Vibrational Frequency Analysis Research Articles

Experimental Dynamic Analysis on a T100 Microturbine Connected With Different Volume Sizes

This paper shows experimental results obtained from a T100 microturbine connected with different volume sizes. The activity was carried out with the test rig developed at the University of Genoa for hybrid system emulation. However, these results apply to all the advanced cycles where a microturbine is connected with an additional external component responsible for volume size increase. Even if the tests were performed with a microturbine, similar analyses can be extended to large size turbines. A modular vessel was used to perform and to compare the tests with different volume sizes. To highlight the volume size effect, preliminary experimental results were carried out considering the transient response due to an on/off bleed valve operation. So, the main differences between system parameters obtained for a bleed line closing operation are compared considering three different volume sizes. The main results reported in this paper are related to surge operations. To produce surge conditions in this test rig, a valve operating in the main air path was closed to generate unstable behavior for the three different volume sizes. Particular focus was devoted to the operational curve plotted on the compressor map. The vibration frequency analysis showed significant amplitude increase not only during surge events but also close to the unstable condition. In details, possible surge precursor indicators were obtained to be used for the detection of risky machine operations. The experimental data collected during these tests are analyzed with the objective of designing control systems to prevent surge conditions.

Excitation device for high frequency vibration analysis: Design and test results

In the present paper, the design and optimization of a high frequency excitation source is presented. The device was developed for a harmonic response analysis test bench, aimed at dynamic characterization and resonance prediction of mechanical structures. A wide frequency range must be covered, depending on the analyzed structure: the range 1–10 kHz was considered in the present work. The device was designed for a test bench aimed at investigating the vibrational response of centrifugal compressor bladed wheels. A really compact solution was needed since the final test bench provides one exciter for each blade (up to 20 devices on the circumference hoop). Both contact and contactless solutions were considered, but only the contact solution was found to fulfill all the specifications. Finally, different stinger solutions were proposed and compared in the paper. The investigated solutions were: a beam stinger (diameter 1 mm); a wire stinger (diameter 0.2 mm); and a ball stinger (diameter 3 mm) with two different support solutions. Experimental tests performed on a device prototype allowed to verify the specifications fulfillment and to choose the best stinger solution for the application.

Dynamic behaviour and seismic design method of a single-layer reticulated shell with semi-rigid joints

Most of the existing studies on reticulated shells with a semi-rigid joint system have been focused on the mechanical properties under static loads. Taking material and geometric nonlinearities into account, the finite element analysis (FEA) model of a single-layer reticulated shell with semi-rigid joints was established using the software ABAQUS and then validated through comparison with the experimental result. Based on the bending stiffness of a bolt-column (BC) joint obtained through experiments, the dynamic behaviour and a seismic design method for single-layer reticulated shells with semi-rigid joints were investigated in this paper. First, analysis of the free vibration frequency of the single-layer latticed domes with semi-rigid bolt-column (BC) joints was conducted based on several different parameters, including joint stiffness, ratio of rise to span, initial geometric imperfection. Second, the seismic internal force coefficient of the members of the semi-rigidly jointed spherical single-layer reticulated shells of different parameters was studied in detail. Finally, the seismic internal force coefficients for spherical single-layer reticulated shells with semi-rigid joints under a common earthquake were derived.

Experimental and numerical analysis of vibration frequency in sandwich composites with different radii of curvature

In this study, free vibration responses of sandwich composite panels with different radius of curvature were presented numerically. The studies were carried out on square flat and curved sandwich panels made of E-glass/epoxy face sheets and polyvinyl chloride foam with three different radii of curvature. Experimental studies were used to verify the numerical results. Vibration tests were performed on flat and curved sandwich panels under free–free boundary conditions. The experimental data were then compared with finite element simulation, which was conducted by ANSYS finite element software and it was shown that the numerical analysis results agree well with the experimental ones. Effect of the curvature on natural frequencies under different boundary conditions (all edge free, simply supported, and fully clamped) was investigated numerically. Results indicated that the natural frequencies and corresponding mode shapes were affected by boundary conditions and curvature of the panel. For all boundary conditions, the variation of curvature had smaller effect on the natural frequency of the first mode than those of the other modes.

