Journal of Mechanical Engineering 57 (2011) 6

 

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Numerical Prediction of Non-Cavitating and Cavitating Vortex Rope in a Francis Turbine Draft Tube

Authors - Dragica Jošt – Andrej Lipej

Abstract

The paper presents a prediction of vortex rope in a draft tube obtained by the numerical flow analysis. The main goal of the research was to numerically predict pressure pulsation amplitude versus different guide vanes openings and compare the results with experimental ones. Three turbulent models (SAS-SST, ω-RSM and LES) were used. Also the effect of different domain configurations, grid density and time step size on results was examined. At first analysis was done without cavitation, while later at one operating point the cavitation model was included.

Keywords - Francis turbine, vortex rope, cavitation, pressure pulsation, turbulent models

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 445-456
DOI:10.5545/sv-jme.2010.068

 Numerical Prediction of Non-Cavitating and Cavitating Vortex Rope in a Francis Turbine Draft Tube (pdf)

 

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A Methodology for Quantifying the Kinematic Position Errors due to Manufacturing and Assembly Tolerances

Authors - Paulo Flores

Abstract

A systematic and general methodology for kinematic position errors analysis of multibody systems is investigated throughout this work, taking into account the influence of the manufacturing and assemble tolerances on the performance of planar mechanisms. The generalized Cartesian coordinates are used to mathematically formulate kinematic constraints and equations of motion of the multibody systems. Thus, the systems are defined by a set of generalized coordinates, which represents the instantaneous positions of all bodies, together with a set of generalized dimensional parameters that defines the functional dimensions of the system. These generalized dimensional parameters take into account the tolerances associated with the lengths, fixed angles, diameters and distance between centers, among others. This paper highlights the relation among kinematic constraints, dimensional parameters and output kinematic parameters. Based on the theory of dimensional tolerances, the variation of the geometrical dimensions is regarded as a tolerance grade with an interval associated with each dimension and, consequently, a kinematic amplitude variation for the bodies’ position. The methodology presented is implemented in a computational code developed for kinematic analysis of multibody systems, capable of automatically generating and solving the equations of motion for general multibody systems. Finally, a slider-crank mechanism is used as a numerical example to demonstrate the accuracy of the presented methodology, as well as to discuss the main assumptions and procedures adopted in this work.

Keywords - positional error, manufacturing tolerances, assembly systems, planar mechanisms

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 457-467
DOI:10.5545/sv-jme.2009.159

 A Methodology for Quantifying the Kinematic Position Errors due to Manufacturing and Assembly Tolerances (pdf)

 

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A Secondary Source Configuration for Control of a Ventilation Fan Noise in Ducts

Authors - Jurij Prezelj ‒ Mirko Čudina

Abstract

The main noise source in heating, ventilation, and air conditioning systems is usually a ventilating fan. Noise, generated by the ventilating fan is transmitted through the duct into the living and working environment. A typical fan noise spectrum consists of a broadband noise, which is superimposed with pure tones. Different methods are available to reduce a transmission of such noise from the ventilating fan into the living and working environment. In this article it is demonstrated how a feedforward active noise control system can be implemented together with a side branch resonator. Effectiveness of the feedforward active noise control system depends on the quality of a reference signal, which should be in a perfect correlation with the primary noise. An acoustic feedback is the main problem of feedforward active noise control systems in ducts. A combined method uses a single loudspeaker to work as a dipole source and a side branch resonator to reduce the acoustic feedback. A side branch resonator reduces noise transmission in a narrowband frequency range as well. In this article, a theoretical background of a dipole source with a side branch resonator is presented, along with some measurement results and simulations of active noise control.

Keywords - active noise control, secondary source, ventilation duct, noise, fan

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 468-476
DOI:10.5545/sv-jme.2009.026

 A Secondary Source Configuration for Control of a Ventilation Fan Noise in Ducts (pdf)

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Fault Detection of an Industrial Heat-Exchanger: A Model-Based Approach

Authors - Dejan Dragan

Abstract

One of the key issues in modelling for fault detection is how to accommodate the level of detail of the model description to suit the diagnostic requirements. The paper addresses a two-stage modelling concept to an industrial heat exchanger, which is located in a tyre factory. Modelling relies on both, prior knowledge and recorded data. During the identification procedure, the estimates of continuous model parameters are calculated by the least squares method and the state variable filters (SVF). It is shown that the estimates are largely invariant of the bandwidth of the SVFs. This greatly reduces the overall modelling effort and makes the whole concept applicable even for less experienced users. The main issues of the modelling procedure are emphasized. Based on the process model, a simple detection system is derived. An excerpt of the results obtained on operating records is given.

