DIAGNOSTYKA Vol. 18, No. 3 (2017)
Table of contents - SCIENTIFIC PAPERS
Clement U MBA, Stefano MARCHESIELLO, Alessandro FASANA, Luigi GARIBALDI
Pages : 3-13

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Abstract (EN)

This study demonstrates how a time domain data based non-linear approach known as Stochastic Resonance (SR) can be effectively used for fault detection in spur gearboxes. SR has just been used recently for fault diagnosis in mechanical systems with a focus on faulty systems. This paper examines the behaviour of SR when it is applied to healthy systems, in particular a healthy gearbox and explores approaches like residual signal and filtered signal computations to aid in the containment of false alarms while improving overall results. Although SR is a time domain procedure, its results also extend to the frequency domain.

Abdellatif RAHMOUNI, Rhali BENAMAR
Pages : 15-20

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Abstract (EN)

Functionally graded materials are used in aircrafts, space vehicles and defence industries because of their good thermal resistance. Geometrically nonlinear free vibration of a functionally graded beam with clamped ends (FGCB) is modeled here by an N-dof discrete system presenting an equivalent isotropic beam, with effective bending and axial stiffness parameters obtained via a homogenization procedure. The discrete model is made of N masses placed at the ends of solid bars connected by rotational springs, presenting the flexural rigidity. Transverse displacements of the bar ends induce a variation in their lengths giving rise to axial forces modeled by longitudinal springs. The nonlinear semi-analytical model previously developed is used to reduce the vibration problem, via application of Hamilton’s principle and spectral analysis, to a nonlinear algebraic system involving the mass and rigidity tensors mij and kij and the nonlinearity tensor bijkl. The material properties of the (FGCB) examined is assumed to be graded according to a power rule of mixture in the thickness direction. The fundamental nonlinear frequency parameters found for the (FGCB) are in a good agreement with previously published results showing the validity of the present equivalent discrete model and its availability for further applications to non-uniform beam.

Pages : 21-29

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Abstract (EN)

This paper concerns the analysis of experimental data, verifying the applicability of signal analysis techniques for condition monitoring of a packaging machine. In particular, the activity focuses on the cutting process that divides a continuous flow of packaging paper into single packages. The cutting process is made by a steel knife driven by a hydraulic system. Actually, the knives are frequently substituted, causing frequent stops of the machine and consequent lost production costs. The aim of this paper is to develop a diagnostic procedure to assess the wearing condition of blades, reducing the stops for maintenance. The packaging machine was provided with pressure sensor that monitors the hydraulic system driving the blade. Processing the pressure data comprises three main steps: the selection of scalar quantities that could be indicative of the condition of the knife. A clustering analysis was used to set up a threshold between unfaulted and faulted knives. Finally, a Support Vector Machine (SVM) model was applied to classify the technical condition of knife during its lifetime.

Pages : 31-37

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Abstract (EN)

The objective of this paper is focused on the computer modelling and dynamic simulation of a coach with damaged wheel and the assessment of these negative effects on a track. The article is composed of two parts. Firstly, problems about the operation of rolling stocks with damaged wheels are described. There are also mentioned diagnostic systems installed on a track for detection and assessment their negative impacts on a track. The second part of the article is dedicated to computer modelling of a coach running on a railway track with the damaged wheel, in this case with the wheel-flat. For these purposes the virtual model of a coach were created. After simulations of its running there were performed analyses needed for the evaluation of its negative impacts on a railway track.

Pages : 39-46

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Abstract (EN)

The present paper introduces a discrete physical model to approach the problem of nonlinear vibrations of cracked beams resting on elastic foundations. It consists of a beam made of several small bars, evenly spaced, connected by spiral springs, presenting the beam bending stiffness. The crack is modeled by a spiral spring with a reduced stiffness and the Winkler soil stiffness is modeled using linear vertical springs. Concentrated masses, presenting the inertia of the beam, are located at the bar ends. The nonlinear effect, due to the axial forces in the bars resulting from the change in their length, is presented by longitudinal springs. This model has the advantage of simplifying parametric studies, because of its discrete nature, allowing any modification in the mass and the stiffness matrices, and in the nonlinearity tensor, to be made separately. After establishing the model, various practical applications are performed without the need of going through all the formulation again. Numerical linear and nonlinear results are given, corresponding to a cracked simply supported beam.

Pages : 47-53

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Abstract (EN)

The article provides a discussion on oscillatory methods used for technical condition assessment of shock absorbers in automotive vehicles, focusing primarily on free vibration methods. It comments on results of simulation studies of a simple two-mass model conducted by application of a pulse input function. Results of experimental tests have also been provided in the paper. The foregoing tests consisted in recording of accelerations of the body of an automotive vehicle equipped with a shock absorber enabling simulation of shock absorbing liquid leakage. The follow-up analyses were conducted to establish the decrement of damping as well as the damping coefficient.

Pages : 55-61

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Abstract (EN)

The paper presents results of dynamic researches conducted on test bed of rotor system. The aim of research was to identify the impact of damping washers to natural frequency of the system. The first part of paper treats with measurements of rotor system in non-stationary states and the second one is about vibration performances parameters in stationary states. Article presents an example of approach to the problem conducted in laboratory conditions, the results of which can be easily transferred on board of a ship or vessel.

