material_metrics.hpp

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// Copyright (c) 2010-2023, Lawrence Livermore National Security, LLC. Produced
// at the Lawrence Livermore National Laboratory. All Rights reserved. See files
// LICENSE and NOTICE for details. LLNL-CODE-806117.
//
// This file is part of the MFEM library. For more information and source code
// availability visit https://mfem.org.
//
// MFEM is free software; you can redistribute it and/or modify it under the
// terms of the BSD-3 license. We welcome feedback and contributions, see file
// CONTRIBUTING.md for details

#ifndef MATERIAL_METRICS_HPP
#define MATERIAL_METRICS_HPP

#include <random>
#include <vector>
#include "mfem.hpp"

namespace mfem
{

/// Class that implements an edge defined by a start and end point.
class Edge
{
public:
   Edge(const Vector &start, const Vector &end) : start_(start), end_(end) {}

   /// Compute the distance between a point and the edge.
   double GetDistanceTo(const Vector &x) const;

private:
   const Vector &start_;
   const Vector &end_;
};

/// Virtual class to define the interface for defining the material topology.
class MaterialTopology
{
public:
   virtual ~MaterialTopology() = default;

   /// Compute the metric rho describing the material topology.
   virtual double ComputeMetric(const Vector &x) = 0;
};

/// Class that implements the particle topology.
class ParticleTopology : public MaterialTopology
{
public:
   /// Constructor. The length of the vectors random_positions and
   /// random_rotations must be 3x and 9x number_of_particles,
   /// respectively. They implicitly define the number of the particles.
   /// @param[in]  (length_x, length_y, length_z) - particle shape
   /// @param[in]  random_positions - vector with random positions for particles
   /// @param[in]  random_rotations - vector with random rotations for particles
   ParticleTopology(double length_x, double length_y, double length_z,
                    std::vector<double> &random_positions,
                    std::vector<double> &random_rotations)
      : particle_shape_({length_x, length_y, length_z}),
   number_of_particles_(random_positions.size() / 3u)
   {
      Initialize(random_positions, random_rotations);
   }

   /// Compute the metric rho describing the particle topology. For a vector x,
   /// this function returns the shortest distance to any of the particles. The
   /// individual is computed as || A_k (x-x_k) ||_2. (A allows do distort the
   /// particle shape.)
   double ComputeMetric(const Vector &x) final;

private:
   /// Initialize the particle topology with positions x_k and matrices A_k.
   void Initialize(std::vector<double> &random_positions,
                   std::vector<double> &random_rotations);

   std::vector<Vector> particle_positions_;          // A_k * x_k, scaled!
   std::vector<DenseMatrix> particle_orientations_;  // Random rotations of shape
   Vector particle_shape_;       // The shape of the particle.
   size_t number_of_particles_;  // The number of particles.
};

/// Class for the topology of a an octet truss. This class assumes the domain is
/// a cube [0,1]^3.
class OctetTrussTopology : public MaterialTopology
{
public:
   OctetTrussTopology() { Initialize(); }

   // Compute the distance, i.e. distance to the closest edge.
   double ComputeMetric(const Vector &x) final;

private:
   /// Initialize the topology, e.g. define the edges.
   void Initialize();

   /// To account for the periodicity, this function creates ghost points for
   /// the distance computation, e.g. ( x[0] ± 1, x[1] ± 1, x[2] ± 1).
   void CreatePeriodicPoints(const Vector &x,
                             std::vector<Vector> &periodic_points) const;

   std::vector<Vector> points_;  // The points of the octet truss.
   std::vector<Edge> edges_;     // The edges of the octet truss.
};

}  // namespace mfem

#endif  // MATERIAL_METRICS_HPP