Analysis Of Vibrational Modes Research Articles

Bandgap tuning and in-plane wave propagation of chiral and anti-chiral hybrid metamaterials with assembled six oscillators

In this paper, a hybrid acoustic metamaterial consisting of chiral and anti-chiral ligaments is proposed. The bandgap properties of the hybrid chiral and anti-chiral structure with and without oscillator intercalation are calculated using Bloch’s theorem and the finite element method, and the structure is verified and evaluated to have good vibration attenuation performance by means of transfer functions and stress clouds. By adjusting the resonant oscillator configuration and applying active strain, the structure is verified to have tunable capability, which provides a simple and easy scheme for bandgap tunability analysis. Finally, a comprehensive analysis of the structural vibration mode, phase constant plane, group velocity, phase velocity and wave propagation direction diagram lead to the conclusion that the directional and regional nature of wave propagation is responsible for the bandgap opening. The new structure in this paper provides a new way of thinking for vibration and noise reduction, and also provides a practical solution for bandgap adjustment. The comprehensive analysis of wave propagation also presents theoretical and technical support for the subsequent structure and bandgap optimization.

Defect study of phosphorous doped a-Si:H thin films using cathodoluminescence, IR and Raman spectroscopy

The phosphorous (P) doping induced defects and deviation in microstructural properties of a-Si:H films have been investigated by Infrared (IR), Raman and Cathodoluminescence (CL) spectroscopy. The analysis of local vibration mode of IR and Raman spectra points out the evolution of defects and cluster structure with a P-doping in a-Si:H films. Undoped a-Si: H films show no CL spectra while it emerges in P-doped films. Intensification in CL spectra with P-doping intimates that the crystallites and defects in films are the origin of CL spectra. CL peaks are emanated from intrinsic structural defects, interstitial cations and two-fold coordinated silicon in films. Peaks at 784 nm and 945 nm in CL spectra are originated from Si micro-crystals.

Circuit Simulator Compatible Model for the Ring-Dot Piezoelectric Transformer

A lumped-element equivalent circuit model for the ring-dot piezoelectric transformer (PT) is derived based on a one-dimensional analysis of the radial vibration mode. Initially, equations for the magnitudes of force, vibration velocity at the boundaries of each Section of the device are derived based on the piezoelectric constitutive equations and using Kirchhoff plate theory. Similarly, equations for the amplitudes of input and output currents are derived from the electric displacement field and Gauss’ law. From this analytical approach, an equivalent circuit model is developed and, using a Taylor expansion, approximated as the Mason equivalent circuit. A key contribution of this work is the development of a circuit simulator compatible model which can be used by electronic engineers, without in-depth knowledge of the underlying material science, to design ring-dot PTs for power conversion applications. The resulting model is verified against both COMSOL finite element simulations and experimental impedance measurements. Compared to COMSOL, the model estimates the resonant circuit elements to within 1% and the input and output capacitance are estimated to within 10%. Experimental results match the simulation to within 10% for most parameters, and 1% for resonant frequency. [2022-0154]

Transverse vibration modes analysis and acoustic response in optical fibers

Fiber optic sensors are often used as acoustic sensors to detect sound waves because of their apparent advantages, such as anti-electromagnetic interference and strong adaptation to the environment. The transverse vibration mode of the fiber caused by the acoustic wave can be obtained, and the principle of the optical fiber sensor to detect the acoustic wave signal was explored by using a simple model. It is found that the acoustic wave can effectively cause the change in birefringence of the fiber only when the number of azimuthal modes is 2, and the acoustic wave was detected by using a fiber sensor. It is found, by analyzing the detection mechanism, that the spectral width is proportional to the acoustic impedance of the surrounding medium, and the acoustic interaction between the TR22 mode and the surrounding medium is much weaker than that of the TR21 mode. This provides a theoretical basis for the detection of acoustic signals by fiber optic sensors.

