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1.
Charpy toughness and microstructure of vibrated weld metal
Bogdan Pučko, Vladimir Gliha, 2006, izvirni znanstveni članek

Opis: Vibration during welding can be used to obtain certain changes in mechanical properties of weld metal. Research work on the influence of vibration on the secondary microstructure of welds and hence on the Charpy toughness was performed. Vibration during welding exhibits positive effects on the microstructure constituent formation. Multipass welding was simulated with reheating of the original single pass weld in order to obtain similar microstructure to multipass welds. Microstructures were examined with an optical microscope. Additionally, fractographic examination of the rupture of Charpy specimens was performed. Changes in the microstructure according to vibration were observed which affect toughness of the weld metal. Vibration during welding was rated more effective in the case of reheating the weld metal, which is the case in multipass welding.
Ključne besede: welding, welded joints, mechanical properties of metals, ferrite, vibration, microstructure, toughness, notched bar testing, weld metal
Objavljeno: 31.05.2012; Ogledov: 1439; Prenosov: 68
URL Povezava na celotno besedilo

2.
SMC with disturbance observer for a linear belt drive
Aleš Hace, Karel Jezernik, Asif Šabanović, 2007, izvirni znanstveni članek

Opis: Accurate position tracking control of a linear belt-driven servomechanism can cause vibrations in the drive response due to compliance and elasticity introduced by force transmission through the belt. This paper proposes a new control algorithm that has been designed by Sliding Mode Control theory. Though it has been proved to assure robust and vibration-free operation, position error peaks still appear at velocity reversals due to nonlinear friction phenomenon. Thus, the control scheme has been extended by asymptotic disturbance observer. The experiments presented in the paper show improved position tracking error response while maintaining vibration suppression.
Ključne besede: motion control, disturbance observer, sliding mode control, timing-belt drive, vibration suppression
Objavljeno: 31.05.2012; Ogledov: 1193; Prenosov: 71
URL Povezava na celotno besedilo

3.
The vibrations of microbeams and nanotubes
Jurij Avsec, 2011, izvirni znanstveni članek

Opis: 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.
Ključne besede: vibrations of microbeams, vibrations of nanotubes, rotor vibration, thermomechanics, nanomechanics
Objavljeno: 05.06.2012; Ogledov: 1184; Prenosov: 20
URL Povezava na celotno besedilo

4.
Nonlinear vibrational analysis of diesel valve gear
Jurij Avsec, Zdravko Praunseis, Milan Marčič, 2011, izvirni znanstveni članek

Opis: A valve gear system is currently more or less a classical mechanical system in a majority of diesel engines. In our case, diesel engine durability test was carried out incorporating a conventional valve gear. After the 3000-hour engine test, the manifestations of an intensive wear detected on the exhaust side of the valve gear. The wear of the exhaust cam was particularly intensive right under the top. As evident from dynamical analysis and experimental data of the valve gear the loads are excessive mainly on the exhaust cam. The assessment of the minimum oil film thickness at the top of the exhaust cam does not provide any favorable results. As the largest loads are exerted at the top of the cam, where the highest wear was measured, it is necessary to reduce the normal stresses and improve the lubrication properties. Dynamic valve gear analysis was performed in order to estimate cam wear intensity and to compare the new cam designs with the existing ones. The model of the actual valve gear design can be represented by means of the partial differential equations. We used a vibrational system with three degrees of freedom. Partial differential equations were solved by means of finite differences and Runge-Kutta methods. Vibrational analysis allows studying kinematic and dynamic behavior of the nonlinear spring and nonlinearity of the damping forces in the valve gear system. The presented theory will be applied in the future research works for determining the conditions for chaotic behavior of the valve gear system. The dynamic model of the valve gear was used to analyze the causes of the excessive wear. Since the cam, designed in accordance with the polysine curve, offered too few possibilities for an optimum cam profile, we wanted to manufacture a completely new type of cam with more possibilities for an optimum adjustment. At the same time, we attempted to summarize some findings on the dependence of the cam design on the fuel consumption and valve gear noise. Thereby a new MULTICAM cam was developed. Contrary to the conventional theory of polysine cam, the motion in the MULTICAM cam can be written by means of seven curves. The analysis of Hertz pressures provides more favorable results for the MULTICAM cam profile. By using the new cam profile the Hertz pressures were substantially reduced. The top of the cam is subjected to the lowest loads with the MULTICAM curve shape. In spite of a higher contact force the normal stresses are lower mainly due to the higher radius of cam curvature. Dynamic analysis demonstrates that both newly designed cams exhibit lower stresses at the top of the cam and better lubrication properties, whereas the flow geometrical cross-sections and the other control values remain similar for all three cam versions.
Ključne besede: disel valve gear vibration, nonlinearity, cam design, valve gear dynamics
Objavljeno: 05.06.2012; Ogledov: 1564; Prenosov: 21
URL Povezava na celotno besedilo

