DIAGNOSTYKA Vol. 15, No. 3 (2014)
Table of contents - SCIENTIFIC PAPERS
Grzegorz Żak, Jakub Obuchowski, Agnieszka Wyłomańska, Radosław Zimroz
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Abstract (EN)
W artykule zaprezentowano nową metodę selekcji informacyjnego pasma częstotliwościowego. Jest ona odpowiednia dla sygnałów drganiowych z maszyny uszkodzonej zawierających impulsy, nawet kiedy są one niewidoczne w dziedzinie czasu, tzn. kiedy wysokoenergetyczne drgania innych elementów zakłócają sygnał informacyjny. Pierwszym krokiem zaproponowanej metody jest dekompozycja sygnału na składowe o prostszej strukturze i ich analiza za pomocą narzędzi statystycznych, tj. modelu ARMA i rozkładu alfa-stabilnego. Wybór tego rozkładu jest umotywowany zdolnością modelowania danych ciężko ogonowych, tzn. sygnałów, w których występują impulsy. Metodę zilustrowano analizą rzeczywistych sygnałów z drganiowych maszyn górniczych. Potwierdzono efektywność zaproponowanej metody statystycznej w kontekście selekcji informacyjnego pasma częstotliwościowego w obecności wysokoenergetycznych zakłóceń.

Jacek CABAN, Paweł DROŹDZIEL, Dalibor BARTA, Štefan LIŠČÁK
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Abstract (EN)
Drivers very often disregard the condition of tires and the value of the prevailing pressure in them. Changes in the value of air pressure in a tire have a significant impact on driving comfort, fuel efficiency and road safety. The article presents selected pressure control systems used in automotive vehicles, based on a literature review and the authors\' experience.

Krzysztof MENDROK
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Abstract (EN)
The structural health monitoring systems seeks to increase the accuracy of diagnosis. Increasingly, raw information about the occurrence of damage is not sufficient. The aim is to determine its location, identification, and even predictions about its propagation. Based on these requirements already in 1993 Rytter [1] proposed the classification of monitoring systems by dividing them into levels from 1 (detection) to 4 (prognosis). To meet the assumptions a method of fault location using local modal filters was developed [2], which was the extension of damage detection method based on spatial filtering [3]. The method of local modal filters correctly locates damage on the object. However, there is a possibility that the multiple damage can occur in the object. In this paper the author will answer the question whether this method will be effective in this type of situation. In the simulations consecutively damages of varying size and location were introduced in the object and it was checked whether they are detectable, and as their increasing number affects the accuracy of location.

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Abstract (EN)
Structures of rail vehicles are designed for a useful structural life of 30 years. However, structural problems which reduce the mechanical performance of the structure might appear due to normal operation conditions and, in some cases, make it unsuitable for a safe operation. This document presents the structural diagnosis of a metro system and the method for the redesign of structural elements of rail vehicles that was derived from this diagnosis, so that the structural performance of both the element and the whole structure is improved. It is based on the European standards related with aluminium and railway applications, and considers the necessary aspects to produce a safe solution for the final design.

Wojciech SAWCZUK
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Abstract (EN)
The article presents a new method for diagnosis of the wear of friction pads through analysis of the braking vibration during braking with the constant braking power and during braking to stop by making the analysis of signals in the amplitude domain. At the time of research there are vibration acceleration generated by the caliper with  brake pads during braking.

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Abstract (EN)
Marine diesel engines are generators of mechanical energy, but also are generators of toxic
compounds into the atmosphere. The composition of the exhaust gas may be a carrier of diagnostic
information about the condition of functional systems of the engine. Results of the classification
and selection of diagnostic signals for selected marine engine malfunctions are presented. The
analysis was based on results of laboratory tests. Mentioned classification was able to isolate
symptoms of malfunctions of marine 4-stroke diesel engine in the composition of the exhaust gas.
Complementary detection signals are exhaust gas temperature behind each cylinder. The
conclusion of this work is the ability to detect by this method such engine malfunctions as the
throttling the air intake duct, the throttling of the exhaust gas duct, the decreasing and the
increasing of fuel injection pressure on the selected cylinder, chocked or discalibrated fuel injector,
the leakage of the fuel pump, changing of the fuel injection timing and exhaust and inlet valves

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Abstract (EN)
This article contains a short description of available diagnostic methods according to which the
technical condition of car shock absorbers is analysed. In Polish diagnostic stands, the devices
operating based on Eusama method are commonly used. This method has many advantages, but it
also has certain limitations about which the analyst should know. The paper presents the analysis
showing how the failure to observe the accepted in regulations way of examining influences the
value of damping of shock absorbers.

Mateusz MARZEC, Tadeusz UHL, Dariusz MICHALAK
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Abstract (EN)
Constantly increasing maintenance costs impose optimal maintenance policy planning. One possible way which helps to minimize maintenance costs and prevent bus fleet availability is analysis of historical maintenance records, which contain information about failures and performed repairs. In many cases this data have free text form and their analysis require individual log-by-log examination of their content. In order to automate this process, text mining methods can be applied. But, accuracy of the analysis depends on data quality and employed methods and should be tested before using this approach. This is especially important when the service decisions, which influence safety and maintenance costs, are made on this basis.
The aim of this paper is to determine whether existing and currently used text-mining methods are sufficiently accurate to be used in classification of unstructured urban bus maintenance and repair data. For that purpose the case study and literature review has been conducted.
The study shows great capabilities of proposed classification model. The model has 99% of accuracy and can be applied to support maintenance decisions.

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Abstract (EN)
The paper presents results of analysis how sea waves affect variation of angular speed of a propulsion shaft of the ship during sea passage. That information is necessary to evaluate the level of credibility of measurements taken as reference value for detection of main engine combustion failures and evaluation of cylinders’ contribution to total power based on shaft’s angular speed irregularity observations. Utilization of IAS (Instantaneous Angular Speed) for diagnostic purposes is mostly based on comparison of actual state measurement with characteristics taken during healthy engine run in certain outer conditions. For marine propulsion set, the weather deriving factor, having impact at angular speed of the shaft, is torque variation caused by changes of propeller’s draught due to pitch of the hull. The aim of analysis was to evaluate how pitching frequency affect run of IAS and how to process obtained data to eliminate harmonics deriving from sea waving.

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Abstract (EN)
The aim of this paper is to show methodology of forecasting with various horizon of prediction
using grey system theory, basing on practical application to vibration condition monitoring
problems. The method of forecasting was based on GM(1,1) prognostic models with various
window lengths for estimating model parameters. The model GM(1,1) is very effective where we
have only few data, incomplete, and with low accuracy. The moving window method applied to
GM(1,1) model enables to adapt to changes in data trend. However, selecting an inappropriate
window length can result in excessive forecast errors. The applied algorithm is based on tracking
the current prediction error for models having various window lengths, and then eliminating the
models for which the error of prediction caused by the loss of adequacy of the model to the data
increases excessively.

Original Research Article : test
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Abstract (EN)