Low‐Frequency Vibration and Noise Reduction and Wave Propagation Properties of Hexagonal Hybrid Metamaterials with Local Resonance Strips

Based on the idea of local resonance, a class of hybrid acoustic metamaterials with interposed resonant strips is proposed in this article, and the bandgap characteristics and transmission properties are calculated by combining Bloch's theorem and lattice theory. The new structure is verified to have low‐frequency damping and noise reduction capability through the analysis of the stress cloud diagram at specific frequencies in the bandgap range. A comprehensive analysis of vibration modes, phase constant surfaces, group velocity, phase velocity, and wave propagation direction diagram is used to explore the wave propagation and bandgap opening mechanism, providing technical support and theoretical basis for subsequent bandgap optimization and structural improvement. The results show that this structure can open multiple bandgaps in the low‐frequency range below 500 Hz, and the stepped design of the single‐cell structure and the introduction of resonant strips provide a new design idea for low‐frequency vibration and noise reduction.

A novel index for vibration-based damage detection technique in laminated composite plates under forced vibrations: experimental study

In this study, vibration modal analysis has been used to experimentally investigate the detection of fiber breakage (FB) and delamination in laminated composite plates. The modal analysis was performed on two arrangement styles of carbon fiber reinforced polymer (CFRP) laminated plates under forced vibrations. The main contribution in this study is that a new index named Improved Curvature Damage Factor (ICDF) was introduced to detect and localize damages in composite structures. It is a developed version of an earlier index based on the change in mode shape curvature (MSC) of dynamic response. To include the effect of more than one mode shape Cumulative Improved Damage Factor (CICDF) was proposed. The ICDF index was validated with a number of earlier studies that investigated the damage detection in different structures in order to approve the efficiency of this index. A scanning laser vibrometer was also used to experimentally examine the modal-based and forced responses for intact and damaged plates. Various experimental tests were used to verify the advantages of the proposed methodology and its use in structural health monitoring. In addition, the analysis of experimental results showed that the mutation caused by FB is almost double that of the value of delamination peaking.

Research on noise control of automobile exhaust system under idling condition based on modal analysis

Correlational studies of vibration characteristics theory of exhaust system, optimization design of idling vibration control and the noise test analysis were conducted to solve the problems of body vibration and exhaust noise under idling condition. Firstly, the analysis of vibration mode, dynamic response and vibration transfer of exhaust system were carried out by using the simulation analysis, and the location of the exhaust system hangers were verified. Furthermore, the structure optimization schemes of exhaust system were proposed for exhaust noise reduction under idling condition based on control of local stiffness optimization, constraint location optimization and system global stiffness optimization. Finally, the interior and exhaust noise and system vibration of optimization schemes were tested under idling condition, and the exhaust noise was verified under rapid acceleration condition respectively. Meanwhile, the vibration response of exhaust system was analyzed. Results showed that the optimization schemes had better noise attenuation effect than the original scheme under idling and rapid acceleration conditions, indicating that it was necessary not only to effectively avoid the idling frequency interval of engine, but also to improve the structural stiffness and the vibration of local structure according to the vibration mode, and minimize the modification of the internal structure of the exhaust system.

Theoretical insights into the stability of buckled tetragonal graphene and the prediction of novel carbon allotropes.

Buckled tetragonal graphene (BTG), a novel allotrope of graphene, has been reported to possess Dirac-like fermions and high Fermi velocities. However, the stability of BTG is still controversial. Here, first principles calculations and ab initio molecular dynamics (AIMD) were performed to study the stability of three kinds of tetragonal graphenes (TGs), including planar tetragonal graphene (PTG), BTG reported by Liu et al. [Phys. Rev. Lett., 2012, 108, 225505] and the novel BTG constructed by us. For the two BTGs, phonon dispersions predict that they are stable, but this conclusion is contradictory with the results of energy analysis, vibrational mode analysis and AIMD simulations. Our electronic structure analysis shows that the delocalized Π bonds formed by unbonded pz electrons drive the stability of PTG and may induce the transformation of the two BTGs into PTG. Our further study of phonon dispersions on planar hexagonal graphene (PHG) and buckled hexagonal graphene (BHG) indicates that the phonon dispersion at 0 K may have some limitations in predicting the stability of 2D carbon materials and thus cannot accurately describe the stability of BTGs. In addition, we have predicted several hydrogenated and fluorinated TGs, and theoretically demonstrated that chemical modification can make metallic PTG become a semiconductor with a certain bandgap. Moreover, the bandgaps of these new materials can be further regulated by increasing the thickness of the carbon atomic layer, which makes them promising for semiconductor devices and energy storage.

