4.1.3. Input file formats

OpenFAST uses two primary input file formats: value column where the first value on the line is read, and key+value where a value and keyword pair are read. Both formats are line number based where a specific input is expected on a specific line, with some exceptions. Value column input files

Only the first column in a value column based input file is read. This is the historical format used by OpenFAST and its predecessors (the keyword was often referenced in the source code and documentation, but OpenFAST did not process the keyword or description). Everything after the first value read is simply ignored by the code. This allowed the user to keep old values while modifying things. So for example, and input line like

2       20   TMax            - Total run time (s)

would be read as 2 and the 20 and everything after it ignored.

This format and associated parsing methodology is somewhat limited in informing the user of errors in parsing, and limited the ability to pass entire inpute files as text strings from another code (such as a Python driver code). Key + Value input files

The first two columns are read in key + value input files. One of these two columns must contain the exact keyword, and the other must contain the value that corresponds to it. For example, an input line

20   TMax            - Total run time (s)

is equivalent to

TMax         20            - Total run time (s)

One additional feature of this input file format is the ability to add an arbitrary number of comment lines wherever the user wishes. Any line starting with !, #, or % will be treated as a comment line and ignored. For example,

! This is a comment line that will be skipped
        %  and this is also a comment line that will be skipped
# as is this comment line
       20   TMax            - Total run time (s)
! the first two columns in the above line will be read as the value + key

The parser for this format of input file also tracks which lines were comments, and which lines contained the value and key pair. If a keyname is not found the parser will return an error with information about which line it was reading from. Modules using Key + Value Format

The following modules use the key + value format input files (all other modules use the value column format):


Input file


Main AD15 input file


Airfoil files


Main HD input file


Main IfW input file


Uniform wind input file


Bladed wind summary file


Main ServoDyn input file


Structural control submodule input file


Structural control sumbodule prescribed force input file


SubDyn SSI matrix input files

Note that key + value format and value column input files can be identical if the value is stated before the key. Reasons for change

The main reason for the change in the input file parsing was to allow for the passing of a complete input file in memory from a wrapper code into OpenFAST or a module. For example, when including the AeroDyn module into a Python code, the input file can be passed in directly in memory without writing to disk first. This helps reduce the IO overhead in optimization loops where the module might be called many times sequentially with very small changes to the input file. NOTE: this is still a work in progress, so not all modules can be linked this way yet.

To accomplish this, the file parser written by Marshall Buhl for parsing airfoil tables in AeroDyn 15 in FAST8 was used. This parser included the more robust key + value input format. Troubleshooting input files

When troubleshooting an input file error, try the following procedure:

  1. An error message containing a line number and variable name, the file format being parsed is a key + value format. Check that the key is spelled exactly as the input file. See Section below.

  2. An error message containing only the variable name but no line number is a value column input file format. See Section below.

  3. Turn on echo option in the input file and check the resulting .ech for which line the file parsing stopped at. This may help isolate where the input file parsing failed when no line number is given in the error message.

  4. Compare the problematic input file with an input file of the same type from the regression test suite distributed with OpenFAST. See section Section 3 for details on the regression tests, or check the repository at r-test .