Microscopic origin of macroscopic strength in granular materials

This study attempts to develop an analytical study about the behavior of arbitrary shape and size noncohesive two-dimensional granular materials. Several mechanical properties and relations are unraveled by connecting micro- and macroscales in an explicit fashion that, at the same time, provides the basis for an analytical–theoretical multiscale framework. Furthermore, this study is based on three main ideas that are developed and connected progressively, namely, the obtention of explicit expressions that enable us to relate microscale parameters, such as contact forces and fabric, to stress and strain as macro (continuum) physical properties. Then, with these powerful tools, physical connections and relations between the mentioned microparameters and macroconstitutive parameters such as friction angle, dilatancy, and critical state are established

A Nonlinear Lagrangian Model for Plane Frames Pre-desing

We propose a nonlinear lagrangian model that takes into account the dynamic interactions between the soil and a n-storey plane frame, which may be subjected to a seismic excitation through the soil. First, the interaction of the soil with the structure is modeled through a combination of springs and dampers representing the characteristics of the soil. In this model, the masses and stiffnesses of the structure elements are condensed to facilitate the analysis. Second, the Euler-Lagrange equations of the system are formulated and generalized for n floors. Third, these equations are discretized using the finite difference method to solve them using the Newton-Raphson method at each time step, during and after the seismic excitation, thus, determining the positions of each concentrated mass of the system. In addition, a linearization of the governing equations is performed in order to compare these results with those of the nonlinear model. Finally, the nonlinear model is used for the analysis of a 10-storey building, which has already been designed for linear geometric and material behaviors. For this analysis, the corrected acceleration record of the 2016 Pedernales (Ecuador) earthquake is used

Towards a more accurate characterization of granular media 2.0: Involving AI in the process

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Automated Additive Construction (AAC) for Earth and Space Using In-situ Resources

Using Automated Additive Construction (AAC), low-fidelity large-scale compressive structures can be produced out of a wide variety of materials found in the environment. Compressionintensive structures need not utilize materials that have tight specifications for internal force management, meaning that the production of the building materials do not require costly methods for their preparation. Where a certain degree of surface roughness can be tolerated, lower-fidelity numerical control of deposited materials can provide a low-cost means for automating building processes, which can be utilized in remote or extreme environments on Earth or in Space. For space missions where every kilogram of mass must be lifted out of Earth’s gravity well, the promise of using in-situ materials for the construction of outposts, facilities, and installations could prove to be enabling if significant reduction of payload mass can be achieved. In a 2015 workshop sponsored by the Keck nstitute for Space Studies, on the topic of Three Dimensional (3D) Additive Construction For Space Using In-situ Resources, was conducted with additive construction experts from around the globe in attendance. The workshop explored disparate efforts, methods, and technologies and established a proposed framework for the field of Additive Construction Using In-situ Resources. This paper defines the field of Automated Additive Construction Using In-situ Resources, describes the state-of-the-art for various methods, establishes a vision for future efforts, identifies gaps in current technologies, explores investment opportunities, and proposes potential technology demonstration missions for terrestrial, International Space Station (ISS), lunar, deep space zero-gravity, and Mars environments

Elementos de cálculo numérico

Mucho tiempo ha transcurrido desde que el conocimiento de los Métodos Numéricos pasó de ser un asunto netamente teórico a uno completamente aplicativo, la llegada y desarrollo de los ordenadores ha permitido que esta herramienta matemática se convierta en una de las técnicas más poderosas de la actualidad para la solución de diversos problemas de Física e Ingeniería. Las técnicas de solución analítica de las diferentes ecuaciones diferenciales que gobiernan los problemas físicos, si bien proporcionan información en cualquier punto del dominio a tratar, o la denominada “Solución Exacta” porque no comprenden aproximaciones, sin embargo, en muchos de los casos esta solución no representa un problema del mundo real que difiere, en este caso, del matemático, ya que este último no vendría a ser más que una representación idealizada y por tanto la “Solución Exacta” se ver ́ıa comprometida al nivel de simplificación del modelo matemático. Bien podría decirse que un modelo real de un problema Físico puede llegar a tener una solución m ́as precisa que la solución de un modelo matemático muy simplificado, es decir, se trata de obviar cualquier efecto que conduzca a complicaciones matemáticas como por ejemplo las no linealidades y, por ende, la solución analítica de estos problemas se verá afectada

Microscopic Origin of Macroscopic Strength in Granular Media: A Numerical and Analytical Approach

