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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.
A computationally efficient method for delineating irregularly shaped spatial clusters
(Springer Berlin Heidelberg, 2011-12-01) Duque, Juan C.; Aldstadt, Jared; Velasquez, Ermilson; Franco, Jose L.; Betancourt, Alejandro; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
In this paper, we present an efficiency improvement for the algorithm called AMOEBA, A Multidirectional Optimum Ecotope-Based Algorithm, devised by Aldstadt and Getis (Geogr Anal 38(4):327-343, 2006). AMOEBA embeds a local spatial autocorrelation statistic in an iterative procedure in order to identify spatial clusters (ecotopes) of related spatial units. We provide an analysis of the computational complexity of the original AMOEBA and develop an alternative formulation that reduces computational time without losing optimality. Empirical evidence is provided using georeferenced socio-demographic data in Accra, Ghana. © 2010 Springer-Verlag.
A General-Purpose Element-Based Approach to Compute Dispersion Relations in Periodic Materials with Existing Finite Element Codes
(World Scientific Publishing Co. Pte Ltd, 2019-01-01) Valencia C.; Gomez J.; Guarín-Zapata N.; Mecánica Aplicada
The numerical determination of dispersion relations in periodic materials via the finite element method is a difficult task in most standard codes. Here, we propose a novel technique which allows the computation of these band structures from local elemental subroutines in contrast with existing methods which impose Bloch boundary conditions on the global arrays. The proposed local approach is thus readily applicable to several physical contexts and space dimensionalities. Here we present the details of this element-based algorithm and provide verification results for three different kinematic assumptions applied to phononic crystals in a classical and a micropolar elastic medium. The paper also includes in the form of supplementary material, a fully-coded user subroutine and a test-problem to be used in a commercial finite element code. © 2019 IMACS.
A novel simple procedure to consider seismic soil structure interaction effects in 2D models
(SPRINGER, 2014-09-01) Diego Jaramillo, Juan; David Gomez, Juan; Restrepo, Doriam; Rivera, Santiago; Mecánica Aplicada
A method is proposed to estimate the seismic soil-structure-interaction (SSI) effects for use in engineering practice. It is applicable to 2D structures subjected to vertically incident shear waves supported by homogenous half-spaces. The method is attractive since it keeps the simplicity of the spectral approach, overcomes some of the difficulties and inaccuracies of existing classical techniques and yet it considers a physically consistent excitation. This level of simplicity is achieved through a response spectra modification factor that can be applied to the free-field 5%-damped response spectra to yield design spectral ordinates that take into account the scattered motions introduced by the interaction effects. The modification factor is representative of the Transfer Function (TF) between the structural relative displacements and the free-field motion, which is described in terms of its maximum amplitude and associated frequency. Expressions to compute the modification factor by practicing engineers are proposed based upon a parametric study using 576 cases representative of actual structures. The method is tested in 10 cases spanning a wide range of common fundamental vibration periods. © 2014, Institute of Engineering Mechanics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg.
A novel simple procedure to consider soil structure interaction effects in 2D models. Accepted in Earthquake Engineering and Engineering Vibration
(SPRINGER, 2014-09-01) GOMEZ, JUAN DAVID; Mecánica Aplicada
A review of regional science applications of satellite remote sensing in urban settings
(Elsevier Sci Ltd, 2013-01) Patino, J. E.; Duque, Juan C.; Universidad EAFIT. Escuela de Economía y Finanzas. Research in Spatial Economics (RiSE), Carrera 49 7 Sur-50, Medellín, Colombia.; Universidad EAFIT. Departamento de Economía y Finanzas; Patino, J.E. (jpatinoq@eafit.edu.co); Duque, Juan C. (jduquec1@eafit.edu.co); Research in Spatial Economics (RiSE); Research in Spatial Economics (RISE)
This paper reviews the potential applications of satellite remote sensing to regional science research in urban settings. Regional science is the study of social problems that have a spatial dimension. The availability of satellite remote sensing data has increased significantly in the last two decades, and these data constitute a useful data source for mapping the composition of urban settings and analyzing changes over time. The increasing spatial resolution of commercial satellite imagery has influenced the emergence of new research and applications of regional science in urban settlements because it is now possible to identify individual objects of the urban fabric. The most common applications found in the literature are the detection of urban deprivation hot spots, quality of life index assessment, urban growth analysis, house value estimation, urban population estimation and urban social vulnerability assessment. The satellite remote sensing imagery used in these applications has medium, high or very high spatial resolution, such as images from Landsat MSS, Landsat TM and ETM+, SPOT, ASTER, IRS, Ikonos and QuickBird. Consistent relationships between socio-economic variables derived from censuses and field surveys and proxy variables of vegetation coverage measured from satellite remote sensing data have been found in several cities in the US. Different approaches and techniques have been applied successfully around the world, but local research is always needed to account for the unique elements of each place. Spectral mixture analysis, object-oriented classifications and image texture measures are some of the techniques of image processing that have been implemented with good results. Many regional scientists remain skeptical that satellite remote sensing will produce useful information for their work. More local research is needed to demonstrate the real potential and utility of satellite remote sensing for regional science in urban environments.
