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414 lines
20 KiB
TeX
414 lines
20 KiB
TeX
\section[Fully-coupled model]{Solving a problem using a Fully-Coupled Model}\label{tutorial-coupled}
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The process of solving a problem using \Dumux can be roughly divided into four parts:
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\begin{enumerate}
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\item The geometry of the problem and correspondingly a grid have to be defined.
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\item Material properties and constitutive relationships have to be selected.
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\item Boundary conditions as well as initial conditions have to be defined.
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\item A suitable model has to be chosen.
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\end{enumerate}
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The problem that is solved in this tutorial is illustrated in Figure \ref{tutorial-coupled:problemfigure}. A rectangular domain with no flow boundaries on the top and on the bottom which is initially saturated with oil is considered. Water infiltrates from the left side into the domain. Gravity effects as well as capillarity effects are neglected.
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\begin{figure}[h]
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\psfrag{x}{x}
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\psfrag{y}{y}
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\psfrag{no flow}{no flow}
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\psfrag{water}{\textbf{water}}
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\psfrag{oil}{\textcolor{white}{\textbf{oil}}}
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\psfrag{p_w = 2 x 10^5 [Pa]}{$p_w = 2 \times 10^5$ [Pa]}
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\psfrag{p_w_initial = 2 x 10^5 [Pa]}{\textcolor{white}{\textbf{$\mathbf{p_{w_{initial}} = 2 \times 10^5}$ [Pa]}}}
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\psfrag{S_n = 0}{$S_n = 0$}
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\psfrag{S_n_initial = 0}{\textcolor{white}{$\mathbf{S_{n_{initial}} = 1}$}}
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\psfrag{q_w = 0 [kg/m^2s]}{$q_w = 0$ $\left[\frac{\textnormal{kg}}{\textnormal{m}^2 \textnormal{s}}\right]$}
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\psfrag{q_n = -3 x 10^-4 [kg/m^2s]}{$q_n = -3 \times 10^-4$ $\left[\frac{\textnormal{kg}}{\textnormal{m}^2 \textnormal{s}}\right]$}
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\centering
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\includegraphics[width=0.9\linewidth,keepaspectratio]{EPS/tutorial-problemconfiguration}
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\caption{Geometry of the tutorial problem with initial and boundary conditions.}\label{tutorial-coupled:problemfigure}
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\end{figure}
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The equations that are solved here are the mass balances of oil and
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water:
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\begin{align}
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\label{massbalancewater}
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\frac {\partial (\phi \, S_{w}\, \varrho_{w})}{\partial t}
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+
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\nabla \cdot \left( \varrho_{w} \, \frac{k_{rw}}{\mu_{w}} \, \mathbf{K}\;\nabla p \right)
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-
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q
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& =
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0 \\
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\label{massbalanceoil}
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\frac {\partial (\phi \, S_{o}\, \varrho_{o})}{\partial t}
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+
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\nabla \cdot \left( \varrho_{o} \, \frac{k_{ro}}{\mu_{o}} \, \mathbf{K}\;\nabla p \right)
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-
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q
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& =
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0
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\end{align}
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\subsection{The main file}
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Listing \ref{tutorial-coupled:mainfile} shows the main file
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\texttt{tutorial/tutorial\_coupled.cc} for the coupled two-phase
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model. This file needs to be executed to solve the problem described
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above.
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\begin{lst}[File tutorial/tutorial\_coupled.cc]\label{tutorial-coupled:mainfile} \mbox{}
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\lstinputlisting[basicstyle=\ttfamily\scriptsize,numbers=left,
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numberstyle=\tiny, numbersep=5pt, firstline=18]{../../tutorial/tutorial_coupled.cc}
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\end{lst}
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From line \ref{tutorial-coupled:include-begin} to line
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\ref{tutorial-coupled:include-end} the Dune and \Dumux files which
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contain the needed functions and classes are included.
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At line \ref{tutorial-coupled:set-type-tag} the type tag of the
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problem which is going to be simulated is set. All other data types
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can be retrieved by the \Dumux property system and only depend on this
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single type tag. Retrieving them is done between line
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\ref{tutorial-coupled:retrieve-types-begin} and
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\ref{tutorial-coupled:retrieve-types-end}. For an introduction to the
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property system, see section \ref{sec:propertysytem}.
