Analysis Of Vibroacoustic Signals Research Articles

Power Transformers OLTC Condition Monitoring Based on Feature Extraction from Vibro-Acoustic Signals: Main Peaks and Euclidean Distance.

The detection of On-Load Tap-Changer (OLTC) faults at an early stage plays a significant role in the maintenance of power transformers, which is the most strategic component of the power network substations. Among the OLTC fault detection methods, vibro-acoustic signal analysis is known as a performant approach with the ability to detect many faults of different types. Extracting the characteristic features from the measured vibro-acoustic signal envelopes is a promising approach to precisely diagnose OLTC faults. The present research work is focused on developing a methodology to detect, locate, and track changes in on-line monitored vibro-acoustic signal envelopes based on the main peaks extraction and Euclidean distance analysis. OLTC monitoring systems have been installed on power transformers in services which allowed the recording of a rich dataset of vibro-acoustic signal envelopes in real time. The proposed approach was applied on six different datasets and a detailed analysis is reported. The results demonstrate the capability of the proposed approach in recognizing, following, and localizing the faults that cause changes in the vibro-acoustic signal envelopes over time.

MODELS FOR ASSESSING THE PRESENCE OF DEFECTS IN BEARING SUPPORTS OF AIRCRAFT GAS TURBINE ENGINES

Increasing the level of reliability of aviation equipment is quite relevant, but at the same time a difficult task. Aircraft engines (AD) are removed from operation every year if they have not exhausted their established resources and service life. As a rule, the reasons for early termination of operation are defects and malfunctions of individual engine components, their mechanical damage, as well as human errors that lead to a malfunction of the engines. From the performed analysis of the causes of failures and damages of the engines of operational-tactical aviation aircraft, it can be concluded that in the vast majority of cases, the failures manifested themselves in increased vibration, which indicated the destruction of the bearing supports of the compressor and turbine rotors, the failure of which may lead to shutdown and damage to the gas turbine engine. Such consequences adversely affect flight safety and can lead to both the loss of the aircraft and the death of the crew. The specifics of the placement of the bearing supports of the GTE rotors greatly complicates their diagnostics in the framework of non-destructive testing. New models are proposed for assessing the presence of defects in the bearing supports of the rotors of aircraft gas turbine engines, based on the analysis of vibroacoustic signals in the frequency and time domains. A software and hardware complex has been created that allows diagnosing the technical condition of the bearing supports of the rotors of aircraft gas turbine engines.

Choice of method for determining the concentration and fractional composition of dust and gas flow

The presence of industrial dust in concentrations exceeding the MPC leads to environmental pollution and threatens environmental safety. The article presents a method for determining the concentration and fractional composition of the dust and gas flow. The essence of the described method lies in the registration and analysis of vibroacoustic signals that occur due to vibrations of parts of the measuring system. The principle of operation of the system is based on the transmission of shock acts of oscillation generation along a chain that includes dust particles, a boundary layer, a dust pipeline wall, and, finally, a piezoceramic sensor of the system. The disperse composition of dust can be determined by two mathematical models (Fourier polynomials) - one reflects the energy spectrum, the other - the amplitude-phase. These polynomials are obtained by applying the Laplace transform to the signal and actually reveal the physical meaning of the process of formation of harmonics in the frequency subspectra. The processing of an acoustic signal on a computer by a fast discrete Fourier transform leads to an accurate description and calculation of the amplitude-frequency spectrum in real time. The main task is to isolate the frequency subspectra, consisting of the main and timbre harmonics for dust monofractions. The method of static moments is used to refine and form the frequency package of the main harmonics. The implementation of the method is carried out on a laboratory stand during the transfer of a dust-gas flow with pure monofractions and with a stepwise increase in concentration, the amplitudes of the main and timbre harmonics increase, which forms the frequency subspectrum of the analyzed dust monofraction. For further analysis and processing of AS spectra, a block diagram of an algorithm for determining the fractional composition of a moving dust and gas flow has been developed.

