Examinando por Autor "Gomez, J."
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Ítem 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 AplicadaThe 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.Ítem Evaluation of the Spectral Finite Element Method with the Theory of Phononic Crystals(World Scientific Publishing Co. Pte Ltd, 2015-06-01) Guarín-Zapata, N.; Gomez, J.; Mecánica AplicadaWe evaluated the performance of the classical and spectral finite element method in the simulation of elastodynamic problems. We used as a quality measure their ability to capture the actual dispersive behavior of the material. Four different materials are studied: a homogeneous non-dispersive material, a bilayer material, and composite materials consisting of an aluminum matrix and brass inclusions or voids. To obtain the dispersion properties, spatial periodicity is assumed so the analysis is conducted using Floquet-Bloch principles. The effects in the dispersion properties of the lumping process for the mass matrices resulting from the classical finite element method are also investigated, since that is a common practice when the problem is solved with explicit time marching schemes. At high frequencies the predictions with the spectral technique exactly match the analytical dispersion curves, while the classical method does not. This occurs even at the same computational demands. At low frequencies however, the results from both the classical (consistent or mass-lumped) and spectral finite element coincide with the analytically determined curves.Ítem Numerical Modeling of Wave Reflection in a Dispersive Micropolar Half-Space(2012-07-13) Velez, Francisco Javier; Gomez, J.; Guarin, Nicolas; Velez, Francisco Javier; Gomez, J.; Guarin, Nicolas; Universidad EAFIT. Departamento de Ingeniería Mecánica; Mecánica AplicadaIn this work wave propagation is studied considering the role played by the microstructural entities described by a non-classical solid, like the Cosserat or micropolar medium [1].Ítem The scattering of SH waves by a finite crack with a superposition-based diffraction technique(Akademie Ved Ceske Republiky, 2017-01-01) Valencia, C.; Gomez, J.; Jaramillo, J.; Saenz, M.; Vergara, J.; Mecánica AplicadaThe problem of diffraction of cylindrical and plane horizontally polarized shear waves (SH waves) by a finite crack embedded in a plane bidimensional elastic full-space is revisited. Particularly, we construct an approximate solution by the addition of independent diffracted terms. In our method the derivation of the fundamental case of a semi-infinite crack obtained as a degenerate case of a generalized wedge is first considered. This result is then used as a building block to compute the diffraction of the main incident waves. The interaction between the opposite edges of the crack is later considered in terms of a series, one term at a time until a desired tolerance is reached. Moreover, we propose a procedure to determine the number of required interactions as a function of frequency. The solution derived with the superposition technique is shown to be effective at low and high frequencies and as shown by comparisons with a direct boundary element method software, highly accurate solutions are obtained after retaining just a few terms of the infinite series. © 2017, Institute of Geophysics of the ASCR, v.v.i.Ítem Shear wave filtering in naturally-occurring Bouligand structures.(ELSEVIER SCI LTD, 2015-09-01) Guarín-Zapata, N.; Gomez, J.; Yaraghi, N.; Kisailus, D.; Zavattieri, P.D.; Mecánica AplicadaWave propagation was investigated in the Bouligand-like structure from within the dactyl club of the stomatopod, a crustacean that is known to smash their heavily shelled preys with high accelerations. We incorporate the layered nature in a unitary material cell through the propagator matrix formalism while the periodic nature of the material is considered via Bloch boundary conditions as applied in the theory of solid state physics. Our results show that these materials exhibit bandgaps at frequencies related to the stress pulse generated by the impact of the dactyl club to its prey, and therefore exhibiting wave filtering in addition to the already known mechanisms of macroscopic isotropic behavior and toughness.Ítem Spatiotemporal Modeling of Urban Growth Using Machine Learning(MDPI AG, 2019-12-28) Duque, J.; Jorge E. Patino; Gomez, J.; Passos, S.; Universidad EAFIT. Departamento de Economía y Finanzas; Research in Spatial Economics (RISE)This paper presents a general framework for modeling the growth of three important variables for cities: population distribution, binary urban footprint, and urban footprint in color. The framework models the population distribution as a spatiotemporal regression problem using machine learning, and it obtains the binary urban footprint from the population distribution through a binary classifier plus a temporal correction for existing urban regions. The framework estimates the urban footprint in color from its previous value, as well as from past and current values of the binary urban footprint using a semantic inpainting algorithm. By combining this framework with free data from the Landsat archive and the Global Human Settlement Layer framework, interested users can get approximate growth predictions of any city in the world. These predictions can be improved with the inclusion in the framework of additional spatially distributed input variables over time subject to availability. Unlike widely used growth models based on cellular automata, there are two main advantages of using the proposed machine learning-based framework. Firstly, it does not require to define rules a priori because the model learns the dynamics of growth directly from the historical data. Secondly, it is very easy to train new machine learning models using different explanatory input variables to assess their impact. As a proof of concept, we tested the framework in Valledupar and Rionegro, two Latin American cities located in Colombia with different geomorphological characteristics, and found that the model predictions were in close agreement with the ground-truth based on performance metrics, such as the root-mean-square error, zero-mean normalized cross-correlation, Pearson's correlation coefficient for continuous variables, and a few others for discrete variables such as the intersection over union, accuracy, and the f1 metric. In summary, our framework for modeling urban growth is flexible, allows sensitivity analyses, and can help policymakers worldwide to assess different what-if scenarios during the planning cycle of sustainable and resilient cities. © 2019 by the authors.Ítem Spectral element method for dispersion relations of phononic crystals(2012-07-13) Guarin, Nicolas; Gomez, J.; Guarin, Nicolas; Gomez, J.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Mecánica AplicadaThe mechanical response of heterogeneous solids below a given length scale starts to be controlled by the existing microstructure. In the case of periodic heterogeneities the materials are known as phononic crystalsÍtem Thermodynamics Theory for Damage Evolution in Solids(Springer New York, 2015-01-01) Basaran, Cemal; Nie, Shihua; Gomez, J.; Gunel, Eray; Shidong Li; Minghui Lin; Hong Tang; Chengyong Yan; Wei Yao; Hua Ye; Basaran, Cemal; Nie, Shihua; Gomez, J.; Gunel, Eray; Shidong Li; Minghui Lin; Hong Tang; Chengyong Yan; Wei Yao; Hua Ye; Universidad EAFIT. Departamento de Ingeniería Mecánica; Mecánica AplicadaIn this chapter the thermodynamic theory behind damage mechanics is presented. The presented damage evolution model is purely physical, rather than empirical. Entropy production rate is used as a damage metric.