Modal analysis of vibrations and evaluation of vibration activity of the platform and propeller of an RW-UAS aerial robot

The quadrocopter used to perform mine surveying and geodetic work, to develop a non-contact ore sampling technology based on the use of an intelligent unmanned aerial vehicle equipped with technical vision and a specialized X-ray fluorescent energy-dispersive device installed on it. In this work, the equations of quadrocopter dynamics under load derived, and the influence of dynamic disturbances on SSS propellers carried out. The analysis of torques on four propellers carried out. The equations of dynamics of 4 rotors of the RW-UAS robot (quadcopter) are written on the basis of the Lagrange-Maxwell equations. An analysis of the control moments carried out, which makes it possible to implement horizontal and vertical flights of the quadrocopter. The simulation carried out using the Maple analytical computing environment. Based on the modal analysis of the equations of dynamics of the air robot, the results obtained where the ranges of wave disturbances on the air vehicle are determined and the SSS of the blades and their elastoplastic displacement obtained. The conducted research shows the need for a detailed study of dynamic processes on an air robot, the behavior of the rotor system is especially important.

Optimization of Wing Structure Based on Fluid-solid Coupling and Vibration Model

With the development of ages, human beings have made more efforts to develop the sky, and aircraft is widely used as the main tool for human beings to set foot in the sky. Therefore, optimizing wing structure is positive for saving resources and improving efficiency. In this paper, by establishing the conventional wing structure model and the wing model after changing its rib density, we compared results based on fluid-solid coupling and vibration mode analysis. It is found that: The wing structure optimization should appropriately increase or decrease the wing-rib aperture (i.e., increase/decrease by 10%) based on ensuring the flight performance of the wing, and it can effectively reduce the overall deformation of the wing and ensure the flight performance of the wing, which provides a valuable reference for the design of the wing structure.

Finite element mesh refinement for in-plane and out-of-plane vibration of variable geometrical Timoshenko beams based on superconvergent vibration modes

PurposeIn this paper, a superconvergent patch recovery method is proposed for superconvergent solutions of modes in the finite element post-processing stage of variable geometrical Timoshenko beams. The proposed superconvergent patch recovery method improves the solution speed and accuracy of the finite element analysis of a curved beam. The free vibration and natural frequency of the beam were considered for studying forced vibrations and structural resonance. Beam vibration mode analysis was performed for high-precision vibration mode solutions and frequency values. The proposed method can be used to compute beam vibration modes of beams with different shapes and boundary conditions as well as variable cross sections and curvatures. The purpose of this paper is to address these issues.Design/methodology/approachAn adaptive method was proposed to analyse the in-plane and out-of-plane free vibrations of the variable geometrical Timoshenko beams. In the post-processing stage of the displacement-based finite element method, the superconvergent patch recovery method and high-order shape function interpolation technique were used to obtain the superconvergent solution of mode (displacement). The superconvergent solution of mode was used to estimate the error of the finite element solution of mode in the energy form under the current mesh. Furthermore, an adaptive mesh refinement was proposed by mesh subdivision to derive an optimised mesh and accurate finite element solution to meet the preset error tolerance.FindingsThe results computed using the proposed algorithm were in good agreement with those computed using other high-precision algorithms, thus validating the accuracy of the proposed algorithm for beam analysis. The numerical analysis of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams helped verify that the solutions of frequencies were consistent with the results obtained using other specially developed methods. The proposed method is well suited for the mesh refinement analysis of a curved beam structure for analysing the changes in high-order vibration mode. The parts where the vibration mode changed significantly were locally densified; a relatively fine mesh division was adopted that validated the reliability of the mesh optimisation processing of the proposed algorithm.Originality/valueThe proposed algorithm can obtain high-precision vibration solutions of variable geometrical Timoshenko beams based on more optimized and reasonable meshes than the conventional finite element method. Furthermore, it can be used for vibration problems of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams. The proposed algorithm can be extended for application in superconvergent computation and adaptive analysis of finite element solutions of general structures and solid deformation fields and used for adaptive analysis of more complex plates, shells and three-dimensional structures. Additionally, this method can analyse the vibration and stability of curved members with crack damage to obtain high-precision vibration modes and instability modes under damage defects.

