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Product development through multi-criteria analysis
Tomaž Kostanjevec, Andrej Polajnar, Andrej Sarjaš, 2008, izvirni znanstveni članek

Opis: The trend regarding the development of sanitary fittings is forecasted by the use of a developed model of multi-criteria analysis. In this analysis a multi-dimensional space is used, which enables the establishment of a time argument in comparison to product parameters. The establishment of product parameters is achieved by means of internal company information and market needs. In this way it is possible to establish an innovative environment for the development of new products. This paper indicates various ways of dealing with product development, on the basis of which the method of multi-criteria analysis for establishing future trends in product development is acquired.
Ključne besede: sanitary fittings, product development, multi criteria analysis, multi-dimensional space
Objavljeno: 31.05.2012; Ogledov: 1368; Prenosov: 29
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Thread gauge calibration for industrial applications
Tadeja Primožič Merkač, Bojan Ačko, 2010, izvirni znanstveni članek

Opis: 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.
Ključne besede: thread ring gauge, calibration, pitch diameter, measurement uncertainty, dimensional measurements
Objavljeno: 31.05.2012; Ogledov: 1245; Prenosov: 19
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Useful measures in the field of time and dimensional rationalisation of manual training lessons
Samo Fošnarič, Jurij Planinšec, 2010, izvirni znanstveni članek

Opis: Schoolwork, especially lessons in manual skills is often associated with various ergonomics stresses. These stresses are the result not only of school obligations but also of the physical working environment and inadequate lesson planning. Much can be done in this field if certain approaches are taken into consideration at the work planning stage. Thus we can use certain analytical methods, such as the Method of Temporary Observations (Multi-Moment Method) and OWAS (a method for the evaluation of postural load during work), when positioning stressful lesson factors. This can be done in arelatively simple way in the field of time rationalisation as well as in the field of dimensional work adjustment to pupils. Research results in this papershow that by using a planned directed approach in this field, it is possible to achieve, a higher level of efficiency with normal levels of fatigue.
Ključne besede: dimensional rationalisation, manual skills lessons, pupils, technology and design education, time rationalisation
Objavljeno: 07.06.2012; Ogledov: 913; Prenosov: 64
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Dynamical and statistical properties of time-dependent one-dimensional nonlinear Hamilton systems
Dimitrios Andresas, 2015, doktorska disertacija

Opis: We study the one-dimensional time-dependent Hamiltonian systems and their statistical behaviour, assuming the microcanonical ensemble of initial conditions and describing the evolution of the energy distribution in three characteristic cases: 1) parametric kick, which by definition means a discontinuous jump of a control parameter of the system, 2) linear driving, and 3) periodic driving. For the first case we specifically analyze the change of the adiabatic invariant (the canonical action) of the system under a parametric kick: A conjecture has been put forward by Papamikos and Robnik (2011) that the action at the mean energy always increases, which means, for the given statistical ensemble, that the Gibbs entropy in the mean increases (PR property). By means of a detailed rigorous analysis of a great number of case studies we show that the conjecture largely is satisfied, except if either the potential is not smooth enough (e.g. has discontinuous first derivative), or if the energy is too close to a stationary point of the potential (separatrix in the phase space). We formulate the conjecture in full generality, and perform the local theoretical analysis by introducing the ABR property. For the linear driving we study first 1D Hamilton systems with homogeneous power law potential and their statistical behaviour under monotonically increasing time-dependent function A(t) (prefactor of the potential). We used the nonlinear WKB-like method by Papamikos and Robnik J. Phys. A: Math. Theor., 44:315102, (2012) and following a previous work by Papamikos G and Robnik M J. Phys. A: Math. Theor., 45:015206, (2011) we specifically analyze the mean energy, the variance and the adiabatic invariant (action) of the system for large time t→∞. We also show analytically that the mean energy and the variance increase as powers of A(t), while the action oscillates and finally remains constant. By means of a number of detailed case studies we show that the theoretical prediction is correct. For the periodic driving cases we study the 1D periodic quartic oscillator and its statistical behaviour under periodic time-dependent function A(t) (prefactor of the potential). We compare the results for three different drivings, the periodic parametrically kicked case (discontinuous jumps of $A(t)$), the piecewise linear case (sawtooth), and the smooth case (harmonic). Considering the Floquet map and the energy distribution we perform careful numerical analysis using the 8th order symplectic integrator and present the phase portraits for each case, the evolution of the average energy and the distribution function of the final energies. In the case where we see a large region of chaos connected to infinity, we indeed find escape orbits going to infinity, meaning that the energy growth can be unbounded, and is typically exponential in time. The main results are published in two papers: Andresas, Batistić and Robnik Phys. Rev. E, 89:062927, (2014) and Andresas and Robnik J. Phys. A: Math. Theor., 47:355102, (2014).
Ključne besede: one-dimensional nonlinear Hamiltonian systems, adiabatic invariant, parametric kick, periodic driving, linear driving, energy distribution, WKB method, action
Objavljeno: 02.03.2015; Ogledov: 1378; Prenosov: 34
.pdf Celotno besedilo (11,07 MB)

