ViscousDamping.hpp

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#pragma once
 
#include <polyfem/assembler/Assembler.hpp>
 
// non linear NeoHookean material model
namespace polyfem
{
    namespace assembler
    {
        class ViscousDamping : public NLAssembler
        {
        public:
            using NLAssembler::assemble_energy;
            using NLAssembler::assemble_gradient;
            using NLAssembler::assemble_hessian;
            using NLAssembler::compute_energy;
 
            std::string name() const override { return "ViscousDamping"; }
            std::map<std::string, ParamFunc> parameters() const override { return std::map<std::string, ParamFunc>(); }
 
            ViscousDamping() = default;
 
            // energy, gradient, and hessian used in newton method
            double compute_energy(const NonLinearAssemblerData &data) const override;
            virtual Eigen::MatrixXd assemble_hessian(const NonLinearAssemblerData &data) const override;
            virtual Eigen::VectorXd assemble_gradient(const NonLinearAssemblerData &data) const override;
 
            // sets material params
            void add_multimaterial(const int index, const json &params, const Units &units) override;
            void set_params(const double psi, const double phi)
            {
                damping_params_[0] = psi;
                damping_params_[1] = phi;
            }
 
            void compute_stress_grad(const OptAssemblerData &data,
                                     const Eigen::MatrixXd &prev_grad_u_i,
                                     Eigen::MatrixXd &stress,
                                     Eigen::MatrixXd &result) const override;
 
            void compute_stress_prev_grad(const OptAssemblerData &data,
                                          const Eigen::MatrixXd &prev_grad_u_i,
                                          Eigen::MatrixXd &result) const override;
 
            static void compute_dstress_dpsi_dphi(const OptAssemblerData &data,
                                                  const Eigen::MatrixXd &prev_grad_u_i,
                                                  Eigen::MatrixXd &dstress_dpsi,
                                                  Eigen::MatrixXd &dstress_dphi);
 
            double get_psi() const { return damping_params_[0]; }
            double get_phi() const { return damping_params_[1]; }
 
            bool is_valid() const { return (damping_params_[0] > 0) && (damping_params_[1] > 0); }
 
            const DampingParameters &damping_params() const { return damping_params_; }
 
        protected:
            // material parameters controlling shear and bulk damping
            // double psi_ = 0, phi_ = 0;
            DampingParameters damping_params_;
 
            void compute_stress_aux(const Eigen::MatrixXd &F, const Eigen::MatrixXd &dFdt, Eigen::MatrixXd &dRdF, Eigen::MatrixXd &dRdFdot) const;
            void compute_stress_grad_aux(const Eigen::MatrixXd &F, const Eigen::MatrixXd &dFdt, Eigen::MatrixXd &d2RdF2, Eigen::MatrixXd &d2RdFdFdot, Eigen::MatrixXd &d2RdFdot2) const;
        };
 
        class ViscousDampingPrev : public ViscousDamping
        {
        public:
            using NLAssembler::assemble_energy;
            using NLAssembler::assemble_gradient;
            using NLAssembler::assemble_hessian;
            using ViscousDamping::compute_energy;
 
            // energy, gradient, and hessian used in newton method
            Eigen::MatrixXd assemble_hessian(const NonLinearAssemblerData &data) const override;
            Eigen::VectorXd assemble_gradient(const NonLinearAssemblerData &data) const override;
        };
    } // namespace assembler
} // namespace polyfem