Modelling geomechanics of residual soils with DMT tests

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Universidade de Aveiro, Instituto Politécnico da Guarda. 200

Research reports: 1991 NASA/ASEE Summer Faculty Fellowship Program

The basic objectives of the programs, which are in the 28th year of operation nationally, are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA Centers. The faculty fellows spent 10 weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague. This is a compilation of their research reports for summer 1991

Radial Turbine Thermo-Mechanical Stress Optimization by Multidisciplinary Discrete Adjoint Method

This paper addresses the problem of the design optimization of turbomachinery components under thermo-mechanical constraints, with focus on a radial turbine impeller for turbocharger applications. Typically, turbine components operate at high temperatures and are exposed to important thermal gradients, leading to thermal stresses. Dealing with such structural requirements necessitates the optimization algorithms to operate a coupling between fluid and structural solvers that is computationally intensive. To reduce the cost during the optimization, a novel multiphysics gradient-based approach is developed in this work, integrating a Conjugate Heat Transfer procedure by means of a partitioned coupling technique. The discrete adjoint framework allows for the ecient computation of the gradients of the thermo-mechanical constraint with respect to a large number of design variables. The contribution of the thermal strains to the sensitivities of the cost function extends the multidisciplinary outlook of the optimization and the accuracy of its predictions, with the aim of reducing the empirical safety factors applied to the design process. Finally, a turbine impeller is analyzed in a demanding operative condition and the gradient information results in a perturbation of the grid coordinates, reducing the stresses at the rotor back-plate, as a demonstration of the suitability of the presented method

Buckling of cylindrical shells under non-uniform lateral pressures

This thesis presents static equilibrium and stability analyses of cylindrical shells subjected to non-uniform external pressures. This problem is of practical importance in the design of launch vehicles, oil storage tanks, cooling towers subjected to wind loads and other engineering structures submerged in flowing water. The non-uniform pressure distributions considered are due to: (a) wind at high Reynolds numbers; (b) flow of water on submerged cylinders. In the static equilibrium analysis for the pre-buckled state both Donnell and Flugge shell theories are employed. The results of pre-buckle deformations and stress resultants, when compared with results obtained using beam or semi-membrane theories show that the beam theory is inadequate and unsafe, whereas the semi-membrane theory is conservative and safe for wind loaded structures. [Continues.