Contrast Estimation in Vibroacoustic Signals for Diagnosing Early Faults of Short-Circuited Turns in Transformers under Different Load Conditions

The transformer is one of the most important electrical machines in electrical systems. Its proper operation is fundamental for the distribution and transmission of electrical energy. During its service life, it is under continuous electrical and mechanical stresses that can produce diverse types of damage. Among them, short-circuited turns (SCTs) in the windings are one of the main causes of the transformer fault; therefore, their detection in an early stage can help to increase the transformer life and reduce the maintenance costs. In this regard, this paper proposes a signal processing-based methodology to detect early SCTs (i.e., damage of low severity) through the analysis of vibroacoustic signals in steady state under different load conditions, i.e., no load, linear load, nonlinear load, and both linear and nonlinear loads, where the transformer is adapted to emulate different conditions, i.e., healthy (0 SCTs) and with damage of low severity (1 and 2 SCTs). In the signal processing stage, the contrast index is analyzed as a fault indicator, where the Unser and Tamura definitions are tested. For the automatic classification of the obtained indices, an artificial neural network is used. It showed better results than the ones provided by a support vector machine. Results demonstrate that the contrast estimation is suitable as a fault indicator for all the load conditions since 89.78% of accuracy is obtained if the Unser definition is used.

Identification of operating mode of a petrol chainsaw based on short-time parametrization and analysis of vibro-acoustic signals

Petrol chainsaws during operation, regardless of the type of their drive and power, generate vibrations and noise that usually exceed the permissible values which are specified in standards and/or regulations. The values of vibration accelerations and emitted noise levels declared by the manufacturers are determined in standardized conditions and they may significantly differ from the values affecting operators. In order to determine the actual impact on operators of chainsaws under nominal operating conditions (in situ) one have to identify the percentages of the chainsaw's operating modes: Idle – ID, Full load – FL, Racing – RA. The article presents the methodology of identifying the operating modes of petrol chainsaws based on recorded vibroacoustic signals. Moreover, a method of identifying these states based on a tachometric signal has been proposed. Different approaches were considered to the identification of operating modes. Basic method is based on tracking of changes of the instantaneous values of vector sums of frequency-weighted values of RMS vibration accelerations – ahv and linear sound pressure levels – Lp. Advanced methods are based on short-time analysis and parametrization in frequency bands of the acoustic signal, as well as the time–frequency maps of vibration and acoustic signals. Discriminants of vibroacoustic signal were determined that allowed us to identify the operating mode of the chainsaw.

Nonlinear analysis of cylindrical gear dynamics under varying tooth breakage

Linear and nonlinear analyses served to detect the degree of tooth damage in a cylindrical gear. The gear in question is widely used in industrial applications and is often subject to gear tooth damage. Multiple-sourced vibrations affecting the test stand may distort or conceal the vibration components responsible for tooth failure. Given its construction, the test stand offers low stiffness, and additional control and measurement equipment further contribute to overall vibrations. Therefore, the vibration signal is likely to contain various disturbances, which further hinder correct diagnosis. Basic vibroacoustic signal analysis methods, which were employed at a preliminary stage, failed to produce unambiguous and satisfactory results. Hence, nonlinear recurrence analysis of gear operation dynamics was applied. It is assumed that the occurrence of damage to the gear will impede the regularity of drive transmission. The adopted research method addresses the limitations of a two-state diagnosis of gear condition (no damage/damage) by allowing the extent of gear tooth damage to be specified.

Estimation of differences in selected indices of vibroacoustic signals between healthy and osteoarthritic patellofemoral joints as a potential non-invasive diagnostic tool

Osteoarthritis (OA) is currently the most generic form of joint disease. It is a complex process in which degenerative changes occur in the articular cartilage [AC], subchondral bone, and synovial membrane and can lead to permanent joint failure. The primary and most commonly used method of diagnosing degenerative changes is classic radiography. Magnetic resonance imaging (MRI) may be used to assess the extent of damage to joint surfaces, but this method is limited by the availability of specialised equipment and the excessive cost of the examination. Arthroscopy, an invasive procedure, is considered the “gold standard” in joint diagnosis. The occurrence of degenerative changes is closely related to the friction and lubrication processes within the joint. The main causes of osteoarthritis are a change or lack of synovial fluid, deformation of the joint bones, local damage to the articular cartilage, and a change in the mechanical properties of the articular cartilage due to water loss from the damaged superficial layer. An alternative, non-invasive method that allows for a delicate assessment of the condition of moving joints is vibroarthrography (VAG). The analysis of vibroacoustic signals generated by moving joint surfaces has an immense potential in the non-invasive assessment of the degree of damage to articular cartilage, meniscus and ligaments and the general diagnosis of degenerative diseases. The purpose of this study is to analyse and statistically compare the basic characteristics of vibroacoustic signals recorded with a CM-01B contact microphone placed on the patella for motion in the 90°–0°–90° range in a closed kinetic chain (CKC) in a control group (HC) and a group of patients diagnosed with osteoarthritis (OA), qualified for the knee alloplasty.