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The first thing which should be done at run time is to initialize the
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message passing interface using DUNE's \texttt{MPIHelper} class. Line
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\ref{tutorial-coupled:init-mpi} is essential if the simulation is
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intended to be run on more than one processor at the same time. Next,
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the command line arguments are parsed starting at line
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\ref{tutorial-coupled:parse-args-begin} until line
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\ref{tutorial-coupled:parse-args-end}. In this example, it is checked if and
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from which time on a previous run of the simulation should be restarted. Furthermore, we
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parse the time when the simulation ends and the initial time step size.
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After this, a grid is created in line
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\ref{tutorial-coupled:create-grid} and the problem is instantiated for
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its leaf grid view in line \ref{tutorial-coupled:instantiate-problem}.
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Finally, on line \ref{tutorial-coupled:restart} a state written to
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disk by a previous simulation run is restored if requested by the user.
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The simulation procedure is started at line
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\ref{tutorial-coupled:execute}.
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\subsection{The problem class}
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When solving a problem using \Dumux, the most important file is the
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so-called \textit{problem file} as shown in listing
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\ref{tutorial-coupled:problemfile} of
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\texttt{tutorialproblem\_coupled.hh}.
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\begin{lst}[File tutorial/tutorialproblem\_coupled.hh]\label{tutorial-coupled:problemfile} \mbox{}
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\lstinputlisting[basicstyle=\ttfamily\scriptsize,numbers=left,
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numberstyle=\tiny, numbersep=5pt, firstline=17]{../../tutorial/tutorialproblem_coupled.hh}
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\end{lst}
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First, a new type tag is created for the problem in line
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\ref{tutorial-coupled:create-type-tag}. In this case, the new type
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tag inherits all properties defined for the \texttt{BoxTwoP} type tag,
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which means that for this problem the two-phase box model is chosen as
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discretization scheme. On line \ref{tutorial-coupled:set-problem}, a
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problem class is attached to the new type tag, while the grid which
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is going to be used is defined in line \ref{tutorial-coupled:set-grid} --
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in this case it's \texttt{SGrid}. Since there's no uniform
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mechanism to allocate grids in \Dune, the \texttt{Grid} property also contains
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a static \texttt{create()} method which provides just that. Next,
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the appropriate fluid system, that specifies both information about
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the fluid mixture as well as about the pure substances, has to be chosen
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in line \ref{tutorial-coupled:set-fluidsystem}. For all parameters that
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depend on space, such as the properties of the soil, the specific spatial
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parameters for the problem of interest are specified in line
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\ref{tutorial-coupled:set-spatialparameters}. The final property on line line
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\ref{tutorial-coupled:gravity} is optional and tells the model not to
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use gravity.
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Parameters which are specific to a set-up -- like boundary and initial
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conditions, source terms or temperature within the domain -- but are
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required to solve the differential equations of the models are
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specified via a \textit{problem} class. If the two-phase box model is
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used, this class must be derived from \texttt{TwoPBoxProblem} as done
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on line \ref{tutorial-coupled:def-problem}.
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The problem class always has at least five methods:
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\begin{itemize}
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\item A method \texttt{boundaryTypes()} specifying the kind of
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boundary conditions to be used for a boundary segment
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\item A method \texttt{dirichlet()} specifying the actual values for
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the Dirichlet conditions on a boundary segment
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\item A method \texttt{neumann()} specifying the actual values for
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the Neumann conditions on a boundary segment
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\item A method for source or sink terms called \texttt{source()}
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\item A method called \texttt{initial()} for specifying the initial
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condition.
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\end{itemize}
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Methods which make statements about boundary segments of the grid (i.e.
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\texttt{boundaryTypes()}, \texttt{dirichlet()} and \texttt{neumann()}) get
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six parameters. The first parameter differs if the type of the boundary condition
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is defined \texttt{boundaryTypes()}:
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\begin{description}
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\item[BCtypes:] A container which stores the type of the boundary condition
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for each equation. For the typical case where all equations have the same boundary
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condition at a certain position, there are two methods that set the appropriate conditions
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for all primary variables / equations: Either \texttt{setAllDirichlet()} or \texttt{setAllNeumann()}.
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\item[element:] The element of the grid where the boundary segment
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is located.
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\item[fvElemGeometry:] The finite-volume geometry induced on the
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finite element by the box scheme.
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\item[isIt:] The \texttt{IntersectionIterator} of the boundary
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segement as given by the grid
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\item[scvIdx:] The index of the sub-control volume in
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\texttt{fvElementGeometry} adjacent to the boundary segment.
