Attenuation Zones Research Articles

Interaction of Bragg scattering bandgaps and local resonators in mono-coupled periodic structures

Periodic structures have gained attention in the research community since they show attenuation zones in their frequency response, called bandgaps. In this paper, the interactions of two mechanisms of bandgap formation in mono-coupled periodic structures are examined, i.e., Bragg scattering and local resonators. With reference to longitudinal elastic waves, an analytical study is carried out to describe in detail the formation of bandgaps. Local resonators are implemented via piezoelectric inserts shunted with a resonating electrical circuit for which a non-traditional model is needed since the study concerns higher frequencies with respect to those of the subwavelength regime. Design maps and tuning formulas are developed not only for the case of infinite structures, but also for the finite case, highlighting the role of the number of unit cells and that of resonances in the attenuation zones. Among the possible tuning strategies of local resonators, it is shown that the mutual influence between elastic and electric parameters is able to produce a wider attenuation zone, bridging Bragg scattering bandgaps thanks to the effect of local resonators. The analytical findings of this paper are validated with numerical results in an example application.

A Novel Application of Multi-Resonant Dissipative Elastic Metahousing for Bearings

Bearing as an important machine element is widely used for industrial and automotive applications. At certain operational speed, bearings induce disturbing vibrations and noises that affect machine service life, productivity and passenger comfort in case of vehicle applications. Dissipative elastic metamaterials have caught considerable attention of scientific community due to their effective medium properties and peculiar dynamic characteristics including frequency bandgaps that can be effectively applied to attenuate and control undesirable vibration and noises. Although a substantial amount of theoretical work for effective medium characteristics and dynamic properties of acoustic/elastic metamaterials has been reported, the practical design and application of these composite structures for real-life engineering problems still remain unexplored. The present study intends to investigate a potential application of dissipative elastic metamaterials in controlling the bearing-generated vibration and noises over an ultrawide frequency range. The study is based on a simple analytical model together with rigorous finite element numerical simulations. It has been established that the dissipative characteristic of resonant system caused by larger material mismatch broadens the local resonance bandgaps beyond the bounding resonance frequency at the cost of wave transmission. In order to achieve broadband vibration and noise control, multi-resonant composite structures are embedded inside the bearing housing in five different layers. The reported results revealed the presence of broadband wave attenuation zone distributed from 3 to 52 kHz with consideration of material damping. The bearing-generated vibration and noises lying inside the wave attenuation zone will be mitigated. This feasibility study provides a new concept for the design and application of acoustic/elastic metamaterials in the bearing industry to improve machine service life and to enhance productivity and passenger comfort.

A robust approach to estimate Q from surface seismic data and inverse Q filtering for resolution enhancement

Accurate estimation of seismic quality factor (Q) is important in seismic data processing to correct for the velocity dispersion effects and to compensate for absorption losses through inverse Q filtering. To estimate it, often logarithmic spectral ratios of the non-stationary seismic signal between two depth levels are linearly inverted. As these ratios are usually derived from the standard Fourier transform (FT) which has a poor time-frequency resolution, this can lead to biased Q estimation. We have calculated spectral ratios from the high-resolution time-frequency spectrum using the Stockwell transform (ST). We then non-linearly inverted these improved spectral ratios to estimate Q using the Levenberg-Marquardt (LM) method. For a synthetic wedge model, results demonstrate a reasonable improvement in the accuracy of Q estimation with the combined ST-LM approach. Application on a real P-wave reflection seismic dataset revealed an anomalous attenuation zone of very low Q (29–75) values. Inverse Q filtering using the estimated Q profile has enhanced the seismic resolution below it and minimized the differential viscous losses. Frequency slice filtering on Q compensated data has improved the S/N ratio and hence the amplitude fidelity of reflectors.

