Construction of polynomial spline spaces over quadtree and octree T-meshes

[EN]We present a new strategy for constructing tensor product spline spaces over quadtree and octree T-meshes. The proposed technique includes some simple rules for inferring local knot vectors to define spline blending functions. These rules allow to obtain for a given T-mesh a set of cubic spline functions that span a space with nice properties: it can reproduce cubic polynomials, the functions are C2-continuous, linearly independent, and spaces spanned by nested T-meshes are also nested. In order to span spaces with these properties applying the proposed rules, the T-mesh should fulfill the only requirement of being a 0-balanced quadtree or octree. ..

A simple strategy for defining polynomial spline spaces over hierarchical T-meses

[EN]We present a new strategy for constructing spline spaces over hierarchical T-meshes with quad- and octree subdivision scheme. The proposed technique includes some simple rules for inferring local knot vectors to define C 2 -continuous cubic tensor product spline blending functions. Our conjecture is that these rules allow to obtain, for a given T-mesh, a set of linearly independent spline functions with the property that spaces spanned by nested T-meshes are also nested, and therefore, the functions can reproduce cubic polynomials. In order to span spaces with these properties applying the proposed rules, the T-mesh should fulfill the only requirement of being a 0- balanced mesh...

High-resolution simulation of stack pollutant emissions

[EN]A three-dimensional air pollution model for the short-term simulation of emission, transport and reaction of pollutants is presented. In the finite element simulation of these environmental processes over a complex terrain, a mesh generator capable of adapting itself to the topographic characteristics is essential, A local refinement of tetrahedra is used in order to capture the plume rise. Then a wind field is computed by using a mass-consistent model and perturbing its vertical component to introduce the plume rise effect. Finally, an Eulerian convection-diffusionreaction model is used to simulate the pollutant dispersion…

Extensión del método del mecano para análisis isogeométrico con T-splines

Congresos y conferencias

Mesh Generation for Isogeometric Analysis with T-spline

[EN]The application of the Isogeometric Analysis (IA) with T-splines [1] demands a partition of the parametric space, C, in a tiling containing T-junctions denominated T-mesh. The T-splines are used both for the geometric modelization of the physical domain, D, and the basis of the numerical approximation. They have the advantage over the NURBS of allowing local refinement. In this work we propose a procedure to construct T-spline representations of complex domains in order to be applied to the resolution of elliptic PDE with IA. In precedent works [2, 3] we accomplished this task by using a tetrahedral parametrization…

Local scale finite element modelling of stack pollutant emissions

Congresos y conferencias

Comparación del método del mecano con otras técnicas convencionales de generación de mallas

Congresos y conferencias

Modelización de sólidos mediante estructura Octree

[EN]En este trabajo presentamos un procedimiento para la modelización de sólidos con geometríacompleja mediante una estructura octree [1]. Partiendo de una triangulación superficial del sólido, se construye una malla de hexaedros que aproxima la geometría con una precisión indicada. Para ello se emplea una división recursiva del espacio con una estructura octree. Inicialmente se lleva a cabo una traslación y escalado de la triangulación al cubo inicial [0,1]3 donde se construye el octree...

Untangling and smoothing of quadrilateral and hexahedral meshes

[EN]In this paper, we extend a simultaneous untangling and smoothing technique previously developed for triangular and tetrahedral meshes to quadrilateral and hexahedral ones. Specifically, we present a technique that iteratively untangles and smooths a given quadrilateral or hexahedral mesh by minimizing an objective function defined in terms of a modification of an algebraic quality measure. The proposed method optimizes the mesh quality by a local node relocation process. That is, without modifying the mesh connectivity. Finally, we present several examples to show that the proposed technique obtains valid meshes composed by high-quality quadrilaterals and hexahedra, even when we start from tangled meshes…