Qualitative Studies of Some Polynomial Systems of Ordinary Differential Equations
Maša Dukarić, 2016, doktorska disertacija

Opis: This doctoral dissertation is devoted to the studies of some qualitative properties of certain polynomial systems of ordinary differential equations. The main problems that are considered in this thesis are the problems of integrability and cyclicity. Some results on the classification of the global phase portraits of a family of cubic systems are presented as well. In the first chapter basic notions and results of the qualitative theory of systems of ODE's are introduced. Since one of important tools for our study of these problems is the commutative computational algebra, some main notions and properties of polynomial ideals and their varieties, including various algorithms related to them, are also presented in the introduction. In the second chapter methods for investigation of trajectories near degenerated singularities are presented. They are further used for the classification of global phase portraits of a family of cubic systems with the nilpotent center at the origin. In the third chapter the main problem of these thesis is studied, the problem of integrability. The problem of integrability which is connected to the problem of distinguishing between a center and a focus is studied for two different families of cubic polynomial systems of ODE's. With the computational algebra approach the necessary conditions for the existence of the first integral of these systems were obtained. For all but one condition was proven, using various approaches, the existence of the first integrals. The center problem for the real systems can be generalized to the complex systems. The origin of the system obtained after the complexification of the real system is the so-called 1:-1 resonant singular point, from which one additional generalization follows. This is the generalization to the p:-q resonant center. In the third chapter the :-3 resonant singular point of a quadratic family of complex systems is studied. The fourth chapter is devoted to the study of the problem of integrability of a three dimensional polynomial system with quadratic nonlinearities. The problem of existence of two independent first integrals and the existence of one first integral in the system was investigated. In the last chapter local bifurcations of limit cycles of a family of cubic systems are studied. Estimations for the number of limit cycles bifurcated from each components of the center variety are obtained.
Ključne besede: planar systems of ODE's, higher dimensional systems of ODE's, phase portrait, nilpotent center, limit cylces, Poincaré compactification, center problem, Bautin ideal, focus quantities, time-reversibility, integrability problem, Darboux method, linearizability, limit cycle, cyclicity
Objavljeno: 19.07.2016; Ogledov: 872; Prenosov: 90
.pdf Celotno besedilo (12,26 MB)

Case study of data warehouse development for monitoring of energy consumption in public buildings
Goran Kovačić, 2016, magistrsko delo

Opis: The goal of this case study was to examine which implementation of the data warehouse will yield better results in the observed scenario – monitoring of energy consumption in public buildings. Data warehouse (DW) is a type of database created with the goal of preparing data for analysis and reporting. We implemented two versions of DW, one based on the star and the other on the snowflake schema model. Series of tests were conducted to evaluate implemented solutions. Statistical analysis showed that for the observed scenarios, implementation based on snowflake schema performs better, in both shorter ETL execution time and smaller size of DW.
Ključne besede: data warehouse, dimensional model, star schema, snowflake schema, ETL process
Objavljeno: 04.07.2016; Ogledov: 425; Prenosov: 45
.pdf Celotno besedilo (2,11 MB)

Prediction of dimensional deviation of workpiece using regression, ANN and PSO models in turning operation
David Močnik, Matej Paulič, Simon Klančnik, Jože Balič, 2014, izvirni znanstveni članek

