An experimental and numerical investigation of heat transfer enhancement in a three dimensional channel using wall mounted porous baffles was conducted. The module average heat transfer coefficients were measured in a uniformly heated rectangular channel with staggered positioned porous baffles. A numerical procedure was implemented, in conjunction with a commercially available Navier-Stokes solver, to model the turbulent flow in porous media. The Brinkman-Forchheimer-Extended Darcy model was used for modeling fluid flow through the porous baffles. Conventional, oneequation, and two-equation models were used for heat transfer modeling. The accuracy and characteristics of each model were investigated and discussed. The results were compared with experimental data. Baffles were mounted alternatively on the top and bottom walls. Heat transfer coefficients and pressure loss for periodically fully developed flow and heat transfer were obtained for different pore densities (10, 20, and 40 pores per inch (PPI)) with two different baffle heights ( / h h B D = 1/3 and 2/3), and two baffle thicknesses ( / t h B D = 1/3 and 1/12). The Reynolds number (Re) was varied from 20,000 to 50,000. To compare the effect of foam metal baffles, the data for conventional solid-type baffles was obtained for ( / t h B D =1/3). The maximum uncertainties associated with the module Nusselt number and friction factor were 5.8% and 4.3%, respectively. The experimental procedure was validated by comparing the data for the straight channel without baffles ( / h h B D = 0) with those in the literature. The use of porous baffles resulted in heat transfer enhancement as high as 300% compared to heat transfer in straight channels without baffles. However, the heat transfer enhancement per unit increase in pumping power was less than one for the range of parameters studied in this work. Correlation equations were developed for the heat transfer enhancement ratio and the heat transfer enhancement per unit increase in pumping power in terms of Reynolds number. The conventional theoretical model, the dispersion conductivity model, and the modified two-phase model using the local thermal non-equilibrium theory were considered. The results from each model were compared against the experimental data, and compared to each other to investigate the efficiency of each model. Also, the characteristics of each model were discussed.

Unintentional drop of munitions could be encountered during the storage, transportation, and loading processes. In such an impact, malfunctioning of crucial components of munitions is the worst scenario that may be encountered and level of loads should not reach to critical levels. From two possible methods, experimental one is not frequently applied owing to high cost of money and time. On the contrary, particularly in last couple of years, interest is shifted to numerical simulations such as finite element method. In this thesis, foam materials will be investigated as energy absorbers to reduce the effect of loads during the impact. However, modeling the behavior of foam materials by FE codes is a challenging task. In other words, more than a few material parameters which are not commonly specified in literature are sufficient to represent the behavior of foams in an appropriate way. For this reason, material characteristics of the selected two foam materials, expanded polypropylene and v polyethylene, have been obtained in this study. Characterization of EPP and PE is followed by the selection of the appropriate material models in LS-DYNA which is a nonlinear explicit finite element code. Drop tests of munitions on which initially specified foam materials are integrated were done to identify the load levels. Validation of drop tests which are explained in detail in this thesis has been accomplished by LS-DYNA. Final section of the thesis is related to optimization of the foam geometry which will provide reducing load levels to allowable limits. After optimization studies, three alternative geometries which succeed in to reduce loads to allowable load levels were reached. Finally, one of three alternatives is selected considering cost and manufacturing difficulties.

