StateSolveNavierStokes.cpp

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#include <polyfem/State.hpp>
 
#include <polyfem/assembler/Laplacian.hpp>
#include <polyfem/assembler/Mass.hpp>
#include <polyfem/assembler/Stokes.hpp>
#include <polyfem/assembler/NavierStokes.hpp>
 
#include <polyfem/solver/NavierStokesSolver.hpp>
#include <polyfem/solver/OperatorSplittingSolver.hpp>
#include <polyfem/solver/TransientNavierStokesSolver.hpp>
#include <polyfem/time_integrator/BDF.hpp>
#include <polyfem/autogen/auto_p_bases.hpp>
#include <polyfem/autogen/auto_q_bases.hpp>
 
namespace polyfem
{
    using namespace solver;
    using namespace time_integrator;
 
    void State::solve_navier_stokes(Eigen::MatrixXd &sol, Eigen::MatrixXd &pressure)
    {
        assert(!problem->is_time_dependent());
        assert(assembler->name() == "NavierStokes");
 
        assert(solve_data.rhs_assembler != nullptr);
        solve_data.rhs_assembler->set_bc(
            local_boundary, boundary_nodes, n_boundary_samples(), local_neumann_boundary, rhs);
 
        std::shared_ptr<assembler::Assembler> velocity_stokes_assembler = std::make_shared<assembler::StokesVelocity>();
        set_materials(*velocity_stokes_assembler);
 
        Eigen::VectorXd x;
        solver::NavierStokesSolver ns_solver(args["solver"]);
        ns_solver.minimize(n_bases, n_pressure_bases,
                           bases, pressure_bases,
                           geom_bases(),
                           *velocity_stokes_assembler,
                           *dynamic_cast<assembler::NavierStokesVelocity *>(assembler.get()),
                           *mixed_assembler,
                           *pressure_assembler,
                           ass_vals_cache,
                           pressure_ass_vals_cache,
                           boundary_nodes,
                           use_avg_pressure,
                           mesh->dimension(),
                           mesh->is_volume(),
                           rhs, x);
 
        sol = x;
        sol_to_pressure(sol, pressure);
    }
 
    void State::solve_transient_navier_stokes_split(const int time_steps, const double dt, Eigen::MatrixXd &sol, Eigen::MatrixXd &pressure)
    {
        assert(assembler->name() == "OperatorSplitting" && problem->is_time_dependent());
 
        Eigen::MatrixXd local_pts;
        auto &gbases = geom_bases();
        if (mesh->dimension() == 2)
        {
            if (gbases[0].bases.size() == 3)
                autogen::p_nodes_2d(args["space"]["discr_order"], local_pts);
            else
                autogen::q_nodes_2d(args["space"]["discr_order"], local_pts);
        }
        else
        {
            if (gbases[0].bases.size() == 4)
                autogen::p_nodes_3d(args["space"]["discr_order"], local_pts);
            else
                autogen::q_nodes_3d(args["space"]["discr_order"], local_pts);
        }
 
        std::vector<int> bnd_nodes;
        bnd_nodes.reserve(boundary_nodes.size() / mesh->dimension());
        for (auto it = boundary_nodes.begin(); it != boundary_nodes.end(); it++)
        {
            if (!(*it % mesh->dimension()))
                continue;
            bnd_nodes.push_back(*it / mesh->dimension());
        }
 
        const int dim = mesh->dimension();
        const int n_el = int(bases.size());       // number of elements
        const int shape = gbases[0].bases.size(); // number of geometry vertices in an element
 
        auto fluid_assembler = std::dynamic_pointer_cast<assembler::OperatorSplitting>(assembler);
        if (!fluid_assembler)
            log_and_throw_error("Invalid assembler {}!", assembler->name());
        // TODO
        double viscosity_ = fluid_assembler->viscosity()(0, 0, 0, 0, 0);
        assert(viscosity_ >= 0);
 
        logger().info("Matrices assembly...");
        StiffnessMatrix stiffness_viscosity, mixed_stiffness, velocity_mass, stiffness;
 
        build_stiffness_mat(stiffness);
        // coefficient matrix of viscosity
        assembler::Laplacian lapl_assembler;
        lapl_assembler.set_size(1);
        lapl_assembler.assemble(mesh->is_volume(), n_bases, bases, gbases, ass_vals_cache, 0, stiffness_viscosity);
        mass_matrix_assembler->set_size(1);
        mass_matrix_assembler->assemble(mesh->is_volume(), n_bases, bases, gbases, mass_ass_vals_cache, 0, mass, true);
 
        // coefficient matrix of pressure projection
        lapl_assembler.assemble(mesh->is_volume(), n_pressure_bases, pressure_bases, gbases, pressure_ass_vals_cache, 0, stiffness);
 
        // matrix used to calculate divergence of velocity
        mixed_assembler->assemble(mesh->is_volume(), n_pressure_bases, n_bases, pressure_bases, bases, gbases,
                                  pressure_ass_vals_cache, ass_vals_cache, 0, mixed_stiffness);
        mass_matrix_assembler->set_size(mesh->dimension());
        mass_matrix_assembler->assemble(mesh->is_volume(), n_bases, bases, gbases, mass_ass_vals_cache, 0, velocity_mass, true);
        mixed_stiffness = mixed_stiffness.transpose();
        logger().info("Matrices assembly ends!");
 
        solver::OperatorSplittingSolver ss(
            *mesh, shape, n_el, local_boundary, boundary_nodes, pressure_boundary_nodes, bnd_nodes, mass,
            stiffness_viscosity, stiffness, velocity_mass, dt, viscosity_, args["solver"]["linear"]);
 
