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Патент USA US3087578

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April 30, 1963
G. KURTZE
3,087,568
VIBRATION-DAMPED STRUCTURE
Filed March 23. 1959
INVEN TOR.
BY
UEN Tl-IER KURTZE
A T'TOI‘FNEV
3,087,568
United States Patent 0 " ice
Patented Apr. 30, 1963
1
2
3,687,568
viscosity means no motion of the medium; i.e. ?rm
coupling of rthe plates 1 and 3. It has been found that
VIBRATION-DAMPED STRUCTURE
Guenther Kurtze, Arlington, Mass, assignor to Bolt
Beranek and Newman, inn, Cambridge, Mass, a cer
poration of Massachusetts
Filed Mar. 23, 1959, Ser. No. 301,197
7 Claims. (Cl. 181-33)
there exists an optimum value of the viscosity for which
maximum damping is obtained. Analysis shows that
the damping, expressed by the loss tangent 1; of the
composite structure 1, 3, 5, increases with square of
frequency, passes a maximum, and then decreases sub
stantially linearly with further increasing frequency.
The present invention relates to vibration-damped
Under the condition cIEZCZ, the vibrational (angular)
structures and, more particularly, to damping with the 10 frequency w of maximum attenuation is approximately
aid of viscous media.
given by
Damping of structure-borne sound vibrations is usually
obtained by covering the structural elements with layers
._ ps1
is 2%;2
or coatings of sound-dissipative materials. in this way,
energy is withdrawn from the sound~vibration waves by 15 and the loss tangent at this frequency is
irreversible deformations of these coatings. The terms
‘° _d1vI2<\/Z+ pd pd 2)
1r/)\1
“sound” and “vibrations,” as herein employed, are in
tended to connote generically all types of elastic vibra
tions and the like, whether audible, sub-audible or super
audible.
20 where
The present invention, on the other hand, is more par
ticularly concerned with the damping of double-walled
p=density of the viscous medium 5,
improved vibration-damped structure.
Mzbending wavelength in plate ‘1.
(1)
(2)
d=thickness of the viscous medium 5,
structures and the like, and involves the use of viscous
n=viscosity of the medium 5,
materials as dissipative media.
An object of the invention is to provide a new and 25 M2=mass per unit area of plate 3, and
A further object is to provide for the damping of
double walls, partitions, panels, surfaces and the like,
all hereinafter referred to by the generic term “plates
and the like.”
Still an additional object is to provide a novel appar
atus for damping vibrations traveling along any pair
of vibration-wave propagating paths, whether of plate
con?guration or of other con?guration for permitting the
passage of sound or vibration waves therealong.
Equation 2 shows that the maximum obtainable damp
ing its proportional to 1/)“ and hence decreases with de
creasing frequency. This may be disadvantageous when
30 damping at low frequencies is desired. For such cases,
; the disadvantage can be obviated, in accordance with the
invention, by partitioning or subdividing the medium 5
with partitions, such as, for example, foam plastic
separators 7, FIG. 2, with closed, air-?lled cells 9. A
35 representative embodiment employed steel plates 1, 3
Other and further objects will be discussed hereinafter
that were each 1 cm. thick, but with stiffness differing by
and will be more particularly pointed out in the appended
a factor of ten, and a liquid medium 5 of silicon oil 1
claims.
cm. thick and of viscosity ,uz668.
The invention will now be described in connection
The partitions 7 are disposed at intervals I only along
with the accompanying drawing, FIG. 1 of which is a 40 one direction (shown longitudinally spaced), the distance
transverse section of a damped double-plate structure
or separation I being much less than the wavelengths of
constructed in accordance with the present invention;
the band of frequencies to be damped. The partitions
and
7 may also be of other materials, though they must have
FIG. 2 is a similar view of a preferred modi?cation.
the property of being soft or highly compressible com
Referring to the drawing, the invention is illustrated
pared With the viscous liquid or other medium 5 in order
as applied to a double-plate structure, though it is to be
to decouple adjacent medium regions from one another.
understood that the teachings hereof may equally well
The construction of FIG. 2 yields a wider or broader
be applied to other pairs of vibration-propagating path
band frequency range of effective damping than for the
structures, including rods, tubes, pipes and the like, to
construction of FIG. 1. Assuming again, that clé2cg,
mention but a few.
the frequency w of maximum damping is given sub
The plates 1 and ‘3 are shown gen
erally co-extensive and of somewhat dilferent thickness
so that the vibration-propagation or bending-wave ve
locity along the plates, say from one end to the other,
is substantially different; in this case, the velocity C1
stantially by
12”
1
“ pdz \/1+ 1201M2
p12
(
along the plate 1 is faster or greater than the velocity
C2 along the plate 3. Different velocities can also be
and the maximum obtainable loss tangent is
obtained in other ways, as by using different materials,
1
diiferent temperatures, and other techniques.
