Frequency Vibration Measurement Research Articles

Effective Condition Monitoring Methods for Diesel Main Bearing -High Frequency Vibration Measurement and Wear Particle Detection

Extension on overhaul inspection period of the main bearing of main diesel engine is highly desired by carrying out its condition monitoring. The effective condition monitoring method is required instead of the temperature method which rises out the warning alarm after bearings appeared in critical condition. It was found also for plane bearing that the contact between the shaft and bearing may occur locally even in the oil film lubrication state. Result from this study, the high frequency vibration measurement and wear particle detection in lubrication oil were suggested to be the effective condition monitoring methods.

Research on the amplitude frequency characteristics compensation based on wavelet neural network for vibration velocity transducer

A method of amplitude frequency characteristics compensation is presented to realize ultra-low frequency vibration measurement based on wavelet neural network(WNN) for vibration velocity transducer. In this method, a dynamic compensation network can be set up according to measurement data of dynamic response of vibration velocity transducer. The compensation principle is introduced and the geometrical structure of the network is analyzed and the algorithms for the training and initialization of network parameters are given. The weights of network, scale factor and displacement factor are trained by the steepest descent method and the network parameters initialization is integrated with the wavelet type, time-frequency parameters of wavelet and the training samples. The results show that the proposed wavelet neural network has good robustness, on-line correction ability, and higher precision and faster training speed than the BP neural network when used in the amplitude frequency characteristics compensation of vibration velocity transducer, and has practical value in measurement field.

Vibration control of a cantilever beam using multiple model adaptive resonant control

In this paper, a multiple model approach is utilised to improve the transient performance of an adaptive resonant controller. The proposed controller, Multiple Model Adaptive Resonant Controller (MMARC), is applied to attenuate vibrations in a cantilever beam structure with large varying parameters. On-line estimation of the structure’s natural frequencies is used to up-date the adaptive resonant controller’s parameters. A very simple supervisor scheme based on the system’s vibration frequency measurement is proposed to reduce the computation burden of the multiple model strategy. Simulation results show that the proposed MMARC strategy can achieve better transient response than a single adaptive controller.

Structure and Dynamics — An Atomic View of Materials

Preface 1. Introduction 2. Structure of materials 3. Formal description of crystal structures 4. The reciprocal lattice 5. Atomic bonding in crystals 6. Diffraction 7. Physical properties 8. Lattice dynamics 10. Experimental methods for measurements of vibrational frequencies 11. Anharmonic interactions 12. Displacive phase transitions A. Real crystals! B. Fourier analysis C. Schoenflies representation of the point groups D. Rhombohedral, trigonal and hexagonal unit cells E. Space groups F. Lattice energy minimization G. Some note on the variational theorem H. Ewald Sphere I. The Wilson Plot J. Diffraction from isotropic materials K. Calculation of physical properties L. Partition function: some key results M. Lattice sums N. Mean-square atomic displacement and temperature factors

Correlation between free oscillation frequency and stiffness in high temperature superconducting bearings

A superconducting magnetic bearing is a dynamic system, which undergoes vibrations at various frequencies during its operation. In this study, we investigated the free vibration frequency modes of a permanent magnet (PM) levitated over a high temperature superconductor (HTS) where the vibration was provided by the seismic activities of the earth. The amplitude of the vibration was less than 1 μm as measured by a vibrometer. A disk shaped PM was levitated over a melt-textured HTS YBCO (yttrium barium copper oxide). The experimental setup was adopted to do the fast Fourier transform analysis of the vibration characteristics of the levitated PM. A cross-coupling between the vibration frequency modes of vertical, lateral and angular is observed in all respective directions for any particular vibration frequency measurement. The results indicate that all the vibration modes are actually the combination of the pure vibration frequency modes. The theoretical predictions based on the frozen-image concept show that the ratio of the vertical to lateral stiffness should be higher than 2 in the dynamic case, which is observed experimentally.

Surface Tension of Liquid Alumina from Contactless Techniques

New data for the surface tension of liquid alumina from 2300 to 3200 K are reported. Aerodynamic levitation of CO2 laser-heated liquid drops allowed contactless measurement of vibration frequencies directly related to surface tension. Consistent data were obtained on drops of different mass ranging from 20 to 160 mg. It was also shown that the oxydo-reducing character of the atmosphere does not modify the results within experimental uncertainty.

