Faculty of Mechanical Engineering

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New Derivative-free Nonmonotone Line Search Methods for Unconstrained Minimization
(2013)
Nikolovski, Filip
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Two new derivative-free nonmonotone line search methods for unconstrained optimization are proposed and analyzed. Convergence is established under standard conditions. Numerical results show good performance of the proposed methods.
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A Line Search Method with Memory for Unconstrained Optimization of Noisy Functions
(Union of Mathematicians of Macedonia, 2015)
Natasa Krejic
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Zorana Luzanin
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Nikolovski, Filip
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We propose a new line search method for unconstrained optimization of noisy functions. The nonmonotone line search rule is based on Ulbrich’s nonmonotone component [SIAM J. on Optimiz., 11 (4) (2001), 889–917]. The method uses only nosy functional values. Convergence under standard assumptions is established. Computational results show a good performance of the method compared with the monotone one.
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Complex-step derivative approximation in noisy environment
(Elsevier BV, 2018-01)
Nikolovski, Filip
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The complex-step derivative approximation is a powerful method for derivative approximations which has been successfully implemented in deterministic numerical algorithms. We explore and analyze its implementation in noisy environment through examples, error analysis and application to optimization methods. Numerical results show a promising performance of the complex-step gradient approximation in noisy environment.
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A nonmonotone line search method for noisy minimization
(Springer Science and Business Media LLC, 2015-01-24)
Krejić, Nataša
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Lužanin, Zorana
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Nikolovski, Filip
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A nonmonotone line search method for optimization in noisy environment is proposed. The method is defined for arbitrary search directions and uses only the noisy function values. Convergence of the proposed method is established under a set of standard assumptions. The computational issues are considered and the presented numerical results affirm that nonmonotone strategies are worth considering. Four different line search rules with three different directions are compared numerically. The influence of nonmonotonicity is discussed.
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SIMULATION OF AN ACTUATOR & DRIVE OF A WIRE DRAWING MACHINE’S MECHATRONIC SYSTEM USING MATLAB/SIMULINK
(Mechanical Engineering – Scientific Journal, 2014-02)
Goce Tasevski; Zlatko Petreski; Dejan Shishkovski
Simulation of a mechatronic system actuator, implemented in a wire drawing machine, developed in Matlab/Simulink environment is presented in this paper. AC induction motor with vector control drive is chosen as an actuator. Mathematical model of the actuator is expressed in d-q reference frame rotating at synchronous speed. Diagrams for calculation of the important parameters for the simulation of the actuator were constructed. Simulation results from the model behaviour were discussed in comparison with the specified parameters by the manufacturer of the existing actuator integrated in such mechatronic system.
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Experimental Measurements of System Dynamics Between Two Stages of Wire Drawing Machine
(Walter de Gruyter GmbH, 2015-03-01)
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Shishkovski, Dejan
<jats:title>Abstract</jats:title> <jats:p>In multi-stage wire drawing machines productivity growth can be achieved at higher drawing speeds by preventing wire breakage during the process. One disadvantage of high-speed wire drawing is the requirement imposed by machine dynamics in terms of its stability and reliability during operation. Tensile forces in the wire must maintained by fast synchronization of all capstans speed. In this process, the displacement sensors play the main role in providing the control system with feedback information about the wire condition. In this study, the influences between the sensors and actuator driven capstans have been studied, and tuner roll concept of a wire drawing machine was experimentally investigated. To this aim, measurements were carried out on two drawing stages at different drawing speeds and obtained results were presented. These results clearly show the fast changes of the capstans speed and the angular displacements of the rollers that tighten the wire, which only confirms the high dynamics of the wire drawing machine.</jats:p>
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Development of system for displacement measurement of a cantilever beam with strain gauge sensor
(Mechanical Engineering – Scientific Journal, 2015)
Dejan Shishkovski; Zlatko Petreski; Goce Tasevski
In this paper, strain gauge based experimental system for displacement measurement of a cantilever beam was developed. The system comprises strain gauge sensors, signal conditioning module and data acquisition unit. Two strain gauges installed at the beam surface are connected in Wheatstone half-bridge configuration. Signal conditioning process is described in details along with the procedure for signal processing. Eventually, experimental investigations were conducted to verify the analytical gained results and certain conclusions were drawn.