Comparison of hydrogen- and halogen-bonding interactions in the complexes of the substituted carbonyl compounds with hypohalous acids and monohaloamines

An ab initio study of the complexes formed by hypohalous acids and monohaloamines (designated as HAX where A = O or NH and X = Cl, Br, or I) with RCHO (R = H, CH3, OCH3, and NH2) carbonyl compounds has been carried out at the MP2/aug-cc-pVTZ computational level for comparative study on hydrogen bonds with halogen bonds. Two types of complexes are formed by their combination –RCHO···HAX and RCHO···XAH (A = O or NH) named as hydrogen-bonded and halogen-bonded, respectively, although other weak interactions also coexist in both types of complexes. Analysis of the BSSE-corrected interaction energies reveals that hydrogen bond strength decreases with an increase in size of X atom (i.e., HACl > HABr > HAI) while reverse trend is indicated for halogen-bonded complexes (HACl < HABr < HAI). For the carbonyl compounds, the interaction energies for both hydrogen- and halogen-bonded complexes follow the same order of HCHO < CH3CHO < (CH3O)CHO < (H2N)CHO. Vibrational frequency analysis suggests that both the H-O and H-N bonds are red-shifted while C–H bonds are blue-shifted in hydrogen-bonded complexes. Similarly, the X-O/X-N and C-H bonds are red- and blue-shifted respectively in halogen-bonded; however, the magnitude of red shift for X-O and X-N bonds in halogen-bonded complexes is much smaller than that of H-O and H-N bonds in hydrogen-bonded complexes. The MEP, NBO, and AIMALL methods have been utilized to understand structure, properties, and nature of the interaction stabilizing these two types of the complexes. Relationship of the interaction energies with MEP, charge transfer (CT), and change in % s character obtained from NBO analysis is also drawn for both complexes.

Vibrational frequency analysis of finite elastic tube filled with compressible viscous fluid

The vibrational frequency analysis of finite elastic tube filled with compressible viscous fluid has received plenty of attention in recent years. To apply frequency analysis to defect detection for example, it is necessary to investigate the vibrational behavior under appropriate boundary conditions. In this paper, we present a detailed theoretical study of the three dimensional modal analysis of compressible fluid within an elastic cylinder. The dispersion equations of flexural, torsional and longitudinal modes are derived by elastodynamic theory and the unsteady Stokes equation. The symbolic software Mathematica is used in order to find the coupled vibration frequencies. The dispersion equation is deduced and analytically solved. The finite element results are compared with the present method for validation and an acceptable match between them are obtained.

A systematic investigation on the structure, energy, aromaticity, and stability of substituted X5Y5C10 nanocages (X=B, Al, Ga, and Y=N, P, As)

AbstractDensity functional theory (DFT) calculations are applied to devise highly doped Cs symmetry X5Y5C10 (X=B, Al, Ga, and Y=N, P, As) heterofullerenes where the substituents are completely linked to each other by means of strong X–Y bonds in equatorial position. The structural stabilities, geometry, and electronic properties of these systems are compared and contrasted at the B3LYP/AUG‐cc‐pVTZ, B3LYP/6‐311++G**, B3LYP/6‐311+G*, and B3PW91/6‐311+G* computational levels. Vibrational frequency analysis confirms that all of these nonsegregated nanocages are real minima. B5N5C10 immerges with the highest HOMO‐LUMO energy separation (2.18 eV). Hence, it is predicted to be the most chemically stable against electronic excitation. In contrast, Al5N5C10 that appears with the narrowest band gaps (1.13 eV), the highest conductivity, and the most charge transfer is the best candidate for hydrogen storage. Assuming the heat of atomization, B5N5C10 is expected to be the most thermodynamically stable heterofullerene. The nucleus‐independent chemical shift calculations at cage center and 1 Å above the cage center are exhibited the most negative value of NICS (0), NICS (1) (−28.08 and −37.80 ppm, respectively) and the most aromaticity for Ga5N5C10 heterofullerene.

An integrated theoretical and experimental investigation of insensitive munition compounds adsorption on cellulose, cellulose triacetate, chitin and chitosan surfaces

This manuscript reports results of combined computational chemistry and batch adsorption investigation of insensitive munition compounds, 2,4-dinitroanisole (DNAN), triaminotrinitrobenzene (TATB), 1,1-diamino-2,2-dinitroethene (FOX-7) and nitroguanidine (NQ), and traditional munition compound 2,4,6-trinitrotoluene (TNT) on the surfaces of cellulose, cellulose triacetate, chitin and chitosan biopolymers. Cellulose, cellulose triacetate, chitin and chitosan were modeled as trimeric form of the linear chain of 4C1 chair conformation of β-d-glucopyranos, its triacetate form, β-N-acetylglucosamine and D-glucosamine, respectively, in the 1➔4 linkage. Geometries were optimized at the M062X functional level of the density functional theory (DFT) using the 6-31G(d,p) basis set in the gas phase and in the bulk water solution using the conductor-like polarizable continuum model (CPCM) approach. The nature of potential energy surfaces of the optimized geometries were ascertained through the harmonic vibrational frequency analysis. The basis set superposition error (BSSE) corrected interaction energies were obtained using the 6-311G(d,p) basis set at the same theoretical level. The computed BSSE in the gas phase was used to correct interaction energy in the bulk water solution. Computed and experimental results regarding the ability of considered surfaces in adsorbing the insensitive munitions compounds are discussed.

