Frequency Spectrum Of Vibrations Research Articles

Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis

This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.

Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis

This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.

Z변환을 이용한 시간영역에서의 승차감 평가

철도차량의 승차감은 승객이 느끼는 감정이므로 물리적인 진동의 크기뿐만 아니라 인간의 감응도(느낌)도 고려하여야 하며, 이러한 진동에 대한 인간의 감응도를 나타낸 것이 주파수 보정곡선이다. 주파수 보정곡선은 라플라스 변환형태의 전달함수이기 때문에 이 전달함수를 직접 사용하여 시간 영역에서의 승차감의 평가가 불가능하다. 이를 해결하기 위해서 본 논문에서는 라플라스 변환형태의 전달함수를 시간 영역에서 사용할 수 있는 전달함수로 변환하는 방법을 제시하고 다양한 예제를 통해 이 방법에 대한 타당성을 입증하였다. In evaluating the ride comfort of railway vehicles, relationship between passenger's feeling and vibration characteristics is very important because human feeling is dependent on frequency spectrum of vibration. Therefore, the weighing curves in frequency domain are used to evaluate the ride comfort of railway vehicles. These curves have been defined in the Laplace transfer functions. It is necessary to convert the Laplace weighing function to the z weighing function in order to obtain the rms value in the time domain. In the present paper, we have applied Tustin's approximation to transform the Laplace weighing function to the z weighing and validated this method by reviewing the various cases.

Nonlinear vibrations and heating phenomena of cracks in metal plates excited by intensive ultrasonic pulses.

When thin metal plates are excited by intensive ultrasonic pulses, nonlinear vibration phenomena are observed in experiments. As the plates contain cracks, the frictional heating of both faces of the crack appears under the excitation of the ultrasonic pulses. Based on the experimental conditions, a finite element modeling is established and transient dynamic analyzes are performed to explore the generation mechanism of the nonlinear vibrations including superharmonics, subharmonics, and chaotics, as well as the heating phenomena of the cracks. A piezoelectric‐thermal analogy method is used to simulate the high‐power ultrasonic transducer excitation, and a contact‐impact algorithm is used to simulate the dynamical interaction between the ultrasonic horn and plate as well as between both sides of the cracks. By analyzing the vibration velocity waveforms, vibration frequency spectra, and contact force waveform, it can be found that the waveform distortion of the intermittent contact forces between the horn ...

Neural Network–Based Intelligent Compaction Analyzer for Estimating Compaction Quality of Hot Asphalt Mixes

Continuous real-time estimating of compaction quality during the construction of a hot mix asphalt (HMA) pavement is addressed in this paper. The densification of asphalt pavements during construction usually is accomplished by using vibratory compactors. During compaction, the compactor and the asphalt mat form a coupled system whose dynamics are influenced by the changing stiffness of the mat. The measured vibrations of the compactor along with process parameters such as lift thickness, mix type, mix temperature, and compaction pressure can be used to predict the asphalt mat density. Contrary to existing techniques in the literature in which a model is developed to fit experimental data and to predict mat density, a neural network-based approach is adopted that is model-free and uses pattern-recognition techniques to estimate density. The neural network is designed to read the entire frequency spectrum of roller vibrations and to classify these vibrations into different levels. The intelligent asphalt c...

Dependence of the frequency spectrum of small amplitude vibrations superimposed on finite deformations of a nonlinear, cylindrical elastic body on residual stress

We model and analyze the response of nonlinear, residually stressed elastic bodies subjected to small amplitude vibrations superimposed upon large deformations. The problem derives from modeling the use of intravascular ultrasound (IVUS) imaging to interrogate atherosclerotic plaques in vivo in large arteries. The goal of this investigation is twofold: (i) introduce a modeling framework for residual stress that unlike traditional Fung type classical opening angle models may be used for a diseased artery, and (ii) investigate the sensitivity of the spectra of small amplitude high frequency time harmonic vibrations superimposed on a large deformation to the details of the residual stress stored in arteries through a numerical simulation using physiologic parameter values under both low and high blood pressure loadings. The modeling framework also points the way towards an inverse problem using IVUS techniques to estimate residual stress in healthy and diseased arteries.

A Method of Measurement and Monitoring to the Train's Vibration Frequency Spectrum-Varying Fault

In condition monitoring of train, because of load change, speed fluctuation and other effect factors, it may cause vibration frequency spectrum migration. If using the common vibration signal acquisition and spectral analysis method to this fault, there will be a result of characteristic spectral smearing, which will lead to misdiagnosis or missed diagnosis. To solve this problem, the vibration mechanism of spectrum-varying fault was discussed. This paper studies a pulse-triggered sampling method of integral periodic signal, the equal angle re-sampling method and other appropriate signal processing method. The feasibility and validity of this method and technology has been verified by the application in Liuzhou Railway Bureau .

