Patent Application
20240003403
The disclosure generally relates to vibration attenuation systems and, more particularly, to passive low frequency and broadband vibration attenuation systems.
This section provides background information related to the present disclosure which is not necessarily prior art.
The ability to achieve broadband vibration attenuation has always been a long-standing challenge in the structural dynamics community. Active and semi-active techniques are capable of extending the operating range and providing some level of adaptation to specific operating conditions. However, they also impose more elaborate system configurations, typically involving added electronics and control logics that increase complexity, probability of false alarms and failure. Conversely, passive systems are simple, robust, and reliable but do not offer the same flexibility to different operating conditions and do not allow achieving broad operating ranges. The aerospace and automotive industries, which predominantly use lightweight structures, have struggled with attenuating low frequency vibrations. Low frequency flexural wave propagation through flexible lightweight structures may cause structural instability, structure radiated noise, and structural damage. The search for a vibration attenuation system capable of combining the benefits of both active and passive methods without inheriting the corresponding disadvantages has been a long-standing challenge in structural dynamics.
In recent years, Acoustic Black Holes (ABH) have rapidly emerged as an effective passive technique to either dissipate or harvest mechanical energy in thin wall structures. The characteristic dimension of an ABH (typically its diameter, in the case of an axisymmetric design) is strictly connected to its cut-on frequency, which is the value below which the ABH cannot affect (i.e., slow down) the incoming wave. From a general perspective, the lower the desired cut-on frequency, the larger the required diameter of the ABH.
This frequency condition is probably more conveniently restated in terms of a cut-on wavelength. Theoretical and experimental results have shown that in order for the ABH to interact with the incoming wave, the wavelength should be about the ABH diameter or smaller. However, design and manufacturing constraints impose stringent limitations on the maximum ABH diameter usable in practical applications, and consequently on the lowest achievable cut-on frequency. It follows that structures with embedded ABHs can perform well in the mid and high-frequency ranges (or, equivalently, the medium to short wavelengths), but perform poorly in the low frequency range (i.e., when wavelengths are longer than the ABH diameter).
Previous studies have explored the dynamic behavior of an ABH metastructure, that is a continuum thin-walled structure integrated with periodic arrangements of ABHs. These works explored the role that periodic arrangements of ABHs can play in tailoring the dispersion properties of the host structure and controlling the propagation of elastic waves. In a follow-up study, it was also shown that periodic ABH elements can also lead to metastructures with unusual effective material properties. Later, separate studies observed that the periodic arrangement of ABHs can introduce locally resonant bandgaps below the ABH cut-on frequency. The use of interconnected double ABH indentations was also explored as a way to couple local resonance and Bragg's scattering effects to widen bandgaps in frequency ranges below the cut-on frequency of the individual ABH.
While recent studies have recognized the potential of periodic arrangements of ABHs to achieve passive vibration attenuation at low frequency (that is below the cut-on frequency of the individual ABH unit), it was found that the overall dynamic performances were still limited by the number of unit cells in these periodic grids. This limitation can be attributed to the spatial constraint restricting the number of unit cells in a finite size domain and, as a consequence, in a limit on the longest wavelength (lowest frequency) affected by the periodic ABH metastructure. It appears that, while ABH metastructures exhibit interesting features capable of extending the performance of passive vibration attenuation methodologies towards the lower end of the frequency spectrum, the intrinsic dependence of the performance of ABH periodic structures on the spatial periodicity and on the dimensions of the unit cell (hence of the individual ABH) is still a limiting factor to achieve satisfactory performance in the low frequency regime, or otherwise known as being below a cut-off frequency.
An opportunity to overcome this latter limitation is offered by the concept of intentional nonlocality that was recently introduced and explored in the context of elastic metasurfaces. Generally speaking, the concept of nonlocal actions is very general and applies to many different branches of physics. At its core, the nonlocal response of a system builds upon the concept of action at a distance which means that the response of the system at a point depends on the state of the system at distant points. In nonlocal elasticity, this concept could be stated observing that the state of stress at a point of a continuum is affected by the distribution of strain at distant points. While different areas of applications (e.g., molecular mechanics or microcontinuum theories) can approach this concept from different perspectives and by using different mathematical tools, the overall concept remain unchanged independently of the length scale of the system.
Previous studies also showed that the introduction of macroscopic nonlocal forces could lead to effective elastic material properties of the metasurface that are functions of both wavelength and frequency. This dependence could be exploited to achieve a remarkably broadband operating range. While the metasurface operated in a much different frequency range, compared to the current ABH metastructure, the operating wavelength was still significantly larger than the characteristic width of the metasurface, hence dictating deeply subwavelength operating conditions. Considering that, in the low frequency range, also the ABH metastructure operates under subwavelength conditions, it is expected that a similar concept of intentional nonlocality could be applicable to ABH metastructures and significantly expand their operating dynamic range.
Accordingly, there is a continuing need for a vibration attenuation system that is configured to attenuate vibrations in a passive manner. Desirably, the vibration attenuation system may be configured to attenuate low-frequency vibrations.
