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uARMSolver: a framework for association rule mining
Iztok Fister, Iztok Fister, 2020, elaborat, predštudija, študija

Ključne besede: association rule mining, categorical attributes, numerical attributes, software framework, optimization
Objavljeno: 17.03.2021; Ogledov: 39; Prenosov: 4
.pdf Celotno besedilo (462,21 KB)
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Discovering associations in COVID-19 related research papers
Iztok Fister, Karin Fister, Iztok Fister, 2020, elaborat, predštudija, študija

Ključne besede: data science, metro maps, optimization
Objavljeno: 15.03.2021; Ogledov: 36; Prenosov: 5
.pdf Celotno besedilo (475,27 KB)
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An analysis of exploration and exploitation using attraction basins on 2D and 3D continuous functions
Mihael Baketarić, 2020, magistrsko delo

Opis: In this thesis we were discussing an analysis of numerical optimization algorithms from the most important aspect, that is exploration and exploitation. We focused on 2-dimensional and 3-dimensional unconstrained continuous functions, which were used to test the recently proposed metric based on attraction basins. The metric does not need any user-defined parameters. Attraction basins were expounded more profoundly and extensively. Our algorithm to calculate them consists of three steps such as making potential boundaries, filling, and then removing false boundaries from attraction basins. Results show that our algorithm is barely satisfying, depends on a particular problem function used. For example, attraction basins from Rastrigin, Schwefel, Ackley and similar functions (including all unimodal ones) were calculated accurately, while more special functions like Michalewicz, Shubert and Branin were proved to be not so easy. Further, we arbitrarly selected two algorithms, Particle Swarm Optimization and Self-adapting Differential Evolution, not for comparative study, rather to test the metric based on attraction basins. Results implied the relevance of recently proposed metric, and opened us a fruitful field for further investigation.
Ključne besede: exploration, exploitation, attraction basins, optimization, metaheuristic
Objavljeno: 04.11.2020; Ogledov: 83; Prenosov: 21
.pdf Celotno besedilo (1,76 MB)

Optimization of the distribution network operation by integration of distributed energy resources and participation of active elements
Nevena Srećković, 2020, doktorska disertacija

Opis: Distribution Networks (DNs) are evolving from a once passive to an active part of the electricity network. This evolution is driven by the current political and environmental decisions, Directives and Incentives, as well as the technological development, observed in the everincreasing integration of renewable energy resources, advanced network control and measurement devices, the upcoming energy exibility market, etc. This Doctoral Thesis deals with the problem of optimization of the technical aspects of a DN operation, enabled by the proliferated integration of the photovoltaic systems (PV) and other active devices. The main objective of the Thesis is the optimization of a DN operation in terms of minimization of electrical energy losses while ensuring the proper voltage profiles and preventing thermal overloadingof lines. Therefore, three Differential Evolution-based optimization procedures were developed and tested on real medium and low voltage DNs. The first methodology determines the optimal rooftop surfaces for the installation of PV systems, yielding minimum annual energy losses. It is based on the simultaneous consideration of high-resolution spatio-temporal solar and PV potential data, as well as long-term measured profiles of consumption and generation of electrical energy within the network of a given configuration. The second algorithm minimizes network losses in a time-discrete operation point, by determining the optimal operation of the following active elements: PV systems capable of cooperation in reactive power provision, On-Load Tap Changer equipped transformer substations and remotely controlled switches for network reconfiguration. The final algorithm was developed by a proper consolidation of the first two approaches, yielding the synergistic effects expressed as the increase of loss reduction and network exibility. The results of the performed case studies show that the locations of the highest suitability for PV installation with respect to the solar energy availability, are not necessarily the best choice from the network operation standpoint. Therefore, both standpoints should be considered simultaneously when choosing the rooftop surfaces for PV installation. Furthermore, by determining optimal hourly operation of the considered active elements, not only the additional reduction of annual network losses was achieved, but also increased accommodation of the PV systems that doesn't violate operation constraints.
Ključne besede: distribution network, optimization of operation, active network elements, PV system placement, minimization of losses
Objavljeno: 11.06.2020; Ogledov: 486; Prenosov: 138
.pdf Celotno besedilo (44,58 MB)

Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy
Damir Skuhala, 2020, magistrsko delo

Opis: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation.
Ključne besede: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness
Objavljeno: 11.05.2020; Ogledov: 382; Prenosov: 105
.pdf Celotno besedilo (25,14 MB)

Peter Fajs, 2019, magistrsko delo

Opis: The objective of the master thesis is to determine the filling properties of injection moulding process for newly created material, and to understand how the variation of processing parameters affects the flow possibilities. In thesis two materials were analysed, i.e. neat PLA material, which was used as a benchmark material and newly created composite CitrusPLA that is based on biodegradable PLA matrix and reinforced with citrus fibres. To fulfil the aim, the virtual and experimental design of experiment with the Taguchi methodology was conducted with use of spiral flow test, where the flow length of material through mould cavity was observed. The experimental results were the basis for the accuracy validation of numerical results and also to determine the optimum process parameters for injection moulding products with best flow conditions through statistical evaluation. It has been concluded that the newly created composite has lower viscosity compared to benchmark virgin PLA which results in better flow conditions in spiral flow test analysis. Both materials have the same optimal conditions in terms of flow conditions. The contribution of mould temperature is in both cases negligible. However, other two variated parameters i.e. melt temperature and injection speed have higher influence on filling characteristics for both materials.
Ključne besede: injection moulding optimization, material characterization, Moldflow, injection moulding simulations, Taguchi DOE, bio-composites, citrus waste fibres, PLA
Objavljeno: 07.06.2019; Ogledov: 595; Prenosov: 0

Dušica Mirković, 2019, doktorska disertacija

Opis: The aim of this doctoral research was to develop and optimize parenteral nanoemulsions as well as the total parenteral nutrition (TPN) admixture containing a nanoemulsion obtained in the course of the optimization process (hereinafter referred to as optimal nanoemulsion), and to examine their physicochemical and biological quality as well. In addition, the quality of the prepared nanoemulsions was compared with the quality of the industrial nanoemulsion (Lipofundin® MCT/LCT 20%), and, in the end, the TPN admixture initially prepared was also compared with the admixture into which the industrial emulsion was incorporated. Parenteral nanoemulsions that were considered in this dissertation were prepared by the high-pressure homogenization method. This method is the most widely applied method for the production of nanoemulsions due to the shortest length of homogenization time, the best-obtained homogeneity of the product and the smallest droplet diameter. For the nanoemulsion formulation, preparation and optimization purposes, by using, firstly, the concept of the computer-generated fractional design, and, after that, the full experimental design, the assessment of both direct effects of different formulation and process parameters (the oil phase type, the emulsifier type and concentration, a number of homogenization cycles and the pressure under which homogenization was carried out) as well as the effects of their interactions on the characteristics of prepared nanoemulsions was performed. Monitoring the nanoemulsion physical and chemical stability parameters was carried out immediately after their preparation, and then after 10, 30 and 60 days. It included the visual inspection, the measurement of the droplet diameter (the mean and volume droplet diameter), the polydispersity index, the ζ-potential, the pH value, the electrical conductivity, and the peroxide number. After the preparation and after 60 days, the biological evaluation (the sterility test and the endotoxic test) of the prepared nanoemulsions was carried out. As far as the characterization of the TPN admixture is concerned, it included practically the same parameters. The dynamics of monitoring the characteristics of the TPN admixture was determined on the basis of practical needs of hospitalized patients (0h, 24h and 72h). The scope and comprehensiveness of this issue indicated the need to divide the doctoral dissertation into three basic stages. The first stage was preliminary. Using the 24-1 fractional factorial design, nanoemulsions for the parenteral nutrition were prepared. They contained either a combination of soybean and fish oil, or a combination of medium chain triglycerides and fish oil. In addition, the type and the amount of an emulsifier used, a number of high-pressure homogenization cycles, and the homogenization pressure, were also varied. The measurement of the above-mentioned parameters for the industrial nanoemulsion was parallely carried out (Lipofundin® MCT/LCT 20%). The objective of this part of the research was to identify critical numerical factors having the most significant effect on the characteristics that define the prepared parenteral nanoemulsions. Parameters that were singled out as the result of this stage of the research (the emulsifier concentration and a number of homogenization cycles) were used as independent variables in the second stage of the research.
Ključne besede: nanoemulsions, total parenteral nutrition admixtures, high pressure homogenization, design of experiments, optimization, analysis of variance, artificial neural networks
Objavljeno: 07.06.2019; Ogledov: 10731; Prenosov: 0
.pdf Celotno besedilo (2,82 MB)

