93 research outputs found

    A primer on CFD-DEM for polymer-filled suspensions

    Get PDF
    This work reports on an evaluation of the computational fluid dynamics–discrete element method (CFD-DEM) numerical approach to study the behavior of polymer-filled suspensions in a parallel-plate rheometer. For this purpose, an open-source CFD-DEM solver is used to model the behavior of such suspensions considering different particle volume fractions and different types of fluid rheology. We first validate the numerical approach for the single-phase flow of the continuum phase (fluid phase) by comparing the fluid’s azimuthal velocity and shear stress components obtained from the open-source solver against the analytical expressions given in cylindrical coordinates. In addition, we compare the numerical torque given by the numerical procedure with analytical expressions obtained for Newtonian and power law fluids. For both cases, there is a remarkable agreement between the numerical and analytical results. Subsequently, we investigated the effects of the particle volume fraction on the rheology of the suspension. The numerical results agree well with the experimentally measured ones and show a yield stress phenomenon with the increase of the particle volume fraction.This research was funded by FEDER through the COMPETE 2020 Programme and National Funds through FCT (Portuguese Foundation for Science and Technology) under projects UID-B/05256/2020, UID-P/05256/2020, UIDB/ 00013/2020, UIDP/00013/2020, UIDB/00532/ 2020, PTDC/EMS-ENE/3362/2014–POCI-01-0145-FEDER-016665

    Uma análise dos aspectos distributivos da aposentadoria por tempo de contribuição do INSS com o emprego de matemática atuarial

    Get PDF
    O objetivo do artigo é o cálculo de parâmetros usualmente adotados na literatura sobre previdência social, como as taxas de reposição previdenciária, alíquotas de contribuição atuarialmente justa e valores presentes de contribuições e de benefícios, para o caso brasileiro. Os cálculos são feitos para a Aposentadoria por Tempo de Contribuição (ATC) do Regime Geral de Previdência Social (RGPS) do INSS. Com tal finalidade, é construído um modelo atuarial simples para um regime previdenciário de repartição. O diferencial deste artigo em relação a trabalhos anteriores que empregavam modelos deterministas é a modelagem dos fluxos previdenciários, feita por meio de técnicas de matemática atuarial, incorporando o risco biométrico. Os cálculos são feitos para diferentes combinações de gênero, idade de início da vida laboral, renda e taxa de desconto. Os resultados mostram que as alíquotas de contribuição do RGPS, (28% a 31%), são mais do que suficientes para financiar a ATC, principalmente para os homens de renda mais elevada e que iniciaram sua vida ativa mais tarde. Os resultados fornecem evidências que as taxas de reposição (próximas a 0,5) são similares às verificadas em países desenvolvidos. Os resultados permitem três conclusões principais. A primeira é que o sistema previdenciário tem impactos distributivos intrageracionais, particularmente no tocante a gênero. A segunda é que parece ser razoável pensar em equiparação nas regras da ATC para homens e mulheres. Em terceiro lugar deve-se atentar para a influência do Fator Previdenciário sobre as questões distributivas

    Advanced polymer simulation and processing

    Get PDF
    [Excerpt] Polymer processing techniques are of paramount importance in the manufacture of polymer parts. The key focus is on producing parts with the desired quality, which usually refers to mechanical performance, dimensional conformity, and appearance. To maximize the overall efficiency of polymer processing techniques, advanced modeling codes are needed along with experimental setups to simulate and optimize the processes. [...]This research was funded by FEDER through the COMPETE 2020 Programme and National Funds through FCT-Portuguese Foundation for Science and Technology under the projects UIDB/05256/2020 and UIDP/05256/2020. It was also funded by FCT through CMAT (Centre of Mathematics of the University of Minho) through projects UIDB/00013/2020 and UIDP/00013/2020

    Hydrodynamic entrance length for laminar flow in microchannels with rectangular cross section

