Resonant Peak Amplitude Research Articles

Numerical study on honeycomb membrane-type acoustic metamaterial with added mass

This paper presents numerical investigations on the transmission loss (TL) of a honeycomb structure with embedded membrane to which small masses are attached. The structure is a lightweight honeycomb membrane-type acoustic metamaterial that presents excellent transmission loss especially at low frequencies. The added mass is a solid material that is attached to the membrane, which is modelled as a linear isotropic elastic material with fixed boundary conditions. The influences of the membrane material properties and of the added mass parameters on the transmission loss are presented. It is demonstrated that the resonant peak amplitude of the transmission loss and its frequency band can be controlled by the properties of the added mass. The various numerical simulation results of configurations with and without added masses as well as various membrane elastic properties are compared. The honeycomb structure used in this study constitutes generally the core layer in sandwich honeycomb panels. While the TL of the honeycomb structure alone is zero, due to the open cell distribution, the integration of a membrane within the honeycomb with added masses induces a significant improvement of the transmission loss. This lightweight metamaterial is shown to attenuate the low frequency noise.

Linear and nonlinear optical absorption coefficients in InGaN/GaN quantum wells: Interplay between intense laser field and higher-order anharmonic potentials

This computational investigation delves into the electronic and optical attributes of InGaN/GaN nanostructures subjected to both harmonic and anharmonic confinement potentials, coupled with the influence of a nonresonant intense laser field (ILF). The theoretical framework incorporates higher-order anharmonic terms, specifically quartic and sextic terms. The solutions to the Schrödinger equation have been computed employing the finite element method and the effective mass theory. Moreover, linear and third-order nonlinear optical absorption coefficients are derived via a density matrix expansion. Our analysis reveals the feasibility of manipulating electronic and optical properties by adjusting confinement potential parameters, system attributes, and laser field intensity. In addition, the ILF induces remarkable modifications, characterized by reduced resonance peak amplitudes and a blue shift in absorption coefficients. Intriguingly, regardless of potential harmonicity, the impact of incident electromagnetic intensity is notably more pronounced in the absence of the ILF. These findings hold significant promise for advancing theoretical predictions, providing valuable insights into the intricate interplay between confinement potentials, laser fields, and their effects on electronic and optical behaviors within nanostructures.

Design and vibration control of aeroengine bracket with variable stiffness based on shape memory alloy

The aeroengine bracket is a vital connector, which plays a key role in supporting and transmitting loads. In this paper, a bracket with variable stiffness for vibration control of aeroengine accessory is designed. Firstly, the topology optimization for the initial model of the aeroengine bracket is carried out, and the quality of the bracket was reduced by 84.78% while meeting the strength requirements. After that, part of the material of the bracket was replaced by shape memory alloy (SMA) to design the bracket with variable stiffness. It is found that with the increase in temperature, the stiffness of the designed bracket with variable stiffness increases by about 36%, and maximum von Mises stress and deformation of the bracket have decreased. Finally, the integrated modeling of aeroengine casing-bracket-accessory is carried out. Under single and coupled fault frequencies, the amplitude of the accessory is reduced by 57.5% and 63.1%, respectively. The frequency sweep at different temperatures shows that as the temperature increases, the resonance frequency changed from 74.6 Hz to 89.1 Hz and the resonance peak amplitude decreased by 17.7%.

Zero-energy states in graphene quantum dot with wedge disclination

We show that wedge disclination affects the density of states for fermions that are electrostatically confined in graphene quantum dots. By considering a magnetic flux and solving the Dirac equation, we determine the eigenspinors. These are used for large arguments to derive an approximate scattering matrix, which allows us to get the density of states. Under various conditions, it is found that the density of states exhibits several resonance peaks. In particular, it is shown that the wedge disclination is able to change the amplitude, width, and positions of resonance peaks.