Theoretical estimates of equilibrium Fe-isotope fractionations from vibrational spectroscopy

The magnitude and direction of equilibrium iron-isotope (54Fe–56Fe) fractionations among simple iron-bearing complexes and α-Fe metal are calculated using a combination of force-field modeling and existing infrared, Raman, and inelastic neutron scattering measurements of vibrational frequencies. Fractionations of up to several per mil are predicted between complexes in which iron is bonded to different ligands (i.e. 4 per mil for [Fe(H2O)6]3+ vs. [FeCl4]− at 25°C). Similar fractionations are predicted between the different oxidation states of iron. The heavy iron isotopes will be concentrated in complexes with high-frequency metal-ligand stretching vibrations, which means that 56Fe/54Fe will be higher in complexes with strongly bonding ligands such as CN− and H2O relative to complexes with weakly bonding ligands like Cl− and Br−. 56Fe/54Fe will also usually be higher in Fe(III) compounds than in Fe(II)-bearing species; the Fe(II) and Fe(III) hexacyano complexes are exceptions to this rule of thumb. Heavy iron isotopes will be concentrated in sites of 4-fold coordination relative to 6-fold coordination. Model results for a ferrous hexacyanide complex, [Fe(CN)6]4−, are in agreement with predictions based on Mössbauer spectra (Polyakov, 1997), suggesting that both approaches give reasonable estimates of iron-isotope partitioning behavior.

Kinetics of CO and NO Ligation with the Cys331 → Ala Mutant of Neuronal Nitric-oxide Synthase

Nitric-oxide synthases (NOS) catalyze the conversion of l-arginine to NO, which then stimulates many physiological processes. In the active form, each NOS is a dimer; each strand has both a heme-binding oxygenase domain and a reductase domain. In neuronal NOS (nNOS), there is a conserved cysteine motif (CX(4)C) that participates in a ZnS(4) center, which stabilizes the dimer interface and/or the flavoprotein-heme domain interface. Previously, the Cys(331) --> Ala mutant was produced, and it proved to be inactive in catalysis and to have structural defects that disrupt the binding of l-Arg and tetrahydrobiopterin (BH(4)). Because binding l-Arg and BH(4) to wild type nNOS profoundly affects CO binding with little effect on NO binding, ligand binding to the mutant was characterized as follows. 1) The mutant initially has behavior different from native protein but reminiscent of isolated heme domain subchains. 2) Adding l-Arg and BH(4) has little effect immediately but substantial effect after extended incubation. 3) Incubation for 12 h restores behavior similar but not quite identical to that of wild type nNOS. Such incubation was shown previously to restore most but not all catalytic activity. These kinetic studies substantiate the hypothesis that zinc content is related to a structural rather than a catalytic role in maintaining active nNOS.

A Technique for Determining the Elastic and Dissipative Properties of Orthotropic Composites in Shear

A new method is presented for the characterization of three principal complex shear moduli of linear viscoelastic orthotropic materials, which is based on the measurement of complex torsional vibration frequencies of three rods of rectangular cross section. The rod-type test specimens are cut out from a composite plate along the principal material axes in the reinforcement plane. It is shown that the torsional stiffness of an elastic rod can be calculated not only by means of the Saint-Venant torsion theory, but also using a relationship obtained from the Reissner-Mindlin theory of plates. The transfer to a viscoelastic model of the material with complex moduli is realized with the help of the correspondence principle. By applying a numerical sensitivity analysis of natural frequencies to the shear moduli, the advisable width-to-thickness ratios of the specimens are found. As an illustration of data processing, the dynamic shear moduli and the loss factors for a GFRP fabric with an epoxy matrix are calculated. A comparison of the method offered with some known static and dynamic methods for determining the shear moduli of orthotropic materials is given.

DETERMINATION OF ELASTIC CONSTANTS OF MATERIALS ON SPECIMENS IN THE SHAPE OF SQUARE PLATES

The results of investigation of the natural vibration frequency spectrum for square plates have been stated. Calculation formulae have been derived and methods for measurements of elastic constants of materials by the results of measurements of bending vibration frequencies for square plates have been developed. The methods include measurements of natural frequencies of two bending vibration modes: with two nodal planes (the lowest vibration mode) and with one nodal circumference, Recommendations on the choice of apparatus for measurements have been given and engineering formulae for calculations have been offered. The results of measurements according to developed methods have been presented for a number of known and new ceramic materials.