    Get PDF
    This work presents a detailed numerical investigation on the required development length (L=L/B) in laminar Newtonian fluid flow in microchannels with rectangular cross section and different aspect ratios (AR). The advent of new microfluidic technologies shifted the practical Reynolds numbers (Re) to the range of unitary (and even lower) orders of magnitude, i.e., creeping flow conditions. Therefore, accurate estimations of L at Re≤O(1) are important for microsystem design. At such low Reynolds numbers, in which inertial forces are less dominant than viscous forces, flow characteristics become necessarily different from those at the macroscale where Re is typically much larger. A judicious choice of mesh refinement and adequate numerical methods allowed obtaining accurate results and a general correlation for estimating L, valid in the ranges 0≤Re≤2000 and 0.1≤AR≤1, thus covering applications in both macro and microfluidics.The authors acknowledge the support by CEFT (Centro de Estudos de Fenómenos de Transporte) and Project PTDC/EMS-ENE/3362/2014—POCI-01-0145-FEDER-016665, funded by FEDER funds through COMPETE2020 “Programa Operacional Competitividade e Internacionaliza” (POCI) and by national funds through FCT “Fundac ao para a Ciência e a Tecnologia”, I.P. L.L. Ferrás would also like to thank FCT for financial support through scholarship SFRH/BPD/100353/2014 and projects UIDB/00013/2020 and UIDP/00013/2020. A. Sucena, A. M. Afonso, M. M. Alves and F. T. Pinho are also grateful to FCT for funding through projects UIDB/00532/2020 and UIDP/00532/2020. A. Sucena thanks FCT for the Ph.D. Grant SFRH/BD/115547/201

    Semi-analytical solutions for the poiseuille-couette flow of a generalised Phan-Thien-Tanner fluid

    Get PDF
    This work presents new analytical and semi-analytical solutions for the pure Couette and Poiseuille-Couette flows, described by the recently proposed (Ferras et al., A Generalised Phan-Thien-Tanner Model, JNNFM 2019) viscoelastic model, known as the generalised Phan-Thien-Tanner constitutive equation. This generalised version considers the Mittag-Leffler function instead of the classical linear or exponential functions of the trace of the stress tensor, and provides one or two new fitting constants in order to achieve additional fitting flexibility. The analytical solutions derived in this work allow a better understanding of the model, and therefore contribute to improve the modelling of complex materials, and will provide an interesting challenge to computational rheologists, to benchmarking and to code verification.This research was funded by FEDER through COMPETE2020-Programa Operacional Competitividade e Internacionalizacao (POCI) and by national funds through FCT-Fundacao para a Ciencia e a Tecnologia, I. P. through Projects PTDC/EMS-ENE/3362/2014, POCI-01-0145-FEDER-016665, UID-MAT-00013/2013, and UID/MAT/00297/2013 as well as grant number SFRH/BPD/100353/2014. This work was partially supported by the Fundacao para a Ciencia e a Tecnologia (Portuguese Foundation for Science and Technology) through the project UID/MAT/00297/2019 (Centro de Matematica e Aplicacoes)

    Slip flows of Newtonian and viscoelastic fluids in a 4:1 contraction

    Get PDF
    This work presents a numerical study of the 4:1 planar contraction flow of a viscoelastic fluid described by the simplified Phan-Thien–Tanner model under the influence of slip boundary conditions at the channel walls. The linear Navier slip law was considered with the dimensionless slip coefficient varying in the range ½0; 4500. The simulations were carried out for a small constant Reynolds number of 0.04 and Deborah numbers (De) varying between 0 and 5. Convergence could not be achieved for higher values of the Deborah number, especially for large values of the slip coefficient, due to the large stress gradients near the singularity of the reentrant corner. Increasing the slip coefficient leads to the formation of two vortices, a corner and a lip vortex. The lip vortex grows with increasing slip until it absorbs the corner vortex, creating a single large vortex that continues to increase in size and intensity. In the range De = 3–5 no lip vortex was formed. The flow is characterized in detail for De ¼ 1 as function of the slip coefficient, while for the remaining De only the main features are shown for specific values of the slip coefficient.The authors gratefully acknowledge funding by COMPETE, FEDER and Fundacao para a Ciencia e a Tecnologia (FCT) through projects PEst-C/CTM/LA0025/2013 (Strategic Project - LA 25 - 2013-2014, PTDC/EME-MFE/113988/2009 and PTDC/EME-MFE/114322/2009. AMA would also like to thank FCT for the financial support through the scholarship SFRH/BPD/75436/2010

    Giant Post-Traumatic Frontoethmoid Osteoma: Diagnostic, Therapeutic and Reconstructive Approach

    Get PDF
    Paranasal sinus osteomas are rare, slow-growing and benign lesions with potentially serious complications. They usually remain asymptomatic but when osteomas grow they can lead to local complications and cause evident aesthetic deformity due to the direct mass effect and in these situations, surgery is required. This is a report of a 30-year-old man with a rare giant post-traumatic osteoma that occupies the right nasal fossa, ethmoidal cells and frontal sinuses with extension into the right orbit
    corecore