Tuned mass damper on spacecraft reaction wheel assembly

Considering the wide frequency range and time-varying characteristics of reaction wheel assembly (RWA) micro-vibrations, an embedded tuned mass damper (TMD) was proposed herein to reduce the influence of the RWA micro-vibration effect on spacecraft. First, dynamics model of the RWA and a mechanical model of the angular contact ball bearing were constructed, and the time-varying characteristics of the RWA were theoretically analyzed. Based on single- and multiple-degree-of-freedom vibration absorption dynamics models, it was shown that the TMD could be applied to the vibration suppression of the RWA’s multi-modal and time-varying state by changing the design parameters of the TMD. Based on the RWA single-degree-of-freedom equivalent dynamics model, the effects of the TMD natural frequency and damping on the displacement amplitude ratio of the RWA were analyzed, and the sensitivities of the RWA resonance peak amplitude and resonance frequency to the two parameters were analyzed by the Sobol sensitivity analysis method. Then, according to the analysis results, the structural design of the TMD in the RWA was guided, and a test platform was built to obtain the RWA micro-vibration data. Finally, a normalized amplitude-frequency response identification algorithm was used to eliminate the effects of non-linearities in the experimental data and to identify the RWA dynamics in a time-varying state, thus obtaining the RWA amplitude–frequency response curve and verifying the results of the theoretical analysis. Theoretical and experimental data showed that the addition of a TMD structure with variable damping and stiffness within the RWA allowed for micro-vibration suppression for arbitrary modes and improved the RWA vibration characteristics. This could provide convenience for different specifications of RWA vibration suppression as well as reference for further research on the effective application of TMDs in RWAs.

Enhancing the Terahertz Absorption Spectrum Based on the Low Refractive Index All-Dielectric Metasurface

We presented an angle-multiplexing low refractive index dielectric metasurface for terahertz absorption spectrum enhancement of lactose with high Q resonance properties. The unit cell structure of the acrylonitrile butadiene styrene (ABS) square structure is designed and optimized. The resonant peak shifts of the dielectric metasurface are analyzed by changing the incident angle of the terahertz wave. Then the α-lactose films with different thicknesses are added to investigate the enhancement effect. The resonant peak amplitude of the angle-multiplexing low refractive index dielectric metasurface absorption spectrum changes greatly with the absorption spectrum of the samples. The results illustrate that the enhanced absorption spectrum formed by the linked envelope can be up to 45 times stronger than that without the unit cell structures and also exhibits a high-quality factor. The proposed dielectric metasurface provides great potential in enhancing the terahertz absorption spectrum.

Fuzzy Clustering Analysis of HVSR Data for Seismic Microzonation at Lahore City

A microzonation study deals with the classification of hazards in a town or city in terms of surface ground motions that result from amplification and resonance frequency in soils against seismic tremors. This paper presents the result of a microzonation study in terms of resonance frequency and peak amplitude for Lahore city, Pakistan. In order to recognize the local soil effects of the covered geology at 159 sites in Lahore city, the horizontal-to-vertical spectral ratio (HVSR) Nakamura method was implemented. A fuzzy C-mean (FCM) clustering algorithm was adopted to obtain the best cluster solution of the analyzed HVSR parameters. The results of the Silhouette Index suggest that the FCM clustering solution of observation data points is more consistent. The results of clustering reveal three solutions. Clusters 1 and 2 reveal that a major part of the research area possesses low to moderate frequencies (0.66–1.03 Hz) with a peak amplitude of 2.25–4.38 mm, indicating the presence of soft to hard rock and thick alluvial sedimentary cover. Cluster 3 reveals the presence of soft to compact rocks (with frequencies and amplitudes of 0.73–1.03 Hz and 3.02–4.11 mm, respectively) overlaying the bedrock. Lahore city has 60% of soil cover with an amplitude of 2–3 mm (for the central part) and about 40% of 3–4 mm in the northern, southern, and southwest portions. According to the NEHRP soil classification code of 1997, a major part of the city has stiff nature of the soil, while a few places reveal the presence of very dense soil. The maps produced in this study will provide expected ground motion-related useful information to reduce the seismic risk for infrastructure in Lahore city.

