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No description available.

The response of wide flange steel columns subjected to constant axial loads and lateral blast loads was examined. The finite element program ABAQUS was used to model W8x40 sections with different slendernesses and boundary conditions. For the response calculations, a constant axial force was first applied to the column and the equilibrium state was determined. Next, a short duration, lateral blast load was applied and the response time history was calculated. Changes in displacement time histories and plastic hinge formations resulting from varying the axial load were examined. The cases studied include single-span and two-span columns. In addition to ideal boundary conditions, columns with linear elastic, rotational supports were also studied. Non-uniform blast loads were considered. Major axis, minor axis, and biaxial bending were investigated. The effects of strain rate and residual stresses were examined. The results for each column configuration are presented as a set of curves showing the critical blast impulse versus axial load. The critical blast impulse is defined as the impulse that either causes the column to collapse or to exceed the limiting deflection criterion. A major goal of this effort was to develop simplified design and analysis methods. To accomplish this, two single-degree-of-freedom approaches that include the effects of the axial load were derived. The first uses a bilinear resistance function that is similar to the one used for beam analysis. This approach provides a rough estimate of the critical impulse and is suitable only for preliminary design or quick vulnerability calculations. The second approach uses a nonlinear resistance function that accounts for the gradual yielding that occurs during the dynamic response. This approach can be easily implemented in a simple computer program or spreadsheet and provides close agreement with the results from the finite element method. / Ph. D.

A full understanding of chemical reaction dynamics at the gas/organic-surface interface requires knowledge of energy-transfer processes that happen during the initial gas/surface collision. We have examined the influence of mass and rovibrational motion on the energy-transfer dynamics of gas-phase species scattering from model organic surfaces using theory and experiment. Molecular-beam scattering techniques were used to investigate the rare gases, Ne, Ar, Kr, and Xe, and the diatomics, N₂ and CO, in collisions with CH₃- and CF₃-terminated self-assembled monolayer (SAM) surfaces. Complementary molecular-dynamics simulations were employed to gain an atomistic view of the collisions and elucidate mechanistic details not observable with our current experimental apparatus. We developed a systematic approach for obtaining highly accurate analytic intermolecular potential-energy surfaces, derived from high-quality ab initio data, for use in our classical-trajectory simulations. Results of rare gas scattering experiments and simulations indicate mass to be the determining factor in the energy-transfer dynamics, while other aspects of the potential-energy surface play only a minor role. Additionally, electronic-structure calculations were used to correlate features of the potential-energy surface with the energy-transfer behavior of atoms and small molecules scattering from polar and non-polar SAM surfaces. Collisions of diatomic molecules with SAMs are seen to be vibrationally adiabatic, however translational energy transfer to and from rotational modes of the gas species, while relatively weak, is readily apparent. Examination of the alignment and orientation of the final rotational angular momentum of the gas species reveals that the collisions induce a stereodynamic preference for the expected "cartwheel" motion, as well as a surprising propensity for "corkscrew" or "propeller" motion. The calculated stereodynamic trends suggest that the CH₃-SAM is effectively more corrugated than the CF₃-SAM. Finally, the feasibility for collisional-energy promoted, direct gas/organic-surface reactions was interrogated using the 1,3-dipolar azide-alkyne cycloaddition reaction. We found that geometrical constraints prevented the reaction from proceeding at the probed conditions. / Ph. D.

Coordinated movements of epithelial tissue are linked with active matter processes. We here consider the influence of curvature on the spatiotemporal arrangements and the shapes of the cells. The cells are represented by a multiphase field model which is defined on the surface of a sphere. Besides the classical solid and liquid phases, which depend on the curvature of the sphere, on mechanical properties of the cells and the strength of activity, we identify a phase of global rotation. This rotation provides a coordinated cellular movement which can be linked to tissue morphogenesis. This investigation on a sphere is a first step to investigate the delicate interplay between topological constraints, geometric properties and collective motion. Besides the rotational state we also analyse positional defects, identify global nematic order and study the associated orientational defects.