Evaluation of Wear of Disc Brake Friction Linings and the Variability of the Friction Coefficient on the Basis of Vibroacoustic Signals

The article presents the results of friction and vibroacoustic tests of a railway disc brake carried out on a brake stand. The vibration signal generated by the friction linings provides information on their wear and offers evaluation of the braking process, i.e., changes in the average friction coefficient. The algorithm presents simple regression linear and non-linear models for the thickness of the friction linings and the average coefficient of friction based on the effective value of vibration acceleration. The vibration acceleration signals were analyzed in the amplitude and frequency domains. In both cases, satisfactory values of the dynamics of changes above 6 dB were obtained. In the case of spectral analysis using a mid-band filter, more accurate models of the friction lining thickness and the average coefficient of friction were obtained. However, the spectral analysis does not allow the estimation of the lining thickness and the friction coefficient at low braking speeds, i.e., 50 and 80 km/h. The analysis of amplitudes leads to the determination of models in the entire braking speed range from 50 to 200 km/h, despite the lower accuracy compared to the model, based on the spectral analysis. The vibroacoustic literature presents methods of diagnosis of the wear of various machine elements such as bearings or friction linings, based on amplitude or frequency analysis of vibrations. These signal analysis methods have their limitations with regard to their scope of use and the accuracy of diagnosis. There are no cases of simultaneous use of different methods of analysis. This article presents the simultaneous application of the amplitude and frequency methods in the analysis of vibroacoustic signals generated by brake linings. Moreover, algorithms for assessing the wear of friction linings and the average coefficient of friction were presented. The algorithm enables determination of the time at which the friction linings should be replaced with new ones. The final algorithm analyzes the vibration acceleration signals using both amplitude analysis for low braking speeds, as well as spectral analysis for medium and high braking speeds.

The method of fundamental harmonic frequency determination

Analysis of vibroacoustic signals is one of the more frequently used mechanical devices diagnostic methods occurring among others in car diagnostics. Often, it happens that the most important element of the recorded course is the fundamental harmonic frequency of vibrations. Fundamental frequency indicates the main process related to the operation of the device and allows to follow its course. In the article the author's method of determining the fundamental frequency in the signal will be presented which is the subject of a patent application. Its theoretical basis and application examples were discussed comparing the accuracy of its use with the accuracy of other methods. The frequency range where the method finds application is shown. That is, where its accuracy turns out to be better than the accuracy of popular used methods to fundamental harmonic frequency determination.

ДІАГНОСТИКА ТУРБОКОМПРЕСОРА ДИЗЕЛЬНОГО ДВИГУНА ЗА ДОПОМОГОЮ АНАЛІЗУ ВІБРОАКУСТИЧНОГО СПЕКТРУ

The method considered in the article consists in the analysis of the vibroacoustic signal generated by the compressor of the gas turbocharger during the operation of the diesel engine under load. Spectral analysis shows that the compressor blades generate vibrations that are always present in the spectrum of the general vibration of a gas turbocharger, regardless of its technical condition. The "blade" harmonic in the spectrum corresponding to these oscillations is determined using the method of limitations. The then calculated instantaneous rotor speed of the turbocharger makes it possible to analyze the amplitude of the fundamental harmonic in the spectrum. For numerical analysis of the amplitude of the fundamental harmonic, the power leakage of the discrete spectrum is eliminated. Further analysis of the amplitude of the fundamental harmonic makes it possible to quickly assess the level of vibration of the rotor during operation. The first part of the experiment was carried out on a ship's main diesel engine 5S60MC at a crankshaft speed of 85 min-1. The recording and analysis of vibroacoustic signals from the TCA 66-20072 turbocharger was carried out. The analysis showed the possibility of highly accurate determination of the rotational speed and the relative amplitude of the turbocharger shaft oscillations. The second part of the experiment was carried out on an experimental stand, which is based on a KamAZ-740.10 engine with an original pressurization system. A turbocharger of the TKR-11 type is used as a pressurization unit. As a result of the experiment, it was shown that the method of diagnosing the operation of a turbocharger, which is based on the analysis of a vibroacoustic signal, can be extended not only to turbochargers of low-speed engines, but also to turbochargers of high-speed diesel engines. In this case, the spectrum of the measured signal contains harmonics, the frequencies of which make it possible to determine the crankshaft rotation frequency. It is also shown that measuring the signal outside the compressor, close to its casing, makes it possible to obtain all the necessary diagnostic parameters as accurately as when measuring the signal directly at the inlet to the compressor wheel. The method can be used in practice. To implement it, a smartphone and a computer with special software are enough. The proposed method can be used as the basis for a system for continuous monitoring of the frequency and vibration level of a marine diesel engine turbocharger.