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\item[boundaryFaceIdx:] The index of the boundary face in
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\texttt{fvElementGeometry} which represents the boundary segment.
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\end{description}
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After the type of the boundary condition is defined, their values have to be
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assigned with the methods \texttt{dirichlet()} and \texttt{neumann()} which only differ
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by the first function parameter:
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\begin{description}
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\item[values:] A vector which stores the result of the method. What
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the values in this vector means is dependent on the method: For
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\texttt{dirichlet()} it contains the values of the primary
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variables, for \texttt{neumann()} the mass fluxes per area unit
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over the boundary segment.
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\end{description}
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Similarly, the \texttt{initial()} and \texttt{source()} methods
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specify properties of sub-control volumes and thus only get
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\texttt{values}, \texttt{element}, \texttt{fvElemGeom} and
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\texttt{scvIdx} as parameters.
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In addition to these five methods, there might be some model-specific
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methods. If the isothermal two-phase model is used, this includes
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for example a \texttt{temperature()} method which returns the temperature in Kelvin
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of the fluids and the rock matrix in the domain. This temperature is
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then used by the model to calculate fluid properties which possibly
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depend on it, e.g. density.
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\subsection{Defining fluid properties}\label{tutorial-coupled:description-fluid-class}
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The \Dumux distribution includes some common substances which can be used
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out of the box. The properties of the pure substances (such as the component
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nitrogen, water, or pseudo-component air) are stored in header files in
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the folder \verb+dumux/material/components+. Each of these files
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defines a class with the same name as the component but starting with a capital
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letter, e.g. \texttt{Water}, and are derived from \texttt{Component}.
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Most often, when two or more components are considered, fluid interactions
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such as solubility effects come into play and properties of mixtures such as
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the density are of interest. These interactions are defined in
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a specific \verb+fluidsystem+ in the folder \verb+dumux/material/fluidsystems+.
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It features methods returning fluid properties like density, enthalpy, viscosity,
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etc. by accessing the pure components as well as binary coefficients such as
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Henry or diffusion coefficients, which are stored in
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\verb+dumux/material/binarycoefficients+. New fluids which are not yet
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available in the \Dumux distribution can be defined analogously.
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% In this example, a class for the definition of a two-phase system is used. This allows the choice
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% of the two components oil and water and to access the parameters that are relevant for the two-phase model.
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\subsection{The definition of the parameters that are dependent on space}\label{tutorial-coupled:description-spatialParameters}
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In \Dumux, the properties of the porous medium such as \textit{intrinsic
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permeability}, the \textit{porosity}, the \textit{heat capacity} as
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well as the \textit{heat conductivity} can be defined in space using a
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so-called \texttt{spatial parameters} class. However, because the soil
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also has an effect on the material laws of the fluids (e.g. \textit{capillarity}),
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their selection and definition of their attributes (e.g. \textit{residual
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saturations}) are also accomplished in the spatial parameters.
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The base class \texttt{Dumux::BoxSpatialParameters<TypeTag>} holds a general
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averaging procedure for vertex-centered box-methods.
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Listing \ref{tutorial-coupled:spatialparametersfile} shows the file
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\verb+tutorialspatialparameters_coupled.hh+:
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\begin{lst}[File tutorial/tutorialspatialparameters\_coupled.hh]\label{tutorial-coupled:spatialparametersfile} \mbox{}
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\lstinputlisting[basicstyle=\ttfamily\scriptsize,numbers=left,
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numberstyle=\tiny, numbersep=5pt, firstline=16]{../../tutorial/tutorialspatialparameters_coupled.hh}
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\end{lst}
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First, a certain material law that best describes the problem at hand has to
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be selected in line \ref{tutorial-coupled:rawlaw}\label{tutorial-coupled:materialLaw}.
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\Dumux provides several material laws in the folder
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\verb+dumux/material/fluidmatrixinteractions+.
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The selected one, here it is a simple linear relation, is included
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in line \ref{tutorial-coupled:rawLawInclude}. After the selection,
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an adapter in line \ref{tutorial-coupled:eff2abs} translates the raw
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law to effective values (residual saturations are considered). As the
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applied raw law knows best which kind of parameters are necessary,
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it provides a parameter class \texttt{LinearMaterialParams} that is
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accessible via the member \texttt{Params} and defined in line
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\ref{tutorial-coupled:matLawObjectType}. The material law object
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could now be instantiated correctly as a private object
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in line \ref{tutorial-coupled:matParamsObject}.