Locally Resonant Periodic Wave Barriers for Vibration Isolation in Subway Engineering

Subway transportation is being promoted worldwide to effectively solve urban congestion. However, the vibration induced by subway traffic has caused a major adverse impact on building safety, precision instrument operation and human health. Wave barriers have been proven effective in mitigating ground vibration, whereas they have some limitations in achieving ideal attenuation zone and high efficiency to cover the low-frequency vibration in underground railway system. Based on locally resonant phononic crystals theory, this paper designs three-component locally resonant periodic wave barriers (LRPWBs), and investigates the effects of geometrical and material parameters on the bandgap features in detail. The band structures are calculated using improved plane wave expansion (IPWE), the transmission spectra and vibration modes are obtained by finite element method (FEM). The results indicate LRPWBs are able to give lower and wider bandgap to cover the main frequency of subway environment, which is proved by time and frequency domain analysis. For the bandgap mechanism, the local resonance features of LRPWBs result in the energy conversion between kinetic energy and elastic strain energy, thus the elastic wave energy is localized in resonance unit and then the locally resonant bandgap is created. In addition, the bandgap can be adjusted by carefully selecting proper geometrical and material parameters to actualize low-frequency broadband attenuation. Further studies about multi-oscillator system indicate that the appropriate combination of multiple LRPWBs are conductive to diverse and broad bandgaps. The investigations can provide inspiration for periodic wave barriers design in multi-frequency vibration attenuation field.

Seismic mitigation performance of periodic foundations with inertial amplification mechanism considering superstructure-foundation interaction

The periodic foundation is a novel seismic isolation technology which uses the filtering characteristics of periodic structures. In order to solve the shortcomings of the existing attenuation mechanism, and to have a better attenuation effect on the main frequency band of ground motions, a periodic foundation based on the inertial amplification mechanism (IAPF) is proposed. The seismic mitigation performance of IAPF is studied by frequency response analysis. The sensitivity analysis and optimization of the interactive system which is composed of IAPF and superstructure are also carried out. The performance of the IAPF interactive system is compared with that of the interactive system composed of the local resonance periodic foundation and superstructure. The results show that IAPF does not require a large resonator mass to mitigate structural response. In addition, proper additional damping can significantly reduce the resonance peak and has negligible effect on the attenuation depth, which makes up for the shortcoming that the periodic foundation will amplify the response at the resonance peaks outside the attenuation zone to some extent.

The Characteristics of the Short-Period S-wave Attenuation Field in the Lithosphere of Turkmenistan and Northeastern Iran and their Relation to Seismicity

The characteristics of the short-period S-wave attenuation field in the lithosphere of Turkmenistan and northeastern Iran are considered. The data obtained by the Karatau station at distances of up to 1750 km were used. The ratios of the maximum amplitudes of Pn and Sn waves (Sn/Pn parameter) were analyzed. The correlation dependence of this parameter on distance has been obtained. These data are compared with data for the regions of Caucasus, Pamir, and the Baikal Rift Zone. The West Turkmenian depression experiences significantly lower attenuation; the Turan Plate shows an intermediate level and the Alborz Range has a higher level. It is shown that attenuation in the source zones decreases considerably with time after large earthquakes. A zone of higher attenuation has been identified in the eastern Alborz Range; it is probably related to preparation of a large earthquake. The connection of heterogeneities in the attenuation field with deep-seated fluids migration is discussed.

Основные дайковые серии северной части Чакылкалянского мегаблока и их потенциальная рудоносность (на примере Яхтонского дайкового роя, Южный Узбекистан)

The study of mineralogical and geochemical properties of gold deposits is an urgent task for the geological industry, especially in the new areas under study. Without reliable information about the geological factors that lead to the formation of ore deposits and the mechanisms of deposit accumulation, it is impossible to ensure reliable scientific forecasting of the mineral potential of the regions, the effective creation of mineral resources of enterprises and mining, the stable operation of the mining industry. Our study of gold deposits was aimed at understanding these important issues of the ore formation problem. This is the urgency of the case. The role of the dictators of the Yakhton ore deposit as important structural material and mineral components of the leading types of ore-magmatic systems is being assessed. A peculiar feature of the geological structure of the ore area is the close paragenetic relationship of mineralization by rocks of the dike kids complex. Mineralization is localized in two stages and has bimetallic properties (gold, tungsten). The mineralization in the upper layer is localized in the corpus carbonate rocks of Yakhton (mainly garnet-pyroxene content). In the lower stage, mineralization is governed by a northeastern tectonic attenuation zone, which includes area concentrations of Au and W and areal mineralized zones that are part of the dike of the Yakhton region. Determining the spatial, age, and genetic relationships of mineralization with magmatism is a major problem of metallogeny.