(4)
7]='—'———__——-_:
Where different bending wave velocities are involved,
P12
p12
60
there will be phase shifts between the bending-wave
motion of the two plates which increase with increasing
According to Equation 4, 7; no longer depends on fre
distance from the source end, resulting in relative mo
quency so that the same amount of maximum damping
tions of the two plates with respect to each other. If
can be obtained at any frequency by proper choice of
these two plates 1 and 3 are coupled over a substantial
[.L in Equation 3.
portion of the region separating them by a viscous
If the plates 1 and 3 are made of light-transmitting
medium 5, as of viscous liquid, plastic, semi-solid ma—
material, such as transparent or translucent glass and the
terial, etc., an alternating ?ow will be generated by this
like, and the medium 5 is also light-transmitting, such
relative motion, and the viscosity of the medium 5 will
as, for example, a clear mineral oil of su?icient viscosity,
give rise to energy losses.
It will be observed that losses do not occur in the 70 a sealed unit 1, 3. 5 could well serve as a vibration
damped window or the like.
theoretical limiting cases of zero and in?nite viscosity,
Further modi?cations will occur to those skilled in
since zero viscosity means no dissipation, and in?nite
ZN/WI; 12am“)
3,087,568
4
a
the art and all such are considered to fall within the
spirit and scope of the invention as de?ned in the ap
pended claims. The terms “steel-like” and “liquid-oil
like” as employed in the claims are intended to embrace
materials which are like steel or like liquid oil, respec
tively, in the function performed by the designated ele
ments in the panel of the invention. For example, as
stated above the spaced layers may be formed of gl-ass,
which is “steel-like” as to stif?ness and rigidity when
stantially greater than the overall bending stiffness of
the other layer, whereby the acoustic bending wave prop
agating velocity 01 of one layer is substantially greater
than the acoustic bending wave propagating velocity 02
of the other layer and the phases of acoustic vibrations
along said layers are different, and a plurality of spaced
partitions extending between said layers and dividing
said viscous material, the compressibility of said parti
tions being substantially greater than that of said viscous
compared to a viscous liquid-oil-like material, including l0 material, said panel having maximum damping at said
predetermined acoustic frequency determined substan
the oils, plastics, or semi-solids described.
tially by the relationship:
What is claimed is:
1. An acoustic panel for damping a predetermined
acoustic frequency f with a maximum degree of damping
pd2 / 1203M»
and frequencies above and below said predetermined 15
,,_
_____
frequency with substantial, but lesser damping, compris
p
ing a pair of layers of stiff steel-like sheet material spaced
apart, and a body of viscous liquid-oil-like material be
tween and continuously contacting said layers, both‘ said
layers being much more rigid than said viscous material, 20
where w=21rf, p is the density of the viscous material,
one of said layers having an overall bending stiffness
partitions.
:1 is the thickness of the viscous material, a is the viscosity
of the viscous material, M2 is the mass per unit area of
this slower-velocity layer, and l is the spacing of the
substantially greater than the overall bending stiffness of
5. The panel of claim 4, said partitions being formed
the other layer, whereby the acoustic bending wave prop
of soft cellular material.
agating velocity C1 of one layer is substantially greater
6. The panel of claim 4, said partitions being formed
than the acoustic bending wave propagating velocity C2 25 of foam plastic.
of the other layer and the phases of acoustic vibrations
7. The panel of claim 4, the spacing of said partitions
along said layers are different, said panel having maxi
being less than the wave length corresponding to said
mum damping at said predetermined acoustic frequency
frequencies.
determined substantially by the relationship:
30
References Cited in the ?le of this patent
drag/913+ 1%)2%_a)
“11M,
4
pd pd 2
where w:21rf, p is the density‘of the viscous material,
d is the thickness of the viscous material, p. is the vis
UNITED STATES PATENTS
1,193,013
2,407,400
2,724,670
Grant ________________ __ Aug. 1, 1916
Chamberlain ________ __ Sept. 10, 1946
Mason ______________ __ Nov. 22, 1955
unit area of the slower-velocity layer.
2. The panel of claim 1, said sheet material and said
2,850,109
Benjamin ___- _________ __ Sept. 2, 1958
viscous material being light-transmitting.
3. The panel of'claim 1, said layers having different
40
thicknesses.
754,299
1,135,422
Great Britain __________ __ Aug. 8, 1956
France ______________ __ Dec. 17, 1956
cosity of the viscous material, and M2 is the mass per 35
4. An acoustic panel for damping a predetermined
acoustic frequency f with a maximum degree of damping
and frequencies ‘above and below said predetermined
FOREIGN PATENTS
OTHER REFERENCES
Cyril M. Harris: Handbook of Noise Control (Mc
Graw-Hill Book Company, Inc., New York, 1957), pages
frequency with substantial, but lesser damping, compris
ing a pair of layers of stiff steel-like sheet material spaced 45 12-1, 12-2, 12-8 through 12-10 and 14-13 through
and continuously contacting said layers, both said layers
14-18.
S. Timoshenko: Vibration Problems in Engineering
being much more rigid than said viscous material, one
of said layers having an overall bending stiffness sub
pages 210-220.
apart, a body of viscous liquid-oil-like material between
(D. Van Nostrand Company, Inc., New York, 1955),
Third edition.
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