It’s all in that 38-line header. Have you read this? SQP method using particles_input. data imports the particle position, but cannot be successfully read - #5 by cgw
The solver expects the data to start on line 39 so the header must be present and the first line must say Version 3.0
The table which starts with
Variable Read(T/F) Default value (when Read=F)
controls whether variables are read from the file (column must be present) or whether a default is applied to all particles (no column for that variable).
Here’s a full V3 particle_input.dat file which you can examine:
https://mfix.netl.doe.gov/forum/uploads/short-url/omGPgpFzQMd5e8ukRgSB1hZqMv4.dat
You basically want to take the first part of that file, set the values in the header correctly (# of particles, default values, etc) and then replace the data in that file with the data you have generated.