Improving Long-term Monitoring of Contaminated Groundwater at Sites where Attenuation-based Remedies are Deployed.

This study presents an effective approach to tackle the challenge of long-term monitoring of contaminated groundwater sites where remediation leaves residual contamination in the subsurface. Traditional long-term monitoring of contaminated groundwater sites focuses on measuring contaminant concentrations and is applicable to sites where contaminant mass is removed or degraded to a level below the regulatory standard. The traditional approach is less effective at sites where risk from metals or radionuclides continues to exist in the subsurface after remedial goals are achieved. We propose a long-term monitoring strategy for this type of waste site that focuses on measuring the hydrological and geochemical parameters that control attenuation or remobilization of contaminants while de-emphasizing contaminant-concentration measurements. We demonstrate how this approach would be more effective than traditional long-term monitoring, using a site in South Carolina, USA, where groundwater is contaminated by several radionuclides. A comprehensive enhanced attenuation remedy has been implemented at the site to minimize discharge of contamination to surface water. The immobilization of contaminants occurs in three locations by manipulation of hydrological and geochemical parameters, as well as by natural attenuation processes. Deployment of our proposed long-term monitoring strategy will combine subsurface and surface measurements using spectroscopic tools, geophysical tools, and sensors to monitor the parameters controlling contaminant attenuation. The advantage of this approach is that it will detect the potential for contaminant remobilization from engineered and natural attenuation zones, allowing potential adverse changes to be mitigated before contaminant attenuation is reversed.

The impact of resonant additions’ footprint on the stop band behavior of 1D locally resonant metamaterial realizations

Metamaterials have been proven to hold potential to enhance the Noise, Vibration and Harshness (NVH) performance in several applications, as they can create stop bands, which lead to frequency zones of pronounced noise and/or vibration attenuation. This paper investigates the influence of the footprint between resonant inclusions and host structure on the stop band behavior of metamaterials. The impact of this design feature is assessed both numerically and experimentally. Numerically, it is shown that by increasing the footprint, the stop bands (SB) become narrower and shift to higher frequencies. Applied to finite structures, it is shown that the zones of pronounced vibration attenuation tend to follow the changes in the stop band limits. The experimental validation is performed on metamaterial beams and the results comply with the numerical model. This investigation demonstrates that the footprint of resonators is a design parameter which can have a beneficial effect when taken into account during the design stage of matematerials.

Vibration attenuation analysis of periodic underground barriers using complex band diagrams

Vibrations propagating underground may have harmful effects on adjacent buildings and human health. Recently, the notion of phononic crystals has been introduced and applied to isolate vibrations below the ground. In this paper, considering the viscoelastic material model, the complex band diagrams are suggested to analyse the transportation of vibrations in the composite foundation consist of soil and different underground structures. In the complex band diagram, the minimum imaginary part of the wave vectors is taken as the index to measure the ability of the pile group to weaken vibrations. Several types of underground barriers, including circular piles, continuous walls, and multi-layer piles, are analysed. The result shows that multi-layer piles can induce local resonance and achieve an attenuation zone at the low-frequency level. The attenuation effect of periodic barriers is then verified by transmission models. The results show that the complex band diagrams can quantitatively evaluate the isolation effect of periodic barriers, which is beyond the capability of classic band diagrams.

