Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ACOUSTIC ANTENNA ELEMENT FOR EMITTING AND/OR RECEIVING
WAVES UNDER WATER AND ASSOCIATED ACOUSTIC ANTENNA
The present invention concerns an acoustic antenna for emitting
and/or receiving medium-frequency waves under water.
Such an antenna is intended to detect and to locate underwater
sources of acoustic noise, for example. To obtain good performance both in
detection and in location, it is necessary to work over a spectrum of low or
medium frequencies and to have an antenna the gain of which is high in
order to obtain a satisfactory signal to noise ratio (in numerous applications
a
gain of 20 dB is necessary). By medium frequencies is meant frequencies
lower than 12 kHz.
At present, acoustic antennas for receiving underwater waves
include acoustic sensors that will be referred to as acoustic panels in the
remainder of the text. These acoustic sensors include at least one acoustic
pick-up enclosed in a flexible material coating. The assembly thus constituted
forms an acoustic panel referred to as an acoustic panel. An acoustic panel
has a globally rectangular shape.
The acoustic panels are mounted on a support, for example on the
hull of a submarine. The acoustic panels have a degree of freedom in
bending so as to be able to mate with the shape of this hull.
The panels are held against the wall by clamping them by means
of two flanges attached along the longer sides of the acoustic panels. The
acoustic panels are sandwiched between the flanges and the hull of the
submarine. The ends of the flanges are mounted on rails on either side of the
panels extending longitudinally in the direction of the width of the panels.
The flanges have a curved shape approximating the curvature of
the submarine, which enables them to clamp the acoustic panels against the
hull of the submarine.
Now, at present, rigid metal flanges are used. They provide
effective clamping of the acoustic panels only on a hull having a
predetermined curvature.
This clamping solution has a certain number of disadvantages.
Because of manufacturing tolerances in respect of the hull of a submarine
and also the flanges, it can happen that the clamping of the acoustic panels
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is not efficacious. If the curvature of the huit is less than foreseen (radius
of
curvature greater than foreseen) or if the curvature of the flanges is greater
than foreseen (radius of curvature less than foreseen), the acoustic panels
are not correctly clamped against the hull of the submarine. Knowing also
that the acoustic panels may be deformed because of hydrodynamic
disturbances, there is therefore a risk of the panels escaping from their
fixing
flanges.
On the other hand, if the curvature of the hull is greater than
foreseen (radius of curvature less than foreseen) or if the curvature of the
la flanges is less than foreseen (radius of curvature greater than
foreseen), the
acoustic panels clamp the panels too firmly, which leads to premature wear
of the panels.
Moreover, it is necessary to provide different flanges for different
submarines the hulls of which have different radii of curvature or for a
single
submarine the hull of which has a varying radius of curvature.
The object of the invention is to remedy the aforementioned
disadvantages.
To this end, the invention consists in an acoustic antenna element for
receiving and/or emitting low-frequency underwater waves, comprising an
acoustic panel formed by at least one acoustic pick-up enclosed in a flexible
jacket, said acoustic panel being generally rectangular and being mounted
against a curved support by means of a mounting device including a
clamping device comprising at least two flanges the ends of which are
mounted on said support. The respective flanges comprise at least one tie
between the two ends thereof and the clamping device comprises means for
adjusting the tension of said ties between the two respective ends thereof,
the flanges being arranged so that the support is curved between the two
respective ends of said ties and so that the panel is clamped against the
support by said ties when they are under tension.
Thus a single clamping device can be provided for clamping
acoustic panels to supports having different radii of curvature. A single
device
can be used on a submarine having a varying radius of curvature or on
different submarines having different radii of curvature. Moreover, the
clamping device clamps the panel against the huit of the submarine even if
the latter features irregularities and is not perfectly convex. Also, this
,
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clamping device makes it possible to prevent premature wear of the acoustic
panels by the means for adjusting the tension of the ties.
An antenna in accordance with the invention comprising one or
more elements in accordance with the invention is therefore of low cost and
resistant to hydrodynamic stresses (because the acoustic panels are firmly
clamped against their support).
Moreover, the antenna in accordance with the invention has good
acoustic performance because of the use of ties.
At least one of said ties advantageously takes the form of a
flexible strip.
At least one of said ties advantageously takes the form of a metal
Cele sheathed by means of a flexible sheath.
At least one of said flanges advantageously consists of a tie.
At least one of said ties is advantageously fastened to the panel.
The panel is advantageously sandwiched between at least one of
said ties and the support.