Differential evolution and large-scale optimization applications
Aleš Zamuda, raziskovalni ali dokumentarni film, zvočna ali video publikacija

Opis: Differential Evolution (DE) is one of the most popular, high-performance optimization algorithms with variants that have been outperforming others for years. As a result, DE has grown to accommodate wide usage for a variety of disciplines across scientific fields. Differential Evolution and Large-Scale Optimization Applications presents a research-based overview and cross-disciplinary applications of optimization algorithms. Emphasizing applications of Differential Evolution (DE) across sectors and laying the foundation for further use of DE algorithms in real-world settings, this video is an essential resource for researchers, engineers, and graduate-level students. Topics Covered : Algorithms, Optimization, Parallel Differential Evolution, Performance Improvement, Stochastic Methods, Tree Model Reconstruction.
Ključne besede: differential Evolution, optimization, algorithms, stochastic methods, tree models, tree model reconstruction
Objavljeno: 14.05.2019; Ogledov: 484; Prenosov: 147
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A practical method for the optimal design of continuous footing using ant-colony optimization
Boonchai Ukritchon, Suraparb Keawsawasvong, 2016, izvirni znanstveni članek

Opis: The objective of this paper is to present a practical method for the optimal design of a continuous footing subjected to vertical and horizontal loads. The design problem of finding the optimal size of footing as well as the minimum steel reinforcement is formulated in a nonlinear minimization form. The continuous footing is subjected to the vertical and horizontal loads acting on the top of the column. There are four design variables in the design problem, i.e., the width of the footing, the thickness of the footing, the soil-embedment depth, and the amount of steel reinforcement. The required geotechnical constraints include the bearing capacity, overturning, as well as global sliding and local sliding at the footing corners. Short-term stability and long-term stability are considered simultaneously in the same formulation. The structural constraints are enforced to control the shear force and bending moment within the section resistance. The formulation of the problem’s constraints leads to the nonlinear programming, whose objective function is to minimize the total cost of the footing material, including the concrete and steel reinforcement. The optimal solution is solved using the ant-colony optimization algorithm MIDACO. The proposed optimization method is demonstrated through the actual design of the footing for supporting a large machine moving on rails.
Ključne besede: optimal design, footing, stability, nonlinear programming, ant-colony optimization
Objavljeno: 18.06.2018; Ogledov: 420; Prenosov: 36
.pdf Celotno besedilo (446,51 KB)
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Design optimization for symmetrical gravity retaining walls
Erol Sadoğlu, 2014, izvirni znanstveni članek

Opis: The optimization for symmetrical gravity retaining walls of different heights is examined in this study. For this purpose, an optimization problem of continuous functions is developed. The continuous functions are the objective function defined as the cross-sectional area of the wall and the constraint functions derived from external stability and internal stability verifications. The verifications are listed as the overturning, the forward sliding, the bearing capacity, the shears in the stem and the bendings in the stem. The heights of the walls are selected as 2.0, 3.0, and 4.0 m in order to investigate the outline of the optimum cross-section and the effect of the wall height on the outline. Additionally, the physical and mechanical properties of the soil are kept constant in order to compare only the effect of the height on the geometry. The upper and lower bounds of the solution space are specified to be as wide as possible and the minimum dimensions suggested for the gravity retaining walls are not taken into account. A common feature of the optimum cross-sections of walls with different heights is to have a very wide lower part like a wall foundation and a slender stem. However, other than the forward sliding constraint, the bending constraints are active at the optimum values of the variables.
Ključne besede: gravity retaining wall, nonlinear optimization, continuous variables, interior point method
Objavljeno: 14.06.2018; Ogledov: 446; Prenosov: 45
.pdf Celotno besedilo (168,77 KB)
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