Study of tunable locally resonant metamaterials: Effects of spider-web and snowflake hierarchies

The present research is an effort to enhance and control locally resonant bandgaps in periodic metamaterials of hexagonal and triangular topologies by introducing spider-web and snowflake-inspired hierarchies to the conventional geometries. Due to their low connectivity number, hexagonal lattice structures are unable to exhibit locally resonant bandgaps. By introducing the spider-web hierarchy, the connectivity number of the structure is increased, and the constituting beams act as local resonators. Thus, the hexagonal lattice structure can attenuate propagating waves in desirable frequency ranges by localizing the wave energy in the constituent beams. As a result, better wave-filtering performance is achieved by introducing hierarchy to hexagonal lattices. Furthermore, the snowflake hierarchical triangular lattice structures exhibit new tunable attenuation zones for which the locations depend on the mechanical and geometrical parameters. The finite element method and Bloch’s theorem are applied to analyze the wave propagation in the considered architected structures. Moreover, theoretical formulations are presented to predict the locations of each locally resonant bandgaps. It is shown that by changing the mechanical and geometrical parameters of the added hierarchical structures, the locally resonant bandgaps can be perfectly tuned to the desired frequencies in the long-wavelength region. Finally, two theoretical diagrams are proposed to represent initial design concepts of tunable acoustic/elastic metamaterials of hexagonal and triangular unit cells with maximum bandgap widths in low frequencies. To present a more comprehensive analysis of the wave propagation in hierarchical structures, the effects of imaginary wave-vector components on the dispersion curves and attenuation behavior of each topology are also investigated. The results of the current study enable the engineers to design architected periodic structures with the ability to present bandgaps in desired frequencies, which has been the goal of structural engineers for years.

Spectral-Domain Optical Coherence Tomography Is More Sensitive for Hydroxychloroquine-Related Structural Abnormalities Than Short-Wavelength and Near-Infrared Autofluorescence.

PurposeTo analyze the appearance of structural abnormalities due to hydroxychloroquine (HCQ) toxicity by spectral-domain optical coherence tomography (SD-OCT) and short-wavelength autofluorescence (SW-AF) and near-infrared fundus autofluorescence (NIR-AF) imaging.MethodsThis retrospective cohort study included 88 eyes from 44 patients who had a history of or were currently taking HCQ. SD-OCT, SW-AF, and NIR-AF images were analyzed by two independent graders for the detection of HCQ-associated abnormalities.ResultsSixty eyes (30 patients, 68%) presented with no abnormalities for either imaging modality. Twenty eyes (10 patients, 23%) presented with parafoveal abnormalities (ellipsoid zone attenuation and/or interdigitation zone continuity loss) in SD-OCT scans but with qualitatively normal SW-AF and NIR-AF images. Eight eyes (four patients, 9%) presented with bull's-eye maculopathy in SW-AF and NIR-AF images, with corresponding outer retinal structures disrupted parafoveally in SD-OCT scans (“flying saucer” sign). No patients presented with normal SD-OCT scans and concurrent abnormalities in SW-AF or NIR-AF images.ConclusionsSD-OCT was more sensitive in detecting structural abnormalities than either SW-AF or NIR-AF imaging, suggesting its superiority as a screening imaging modality for HCQ toxicity. Maculopathy and abnormalities in the retinal pigment epithelium from HCQ toxicity can be appreciated in both SW-AF and NIR-AF images.Translational RelevanceAlthough debate exists regarding the best imaging modalities for screening patients for potential HCQ toxicity, our study supports the use of SD-OCT over both SW-AF and NIR-AF imaging as a screening modality.

Crustal deformation in the Rio de la Plata estuarine (South Atlantic passive margin) and the associated seismicity as a consequence of an isostatic readjustment

The Río de la Plata estuarine has been the epicenter of the 30 November 2018 intra-crustal earthquake with a magnitude and focal depth of 3.7 and 19 km (±6 km), respectively, which alerted the Buenos Aires city population. This area has also been the locus of a series of earthquakes with magnitudes ranging from 3.7 to 5, and particularly the 1888 earthquake, probably with an epicenter near the axis of the estuarine. These earthquakes occur in the Salado basin area, an aulacogen basin associated with the early stages of the South Atlantic spreading in late Early Cretaceous times, that subsided all through the Cenozoic. Previous gravimetric analyses revealed that this basin is characterized by an important crustal attenuation zone. From a new gravimetric analysis, using satellite gravity data, we find isostatic anomalies associated with this section of the Atlantic passive margin. Therefore, we propose that the origin of these earthquakes is the isostatic readjustment of this aulacogen type basin, a process that could have reactivated shallow crustal structures. From a preliminary evaluation, we estimate that the Salado basin would subsidize other ~2 km to compensate for the measured thick anti-root, constituting a crucial seismogenic source that should be considered due to the demographical and economic importance of the region.

