Fundamental Vibrations Research Articles

Spectra of CO2‐Kr in the 4.3 μm region: Intermolecular Bend and Symmetry Breaking of the Intramolecular CO2 Bend

AbstractThe infrared spectrum of CO2‐Kr complex is studied in the region of the carbon dioxide ν3 fundamental vibration (≈2350 cm−1). Tunable IR radiation from an OPO is employed to record absorption spectrum of the complex generated in a pulsed supersonic slit jet. The spectrum exhibits broadening and splitting of transitions due to mass dependence of the five Kr isotopes with natural abundances exceeding 2 %. Good simulation of the spectrum is achieved by scaling the vibrational and rotational parameters. This scaling model is particularly important for the combination band involving the intermolecular bending mode where many isotope splittings are observed. As with other CO2‐rare gas complexes, we also observe weak hot bands of CO2‐Kr transitions corresponding to the hot band originating in the CO2 intramolecular bend. From these we determine a splitting of 1.418 cm−1 between the in‐plane and out‐of‐plane bend of CO2, due to the neighboring Kr atom.

Direct FE numerical simulation for dynamic instability of frame structures

Dynamic instability analysis of structures has been a critical issue in the application of engineering and mechanical designs. Can we directly simulate the dynamic stability of structures like buckling analysis in finite element software? To address this question, in this study, we explore the dynamic instability of frame structures, discretized into finite element structures, through developing a direct FE numerical simulation procedure. Benefiting from the advances of eigenvalue analysis of partial differential equations and finite element technology, a direct numerical simulation procedure is developed by using Floquet theorem, harmonic balance methods and finite element method. Dynamic instability characteristics of frame structures, concerning fundamental vibration, multi-mode coupling vibration and flexural-torsional vibration deformation due to their spatial characteristics, are thoroughly investigated. The results reveal that, the developed procedure can achieve dynamic stability analysis of damped and non-damped structures. Frame's flexural-torsional vibration deformation can significantly enlarge the size and instability intensity of unstable regions, threatening dynamic stability of frame structures. Moreover, damping ratio has a slight impact on instability mitigation of the frame induced by flexural-torsional vibration. Unstable regions of mode-coupling vibration of frame have a hidden attribute. No existing approximate formula can be available to estimate instability regions of frame's flexural-torsional vibration and mode-coupling vibration. The dynamic instability index presented here can characterize unstable regions intuitively. The proposed insights can provide design guidelines for frame structures, the developed direct FE simulation procedure may be insightful for extending to explore instability mechanisms of generalized structures with complex forms owing to parametric resonance.

Spectroscopic characterization (IR, UV-Vis), and HOMO-LUMO, MEP, NLO, NBO Analysis and the Antifungal Activity for 4-Bromo-N-(2-nitrophenyl) benzamide; Using DFT Modeling and In silico Molecular Docking

In this study, the density functional theory was used to explore the spectral and electronic properties of the title molecule, as well as a molecular docking technique to evaluate its antifungal activity. The fundamental vibrations were assigned based on the calculated vibrational spectra. The maximum absorption peak in the UV–Visible spectra was detected at 238.165 nm and caused by electronic transitions from HOMO to LUMO+1. The calculated quantum chemical parameters indicated considerable chemical activity, such as a small band gap and high electrophilicity value. The title molecule has a high level of electrophile nature, as revealed by its high electrophilicity value (7.32 eV) and MEP analysis. The third-order NLO polarizability analysis demonstrated significant potential for NLO applications. NBO analysis was conducted to analyze a complete molecular description and intermolecular interactions resulting from hyper-conjugative interactions and charge delocalization of the molecule. The calculated physicochemical properties of Lipinski's rule revealed a favorable character of drug-likeness. The molecular docking study confirmed the strong inhibitory potential (-8.05 Kcal/Mol) for the title molecule against 14α-demethylase, the main target enzyme for antifungal medications. In the reported protein-ligand interaction, the presence of a halogen bond with the bromine atom indicated the halogenated character of the studied molecule. These findings point to a high level of antifungal activity.

