DIAGNOSTYKA Vol. 18, No. 4 (2017)
Table of contents - SCIENTIFIC PAPERS
Mohamed Ben RAHMOUNE, Ahmed HAFAIFA, Kouzou ABDELLAH, XiaoQi CHEN
Pages : 3-10

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Abstract (EN)

The automatic engineering known a very rapid progress with the consequent development of numerical methods and computer systems, by the growth of computational capacity. In this context, this work proposes a strategy of predictive control of the high-pressure shaft speed of a gas turbine using artificial neural networks in order to monitor the vibratory behavior of this rotating machine. This approach makes it possible to ensure the stability of this turbine under real conditions and to detect any deviation of their dynamic behavior from the margin of safety. This approach makes it possible to include the control limitations on the turbine variables in the modeling step of the high-speed shaft speed controller.


Moussa GUEBAILIA, Nouredine OUELAA
Pages : 11-17

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Abstract (EN)

Several dynamic effects can be generated and simply observed by the passage of an external mobile exciter forces with different speeds on the surface of an orthotropic continuous plate. In the present paper one illustrates the dynamic behaviour of a thin, orthotropic, multi-span plate, subjected to the passage of moving exciters. In this model, the roughness of the surface of the plate is considered as the contact surface between mobile exciter and the plate. The modal and Newmark integration methods are used in order to solve the coupled plate–exciter equations of motion. One presents especially results which show clearly the influence of the surface states on the dynamic behaviour of the plate and also the generated interaction forces due to the surface roughness. In this paper one presents also the influence of the mobile exciter speeds on the plate dynamic response.


Miroslav BLATNICKY, Dalibor BARTA, Jan DIZO, Pawel DROZDZIEL
Pages : 19-26

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Abstract (EN)

The paper deals with analytical determination of the stress concentrator location on a sample serving for diagnosing multiaxial fatigue lifespan of aluminium alloys, which are applied for reducing weight of road and rail vehicle constructions for acquiring decrease of fuel consumption. This article put emphasis on significance of appropriate sample design and notch location according to the material type and mounting in the testing device. It operates also with suitable welding technology selection and thus ensures input parameters for numerical simulations of selected welding technology. The aim of numerical simulations is obtaining important information that will serve for detailed fatigue lifespan prediction in comparison of base and weld material.


Jairo A GRAJALES, Héctor F QUINTERO, Juan F LÓPEZ, Carlos A ROMERO, Edison HENAO, Oscar CARDONA
Pages : 27-36

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Abstract (EN)

Fault diagnosis of an internal combustion engine is proposed herein by means of vibration analysis and a comparative analysis of normal operation and induced misfire scenarios. In order to validate previous works on misfire with pure gasoline, measurements also included tests performed with ethanol-gasoline fuel blends. According to results, changes in the fuel mix seem to have little impact on the performance and behaviour of the engine. And additionally, the particular frequency components that allowed differentiation between normal and faulty conditions were also present on all the fuel blends tested. Fast Fourier Transform was applied to obtain the frequency domain of the signal as a previous step to the subsequent identification process based on statistical characteristics extraction. A fuel blend classification method based on the analysis of the vibration signals of the engine was studied using envelope, Spike Energy and Peak Value techniques. Differentiation was possible with the extraction of the statistical features of the Peak Value spectrum of the longitudinal acceleration with a specific filter selection.


Jarosław ŁUKASIAK, Adam ROSIŃSKI
Pages : 37-42

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Abstract (EN)

This paper presented issues concerning the operation process of electronic safety systems. The particular attention was paid to the issues related to periodic inspections and rationalisation of the readiness index value. The analysis of current reliability and operation models allowed to conclude that a thesis, which also takes into account information obtained from diagnostic subsystems, is right. This approach made it possible to develop a graph of relationships in the system including diagnostic information.


