Prediction of wear via DEM and phenomenological models

The Discrete Element Method (DEM) is a computational method used to describe the movement of a large number of particle of different sized and shapes, which interact through a contact model. Among other applications, in the field of mining DEM have been used extensively for predicting the trajectory of material inside Semi-Autogenous Grinding (SAG) mills and in the chutes of minerals transfer. However, no calculations that predict the wear of the enclosing walls have been performed to date. After an extensive review of the literature, a methodology to predict wear via DEM and phenomenological wear models has been developed. The decision was taken to use Archard's model (one of the simplest yet most accurate models proposed to date) in the context of DEM. Given that the wear occurs in a matter of weeks or months, and that a DEM run of even a minute can consume copious amounts of computer resources, a separation of timescales was implemented. For each stage of the overall cycle, the present configuration is run for a relatively small amount of physical time (from T0 to T1) in order to get the statistics of wear. For a mill, this could be a few rotations. For all the faces on the boundaries, the wear is updated every time step. At the end of the DEM run, the total change in volume is used to compute a `recession speed' for each face. The recession speed is then used to extrapolate the recession distance (i.e. the wear) from T0 to a much larger time T2. Once the surface is moved via the recession distance, the run is restarted and the cycle repeats. The result obtained to date show that the methodology is able to compute realistic wear patterns with CPU requirements that are acceptable in an engineering design environment.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Prediction of wear via DEM and phenomenological models

The Discrete Element Method (DEM) is a computational method used to describe the movement of a large number of particle of different sized and shapes, which interact through a contact model. Among other applications, in the field of mining DEM have been used extensively for predicting the trajectory of material inside Semi-Autogenous Grinding (SAG) mills and in the chutes of minerals transfer. However, no calculations that predict the wear of the enclosing walls have been performed to date. After an extensive review of the literature, a methodology to predict wear via DEM and phenomenological wear models has been developed. The decision was taken to use Archard's model (one of the simplest yet most accurate models proposed to date) in the context of DEM. Given that the wear occurs in a matter of weeks or months, and that a DEM run of even a minute can consume copious amounts of computer resources, a separation of timescales was implemented. For each stage of the overall cycle, the present configuration is run for a relatively small amount of physical time (from T0 to T1) in order to get the statistics of wear. For a mill, this could be a few rotations. For all the faces on the boundaries, the wear is updated every time step. At the end of the DEM run, the total change in volume is used to compute a `recession speed' for each face. The recession speed is then used to extrapolate the recession distance (i.e. the wear) from T0 to a much larger time T2. Once the surface is moved via the recession distance, the run is restarted and the cycle repeats. The result obtained to date show that the methodology is able to compute realistic wear patterns with CPU requirements that are acceptable in an engineering design environment.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Improvements in speed and scalability of a DEM code

A number of near-optimal techniques were implemented to reduce computing times for the Discrete Element Method (DEM) code named DESOL. Among these, the following showed the largest improvements: multilevel bins, periodic rebuild, trimming and Symmetric Multiprocessor (SMP) parallelization. These improvements have led to Central Processing Unit (CPU) reduction of the order of 1:3-1:5 on scalar machines, while also showing excellent scalability up to the point of memory saturation, which on current Intel Xeon processors occurs at approximately 8 cores for double precision and 16 cores for single precision.Publicado en: Mecánica Computacional vol. XXXV, no. 10.Facultad de Ingenierí

Prediction of wear via DEM and phenomenological models

The Discrete Element Method (DEM) is a computational method used to describe the movement of a large number of particle of different sized and shapes, which interact through a contact model. Among other applications, in the field of mining DEM have been used extensively for predicting the trajectory of material inside Semi-Autogenous Grinding (SAG) mills and in the chutes of minerals transfer. However, no calculations that predict the wear of the enclosing walls have been performed to date. After an extensive review of the literature, a methodology to predict wear via DEM and phenomenological wear models has been developed. The decision was taken to use Archard's model (one of the simplest yet most accurate models proposed to date) in the context of DEM. Given that the wear occurs in a matter of weeks or months, and that a DEM run of even a minute can consume copious amounts of computer resources, a separation of timescales was implemented. For each stage of the overall cycle, the present configuration is run for a relatively small amount of physical time (from T0 to T1) in order to get the statistics of wear. For a mill, this could be a few rotations. For all the faces on the boundaries, the wear is updated every time step. At the end of the DEM run, the total change in volume is used to compute a `recession speed' for each face. The recession speed is then used to extrapolate the recession distance (i.e. the wear) from T0 to a much larger time T2. Once the surface is moved via the recession distance, the run is restarted and the cycle repeats. The result obtained to date show that the methodology is able to compute realistic wear patterns with CPU requirements that are acceptable in an engineering design environment.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Improvements in speed and scalability of a DEM code