Experimental proof of emergent subharmonic attenuation zones in a nonlinear locally resonant metamaterial

High-performance locally resonant metamaterials represent the next frontier in materials technology due to their extraordinary properties obtained through materials design, enabling a variety of potential applications. The most exceptional feature of locally resonant metamaterials is the subwavelength size of their unit cells, which allows to overcome the limits in wave focusing, imaging and sound/vibration isolation. To respond to the fast evolution of these artificial materials and the increasing need for advanced and exceptional properties, the emergence of a new mechanism for wave mitigation and control consisting in a nonlinear interaction between propagating and evanescent waves has recently been theoretically demonstrated. Here, we present the experimental proof of this phenomenon: the appearance of a subharmonic transmission attenuation zone due to energy exchange induced by autoparametric resonance. These results pave the path to a new generation of nonlinear locally resonant metamaterials.

Dissipative Multiresonant Pillared and Trampoline Metamaterials With Amplified Local Resonance Bandgaps and Broadband Vibration Attenuation

AbstractThe present study deals with the analysis of dissipative multiresonant pillared and trampoline effect–enhanced elastic metamaterials for the amplification of local resonance bandgaps. The study is conducted through a finite element–based numerical technique and substantiated with a discrete mass-in-mass analytical model. The band structures and wave dispersion characteristics of the multiresonant pillars erected on a thin elastic plate foundation are analyzed. Compared to a single-resonant metamaterial, this multiresonant structure innovatively creates wider bandgaps due to the coupling of resonance frequencies of the pillar modes with the base plate. For trampoline metamaterials, a periodic array of holes is made inside the plate. The holes forge the plate to work as a compliance base that enhances the system resonance frequency through intensive vibration of pillar-plate structure resulting in further amplified local resonance bandgaps. The enlargement of bandgaps also depends upon the height of the pillar and diameter of holes. Extremely wide low-frequency bandgaps can be achieved for a larger pillar height and a bigger hole diameter. Through a frequency response study, reported bandgaps are compared and an infinite unit cell model (band structure) is validated. The introduction of material loss factor (material damping) resulted in a broadband vibration attenuation zone spread throughout the frequency spectrum. Compared to a standard multiresonant pillared-plate model, the bandgap amplification caused by the trampoline effect induces a relatively larger bandwidth, and this superior characteristic together with the dissipative nature of the medium may facilitate potential design outcomes for manipulating subwavelength metamaterial properties over a broad range of frequencies.

Broadening the attenuation range of acoustic metafoams through graded microstructures

Low frequency sound attenuation is a challenging task, because of the severe mass, stiffness and volume constraints on the absorbing and/or reflecting barriers. Recently, significant improvements in low frequency sound attenuation has been achieved by introducing the acoustic metafoam concept, which combines the mechanism of conventional acoustic foams - high viscothermal dissipation - with the working principle of locally resonant acoustic metamaterials - wave attenuation at low frequencies. However, the attenuation improvement provided by periodic materials containing identical resonators is confined to a narrow frequency range. To overcome this limitation, graded acoustic metafoams are proposed and studied here, where a distribution of local resonators with varying properties (mass and stiffness) is introduced. It is demonstrated that, through a suitable design of mass and stiffness distribution of the resonators, the broadening of the frequency attenuation ranges can be effectively achieved. Graded acoustic metafoams are, therefore, a natural development direction for achieving broad frequency attenuation zones.