Structural and photocatalytic properties and X-ray absorption spectroscopic study of BiVO4 nanoparticles incorporated with Fe synthesized by sonochemical method

In this work, Fe-incorporated BiVO4 nanoparticles with different Fe-loading contents (0–4%) were synthesized via one-step sonochemical process. Crystal structure of all samples was investigated by X-ray diffraction technique (XRD). XRD patterns obviously show the main structure of monoclinic BiVO4 structure. The secondary phase is found in the form of Fe-based oxide as a hematite Fe2O3 phase at for Fe-loading contents ≥ 2%. Relevant chemical bonding of as-synthesized samples was carried out by Raman spectroscopy indicating the fundamental vibration with various vibration modes of VO43− tetrahedron and V–O band, respectively. Morphological structure of pure BiVO4 shows rod-like structure while 1–4%Fe-incorporated BiVO4 display different morphologies. The chemical compositions and oxidation numbers of all elements of the samples were carried out via X-ray photoelectron spectroscopy (XPS). XPS spectra indicate the existence of all elements on their surface and the oxidation states of all elements are clearly scrutinized. Local structure of all samples was investigated to interrogate the local atomic site of Fe atoms by X-ray absorption spectroscopy (XAS). The normalized Fe K-edge XANES spectra of all samples indicate that the local atomic site of Fe atoms would not replace in local sites of either Bi or V sites in BiVO4 crystal verified by simulated XANES spectra. However, the specific features of measured XANES spectra of all samples corresponds to the Fe K-edge XANES spectra of Fe2O3 and BiFeO3 structure suggesting that local structure of all samples are formed to Fe-based oxide between Fe2O3 and BiFeO3 structure. Fitting EXAFS spectra of 1–4%Fe-incorporated were practically conducted by artemis program with Fe2O3 and BiFeO3 used as structural models to identify local atomic environment of Fe atoms. Results show agreeable fitting with their structural models and reveal pertinent information of localization of Fe atoms. Optical properties of the samples were analyzed by UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS). DRS results exhibit the absorption edge in visible range of all samples. Meanwhile, influence of Fe loading contents into pure BiVO4 displays to confirm the red-shift on the absorption edge in visible range to higher wavelength, which suggests the lower optical band gap of pure BiVO4. The optimized photocatalytic degradation of RhB was performed by 4%Fe–BiVO4 with 82% decolorization under visible-light irradiation within 10 min and exhibited rate constant at 0.150 min−1.

The Effect of the Material Periodic Structure on Free Vibrations of Thin Plates with Different Boundary Conditions.

Thin elastic periodic plates are considered in this paper. Since the plates have a microstructure, the effect of its size on behaviour of the plates can play a crucial role. To take into account this effect, the tolerance modelling method is applied. This method allows us to obtain model equations with constant coefficients, which involve terms dependent of the microstructure size. Using the model equations, not only can formulas of fundamental lower-order vibration frequencies be obtained, but also formulas of higher-order vibration frequencies related to the microstructure. In this paper, the effect of the material periodic microstructure on free vibration frequencies for various boundary conditions of the plates was analysed. To obtain proper formulas of frequencies, the Ritz method is applied. Moreover, some results are compared to the results calculated using the FEM.

New Equivalent Circuit of a Cymbal Transducer Incorporating the Third Harmonic Mode of Vibration

A cymbal transducer is composed of a pair of metal caps and a piezoceramic disk. Cymbal transducers arranged in an array exhibit broadband characteristics. Although the finite element method has been widely used for analyzing the transducer and its array, an equivalent circuit that allows efficient analysis was recently developed. However, this previously reported circuit was based solely on the fundamental vibration mode of the transducer, and is thus unsuitable for analyzing the broadband characteristics of the cymbal array. Therefore, to overcome this limitation, a new broadband equivalent circuit for the cymbal transducer was devised in the present study. The new circuit was constructed by incorporating terms related to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{\text {rd}}$ </tex-math></inline-formula> harmonic vibration mode of the cap and corresponding radiation impedance into the existing equivalent circuit. The validity of this novel circuit was verified by comparing the analysis results with those obtained from the measurement of acoustic characteristics exhibited by a cymbal-transducer specimen. Compared with the previous circuit, the new equivalent circuit allows more accurate analysis and design of a cymbal transducer over a wider frequency range.

