Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an impact damper
comprising a bed plate attached to an object of
damping forming a main vibration system with a main
natural frequency, an additional weight, additional
S elastic means supporting the additional weight so as
to be able to vibrate the same in the same direction
as the vibration o the object of damping, mounting
means for mounting the additional elastic means on
the bed plate, and stop means mounted on the bed
plate to strike against the additicnal weight in
vibration.
From a vibrational point of view, the object
of damping may be regarded as a main vibration system
including a main weight and main elastic means and
having the main natural frequency. Likewise, the
impact damper of the invention may be regarded as an
additional vibration system including the additional
weight and additional elastic means and having the
addltional natural frequency.
The impact damper is attached to the object of
damping, and vibrates in concert with the object so that
the additlonal weight strikes against the object to damp
the same with high efficiency.
In the well-known impact damper of this type, the
frequency range to provide a satisfactory damping effect
is restricted to limit the fields of application unless
the characteristics of the main and additional vibration
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systems and the relative positions of the object of
damping and the additional weight are determined
properly.
The object of this invention is to provide an
impact damper free from the aforementioned drawbacks of
the prior art impact damper and capable of producing a
satisfactory damping efEect throughout a wide frequency
range.
To this end, an impact damper according to this
invention is so constructed that the natural frequencies
and relative positions of the main and additional
vibration systems fulfill the following two
requirements:
(1) The distance between the additional weight
and the stop means as measured when the
object of damping and the additional weight
are not vibrating is to range from 0% (in
this case the additional weight is in contact
with the object) to 80% of the resonance
amplltude of the object without impact damper.
(2) The additional natural frequency of the
:: additional vibration system is to range
from 60% to 80% of the main natural
frequency of the main vibration system.
When the impact damper of the above-mentioned
construction is attached to the object of damping, the
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object and the additional weight strike against each
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other during vibration, so that the amplitude of the
object is attenuated by a change of momentum thereof
and an energy loss caused by the impact. With the
aforesaid construction, moreover, the object of damping
can effectively be damped and prohibited from vibrating
with a great amplitude in a wide frequen~y range
including frequencies higher or lower than the main
natural frequency, not to mention the main natural
frequency.
The requirements of the impact damper are induced
from quite many tests conducted with regard to a lot
of other parameters than them. Effects obtained with
use of this impact damper will be mentioned later in
conjunction with the preferred embodiment of the
invention.
This invention can be more fully understood from
the following detailed description when taken in
conjunction with the accompanying drawings, in which:
Fig. 1 is a side view of an impact damper according
to this invention;
Fig. 2 is a side view of the impact damper of
Fig. 1 attached to a pipe to be damped;
Fig. 3 is a sectional view taken along line 3-3 of
Flg. 2;
Fig. 4 shows a testing device for the impact
damper;
Fig. 5 lS a graph showing the relationship between
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the resonance magnification ~ and the specific frequency
ratio n between the additionai vibration system natural
frequency and main vibration system natural frequency;
and
Fig. 6 is a graph showing the relationship between
the space ratio and damping ratio y obtained with
use of various values of the ratio ~.
Fig~ 1 shows an impact damper 10 according to an
embodiment of this invention. In Fig. 1, a bed plate
lOa is mounted with a retaining stand 14 retaining an
additional elastic means or an additional spring 12,
and a screw retaining stand 18 rotatably supporting
a screw rod 16. The additional spring 12 is a leaf
spring which extends in the horizontal direction of
Fig. 1, and has an additional weight 20 fixed on the
left end portion thereof. The right end portion of
the additional spring 12 is fixed between the retaining
stand 14 and a retaining member 22 by means of a clamp
screw 24 so as to be adjustable for the location of
the weight 20 in a desired horizontal position. The
retaining member 22, the retaining stand 14, and the
clamp screw 24 form a mounting means for mounting the
weight 20 and the spring 12. A nut 30 is attached
tight by means of a screw 32 to the right end portion
of the spring 12 which is projected to the right side
of the mounting means. A threaded portion 34 of the
screw rod 16 is screwed in the nut 30. The screw rod
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16 is rotatably held by the screw retaining stand 1
so as not to move horizontally, and can easily be
rotated by means of a square portion 36 protruding
from the right end of the screw rod 16. The effective
length of the spring 12 can be varied by loosening
the clamp screw 24 and rotating the square portion
36 by means of a suitable tool. A tapped hole 40 is
vertically bored through the left end portion of the
bed plate lOa, and a stop 46 is fixed on a base 44 on
the top of a screw 42 which is fitted in the tapped
hole 40. The stop 46, the base 44, and the screw
42 form a stop member. The vertical position of the
stop 46 is set by rotating the screw 42 and fixed by
means of a setscrew 45 so that the weight 20 attached
to the tip of the spring 12 can strike against the
stop 46 with proper strength when it moves downward
by vibration. The space between the under surface of
the weight 20 and the top surface of the stop 46 as
measured when the weight 20 is not vibrating is
designated by d in Fig. 1.
