SV - JME 55 (2009)9

SV-JME-9-2009 in digital form »

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Performance Analysis of the Reheat-Stop-Valve Mechanism under Dimensional Tolerance, Misalignment and Thermal Impact

Corresponding author - Xu Dong

Authors - Jin Ye

Abstract

The reheat-stop-valve (RHSV) mechanism is a principal component in a steam turbine unit which controls the running state. Mechanical jamming and incompletence often occur during closing the mechanism. This paper proposes a method to quantitatively investigate the cumulative effect of dimensional tolerance, misalignment and thermal impact on the dynamic performance with shaft and bearing pairs in a RHSV mechanism. Finite element method is employed to study the effect of thermal impact on the clearance of the shaft and bearing pairs. Then, we calculate the clearance of the shaft and bearing pairs considering thermal impact and dimensional tolerance. Based on the non-linear clearance and misalignment, a model named compensation cone is developed to establish the multi-support mechanism of the shaft and bearings system. The method is demonstrated by applying to the RHSV mechanism in a supercritical steam turbine unit. The results indicate that the combined effect of dimensional tolerance, misalignment and thermal impact exerts great effect on the performance of mechanism.

Keywords - dimensional tolerance, misalignment, thermal impact, clearance, performance

Paper's information

Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 507-520 
UDC 621.646.2:621.165

 Performance Analysis of the Reheat-Stop-Valve Mechanism under Dimensional Tolerance, Misalignment and Thermal Impact (pdf)

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Emergent Synthesis Based Multi-Objective Design of the Manufacturing System Shop-Floor

Corresponding author - Zlatan Car

Authors - Branimir Barišić, Miroslaw Rucki

Abstract

This article presents a new approach for multi-objective design of the manufacturing system shop-floor. The proposed model for multi-objective design is based on the Emergent Synthesis approach. Emergent Synthesis related approaches use both, bottom-up and top-down features, unlike traditional analytical, deterministic approaches based on top-down problem decomposing. Based on the proposed approach a simulation model has been built and analysed. The Genetic Algorithm (GA) has been implemented in the proposed model for in final optimization process. From the obtained results of the simulation it can be concluded that with the utilization of the proposed approach for adaptable design  the model has a high level of multi-objective adaptation in the design of the manufacturing system shop-floor. One of the major characteristics of the here proposed approach for multi-objective design of the manufacturing system is that the model has the ability for a simultaneous  influence on the design and adaptation of the shop-floor layout and that it adapts to scheduling rules.

Keywords - multi-objective design, Emergent Synthesis, BMS, genetic algorithm

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 521-528
UDC 658.5

 Emergent Synthesis Based Multi-Objective Design of the Manufacturing System Shop-Floor (pdf)

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Some Statistical Aspects of Firecracker Noise

Corresponding author - Ferdinand Deželak

Authors - Jurij Prezelj, Mirko Čudina

Abstract

Since firecracker explosions have the characteristics of an impulse noise, they can cause hearing loss, serious personal injuries, fire hazards, annoyance, and even death. Their peak sound pressure levels at a distance of some meters can exceed the limit value of 140 dB, at which hearing protection is necessary. This article deals with some noise aspects resulting from firecracker explosions, which were measured during New Year's Eve. Apart from principal factors influencing the acoustic power of such an explosion, some new statistical aspects are described. A special emphasis is given to the probability distribution function of peak sound pressure levels, originating from a great number of firecracker explosions. Generally, the probability distribution closely follows the Rayleigh distribution, but when the number of explosions in unit time is high enough, it tends to a Gaussian distribution. Such transition is accelerated when reflections are taken into account, since in this case the number of peaks between two sequential zero crossings of sound pressure increases.

Keywords - firecrackers, explosions, statistics, prediction, noise level

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 529-541
UDC 534.6: 662.15

 Some Statistical Aspects of Firecracker Noise (pdf)

 

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Reward Level Evaluation of Parallel Systems

Corresponding author - Vasov Ljubiša
Authors - Stojiljković Branimir, Mitrović Časlav

Abstract

In the presented model of the utilization process of parallel systems, the inherent characteristics of system reliability and maintainability as well as repair shop capacity are included. For the system required to perform a desired function and produce certain yield an achieved reward level is proposed as a measure of the utilization process quality by introducing a referent reward concept. System modeling is accomplished by applying Markov Techniques, and several elements are incorporated: failure and repair rates as well as repair shop capacity. By getting closed-form mathematical expressions for system state probabilities and the achieved reward level, an investigation of reliability, maintainability and repair shop capacity on the achieved reward level and system availability is done.