Nondestructive detection of weak joints in adhesively bonded composite structures

Some aspects of research and progress in adhesive bonding of composite structures are summarized with emphasis on defects, mechanisms, modeling, and nondestructive evaluation methods. The application of vibration damping and frequency measurements in nondestructive detection of degraded adhesive joints is emphasized. Unlike our previous reported research on void-degraded adhesively bonded composite models, this paper focuses on the composite structures with weak bonding defects.

An approach for vibration measurement based on laser frequencysplitting technology

An approach for vibration measurement based on He-Ne laserfrequency splitting technology is presented and experiments have been performed.While a quartz crystal wedge, which is placed in the laser cavity, vibrateswith the object to be measured, the frequency difference of the laser ismodulated by the vibration signal. The vibration signal is restored bydemodulating the laser frequency difference signal. In the experiments a15 nm resolution and a ±1.6×10-4 reproducibility of thevibrational amplitude are obtained with the system. The frequency range ofvibration measurement is only up to the limit of mechanical structures. Themethod has a good potential prospect for application in high-resolution, lowor middle frequency vibration measurement.

Photooxidation of Toluene and p-Xylene in Cation-Exchanged Zeolites X, Y, ZSM-5, and Beta: The Role of Zeolite Physicochemical Properties in Product Yield and Selectivity

The photooxidation of toluene and p-xylene with molecular oxygen and visible light has been investigated in several cation-exchanged zeolites. In general, the yield of the photooxidation products, for fixed irradiation time and intensity, was found to correlate with the electric field intensity at the cation sites within the zeolites. On the basis of measurements of CO vibrational frequencies, electric fields of approximately 3−7 V nm-1 are indicated for the cation-exchanged zeolites X, Y, ZSM-5, and Beta used in these studies. These large electric fields are thought to promote photooxidation by stabilizing an intermolecular charge transfer state (R+·O2-) that is formed upon excitation with visible light. The measured electric field was found to correlate with the product yield and was highest in divalent cation-exchanged zeolites with high Si/Al ratios, such as BaZSM-5 and BaBeta. For zeolites containing the same cation, the selectivity of toluene to form benzaldehyde and p-xylene to form p-tolualdehyde ...

Development of experimental techniques to minimise the leakage errors involved in FFT based measurements

Leakage errors arise from the processing of signals that are not periodic in the time window of a fast fourier transform (FFT) analyser, since FFT assumes a periodic waveform within the window period. If this is not the case then errors will occur. To enable FFT to calculate the magnitude spectrum more accurately it is necessary to force a nonperiodic waveform to become periodic within the window period. The goal of this study is to look for ways of minimising leakage errors involved in frequency response and vibration measurements by improving the quality of measurements. In the first part of the study, the characteristics and function of the time windows are considered. Then, in the second part, the application of these time windows to the specific case study of a washing machine is considered. Comparison of results enables us to determine the optimum time windows that fit our requirements. Results indicate that choosing the proper time window can decrease the leakage errors dramatically, and special signal processing techniques, which take into account properties of the input signals, can help us to overcome the major problems of noise and truncation that lead to the leakage.

Mechanical Performance of External Fixators With Wires for the Treatment of Bone Fractures—Part II: Wire Tension and Slippage

The work shows correct procedures needed in order to gather reliable data from measurement of displacements versus axial load in a laboratory mounting of the Ilizarov external fixator. The mechanism of settling after load cycling is investigated. Detension under load is a major problem of wires. By means of vibration frequency measurements, tests on single wire allow determination of reduction in wire tension due to transverse loading: it is found that, almost independently from the amount of clamp tightening, the tension reaches a lower limit related only to the transverse load and not related to pretension. It is shown that, for higher clamp tightening torques, wire detension must be attributed to permanent plastic deformation of the wires; moreover, it is shown that the unavoidable errors in the spacing of the tensioned wires lead to marked decrease of their stiffness under transverse load.