At least one of said ties is advantageously at least partially
accommodated in a channel opening onto the face of the panel facing the
environment external to the support, referred to as the external face.
At least one of said ties is advantageously flush with the external
face of the panel.
The volume of said passage that is not occupied by said at least
one of said ties is advantageously caulked by means of a caulking material
so that the surface formed by the caulking material and said at least one of
said ties is flush with the external face of the panel.
At least one of said ties is advantageously at least partially
accommodated in a passage extending over all the length or over ail the
width of said panel.
The clamping means advantageously comprise at least three
flanges.
The flanges are advantageously adapted to clamp the panel
against the support exclusively via said ties under tension.
The invention also consists in an antenna comprising a plurality of
elements according to the invention.
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The invention also consists in a ship equipped with an antenna
according to the invention.
The invention further consists in a method of mounting an acoustic
panel formed by at least one acoustic pick-up enclosed in a flexible jacket,
said acoustic panel being globally rectangular, against a curved support,
comprising:
- a step in which the panel is attached to a support,
- a step in which the panel is clamped against the support by means of a
clamping device comprising at least two fianges each comprising at least one
tie between its two ends and means for adjusting the tension of said ties
between their respective two ends, said clamping step comprising a step
during which said flanges are arranged se that the support is curved between
the respective two ends of said ties and so as to clamp the panel against the
support via said ties under tension,
said ties being fastened to the panel when the panel is mounted on the
support.
Other features and advantages of the invention will become
apparent on reading the following detailed description, given by way of
nonlimiting example and with reference to the appended drawings, in which:
- figure 1 represents diagrammatically an antenna in accordance
with the invention,
- figure 2 represents diagrammatically an antenna element in
accordance with one embodiment of the invention,
- figure 3 represents a diagrammatic exploded view of means
contained in the dashed-line bubble in figure 2,
- figure 4 represents diagrammatically a portion of an element in
accordance with a variant of the invention,
- figure 5 represents diagrammatically a view in section on the
plane M of the element represented in figure 2,
- figure 6 represents a variant of the figure 5 sectional view.
From one figure to another, the same elements are identified by
the same references.
Figure 1 represents diagrammatically an acoustic antenna 2 in
accordance with the invention for receiving underwater waves. This antenna
2 is formed of a succession of acoustic panels 4 pressed against a support 3
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by means of mounting devices comprising clamping devices flot represented
in figure 1.
ln the example represented in figure 1, the support 3 is the watt of
the huit of a submarine 1. Here the panels are mounted on one flank of the
In figure 2 there has been represented an element of the acoustic
antenna, said element comprising an acoustic panel 4 and one example of a
To be more precise, the panels have the overall shape of a thin
rectangular parallelepiped. By thin parallelepiped is meant a parallelepiped
They have two opposite longer sides 5 (extending in the direction
of the height of the panels) and two opposite shorter sides 6 (extending in
the
Given that the huit of a submarine has a curved shape, the panels
have a degree of freedom in bending so as to mate with the shape of the huit
of the submarine. In the embodiment in the figures, the submarine has a
cylindrical general shape with its axis X corresponding to the axis of the
25 submarine. In this embodiment, the shorter edges 6 of the panels 4 are
parallel to this axis X. In other words, the support 3 is convex between the
shorter sides 6 of the panels 4. Here the degree of freedom in bending of the
panels 4 is therefore a degree of freedom in rotation about an axis parallel
to
the shorter edges 6.
30 A variant would consist in disposing panels on a convex support
between its two longer edges 5. The panels would then have to have a
degree of freedom in bending about an axis parallel to these longer sides.
The acoustic panels are known to the person skilled in the art. A
brief, non-limiting description of them is given hereinafter.
I
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The acoustic panels are acoustic sensors. They comprise at least
one acoustic pick-up, for example a plurality of acoustic pick-ups.
Point-type acoustic pick-ups may be used, for example, such as
simple hydrophones, for example, or area-type pick-ups. The acoustic pick-
ups are enclosed in a watertight flexible jacket for protecting the acoustic
pick-ups from moisture.
The flexible jacket is a homogeneous structure, for example. It
may equally be a composite structure comprising an exterior envelope
enclosing at least one packing material, the pick-ups being embedded in a
packing material. In the case of a composite jacket, the exterior jacket
serves
as a mold for the packing material or materials that it encloses.
The pick-ups may be embedded in a packing material in the form
of a soft polyurethane. By soft polyurethane is meant a polyurethane the
Shore A hardness of which is typically less than 50.
