Note: Descriptions are shown in the official language in which they were submitted.
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~ The present inven-tion relates to the reduction of l;.cLuid
: wave heights and more particularly :rela-tes -to the reduction of
.~ea water wave heights in the vicinity of m~.rine installations
~md the like.
Wave reduction devices may be scaled to protec-t operatiol1s
varying frorn oil dril].ing and production platforms, loading
.. buoys, ship ~alvage and similar open sea m.qrine operations in
exposed ocean locations to fish farms or yichtlDarin~s in estuaries~
It is an object of the present invention to provide a
floating wave reduction system which substantially dissipates
wave energy whereby the wave height is reduced during its passage
to~.rards the installation being protected.
-. Thus according to the present invention there is provided
a wave reduction device comprising one or more flexible containers ~.
: which are adapted to be partially or wholly filled with a liquid and
means for joining them in a side by side relation~hip and mean~ for
rendering the containers buoyant, the upper and lo-iTer faces of
each container being drawn towards each other at a number of
- pucker points so as to form a puckered surface structure whereby
a resistance to liquid motion inside each container is created.
~ The con-tainers are preferably suspended so -that, in still
--- water, the upper surface of the container is a~rash or down to a .
maxirnum depth of 1/1Oth of the beam of the device. (The beam
is defined as the dimensi.on of the device ~Ihich lies a:l.on~ -the
direction of the ;.ncident wave to be reduced in height and the
length is the dimension at right angles to the beam alon~ the
wave crests). ~:
The containers are suitably constructed from a flexible
fabric so that, ~Jhen filled, a pattern of joins or pucker points
bet~een the upper and lo-rer sheets of -the container cause the top
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and bottom surfaces to become puckered. Their internal structure
provides a resistance to the free movement of liquid within the
container but most preferably no bulkhead should be incorporated
,
which completely prevents liquid flow from front to back i.e.
in the bea~ direction.
The upper and lower surfaces of the container are connected
90 as to provide a resistance to liquid flow within the container
and preferably the upper and lower surfaces of the containers
are joined 90 that the thickness of the container at the pucker
point i9 from 0 to 50~ of the inflated maximum thickness of the
container. By inflated maximum thickness is meant the thickness
of the container when at its total volume (as hereinafter
defined). This may be achieved, for example, by joining the
opposite faces by use of a ring weld. Each pucker point may
be of any suitable shape e.g. circular, hexagonal, elliptical
or rectangular with curved ends. If asymmetrical shapes are used
the largest dimension of said shape is preferably at right
.,., ~
angles to the beam of the device. AlternativeIy the upper and
lower surfaces may ~imply be drawn closer together by e.g. a
suitable form of clip, moulding or grommet to provide the resistance
to liquid flow in the container without the opposite surfaces
touching. The area of the pucker points comprises from 2 to
30~ of the total surface area of the container. In one embodiment
of the invention, the pucker points are preferably arranged in
parallel rows and in another preferred embodiment each row is
staggered with respect to each other.
Preferably the joins or pucker points between the upper
and lower ~u~faces have holes pas~ingthrough them 90 that in use
of the device, the liquid whose wave height is to be reduced can
- 30 pass through said holes. These holes, preferably, have an area
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of 1 to 50~ of the total surface area of said upper and lower
surfaces of the device. The presence of the holes help~ to
reduce the tendency of the container to dive when subjected to
~ water currents. Also the wave reduction device may h~ve a flexible
- flotation collar, e.~. of a closed cell foam, arounds its
- periphery to further reduce any dippin~ tendency.
The container is designed to have a beam and length several
times greater than its thickness when filled with liquid and
preferably each container ha3 a beam from 10 to 30 times the
maximum container thickness when filled with liquid. The
containers u~ually have a larger beaM than length but containers
having a greater length than beam may be used.
Any length of breakwater may be constructed by joining
the containersto~ether to obtain the required protection. Preferably
the joins should be made along the beam direction.
oont~ners may be moored 90 as to lie close to each other
with a uniform or varying gap between them to build up a larger
area of effective breakwater.
Buoyancy for the containers may be locali3ed or distributed. ,
In one embodiment the buoyancy takes the form of a closed cell
- foam which is distributed over the surfaces of the containers.
