Vibroacoustic Method Research Articles

Diagnosis of Technical Condition of Power Transformers Based on the Analysis of Vibroacoustic Signals Measured in Transient Operating Conditions

The issue of an effective assessment of the technical condition of the mechanical structure of the power transformer core and windings originated the research work discussed in this paper. This publication presents the results which indicate the possibility of developing a new and noninvasive diagnostic method of the transformer active part. The method developed is based on the time-frequency analysis results of the mechanical vibrations measured of the monitored appliance. The registration of vibrations is performed during switching the transformer monitored into idle operation. This paper characterizes the power object under study, the measuring system applied, and discusses a new methodology of assessment of the technical condition of the core and windings using a modified vibroacoustic method. The original measurement results presented in this paper were obtained during switching on a 200-kVA transformer in laboratory conditions. The analysis of the signals measured was carried out for four operating conditions of the transformer under study: 1) with the core pressed by the manufacturer; 2) with the core with loose screws fixing the upper yoke; 3) with the core with loose screws fixing the upper and lower yokes; and 4) with the core with loose screws fixing the upper and lower yokes with a simultaneous unpressing of the windings of the upper voltage side.

Time-Frequency Analysis of Mechanical Vibrations of the Dry Type Power Transformer Core

The paper presents research results referring to the development of a non-invasive method of assessment of the power transformer core technical condition based on the analysis of the mechanical vibrations registered. It characterizes the power object under study, the measuring system used and the developed methodology of assessment of the core pressing degree using the vibroacoustic method. The original results of the time–frequency analysis of the vibroacoustic signals presented in the paper were obtained during switching on a real 800 kVA dry type power transformer in laboratory conditions. The analysis of the signals registered was carried out for three states of its operation: the core pressed by the manufacturer, the core with loose screws fixing the upper yoke and the core with separated upper yoke beams.

Vibroacoustic methods of assessing valve clearance in combustion engines* An analysis of signals in the area of frequency

This article presents results of research referring to applying selected frequency characteristics of signal of vibration accelerations of combustion engine’s head to assess valve clearance of combustion engine. The authors indicate necessity to perform preliminary preparations of signal of vibration accelerations before carrying out frequency analyses in order to decrease the risk of inaccurate analysis.

Diagnostics of GTE turbine blades using a new vibroacoustic method

The results of development and application of a new vibroacoustic method for diagnostics of the technical condition of aircraft GTE turbine blades are presented.

Vibroacoustic Measurements in a Transient State οf Transformer Operation

The subject matter of this paper refers to the assessment of the technical condition of a power transformer core and windings based on vibroacoustic measurements taken during a transient operation state of the appliance diagnosed — at a transformer unit switch on. The paper presents preliminary results of the research work carried out, which aims at elaborating a new diagnostic and assessment method of the degree of the transformer core and winding pressing using the so-called modified vibroacoustic method. The paper characterizes the measurement path and the assessment method of the core and winding pressing degree based on the selected analyses of the vibroacoustic signal registered. The original research results presented in the paper were obtained at a real 400 kV A power transformer switch on in laboratory conditions — for a regular operation condition and for modeled core damage.

THE REQUIRED NUMBER DETERMINATION OF MEASUREMENTS FOR ADVANCED VIBRO AND ACOUSTIC METHOD OF DIAGNOSTICS OF REINFORCED CONCRETE OF THE CONTACT ENVIRONMENT

The necessary quantity of making shocks on a support by the improved vibroacoustic method of detecting defective supports of the contact electric mains has been investigated.

Diagnosing of misfire events in compression-ignition engines with the help of vibroacoustic methods in the aspect of OBD system application in diesel locomotives

The article concerns the possibilities of use of the method being able to assess of the combustion process and its lack in internal combustion engines of railway traction vehicles, that bases on the use of vibration signal parameters. The paper includes the results of research conducted on the engine test bench with a single cylinder research and compression-ignition engine with direct injection, and tests for the engine of a diesel locomotive in the exploitation condition. Possibility of the vibration signal estimators application to the assessment of a combustion process lack in an internal combustion engine and a high reliability of combustion process diagnostics basing on the above method have been proved.

Removal of excess product water in a PEM fuel cell stack by vibrational and acoustical methods

The research presented here investigates the use of vibro-acoustic methods to improve the performance of a PEM fuel cell by enhancing water removal from the active reaction sites within the fuel cell. Removing the water increases the available reaction sites and thus increases the available power for a given operating condition. To examine the new water removal methods, first, the production of water in fuel cells and current water removal methods are reviewed. Then, the new methods are proposed that are based on structural and acoustical excitation of the stack. Specifically, the use of flexural waves, acoustic waves and surface waves to remove water from a fuel cell stack are examined. Analytical formulations are given in order to calculate the excitation frequency and amplitude required to move a droplet resting on a vibrating bipolar plate. Depending on the droplet radius and other parameters, it is estimated that a water droplet resting on a bipolar plate can be moved by structural displacement levels as low as 1 μm. The different approaches to droplet removal are compared in terms of the minimum vibration energy required per droplet. Water production in a commercial fuel cell stack is then estimated and used as a test case to compare the power required to effect removal of a certain number of droplets with the amount of power produced by the stack. It is shown that a water droplet clogging a plate channel may be moved with parasitic power requirements as low as 21 mW. For each method, the energy required to effect droplet removal is quite small, although among the three, the use of surface acoustic waves may be the best option in terms of minimal vibration energy and implementation feasibility.

Oscillogram-Period Method for Determining Kinds of Graphitized Iron

The microstructure of graphitized iron is studied by a vibroacoustic oscillogram-period method. It is shown that the method is suitable for evaluating the strength of iron on the basis of a derived relation between the standard coefficient of the period of sound and the ultimate rupture strength.