The vibration frequency analysis of the screw feeding system with spring supports

Ball screw feeding system has wide application in machine tools, and its dynamic research is very important. The drive screw can be seen as a rotating Timoshenko beam under the pre-tension force. Considering the bearing stiffness, the boundary condition of the screw is spring supported. Also, considering the contact deformation between the screw and the worktable and the worktable moving, the screw is added an intermediate moving spring-mass system. Using boundary conditions and continuity conditions, the lateral and longitudinal frequency equations of the screw feeding system are derived considering the effect of gyroscope, the pre-tension force, the bearing stiffness, the contact between the worktable and the screw and the moving of the worktable. The effect of the system parameters on the natural frequency is studied. The diameter, the pre-tension force, the bearing stiffness, the contact stiffness and the rotational speed of the screw have effect on the vibration frequency and the frequency varies when the worktable moves along the screw from the left to the right end. This work supplies a base for designing the drive system to avoid resonance and to improve the stability of the system.

Study on collision of threaded connection during impact

For the threaded connection, elastic model and collision model were established. According to elastic deflection of thread, the axial load distribution of thread was determined and the stiffness of threaded connection was calculated. Meanwhile, collision model for threaded connection was proposed, and the calculation methods of collision time and collision force were given. Through tensile tests of threaded connections and impact experiments of projectiles penetrating into concrete targets, thread stiffness and deceleration data were obtained respectively. At the same time, finite element model were created to study the collision process on the interface of threaded connection between projectile and fuze. In order to obtain the time-frequency characteristic of deceleration, the wavelet analysis for measured deceleration and the vibration frequency analysis for projectile and fuze were conducted. The good agreement among the calculation value, finite element analysis and experiment data proved that the thread collision between projectile and fuze really exist and have very serious influence for the measured deceleration.

Research on Variable Preload Device for Spindle Bearing by Piezoelectric Actuators

The bearing preload has significant influence on dynamic performance of motorized spindle. The dynamic performance and the life of bearing can be significant improve if the bearing preload can change according to the different conditions. The main purpose of this paper is to calculate the minimum bearing preload to prevent gyroscopic rotation and study the natural frequency and mode analysis of spindle vibration. Perform the experiments of variable bearing preload device based on piezoelectric actuators. Research the mechanical characteristic of piezoelectric actuators. Providing theory for improving the performance of the motorized spindle by controlling the bearing preload .

Finite element analysis for structural modification and control resonance of a vertical pump

The main objective of this research was to evaluate and enhance dynamic performance for a vertical pumping unit. The original electric motor of the pump unit had been replaced by another one different in design and weights. Vibration has been increased greatly after installing the new motor. Consequently, it is necessary to estimate the change in the vibration characteristics owing to the difference in the boundary conditions of the new motor. Measured vibration levels and frequency analysis were dangerous at 1× due to resonance problem. Finite Element Analysis was used to model the motor structure in order to find its natural frequencies and mode shapes. The results confirm that the third natural frequency is very close to 1× operating speed with deviation about 1%. To solve the resonance problem, it was recommended to increase the structure stiffness. The results after modifications confirmed that the overall vibration level decreases by 89%.

Au20Si12: A hollow Catalan pentakis dodecahedron

A stable hollow Au20Si12 cage with Ih symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au20Si12 structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au20Si12 cage. The cage-like Au20Si12 structure may have potential applications in semiconductor industry and microelectronics.

Modal analysis of dislocation vibration and reaction attempt frequency

Transition state theory is a fundamental approach for temporal coarse-graining. It estimates the reaction rate for a transition processes by quantifying the activation free energy and attempt frequency for the unit process. To calculate the transition rate of a gliding dislocation, the attempt frequency is often obtained from line tension estimates of dislocation vibrations, a highly simplified model of dislocation behavior. This work revisits the calculation of attempt frequency for a dislocation bypassing an obstacle, in this case a self-interstitial atom (SIA) loop. First, a direct calculation of the vibrational characteristics of a finite pinned dislocation segment is compared to line tension estimates before moving to the more complex case of dislocation-obstacle bypass. The entropic factor associated with the attempt frequency is calculated for a finite dislocation segment and for an infinite glide dislocation interacting with an SIA loop. It is found to be dislocation length independent for three cases of dislocation-self interstitial atom (SIA) loop interactions.

Hexacarbonyls of Mo, W, and Sg: Metal-CO Bonding Revisited.

