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Kaunas, Lithuania

Palevicius R.,Kaunas University of Technology | Palevicius R.,Kaunas Technical College | Ragulskis K.,Lithuanian Academy of Sciences
Journal of Vibroengineering | Year: 2012

Planetary type vibration excitation systems are analyzed in the paper. It is shown that resonance vibrations in such systems can occur in the regime of self-resonance, which is understood as a mode of motion when the angular frequency of a driving shaft is high, but the generated vibration frequency is relatively low. Theoretical investigations of the effect of selfresonance enabled to define the conditions of existence and stability of such motion modes in planetary vibroexciter. Such principle of vibration excitation can be successfully exploited in different areas of engineering as it eliminates the necessity of complex and expensive vibration control and stabilization equipment. © VIBROENGINEERING.

Snitka V.,Kaunas University of Technology | Mizariene V.,Kaunas University of Technology | Bruzaite I.,Vilnius Gediminas Technical University | Lendraitis V.,Kaunas Technical College | Rackaitis M.,Bridgestone
International Journal of Nanomanufacturing | Year: 2010

In this work, the porphyrin nanotubes were built by ionic self-assembly in acidic aqueous solution of two oppositely charged non-metal porphyrins, namely, the anionic meso-tetra (4-sulfonatophenyl) porphine dihydrochloride (TPPS 4) and cationic meso-tetra (4-pyridyl) porphine (T4MPyP). The electrostatic forces between these porphyrin blocks contribute to the formation of porphyrin aggregates in the form of nanosheets and nanotubes, enhance the structural stability of these nanostructures. The nanosheets thickness approximately varies in the range of 3-15 nm and the sheets diameter up to 1 micron. Using the TEM and SEM, it was revealed that the mechanism of nanotubes formation is based on the wrapping of nanosheets in multiwall cigar-like structures. The porphyrin nanotubes obtained are hollow structures with a length from 200 nm up to 1,000 nm and have a diameter in the range of 50-140 nm with 20-40 nm thick walls. TEM images confirm a hollow tubular structure of the aggregates. Copyright © 2010 Interscience Enterprises Ltd.

Dauksys G.,Kaunas University of Technology | Dauksys G.,Kaunas Technical College | Jonaitis A.,Kaunas University of Technology | Gudzius S.,Kaunas University of Technology | Morkvenas A.,Kaunas University of Technology
Elektronika ir Elektrotechnika | Year: 2016

It is well known the use of on-line partial discharge (PD) measurements as an indicator of stator winding insulation condition. The scheduled PD measurements could be used as a test to evaluate the quality of the equipment. The test results could help to diagnose the insulation problems in motors and generators for corresponding action before failure occurs. Although a number of PD measurement methods exists, but the tests results of on operating rotating machines can be influenced by conditions such as humidity, temperature, terminal voltage, and load. This paper describes the development of PD imitation mathematical model in stator insulation. The experimental investigation with physical model was performed for adequacy assessment. The capacitive sensor was used for PD online monitoring.

Kargaudas V.,Kaunas University of Technology | Zmuida M.,Kaunas University of Technology | Zmuida M.,Kaunas Technical College
Mechanika | Year: 2012

Vibrations of elastic plate and compressible fluid are investigated. Compressibility of the fluid influences eigenmodes and to some degree eigenfrequencies also, while density of the fluid eigenfrequencies changes more than eigenmodes. Calculations of steel plate vibrations in water and wood plate vibrations in air are presented, influence of the water and the air compressibility discussed. Interaction of plate eigenmodes in vacuum is represented by hydrodynamic matrix, entries of which depend on sound wave speed in fluid. Eigenmodes of the plate in vacuum and eigenmodes in incompressible fluid can be applied as base functions of the investigation, but the set of eigenmodes of the plate in compressible fluid does not form a set of complete orthogonal base functions.

Dauksys G.,Kaunas University of Technology | Dauksys G.,Kaunas Technical College | Jonaitis A.,Kaunas University of Technology
Elektronika ir Elektrotechnika | Year: 2013

The solid insulations of electrical equipment are perpetually affected by various duration overvoltages. Electric stress of insulation depends on its thickness and amplitude of applied voltage. The damaged solid insulation may also influence characteristic parameters of partial discharges. The characteristic parameters of solid insulation quality should be permanently evaluated. Partial discharge monitoring provides reliable information necessary for basic maintenance of stator windings of motors and generators. Submitted paper deals with partial discharge measurements in stator windings during the increasing of applied voltage.

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