Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Apparatus for generating power from sea currents
The invention relates to an apparatus for generat-
ing power from sea currents, comprising a structure having a
buoyancy provided by buoyancy members, support members sup-
porting water turbines and mooring means for mooring the
structure to a fixed point.
In the field of generating power from sea cur-
rents, many different types of apparatus have been proposed
in the past, each with specific advantages and disad-
vantages.
It is an object of the present invention to pro-
vide a novel type of apparatus for generating power from sea
currents.
Thus, in accordance with the present invention an
apparatus is provided which is characterized in that the
buoyancy members comprise an elongate main floating body and
at least one elongate auxiliary floating body, wherein the
auxiliary floating body is positioned above the main float-
ing body in a vertical plane extending through the main
floating body and wherein the main floating body and auxil-
iary floating body are interconnected by at least one verti-
cally extending strut.
The apparatus according to the present invention
has a stable position in the water, due to the relative po-
sitions between the main floating body and auxiliary float-
ing body. The cross-section of the main floating body and/or
auxiliary floating body may be substantially cylindrical.
In a preferred embodiment the main and auxiliary
floating bodies extend substantially horizontally and in
parallel to each other. As such the drag experienced and
generated by the floating bodies is minimised.
In a specific embodiment of the apparatus accord-
ing to the present invention, the overall buoyancy of the
structure is such that the auxiliary floating body in an op-
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erational position of the apparatus extends partly above and
partly below water level.
The indication "operational position" relates to a
position of the apparatus in which its water turbines are at
the required depth for generating power. Because in such a
position a part of the auxiliary floating body still is lo-
cated above water level, a downward movement of the struc-
ture (for example caused by a force acting on the water tur-
bines) automatically will lead to an increase of the buoy-
ance counteracting such a downward movement. An upward move-
ment, to the contrary, will lead to a decrease of the buoy-
ancy. Thus, there will be a stabilizing effect. Because of
the position of the auxiliary floating body vertically above
the main floating body, the auxiliary floating body is also
very effective in compensating (or preventing) other motions
of the structure, such as for example (excessive) rolling of
the structure.
In another embodiment the at least one strut pro-
vides a passage for a person between the interior of the
auxiliary floating body and the interior of the main float-
ing body which is sealed against surrounding seawater. For
example such a passage is provided with a ladder enabling a
person to reach the interior of the main floating body.
In such an embodiment, then, it further is con-
ceivable that the auxiliary floating body is provided with
an access opening which can be closed and opened by a clo-
sure, such as for example a hatch, which in the operational
position of the apparatus is located above water level. As a
result it is possible to gain access to the passage within
the strut (and to the main floating body), even in an opera-
tional position of the apparatus.
It also is possible that the auxiliary floating
body in the vicinity of the access opening is provided with
a mooring structure for a vessel. This allows to moor a ves-
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sel (for example bringing maintenance personnel and equip-
ment to the apparatus) to the auxiliary floating body.
The apparatus generally will comprise equipment,
such as electric equipment, and this may mainly be located
in the interior of the main floating body. One of the ad-
vantages of positioning such equipment in the main floating
body is the resulting low position of the centre of gravity
of the structure, adding to an improved stability thereof.
For further optimising the structural integrity
and strength of the structure, it is possible that the appa-
ratus is provided with two struts spaced apart in the longi-
tudinal direction of the main and auxiliary floating bodies.
When the at least one strut has an oval cross sec-
tion, the drag can be minimised, whereas further such a
cross section may increase the azimuthal stabilisation of
the apparatus.
In one embodiment of the apparatus according to
the present invention, the support members for the water
turbines comprise at least one pair of cross beams extending
in opposite directions outwardly from the main floating
body. Each cross beam generally will support at least one
water turbine, but it is also conceivable that a cross beam
supports a number of water turbines. The position of these
cross beams on the main floating body leads to a stabile ap-
paratus with a low centre of gravity.
It may be advantageous when the cross beams are
attached to an upper part of the main floating body.
In yet another embodiment the cross beams extend
inclined upwardly from the main floating body with an angle
with respect to the horizontal of at most 10 , and prefera-
bly said angle is at most 5 . This also has a stabilising
effect on the position of the apparatus.
Preferably the water turbines are mounted on an
upper surface of the cross beams. As a result the water tur-
bines will surface early when the entire apparatus moves up-
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wardly (for example by increasing its buoyancy), and will be
readily accessible for maintenance or repairs without the
need for any additional movement or displacement thereof
(such as, for example, a rotation around a horizontal axis
which requires a complicated structure prone to malfunc-
tions).
The cross beams may be provided with a controlla-
ble ballasting system. Likewise, the main floating body may
comprise controllable ballasting means. Such a system or
means may be used to change the buoyancy of the apparatus
for moving it vertically upward or downward or for trimming
purposes.
When the apparatus is provided with only one pair
of cross beams, these may, as seen in the direction of the
sea current, be attached to the rear half of the main float-
ing body.
The cross beams may be substantially wing shaped
and taper outwardly. As a result they may function essen-
tially as hydrofoils for helping in determining or control-
ling the position of the apparatus.
The mooring means may comprise mooring lines at-
tached to the forward and rearward ends of the main floating
body.
Finally it is conceivable that the apparatus com-
prises only one auxiliary floating body.