Compensation for discarded singular values in vibro-acoustic inverse methods

The paper addresses the inverse problem where source strengths are back-calculated from a sound pressure field sampled at several points. Regularization techniques, such as singular value discarding or Tikhonov regularization, are commonly used to improve estimates of source strength in such situations. However, over-regularization can result in even worse errors. A simple procedure is proposed here to compensate for errors of over-regularization. The basis is to constrain the solution such that the spatial mean of the measured and reconstructed sound pressure are equal. In other words, to set the overall sound power of the equivalent (calculated) sources equal to that of the real source. It is argued that the overall sound power is the most stable and reliable quantity on which to base source strength estimates. Examples of both singular value discarding and Tikhonov regularization are given.

Application of nonlinear phenomena induced by focused ultrasound to bone imaging

A tissue deformability image is obtained with the vibroacoustography imaging method using mechanical low-frequency ( LF) excitation. This ultrasonic excitation is created locally by means of a focused annular array emitting two primary beams at two close frequencies, f 1 and f 2 ( f 2 = f 1 + f LF ). The LF acoustic emission resulting from the vibration of the medium is detected by a sensitive hydrophone and then used to form the image. This noninvasive imaging method was demonstrated in this study to be suitable for bone imaging, with x and y transverse resolutions less than 300 μm. Two bone sites susceptible to demineralization were tested: the calcaneus and the neck of the femur. The vibroacoustic method provides valuable ultrasonic images regarding the structure and the elastic properties of bone tissue. Correlation was made between vibroacoustic bone images, performed in vitro, and images acquired by other imaging methods ( i.e., bone ultrasound attenuation and x-ray computerized tomography (CT)). Moreover, the amplitudes of vibroacoustic signals radiating from phosphocalcic ceramic samples (bone substitute) of different porosity were evaluated. The good correlation between these results and the description of our images and the quality of vibroacoustic images indicate that bone decalcification could be detected using vibroacoustography.

Monitoring wood decay in poles by the vibroacoustic response method

Despite recent advances in the development of new materials, wood continues to be used globally for the support of overhead cable networks used by telecommunications and electrical utility companies. As a natural material, wood is subject to decay and will eventually fail, causing disruption to services and danger to public and company personnel. The traditional method of testing poles for decay involves hitting them with a hammer and listening to the sound that results. However, evidence suggests that a large number of poles are replaced unnecessarily and a significant number of poles continue to fail unexpectedly in service. Therefore, a more accurate method for assessing the structural integrity of wooden poles is required. The underlying physical principles behind the ‘pole tester's approach’ have been identified and used in the development of a decay meter to enable objective monitoring of decay in wooden poles.

Usage of Wigner–Ville distribution for vibroacoustical forced oscillation diagnostics of cracks

For diagnostics of fatigue cracks using vibration and noise, the new low-frequency vibroacoustical method of forced oscillations with nonstationary excitation is considered. The usage of an advanced time-frequency signal-processing technique based on Wigner–Ville distribution is proposed and developed to improve the effectiveness of diagnostics. The simulation results are presented.

Vibroacoustical preventive method for non-destructive testing and evaluation of rotative bladed systems

Method uses spectral component parameters of vibroacoustical noise of systems as features. Estimation of mentioned parameters allows evaluation of the levels of mechanical and aerodynamic loadings of rotative bladed systems. Experimental results with aircraft gas turbine engine are presented.

Passive–active low-frequency vibroacoustical fault diagnosis method

The presented work is dedicated to the development of the new passive–active low-frequency automatic vibroacoustical early fault diagnosis method of helicopter engine units (compressor stages, turbine stages). The proposed method is based on signal processing of the rotating details of acoustic noise in the low-frequency range (0–25 kHz). There are two important characteristics of this method: (a) it uses a nonstationary narrow-band vibration excitation with variable central frequency, and (b) this excitation is provided by rotating rotor, and user of the method will vary the central frequency, and (b) this excitation is provided by rotating rotor, and user of the method will vary the central frequency of rotor rotation. The basis for using this method is the fact that, at the presence of fault (for example, fatigue crack) in testing details, parameters of arising free and forced oscillations change (nonzero spectral amplitudes of higher harmonics). The new analytical dependencies of testing object oscillation parameters from the relative crack size and parameters of nonstationary excitation are received. A multidimensional testing data vector for diagnostics and evaluation of faults is proposed and investigated.

Nonlinear vibroacoustical free oscillation method for crack detection and evaluation

For detection and evaluation of cracks, the vibroacoustical method of free oscillations, based on nonlinear dynamics of a tested object, is widely used. However, in spite of wide practical application, the theoretical basis of this method is insufficiently investigated. The theoretical research of the decrement of the damped nonlinear free oscillations is given in the presence of a crack in a tested object. New generalizations of the decrement for nonlinear oscillations are proposed and investigated. New analytical expressions between the decrement and relative size of a crack, factors of damping, and the natural frequency of a tested object without a crack are received, on the basis of which a new testing feature is proposed and investigated. The cases of small and large damping are considered. The results obtained allow one to explain the phenomena that appeared at the method usage. [Work supported in part by the John D. and Catherine T. MacArthur Foundation.]

The Need for New Vibro-Acoustic Test Methods Due to the Increasing Use of Automatized Electrical Drives

The Need for New Vibro-Acoustic Test Methods Due to the Increasing Use of Automatized Electrical Drives

Using the resonance vibroacoustic method for nondestructive inspection of separation of coatings of polyurethane foam materials

Using the resonance vibroacoustic method for nondestructive inspection of separation of coatings of polyurethane foam materials

Vibroacoustic methods for monitoring the technical state of hydroelectric generators

Vibroacoustic methods for monitoring the technical state of hydroelectric generators