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Discrete optimization with fuzzy constraints
Primož Jelušič, Bojan Žlender, 2017, original scientific article

Abstract: The primary benefit of fuzzy systems theory is to approximate system behavior where analytic functions or numerical relations do not exist. In this paper, heuristic fuzzy rules were used with the intention of improving the performance of optimization models, introducing experiential rules acquired from experts and utilizing recommendations. The aim of this paper was to define soft constraints using an adaptive network-based fuzzy inference system (ANFIS). This newly-developed soft constraint was applied to discrete optimization for obtaining optimal solutions. Even though the computational model is based on advanced computational technologies including fuzzy logic, neural networks and discrete optimization, it can be used to solve real-world problems of great interest for design engineers. The proposed computational model was used to find the minimum weight solutions for simply-supported laterally-restrained beams.
Keywords: uncertainty, discrete optimization, neuro-fuzzy technique, structural optimization
Published: 09.08.2017; Views: 756; Downloads: 302
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Multi-objective synthesis of company’s supply-networks based on integration of renewable resources
Annamaria Vujanović, 2017, doctoral dissertation

Abstract: The aim of this doctoral dissertation was to develop a general methodology for sustainable integration of company's supply networks into nearby regional networks by i) integrating renewables, thereby increasing company's energy self-sufficiency, ii) by performing multi-objective synthesis in order to obtain economically efficient and yet environmentally benign or even unburdening solutions, and iii) to perform dynamic and stochastic synthesis under uncertainties in dynamically changing market conditions in order to obtain more reliable and realistic solutions. The research work is directly interlinked with a large-scale European meat producing company Perutnina Ptuj d.d., which is located in the heart of Slovenia. The aim of the first part was to integrate renewables into companies’ supply-networks at regional level in order to maximize the self-sufficiencies of their energy supplies. This concerns companies’ activities from the use of natural resources to supplying their final products to the customers being interlinked with their regional networks. A Mixed-Integer Linear Programming (MILP) model has been developed for the integration of both the companies’ and surrounding regional supply-networks and the utilization of different types of renewables as sources for the companies’ energy supplies. The potential renewable energy sources, which are located within companies surrounding region are solar, biomass, organic and animal wastes. The result indicates that by sufficient integration of renewables into companies’ supply networks, profitable and yet energy self-sufficient solutions can be obtained. The second part presents the multi-objective synthesis of a company’s supply-network by integrating renewables and accounting for several environmental footprints. A previously developed model for achieving energy self-sufficiency by integrating renewables into companies’ supply-networks has been extended for the evaluation of environmental impacts, such as energy, carbon, nitrogen, and water footprints. The achievement of an energy self-sufficient supply-network has been considered whilst significantly reducing environmental impacts. Direct (burdening) and indirect (unburdening) effects that form total effects on the environment are considered for the evaluation of environmental footprints. This approach identifies those alternative energy production technologies that are more profitable and environmentally more benign with significant unburdening capabilities. The results showed significant unburdening of the environment in terms of carbon and nitrogen footprints; however, higher burdening in terms of the water footprint. The third part presents a multi-objective MILP synthesis of a dynamic supply-network under uncertainty applied to the company. The previously-developed multi-objective model for achieving energy self-sufficiency by integrating renewables into companies’ supply-networks has now been extended to account for the dynamic consideration of variable supply and demand over the year, for uncertainties related to products’ demand and sun radiation, and for multi-objective optimisation, in order to obtain the most sustainable company’s supply-network. The sustainable synthesis of a company’s network is performed regarding the integration of the renewables such as biomass and other wastes, and solar energy. The obtained solutions are those reflecting maximal profit, reflecting constantly-changing dynamic market conditions, accounting for several uncertain parameters, and protecting the environment.
Keywords: Company's supply network, Renewables, Environmental Impacts, Dynamic synthesis, Flexibility, Multi-objective optimisation, Uncertainty
Published: 21.07.2017; Views: 968; Downloads: 118
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Decision making under conditions of uncertainty in agriculture
Karmen Pažek, Črtomir Rozman, 2009, review article

