2,252 research outputs found
Sample sort on meshes
This paper provides an overview of lower and upper bounds for mesh-connected processor networks. Most attention goes to routing and sorting problems, but other problems are mentioned as well. Results from 1977 to 1995 are covered. We provide numerous results, references and open problems. The text is completed with an index. This is a worked-out version of the author's contribution to a joint paper with Grammatikakis, Hsu and Kraetzl on multicomputer routing, submitted to JPDC
Implicit solvers for unstructured meshes
Implicit methods were developed and tested for unstructured mesh computations. The approximate system which arises from the Newton linearization of the nonlinear evolution operator is solved by using the preconditioned GMRES (Generalized Minimum Residual) technique. Three different preconditioners were studied, namely, the incomplete LU factorization (ILU), block diagonal factorization, and the symmetric successive over relaxation (SSOR). The preconditioners were optimized to have good vectorization properties. SSOR and ILU were also studied as iterative schemes. The various methods are compared over a wide range of problems. Ordering of the unknowns, which affects the convergence of these sparse matrix iterative methods, is also studied. Results are presented for inviscid and turbulent viscous calculations on single and multielement airfoil configurations using globally and adaptively generated meshes
Mesh Connected Computers With Multiple Fixed Buses: Packet Routing, Sorting and Selection
Mesh connected computers have become attractive models of computing because of their varied special features. In this paper we consider two variations of the mesh model: 1) a mesh with fixed buses, and 2) a mesh with reconfigurable buses. Both these models have been the subject matter of extensive previous research. We solve numerous important problems related to packet routing, sorting, and selection on these models. In particular, we provide lower bounds and very nearly matching upper bounds for the following problems on both these models: 1) Routing on a linear array; and 2) k-k routing, k-k sorting, and cut through routing on a 2D mesh for any k ≥ 12. We provide an improved algorithm for 1-1 routing and a matching sorting algorithm. In addition we present greedy algorithms for 1-1 routing, k-k routing, cut through routing, and k-k sorting that are better on average and supply matching lower bounds. We also show that sorting can be performed in logarithmic time on a mesh with fixed buses. As a consequence we present an optimal randomized selection algorithm. In addition we provide a selection algorithm for the mesh with reconfigurable buses whose time bound is significantly better than the existing ones. Our algorithms have considerably better time bounds than many existing best known algorithms
Suppression of von K\'arm\'an vortex streets past porous rectangular cylinders
Although the stability properties of the wake past impervious bluff bodies
have been widely examined in the literature, similar analyses regarding the
flow around and through porous ones are still lacking. In this work, the effect
of the porosity and permeability on the wake patterns of porous rectangular
cylinders is numerically investigated at low to moderate Reynolds numbers in
the framework of direct numerical simulation combined with local and global
stability analyses. A modified Darcy-Brinkman formulation is employed here so
as to describe the flow behavior inside the porous media, where also the
convective terms are retained to correctly account for the inertial effects at
high values of permeability. Different aspect ratios of the cylinder are
considered, varying the thickness-to-height ratios, t/d, from 0.01 (flat plate)
to 1.0 (square cylinder). The results show that the permeability of the bodies
has a strong effect in modifying the characteristics of the wakes and of the
associated flow instabilities, while the porosity weakly affects the resulting
flow patterns. In particular, the fluid flows through the porous bodies and,
thus, as the permeability is progressively increased, the recirculation
regions, initially attached to the rear part of the bodies, at first detach
from the body and, eventually, disappear even in the near wakes. Global
stability analyses lead to the identification of critical values of the
permeability above which any linear instability is prevented. Moreover, a
different scaling of the non-dimensional permeability allows to identify a
general threshold for all the configurations here studied that ensures the
suppression of vortex shedding, at least in the considered parameter space.Comment: 31 pages and 17 figure
Implicit solutions with consistent additive and multiplicative components
Use of multiple-point-constraint
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