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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: 3839; Downloads: 270
.pdf Full text (13,21 MB)

2.
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: 1434; Downloads: 73
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3.
Characterization of open-cell cellular material structures with pore fillers
Matej Vesenjak, Andreas Öchsner, Zoran Ren, 2008, original scientific article

Abstract: Due to their mechanical properties, cellular material structures are often used in automotive, aerospace, ship and railway industries, as elements for deformational energy absorption. New advanced cellular material structures have been evaluated and characterised in the scope of this study in order to determine their energy absorption capability through the deformation process. Parametric computational simulations in the framework of the finite element method have been used for this purpose. Newly developed computational models of regular open-cell cellular material structures considering viscous pore fillers have been developed and their response under impact conditions was analysed using the explicit code LS-DYNA. The results of the performed study show that introduction of viscous fillers indeed increases the energy absorption capability of open-cellular material structures. Additionally, it was determined that the size of the cellular material (number of cells) dramatically influences the cellular structure response and that the filler influence is stronger in cellular structures with higher relative density.
Keywords: cellular materials, computer simulation, deformation, mechanical properties
Published: 31.05.2012; Views: 1032; Downloads: 59
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4.
Computer-aided analysis of the forging process
Matjaž Šraml, Janez Stupan, Iztok Potrč, Janez Kramberger, 2004, original scientific article

Abstract: This paper presents computer simulation of the forging process using the finite volume method (FVM). The process of forging is highly non-linear, where both large deformations and continuously changing boundary conditions occur. In most practical cases, the initial billet shape is relatively simple, but the final shape of the end product is often geometrically complex, to the extent that it is commonly obtained using multiple forming stages. Examples of the numerical simulation of the forged pieces provided were created using Msc/SuperForge computer code. The main results of the analysis are deformed shape, temperature, pressure, effective plastic strain, effective stress and forces acting on the die.
Keywords: forging, computer simulation, finite volume method, deformation, stresses, material flow, industrial applications
Published: 01.06.2012; Views: 1177; Downloads: 72
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5.
Computer simulation of needle and take-up lever mechanism using the ADAMS software package
Darja Žunič-Lojen, Karl Gotlih, 2003, original scientific article

Abstract: A knowledge of the interactions between a sewing machinećs mechanisms and the sewing thread in the stitch formation process should help us to understand thread loadings in the sewing process. The aim of this work is to analyse the needle bar's kinematics with the thread take-up lever by using computer simulation. A cyclogram was drawn on the basis of modelling and kinematic simulation of a needle bar with a thread take-up lever, and measurements of the thread tension forces in the sewing process. This cyclogram enables analysis of the interactions between the thread and the elements of the sewing machine. The results of these simulations are curves that describe the movements at characteristic points on the mechanism. These give the possibility of pinpointing the exact positions of the mechanism's elements with respect to the main shaft rotation in the sewing machine.
Keywords: textiles, garment manufacturing, sewing, thread, stitch fomation, thread loading, cyclogram, computer simulation
Published: 01.06.2012; Views: 1408; Downloads: 19
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6.
Design of Lyapunov based nonlinear velocity control of electrohydraulic velocity servo systems
Edvard Detiček, Nenad Gubeljak, Mitja Kastrevc, 2017, original scientific article

Abstract: Development of a hydraulically driven process of steel centrifugal die casting industry requires accurate response of position in time. In the frame of preliminary investigations the analysis and control of electrohydraulic velocity servo system is considered in the presence of flow nonlinearities and internal friction. The nonlinear and uncertainty characteristics make the conventional controller not yield to the system high requirements. Two different nonlinear design procedures are employed: feedback linearization and backstepping. It is shown that both these techniques can be successfully used to stabilize any chosen operating point of the system. Additionally, invaluable new insights are gained about the dynamics of the system under consideration. This illustrates that the true potential of constructive nonlinear design lies far beyond the mere task of achieving a desired control objective. All derived results are validated by computer simulation of the nonlinear mathematical model of the system.
Keywords: computer simulation, electro-hydraulic velocity servo system, integrator backstepping, Lyapunov methods, velocity control
Published: 11.07.2017; Views: 453; Downloads: 254
.pdf Full text (1,52 MB)
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