Preferably the foam is distributed evenly and over either the
upper surface or the lower surface of the containers. The foam ;~
may be cut away at the puckers. Alternatively the upper and lower
sheets of the containers may contain distributed buovancy in th~
form of many air filled pockets.
In R second embodiment of the invent;on, flexible air
chambers may be connected to the containers at the join~ between
module~. Float3 may be incorporated in some or all of the
depressions in the puckered structure of the inflated containers.
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In order to cause wave reduction over the range of condition~
encountered at a chosen location the device is desirably dimensioned
to produce the required performance for the longest wave length
and greatest wave height (crest to trough) specified for reduction
at the location,
The thicknes~ of the container is preferably 0.3 to 10 metres.
The beam dimension should be, preferably, 10 to 200 metres.
The overall length of the breakwater installation, one or more
discrete length units, is determined bv the area of protected
water required. The shape of the complete breakwater installation
may be straight or curved. The overall shape is determined by
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the shape of the containers and the deployment positions of the
mooring lines.
The containers are preferably made from a polymer coated
synthetic fabric in which the polymer may be in the form of a
closed cell foam. Preferred fabrics are polyester and nylons
and the most preferred material is nylon reinforced rubber sheet.
Typcial thicknesses used are from 0.5 to 20 mm. Alternatively
non~reinforced elastic polymer sheets e.g. a rubber, may be used
which when filled have the characteristics of a balloon or bladder.
Again the polymer may be in the form of a closed cell foam.
The mooring lines may be connected to flexible load
distributing spar~ incorporated into the beam edges of
the containers. ~owever, in a preferred embodiment mooring may
- be achievsd by passing a primary line between two points whichmay be anchors or vessels and taking a number of secondary lines
from the primary line to the nearest edge of the breakwater.
These secondary lines are adjusted in length ~o as to pull
the primary line into a shallow curve and the edge of the
breakwater is held in the desired shape. Netting may be used
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as a substitute ~or the secondary lines. This arran~ement may
be duplicated to moor other edges of the breakwater if necessary.
In an alternative embodiment, the edge of the breakwater may be
fabricated in a curve so as to eliminate need for secondary lines.
The fill of the liquid within the containers is preferably
greater than 7~% of the total volume and may be increased to
give static filling pressures in the bag of up to 3 p3i above
atmospheric pressure at the top surface of the container liquid.
By total volume of the container is meant the volume of the container
when floating on the liquid surface and filled with liquid to
- an internal pressure of 0.5 p~i above atmospheric pressure at
the top surface of the container liquid.
The invention also includes a method of liquid wave reduction
whereby:
(a) a wave reduction device (as hereinbefore described)
i9 deployed with it3 length at right angles to the
incident wave direction, and
(b) most of the upper surfaces of the device being
- awash or below the still liquid level.
2 0 The invention will now be described by way of example
only with reference to Figures 1 to 6 of the accompanying drawings.
Figure 1 shows a plan view of a type A container having pucker
points in a 4 - 5 configuration.
Figure 2 shows a plan view of a t~pe B container having pucker
points in a 5 - 6 configuration.
Figure 3 shows a plan view of a deployed breakwater comprising
5 type A and 5 type B containers with associated buoys and
mooring lines.
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Figure 4 ~hows the relationship between wave height reduction,
wavelength and liquid fill for a breakwater ~igure 5 illustrates
a number of different ways of for~ing the pucker points of the
containers and Figure 6 shows a diagrammatic representation of
a four container breakwater when deployed on open water. Figure
1 shows a type A container 1 measuring about 5.8 X 12 metres.
The containers 1 were made from a nylon fabric coated with a
656 gram/m2 polychloroprene/natural rubber blend. The tensile
strength of the fabric was of the order 63 kg/on warp and 36
kg/cm weft, trouser tear 23 kg.
Distributive buoyancy for type A containers was provided
by means of (not shown) 9mm thick ethylene vinylacetate (EVA)
- closed cell foam affixed to the top inside face of containers
Al and A2 and to the outside lower face of containers A3, A4
and A5. The buoyancy provided by the foam was about 600 kg
per container.