Teresa FRAS, Leszek J. FRAS, Norbert FADERL
Pages : 63-68

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Abstract (EN)

Monolithic, homogenous ballistic shields consisting of a single thick, high-hardness and high-strength steel plate are rarely applied in modern combat vehicles. Currently, a popular armour concept is a multi-layered shield since it is expected that the kinetic energy of a threat may be dissipated by transmission through materials with different properties and also by multiple interface reflections. Searching for a maximum ballistic protection at minimum weight inspires applications of various materials which complementary behaviour provides a high protective efficiency without excessive mass. The preliminary experimental investigation presented in the paper aimed to verify behaviour of two prototyped laminated armours under impacts of small-calibre projectiles (cal. 7.62). The main interest lied in impact properties of materials proposed as the intermediate layer. The first tested concept was a laminated steel armour with the 10 mm thick rubber interlayer. In the second armour, the intermediate layer consisted of a magnetorheological fluid.

Tomasz PIŁAT, Grzegorz GRZECZKA, Adam POLAK
Pages : 69-75

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Abstract (EN)

Despite the invention of new chemical sources of electricity, acid batteries, due to their price, are still widely used. They are also used on conventional submarines as the primary source of power. Due to their properties, lead-acid batteries require a lot of attention during their operation, including charging according to fairly rigorous rules. Because of their special operating conditions on submarines, it is not possible to maintain optimal conditions for such batteries. The battery’s integrated management system allows for remote and online monitoring. However, it gives only general information about how much energy remains in the battery for the use in operating conditions. The submarine’s operational capabilities, such as range and operation time, depend to a great extent on battery capacity, therefore, the information of its condition and status is very important.

The proposed method of evaluating the capacity of lead-acid batteries allows them to be processed during their operation, without the need of a time-consuming and expensive capacity test. The authors proposed an original algorithm for evaluating the battery capacity, based on measurement data from a typical monitoring system, assembled with a battery on a ship. The measurements needed to implement the proposed algorithm are already implemented in the existing battery monitoring system – no additional equipment is required. Based on the results of the proposed method, it will be possible to easily determine how much energy is available for the submarine, what is crucial in planning combat missions at the sea.

Pages : 77-83

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Abstract (EN)

Cavitation is a common cause of failure in centrifugal pumps. Because of interaction of several mechanical parts and fluid, the vibration signal of a centrifugal pump is complicated. In this paper, the vibrations of a transparent-casing centrifugal pump are studied. Three states are studied experimentally: no cavitation, limited cavitation and developed cavitation. Each case was also confirmed by visually inspecting the cavitation bubbles. The vibrations of the pump was acquired by using an accelerometer that was attached to the casing. Discrete wavelet transform (DWT) analysis and empirical mode decomposition (EMD) are used to extract classification features from the acquired signals. Using these features, an artificial neural network (ANN) successfully diagnosed the cavitation condition of the pump. Finally, EEMD is also implemented. The results showed the success of EMD and DWT in cavitation diagnosis. The output of EEMD does not show significant change comparing to EMD.

Pages : 85-91

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Abstract (EN)

The article deals with the examination of the state of the ball track at the heavy machine ZP 6600/Z79. This kind of machines are located in Doly Bílina. Article presents results of material exams which were taken on given samples and it describes the progress and results of the numeric calculations for the state of tenseness. The material tests were realized in an external cooperation. The numeric simulation of the tenseness was made in the VÚHU a. s. on the 3D model of the contact by a method of the ultimate elements. The used method works with the ending parts at the bottom of part of the ball track when it touches the ball. To determine the internal and contact forces in the ball and the bottom part of the ball track we used the software called COSMOS/DesignStar ver. 6.0. The result was an evidence for the decision about the depth of the turned layer of the material in order to create a new groove of the bottom part of the ball track.

Pages : 93-98

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Abstract (EN)

As a result of a job commissioned by an external company, over the period of one year 3 measurements were performed on a steel-cord conveyor belt in one of Polish underground copper ore mines. The tests were performed with the DIAGBELT system for automatic belt diagnostics which was developed at Wroclaw University of Science and Technology.

The non-invasive tests revealed that new damage developed in the belt core and that the already existing damage became more extensive. The factor of mean defect number per 1 meter of belt or the number of defects on a given belt section are not sufficient to effectively describe belt technical condition. Quantitative information should be extended with the total surface area of the defects. The analysis of the test results showed that estimations based on 3 measurements are insufficient and that verification should be performed after more measurements are obtained. In addition, the estimations for the complete belt loop are only approximate, as the damaged sections were cut out in the periods between the measurements and replaced with new, undamaged sections.

Research has shown increase in the number of defects that amounted to 33.17% and total surface area of all defects increased by 57.35% over a period of 9 months.

Pages : 99-105

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Abstract (EN)

The need for continuous improvement of product quality, reliability and safety arises and above all a company’s desire to improve its market position and customer satisfaction. These issues require product manufacturers to perform risk analyses that identify and minimize part/system failures throughout the product‘s life cycle. In the paper we will apply the Failure Modes and Effects Analysis (FMEA) for analysis of combustion engine failures. We analyzed 15 different types of cars in which the 2.0 TDI was equipped.

On the basis of the obtained data, we evaluated the most disturbing parts of the combustion engine and on these elements we determined the probability of occurrence of a fault which is one of the factors determining the Risk Priority Number (RPN).