Fluid-structure interaction simulation of prosthetic aortic valves : comparison between immersed boundary and arbitrary Lagrangian-Eulerian techniques for the mesh representation

In recent years the role of FSI (fluid-structure interaction) simulations in the analysis of the fluid-mechanics of heart valves is becoming more and more important, being able to capture the interaction between the blood and both the surrounding biological tissues and the valve itself. When setting up an FSI simulation, several choices have to be made to select the most suitable approach for the case of interest: in particular, to simulate flexible leaflet cardiac valves, the type of discretization of the fluid domain is crucial, which can be described with an ALE (Arbitrary Lagrangian-Eulerian) or an Eulerian formulation. The majority of the reported 3D heart valve FSI simulations are performed with the Eulerian formulation, allowing for large deformations of the domains without compromising the quality of the fluid grid. Nevertheless, it is known that the ALE-FSI approach guarantees more accurate results at the interface between the solid and the fluid. The goal of this paper is to describe the same aortic valve model in the two cases, comparing the performances of an ALE-based FSI solution and an Eulerian-based FSI approach. After a first simplified 2D case, the aortic geometry was considered in a full 3D set-up. The model was kept as similar as possible in the two settings, to better compare the simulations' outcomes. Although for the 2D case the differences were unsubstantial, in our experience the performance of a full 3D ALE-FSI simulation was significantly limited by the technical problems and requirements inherent to the ALE formulation, mainly related to the mesh motion and deformation of the fluid domain. As a secondary outcome of this work, it is important to point out that the choice of the solver also influenced the reliability of the final results

State-of-the-art in aerodynamic shape optimisation methods

Aerodynamic optimisation has become an indispensable component for any aerodynamic design over the past 60 years, with applications to aircraft, cars, trains, bridges, wind turbines, internal pipe flows, and cavities, among others, and is thus relevant in many facets of technology. With advancements in computational power, automated design optimisation procedures have become more competent, however, there is an ambiguity and bias throughout the literature with regards to relative performance of optimisation architectures and employed algorithms. This paper provides a well-balanced critical review of the dominant optimisation approaches that have been integrated with aerodynamic theory for the purpose of shape optimisation. A total of 229 papers, published in more than 120 journals and conference proceedings, have been classified into 6 different optimisation algorithm approaches. The material cited includes some of the most well-established authors and publications in the field of aerodynamic optimisation. This paper aims to eliminate bias toward certain algorithms by analysing the limitations, drawbacks, and the benefits of the most utilised optimisation approaches. This review provides comprehensive but straightforward insight for non-specialists and reference detailing the current state for specialist practitioners

JIGSAW-GEO (1.0): locally orthogonal staggered unstructured grid generation for general circulation modelling on the sphere

An algorithm for the generation of non-uniform, locally-orthogonal staggered unstructured spheroidal grids is described. This technique is designed to generate very high-quality staggered Voronoi/Delaunay meshes appropriate for general circulation modelling on the sphere, including applications to atmospheric simulation, ocean-modelling and numerical weather prediction. Using a recently developed Frontal-Delaunay refinement technique, a method for the construction of high-quality unstructured spheroidal Delaunay triangulations is introduced. A locally-orthogonal polygonal grid, derived from the associated Voronoi diagram, is computed as the staggered dual. It is shown that use of the Frontal-Delaunay refinement technique allows for the generation of very high-quality unstructured triangulations, satisfying a-priori bounds on element size and shape. Grid-quality is further improved through the application of hill-climbing type optimisation techniques. Overall, the algorithm is shown to produce grids with very high element quality and smooth grading characteristics, while imposing relatively low computational expense. A selection of uniform and non-uniform spheroidal grids appropriate for high-resolution, multi-scale general circulation modelling are presented. These grids are shown to satisfy the geometric constraints associated with contemporary unstructured C-grid type finite-volume models, including the Model for Prediction Across Scales (MPAS-O). The use of user-defined mesh-spacing functions to generate smoothly graded, non-uniform grids for multi-resolution type studies is discussed in detail.Comment: Final revisions, as per: Engwirda, D.: JIGSAW-GEO (1.0): locally orthogonal staggered unstructured grid generation for general circulation modelling on the sphere, Geosci. Model Dev., 10, 2117-2140, https://doi.org/10.5194/gmd-10-2117-2017, 201

