# Parametric runs using CPL¶

CPL provides two classes CMLSimulation and CMLSimCollection that can be used to create workflows that can automate the CFD analysis process. It also provides an implementation of CMLSimCollection called CMLParametricRun that can be used to automate running a parametric study over several variables and managing the analysis as a group. These classes serve as simple examples for the user to derive sub-classes from CPL to develop their own custom workflows.

The parametric run capability is also accessible from the command-line via caelus_sim. This tutorial provides a step-by-step walkthrough of exercising CPL’s parametric run capabilities through the command-line. This tutorial will demonstrate an example of generating airfoil polars for a range of angles of attack at different Reynolds numbers. In addition to varying, the angle of attack and Reynolds number, it will also show how to specify other flow parameters through CPL.

## Preliminaries¶

To use CPL’s parametric run interface, the user needs to provide a simulation configuration file (in YAML format), and a case template directory (similar to the one used with caelus clone command).

To follow along with this tutorial, we recommend that the user download the parametric run setup file and a case template. For the purposes of this tutorial we will assume that the user is executing the commands from within $HOME/run directory. Once downloaded please unzip the zip file. # Files downloaded for the tutorial walkthrough bash:/tmp/run$ ls
airfoil_demo.zip caelus_sim.yaml

# Unzip the file
bash:/tmp/run$unzip airfoil_demo.zip Archive: airfoil_demo.zip creating: airfoil_template/ creating: airfoil_template/0.orig/ inflating: airfoil_template/0.orig/k inflating: airfoil_template/0.orig/nut inflating: airfoil_template/0.orig/omega inflating: airfoil_template/0.orig/p inflating: airfoil_template/0.orig/U inflating: airfoil_template/cmlControls creating: airfoil_template/constant/ creating: airfoil_template/constant/polyMesh/ inflating: airfoil_template/constant/polyMesh/boundary inflating: airfoil_template/constant/polyMesh/faces.gz inflating: airfoil_template/constant/polyMesh/neighbour.gz inflating: airfoil_template/constant/polyMesh/owner.gz inflating: airfoil_template/constant/polyMesh/points.gz inflating: airfoil_template/constant/RASProperties inflating: airfoil_template/constant/transportProperties inflating: airfoil_template/constant/turbulenceProperties creating: airfoil_template/system/ inflating: airfoil_template/system/controlDict inflating: airfoil_template/system/decomposeParDict inflating: airfoil_template/system/fvSchemes inflating: airfoil_template/system/fvSolution  ### Preparing a case template directory¶ In order to simplify the process of setting up parametric run, CPL assumes that all user-configurable entries are provided in cmlControls within the case directory. Other files within the case directory use the #include option to include this file and use variable replacement macro syntax $variable to interface with the parametric run utility. In this airfoil demonstration example, a cmlControls that will be used is shown below:

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 FoamFile { version 2.0; format ascii; class dictionary; object "cmlControls"; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // density 1.225; Uinf 15.0; chord 1.0; Re 1000000.0; aoa 0.0; turbKe 3.75e-07; velVector (15.0 0.0 0.0); nuValue 1.0e7; turbulenceModel kOmegaSST; // ************************************************************************* // 

An example of using this file to set the turbulence model in constant/RASProperties is shown below:

FoamFile
{
version     2.0;
format      ascii;
class       dictionary;
location    "constant";
object      RASProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#include "../cmlControls"

RASModel        $turbulenceModel; turbulence on; printCoeffs on; kMin 1.e-20; // ************************************************************************* //  Notice how the cmlControls file is included in line 11, and the property RASModel is set with $turbulenceModel (see line 27 in cmlControls snippet above). The user is referred to constant/transportProperties, 0.orig/U, 0.orig/k, and functions section of system/controlDict for further examples of how the inputs from cmlControls is used to customize the case.

Tip

Currently, cmlControls and CPL’s dictionary manipulation capabilities are restricted to text files only. If you want to customize binary files within 0/ directory, then we recommend using cmlControls to modify system/changeDictionaryDict and execute CML’s changeDictionary executable in the pre-processing phase to modify binary files.

Note

With newer versions of OpenFOAM, the RANS inputs must be part of the constant/turbulenceProperties file.

