Note: Descriptions are shown in the official language in which they were submitted.
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UNDERWATER SEDIMENT MANAGEMENT
The present invention comprises to an apparatus for carrying out controlled
excavation and movement of loose bed material in marine, river, lake and
similar
underwater environments. Modifying the underwater bed topography, by selective
removal of bed material from one axea and deposition in another, comes under
the
ambit of sediment management. The present apparatus is designed for sediment
management operations, primarily, in shallow water (1-SOm water-depth).
The herein-described apparatus incorporates an embodiment of a means for
dredging,
scouring, excavation and cleaning, described more particularly in
PCT/GB2003/005030. In the latter document the embodiment, namely a ducted-
propeller, is described in more detail, together with various alternative
modes of
operation and means of deployment. The herein-described apparatus can be seen
as
providing a suspended underwater vehicle deployment means, for bring to bear
the
operation of the ducted-propeller.
As such, the present invention is deployable in a similar manner to the Wing
Dredger
described in U.S. Patent No. 6125560, in terms of deployment from a floating
vessel
by means of suspension wires for the purpose of controlling the direction of
the
propeller jets) relative to the bed. A further similarity exists with the Wing
Dredger
in the design of the propeller and the duct, and in having the propeller
mounted at the
outlet end of the duct. However, the present invention differs from the Wing
Dredger
in being designed specifically for use in shallow water, in being more
versatile in
terms of single- and multiple jet operation and in embracing a wholly new and
novel
approach to propeller jetting.
This new approach recognises and takes advantage of the fact that the jet
created by
the said ducted-propeller, is not simply a thrust means. Rather, it is a
complex
swirling flow, which includes a number of embedded vortical flow elements. The
various ways in which the said swirling jet can be modified and can be used
for
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excavation and controlled movement of bed material are described, more
particularly,
in PCT/GB2003/005030. Suffice it to say, swirl imbues the jet with certain
behavioural characteristics, which when properly directed can be highly
beneficial for
a range of sediment management operations.
In its broadest sense, the present invention provides an apparatus comprising
a body
having a bottom face and comprising an outlet flow path in which is mounted
thrust
means to direct, in use, a wash of water downwards towards an area of sea or
river
bed or the like, orientation means to connect said apparatus, in use, to a
support means
to orientate said apparatus with respect to the sea or river bed, and at least
one inlet
flow path through which water is supplied, in use, to the thrust means;
characterised
in that the inlet and outlet flow paths are provided with respective openings
in the
bottom face of the body; in that at least a portion of the outlet flow path
comprises a
duct; and in that the thrust means comprises a propeller mounted within the
duct.
Preferably, the inlet and outlet flow paths are parallel, but of opposite
directions.
Preferably, the duct is formed with an outlet in the undersurface of a central
section of
the body.
Suitably, an adjustable flow regulator is provided adjacent the inlet of the
inlet flow
path. Typically, the flow regulator comprises a louvre assembly.
In one particular embodiment, the body is in the form of a wing having an
angled face
at at least one of leading and trailing edges thereof. Such face or faces may
be
provided by means of an additional wing profile attachment to the body.
Suitably, the apparatus is of simple box-like construction, being made from
steel
plate, with one ducted propeller unit per apparatus. The design is preferably
such that
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two or more units can be easily coupled together in different configurations
for
multiple j etting operations. In order to be able to operate in very shallow
water and
yet maintain a reasonable distance from the bed, the apparatus is designed
with
intakes on the underside that face downwards. Provided the apparatus is
initially
filled with water (primed) it can continue to operate when lifted partway
above the
waterline, since water will continue to siphon through the body of the
apparatus and
into the propeller duct. Adjustable opening louvre plates over the intakes
provide
protection from ingress of debris and also a means for preventing rotation of
the
apparatus (countering the propeller torque) when operating in single jetting
mode.
More importantly, they also provide a means for controlling the rate of water
flow
through the propeller duct.
