You have several options, however the easiest one can be:
1) you identify the particles of the wall with Id or Mk 2) you use PartVTK to compute the ACE of those particles (Id or Mk) so you will create XXX output files, for example in ASCII format 3) you can load the ASCII files with a program (C++ or Matlab) where for each output file (each output instant) you will perform the summation of ACE of all those particles and you will get the Total force at that tiem step as FORCE(t)=SUM(ACE)*mass where mass is the mass of the boundary particles
Comments
1) you identify the particles of the wall with Id or Mk
2) you use PartVTK to compute the ACE of those particles (Id or Mk) so you will create XXX output files, for example in ASCII format
3) you can load the ASCII files with a program (C++ or Matlab) where for each output file (each output instant) you will perform the summation of ACE of all those particles and you will get the Total force at that tiem step as
FORCE(t)=SUM(ACE)*mass
where mass is the mass of the boundary particles
Regards