Abstract: In decision under uncertainty individual decision makers (farmers) have to choose one of a set number of alternatives with complete information about their outcomes but in the absence of any information or data about the probabilities of the various state of nature. This paper examines a decision making under uncertainty in agriculture. The classical approaches of Wald’s, Hurwicz’s, Maximax, Savage’s and Laplace’s are discussed and compared in case study of oil pumpkin production and selling of pumpkin oil. The computational complexity and usefulness of the criterion are further presented. The article is concluded with aggregate the results of all observed criteria and business alternatives in the conditions of uncertainty, where the business alternative 1 is suggested.
Keywords: uncertainty, Wald’s, Hurwicz’s, Maximax, Savage’s and Laplace’s criterion, decision support system, agriculture, oil crops
Published: 20.07.2017; Views: 552; Downloads: 76
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Optimal robust motion controller design using multi-objective genetic algorithm
Andrej Sarjaš, Rajko Svečko, Amor Chowdhury, 2014, original scientific article

Abstract: This paper describes the use of a multi-objective genetic algorithm for robust motion controller design. Motion controller structure is based on a disturbance observer in an RIC framework. The RIC approach is presented in the form with internal and external feedback loops, in which an internal disturbance rejection controller and an external performance controller must be synthesised. This paper involves novel objectives for robustness and performance assessments for such an approach. Objective functions for the robustness property of RIC are based on simple even polynomials with non-negativity conditions. Regional pole placement method is presented with the aims of controllers% structures simplification and their additional arbitrary selection. Regional pole placement involves arbitrary selection of central polynomials for both loops, with additional admissible region of the optimized pole location. Polynomial deviation between selected and optimized polynomials is measured with derived performance objective functions. A multi-objective function is composed of different unrelated criteria such as, robust stability, controllers' stability and time performance indexes of closed loops. The design of controllers and multi-objective optimization procedure involve a set of the objectives, which are optimized simultaneously with a genetic algorithm - Differential evolution.
Keywords: disturbance observer, DOB, uncertainty systems, optimal robust control, multi-objective optimization, differential evolution
Published: 15.06.2017; Views: 699; Downloads: 289
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Contingency factors influencing implementation of physical asset management practices
Damjan Maletič, Matjaž Maletič, Basim Al-Najjar, Katerina Gotzamani, Maria Gianni, Kalinowski, Boštjan Gomišček, 2017, original scientific article

Abstract: Purpose: The purpose of this empirical study is to examine the role of two contingency factors, i.e. uncertainty and competitiveness in relation to physical asset management (PAM) practices as well as to maintenance key performance indicators. The research is based on a premise that PAM, which was defined by risk management practices, performance assessment practices, life cycle management practices, and policy & strategy practices, has become an indispensable element of strategic thinking of asset owners as well as maintenance and asset managers. The purpose of this study is to advance the understanding of how organizations that face high or low level of uncertainty and competitiveness respond in terms of PAM deployment. Methodology/Approach: This study employed a data set based on a large-scale survey among organizations in six European countries (i.e. Slovenia, Poland, Greece, Sweden, Turkey and Slovakia). Data were collected from 138 organizations located in the above-mentioned countries to conduct the study. Findings: The results show that organizations that are faced with high level of uncertainty and competitiveness are more engaged in the deployment of PAM practices. Moreover, results show that when organizations are facing high levels of competitiveness they are using KPIs to a greater extent than organizations under low levels of competitiveness. Originality/value: From a theoretical perspective, this study contributes to the contingency theory by providing empirical evidence whether a context-dependent approach to PAM is needed. The findings also provide insights for managers on how to respond to the competitive pressure as well as how to customize PAM practices in order to adapt to the changes in dynamic organizational environment.
Keywords: physical asset management, maintenance, uncertainty, competitiveness
Published: 06.04.2017; Views: 932; Downloads: 308
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Possibilities of using three-dimensional optical scanning in complex geometrical inspection
Tomaž Brajlih, Tadej Tasič, Igor Drstvenšek, Bogdan Valentan, Miodrag Hadžistević, Vojko Pogačar, Jože Balič, Bojan Ačko, 2011, original scientific article

