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Editorial Office

University of Ljubljana
Faculty of Mechanical Engineering
Journal of Mechanical Engineering

Aškerčeva 6,

SI-1000 Ljubljana
Slovenia

P: +386 1 4771 137
E: info@sv-jme.eu



The journal is subsidized by Slovenian Research Agency.

 
ISSN: 0039-2480

Journal of Mechanical Engineering 63 (2017) 4

 

 

 


 

The Validation of Numerical Methodology for Oven Design Optimization Using Numerical Simulations and Baking Experiments

Authors - Uroš Kokolj* – Leopold Škerget– Jure Ravnik


Abstract

In this paper, we will present the validation of numerical methodology for the improvement of baking performance of a forced convection oven. The baking performance will be assessed as the degree of uniformity between browning and temperature distribution in the oven. We found a linear relationship between the experimentally measured grade of browning and the simulated temperature distribution. Six different designs of oven fan cover were compared through numerical simulations, where a time-dependent 3D numerical model with radiative and convective heat transfers mechanism was used. The results were used in a linear model to estimate the grade of browning. The results were validated with the experimental measurements of baked shortbread using an old and improved-upon oven design. The grade of browning was determined experimentally by the colour contrasts method, based on the colour space CIE L*a*b. The results show that the improved fan cover performs better than the existing fan cover.

Keywords - computational fluid dynamics, baking, oven, heat transfer, shortbread, optimization

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 215-224, SI 33
DOI:10.5545/sv-jme.2016.4089

 

pdfThe Validation of Numerical Methodology for Oven Design Optimization Using Numerical Simulations and Baking Experiments (.pdf 2.0MB)

 


  

Pneumatic Muscle-Actuated Adjustable Compliant Gripper System for Assembly Operations

Authors - Tudor Deaconescu* – Andrea Deaconescu


Abstract

The aim of this paper is to present and discuss an innovative, constructive solution for a gripper system that can be attached to an industrial robot for assembly operations. The construction of this gripper system is based on a linear pneumatic muscle used as the actuator and the transmission of motion by gear-and-rack mechanisms. Air compressibility renders pneumatic muscle behaviour inherently compliant; this favours automated assembly applications as it allows the correction of inevitable lateral and angular misalignments in mating operations. Therefore, the jamming of a peg-like object can be avoided when this is introduced into a hole with tight clearance. In addition to the construction of the gripper system, this paper discusses its actuation, as well other characteristics.

Keywords - assembly, compliance, grippers, manipulators, pneumatic muscles, stiffness

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 225-234, SI 34
DOI:10.5545/sv-jme.2016.4239

 

pdfPneumatic Muscle-Actuated Adjustable Compliant Gripper System for Assembly Operations (.pdf 1.3MB)

 


 

Performance Index in MHD Duct Nanofluid Flow Past a Bluff Body at High Re

Authors - Kozhikkatil Sunil Arjun* – Rakesh Kumar


Abstract

The quasi-two-dimensional Al2O3-water nanofluid magneto hydro-dynamics (MHD) flowing over a circular cylinder at higher Reynolds number has been modelled using Ansys FLUENT 15.0 in a rectangular duct to determine the viability of heat transfer enhancement. The effect of the numerical simulations on performance indices were analysed for the range of 1000 ≤Re≤3000 Reynolds numbers, 10 ≤Ha≤100 modified Hartmann numbers, 0.5 ≤φ ≤2 nanoparticle volume concentrations, 0.1 ≤β≤0.4 blockage ratios, 1 ≤γ≤0.25 position ratios, 0.75 ≤G/d≤ 1.5 gap ratios and 0 ≤ d≤10 distance downstream of cylinder along heated duct wall. The results are presented graphically and discussed quantitatively. Grid independence is achieved with the domain having 3 upstream and 20 downstream cylinder diameter distance lengths with element polynomial degree 7 with respect to mean drag coefficient and Strouhal number. Cylinder placement with gaps to the heated wall of diameters between 0.75 and 1.25 and 10 diameters downstream of cylinder performed best, achieving 117 % enhancement of the performance indices at Re=3000, Ha =20, φ =2 %, β= 0.4, γ= 1 and G/d=1. The performance indices were greater than one for all the cases tested, which indicates that the heat transfer enhancement for this flow is viable. The Nusselt number values of the present study were compared with the analytical and experimental data published earlier and found to be in perfect agreement validating the reliability of the present model

Keywords - computational fluid dynamics, heat transfer enhancement, bluff body, circular cylinder, magneto hydro-dynamics

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 235-247, SI 35
DOI:10.5545/sv-jme.2016.4258

 

pdfPerformance Index in MHD Duct Nanofluid Flow Past a Bluff Body at High Re (.pdf 718KB)

 


 

Reliability Assessment of Bearings Based on Performance Degradation Values under Small Samples

Authors - Luosheng Qin – Xuejin Shen* – Xiaoyang Chen – Pandong Gao


Abstract

It is difficult to obtain the lifetime data of a long lifetime bearing from a test with limited time. Therefore, to apply the method of reliability assessment based on lifetime data to the high reliability and long lifetime bearings would be impractical. The performance degradation data, which contains reliability information, could be used in the reliability assessment. However, the methods based on performance degradation data are often applied in a large sample situation. In this paper, a method suitable for a small-sample situation based on a distribution-based degradation model and a bootstrapping method combined with the Monte Carlo method (DDBMC) is proposed. This method is put forward to enlarge the sample size and estimate the distribution parameters. Then, the function between distribution parameters and time can be obtained by using the least square method. In this paper, the reliability of the ball bearings under a small sample is assessed to verify the proposed method. Finally, the proposed methodology was applied to assessing the reliability of bearings and shown to be efficient in the reliability assessment of bearings under small samples

