[cig-commits] commit 2489 by bangerth to /var/svn/dealii/aspect

[dealii.demon at gmail.com]

Revision 2489

Get the sign right in the computation of dynamic topography. It is easy to convince oneself that we want a minus sign by just considering a divergent flow at a ridge (or a convergent flow at a subduction zone) that the sign in front of sigma_rr must be negative. The confusion with the literature is due to the fact that our coordinate system has z pointing out of the domain (i.e., height) whereas others denote z as the depth.

U   trunk/aspect/source/postprocess/dynamic_topography.cc
U   trunk/aspect/source/postprocess/visualization/dynamic_topography.cc


http://www.dealii.org/websvn/revision.php?repname=Aspect+Repository&path=%2F&rev=2489&peg=2489

Diff:
Modified: trunk/aspect/source/postprocess/dynamic_topography.cc
===================================================================
--- trunk/aspect/source/postprocess/dynamic_topography.cc	2014-04-12 11:39:37 UTC (rev 2488)
+++ trunk/aspect/source/postprocess/dynamic_topography.cc	2014-04-12 11:51:31 UTC (rev 2489)
@@ -106,7 +106,7 @@
                   const Tensor<1,dim> gravity_direction = gravity/gravity.norm();
 
                   const double sigma_rr           = gravity_direction * (stress * gravity_direction);
-                  const double dynamic_topography = sigma_rr / gravity.norm() / density;
+                  const double dynamic_topography = -sigma_rr / gravity.norm() / density;
 
                   output << location
                          << ' '

Modified: trunk/aspect/source/postprocess/visualization/dynamic_topography.cc
===================================================================
--- trunk/aspect/source/postprocess/visualization/dynamic_topography.cc	2014-04-12 11:39:37 UTC (rev 2488)
+++ trunk/aspect/source/postprocess/visualization/dynamic_topography.cc	2014-04-12 11:51:31 UTC (rev 2489)
@@ -98,7 +98,7 @@
             const Tensor<1,dim> gravity_direction = gravity/gravity.norm();
 
             const double sigma_rr           = gravity_direction * (stress * gravity_direction);
-            const double dynamic_topography = sigma_rr / gravity.norm() / density;
+            const double dynamic_topography = -sigma_rr / gravity.norm() / density;
 
             computed_quantities[q](0) = dynamic_topography;
           }