A simple fibre optic sensor for measurement of vibrational frequencies

A non-contact non-interferometric fibre optic vibration sensor is described which is constructed from a 50/125 mu m multimode communication grade directional coupler, a modulated 820 nm LED and a PIN photodiode module. The sensing fibre is one arm of the directional coupler. The sensor is designed to detect small proximity variations between an unprepared reflective surface and the end of the sensing fibre. Vibrations of amplitude 1 mu m for mirrored surfaces and 4 mu m for unpolished aluminium can be detected for a sensor located approximately 50 mu m from the vibrating surface. The sensor output is reasonably linear for vibration amplitudes up to about 0.2 mm. The sensor uses synchronous detection circuitry based on common, low cost integrated circuits to improve the output signal-to-noise ratio by a factor of ten. The design of the vibration sensor is described in sufficient detail for it to be easily reconstructed at minimum expense.

A Monitor for Indirect Measurement of Cable Vibration Frequency and Tension

A non-contact cable tension monitor was designed, constructed, and evaluated. Such a monitor could be used to warn machine operators of unsafe cable tension or to inform operators of current cable tension for more efficient operation. The vibration frequency of a cable between supports varies with tension. A scanning laser beam and optical sensors were used to monitor the instantaneous transverse position of a vibrating cable. The period of oscillation of the cable was then determined from the sequence of position measurements. Tests were conducted for simulated center-to-center cable displacements from 13 mm to 50 mm, at both 5 and 15 Hz. Monitor output was within 10% of the actual period value 79% of the time under the most ideal conditions of 50 mm displacement and 15 Hz frequency. Performance deteriorated as either displacement or frequency decreased. Only 23% of the results were within 10% of the actual period value under the least favorable conditions of 13 mm displacement and 5 Hz frequency.

Application of ‘SPATE’ to high frequency vibration measurement of aero engine components : Turner, S.R.; Pollard, N.G. Stress Analysis by Thermoelastic Techniques, Proceedings of a Conference, London (United Kingdom), 17–18 Feb. 1987. pp. 162–178. Edited by B.C. Gasper. Proceeding of SPIE - The International Society for Optical Engineering, Vol. 731 (1987)

Application of ‘SPATE’ to high frequency vibration measurement of aero engine components : Turner, S.R.; Pollard, N.G. Stress Analysis by Thermoelastic Techniques, Proceedings of a Conference, London (United Kingdom), 17–18 Feb. 1987. pp. 162–178. Edited by B.C. Gasper. Proceeding of SPIE - The International Society for Optical Engineering, Vol. 731 (1987)

The Differential – Piezoelectric Accelerometers Used for Environmental Vibration and Human Vibration Measurements

A prototype of a low frequency differential-piezoelectric accelerometer is described. It has the function that the vibration signals can be transformed to a pair of push-pull signals which are out of phase. But for the non-vibration signals, such as the environmental temperature transient sensitivity, the out-puts are all in phase. Owing to the difference in phase, the non-vibration signals can be separated out and thus can be compensated directly. The experimental results show that the temperature transient sensitivity can be reduced to 6.4 times and 9.3 times when the lower limiting frequencies are 0.3 Hz and 0.08 Hz respectively. Combining with other measures, the temperature transient sensitivity of the accelerometer is quite low and therefore it can be neglected in most low frequency vibration measurement applications. After analyzing the compensation of the transverse sensitivity and acoustic sensitivity, it is concluded that these effects are not significant in practical use. Meanwhile, a predicting method for calculating the natural frequency is described. Some experimental products of this structure have been used effectively in the measurements of human vibration and environmental vibration.

Use of Frequency Data to Predict Buckling

Vibration frequency measurements are sometimes used to nondestructively predict buckling loads. Various powers of the fundamental frequency may be plotted as a function of the load. A curve-fitting procedure may be applied to obtain estimates of the buckling load, which occurs when the fundamental frequency decreases to zero. Often such predictions lead to a value that is higher than the actual buckling load. It would be useful if both lower and upper bounds on the buckling load could be obtained from the vibration data. In this technical note, the convexity properties of the curves of load versus a power of the frequency are utilized to predict such bounds. These ideas are demonstrated on typical curves associated with buckling at a limit point and a bifurcation point. The curves are derived from an example of a shallow elastic arch with pinned ends and a sinusoidal initial shape, which is subjected to a sinusoidal distributed load.