OpenFAST ZMQ connection (1 WT)

[lorenzoschena]

yes

Feature or improvement description

This update enables ZMQ communication with OpenFAST. Two connections are possible:

1. PUB-SUB: OpenFAST results are published to a socket and all subscriber can receive updates in real-time
2. REQ-REP: OpenFAST can query with specific requests a socket.

Both updates can follow different time steps, default is intended to be the DT input of openfast.

FAST_Registry has been modified to handle all variables that are useful in the context of these communications. The .fst templates are to be found in /zmq_coupling_tests/templatesDir/.

In this PR, the communication is possible for only single wind turbines; developments to FAST.Farm is going to follow.

Related issue, if one exists

Impacted areas of the software

Most of the modifications made are in FAST_Subs. However, minor adjustments have also been made to ServoDyn to handle possible override from ZMQ.

Additional supporting information

Needs two requirements:

1. cJSON: to compact inbound and outbound message with JSON format
2. ZMQ: to open connection sockets in C Language. The connections are handled by C modules and imported in Fortran.

A brief white paper will be added in the documentation to use this module.

Test results, if applicable

• ex01 tests consistency between received values via PUB-SUB socket and output of OpenFAST.
• ex02 tests consistency between sent values via REQ-REP socket and input received by OpenFAST.
• ex03 tests both connections at the same time.

[andrew-platt]

Does this PR add to #2153, or replace it?

Apologies for our delays on merging #2153. I am a little behind on merges.

[lorenzoschena]

Hello Andy,

No problems at all! It replaces is, we can delete the previous one.