### Inputs for setting up parametric run¶

The first step to creating a parametric analysis directory structure is to execute the caelus_sim setup command. By default, this command will attempt to load the analysis configuration from the caelus_sim.yaml. The user can, however, change this by providing an alternate file with the -f flag. The contents of the caelus_sim.yaml used for this demo is shown below.

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 # -*- mode: yaml -*- # caelus_sim requires a simulation section in YAML file simulation: # Name of the parametric run top-level directory. Can also set using -n flag # at command line which takes precedence sim_name: airfoil_demo # The template directory for creating case directories. Requires 'path' # argument. Other optional variables can be provided to control clone behavior template: path: "./airfoil_template" # copy_polymesh: no # copy_zero: no # copy_scripts: no # extra_patterns: ["*.py"] # This section details the parametric run options simulation_setup: # User defined format for case directory names case_format: "Re_{Re:.1e}/aoa_{aoa:+06.2f}" # The matrix of runs run_matrix: - Re: [1.0e6, 2.0e6] aoa: start: 0.0 stop: 2.0 step: 2.0 # Only run one Re for the negative AOA - Re: [1.0e6] aoa: [-4.0, -2.0] # Other parameters that are passed to cmlControls file constant_parameters: density: 1.225 Uinf: 15.0 chord: 1.0 turbKe: 3.75e-07 turbulenceModel: kOmegaSST # User-defined transformations on the variables apply_transforms: transform_type: code # Only pass these variables to cmlControls extract_vars: [velVector, Re, nuValue, liftVector, dragVector] # Python code that is executed before generating case parameters code: | Re = float(Re) aoaRad = np.radians(aoa) Ux = Uinf * np.cos(aoaRad) Uy = Uinf * np.sin(aoaRad) velVector = np.array([Ux, Uy, 0.0]) nuValue = Uinf / Re liftVector = np.array([-np.sin(aoaRad), np.cos(aoaRad), 0.0]) dragVector = np.array([np.cos(aoaRad), np.sin(aoaRad), 0.0]) # Configuration for running each case within this analysis group run_configuration: # Number of MPI ranks for parallel runs num_ranks: 2 # Extra MPI arguments passed during parallel runs # mpi_extra_args: -machinefile mymachines # Should the case be reconstructed on successful run reconstruct: no # Modify the default template input files change_inputs: controlDict: endTime: 1 writeFormat: binary # Pre-processing actions to be performed before solve. The syntax is similar # to the Tasks YAML interface. Note, the case manager will automatically # perform decomposition and similar tasks. Users only need to provide # non-standard pre-processing actions (e.g., copy actions, changeDictionary, # or mesh generation) during the prep phase. prep: - copy_tree: src: "0.orig" dest: "0" # Perform the solve solve: simpleSolver # solve: # - solver: potentialSolver # solver_args: "-initializeUBCs -noFunctionObjects" # - solver: pimpleSolver # Similar to prep, perform post-processing actions # post: # - run_command: # cmd_name: "python ./my_post_process.py" 

The input file must contain one section simulation that provides all the information necessary for setting up and executing the parametric run. The simulation dictionary contains the following major sections:

sim_name

The name of the parametric analysis group. The program creates a unique run directory with this name. This parameter can also be overridden from the command line.

template

Details of the case template that will be used to create the individual case directories. It must contain one mandatory entry: path, that is the path to the template case directory. In this demo we will use the airfoil_template that we unzipped from the airfoil_demo.zip. Additional parameters are passed to control the cloning of the template directory and are similar to caelus clone command.

simulation_setup

This section contains the details of the parametric run. case_template is a template suitable to be processed by python str.format() method.

run_matrix contains the list of parametric combinations that will be run. In this example, we will run two angles of attack for each of the two Reynolds numbers specified. Each entry in the list generates all possible combinations of runs possible, and these are sub-groups of parametric runs. User can provide multiple entries in the list to generate additional custom combinations.

constant_parameters, if present, are variables that that will be populated in addition to the variable parameters (in run_matrix) when setting up the case.