        /* initialize solution */
        pressure = Eigen::MatrixXd::Zero(n_pressure_bases, 1);
 
        const int n_b_samples = n_boundary_samples();
        for (int t = 1; t <= time_steps; t++)
        {
            double time = t * dt;
            logger().info("{}/{} steps, t={}s", t, time_steps, time);
 
            /* advection */
            logger().info("Advection...");
            if (args["space"]["advanced"]["use_particle_advection"])
                ss.advection_FLIP(*mesh, gbases, bases, sol, dt, local_pts);
            else
                ss.advection(*mesh, gbases, bases, sol, dt, local_pts);
            logger().info("Advection finished!");
 
            /* apply boundary condition */
            solve_data.rhs_assembler->set_bc(
                local_boundary, boundary_nodes, n_b_samples, local_neumann_boundary, sol, Eigen::MatrixXd(), time);
 
            /* viscosity */
            logger().info("Solving diffusion...");
            if (viscosity_ > 0)
                ss.solve_diffusion_1st(mass, bnd_nodes, sol);
            logger().info("Diffusion solved!");
 
            /* external force */
            ss.external_force(*mesh, *assembler, gbases, bases, dt, sol, local_pts, problem, time);
 
            /* incompressibility */
            logger().info("Pressure projection...");
            ss.solve_pressure(mixed_stiffness, pressure_boundary_nodes, sol, pressure);
 
            ss.projection(n_bases, gbases, bases, pressure_bases, local_pts, pressure, sol);
            // ss.projection(velocity_mass, mixed_stiffness, boundary_nodes, sol, pressure);
            logger().info("Pressure projection finished!");
 
            pressure = pressure / dt;
 
            /* apply boundary condition */
            solve_data.rhs_assembler->set_bc(
                local_boundary, boundary_nodes, n_b_samples, local_neumann_boundary, sol, Eigen::MatrixXd(), time);
 
            /* export to vtu */
            save_timestep(time, t, 0, dt, sol, pressure);
        }
    }
 
    void State::solve_transient_navier_stokes(const int time_steps, const double t0, const double dt, Eigen::MatrixXd &sol, Eigen::MatrixXd &pressure)
    {
        assert(assembler->name() == "NavierStokes" && problem->is_time_dependent());
 
        const auto &gbases = geom_bases();
        Eigen::MatrixXd current_rhs = rhs;
 
        StiffnessMatrix velocity_mass;
        // TODO mass might not be constant
        mass_matrix_assembler->assemble(mesh->is_volume(), n_bases, bases, gbases, mass_ass_vals_cache, 0, velocity_mass, true);
 
        StiffnessMatrix velocity_stiffness, mixed_stiffness, pressure_stiffness;
 
        Eigen::VectorXd prev_sol;
 
        BDF time_integrator;
        if (args["time"]["integrator"].is_object() && args["time"]["integrator"]["type"] == "BDF")
            time_integrator.set_parameters(args["time"]["integrator"]);
        time_integrator.init(sol, Eigen::VectorXd::Zero(sol.size()), Eigen::VectorXd::Zero(sol.size()), dt);
 
        std::shared_ptr<assembler::Assembler> velocity_stokes_assembler = std::make_shared<assembler::StokesVelocity>();
        set_materials(*velocity_stokes_assembler);
 
        mixed_assembler->assemble(mesh->is_volume(), n_pressure_bases, n_bases, pressure_bases, bases, gbases,
                                  pressure_ass_vals_cache, ass_vals_cache, 0, mixed_stiffness);
        pressure_assembler->assemble(mesh->is_volume(), n_pressure_bases, pressure_bases, gbases, pressure_ass_vals_cache, 0,
                                     pressure_stiffness);
 
        solver::TransientNavierStokesSolver ns_solver(args["solver"]);
        const int n_larger = n_pressure_bases + (use_avg_pressure ? 1 : 0);
 
        const int n_b_samples = n_boundary_samples();
 
        for (int t = 1; t <= time_steps; ++t)
        {
            double time = t0 + t * dt;
            double current_dt = dt;
 
            velocity_stokes_assembler->assemble(mesh->is_volume(), n_bases, bases, gbases, ass_vals_cache, time, velocity_stiffness);
 
            logger().info("{}/{} steps, dt={}s t={}s", t, time_steps, current_dt, time);
 
            prev_sol = time_integrator.weighted_sum_x_prevs();
            solve_data.rhs_assembler->compute_energy_grad(
                local_boundary, boundary_nodes, mass_matrix_assembler->density(), n_b_samples, local_neumann_boundary, rhs, time, current_rhs);
            solve_data.rhs_assembler->set_bc(
                local_boundary, boundary_nodes, n_b_samples, local_neumann_boundary, current_rhs, Eigen::MatrixXd(), time);
 
            const int prev_size = current_rhs.size();
            if (prev_size != rhs.size())
            {
                current_rhs.conservativeResize(prev_size + n_larger, current_rhs.cols());
                current_rhs.block(prev_size, 0, n_larger, current_rhs.cols()).setZero();
            }
 
            Eigen::VectorXd tmp_sol;
            ns_solver.minimize(
                n_bases, n_pressure_bases,
                time,
                bases, geom_bases(),
                *dynamic_cast<assembler::NavierStokesVelocity *>(assembler.get()),
                ass_vals_cache,
                boundary_nodes,
                use_avg_pressure,
                mesh->dimension(),
                mesh->is_volume(),
                sqrt(time_integrator.acceleration_scaling()), prev_sol, velocity_stiffness, mixed_stiffness,
                pressure_stiffness, velocity_mass, current_rhs, tmp_sol);
            sol = tmp_sol;
            time_integrator.update_quantities(sol.topRows(n_bases * mesh->dimension()));
            sol_to_pressure(sol, pressure);
 
            save_timestep(time, t, t0, dt, sol, pressure);
        }
    }
} // namespace polyfem