A number of near-optimal techniques were implemented to reduce computing times for the Discrete Element Method (DEM) code named DESOL. Among these, the following showed the largest improvements: multilevel bins, periodic rebuild, trimming and Symmetric Multiprocessor (SMP) parallelization. These improvements have led to Central Processing Unit (CPU) reduction of the order of 1:3-1:5 on scalar machines, while also showing excellent scalability up to the point of memory saturation, which on current Intel Xeon processors occurs at approximately 8 cores for double precision and 16 cores for single precision.Publicado en: Mecánica Computacional vol. XXXV, no. 10.Facultad de Ingenierí

Comparative analysis between themaxent and the weighted least square shape functions in acollocation meshless method

En el presente artículo se analiza el comportamiento de la función de forma basada en el principio de máxima entropía (maxent), en el contexto de un método sin malla con un esquema de colocación, comparando su resultado con la función de forma tradicional basada en mínimos cuadrados ponderados fijos (FWLS). La función de forma maxent considerada en el presente trabajo posee ciertas propiedades deseables para formulaciones sin malla basadas en un esquema de colocación, como lo son su positividad, suavidad y aspecto uniforme, para distintos tipos de discretizaciones. Además, en los contornos, la aproximación no depende de las funciones de forma de los nodos interiores del dominio, propiedad que se conoce como reducción de la función de forma sobre el contorno. Para comparar este tipo de funciones se han desarrollado ejemplos que incluyen la resolución de ecuaciones elípticas de segundo orden, en 1D y 2D. Los resultados numéricos muestran un mejor comportamiento de la función de forma maxent en comparación con la de FWLS, en particular en cuanto a la convergencia y estabilidad del método sin malla de colocación resultante.In this article the behavior of a shape function based on the maximum entropy principle (maxent) is analyzed in a meshless collocation method, compared with a traditional fixed weighted least square shape function (FWLS). The maxent shape function used in this work has certain properties that are desired in a meshless collocation method, for example the positivity, the smooth and uniform aspect for different discretizations. Further, in the boundary, the approximation not depends of the shape function of the interior nodes, this property is know as a reduction of the shape function on the boundary. To compare this type of function, it was developed examples that include the solution of eliptical second order equations in 1D and 2D. The numerical results shown a better behavior of the maxent shape function compared with the FWLS, particularly in terms of the convergence and stability of the meshless collocations method that result.Peer Reviewe

A finite point method for elasticity problems

The basis of the finite point method (FPM) for the fully meshless solution of elasticity problems in structural mechanics is described. A stabilization technique based on a finite calculus procedure is used to improve the quality of the numerical solution. The efficiency and accuracy of the stabilized FPM in the meshless analysis of simple linear elastic structural problems is shown in some examples of applications

Adaptividad En El Método Sin Malla De Puntos Finitos

En este trabajo se presentan un estimador del error a posteriori y un proceso de refinamiento adaptivo para el método sin malla de puntos finitos (MPF). El indicador del error se formula a partir de la evaluación del funcional de mínimos cuadrados, utilizado en el cálculo de la función de forma. Nuevos grados de libertad o nodos adicionales pueden ser incorporados sin dificultad en las regiones donde el estimador del error presenta un valor elevado, mediante las técnicas de refinamiento h y p. La validez del estimador del error propuesto se demuestra, mediante el desarrollo de problemas de la mecánica de sólidos y fluidos tanto 2D como 3D, utilizando un proceso de refinamiento adaptivo de la solució

Adaptive methodology for meshless finite point method

In this work, a posteriori error estimator and an adaptive refinement process for the meshless finite point method (FPM), which is based on point collocation, are presented. The error indicator is formulated by the least-squares functional evaluation, used in the shape function development. New degrees of freedom or additional points can be incorporated without difficulty, in zones where the error estimator presents a high value, by means of h–p refinement processes. The validity of the proposed error estimator can be demonstrated by developments of numerical problems in mechanics of solids, using an adaptive refinement process of the solution

A Precision Measurement of the Lambda_c Baryon Mass

The $\Lambda_c^+$ baryon mass is measured using $\Lambda_c^+\to\Lambda K^0_S K^+$ and $\Lambda_c^+\to\Sigma^0 K^0_S K^+$ decays reconstructed in 232 fb$^{-1}$ of data collected with the BaBar detector at the PEP-II asymmetric-energy $e^+e^-$ storage ring. The $\Lambda_c^+$ mass is measured to be $2286.46\pm0.14\mathrm{MeV}/c^2$. The dominant systematic uncertainties arise from the amount of material in the tracking volume and from the magnetic field strength.Comment: 14 pages, 8 postscript figures, submitted to Phys. Rev.