Peripheral buoyancy of about 8 kg/metre was provided by
6000 x 150 x 60 mm blocks of EVA foam laced to the edges of
; the containers.
The pucker points ? were formed in a 4 - 5 arrangement
around 300 mm diameter holes 3 by cold bonding a fabric reinforced
grommet to the top and bottom surfaces of the container (see
~igure 5. The distance between the edges of the holes 3 was
-~ 850 mm and gave a maximum inflated thickness of the container
of 540 mm. Valves 4, 5 were incorporated for filling and monitoring
internal pressure and zippers 6 were used for rapid emptying
of the container.
The details of construction of the type A containers
are shown in the Table 1.
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Figure 2 shows a type B container 7 of similar dimensions
to the type ~ container 1. Two similar nylon/butyl rubber/nylon
sandwhich materials were used for construction of the container.
(I) The tensile strength was of the order 40 kg/cm (warp) and
36 kg/cm (weft)-and the trouser tear was 22 kg., (II) the
tensile strength was 57 kg/cm (warp and weft) and the trouser
tear was 34 kg (warp) and 27 kg (weft).
Distributive buoyancy for the type 3 containers was
provided by means of 6 mm thick EVA foam with a buoyancy of
400 kg/container affixed to the external lower face of the
container 7.
Peripheral buoyancy, filling and pressure relief valves
were similar to the type ~ containers. Details of construction
of the type B containers are shown in the Table 1.
The pucker points 8 were formed in a 5 - 6 arrangement
around 300 mm diameter holes 9, The pucker points 8 were
stitched circular doublers (Figure 5) cold bonded in position
- with the circular holes 9 cut out after the bonding.
Figure 3 shows a breakwater 10 comprising ten flexible
water filled containers 11 joined in parallel with small gaps
between. Five of the containers are of type A (A1 to 5) and ~
the other five are of type B (B6 to 10). The total array of ,
containers has dimensions of about 63 x 11 metres. The buoyancy
of the container was such that the upper surfaces were awash~
The mooring system for the breakwater was made up as
follows. Four primary ropes 12 of 20 mm diameter polypropylene
were held in parabolic form by moorings and buoys 13. The
edges of the containers 11 were attached to the primary ropes ~;
12 by 6 mm diameter nylon lines 14 in a zig-zag configuration.
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This arrangement keeps the breakwater in its configuration
when subjected to wave and tidal forces.
When the breakwater 10 had been deployed and moored,
the individual containers 11 were then filled with water.
Ten sealed foam filled 25 litre plastic buckets each containing
a 35 ampere-hour, 12 volt accumulator on the inside and a 12V,
- 6800 litre/hour bilge pump on the autside were used to fill
the breakwater. The initial filling took about 3 hours.
The performance of the breakwater was assessed by wave
rider buoys 15 placed in front of and behind the brea~later
and to one side where a reference buoy was not under any
influence from the breakwater. Examples of the results obtained `
for a sea trial are indicated in the following Table 2. ~-
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Figure 4 shows results obtained for wave reduction and
~ L/B ratio where L i9 the water wavelength and B is the beam dimension
- of tha breakwater using a wave tank at different water fills.
The breakwater comprised three containers. Each container was
formed from two 2078 X 1219 mm sheets of nylon reinforced polyvinyl
-~ chloride welded along their edges. The pucker points consisted
of 64 mm diameter welded rings in a 3 - 4 parallel row formatlon.
Buoyancy was provided by strips of 2 - 3 mm closed cell plastic
foam bonded to the upper or lower surfaces of the containers.
The wave tank used had a length of 15.2 metres, a width
of 3.6 metres and a water depth of 900 mm. Waveq were generated
at one end by an hydraulically driven cam and at the other end
a beach minimised wave reflection.
The results show an increase of wave height absorbed with
degree of water fill up to a fill of 22 gallons. At greater
fill~ the wave height reduction diminishes. The total fill
volume of the container was considered to be 28 gallons.
Figure 5 (a) and (b) shows two ways of fabricating the
pucker points, in which in Figure 5 (a), the upper and lower ~urfaces
of fabric are cold bonded to a partly reinforced rubber grommet,
and in Figure 5 (b), the upper and lower surfaces of the fabric
are cold bonded to a circular stitched doubler.
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