Changes between Version 4 and Version 5 of palm

Timestamp:

Dec 7, 2017 8:36:11 AM (7 years ago)

Author:

maronga

Comment:

--

palm

@@ -17 +17 @@
 
 Following Monin-Obukhov similarity theory (MOST) a constant flux layer can be assumed as boundary condition between the surface and the first grid level where scalars and horizontal velocities are defined. In PALM we assume that MOST can be also applied locally and we therefore calculate local fluxes, velocities, and scaling parameters. This scheme involves calculation of the Obukhov length ''L'', which can be either done based on variables of the previous time step ("circular"), via a Newton iteration method, or via a look-up table for the stability parameter ''z/L''.
+
+== Parallelization and scaling==
+The parallelization of the code is achieved by a 2-D domain decomposition method along the x and y direction with equally sized subdomains. Ghost layers are added at the side boundaries of the subdomains in order to account for the local data dependencies, which are caused by the need to compute finite differences at these positions. The number of ghost layers that are used in PALM depend on the order of the advection scheme, with three layers for the 5th-order Wicker-Skamarock scheme. Ghost layer data are exchanged after every time step. Data exchange between proecessor cores is realized using the Message Passing Interface (MPI). Additional loop vectorization via OpenMP is realized which also allows a so-called hybrid parallelization.
+
+PALM shows excellent scaling which was tested for up to 50,000 processor cores [wiki:doc/tec/parallel#Parallelizationandoptimizationdetails (details)].
 
 == External forcing and nesting ==