General Dynamic Scene Reconstruction from Multiple View Video

This paper introduces a general approach to dynamic scene reconstruction from multiple moving cameras without prior knowledge or limiting constraints on the scene structure, appearance, or illumination. Existing techniques for dynamic scene reconstruction from multiple wide-baseline camera views primarily focus on accurate reconstruction in controlled environments, where the cameras are fixed and calibrated and background is known. These approaches are not robust for general dynamic scenes captured with sparse moving cameras. Previous approaches for outdoor dynamic scene reconstruction assume prior knowledge of the static background appearance and structure. The primary contributions of this paper are twofold: an automatic method for initial coarse dynamic scene segmentation and reconstruction without prior knowledge of background appearance or structure; and a general robust approach for joint segmentation refinement and dense reconstruction of dynamic scenes from multiple wide-baseline static or moving cameras. Evaluation is performed on a variety of indoor and outdoor scenes with cluttered backgrounds and multiple dynamic non-rigid objects such as people. Comparison with state-of-the-art approaches demonstrates improved accuracy in both multiple view segmentation and dense reconstruction. The proposed approach also eliminates the requirement for prior knowledge of scene structure and appearance

Proposals for Flashflood Management in Western Argentina: Case Study: The Metropolitan Area of Greater Mendoza

Las cuencas hidrográficas situadas en el oeste del Gran Mendoza (Argentina) son ejemplos típicos de las zonas directa o indirectamente afectadas por inundaciones repentinas. Gran Mendoza está invadiendo zonas con un relieve pronunciado (vertiente oriental de la Precordillera, el piedemonte y otras unidades menores) con fuertes presiones humanas en un entorno frágil. Hoy en día, la parte occidental del Gran Mendoza se cubre con superficies pavimentadas y edificios, poniendo en peligro la ciudad situada aguas abajo. Con el fin de mitigar los efectos negativos del uso y ocupación del piedemonte, un conjunto de medidas estructurales y no estructurales y un modelo de planificación urbana, con nuevas propuestas de desarrollo y arquitectura urbana, se han ideado. Estas medidas implican el control de inundaciones, control de la erosión, la repoblación forestal, la gestión del hábitat, control de las prácticas de extracción (agregados, fauna, vegetación, etc.) y la educación. El nuevo modelo de planificación urbana se basa en la preservación del carácter natural de la tierra y el manejo adecuado de los excedentes de agua (detección de escorrentía en el área de origen, la retención de sistema de drenaje, lo que aumenta la capacidad de drenaje y reducir al mínimo los impactos en entornos de aguas abajo, y la creación de áreas para amortiguar el escurrimiento). Muchas de estas medidas se han desarrollado y demostrado éxito a nivel local.Fil: Vich, Alberto Ismael Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Instituto de Estudios del Ambiente y los Recursos Naturales; ArgentinaFil: López Rodríguez, Mariela Beatriz. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Instituto Cartografía, Investigación y Formación para el Ordenamiento Territorial; ArgentinaFil: Lauro, Carolina. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Instituto de Estudios del Ambiente y los Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Vaccarino Pasquali, Emilce Liliana Belén. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Instituto de Estudios del Ambiente y los Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentin

3D FEM Simulation of shape rolling using an ALE method

The shape rolling of stator vanes has been modelled in 3D using the finite\ud element method. Till now only the rolling of straight vanes, which have a constant cross section, is studied. Therefore this rolling process can be considered as a stationary process. Such processes can be described as a flow problem using the Arbitrary Lagrangian Eulerian (ALE) formulation. This makes it possible to follow free surfaces and to adapt the mesh in order to avoid large element distortions, to keep or create refinements were needed. The mesh topology however remains constant during a simulation. Topics of the ALE formulation such as mesh relocation, transfer of state variables etc. will be addressed in the paper. The tools are modelled as deformable bodies, as tool deformation is the most important reason for the deviation of the vane dimensions from the required dimensions. 3D FEM simulations have been carried out of the rolling of a test vane. Some characteristic results, such as material flow, tool deformations, stresses and strains, will be shown