Constitutive modeling in granular materials has historically been based on macroscopic experimental observations that, while being usually effective at predicting the bulk behavior of these type of materials, suffer important limitations when it comes to understanding the physics behind grain-to-grain interactions that induce the material to macroscopically behave in a given way when subjected to certain boundary conditions. The advent of the discrete element method (DEM) in the late 1970s helped scientists and engineers to gain a deeper insight into some of the most fundamental mechanisms furnishing the grain scale. However, one of the most critical limitations of classical DEM schemes has been their inability to account for complex grain morphologies. Instead, simplified geometries such as discs, spheres, and polyhedra have typically been used. Fortunately, in the last fifteen years, there has been an increasing development of new computational as well as experimental techniques, such as non-uniform rational basis splines (NURBS) and 3D X-ray Computed Tomography (3DXRCT), which are contributing to create new tools that enable the inclusion of complex grain morphologies into DEM schemes. Yet, as the scientific community is still developing these new tools, there is still a gap in thoroughly understanding the physical relations connecting grain and continuum scales as well as in the development of discrete techniques that can predict the emergent behavior of granular materials without resorting to phenomenology, but rather can directly unravel the micro-mechanical origin of macroscopic behavior. In order to contribute towards closing the aforementioned gap, we have developed a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media, where typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for better understanding and modeling granular media. In the same way, we utilize a new DEM scheme (LS-DEM) that takes advantage of a mathematical technique called level set (LS) to enable the inclusion of real grain shapes into a classical discrete element method. After calibrating LS-DEM with respect to real experimental results, we exploit part of its potential to study the dependency of critical state (CS) parameters such as the critical state line (CSL) slope, CSL intercept, and CS friction angle on the grain's morphology, i.e., sphericity, roundness, and regularity. Finally, we introduce a first computational algorithm to ``clone'' the grain morphologies of a sample of real digital grains. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same morphological features (e.g., roundness and aspect ratio) displayed by their real parents and can be included into a DEM simulation of a given mechanical phenomenon. In turn, this will help with the development of discrete techniques that can directly predict the engineering scale behavior of granular media without resorting to phenomenology.</p

Desagües urbanos

Este documento trae un resumen de los aspectos mas importantes a considerar en el momento de seleccionar una bomba centrifuga, haciendo mayor hincapié en lo que corresponde a Pre Selección y a la Altura Neta Positiva de Aspiración (ANPA). Se tomaron en cuenta las teorías básicas de donde salen todas las ecuaciones fundamentales que gobiernan el comportamiento de una bomba, de manera que el lector, sea este profesional de la ingeniería o estudiante, tenga una clara visión de las bombas centrifugas y los fenómenos que se dan en el funcionamiento de las mismas. Se consideran temas que no tiene una influencia directa en la selección de los equipos de bombeo, pero que son de importancia indiscutible en el momento de su elección; estos temas son: Golpe de Ariete y Estaciones de Bombeo. El presente trae un Ejercicio Compilador, en donde se resuelve de una manera clara y completa todos los pasos a seguir en el momento de seleccionar una bomba para el caso presentado en el mismo; compilando la mayor parte de los temas tratados en este texto. Se da también el tratamiento debido a la Altura Manométrica, de sumo interés en el momento de diseñar y seleccionar una bomba o un sistema de bombeo. Esperando que el presente contribuya a resaltar la importancia de los equipos de bombeo, muchas de las veces llevada a menos, se desarrollará a continuación, de una manera clara toda la problemática de la Selección de Bombas Centrifugas.Ingeniero CivilCuenc

A micro-mechanical study of peak strength and critical state

We present a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media. Typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for a better understanding and modeling of granular materials. These multi-scale relations are derived in three steps. First, explicit relations between macroscopic stress and strain rate with the corresponding grain-scale mechanics are established. Second, these relations are used in conjunction with the non-associative Mohr–Coulomb criterion to explicitly connect internal friction and dilation angles to the micro-mechanics. Third, the mentioned explicit connections are applied to investigate, understand, and derive micro-mechanical conditions for peak strength, critical state, and residual strength

A micro-mechanical study of peak strength and critical state

We present a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media. Typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for a better understanding and modeling of granular materials. These multi-scale relations are derived in three steps. First, explicit relations between macroscopic stress and strain rate with the corresponding grain-scale mechanics are established. Second, these relations are used in conjunction with the non-associative Mohr–Coulomb criterion to explicitly connect internal friction and dilation angles to the micro-mechanics. Third, the mentioned explicit connections are applied to investigate, understand, and derive micro-mechanical conditions for peak strength, critical state, and residual strength