PALM

The software PALM is a large-eddy simulation (LES) model for atmospheric and oceanic flows developed at the Institute of Meteorology and Climatology of the Leibniz Universität Hannover.

Installation

Please download and follow the follwing pdf-document for detailled instructions for the installation of PALM:

• Installation of PALM on FLOW

SGE scripts

Sample SGE scripts for submitting PALM jobs can be found here:

• palm.sge (for standard version of PALM)

• palm_simple.sge (only for simple version of PALM - see installation guide for more information)

Please copy the sample script to your working directory (as palm.sge or <different-name>.sge). For carrying out the test run (to verify the installation), the script does not need to be modified. Please see the installation guide for instructions on how to modify the script for different runs.

Runtime estimation

The runtime of PALM (which is needed for the SGE script and for mrun) can be estimated by

$T_{CPU}[{\mbox{s}}]=c_{PALM,FLOW}{\frac {N_{Iterations}\cdot N_{Points}}{N_{CPU}}}$

where the constant c_{PALM,FLOW} is approximately

$c_{PALM,FLOW}\approx 8\cdot 10^{-6}{\mbox{s}}$

This value is a first guess from a sample of simulation data. However, this number might have to be corrected in the future. It depends on additional parameters as amount of output data and complexity of user-defined code.

The number of points is defined by the product of the grid points in x-, y- and z-direction

$N_{Points}=N_{x}\cdot N_{y}\cdot N_{z}$

The number of iterations can be calculated by

$N_{Iterations}={\frac {T_{total}}{\Delta t}}$

with the physical simulation time T_{total} and the timestep size \Delta t. The timestep size \Delta t can (in most cases) be estimated by the Courant-Friedrichs-Levy like criteria

$\Delta t={\frac {\max \left(\Delta x\right)}{2{\bar {u}}_{max}}}={\frac {\max \left({\frac {L_{x}}{N_{x}}},{\frac {L_{y}}{N_{y}}},{\frac {L_{z}}{N_{z}}}\right)}{2{\bar {u}}_{max}}}$

where L and N are the length of the simulated domain and resolution in x-, y- and z-direction, respectively. The velocity \bar u_{max} is the maximal windspeed of the simulation.

Note: In the time estimation the scaling is assumed to be linear which is not true for large number of used CPU cores and small resolutions (O(10⁵) points/core). In this case the constant could be larger.

Known issues

• With the Intel Compiler 12.0.0 the compiler flag -no-prec-div and -np-prec-sqrt can lead to different results for same runs. Please don't use these flags. Note that the flags will automatically be set when using the compiler option -fast. In this case you should set -prec-div and -prec-sqrt.

Tutorials

Here are slides from the last training at ForWind in April 2012.

Day 1

• Fundamentals of LES
• Introduction
• Overview
• Installation on FLOW (Please see above for actual installation rules)
• Introduction to NCL

Day 2

• Exercise: Neutral boundary layer
• Numerical boundary conditions
• Program control
• Program structure
• Runs with mrun (part 1)
• Runs with mrun (part 2)

Day 3

• Parallelization
• Debugging
• Non-cyclic boundary conditions
• Restarts with mrun
• Interface Exercise
• User defined code
• LES of wake flows

External Links

• PALM homepage