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In line \ref{tutorial-coupled:permeability} the function returning the
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intrinsic permeability can be found. As can be seen, the function has
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to be called with three different arguments.
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(\texttt{Element}) is again the current element, which also holds information
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about its geometry and position, the second argument
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(\texttt{fvElemGeom}) holds information about the finite-volume geometry induced
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by the box-method, and the third defines the index of the current sub-control
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volume. The intrinsic permeability is a tensor and is thus returned in form of
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a $\texttt{dim} \times \texttt{dim}$-matrix where \texttt{dim} is the dimension
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of the problem.\\
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The function \texttt{porosity()} defined in line
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\ref{tutorial-coupled:porosity} is called with the same arguments as
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the permeability function described before and returns the porosity
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dependent on the position in the domain.\\
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Next, the method \texttt{materialLawParams()} defines in line
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\ref{tutorial-coupled:matLawParams} which object of a considered
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material law should be applied at this specific position.
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While the selection of the type of this object was already explained (see
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\ref{tutorial-coupled:materialLaw}), some specific parameter
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values of the applied material law are still needed. This is
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done in the constructor body (line \ref{tutorial-coupled:setLawParams}).
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Depending on the type of the \texttt{materialLaw} object, the adequate \texttt{set}-methods
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are provided by the object to access all necessary parameters
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for the applied material law.
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\subsection{Exercises}
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\label{tutorial-coupled:exercises}
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The following exercises will give you the opportunity to learn how you
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can change soil parameters, boundary conditions and fluid properties
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in \Dumux. For each exercise you can find the output file of the last
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timestep in the directory \texttt{tutorial/results/coupled}.
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\subsubsection{Exercise 1}
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\renewcommand{\labelenumi}{\alph{enumi})} For Exercise 1 you only have
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to make some small changes in the tutorial files. To get an
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impression what the results should look like you can first run the
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original version of the fully-coupled tutorial model by typing
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\texttt{./tutorial\_coupled}. For the visualisation with paraview
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please refer to \ref{quick-start-guide}.
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\begin{enumerate}
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\item \textbf{Changing the Model Domain and the Boundary Conditions} \\
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Change the size of the model domain so that you get a rectangle with
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edge lengths of $\text{x} = 400 m$ and $\text{y} = 500 m$ and with
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discretization lengths of $\Delta \text{x} = 20$ m and $\Delta
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\text{y} = 20$ m.
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Change the boundary conditions in the file
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\texttt{tutorialproblem\_coupled.hh} so that water enters from the
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bottom and oil is extracted from the top boundary. The right and the
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left boundary should be closed for water and oil fluxes.
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Compile the main file by typing \texttt{make tutorial\_coupled} and
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run the model.
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\item \textbf{Changing Fluids} \\
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Now you can change the fluids. Use \texttt{Carbon dioxide} instead of
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\texttt{Nitrogen} and \texttt{Brine} instead of \texttt{Water}. To do
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that you have to change the problem file
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\texttt{tutorialproblem\_coupled.hh} and choose another \texttt{fluid system}.
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If you want to take a closer look how the fluid systems are defined
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and which fluids are already available please look into the folder \verb+dumux/material/fluidsystems/+
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for an example.
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\item \textbf{Changing Constitutive Relations} \\
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Use a regularized Brooks-Corey law with $\lambda = 2$ and entry pressure $p_e =
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0.0$ instead of using an unregularized linear law for the
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relative-permeability saturation relationship. To do that you have
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to change the file \texttt{tutorialspatialparameters\_coupled.hh}.
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You can find the material laws in the folder
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\verb+dumux/material/fluidmatrixinteractions+. The necessary parameters
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of the Brooks-Corey law and the respective \texttt{set}-functions can be found
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in the file \verb+dumux/material/fluidmatrixinteractions/2p/brookscoreyparams.hh+.
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\item \textbf{Heterogeneities} \\
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Set up a model domain with the soil properties given in Figure
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\ref{tutorial-coupled:exercise1_d}. Adjust the boundary conditions
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so that water is still flowing from the bottom to the top of the
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domain. You can use the fluids of exercise 1b) and the constitutive
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relationship of exercise 1c).