Calculations of the first bond dissociation energies (FBDEs) and other molecular properties of M(CO)6, where M = Mo, W, and Sg, have been performed using a variety of nonrelativistic and relativistic methods, such as ZORA-DFT, X2c+AMFI-CCSD(T), and Dirac-Coulomb density functional theory. The aim of the study is to assist experiments on the measurements of the FBDE of Sg(CO)6. We have found that, different from the results published earlier, the metal-CO bond in Sg(CO)6 should be weaker than that in W(CO)6. A comparison of the relativistic and nonrelativistic FBDE values, as well as molecular orbital and vibrational frequency analyses within both the nonrelativistic and relativistic approaches, have shown that this is a relativistic, predominantly scalar, effect causing weaker d(M) → π(CO) back-bonding in Sg(CO)6 than in the lighter homologues. Good agreement between the calculated FBDEs in this work and the experimental FBDEs for the Mo and W compounds gives credit to the present FBDE of Sg(CO)6, which should serve as guidance for ongoing experiments.

Using technique vibration diagnostics for assessing the quality of power transmission line supports repairs

The considered method for assessing the quality of the repair work to restore the rack supports of transmission lines is based on the method of vibration diagnostics. Power transmission line supports with a symmetrical destruction of the protective layer of concrete in the ground in violation of the construction section were chosen as an object. Finite element modelling package Ansys was used in assessing the quality of repair work. The example of evaluating the quality of repair using the relative adhesion defective area design criteria in the analysis of natural vibration frequencies is given.

Finite Element Analysis and Optimal Design for the Frame of SX360 Dump Trucks

As bearing foundations of autos, the frame bears various forces and torques transmitted from engine, clutch, body, and cargo container. Analysis of natural vibration frequency and dynamic mode of the frame is an important process to ensure operating capabilities of autos. It is hard to yield accurate analysis results with traditional methods. However, the FEA software ABAQUS can provide accurate frame stress distributions, frame deflection laws at its two ends and the middle point, and transient frame dynamics. Most of previous finite element analysis only focused on frame mass and model optimization analysis, lacking of vibration and mode analysis. In this paper the large-scale software ABAQUS was used to analyze the natural vibration frequency and dynamic mode of the frame of SX360 dump trucks, providing necessary theoretic basis for optimal design of the frame.

Electronic and Optical Properties of VSc2N@C68 Fullerene

We report a detailed investigation of structural, electronic, and spectroscopic properties of VSc2N@C68 endohedral fullerene. First, the candidate structures of the ground state are obtained using a systematic approach in which 900 isomers of endohedral fullerenes were screened for their energetic stability. The stability of some of the most promising isomers was studied using density functional theory at the all-electron level using large polarized Gaussian basis sets. Although the dopant vanadium atom is also in the same charge state as Sc, the doping changes the structure and the spin state from that of Sc3N@C68. The d-orbitals of the V atom lead to a spin state with spin moment of 2 μB for the endohedral fullerene. The spin–orbit coupling strength is, however, weak, leading to vanishingly small zero-field splitting of the spin levels. The ionization energy, electron affinity, and the quasi-particle gap of the most stable isomer are comparable to those of C60. The vibrational frequency analysis shows t...

Defect-caused alteration of a composite unit modal parameters

Abstract This paper presents research on diagnostic parameters for monitoring conditions of a light aircraft engine blade made of composite materials (CM) in flight. This study covers the modal parameters investigation of the blades in the frequency range of 30–60 Hz. Using the Doppler Effect the vibration response between the used blades and a new blade was compared. The used blades demonstrated a fourfold increase in amplitude of resonant vibration in the first bending mode. The amplitude growth of the first bending mode resonant vibration can be used as a diagnostic sign of emerging defects. The ease of amplitude and frequency analysis of a blade resonant vibration in flight conditions will allow researchers to develop an express-control device for technical condition analysis of CM blades while in air.

Observations of vibration velocity on wind turbine with propagated sound to surroundings

The authors newly tried measurements of the excited vibration on many parts of wind turbine such as outside surface of nacelle storing power generation system and tall tower by using a laser Doppler vibration meter. Observation and analysis of the natural vibration frequencies of blade in the stopping were done. Observations on sound in surroundings of wind turbine were also done. FFT analyses on them with high resolution to obtain detailed frequency characteristics and to know the relations between vibration velocity and propagated sound to surroundings were done in addition to ordinal spectral analyses. Sharp spectra at near 1 Hz as slightly lower or higher were appeared in the analysed results on blade and tower. In both the analyzed results of vibration velocity on wind turbine and propagated sound, a lot of sharp spectral peaks were recognized in wide frequency range from very low frequency to several hundreds of hertz with high coherencies between vibration velocity and propagated sound at their peak spectral frequencies. Certain values of coherency were remained even for the case of sound received in about 200 m distant from a wind turbine. These observed results would be effective for understanding key parts to make sound radiation lower.