Communications – electrical: acoustic wave systems and devices – Sonar counter-measures
Reexamination Certificate
2000-10-26
2002-04-30
Pihulic, Daniel T (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Sonar counter-measures
Reexamination Certificate
active
06381196
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for damping vibration, more particularly for attenuating acoustic vibration such as structureborne noise.
Vibrations can cause problems such as structural weakening, metal fatigue and bothersome noise. Of particular note are situations wherein a power-driven source (e.g., a motor) produces a frequency at which an attached structure naturally vibrates, a phenomenon known as “resonance.”
Various types of passive damping treatments have been known to be effective in reducing the amplitude of vibrations at resonant frequencies. Among the known effective passive damping methodologies are freelayer damping, constrained layer damping, tuned damping and direct-load-path damping.
According to freelayer damping, damping material is positioned on the to-be-damped structure. When the structure is excited, the damping material and the structure vibrate together. This causes the damping material to stretch and compress, resulting in the dissipation of vibration energy as heat
According to constrained layer damping, damping material is positioned against the structure and covered with a constraining layer, such as a metal sheet In other words, the damping material is sandwiched between the constraining layer and the structure. The mechanism between the constraining layer and the structure is shear in nature.
According to tuned damping, damping material acts as a spring-mass system which is tuned to vibrate at a frequency of interest, e.g., the same frequency as the structural vibration of the structure on which it is mounted. The tuned damper vibrates out-of-phase with the structure and applies a force opposite the motion of the structure.
According to direct-load-path damping, a discrete location of the structure is damped by load-bearing damping material. In contrast, freelayer damping and constrained layer damping afford area coverage of the structure.
Generally, tuned damping provides narrowband damping, designed to concentrate damping where most needed, i.e., at the frequencies of resonance modes. By comparison, freelayer damping, constrained layer damping and direct-load-path damping provide broadband damping, designed to afford more moderate damping over a wider range of frequencies.
The United States Navy has recently begun evaluating new mechanisms in association with a family of damping treatments, viz., entrained damping, which utilizes particulate material. According to entrained damping, a hollow space in a structure to be damped is filled with particulate damping material. Particles such as sand or polymeric (e.g., viscoelastic) beads have been demonstrated by the U.S. Navy to provide effective structureborne noise attenuation when used as a filler for noise-critical structures.
In particular, the U.S. Navy has experimentally found that this particle-filler type of damping treatment can be adapted to effectuate a kind of tuned damping; that is, the particle filler can act as a tuned absorber, wherein the vibration of the structure couples into the particle filler. At the fundamental frequencies, where the structural vibration coincides with the standing wave resonance modes through the thickness of the particle filler, very high levels of structural damping have been achieved in proprietary testing conducted by the U.S. Navy.
The mechanisms associated with the above-described “particle-type” tuned damping are not clearly understood; nevertheless, considered likely by U.S. Navy researchers are several mechanisms which influence the high levels of damping obtained.
One mechanism associated with tuned-particle-type damping is believed to be the relative rigid body displacement between the particles of the filler, which adds a frictional or coulomb-type damping to the structure. This mechanism is likely the dominant one for a structure filled with sand; the sand particles, made of quartz or other mineral base material, are very stiff with extremely low levels of inherent material damping.
Another mechanism associated with tuned-particle-type damping is believed to be present for viscoelastic-type filler materials. This effect also occurs at the interface of the individual particles. When an acoustic wave is transmitted through a solid material, the pressure is relatively evenly distributed through the material across any section whose dimensions are small relative to the wavelength. In the case of a medium made up of particles, however, the point contact between each particle forces a pressure concentration and subsequent strain-increase at each particle interface as the pressure wave is transmitted. The strain concentration at each contact point has the effect of multiplying the viscoelastic effect of the base material over an equivalent solid material.
Hence, the U.S. Navy has been evaluating, with good success, the application of free viscoelastic particle damping treatments to entraining structures (i.e., structures which can be filled). The U.S. Navy has especially been assessing the application of free viscoelastic particle damping treatments of a tuned-particle-type to entraining structures. The U.S. Navy is currently desirous of effectuating, with respect to non-entraining structures (i.e., structures which cannot be filled, such as plates, or piping having working fluid inside), damping treatments having attributes of both entrained damping and tuned damping.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for effectuating, with respect to a non-entraining structure, a damping treatment which is similarly effective as is a tuned-particle-type damping treatment with respect to an entraining structure.
It is a further object of the present invention to provide such method and apparatus which effectuate same in an efficient and effective manner.
In accordance with many embodiments of the present invention, a passive vibration damping device comprises plural viscoelastic particles which generally cohere with one another. At least substantially every said particle is characterized by: (a) adherent communication with at least one other particle; (b) adjacency to at least one separation between the particle and at least one other particle; and, (c) at least one of: (i) an approximate shear modulus in the range between about 10 p.s.i. and about 100,000 p.s.i. inclusive; and, (ii) an approximate loss factor in the range between about 0.05 and about 1.5 inclusive. According to typical practice, the adherent communication includes a contact region between two particles, and a bond region between the two particles, whereing the bond region is at least approximately commensurate with the contact region. Frequent inventive practice prescribes particle sizes wherein at least substantially every particle is characterized by size (as taken along its greatest dimension) in the range between about 0.05 inches and about 0.5 inches inclusive.
Further provided by the present invention is a method for effectuating passive damping of an object The method comprises: (a) providing a device including plural viscoelastic particles which generally cohere with one another; and (b) coupling the device with the object. At least substantially every particle is characterized by: (a) adherent communication with at least one other particle; (b) adjacency to at least one separation between the particle and at least one other particle; and, (c) at least one of: an approximate shear modulus in the range between about 10 p.s.i. and about 100,000 p.s.i. inclusive; and an approximate loss factor in the range between about 0.05 and about 1.5 inclusive. Typically according to inventive practice, at least substantially every said particle is characterized by size in the range between about 0.05 inches and about 0.5 inches inclusive.
Further provided by the present invention is a method for making a device suitable for passively damping a structure. The method comprises: (a) providing plural viscoelastic particles; (b) placing the particles in a mold; and (c)
Drake Michael L.
Hein Kenneth D.
Stack Christopher F.
Kaiser Howard
Pihulic Daniel T
The United States of America as represented by the Secretary of
LandOfFree
Sintered viscoelastic particle vibration damping treatment does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sintered viscoelastic particle vibration damping treatment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sintered viscoelastic particle vibration damping treatment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2930088