DSpace Collection:http://hdl.handle.net/10174/9952024-03-29T15:55:11Z2024-03-29T15:55:11ZProblems associated with the contrast between thermal and mechanical properties of materialsDuque, Maria Rosahttp://hdl.handle.net/10174/364592024-03-19T15:03:17Z2023-01-01T00:00:00ZTitle: Problems associated with the contrast between thermal and mechanical properties of materials
Authors: Duque, Maria Rosa
Abstract: The present work consists in the study of thermal and mechanical properties of a body
consisting of equal volume of two materials with different thermal and mechanical
properties, placed in physical contact. The materials are subjected to a common thermal
source but, due to their density and specific heat capacity, their temperatures will suffer
different variations. This work studies the changes occurring near the contact zone of the
two materials. In addition to different volume increases (pressure increases) in the two
materials, different values of thermal conductivity must be considered and shear stresses
of thermal origin, with different values in the two materials must be studied near the
contact zone. The work studies the changes observed near the contact area of the two
materials considering different values of heat supplied . Changes of thermal conductivity
and specific heat capacity values with temperature are considered but variations with
pressure increase are not. The hypothesis of introducing a third element (water) into pre existing cracks dilated with the initial heating is also studied.2023-01-01T00:00:00ZAlteração de temperatura do solo associada a variações de intensidade de fontes internasDuque, Maria Rosahttp://hdl.handle.net/10174/364582024-03-19T15:01:34Z2024-01-01T00:00:00ZTitle: Alteração de temperatura do solo associada a variações de intensidade de fontes internas
Authors: Duque, Maria Rosa
Abstract: A temperatura medida no solo abaixo da superfície, resulta das transferências de energia
térmica proveniente do Sol propagando-se por condução até ao ponto onde é feita a
medição, e energia térmica proveniente do interior da Terra que se propaga por condução,
em sentido oposto, até à superfície. O presente trabalho fala apenas desta última
transferência de energia. As fontes térmicas no interior da Terra são essencialmente
energia proveniente de zonas mais internas, relacionada com o processo de formação e
desenvolvimento do planeta, reações químicas e fontes radioativas. Sabendo a
concentração dos isótopos radioativos responsáveis pela libertação de energia térmica,
235U, 238U, 232Th e 40K, é possível obter-se a “produção de calor” associada ao decaimento
radioativo. A diminuição secular do fluxo de calor proveniente do manto pode ser obtida
através de uma lei exponencial com uma constante de decaimento de 3 G ano-1
. Utilizando
a informação referida, tendo em conta os fluxos de calor proveniente do manto nos tempos
atuais, podemos obter informação sobre o fluxo de calor e a temperatura no passado. O
presente estudo remonta até há 4 milhões de anos (idade atribuída aos Australopithecus)
terminando cerca de 300 000 anos atrás (idade dos vestígios mais antigos de Homo
Sapiens). As diferenças entre o fluxo atual na superfície e o fluxo no passado permitem
inferir a sua influência na camada de ar junto ao solo e também junto ao fundo oceânico.2024-01-01T00:00:00ZCFD Analysis of Perforated Plates and Open-Cell Materials AerodynamicsAntonio, F. Miguelhttp://hdl.handle.net/10174/358072023-12-20T11:11:37Z2023-01-01T00:00:00ZTitle: CFD Analysis of Perforated Plates and Open-Cell Materials Aerodynamics
Authors: Antonio, F. Miguel
Abstract: In this paper, a numerical study of fluid flow through perforated panels with square holes and open-cell material with cubic cells is presented. Structures with a wide variety of porosities (0.15<E<0.94) and Reynolds numbers (0.01<Re<6000) are studied. Among the various outcomes obtained, the results indicate that pressure gradient vs Reynolds number exhibits three different forms of variation, including linear (Re<1), nonlinear (1≤Re<4000), and one where the pressure gradient is virtually constant with the Reynolds number (Re≥4000). The results were provided in terms of loss factor, but also of intrinsic permeability and the Forchheimer coefficient. Relationships that connect porosity to the loss factor, intrinsic permeability, and Forchheimer coefficient are also presented. These findings may prove useful in better understanding the flow behaviors in perforated panels and cell metal foams, which have a wide range of applications.2023-01-01T00:00:00ZDelocalization of topological surface states by diagonal disorder in nodal loop semimetalsSilva, João S.Araújo, Miguel A. N.Gonçalves, MiguelRibeiro, PedroCastro, Eduardo V.http://hdl.handle.net/10174/357152023-11-22T11:12:38Z2023-01-30T00:00:00ZTitle: Delocalization of topological surface states by diagonal disorder in nodal loop semimetals
Authors: Silva, João S.; Araújo, Miguel A. N.; Gonçalves, Miguel; Ribeiro, Pedro; Castro, Eduardo V.
Abstract: The effect of Anderson diagonal disorder on the topological surface (drumhead) states of a Weyl nodal loop semimetal (SM) is addressed. Since diagonal disorder breaks chiral symmetry, a winding number cannot be defined. Seen as a perturbation, the weak random potential mixes the clean exponentially localized drumhead states of the SM, thereby producing two effects: (i) the algebraic decay of the surface states into the bulk and (ii) a broadening of the low energy density of surface states of the open system due to degeneracy lifting. This behavior persists with increasing disorder, up to the bulk SM-to-metal transition at the critical disorder
Wc. Above Wc, the surface states hybridize with bulk states and become extended into the bulk.2023-01-30T00:00:00Z