The propeller is driven by a high-pressure hydraulic motor, wluch is located
axially
within the duct. The use of a hydraulic motor is an integral part of the
overall design
of the apparatus, since it enables a very compact and light-weight
construction
(compared to the aforementioned Wing Dredger) and also provides for variable
speed
and direction control over propeller rotation. The apparatus can also be more
easily
fitted with the means to modify the behaviour of the jet: to create a straight-
sided or
wide-angle jet, as required.
The above and other aspects of the present invention will now be described by
way of
example only and with reference to the accompanying drawings, in which:
Figure 1 shows an oblique underside view of the exterior of an apparatus in
accordance with the present invention.
Figure 2 shows an oblique topside view of the exterior of the apparatus of
Figure 1.
Figures 3 and 4 show sectional views through the apparatus of Figure 1. Figure
3 is a
vertical section on the long axis, and Figure 4 is a horizontal section at mid-
level.
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Figures 5, 6 and 7 show sectional views through one of the intakes to
illustrate the
louvre plates and the mechanism controlling the degree of opening of these
plates.
Figure 5 shows the louvre plates fully open (against the bar stop), Figure 6
shows the
louvre plates half open (against the bar stop), and Figure 7 shows the louvre
plates
shut (with no flow through the intakes).
Figures 8 and 9 show, in diagrammatic form, the water-flow circulation through
the
apparatus of Figure 1 depending on the direction of rotation of the propeller.
Figures
8 shows normal flow jetting, and Figure 9 shows reverse flow filling
(priming).
Figures 10 to 13 shows various ways in which the apparatus can be suspended
from a
vessel and various ways in which multiple units can be coupled together.
Figures l and 2 show an embodiment of the apparatus of the present invention
including a rectangular body or tank 10 of generally light-weight
construction; steel
plate being a suitable construction material. The dimensions of the tank, as
shown,
are in the ratio: length 3; width 2; height 1.5. It is envisaged that these
dimensions
would be represented by metres, however the overall size of the tank is not
critical to
the operation of the apparatus and may be any convenient size or, indeed,
shape
To provide added stiffness to the construction, as shown in Figures 1 and 2,
side
plates 12, and top and bottom plates 13 and 14, are joined by angled plates
15. This
has the added benefit that on the inside of the tank the lower sides slope
inwards
creating a partial hopper effect. Material carried in-board in suspension with
the
intake flow (see Figure 8) that might otherwise settle inside the tank, in the
angle
between the sides and base, is encouraged to slip down towards the intalce and
so be
re-suspended by the intake flow.
Reference to Figure 3 shows that the hopper effect is completed by angled
fillets 47
placed along the contact between end plates 16 and bottom plate 14 and between
bottom plate 14 and central bulkhead plate 45.
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Various attachment points are provided on the outside of the tank, as
indicated in
Figures l and 2. There are four corner attachment points 17 at each end,
formed by
' the proj ections of end plates 16, and four centre attachment points 18,
which comprise
5 triangular plates 19 welded to angle plates 15. The position and orientation
of
triangular plates 19 correspond internally to bulkhead plate 45. Smaller
triangular
fillet plates 20 provide added lateral stiffness to each of the suppout
points.
Referring to Figure 2, it can be seen that two hatch-covers 22 are provided on
top of
the tank that give access, via associated openings in top plate 13, to the
inside of the
tank. These hatch covers are of conventional construction, but are designed
specifically to provide an air-tight seal to the tank when fully closed. Also
on the top
of the tank are two grab rails 23 that run along the outer long edge of top
plate 13.
These are formed of steel pipe and are attached at their two ends and at
intermediate
locations in such a way that there is communication between the inside of the
tank
and the bore of the pipes. Set onto the top of the grab rail pipes towards
each end, are
short, internally threaded, spigot pipes 24, into which non-return valves (not
shown)
can be screwed. The non-return valves are designed to allow egress (venting)
from
the tanlc of air and water, but not ingress. Their function and operation will
be
described later.
