Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02949735 2016-12-19
P343125Per
Improvements in Underwater Connections
TECHNICAL FIELD
This invention relates to underwater connections, in particular connections
associated
with tidal turbines and the like. Such connections may be mechanical, for
example to
couple a tidal turbine assembly to an underwater anchorage. Such connections
may
also convey services, for example, to couple a turbine generator to an
underwater
power supply cable and the like; the service connection may be one or more of,
for
example, electrical hydraulic and pneumatic.
BACKGROUND TO THE INVENTION
Underwater turbine generators have been proposed to generate electricity from
stream
flows, for example tidal flows. In general a turbine assembly is coupled to an
underwater anchorage, and is arranged to float in the stream flow below the
surface of
the water. In one common arrangement the turbine assembly is connected to the
anchorage by a tether, and trails in the stream flow; the turbine assembly may
be free
to pitch roll and yaw according to prevailing stream flow conditions, for
example by
provision of suitable pivots at the ends of the tether. The tether may be
rigid or
flexible.
One characteristic of an underwater turbine is that it must be transported to
the
operating site and coupled to an anchorage. The latter operation is somewhat
problematic since a large turbine array may displace several hundred tonnes
and be
difficult to manage in a strong current. Furthermore it may be necessary to
uncouple
the anchorage to permit the turbine assembly to be removed for repair and/or
replacement.
Underwater conditions are not favourable to mechanical devices, but
nevertheless it is
essential to ensure that uncoupling of an anchorage can be effected on demand,
even
after several years' immersion in sea water. Corrosion resistant materials are
relatively
expensive, and may lack the material properties of toughness, resilience and
fatigue
resistance which are essential to an adequate mechanical life underwater.
Sealing of
moving mechanical devices, such as actuators, is problematic and cannot be
relied
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upon. Furthermore power is required for such devices, and thus introduces
additional
difficulties, especially if far from shore in a relatively hostile
environment.
What is required is an inexpensive and reliable means and method of coupling
and
uncoupling an underwater device with respect to an underwater anchorage.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided underwater
actuator and
an underwater device, the actuator having a latch to releasably couple the
actuator to
the underwater device, and a driver to engage and disengage a retaining member
associated with an underwater anchorage of a tidal energy device whereby said
underwater device is adapted to be coupled and uncoupled with said underwater
anchorage, and whereby said underwater actuator is adapted to be removed from
said
underwater device on demand, the actuator further including a suspension cable
for
attachment to a floating winch and wherein said underwater device comprises a
turbine generator and a tether for attaching said turbine generator in said
underwater
anchorage, said latch being engageable at the free end of said tether.
The invention essentially allows the moving parts of an engaging and
disengaging
device to be mounted on a removable actuator, which may thus be lowered and
raised
only when a connection or disconnection of the anchorage is required.
Furthermore,
by latching to the underwater device, the invention provides a secondary
benefit of
retaining the device in the stream flow before and after connection. The
actuator may
thus be used for raising and lowering the underwater device, or a part
thereof, with
respect to the anchorage. In the case of an underwater turbine, the actuator
may be
latched to the free end of a tether prior to connection with an anchorage, and
after
disconnection from an anchorage.
In one embodiment the actuator is connected by the suspension cable to a
floating
vessel, such as a barge or boat. A power connection for the actuator may be
provided
from the vessel, and may be electrical, hydraulic or pneumatic.
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The actuator may include a transverse arm to provide for contact between the
actuator
and anchorage by drifting in the stream flow. The transverse arm may act as a
catcher,
and engage an upstanding element of the anchorage, such as a pin. Such an arm
may
define a vee or fork to guide the device and anchorage into substantial
alignment. The
arm may be compliant or have a compliant element to ensure engagement with the
anchorage without substantial shock; the arm may be controllable, such as by
moving
elements, to allow engagement with the anchorage in a progressive manner or at
a
desired rate.
The retaining member may be associated with the device, with the anchorage, or
with
the actuator. In one embodiment the retaining device is mounted on the
actuator prior
to engagement with the anchorage and after disengagement from the anchorage;
such
an arrangement allows the retaining device to be brought to the surface
periodically
for cleaning and for maintenance.
According to a second aspect of the invention there is provided a method of
unmaking
an underwater connection between an underwater device and an underwater
anchorage
of a tidal energy device, said underwater device comprising a turbine
generator and a
tether for attaching said turbine generator in said underwater anchorage, the
method
comprising:
lowering an actuator to said anchorage;
attaching said actuator to said underwater device at a free end of said
tether, at
said anchorage;
unlatching said underwater device by moving a retaining member to a
disengaged condition with said actuator; and
raising said actuator to disengage said device and anchorage.
The method of the invention allows for a minimum of moving underwater
components
associated with the engagement of the anchorage and underwater device,
typically just
a sliding key, pin, clip or friction element.