Dual Band MEMS Directional Acoustic Sensor for Near Resonance Operation.

In this paper, we report on the design and characterization of a microelectromechanical systems (MEMS) directional sensor inspired by the tympana configuration of the parasitic fly Ormia ochracea. The sensor is meant to be operated at resonance and act as a natural filter for the undesirable frequency bands. By means of breaking the symmetry of a pair of coupled bridged membranes, two independent bending vibrational modes can be excited. The electronic output, obtained by the transduction of the vibration to differential capacitance and then voltage through charge amplifiers, can be manipulated to tailor the frequency response of the sensor. Four different frequency characteristics were demonstrated. The sensor exhibits, at resonance, mechanical sensitivity around 6 μm/Pa and electrical sensitivity around 13 V/Pa. The noise was thoroughly characterized, and it was found that the sensor die, rather than the fundamental vibration, induces the predominant part of the noise. The computed average signal-to-noise (SNR) ratio in the pass band is about 91 dB. This result, in combination with an accurate dipole-like directional response, indicates that this type of directional sensor can be designed to exhibit high SNR and selectable frequency responses demanded by different applications.

Energy Landscape and Structural and Spectroscopic Characterization of Diazirine and Its Cyclic Isomers

Identifying new nitrogenated hydrocarbon molecules in the interstellar medium (ISM) is challenging because of the lack of comprehensive spectroscopic data from experiments. In this computational work, we focus on investigating the structures, relative energies, spectroscopic constants, and energy landscape of the cyclic isomers of diazirine (c-CH2N2) using ab initio quantum chemical methods. Density functional theory (DFT) methods and coupled cluster theory with singles and doubles including perturbative triples [CCSD(T)] and CCSD(T) with the explicitly correlated F12b correction [CCSD(T)-F12b] were employed for this purpose along with large correlation consistent cc-pVTZ, cc-pVQZ, and cc-pV5Z basis sets. Harmonic vibrational frequencies, infrared vibrational intensities, rotational constants, and dipole moments are reported. Anharmonic vibrational fundamentals along with centrifugal distortion constants, and vibration-rotation interaction constants are also reported for all the cyclic isomers. The energies computed with the CCSD(T) and CCSD(T)-F12b methods were extrapolated to the one-particle complete basis set (CBS) limit following a three-point formula. At the CCSD(T)-F12b/CBS level of theory, the 3,3H-diazirine (c-CH2N2) is the lowest energy cyclic isomer followed by 1,3H-diazirine, (E)-1,2H-diazirine, and (Z)-1,2H-diazirine, which are 20.1, 47.8, and 51.3 kcal mol-1 above the 3,3H-diazirine, respectively. Accurate structures and spectroscopic constants that are reported here could be useful for future identification of these cyclic nitrogenated organic molecules in the interstellar medium or circumstellar disks.

On the Use of the H/V Spectral Ratio Method to Estimate the Fundamental Frequency of Tailings Dams

ABSTRACT This paper analyses the feasibility of estimating the fundamental frequency of an 85 m high cycloned-sand tailings dam located in the Central-North area of Chile using the single-station H/V Spectral Ratio Method (HVSR), calculated from seismic ambient noise and earthquakes recorded by a temporal seismic array deployed along the embankment crest, the downstream slope, and the dam toe, directly over the foundation soil. The fundamental vibration frequencies obtained from the HVSRs show consistency with results from the Standard Spectral Ratio method (SSR) calculated between the crest and the toe using the available earthquake records, particularly in the dam central part.