Finally, apply_transforms is an optional section, that uses valid python code snippets to perform user-defined transformations to the variables in run_matrix and constant_parameters to generate dependent variables or perform additional processing. After transformation, by default, all variables introduced by the python code is extracted and passed along with constant_parameters and variables in run_matrix to cmlControls. However, if the user has imported modules or defined functions, this could lead to error. So it is recommended that the user manually specify the variables to extracted through the extract_vars option in apply_transforms section.

run_configuration

This section contains the details on how each case is executed after setup. It has a general section that has information regarding parallel run setup etc.

change_inputs lists changes to be performed to input files cloned from the template directory. This step is performed after setting up case directory, but before execution of any pre-processing or solve tasks.

prep contains tasks (see Caelus Tasks) that must be executed before decomposing and executing the case. Note that the user need not specify the decomposePar task, as this is handled automatically by the parametric run interface.

solve indicates the name of the solver that is used to run these cases. It can also accept a list entry with multiple solvers (e.g., running potentialSolver before simpleSolver, etc.)

post is similar to prep but are tasks that are executed after a successful solver completion.

## Setting up a parametric run¶

Now that we have the requisite inputs for setting up a parametric run, we will use caelus_sim setup command to setup a case (see caelus_sim – Parametric Run CLI for more details).

bash:/tmp/run$caelus_sim setup INFO: Caelus Python Library (CPL) v0.1.1 # # Output deleted # INFO: Successfully setup simulation: airfoil_demo (6)  On successful execution, you should see a new directory airfoil_demo that contains six Caelus case directories for the various combinations of Reynolds number and angles of attack. User can query the status of the analysis by executing the status sub-command. bash:/tmp/run/airfoil_demo$ ls
Re_1.0e+06      Re_2.0e+06      caelus_sim.yaml
bash:/tmp/run/airfoil_demo$caelus_sim status INFO: Caelus Python Library (CPL) v0.1.1 Run status for: airfoil_demo Directory: /private/tmp/run/airfoil_demo =============================================== #. NAME STATUS =============================================== 1. Re_1.0e+06/aoa_+00.00 Setup 2. Re_1.0e+06/aoa_+02.00 Setup 3. Re_2.0e+06/aoa_+00.00 Setup 4. Re_2.0e+06/aoa_+02.00 Setup 5. Re_1.0e+06/aoa_-04.00 Setup 6. Re_1.0e+06/aoa_-02.00 Setup =============================================== TOTAL = 6; SUCCESS = 0; FAILED = 0 ===============================================  For a description of the various status tags, please consult caelus_sim status documentation. Note 1. If you are running from a directory outside of airfoil_demo then provide the case path using the -d option to caelus_sim status -d. You don’t need to provide this if you were, say, within airfoil_demo/Re_1.0e+06 directory or any of the subdirectories. 2. Setup sub-command allows the user to immediately perform prep tasks or submit the solve jobs immediately upon setup using the -p or -s flags during the invocation of setup. ## Prep, solve, and post¶ Now that the cases as setup, the user can examine the auto-generated case directories to ensure everything is setup properly and can run the simulation by just invoking the solve sub-command. CPL will detect if pre-processing and case decomposition haven’t been performed and will perform these tasks. User also has the option to explicitly invoke the prep task separately from command line. Without any arguments, these sub-commands will choose all the cases within a parametric run for execution. User can, however, pass shell-style wildcard arguments to select a subset of cases where the command is executed. In this tutorial, we will demonstrate this behavior by executing prep only on the cases where $$Re = 2\times 10^6$$. # # Submit prep only for Re=2e6 # bash:/tmp/run/airfoil_demo$ caelus_sim prep 'Re_2.0*/*'
INFO: Caelus Python Library (CPL) v0.1.144-g41f57bc-dirty
INFO: Executing pre-processing tasks for case: Re_2.0e+06/aoa_+00.00
INFO: Writing Caelus input file: system/decomposeParDict
INFO: Decomposing case: Re_2.0e+06/aoa_+00.00
INFO: Executing pre-processing tasks for case: Re_2.0e+06/aoa_+02.00
INFO: Writing Caelus input file: system/decomposeParDict
INFO: Decomposing case: Re_2.0e+06/aoa_+02.00