DIESEL ENGINES DIAGNOSIS AND IMPROVEMENT OF REPAIR AND OPERATION

Introduction. In the practice of operating and repairing locomotive diesel engines there are cases when a diesel engine is put into operation after repair works with a set of defects of the high-pressure fuel equipment, the cylinder-piston group and the valve timing gear, and rather large uneven distribution of power over the cylinders which has not been fully remedied. It is known that during operation, especially in conditions of frequent load changes, the number of operational defects increases. Hard-to-detect defects in the fuel equipment, the cylinder-piston group and the valve timing gear lead to an uneven distribution of power over the cylinders, an increase in the overall level vibration, a significant increase in specific fuel consumption and an even greater soot emission and hazardous substances during transient conditions. Moreover, routine maintenance work does not always eliminate all defects on the engine, because, firstly, there is no detailed picture of the defects of the individual components before the repairs and, secondly, there is no parametric testing of the condition of the high-pressure fuel equipment, the cylinder-piston group and the valve timing gear after repair work. Purpose. The task of the effective and reliable diagnostics of the technical condition of the engine components before carrying out repair work to accurately detail the scope of the upcoming repair is crucial as well as the subsequent quality control of the repairs, as a result of which the remaining unresolved defects can be identified. After eliminating defects, it is necessary to evenly distribute the load between the cylinders, which should done by balancing the mean indicated pressure Pi (MIP) with the permissible pressure deviations Pz at the end of compression Pc and exhaust gas temperatures Texh. Results. The research of the working process undertaken by the staff of the Department of Ship Power Plants and Technical Maintenance of Odessa National Maritime University showed that during rheostat tests of K6S310DR diesel engines it is possible to promptly obtain reliable diagnostic information. This is done by using parallel analysis of the pressure-volume diagrams and vibration records of the high-pressure fuel equipment, the cylinder-piston group and the valve timing gear. The spectral analysis of vibroacoustic signals of the gas turbocharger and the analytical method for eliminating the effect of power leakage in the discrete spectrum allows for on-line diagnostics of the oscillation level of the gas turbocharger rotor. Conclusions. These methods, implemented in the DEPAS system developed by the specialists of Odessa National Maritime University, can be effectively used in practice of operating locomotive diesel engines.

Diagnosing wind turbine condition employing a neural network to the analysis of vibroacoustic signals

It is important from the economic point of view to detect damage early in the wind turbines before failures occur. For this purpose, a monitoring device was built that analyzes both acoustic signals acquired from the built-in non-contact acoustic intensity probe, as well as from the accelerometers, mounted on the internal devices in the nacelle. The signals collected in this way are used for long-term training of the autoencoder neural network. The appropriately trained network automatically detects deviations, signaling them to technical service. The applied methods of analysis of vibroacoustic signals and neural network training are the subject of the presented paper. In addition, the motion magnification of video is used for extracting information on vibrations of the whole wind turbine construction. Finally, spectral analysis is applied for detecting unnatural components presence meaning defects in both: visual and vibroacoustic representations. The process of reduction and construction of a wind turbine model is discussed with a particular emphasis on application to perform extensive tests of the developed methods and algorithms. [The research was subsidized by the Polish National Centre for Research and Development within the project “STEO—System for Technical and Economic Optimization of Distributed Renewable Energy Sources”, No. POIR.01.02.00-00-0357/16.]

