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1.
Approach to optimization of cutting conditions by using artificial neural networks
Franc Čuš, Uroš Župerl, 2006, izvirni znanstveni članek

Opis: Optimum selection of cutting conditions importantly contribute to the increase of productivity and the reduction of costs, therefore utmost attention is paid to this problem in this contribution. In this paper, a neural network-based approach to complex optimization of cutting parameters is proposed. It describes the multi-objective technique of optimization of cutting conditions by means of the neural networks taking into consideration the technological, economic and organizational limitations. To reach higher precision of the predicted results, a neural optimization algorithm is developed and presented to ensure simple, fast and efficient optimization of all important turning parameters. The approach is suitable for fast determination of optimum cutting parameters during machining, where there is not enough time for deep analysis. To demonstrate the procedure and performance of the neural network approach, an illustrative example is discussed in detail.
Ključne besede: optimization, cutting parameter optimization, genetic algorithm, cutting parameters, neural network algorithm, machining, metal cutting
Objavljeno: 30.05.2012; Ogledov: 1398; Prenosov: 69
URL Povezava na celotno besedilo

2.
The effect of small flaws on the fatigue strength of HAZ at the weld toe
Vladimir Gliha, 2007, izvirni znanstveni članek

Opis: The effects of small artificial surface flaws on the fatigue strength of HAZ material are studied. The samples of coarse grain HAZ material were prepared using a welding thermal-cycle simulator. The artificial flaws were produced byindenting with a Vickers pyramid at different loads as either single indentations or as a series. The size of the flaws did not exceed the primary austenitic grain size of the material, which is the most relevant microstructural unit of carbon steels. The dependence of the experimentally determined bending fatigue strength of treated coarse grain HAZ materials on the properly evaluated size of the artificial flaws was compared with the law of long-crack propagation. The biggest flaws evaluated with the flaw-size parameter ?area ? 100 m are still small for the studied coarse grain HAZ. In further experimental work, the effects of flaw size and the effects of residual stresses should be analysed separately.
Ključne besede: welding, welded joints, coarse grained HAZ, crack initiation, flaw-size parameter, small surface flaws, stress intensity range, Vickers indentation, weld toe
Objavljeno: 31.05.2012; Ogledov: 1053; Prenosov: 44
URL Povezava na celotno besedilo

3.
Characterization of corrosion processes by current noise wavelet-based fractaland correlation analysis
Peter Planinšič, Aljana Petek, 2008, izvirni znanstveni članek

Opis: Electrochemical noise data in the presence of pitting, general corrosion and passivity were analyzed using the discrete wavelet transform. The registered current noise was decomposed into a set of band-limited details, which contain information about corrosion events occurring at a determined time-scale. It has been observed that the signal variance and variances of details depend on the intensity of processes. Distribution of the signal energy among different details was characteristic for the particular type of corrosion. The characterization of corrosion processes on the basis of in the wavelet domain calculated Hurst parameter H and fractal dimension, D, of electrochemical noise signals has been established. It is concluded that general corrosion is a stationary random process with a weak persistence and D= 2.14, whereas pitting corrosion is a non-stationary process with a long memory effect and D = 1.07. Passivity is a non-stationary process near to the Brownian motion with D = 1.56. The persistence features of electrochemical noise signals were explained also by correlation coefficients calculated between signals obtained by discrete wavelet multiresolution decomposition.
Ključne besede: elektrokemijski šum, valčki, Hurstov parameter, fraktalna dimenzija, korelacijski koeficient, korozija, electrochemical noise, wavelets, Hurst parameter, fractal dimension, correlation coefficients, corrosion
Objavljeno: 31.05.2012; Ogledov: 1193; Prenosov: 59
URL Povezava na celotno besedilo

4.
Use of genetic algorithm for fitting Sovova's mass transfer model
Dejan Hrnčič, Marjan Mernik, Maša Knez Hrnčič, 2010, izvirni znanstveni članek