Free and forced vibrations of composite cylindrical–cylindrical​ shells with partial bolt loosening connections: Theoretical and experimental investigation

In the present study, the free and forced vibrations of composite cylindrical–cylindrical shells with partial bolt loosening connections are investigated both experimentally and theoretically. Initially, a theoretical model is proposed based on the assumption of primary and secondary connection springs with reduced stiffnesses related to different loosening positions of connection bolts. The equation of motion is derived for predicting the fundamental frequencies, mode shapes, and vibration displacement responses on the basis of the Rayleigh–Ritz method, the Jacobian polynomial approach, the modal superposition technique, etc. To ensure the calculation accuracy of the present model, a convergence study is conducted to determine the truncation number. Also, to give a solid validation of the model, some detailed tests, such as the pulse, sweeping-frequency, and resonant excitations, are conducted on a combined shell specimen, which is obtained by assembling two different composite cylindrical shells via twelve M8 bolts, with a torque wrench being adopted to control the torques in the connection bolts to achieve the desired partial bolt loosening effect. By comparing the calculated and tested results, it can be found that the present model is reliable to predict the structural dynamic parameters because the calculation errors of natural frequencies and resonant displacements are less than 7.4 and 11.9 %, respectively. Finally, the impact of critical bolt loosening parameters on vibration characteristics of the combined shells is evaluated, with some important conclusions being highlighted to illustrate the reduction mechanism of dynamic properties as the partial bolt loosening degree and number increase or the loosening pattern becomes more complex.

Inharmonicity in plucked guitar strings

We have considered the vibration of various types of pinned guitar strings and have investigated the deviation of the partials from integer multiples of the string's fundamental vibration frequency. We measured the inharmonicity parameter B and compared it to a direct calculation based on a model equation. We generally found very good agreement between the two determinations of B for monofilament strings, but perhaps not surprisingly, we find rather poor agreement for wound strings. Furthermore, we show that the methodology used to carry out this experiment can easily serve as the basis for an upper division physics laboratory on physical acoustics including a more thorough investigation of the classical wave equation in a real-world application.

An indirect method to determine nonlinearly elastic shear stress-strain constitutive relationships for nonlinear torsional vibration of nonlinearly elastic shafts

PurposeIn this paper, the authors aim to propose an effective method to indirectly determine nonlinear elastic shear stress-strain constitutive relationships for nonlinear elasticity materials, and then study the nonlinear free torsional vibration of Al–1%Si shaft.Design/methodology/approachIn this study the authors use BoxLucas1 model to fit the determined-experimentally nonlinear elastic normal stress–strain constitutive relationship curve of Al–1%Si, a typical case of isotropic nonlinear elasticity materials, and then derive its nonlinear shear stress-strain constitutive relationships based on the fitting constitutive relationships and general equations of plane-stress and plane-strain transformation. Hamilton’s principle is utilized to gain nonlinear governing equation and boundary conditions for free torsional vibration of Al–1%Si shaft. Differential quadrature method and an iterative algorithm are employed to numerically solve the gained equations of motion.Findings The effect of four variables, namely dimensionless fundamental vibration amplitude , radius and length , and nonlinear-elasticity intensity factor , on frequencies and mode shapes of the shafts is obtained. Numerical results are in good agreement with reference solutions, and show that compared with linearly elastic shear stress-strain constitutive relationships of the shafts made of the nonlinear elasticity materials, its actual nonlinearly elastic shear stress-strain constitutive relationships have smaller torsion frequencies. In addition, but having opposite hardening effect, the rest of the four variables have softening effect on nonlinearly elastic torsion frequencies. Eventually, taking into account nonlinearly elastic shear stress-strain constitutive relationships, changes of the four factors, i.e. , , and , cause inflation and deflation behaviors of mode shapes in nonlinear free torsional vibration.Originality/valueThe study could provide a reference for indirectly determining nonlinear elastic shear stress-strain constitutive relationships for nonlinear elasticity materials and for structure design of torsional shaft made of nonlinear elasticity materials.

Use of Artificial Neural Networks and Response Surface Methodology for Evaluating the Reliability Index of Steel Wind Towers

The estimation of structural reliability is a process that requires a large number of computational hours when statistical data are not available since it is necessary to perform a large amount of analysis or numerical simulations to estimate parameters related to the reliability. A methodology is proposed for estimating the structural reliability index, as well as the demand and structural capacity factors inherent to the structure, given the fundamental vibration period and the height of the structure, by using artificial neural networks (ANN) and, alternatively, the response surface method (RSM). Both approaches are applied to steel wind turbine towers. For the cases studied, ANN allow evaluating the reliability index and both the demand and structural capacity factors with greater accuracy than when using RSM.