Opis: As manufacturing companies pursue higher-quality products, they spend much of their efforts monitoring and controlling dimensional accuracy. In the present work for dimensional deviation prediction of workpiece in turning 11SMn30 steel, the conventional deterministic approach, such as multiple linear regression and two artificial intelligence techniques, back-propagation feed-forward artificial neural network (ANN) and particle swarm optimization (PSO) have been used. Spindle speed, feed rate, depth of cut, pressure of cooling lubrication fluid and number of produced parts were taken as input parameters and dimensional deviation of workpiece as an output parameter. Significance of a single parameter and their interactive influences on dimensional deviation were statistically analysed and values predicted from regression, ANN and PSO models were compared with experimental results to estimate prediction accuracy. A predictive PSO based model showed better predictions than two remaining models. However, all three models can be used for the prediction of dimensional deviation in turning.
Ključne besede: artificial neural network, dimensional dviation, particle swarm optimization, regression
Objavljeno: 12.07.2017; Ogledov: 289; Prenosov: 81
.pdf Celotno besedilo (1,17 MB)
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Limit cycle bifurcated from a center in a three dimensional system
Bo Sang, Brigita Ferčec, Qin-Long Wang, 2016, izvirni znanstveni članek

Opis: Based on the pseudo-division algorithm, we introduce a method for computing focal values of a class of 3-dimensional autonomous systems. Using the $Є^1$-order focal values computation, we determine the number of limit cycles bifurcating from each component of the center variety (obtained by Mahdi et al). It is shown that at most four limit cycles can be bifurcated from the center with identical quadratic perturbations and that the bound is sharp.
Ključne besede: algorithms, three dimensional systems, focal value, limit cycle, Hopf bifurcation, center
Objavljeno: 08.08.2017; Ogledov: 913; Prenosov: 79
.pdf Celotno besedilo (236,33 KB)
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Determination of passive earth pressure using three-dimensional failure mechanism
Helena Vrecl-Kojc, Stanislav Škrabl, 2007, izvirni znanstveni članek

Opis: This paper presents a modified three-dimensional (3D) failure mechanism for determining the 3D passive earth pressure coefficient using the upper bound theorem within the framework of the limit analysis theory. The translational kinematically admissible failure mechanism generalized with a depth of h = 1.0 is considered in the analysis. The mechanism geometry presents a volume of rigid blocks composed of the central body and two lateral rigid bodies, which are connected by a common velocity field. The front surface of the central body interacts with the retaining wall, while the upper surface can be loaded by surcharge loading. The lateral body segments represent four- and three-sided polygons in the cross section of the central body; therefore, they define the polygonal failure surface of the central part. At the outer side, each segment of the lateral body is bounded by infinitesimally spaced rigid half-cones that describe the envelope of a family of half-cones. The numerical results of 3D passive earth pressure limit values are presented by non-dimensional coefficients of passive earth pressure influenced by the soil weight Kpg and a coefficient of passive earth pressure influenced by the surcharge Kpq. This research was intended to improve the lowest values obtained until now using the limit analysis theory. The results are presentedin a graphical form depending on the geometrical parameters and soil properties. A brief description of two world-recognized failure mechanisms based on the limit analysis approach, and the comparison of three failure mechanism results are also presented.
Ključne besede: soil mechanics, passive earth pressure, upper bound theorem, optimization, three-dimensional failure mechanism
Objavljeno: 18.05.2018; Ogledov: 263; Prenosov: 20
.pdf Celotno besedilo (504,97 KB)
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A fundamental study of the performance of X-section cast-in-place concrete single piles
Yu Wang, Yaru Lv, Dongdong Zhang, Jieying Zhou, 2016, izvirni znanstveni članek

Opis: X-section cast-in-place concrete (XCC) piles are used because they have a higher bearing capacity than circularsection cast-in-place concrete (CCC) piles of the same cross-sectional area. Although the bearing capacity of XCC piles has been studied, the performance of XCC single piles, especially for the stress-transfer mechanism dependent on the geometrical effects, is still not fully understood. This paper reports two comparative field static load tests on an XCC and a CCC single pile of the same cross-sectional area. In addition, corresponding threedimensional numerical back-analyses are performed to provide a fundamental understanding. The measured and computed results reveal that the XCC single pile has an approximately 25% higher ultimate bearing capacity than the CCC single pile. This is because the XCC single pile has an approximately 20% larger total side resistance, which is caused by a 60% larger pile perimeter and a slightly smaller unit side resistance. Lateral soil arching effects are developed, causing a non-uniform effective normal stress and a shear stress across the circumference of the XCC single pile. It is suggested that XCC single piles have a higher efficiency in terms of material saving compared with CCC single piles.
Ključne besede: X-section cast-in-place concrete pile, field static load test, three-dimensional numerical back-analysis, stresstransfer mechanism, side resistance, soil arching
Objavljeno: 15.06.2018; Ogledov: 379; Prenosov: 20
.pdf Celotno besedilo (485,57 KB)
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