 <OpenGeoSysProject>

   <meshes>

     <mesh>square_1x1_quad8_1e2.vtu</mesh>

     <mesh>square_1x1_geometry_left.vtu</mesh>

   </meshes>

   <processes>

     <process>

       <name>LF_GAS</name>

       <type>LIQUID_FLOW</type>

       <integration_order>3</integration_order>

       <equation_balance_type>mass</equation_balance_type>

       <process_variables>

         <process_variable>pressure</process_variable>

       </process_variables>

       <secondary_variables>

         <secondary_variable internal_name="darcy_velocity" output_name="v" />

       </secondary_variables>

       <specific_body_force>0 0</specific_body_force>

     </process>

   </processes>

   <media>

     <medium>

       <phases>

         <phase>

           <type>Gas</type>

           <properties>

             <property>

               <name>viscosity</name>

               <type>Constant</type>

               <value>1e-5</value>

             </property>

             <property>

               <name>density</name>

               <type>IdealGasLaw</type>

             </property>

             <property>

               <name>molar_mass</name>

               <type>Constant</type>

               <value>0.028964397787206768</value>

             </property>

           </properties>

         </phase>

         <phase>

           <type>Solid</type>

           <properties>

             <property>

               <name>density</name>

               <type>Constant</type>

               <value>2.17e3</value>

             </property>

           </properties>

         </phase>

       </phases>

       <properties>

         <property>

           <name>porosity</name>

           <type>Constant</type>

           <value>0.03</value>

         </property>

         <property>

           <name>reference_temperature</name>

           <type>Constant</type>

           <value>293.15</value>

         </property>

         <property>

           <name>permeability</name>

           <type>Constant</type>

           <value>1e-4</value>

         </property>

         <property>

           <name>storage</name>

           <type>Constant</type>

           <value>0.0</value>

         </property>

       </properties>

     </medium>

   </media>

   <time_loop>

     <processes>

       <process ref="LF_GAS">

         <nonlinear_solver>basic_picard</nonlinear_solver>

         <convergence_criterion>

           <type>DeltaX</type>

           <norm_type>NORM2</norm_type>

           <reltol>1.e-6</reltol>

         </convergence_criterion>

         <time_discretization>

           <type>BackwardEuler</type>

         </time_discretization>

         <time_stepping>

           <type>FixedTimeStepping</type>

           <t_initial>0</t_initial>

           <t_end>100</t_end>

           <timesteps>

             <pair>

               <repeat>1</repeat>

               <delta_t>0.1</delta_t>

             </pair>

           </timesteps>

         </time_stepping>

       </process>

     </processes>

     <output>

       <type>VTK</type>

       <prefix>gas_flow</prefix>

       <timesteps>

         <pair>

           <repeat>1</repeat>

           <each_steps>1000</each_steps>

         </pair>

       </timesteps>

       <variables>

         <variable>pressure</variable>

         <variable>velocity</variable>

       </variables>

       <suffix>ts{:timestep}_t_{:time}</suffix>

     </output>

   </time_loop>

   <parameters>

     <parameter>

       <name>pressure0</name>

       <type>Constant</type>

       <values>1e5</values>

     </parameter>

     <parameter>

       <name>zero</name>

       <type>Constant</type>

       <value>0</value>

     </parameter>

     <parameter>

       <name>flux</name>

       <type>Constant</type>

       <value>1e-3</value>

     </parameter>

   </parameters>

   <process_variables>

     <process_variable>

       <name>pressure</name>

       <components>1</components>

       <order>2</order>

       <initial_condition>pressure0</initial_condition>

       <boundary_conditions>

         <boundary_condition>

           <mesh>square_1x1_geometry_left</mesh>

           <type>Neumann</type>

           <parameter>flux</parameter>

         </boundary_condition>

       </boundary_conditions>

     </process_variable>

   </process_variables>

   <nonlinear_solvers>

     <nonlinear_solver>

       <name>basic_picard</name>

       <type>Picard</type>

       <max_iter>100</max_iter>

       <linear_solver>general_linear_solver</linear_solver>

     </nonlinear_solver>

   </nonlinear_solvers>

   <linear_solvers>

     <linear_solver>

       <name>general_linear_solver</name>

       <lis>-i bicgstab -p ilu -tol 1e-16 -maxiter 10000</lis>

       <eigen>

         <solver_type>BiCGSTAB</solver_type>

         <precon_type>ILUT</precon_type>

         <max_iteration_step>3000</max_iteration_step>

         <error_tolerance>1e-18</error_tolerance>

       </eigen>

     </linear_solver>

   </linear_solvers>

 </OpenGeoSysProject>