The effects of roughness on the area of contact and on the elastostatic friction: FEM simulation of micro-scale rough contact and real world applications

Roughness is everywhere. Every object, every surface we touch or look at, is rough. Even when it looks smooth and flat, if analyzed at the proper length scale, it will reveal roughness. Thus, macro-scale, micro-scale, and even nano-scale roughness exist. What is even more fascinating, is that most of the rough structures, which can be observed at a given length scale, repeat themselves at smaller length scales, as in a fractal. The first implication of the rough nature of surfaces is that what we perceive as a full, solid, and smooth contact area, is in reality a collection of fragmented microscopical contact patches, composed of single contact points. Given its intrinsic complexity, the modeling of the real area of contact has been the subject of a huge amount of studies, which yielded different and contrasting results. As it is easy to imagine, the real area of contact is crucial for many real-world applications, such as the prediction of wear and fretting, charge and heat conduction, and frictional effect.Let alone think of how an acting load is normally believed to be uniformly distributed over the contact surface, and how variable and uneven it must, in reality, appear at microscopic length scales. The importance of roughness, together with our knowledge in parallel computing and fast solution methods, are the premises of the current work. In this study, we analyze rough contact between realistic surfaces, and we resolve it numerically at micro-scale, to understand its meso- and macro-scale effects. We do this by means of the Finite Element Method, in combination with an optimal multi-grid strategy and a spatial decomposition to perform the computations on highly parallel super-computers. We concentrate on the type of surfaces for which it is believed that molecular and chemical effects can be neglected.We simulate the contact between an elastic cube and diverse rigid rough surfaces, under different loading conditions, and we derive empirical laws which describe the influence of well known roughness parameters on important features such as contact evolution and static friction production. We also define bounds on the uncertainty of our measurements, to make clear the level up to which our predictions have to be considered reliable and applicable. Literature on roughness is densely populated by models, approaches, and theoretical predictions about the evolution of the real area of contact. An exhaustive comparison of our results with such corpus of works, articles, books, and theses would be infeasible. We therefore compare our results on the real area of contact to the predictions of two widely accepted theories (one by B. N. J. Persson, the other by A. W. Bush, R. D. Gibson, and T. R. Thomas), which have often proved to be interpretable as asymptotical bounds, for systems at low pressures. For large pressures, and consequent large areas of contact, we also compare our results to the newly developed and semi-empirical theory by Yastrebov, Molinari, and Anciaux. Finally, we test our method on the real world problem of tyre-asphalt interactions on wet roads, comparing the results obtained by our method to data from other studies, collected on real highways and runways, and to a theoretical model, which is close, in the assumptions, to our numerical experiments

An Edge and Fog Computing Platform for Effective Deployment of 360 Video Applications

This paper has been presented at: Seventh International Workshop on Cloud Technologies and Energy Efficiency in Mobile Communication Networks (CLEEN 2019). How cloudy and green will mobile network and services be? 15 April 2019 - Marrakech, MoroccoIn press / En prensaImmersive video applications based on 360 video streaming require high-bandwidth, high-reliability and lowlatency 5G connectivity but also flexible, low-latency and costeffective computing deployment. This paper proposes a novel solution for decomposing and distributing the end-to-end 360 video streaming service across three computing tiers, namely cloud, edge and constrained fog, in order of proximity to the end user client. The streaming service is aided with an adaptive viewport technique. The proposed solution is based on the H2020 5G-CORAL system architecture using micro-services-based design and a unified orchestration and control across all three tiers based on Fog05. Performance evaluation of the proposed solution shows noticeable reduction in bandwidth consumption, energy consumption, and deployment costs, as compared to a solution where the streaming service is all delivered out of one computing location such as the Cloud.This work has been partially funded by the H2020 collaborative Europe/Taiwan research project 5G-CORAL (grant num. 761586)

In Situ Framework for Coupling Simulation and Machine Learning with Application to CFD

Recent years have seen many successful applications of machine learning (ML) to facilitate fluid dynamic computations. As simulations grow, generating new training datasets for traditional offline learning creates I/O and storage bottlenecks. Additionally, performing inference at runtime requires non-trivial coupling of ML framework libraries with simulation codes. This work offers a solution to both limitations by simplifying this coupling and enabling in situ training and inference workflows on heterogeneous clusters. Leveraging SmartSim, the presented framework deploys a database to store data and ML models in memory, thus circumventing the file system. On the Polaris supercomputer, we demonstrate perfect scaling efficiency to the full machine size of the data transfer and inference costs thanks to a novel co-located deployment of the database. Moreover, we train an autoencoder in situ from a turbulent flow simulation, showing that the framework overhead is negligible relative to a solver time step and training epoch

Repercusión de la inundación ocurrida en La Plata en el año 2013 sobre la sensibilidad cutánea a hongos aerógenos en pacientes alérgicos respiratorios

En La Plata, entre el 2 y el 3 de abril del 2013 cayeron 400 mm de agua provocando una inundación masiva y nunca vista. Más de la mitad de la ciudad bajo agua. En algunos lugares llegó a superar los 2 metros. Los problemas de la calidad del aire del interior de los ambientes son reconocidos como importantes factores de riesgo para la salud humana. La exposición a los contaminantes microbianos puede estar asociada con síntomas respiratorios en pacientes alérgicos. La humedad y el moho del interior son problemas comunes en todo el mundo. La evidencia indica que la humedad y el moho en el hogar podrían ser determinantes en el desarrollo de asma.Facultad de Ciencias Médica

Repercusión de la inundación ocurrida en La Plata en el año 2013 sobre la sensibilidad cutánea a hongos aerógenos en pacientes alérgicos respiratorios

En La Plata, entre el 2 y el 3 de abril del 2013 cayeron 400 mm de agua provocando una inundación masiva y nunca vista. Más de la mitad de la ciudad bajo agua. En algunos lugares llegó a superar los 2 metros. Los problemas de la calidad del aire del interior de los ambientes son reconocidos como importantes factores de riesgo para la salud humana. La exposición a los contaminantes microbianos puede estar asociada con síntomas respiratorios en pacientes alérgicos. La humedad y el moho del interior son problemas comunes en todo el mundo. La evidencia indica que la humedad y el moho en el hogar podrían ser determinantes en el desarrollo de asma.Facultad de Ciencias Médica

Repercusión de la inundación ocurrida en La Plata en el año 2013 sobre la sensibilidad cutánea a hongos aerógenos en pacientes alérgicos respiratorios

En La Plata, entre el 2 y el 3 de abril del 2013 cayeron 400 mm de agua provocando una inundación masiva y nunca vista. Más de la mitad de la ciudad bajo agua. En algunos lugares llegó a superar los 2 metros. Los problemas de la calidad del aire del interior de los ambientes son reconocidos como importantes factores de riesgo para la salud humana. La exposición a los contaminantes microbianos puede estar asociada con síntomas respiratorios en pacientes alérgicos. La humedad y el moho del interior son problemas comunes en todo el mundo. La evidencia indica que la humedad y el moho en el hogar podrían ser determinantes en el desarrollo de asma.Facultad de Ciencias Médica

Efficiently combining Machine Learning with OpenFOAM using SmartSim - Slides

Slides: 18th OpenFOAM Workshop - Efficiently combining Machine Learning with OpenFOAM using SmartSim1.