Keywords - reward level, parallel system, availability, Markov model

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 542-548
UDC 519.217

 Reward Level Evaluation of Parallel Systems (pdf)

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Numerical Simulation of Crack Modeling using Extended Finite Element Method

Corresponding author - Gordana Jovičić

Authors - Miroslav Živković, Nebojša Jovičić

Abstract

For numerical simulation of crack modeling in Fracture Mechanics the eXtended Finite Element Method (X-FEM) has recently been accepted as the new powerful and efficiency methodology. Following the new approach, a discontinuous function and the asymptotic crack-tip displacement functions are added to the conventional finite element approximation. This enables the domain to be modeled by finite elements with no explicit meshing of the crack faces. In the paper we present the details of implementation of the X-FEM algorithm in our in-house finite elements based software. Also, we investigated the impact of the node enrichment variations on results of the developed numerical procedure. In order to evaluate computational accuracy, numerical results for the Stress Intensity Factors (SIF) are compared with both theoretical and conventional finite element data. For the calculation of the Stress Intensity Factors, we used the J-Equivalent Domain Integral (J-EDI) Method. Computational geometry issues associated with the representation of the crack and the enrichment of the finite element approximation are discussed in detail. Obtained numerical results have shown a good agreement with benchmark solutions.

Keywords - extended finite element method, node enrichment, stress intensity factor, j-equivalen domain integral method

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 549-554
UDC 620.178

 Numerical Simulation of Crack Modeling using Extended Finite Element Method (pdf)

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The Application of the Root Locus Method for the Design of Pitch Controller of an F-104A Aircraft

Corresponding author - Branimir Stojiljković

Avtorji - Ljubiša Vasov, Časlav Mitrović, Dragan Cvetković

Abstract

This paper presents an application of the root locus technique for the design of a feedback control system of an F-104A aircraft. The analysis of the longitudinal aircraft stability was performed for the Single Input Single Output (SISO) open-loop system, using linearised equations of aircraft motion and aerodynamic derivatives of an F-104A aircraft taken from the NASA report [1]. The dynamical behavior of the open-loop system was unsatisfactory and led to the introduction of the feedback control system. The closed-loop system was designed using the root locus technique, developed by Evans in 1948. The transfer function parameters of each element of the feedback control system are determined according to previously set design requirements. Although, the analysis of the closed-loop step response showed that all of the design requirements were realised, the controller designed within the proposed control system structure is not the only one, and there are different controller designs that lead to a satisfactory solution.

Keywords - controller synthesis, root locus, stability derivatives, longitudinal dynamical stability

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 555-560
UDC 629.7.062

 The Application of the Root Locus Method for the Design of Pitch Controller of an F-104A Aircraft (pdf)

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Intelligent Interfacing Module of Process Capability among Product and Process Development Systems in Virtual Environment

Corresponding author - Algirdas Bargelis

Authors - Petri Kuosmanen, Andrius Stasiškis

Abstract
An intelligent interfacing module of process capability (IIMPC) between product and process design systems in virtual prototyping environment has been developed on the basis of the knowledge acquired at different organizations involved in new product development. The paper considers contradictions both, in product design procedure when seeking its best performance and in the principles of design for assembling (DFA) and design for manufacturability (DFM), whereas, when facilitating the product assembling process, the fabrication process of product parts becomes more complicated. This research can help to find the best decision of quality and lean manufacturing among available product and process alternatives. Mathematical formalization of a developed interfacing module is provided and appropriate software is created. The proposed interfacing module is being implemented for the integration of computer aided design (CAD) and computer aided process planning (CAPP) systems. IIMPC is used in industry and in study processes in universities.

Keywords - intelligent interfacing module, product and process development, integration, process capability, quality, virtual environment

Paper's information
Strojniški vestnik - Journal of Mechanical Engineering 55(2009)9, 561-569
UDC 658.5

 Intelligent Interfacing Module of Process Capability among Product and Process Development Systems in Virtual Environment (pdf)

 

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