Substrate-Dependent Conformational Switch of the Noncubane [4Fe-4S] Cluster in Heterodisulfide Reductase HdrB

The noncubane [4Fe-4S] cluster identified in the active site of heterodisulfide reductase (HdrB) displays a unique geometry among Fe-S cofactors found in metalloproteins. Here we employ resonance Raman (RR) spectroscopy and density functional theory (DFT) calculations to probe structural, electronic, and vibrational properties of the noncubane cluster in HdrB from a non-methanogenic Desulfovibrio vulgaris (Dv) Hildenborough organism. The immediate protein environment of the two neighboring clusters in DvHdrB is predicted using homology modeling. We demonstrate that in the absence of substrate, the oxidized [4Fe-4S]3+ cluster adopts a "closed" conformation. Upon substrate coordination at the "special" iron center, the cluster core translates to an "open" structure, facilitated by the "supernumerary" cysteine ligand switch from iron-bridging to iron-terminal mode. The observed RR fingerprint of the noncubane cluster, supported by Fe-S vibrational mode analysis, will advance future studies of enzymes containing this unusual cofactor.

Relativistic density functional investigation of the mono-lanthanum silicide clusters LaSin (n=1-6): geometries, electronic properties and IR spectra

The mono-lanthanum silicide clusters LaSin (n=1-6) have been studied adopting the relativistic density functional calculation with generalized gradient approximation. Considering different spin configurations, we calculated and discussed the equilibrium geometries, charge populations, the HOMO-LUMO gaps, as well as infrared (IR) absorption spectra of LaSin (n=1-6) clusters. It is found that: the lowest-lying LaSin (n=1-6) clusters basically maintain a similar framework to the low-lying Sin+1 clusters, and the La atoms prefer the surface sites. The relative stabilities are investigated based on the calculation of fragmentation energies and, showing that LaSi2, LaSi4, and LaSi5 clusters have enhanced stabilities. Charge populations analysis shows that the charges transfer from La atom to Sin framework and the La atom acts as an electron donor. HOMO-LUMO gaps indicate that LaSi2 and LaSi5 clusters have higher chemical stabilities. IR absorption spectrum and vibrational mode analysis show that the highest frequency absorption peaks all correspond to the breathing mode of the silicon framework, and the characteristic infrared absorption peaks caused by La atom vibration, except for LaSi dimer, all appeared in the low-frequency region.

Broadband infrared absorption spectroscopy of low-frequency inter-molecular vibrations in crystalline poly(L-lactide)

The broadband vibrations of poly l-lactide (PLLA) were investigated by terahertz (THz) spectroscopy in the range of 2–16 THz, infrared (IR) spectroscopy, density functional theory (DFT), and classical molecular dynamics (MD) simulations. Characteristic functional group peaks were observed in the IR spectra, which were independent of the crystallinity. A simple model analysis utilizing DFT calculations with an isolated l-lactide monomer and MD simulations for nine polymer chains in a unit cell were performed to investigate the origin of intra-molecular vibrations between molecular chains. Experimentally observed peaks in the THz region were assigned to the inter- and intra-molecular vibration modes. Results showed that classical MD calculations are a particularly powerful tool for the vibrational-mode analysis of inter-molecular interactions.