For example, an exterior jacket made of neoprene rubber or
neoprene rubber and a hard polyurethane, typically having a Shore hardness
of at least 70, may be used, the hard polyurethane serving to fill the space
formed by the exterior jacket.
The device for clamping an acoustic panel against its support will
now be described in more detail with reference to figure 2.
The device for clamping an acoustic panel comprises two flanges
7 mounted on the support 3. Each clamp comprises between its two ends at
least one tie 8. The flanges provide the interface between the acoustic panel
and the rest of the submarine 10.
By tie 7 is meant a flexible, i.e. bendable, object of elongate
shape. This refers to metal, for example steel, cables, for example. These
cables may advantageously be coated with a flexible sheath, for example
made of rubber. This sheath then makes it possible to prevent the ties from
damaging the panel 4 when they clamp the panel against the support 3.
The ties may form flexible strips, in which case they are referred to
as straps, or have a round section. The use of straps makes it possible to
distribute the pressure forces exerted by the ties on the acoustic panel. This
makes it possible to ensure good retention of the panel without causing
premature wear thereof.
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Moreover, the use of ties (straps or cables) also has acoustic
advantages. They degrade acoustic performance less than a rigid flange, in
particular if acoustic pick-ups disposed in the acoustic panel are sandwiched
between a tie and the support.
The ties are advantageously made from a material that is
optimized with regard to the acoustic performance required on the panel.
Cloth, polypropylene or polyester straps are used, for example. Composite
material, for example glass fiber or carbon fiber, cables are used, for
example.
The ties advantageously have a maximum width of 5 cm and a
maximum thickness of 1 cm. These sections make it possible to preserve
good acoustic performance even at high frequencies, in particular if acoustic
pick-ups disposed in the acoustic panel are sandwiched between a tie and
the support. Acoustic performance degraded by around 1 dB is acceptable.
The clamping device further comprises means for adjusting the
tension of the ties between their respective two ends. These means are
adapted to tension the ties longitudinally between their respective ends and
to adjust this tension.
The flanges 7 are such that the support is curved between the
respective two ends of the ties and the flanges clamp the panel against the
support via the ties when the ties are under tension.
In the non-limiting embodiment of figure 2, the flanges 7 consist of
a tie. The clamping effect is obtained by exerting a longitudinal tension in
the
flange, which results in a force in the radial direction of the hull of the
submarine. By virtue of the traction force at its two ends 8 the flange 7
tends
to take the shortest line, the effect of which is to sandwich the panel 4
between the flanges 7, here the ties, and the support 3.
The flanges 7 extend continuously from a first edge to the opposite
edge of the panel, between which the support is curved. In other words, a
convex line joins the respective two ends of the ties. In the figure 2
embodiment, the first edge and the opposite second edge are respective
shorter edges 6 of the panel. In other words, in this embodiment, the flanges
7 extend continuously over all the length of the panel. In a variant, however,
the flanges could extend continuously over all the width of the panel, for
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example, if the support were curved between the two longer edges of the
panel.
When the flanges 7 are tensioned between their respective ends,
because of the convexity of the support between their two respective ends,
they are automatically clamped against the panel 4, which holds the panel 4
against the support 3. In fact, by exerting a longitudinal tension in the
flange
that is reflected in a traction force tangential to the hull of the submarine
at
each end of the flange, the flange tends to take the shortest line and se
clamps the panel against the support.
In the figure 2 embodiment, the flanges 7 are disposed in the
vicinity of the respective two longer sides 5 of the panel 4. They extend
along
these longer sides.
Alternatively, the clamping means comprise more than two flanges
7. For example, an additional flange 7 may be disposed in the central part of
the panel 4, for example along the longer sides 5, although this is flot
limiting
on the invention.
Providing three flanges ensures improved retention of the panels
against the wall of the submarine. It is then possible to use larger acoustic
panels.
Increasing the size of the panels addresses the requirement to
dispose more individual hydrophones within the same jacket, which also
makes it possible to reduce considerably the cost of the antenna, the latter
being directly related to the number of objects (panels) installed on the
submarine.
Panels having a height between 1 m and 2 m are preferably used.
If the panels are fixed by means of two flanges, panels are
preferably used having a width between 40 cm and 60 cm. If the panels are
fixed by means of more than two flanges, panels are preferably used having
a width between 60 cm and 150 cm.