Torsional Vibrations Caused by Geared Coupling in a Shaft Train Driven by a Steam Turbine

Rotating machines that include geared shaft-trains can be affected by a dynamic behavior that is influenced by coupling effects between lateral and torsional vibrations. These latter vibrations are rarely measured by means of permanent probes in industrial machines; therefore, these phenomena can be often pointed out only by detecting abnormal harmonic components in the frequency spectrum of the lateral vibrations measured during common monitoring activities. Then, the diagnosis of the occurrence of coupling effects between torsional and lateral vibrations can be supported by the results provided by model-based techniques. In this paper, the results of the analysis of the dynamic behavior of a small power unit that was affected by abnormal lateral vibrations caused by the excitation of torsional normal modes of the geared shaft-train are shown and discussed.

The Influence of Ethanol–Gasoline Blends on Spark Ignition Engine Vibration Characteristics and Noise Emissions

Engine vibration characteristics and noise emission of a two stroke spark ignition engine were investigated by using blends of ethanol–gasoline–oil (25% E–70% G–5% O and 50% E–45% G–5% O) and pure gasoline. Engine test conditions were 0.86 kW (5.5 Nm) at 1,500 rpm, 1.25 kW (6.0 Nm) at 2,000 rpm, and 1.83 kW (7.0 Nm) at 2,500 rpm. A high sensitivity electronic vibration analysis system was used for measurement of frequency spectrum of the spark ignition engine vibration. Higher octane number, lower sulphur content, and higher oxygen content were important advantages of blend fuels. Experiment results indicated that when the blend fuels were used, vibration characteristics of the engine changed significantly at 1,500 and 2,500 rpm. In general, in comparison with gasoline, vibration amplitudes and noise emission of the engine with the blend fuels showed a trend of increasing. These results are probably due to oxygen content and higher latent heat of evaporation of ethanol, in which the increasing rate of pressure (dp/dt) and peak pressure values in the cylinder rise during the combustion processes. There was a relation between vibration and noise emissions, due to the increasing trend of them at the same test condition.

Some dynamics problems of monocrystalline turbine blades

Consideration is given to general problems for providing the dynamic strength of monocrystalline gas-turbine blades which are caused by anisotropy of the material and manufacturing deviations of the directions of crystallographic axes, specifically, features of the vibration frequency spectrum of blades and detuning frequencies from resonances, role of the slip system in a crystal on the evaluation of fatigue damage, analysis of data of fatigue tests and strain measurement, and a rational approach to evaluation of the margin of the fatigue strength of blades by maximum tangential stresses.

Investigations of Low-Frequency Vibrational Dynamics and Ligand Binding Kinetics of Cystathionine β-Synthase

Vibrational coherence spectroscopy is used to study the low frequency dynamics of the truncated dimer of human cystathionine beta-synthase (CBS). CBS is a pyridoxal-5'-phosphate-dependent heme enzyme with cysteine and histidine axial ligands that catalyzes the condensation of serine and homocysteine to form cystathionine. A strong correlation between the "detuned" coherence spectrum (which probes higher frequencies) and the Raman spectrum is demonstrated, and a rich pattern of modes below 200 cm(-1) is revealed. Normal coordinate structural decomposition (NSD) of the ferric CBS crystal structure predicts the enhancement of normal modes with significant heme "doming", "ruffling", and "saddling" content, and they are observed in the coherence spectra near approximately 40, approximately 60, and approximately 90 cm(-1). When pH is varied, the relative intensities and frequencies of the low frequency heme modes indicate the presence of a unique protein-induced heme structural perturbation near pH 7 that differs from what is observed at higher or lower pH. For ferric CBS, we observe a new mode near approximately 25 cm(-1), possibly involving the response of the protein, which exhibits a phase jump of approximately pi for excitation on the blue and red side of the Soret band maximum. The low frequency vibrational coherence spectrum of ferrous CBS is also presented, along with our efforts to probe its NO-bound complex. The CO geminate rebinding kinetics of CBS are similar to the CO-bound form of the gene activator protein CooA, but with the appearance of a significant additional kinetic inhomogeneity. Analysis of this inhomogeneity suggests that it arises from the two subunits of CBS and leads to a factor of approximately 20 for the ratio of the average CO geminate rebinding rates of the two subunits.

