DIAGNOSTYKA Vol. 18, No. 1 (2017)
Table of contents - SCIENTIFIC PAPERS
Jacek WODECKI, Rafał ZDUNEK, Agnieszka WYŁOMAŃSKA, Radosław ZIMROZ
Pages : 3-8

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Abstract (EN)
Information extraction is a very important problem nowadays. In diagnostics, it is particularly useful when one desires to isolate information about machine damage from a measured diagnostic signal. The method presented in this paper utilizes the idea that is based on a very important topic in numerical algebra, which is nonnegative matrix factorization. When applied to the matrix of multidimensional representation of the measured data, it can extract very useful information about the events which occur in the signal and are not recognizable otherwise. In the presented methodology, we use the algorithm called Semi-Binary Nonnegative Matrix Factorization (SB-NMF), and apply it to a time-frequency representation of the real-life vibration signal measured on faulty bearing operating in a belt conveyor driving station. Detected impulses of local damage are clearly identifiable. Performance of the algorithm is very satisfying in terms of time efficiency and output signal quality.

Matteo MANA, Emanuele PICCIONI, Ludovico TERZI
Pages : 9-16

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Abstract (EN)

Wind turbines undergo dynamic loads along all the phases of transformation of wind kinetic energy into power output to be fed into the grid. Gearbox breakdowns are one of the most common and most severe causes of energy losses and it is therefore crucial to prevent and forecast them. Straightforward vibration analysis is very demanding by the point of view of technology, costs and complexity of signal denoising. A considerable keystone in fault diagnosis is the analysis of Supervisory Control And Data Acquisition (SCADA) systems. In particular, thermal behaviour of wind turbines fits well with the common time scale of SCADA data; heating trends are fairly responsive as a consequence of rotor vibration. Machine learning techniques applied to SCADA data are very powerful in reconstructing inputs – output dependency. On these grounds, in this work an Artificial Neural Network approach is proposed for early diagnosis of gearbox faults. The method is validated on the data of a wind farm operating in Italy. It is shown that the method is capable in recognizing incoming faults with a very manageable advance also with data on short time scales.

Pages : 17-24

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Abstract (EN)
Optimal alignment of wind turbines to the wind direction is a crucial condition for the quality of power output and for the health of the turbines. Actually, bad alignment can cause degraded performances and dangerous loads that can affect, on the long run, the mechanical safety of the wind turbine. Supervisory Control And Data Acquisition (SCADA) systems are becoming widespread in modern wind energy technology because of the appreciable costs – benefits ratio. The common time scale of SCADA, yet, usually is not effective for misalignment diagnosis because the wind varies too rapidly. For this reason, misalignment is often diagnosed using ad hoc techniques as LIDAR-based or spinner anemometers. In the present work, it is shown that very useful indications for the diagnosis of misalignment can be obtained also from the SCADA data, without invoking expensive supplementary control techniques. The method is validated on the data set of a wind farm sited in Italy.

Pages : 25-35

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Abstract (EN)
We examine the mathematical model of start processes of the electromechanical system of the ring-ball mill, which was built taking into account the interaction of electromagnetic phenomena in asynchronous motor and mechanical vibrational phenomena. The specifics of transfer of the torque from the motor to the reducer by means of the centrifugal clutch with shot are taken into account in the motion equations of the mechanical system, as well as instability of reduced moment of inertia of the actuating mechanism and parameters of the technological load during filling or emptying of crushing cell. Electromagnetic state of asynchronous motor is described based on magnetic saturation. The mathematical model can be used to predict the fatigue strength of heavy loaded elements of ring-ball mill’s constructions. Substantiated practical recommendations aimed at reducing the dynamic loads of the main shaft of the mill.

Przemysław GONEK, Mateusz LISOWSKI, Tadeusz UHL
Pages : 37-44

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Abstract (EN)
This paper presents an idea of wirelessly powered mobile sensors utilizing cloud management system similar to the swarm robotics. Sensors are based on the previously developed wireless passive sensors working with RFID protocol in the HF range. Preliminary research presented in this paper is related to the energy harvesting efficiency evaluation and the possibility to wirelessly power an electric motor. Performed experiments show that the magnetic field generated by the RFID reader antenna provides enough amount of energy not only to perform communication, measurements and computation, but to power the actuators as well. Achieved results state a base for further investigation in the area of wireless passive mobile sensors.

Henryk Franciszek TYLICKI, Ryszard MOKRZYCKI
Pages : 45-50

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Abstract (EN)
The following article presents an original method of resolving the problem connected with production line machines life maintenance with the use of state forecasting procedures. The research problem undertaken in this article focuses on defining and describing how to maintain a usability state for production line machinery used in industries on the example of the Philips Lighting Poland S.A. in Piła. The defined problems could probably be eliminated by shifting from a planed-preventive strategy to a state-based machinery usage strategy. To implement the second course of action it is necessary to develop suitable procedures monitoring the state of machines used in production lines, including procedures of their state evaluation and state prognosis.

Pages : 51-58

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Abstract (EN)
This article presents the experimental research on ball bearings, which could be applied in vapour microturbines operating in CHP systems. The bearings are of three kinds, according to their constructional solution: 1.  all-steel (all components are made of steel); 2. ceramic-steel-hybrid (ceramic balls,  steel cage and races); 3.  all-ceramic (the balls, as well as external and internal races, are made from ceramic silicon nitride – Si3N4, while the cage is made of PTFE). The test rig and the research method were discussed. In order to have a better picture of vibrations of the rotor-bearing system, we applied the bearing system with a flexible rotor. That option entailed some difficulties, however. In each case, both the analysis of the ball bearings\' properties and of the impact of ceramic components on the dynamic performance of the rotor was carried out. The results of these analyses are presented in the following forms: displacement amplitudes of the rotor, colormap graphs of the type Order Spectrum Analysis and three-dimensional vibration trajectories. The bearings were analysed on the basis of colormap graphs, while the analysis of the rotating rotor was conducted using graphs depicting 3D vibration trajectories and displacement amplitudes at the disk location. As a result of all this work that we have mentioned, useful information on the possible application of tested bearings for vapour microturbines has been gained.