5.
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, izvirni znanstveni članek

Opis: 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.
Ključne besede: biology, zoology, receptors, chordotonal organs, vibrations, vibratory signals, transmission of vibrations, reception of vibrations, electrophysiology, substrate vibration, antlions, Myrmeleontidae, sand, substrate vibration, particle size
Objavljeno: 07.06.2012; Ogledov: 1313; Prenosov: 63
URL Povezava na celotno besedilo

6.
Emergency gate vibration of the pipe-turbine model
Andrej Predin, Roman Klasinc, 2000, izvirni znanstveni članek

Opis: 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.
Ključne besede: water turbines, emergency gates, vibrations, vibration measurement
Objavljeno: 15.06.2017; Ogledov: 325; Prenosov: 185
.pdf Celotno besedilo (2,45 MB)
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7.
Charpy toughness of vibrated microstructures
Bogdan Pučko, Vladimir Gliha, 2005, izvirni znanstveni članek

Opis: The aim of this study was to investigate the influence of vibration on impact toughness of weld metal. Studies were carried out on two welds, of which one had been welded with applying vibration during welding. From test plates samples were made to simulate heat affect in combination with or without vibration after solidification. In this way conditions at multi-pass welding were simulated. According to different conditions Charpy toughness on non standard specimens and fracture appearance were observed. Vibration during welding benefits impact energy of weld metal, especially if weld metal undergoes further heatb treatment.
Ključne besede: welded joints, impact toughness, vibration, Charpy toughness, SAW
Objavljeno: 03.07.2017; Ogledov: 250; Prenosov: 58
.pdf Celotno besedilo (118,79 KB)
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8.
Designing the gear body structure to control vibration behaviour
Riad Ramadani, 2018, doktorska disertacija

Opis: This research presents a new approach aiming to reduce gear vibration as well as its weight by modifying the gear body structure. The primary objective was to reduce vibration and noise emission of spur gears. For this purpose, a solid gear body was replaced by a cellular lattice structure, which was expected to raise the torsional elasticity of the gear body. The cellular lattice structure was designed and optimized by FE-based topology optimization software CAESS ProTOp, which is based on strain energy control. For experimental purposes, the optimized gear was produced from Titanium alloy Ti-6Al-4V ELI by using Selective Laser Melting technique. A polymer matrix was added to increase the damping of the structure. In order to test the gears, a new test rig with closed loop was conceived, designed and produced. The test rig is equipped with two gear pairs: with the tested one and with the driving one. The gears have been run and tested at different speeds and torque. The acceleration, strain and sound pressure of a running gear pair was measured. The final processing of the signal was done by a specially developed software based on LabView. By employing the fast Fourier transformation the time signal of acceleration, strain and sound pressure has been converted to the frequency spectrum and time frequency spectrogram. The results obtained by testing the solid and cellular lattice gear body were compared. It was experimentally confirmed that the cellular lattice structure of a gear body and addition of a polymer matrix may significantly reduce the vibration.
Ključne besede: Gear vibration, cellular lattice structure, topology optimization, test rig
Objavljeno: 27.02.2018; Ogledov: 678; Prenosov: 97
.pdf Celotno besedilo (13,76 MB)

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