Opis: A genetic algorithm with resizable population has been applied to the estimation of parameters for Sovovaćs mass transfer model. The comparison of results between a genetic algorithm and a global optimizer from the literatureshows that a genetic algorithm performs as good as or better than a global optimizer on a given set of problems. Other benefits of the genetic algorithm, for mass transfer modeling, are simplicity, robustness and efficiency.
Ključne besede: Sovova's mass transfer model, genetic algorithm, parameter estimation
Objavljeno: 31.05.2012; Ogledov: 1033; Prenosov: 26
.pdf Celotno besedilo (718,52 KB)
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Population size reduction for the differential evolution algorithm
Janez Brest, Mirjam Sepesy Maučec, 2008, izvirni znanstveni članek

Opis: This paper studies the efficiency of a recently defined population-based direct global optimization method called Differential Evolution with self-adaptive control parameters. The original version uses fixed population size but a method for gradually reducing population size is proposed in this paper. It improves the efficiency and robustness of the algorithm and can be applied to any variant of a Differential Evolution algorithm. The proposed modification is tested on commonly used benchmark problems for unconstrained optimization and compared with other optimization methods such as Evolutionary Algorithms and Evolution Strategies.
Ključne besede: differential evolution, control parameter, fitness function, global function optimization, self-adaptation, population size
Objavljeno: 01.06.2012; Ogledov: 1180; Prenosov: 60
URL Povezava na celotno besedilo

7.
Performance comparison of self-adaptive and adaptive differential evolution algorithms
Janez Brest, Borko Bošković, Sašo Greiner, Viljem Žumer, Mirjam Sepesy Maučec, 2007, izvirni znanstveni članek

Opis: Differential evolution (DE) has been shown to be a simple, yet powerful, evolutionary algorithm for global optimization. for many real problems. Adaptation, especially self-adaptation, has been found to be highly beneficial for adjusting control parameters, especially when done without any user interaction. This paper presents differential evolution algorithms, whichuse different adaptive or self-adaptive mechanisms applied to the control parameters. Detailed performance comparisons of these algorithms on the benchmark functions are outlined.
Ključne besede: differential evolution, control parameter, fitness function, optimization, self-adaption
Objavljeno: 01.06.2012; Ogledov: 1239; Prenosov: 52
URL Povezava na celotno besedilo

8.
Optimal reactor systems for Van de Vusse reaction scheme with multicomponent feed
Duško Bikić, Branko Butinar, Peter Glavič, 2002, izvirni znanstveni članek

Opis: In the present paper, product yield in the Van de Vusse reaction scheme with multicomponent feed has been studied. The optimal reactor structures have been found by investigating optimality conditions. The optimum product yield and criteria for selecting an appropriate reaction system have been obtained as functions of kinetic parameters. On the basis of optimization results the parameter space has been classified into regions indicating optimum reactor structure.
Ključne besede: optimal reactor structure, optimum product yield, multicomponent feed, parameter space, Van der Vusse reaction
Objavljeno: 01.06.2012; Ogledov: 1464; Prenosov: 69
URL Povezava na celotno besedilo

9.
Posodobitev informacijskega sistema za optimizacijo organizacije prevozov v invalidski organizaciji
Tadej Korošec, 2012, magistrsko delo

Opis: Magistrsko delo je koncipirano na dveh segmentih. Prvi podrobneje obravnava sedanji informacijski sistem (IS) za organizacijo prevozov v invalidski organizaciji, drugi pa predlaga rešitve za njegovo posodobitev v smeri avtomatiziranega razporejanja zahtevkov za prevoz (ZZP). Posodobitev IS smo predvideli z implementacijo petih algoritmov za avtomatizirano razporejanje ZZP, ki temeljijo na kontroli porabe razpoložljivih virov (kapacitete vozil, specifikacije uporabnikov prevozov in voznikov), hkrati pa uvajajo različne postopke optimizacije. Pri tem si pomagamo z vpeljavo pojmov statičnih in dinamičnih časovnih parametrov in ustreznimi izračuni nad podatki o zgodovini realiziranih prevozov. Evidenten primer uporabe optimizacijskega postopka je tudi integracija Googleove storitve, s katero pridobimo ustrezen optimiziran podatek poti ali časa, ko razporejamo ZZP ustreznemu vozilu, uporaba koncepta sistema za podporo odločanju pa nam pomaga upoštevati prenekatere pogoje v fazi razporejanja ZZP. Poleg predstavitve novih algoritmov je rezultat tega dela tudi izdelava študije izvedljivosti implementacije predlaganih posodobitev na sedanjem informacijskem sistemu v invalidski organizaciji.
Ključne besede: informacijski sistem, optimizacija, prevozi, časovni parameter, Google
Objavljeno: 14.02.2013; Ogledov: 1139; Prenosov: 50
.pdf Celotno besedilo (4,78 MB)

