1,395 research outputs found
Recent Advances in Graph Partitioning
We survey recent trends in practical algorithms for balanced graph
partitioning together with applications and future research directions
Depth map compression via 3D region-based representation
In 3D video, view synthesis is used to create new virtual views between
encoded camera views. Errors in the coding of the depth maps introduce
geometry inconsistencies in synthesized views. In this paper, a new 3D plane
representation of the scene is presented which improves the performance of
current standard video codecs in the view synthesis domain. Two image segmentation
algorithms are proposed for generating a color and depth segmentation.
Using both partitions, depth maps are segmented into regions without
sharp discontinuities without having to explicitly signal all depth edges. The
resulting regions are represented using a planar model in the 3D world scene.
This 3D representation allows an efficient encoding while preserving the 3D
characteristics of the scene. The 3D planes open up the possibility to code
multiview images with a unique representation.Postprint (author's final draft
A novel highly efficient Lagrangian model for massively multidomain simulations: parallel context
A new method for the simulation of evolving multi-domains problems has been
introduced in a previous work (RealIMotion), Florez et al. (2020). In this
article further developments of the model will be presented. The main focus
here is a robust parallel implementation using a distributed-memory approach
with the Message Passing Interface (MPI) library OpenMPI. The original 2D
sequential methodology consists in a modified front-tracking approach where the
main originality is that not only interfaces between domains are discretized
but their interiors are also meshed. The interfaces are tracked based on the
topological degree of each node on the mesh and the remeshing and topological
changes of the domains are driven by selective local operations performed over
an element patch. The accuracy and the performance of the sequential method has
proven very promising in Florez et al. (2020). In this article a parallel
implementation will be discussed and tested in context of motion by curvature
flow for polycrystals, i.e. by considering Grain Growth (GG) mechanism. Results
of the performance of the model are given and comparisons with other approaches
in the literature are discussed
Aspects of Unstructured Grids and Finite-Volume Solvers for the Euler and Navier-Stokes Equations
One of the major achievements in engineering science has been the development of computer algorithms for solving nonlinear differential equations such as the Navier-Stokes equations. In the past, limited computer resources have motivated the development of efficient numerical schemes in computational fluid dynamics (CFD) utilizing structured meshes. The use of structured meshes greatly simplifies the implementation of CFD algorithms on conventional computers. Unstructured grids on the other hand offer an alternative to modeling complex geometries. Unstructured meshes have irregular connectivity and usually contain combinations of triangles, quadrilaterals, tetrahedra, and hexahedra. The generation and use of unstructured grids poses new challenges in CFD. The purpose of this note is to present recent developments in the unstructured grid generation and flow solution technology
Mesoscale modelling of a masonry building subjected to earthquake loading
Masonry structures constitute an important part of the built environment and architectural heritage in seismic areas. A large number of these old structures showed inadequate performance and suffered substantial damage under past earthquakes. Realistic numerical models are required for accurate response predictions and for addressing the implementation of effective strengthening solutions. A comprehensive mesoscale modeling strategy explicitly allowing for masonry bond is presented in this paper. It is based on advanced nonlinear material models for interface elements simulating cracks in mortar joints and brick/block units under cyclic loading. Moreover, domain decomposition and mesh tying techniques are used to enhance computational efficiency in detailed nonlinear simulations. The potential of this approach is shown with reference to a case study of a full-scale unreinforced masonry building previously tested in laboratory under pseudodynamic loading. The results obtained confirm that the proposed modeling strategy for brick/block-masonry structures leads to accurate representations of the seismic response of three-dimensional (3D) building structures, both at the local and global levels. The numerical-experimental comparisons show that this detailed modeling approach enables remarkably accurate predictions of the actual dynamic characteristics, along with the main resisting mechanisms and crack patterns
Layered Fields for Natural Tessellations on Surfaces
Mimicking natural tessellation patterns is a fascinating multi-disciplinary
problem. Geometric methods aiming at reproducing such partitions on surface
meshes are commonly based on the Voronoi model and its variants, and are often
faced with challenging issues such as metric estimation, geometric, topological
complications, and most critically parallelization. In this paper, we introduce
an alternate model which may be of value for resolving these issues. We drop
the assumption that regions need to be separated by lines. Instead, we regard
region boundaries as narrow bands and we model the partition as a set of smooth
functions layered over the surface. Given an initial set of seeds or regions,
the partition emerges as the solution of a time dependent set of partial
differential equations describing concurrently evolving fronts on the surface.
Our solution does not require geodesic estimation, elaborate numerical solvers,
or complicated bookkeeping data structures. The cost per time-iteration is
dominated by the multiplication and addition of two sparse matrices. Extension
of our approach in a Lloyd's algorithm fashion can be easily achieved and the
extraction of the dual mesh can be conveniently preformed in parallel through
matrix algebra. As our approach relies mainly on basic linear algebra kernels,
it lends itself to efficient implementation on modern graphics hardware.Comment: Natural tessellations, surface fields, Voronoi diagrams, Lloyd's
algorith
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