Index: palm/trunk/DOC/app/chapter_2.0.html =================================================================== --- palm/trunk/DOC/app/chapter_2.0.html (revision 54) +++ palm/trunk/DOC/app/chapter_2.0.html (revision 62) @@ -1,24 +1,15 @@ - -
- -LES models generally permit the +
LES models +generally permit the simulation of turbulent flows, whereby those eddies, that carry the main energy are resolved by the numerical grid. Only the @@ -28,10 +19,13 @@ simulated directly (they are explicitly resolved) and their effects are represented by the advection terms.
-PALM is based on the +
PALM is +based on the non-hydrostatic incompressible Boussinesq equations. It contains a water cycle with cloud formation and takes into account infrared radiative cooling in cloudy conditions. The model has six prognostic -quantities in total u,v,w, liquid water potential temperature -Θl (BETTS, +quantities in total – u,v,w, liquid water potential +temperature +Θl +(BETTS, 1973), total water content q and subgrid-scale turbulent kinetic energy e. The @@ -45,5 +39,5 @@ 1993). The water cycle is closed by using a simplified version of KESSLERs scheme (KESSLER, 1965; 1969) to parameterize precipitation -processes (MÜLLER and CHLOND, 1996). Incompressibility is +processes (MÜLLER and CHLOND, 1996). Incompressibility is applied by means of a Poisson equation for pressure, which is solved with a direct method (SCHUMANN and SWEET, 1988). The Poisson equation @@ -58,5 +52,6 @@ horizontal directions. At the lower surface, either temperature/ humidity or their respective fluxes can be prescribed.
-The advection terms +
The +advection terms are treated by the scheme proposed by PIACSEK and WILLIAMS (1970), which conserves the integral of linear and quadratic quantities up to @@ -66,10 +61,12 @@ with the third-order Runge-Kutta scheme. A second-order Runge-Kutta scheme, a leapfrog scheme and an Euler scheme are also implemented.
-By default, the time step is computed +
By default, the time step is +computed with respect to the different criteria (CFL, diffusion) and adapted automatically. In case of a non-zero geostrophic wind the coordinate system can be moved along with the mean wind in order to maximize the time step (Galilei-Transformation).
-In principle a model +
In +principle a model run is carried out in the following way: After reading the control parameters given by the user, all prognostic variables are @@ -90,10 +87,11 @@ corrected with the help of the pressure solver. Following this, all diagnostic turbulence quantities including possible -Prandtl-layerquantities are computed. At the end of a time +Prandtl-layer–quantities are computed. At the end of a time step the data output requested by the user is made (e.g. statistic of analyses for control purposes or profiles and/or graphics data). If the given end-time was reached, binary data maybe be saved for restart.
-The model is based +
The +model is based on the originally non-parallel LES model which has been operated at the institute since 1989 @@ -109,9 +107,11 @@ Users can choose between a two- and a one-dimensional domain decomposition. A 1D-decomposition is preferred on machines with a -slow network interconnection. In case of a 1D-decomposition, the +slow network interconnection. In case of a 1D-decomposition, +the grid points along x direction are distributed among the individual processors, but in y- and z-direction all respective grid points belong to the same PE.
-The calculation of central differences or +
The calculation of central +differences or non-local arithmetic operations (e.g. global sums, FFT) demands communication and an appropriate data exchange @@ -126,23 +126,16 @@ y-direction, the data which lie distributed on the individual central processing elements, have to be collected and/or relocated before. -This happens by means of the routine MPI_ALLTOALLV. Certain +This happens by means of the routine MPI_ALLTOALLV. +Certain global operations like e.g. the search for absolute maxima or minima within the 3D-arrays likewise require the employment of special MPI routines (MPI_ALLREDUCE).
-Further details of the internal model +
Further details of the
+internal model
structure are described in the technical/numerical
documentation.
Last
-change: 14/04/05 (SR)
-
Last
+change: $Id$
+