10.
STABILITY AND METASTABILITY OF NEMATIC GLASSES
Amid Ranjkesh Siahkal, 2014, doktorska disertacija

Opis: Structures exhibiting continuous symmetry breaking are extremely susceptible to various perturbations. The reason behind is the existence of Goldstone modes in the gauge component of the order parameter describing broken symmetry. The so-called Larkin-Imry–Ma argument claims that even infinitesimally weak random field-type disorder destroys long range order (LRO) which would otherwise be present in the absence of random disorder. Furthermore, it claims that the system breaks into domain type configuration having short range order (SRO), where the characteristic domain size scales as ksi= W^-2/(4-d). Here W measures the strength of random field interaction and d is the dimensionality of space. However, some studies claim that structures with quasi long range order (QLRO) are established instead of SRO. The main focus of this doctor thesis is the character of nematic structures in the random field. I studied theoretically and numerically nematic structures that are obtained by continuous symmetry breaking in orientational degrees of freedom on decreasing the temperature T, starting from the ordinary liquid, the so called isotropic phase. In particular, I investigated conditions for which the Larkin-Imry-Ma theorem holds true. So far statistical interpretations of such systems have typically used two different semi- microscopic type models: i) the Random Anisotropic Nematic (RAN) and ii) the Sprinkled Silica Spin (SSS) model. The RAN model is a Lebwohl-Lasher (LL) model with nematic molecules locally coupled with uncorrelated random anisotropic field at each site, while the SSS model has a finite concentration of impurities frozen in random directions. I used a three dimensional (d = 3) model intermediate between SSS and RAN models, with finite concentration p of frozen impurities, where p < pc (pc stands for the percolation threshold). The simulations were performed at different temperatures for temperature-quenched (TQH) and field-quenched histories (FQH), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Numerically, I studied the impact of control parameters (T, p, W) and history of samples (TQH, FQH, AH) on structural properties of the system. Within the model I was varying p, temperature T, interaction strength W and also sample histories. From final configurations, I calculated orientational order parameters and two-point correlation functions. Next, I estimated the size of the Larkin-Imry-Ma domains d. Finite size-scaling was also used to determine the range of the orientational ordering, as a function of W, p, T and sample history. The main results of my study are the following. In general, the system exhibited strong memory effects, indicating important role of history of samples. Furthermore, obtained results were relatively robust (from macroscopic point of view), indicating substantial energy barriers among competing states. On increasing the strength W, I typically obtained the following sequence of orders: LRO, QLRO, and SRO. For some concentrations p,however, SRO was absent. The crossover anchoring strength between QLRO and SRO strongly depends on history of samples, and it has the lowest values for TQH. From my simulations it follows that for the model used the Larkin-Imry-Ma argument holds only in limited range of model parameters. In most cases I obtain QLRO instead of SRO. However, in all structures there is imprint of Larkin-Imry-Ma domains, exhibiting scaling d  1/ (W2p) in the weak anchoring regime. This suggests that we do not have a “classical ” QLRO with algebraic decay with distance. Similar results were obtained in the studies of magnetic systems.
Ključne besede: nematic liquid crystals, topological defect, order parameter, symmetry breaking, domains, Random field, larkin-Imry–Ma theorem, speroNematics
Objavljeno: 15.07.2014; Ogledov: 1045; Prenosov: 71
.pdf Celotno besedilo (2,86 MB)

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