[cig-commits] commit 2056 by bangerth to /var/svn/dealii/aspect

[dealii.demon at gmail.com]

Revision 2056

Document better.

U   trunk/aspect/tests/compressibility_iterated_stokes.cc
U   trunk/aspect/tests/compressibility_iterated_stokes.prm


http://www.dealii.org/websvn/revision.php?repname=Aspect+Repository&path=%2F&rev=2056&peg=2056

Diff:
Modified: trunk/aspect/tests/compressibility_iterated_stokes.cc
===================================================================
--- trunk/aspect/tests/compressibility_iterated_stokes.cc	2013-11-26 13:23:40 UTC (rev 2055)
+++ trunk/aspect/tests/compressibility_iterated_stokes.cc	2013-11-26 13:28:26 UTC (rev 2056)
@@ -63,7 +63,6 @@
     {
       // compressibility = 1/rho drho/dp
       return  0.01;
-;
     }
 
     template <int dim>

Modified: trunk/aspect/tests/compressibility_iterated_stokes.prm
===================================================================
--- trunk/aspect/tests/compressibility_iterated_stokes.prm	2013-11-26 13:23:40 UTC (rev 2055)
+++ trunk/aspect/tests/compressibility_iterated_stokes.prm	2013-11-26 13:28:26 UTC (rev 2056)
@@ -1,15 +1,24 @@
 # A variation on the 'compressibility' testcase. here, we compute not
 # only the first iteration of a nonlinear fixed point scheme, but in
-# fact the first two. The second iteration should have a better guess
-# u^* for the continuity equation,
-#    div u = -1/rho drho/dp u^* . g
-# and so should lead to an upward expansion of the flux. 
+# fact the first several. This should iterate out the
+# continuity equation,
+#    div u = -1/rho drho/dp u^ . g
+# and so should lead to an upward expansion of the flux.
 #
 # with the original testcase, the iteration does not converge. rather,
 # we need a much smaller compressibility to make things converge. we
-# choose a compressibility so that the density is
+# choose a velocity profile
+#   u_y = 1+z/100
+# with corresponding density profile
+#   rho = 1/(1+z/100)
+# so that the continuity equation is satisfied. From the density one
+# can compute a pressure profile (here, the pressure equals the hydrostatic
+# pressure because all second derivatives of the velocity vanish). This gives
+# p(z), which we can invert for z=z(p) and enter into the density equation
+# to get
 #   rho = 10.0/11.0*exp(pressure/100.0)
-# which corresponds to compressibility=0.01
+# which corresponds to compressibility=0.01. This is implemented in
+# the .cc file corresponding to this testcase.
 
 set Dimension = 2
 set CFL number                             = 1.0