In concordance with the instant disclosure, a vibration attenuation system that is configured to attenuate vibrations in a passive manner, has surprisingly been discovered. Desirably, the nonlocal acoustic black hole metastructure system may attenuate vibrations in a broad low-frequency range.
The vibration attenuation system includes a load bearing layer, a non-load bearing layer, and a rigid beam connector. In a specific example, the non-load bearing layer may be flexible. The load bearing layer may have a first density and a first stiffness. The non-load bearing layer may have a second density and a second stiffness, the second density may be lower the first density. The rigid beam connector may have a third density and a third stiffness. In a more specific example, the rigid beam connector may be constructed from an available material with the lowest density and the highest stiffness when compared to the first density and stiffness and/or the second density and stiffness. The rigid beam connector couples the load bearing layer to the non-load bearing layer. The coupling of the non-load bearing layer to the load bearing layer through the use of the rigid beam connector may provide a nonlocal connection to transfer energy from the load bearing layer to the non-load bearing layer.
Various ways of using the vibration attenuation system are provided. For instance, a method may include a step of providing a load bearing layer, a non-load bearing layer, and a rigid beam connector. The load bearing layer may have a first density and a first stiffness. The non-load bearing layer may have a second density and a second stiffness. The rigid beam connector may have a third density and a third stiffness. The rigid beam connector may couple the load bearing layer to the non-load bearing layer. In a specific example, the rigid beam connector may couple an Acoustic Black Hole (ABH) metastructure of the load bearing layer to the non-load bearing layer. An external load-induced vibration may be accepted in the load bearing layer. The vibration energy may then be transferred through the rigid beam connector to the non-load bearing layer. Next, the vibration may be localized in the non-load bearing and attenuated using viscoelastic damping layers.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations and are not intended to limit the scope of the present disclosure.
The following description of technology is merely exemplary in nature of the subject matter, manufacture, and use of one or more inventions, and is not intended to limit the scope, application, or uses of any specific invention claimed in this application or in such other applications as may be filed claiming priority to this application, or patents issuing therefrom. Regarding methods disclosed, the order of the steps presented is exemplary in nature, and thus, the order of the steps can be different in various embodiments, including where certain steps can be simultaneously performed. “A” and “an” as used herein indicate “at least one” of the item is present; a plurality of such items may be present, when possible. Except where otherwise expressly indicated, all numerical quantities in this description are to be understood as modified by the word “about” and all geometric and spatial descriptors are to be understood as modified by the word “substantially” in describing the broadest scope of the technology. “About” when applied to numerical values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by “about” and/or “substantially” is not otherwise understood in the art with this ordinary meaning, then “about” and/or “substantially” as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters.
Although the open-ended term “comprising,” as a synonym of non-restrictive terms such as including, containing, or having, is used herein to describe and claim embodiments of the present technology, embodiments may alternatively be described using more limiting terms such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting materials, components, or process steps, the present technology also specifically includes embodiments consisting of, or consisting essentially of, such materials, components, or process steps excluding additional materials, components or processes (for consisting of) and excluding additional materials, components or processes affecting the significant properties of the embodiment (for consisting essentially of), even though such additional materials, components or processes are not explicitly recited in this application. For example, recitation of a composition or process reciting elements A, B and C specifically envisions embodiments consisting of, and consisting essentially of, A, B and C, excluding an element D that may be recited in the art, even though element D is not explicitly described as being excluded herein.
As referred to herein, disclosures of ranges are, unless specified otherwise, inclusive of endpoints and include all distinct values and further divided ranges within the entire range. Thus, for example, a range of “from A to B” or “from about A to about B” is inclusive of A and of B. Disclosure of values and ranges of values for specific parameters (such as amounts, weight percentages, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that Parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping, or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if Parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9,1-8,1-3,1-2,2-10,2-8,2-3,3-10,3-9, and so on.
When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected, or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments.
Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the FIG. is turned over, elements described as “below,” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
As shown in
A possible idealized 1D discrete model of the nonlocal Acoustic Black Hole (ABH) metastructure is illustrated in
The vibration attenuation system 100 may include various ways to attenuate a vibration while maintaining the strength of the load bearing layer 102. For instance, the second density may be less than the first density. In a more specific non-limiting example, the third density may be less than the first density. In a specific example, the third stiffness of the rigid beam connector 108 may be greater than each of the first stiffness of the load bearing layer 102 and the second stiffness of the non-load bearing layer 104, 106. In a more specific example, the first stiffness of the load bearing layer 102 may be greater than the second stiffness of the non-load bearing layer 104, 106, yet still lesser than the third stiffness of the rigid beam connector 108. Additionally, the shape of the vibration attenuation system 100 may be configured to further attenuate a vibration. The load bearing layer 102 may be a primary thin-walled structure for which broadband vibration attenuation performance is sought. As shown in
In certain circumstances, the non-load bearing layer 104, 106 may be configured to control the distribution of nonlocal forces. As shown in
As shown in
The non-load bearing layer 104, 106 may be connected to the load bearing layer 102 by the rigid beam connectors 108. In a practical implementation, the rigid beam connectors 108 may be designed as structural linkages having significantly higher stiffness compared to the layers 102, 104, 106, for example, a ratio of E of connector: ELBL=12:1. Here, E is Young's modulus between the load bearing layer 102 and the supporting structure. Their spacing influences where the nonlocal forces mediated by the non-load bearing layer 104, 106 are transferred to the load bearing layer 102. Both the number and location of these rigid beam connectors 108 may be treated as design variables whose values would be obtained by means of an optimization approach. From a more qualitative perspective, these links allow the vibrational energy to flow between the two layers 102, 104, 106, hence it is reasonable to locate these rigid beam connectors 108 close to structural locations on the load bearing layer 102 with high energy density. Equivalently, given that nonlocal forces are driven by the state of strain within the horizon of nonlocality, rigid beam connectors 108 may be optimally located in regions with high strain energy density. As a non-limiting example, the center points of ABH tapers 110 (known to be points with high energy density) may be optimal locations of interest to place the rigid beam connectors 108. One skilled in the art may select other suitable number, locations, or positions for the rigid beam connector 108, within the scope of the present disclosure.