Experimental research on the influence of modal nonlinearities of paintings under mechanical loads

In the traditional transportation of paintings and the design of the packaging systems, paintings are usually assumed to behave like a linear system. In order to verify this hypothesis, in this contribution, by means of a hammer experiment and a sweep excitation experiment to simulate the shock and vibration during transportation, respectively, the modal nonlinearities of two real paintings and a dummy painting are experimentally studied. The experimental results show that paintings can be treated as a linear system only when being subjected to shock, but the modal nonlinearities of paintings cannot be ignored when being subjected to vibration. The general behaviour of the paintings modal nonlinearities is then summarised based on experimental results, and their consequences for painting transportation are discussed. First of all, the offset of the resonance frequency is the most important problem which will lead to failure of the original vibration isolation measures. Further, the decrease in the resonance peak amplitude will increase the probability of the eigenmode being excited. Besides, it is also necessary to attenuate the harmonic vibrations of paintings. Lastly, the different modal characteristics obtained by a sweep with increasing and decreasing frequency make the analysis of different excitation schemes more complicated. Therefore, the identification of the paintings modal nonlinearities is necessary and important.

Resonant Scattering in Proximity-Coupled Graphene/Superconducting Mo2 C Heterostructures.

The realization of high‐quality heterostructures or hybrids of graphene and superconductor is crucial for exploring various novel quantum phenomena and devices engineering. Here, the electronic transport on directly grown high‐quality graphene/Mo2C vertical heterostructures with clean and sharp interface is comprehensively investigated. Owing to the strong interface coupling, the graphene layer feels an effective confinement potential well imposed by two‐dimensional (2D) Mo2C crystal. Employing cross junction device geometry, a series of resonance‐like magnetoresistance peaks are observed at low temperatures. The temperature and gate voltage dependences of the observed resonance peaks give evidence for geometric resonance of electron cyclotron orbits with the formed potential well. Moreover, it is found that both the amplitude of resonance peaks and conductance fluctuation exhibit different temperature‐dependent behaviors below the superconducting transition temperature of 2D Mo2C, indicating the correlation of quantum fluctuations and superconductivity. This study offers a promising route toward integrating graphene with 2D superconducting materials, and establishes a new way to investigate the interplay of massless Dirac fermion and superconductivity based on graphene/2D superconductor vertical heterostructures.

Independently tunable triple-band infrared perfect absorber based on the square loops-shaped nano-silver structure

Recently, the keen demand for multi-band perfect absorbers in spectroscopy, infrared detection, and other fields has intensified. To meet the energy demand, here we propose an Ag-Dielectric-Ag multilayer triple-band perfect absorber exhibiting perfectly resonance absorption in the near-infrared region. And the numerical calculations indicate that we obtain three resonance absorption peaks (908 nm, 1085 nm, and 1216 nm) with the maximal absorption of 99.09%, 99.84%, and 99.21%, respectively. Based on this, we propose that the physical formation mechanism of three resonance peaks are the Fabry-Pérot resonance effect and Localized surface plasmon polaritons resonance. Theoretically combined with the electromagnetic coupling theory to explain how the resonance-enhanced absorption. At the same time, by the comparison with the complementary structure, it is theoretically proposed that the MIM structure has a Fabry-Pérot resonance effect in the near-infrared region and then computationally verified the Fabry-Pérot formula. Furthermore, we can adjust the amplitude and wavelength of resonance peaks by modifying the geometry unit cell. And our proposed triple-band perfect absorber has some excellent properties, such as high absorptivity, multi-band, tunable, suitability for wide incidence angles, excellent angle tolerance, polarization tolerance, etc. In addition, our TBPA has a simple structure, which simplifies the processing technology and economically saves processing costs. Furthermore, the following simulations investigate the absorption spectrum of our TBPA exhibit property changes significantly as the environment changes. So we can calculate the sensitivity of three modes (sorted by resonance wavelength from short to long) is S1 = 70.09 nm/RIU, S2 = 208.26 nm/RIU, and S3 = 50.06 nm/RIU, respectively. Therefore, we believe that this triple-band perfect absorber can capture maximize optical energy and apply it in devices and materials for light conversions, like plasmon-enhanced photovoltaics, optical absorption switching, and modulator-optical communications.