Abstract: Brezkontaktno optično zajemanje, merjenje in digitalizacija postajajo vedno bolj razširjeni postopki v sistemih zagotavljanja kakovosti. Prednosti optičnega skeniranja v primerjavi s konvencionalnimi kontaktnimi merilnimi postopki so preprosto zajemanje, visoka gostota pridobljenih podatkov ter povezava med povratnim inženirstvom in preverjanjem oblike. Optični skener se zaradi trirazsežnega zajemanja podatkov pogosto obravnava kot alternativa koordinatni merilni napravi. Prednost optičnega skeniranja je predvsem večja hitrost zajemanja podatkov, medtem ko natančnost še ne dosega ravni koordinatne merilne tehnike. Ta prispevek obravnava možnosti uporabe optičnega skenerja pri preverjanju natančnosti izdelave. Predstavljen je primer, pri katerem je za preverjanje natančnosti izdelka uporabljen optični skener GOM ATOS II. V prvem delu prispevka je predstavljeno specifično področje preverjanja natančnosti medicinskih vsadkov. Predstavljene so prednosti, zaradi katerih je optično skeniranje pri takšnih izdelkih primernejše od koordinatnega merjenja. V drugem delu prispevka so predstavljeni rezultati optičnega zajemanja geometrije merilnih kladic ter merilna negotovost postopka. V zadnjem delu je predstavljena neposredna primerjava rezultatov optičnega skeniranja in koordinatnega merjenja krogle. Glede na rezultate merjenja merilnih kladic in primerjave rezultatov merjenja krogle smo dokazali, da je natančnost optičnega skenerja GOM ATOS II primerna za preverjanje oblike medicinskih vsadkov z ozirom na zahtevano natančnost izdelka pred samim operacijskim posegom. Nadaljnje raziskave na tem področju bodo namenjene predvsem ločevanju in vrednotenju merilnih pogreškov optičnega zajemanja, ki so posledica nenatančnosti same naprave ter pogreškov, ki nastajajo zaradi naknadne poobdelave (poligonizacije) zajetih podatkov. Preizkus natančnosti optičnega sistema je bil omejen na merjenje merilnih kladic in na primerjavo meritve krogle s koordinatno merilno napravo. Prispevek predstavlja izvirno področje preverjanja natančnosti izdelave kompleksnih geometrijskih oblik. Predstavljena sta postopek zajemanja in poobdelave podatkov ter metoda preizkusa natančnosti naprave. Prispevek je namenjen vsem, ki se ukvarjajo s preverjanjem kompleksnih geometrijskih oblik, saj se bo z razvojem novih sistemov za optično zajemanje oblik povečevala tudi njihova natančnost. Te naprave bodo zato postajale vedno pomembnejše na širšem področju zagotavljanja kakovosti in ne samo na specifičnem primeru, predstavljenem v tem članku.
Keywords: 3D optical scanning, uncertainty of measurement, geometry inspection, rapid manufacturing, reverse enginering, quality assurance
Published: 10.07.2015; Views: 1016; Downloads: 106
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Uncertainty of nitrate and sulphate measured by ion chromatography in wastewater samples
Brigita Tepuš, Marjana Simonič, 2007, original scientific article

Abstract: This paper presents an evaluation of measurement uncertainty regarding the results of anion (nitrate and sulphate) concentrations in wastewater. Anions were determined by ion chromatography (EN ISO 10304-2, 1996). The major sources of uncertainty regarding the measurement results were identified as contributions to linear least-square or weighted regression lines, precision, trueness, storage conditions, and sampling. Determination of anions in wastewater is very important for the purification procedure, especially the amount of nitrate in waste and potable waters. The determined expanded uncertainty was 6% for nitrate anions and 8.3% for sulphate anions. The difference between measurement uncertainties determined by the two methods, the weighted and linear least-square methods is negligible.
Keywords: wastewater, nitrates, sulphates, measurements, measuring uncertainty
Published: 01.06.2012; Views: 1405; Downloads: 291
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Calibration of electronic levels using a special sine bar
Bojan Ačko, 2005, original scientific article