Erwin WOJTCZAK, Magdalena RUCKA
Pages : 43-49

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Abstract (EN)

The aim of the study is the elastic wave propagation in adhesive joints of metal rods that are one of the simplest kind of glue connections. They are consisted of two metal members and an adhesive layer joining two parts together. The analysis is directed to technical diagnostics of such type of connections. Longitudinal and transversal guided waves were excited in prepared joints. Signals of propagating waves were registered in a couple of points by means of PZT plate sensors. Butt and single lap joints were tested. Single rod was also investigated to compare with adhesive joints. There were two approaches applied for both types of connections: experimental investigations and FEM analysis. In the study, the possibility of the application of guided waves in diagnostics of adhesive joints of metal rods was analysed.


Jacek DYBAŁA, Krzysztof Marcin NADULICZ
Pages : 51-59

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Abstract (EN)

As the quality of welded joints transfers to the load carrying capacity of structures, welded joints naturally become the object of diagnostic tests. Welded joints are mainly tested in order to find out the places with structural or mechanical non-homogeneities. It is caused by the fact that the existence of welding imperfections significantly decreases mechanical properties of the welded joint and especially its fatigue strength.

The paper presents some results of diagnostic tests for welded joints of steel components carried out with the use of passive and active magnetic methods. Faults of the welded joint occurring within a tested object cause the phenomenon of magnetic anomalies existing over a tested surface and this phenomenon has been used to detect welding imperfections. A specially designed measurement matrix consisting of 768 one-axial miniature magnetic field sensors has been used to record the magnetic flux leakage. The paper includes a comparison of the effectiveness of diagnosing using the passive and active magnetic method. Moreover, it was shown that the magnetic diagnostics provides rapid inspection of quality of welded joints with no need for special preparation of joints for testing which is relevant for its practical applications and results in low costs of such tests.


Roberto MARSILI, Nicola BORGARELLI
Pages : 61-67

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Abstract (EN)

The development of new techniques for the measurement of contact pressure distributions between bodies in contact is of large interest in mechanics, for the design and verify of many couplings between mechanical components. Examples are the contact between tooth of gears, between the balls and rings of ball bearings, between the wheel and rail etc.

In this paper a new measurement technique is proposed, based on the measurement principle known as thermoelasticity. The particular case about the measurement of contact pressure distribution between a ball and a flat plate is discussed. Previous studies was performed in order to examine the contact surface between the two bodies realizing one of the two bodies in contact using an infrared transparent material, with appropriate values of the other mechanical properties. These studies were anyway only qualitative. In the present work, two calibration methodologies are proposed to obtain measures of contact surface stress between a ball and a flat. One of these methodologies is based on experimental test and the other one is based also on analytic results. The measured stress behaviours are in agreement with the classic Hertz theory; relative uncertainty is smaller than 0.1. This allows to obtain first quantitative results of contact pressure distribution by using thermoelasticity.


Robert BARAŃSKI, Anna GRZECZKA
Pages : 69-77

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Abstract (EN)

Recently, there has been a noticeable increase in interest in solutions utilizing electrical signals accompanying muscle activity. Electromyography (EMG) is a technique for recording, analysis and evaluating the electrical activity produced by striated muscle. Its great popularity is due, among other, to the ability to measure with non-invasive electrodes (called as sEMG surface electromyography). However, the limitations of this method are the high costs of specialized measuring equipment, and in particular the systems of bioelectric signal preamplifier circuits.

The work presents the design of a low budget EMG signal amplifier. It has been designed and validated in accordance with ISEK (International Society of Electrophysiology and Kinesiology) and SENIAM (Surface ElectroMyGraphy for Non-Invasive Assessment of Muscles).


