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1.
Using neural networks in the process of calibrating the microsimulation models in the analysis and design of roundabouts in urban areas
Irena Ištoka Otković, 2011, dissertation

Abstract: The thesis researches the application of neural networks in computer program calibration of traffic micro-simulation models. The calibration process is designed on the basis of the VISSIM micro-simulation model of local urban roundabouts. From the five analyzed methods of computer program calibration, Methods I, II and V were selected for a more detailed research. The three chosen calibration methods varied the number of outgoing traffic indicators predicted by neural networks and a number of neural networks in the computer program calibration procedure. Within the calibration program, the task of neural networks was to predict the output of VISSIM simulations for selected functional traffic parameters - traveling time between the measurement points and queue parameters (maximum queue and number of stopping at the roundabout entrance). The Databases for neural network training consisted of 1379 combinations of input parameters whereas the number of output indicators of VISSIM simulations was varied. The neural networks (176 of them) were trained and compared for the calibration process according to training and generalization criteria. The best neural network for each calibration method was chosen by using the two-phase validation of neural networks. The Method I is the calibration method based on calibration of a traffic indicator -traveling time and it enables validation related to the second observed indicator – queue parameters. Methods II and V connect the previously described calibration and validation procedures in one calibration process which calibrates input parameters according to two traffic indicators. Validation of the analyzed calibration methods was performed on three new sets of measured data - two sets at the same roundabout and one set on another location. The best results in validation of computer program calibration were achieved by the Method I which is the recommended method for computer program calibration. The modeling results of selected traffic parameters obtained by calibrated VISSIM traffic model were compared with: values obtained by measurements in the field, the existing analysis methods of operational roundabouts characteristics (Lausanne method, Kimber-Hollis, HCM) and modeling by the uncalibrated VISSIM model. The calibrated model shows good correspondence with measured values in real traffic conditions. The efficiency of the calibration process was confirmed by comparing the measured and modeled values of delays, of an independent traffic indicator that was not used in the process of calibration and validation of traffic micro-simulation models. There is also an example of using the calibrated model in the impact analysis of pedestrian flows on conflicting input and output flows of vehicles in the roundabout. Different traffic scenarios were analyzed in the real and anticipated traffic conditions.
Keywords: traffic models, traffic micro-simulation, calibration of the VISSIM model, computer program calibration method, neural networks in the calibration process, micro-simulation of roundabouts, traffic modeling parameters, driving time, queue parameters, delay
Published: 02.06.2011; Views: 3541; Downloads: 242
.pdf Full text (13,21 MB)

2.
Product development simulation with multicriteria analysis
Tomaž Kostanjevec, Andrej Polajnar, Metka Kostanjevec, 2009, original scientific article

Abstract: Effective product development rests on a productćs design ability to create a positive product experience. This involves complex transformation of product information from customers to engineers to production to sales and back to customers. This work presents the concept of simulating the development of a new product. The multicriteria analysis of product development in a multi-dimensional space is being used. Based on simulation, the model shows in which direction the product will be developed on the basis of existing information. In the set multi-dimensional space, in which each observation parameter has a designated polar dimensional in terms of dependence on time, development on the basis of selected products is simulated. In an innovative way and in the case of sanitary fittings, simulation of the development of a new product in the early stages of design ideas is shown.
Keywords: product development, simulation, multicriteria analysis, multidimensional space
Published: 31.05.2012; Views: 1152; Downloads: 33
URL Link to full text

3.
Analytical hierarchy process as a tool for selecting and evaluating projects
Iztok Palčič, Bojan Lalić, 2009, original scientific article

Abstract: This paper explains the reasons for selecting the right project to conduct business in various organisations. It presents several methods for evaluating and selecting projects. A special focus is on Analytical Hierarchy Process (AHP) method that is becoming increasingly important tool in different decision-making situations. We have used this method in project management anddeveloped a project evaluation and selecting process. We have also developed a simple application in MS Excel that helps with calculating projectsć total priority grade. This tool helps us with simulating project importance based on changes in perception of the criteria.
Keywords: project selection, project evaluation, analytical hierarchy process, criteria simulation
Published: 31.05.2012; Views: 1032; Downloads: 21
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4.
Numerical analysis of injection characteristics using biodiesel fuel
Breda Kegl, 2006, original scientific article

