Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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l SPECIFICATIONS
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1. TITLE OF THE INVENTION
Device for absorbing the energy of floating bodies
approaching the coast wall.
2. ~ACKGROUND I~F THE INVENTION
(1) Field of the invention
This invention relates to coastal energy absorption
devices for ab,orbing the kinetic energy of the floating
bodies such as ships approaching a coast line.
1., .
10 (2) Description of the prior art
Fenders are well known as the devices for absorbing
the kinetic energy of ~ships approaching a coast. These are
made of spring materials and are provided on the sides of the
coast walls or pier wàlls so that the impact energy of the
ships approach:ng these walls is absorbed by the springs in
the form of displacement energy. Recently, since the ships
are b coming larger in size, the spring cons~ants of the
fendersare also being increased.
; However, if the spring constants of the fenders
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1 are increased, although large amounts of kinetic ener~y
can be absorbed from large ships the reactive force on the
shore or pier wall will also become very large thereby
requi~ing that these walls be built consider~bly stronger.
Furthermore, when the fender spring constants
are increased, the ratio of the spring constant of the
fender to that of the mooring system will also become large,
say, from 100:1 to 1000:1, as a result of which the move-
ment of the moored ship due to the force of waves will not
be limited to only swaying but also will consist of subharmonic
motion which is large movement of the ship with oscillatory
periods lar~er than the characteristic period of the mooring
system which is caused by the spring constant of the mooring
system being smaller than the spring cons-tant of the fender
an~ by the large assymetry of the mooring system.
As an available means for relievin~ an impulsive
force of a ship on a pier wall, there is a so-called
absorber type system with a dash-pot provided additionally
on the fender. However, this system is effective only in
relieving the impulsive force of the ship, and no more,
and hence, does not compensate for external forces exerted
on a ship's motion at the time of mooring. 'rherefore, the
above-mentioned problems where there is only a fender, and
particularly, the peculiar motion of the ship, are still not
thoroughly solved thereby.
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1 In view of the above-mentioned drawbacks prevailing
in conventional devicesl it is an object of the invention to
pro~,ide an energy absorbing device for an approaching
floating body wherein a large amount of kinetic energy can
be absorbed from an approaching floating body by using a
fender with a small spring constan-t, whereby the maximum
reactive force.on a pier wall is reduced, and thus, the
fender can be reduced in size.
Another object of the invention is to provide an
energy absorbing device for a floa-ting body wherein a mooring
system is symmetrical, and thus, movement of floatir,g bodies
can be minimized.
In order to attain the above-mentioned objects, the
invention relates to an improvemen-t characterized by a
fender for absorbing kinetic energy of an approaching floating
body, the fender including spring means disposed on a side
surface of a coast or pier wall, and displaceable ~)y the
approaching body; dash-pot means on the side surface for
dissipating the energy by means of a resistance of i.nternal
fluids; and the fender has a spring constant KO w.ith a
magnitude substantially close to the magnitude of a spring
constant Kl of a mooring sys-tem for the floating body,
the~~eby decreasing the quantity of energy to be absorbed
by the device at the time o~ a mooring operation and also
considerably decreasing motion of the floa-ting body due to
fluctuating external forces.
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1 (4) Brief description of drawings
Figure 1 shows the schematic outline of the device
of this invention in a sample application. Figure 2 shows
the isometric view of an actual device of Figure 1. Figure
. 3 is a graph showing the energ~ absorption by the fender
from a floating body approaching the coast. Figure 4 is
a graph showing the maximum reactive force acting on the
coast walls and the approaching floating body. Figure 5
is a graph showing the displacement of -the fender due to
the impact of the
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1 approaching floating body. Figure 6 shows the cross-
-sectional view of the device in another example of
application of this invention. Figure 7 shows the cross-
-sectional view of the device in yet another example of
application of this invention. Figure 8 shows the cross-
-sectional view of the dash-pot used in another example
of application of this invention. Figure 9 shows the
schematic diagram of yet another example of application of
this invention.
3. DETAILED DESCRIPTION
The following is a detailed description of this
invention based on the examples of application shown in the
figures below.
