PUBLICACIONES

Investigaciones realizadas con el uso de recursos computacionales del sistema HPC-MODEMAT

A generalized three-dimensional discrete element method with electrostatic induced cohesion

Many granular materials can be electrostatically charged when colliding as part of several dust handling processes (Pei et al. in Powder Technol 248:34–43, 2013). The attractive and repulsive forces that result from this handling can lead to the aggregation or segregation of the grains (Grzybowski et al. in Nat Mater 2(4):241–245, 2003) and to an unanticipated grain dispersion (Wu et al. in Ind Eng Chem Res 47(15):5005–5015, 2008). Therefore, understanding the kinematics and dynamics of electrically charged grains is very important in the processing of materials with electrostatic induced cohesion (Pei et al. in AIChE J 61(6):1792–1803, 2015). The present work introduces a new level set-based discrete element method which enables us, for the first time, to a generalized modeling and computational simulation of real three-dimensional cohesive granular media such as clays.

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An Empirical Model for Rainfall Maximums Conditioned to Tropospheric Water Vapor Over the Eastern Pacific Ocean

One of the most difficult weather variables to predict is rain, particularly intense rain. The main limitation is the complexity of the fluid dynamic equations used by predictive models with increasing uncertainties over time, especially in the description of brief, local, and high intensity precipitation events. Although computational, instrumental and theoretical improvements have been developed for models, it is still a challenge to estimate high intensity rainfall events, especially in terms of determining the maximum rainfall rates and the location of the event. Within this context, this research presents a statistical and relationship analysis of rainfall intensity rates, total precipitable water (TPW), and sea surface temperature (SST) over the ocean. An empirical model to estimate the maximum rainfall rates conditioned to TPW values is developed. The performance of the maximum rainfall rate model is spatially evaluated for a case study. High-resolution TRMM 2A12 satellite data with a resolution of 5.1 × 5.1 km and 1.67 s was used from January 2009 to December 2012, over the Eastern Pacific Niño area in the tropical Pacific Ocean (0–5°S; 90–81°W), comprising 326,092 rain pixels. After applying the model selection methodology, i.e., the Akaike Information Criterion (AIC) and the Bayesian Information Criterion (BIC), an empirical exponential model between the maximum possible rain rates conditioned to TPW was found with R2 = 0.96, indicating that the amount of TPW determines the maximum amount of rain that the atmosphere can precipitate exponentially. Spatially, this model unequivocally locates the rain event; however, the rainfall intensity is underestimated in the convective nucleus of the cloud. Thus, these results provide an additional constraint for maximum rain intensity values that should be adopted in dynamic models, improving the quantification of heavy rainfall event intensities and the correct location of these events

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Numerical Flow Characterization Around a Type 209 Submarine Using OpenFOAM

The safety of underwater operation depends on the accuracy of its speed logs which depends on the location of its probe and the calibration thoroughness. Thus, probes are placed in areas where the flow of water is smooth, continuous, without high velocity gradients, air bubbles, or vortical structures. In the present work, the flow around two different submarines is numerically described in deep-water and near-surface conditions to identify hull zones where probes could be installed. First, the numerical setup of a multiphase solver supplied with OpenFOAM v7 was verified and validated using the DARPA SUBOFF-5470 submarine at scaled model including the hull and sail configuration at H/D = 5.4 and Fr = 0.466. Later, the grid sensitivity of the resistance was assessed for the full-scale Type 209/1300 submarine at H/D = 0.347 and Fr = 0.194. Free-surface effect on resistance and flow characteristics was evaluated by comparing different operational conditions. Results shows that the bow and near free-surface regions should be avoided due to high flow velocity gradient, pressure fluctuations, and large turbulent vortical structures. Moreover, free-surface effect is stronger close to the bow nose. In conclusion, the probe could be installed in the acceleration region where the local flow velocity is 15% higher than the navigation speed at surface condition. A 4% correction factor should be applied to the probe readings to compensate free-surface effect.

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Análisis de inestabilidades two-stream en los casos límite de beam-plasma y gentle-bump en plasmas cinéticos no colisionales, usando algoritmos tipo Particle-in-Cell no relativistas

Un plasma espacial puede ser descrito analíticamente mediante una aproximación cinética. En este régimen, el comportamiento del plasma está gobernado por una ecuación de Vlasov para cada especie de partícula que lo componen. El estudio que se desarrolla en este documento tiene dos componentes: uno analítico y el otro numérico. En ambos escenarios analizamos la inestabilidad two-stream, en los casos límite beam-plasma y gentle-bump. Para el tratamiento no lineal hemos implementado un código cinéticos tipo Particle-in-Cell en el servidor de cálculo numérico del Departamento de Física de la Escuela Politécnica Nacional. Las simulaciones numéricas desarrolladas en este estudio muestran que el código implementado es estable y reproduce adecuadamente la física de estos casos límite

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A geometry-based algorithm for cloning real grains 2.0

We introduce an improved version of a computational algorithm that “clones”/generates an arbitrary number of new digital grains from a sample of real digitalized granular material. Our improved algorithm produces “cloned” grains that more accurately approach the morphological features displayed by their parents. Now, the “cloned” grains were also included in a discrete element method simulation of a triaxial test and showed similar mechanical behavior compared to the one displayed by the original (parent) sample. Thus, the present work is divided in four parts. First, we compute multivariable probability density functions from the parents’ morphological parameters (morphological DNA), i.e., aspect ratio, roundness, volume-surface ratio, and particle diameter. Second, an improved, now parallelized and better tuned version of the geometric stochastic cloning algorithm (Jerves et al. in Granul Matter, 2017. https://doi.org/10.1007/s10035-017-0716-7), which is based on the aforementioned multivariable distributions and that, in the same way, introduces an enhanced radii sampling process, as well as a new quality control test based on the volume-surface ratio is discussed. Third, morphological DNA of the grains (i.e., aspect ratio, roundness, volume-surface ratio and particle diameter) is also extracted from the new “cloned” grains and compared to the one obtained from the parent sample. Fourth, clones and parents are subjected to a triaxial compression tests using a level set discrete element scheme (3DLS-DEM), and then, compared in terms of their mechanical response. Finally, the error of the “clones” in the morphology and mechanical behavior is analyzed and discussed for future improvements.

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First Order Methods for High Resolution Image Denoising

In this paper we are interested in comparing the performance of some of the most relevant first order non-smooth optimization methods applied to the Rudin, Osher and Fatemi (ROF) Image Denoising Model and a Primal-Dual Chambolle-Pock Image Denoising Model. Because of the properties of the resulting numerical schemes it is possible to handle these computations pixelwise, allowing implementations based on parallel paradigms which are helpful in the context of high resolution imaging.

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