Also on the top of the tanlc and attached to top plate 13 by means of multiple
bolts, is
a circular plate 25. Circular plate 25, when removed, gives access to the
inside of the
tank for the purpose of removing the propeller duct unit. The circular opening
in top
plate 13 that is covered by circular plate 25 is, therefore, slightly larger
in diameter
than the widest lateral dimension of the propeller duct. Circular plate 25 is
fitted with
a rubber gaslcet designed to effect an air-tight seal.
Also formed centrally in circular plate 25 are three circular openings set out
in
triangular fashion, which provide penetrations for the three hydraulic hoses
that
connect to the motor (two high-pressure power hoses and one low-pressure
casing
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drain hose). Split flanges 26, formed of rigid plastic, and bolted to circular
plate 25
over each opening, encircle each hose and provide an air-tight seal where the
hoses
enter the tank. Split flanges 26 also serve to secure the hoses at the point
of entry to
the tank, thus preventing any rislc of chaffing of the hoses against metal
edges. Split
flanges 26 can be more clearly seen in Figure 3.
Completing the appurtenances on the top of the tank, as shown in Figure 2, is
a small
detachable stool-like structure 27, consisting of a circular ring supported by
means of
struts at a fixed distance above the top plate. The hydraulic hoses pass
through the
ring and are loosely supported in such a way that over-bending, or kinking, of
the
hoses at the point of entry into the tank is prevented.
Referring to Figure 1, the circular outlet 28 of the propeller duct can be
seen to be
centrally located on the underside of the tank. Also the position of the
propeller 29,
just inboard of the duct openings can be clearly seen. It should be noted that
there are
no rigid obstructions (vanes, struts or other protrusions) in way of the
propeller jet,
within or below the outlet end of the duct.
Located either side of the propeller duct outlet 28, are two water intakes 30.
These
are rectangular in shape and are of such a size that one on its own would
provide for
unhindered flow of water into the propeller duct, when the propeller is
rotating at full
speed. Attached to the bottom plate 14 and extending vertically over each
opening
are three thick metal grill plates 31. These are designed to prevent large
items of
debris, or obstructions sticlcing up from the seabed, from penetrating the
intakes.
They are also designed to take the weight of the apparatus when the latter is
placed
on-deck or onto a hard-standing surface. If the apparatus were to be placed on
a soft
surface, wooden sleepers would be used to prevent the grill plates from
penetrating
into the surface.
Figure 1 also shows that immediately inboard of the intakes 30 are multiple
louvre
plates 32, which extend across each intake. These are designed to prevent
ingress of
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smaller debris that might otherwise pass between the thick metal grill plates
31. Each
louvre plate has a hinge attachment to the bottom of the tank at either end,
such that
each plate is free to rotate about a hinge-line coincident with the bottom
edge of the
plate. A detail of this hinge attachment is shown. in Figures 5 to 7.
Referring to Figures 5 it can be seen that a simple horizontal bar stop 33,
supported at
either end on pillars 34, allows adjustment of the amount of opening of the
louvre
plates 32. Each pillar 34 has a series of holes drilled into it to allow the
bar to be
secured at different heights above the base of the tank. As presently
designed,
adjustment of the amount of louvre plate opening has to be by hand, requiring
man
access through the hatch covers with the apparatus on deck. It is envisaged
that in
due course a remotely operated louvre adjustment mechanism will be adopted.
When the louvre plates are lying flat (Figure 7), the intakes are effectively
closed,
save for minor leakage at the edges of the plates. This leakage is useful in
that during
reverse circulation flow (see below) it allows any residual sediment that may
have
collected in the bottom of the tank to be flushed out. When the louvre plates
are
pointing nearly vertically upwards (Figure 5), the intakes are fully open,
allowing
unhindered flow to the propeller duct. When no water is being drawn through
the
intakes, self weight causes the plates to fall shut and adopt the imbricate
arrangement
shown in Figure 7.
It should be noted that the louvre plates are set in such a way that they face
in
opposing directions over each intake. While this is of little consequence when
the
plates are fully closed or fully open, it will be appreciated that with the
louvre plates
at intermediate positions (Figure 6), water entering the intake is forced to
do so at an
angle, which will be opposed on the two sides. Opposed deflection of the
intake
water flow imparts a turning moment to the apparatus, which helps to counter
any
tendency for rotation in the opposite direction induced by the propeller.