Figures 1 and 2 show the device in an example of
application of this invention. As can be seen in Fi~ure 1,
such a device consists of fenders 3 and dash-pots 7
installed on the side wall 2 of the coast body 1, so that
the fenders 3 and the dash-pots 7 are constructed integrally
Further, the fender 3 is constructed of spring materials 4
made of elastic material such as rubber of length ~0 cm and
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1 ~iameter 100 cm, a fixing plate 5 fixed to the rear end of
the sprin~ material ~, and a face plate 6 affixed to the
other end of the spring material 4, as is shown in Figure 2.
The entire assembly is fixed to the coast side wall 2 by
affixing the fixing plate 5 to the former horizontally.
As will be apparent from what is described herein-
ar-ter, a low spring constant is selected for the fender 3
as compared with a conventional one, which is retained
substan-tially close to a spring constant of the mooring
syste,m, -that is, with a ratio within the range of about
one in several tens up t~ several tens.
The dash-po-ts 7 are four in number and are provided
at equal intervals around the periphery of the spring
material 4 of the fender 3. Each dash-pot 7 consists of a
hermetically sealed cylinder 8 containing some gas or
VlSCOUS fluid whose rear end is affixed to the fixin~ plate
5, a piston 9 that can move inside the cylinder ~, and
a piston rod 10 which is connected at one end to the piston
9 and to the face plate 6 at the other end so that the
fixing plate 5 and the face plate 6 are maintained at
right angles to each of the dash-pots.
Each of the pistons 9 contains orifices marked 9a
in the figure. These orifices result in creatin~ some
re~istance to the movement of the piston within the cylinder
and also serve to reduce the loa~ on the piston rods 10
durin~ such movement o~ the piston 9. The orifices 9a
formed on the pistGn 9 will not change in number and shape
when a fluid or the like passes in a compression process,
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1 and hence, are unchanged during any stroke of piston rod 10.
Also, it goes withou-t saying -that some form of well known
technique is used for sealing as well as lubricating the
hole in the front end of the cylinder 8 through which the
pis~on rod ln can move freely.
_ 5a -
1 When the face plate 6 is pressed due to the ship's
body ~, the spring material 4 and the dash-pot 7 are compressed
simul-~aneously, and the kinetic energy of the ship's body 1
will not only be converted into the displacement energy of ~he
spring material 4 but is also dissipated due to the resistance
of th~ dash-po-t 7. Therefore, compared to a conventional
device consisting of only a fender, the spring constant of the
sprinS material 4 of the fender 3 can be made considerably
small as is explained below using the graphs shown in Figures
3 to 5.
Figures 3 to 5 are the results of numerical
simulation of the case when the ship is approaching the coast
wall with its side surface parallel to the coast wall. The
numerical parameters used in the calculation and the method
of calculation are as follows.
Parameters used in calculation :
(a) Mooring system model : Ship length (L) = 144 m;
ship breadth (B) = 27.3 m; total depth (D) = 18 m;
draft (d) = 5.4 m; Mass (M) = 22,Q00 tons.
(b) Banking model : Distance between ship and shore =
4.8 m; ship speed at the time of impact = 15 ~m/s.
Method of calculation :
Obtained by time-series analysis using the dynamic
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1 equations ~1) of Cummins:
~ t
, ( M kj t 7rLkj ) x j ~J kkj ( t ~ ) d ~ t Cl<J X iJ
_ 00
= fk (w) c~swt
(1< - 1 ,2, 6)
5 where Mkj and Ck; are the k-jth elements of the inertial
matrix and the hydrostatic reactive force coefficient matrix,
respectively. Also, mkj and Kkj(t) are the corresponding
non-variant mass and delay function coefficients, respectively.
The graph in Figure 3 shows the relationship
between the spring constant of the fender and the energy
absorbed as calculated according to the above parameters
of calculation and method of calculation, and is dra~
with the spring constant K'f of the fender along the
horizontal axis and the kinetic energy E of the ship to be
absorbed by the fender (energy absorbed by the devic~)
along the vertical axis. The continuous-line curve is ~or
the conven-tional device consisting of only the fender, the
dashed-line curve with one dot between the dashes is for
the ~ase of a ~cnder with dash-pots with the attenuation
coefficient of the dash-pot being C'df = 278.9, ~f sec/m the dashed-
-line curve with two dots between the dashes is for the
case of the same fender with dash-pots having an attenuation
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1 coerficient of C'df = 557.8 tf sec/m, the dashed line curve with
three dots between the dashes is for the case of the
dash-pots having an attenuation coefficient of C'~ = 1115.~ tf sec/m,
and the hori70ntal dashed line indicates the estimated
kinetic energy of the ship approaching -the coast as calcu-
lated according to the equation E = M V2/2g where M is the
virtual weight of the ship evaluated according to Sterlin's
equation.