Vibration mitigation in saturated soil by periodic in-filled pipe pile barriers

Abstract The complex dispersion relations and vibration mitigation properties of periodic in-filled pipe pile barrier in fluid-saturated poroelastic soil are investigated. The periodic structure theory is adopted and the viscosity of the in-filled materials is taken into account by using the Kelvin-Voigt model. The local resonance attenuation zones (LRAZs) covering the resonance frequency of the inner oscillator are obtained and then broadened by properly designing the viscosity of the in-filled materials. The influences of the typical geometry and material parameters of the pile barriers on the LRAZs are comprehensively studied. To validate the efficiency of LRAZs, the dynamic responses of a finite periodic pipe pile system are numerically simulated by conducting the time-history analysis. Taking the viscosity of the rubber into account, it is found that the attenuation parameter is suppressed in the LRAZs and enlarged outside of the LRAZs. In addition, the propagation of shear-waves can be effectively reduced in the LRAZs below 20 Hz when filling the pipe piles with soft materials. The findings of this study present a proper way to design periodic pipe pile barriers in saturated soil for ambient vibration attenuation, especially in the low-frequency range.

New Engineering Solutions for the Traction Electric Drive of a Gazelle-Next Medium-Duty Van

A procedure for choosing the optimal gear ratio for a reducing gear train is proposed for the traction electric drive of the workshop electric automobile based on the GAZ A22R22/32 chassis and its modified versions, taking into account the requirements for the top linear speed of the automobile, acceleration, and power plant energy efficiency that will allow achieving a required reserve. The optimization procedure consists of three phases. In phase one, the traction electric drive’s top speed was achieved. Then, the time was minimized for which the electric drive reached the rated speed. In phase two, the gear ratio was adjusted proceeding from the conditions in which the drive was used in the field attenuation zone. Taking into account the system’s operation in the attenuation mode against the loss minimization criteria, the procedure of selecting the gear ratio allowed reaching a cruising range of 200 km and the traction electric drive’s acceleration to the rated speed in 9 s. A charge control system is proposed that allows making the battery work stably in operational and charge modes. It is confirmed by experiment that, at a cell imbalance of no more than 3%, the full balancing takes only up to 4 min.

Vibration Attenuation and Amplification of One-Dimensional Uncoupled and Coupled Systems with Optimal Metafoundations

Finite locally resonant metafoundations represent an innovative solution for structural seismic response mitigation based on their filtering capabilities at selected frequency ranges. They inherit the filtering properties of periodic foundations and bands in which response amplitudes are reduced, the so-called attenuation zones. Nonetheless, other bands of vibration-induced resonances amplify the components of superstructure response and are generally named nonattenuation zones. Both frequency bandwidths and amplification depend on the dynamic properties of metafoundations and superstructures as well as their coupling. Thus, in order to shed light on the mechanisms of seismic mitigation of coupled systems endowed with optimal metafoundations, this paper explores both elastic uncoupled and coupled unit-cell chains in the frequency domain based on the analysis of various transfer functions. Moreover, to address uncertainty at the excitation level, time history analyses are performed with a set of natural accelerograms that characterize operating basis earthquakes; thus, response contributions from both attenuation zones and nonattenuation zones can be distinguished by relating response variances to peak responses. Eventually, the attenuation effects of optimal metafoundations, frequency shift of superstructures due to unit cells of metafoundations, and coupling of both attenuation zones and nonattenuation zones are analyzed in depth.

A global sensitivity analysis method based on the Gauss-Lobatto integration and its application in layered periodic foundations with initial stress

A global sensitivity analysis method based on the Gauss-Lobatto integration is proposed and applied to study the attenuation zones of layered periodic foundations including the effect of initial stress. Comparisons with existing results of a mathematical model in previous studies are conducted to validate the proposed method, and the accuracy of the proposed method is found to be superior to the extensively used Monte Carlo simulation method in the global sensitivity analysis. Global sensitivity analyses of the lower bound frequency, width and maximum attenuation coefficient of the first attenuation zone are conducted considering five input parameters. The relative importance of every individual parameter and their interactions in determining the first attenuation zone are examined. Moreover, fitting equations of the lower bound frequency, width and maximum attenuation coefficient of the first attenuation zone are developed as guidelines to design layered periodic foundations with initial stress.