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eWoms hereby declares full independence. Humor aside, the main technical advantage of this is, that it is now possible to easily install both, Dumux and eWoms on a system using a package management system without bad tricks.
94 lines
4.8 KiB
TeX
94 lines
4.8 KiB
TeX
\chapter{Introduction}
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\eWoms~\cite{EWOMS-HP} a generic simulation framework using continuum
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mechanical approaches with a focus on multi-phase fluid flow and
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transport processes in porous media. \eWoms is also an integral part
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of the open porous media initiative~\cite{OPM-HP} for which it
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implements the fully-implicit discretization schemes. \eWoms is based
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on the source code of the \Dumux~\cite{DUMUX-HP} simulation framework
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and aims to be a proper superset of \Dumux when it comes to features,
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while at the same time it delivers better performance and a
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higher-quality code base. To ease porting features from \Dumux to
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\eWoms, the \eWoms source code uses very similar naming and style
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conventions as the one of \Dumux.
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Besides being a generic simulation framework, \eWoms also aims to to
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deliver top-notch computational performance, high flexibility, a sound
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software architecture and the ability to run on anything from single
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processor systems to highly parallel supercomputers with specialized
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hardware architectures. The means to achieve these somewhat
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contradictory goals are the thorough use of object oriented design in
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conjunction with template programming. These requirements motivated
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the decision to implement \eWoms using the \Cplusplus programming
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language.
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One of the more complex issues when dealing with parallel continuum
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models for partial differential equations, is the management of the
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grids used for the spatial discretization. To date, no generic and
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efficient approach exists for all possible cases, which lead to \eWoms
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being build on top of \Dune, the \textbf{D}istributed and
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\textbf{U}nified \textbf{N}umerics
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\textbf{E}nvironment~\cite{DUNE-HP}. Instead of trying to implement a
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grid for everything, \Dune defines a generic \Cplusplus interface to
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grids, and provides adapters to several existing grid management
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libraries such as UG~\cite{UG-HP}, ALBERTA~\cite{ALBERTA-HP} or
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ALUGrid~\cite{ALUGRID-HP}. DUNE also extensively uses template
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programming in order to achieve minimal overhead when accessing the
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underlying grid libraries\footnote{In fact, the performance penalty
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resulting from the use of \Dune's grid interface is usually
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negligible~\cite{BURRI2006}.}.
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\begin{figure}[hbt]
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\centering
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\includegraphics[width=.5\linewidth, keepaspectratio]{EPS/dunedesign}
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\caption{
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\label{fig:dune-design}
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A high-level overview of \Dune's design is available on the project's
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web site~\cite{DUNE-HP}.
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}
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\end{figure}
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DUNE's grid interface is independent of the spatial dimension of the
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underlying grid. For this purpose, it uses the concept of
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co-dimensional entities. Roughly speaking, an entity of co-dimension
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$0$ constitutes a cell, co-dimension $1$ entities are faces between
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cells, co-dimension $1$ are edges, and so on until co-dimension $n$
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which are the cell's vertices. The \Dune grid interface generally
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assumes that all entities are convex polytopes, which means that it
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must be possible to express each entity as the convex hull of a set of
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vertices. For the sake of efficiency, all entities are further expressed in terms
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of so-called reference elements which are transformed to the actual
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spatial incarnation within the grid by a so-called geometry
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function. Here, a reference element for an
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entity can be thought of as a prototype for the actual grid
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entity. For example, if we used a grid which applied hexahedrons as cells,
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the reference element for each cell would be the unit cube $[0, 1]^3$
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and the geometry function would scale and translate the cube so that
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it matches the grid's cell. For a more thorough description of \Dune's
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grid definition, see~\cite{BASTIAN2008}.
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In addition to the grid interface, \Dune also provides quite a few
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additional modules; In the context of this handbook the
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\texttt{dune-localfunctions} and \texttt{dune-istl} modules are
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probably the most relevant. \texttt{dune-localfunctions} provides a
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set of generic finite element shape functions, while
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\texttt{dune-istl} is the \textbf{I}terative \textbf{S}olver
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\textbf{T}emplate \textbf{L}ibrary and provides generic, highly
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optimized linear algebra routines for solving linear systems of
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equations.
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\eWoms comes in form of a module \Dune module '\texttt{ewoms}'. It
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depends on the \Dune core modules \texttt{dune-common},
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\texttt{dune-grid}, \texttt{dune-istl}, and on
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\texttt{dune-localfunctions}. The main intention of \eWoms is to
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provide a framework for an easy and efficient implementation of new
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physical models for porous media flow problems, ranging from problem
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formulation and the selection of spatial and temporal discretization
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schemes as well as nonlinear and linear solvers, to general concepts
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for model coupling. Moreover, \eWoms includes ready-to-use numerical
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models and a few example applications.
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%%% Local Variables:
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%%% mode: latex
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%%% TeX-master: "ewoms-handbook"
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%%% End:
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