Journal of Mechanical Engineering 56 (2010) 6

SV-JME-6-2010 in digital form »

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An Optimal Main Helicopter Rotor Projection Model Obtained by Viscous Effects and Unsteady Lift Simulation

Corresponding author - Časlav Mitrović

Authors - Aleksandar Bengin - Dragan Cvetković - Dragoljub Bekrić

Abstract

 

This paper presents an airfoil model which provides a method for optimal main helicopter rotor projection by viscous effect and unsteady lift simulation through algorithm and set of program entireties, applicable to the ideological and main project of helicopter rotor. Based on real rotors theoretical consideration and the, numerical analysis considerations in this paper can be applied with sufficient accuracy in the analysis and constructive realizations of helicopter rotor in real conditions. The method for unsteady viscous flow simulations by inviscid techniques is developed.
The aim of this paper is to determine helicopter rotor blade lift with the highest possible accuracy by using a singularity method and to define an optimal conception model of aerodynamic rotor projection corresponding to rotor behavior in real conditions and with sufficient quality from the aspect of engineer use.

Keywords - unsteady lift, viscous effect simulation, potential flow, lifting surface, panel method, free-wake model, main helicopter rotor aerodynamics

Paper's information

 

Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC 629.735.45

 An Optimal Main Helicopter Rotor Projection Model Obtained by Viscous Effects and Unsteady Lift Simulation (pdf)

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Analysis of Die Casting Tool Material

Corresponding author - Mitja Muhič

Authors - Janez Tušek - Franc Kosel - Damjan Klobčar

Abstract

This paper deals with defects produced in aluminium alloy die casting dies during die operation. The most frequent defect is thermal fatigue cracking. Hardness and toughness is measured on specimens cut from different parts of used die casting die.
The results show a significant difference in material microstructure and hardness between the surface and the core. The intense martensite tempering is observed on the die surface, while the core material microstructure remains unchanged. A considerable hardness drop is measured on the material surface and no change is observed in the depth of six millimetres from surface.

Keywords - die casting, die defect, thermal fatigue, surface cracks

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC

 Analysis of Die Casting Tool Material (pdf)

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Analysis of Ex-Vessel Steam Explosion Pressure Loads

Corresponding author - Mitja Uršič

Authors - Matjaž Leskovar

Abstract

An ex-vessel steam explosion in a nuclear power plant may develop when the reactor vessel fails and the molten core interacts with the coolant water in the reactor vessel. At the fuel coolant interaction a part of the corium energy is intensively transferred to water in a very short time scale. The water vaporizes at high pressure and expands, inducing potentially severe dynamic loadings on surrounding systems, structures and components that may lead to an early release of radioactive material into the environment.
To get a better understanding of the ex-vessel steam explosion phenomenon, various scenarios analyses for a typical pressurized water reactor cavity were made. A detailed analysis was performed varying the melt release location, the cavity water temperature, the primary system over-pressure at vessel failure and the triggering time for explosion calculations. The main purpose of the analysis was to determine the most challenging ex-vessel steam explosion cases and to estimate the expected pressure loadings on the cavity walls. The performed analysis shows that for some ex-vessel steam explosion scenarios significantly higher pressure loads are predicted than were obtained in the OECD programme SERENA.
The detailed analysis of the most challenging central melt pour scenario revealed that the calculated high pressure loads are also a consequence of the axial symmetric geometry of the cavity model and the probably over-predicted melt droplets amount involved in the steam explosion.

Keywords - fuel-coolant interaction, steam explosion, severe accident, simulation

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC 621.039.536.2:004.94

 Analysis of Ex-Vessel Steam Explosion Pressure Loads (pdf)

 

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Application of Artificial Neural Networks in the Prediction of Critical Buckling Loads of Helical Compression Springs

Corresponding author - Turgay Ibrikçi
Authors - Selim Saçma - Vebil Yıldırım - Tarkan Koca

Abstract

This paper proposes the use of artificial neural networks (ANN) to perfectly predict the critical buckling loads of cylindrical isotropic helical spring with fixed ends and with circular sections, and with large pitch angles. The buckling equations of cylindrical isotropic helical springs loaded axially consist of a set of twelve linear differential equations. As finding a solution in an analytical manner is too difficult, numerical solution in an exact manner based on the transfer-matrix method to collect consistent dimensionless numerical data for the training process is used. In this way almost perfect weight values are obtained to predict the non-dimensional buckling loads. A good agreement is observed with the data available in the literature.