In the nonlimiting example represented in figure 2, the means for
adjusting the tension of the ties between their two ends comprise threaded
tips 8 fastened to respective ends of the flanges 7. Each threaded tip 8
cooperates with a nut 9 butted against abutment members 10 to retain the
ends of the flanges 7 relative to the support 3 and to tension them between
their two ends.
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In the figure 2 embodiment, these elements are seen for only one
end of each flange 7. However, these elements and how they function are
the same at each end of each flange. The elements contained in the dashed-
line bubble in figure 2 are represented in more detail in an exploded view in
figure 3.
The abutment members are rails (or studs) 10 disposed on either
side of the panel 4 and contiguous with the respective shorter edges 6 of the
panel 4. The rails 10 are fastened to the hull of the submarine and extend
longitudinally parallel to the axis of the submarine. These rails also have a
lo function of
orienting the panel 4. In fact, the shorter edges 6 of the panels are
abutted against the faces of these rails that are adjacent the shorter sides
of
the panels.
The rails 10 have faces 11 opposite the shorter edges 6 of the
panels that are globally perpendicular to the wall of the submarine.
The threaded tips 8 penetrate passages 14 provided in these rails
10 and the nuts 9 are abutted against the faces of the rails opposite the
shorter edges 6 of the panels.
Accordingly, when the nuts 9 are screwed onto the two threaded
tips 8 of a tie, because the nuts 9 are abutted against the abutment members
10, traction forces globally tangential to the wall of the submarine are
exerted
on these tips 8. The components of these tangential traction forces along a
straight line segment connecting the points of application of the force
between the tips and the nuts 9 are in opposition, the effect of which is to
tension the ties 7.
It may be noted that, as the nuts 9 are abutted against the
abutment members 10 fastened to the support 3, the means for adjusting the
tension of the ties 7 also constitute means for retaining the ends of the
flanges fixed relative to the support 3, i.e. means for mounting these ends on
the support 3.
Accordingly, because of the curvature of the hull of the submarine
between the two ends of each flange 7, each flange under tension is
automatically pressed against the acoustic panel and therefore clamps the
acoustic panel against the hull of the submarine.
Moreover, the threaded rods 8 have a predetermined length. This
makes it possible to adjust the lengths of the ties 7 between their two ends,
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the effect of which is to tension the ties 7 even if the hull of the submarine
has different radii of curvature. Moreover, this feature makes it possible to
adjust the pressure exerted by the ties 7 on the panel 4.
Thus a single clamping device may be provided to clamp the
5 acoustic panels 4 onto supports having different radii of curvature. A
single
device may be used on a submarine having a varying radius of curvature or
on different submarines having different radii of curvature. Moreover, the
clamping device clamps the panel against the hull of the submarine even if
the latter features irregularities and is not perfectly convex. Moreover, this
10 clamping device makes it possible to prevent premature wear of the
acoustic
panels by the means for adjusting the tension of the ties.
An antenna in accordance with the invention comprising one or
more elements in accordance with the invention is therefore of low cost and
resistant to hydrodynamic stresses (because the acoustic panels are well
clamped against their support).
Moreover, the antenna in accordance with the invention has good
acoustic performance because of the use of ties.
Alternatively, ties may first be provided fastened at one of their
ends only to a threaded rod adapted to cooperate with a nut as described
above so as to fix said end to the support and to adjust the tension of the
tie
between its two ends, the second end being made fixed relative to the
support by other fixing means.
In the embodiment described above, the flange consists of a tie.
Alternatively, the flange comprises between its two ends one or more ties
and means for adjusting the tension of the ties.
One example of this variant is represented in figure 4, which
represents a portion of a panel 4 installed as in figure 1.
In this example, the clamping device comprises means 108a, 108b
for fixing the respective ends of a flange 107 to respective rails 100a, 100b
fastened to the support'3, flot shown. The flange 107 extends continuously
over ail the length of the panel 4 between its shorter edges 6. To be more
precise, it extends parallel to the longer sides 5 of the panel 4.
The flange 107 comprises a tie 110. The tie 110 extends
continuously over ail the length of the panel.
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As in the previous embodiment, the flange 107 is adapted to
clamp the panel 4 against the support 3 via the tie 110 when the tie 110 is
tensioned. Firstly, the flange 107 is such that the support is curved between
the two ends of the tie 110. More generally, in this embodiment, the support 3
is curved between the two ends of the flange.
Moreover, the panel is sandwiched between the flange 107 and
the support 3.