An investigation on 3-hydroxybenzaldehyde for exploring terahertz low-frequency vibration modes with quasi-harmonic approximation method

3-Hydroxybenzaldehyde (3-HBA) was investigated in the range of 0.6–2.8 THz by terahertz time-domain spectroscopy (THz-TDS) and solid-state density functional theory (ss-DFT) with first-principles calculation. Four distinct peaks were found respectively, and among them, the intensity disparity between experiment and simulation spectra at 2.04 THz was recognized as the biggest inconsistency. Considering thermal behavior can be responsible for this, quasi-harmonic approximation (QHA) method was introduced to mimic the unit cell volume expansion. According to vibrational modes analysis, it was ascertained that the biggest vibrational modes discrepancy was also located at 2.04 THz. Molecules in 0% and 4% unit cell expansion exhibit an opposite rotational direction in a-b plane compared with 2% unit cell expansion. Noncovalent intermolecular interactions were investigated with independent gradient model (IGM), and the result indicates that hydrogen bonding is the dominating noncovalent interaction of 3-HBA. While calculating systematic potential energy to the displaced bonds stretching involving hydrogen atoms, it was found the anomalous potential energy variation to the bond stretching provides a possible explanation for the rotation direction divergence, that is, the rotation direction divergence can be related to some hydrogen atoms seeking lower overall potential energy around their equilibrium positions during bond stretching in response to the variational intermolecular van der Waals force. This research combined THz-TDS with the quasi-harmonic approximation method, elucidating the principle of vibrational characteristics in different volumes, which is beneficial to the investigation of the terahertz low-frequency vibration to thermal behavior as a reference in biochemistry and other fields.

Modal analysis of beam-like structures using multipoint dynamic testing vision system based on composite fringe pattern

A multipoint dynamic testing vision-based system for beam-like structures based on composite fringe pattern (CFP) was proposed. The CFP was decorated on the surface of a beam as a sensor, whose image sequences were captured by a camera for dynamic identification. The CFP consists of two cosine fringe patterns. The fringes on both sides of the CFP are used to locate the measuring positions and the middle one is used to measure the spatial displacement of structures. The key advantage of the proposed method is that it can measure multipoint vibration information along the length direction of the beam at one measurement without point-by-point scanning. Experiments on two different beams were carried out, and the results show that the method can get multipoint vibration information and the modal shapes of the beam. Therefore, the vision and CFP-based measurement method is suitable for vibration monitoring and modal analysis of beam-like structures.

Suppression of thermoacoustic instabilities by flame-structure interaction

We present here an experimental study of the influence of the aeroelastic coupling between the combustion chamber walls and the acoustic fluid field on the onset and development of thermoacoustic instabilities in stoichiometric propane-air premixed flames. A horizontal quasi-two-dimensional Hele–Shaw chamber formed by two parallel plates separated a small distance h is used. The flames are ignited at the open end, in contact with the atmosphere, and propagate towards the opposite closed end. The experiments reveal three distinct propagation regimes determined by the stiffness of the plates and the evolution of the pressure perturbation generated during ignition: (i) for sufficiently rigid plates, we observed secondary acoustic instabilities with large amplitude oscillations in the direction of propagation of the flame; for flexible enough walls to be compliant with ignition-related pressure changes, (ii) the propagation of the flame undergoes small-amplitude oscillations (primary acoustic instabilities) along the channel or (iii) it is smooth with no oscillations whatsoever. The flexural rigidity of the plate is modified experimentally by changing both the width W and thickness hw of the top plate of the Hele–Shaw cell. The data recorded by the pressure transducer and the accelerometer is used to plot a stability map in the W−hw parametric space to define the combination of structural parameters that triggers the onset of thermoacoustic instabilities. Our experimental measurements, supplemented with results from a theoretical analysis of the walls vibration modes, indicated that deformation-induced volume changes of around 0.1% of the volume of the Hele–Shaw cell are sufficient to suppress thermoacoustic instabilities.

