54,247 research outputs found
Construction of a -adaptive continuous Residual Distribution scheme
A \textit{p}-adaptive continuous Residual Distribution scheme is proposed in this paper.Under certain conditions, primarily the expression of the total residual on a given element into residuals on the sub-elements of and the use of a suitable combination of quadrature formulas,it is possible to change locally the degree of the polynomial approximation of the solution.The discrete solution can then be considered non continuous across the interface of elements of different orders, while the numerical scheme still verifies the hypothesis of the discrete Lax-Wendroff theorem which ensures its convergenceto a correct weak solution.We detail the theoretical material and the construction of our \textit{p}-adaptive method in the frame of a continuous Residual Distribution scheme. Different test cases for non-linear equations at different flow velocities demonstrate numerically the validity of the theoretical results
A posteriori modeling error estimates in the optimization of two-scale elastic composite materials
The a posteriori analysis of the discretization error and the modeling error
is studied for a compliance cost functional in the context of the optimization
of composite elastic materials and a two-scale linearized elasticity model. A
mechanically simple, parametrized microscopic supporting structure is chosen
and the parameters describing the structure are determined minimizing the
compliance objective. An a posteriori error estimate is derived which includes
the modeling error caused by the replacement of a nested laminate
microstructure by this considerably simpler microstructure. Indeed, nested
laminates are known to realize the minimal compliance and provide a benchmark
for the quality of the microstructures. To estimate the local difference in the
compliance functional the dual weighted residual approach is used. Different
numerical experiments show that the resulting adaptive scheme leads to simple
parametrized microscopic supporting structures that can compete with the
optimal nested laminate construction. The derived a posteriori error indicators
allow to verify that the suggested simplified microstructures achieve the
optimal value of the compliance up to a few percent. Furthermore, it is shown
how discretization error and modeling error can be balanced by choosing an
optimal level of grid refinement. Our two scale results with a single scale
microstructure can provide guidance towards the design of a producible
macroscopic fine scale pattern
An adaptive GMsFEM for high-contrast flow problems
In this paper, we derive an a-posteriori error indicator for the Generalized
Multiscale Finite Element Method (GMsFEM) framework. This error indicator is
further used to develop an adaptive enrichment algorithm for the linear
elliptic equation with multiscale high-contrast coefficients. The GMsFEM, which
has recently been introduced in [12], allows solving multiscale
parameter-dependent problems at a reduced computational cost by constructing a
reduced-order representation of the solution on a coarse grid. The main idea of
the method consists of (1) the construction of snapshot space, (2) the
construction of the offline space, and (3) the construction of the online space
(the latter for parameter-dependent problems). In [12], it was shown that the
GMsFEM provides a flexible tool to solve multiscale problems with a complex
input space by generating appropriate snapshot, offline, and online spaces. In
this paper, we study an adaptive enrichment procedure and derive an
a-posteriori error indicator which gives an estimate of the local error over
coarse grid regions. We consider two kinds of error indicators where one is
based on the -norm of the local residual and the other is based on the
weighted -norm of the local residual where the weight is related to the
coefficient of the elliptic equation. We show that the use of weighted
-norm residual gives a more robust error indicator which works well for
cases with high contrast media. The convergence analysis of the method is
given. In our analysis, we do not consider the error due to the fine-grid
discretization of local problems and only study the errors due to the
enrichment. Numerical results are presented that demonstrate the robustness of
the proposed error indicators.Comment: 26 page
A Direct Multigrid Poisson Solver for Oct-Tree Adaptive Meshes
We describe a finite-volume method for solving the Poisson equation on
oct-tree adaptive meshes using direct solvers for individual mesh blocks. The
method is a modified version of the method presented by Huang and Greengard
(2000), which works with finite-difference meshes and does not allow for shared
boundaries between refined patches. Our algorithm is implemented within the
FLASH code framework and makes use of the PARAMESH library, permitting
efficient use of parallel computers. We describe the algorithm and present test
results that demonstrate its accuracy.Comment: 10 pages, 6 figures, accepted by the Astrophysical Journal; minor
revisions in response to referee's comments; added char
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