According to this graph, the energy E to be
absorbed by the fender varies very sharply with the spring
constant K'f of the fender in the case of the device using
only the fender. In particular, in this case, E increases
drastically as K'f becomes small and significantly exceeds
the estimated kinetic energy of the ship. Also, as K'f
is increased beyond about 10,000 tf/m, E decreases to values
below the estimated kinetic energy of the ship. This is
due to the fact that the wave drag decreases as the displa-
cement of the ship increases towards the fender. Therefore,
kf a fender with small K'f is used, E increases despite the
fact that the actual energy absorption capability of the
fender is low thus rendering the fender ineffective as an
energy absorption device. In view of this fact, fenders
with larger values of K'f are used with ships of larger
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1 tonnage, etc.
On the other hand, in the case of the devices
pro?osed in this invention, E decreases as the attenuation
coe_~icient C'df of the dash-pots is increased, and the
value of K'f can be freely selected as long as C'df is
above 278.9 tf-sec/m since in that case E is always below
the estimated kinetic energy of the ship. In addition,
this phenomenon is particu:.arl~ pronounced when K'f is
lower than 500 tf/m. As a consequence, the energy to be
absorbed by the fender can be decreased by using dash-pots
with high values of attenuation coefficient C'df and a
fender with a low value of K'f.
Figure 4 shows the relationship between the
maximum reactive force on t:he coast wall as well as on the
ship body and the spring c~onstant K'f of the fender.
The graph is plotted with t:he spring constant K'f along the
horizontal axis and the abc)ve mentioned reactive force Ff
along the vertical axis. q'he continuous-line curve is for
the conventional device whi.le the dashed-line curve with one
dot between the dashes is for the device of :this invention
and shows the reactive force component of the fender only.
The dashed-line curve represents the reactive force of th~
combination of the fender and the dash-pots in this invention.
(C'df of the dash-pots is 1115.4 tf-sec/m.)
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1 According to this figure, it is obvious that the
peak value of the reactive force is lower in a device built
according to this invention than in a conventional device.
In addition, it should be noted that the actual value of K'f
of the fender used in a device of this invention is much lower
than that of the fender used in a conventional device and hence
the lowering of the reactive force is much more significant
than a first glance of these curves indicate.
Figure 5 is a graph showing the relationship between
the relative displacement of the fender (shown along the
vertical axis) and the spring constant K'~ of the fender
(shown along the horizontal axis). The various curves in
this graph have the same connotation as t-he curves in Figure 3.
As can be seen from this figure, the relative displa-
cement increases as the spring constatn K'f is decreased
However, it is obvious that the change in the relative
displacement with a corresponding change in the spring
constant is much smaller in a device with dash-pats as per
this invention. There~ore, it can be concluded that even if
a fender with the same spring constant is used in a device
as per this inventian as a fender in a conventional device,
the overall size of the device can be reduced~
Next, the following table shows the comparison of
3~
1 a nu.mber of data obtained for the conventional device and
a aeviee according to this invention at the time of impact
between the ship and the coast wall and at the time of
mooring when the ship is swaying due to the force of waves.
S (V = 15 cm/sec when the ship is approaching the coast wall,
and T = 14 seconds and H = 1.2 m when the ship is moored.)
The clata in the column marked (A) is for a conventional
device in which case the mooring system is considerably
assy~metrical since thc spring constant of the fender is
10 K'f = 2,939 tf,~m and the spring cons-tant of the mooring
lines K'l is 3 7 tf/m. The data in the column marked (B)
is for a device accorcling to this invention in which case
K'l = 3.7 tf/m, X'f = 73.4 tf/m, and the attenuation
eoeffieient of the dash-pots is C'df = 279 tf-see/m.
