GenericFiber.hpp

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#pragma once
 
#include <polyfem/assembler/GenericElastic.hpp>
#include <polyfem/assembler/MatParams.hpp>
 
namespace polyfem::assembler
{
    template <typename FiberModel>
    class GenericFiber : public GenericElastic<FiberModel>
    {
    public:
        GenericFiber();
        virtual ~GenericFiber() = default;
 
        // sets material params
        virtual void add_multimaterial(const int index, const json &params, const Units &units) override;
        virtual void set_size(const int size) override;
 
    protected:
        template <typename T>
        T I4Bar(const RowVectorNd &p,
                const double t,
                const int el_id,
                const DefGradMatrix<T> &def_grad) const
        {
            const T J = polyfem::utils::determinant(def_grad);
            const auto Cbar = (def_grad.transpose() * def_grad / pow(J, 2.0 / 3.0)).eval();
 
            const auto a_tmp = fiber_direction_(p, p, t, el_id);
            assert(a_tmp.rows() == this->size() && a_tmp.cols() == 1);
            Eigen::Matrix<T, Eigen::Dynamic, 1, 0, 3, 1> a(a_tmp.rows(), a_tmp.cols());
            for (int i = 0; i < a.size(); ++i)
                a(i) = T(a_tmp(i));
 
            const Eigen::Matrix<T, 1, 1> tmp = a.transpose() * Cbar * a;
            assert(tmp.rows() == 1 && tmp.cols() == 1);
            return tmp(0, 0);
        }
 
        FiberDirection fiber_direction_;
    };
} // namespace polyfem::assembler