Needless to
say, the direction of angling of the louvre plates has to be co-ordinated with
the
direction of rotation of the propeller.
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Lastly, in referring to Figure 1, it should be noted that surrounding the
outlet end of
the propeller duct is a flange plate 35 directly welded to the bottom plate
14. Flange
plate 35 has a series of tapped holes drilled into it. The purpose of the
flange plate is
to allow attachment of a flared nozzle, the function of wluch is discussed in
PCTlGB2003/005030.
Reference to Figure 3 shows the inside of the tank in vertical section to
illustrate the
disposition of the propeller duct 36 and motor 37. The propeller duct 36 can
be seen
to have a vertical length approximately 2/3 the height of the tank, and to
have a
belhnouth 38 at the top (inlet end) to facilitate the inflow of water. Motor
37 is
axially positioned in the duct with its shaft (not seen) facing downwards and
the high
pressure hydraulic fluid ports (for attachment of the two high-pressure hoses
3 8)
facing upwards. A side-tap on the motor (not shown) provides attachment for
the
casing drain hose 39 (see Figure 2).
Motor 37 is supported axially within the duct by means of collar 40 to which
the
motor is secured by a ring of axial bolts, and the collar is secured to the
inside of the
duct by means of angled fin plates 41. The fin plates are vertically set in
order to
present a limited surface area to the direction of flow and their edges axe
also
chamfered to further minimise flow obstruction. There are five supporting fin
plates
41, equally spaced; this number being purposely chosen to provide both a rigid
axial
support to the motor and an non-equal or non-multiple of the propeller blade
number
(four-bladed propeller): the latter being good engineering practise in terms
of ducted
propeller design. The arrangement of the fin plates can be better seen in
horizontal
section, in Figure 4.
The motor can be seen to taper downwaxd at its front end, forming a smooth
transition
with the hub of the propeller 29. The smooth profile of the motor and
propeller hub
matches the shape of the duct, giving a uniform width of annulus between the
motor
and the duct.
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The duct, complete with motor, can be detached from the tank and removed
through
the top of the tank. The duct has three rings 42 welded around its outer
circumference. These are designed, partly, to maintain the ovality of the duct
both
during and following fabrication. The uppermost ring also gives added
stiffness to the
duct at the point of fixity of the angled motor support fin plates, while the
lowermost
ring also acts as a seating flange when the duct is installed into the tank.
This
lowermost ring has two holes drilled into it that act as stabbing guides for
pegs 43
(indicated by small arrows) that stick up from a landing flange 44 on the
bottom of the
tank. The two upper rings also have holes drilled in them to enable the duct
to be
rigidly secured on either side to the central vertical bulkhead plate 45.
Angled
brackets 46, in pairs, provide the means for bolting the propeller duct to the
bulkhead
plate and can be seen in Figure 4.
Also visible in Figure 3 are the fillets 47, which complete the hopper-like
form of the
tank base around each intake, as can be better seen in Figure 4. The fillets
may be of
any suitable material, such as concrete, and may be removable or cast in situ.
Lastly, in referring to Figure 3, it should be noted that while bulkhead plate
45 only
extends inwards as far as the propeller duct, it stretches the full height of
the tank; and
thus effectively divides the tank into two separate compartments below the top
level
of the propeller duct. Directly over the top of the propeller duct, however,
there is
free communication between the two halves of the tank.
The workings of the apparatus will now be briefly described by reference to
Figures 8
and 9. In the first instance, it will be assumed that the apparatus is being
operated in
sufficient depth of water that the siphonic action is not required.
Figure 8 shows that when the propeller is rotating, such as to produce a
downward jet
of water, water is drawn through intakes 30; circulates through each side of
the tanlc;
enters the top of the propeller duct through bellmouth inlet 38; travels
through duct 36
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and is forced out through duct outlet 28. The reduction in pressure inside the
tanlc
caused by the rotation of the propeller (acting like an axial flow pump)
causes louvre
plates 32 to open as far as paired bar stops 33 will allow. Water is thus
sucked
upwards into the tank at a rate determined by the speed of rotation of the
propeller and
5 the degree of opening of the louvres.