(A) (B)
o ~ Energy absorbed by fender (t~) 29.6 13.6
3 ~ ~ Peak reaetive foree of fender
w (and dash~pot) (tf) 208.5 41
o Maximum displacement of fender(m) 0.14 ~.6
. __. . . _
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l ~--l l
1 ~ ~ Sway amplitude (m) 27.94.1
Peak reactive force of
s ~ fender (and dash-pot) (tf) 1300 163.1
c ~ c Maximum tension on the
,~ a) o
¦ _ mooring lines (tf) 97.07.1 l
From the above table it is apparent ~hat in the case of the
device built ac~ording to this invention, not only the
peak reactive force on the coast walls is reduced but also
the amplitude of swaying of the ship.when moored is lower.
Figures 6 and 7 show two other examples of
application of this invention in both of which dash-pots
17 and 27 are provided within the fenders 13 and 23, and
these dah-pots and fenders are made so that they return to
their normal shapes after being compressed once due to the
impact between the ship and the coast wall before the ship
collides again with the coast wallO
Firstly, in the example of application shown in.
Figure 6, the dash-pot 17 is constructed such that a bypass
path 11 is provided below the sealed cylinder 18. This
bypass path 11 links the compression chamber 18a and the
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1 expansion chamber 18b of the cylinder 18. Within -this
byp2ss pa-th 11 is provided a one-way valve 12 which gets
closed when the piston 19 moves in the direction of the
arrow Y so as to compress the fluid in the cylinder's
comp-ession chamber 18a, and gets opened when the piston
19 moves in the opposite direction marked by the arrow X.
As a result of this construction, when the face
plate 16gets compressed toward the coast wall due to the
im?act of the ship, the one-way valve 12 in the bypass
path 11 will become closed and the fluid in the compression
ch~mber lSa flows slowly into the expansion chamber 18b
vi~ the orifices l9a in the piston 19 thereby causing the
impact energy of the ship to be dissipated.
Next, when the ship recoils and moves away from
the device, both the dash-pot and the fender start to go
back to their original shapes. At this time r since the
one-way valve 12 in the bypass path 11 gets opened, the
fluid in the dash-pot 17 does not offer any resistance to
the movement of the piston and quickly returns to the
compression chamber 18a, and hence the dash-pot 17 returns
quickly and easily to its normal position due only to ~he
force of the fender 13.
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1 In the application example shown in Figure 7,
belcw the cylinder 28 of the dash-pot 27 is provided an
auxiliary cylinder 22 which houses in it in a freely
movable fashion a bypass path body 21 to be describe~l
further below. The said bypass path body 21 inserted
within the auxiliary cylinder 22 contains a`bypass path 21a
which links the expansion chamber 28b and the compression
chamber 28a of the cylinder 2~. Also, an actuating r.od 20
is fixed to the side of the bypass path body 21 facing the
side of the device that opposes the approaching ship's
side wall. The other end of the bypass path body 21 butts
against a spring 22a within the auxiliary cylinder ;'2.
The front end 20a of the above mentioned actual:ing
rod 20 passes through a large enough hole 26a in the
face plate 26 and projects beyond the surface of the face
plate 26. When the slde of the ship comes into con-tact
with the face plate, it first pushes in the actuating rod
against the force of the spring 22a whereby the bypa~;s path
body 21 will be moved in the leftward direction in the
figure. On the other hand, when there is no load on the
dash-pot 27 the bypass path body 21 will be in such a
position that the bypass path 21a in it lin~s the compression
chamber 28a and the expansion chamber 28b of the cylinder 28.
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1 sut, -~hen the actuatin~ rod 20 has been pushed in due to
the pressure of the side wall of the ship on the front end
20~ of the actuating rod 20., the two openings 21c and 21b
of the bypass path 21a will move away from the two openings
28c and 28d in the wall of the cylinder 28thereby isolating
the ccmpression chamber 28a and the expansion chamber 28b
of the cylinder 28. In this condition, the extent of
linkage between the two chambers of the cylinder can be varied
from completely closed to partially closed by appropriately
selecting the amount of projecticn of the front end 2~a of
the actuating rod 20 .
Further, in this example of applicatlon of this
invention when the ship approaches the facing plate 26 of
this device, it first closes the byapass path between the
two chambers of the cylinder 28 of the dash-pot 27 and the
operation of the dash-pot thereafter when the face plate
26 is further pushed in will be the same as in the previous
examples of application of this invention.
