
5. Apparatus according to claim 2 or claim 3 including a plurality of said compartments
(5a-5g) surrounding said buoyant member (1), characterised by a damper skirt member
(4) extending generally horizontally around said buoyant member (1) to form a base
for each said compartment (5a-5g), the lower openings (6) being formed between said
base and side walls of the compartments.
6. Apparatus according to any one of claims 1 to 5 characterised by a payload (3)
carried by and below said buoyant member (1), said payload (3) being connected to
said buoyant member by decoupling means (8) operative to decouple motions of the payload
and the buoyant member from one another over a given angular range.
7. Apparatus according to claim 6 characterised in that said decoupling means is a
flexible member (8) connected at an upper end (8b) to a rigid portion (9) of said
buoyant member (1) and at a lower end to said payload (3), said flexible member extending
through a collar (33) of a housing (32) of said payload, and in that said rigid portion
(9) has a bumper (91) positioned to engage said collar (33) when relative angular
movement betweeh' the rigid portion (9) and the payload housing (32) attains a predetermined
angle.
8. Apparatus according to claim 6 or claim 7 characterised in that said payload (3)
has a housing (32) including a chamber (33) within which said buoyant member (1) is
stored when the apparatus is in an undeployed state.
9. Apparatus according to any one of claims 6 to 8 characterised in that said device
to be supported is an antenna (2) supported by said support means of said buoyant
member (1), in that said payload (3) includes an r.f. signal generator (31) and in
that said generator is electrically connected to said antenna.
10. Apparatus according to any one of the preceding claims characterised in that the
under surface of the buoyant member (1) is substantially concave (15).
11. Apparatus according to claim 10 characterised in that the buoyant member is a
flotation bag (1) having internal straps (13) connected between the bag walls (131)
and the central portion of the bottom of the bag (16) to pull the under surface upwardly
into said substantially concave condition (15).
12. Apparatus for the substantially stable support of a device (2) in a fluid medium,
said apparatus including:
a buoyant member (1);
support means associated with the buoyant member for supporting the device (2) to
be supported; and
a payload (3) positioned below the buoyant member (1);
characterised in that:
said payload (3) is connected to said buoyant member (1) by decoupling means (8) operative
to decouple motions of the payload and the buoyant member from one another over a
given angular range.