Abstract: Electronic levels are designated for the precise measurement of inclination angles within the range of +- 3 mm/m. They are very often used for checking the straightness of machine tool guides as well as the flatness of different kindsof machine tool tables and surface plates. Typical resolution of such instruments is 1 m/m. Electronic levels are calibrated by using very precise angle generators. One such generator is a sine bar. Sine bars are cheap and enable fast and simple calibrations. Commercial sine bars however are not precise enough. We, therefore, decided to design a special sine bar, which would be able to generate angles within an uncertainty of 1 mžm. This sine barwas designed by the laboratory staff and manufactured in our workroom. We have also created a calibration procedure, which has already been accredited. Uncertainty analysis, including experimental measurements, shows that the planned uncertainty has been reached. The sine bar design, calibration procedure and uncertainty evaluation are presented in this article.
Keywords: production measurements, measuring uncertainty, calibration, inclination angles, flatness measurements, sine bar, electronic level
Published: 01.06.2012; Views: 2066; Downloads: 91
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Thread gauge calibration for industrial applications
Tadeja Primožič Merkač, Bojan Ačko, 2010, original scientific article

Abstract: There are two most commonly used methods for calibration of thread rings, with different measuring uncertainty. The method of mechanical sensing with two balls is mostly used on one-axial measuring machines and on coordinate measuring machines. However, the method of calculating the core diameter of the thread ring combined with the technique of adaptation (in accordance with the method of the smallest squares) is used on the profile scanner. The required tolerances, which are very narrow for adjustable and laboratory thread ring, so the measuring uncertainty may be too high when using the method of mechanical sensing with two balls, and the low quality of some control rings, are the decisive factors for choosing an appropriate method in the industry. This also depends on the laboratoryćs capability of executing a specific method. The measurements of the core diameter of thread rings, which are the main topic of this article, were included into an international inter-comparison in which the main subject was the same thread ring as the one mentioned in this article.
Keywords: thread ring gauge, calibration, pitch diameter, measurement uncertainty, dimensional measurements
Published: 31.05.2012; Views: 1592; Downloads: 28
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Measurement uncertainty in calibration of measurement surface plates flatness
Andrej Gusel, Bojan Ačko, Vedran Mudronja, 2009, original scientific article

Abstract: Ravno merilno površino, kot je to na primer merilna plošča, lahko smatramo kot izhodišče za izvajanje večine meritev oblike in lege merjenih objektov. Da bi merilne plošče v ta namen zadovoljivo uporabljali, moramo najprej zagotoviti, da so res ravne in primerne za meritve. Ravnost merilne ploskve ugotavljamo posredno, tako da najprej določimo premost posameznih linij, ki so sestavni del merilne mreže. Te linije so še dodatno razdeljene na merilne korake, ki so prirejeni meram merilne opreme. Premost merilne linije izračunamo z merjenjem nagiba posameznega merilnega položaja za vsako linijo posebej, neravnost celotne površine pa tako, da rezultate po linijah povežemo v celoto. Osnove, postopki in merilne naprave za izvajanje meritev so torej znani, neznanka pa ostaja negotovost tovrstne kalibracije merilne površine. Meritev brez ustrezno izražene negotovosti ne pomeni ničesar, zato moramo zagotoviti, da bomo lahko negotovost določili. Pričujoči članek predstavlja nov pristop določanja merilne negotovosti pri merjenju ravnosti, ki temelji na uporabi metode Monte Carlo. Pri tem celoten merilni sistem razstavimo na posamezne komponente ter ocenimo njihovo veličino in vplive le teh, meritve pa simuliramo. Zanima nas tudi vpliv parametrov merilne mreže na meritev.
Keywords: production measurements, length measurements, measuring uncertainty, calibration, uncertainty measurement, flatness measurement
Published: 31.05.2012; Views: 1509; Downloads: 32
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