Применение фильтра Калмана в задаче технической диагностики двигателей внутреннего сгорания

The paper deals with the problem of filtering vibroacoustic signals of an internal combustion engine (ICE) using an adaptive Kalman filter in order to further use the filtered array to solve the problem of technical diagnostics of ICE. The results of the simulation of an adaptive filter in the MATLAB / Simulink software environment of a real vibro-acoustic signal of the engine of an Opel Vectra brand are also given. Implemented a device based on the Arduino Mega microcontroller, which was used to process the field observations of the object of study – ICE. The development of methods for the operational determination of the technical state of internal combustion engines (ICE), first of all automobiles, is currently being given special attention in connection with ensuring not only the reliability of the latter, but also increasing requirements for the economically and environmentally friendly ICE. These methods should allow to carry out diagnostics of the technical condition of the vehicle’s internal combustion engine and to make timely adjustments to the systems and components of the internal combustion engine thereby increasing the operational performance and service life of the object. Environments of various methods for diagnosing the technical condition of internal combustion engines of particular importance are the method based on the analysis of vibroacoustic signals, which allows indiscriminate monitoring of components and interfaces of an internal combustion engine. It should be noted that the analyzed vibro-acoustic signals of the internal combustion engine are mutually correlated in terms of the operation of the internal combustion engine assemblies. Therefore, in order to adequately establish and localize the location of a defect in the internal combustion engine, it is necessary to first isolate the useful signal in the conditions of the mutual influence of non-stationary vibro-acoustic signals generated by various engine components.

Autocorrelation Analysis of Vibro-Acoustic Signals Measured in a Test Field for Water Leak Detection

Reducing losses in water distribution networks is a worldwide challenge and all utilities are developing proper strategies for the active control of leaks. Temporary or permanent grids of units for the continuous monitoring of pipelines through vibro-acoustic measurements are probably the most commonly adopted leak detection systems. Such systems generally rely on the definition of proper thresholds to detect increments in the vibration levels associated with leaks. Since the thresholds are strongly dependent on the local boundary conditions of the monitored network, the initial setup is costly and time consuming, and the risk of undetected leaks or false alarms increases. This work aims to investigate leak detection methods based on the inherent properties of the measured signals instead of their relative amplitude. In particular, the possibility of detecting water leaks in small-diameter plastic pipes by analyzing the autocorrelation function of vibro-acoustic signals is assessed. An experimental campaign is conducted in a full-scale test facility that simulates the actual network. The measurements concerning artificially generated leaks are attained by two accelerometers and one hydrophone. The experimental results confirm the effectiveness of the proposed approach, which is therefore proven as a promising tool for leak detection.

Use of incremental decomposition and spectrogram in vibroacoustic signal analysis in knee joint disease examination

Use of incremental decomposition and spectrogram in vibroacoustic signal analysis in knee joint disease examination

Determination of elastic mechanical characteristics of surface coatings from analysis of signals obtained by impulse excitation

Most of the surface coatings are based on the synthetic polymers, which are substances composed from very large molecules that form tough, flexible, adhesive films when applied to surfaces. The other components of surface coverings materials are pigments that provide colour, opacity, gloss and other properties. Surface coatings are two-phase composite materials: constitute a polymer matrix on the one side, and on the other side of the pigments and additives dispersed in the matrix. Their role is not only aesthetically but also to ensure anticorrosive protection or even improve some mechanical properties of coated surfaces. In this paper it will follow, starting from the mechanical properties of the substrate, the metallic sheet in general, to determine the new properties of the assembly of substrate and the two coating layers, also the determination of mechanical properties of the layers. From the analysis of vibroacoustic signals obtained by the impulse excitation of the sample, one can determine the elasticity modulus. These results come to validate the results based on finite element analysis (FEA) of the same samples.

On the use of signal smoothness estimates and signal similarity in bearing fault detection

The concepts of signal smoothness and signal similarity are very common in digital signal processing. In this paper, both concepts have been explored in the ball bearing failure diagnostics, where the bearing fault, bearing inner race and outer race faults were analysed. It was found out that the signal smoothness and the signal similarity estimates might reduce computational tolerance in the vibro-acoustic signal analysis. On this basis, numerous experiments have been carried out to demonstrate usefulness of the above-mentioned estimates (as useful parameters of signal features) in the signal quality analysis.