Hereinafter the invention will be elucidated while
referring to the drawing, in which:
Figure 1 illustrates in a perspective view from
behind and partly cut away an embodiment of the apparatus
according to the present invention;
Figure 2 shows a frontal view of the apparatus
from figure 1;
Figure 3 shows a side view of the apparatus from
figure 1, and
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Figure 4 shows a top plan view of the apparatus
from figure 1.
The apparatus for generating power from sea cur-
rents illustrated in the figures basically comprises a
5 structure having a buoyancy provided by buoyancy members,
support members supporting water turbines and mooring means
for mooring the structure to a fixed point. Before discuss-
ing these parts in detail below, it is noted that the struc-
ture apart from its buoyancy members also may comprise other
parts which do not or only in a limited sense contribute to
the overall buoyancy of the structure.
The buoyancy members firstly comprise an elongate,
in the present embodiment substantially cylindrical, main
floating body 1 of which the rear end is depicted at the
left in figures 1,3 and 4. Rear mooring line connectors 2
and forward mooring line connectors 3 are provided in the
main floating body 1 for guiding and attaching first ends of
mooring lines 4 of which opposite second ends are attached
to a fixed point, for example on the seabed (not illustrat-
ed) or another stationary construction. The mooring line
connectors 2,3 may be provided with mooring lines pull in
and tensioning means (for example located within the main
floating body 1).
The main floating body 1 provides a defined buoy-
ancy which can be set at a required level by rear and for-
ward controllable ballast tanks 5 and 6, respectively, which
also may be used for trimming the apparatus.
In the interior of the main floating body 1 a
chamber 7 may be provided for housing equipment, such as
electric equipment.
The buoyancy members of the structure further com-
prise a single elongate, also substantially cylindrical,
auxiliary floating body 8 which is positioned above the main
floating body 1 in a vertical plane extending through the
main floating body.
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The main floating body 1 and auxiliary floating
body 8 are interconnected by two vertically extending struts
9 and 10 spaced apart in the longitudinal direction of the
main and auxiliary floating bodies (and in the illustrated
embodiment having an oval cross section). As appears best
from figures 1 and 3, the main and auxiliary floating bodies
1,8 extend substantially horizontally and in parallel to
each other (in an operational position of the apparatus).
The overall buoyancy of the structure is such that
the auxiliary floating body 8 in an operational position of
the apparatus extends partly above .and partly below water
level 15 (see figure 3).
The struts 9,10 each provide a passage 11 for a
person (for example equipped with a ladder 12) between the
interior of the auxiliary floating body 8 and the interior
of the main floating body 1. The structure of the struts is
, such that these passages 11 are sealed against surrounding
seawater, as a result of which the interior of the main
floating body 1 and the equipment chamber 7 too can be
reached by personnel when the apparatus is in the substan-
tially submersed operational position illustrated best in
figures 2 and 3.
The auxiliary floating body 8 is provided with an
access opening 13 which can be closed and opened by a clo-
sure, such as for example a hatch 14, and which in the oper-
ational position of the apparatus is located above water
level 15. In the vicinity of said access opening 13 the aux-
iliary floating body 8 is provided with a mooring structure
16 for a vessel (see figure 2). Further a crane 17 is shown
and navigation members 18 (see figure 3).
The apparatus further is provided with support
members for water turbines 19. Said support members comprise
two cross beams 20 extending in opposite directions outward-
ly from the main floating body 1. As appears best from fig-
ure 2, the cross beams 20 are attached to an upper part of
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the main floating body 1 and extend inclined upwardly from
the main floating body 1 with an angle a with respect to the
horizontal of at most 100, and in the present embodiment at
most 5 .
In the illustrated embodiment the cross beams 20
are, as seen in the direction of the sea current, attached
to the rear half of the main floating body 1. Further figure
4 clearly shows that the cross beams 20 are substantially
wing shaped and taper outwardly.
The water turbines 19 are mounted on an upper sur-
face of the cross beams.
The cross beams 20 may be provided with a control-
lable ballasting system, for example interior ballast tanks
(not visible) for aiding in the control of the overall buoy-
ancy of the structure and for trimming purposes.
As shown in figures 2 and 3, the main floating
body 1 further comprises an umbilical bell mouth 21 at which
an umbilical line 22 is connected to the apparatus.
In the operational position of the apparatus, the
water turbines 19 are at the required depth beneath water
level 15 for an operation under optimal working conditions.
The auxiliary floating body 8 provides an added stability to
the entire apparatus, and also allows access to the interior
of the structure (especially the interior of the main float-
ing body 10) without the need to leave the operational posi-
tion. However, if for example maintenance of the water tur-
bines 19 is required, the overall buoyancy of the structure
may be increased in such a manner that the apparatus rises
until the water turbines have surfaced. Thus there is no
need for attaching the water turbines 19 to the structure in
a movable manner (e.g. rotatable manner, which has the dis-
advantage that the water turbines assume a tilted position
with the risk of a detrimental displacement of lubricant
within the water turbines).
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The invention is not limited to the embodiment de-
scribed before which may be varied widely within the scope
of the invention as defined by the appending claims. For ex-
ample, the wind turbines 19 may be counter rotating to real-
ise symmetrical forces on the apparatus. The number of water
turbines 19 and cross beams 20 may differ from what has been
illustrated. The position of the water turbines relative to
the cross beams also may differ, and if a cross beam sup-
ports more than one water turbine, these may be positioned
on the upper and lower surface of the respective cross beam.
Finally, although horizontal water turbines with forward
facing blades are illustrated, also other types of water
turbines are considered to be within the scope of the inven-
tion.