Yes / A 2D coupled temperature-displacement FE model is developed for a pad-disc brake system based on a restricted rotational pad boundary condition. The evolution of pressure, heat flux, and temperature along the contact interface during braking applications is analysed with the FE model. Results indicate that different rotational pad boundary conditions significantly impact the interface pressure distribution, which in turn affects interface temperature and heat flux distributions, and suggest that a particular pad rotation condition is most appropriate for accurately modelling friction braking processes. The importance of the thermal contact conductance in the analysis of heat transfer in friction braking is established, and it is confirmed that the heat partition ratio is not uniformly distributed along the interface under normal and high interface thermal conductance conditions.

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No description available.

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L’impact de la perte racinaire sur l’ancrage d’Eugenia grandis Wight et de Pinus pinaster Ait ainsi que la capacité de trois différentes espèces d’arbres (Fagus sylvatica L, Abies alba Mill et Picea abies L) à résister au déracinement ou à la rupture sous l’effet d’un éboulement en pente raide ont été étudiés au moyen de tests de treuillage et le creusement de tranchées (tree winching and trenching tests) et les résultats ont été corrélés avec la structure du système racinaire. Aucune différence n’a été observée entre TMcrit et la distance de creusement de tranchée sur E. grandis. Les résultats obtenus ont révélé qu’en termes de rigidité rotationnelle de l’ancrage des arbres (TARS) et de TMcrit, la stabilité mécanique n’a pas été significativement affectée par le creusement de tranchées en sol argilo-sableux en raison de la profondeur d’enracinement des racines pivotantes (« sinker roots ») qui se sont formées près du tronc et en raison de la taille de la plaque racinaire qui augmente la rigidité et constitue donc une composante importante de l’ancrage d’E. grandis. Toutefois, pour P. pinaster, la stabilité mécanique a été significativement affectée par le creusement de tranchée, probablement en raison de la coupe des racines latérales qui a considérablement altéré la taille de la plaque racinaire et, en conséquence, la somme des surfaces en section (CSA= cross-sectional area) de la plupart des racines latérales et d’un certain nombre de racines traçantes, ce qui constitue une des composantes essentielles de l’ancrage d’arbres P. pinaster adultes plantés en podzol sableux. Pour les espèces forestières de protection plantées en pente raide, les résultats obtenus ont révélé que les espèces d’arbre présentant un système racinaire profondément enfoui et fortement ramifié avec une grande proportion de racines obliques (par exemple, le hêtre et le sapin pectiné) seront mieux ancrées et auront une meilleure fonction anti-éboulement que epicéa commun qui possède un système racinaire superficiel et peu profond. Les connaissances apportées par cette étude peuvent être utilisées pour la sélection et la production d’arbres qui résistent aux risques naturels ainsi qu’aux risques provoqués par l’Homme. / The impact of root loss on tree anchorage on Eugenia grandis Wight and Pinus pinaster Ait and the ability of three different trees species (Fagus sylvatica L, Abies alba Mill and Picea abies L) to resist uprooting or breakage due to rockfall on steep slopes were investigated using tree winching and trenching tests and results correlated to root system architecture. No differences were found between TMcrit and trenching distance in E. grandis trees. The results showed that in terms of Tree Anchorage Rotational Stiffness (TARS) and TMcrit, mechanical stability was not significantly affected by trenching on sandy clay soil, due to rooting depth of the sinkers which occurred close to the trunk and root plate size which provide greater stiffness thus play a major component of anchorage in E. grandis. However, in P. pinaster, mechanical stability was significantly affected by trenching, possibly due to severing of lateral roots greatly altered the size of the root plate and subsequently root CSA of major lateral roots and number of sinkers, which are crucial components in anchorage of mature P. pinaster trees grown on sandy podzol soil. For protection forest species grown on steep slopes, the results showed that tree species with deep, highly branched root systems with a higher proportion of oblique roots (e.g. European beech and Silver fir) will be better anchored and provide better protective function against rockfall as compared to Norway spruce that possessed a superficial plate-like root system. The knowledge gained from this study can be utilized in selection and production of trees which are resistant to both man made or natural hazards.