Dependence of Piezoelectric Discs Electrical Impedance on Mechanical Loading Condition

The piezoelectric effect, along with its associated materials, fascinated researchers in all areas of basic sciences and engineering due to its interesting properties and promising potentials. Sensing, actuation, and energy harvesting are major implementations of piezoelectric structures in structural health monitoring, wearable devices, and self-powered systems, to name only a few. The electrical or mechanical impedance of its structure plays an important role in deriving its equivalent model, which in turn helps to predict its behavior for any system-level application, such as with respect to the rectifiers containing diodes and switches, which represent a nonlinear electrical load. In this paper, we study the electrical impedance response of different sizes of commercial piezoelectric discs for a wide range of frequencies (without and with mechanical load for 0.1–1000 with resolution 20 ). It shows significant changes in the position of resonant frequency and amplitude of resonant peaks for different diameters of discs and under varying mechanical load conditions, implying variations in the mechanical boundary conditions on the structure. The highlight of our work is the proposed electrical equivalent circuit model for varying mechanically loaded conditions with the help of impedance technique. Our approach is simple and reliable, such that it is suitable for any structure whose accurate material properties and dimensions are unknown.

Novel resonance stability criterion for the 2D magnetically levitated servo-proportional valve

The leakage of the pilot stage of the 2D valve mainly depends on the size of its initial opening. According to the Routh criterion, the pilot stage of the two-dimensional magnetically levitated servo-proportional valve (2D-MSP valve) needs to be designed to have certain positive values to increase the damping ratio to improve valve stability, which leads to the leakage flow representing a non-negligible power loss. In order to reduce leakage flow and achieve goal of energy saving, this paper presents a novel resonance stability criterion by considering nonlinear characteristics of the fluid dynamic system. First, the 2D-MSP valve is regarded as a three-way valve-controlled differential cylinder system. Based on the frequency response of the resonance state, the energy conservation method is used to solve the flow “backfilling” area, the motion equation of the cylinder piston (valve spool displacement) and the pressure waveform of the sensing chamber under different opening and pressure amplitude ratio. Then, the analytical expression of the resonance peak amplitude is obtained and the resonance stability criterion is deduced. The result is compared with the Routh stability criterion, which illustrates that the positive openings of the pilot stage can be reduced to one-third of the original value. The prototype valve is then designed and manufactured based on the resonance stability criterion. The dynamic and static characteristics under different system pressures are measured. Experimental results show that the prototype valve is an over-damped system without any overshoot, which has excellent working stability, and its static and dynamic performance can meet the demands of the industry servo-proportional control system. The research work validates the effectiveness of the proposed resonance stability criterion.

Study on dynamic characteristics of bio-inspired vibration isolation platform

Inspired by the body movement of the kangaroo, a multi-degree-of-freedom vibration isolation platform containing three units, that is, a protected object, a nonlinear energy sink, and an X-shaped structure, has been modeled, and the differential equations of the system have been given in the form of uniform relative coordinates. Furthermore, the displacement transmissibility analysis and numerical calculation are supported by the method of harmonic balance and Runge–Kutta algorithm, which shows that (a) there are nonlinear behaviors and resonant phenomenon in the time–frequency response and (b) quasi-periodic motion may be a predictor of periodic steady-state response or strong resonance, and the displacement evolution before quasi-periodic motion may be used to distinguish the two phenomena. In addition, based on the numerical method, the system energy changes in a selected frequency are discussed. Finally, the correctness of the theoretical analysis is verified by simulation data in Adams. Taken together, these results demonstrate that the dynamic characteristics are adjustable and designable of structural parameters in a specific frequency band and can provide a useful way to reduce the amplitude of resonant peaks and improve the vibration isolation performance for practical engineering applications.

