Volume 9, number 1 (2015)
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Item Aerodynamic loading acting on the stator vane in the variable nozzle turbine flow(University of West Bohemia, 2015) Žatko, Miroslav;The purpose of this paper is to evaluate an aerodynamic loading acting on the stator vanes of the turbocharger using variable nozzle turbine (VNT). Computational fluid dynamic (CFD) is applied using commercial software ANSYS CFX. A full turbine stage CFD model is used to investigate the aerodynamic loading in several operating points for different stator vane positions. Results are compared with the measurement on the Gas Stand testing rig. This device burns natural gas and produces a stable flow at very high temperatures. This excludes the impact of the engine control management, the engine vibrations, and the flow pulsations on measured values. A comparison of measured and simulated vane aerodynamic loading provides a very good correlation. These encouraging results show a high potential of CFD methods for further development and optimization of VNT mechanism.
Item Wall heat transfer in gas-fired furnaces: Effect of radiation modelling(University of West Bohemia, 2015) Vondál, Jiří; Hájek, Jiří;The purpose of this work is to study heat transfer to cooled walls in a MW-scale laboratory furnace with a dominating thermal radiation component. Experiment is performed in a specially designed combustion chamber with segmental water-cooled walls and profile of absor bed heat flux is measured along the flame. Non-premixed natural gas flame is stabilized by a guide-vane swirler. The unsteady governing equations of turbulent flow are solved by a finite-volume code with a two-equation k - ε realizable turbulence model, a combination of first-order and second-order upwind schemes and implicit time integration. The coupling of pressure with velocity is treated by SIMPLE (semi-implicit method for pressure-linked equations) algorithm. Radiative heat transfer as the main heat transfer method is modelled with special care by discr ete ordinates method and gas absorption coefficient is calculated by two alternatives of WSGGM (weighted sum of g rey gases model). The predicted total heat transfer rate is found to depend strongly on method chosen for the computation of mean beam length. The results of numerical simulations show that overall heat transfer in a process furnace can be su ccessfully predicted, while heat flux profile along the flame is more difficult to predi ct accurately. Good engineering accuracy is nevertheless achievable with reasonable computational resources. The trend of deviations is reported, which is useful for the interpretation of practi cal predictions of process furnaces (fired heaters).Item Optimization of plated steel beams using metamodels and modern optimization methods(University of West Bohemia, 2015) Šťastný, Antonín;This paper deals with metamodel-based optimization of plated steel beams. The first part of the article explains the principle of the metamodel-based optimization approach and also provides basic information on incorporated sub-methods such as design of experiments (DOE), math ematical approximation methods and mathematical opti- mization methods. Since optimized sections tend to be slender and thus susceptible to buckling, special attention is paid to the buckling evaluation. Both linear and nonlinear buckling analyses are employed. The nonlinear buckling analysis addresses detrimental influence of imperfections on the limit load by introducing equivalent geometric imperfections into the finite element (FE) model. The s hapes and magnitudes of these imperfections are based on recommendations for plated beams given in Eurocode 3 (EC3). The practical part of the article illustrates the approach on step by step basis using an example of spreader beam weight optimization. It is shown that simple metamodels can efficiently substitute the FE model in optimization, thereby making the process very fast. The parametric FE models are developed in the Ansys Parametric Design Language (APDL). The governing algorithm, as well as most of the mathematical sub-methods, is realized in the Matlab software.Item Frontal impact response of a virtual low percentile six years old human thorax developed by automatic down-scaling(University of West Bohemia, 2015) Špička, Jan; Maňas, Jaroslav; Hynčík, Luděk;Traffic accidents cause one of the highest numbers of severe injuries in thewhole population spectrum. The numbers of deaths and seriously injured citizens prove that traffic accidents and their consequences are still a serious problem to be solved. The paper contributes to the field of vehicle safety technology with a virtual approach. Exploitation of the previously developed scaling algorithm enables the creation of a specific anthropometric model based on a validated reference model. The aim of the paper is to prove the biofidelity of the small percentile six years old virtual human model developed by automatic down-scaling in a frontal impact. For the automatically developed six years old virtual specific anthropometricmodel, the Kroell impact test is simulated and the results are compared to the experimental data. The chosen approach shows good correspondence of the scaled model performance to the experimental corridors.Item Blade couple with dry friction connection(University of West Bohemia, 2015) Půst, Ladislav; Pešek, Luděk; Radolfová, Alena;Vibration of a blade couple damped by a dry friction contact in the shroud is investigated by means of hysteresis loops and response curves analysis. The studied system is excited by one harmonic external force in a frequency range near to the lowest eigenfrequency of real blades. Blades are connected by means of a damping element consisting of dry friction part linked in series with linear spring. This “stick-slip” damping element is supposed to be either weightless or of a very small mass which models the mass of elastically deformed parts of contacting bodies near the friction surface. Two approximate mathematical models of “stick-slip” dry friction elements are suggested and analysed. The response curves of blade couple connected by stick-slip damping element are presented for different values of slip friction forces and two values of mass of elastically deformed parts.Item Modelling of flexi-coil springs with rubber-metal pads in a locomotive running gear(University of West Bohemia, 2015) Michálek, Tomáš; Zelenka, Jaromír;Nowadays, flexi-coil springs are commonly used in the secondary suspension stage of railway vehicles. Lateral stiffness of these springs is influenced by means of their design parameters (number of coils, height, mean diameter of coils, wire diameter etc.) and it is often suitable to modify this stiffness in such way, that the suspension shows various lateral stiffness in different directions (i.e., longitudinally vs. laterally in the vehicle-related coordinate system). Therefore, these springs are often supplemented with some kind of rubber-metal pads. This paper deals with modelling of the flexi-coil springs supplemented with tilting rubber-metal tilting pads applied in running gear of an electric locomotive as well as with consequences of application of that solution of the secondary suspension from the point of view of the vehicle running performance. This analysis is performed by means of multi-body simulations and the description of lateral stiffness characteristics of the springs is based on results of experimental measurements of these characteristics performed in heavy laboratories of the Jan Perner Transport Faculty of the University of Pardubice.Item Evaluation of human thorax FE model in various impact scenarios(University of West Bohemia, 2015) Jansová, Magdalena; Hynčík, Luděk; Čechová, Hana; Toczyski, J.; Gierczycka-Zbrozek, D.; Baudrit, P.;The study focused on the validation of the 50 th percentile male model — a detailed FE model of the thoracic segment of the human body developed within project Development of a Finite Element Model of the Human Thorax and Upper Extremities (THOMO) co-funded by the European Commission (7 th Framework Programme). The model response was tested in three impact scenarios: frontal, lateral and oblique. The resulting impactor contact force vs. time and chest deflection vs. time responses were compared with experimental results. The strain profile of the 5th rib was checked with lateral and oblique strain profiles from post-mortem human subject (PMHS) experiments. The influence of heart and lungs on the mechanical response of the model was assessed and the material data configuration, giving the most biofidelic thorax behaviour, was identified.