In certain circumstances, the non-load bearing layer 104, 106 may include a viscoelastic layer 114 configured to further dampen and/or attenuate the vibration. In a specific example, the viscoelastic layer 114 may be disposed on the non-load bearing ABH 112 of the non-load bearing layer 104, 106 to attenuate the localized energy in the non-load bearing layer 104, 106. It is contemplated that a plurality of viscoelastic layers 114 may be utilized on the non-load bearing layer 104, 106. The viscoelastic layer 114 may be constructed from any viscoelastic/dampening materials, such as rubber and/or polyurethane. In another specific example, the viscoelastic layer 114 may be disposed on the load bearing layer 102. In a more specific example, the viscoelastic layer 114 may include a plurality of viscoelastic layers 114 disposed on the load bearing layer 102. In an even more specific example, the viscoelastic layer 114 may be disposed on each of the load bearing layer 102 and the non-load bearing layer 104, 106. One skilled in the art may select other suitable materials to construct the viscoelastic layer 114, within the scope of the present disclosure.
Various ways of using the vibration attenuation system 100 are provided. For instance, as shown in
Advantageously, the vibration attenuation system 100 utilizes intentional nonlocality to improve the broadband and low frequency attenuation performance of ABH metastructures 112, 114. In a specific example, the nonlocal design integrates a local ABH metastructure, which leverages multiple periodic ABH tapers 110, with additional flexible layers 104, 106 intentionally introduced to achieve a nonlocal dynamic behavior. The new structural design implements, at the macroscopic scale, an equivalent concept of action at a distance typically seen in systems with prominent scale effects. In linear elasticity, the traditional material nonlocality is mathematically defined as a function of the location-dependent nonlocal attenuation function. However, as the nonlocal behavior of the vibration attenuation system 100 was achieved by using geometrically tailored physical connections, a semi-analytical methodology was developed to extract the effective dynamic nonlocal attenuation functions endowed with both spatial and temporal dependence. The qualitative agreement between the semi-analytical and the numerical dispersion structure of an infinite nonlocal ABH metastructure allowed validating the semi-analytical technique. While this method could certainly be useful to obtain homogenized models of large-scale nonlocal ABH metastructures, in the present disclosure its development was motivated by the understanding of the effects that different design parameters have on the occurrence of the nonlocal behavior.
In a specific, non-limiting example, the additional nonlocal layer (the non-load bearing layer 104, 106) may increase the overall weight of the system 100 by around fifteen percent for a flat plate configuration and around twenty six percent for a tapered/concave surface plate configuration. However, with continued reference to the non-limiting example, an average reduction of around twenty-seven percent for a nonlocal flat plate configuration and around forty percent for a nonlocal tapered/concave surface plate configuration in the steady state response amplitude was obtained for the nonlocal design in the low-frequency range. Accordingly, the results clearly indicate that the vibration response of ABH metastructures can be significantly attenuated via the nonlocal design.
Another very remarkable effect is observed on the position of the first frequency bandgap. In another specific, non-limiting example, the local ABH metastructure (tapered load bearing plate 102) may present a first bandgap around 170 Hz (center frequency), the nonlocal design can reduce its center frequency to approximately 2 Hz (a 98% reduction). The width and location of the bandgaps at low frequencies could be tuned by selecting the type of non-load bearing layer 104, 106 and its geometrical parameters. The present disclosure particularly describes how the combination of intentional (macroscopic) nonlocality and of ABH technology can achieve very low frequency bandgaps without compromising the structural integrity of the system 100. Desirably, this characteristic can be very useful for structural dynamics applications and passive vibration control.
Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Equivalent changes, modifications and variations of some embodiments, materials, compositions, and methods can be made within the scope of the present technology, with substantially similar results.
The present application is a U.S. non-provisional application which claims the benefit of U.S. provisional application Ser. No. 63/357,720, filed Jul. 1, 2022, the content of which is incorporated by reference herein in its entirety.
This invention was made with government support under 1621909 and 1761423 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63357720 | Jul 2022 | US |