VMWare e tecniche di virtualizzazione: un caso di studio

Il lavoro svolto da Fabrizio Amici ha suscitato immediatamente il mio interesse in primo luogo perché quando si parla di virtualizzazione con vari fornitori e commerciali, questi la indicano come una soluzione che possa coprire a 360 gradi le esigenze di un Datacenter. Questo è vero nella misura in cui il progetto di virtualizzazione e consolidamento dei Server sia svolto sotto certi criteri progettuali. Per esperienza personale non ho trovato in letteratura lavori che potessero fornire indicazioni approfondite sui parametri da considerare per una corretta progettazione di sistemi di virtualizzazione, spesso ci si avvale di vari fornitori che accennano ad eventuali criticità. Un lavoro come quello proposto da Fabrizio va esattamente nella direzione di rispondere a quelle domande che nascono quando si affronta la tematica della virtualizzazione e soprattutto cerca di capire quali siano i limiti intrinseci della virtualizzazione. In particolare nei vari confronti che, con piacere, ho avuto con Fabrizio, il mio suggerimento è stato quello di esasperare il sistema che aveva assemblato, caricando i test sino ad osservarne i limiti. Dai vari test sono emerse sia conferme, sia inaspettati comportamenti del sistema che rendono ancora più chiaro che solo una prova sperimentale può essere il banco di prova di un sistema complesso. L'elemento che colpisce maggiormente analizzando i risultati è il diverso comportamento in funzione delle CPU utilizzate. I risultati indicano chiaramente che le prestazioni sono fortemente influenzate da come si distribuiscono i core nelle macchine virtuali. Dalla lettura dei risultati viene confermato che i sistemi virtualizzati devono essere progettati per non raggiungere il 70-80% della componente più critica (RAM, CPU) ma anche che sono fortemente sensibili alle disponibilità prestazionali dei sistemi al contorno (Rete, SAN/Dischi). L'approccio metodico sperimentale ed i risultati forniscono una serie di elementi che permettono di affrontare la tematica della virtualizzazione in un quadro generale più solido, offrendo fra l'altro spunti di ricerca ulteriori anche in previsione di nuove soluzioni che vari costruttori, sviluppatori e system integrator proporranno nei prossimi anni. Ing. Massimiliano Casali Esperto di Gestione ICT, Pubblica Amministrazione,Repubblica di San Marino

Wind forecasting over complex terrain

[EN]In this paper we introduce a new methodology for wind field forecasting over complex terrain. The idea is to use the predictions of the HARMONIE mesoscale model as the input data for an adaptive finite element mass consistent wind model [1, 2]. A description of the HARMONIE Non-Hydrostatic Dynamics can be found in [3]. The HARMONIE results (obtained with a maximum resolution about 1 Km) are refined in a local scale (about a few meters)...

Advances of the meccano method for isogeometric analysis of irregular planar domains

[EN]We present advances of the meccano method for T-spline modelling and analysis of complex geometries. We consider a planar domain composed by several irregular sub-domains. These sub-regions are defined by their boundaries and can represent different materials. The bivariate T-spline representation of the whole physical domain is constructed from a square. In this procedure, a T-mesh optimization method is crucial. We show results of an elliptic problem by using a quadtree local T-mesh refinement technique…

Adaptive T-spline refinement for isogeometric analysis in planar geometries

[EN]We present a new strategy, based on the meccano method [1, 2, 3], to construct a T-spline parameterization of 2D geometries for the application of isogeometric analysis. The proposed method only demands a boundary representation of the geometry as input data. The algorithm obtains, as a result, high quality parametric transformation between 2D objects and the parametric domain, the unit square. The key of the method lies in defining an isomorphic transformation between the parametric and physical T-mesh finding the optimal position of the interior nodes by applying a new T-mesh untangling and smoothing procedure. Bivariate T-spline representation is calculated by imposing the interpolation conditions on points sited both on the interior and on the boundary of the geometry…

Mesh Generation and Isogeometric Analysis

[EN]We present advances of the meccano method [1,2] for tetrahedral mesh generation and volumetric parameterization of solids. The method combines several former procedures: a mapping from the meccano boundary to the solid surface, a 3-D local refinement algorithm and a simultaneous mesh untangling and smoothing. The key of the method lies in defining a one-to-one volumetric transformation between the parametric and physical domains. Results with adaptive finite elements will be shown for several engineering problems. In addition, the application of the method to T-spline modelling and isogeometric analysis [3,4] of complex geometries will be introduced…