LinearElasticity.hpp

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#pragma once
 
#include <polyfem/assembler/Assembler.hpp>
#include <polyfem/assembler/MatParams.hpp>
#include <polyfem/utils/AutodiffTypes.hpp>
#include <polyfem/utils/ElasticityUtils.hpp>
 
// local assembler for linear elasticity
namespace polyfem::assembler
{
    class LinearElasticity : public LinearAssembler, NLAssembler, ElasticityAssembler
    {
    public:
        using LinearAssembler::assemble;
        using NLAssembler::assemble_energy;
        using NLAssembler::assemble_gradient;
        using NLAssembler::assemble_hessian;
 
        // vals stores the evaluation for that element
        // da contains both the quadrature weight and the change of metric in the integral
        Eigen::Matrix<double, Eigen::Dynamic, 1, 0, 9, 1>
        assemble(const LinearAssemblerData &data) const override;
 
        // compute elastic energy
        double compute_energy(const NonLinearAssemblerData &data) const override;
        // neccessary for mixing linear model with non-linear collision response
        Eigen::MatrixXd assemble_hessian(const NonLinearAssemblerData &data) const override;
        // compute gradient of elastic energy, as assembler
        Eigen::VectorXd assemble_gradient(const NonLinearAssemblerData &data) const override;
 
        // kernel of the pde, used in kernel problem
        Eigen::Matrix<AutodiffScalarGrad, Eigen::Dynamic, 1, 0, 3, 1> kernel(const int dim, const AutodiffGradPt &r, const AutodiffScalarGrad &) const override;
 
        // uses autodiff to compute the rhs for a fabbricated solution
        // uses autogenerated code to compute div(sigma)
        // pt is the evaluation of the solution at a point
        VectorNd compute_rhs(const AutodiffHessianPt &pt) const override;
 
        void compute_stiffness_value(const double t,
                                     const assembler::ElementAssemblyValues &vals,
                                     const Eigen::MatrixXd &local_pts,
                                     const Eigen::MatrixXd &displacement,
                                     Eigen::MatrixXd &tensor) const override;
 
        void compute_stress_grad_multiply_mat(const OptAssemblerData &data,
                                              const Eigen::MatrixXd &mat,
                                              Eigen::MatrixXd &stress,
                                              Eigen::MatrixXd &result) const override;
 
        void compute_stress_grad_multiply_stress(const OptAssemblerData &data,
                                                 Eigen::MatrixXd &stress,
                                                 Eigen::MatrixXd &result) const override;
 
        void compute_dstress_dmu_dlambda(const OptAssemblerData &data,
                                         Eigen::MatrixXd &dstress_dmu,
                                         Eigen::MatrixXd &dstress_dlambda) const override;
 
        // inialize material parameter
        void add_multimaterial(const int index, const json &params, const Units &units) override;
 
        // class that stores and compute lame parameters per point
        const LameParameters &lame_params() const { return params_; }
        void set_params(const LameParameters &params) { params_ = params; }
 
        void update_lame_params(const Eigen::MatrixXd &lambdas, const Eigen::MatrixXd &mus) override
        {
            params_.lambda_mat_ = lambdas;
            params_.mu_mat_ = mus;
        }
 
        virtual bool is_linear() const override { return true; }
 
        std::string name() const override { return "LinearElasticity"; }
        bool allow_inversion() const override { return true; }
        std::map<std::string, ParamFunc> parameters() const override;
 
        void assign_stress_tensor(const OutputData &data,
                                  const int all_size,
                                  const ElasticityTensorType &type,
                                  Eigen::MatrixXd &all,
                                  const std::function<Eigen::MatrixXd(const Eigen::MatrixXd &)> &fun) const override;
 
    private:
        // class that stores and compute lame parameters per point
        LameParameters params_;
 
        // aux function that computes energy
        // double compute_energy is the same with T=double
        // assemble_gradient is the same with T=DScalar1 and return .getGradient()
        template <typename T>
        T compute_energy_aux(const NonLinearAssemblerData &data) const;
    };
} // namespace polyfem::assembler