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REVERSE ENGINEERING – AN EFFECTIVE TOOL FOR DESIGN AND DEVELOPMENT OF MECHANICAL PARTS
(A CTA TECHNICA CORVINIENSIS – Bulletin of Engineering, 2018-04)
The Reverse Engineering has already found an extensive application in industry and other different fields. Reverse engineering (RE) is a process of taking the existing physical model and reproducing its surface geometry in three-dimensional (3D) data file on a computer-aided design (CAD) system. This paper will analyze the real situation in one industrial plant and provide comparative analysis of the application of current measuring methods and possibility of incorporating digital measurement. The Reverse Engineering (RE) is based on a method of reducing the time of dimensioning and modeling of mechanical parts which can be complex by geometry or dimensionally very accurate. In this paper we can give some practical examples of parts that are really produced in one manufacturing factory. Recommendation for digitalization will be of crucial importance for every company in its measurement and quality control activities
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ANALYSIS OF ENTREPRENEURIAL EDUCATORS FOR BOOSTING THE ENTREPRENEURIAL POTENTIAL IN EUROPE
(IATED, 2019-11)
Stankovska, Ivana
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Polenakovik, Liljana
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Polenakovik, Radmil
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Shterjova, Nastasija
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Velkovski, Trajce
The development of entrepreneurial capacity is one of the key policy objectives for the EU and Member states. In order to provide shared definition of the entrepreneurship as a competence, as well as to raise consensus among all stakeholders and to establish a bridge between the worlds of education and work, the EntreComp framework was developed and established. However, of a great importance for the quality and success of the development of entrepreneurial capacities in the EU is the level of entrepreneurial development of the teachers and other educators in both, formal and informal educational sectors. This research aimed to investigate the needs and requirements among the teachers and educators, which will serve for the development of a competence-based framework outlining the skills that teachers can use to facilitate entrepreneurial learning in the classroom, supporting by extensive user testing with learners, teachers, leaders, community and business. For this purpose, the quantitative research methodology consisted of online questionnaire was designed and implemented among the educators from primary and secondary schools in four European countries: United Kingdom, Belgium, Republic of Macedonia and Spain. The focus of the survey was targeted to assessing different factors/options for continuing professional development and the current level of development of the entrepreneurial competences listed in the EntreComp framework among the respondents’ learners. The collected dataset was analysed from two perspectives. Firstly, the country-specific responses were observed separately and comparatively among different countries. Secondly, the answers were classified according to the role of the respondents in the educational systems, and relevant role-specific findings were brought to light for the role categories that were represented with significant number of respondents. The results revealed interesting country-specific and sector-specific conclusions that will provide useful recommendations and advices in the transformation of the EntreComp framework to the EntreCompEdu professional entrepreneurial skills framework. The application of the EntreCompEdu framework to the educational sector in the European modern societies will drive them in their strategic exertions for building creative and entrepreneurial mindsets and bridging in real-life context with the teaching.
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Assessment of the Thermal Processing Behavior of Tobacco Waste
(American Chemical Society (ACS), 2012-09-11)
Strezov, Vladimir
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Popovic, Emilija
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Filkoski, Risto V.
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Shah, Pushan
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Evans, Tim
Pyrolysis of tobacco waste can provide an effective management option, as it produces biogas and bio-oils, which can be subsequently applied for energy recovery, and biochar, which can be used for carbon sequestration when stored in soils. This work assesses the pyrolysis behavior of tobacco waste and reveals four stage pyrolysis mechanism consisting of dehydration (<200 °C), torrefaction (≈300 °C), charring (≈500 °C), and carbonization (≈750 °C). The calorific value of the evolved biogas products at the charring temperature of 500 °C was estimated to be reasonably high and the products can be combusted to generate energy required to self-sustain the pyrolysis process. The bio-oils contained complex chemical structure consisting of nicotine, phenols, and organic acids. The biochar product exhibited enrichment in the fixed carbon, ash, and nutrients P and K, while N remained at relatively constant concentration throughout the pyrolysis process.

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