The Ritz formulation applied to the study of the vibration frequency characteristics of functionally graded circular cylindrical shells

In this article vibration frequencies of functionally graded circular cylindrical shells are analysed and studied using the Ritz formulation. Since closed-form solutions are limited to simple cases, an approximate method is employed to solve the shell problem, and numerical evaluation is carried out using a direct variational method. Axial modal dependence is chosen in terms of Ritz polynomials to ascertain a rapid convergence of the method. Sanders and Budiansky's thin shell theory is utilized for strain—displacement and curvature—displacement relations. Functionally graded material characteristics for the constituent materials are distributed in accordance with a volume fraction law. Influence of boundary conditions and volume fraction exponents on the vibration frequency spectra is analysed. The present results are compared with some previous works and excellent agreement is found.

Interpretation of temperature-dependent low frequency vibrational spectrum of solid-state benzoic acid dimer

Temperature-dependent low frequency vibrational absorption spectrum of solid-state benzoic acid dimer has been interpreted, using ab initio method at the MP2 level, density-functional-theory (DFT) calculations done by different DFT functionals (PBE, B3LYP, and MPWB1K) including the anharmonic potential, and DFT-based periodic wave function calculations. The assignment is successful by assuming that the vibrational absorption signals at room temperature are from dimer molecules under packing force by neighboring molecules in crystal and that those at low temperature are from intralayer tetramers connected by weak hydrogen bond and/or a periodic order form via hydrogen-bonded network.

On the influence of a transverse magnetic field on the vibration spectra of shallow shells

In the design of electric machines, devices, and plasma generator bearing constructions, it is sometimes necessary to study the influence of magnetic fields on the vibration frequency spectra of thin-walled elements. The main equations of magnetoelastic vibrations of plates and shells are given in [1], where the influence of the magnetic field on the fundamental frequencies and vibration shapes is also studied. When studying the higher frequencies and vibration modes of plates and shells, it is very efficient to use Bolotin’s asymptotic method [2–4]. A survey of studies of its applications to problems of elastic system vibrations and stability can be found in [5, 6]. Bolotin’s asymptotic method was used to obtain estimates for the density of natural frequencies of shallow shell vibrations [3] and to study the influence of the membrane stressed state on the distribution of frequencies of cylindrical and spherical shells vibrations [7, 8]. In a similar way, the influence of the longitudinal magnetic field on the distribution of plate and shell vibration frequencies was studied [9, 10]. It was shown that there is a decrease in the vibration frequencies of cylindrical shells under the action of a longitudinal magnetic field, and the accumulation point of the natural frequencies moves towards the region of lower frequencies [10]. In the present paper, we study the influence of a transverse magnetic field on the distribution of natural frequencies of shallow cylindrical and spherical shells, obtain asymptotic estimates for the density of natural frequencies of shell vibrations, and compare the obtained results with the empirical numerical results.

Hydrogen Bonds and Vibrations of Water on (110) Rutile

We study the relation between the hydrogen bonding and the vibrational frequency spectra of water on the (110) surface of rutile (α-TiO2) with three structural layers of adsorbed water. Using ab initio molecular dynamics simulations at 280, 300, and 320 K, we find strong, crystallographically controlled adsorption sites, in general agreement with synchrotron X-ray and classical molecular dynamics simulations. We demonstrate that these sites are produced by strong hydrogen bonds formed between the surface oxygen atoms and the sorbed water molecules. The strength of these bonds is manifested by substantial broadening of the stretching mode vibrational band. The overall vibrational spectrum obtained from our simulations is in good agreement with inelastic neutron scattering experiments. We correlate the vibrational spectrum with different bonds at the surface to transform these vibrational measurements into a spectroscopy of surface interactions.

Frequency information in the vibration-cued escape hatching of red-eyed treefrogs

Incidental acoustic and vibrational cues generated by predators are a potential source of information for prey assessing risk. Substrate vibrations should be excited by most predators, and frequency, amplitude or temporal properties could allow prey to distinguish predator from benign-source vibrations. Red-eyed treefrog embryos detect egg predators using vibrations excited during attacks, hatching rapidly and prematurely to escape. We recorded vibrations in egg clutches during attacks by five species of predators and three common types of benign physical disturbance. We analyzed their frequency distributions to assess if and how frequency properties could be used to discriminate between vibration sources and used vibration playbacks to examine the effects of frequency properties on the escape hatching response. Vibrations produced by predators and benign disturbances generally have broad and overlapping frequency distributions, and all frequencies excited by attacks are also excited by benign disturbances. Decision rules based on the frequency distribution of vibrations alone would therefore result in either high levels of hatching in response to benign vibrations (false alarms) or common failures to hatch in response to predators (missed cues). Nevertheless, embryos hatch in response to predator and not benign disturbances in nature, and our playback results show that vibration frequency information is an important component of their hatching decision. Embryos combine frequency with temporal information to refine their hatching response. Moreover, comparing frequency spectra of predator and benign vibrations suggests that the presence of energy in frequencies outside the range characteristic of attacks might serve as an indicator of benign disturbance.

