Journal of Mechanical Engineering 57 (2011) 12

 

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Pipistrel Taurus G4: on Creation and Evolution of the Winning Aeroplane of NASA Green Flight Challenge 2011

Authors - Tine Tomažič – Vid Plevnik – Gregor Veble – Jure Tomažič – Franc Popit – Sašo Kolar – Radivoj Kikelj – Jacob W. Langelaan – Kirk Miles

Abstract

The paper presents the journey of the Pipistrel’s Taurus G4, the World’s first four-seat electric aeroplane and winner of the NASA Green Flight Challenge 2011, sponsored by Google, from idea to completion of competition. At the beginning, the race event and qualification requirements are presented. The selection of the aeroplane’s configuration and sizing is discussed, and emphasis given to the unique twin-fuselage configuration. Next, the architecture of the electrical systems on board the aeroplane, including the large battery pack and propulsion elements is presented. In the second part of the paper, authors give an insight to the 40-hour flight test, the challenges encountered and the preparation to the race event itself. A non-linear mathematical performance model was developed to predict performance of the Taurus G4 during the two race events and used for flight planning and in-flight online performance optimisation. Instead of the conclusion, the results of the NASA Green Flight Challenge 2011 are presented and discussed, together with a comparison to other participating teams’ results.

Keywords - electric aeroplane, structural efficiency, NASA Green Flight Challenge 2011, large battery pack, performance modelling, flight test

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 869-878
DOI:10.5545/sv-jme.2011.212

Pipistrel Taurus G4: on Creation and Evolution of the Winning Aeroplane of NASA Green Flight Challenge 2011 (pdf)

 

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Kinematics and Dynamics of the Quasi-Passive Biped “PASIBOT”

Authors - Jesús Meneses – Cristina Castejón – Eduardo Corral – Higinio Rubio – Juan Carlos García-Prada

Abstract

A quasi-passive biped (having only one actuator) developed into a Spanish project called “PASIBOT” [1] is presented in this article. We focus on the PASIBOT’s topology, kinematics and dynamics, and we describe a program designed for carrying out the corresponding calculations. This code provides for all kinematic and dynamic data, as functions of time, along one step: position, velocity and acceleration of all members, as well as all the forces and torques on each of them, motor torque included. This latter information has helped us to choose the required motor, as this choice depends on some parameters of interest that can be modified in the program, like density or link dimensions. Also, we will be able to get strain-stress data in all links in the course of a step, and then optimize those dimensions. To finish, some results are also presented that confirm the interest of the developed code.

Keywords - mechanism analysis, quasi-passive biped, walking robots

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 879-887
DOI:10.5545/sv-jme.2010.210

Kinematics and Dynamics of the Quasi-Passive Biped “PASIBOT” (pdf)

 

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Finite Element Analysis of a Tire Steady Rolling on the Drum and Comparison with Experiment

Authors - Nikola Korunović – Miroslav Trajanović – Miloš Stojković – Dragan Mišić – Jelena Milovanović

Abstract

A finite element (FE) model for analysis of tire rolling on the drum, based on a specially developed CAD model, is presented in the paper. All the changes performed on the geometry of CAD model are automatically propagated to FE model. This makes the FE model very suitable for parametric studies, which help tire designer to quickly find the optimal values of tire design parameters. In this way the tire design process is shortened and the quality of resulting tires improved. The results of finite element analyses conducted on the model have directly been compared to experimental ones, confirming model validity. Equipment and methods used for experimental determination of braking and cornering characteristics of the tire as well as for experimental determination of friction coefficient of tire tread have been shown. The difference between experimental and numerical results was smaller after the calibration of friction coefficient had been performed and in such a way a further improvement of the existing model was achieved.

Keywords - finite element analysis (FEA), tire design, steady-state rolling (SSR), cornering, braking, parametric

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 888-897
DOI: 10.5545/sv-jme.2011.124

Finite Element Analysis of a Tire Steady Rolling on the Drum and Comparison with Experiment (pdf)

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Influence of the Milling Strategy on the Durability of Forging Tools

Authors - Ivo Pahole ‒ Dejan Studenčnik ‒ Karl Gotlih ‒ Mirko Ficko ‒ Jože Balič

Abstract

The quality of a tool’s surface has a direct influence on the number of well-produced parts. For the machining of an active tool surface, two technological processes are used: electrical discharge machining and high-speed milling. These two processes are used when machining new tools and for the repairing of used forging tools. In both cases, the material has already been thermally treated, so it has to be used for hard milling. Practical experience shows that the milling strategy has a big influence on the durability of a forging tool. This paper shows the influence of the CNC machining direction during high-speed milling on the durability of the engraving within the forging tool. In some cases the correct milling strategy can increase the durability of the forging tool by about one third.

Keywords - forging tools, surface quality, high speed cutting, CNC milling

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 898-903
DOI:10.5545/sv-jme.2010.078

Influence of the Milling Strategy on the Durability of Forging Tools (pdf)

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Polycrystalline Cubic Boron Nitride (PCBN) Tool Life and Wear in Turning of Amorphous-Crystalline Iron-Based Coatings

Authors - Ljubodrag Tanovic ‒ Pavao Bojanic ‒ Radovan Puzovic ‒ Sergey Klimenko

Abstract

The paper presents PCBN-Ciborit cutting tools life and wear test results. The effects of the machining regime when turning amorphous-crystalline Fe80B20 and Fe79Cr16B5 coating systems applied to conventional workpiece materials were assessed. It has been shown that the observed tool wear mechanisms are complex in their character and are dominated by abrasive-mechanical, adhesive and chemical effects in the cutting zone. Under changing turning conditions tool life is affected by the structural-phase composition and by the non-homogeneous structure of the coating. Specifically, when turning gas-flame coatings deposited with a Fe80B20 electrode and electro-arc coatings with a Fe79Cr16B5 electrode the lowest wear and the highest tool life was achieved at cutting speeds of v = 1.1 to 1.2 m/s and a back rake angle of γ = –10º. It has been demonstrated that a change of the back rake angle from γ = 0 to –10º does not have a great effect on tool life contrary to the case with γ = -20º.