Keywords - buckling, critical buckling load, helical spring, artificial neural networks, design, coil spring

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC 629.4.027.31-272.2:531.2:004.8

 Application of Artificial Neural Networks in the Prediction of Critical Buckling Loads of Helical Compression Springs (pdf)

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Simulation of Transient Flow in Hydroelectric Power Plants Using Unsteady Friction

Corresponding author - Alireza Riasi

Authors - Mehrdad Raisee - Ahmad Nourbakhsh

Abstract

In this paper the influence of surge tanks on transient flow generated by changing turbine gate opening has been numerically studied. For this purpose, the governing equations of transient flow are solved using the method of characteristics and considering unsteady friction. The surge tank and the hydraulic turbine are considered as internal boundary conditions. Comparison of transient results for pressure oscillations with the available experimental data shows good agreement. The surge tanks lower down the pressure levels at the upstream side of turbine and stabilize the pressure at the downstream side. Also, surge tanks delay the time occurrence of the maximum and minimum pressure. Finally, the effect of wicket gate closing followed by wicket gate opening on the so called speed no load operation (SNLO) on the transient flow is investigated and transient conditions improved by this sequence are found.

Keywords - hydraulic turbine, hyperbolic PDE, surge tank, transient flow, unsteady friction

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC

 Simulation of Transient Flow in Hydroelectric Power Plants Using Unsteady Friction (pdf)

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The Optimization of Machining Parameters Using the Taguchi Method For Surface Roughness of AISI 8660 Hardened Alloy Steel

Corresponding author - Ali Riza Motorcu

Abstract

The surface roughness in the turning of AISI 8660 hardened alloy steels by ceramic based cutting tools was investigated in terms of main cutting parameters such as cutting speed, feed rate, depth of cut in addition to tool’s nose radius, using a statistical approach. Machining tests were carried out with PVD-coated ceramic cutting tools under different conditions. An orthogonal design, signal-to-noise ratio and analysis of variance were employed to find out the effective cutting parameters and nose radius on the surface roughness.
The obtained results indicate that the feed rate was found to be the dominant factor among controllable factors on the surface roughness, followed by depth of cut and tool’s nose radius. However, the cutting speed showed an insignificant effect. Furthermore, the interaction of feed rate/depth of cut was found to be significant on the surface finish due to surface hardening of steel. Optimal testing parameters for surface roughness could be calculated. Moreover, the second order regression model also shows that the predicted values were very close to the experimental one for surface roughness.

Keywords - ceramic cutting tools, surface roughness model, Taguchi method, hardened alloy steel

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC

 The Optimization of Machining Parameters Using the Taguchi Method For Surface Roughness of AISI 8660 Hardened Alloy Steel (pdf)

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Conceptual Framework for NPN Logic Based Decision Analysis

Corresponding author - Goran Devedžić

Authors - Miodrag Manić - Dejan Tanikić - Lozica Ivanović - Nenad Mirić

Abstract
The paper presents the methodology for multicriteria decision analysis based on negative-positive-neutral (NPN) logic, which is an extension of both crisp and fuzzy logic. As the basic modeling framework we use fuzzy cognitive maps (FCM) which are a set of meaningful concepts, connected to form a network, with fuzzy weighted links measuring the strength and direction of effect of cause concept over target concept. Introducing NPN logic to FCM modeling framework provides the possibility to measure, the so-called, side effect of each decision-making path. This information additionally describes under what mutual conditions between concepts FCM settles down in equilibrium. An illustrative example from the real industrial environment related to metal cutting process planning parameters analysis demonstrates the potential of the methodology.

Keywords - NPN logic and NPN relations, Fuzzy Cognitive Maps, Decision Analysis, Process Planning

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC

 Conceptual Framework for NPN Logic Based Decision Analysis (pdf)

 

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Methods of Shaping the Metrological Characteristics of Air Gages

Corresponding author - Czeslaw Janusz Jermak

Abstract
The paper presents the results of investigations on the influence of most important geometrical parameters on the metrological properties of the air gauges. Among others, the diameters of the inlet and measuring nozzles were taken into consideration, as well as the normalized outer diameter of the measuring nozzle. The influence of the ratio of measuring nozzle to inlet nozzle on the metrological properties. In the analysis, the following features were taken into consideration: measuring range of the air gauge, multiplication and the initial slot width corresponding with the beginning of measuring range. As a result of investigation, some recommendations on the air gauge choice dependent on the particular measuring task are presented in the final part of the paper.

Keywords - air gauge, dimensional measurement, metrology, uncertainty, static metrological properties

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 56(2010)6
UDC

 Methods of Shaping the Metrological Characteristics of Air Gages (pdf)

 

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