GB.H

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#ifndef MODEL_INTERFACE_GB_H
#define MODEL_INTERFACE_GB_H
 
#include <AMReX.H>
#include <AMReX_AmrCore.H>
 
#include <eigen3/Eigen/Eigenvalues>
 
#include <iostream>
#include <fstream>
 
namespace Model
{
namespace Interface
{
namespace GB
{
class GB
{
public:
    GB() {};
    virtual ~GB() {};
    virtual Set::Scalar W(const Set::Scalar theta) const = 0;
    virtual Set::Scalar DW(const Set::Scalar theta) const = 0;
    virtual Set::Scalar DDW(const Set::Scalar theta) const = 0;
    virtual Set::Scalar W(const Set::Vector& a_n) const { return W(atan2(a_n(1), a_n(0))); };
    virtual Set::Scalar DW(const Set::Vector&, const Set::Vector&) const { return NAN; };
    virtual Set::Scalar DDW(const Set::Vector&, const Set::Vector&) const { return NAN; };
 
    void ExportToFile(std::string filename, amrex::Real dTheta)
    {
        std::ofstream outFile;
        outFile.open(filename);
 
        for (amrex::Real theta = 0; theta < 2 * pi; theta = theta + dTheta)
        {
            outFile << theta << " " << W(theta) << std::endl;
        }
        outFile.close();
    }
 
    enum Regularization { Wilhelm, K23 };
 
    // Return anisotropic driving force, regularization
    std::tuple<Set::Scalar, Set::Scalar>
        DrivingForce(const Set::Vector& Deta, const Set::Matrix& DDeta, const Set::Matrix4<AMREX_SPACEDIM, Set::Sym::Full>& DDDDeta)
    {
#if AMREX_SPACEDIM == 2
        Set::Scalar Theta = atan2(Deta(1), Deta(0));
        Set::Scalar sigma = /*pf.l_gb*0.75**/W(Theta);
        Set::Scalar Dsigma = /*pf.l_gb*0.75**/DW(Theta);
        Set::Scalar DDsigma = /*pf.l_gb*0.75**/DDW(Theta);
        Set::Scalar sinTheta = sin(Theta);
        Set::Scalar cosTheta = cos(Theta);
        Set::Scalar sin2Theta = sinTheta * sinTheta;
        Set::Scalar cos2Theta = cosTheta * cosTheta;
        Set::Scalar cosThetasinTheta = cosTheta * sinTheta;
 
        Set::Scalar boundary_term =
            -(sigma * DDeta.trace() +
                Dsigma * (cos(2.0 * Theta) * DDeta(0, 1) + 0.5 * sin(2.0 * Theta) * (DDeta(1, 1) - DDeta(0, 0))) +
                0.5 * DDsigma * (sin2Theta * DDeta(0, 0) - 2. * cosThetasinTheta * DDeta(0, 1) + cos2Theta * DDeta(1, 1)));
 
        Set::Scalar curvature_term =
            DDDDeta(0, 0, 0, 0) * (sin2Theta * sin2Theta) +
            DDDDeta(0, 0, 0, 1) * (4.0 * sin2Theta * cosThetasinTheta) +
            DDDDeta(0, 0, 1, 1) * (6.0 * sin2Theta * cos2Theta) +
            DDDDeta(0, 1, 1, 1) * (4.0 * cosThetasinTheta * cos2Theta) +
            DDDDeta(1, 1, 1, 1) * (cos2Theta * cos2Theta);
        return std::make_tuple(boundary_term, curvature_term);
 
#elif AMREX_SPACEDIM == 3
 
        Set::Vector normal = Deta / Deta.lpNorm<2>();
 
        // GRAHM-SCHMIDT PROCESS to get orthonormal basis
        const Set::Vector e1(1, 0, 0), e2(0, 1, 0), e3(0, 0, 1);
        Set::Vector _t2, _t3;
        if (fabs(normal(0)) > fabs(normal(1)) && fabs(normal(0)) > fabs(normal(2)))
        {
            _t2 = e2 - normal.dot(e2) * normal; _t2 /= _t2.lpNorm<2>();
            _t3 = e3 - normal.dot(e3) * normal - _t2.dot(e3) * _t2; _t3 /= _t3.lpNorm<2>();
        }
        else if (fabs(normal(1)) > fabs(normal(0)) && fabs(normal(1)) > fabs(normal(2)))
        {
            _t2 = e1 - normal.dot(e1) * normal; _t2 /= _t2.lpNorm<2>();
            _t3 = e3 - normal.dot(e3) * normal - _t2.dot(e3) * _t2; _t3 /= _t3.lpNorm<2>();
        }
        else
        {
            _t2 = e1 - normal.dot(e1) * normal; _t2 /= _t2.lpNorm<2>();
            _t3 = e2 - normal.dot(e2) * normal - _t2.dot(e2) * _t2; _t3 /= _t3.lpNorm<2>();
        }
 
        // Compute Hessian projected into tangent space (spanned by _t1,_t2)
        Eigen::Matrix2d DDeta2D;
        DDeta2D <<
            _t2.dot(DDeta * _t2), _t2.dot(DDeta * _t3),
            _t3.dot(DDeta * _t2), _t3.dot(DDeta * _t3);
        Eigen::SelfAdjointEigenSolver<Eigen::Matrix2d> eigensolver(2);
        eigensolver.computeDirect(DDeta2D);
        Eigen::Matrix2d eigenvecs = eigensolver.eigenvectors();
 
        // Compute tangent vectors embedded in R^3
        Set::Vector t2 = _t2 * eigenvecs(0, 0) + _t3 * eigenvecs(0, 1),
            t3 = _t2 * eigenvecs(1, 0) + _t3 * eigenvecs(1, 1);
 
        // Compute components of second Hessian in t2,t3 directions
        Set::Scalar DH2 = 0.0, DH3 = 0.0;
        Set::Scalar DH23 = 0.0;
        for (int p = 0; p < 3; p++)
            for (int q = 0; q < 3; q++)
                for (int r = 0; r < 3; r++)
                    for (int s = 0; s < 3; s++)
                    {
                        DH2 += DDDDeta(p, q, r, s) * t2(p) * t2(q) * t2(r) * t2(s);
                        DH3 += DDDDeta(p, q, r, s) * t3(p) * t3(q) * t3(r) * t3(s);
                        DH23 += DDDDeta(p, q, r, s) * t2(p) * t2(q) * t3(r) * t3(s);
                    }
 
        Set::Scalar sigma = W(normal);
        Set::Scalar DDK2 = DDW(normal, _t2);
        Set::Scalar DDK3 = DDW(normal, _t3);
 
        // GB energy anisotropy term
        Set::Scalar gbenergy_df = -sigma * DDeta.trace() - DDK2 * DDeta2D(0, 0) - DDK3 * DDeta2D(1, 1);
 
        // Second order curvature term
        Set::Scalar reg_df = NAN;
        if (regularization == Regularization::Wilhelm) reg_df = DH2 + DH3 + 2.0 * DH23;
        else if (regularization == Regularization::K23) reg_df = DH2 + DH3;
 
        return std::make_tuple(gbenergy_df, reg_df);
 
#endif
    }
 
 
protected:
    static constexpr amrex::Real pi = 3.14159265359;
    Regularization regularization = Regularization::Wilhelm;
};
}
}
}
 
#endif