To be more precise, the panel 4 is sandwiched between the tie
110 and the support 3. The tie 110 extends continuously over ail the length of
the panel 4 between its shorter edges 6. Accordingly, when the tie is
tensioned, the flange clamps the panel 4 via the tie 110.
The means for adjusting the tension of the tie 110 between its two
ends comprise a cable tensioner 112. A cable tensioner conventionally
comprises two threaded rods that screw into the same threaded body. When
the free body is turned between the two rods, this tends to screw each of the
rods into the body. The two rods move toward each other and the length of
the device is reduced.
A first end of the cable tensioner constitutes a first end of the flange
107 and is fixed to the support by first fixing means 108b. The second end of
the tensioner 112 is fixed to a first end of the tie 110 by means of a hook
device 111. The second end of the tie 110 constitutes the second end of the
flange 107 and is fixed to the support by means of the second fixing means
108a.
When the length of the tensioner 112 is reduced, it tensions the tie
110 between its two ends. Because the hull of the submarine is curved
between the two ends of the tie, the tie then clamps the panel 4 against the
support 3. The flange therefore clamps the panel 4 against the support via
the tie 110 alone.
Alternatively, the means for adjusting the tension of the tie may be
disposed between the two shorter edges 6 of the panel 4. The flange then
clamps the panel via the tie and via the means for adjusting the tension of
the
tie when the tie is tensioned. However, the acoustic performance of the
device is improved if the flange clamps the panel only by means of the tie.
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Generally speaking, an adjustable clamp or a ratchet-type
clamping device or a cable tensioner may be installed between the two fixed
ends of the flange.
Each flange may comprise one or more ties and means for
adjusting the tension of the tie or ties.
The acoustic panels have an internat face, flot visible in the
figures, disposed against the watt of the huit of the submarine and an
externat
face 12, visible in figures 2 and 4, facing the exterior environment of the
submarine, or more generally externat to the support.
The externat face 12 of the acoustic panels is advantageously
plane at least in its central part. This feature is necessary to disturb the
hydrodynamics of the submarine as little as possible.
As represented in figure 2 and in figure 5, representing a section
of the element from figure 2 on the plane M, the ties are advantageously at
least partially accommodated in channels 13 opening onto the externat face
12 of the panel 4. Here the channels 13 extend over ail the length of the
panel 4 but they could extend over ail its width. The ties 7 are
advantageously flush with the externat face 12 of the panel 4.
This feature makes it possible to limit the disturbance of the
hydrodynamics of the submarine caused by the antenna.
However, the surface formed by the ties 7 and the externat face of
the panel 4 is flot necessarily plane. This is the case if the channeis are
wider
than the ties that are accommodated in them, for example, as represented in
figure 5.
The volume of a channel 13 that is flot occupied by a tie 7 is
advantageously caulked with a caulking material so that the surface formed
by the caulking material and the ties 7 is flush with the externat face of the
panel.
The ties are advantageously fastened to the panel that they clamp.
This solution is very advantageous in terms of the simplicity of mounting the
antenna on its support. A single step is necessary to attach the panel and the
ties to the watt of the submarine. It is net necessary to attach these
elements
separately.
The invention also consists in a method of mounting an acoustic
panel on a support, comprising:
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- a step in which the panel is attached to a support,
- a step in which the panel is clamped against the support by
means of a clamping device comprising at least two flanges each comprising
at least one tie between its two ends and means for adjusting the tension of
said ties between their respective two ends, said clamping step comprising a
step in which said flanges are arranged so that the support is curved
between the respective two ends of said ties and sa as to clamp the panel
against the support via said ties under tension.
The ties are advantageously fastened to the panel when the panel
is mounted on the support.
In an even more advantageous solution, it is the flanges that are
fastened to the panel that they clamp.
It is possible, for example, in the solutions described above, to fix,
for example, to glue, the ties to the panels that they are intended to clamp.
In a variant represented in figure 6, the ties 7 are at least partially
accommodated in passages 130 inside the panel 4 and extending over all the
length or the width (if the support is curved between the longer edges of the
panel 4). The passages open on either side of the acoustic panel.
This feature is advantageous bath in terms of simplicity of
mounting but also because it limits the disturbance to the hydrodynamics of
the submarine caused by the antenna. In fact, because the passages are
inside the panel, no element of the clamping device covers the external face
of the panel.
Moreover, because the ties 7 extend over all the length of the
acoustic panel in the passages 130 inside the panel 4, they automatically
clamp the panel against the support when they are tensioned by virtue of
coming to bear on the surface of the passage.
