Examinando por Autor "Restrepo, D."
Mostrando 1 - 8 de 8
Resultados por página
Opciones de ordenación
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 Earthquake ground-motion simulation including nonlinear soil effects under idealized conditions with application to two case studies(SEISMOLOGICAL SOC AMER, 2012-11-01) Taborda, R.; Bielak, J.; Restrepo, D.; Mecánica Aplicada[No abstract available]Ítem Effects of realistic topography on the ground motion of the Colombian Andes - A case study at the Aburra Valley, Antioquia(OXFORD UNIV PRESS, 2016-03-01) Restrepo, D.; Bielak, J.; Serrano, R.; Gómez, J.; Jaramillo, J.; Mecánica AplicadaThis paper presents a set of deterministic 3-D ground motion simulations for the greater metropolitan area of Medellin in the Aburra Valley, an earthquake-prone region of the Colombian Andes that exhibits moderate-to-strong topographic irregularities. We created the velocity model of the Aburra Valley region (version 1) using the geological structures as a basis for determining the shear wave velocity. The irregular surficial topography is considered by means of a fictitious domain strategy. The simulations cover a 50 x 50 x 25 km(3) volume, and four M-w = 5 rupture scenarios along a segment of the Romeral fault, a significant source of seismic activity in Colombia. In order to examine the sensitivity of ground motion to the irregular topography and the 3-D effects of the valley, each earthquake scenario was simulated with three different models: (i) realistic 3-D velocity structure plus realistic topography, (ii) realistic 3-D velocity structure without topography, and (iii) homogeneous half-space with realistic topography. Our results show how surface topography affects the ground response. In particular, our findings highlight the importance of the combined interaction between source-effects, source-directivity, focusing, soft-soil conditions, and 3-D topography. We provide quantitative evidence of this interaction and show that topographic amplification factors can be as high as 500 per cent at some locations. In other areas within the valley, the topographic effects result in relative reductions, but these lie in the 0-150 per cent range.Ítem Influence of preprocessing and segmentation on the complexity of the learning machines in medical imaging(Indian Society for Development and Environment Research) Paniagua, J.; Restrepo, D.; Ariza, L.; Jose Garcés E; Diaz, C.; Diana Serna Higuita; Wiston Arrazola; Sebastian Arango; Ramiro Vélez Koeppel; Miguel Mejia; Wayner Barrios; Jesus Vargas Bonilla; Quintero, Olga Lucia; Universidad EAFIT. Departamento de Geología; Ciencias del MarÍtem Influence of preprocessing and segmentation on the complexity of the learning machines in medical imaging(Indian Society for Development and Environment Research) Paniagua, J.; Restrepo, D.; Ariza, L.; Jose Garcés E; Diaz, C.; Diana Serna Higuita; Wiston Arrazola; Sebastian Arango; Ramiro Vélez Koeppel; Miguel Mejia; Wayner Barrios; Jesus Vargas Bonilla; Quintero, Olga Lucia; Universidad EAFIT. Escuela de Ciencias; Modelado MatemáticoÍtem Influence of preprocessing and segmentation on the complexity of the learning machines in medical imaging(Indian Society for Development and Environment Research) Paniagua, J.; Restrepo, D.; Ariza, L.; Jose Garcés E; Diaz, C.; Diana Serna Higuita; Wiston Arrazola; Sebastian Arango; Ramiro Vélez Koeppel; Miguel Mejia; Wayner Barrios; Jesus Vargas Bonilla; Quintero, Olga Lucia; Paniagua, J.; Restrepo, D.; Ariza, L.; Jose Garcés E; Diaz, C.; Diana Serna Higuita; Wiston Arrazola; Sebastian Arango; Ramiro Vélez Koeppel; Miguel Mejia; Wayner Barrios; Jesus Vargas Bonilla; Quintero, Olga Lucia; Universidad EAFIT. Departamento de Ingeniería de Sistemas; I+D+I en Tecnologías de la Información y las ComunicacionesÍtem Multiaxial cyclic plasticity in accordance with 1D hyperbolic models and Masing criteria(John Wiley and Sons Ltd, 2018-12-10) Restrepo, D.; Taborda, R.; Mecánica AplicadaBounding surface plasticity models based on one-dimensional hardening functions are broadly accepted as a valid approach to represent the multiaxial cyclic behavior of undrained cohesive soils. However, under certain conditions, these models may exhibit deviations from the expected stress path. This makes them inadequate to meet traditional hysteretic rules. Current solutions to this problem impose thresholds to help adjust the stress path by introducing additional memory variables. This article presents a formulation that achieves the same goal without the need of such additional variables. The proposed formulation operates on a generic hardening function under multiaxial loading while preserving the simplicity inherited from pure deviatoric bounding surface models. In addition, the approach presented here allows the implementation of Masing-type rules, as well as the use of reduction factors to mitigate the overdamping effects of large hysteresis loops. The formulation is tested using well-known hyperbolic backbone functions under radial and nonradial multiaxial loading cycles, and it is shown to have good agreement with reference solutions. © 2018 John Wiley & Sons, Ltd.Ítem Symmetrical Observability of Kinematic Parameters in Symmetrical Parallel Mechanisms(Editora Edgard Blücher Ltda., 2014-05) Durango, S.; Restrepo, D.; Ruíz, O.; Restrepo-Giraldo, J.; Achiche, S.; Universidad EAFIT. Departamento de Ingeniería Mecánica; Laboratorio CAD/CAM/CAEThis article presents an application of symmetry group theory in kinematic identification of parallel mechanisms of nlegs legs -- Kinematic Identification implies the estimation of the actual geometrical parameters (as opposed to nominal ones) of a physical mechanism -- For a symmetric mechanism, KI requires configuring sets of leg positions with symmetrical observability – This article presents as main contributions: (i) a conjecture that allows mapping the symmetries of the mechanism into the active-joint workspace, (ii) a set of necessary conditions to express leg parameters in coordinate systems which allow symmetrical observability, and (iii) a procedure for exploiting symmetries in pose selection for kinematic identification of symmetrical parallel mechanisms -- For the kinematic identification itself, we adopt a divide-and-conquer (DC) identification protocol -discussed by us in another publication- in which each leg of the mechanism is independently identified by using the inverse calibration method -- In this article we emphasize how to exploit the symmetries existent in (nlegs − 1) legs of the parallel mechanism allowing to apply to other legs the symmetry-transformed sample protocol used for the kinematic identification of a reference leg -- The symmetrical observability of sets of leg parameters allows to reduce the costs of the pose selection procedure by a factor of (1/nlegs) compared to a complete DC procedure in which the poses of each leg are selected independently -- The pose selection is carried out only for the reference leg -- For the (nlegs−1) remaining legs the poses are dictated by symmetry operations performed onto the poses of the reference leg -- An application of the symmetrical observability is presented through the simulated kinematic identification of a 3RRR symmetrical parallel mechanism