DFT simulation of barrier heights, infrared and Raman spectra, and investigation of vibrational characteristics of 2-((2-aminopyridin-3-yl) methylene) hydrazinecarbothioamide and its N-methyl variant

ABSTRACT Fourier transform infrared spectra, for 2-((2-aminopyridin-3-yl) methylene) hydrazinecarbothioamide (APHT) and 2((2-aminopyridin-3-yl) methylene)-N-methylhydrazinecarbothioamide (APMHT), were recorded in the spectral range 4000–400 cm−1. Their Raman counterparts were measured in the spectral region 4000–50 cm−1. Preliminary values of dihedral angles around five rotating bonds C–NH2 pyridyl C–CN, N–N, N–CS and C–NH2 aliphatic in APHT, required for initiating geometry optimization, were obtained by pairing successive bonds and evaluating torsional potential energy for various values of dihedral angle around these bonds in the entire conformational space spanning 0° to 360°. Barrier heights, around five rotating bonds in APHT and six rotating bonds in APMHT were computed, making torsional scans in conformational space from 0° to 360°. This indicated existence of two rotational isomers for APMHT. General valence force field, harmonic vibrational fundamentals, potential energy distribution (PED), along with infrared and Raman intensities were determined using DFT/B3LYP/6-311++G(d,p) level of theory for both the molecules. Good agreement was found between measured and simulated spectra, for APHT and APMHT. This was also true for corresponding Raman spectra. The rms error between experimental and theoretical vibrational frequencies was 9.00 and 6.70 cm−1, for APHT and APMHT, respectively. All vibrational fundamentals were assigned unambiguously, on the basis of computed PED, eigenvectors, and literature range for the first time. These assignments were further supported by comparing with attribution of corresponding bonds in the parent molecule pyridine and a related molecule 2-((2-aminopyridin-3-yl)methylene)-N-ethylhydrazinecarbothioamide, wherever possible.

High cycle fatigue performance evaluation of a laser powder bed fusion manufactured Ti-6Al-4V bracket for aero-engine applications

Due to the stringent certification requirements and complex engine operating environment, the design of AM components for aero-engine application remains a challenging task. The high cycle fatigue performance of a weight-optimised bracket made using the Laser Powder Bed Fusion (LPBF) process was studied through shaker table testing. The results are discussed together with the observed mechanical and fatigue strengths in conjunction with material characterisation of microstructure, surface roughness, defects, micro-hardness and fracture surfaces. The debits in mechanical and fatigue strengths are expected due to process dependent surface roughness and the density of defects present. From the shaker table test results, it was concluded that the proposed weight-optimised LPBF bracket is capable of meeting the performance targets. The fundamental vibration mode of the bracket assembly was 84 Hz, which was much higher than the 1st Low Pressure shaft speed (48 Hz) of the target engine and thus avoids potential resonance. The bracket achieved its target inertial g load capability of 20 g and it was demonstrated that the bracket had enough redundancy in its load transfer paths should a strut fail during service of the engine. Lack of fusion voids and micro-cracks present on or near the surface were the prime sites for crack initiation. It has been shown that the as-built surface can cause a significant reduction (up to 40%) in the fatigue strength when compared to machined Ti-6Al-4V. A safe life regime for LPBF component design has been presented based on the Kitagawa-Takahasi diagram, modified using the Chapetti curve, which effectively links the material fatigue properties and performance of LPBF parts with intrinsic defects.

Comparison of Computational and Previous Experimental Studies on Naphthyl Pyridyl Pyrazole (NPP)

The naphthyl pyridyl pyrazole (NPP) was the subject of a theoretical inquiry. The data determined through the calculations were supported by experimental results from 1HNMR and X-Ray techniques. Geometrical parameters and optimized energies for the NPP molecule were determined via density functional theory (DFT) at the B3LYP 6-311++G (d, p) level of theory. The vibrational spectra were obtained and the fundamental vibrations were assigned. 1HNMR chemical shifts were recorded by using the gauge-invariant atomic orbital (GIAO) method. Further, electronic properties such as HOMO and LUMO energies were determined via time-dependent density functional theory (TD-DFT). The results of the calculations were found to be comparable to the experimental results obtained.