Andrzej GĘBURA
Pages : 59-66

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Abstract (EN)
The  article describes test results of   rolling bearings conducted on turbojets, with the simultaneous use of two diagnostics methods: FAM-C and FDM-A [7]. For these methods, no installation of additional sensors on the aircraft is needed – the on-board electric generators are used as sensors. The „FAM-C” method uses the aircraft’s alternating current (AC) tachometer generator, whereas the “FDM-A” method uses the direct current (DC) commutator-type generator. Spectrum of angular velocity of individual bearings manifests itself in  high frequency ranges (60-240 Hz for the tachometer generator, 3-10 kHz for the DC generator), making the oscillation signal resistant to noise. This frequency modulated signal can be picked up by measuring instruments in any point of the aircraft electrical system. After detection the initial signal is obtained. Measurement analysis can be easily automated [10]. During detection, the carrier frequency is filtered off. Currently, with the simultaneous use of correlated FAM-C and FDM-A methods, four models of rolling bearings wear can be detected: increase of aggregate friction, seizure of rolling elements, increase of radial clearances, increase of axial clearance. This division was made on the basis of observing the technical condition of rolling bearings on many (around 30) turbojets during its normal operation.

Pages : 67-72

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Abstract (EN)

Speed limitations imposed upon vehicles using the road network are practically brought down to a road administrator defining a certain presupposed discrete value. The latter is typically dependent on the arrangement of linear road infrastructure elements and local development (visibility), the road pavement condition and the roadway geometry. Such a limitation is sometimes consequential to excessive noise or technical specificity of an infrastructure element, which is the case of bridges, tunnels etc. Every officially imposed speed limit set at a too high level against the legitimate requirements (needs) causes considerable losses in terms of traffic flow and affects (also negatively) the behaviour of drivers. From a cognitive perspective, a lower and unjustified speed limit causing irritation among vehicle drivers may not necessarily translate into increased traffic safety. Reduction of traffic flow in road network cross-sections stems from the fact that the permissible speed has been limited to a level below the free flow traffic speed, only based on discrete (step) values, and not always the appropriate ones. This article provides a discussion on a method for determining a legitimate speed limit for a road network based on mobile diagnostics of vehicles. It also touches upon the problem of dynamic adjustment of this specific road network parameter, which will prove crucial for intelligent transport systems (ITS) in the nearest future.

Pages : 73-78

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Abstract (EN)
The present work provides an overview on the selected applications of peridynamics to damage modelling and simulations of its propagation in mechanical structures. The theoretical fundamentals of the method are briefly described to highlight its advantages and the scope of practical use in the field of computational mechanics. Selected results of numerical analyses are provided to illustrate demanded capabilities. The perspectives of nonlocal and integral based problem formulations for dynamics are discussed.

Pages : 79-86

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Abstract (EN)
In this article an attempt to diagnose damage to the shock absorbers of a passenger car during road operation with the use of vibration response measurement  has been described. Accelerometers were mounted on the body – sprung mass. Based on the recorded signals, FFT and Cross-Spectrum graphs were prepared. The test was performed for several variants shock absorber damage.
The single-number index of vibration amplitude increase, in the range of resonance frequency, was calculated, based on spectrum analysis. The results are shown as graphs and tables, for different damage types. The realization of measurement and adopted method of damage diagnosis are described.

Pages : 87-93

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Abstract (EN)
Automotive spark plugs are essential ignition circuit components being of importance for combustion engine reliability and performance. The majority of spark plugs have ribbed ceramic insulator to ensure high resistance along the surface from the terminal to the metal shell to minimize leakage current and to provide flashover protection. The leakage current intensity depends on electric field distribution, physical insulator properties and such factors as humidity, insulator contamination or defects in insulation material. Furthermore, leakage current not infrequently interferes with discharge process causing misfire effect being harmful to exhaust manifold components, mainly to catalytic converters. This paper presents simulation results of electric field distribution in ceramic insulator, in silicone rubber boot and in space surrounding a spark plug. Assuming that a spark plug can be considered as an object having cylindrical symmetry the electric field distribution was calculated for a two-dimensional case in accordance with Laplace’s and Poisson’s equations. In this paper, the finite difference method (FDM) for the solution of the Laplace’s equation was applied. The FDM algorithm based on the Liebmann’s method was developed in the MATLAB environment. Presented simulation results can be helpful to automotive spark plugs and high-tension cables manufacturers interested in improvement of insulating properties.

Pages : 95-102

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Abstract (EN)

In the recent years, foil bearings have increasingly been used over a wide variety of different high-speed fluid-flow machinery. Since modern bearings of this type are the complex result of an assembly of several interdependent components, both their theoretical description and their modelling is very problematic. This article provides an analysis of the rotor supported by foil bearings conducted on the basis of an in-house developed numerical model. The model takes into account both structural and flow-related parameters, and makes it possible to determine the characteristics of a foil bearing under various operating conditions. The developed model allows analysing the dynamic performance of different foil bearings, taking into account the lubricating medium\'s properties as well as the geometry and characteristics of structural materials (top foil and bump foil). It gives an opportunity to shape the bearing freely so as to optimise its structure. An example of such an optimisation, which aims to minimise vibration of the rotor, was presented in the article.