strainrate.H

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#ifndef STRAINRATE_H
#define STRAINRATE_H
 
#include "amr-wind/fvm/fvm_utils.H"
#include "AMReX_REAL.H"
 
using namespace amrex::literals;
 
namespace amr_wind::fvm {

template <typename FTypeIn, typename FTypeOut>
struct StrainRate
{
    StrainRate(FTypeOut& strphi, const FTypeIn& phi)
        : m_strphi(strphi), m_phi(phi)
    {
        AMREX_ALWAYS_ASSERT(AMREX_SPACEDIM == m_phi.num_comp());
        AMREX_ALWAYS_ASSERT(m_phi.num_grow() > amrex::IntVect(0));
    }
 
    template <typename Stencil>
    void apply(const int lev, const amrex::MFIter& mfi) const
    {
        const auto& geom = m_phi.repo().mesh().Geom(lev);
        const auto& idx = geom.InvCellSizeArray();
        const auto& strphi = m_strphi(lev).array(mfi);
        const auto& phi = m_phi(lev).const_array(mfi);
 
        const auto& bx_in = mfi.tilebox();
        const auto& bx = Stencil::box(bx_in, geom);
        if (bx.isEmpty()) {
            return;
        }
 
        amrex::ParallelFor(bx, [=] AMREX_GPU_DEVICE(int i, int j, int k) {
            amrex::Real cp1, c, cm1, ux, uy, uz, vx, vy, vz, wx, wy, wz;
            cp1 = Stencil::c00;
            c = Stencil::c01;
            cm1 = Stencil::c02;
 
            ux = (cp1 * phi(i + 1, j, k, 0) + c * phi(i, j, k, 0) +
                  cm1 * phi(i - 1, j, k, 0)) *
                 idx[0];
            vx = (cp1 * phi(i + 1, j, k, 1) + c * phi(i, j, k, 1) +
                  cm1 * phi(i - 1, j, k, 1)) *
                 idx[0];
            wx = (cp1 * phi(i + 1, j, k, 2) + c * phi(i, j, k, 2) +
                  cm1 * phi(i - 1, j, k, 2)) *
                 idx[0];
 
            cp1 = Stencil::c10;
            c = Stencil::c11;
            cm1 = Stencil::c12;
 
            uy = (cp1 * phi(i, j + 1, k, 0) + c * phi(i, j, k, 0) +
                  cm1 * phi(i, j - 1, k, 0)) *
                 idx[1];
            vy = (cp1 * phi(i, j + 1, k, 1) + c * phi(i, j, k, 1) +
                  cm1 * phi(i, j - 1, k, 1)) *
                 idx[1];
            wy = (cp1 * phi(i, j + 1, k, 2) + c * phi(i, j, k, 2) +
                  cm1 * phi(i, j - 1, k, 2)) *
                 idx[1];
 
            cp1 = Stencil::c20;
            c = Stencil::c21;
            cm1 = Stencil::c22;
 
            uz = (cp1 * phi(i, j, k + 1, 0) + c * phi(i, j, k, 0) +
                  cm1 * phi(i, j, k - 1, 0)) *
                 idx[2];
            vz = (cp1 * phi(i, j, k + 1, 1) + c * phi(i, j, k, 1) +
                  cm1 * phi(i, j, k - 1, 1)) *
                 idx[2];
            wz = (cp1 * phi(i, j, k + 1, 2) + c * phi(i, j, k, 2) +
                  cm1 * phi(i, j, k - 1, 2)) *
                 idx[2];
 
            strphi(i, j, k) = std::sqrt(
                (2.0_rt * std::pow(ux, 2.0_rt)) +
                (2.0_rt * std::pow(vy, 2.0_rt)) +
                (2.0_rt * std::pow(wz, 2.0_rt)) + std::pow(uy + vx, 2.0_rt) +
                std::pow(vz + wy, 2.0_rt) + std::pow(wx + uz, 2.0_rt));
        });
    }
 
    FTypeOut& m_strphi;
    const FTypeIn& m_phi;
};

template <typename FTypeIn, typename FTypeOut>
void strainrate(FTypeOut& strphi, const FTypeIn& phi)
{
    BL_PROFILE("amr-wind::fvm::strainrate");
    StrainRate<FTypeIn, FTypeOut> str(strphi, phi);
    impl::apply(str, phi);
}

template <typename FType>
std::unique_ptr<ScratchField> strainrate(const FType& phi)
{
    const std::string gname = phi.name() + "_strainrate";
    auto strphi = phi.repo().create_scratch_field(gname, 1);
    strainrate(*strphi, phi);
    return strphi;
}
 
} // namespace amr_wind::fvm
 
#endif /* STRAINRATE_H */