Since all other points of ingress for water into the tank are sealed, the
louvre plates
provide an effective means for regulating (i.e. reducing) the flow of water
through the
propeller duct for any given speed of rotation of the propeller. The main
reason for
10 wanting to reduce the flow of water through the propeller duct is that the
axial
velocity of the jet is reduced compaxed to its swirl velocity and so the Jet
Swirl
Number is increased (see PCT/GB2003/005030 for a more detailed description of
Jet
Swirl Number). In propeller design parlance, a decrease in flow through the
propeller
disc is referred to as a reduction in propeller advance coefficient (J). One
of the
significant effects of this (as described more particularly in
PCT/GB2003/005030) is
that the behaviour of the jet is changed, making it more susceptible to
breakdown.
When starting the apparatus in very shallow water an initial priming action
may be
necessary, which is illustrated in Figure 9. The propeller is initially
rotated in reverse
at slow to moderate speed. This has the effect of forcing water into the tank
through
the propeller duct. The louvre plates act as (slightly leaky) one-wayvalves
preventing
wholesale egress of water through the intakes. Air and then water are thus
forced out
of the top of the tank through the four non-return valves in vent holes 24.
Once the
tanlc has been filled with water and purged of air (indicated by continuous
spouts of
water from the holes 24) the motor rotation is quickly reversed to begin
normal jetting
operations, as explained by reference to Figure 8. This priming action can
also be
used as an effective way of cleaning (back-washing) residual sediment from the
bottom of the tans; material being flushed out by the leakage flow that occurs
through
the gap between the ends of the louvre plates and the underside of the tank
(see Figure
7).
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Normal jetting, once established, can continue even with much of the tank out
of the
water, because the propeller creates sufficient suction head for water to
siphon into
the propeller duct. The fact that the intakes are placed on the underside of
the tank
also means that there is less likelihood of air being sucked in via a drain-
hole vortex.
Clearly, for this siphonic action to worlc effectively the emergent top of the
tank has to
be fully air-tight.
For most operations, where simple jetting of the bed is required, the
apparatus would
be suspended by one or two pairs of wires from a crane, or A-frame, mounted on
a
support vessel. Figures 10 to 13 show a number of possible support options,
together
with various ways in which several single jet units can be coupled together to
form
multiple units. In Figure 10 a single unit is shown suspended by two wires 4~.
Loops
of chain 49 with their ends attached to the upper corner points 17 provide a
means for
adjusting the roll and pitch of the apparatus. By shackling the wires to links
on one or
other side of the centre point of each loop, forward or backward pitch can be
introduced. By adjusting the length of each chain independently, sideways roll
can be
effected. In this respect, operation similar to that described in U.S. Patent
6125,560 is
achieved.
Single unit operation is intended primarily for pipeline (or cable) jetting
work. For
instance, where a pipeline laid on the seabed is required to be lowered below
the bed
for the purpose of increased protection. The ability to tilt the apparatus
sideways is
important, since by directing the tilted jet just under the pipe as the unit
traverses
along and adjacent to the line of the pipe, material can be displaced to the
fax side of
the pipe to form a levee stockpile. The same material can then be used to
bacl~ll the
trench by jetting from the opposite side with the jet tilted towards the
stockpile and
the trench. Note that a significant advantage of this jetting equipment over
conventional pipeline ploughing equipment is that there is no mechanical
contact with
the pipe.
3O
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In Figure 11 two units are shown coupled together in-line and suspended in
similar
fashion, but with the chains 49 attached to the four upper centre attachment
points 18.
Because the separation of the wires and the attachment arrangement of the
chains is
identical to that for the single unit (shown in Figure 10) a double unit can
be operated
from the same vessel in exactly the same way as a single unit. It is a also a
very
simple matter to couple two units together in-line, by means of four high-
tensile bolts
passing through the four common corner attachment point holes 17.