A stiffness derivative local hypercomplex-variable finite element method for computing the energy release rate
(Elsevier BV, 2019-01-01) Aguirre-Mesa A.M.; Ramirez-Tamayo D.; Garcia M.J.; Montoya A.; Millwater H.; Mecánica Aplicada
A “local” hypercomplex-variable finite element method, L-ZFEM, is proposed for the computation of the energy release rate (ERR) using the stiffness derivative equation. This approach is analogous to the stiffness derivative method proposed by Parks and Hellen but has superior numerical accuracy. In addition, this method is significantly more efficient than the previously published “global” hypercomplex-variable finite element method, ZFEM, in that the global hypercomplex system of FE equations is not assembled nor solved. Instead, the displacement field is computed using a traditional, real-valued finite element method, and the numerical derivative of the stiffness matrix at the element level is only computed for a group of local, surrounding elements to the crack tip by using a Taylor series expansion based on complex numbers or dual numbers. The ERR is then determined as a sum of the element contributions. Derivatives of the ERR with respect to an arbitrary model parameter such as a crack extension, material property, or geometric feature are also available using a combination of the global and local methods, GL-ZFEM. Both L-ZFEM and GL-ZFEM were implemented into the commercial finite element software Abaqus through user defined element subroutines. Numerical results show that the ERR obtained by L-ZFEM has the same accuracy as that estimated through the global ZFEM or the J-integral methods but exhibits superior computational efficiency. © 2019 Elsevier Ltd
A Superposition Based Diffraction Technique to Study Site Effects in Earthquake Engineering
(Hindawi Publishing Corporation, 2016-01-01) Gomez, Juan; Jaramillo, Juan; Mario Saenz; Vergara, Juan; Mecánica Aplicada
A method to study the response of surface topographies submitted to incident SH waves is presented. The method is based on the superposition of diffracted sources described in Jaramillo et al. (2013). Since the technique proceeds in the frequency domain in terms of the superposition of incident, reflected, and diffracted waves, it has been termed like a superposition based diffraction approach. The final solution resulting from the superposition approach takes the form of a series of infinite terms, where each term corresponds to diffractions of increasing order and of decreasing amplitude generated by the interactions between the geometric singularities of the scatterer. A detailed, step-by-step algorithm to apply the method is presented with regard to the simple problem of scattering by a V-shaped canyon. In order to show the accuracy of the method we compare our time and frequency domain results with those obtained from a direct Green's function approach. We show that fast solutions with an error of the order of 6.0% are obtained.
Accelerated Fatigue of Dentin with Exposure to Lactic Acid
(Elsevier BV, 2013-08-01) Orrego, Santiago; Mecánica Aplicada
Agglomeration Economies in the Presence of an Informal Sector The Colombian Case
(ARMAND COLIN, 2019-04-30) Garcia, Gustavo Adolfo; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
Agglomeration economies in the presence of an informal sector: the Colombian case
(ARMAND COLIN, 2019-01-01) Garcia, Gustavo A.; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
This paper analyzes the relationship between agglomeration economies and productivity in the context of a developing country in presence of an informal sector. Using data from Colombia, we examine whether the informal sector achieves benefits from agglomeration economies as well as whether there are differences between the formal and informal sectors in terms of agglomeration returns. We find that agglomeration economies have a significantly positive effect on productivity in the informal sector: informal workers in denser areas will earn approximately 11% more than those in less dense areas.
Algunos conceptos de la econometría espacial y el análisis exploratorio de datos espaciales.
