Patent Application
20210095738
The present invention generally relates to devices for attenuating system vibrations and, more particularly, to devices for attenuating system vibrations at multiple frequencies.
Aircraft are subject to various undesired vibrations at multiple frequencies. Each airplane has a unique signature of normal vibration. This is a consequence of mass distribution and structural stiffness that results in vibration modes at certain frequencies. When external forces act on the airplane, such as normal airflow over the surfaces, very low-level vibrations result. Typically, this is perceived as background noise. More noticeable, but also normal, is the reaction of the airplane to turbulent air, in which the magnitude of the vibration may be larger and thus clearly visible and felt. Engine operation at some spool speeds may result in increased vibration because spool imbalance excites the engine and transmits this vibration throughout the airframe. Finally, the operation of some mechanical components, such as pumps, may be associated with normal noise and vibration.
In some applications, avoiding operating at the aircraft system's modal frequency is difficult if not impossible. Vibration attenuation is desirable to prevent wear to aircraft components and for increased comfort of the occupants of the aircraft. It is most desirable to attenuate vibrations during take-off (because high amplitude vibrations may occur while operating the engines to produce high levels of thrust) and while in flight at cruising speed (because most of the operational time of the aircraft is spent at this speed). In most cases, the frequency of vibration is different during take-off and at cruising speed. There is a need to attenuate the frequency of the overall aircraft assembly to reduce vibrations at the undesired frequencies. The present invention is directed toward meeting these needs.
In one embodiment, a multiple frequency vibration attenuation device is disclosed, comprising: a spring; and a mass attached to the spring; wherein the device comprises at least two natural frequencies; and wherein the mass is not attached to anything other than the spring.
In another embodiment, a device for attenuating vibration frequencies of an aircraft is disclosed, comprising: a spring; and a mass attached to the spring; wherein the device comprises at least two natural frequencies; wherein the mass is not attached to anything other than the spring; and wherein the device is constructed and arranged to attach to the aircraft.
Other embodiments are also disclosed.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings, and specific language will be used to describe that embodiment. It will nevertheless be understood that no limitation of the scope of the invention is intended. Alterations and modifications in the illustrated device, and further applications of the principles of the invention as illustrated therein, as would normally occur to one skilled in the art to which the invention relates are contemplated and desired to be protected. Such alternative embodiments require certain adaptations to the embodiments discussed herein that would be obvious to those skilled in the art.
Various embodiments of the multiple frequency vibration attenuation device disclosed herein may attenuate vibrations at two or more different frequencies.
In some embodiments, the spring 102 and the mass 104 are machined from a single piece of material, such as metal, plastic, or other machinable materials, for example. When making the spring 102 as a machined spring, bar stock is first machined into a thick wall tube form, attachment features are added, and then a helical slot is cut, thereby producing multiple coils. When deflected, these coils provide the desired elasticity. In addition to machining, the multiple frequency vibration attenuation device 100 may be made by other processes, such as 3D printing, molding, and various other methods known in the art.
When using a machined spring, the spring 102 may have any number of starts 106. The spring 102 in
The mass 104 is formed in a non-radially symmetric shape to allow for attenuation at two frequencies. In the illustrated embodiment, the mass 104 is bilobed, with the majority of its mass concentrated in lobes 110A and 110B. Lobe 110A is located 180 degrees from lobe 110B with respect to the longitudinal axis 112 of the multiple frequency vibration attenuation device 100. Altering the size and/or position of these lobes may change the frequencies the device 100 may attenuate. For example, changing the mass lobes or moving them farther out from the longitudinal axis 112 may change the frequencies the device 100 attenuates. Although the illustrated embodiment is bilobed, any non-radially symmetric shape may be used for the mass 104.
The shape and mass of the mass 104 is dependent on the spring rate and lateral bending rate of the spring 102, and the frequencies that are desired to be attenuated. Natural frequency, also known as eigenfrequency, is the frequency at which a system tends to oscillate in the absence of any driving or damping force. Free vibrations of an elastic body are called natural vibrations and occur at the natural frequency. Natural vibrations are different from forced vibrations that happen at a frequency of applied force (forced frequency). If the forced frequency is equal to the natural frequency, the amplitude of vibration increases many fold. This phenomenon is known as resonance.
Machined springs can easily be used in lateral translation. Lateral translation occurs when one end of a spring is anchored and the other end is laterally displaced by a force plus a moment to insure the end faces of the spring remain parallel. In an embodiment, the multiple frequency vibration attenuation device 100 is designed to have two (or more) natural frequencies that match the vibration frequencies of an aircraft that are desired to be attenuated. When subjected to one of these frequencies by the vibrating aircraft, the multiple frequency vibration attenuation device 100 resonates and dissipates much of the vibration energy from the aircraft (or other system) as this energy is used to move the spring 102 and the mass 104. This in turn may lead to better damping across the entire system, for example an aircraft system.
The multiple frequency vibration attenuation device 100 may be tuned to specific operational frequencies of an aircraft system. This may be done by altering either the spring rate or the mass 104 coupled to the spring 102, so that the modal (natural) frequencies of the spring-mass combination match the modal frequencies of the areas of concern around the aircraft system. Using an asymmetric mass may also require that each of the moments of inertia of the mass be determined so that multiple modal frequencies may be achieved.
The multiple frequency vibration attenuation device 100 may oscillate (through lateral translation, for example) at a first frequency on a first transverse axis 114A oriented in a first direction and oscillate (through lateral translation, for example) at a second frequency on a second transverse axis 114B oriented in a second direction, 90 degrees from the first direction. For example, when the aircraft takes off, the spring may oscillate to attenuate the first frequency, then the oscillation may change 90° to attenuate the second frequency while the aircraft is cruising.
In one embodiment, the two frequencies at which the multiple frequency vibration attenuation device 100 oscillates may include 97 Hz and 120 Hz. In one embodiment, the two frequencies at which the multiple frequency vibration attenuation device 100 oscillates may include 97.5 Hz and 120 Hz. In one embodiment, the two frequencies at which the multiple frequency vibration attenuation device 100 oscillates may include 98 Hz and 120 Hz.
The specific dimensions of the mass 104 may be determined using a computer simulated system model, through multiple design iterations, to achieve a design that has a modal response at the desired frequencies of concern. An aircraft system may include 120 multiple frequency vibration attenuation devices 100 installed around the aircraft in some embodiments. Due to the unwanted aircraft system energy being consumed by vibrating the multiple frequency vibration attenuation devices 100, the vibration in the aircraft system may be reduced to acceptable levels.
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.
This application claims priority to U.S. Provisional Application No. 62/906,813, filed Sep. 27, 2019, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62906813 | Sep 2019 | US |
