Program Listing for File SurfaceTension_Akinci2013.cpp

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#include "SurfaceTension_Akinci2013.h"
#include <iostream>
#include "../Simulation.h"
#include "SPlisHSPlasH/BoundaryModel_Akinci2012.h"
#include "SPlisHSPlasH/BoundaryModel_Koschier2017.h"
#include "SPlisHSPlasH/BoundaryModel_Bender2019.h"

using namespace SPH;
using namespace GenParam;

std::string SurfaceTension_Akinci2013::METHOD_NAME = "Akinci et al. 2013";
int SurfaceTension_Akinci2013::SURFACE_TENSION = -1;
int SurfaceTension_Akinci2013::SURFACE_TENSION_BOUNDARY = -1;


SurfaceTension_Akinci2013::SurfaceTension_Akinci2013(FluidModel *model) :
    NonPressureForceBase(model)
{
    m_surfaceTension = static_cast<Real>(0.05);
    m_surfaceTensionBoundary = static_cast<Real>(0.01);
    m_normals.resize(model->numParticles(), Vector3r::Zero());

    model->addField({ "normals", METHOD_NAME, FieldType::Vector3, [&](const unsigned int i) -> Real* { return &m_normals[i][0]; }, false });
}

SurfaceTension_Akinci2013::~SurfaceTension_Akinci2013(void)
{
    m_model->removeFieldByName("normals");
    m_normals.clear();
}

void SurfaceTension_Akinci2013::initParameters()
{
    NonPressureForceBase::initParameters();

    SURFACE_TENSION = createNumericParameter("surfaceTension", "Surface tension coefficient", &m_surfaceTension);
    setGroup(SURFACE_TENSION, "Fluid Model|Surface tension");
    setDescription(SURFACE_TENSION, "Coefficient for the surface tension computation");
    RealParameter* rparam = static_cast<RealParameter*>(getParameter(SURFACE_TENSION));
    rparam->setMinValue(0.0);

    SURFACE_TENSION_BOUNDARY = createNumericParameter("surfaceTensionBoundary", "Boundary surface tension coefficient", &m_surfaceTensionBoundary);
    setGroup(SURFACE_TENSION_BOUNDARY, "Fluid Model|Surface tension");
    setDescription(SURFACE_TENSION_BOUNDARY, "Coefficient for the surface tension computation at the boundary");
    rparam = static_cast<RealParameter*>(getParameter(SURFACE_TENSION_BOUNDARY));
    rparam->setMinValue(0.0);
}


void SurfaceTension_Akinci2013::computeNormals()
{
    Simulation *sim = Simulation::getCurrent();
    const Real supportRadius = sim->getSupportRadius();
    const unsigned int numParticles = m_model->numActiveParticles();
    const unsigned int fluidModelIndex = m_model->getPointSetIndex();
    const unsigned int nFluids = sim->numberOfFluidModels();
    FluidModel *model = m_model;

    // Compute normals
    #pragma omp parallel default(shared)
    {
        #pragma omp for schedule(static)
        for (int i = 0; i < (int)numParticles; i++)
        {
            const Vector3r &xi = m_model->getPosition(i);
            Vector3r &ni = getNormal(i);
            ni.setZero();

            // Fluid
            forall_fluid_neighbors_in_same_phase(
                const Real density_j = m_model->getDensity(neighborIndex);
                ni += m_model->getMass(neighborIndex) / density_j * sim->gradW(xi - xj);
            )
            ni = supportRadius*ni;
        }
    }

}

void SurfaceTension_Akinci2013::step()
{
    Simulation *sim = Simulation::getCurrent();
    const Real density0 = m_model->getDensity0();
    const Real supportRadius = sim->getSupportRadius();
    const unsigned int numParticles = m_model->numActiveParticles();
    const Real k = m_surfaceTension;
    const Real kb = m_surfaceTensionBoundary;
    const unsigned int fluidModelIndex = m_model->getPointSetIndex();
    const unsigned int nFluids = sim->numberOfFluidModels();
    const unsigned int nBoundaries = sim->numberOfBoundaryModels();
    FluidModel *model = m_model;

    computeNormals();

    // Compute forces
    #pragma omp parallel default(shared)
    {
        #pragma omp for schedule(static)
        for (int i = 0; i < (int)numParticles; i++)
        {
            const Vector3r &xi = m_model->getPosition(i);
            const Vector3r &ni = getNormal(i);
            const Real &rhoi = m_model->getDensity(i);
            Vector3r &ai = m_model->getAcceleration(i);

            // Fluid
            forall_fluid_neighbors_in_same_phase(
                const Real &rhoj = m_model->getDensity(neighborIndex);
                const Real K_ij = static_cast<Real>(2.0)*density0 / (rhoi + rhoj);

                Vector3r accel;
                accel.setZero();

                // Cohesion force
                Vector3r xixj = (xi - xj);
                const Real length2 = xixj.squaredNorm();
                if (length2 > 1.0e-9)
                {
                    xixj = (static_cast<Real>(1.0) / sqrt(length2)) * xixj;
                    accel -= k * m_model->getMass(neighborIndex) * xixj * CohesionKernel::W(xi - xj);
                }

                // Curvature
                const Vector3r &nj = getNormal(neighborIndex);
                accel -= k * (ni - nj);

                ai += K_ij * accel;
            );

            // Boundary
            if (sim->getBoundaryHandlingMethod() == BoundaryHandlingMethods::Akinci2012)
            {
                forall_boundary_neighbors(
                    // adhesion force
                    Vector3r xixj = (xi - xj);
                    const Real length2 = xixj.squaredNorm();
                    if (length2 > 1.0e-9)
                    {
                        xixj = ((Real) 1.0 / sqrt(length2)) * xixj;
                        ai -= kb * density0 * bm_neighbor->getVolume(neighborIndex) * xixj * AdhesionKernel::W(xi - xj);
                    }
                );
            }
            else if (sim->getBoundaryHandlingMethod() == BoundaryHandlingMethods::Koschier2017)
            {
                forall_density_maps(
                    Vector3r xixj = xi - xj;
                    const Real length2 = xixj.squaredNorm();
                    if (length2 > 1.0e-9)
                    {
                        xixj = ((Real) 1.0 / sqrt(length2)) * xixj;
                        ai -= kb * density0 * xixj * rho * AdhesionKernel::W_zero() / sim->W_zero();
                    }
                );
            }
            else if (sim->getBoundaryHandlingMethod() == BoundaryHandlingMethods::Bender2019)
            {
                forall_volume_maps(
                    Vector3r xixj = (xi - xj);
                    const Real length2 = xixj.squaredNorm();
                    if (length2 > 1.0e-9)
                    {
                        xixj = ((Real) 1.0 / sqrt(length2)) * xixj;
                        ai -= kb * Vj * density0 * xixj * AdhesionKernel::W(xi - xj);
                    }
                );
            }
        }
    }
}


void SurfaceTension_Akinci2013::reset()
{
}

void SurfaceTension_Akinci2013::performNeighborhoodSearchSort()
{
    const unsigned int numPart = m_model->numActiveParticles();
    if (numPart == 0)
        return;

    Simulation *sim = Simulation::getCurrent();
    auto const& d = sim->getNeighborhoodSearch()->point_set(m_model->getPointSetIndex());
    d.sort_field(&m_normals[0]);
}