Changes between Version 115 and Version 116 of doc/app/initialization_parameters

Timestamp:

Sep 16, 2010 8:37:33 AM (14 years ago)

Author:

raasch

Comment:

--

doc/app/initialization_parameters

@@ -648 +648 @@
 {{{#!td
 Switch to steer the call of the pressure solver.\\\\
-In order to speed-up performance, the Poisson equation for perturbation pressure (see [#psolver psolver]) can be called only at the last substep of multistep Runge-Kutta timestep schemes (see [#timestep_scheme timestep_scheme]) by setting '''call_psolver_at_all_substeps''' = ''.F.''. In many cases, this sufficiently reduces the divergence of the velocity field. Nevertheless, small-scale ripples (2-delta-x) may occur. In this case and in case of non-cyclic lateral boundary conditions, '''call_psolver_at_all_timesteps''' = ''.T.'' should be used. 
+In order to speed-up performance, the Poisson equation for perturbation pressure (see [#psolver psolver]) can be called only at the last substep of multistep Runge-Kutta timestep schemes (see [#timestep_scheme timestep_scheme]) by setting '''call_psolver_at_all_substeps''' = ''.F.''. In many cases, this sufficiently reduces the divergence of the velocity field. Nevertheless, small-scale ripples (2-delta-x) may occur. In this case and in case of non-cyclic lateral boundary conditions, the default value '''call_psolver_at_all_timesteps''' = ''.T.'' should be used. 
 }}}
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@@ -798 +798 @@
 }}}
 {{{#!td
-Grid level at which data shall be gathered on PE0.\\\\
-In case of a run using several PEs and the multigrid method for solving the Poisson equation for perturbation pressure (see [#psolver psolver]), the value of this parameter defines on which grid level the data are gathered on PE0 in order to allow for a further coarsening of the grid. The finest grid defines the largest grid level. By default, the gathering level is determined automatically and displayed in file [../iofiles#RUN_CONTROL RUN_CONTROL]. It is only possible to gather data from a level larger than the one determined automatically. A test run may be neccessary to determine this level.
+Number of Gauss-Seidel iterations to be carried out on each grid level of the multigrid Poisson solver.\\\\
+In case of using the multigrid method for solving the Poisson equation for perturbation pressure (see [#psolver psolver]), this parameter defines the number of Gauss-Seidel iterations to be carried out on each grid level. High numbers give better convergence. The dafault value of ''2'' reduces the divergence of the preliminary velocity field by about 1-2 orders of magnitude, which is sufficient in most cases. The value of '''ngsrb''' has a significant effect on the cpu requirement of the run.
 }}}
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@@ -870 +870 @@
 '' 'sor' ''\\\\
       Successive over relaxation method (SOR). The convergence of this iterative scheme is steered with the parameters [#omega_sor omega_sor], [#nsor_ini nsor_ini] and [#nsor nsor].\\ 
-      Compared to the direct method and the multi-grid method, this scheme needs substantially more computing time. It should only be used for test runs, e.g. if errors in the other pressure solver methods are assumed.\\\\
-      In order to speed-up performance, the Poisson equation is by default only solved at the last substep of a multistep Runge-Kutta scheme (see [#call_psolver at_all_substeps call_psolver at_all_substeps] and [#timestep_scheme timestep_scheme]). 
+      Compared to the direct method and the multi-grid method, this scheme needs substantially more computing time. It should only be used for test runs, e.g. to compare results with the other pressure solver methods.\\\\
+      In case of using a multistep Runge-Kutta timestep scheme (see [#timestep_scheme timestep_scheme]), the Poisson equation is by default solved after each of the substeps. In order to speed-up performance, the Poisson equation may be solved only for the last substep (see [#call_psolver at_all_substeps call_psolver at_all_substeps]). 
 }}}
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