#
# Check status of simulation
#
bash:/tmp/run/airfoil_demo$caelus_sim status INFO: Caelus Python Library (CPL) v0.1.1-44-g41f57bc-dirty Run status for: airfoil_demo Directory: /private/tmp/run/airfoil_demo =============================================== #. NAME STATUS =============================================== 1. Re_1.0e+06/aoa_+00.00 Setup 2. Re_1.0e+06/aoa_+02.00 Setup 3. Re_2.0e+06/aoa_+00.00 Prepped 4. Re_2.0e+06/aoa_+02.00 Prepped 5. Re_1.0e+06/aoa_-04.00 Setup 6. Re_1.0e+06/aoa_-02.00 Setup =============================================== TOTAL = 6; SUCCESS = 0; FAILED = 0 ===============================================  Note the use of single quotes around the wildcard arguments to prevent expansion by the shell when parsing the command line. In the next step, we will directly invoke solve on the positive angle of attack cases for $$Re = 1\times 10^6$$ to demonstrate the automatic invocation of prep if not already performed. # # Submit solve only for positive aoa and Re=1e6 # bash:/tmp/run/airfoil_demo$ caelus_sim solve 'Re_1.0*/aoa_+*'
INFO: Caelus Python Library (CPL) v0.1.1
INFO: Executing pre-processing tasks for case: Re_1.0e+06/aoa_+00.00
INFO: Submitting solver (simpleSolver) for case: Re_1.0e+06/aoa_+00.00
INFO: Executing pre-processing tasks for case: Re_1.0e+06/aoa_+02.00
INFO: Submitting solver (simpleSolver) for case: Re_1.0e+06/aoa_+02.00

#
# Check status of simulation
#
bash:/tmp/run/airfoil_demo$caelus_sim status INFO: Caelus Python Library (CPL) v0.1.1 Run status for: airfoil_demo Directory: /private/tmp/run/airfoil_demo =============================================== #. NAME STATUS =============================================== 1. Re_1.0e+06/aoa_+00.00 Solved 2. Re_1.0e+06/aoa_+02.00 FAILED 3. Re_2.0e+06/aoa_+00.00 Prepped 4. Re_2.0e+06/aoa_+02.00 Prepped 5. Re_1.0e+06/aoa_-04.00 Setup 6. Re_1.0e+06/aoa_-02.00 Setup =============================================== TOTAL = 6; SUCCESS = 0; FAILED = 1 ===============================================  Note For the purposes of demonstration, the endTime is controlDict is set to one timestep. Also a deliberate error was introduced in solve step to demonstrate the FAILED status flag. User can execute the post step and it will only execute post-processing actions on cases that have completed the solve. # # Execute post-processing actions # bash:/tmp/run/airfoil_demo$ caelus_sim post
INFO: Caelus Python Library (CPL) v0.1.1
INFO: Executing post-processing tasks for case: Re_1.0e+06/aoa_+00.00
WARNING: Re_1.0e+06/aoa_+02.00: No previous solve detected, skipping post
WARNING: Re_2.0e+06/aoa_+00.00: No previous solve detected, skipping post
WARNING: Re_2.0e+06/aoa_+02.00: No previous solve detected, skipping post
WARNING: Re_1.0e+06/aoa_-04.00: No previous solve detected, skipping post
WARNING: Re_1.0e+06/aoa_-02.00: No previous solve detected, skipping post

#
# Check status of simulation
#
bash:/tmp/run/airfoil_demo\$ caelus_sim status
INFO: Caelus Python Library (CPL) v0.1.1

Run status for: airfoil_demo
Directory: /private/tmp/run/airfoil_demo
===============================================
#. NAME                     STATUS
===============================================
1. Re_1.0e+06/aoa_+00.00    DONE
2. Re_1.0e+06/aoa_+02.00    FAILED
3. Re_2.0e+06/aoa_+00.00    Prepped
4. Re_2.0e+06/aoa_+02.00    Prepped
5. Re_1.0e+06/aoa_-04.00    Setup
6. Re_1.0e+06/aoa_-02.00    Setup
===============================================
TOTAL = 6; SUCCESS = 1; FAILED = 1
===============================================