Im Rahmen dieser Arbeit wird ein physikalisches Modell für weichelastische EVA-Schaumstoffe entwickelt, das das mechanische Verformungsverhalten (Spannungs-Verformungs-Kurve) bei der Interaktion zwischen Sportler und Sportgerät am Beispiel eines Laufschuhs anwendungsgerecht – d.h. bei hoher Verformung und Belastungsgeschwindigkeit – kennzeichnet. Im Stand der Technik werden als Einflussfaktoren auf das mechanische Verformungsverhalten von Weichschäumen die Parameter Schaumdichte, Zellgröße bzw. Zelldurchmesser, Schaumhärte und Verformungsgeschwindigkeit ermittelt. Diese werden für die vorliegenden vier Versuchsmaterialien analysiert, wobei die letzten zwei Parameter im Modell Berücksichtigung finden. Das Modell setzt sich aus einem Matrix- und einem Gasphasenanteil zusammen. Der Matrixphasenanteil wird experimentell bei der jeweiligen Verformungsgeschwindigkeit bestimmt, wohingegen der Gasphasenanteil der in den Zellen komprimierten Luft auf einem physikalischen Zusammenhang beruht und anhand der gemessenen Schaumhärte und des Atmosphärendrucks bei der jeweiligen Verformung berechnet wird. Die Voraussetzungen für die Verwendung des Modells, zu denen inkompressible Matrixphase, Geschlossenzelligkeit und keine Querausdehnung des Schaums zählen, werden vorab umfangreich geprüft. Zusammenfassend lässt sich aussagen, dass das gewählte Modell eine gute Übereinstimmung mit den experimentell bestimmten Ergebnissen erzielt. Dies wird anhand der Mittelwertes der Differenz von experimentell ermittelten zu modellierten Daten bestimmt, für den ein Wert von 7 % berechnet wird. / The purpose of this doctoral thesis is developing a physical model for flexible foam materials (e.g. ethylene/vinyl acetate foam) characterizing the mechanical deformation behavior (stress-strain-curve) at the interaction between athlete and sports equipment (e.g. running footwear) during high deformation and high loading rate. Previous studies described various parameters influencing the mechanical deformation behavior of flexible foams: foam density, cell size / cell diameter, foam hardness and loading rate. These parameters are being analyzed for the four present foams whereof the last two parameters were considered in the model. The model consists of a matrix phase measured experimentally at required loading rate multiplied with a correction factor and a gas phase of the air compressed in the foam cells which is calculated by atmospheric pressure and foam hardness. The requirements (incompressible matrix phase, closed cells and zero Poisson ratio) for using the model are verified first of all. In conclusion, the developed model presents a good accordance with the experimental data calculated by a mean difference between experimental and modeled data of 7 %.

Im Rahmen dieser Arbeit wird ein physikalisches Modell für weichelastische EVA-Schaumstoffe entwickelt, das das mechanische Verformungsverhalten (Spannungs-Verformungs-Kurve) bei der Interaktion zwischen Sportler und Sportgerät am Beispiel eines Laufschuhs anwendungsgerecht – d.h. bei hoher Verformung und Belastungsgeschwindigkeit – kennzeichnet. Im Stand der Technik werden als Einflussfaktoren auf das mechanische Verformungsverhalten von Weichschäumen die Parameter Schaumdichte, Zellgröße bzw. Zelldurchmesser, Schaumhärte und Verformungsgeschwindigkeit ermittelt. Diese werden für die vorliegenden vier Versuchsmaterialien analysiert, wobei die letzten zwei Parameter im Modell Berücksichtigung finden. Das Modell setzt sich aus einem Matrix- und einem Gasphasenanteil zusammen. Der Matrixphasenanteil wird experimentell bei der jeweiligen Verformungsgeschwindigkeit bestimmt, wohingegen der Gasphasenanteil der in den Zellen komprimierten Luft auf einem physikalischen Zusammenhang beruht und anhand der gemessenen Schaumhärte und des Atmosphärendrucks bei der jeweiligen Verformung berechnet wird. Die Voraussetzungen für die Verwendung des Modells, zu denen inkompressible Matrixphase, Geschlossenzelligkeit und keine Querausdehnung des Schaums zählen, werden vorab umfangreich geprüft. Zusammenfassend lässt sich aussagen, dass das gewählte Modell eine gute Übereinstimmung mit den experimentell bestimmten Ergebnissen erzielt. Dies wird anhand der Mittelwertes der Differenz von experimentell ermittelten zu modellierten Daten bestimmt, für den ein Wert von 7 % berechnet wird. / The purpose of this doctoral thesis is developing a physical model for flexible foam materials (e.g. ethylene/vinyl acetate foam) characterizing the mechanical deformation behavior (stress-strain-curve) at the interaction between athlete and sports equipment (e.g. running footwear) during high deformation and high loading rate. Previous studies described various parameters influencing the mechanical deformation behavior of flexible foams: foam density, cell size / cell diameter, foam hardness and loading rate. These parameters are being analyzed for the four present foams whereof the last two parameters were considered in the model. The model consists of a matrix phase measured experimentally at required loading rate multiplied with a correction factor and a gas phase of the air compressed in the foam cells which is calculated by atmospheric pressure and foam hardness. The requirements (incompressible matrix phase, closed cells and zero Poisson ratio) for using the model are verified first of all. In conclusion, the developed model presents a good accordance with the experimental data calculated by a mean difference between experimental and modeled data of 7 %.