wip: particle dynamics

Particle Dynamics

-----------------

During the DES steps, particle positions are updated using the

`MFIXParticleContainer::EvolveParticles

<https://amrex-codes.github.io/MFIX-Exa/doxygen/class_m_f_i_x_particle_container.html#a158f3f5fa11c262ad6a9909b40a5cd13>`_

method. It's structure is:

.. highlight:: c++

::

    // Set time-step size (subdt) and number (numbsebsteps) for the DES steps

    des_init_time_loop( &time, &dt, &nsubsteps, &subdt, &subdt_io );

    // Temporary storage of forces and torques

    std::map<PairIndex, Vector<Real>> tow;

    std::map<PairIndex, Vector<Real>> fc;

    for (MFIXParIter pti(*this, lev); pti.isValid(); ++pti)

    {

        PairIndex index(pti.index(), pti.LocalTileIndex());

        tow[index] = Vector<Real>();

        fc[index] = Vector<Real>();

    }

    while (n < nsubsteps) // step over number of substeps (DES part)

    {

        // Neighbourlist house-keeping

        if (n % 25 == 0) {

            clearNeighbors(lev);

            Redistribute();

            fillNeighbors(lev);

            buildNeighborList(lev,sort_neighbor_list);

        } else {

            updateNeighbors(lev);

        }

        // Itterate over particles

        for (MFIXParIter pti(*this, lev); pti.isValid(); ++pti)

        {

            // Forces and torques due to particle-wall collisions

            calc_wall_collisions_ls(particles, & ntot, & nrp,

                                    tow[index].dataPtr(), fc[index].dataPtr(), & subdt,

                                    ...

                                    );

            calc_particle_collisions(particles                     , &nrp,

                                     neighbors[index].dataPtr()    , &size_ng,

                                     neighbor_list[index].dataPtr(), &size_nl,

                                     tow[index].dataPtr(), fc[index].dataPtr(), &subdt, &ncoll);

        }

    }