Examinando por Materia "Molecular dynamics"

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    A comparative computational study of blood flow pattern in exemplary textile vascular grafts
    (Taylor and Francis Ltd., 2018-01-01) Valencia, R.A.; García, M.J.; Bustamante, J.; Mecánica Aplicada
    Textile vascular grafts are biomedical devices and play an important role serving as a solution for the partial replacement of damaged arterial vessels. It is believed that the success of a textile vascular graft, in the healing process after implantation, is due to the porous micro-structure of the wall. Although the transport of fluids through textiles is of great technical interest in biomedical applications, little is known about predicting the micro-flow pattern and cellular transport through the wall. The aim of this work is to investigate how the type of fabric, permeability and porosity affect both the local fluid dynamics at several scales and the fluid-particle interaction between platelets in textile grafts, related with the graft occlusion. This study involves both experimental and computational tests. Experimental tests are performed to characterize the permeability and porosity according to the ISO 7198 standard. The numerical process is based on a multi-scale approach where the fluid flow is solved with the Finite Element Method and the discrete particles are solved with the Molecular Dynamic Method. The results have shown that the type of fabric in textile vascular grafts and the degree of porosity and permeability affect both the local fluid dynamics and the level of penetration of platelets through the wall, thus indicating their importance as design parameters. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
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    A comparative computational study of blood flow pattern in exemplary textile vascular grafts
    (Taylor and Francis Ltd., 2018-01-01) R. VALENCIA; M. GARCÍA; J. BUSTAMANTE; R. VALENCIA; M. GARCÍA; J. BUSTAMANTE; Universidad EAFIT. Departamento de Humanidades; Centro de Estudios Urbanos y Ambientales (URBAM)
    Textile vascular grafts are biomedical devices and play an important role serving as a solution for the partial replacement of damaged arterial vessels. It is believed that the success of a textile vascular graft, in the healing process after implantation, is due to the porous micro-structure of the wall. Although the transport of fluids through textiles is of great technical interest in biomedical applications, little is known about predicting the micro-flow pattern and cellular transport through the wall. The aim of this work is to investigate how the type of fabric, permeability and porosity affect both the local fluid dynamics at several scales and the fluid-particle interaction between platelets in textile grafts, related with the graft occlusion. This study involves both experimental and computational tests. Experimental tests are performed to characterize the permeability and porosity according to the ISO 7198 standard. The numerical process is based on a multi-scale approach where the fluid flow is solved with the Finite Element Method and the discrete particles are solved with the Molecular Dynamic Method. The results have shown that the type of fabric in textile vascular grafts and the degree of porosity and permeability affect both the local fluid dynamics and the level of penetration of platelets through the wall, thus indicating their importance as design parameters. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
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    Lagrangian model for predicting the dynamic behavior of cohesive particles in a fluidized confined environment
    (Universidad EAFIT, 2013) Posada Noreña, Juliana; García Ruíz, Manuel Julio
    Titanium dioxide, TiO2, is one of the most important raw materials in the paint production process; also TiO2 is classified as a Geldart C solid type, and it makes its storage and handling more than important not only because of its importance to the process but also because of its complicated nature -- Most common problems encountered handling and storing TiO2 come from the cohesive nature of the solid, which benefits the formation of agglomerates leading to clogging in pipes and storage vessels -- Attempting to simulate TiO2’s handling and storage, a Lagrangian particle simulation began by using a Discrete Element Model -- Understanding the interactions and forces acting on solids when they are dispersed in a gas and then stored, and the agglomerate formation due to cohesive forces were the main purposes of this work -- The particle motion under the influence of gravity and a fluid in motion was simulated with the BBO equation for each of the particles -- The wall-particle collisions were simulated with the equations for exchange of momentum and energy; the particle-particle collisions were simulated with the hard sphere model using as well the equations for exchange of momentum and energy and the agglomerate formation considered the collision model and a cohesion parameter -- Three hypotheses were proposed for the analysis of the interactions acting on the particles and their behavior was compared with results from various authors to conclude on the final validation of the DEM here proposed
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    Predictions of fluidities of amines by molecular simulations: TraPPE-EH vs. OPLS-AA
    (Elsevier B.V., 2018-05-25) Rendón-Calle A.; Orozco G.A.; Builes S.; Universidad EAFIT. Departamento de Ingeniería de Procesos; Desarrollo y Diseño de Procesos
    Amines have several important industrial properties and commercial applications, such as gas sweetening and carbon capture; and the synthesis of: tranquilizers, decongestants, and azo dyes. For the design of many engineering applications, it is important to calculate the density and viscosity of the substances in order to determine how the fluids should be handled, stored, and discarded. In this work, the accuracy of two common force fields for amines, TraPPE-EH and OPLS-AA, was evaluated with respect to their predictions of liquid densities and fluidities for a large set of amine molecules including primary, secondary and tertiary. We propose the use of the reciprocal of viscosity, the fluidity, as a more accurate assessment of the predictions of viscosity at different temperatures. The fluidity was calculated using molecular dynamics in the isothermal-isobaric ensemble (NPT) along with the Green Kubo formalism. The simulation results were compared to available experimental information in order to provide a quantitative study of the force fields accuracy as well as their transferability to amines and thermodynamic conditions different to the ones used in their original parametrization. Overall, liquid densities and fluidities are well reproduced by the TraPPE-EH force field with absolute average deviations of 1.5% and 12%, respectively. However, important deviations were found for the OPLS-AA force field corresponding to 3.6% and 28% for density and fluidity respectively. In order to obtain better estimations of the fluidity, a temperature correction that accounts for the error in the liquid density predictions was proposed. Once the temperature correction was included the average deviation of the fluidity decreased to 10% for TraPPE-EH and to 18% for OPLS-AA. © 2018 Elsevier B.V.
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    Study of Lattice Boltzmann Boundary conditions for fluid structure interaction
    (Universidad EAFIT, 2014) Aguirre Mesa, Andrés Mauricio; García Ruíz, Manuel Julio
    Lattice Boltzmann is a numerical method for the simulation of different physical phenomena, such as incompressible flow -- Despite the fact of being a kinetic method, and therefore of unsteady nature, allows to obtain the solution of steady problems with good accuracy and efficiency -- However, the arising of pressure oscillations during the solution process and the reflective character of some of its boundary conditions have resulted in an active research interest on open boundaries, and outlet conditions in particular -- Fluid structure interaction problems are mostly of unsteady type, so the elimination of spurious pressure oscillations is desirable or even necessary -- The aim of the present work is to show, in the first place, that oscillations occur even without involving solid obstacles in the simulations, although measures to avoid them are taken, like diffusive scaling -- On the other hand, that oscillation-free results are possible to be obtained using the most basic formulation of the method, LBGK, and even conventional reflective conditions, but sacrificing the most widely used tool of the LBM method: the bounce back condition