Synthesis, characterization, vibrational analysis and computational studies of a new Schiff base from pentafluoro benzaldehyde and sulfanilamide

This work presents the characterization of (E)-4-(((perfluorophenyl)methylene)amino)benzenesulfonamide (PFNI) by spectral techniques and quantum chemical calculations. The structure was investigated by FT-IR, UV–Vis and NMR techniques. The geometrical parameters and energies have been obtained from Density functional theory (DFT) B3LYP (cc-pVDZ) basis set calculation. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of potential energy distribution (PED) of the vibrational modes, calculated with VEDA program. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge-independent atomic orbital method (GIAO). The electronic properties such as excitation energies, wavelength performed by Time dependent density functional theory (TD-DFT) results complements with the experimental findings. NBO analysis has been performed for analyzing charge delocalization throughout the molecule. The calculation results were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. To provide information about the interactions between staphylococcus aureus (4EMW) protein and the novel compound theoretically, docking studies were carried out using autodock-4.

Vibrational (Infrared, Raman) and Thermogravimetric Study of Copper Ore from the Deposit at Tchirozerine, Agadez (Niger)

Agadez is the mining region of the republic of Niger in which all kinds of ore are found. Copper would have been exploited and refined in Niger in the 15th century in the province of Azelik, region of Agadez. In this context, it is important to use mew techniques to characterize the mineralogical variability of copper ore. The collected sample was analyzed by X-ray diffraction, Thermogravimetric analysis and spectroscopies (infrared and Raman). The results of the X-ray diffraction of the ore show that the sample corresponds to an association between brochantite and biotite, dominated by brochantite. The thermogravimetric analysis indicates that the sample was stable up to 200°C and above this temperature, the solid decomposed in a series of three decomposition stages. Raman and infrared spectroscopies show the fundamental vibration of sulfate ion which functioning as a unidentate because the effective symmetry is lowered to C3v. &nbsp;

Refinement of the Voigt's hypothesis with respect to copper and latten brass

According to the Voigt’s hypothesis, the coefficient of internal friction of metals is considered to be frequency independent. As a result of experiments with rod specimens made of copper and latten brass, it was found that the coefficient of internal friction decreases according to the hyperbolic law with increasing frequency of the fundamental vibration. Keywords: Voigt's hypothesis, internal friction, vibration strength, copper, latten brass. aktomilin@tpu.ru, kuznetsov@mail.ru, ivkon@tpu.ru, iskonovalenko@tpu.ru

Structural dynamic properties of reinforced concrete tunnel form system buildings

Tunnel form buildings refer to reinforced concrete structures constructed using the tunnel formwork system, which results in a repetitive concrete cellular structure composed only of walls and flat slabs. This widespread low-cost and robust system reaches its popularity for residential buildings in the 70 s and 80 s of the last century. At the time of their design, a 3D finite element analysis has not been conducted. The seismic design relied on building codes that provide approximate fundamental period formula, which commonly depends on structural system type (shear wall, frame), material (steel, reinforced concrete), and the building height. Based on the existing RC tall buildings, both modeling and vibration measurements were carried out to provide a detailed case study as well as to increase the knowledge base of existing buildings frequencies of vibration. The fundamental vibration period obtained from numerical analyses of three real reinforced concrete shear walls buildings (RCSW) located in the Croatian city Osijek, were compared with values obtained using the formulas in the European code EN1998-1:2004 (CEN 2004) and other available literature. Numerical modeling is performed using SAP2000 software. The objectives of the article are experimental identification of the dynamic characteristics (mainly natural frequency) of existing Tunnel form buildings, as well as comparison with values obtained by approximate formulas and a detailed structural model. The results of this study showed a very good agreement between the numerical 3D model and the experimental campaign conducted with the usage of ambient testing. Nevertheless, a serious question arises regarding the confidence of proposed empirical formulas provided in the codes and standards which may lead to imprecise and false results.