EFFECTS OF SIMPLIFIED METHODS FOR HYDRODYNAMIC FORCE ON TRANSFER FUNCTION OF CIRCULAR PIER

The rigid-structure method, Morison method and a method based on approximation of fundamental frequency are applicable simplified methods for the hydrodynamic force of incompressible non-viscous water. To investigate the differences of the above methods, the responsesof elastic cantilever circular piers were compared in the form of frequency domain transfer function, with the exact solutions which based on the radiation theory of incompressible non-viscous water considering structural deformation. Two kinds of size parameters were selected and 84 different sizes of piers were designed. By inputting impulse excitation, the transfer functions of displacement at the bottom, the transfer function of shear force and bending moment at the top were obtained. Then the first two order resonance-peak amplitude and resonance frequency were extracted for error analysis. Through the analysis of the range and variation trend of errors, it is found that:the resonance peak amplitude obtained by the rigid-structure method is more accurate, the resonance period obtained by the method based on approximation of fundamental-frequency is more accurate, and the error of the Morison method is significantly affected by the parameters. In addition, the amplitude of formant obtained by the fundamental frequency approximation is mostly smaller, while the amplitude and period obtained by the Morrison method are mostly larger.

Transfer matrix solution to free-field response of a multi-layered transversely isotropic poroelastic half-plane

Free-field response of a layered medium is of fundamental important for studying wave propagation and SSI problems, however, few researches have been conducted on this subject. In this paper, a transfer matrix method is presented to solve the free-field motion of a multi-layered transversely isotropic (TI) poroelastic half-plane subjected to incident plane qP1-, qP2- and qSV-waves. First, the displacement and stress expressions are obtained by solving the governing differential equations for a TI poroelastic medium. Then, the transfer matrices are derived by the continuity of tractions and displacements at layer interfaces, a transfer matrix solution for free-field response of the multi-layered TI poroelastic half-plane under obliquely incident seismic waves is presented. The free surface of the stratified system can be considered either completely drained or undrained. The accuracy of theoretical formulations is verified through comparison with existing layered TI as well as homogeneous saturated medium models. Numerical examples of varying key parameters are given out to evaluate the ground seismic responses. Results show that both anisotropy and porous property of medium have very important effect on the resonance frequency and peak amplitude. Meanwhile, due to the filtering and amplification mechanism of soil layer to ground motion, thicker layers have a more obvious amplification effect on low-frequency components and a certain "isolation" effect on high-frequency components.

Nonlinear actuation of non-prismatic dielectric elastomeric membrane

ABSTRACT Nowadays, the soft material, dielectric elastomers (DEs) are being used for many engineering applications due to their exceptional properties like high strain rate sensitivity, low power consumption, capable of static force measurement and capability of changing dimensions when subjected to voltage. They have the ability of converting mechanical energy to electrical energy and vice versa. In this article, nonlinear dynamic behavior of viscoelastic tapered DE under mechanical and electromechanical loading is studied. A dynamic model based on standard linear solid model is incorporated for viscoelasticity. Strain energy density of the system is derived from Gent model of hyperelasticity. The tapered DE is analyzed with different values of damping coefficients, ratio of shear moduli of springs, width and height tapers. The effects of tapers greatly put an impact on the dynamic responses of the system. The tapered DEs exhibits damped vibration and weak nonlinearity with an increase in damping force. The dynamic stability of tapered DEs is also studied using phase diagrams, and the results indicated that with an increase in damping force, the dynamic stability changes from a state of aperiodic vibration to quasi-periodic vibration. It is also found that the resonant frequency and peak amplitude reduce with an increase in the damping force.

A Compact Ultra-Long Period Fiber Grating Based on Cascading Up-Tapers

A new ultra-long period fiber grating constructed by a series of up tapers is proposed and demonstrated experimentally. A fiber grating with length of 2mm is fabricated by cascading three up-tapers on a single mode fiber, which is the shortest ultra-long period fiber grating up to now. The effect of periodic error is greatly reduced due to the ultra-long grating pitch. The fabrication repeatability is greatly improved by adopting semi-automated fabrication techniques. Strain and temperature are identified simultaneously by tracing the change of resonant wavelength and attenuation peak amplitude with a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.2~\mu \varepsilon $ </tex-math></inline-formula> and 0.2°C, respectively.