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The invention also comprises a method of unmaking an underwater connection
between an underwater device and an underwater anchorage of a tidal energy
device,
the method comprising:
lowering an actuator to said anchorage;
attaching said actuator to said underwater device at said anchorage;
unlatching said underwater device by moving a retaining member to a
disengaged condition with said actuator; and
raising said actuator to disengage said device and anchorage.
The method of the invention may include making a service connection, for
example an
electrical connection between a cable associated with the anchorage and a
connector
mounted on the underwater device. The service connection may be made and
unmade
automatically upon attachment or detachment of the device, for example by
raising or
lowering said actuator with respect to the anchorage.
BRIEF DESCRIPTION OF DRAWINGS
Other features of the invention will be apparent from the following
description of a
preferred embodiment illustrated by way of example only in the accompanying
drawings, in which:
Fig. 1 is a schematic illustration of an exemplar underwater turbine assembly
and underwater anchorage.
Fig. 2 illustrates the invention with actuator and tether in a connected
condition.
Fig. 3 illustrates the invention with tether and anchorage in coupled
condition,
with actuator connected.
Fig. 4 corresponds to Fig. 3 and shows actuator disconnected.
Fig. 5 illustrates a catcher for the actuator of Figs. 2 to 4.
Fig. 6 illustrates a connection device for the actuator of Figs. 2 to 4.
DESCRIPTION OF AN EMBODIMENT
Fig. 1 illustrates an exemplar and somewhat schematic underwater turbine
assembly
or tidal energy device 10 comprising a tether 11 mounted to an underwater
anchorage
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12 projecting from the underwater surface 13. The tether mounting has
capability for
one or more of pitch, yaw and roll.
The turbine assembly lies in use below the water surface 14, and in this
example
comprises a twin booms 15 having the fore portions 16 joined in a 'Y' shape,
and aft
portions 17 adapted to contain variable ballast. Arms 18 extend from the booms
transversely, and turbine generators 19 are mounted thereon. A suitable
electrical
connection, not shown, connects the turbines to a power cable on the
underwater
surface 13. The booms 15 contain hollow chambers to which water may be
admitted
as ballast 20, so as to adjust the operating height of the turbine assembly.
The turbine
assembly may be for example ballasted to float between a surface maintenance
condition, where the turbine generators are exposed for maintenance, and an
underwater contact condition, where the assembly sits on the underwater
surface; the
latter condition may be appropriate to give stability in strong tidal flows
(arrow 'A') or
in stormy conditions, and the turbine generators may be inactive in the
contact
condition.
The turbine assembly of Fig. 1 comprises the essential elements of an
underwater
stream flow generator, namely a turbine generator 19, a framework 18 to mount
the
turbine generator and a tether 15, 16, 17 for attachment to an anchorage 12.
Many
kinds of such an assembly have been proposed, and in particular the tether may
comprise a single arm, and may be flexible or rigid. The present invention is
not
directed to a particular kind of turbine assembly.
In order to position such an assembly for generation, it must first be
attached to the
anchorage 12.
Fig. 2 illustrates schematically the present invention. A conventional
anchorage 21 is
fixed to the underwater surface, and comprises an upstanding spigot 22. A
tether 23 of
a turbine generator (not shown) terminates at a coupling 24 for engagement
with the
spigot. For simplicity a coupling which allows movement in yaw (about a
vertical
axis) is illustrated, but additional degrees of freedom in pitch and roll may
be
incorporated by provision of suitable pivot axes, for example on the coupling
24. The
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spigot and coupling may be of any suitable shape; for example the spigot may
have a
tapering free end, or the coupling may have a narrowing mouth, so as to ease
mutual
engagement and centralize the components before latching. The anchorage may
comprise other kinds of relatively fixed attachment, and need not cbmprise an
upstanding spigot.
An actuator 25 is suspended by cable 26 from a floating winch, for example on
a boat
or barge, and is attached to the coupling by opposed arms 27 (one shown) which
grip
or otherwise engage the coupling from the side. The arms 27 may be of any
suitable
kind so long as the engagement is secure, and in this example are moved about
a
respective vertical axis by a suitable motor (not shown) which may be
hydraulic,
pneumatic or electric. A single arm or other attachment device may be
provided. The
motor may be a telescopic strut or the like, acting directly to draw the arms
together,
or move them apart. A power supply 28 is provided for the motor from the
surface, for
example from the winch boat or barge. Progressive engagement between the
actuator
and the device is preferred; for example a pointed shape may be stabbed into a
recess,
and the actuator rotated to permit insertion of a locking pin to complete the
latching
operation.
In use the cable 26 supports the weight of the tether 23 and coupling 24; it
is assumed
that the turbine assembly is floating. The actuator 25 is manoeuvred until the
coupling
24 is over the spigot 22, at which point it is lowered so as to be engaged
thereon (as
illustrated in Fig. 3).
