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1

Wavelet transform in vibroacoustic diagnostic of machines

Haller Piotr, Jankowski Antoni, Kaźmierczak Andrzej, Wróbel Radosław

Journal of KONES

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2019

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Vol. 26, No. 1

47--55

EN

This article discusses the use of wavelet decomposition in the diagnostics of vibrometric signals of an engine. Apart from presenting the possibility of using wavelets in diagnostics, the authors take up the subject of the applicability range of processing for stationary signals, which until now has been reserved for non-stationary signals. A unified definition of signal stationarity has been proposed, which is not based on statistics. The authors presented methods of wavelet decomposition of a vibrometric signal of combustion engine vibrations, measured with the use of LDV (Laser Doppler Vibrometry). Laser measurements allows for studying an object without 'touching' its housing. Basing on the relative velocity of engine vibrations, the authors indicate how reliable vibrations are in diagnostics. Despite higher costs, this measurement method gives better results (for specific cases) than acoustic studies. Transform – wavelet decomposition is a solution hardly ever used in machine diagnostics; it is more often applied in medicine and image recognition. The authors presented the differences that can be obtained for different levels of decomposition, and also presented the impact on the engine condition assessment through the use of filtering (windowing) the signal before decomposition.

2

Transmission of vibrations from the engine to the car body

Aleksieva V., Valchanov H., Magdziak-Tokłowicz M., Wróbel J., Włostowski R.

Journal of KONES

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2016

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Vol. 23, No. 4

17--23

EN

Vibrations have become an important factor of vehicles. Vibration tests help identify, and then tune the automotive vehicle to improve the structural strength. Due to the increasing development of vehicles and machines and their widespread use. Increased research-using vibrations due to their low or zero interference with the vehicle under test. Vibration testing is often carried out using Laser Doppler Vibrometry (LDV), a device that is used for contactless measurement of vibration on the surface. The laser beam is directed from the device to the surface of interest, and the amplitude and frequency of vibration are extracted from the Doppler shift frequency of the reflected laser beam due to the movement surface. High values of vibration transmitted from the engine, and the way significantly affect the body of the vehicle and the driver. Article presents results of research carried out on vehicles powered by three different engines and rpm. Tests were carried out on an engine dynamometer in the same environmental conditions. Two of engines were with spark ignition, including one with a supercharged engine and compression ignition engine. The measurements were made using the Laser Doppler Vibrometry using Fast Fourier Transform. The spectrum obtained is used for further analysis to determine the acceleration level at various frequencies. Obtained from Fast Fourier Transform readings used for drawing graphs of frequency V acceleration. The results of the study are interesting and promising, as they show a significant difference in the velocity for spark ignition engines and compression-ignition.

3

NVH application research using accelerometers on a chassis dynamometer

Sitnik L., Wróbel R., Andrych-Zalewska M., Mihaylov V.

Journal of KONES

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2016

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Vol. 23, No. 3

443--448

EN

Accelerometric tests, similarly to laser tests (with regard to human health) are something of novelty. All standards related to this issue refer to sound intensity (measured using specialised microphones). The work presents results of accelerometric tests conducted during driving cycles on an inertial load chassis dynamometer Maha LPS3000. The object of the research was Mazda 3 1.6 (petrol), built in 2010, mileage 70 thousand km. The tests were related to vibration measurements on a chassis dynamometer using various, forced tractive effort (300, 500 and 700 N). No additional signal processing was used (except for operations necessary to create a spectrum) so as to present the whole vibration spectrum with special emphasis on the resonance frequency of human organs. The article presents vibration amplitude measured at the level of the headrest for three forced tractive efforts: 300, 500 and 700 N. The measurements were made at the speed of 60 km/h in the fourth gear (which corresponds to about 2000 rpm). The obtained results, indicate that the maximum value of harmonics fall in the range 85-95 Hz. Hence, they are resonance frequencies of eyeballs. In addition to this, one can state that the values of these harmonics are higher for higher values of forced tractive efforts. This would mean that seats should be additionally stabilised (dampened) to limit the influence of dangerous vibration on a human organism.

4

Principles of piezo-based machinery health monitoring

Ostachowicz W., Wandowski T., Malinowski P.

Transactions of the Institute of Fluid-Flow Machinery

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2015

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nr 127

117--136

EN

In this paper methods used for structural health monitoring of machinery parts are discussed. These methods are based on applications of piezoelectric transducers. Proposed methods are used for assessment of structural machine parts manufactured of carbon fiber reinforced plastics/polymers (CFRP) and glass fiber reinforced plastics/polymers (GFRP). The first discussed method is based on elastic wave propagation and scanning laser vibrometry. This method is based on the fact that any kind of structural discontinuities cause changes in elastic wave propagation within the structure. In the proposed approach elastic waves are generated using piezoelectric transducer and then the waves are registered using scanning laser vibrometer. Here attention was paid on an analysis of elastic wave propagation in simple composite parts and parts with complex structure. The paper presents also results of simulated damage localization. The second method is an electromechanical impedance (EMI) technique. In this case piezoelectric transducer is also effectively used. This transducer is attached to an investigated structure. Due to electromechanical coupling of piezoelectric transducer and a structure, characteristics of mechanical resonances of the structure can be registered through the measurement of electrical parameters of piezoelectric transducer. An initiation of damage causes changes in resonant characteristics of considered structures. As electrical parameter very often impedance, admittance, resistance, conductance or reactance are used. For that purpose electrical impedance analyzer is used. Three parameters have been taken for the analysis. For proposed method effective damage indexes have been proposed.

5

Laser Doppler vibrometry with acoustooptic frequency shift

Kaczmarek P. R., Rogowski T., Antończak A. J., Abramski K. M.

Optica Applicata

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2004

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Vol. 34, nr 3

373-384

EN

This paper describes our experiments and investigations on vibration measurements by laser interferometers. The main objective was to build a simple heterodyne interferometer which would allow vibrations of objects with light scattering surface to be measured. The optimisation procedure of optical setup, basic heterodyne interferometer and results are presented.