Abstract: This paper deals with numerical analysis of injection process using biodieselžmineral diesel fuel blends with the aim to search for the potentialsto reduce engine harmful emissions. The considered fuels are neat biodiesel from rapeseed oil and its blends with mineral diesel D2. For the numerical analysis a one-dimensional mathematical model is employed. In order to model accurately the investigated fuels, the employed empirical expressionsfor their properties are determined by experiments. To verify the mathematical model and the empirical expressions, experiments and numerical simulation are run on a mechanical control diesel fuel injection M system at several operating regimes. Injection process at many different operating regimes and using several fuel blends are then investigated numerically. Attention is focused on the injection characteristics, especially on fuelling,fuelling at some stage of injection, mean injection rate, mean injection pressure, injection delay and injection timing, which influence the most important engine characteristics. The analysis of the obtained results reveals that, while keeping engine performance within acceptable limits, harmful emissions can be reduced by adjusting appropriately pump injection timing in dependence on the biodiesel content. This prediction is also confirmed experimentally.
Keywords: internal combustion engines, Diesel engines, fuel injection, biodiesel fuel, numerical simulation, emission reduction
Published: 31.05.2012; Views: 1041; Downloads: 31
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5.
Two-dimensional velocity-vorticity based LES for the solution of natural convection in a differentially heated enclosure by wavelet transform based BEM and FEM
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2006, original scientific article

Abstract: A wavelet transform based boundary element method (BEM) numerical scheme is proposed for the solution of the kinematics equation of the velocity-vorticityformulation of Navier-Stokes equations. FEM is used to solve the kinetics equations. The proposed numerical approach is used to perform two-dimensional vorticity transfer based large eddy simulation on grids with 105 nodes. Turbulent natural convection in a differentially heated enclosure of aspect ratio 4 for Rayleigh number values Ra=107-109 is simulated. Unstable boundary layer leads to the formation of eddies in the downstream parts of both vertical walls. At the lowest Rayleigh number value an oscillatory flow regime is observed, while the flow becomes increasingly irregular, non-repeating, unsymmetric and chaotic at higher Rayleigh number values. The transition to turbulence is studied with time series plots, temperature-vorticity phase diagrams and with power spectra. The enclosure is found to be only partially turbulent, what is qualitatively shown with second order statistics-Reynolds stresses, turbulent kinetic energy, turbulent heat fluxes and temperature variance. Heat transfer is studied via the average Nusselt number value, its time series and its relationship to the Rayleigh number value.
Keywords: numerical modelling, boundary element method, discrete wavelet transform, large eddy simulation, velocity-vertocity formulation, natural convection
Published: 31.05.2012; Views: 1411; Downloads: 23
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6.
Methodology for determination of anaerobic digestion kinetics using a bench top digester
Marko Tramšek, Andreja Goršek, Peter Glavič, 2007, original scientific article

Abstract: This paper presents a methodology for determining the microbial growth kinetics of an ideal anaerobic process in a non-ideal laboratory anaerobic digester (Armfield). Some laboratory experiments were performed, to confirm the proposed methodology. Having the same zero biomass concentration, some process parameters were changed and their influence on substrate outlet concentration was monitored. The specific growth rate of the biomass, the saturation constant of the substrate, and the yield coefficient were calculated, on the basis of the measured values. These parameters enabled us to perform a dynamic simulation of an anaerobic process in ideal continuously-stirred tank reactors (CSTR). The results represented the mass concentration profiles for substrate and biomass, from which the time required for reaching the steady state (60 d), where the operation is optimal, could be determined. The laboratory anaerobic digester provided operational process data, which are applicable for wastewater treatment plant design purposes.
Keywords: wastewater treatment, anaerobic digester, kinetics, dynamic simulation
Published: 31.05.2012; Views: 1299; Downloads: 42
URL Link to full text

7.
QoS-oriented design of embedded systems with specification PEARL
Roman Gumzej, Wolfgang A. Halang, 2007, original scientific article