An Investigation of Rolling Element Vibrations Caused by Local Defects

In this paper, a shaft-bearing model is developed in order to investigate the rolling element vibrations for an angular contact ball bearing with and without defects. The shaft-bearing assembly is considered as a mass-spring system. The system shows a nonlinear characteristic under dynamic conditions. The equations of motion in radial and axial directions were obtained for shaft and rolling elements, and they were solved simultaneously with a computer simulation program. Additionally, the effect of localized defects on running surfaces (i.e., inner ring, outer ring, and ball) on the vibration of the balls is investigated. Vibration of rolling elements in the radial direction is analyzed in time and frequency domains. Characteristic defect frequencies and their components can be seen in the frequency spectra of rolling element vibrations. Comparison of the obtained results with similar studies available in literature showed reasonable qualitative agreement.

Control of nonlinear vibrations of vibrating ring microgyroscope

The influence of the basement rotation on the variations in the spectrum of vibration frequencies of thin elastic shells and rings was known already at the end of the 19th century [1]. The physical phenomenon of inertness of elastic waves occurring free vibrations of an axisymmetric body, first explained in [2], were practically used in developing new types of gyros [2–6]. The foundations of the theory of wave gyros were laid in [2, 4], and the errors of such gyroscopes for various shapes of the vibrating resonator were studied in [2, 4, 7, 8]. It was shown that the error of the resonator manufacturing (the variable density, thickness, anisotropy of the material elastic properties, etc.) [2, 8] and the geometric nonlinearity of the resonator flexural vibrations studied in [2, 7] lead to splitting of the natural frequency of flexural vibrations [2], which is reflected in the wave picture of the resonator vibrations and characterizes the gyroscope precision.

Elasticity of nuclear medium as a principal macrodynamical promoter of electric pygmy dipole resonance

Motivated by arguments of the nuclear core-layer model formulated in [S.I. Bastrukov, J.A. Maruhn, Z. Phys. A 335 (1990) 139], the macroscopic excitation mechanism of the electric pygmy dipole resonance (PDR) is considered as owing its origin to perturbation-induced effective decomposition of a nucleus into two spherical domains–undisturbed inner region treated as a static core and dynamical layer undergoing elastic shear vibrations. The elastic restoring force is central to the excitation mechanism under consideration and has the same physical meaning as in macroscopic model of nuclear giant resonances involving distortions of the Fermi-sphere providing unified description of isoscalar giant electric and magnetic resonances of multipole degree ℓ⩾2 in terms of two fundamental vibrational modes in an elastic sphere, to wit, as spheroidal (electric) and torsional (magnetic) modes of shear elastic oscillations of the nodeless field of material displacements excited in the entire nucleus volume. In the present Letter focus is placed on the emergence of dipole overtone in the frequency spectrum of spheroidal elastic vibrations as Goldstone soft mode. To emphasis this feature of dipole resonant excitation imprinted in the core-layer model we regain spectral equation for the frequency of spheroidal elastic vibrations trapped in the finite-depth layer, derived in the above paper, but using canonical equation of an elastic continuous medium. The obtained analytic equations for the frequency of dipole vibrational state in question and its excitation strength lead to the following estimates for the PDR energy centroid EPDR(E1)=[31±1]A−1/3 MeV and the total excitation probability BPDR(E1)=[1.85±0.05]10−3Z2A−2/3e2 fm2 throughout the nuclear chart exhibiting fundamental character of this soft dipole mode of nuclear resonant response.

Analysis and Prediction of Vibration-Induced Solder Joint Failure for a Ceramic Column Grid Array Package

Solder joint fatigue failure under vibration loading continues to be a concern in microelectronic industry. Existing literature has not adequately addressed high-cycle fatigue failure of high-lead solder joints, especially under a broad spectrum of vibration frequencies. Also, damage mapping across solder joints in an area-array package has not been effectively studied using numerical models and experimental cross sectioning. This paper aims to develop an experimental and modeling approach that can accurately determine the solder joint behavior of electronic components under vibration conditions. In particular, this paper discusses the out-of-plane sinusoidal vibration experiments at 1G, numerical modeling, and fatigue life prediction for a 42.5×42.5×4mm3 1089 input∕output ceramic column grid array (CCGA) package on a 133×56×2.8mm3 FR4 board. Detailed investigation and characterization involving dye-and-pry analysis, microstructural examination, and numerical modeling enabled the development of a high-cycle stress-based equation for lead-containing CCGA under sinusoidal loading. The developed approach has been applied to a number of cases including a CCGA package with a heat sink as well as a CCGA package subjected to frequency sweeps. It is seen that the predictions from the developed model agree well with experimental data and that the developed model can map the evolution of solder damage across all solder joints and can also provide important design recommendations in terms of solder joint location as well as heat sink attachment.