Efficient limitation of resonant peaks by topology optimization including modal truncation augmentation

In many engineering applications, the dynamic frequency response of systems is of high importance. In this paper, we focus on limiting the extreme values in frequency response functions, which occur at the eigenfrequencies of the system, better known as resonant peaks. Within an optimization, merely sampling the frequency range and limiting the maximum values result in high computational effort. Additionally, the sensitivities of this method are not complete, since only information about the resonance peak amplitude is included. The design dependence with respect to the frequency of the extreme value is missed, thus hampering the convergence. To overcome these difficulties, we propose a constraint which can efficiently and accurately limit resonant peaks in a frequency response function. It has a close relation with eigenfrequency maximization; however, in that case, the amplitudes of the frequency response are unconstrained. In order to keep the computational time low, efficient implementation of this constraint is studied using reduced-order models based on modal truncation and modal truncation augmentation. Furthermore, approximated sensitivities are investigated, resulting in a large computational gain, while still yielding very accurate sensitivities and designs with almost equivalent performance compared with the non-approximated case. Conditions are established for the accuracy and computational efficiency of the proposed methods, depending on the number of peaks to be limited, numbers of inputs and outputs, and whether or not the system input and output are collocated.

Inversion for acoustic parameters of plastic polymer target in water

The high-precision molding capability of complex surfaces and structures makes three-dimensional (3D) printing technology more widely used in underwater acoustic models and structural molding. The plastic polymer material, as the main material in the field of 3D printing, possesses the acoustic parameters that are directly related to the acoustic properties of 3D printed underwater acoustic models and structures. Based on the Rayleigh normal series solution for the acoustic scattering of underwater target and the mechanism analysis of the low-frequency resonance which is associated with subsonic Rayleigh waves on the solid plastic polymer spheres, the sensitivity characteristics of the resonance frequency and amplitude to the wave velocity and attenuation coefficient are obtained at low frequencies. It is shown that the transverse wave velocity and the transverse wave attenuation coefficient both have high inversion accuracy at low values of &lt;i&gt;ka&lt;/i&gt;, where &lt;i&gt;a&lt;/i&gt; is the radius of elastic sphere, as they are quite sensitive to the backscattering resonance frequency and amplitude, respectively. In the frequency band of interest, the backscattering resonance frequency is almost independent of attenuation coefficient. Considering the inversion accuracy, the longitudinal wave velocity and transverse wave velocity are inverted by the resonance frequency separately. Based on these characteristics, the cyclic search method is used to establish an acoustic parameter inversion method for plastic polymer materials, in which the frequency and amplitude of backscattering resonance peak are used as cost functions. Finally, the backscattering acoustic scattering experiment on a solid typical plastic polymer PMMA (methyl methacrylate-acrylic) sphere is conducted in the tank. The experimental results about the backscattering target strength varying with the frequency are in good agreement with the simulation results in a frequency range of 5–20 kHz. The simulation parameters such as the longitudinal wave velocity, transverse wave velocity and attenuation coefficient are obtained by the previously established inversion method. Therefore, the acoustic parameter inversion method provides reliable acoustic parameters for 3D printed underwater acoustic model and structure performance prediction for plastic polymer materials.

Hydrodynamic pressures on arch dam faces with irregular reservoir geometry

A scaled boundary finite element method is developed for the analysis of hydrodynamic pressures acting on arch dam faces with a reservoir of irregular geometry. Water compressibility and reservoir boundary absorption are considered simultaneously. The reservoir is idealized as composed of finite and infinite subdomains. Governing equations for evaluating hydrodynamic pressures of finite fluid domain have been established and the solution procedures are presented. In addition, the boundary conditions at the interface between finite and infinite subdomains are decided. Numerical examples validate the present method with high accuracy and show that the fairly irregular geometry of a reservoir has an important influence on the hydrodynamic pressures acting on the arch dam face. Frequency response functions of the hydrodynamic pressures in the stream and cross-stream directions are evidently influenced by reservoir geometry, while hydrodynamic pressures in the vertical direction are relatively less influenced. Another feature of the frequency response function of hydrodynamic pressures is that the amplitude of resonant peaks is affected much more by reservoir geometry as compared to the resonant frequency. Besides, peak value of hydrodynamic pressures in the arch direction and cantilever direction is also significantly influenced by reservoir geometry. Based on these facts, it can be concluded that the effect of reservoir geometry on hydrodynamic pressure should be considered for seismic design of arch dams.