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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modelagem matem?tica e simula??o num?rica de correntes de gravidade em uma configura??o canal-bacia

Francisco, Ezequiel Pelisoli 12 March 2018 (has links)
Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-03-16T11:45:41Z No. of bitstreams: 1 Tese_Ezequiel_Pelisoli_Francisco.pdf: 24416873 bytes, checksum: 61b6a5e0625a49b1bb008d8f6023eb15 (MD5) / Approved for entry into archive by Tatiana Lopes (tatiana.lopes@pucrs.br) on 2018-04-03T11:57:18Z (GMT) No. of bitstreams: 1 Tese_Ezequiel_Pelisoli_Francisco.pdf: 24416873 bytes, checksum: 61b6a5e0625a49b1bb008d8f6023eb15 (MD5) / Made available in DSpace on 2018-04-03T12:03:22Z (GMT). No. of bitstreams: 1 Tese_Ezequiel_Pelisoli_Francisco.pdf: 24416873 bytes, checksum: 61b6a5e0625a49b1bb008d8f6023eb15 (MD5) Previous issue date: 2018-03-12 / Gravity currents are flows generated by the pressure gradient due density differences between two fluids which are in contact. In this work are presented a set of three-dimensional highly resolved direct numerical simulations of particle-laden gravity currents, solved in an original configuration called channel-basin. The focus is on low concentrations gravity currents, where the density differences are small enough for the Boussinesq approximation may be valid. The mathematical model is based on an Eulerian description of the concentration field by using a transport equation, combined with the incompressible Navier-Stokes equations. The equations are solved by the open-source code Incompact3d, which is based on high-order compact schemes for the concentration and velocity fields discretization, and a spectral method for the pressure field. The adopted mathematical modeling allows the particle sedimentation, however there is no possibility of re-suspension of the particles already deposited, nor the bottom deformation due the growth of the sediment layer thikness. The main goal of this reserach is to know how the initial parameters, such as Reynolds number, settling velocity and channel geometry, affect the dynamics of the current spreading. The results have shown that the spreading form is highly dependent of the settling velocity. For the front velocity of the current, the channel geometry and settling velocity are more important when the Reynolds is lower than when it is higher. The sedimentation rate is highly affected by the settling velocity. The increasing of the Reynolds number mainly affects the size of the turbulent structures such as vortex and lobes. The energy budget is strongly dependent of the settling velocity and slightly dependent of the channel geometry and Reynolds number. / Corrente de gravidade s?o escoamentos que ocorrem devido a um gradiente de press?o gerado, exclusivamente, pela diferen?a na massa espec?fica entre dois fluidos que entram em contato. Neste trabalho ? apresentada uma s?rie de resultados tridimensionais de alta fidedignidade, obtidos atrav?s de simula??o num?rica direta em uma configura??o original, aqui denominada de canal-bacia, a qual busca emular a transi??o entre um escoamento confinado para um n?o confinado. O foco deste estudo est? nas correntes de gravidade de baixas concentra??es, onde as diferen?as de densidade sejam pequenas o suficiente para que a aproxima??o de Boussinesq seja v?lida. O modelo matem?tico baseia-se em uma descri??o Euleriana do campo de concentra??es, que usa uma equa??o de transporte combinada com as equa??es de Navier-Stokes em sua forma incompress?vel. A resolu??o das equa??es ? feita atrav?s do c?digo Incompact3d, o qual baseia-se em esquemas compactos de diferen?as finitas de alta ordem para a solu??o da concentra??o e velocidade, e um m?todo espectral para a solu??o da press?o. O modelo matem?tico adotado permite que as part?culas se depositem no fundo do dom?nio, por?m n?o permite que haja a ressuspens?o nem que o fundo se deforme pelo aumento da espessura da camada de sedimentos. O objetivo proposto nesta Tese ? investigar como os par?metros iniciais, tais como n?mero de Reynolds, velocidade de queda e a geometria do canal de alimenta??o afetam a din?mica de livre espalhamento de correntes conservativas e n?o conservativas. Os resultados mostram que a forma como as correntes se espalham pelo dom?nio ? altamente dependente da velocidade de queda. A velocidade de propaga??o da corrente se mostrou mais dependente da geometria do canal e da velocidade de queda para o menor Reynolds do que para o maior. A taxa de sedimenta??o tamb?m apresentou grande sensibilidade ?s varia??es da velocidade de queda. O aumento no n?mero de Reynolds afetou, principalmente, o tamanho das estruturas turbulentas, tais como v?rtices e lobos. O balan?o de energias ? fortemente dependente da velocidade de queda, sendo pouca a influ?ncia da geometria do canal e do n?mero de Reynolds.
2

Simula??es num?ricas de correntes gravitacionais com elevado n?mero de Reynolds

Frantz, Ricardo Andr? Schuh 09 March 2018 (has links)
Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-06-05T13:28:29Z No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-06-12T12:40:17Z (GMT) No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) / Made available in DSpace on 2018-06-12T12:49:08Z (GMT). No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) Previous issue date: 2018-03-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / This work investigates the method of large-eddy simulation (LES) in the context of gravity currents, which is found necessary since it allows a substantial increase in the order of magnitude of the characteristic Reynolds number used in numerical simulations, approaching them with natural scales, in addition to significantly reducing the computational cost. The implicit large eddy simulation (ILES) methodology, based on the spectral vanishing viscosity model, is unprecedentedly employed in the context of gravity currents, is compared against with explicit methods such as the static and dynamic Smagorisnky. The evaluation of the models is performed based on statistics from a direct numerical simulation (DNS). Results demonstrate that the first model based purely on numerical dissipation, introduced by means of the second order derivative, generates better correlations with the direct simulation. Finally, experimental cases of the literature, in different flow configurations, are reproduced numerically showing good agreement in terms of the front position evolution. / Este trabalho investiga o m?todo de simula??o de grandes escalas (LES) no contexto de correntes gravitacionais. O mesmo se faz necess?rio, visto que possibilita um aumento substancial da ordem de grandeza do n?mero de Reynolds caracter?stico utilizado em simula??es num?ricas, aproximando os mesmos de escalas naturais, al?m de reduzir significativamente o custo computacional dos c?lculos. A avalia??o dos modelos ? realizada utilizando uma base de dados de simula??o num?rica direta (DNS). A metodologia de simula??o de grandes escalas impl?cita (ILES), baseada no modelo de viscosidade turbulenta espectral, ? colocado a prova de maneira in?dita no contexto de correntes de gravidade com m?todos expl?citos dispon?veis na literatura. Resultados demonstram que o mesmo, baseado puramente em dissipa??o num?rica introduzida por meio do comportamento dos esquemas de derivada de segunda ordem, gera melhores correla??es com as estat?sticas baseadas em campos m?dios da simula??o direta. Por fim, casos experimentais da literatura, em diferentes configura??es de escoamento, s?o reproduzidos numericamente.

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