Keywords - cutting, tool wear, tool life, amorphous-crystalline coating

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 904-910
DOI:10.5545/sv-jme.2011.010

Polycrystalline Cubic Boron Nitride (PCBN) Tool Life and Wear in Turning of Amorphous-Crystalline Iron-Based Coatings (pdf)

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Simulation of Water-Gas Shift Membrane Reactor for Integrated Gasification Combined Cycle Plant with CO2 Capture

Authors - Andrej Lotrič ‒ Mihael Sekavčnik ‒ Christian Kunze ‒ Hartmut Spliethoff

Abstract

The effectiveness of energy conversion and carbon dioxide sequestration in Integrated Gasification Combined Cycle (IGCC) is highly dependent on the syngas composition and its further processing. Water gas shift membrane reactor (WGSMR) enables a promising way of syngas-to-hydrogen conversion with favourable carbon dioxide sequestration capabilities. This paper deals with a numerical approach to the modelling of a water gas shift reaction (WGSR) in a membrane reactor which promotes a reaction process by selectively removing hydrogen from the reaction zone through the membrane, making the reaction equilibrium shifting to the product side. Modelling of the WGSR kinetics was based on Bradford mechanism which was used to develop a code within Mathematica programming language to simulate the chemical reactions. The results were implemented as initial and boundary conditions for the tubular WGSMR model designed with Aspen Plus software to analyze the broader system behaviour. On the basis of selected boundary conditions the designed base case model predicts that 89.1% CO conversion can be achieved. Calculations show that more than 70% of carbon monoxide conversion into hydrogen appears along the first 40% of reactor length scale. For isothermal conditions more than two thirds of the heat released by WGSR should be extracted from the first 20% of the reactor length. Sensitivity analysis of the WGSMR was also performed by changing the membrane’s permeance and surface area.

Keywords - IGCC, water-gas shift reaction, membrane reactor

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 911-926
DOI: 10.5545/sv-jme.2011.100

Simulation of Water-Gas Shift Membrane Reactor for Integrated Gasification Combined Cycle Plant with CO2 Capture (pdf)

 

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Investigation on the High Vacuum Tribological Characteristics of Surface Treated Nuclear Grade Stainless Steel Type AISI 316 LN at 25 to 500 °C

Authors - Ayyannan Devaraju – Ayyasamy Elayaperumal – Srinivasan Venugopal – Satish V. Kailas – Joseph Alphonsa

Abstract
Although some researchers have published friction and wear data of Plasma Nitride (PN) coatings, the tribological behavior of PN/PN Pairs in high vacuum environment has not been published so far. In order to bridge this knowledge gap, tribological tests under dry conditions have been conducted on PN/PN Pairs for varying temperatures of 25, 200, 400 and 500 °C in high vacuum (1.6×10-4 bar) environment. The PN coatings showed good wear resistance layer on the ring surface. The PN coatings were removed only from the pin surface for all the tests since it contacts at a point. The friction and wear were low at lower temperatures and it eliminated adhesion between the contact surfaces until the coating was completely removed from the pin surface.

Keywords - nuclear materials, surface treatment, PN layer, elevated temperature, high vacuum, tribological characteristics

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 927-935
DOI: 10.5545/sv-jme.2010.260

Investigation on the High Vacuum Tribological Characteristics of Surface Treated Nuclear Grade Stainless Steel Type AISI 316 LN at 25 to 500 °C (pdf)

 

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Experimental Equipment Research for Cryogenic Joule-Thompson Cryocoolers Comparison in IR Technology Sensors

Authors - Aleksandar Sicovic ‒ Momčilo Milinovic ‒ Olivera Jeremic

Abstract
This paper shows experimental setup for research of Joule-Thompson cryocoolers performances integrated in Dewar vessels with temperature detector simulator of IR sensor. Experimental solutions of transient temperature regimes of detector cooling on cryogenic cooldown temperature by using nitrogen as the coolant have been analyzed. In experiments of transient temperature influences, three principal methods of the fluid flow regulation, were compared. Results of experiments have shown important differences in quality and rate of cooling for IR detector integrated in cooling system with or without coolant flow regulation. The chosen thermodynamic regime parameters in experiments were suitable for the real necessities of detector cooling in IR sensor application. Scheme of the experimental equipment, its components, method of research and monitoring of desired transient function of temperature versus time in cooling (cooldown regime) of detector, and thermodynamic performances of the overall micro-cryogenic cooler are shown in this paper.

Keywords - cool-down regimes, Joule-Thompson micro-cryogenic coolers, sensitive element, cryogenic gasses, temperature measurements, experimentation of transient

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)12, 936-946
DOI: 10.5545/sv-jme.2010.259

Experimental Equipment Research for Cryogenic Joule- Thompson Cryocoolers Comparison in IR Technology Sensors (pdf)

 

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