Keywords - bearings, distribution-based degradation, small sample, bootstrapping method, Monte Carlo method, reliability


Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 248-254, SI 36
DOI:10.5545/sv-jme.2016.3898

 

pdfReliability Assessment of Bearings Based on Performance Degradation Values under Small Samples (.pdf 617KB)




An Experimental Investigation and Numerical Simulation in SPF of AA 5083 Alloy using Programming Logic Control Approach

Authors - Muthusamy Balasubramanian* – Pasupathy Ganesh – Kalimuthu Ramanathan – Velukkudi Santhanam Senthil Kumar

Abstract

A new programming logic control method is proposed to predict the pressure during the superplastic forming process with improved forming characteristics of AA 5083 alloy sheets. The method has produced a better uniformity thickness profile in a complex, multidimensional profile in comparison with existing methods. To optimize pressure during the forming process, it is possible to maintain an optimum strain rate. Accurate control of the magnitude and duration of forming pressure and, as a result, the achievement of uniform thickness distribution in the taper angle, die corner, entry regions, and micro-forming of the multidimensional dome has been proved in this paper. Profiles formed without significant wrinkles and necking have been obtained via the fine adjustment of the applied pressure. The experimentally obtained results, using a multidimensional dome profile, are compared with the finite element method (FEM) simulated results and both are found to be in good agreement. The influence of key factors such as strain rate sensitivity index and friction coefficient on the optimum pressure-time cycle and also on the thickness distribution of the profile have been investigated and optimized. Furthermore, the microstructure was examined in parent metal and superplastically formed components

Keywords - superplastic forming, finite element method, programming logic control circuit, aluminium 5083 alloy, multidimensional dome

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 255-264, SI 37
DOI:10.5545/sv-jme.2016.3721

 

pdfAn Experimental Investigation and Numerical Simulation in SPF of AA 5083 Alloy using Programming Logic Control Approach (.pdf 2.0MB)




A Surveillance of Direct-Firing System for Pulverized-Coal Using Statistically Treated Signals from Intrusive Electrostatic Sensors

Authors - Boštjan Jurjevčič – Andrej Senegačnik – Igor Kuštrin*


Abstract

Operational surveillance of all vital parts of thermal power plants is nowadays more important than any time before due to requirements for their extremely flexible operation resulting from intermittent behaviour of renewable energy sources. New methods for online measuring of pneumatic transport provide new possibilities for control and early fault detection of coal grinding and conveying system in direct-fired power plant boilers. Arrays of intrusive electrostatic sensors are an attractive option due to their inexpensive application and good spatial sensitivity required in large rectangular ducts of pulverized-coal systems. In this study, statistically treated electrostatic signals are used for detection of unexpected change in operating regime of coal grinding and conveying. Model-based and model-free autocorrelation reduction techniques are used to reduce the inherent autocorrelation of data. Forming batch-means of data, a model-free autocorrelation reduction technique is proposed in combination with an autoregressive-integrated-moving-average (ARIMA) method. Residuals between real and ARIMA-model fitted data are entered into exponentially-weighted-moving-average (EWMA) control chart for statistical surveillance of the process. The robust and cost-effective measuring method accompanied with a simple and intuitive control scheme proves to be effective for early fault detection of the pulverized-coal preparation system.

Keywords - ARIMA model, control chart, fan mill, fault detection, pneumatic transport, statistical modelling

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 265-274, SI 38
DOI:10.5545/sv-jme.2016.4264

 

pdfA Surveillance of Direct-Firing System for Pulverized-Coal Using Statistically Treated Signals from Intrusive Electrostatic Sensors (.pdf 1.3MB)

 



Failure Analysis of the Multi-Level Series Rotary Seal Device under High-Pressure Water

Authors - Zenghui Liu – Changlong Du* – Songyong Liu – Hongxiang Jiang

Abstract

High-pressure water jets are used to assist roadheaders in breaking hard rock. The failure life of the high-pressure rotary seal (HPRS) is significant, due to how it affects the safety and efficiency of the roadheader. Here we investigate the mechanical behaviour of the HPRS with a series of experiments. Single-level rotary seal device based studies were conducted to investigate the effect of seal forms, materials, operating pressure and spindle speed on friction torque and leakage. The best seal form from the three kinds of forms was chosen to test the failure life of the multi-level series rotary seal device and the relationships between the operating pressure, spindle speed, temperature, leakage and failure life were analysed. The failure life of rotary seals from Levels 1 to 4 was observed to be 15, 11, 5, and 4 days respectively. The increase in temperature of Levels 1 and 2 was perceived to be slow at the beginning phase of the test, while it rose sharply until the failure occurred, whereas in the case of Levels 3 and 4 it was instantaneous

Keywords - failure analysis, rotary seal, mechanical testing, wear, high pressure

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 63(2017)4, 275-283, SI 39
DOI:10.5545/sv-jme.2016.4012

 

pdfFailure Analysis of the Multi-Level Series Rotary Seal Device under High-Pressure Water (.pdf 1.7MB)

 


 


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Journal of Mechanical Engineering

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SV-JME-10-2017


SV-JME-9-2017


SV-JME-7-8-2017


SV-JME-6-2017

 

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