=
In order to retain the coupling 24 on the spigot 22, a key 29 is advanced by
another
motor of the actuator 25. The kind of key is not important so long as
retention is
assured whilst permitting the desired axes of movement of the coupling on the
spigot.
As illustrated a flat member with a concave leading edge is advanced as key to
engage
a pocket or groove of the spigot 22. Alternatively a pin may be pushed through
a hole
of the spigot. It will be appreciated that the anchorage 21 and coupling 24
are
configured to resist sideways loads generated by operation of the underwater
turbine
assembly 10.
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Once the coupling 24 and spigot 22 are engaged, the actuator 25 is removed by
releasing the arms 27. The actuator is then brought to the surface by winching
in the
cable 26 (Fig. 4). Should it be desired to uncouple the coupling 24 and spigot
22, the
actuator 25 is lowered to the coupling and re-latched thereto by operation of
the
gripping arms 27. Subsequently a motor of the actuator withdraws the key 29,
thus
allowing winching of the cable 26 to draw the coupling 24 off the spigot 22
(Fig. 1).
The key may be part of the coupling 24 or part of the spigot 22, or may be
installed
from the actuator 24, and withdrawn therewith.
The arrangement of the invention has many advantages.
Firstly, no mechanism associated with coupling and uncoupling remains with the
anchorage, and thus not able to be brought to the surface for repair or
replacement: all
that is left underwater is the spigot with its groove or engagement recess
which is
typically made from corrosion resistant material. The key and associated
linkages and
mechanisms that remain with the device can be made from corrosion resistant
material
and can be brought to the surface for repair or replacement.
Secondly, the actuator is removed to the surface after each engagement or
disengagement and can be maintained, cleaned and serviced as often as
necessary.
Thirdly, only one such actuator is required for attachment of each of a
plurality of
turbine assemblies to respective anchorages; this advantage is particularly
useful
where an array of turbines is installed on the underwater surface.
Fourthly, a permanent power supply to the underwater coupling is not required,
thus
obviating cost and maintenance thereof.
Fifthly, when the coupling is released, the tether arm 23 is retained by the
cable 26
and may be winched up for attachment to a barge or other floating structure; a
separate retaining apparatus is accordingly obviated, along with any risk that
the
turbine assembly will float away.
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Fig. 5 illustrates an alternative embodiment including a catcher 31 attached
to the
actuator 25. The catcher 31 comprises a transverse arm which may be flexible,
and
which provides a means of engaging the spigot 22 whilst the assembly is moved
in the
direction thereof prior to attachment. This arrangement avoids the need for
precise
vertical alignment of the actuator and spigot whilst the actuator is winched
down to
the required depth, which may be problematic in a stream flow. The catcher 31
permits the assembly to be lowered to the appropriate depth, and then allowed
to drift
towards the spigot in the stream flow until arrested by contact of the catcher
31 with
the spigot 22. This stabilizes the assembly for positioning and further
lowering
thereof.
In one embodiment the catcher is mounted at an acute angle so as to present a
fork to
the spigot, this arrangement allows the spigot 22 to slide to the apex of the
fork,
whereupon the actuator and spigot will be substantially aligned. A catcher may
be
provided on one or both sides of the actuator.
Fig. 6 illustrates yet another alternative in which one end of a power cable
33 is
carried releasably by an arm 32 of the actuator. Upon connection of the
coupling 24
with the spigot 22, the arm permits attachment of the cable 33 to a junction
box 34
associated with the coupling. Typically a second power cable runs from the
junction
box 34 to the or each turbine generator, for example within a hollow tether
23. The
arm 32 may be mechanized or movable to attach the cable 33, thereby providing
a
power connection from the turbine generator to a power grid or other
electrical
consumer. After connection of the cable 33, the actuator 25 and arm 32 can be
disconnected and winched to the surface as previously described. The cable may
comprise a signalling or control connection for the turbine assembly, for
example to
control the pitch of the blades thereof, and/or may comprise other services
means for
instance pipes or lines carrying hydraulic or pneumatic or fibre optics for
power or
signal transmission.
Any kind of suitable connection arrangement for the cable 33 may be used, for
example a plug and socket, the essential feature being that the actuator
transports and
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couples the free end of the cable before being withdrawn to the surface. The
arrangement may also be used to disconnect the cable 33 on demand, whilst
allowing
the actuator to retain the cable end for, for example, lifting to the surface.
The cable
33 may be automatically attached upon lowering of the coupling on the spigot,
or the
arm 32 may be movable between connecting and disconnecting conditions.
It will be understood that the illustrated embodiment is schematic, and that
materials,
sizes and dimensions of components will be selected according to the required
duty.
Modifications and alternatives are envisaged within the scope of the appended
claims.
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