Diffeomorphism-invariant properties for quasi-linear elliptic operators

For quasi-linear elliptic equations we detect relevant properties which remain invariant under the action of a suitable class of diffeomorphisms. This yields a connection between existence theories for equations with degenerate and non-degenerate coerciveness.Comment: 16 page

A second order scheme for a Robin boundary condition in random walk algorithms

Random Walk (RW) is a common numerical tool for modeling the Advection-Diffusion equation. In this work, we develop a second order scheme for incorporating a heterogeneous reaction (i.e., a Robin boundary condition) in the RW model. In addition, we apply the approach in two test cases. We compare the second order scheme with the first order one as well as with analytical and other numerical solution. We show that the new scheme can reduce the computational error significantly, relative to the first order scheme. This reduction comes at no additional computational cost

Computational analysis of transport in three-dimensional heterogeneous materials: An OpenFOAM®-based simulation framework

Porous and heterogeneous materials are found in many applications from composites, membranes, chemical reactors, and other engineered materials to biological matter and natural subsurface structures. In this work we propose an integrated approach to generate, study and upscale transport equations in random and periodic porous structures. The geometry generation is based on random algorithms or ballistic deposition. In particular, a new algorithm is proposed to generate random packings of ellipsoids with random orientation and tunable porosity and connectivity. The porous structure is then meshed using locally refined Cartesian-based or unstructured strategies. Transport equations are thus solved in a finite-volume formulation with quasi-periodic boundary conditions to simplify the upscaling problem by solving simple closure problems consistent with the classical theory of homogenisation for linear advection–diffusion–reaction operators. Existing simulation codes are extended with novel developments and integrated to produce a fully open-source simulation pipeline. A showcase of a few interesting three-dimensional applications of these computational approaches is then presented. Firstly, convergence properties and the transport and dispersion properties of a periodic arrangement of spheres are studied. Then, heat transfer problems are considered in a pipe with layers of deposited particles of different heights, and in heterogeneous anisotropic materials

Ocorrência do besouro tigre Neotropical, Cylindera suturalis helvaea (W. Horn, 1903) (Coleoptera, Cicindelidae), em bancos de areia do Reservatório da Barragem da Pedra, Rio de Contas, Bahia, Brasil

The occurrence of the tiger beetle Cylindera (Plectographa) suturalis helvaea (W. Horn, 1903) in sandbanks of Reservoir Barragem da Pedra, Bahia, Brazil, is registered. Adult beetles were collected using entomological nets on sandbanks between May and September 2003. Cicindelids are one of the most conspicuous groups among invertebrates. That is why thay are well suited for bioindication of biodiversity as well as of disturbance and modification in terrestrial ecosystems.Neste estudo é registrada a ocorrência do besouro tigre Cylindera (Plectographa) suturalis helvaea (W. Horn, 1903) em bancos de areia no Reservatório da Barragem da Pedra, Bahia, Brasil. Indivíduos adultos foram coletados utilizando-se de redes entomológicas, entre os meses de Maio e Setembro de 2003. Cicindelídeos são um dos mais conspícuos grupos de invertebrados, sendo considerados como bons indicadores de biodiversidade assim como de distúrbios e modificações nos ecossistemas terrestres

SIMULATION OF FLOW AND PARTICLE TRANSPORT AND DEPOSITION IN POROUS MEDIA WITH COMPUTATIONAL FLUID DYNAMICS

The simulation of transport and deposition of colloidal particles in porous media finds important applications in many engineering and environmental problems, such as particle filtration, catalytic processes carried out in filter beds, chromatographic separation and aquifer remediation. This study focuses in particular on remediation of contaminated groundwater via direct injection of nano-sized zerovalent iron particles, which have been shown to be able to efficiently degrade a large variety of contaminants. Application of this technology on full scale applications poses a number of challenges, the most important of which regards the mobility of the particles and their delivery to the contaminated site in the soil. Particles migration is usually quantitatively expressed by a single parameter: the deposition efficiency in the porous bed, whose theoretical reference lies in the classical colloid filtration theory, which moreover further subdivides the process of deposition in the three mechanisms by which particles can reach the solid grain: Brownian diffusion, steric interception, and gravitational sedimentation. This theory, however, has been developed only for very simple geometrical representations of the porous media and a narrow range of fluid conditions. The difficulties in investigating this kind of systems from the experimental point of view have prevented the development of accurate models able to account for the high degree of complexity which characterizes a porous medium, both in the grain arrangement and in their shape. The aim of this study is therefore to simulate the transport of the nanoparticles and their interaction with the porous media (at the microscopic scale), in order to improve the current understanding of these phenomena and obtain predictive models for the deposition efficiency of the colloids on the surface of the grains constituting the porous medium; moreover, eventually, to evaluate the effectiveness of the zerovalent iron technology. Several two and three dimensional microscale (the order of millimiters) representations of grain packings with different degrees of complexity were analyzed. First, two dimensional random arrangements of spheres were considered. Then, the analysis was extended to domains reconstructed from SEM images of a real porous medium. The work was then expanded in three dimensions, first considering simplified domains constituted by irregular packings of spheres, and finally geometries constituted by grains of realistic shapes. These last geometries were created using an algorithm simulating the grain sedimentation process in porous media (Settledyn). Flow field and particle transport was then investigated using finite volume CFD codes (Fluent and OpenFoam), solving the Navier-Stokes equations for the flow and using an Eulerian approach for the colloid transport, eventually obtaining, for each case, an estimate of the colloidal transport efficiency. After having validated the methodology used in this work by comparing our results with proved analytical results available for simplified cases, new predictive equations for each of the individual contributions of the three deposition mechanisms were derived, highlighting the differences from the theoretical model due to the wider range of operating conditions investigated and/or the different geometrical characteristics of the porous media

Aerial LiDAR Technology in Support to Avalanches Prevention and Risk Mitigation: AN Operative Application at "colle della Maddalena" (italy)

Abstract. Snow avalanches are the result of unstable snow masses that detach from steep slopes as consequence of changes in snowpack structure. Nowadays, remote sensing technologies can improve the knowledge of avalanches phenomenon. This work focuses on the use of high point density aerial LiDAR (Light Detection And Ranging) technology as support to avalanche events prevention and risk mitigation, by presenting an operative application at Colle della Maddalena (Italy), along the road SS n. 21, nearby the French state border. The area is often involved in intense avalanche events that adversely impact on traffic and freight transport. For this reason, regional administrations will activate the Avalanche Artificial Detachment Intervention Plan (PIDAV, 2012) in order to prevent and manage the avalanche risk in the study area, also adopting artificial detachment systems. Main aim of the present work was to generate high resolution information related to geomorphological characterization (i.e. digital elevation models, slope and aspect) of avalanche sites derived from LiDAR data processing, that will help involved authorities in the management of the avalanche control plan. Digital elevation models at 0.5 m of spatial resolution were generated together with relative tridimensional models. Secondly, a preliminary investigation about capabilities and limits of LiDAR technology was done in the identification of avalanche sites only relying on geomorphological information directly derived by LiDAR data processing. Results showed that position of avalanche sites were correctly identified while no information could be obtained about the extension of the sliding area and identification of detachment areas