Keywords - industrial heat exchanger, fault detection, condition monitoring, model-based detection, modelling, identification

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6,477-484
DOI:10.5545/sv-jme.2010.128

Fault Detection of an Industrial Heat-Exchanger: A Model-Based Approach (pdf)

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Numerical Methods for TMF Cycle Modeling

Authors - Henrik Zaletelj – Gorazd Fajdiga – Marko Nagode

Abstract

Experimental tests for the endurance evaluation of the machine parts that are exposed to thermomechanical fatigue (TMF) require advanced and expensive testing machines. Numerical methods for the determination of stress-strain material behavior have become very frequent and known due to lower costs. There are several different approaches for the determination of stress-strain behavior. In the article three different numerical methods and their results are presented. The numerical results for different load conditions are compared with the experimental results and the accuracy of the methods can be compared. The Chaboche, Skelton and Prandtl operator approaches are presented, presuming a stabilized elastoplastic response and not including creep. The properties of the model, their weaknesses and possible improvements are also studied in the paper.

Keywords -jcyclic loading, elastoplasticity, kinematic hardening, stress-strain trajectory, thermomechanical fatigue

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 485-494
DOI:10.5545/sv-jme.2010.212

 Numerical Methods for TMF Cycle Modeling (pdf)

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Criticality Analysis of the Elements of the Light Commercial Vehicle Steering Tie-Rod Joint

Authors - Dobrivoje Ćatić – Branislav Jeremić – Zorica Djordjević – Nenad Miloradović

Abstract

The introduction of the paper gives the basic concepts of Failure Modes, Effects and Criticality Analysis - FMECA. Features of elements of mechanical systems regarding failure intensity demand a special approach of quantitative FMECA. The paper presents this approach, applied to the elements of mechanical systems and used for the design of a software package. Criticality analysis of failure modes of light commercial vehicle’s steering tie-rod joint elements was conducted based on the exploitation results and with the use of the previously mentioned method and program. In conclusion, the possibilities of application of the obtained results are presented.

Keywords - reliability, FMECA, steering system of a light commercial vehicle, tie-rod joint

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 495-502
DOI:10.5545/sv-jme.2010.077

 Criticality Analysis of the Elements of the Light Commercial Vehicle Steering Tie-Rod Joint (pdf)

 

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Mathematical Model of an Autoclave

Authors - Aleksander Preglej ‒ Rihard Karba ‒ Igor Steiner ‒ Igor Škrjanc

Abstract
This paper presents the mathematical modelling of the following autoclave processes: heating, cooling and pressure changes. An autoclave is a pressure vessel of a cylindrical form where the composite semi-products are placed on a metal plate above electrical heaters and heated at selected temperatures and under a higher pressure. The purpose of the modelling is to build a mathematical model with which the behaviour of the processes can be simulated and the temperature and pressure control in the autoclave can be improved. Furthermore, using this mathematical model we intend to test advanced uni- and multi-variable control algorithms. The mathematical model is built on the basis of the heat-transfer and pressure-changing theories. While the pressure-changing process is not very complex, the heating and cooling processes involve complex phenomena of heat conduction and convection. In the mathematical model some simplifications were considered and so the heat-transfer correlations past flat plates were used. Most of the data are real and obtained from the autoclave manufacturer, but where not possible, the method of the model’s response fitting to the measured data with the criterion function of the sum of squared errors was used. In this way, to a great extent simulated similarly to the real process responses were obtained. It can be concluded that the obtained mathematical model is usable for the design of a variety of process-control applications.

Keywords - autoclave, mathematical model, heat transfer, convection, conduction, temperature, pressure

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 503-516
DOI:10.5545/sv-jme.2010.182

 Mathematical Model of an Autoclave (pdf)

 

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Theoretical Analysis of Stiffness Constant and Effective Mass for a Round-Folded Beam in MEMS Accelerometer

Authors - Wai Chi Wong ‒ Ishak Abdul Azid ‒ Burhanuddin Yeop Majlis

Abstract
In this paper, the governing equations of stiffness constant and effective mass for a round folded suspension beam in Micro-Electro Mechanical System (MEMS) accelerometer are derived and solved. The stiffness constant is determined by the strain energy and Castigliano’s displacement theorem, whereas the effective mass is determined by the Rayleigh principle. The stiffness constant and the effective mass are solved separately by components and then combined by using the superposition method. The results obtained by the derived equations agree well when compared with the finite element results for several thickness values. The governing equations derived in this paper can be used to predict the natural frequencies and sensitivity of the MEMS-accelerometer.

Keywords - effective mass, folded beam, MEMS-accelerometer, stiffness constant, strain energy

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 57(2011)6, 517-525
DOI:10.5545/sv-jme.2009.151

 Theoretical Analysis of Stiffness Constant and Effective Mass for a Round-Folded Beam in MEMS Accelerometer (pdf)

 

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