Re: Hydrodynamic forces analysis

[Jean-Noël Grad]

Hi,

To the best of my knowledge, there isn't a way to calculate this 
quantity from the Python interface, because the particle coupling code 
that updates particle forces also updates the LB grid and thermostat as 
a side-effect.

If you are familiar with C++ programming, it would be a fun exercise to 
update the particle coupling code to also update a dictionary of 
particle forces. To do so, one would adapt `ParticleCoupling::kernel()` 
to write forces to a `std::unordered_map<int,Utils::Vector3d> obs` using 
particle ids as key.

The particle forces from the LB grid are calculated here:
https://github.com/espressomd/espresso/blob/b70d9e8/src/core/lb/particle_coupling.cpp#L279

One can then accumulate forces with `obs[p.id()] += force_on_particle;` 
and reset all forces to zero as the first step of `couple_particles()` 
with `for(auto &[k,v] : obs){v=Utils::Vector3d{};}`.

Hope this helps,
JN

On 10/30/23 15:18, Ahmad Reza Motezakker wrote:
> Dear EspressoMD Community,
>
>
> I hope this email finds you well. I am working on a project involving 
> nanoparticles and polymers in a cubic box, simulated with LB fluid 
> dynamics and Lennard-Jones forces.
>
>
> I am particularly interested in analyzing the hydrodynamic forces acting 
> on the nanoparticles. Could you share any tips or tools in EspressoMD 
> that would help me isolate and accurately calculate these forces and the 
> net force?
>
>
> Thank you in advance for your assistance.
>
>
> Best,
>
> ARM