Abstract: Only recently have methodical tools adequate to design real-time systems been formally introduced in design methodologies. Naturally, they were present fromthe beginning, but due to the large diversity of embedded systemsć areas of deployment, specially dedicated formalisms have been developed and used. High-level language programming and integration of modeling formalisms into design methods eased the development of more complex real-time applications. With the emerging object-oriented programming languages and design methods, their integration into larger information systems has become more transparent. It was the UML methodology, however, which eventually merged also the design methods and concepts of real-time systems into a consistent whole. It took a large consortium and a long process to persuade industry of the benefits the new integral methodology can offer. On the other hand, there are some trade-offs, and there are some features not completely covered, yet. Here, a different, more straightforward approach to program and design (embedded) real-time systems is presented. Since it emerged from the real-time community, it includes most features relevant there. Independent of the UML profile for schedulability, performance and time specification, a profile was devised for use in PEARL-oriented UML design. The strengths of the mentioned language and design methods for QoS-oriented design of (embedded) real-time systems are emphasised throughout this article.
Keywords: real time systems, embedded systems, quality of service, co-design, co-simulation, safety, dependability, security, timeliness, determinism, readiness, reliability, portability, flexibility, specification PEARL, UML profiles, patterns
Published: 31.05.2012; Views: 1496; Downloads: 32
URL Link to full text

8.
Velocity vorticity-based large eddy simulation with the bounadr element method
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2006, published scientific conference contribution (invited lecture)

Abstract: A large eddy simulation using the velocity-vorticity formulation of the incompressible Navier-Stokes equations in combination with the turbulent heat transfer equation is proposed for the solution of the turbulent natural convection drive flow in a 1:4 enclosure. The system of equations is closed by an enthropy-based subgrid scale model.The Prandtl turbulent number is used to estimate turbulent diffusion in the heat transfer equation. The boundary element method is used to solve the kinematics equation and estimate the boundary vorticity values. The vorticity transport equation is solved by FEM. The numerical example studied in this paper is the onset of a turbulent flow regime occuring at high Rayleigh number values ▫$(Ra=10^7-10^10)$▫. The formation of vortices in the boundary layer is observed, along with buoyancy driven diffusive convective transport. Quantitative comparison with the laminar flow model and the worh of other authors is also presented in terms of Nusselt number value oscillations.
Keywords: fluid mechanics, incompressible viscous fluid, turbulent flow, velocity vorticity formulation, finite element method, large eddy simulation
Published: 31.05.2012; Views: 1135; Downloads: 16
URL Link to full text

9.
Computational modelling of irregular open-cell foam behaviour under impact loading
Matej Borovinšek, Zoran Ren, 2008, original scientific article

Abstract: Cellular structures represent an important class of engineering materials. Typical representative of such structures are metallic foams, which are being increasingly used in many advanced engineering applications due to their low specific weight, appropriate mechanical properties and excellent energy absorption capacity. For optimal design of cellular structures it is necessary to develop proper computational models for use in computational simulations of their behaviour under impact loading. The paper studies the effects of open-cell metallic foam irregularity on deformation behaviour and impact energy absorption during impact loading by means of parametric computational simulations, using the lattice-type modelling of open-cell material structure. The 3D Voronoi technique is used for the reproduction of real, irregular open-cell structure of metallic foams. The method uses as a reference a regular mesh structure and utilises an irregularity parameter to reproduce the irregularity of real open-cell structure. A smoothing technique is introduced to assure proper stability and accuracy of explicit dynamic simulations using the produced lattice models. The effects of the smoothing technique were determined by comparative simulations of smoothed and unsmoothed lattices subjected to dynamic loading.
Keywords: open-cell foam, voronoi tessellation, behaviour, computer simulation
Published: 31.05.2012; Views: 1217; Downloads: 37
URL Link to full text

10.
Boundary element method for thermal flows using k-[epsilon] turbulence models
Matjaž Ramšak, Leopold Škerget, 2008, published scientific conference contribution

Abstract: Purpose - This paper aims to develop a multidomain boundary element method (BEM) for modeling 2D complex turbulent thermal flow using low Reynolds two-equation turbulence models. Design/methodology/approach - The integral boundary domain equations are discretised using mixed boundary elements and a multidomain method also known as a subdomain technique. The resulting system matrix is an overdetermined, sparse block banded and solved using a fast iterative linear least squares solver. Findings - The simulation of a turbulent flow over a backward step is in excellent agreement with the finite volume method using the same turbulent model. A grid consisting of over 100,000 elements could be solved in the order of a few minutes using a 3.0 GhzP4 and 1 GB memory indicating good efficiency. Originality/value - The paper shows, for the first time, that the BEM is applicable to thermal flows using k-▫$epsilon$▫.
Keywords: thermal flow, heat exchange, turbulence, boundary element method, simulation
Published: 31.05.2012; Views: 759; Downloads: 19
URL Link to full text

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