SV - JME 56 (2010) 9

 

SV-JME-9-2010 in digital form »

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Cover plate

The photos show the development of shock waves (bright circular contours) generated in the air above the water surface (dark band in the bottom of the image) irradiated with Er:YAG laser pulses. The dark shape in the upper part of the images is the handpiece of a Er:YAG laser for dental applications. The photos are taken using a novel double exposure shadowgraph method. On each photo, the shock wave is captured at two time instances delayed by 1.56 microseconds.

Recorded in collaboration between: UL-FS COLA and Fotona d.d.

 

 

Infrared Thermography of Cavitation Thermal Effects in Water

Corresponding author - Aljaž Osterman

Authors - Matevž Dular - Marko Hočevar - Brane Širok

Abstract

Although the thermal effects of cavitation are believed to be negligible for cavitation in water, they were successfully experimentally measured using infrared thermography. Cavitation was generated in a small container holding about 500 ml of water. It was oscillated with ultrasonic frequencies of 42 kHz to trigger growth and collapse of bubbles. For the temperature measurements a high-speed thermovision camera was used. It captures light in infrared spectrum with wavelength of 3-5 μm. The frequency of temperature field acquisition was set to 600 Hz. A silicon glass, which is transparent in the infrared light spectrum, was attached to a cylinder and partially submerged into water. Bubbles, which tend to appear in the vicinity of solid surface, appeared on the submerged side of the glass. The visual path for the thermovision camera was: air – silicon glass – water. In this way, the temperatures on the submerged side of the silicon glass where bubble growth and implosions occur could be measured. With the applied thermographic method small but distinctive local decreases of temperature (with magnitudes up to 0.3 K), caused by cavitation, were detected.

Keywords - cavitation, ultrasound, temperature, IR thermography, bubbles

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 527-534
UDC 532.528:544.57:536.5

 

 Infrared Thermography of Cavitation Thermal Effects in Water (pdf)

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Determination of a Light Helicopter Flight Performance at the Preliminary Design Stage

Corresponding author - Zlatko Petrović

Authors - Slobodan Stupar - Ivan Kostić - Aleksandar Simonović

Abstract

Promising solutions for the problem of the extensively time-consuming modern urban transportation has been found in the use of light and very light helicopters. This paper presents a part of the preliminary design methodology, compiled at the Faculty of Mechanical Engineering, University of Belgrade and includes performance calculations of such helicopters. Due to limited budgets and an extremely demanding process of helicopter development, it is highly significantt that during all development stages reliable performance estimates are obtained in order to ensure assigned operational requirements. The scope of this paper is confined to the preliminary design stage, where it is customary to substitute the very complex helicopter rotor dynamics with its averaged mechanical and aerodynamic characteristics and apply certain empirically verified simplifications. Based on this approach, the independent, efficient and reliable computer programs for the calculation of different performance characteristics have been developed. In addition to their application on an actual on-going project, they have also been applied on several existing helicopters of a similar class for a more accurate determination of the empirical input parameters. The applied methodology and obtained results have been presented, verifying the overall algorithm efficiency.

Keywords - light helicopter, flight performance, preliminary design stage

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 535-543
UDC 533.661:629.01

 Determination of a Light Helicopter Flight Performance at the Preliminary Design Stage (pdf)

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The Strength of the Bus Structure with the Determination of Critical Points

Corresponding author - Dušan Mežnar

Authors - Momir Lazovič

Abstract

A monocock structure of an airport bus is a very demanding product as regards its strength. With the application of the FEA method the allegedly critical points of the framework were determined; these especially occurred on the door frameworks. The experimental methods of measuring mechanical deformations confirmed the presumptions that maximum deformations were measured at the points which were previously analysed with the FEA method. The driving regime with a maximum speed of 40 km/h in a circle with a minimum turning radius and a changeable regime of acceleration and braking proved critical. The measurements led to appropriate construction amendments, additional strengthening of the framework and other measures which fulfilled the required strength criteria.

Keywords - buses, motor vehicles, bodies, reinforcements, strength

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 544-550
UDC 629.34:629.021

 The Strength of the Bus Structure with the Determination of Critical Points (pdf)

 

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Pressure Stimulated Current Emissions on Cement Paste Samples under Repetitive Stepwise Compressional Loadings

Corresponding author - A. Kyriazopoulos
Authors - I. Stavrakas, K. Ninos, C Anastasiadis, D. Triantis

Abstract

The electric signals detection technique that is described here was applied on several geomaterials in the past and on cement based materials lately. In this work cement paste samples were studied regarding electric signal emissions during axial stress application processes and specifically when the samples were subjected to repetitive loadings and unloadings in the range where crack opening and propagation processes are established. It was observed that the electric signal was emitted in two stages. Initially, current was emitted simultaneously with the stress step in the form of a spike which gradually returned to its background level. A secondary current emission was recorded while the stress was maintained constant at the high level of each stress step.