Next, when the side wall of the ship's body 1
moves away from the coast wall slowly, ~he side wall of
the ship will still be pushing somewhat against the ace
plate 26 of this device and hence the bypass path 21a will
still remain in the closed state. As a result, -the fluid
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1 in ~he expansion chamber 28b of the cylinder 28 can only
re~u-n to the compression chamber 28a via the orifice 29a
in t~2 piston 29. This causes resistance to the reverse
movement of the piston and slows down the fender and the
dash-pot from returning to their original positions closely
following the movement of the ship away from the face plate.
However, if the ship's side wall moves away from
the face plate 26 faster than the natural rate of reversal
of this device to its normal shape, then the pressure on
the front end 20a of the actuating rod 20 will be released
whereby the bypass path body 21 quickly returns to its
normal positon due to the f~rce of the spring 22a and the
bypass path 21a will be opened thereby bringing the fluid
in the cylinder 2~ to equilibrium ~uickly. This ensures
that there will be no delay in the device returning to its
normal position.
Therefore, in this example of application of this
invention, it is not only possible to make the fender and
dash-pot revert to t~eir normal positons in accordance
with the rate of movement of the ship awa~ from the ~evice,
but also possible to reduce the force of the ~ender trying
to push the ship back into the bay.
It is also to be noted that in this inve~tion
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1 although the attenuating power of the dash-pot 27 is being
con.rolled ~y the orifice 29a in the piston 29, it can be
further controlled by the adjustment of the motion of the
bypass path body 21a. In addition, the orifice 29a in the
pis~on 29 can be eliminated altogether by making the area
of overlap between the openings in the cylinder 28 and the
openings in the bypass path 21a vary continuously with the
movement of th~ bypass path body 21.
Figure 8 shows another example of the return path
for the fluid i.n the cylinder in the application examples
of Figures 6 and 7. In the scheme shown in Figllre 8, no
bypass path is provided as the return path for the fluid,
but a large diameter connecting path 39b is provided in -the
piston 39 itself along with the orifice 39a, and closing
this connecting path 39b when the dash-pot 37
is compressed and openin~ when the dash-pot is released
by provi.ding a one-way valve 40 in front of the connecting
path 39b on the compression chamber side of the piston.
The operation of this device too will be equivalent to
that of the device described above, except that in this
case the construction of the dash-pot becomes much simpler.
In all the applica~ion examples shown in Fi~ures
to 8, the maximum reactive force on the coast walls will
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1 be reduced and the amplitude of swaying of the ship ~Jill be
reduced in the moored condition, as was explained for the
appiication example of Figure 1.
Figure 9 shows the schematic diagram of another
exam?le of application of this invention. In this example,
the dash-pot ~7 is not built integrally with the fender ~3,
but the two are provided separately from each other on the
ccast wall but close to each other on the coast wall 42. In
this example, two sets of fenders ~3 and dash-pots 47 are
provided and operate in the same manner as the example of
a~plication described in Figure 1 with the same results.
As described above, according to the invention, a
fender ~or absorbing energy of an approaching floating body
by means of a spring displacement action is disposed on the
side wall of a coast or pier, and dash-pots for dissipating
the energy by means of the resistance of internal fluids are
also provided additionally thereon, thereby decreasing the
quantity of energy to be absorbed by the device at the time
of a mooring operation. ThereEore, a fender with a small
spring constant can be used; the fender can thus be reduced
in size; the maximum reactive Eorce to a pier or the like at
the time c~ a mooring operation is decreased; and thus,
coastal energy o~ big ships can be absorbed securely without
enhancing the strength oE the pier wall particularly there~or~
Further, since a spring consta~t of the fender is
kept substantially close t~ the spring ~onstant of a mooring
system, the mooring system will be symme~rical, ~nd thus,
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1 movement of the floating body due to waves, or particularly,
a swa-ying due to subharmonic motion can be decreased.
This invention has been described in the above
para~raphs using several examples of application. ~lowever,
the scope of the novel concepts of this invention is not
to be construed to be limited to the examples described
herein since many more design modifications can be effected
based on the spirit of this invention.
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