Note: Descriptions are shown in the official language in which they were submitted.
FIELD OF THE INV~NTION
This invention concerns a floating breakwater with a
pontoon-type float body which is anchored to the sea bottom.
BACKGROUND OF THE INVENTION
(a) Brief Description of Drawinq Related to Prior Art
Figure 1 shows a side cross-sectional view of a
floating breakwater of past design.
(b) Description of the Prior Art
Referring to Fig. 1, the pontoon-type float body (a)
was attached to the sea bottom (c) by a rope or a chain
(b). When incident or incoming waves (d) struck, the
10at body (a) would bob up and down, or laterally in a
left-right direction.
When a wave would pass this breakwater, the incoming
wave (d), when it hit the restrained float body (a),
would produce wave (e). The movement of the float body
(a) would cause wave (f) to be formed. The optimum
conditions which would produce no waves transiting the
~ breakwater would be if float body (a)'s lateral, left-right
sway phase difference with respect to incoming wave (d)
matched the phase difference of the float body's vertical
movement caused by incoming wave (d). With these conditions,
waves (e) and (f) would cancel each other out and there
would be no transiting waves.
However, as Figure 1 shows, a simple pontoon-type
of float body (a~ has only its shape to determine its
wave-breaking properties and it was an objective to
improve upon this floating breakwater by providing a
measure by which these properties could be adjusted.
SUMMARY OF THE INVENTION
Therefore, in this invention's sea bottom-
anchored, pontoon-type floating breakwater, there is a
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left-right sway-reducing tank in the above-mentioned
float body which makes the phase difference of the
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vertical motion of the float body from incoming
waves, approach that of the lateral, left-right,
sway of the float body caused by the same incoming
waves.
~ ore particularly, the invention comprehends
a floating breakwater including a pontoon type
breakwater float body anchored to the sea bottom.
A floating left-right sway reducing tank floats
inside the breakwater float body. Th~ phase
difference between the vertical movements of the
float body and the incoming waves, and that of
the lateral, left-right sway and the incoming waves
are caused to approach each other by the left-right
sway of the sway reducing tank so that the ratio
of the transiting wave to the incoming wave is
reduced.
In the past, it was necessary to employ ballast
water in pontoon type breakwaters to sink them to
a specific draft, but with the floating breakwater
o this invention, it has the advantage of combining
the function of the functional water with that of
ballast water, so it is possible to improve the
cost efficiency.
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BRIEF DESCRIPTION OF THE DRAWINGS OF THE INVENTION
Varlous other objects and many of the attendant
advantages of the present invention will be readily
appreciated as the same becomes better understood by
reference to the following detailed description when
considered in connection with the accompanying
drawings in which like reference characters designate
the same or similar parts throughout all the figures
thereof (Fig. l having been previously described with
relation to the prior art1, and wherein:
Figures 2 - 5 are all figures representing side
cross-sectional views of actual examples of this
invention;
Figure 5 shows a side cross-sectional view of the
action of the floating breakwater of this invention;
and
Figure 7 is a graph which compares the properties
of this invention's breakwater with one of past
design.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figures 2 - 5 are all examples of a side cross-
sectional view of an actual example of this invention.
In each of these figures of floating breakwaters, the
float body (3) is anchored to the sea bottom (l) by a chain
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or rope (2). It is built to include a left-right sway-
reducing tank. The water inside of the tank combines the
ballast water function and that of the functional water (4a).
In each of the examples in Figures 2 - 4, the left-
right sway-xeducing tank (4) is mounted on the inner
plate (3a) of the double-bottom of the pontoon-type
float body (3). As E'igure 5 shows, it would also be
alright to have a left-right sway-reducing tank inside of
a pontoon-type of float body with a single bottom (3)
where it would be in direct contact with the functional
water.
Also, as Figure 4 shows, because there are holes
(5) made in the wall portion of the pontoon-type float
body (3), it is alright if water from the outside is
allowed to come into contact with the left-right sway-
reducing tank.
Based upon the double pendulum theory, by adding
the supplementary pendulum in the form of the left-right
sway-reducing tank (4), it becomes possible to change
the phase lag of the principal pendulum which is the
float body t3) itself.
That is, the functional water (4a) which is enclosed
within the floating breakwater upon being hit by an
incoming wave of short wavelength, moves in a left-right
direction as shown in Figure 6. The phase difference
in the left-right sway of the float body vis-a-vis the
- incoming waves varies with the width Bo of the left-right
sway-reducing tank (4) and the depth (h) of the functional
water when it is at rest.
The characteristic periodicity (T) of the back-
and-forth motion of the functional water (4a) is shown by
the following equation.
T = 2~
.., _
~ Bog tanh Bo
Where: -
Bo is the width of tihe functional water
' h is the depth of the functional water at rest
g is the acceleration of gravity
In this manner, if a left-right sway-reducing
tank (4) is incorporated, the phase difference between
the vertical movement of the float body (3) due to -.
incoming waves and that of the lateral, left-right sway from
incoming waves approach each otherO Due to this, the
transition wave ratio, HT/HI (that is the ratio of the
transiting wave height (HT) and the incoming wave hcight~.
(HI)-can be reduced.
Figure 7 is a graph which compares the experimental
properties of this invention's floating breakwater with a
left-right sway-reduclng tank and those of former floating
breakwaters. In the figure center, curve M shows properties
of a former floating breakwater without a left-right sway-
reducing tank. Curve N shows data for this invention. As
becomes clear from the figure, where the ratio of the
wavelength of the incoming wave ~ and the width (B) of the
float body (3), ~/Bo is within limits which are smaller
than 4,5, the transiting wave ratio, HT/HI maximum height
is reduced by about 17%~
As has been explained in detail above, by -the very
simple measure of adding a left-right sway-reducing tank
to a pontoon-type of floating breakwater, the phase
difference in the vertical motion of the float body caused
by incoming waves and that of the lateral, left-right sway
of the float body caused by incoming waves, can be made
to approach each other so that the wave-breaking
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effectiveness of the breakwater can be increased by a
widé margin. One can also have a breakwater with the same
wave-breaking effectiveness of a past breakwater which is
of smaller size.
Obviously, many modifications and variations of
the present invention are possible in light of the above
teachings. It is therefore to be understood that within
the scope of the appended claims, the invention may be
practiced otherwise than as specifically described herein;
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