Keywords - Pressure Stimulated Current; electric current emissions; cement paste; uniaxial compressional stress

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 551-556
UDC 620.173.25:621.742.48

 Pressure Stimulated Current Emissions on Cement Paste Samples under Repetitive Stepwise Compressional Loadings (pdf)

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Air-Coupled Lamb and Rayleigh Waves for Remote NDE of Defects and Material Elastic Properties

Corresponding author - Igor Solodov

Authors - Daniel Döring - Gerd Busse

Abstract

Conventional air-coupled ultrasound (ACU) is a well-established tool for acoustic NDT and material characterization. Its major shortcoming is concerned with a week penetration into solid materials due to a severe impedance mismatch at the air-solid interface. A dramatic rise in acoustic coupling is obtained by using acoustic mode conversion into plate and surface waves in slanted configurations. In our experiments, an increase of the ultrasound amplitude by up to one order of magnitude was observed in various materials (metals, wood, concrete, composite) under phase matching conditions. On this basis, fully air-coupled configurations are developed and applied for non-contact NDT. The methods based on this principle enable precise measurements of fibre directions and quantification of in-plane anisotropy in composites and natural materials, elastic depth profiling, drying of coatings, advanced imaging of cracked defects and delaminations.

Keywords - air-coupled ultrasonic testing, Lamb and Rayleigh waves, material characterization, elastic anisotropy, elastic depth profiling, process monitoring, NDT imaging

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 557-564
UDC 544.57:539.3

 Air-Coupled Lamb and Rayleigh Waves for Remote NDE of Defects and Material Elastic Properties (pdf)

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Robust IMC Controllers with Optimal Setpoints Tracking and Disturbance Rejection for Industrial Boiler

Corresponding author - Dejan D. Ivezić

Avtorji - Trajko B. Petrović

Abstract

Robust controllers based on Internal Model Control (IMC) theory are developed in this paper to improve the robust performance of industrial boiler system against uncertainties and disturbances. A simplified model of a boiler’s drum unit is developed and transfer matrix realization of its dynamics is obtained for a nominal operational condition. Controllers parameters are selected in accordance with the frequency domain optimization method based on micro-optimality frameworks. The proposed controllers are robust for reference signals and/or for disturbances. Finally, a comparison between the performances of the closed-loop system with designed IMC controllers is obtained.

Keywords - industrial boiler, robust control, internal model control

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 565-574
UDC 621.182

 Robust IMC Controllers with Optimal Setpoints Tracking and Disturbance Rejection for Industrial Boiler (pdf)

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Alternative to the Conventional Heating and Cooling Systems
in Public Buildings

Corresponding author - Mitja Košir

Authors - Aleš Krainer - Mateja Dovjak - Rudolf Perdan - Živa Kristl

Abstract
The paper presents an alternative system for heating and cooling in public buildings. The system was designed for the retrofitted building of the Slovene Ethnographic Museum (SEM) where it was also extensively tested. The installed system includes radiant wall mounted panels for heating and cooling, localized automated tangential fans for cooling and ventilation and a centralized building management system for the regulation and supervision of the performance. The efficiency of the system was thoroughly investigated through a series of experiments conducted prior to the renovation of the building as well as after the museum was put into service. The application of the described system resulted in substantial reduction of energy consumption, better internal thermal conditions and lower investment costs for the Heating, Ventilation and Ait Conditioning (HVAC) system of the entire building.

Keywords - heating, cooling, ventilation, low temperature system, radiant panels

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 575-583
UDC 628.8:697.353:069

 Alternative to the Conventional Heating and Cooling Systems in Public Buildings
(pdf)

 

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The Effects of Machining Parameters on Cutting Forces, Surface Roughness, Built-Up Edge (BUE) and Built-Up Layer (BUL) During Machining AA2014 (T4) Alloy

Corresponding author - Hasan Gökkaya

Abstract
Tool wear, formed in cutting tool during machining processes, affects the surface roughness of the work piece, cutting forces and other output parameters. The effects of the machining parameters cutting speed (Vc) and the feed rate (f) on built-up edge (BUE), built-up layer (BUL), main cutting force (Fc), and surface roughness (Ra) is investigated in this study. The effects of the cutting parameters on cutting force and surface roughness has been examined by the use of Variance Analysis (ANOVA); and their optimum and critical cutting parameters were determined accordingly. AA2014 aluminum alloy was machined with uncoated carbide tools using Computer Numerical Control (CNC) turning machine under dry cutting conditions. Four different cutting speeds (200 m/min, 300 m/min, 400 m/min, and 500 m/min), five different feed rates (0.10 mm/rev, 0.15 mm/rev, 0.20 mm/rev, 0.25 mm/rev, and 0.30 mm/rev) and a constant depth of cut were selected as the machining parameters. BUE and BUL in the cutting tool were formed most at cutting speed 200 m/min and feed rate 0.30 mm/rev. The lowest cutting force was determined as 137 N at cutting speed 500 m/min and feed rate 0.10 mm/rev. The lowest average surface roughness, however, was determined as 0.93 µm at 500 m/min cutting speed and feed rate 0.10 mm/rev.

Keywords - AA2014 alloy, built-up edge (BUE), built-up layer (BUL), cutting force, surface roughness, machining

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)9, 584-593
UDC 621.91:669.71

 The Effects of Machining Parameters on Cutting Forces, Surface Roughness, Built-Up Edge (BUE) and Built-Up Layer (BUL) During Machining AA2014 (T4) Alloy
(pdf)

 

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