A double in-line unit (or indeed a triple in-line unit, as shown in Figure 12)
would be
used primarily for bulls excavation and movement of material. This might
include
pre-sweeping of a corridor through sandwaves for the purpose of preparing a
smoothed profile for laying a large diameter pipeline, or it might include
removal of
material from shoal areas in a navigation channel. Either way, material has
typically
to be removed in large quantities to an agreed level, and in the latter case
the
excavated material has to be deposited below the navigation depth. By
operating two
or more units in-line the jets act in concert to remove a swathe of material.
Typically,
the units would be tilted (pitched) in the direction of forward travel so that
material is
displaced in this direction. No sideways roll would be used, as the objective
is to
create a level surface.
Finally, Figure 13 shows two units coupled together in saddle fashion, metal
struts 50
being used to cross-connect adjacent upper and lower attachment points (17 and
18)
and achieve the desired angle of convergence of the jets. A similar means of
suspension is used, as in the other sketches. Such a converging jet
arrangement would
be employed, for instance, where increased jetting energy was required for
lowering a
pipeline (or possibly exhuming an existing buried pipeline). The focussing of
the two
jets means that excavation energy is concentrated at the point of intersection
of the
two jets.
Advantages of the apparatus for the present invention include:
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1. An improved ability (compared to U.S: Patent 6,125,560) to operate in
shallow
water for the purposes of carrying out underwater jetting excavation and
movement of bed material. Said ability being achieved by means of a short
propeller duct, housed inside an air-tight tank, with the primary water
intakes on
the underside of the tanlc and with the ability to carry out an initial
priming
operation wherein the propeller is reversed to induce filling of the tank.
2. An improved ability and gr eater versatility to operate in single- and
multiple-
jetting configurations, by coupling single jetting units together.
3. An improved ability to control and regulate the velocity of flow through
the
propeller duct and at its outlet end for the purpose of modifying the
behaviour of
the jet. Said control being~exercised by adjusting the degree of opening of
the
louvre plates, which function lilce one-way valves.
4. An ability, stemming from point 3 and the use of various attachments (as
discussed in PCT/GB2003/005030), to carry out very rapid excavation in a wide
range of loose bed materials, with the attendant directional movement of the
excavated material over long distances (100m's).
5. An ability, also stemming from point 3 and the use of various attachments
(as
discussed in PCT/GB2003/005030), to carry out excavation (albeit at a slower
rate) in stiff clay materials that axe otherwise not amenable to excavation by
means of low-pressure water jetting.
6. An ability, equal with U.S. Patent 6,125,560 to operate the apparatus from
a
support vessel by means of a wire suspension system wherein the attitude of
the
apparatus can be adjusted in terms of both pitch and roll. Said capability
being
used for the purpose of sideways displacement of material (such as for
pipeline
jetting) and for forward displacement of material (such as for pre-sweeping
and
sediment management operations).
7. An added benefit, further to point 3, that the said louvre plates also
provide a
means for preventing access of debris into the propeller duct.
An added benefit, further to point 3 and point 7, that the said louvre plates
when
half open also provide a means for preventing rotation of the apparatus by
countering the turning moment induced by the propeller.
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9. The added benefit, further to point 7, wherein thick grill plates over the
intakes
protect from ingress of coarse debris and penetration of seabed obstructions.
Said
grill plates also provide a means for supporting the apparatus when not in
use.
10. A simple body shape that is strong, light-weight and functional (in terms
of
forming an air-tight sealed tank), that is, in effect, self cleaning by having
a
hopper-like base form, that has attachment points strategically placed to
enable
the body to be suspended from wires and chains and coupled to like bodies in
different configurations for the purpose of multiple jetting.
11. A simple means for installing and removing the propeller duct, i.e. for
maintenance purposes, and to enable said propeller duct to be used in other
propeller jetting embodiments (as described in PCT/GB2003/005030).
12. The added benefit, further to the self cleaning ability noted in claim 10,
of using
the priming action, noted in point 1, as a further means for cleaning (back-
washing) the inside of the tank.
