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1.
Method for detecting fatigue crack in gears
Aleš Belšak, Jože Flašker, 2006, original scientific article

Abstract: The most undesirable damage that can occur in gear units is crack in the tooth root as it often makes gear unit operation impossible. Monitoring vibrations can be used to detect defects. Time signals are acquired experimentally and afterwards. Different methods can be used to analyse them. The changes in tooth stiffness caused by a fatigue crack in the tooth root are of significance. The dynamic response of a gear unit with a damaged tooth differs from the one of an undamaged tooth. Amplitudes of time signal are, by time-frequency analysis, presented as a function of frequencies in spectrum.
Keywords: gear drives, fatigue failures, crack initiation, crack propagation, vibrations
Published: 31.05.2012; Views: 1218; Downloads: 65
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2.
Crack identification in gear tooth root using adaptive analysis
Aleš Belšak, Jože Flašker, 2007, original scientific article

Abstract: Problems concerning gear unit operation can result from various typical damages and faults. A crack in the tooth root, which often leads to failure in gear unit operation, is the most undesirable damage caused to gear units. This article deals with fault analyses of gear units with real damages. A laboratory test plant has been prepared. It has been possible to identify certain damages by monitoring vibrations. In concern to a fatigue crack in the tooth root significant changes in tooth stiffness are more expressed. When other faults are present, other dynamic parameters prevail. Signal analysis has been performed also in concern to a non-stationary signal, using the adaptive transformation to signal analysis.
Keywords: machine elements, gears, fatigue crack, fault detection, vibrations, adaptive signal analysis, engineering diagnostics
Published: 31.05.2012; Views: 1343; Downloads: 57
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3.
Thermal vibrational analysis for simply supported beam and clamped beam
Jurij Avsec, Maks Oblak, 2007, original scientific article

Abstract: The presented paper shows how the temperature field in beams has impact on vibrations of beams. Due to the relatively high possible temperature variations in beams we have developed the mathematical model where fundamental thermomechanical properties of state are functions of temperature such as modulus of elasticity, Poisson number, linear expansion coefficient, shear modulus and some other important thermodynamic properties of state. The detailed analysis shows, that also small changes of temperature cause significant changes of natural frequencies for beams. The comparison between our analytical model and experimental data shows good agreement. In the presented paper it is possible to find for the first time in scientific literature the application of the combination of statistical thermodynamics and the theory of vibration at the same time.
Keywords: statistical thermomechanics, vibrations, vibrational theory, temperature effects, simply supported beams, clamped beams, thermomechanical properties
Published: 31.05.2012; Views: 960; Downloads: 66
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4.
Analysis of vibrations and noise to determine the condition of gear units
Aleš Belšak, Jurij Prezelj, 2011, independent scientific component part or a chapter in a monograph

Abstract: The main goal of maintenance is to maintain the characteristics of a technical system at the most favourable or still acceptable level. Maintenance costs can be reduced, operation can become more reliable and the frequency and complexity of damages can be reduced. To evaluate the condition of a technical system, it is necessary to collect precise data, and the to analyse, compare and process this data properly. Gear units are the most frequent machine parts or couplings. They consist of a housing, toothed wheels, bearings and a lubricating system and are of various types and sizes. Durable damages in gear units are often a resulta of the following factors: geometrical deviations or unbalanced component parts, material fatigue, which is a result of engagement of a gear pair, or damages caused to roller bearings. To monitor the condition of mechanical systems, methods for measuring vibrations and noise are usually used; data about a gear unit can be acquired in this way. Afterwards certain tools are used to analyse the data. Features that denote the presence of damages and faults are identified in this way.
Keywords: vibrations, noise source identification, maintenance, gears
Published: 01.06.2012; Views: 1115; Downloads: 56
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5.
Vibration of beams and rotating shafts under thermal effects
Jurij Avsec, 2009, original scientific article

Abstract: Temperature variations can significantly change the dynamic characteristics of structures. In the presented paper we have studied the clamped isotropic rotor under thermal effects. We have studied aluminium and copper beam. Because the expansion is restrained by the clamping, the beam undergoes internal stresses, which induce changes in dynamic characteristics. We have also expanded and developed Marques and Inman model as well as Bahzad and Bastami model. We have taken into account the compound influence of thermal force, axial force in rotating shaft and gyroscopic effect. The behavior of rotating shaft is studied in the temperature range of 250-700 K. The influence of temperature-dependent material properties was considered primarily with respect to temperature variations. The presented research work demonstrates a very good agreement between experimental data and results from our vibrational model. On the basis of the proposed analytical model it is possible to determine the vibrational characteristics in very wide range of temperatures. The reported paper is the first one in scientific literature to consider collectively the combined influence of temperature, gyroscopic effects and rotor speeds on shaft and beam vibrations.
Keywords: beam vibrations, rotor vibrations, temperature effects, mechanics, thermomechanics
Published: 05.06.2012; Views: 2057; Downloads: 52
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6.
The vibrations of microbeams and nanotubes
Jurij Avsec, 2011, original scientific article