(Universidad EAFIT, 2008-10-01) Acevedo, Ingrid; Velásquez, H.; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
El presente artículo es parte del trabajo realizado en el proyecto de Investigación ?Análisis Exploratorio de Datos Espaciales y el Índice de Moran?, el cual es financiado con fondos de la Universidad EAFIT para el año 2008. En este trabajo se presenta
Alternativas fundamentales para cuantificar el riesgo operacional
(Universidad EAFIT, 2010-01-01) Velasquez, Hermilson; Luis Ceferino Franco Arbeláez; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
Análisis del índice general de la bolsa de valores de colombia y sus rendimientos desde la teoría del caos, 2001-2011
(Universidad de Medellín, 2012-01-01) Velasquez, Hermilson; Restrepo, Jorge Humberto; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
El objetivo de este trabajo es presentar un enfoque alternativo para el análisis de las seriesde tiempo en mercados financieros, cuyos fundamentos consideran la posible existencia decaracterísticas de objetos...
Análisis espacial cuantitativo de la transformación de humedales continentales en Colombia
(2016-06-01) Patiño, Jorge Eduardo; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
Análisis espacial de la informalidad laboral intraurbana
(2018-12-01) Garcia, Gustavo Adolfo; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
Análisis espacial de la informalidad laboral intraurbana en Medellín
(2018-12-15) Garcia, G.; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)
Analisis Estructural de una losa vial bajo carga estática y simulación por el método de elementos finitos
(Facultad de Ingenierías del Instituto Tecnológico Metropolitano (ITM), 2009-01-01) Velez, Francisco Javier; Mecánica Aplicada
Analysis of the role of diffraction in topographic site effects using boundary element techniques
(Springer. Seismological Society of China, 2013-10) Gomez, Juan; Jaramillo, Juan Diego; Restrepo, Dorian; Valencia, Camilo; Juan Gomez (jgomezc1@eafit.edu.co); Mecánica Aplicada
The role played by the diffraction field on the problem of seismic site effects is studied. For that purpose we solve and analyze simple scattering problems under P and SV in-plane wave assumptions, using two well known direct boundary-element-based numerical methods. After establishing the difference between scattered and diffracted motions, and introducing the concept of artificious and physically based incoming fields, we obtain the amplitude of the Fourier spectra for the diffracted part of the response: this is achieved after establishing the connection between the spatial distribution of the transfer function over the studied simple topographies and the diffracted field. From the numerical simulations it is observed that this diffracted part of the response is responsible for the amplification of the surface ground motions due to the geometric effect. Furthermore, it is also found that the diffraction field sets in a fingerprint of the topographic effect in the total ground motions. These conclusions are further supported by observations in the time-domain in terms of snapshots of the propagation patterns over the complete computational model. In this sense the geometric singularities are clearly identified as sources of diffraction and for the considered range of dimensionless frequencies it is evident that larger amplifications are obtained for the geometries containing a larger number of diffraction sources thus resulting in a stronger topographic effect. The need for closed-form solutions of canonical problems to construct a robust analysis method based on the diffraction field is identified.
Analysis of the role of diffraction in topographic site effects using boundary element techniques
(Seismological Society of China, 2013-01-01) Gomez, J.; Restrepo, D.; Jaramillo, J.; Valencia, C.; Mecánica Aplicada
The role played by the diffraction field on the problem of seismic site effects is studied. For that purpose we solve and analyze simple scattering problems under PandSVin-plane wave assumptions, using two well known direct boundary-element-based numerical methods. After establishing the difference between scattered and diffracted motions, and introducing the concept of artificious and physically based incoming fields, we obtain the amplitude of the Fourier spectra for the diffracted part of the response: this is achieved after establishing the connection between the spatial distribution of the transfer function over the studied simple topographies and the diffracted field. From the numerical simulations it is observed that this diffracted part of the response is responsible for the amplification of the surface ground motions due to the geometric effect. Furthermore, it is also found that the diffraction field sets in a fingerprint of the topographic effect in the total ground motions. These conclusions are further supported by observations in the time-domain in terms of snapshots of the propagation patterns over the complete computational model. In this sense the geometric singularities are clearly identified as sources of diffraction and for the considered range of dimensionless frequencies it is evident that larger amplifications are obtained for the geometries containing a larger number of diffraction sources thus resulting in a stronger topographic effect. The need for closed-form solutions of canonical problems to construct a robust analysis method based on the diffraction field is identified. © The Seismological Society of China, Institute of Geophysics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg 2013.

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