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\begin{figure}[h]
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\psfrag{K1 =}{K $= 10^{-8}\text{ m}^2$}
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\psfrag{phi1 =}{$\phi = 0.15$}
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\psfrag{K2 =}{\textcolor{white}{K $= 10^{-9}\text{ m}^2$}}
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\psfrag{phi2 =}{\textcolor{white}{$\phi = 0.3$}}
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\psfrag{600 m}{600 m}
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\psfrag{300 m}{300 m}
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\centering
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\includegraphics[width=0.5\linewidth,keepaspectratio]{EPS/exercise1_c.eps}
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\caption{Exercise 1d: Set-up of a model domain with a heterogeneity. $\Delta \text{x} = 20$ m $\Delta \text{y} = 20$ m.}\label{tutorial-coupled:exercise1_d}
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\end{figure}
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\end{enumerate}
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\subsubsection{Exercise 2}
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For this exercise you should create a new proplem file analogous to
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the file \texttt{tutorialproblem\_coupled.hh} and new spatial parameters
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just like \texttt{tutorialspatialparameters\_coupled.hh}. The new problem file needs to
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be included in the file \texttt{tutorial\_coupled.cc}.
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The new file defining spatial parameters should contain the definition
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of a new class, such as \texttt{SpatialParametersEx2}. Make sure that you also adjust the guardian
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macros in the header files (e.g. change \texttt{TUTORIALSPATIALPARAMETERS\_COUPLED} to
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\texttt{SPATIALPARAMETERSEX2}). Besides also adjusting the guardian macros,
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the new problem file should define and use a new type tag for the problem as well as a new problem class
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e.g. \texttt{ProblemEx2}. Make sure you assign your newly defined spatial
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parameter class to the \texttt{SpatialParameters} property for the new
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type tag.
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After this, change the \texttt{create()} method of the \texttt{Grid}
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property so that it matches the domain described
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by figure \ref{tutorial-coupled:ex2_Domain}. Adapt the problem class
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so that the boundary conditions are consistent with figure
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\ref{tutorial-coupled:ex2_BC}. Initially the domain is fully saturated
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with water and the pressure is $p_w = 5 \times 10^5 \text{Pa}$ . Oil
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infiltrates from the left side. Create a grid with $20$ cells in
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$x$-direction and $10$ cells in $y$-direction. The simulation time
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should be set to $4\times 10^7 \text{s}$ with an initial time step size of
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$100 \text{s}$.
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Now include your new problem file in the main file and replace the
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\texttt{TutorialProblemCoupled} type tag by the one you've created and
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compile the program.
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\begin{figure}[h]
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\psfrag{K1}{K $= 10^{-7}\text{ m}^2$}
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\psfrag{phi1}{$\phi = 0.2$}
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\psfrag{Lin}{Linear Law}
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\psfrag{K2}{K $= 10^{-9}\text{ m}^2$}
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\psfrag{phi2}{$\phi = 0.15$}
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\psfrag{BC1}{Brooks Corey Law}
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\psfrag{BC2}{$\lambda = 1.8$, $p_b = 0.0$}
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\psfrag{H1y}{50 m}
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\psfrag{H2y}{15 m}
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\psfrag{H3y}{20 m}
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\psfrag{L1x}{100 m}
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\psfrag{L2x}{50 m}
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\psfrag{L3x}{25 m}
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\centering
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\includegraphics[width=0.8\linewidth,keepaspectratio]{EPS/Ex2_Domain.eps}
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\caption{Set-up of the model domain and the soil parameters}\label{tutorial-coupled:ex2_Domain}
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\end{figure}
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\begin{figure}[h]
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\psfrag{pw}{$p_w = 5 \times 10^5$ \text{Pa}}
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\psfrag{S}{$S_n = 1.0$}
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\psfrag{qw}{$q_w = 2 \times 10^{-4}$ [kg/$\text{m}^2$s]}
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\psfrag{qo}{$q_n = 0.0$ [kg/$\text{m}^2$s]}
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\psfrag{no flow}{no flow}
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\centering
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\includegraphics[width=0.8\linewidth,keepaspectratio]{EPS/Ex2_Boundary.eps}
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\caption{Boundary Conditions}\label{tutorial-coupled:ex2_BC}
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\end{figure}
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\subsubsection{Exercise 3}
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Create a new file for benzene called \texttt{benzene.hh} and implement
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a new fluid system. (You may get a hint by looking at existing fluid
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systems in the directory \verb+/dumux/material/fluidsystems+.)
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Use benzene as a new fluid and run the model of Exercise 2 with water
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and benzene. Benzene has a density of $889.51 \, \text{kg} / \text{m}^3$
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and a viscosity of $0.00112 \, \text{Pa} \; \text{s}$.
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|