Direct and Water-Mediated Adsorption of Stabilizers on SERS-Active Colloidal Bimetallic Plasmonic Nanomaterials: Insight into Citrate-AuAg Interactions from DFT Calculations.

In previous studies, AuAg colloidal nanostar formulations were developed with the two-fold aim of producing optimized surface-enhanced Raman spectroscopy (SERS) substrates and investigating the nature of the capping process itself. Findings demonstrated that the nanoparticle metals are alloyed and neutral, and capping by stabilizers occurs via chemisorption. This study utilizes citrate as the model stabilizer and investigates the mechanistic aspects of its interaction with mono- (Au20) and bimetallic (Au19Ag) surfaces by density functional theory (DFT) calculations. Citrate was modeled according to the colloid's pH and surrounded by a water and sodium first solvation shell. A population of stable cluster-citrate structures was obtained, and energies were refined at the uB3LYP//LANL2TZ(f)/cc-pVTZ level of theory. Solvation was accounted for both explicitly and implicitly by the application of the continuum model SMD. Results indicate that both direct binding and binding by water proxy through the charge-transfer complex formation are thermodynamically favorable. Water participation in citrate adsorption is supported by the adsorption behavior observed experimentally and the comparison between experimental and DFT-simulated IR spectra. Vibrational mode analysis suggests the possible presence of water within a crystal in dried nanostar residues. All ΔGads(aq) indicate a weak chemisorptive process, leading to the hypothesis that citrate could be displaced by analytes during SERS measurements.

Advanced surface FTIR spectroscopy analysis of poly(ethylene)-block-poly(ethylene oxide) thin film adsorbed on gold substrate

This study investigates the thin film adsorption on gold substrate of PE-b-PEO block copolymer. The originality is to use Polarization Modulation – InfraRed Reflection Absorption Spectroscopy (PM-IRRAS) to probe the copolymer thin film conformational state when physisorbed. The PM-IRRAS technology allows to measure surface-specific FTIR spectra of thin films due to differential reflectivity of p- and s-polarized light from interfaces. The anisotropy and the exaltation of the electric field created at the copolymer/metal interface are exploited to infer macromolecular adsorption and conformational changes induced by the adsorption. In addition to spectroscopic analyzes, the surface topology of the thin film of copolymer and the ability of the blocks to crystallize at the solid interface were investigated by Atomic Force Microscopy (AFM). Vibrational modes analysis of the PM-IRRAS spectra unambiguously show first that the PEO sequences of the PE-b-PEO copolymer are adsorbed preferentially on the Au substrate in flatten conformations relative to the substrate surface with an orientation angle of 27° between the main chain axis and the gold substrate and second that the PE sequences of PE blocks are randomly oriented compared to the gold surface and rejected as an amorphous phase to the upper surface of the copolymer film.

Structural Characterization of a Toppling Rock Slab From Array‐Based Ambient Vibration Measurements and Numerical Modal Analysis

AbstractAccurate assessments of the internal structure and boundary conditions of unstable rock slopes are imperative for evaluating landslide hazard scenarios. However, instability characterization at depth remains challenging and is often limited by costly or invasive subsurface investigations. Here, we develop a new approach coupling array‐based ambient vibration modal analysis and numerical modeling to improve structural characterization of rock slope instabilities at depth. We used ambient noise cross‐correlation on 4 hr of seismic data recorded by an array of 30 nodal geophones at a 500‐m‐long toppling rock slab in Utah, USA to identify modal frequencies between 0.8 and 3.5 Hz and derive modal displacements. We show that transverse and longitudinal bending modes span the length of the instability, indicating an interconnected slab. Statistical comparison of field results with outputs from >1,000 finite element models with varying boundary conditions showed that the instability depth varies between 40–70 and 10–20 m in the middle and lateral regions, respectively. Our approach yields new information on the structural conditions of rock cliff and column instabilities at depth, which is not easily obtained by other means but is imperative for change detection monitoring and improved hazard assessments.