# Liquid flow with time dependent boundary conditions and source term

Project file on GitLab

## Motivation

In real world examples the boundary conditions or source terms can vary over time and can be heterogeneous in space. This behaviour can be modelled using the TimeDependentHeterogeneousParameter for boundary conditions or source terms.

## Specification in OGS project file

In the parameter specification section of the project file it is possible to add a parameter type with the type TimedependentHeterogeneousParameter.

<parameter>
<name>ParameterForSourceTerm</name>
<type>TimeDependentHeterogeneousParameter</type>
<time_series>
<pair>
<time>0</time>
<parameter_name>parameter_for_timestep1</parameter_name>
</pair>
<pair>
<time>1</time>
<parameter_name>parameter_for_timestep2</parameter_name>
</pair>
...
<pair>
<time>end_time</time>
<parameter_name>parameter_for_end_time</parameter_name>
</pair>
</time_series>
</parameter>


Of course, the referenced parameters for the particular time steps have to be defined also. Values of the parameter are piecewise linear interpolated.

## Example

This simple example should demonstrate the use of the time depenendent heterogeneous parameter. We start with homogeneous parabolic problem: $$$$s\;\frac{\partial p}{\partial t} + k; \Delta p = q(t,x) \quad \text{in }\Omega$$$$ w.r.t boundary conditions \eqalign{ p(t, x) = g_D(t, x) &\quad \text{on }\Gamma_D,\cr k\;{\partial p(x) \over \partial n} = g_N(x) &\quad \text{on }\Gamma_N, }

The example the domain $\Omega = [0,1]^2$ is a square. On the left ($x=0$) side and the right ($x=1$) side time dependent Dirichlet-type boundary conditions are set. Until half of the simulation time high pressure values are set on the left side and low pressure values on the right side. In the second half of the simulation there are low pressure values on the left side and high pressure values on the right side. Additionally, the source term $q$ acts in the first quarter as a source, in the second quarter as a sink, in the third quarter as a source, and in the last quarter as a sink again.