Now there will be described the operation of the
impact damper. Fig. 2 shows how the impact damper 10
is attached to a pipe 52 as an object of damping. For
~; the simplicity of illustration, the pipe 52 is drawn
in an unduly reduced scale as compared with the impact
damper 10. Fig. 3 is a side sectional view corre-
sponding to Fig. 2. since the impact damper 10 of
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Fig. 2 is substantially the same as the one shown in
Fig. 1, reference numerals are used to designate the
principal members or portions only. The bed plate
lOa of the impact damper 10 is mounted on an upwardly
extending mounting member 50 with a T-shaped section
by means of fitting screws lOb. The mounting member
50 is attached to the pipe 52 by means of fitting
members 58 which each consists of a pair of substan-
tially semicircular curved members 54 embracing the
pipe 52 and bolts and nuts. A multitude of the impact
dampers 10 of the invention are attached to the pipe 52
at suitable intervals so as to damp and prevent the pipe
from vibrating substantially when an external vibration
or shock such as an earthquake shock is applied to the
plant, thereby protecting the pipe from damage. For
example, the pipe may be one of those pipes which are
used in piping systems in plants. In this embodiment,
the additional natural frequency of an additional
vibration system representing the vibrational charac-
teristic of the impact damper is limited from 60%to 80% of the main natural frequency of a main vibration
system representing the vibrational characteristic of
the pipe 52 as the object of damping, and the space d
be~ween the additional weight 20 and the stop 46 as
measured when the weight 20 is not vibrating is limited
;~ to 80% or ~less of the resonance amplitude D of the pipe
52 in vibratlon without impact damping. The ratio ~ of
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the space d to the resonance amplitude D, i.e., d/D = ~,
is referred to as a specific space. Thus, the space d
may be zero.
Now there will be described results of a test on
damping effect conducted with use of the impact damper.
Fig. ~ shows a testing device 100, in which a pipe 106
is rotatably mounted at point B on a support 104
standing on a floor 102, the pipe 106 is vertically
vibrated at the left end or point A with an ampli~ude
of +0.25 mm, the impact damper of the invention is
attached to point C where the amplitude of the pipe
106 is measured on the pipe 106, and the right end
of the pipe 106 is supported at point D (where the
amplitude of the pipe 102 is measured) on a stand 108
by means of a U-bolt. The pipe 106 has a diameter
of 48.6 ~ and a natural frequency of 8.1 Hz, and is
subjected to a weight of 32 kg. In this case, the
resonance amplitude obtained is 4.8 mm.
Fig. 5 is a graph prepared by plotting the change
of the resonance magnification ~ obtained when the
ratio n between the additional natural frequency of
the impact damper and the main natural frequency of
the object of damping is changed where the space d
between the additional load 20 and the stop 46 is
0.8 mm. The resonance magnification is defined as the
ratio of the amplitude of the actual vibration of the
object of damping to the amplitude of the vibration
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applied to the object of damping. As may be seen
from Fig. 5, the resonance magnification ~ is minimized
at a point where n is approximately 0.7, and takes
relatively low values elsewhere. It was confirmed
that substantially the same result may be obtained
where the space d is approximately 0.8 mm or less.
Thereupon, the damping ratio y was measured
for three values of n, 0.6, 0.7 and 0.8, as compared
with the specific space E varying from 0 to 0.8.
Here the damping ratio y is defined as the ratio of
the amplitude of the pipe obtained with use of the
impact damper to the amplitude obtained without the
use of the impact damper. Fig. 6 shows curves
corresponding to the three values of n- The axes
of abscissa and ordinate represent ~ and ~, respec-
tively. Although the measurement was made for more
varied values of E I the plotted spots are thinned out
for the simplicity of illustration. If we have n = 0.6
to 0.8 and ~ = 0 to 0.8, ~ is reduced to approximately
0.5 or less.
As may be seen from the aforesaid test results,
it is resonable to set n within a range 0.6 to 0.8 and
E within a range 0 to 0.8. Namely, according to this
invention, a substantial damping effect may be obtained
for a wide range of the frequency n. 0.6 to 0.8, with
use of ~ ranging from 0 to 0.8.
In the damping effect test, the mass ratio ~ of
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the additional weight to the pipe is 0.027. In testing,
various values are used for ~, and substantially the
same damping effect may be obtained with use of the
values of n and ~ within the aforementioned ranges.
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