Evaluation of the Technical Condition of the Active Part of the High Power Transformer Based on Measurements and Analysis of Vibroacoustic Signals

Abstract This article presents the results of research connected with the development and industrial use of vibroacoustic methods for the evaluation of the technical condition of the active part of transformers. The article presents the results of the analysis of vibrations generated by the high power transformer in which a defect was found on the basis of tests of oil carried out using the chromatography tests. In order to confirm the damage of the active part of this transformer, vibroacoustic measurements were performed in three states of its operation. The measurement using the classical vibroacoustic method included the registration of vibrations at the idle speed and during the load operation of the transformer. The original diagnostic method, so-called the modified vibroacoustic method, was also used during the measurement. The analysis of signals recorded using the classical vibroacoustic method was carried out in the frequency domain by indicating the amplitude of even harmonic vibrations. However, the analysis of signals measured during the commissioning of the transformer was conducted in the time-frequency domain using the short-time Fourier transform (STFT), continuous wavelet transform (CWT), and discrete wavelet transform (DWT). On the basis of the analysis of the results obtained it was stated that the increased level of vibrations of this transformer is a consequence of the loss of rigidity of the mechanical structure of its core.

Designing the technology of express diagnostics of electric train's traction drive by means of fractal analysis

The object of this study was the development of technology of the express diagnostics of the traction drives of electric trains. Its base was obtaining, processing and fractal analysis of vibroacoustic signals, which makes it possible to forecast the period of service of this unit in between planned maintenance works. We carried out the research into the failures of equipment of electric trains in operation, which showed that the share of defects in the traction reducers is the most significant and amounts to 41,2 % of the total number of failures in the carriage part. The method of selection of acoustic components (samples) was created, which makes it possible to separate them from the complete vibroacoustic signal. Its characteristic peculiarity is initial link to the time interval, determining final duration, as well as selection of a number of cyclically repeated components with each rotation of the large gear of the traction drive. Based on the wavelet conversion of detailing coefficients with high content of noise components, we used the method of denoising vibroacoustic samples with the help of soft thresholding. As the diagnostic parameter, the fractal Hurst index is proposed. The process of its determining is described and the maximum ranges of its change from the point of view of persistence are found. Accordingly, the Hurst index's matching one or another range makes it possible to tell the presence or absence of defect in the traction drive, which can be later on, during a regular maintenance, categorized and removed. Thus, the application of the comprehensive technology of the express diagnostics makes it possible to promptly assess the technical condition of the traction drives of electric trains and to forecast their working capacity in between the planned types of repairs.

Joint Motion Quality in Chondromalacia Progression Assessed by Vibroacoustic Signal Analysis

BackgroundBecause of the specific biomechanical environment of the patellofemoral joint, chondral disorders, including chondromalacia, often are observed in this articulation. Chondromalacia via pathologic changes in cartilage may lead to qualitative impairment of knee joint motion. ObjectiveTo determine the patellofemoral joint motion quality in particular chondromalacia stages and to compare with controls. DesignRetrospective, comparative study. SettingVoivodship hospitals, university biomechanical laboratory. PatientsA total of 89 knees with chondromalacia (25 with stage I; 30 with stage II and 34 with stage III) from 50 patients and 64 control healthy knees (from 32 individuals). MethodsVibroacoustic signal pattern analysis of joint motion quality. Main Outcome MeasurementsFor all knees vibroacoustic signals were recorded. Each obtained signal was described by variation of mean square, mean range (R4), and power spectral density for frequency of 50-250 Hz (P1) and 250-450 Hz (P2) parameters. ResultsDifferences between healthy controls and all chondromalacic knees as well as chondromalacia patellae groups were observed as an increase of analyzed parameters (P < .001) with only one exception. No statistically significant difference between control group and stage I of chondromalacia patellae was found. All chondromalacia groups were differentiated by the use of all analyzed parameters (P < .01), whose values correspond to the progress of chondromalacia. ConclusionsChondromalacia generates abnormal vibroacoustic signals, and there seems to be a relationship between the level of signal amplitude as well as frequency and cartilage destruction from the superficial layer to the subchondral bone. Level of EvidenceIV