Dariusz BUCHCZIK, Marek PAWEŁCZYK
Pages : 79-87

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Abstract (EN)

Vibrational diagnostics of machines is usually based on use of accelerometers. Their calibration is required in order to obtain reliable results. This paper presents method for calibration of accelerometers using a multisinusoidal excitation. There is also proposed a procedure for estimating uncertainty of the obtained characteristics. The routine is based on an analysis of signals in the frequency domain using evaluation of cross power spectral density between the signals from the calibrated and standard accelerometer and evaluation of power spectral density of the signal from the standard accelerometer. The procedure allows to determine the nominal sensitivity, amplitude-frequency characteristics and estimate their uncertainties. The experiments were performed using a piezoelectric sensor PCB 338B35, and a sensor based on ADXL 202 capacitive accelerometer constructed at Silesian University of Technology. Results of this study show that the proposed method can be successfully used. The main advantage of the routine is a very short duration of the measurement experiment. Values of estimated relative uncertainties reach several percent. The procedure can be applied when it is necessary to quickly check the sensor characteristics, for example in the field for periodical maintenance of sensors mounted on the machine.


Joanna IWANIEC, Marek IWANIEC
Pages : 89-96

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Abstract (EN)

Currently, for the purposes of recorded ECG signals (electrocardiograms) interpretation, the classical methods involving analysis of geometrical properties of the recorded waveforms in time domain are used. Such an analysis consists in determining the values of parameters describing the heart rate and rhythm. However, these indicators can not be treated as an infallible criterion for diagnosis and, moreover, the limits of increasing the accuracy of ECG analysis by increasing the accuracy of determining its characteristic points have already been reached. Therefore, in the paper, for the purposes of analysis of registered ECG signals and acoustical recordings of heart work, it is proposed to use the recurrence plots and RQA analysis methods that consist in searching for the recurrence properties of the registered signals. Application of the recurrence-based methods is natural due to the cyclic character of the heart work while providing patterns characteristic for different cardiac dysfunctions supported by objective, quantitative measures will contribute to early, credible and reliable classification of cardiovascular dysfunction.


Ryszard BŁAŻEJ, Leszek JURDZIAK, Agata KIRJANÓW, Tomasz KOZŁOWSKI
Pages : 97-102

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Abstract (EN)

Loads acting on the conveyor belt cause it to undergo a continuous process of wear and tear. One of many symptoms indicating such wear and tear is the abrasion of the carrying cover and the pulley cover. Decrements in the belt’s cross-section reduce its puncture resistance, thus increasing the risk of core damage. Early detection of even the slightest damage to belt covers and the evaluation of damage increment may help the user to prepare a more precise schedule of current repairs. Such precision will in turn help to minimize losses due to belt conveyor emergency downtime. This article presents a device for measuring conveyor belt thickness and for evaluating the changes in the belt’s transverse and longitudinal profile. The measurements are performed continuously, along the belt axis. Belt thickness is measured on a flat section, during belt operation. The device may be applied to any type of belt used in mining industry. The measurement device is managed by an application called DiagBeltSonic, specially designed for this purpose. The application allows the user to define some basic information about the conveyor prior to the test. The measurement results show a sectional view of the belt along the length of the complete loop and also show the longitudinal and transverse profile of the tested belt.


Andrzej PUCHALSKI, Iwona KOMORSKA
Pages : 103-110

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Abstract (EN)

Vibrodiagnostic analysis of wearing and/or defects of complex rotating systems confirms the presence of non-linear, nonstationary and multiscale properties as well as long-term correlations of real signals. The recorded time series of vibrations are often of an impulse character. Probability distributions are different than Gaussian distributions and exhibit heavy-tails. These are important sources of multifractal dynamics, requiring advanced, data-based modelling methods. The reliable numerical algorithms, used for calculations of functions of stable distributions and multifractal properties, were applied in the approach presented in the hereby paper. Relations between parameters of stable distributions and singularity spectra indicate the possibility of applying both methods for modelling mechanical vibrations signals in diagnostics of complex systems. The performed investigations confirmed the possibility of modelling and assessing the observed states of the powertrain of vehicles with SI engines, on the bases of parameters of alpha-stable distribution (ASD) and parameterised entropy of mechanical vibrations signals.