Abstract: Temperature variations can significantly change the dynamic characteristics of macro-, micro- and nano-structures. In the presented article we have studied the microbeams and nanotubes under thermal effects. Microbeams and nanotubes will be very important in the future in the fields of MEMS and NEMS. For the physical explanation of vibrations of nanotubes classical mechanics is valid with some limitations. We have taken into account the influence of thermal force, axial force in rotating shaft and also gyroscopic effect. The effect of temperature-dependent material properties was considered primarily with respect to the temperature variations. On the basis of our analytical model it is possible to determine the vibrational characteristics in a very wide range of temperatures. In the presented paper it is shown for the first time in scientific literature the combined influence of temperature, gyroscopic effects and rotor speeds on shaft and beam vibrations.
Keywords: vibrations of microbeams, vibrations of nanotubes, rotor vibration, thermomechanics, nanomechanics
Published: 05.06.2012; Views: 1349; Downloads: 24
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7.
Sand as a medium for transmission of vibratory signals of prey in antlions Euroleon nostras (Neuroptera: Myrmeleontidae)
Dušan Devetak, Bojana Mencinger Vračko, Miha Devetak, Marko Marhl, Andreja Špernjak, 2007, original scientific article

Abstract: European pit-building antlions (Euroleon nostras/ Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species (Tenebrio molitor, Pyrrhocoris apterus, Formica sp. and Trachelipus rathkei) is 0.1-4.5 kHz and acceleration values are in the range ▫$400 {mu}m s^{-2} to 1.5 mm s^{-2}$▫. Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB ▫$cm^{-1}$▫ and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ▫$le 0.23 mm$▫) and 12.3 cm in coarser sand (particle size 1-1.54 mm). The most convenient sands for prey detection are considered to be medium particle-sized sands.
Keywords: biology, zoology, receptors, chordotonal organs, vibrations, vibratory signals, transmission of vibrations, reception of vibrations, electrophysiology, substrate vibration, antlions, Myrmeleontidae, sand, substrate vibration, particle size
Published: 07.06.2012; Views: 1499; Downloads: 78
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8.
Torsional vibrations at guide-vane shaft of pump-turbine model
Andrej Predin, 1997, original scientific article

Abstract: This article focuses on the problem of guide-vane vibrations of reversible pump-turbines, especially, in the pump mode. These vibrations are transmitted to the guide-vane shaft torque. The guide-vane vibrations are caused by the impeller exit flow, which has a turbulent and partly nondeterministic property. Experimentally determined flow velocities at the impeller exit are given. The mathematical models for theoretical torsional vibration prediction formulated using linear and nonlinear differential equations are presented. The results of theoretical calculations are compared with measurements results. The possibility of transferring the parameters from the model to the prototype is discussed.
Keywords: pump-turbines, oscillations, guide-vane shaft, torsional vibrations
Published: 15.06.2017; Views: 470; Downloads: 243
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9.
Emergency gate vibration of the pipe-turbine model
Andrej Predin, Roman Klasinc, 2000, original scientific article

Abstract: The vibration behaviour of an emergency gate situated on a horizontal-shaft Kaplan turbine is studied. The analysis and transfer of the dynamic movements of the gate are quite complex. In particular the behaviour is examined of the emergency gate for the case when the power unit is disconnected from the system or there is a breakdown of the guide vane system at the moment when the maximal head and capacity are achieved. Experimental-numerical methods both in the time domain and in the frequency are employed. Natural vibrations characterize a first zone, corresponding to relatively small gate openings. As the gate opening increases, the vibration behaviour of the gate becomes increasingly dependent on the swirl pulsations in the draft tube of the turbine. Finally, the data transfer from the model to the prototype by use of the dinamic similitude law is discussed.
Keywords: water turbines, emergency gates, vibrations, vibration measurement
Published: 15.06.2017; Views: 447; Downloads: 218
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10.
Influence of vibrations on residual stresses distribution in welded joints
Ivan Samardžić, Tomaž Vuherer, Dejan Marić, Pejo Konjatić, 2015, original scientific article

Abstract: This paper presents research experience related to implementation of vibrations on residual stress relief with the equipment for treatment by vibration method. The paper provides explanation of effects achieved by vibration method when implemented during welding, and elaborates advantages and disadvantages of that method applied after welding process. In order to present effects of vibration on solid structures, there was experimental analysis performed and compared with heat treatment.
Keywords: welding, vibrations, residual stress, heat treatment
Published: 03.07.2017; Views: 344; Downloads: 64
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