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equation.h
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equation.h
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//
// Created by Maxim Masterov on 24/01/2023.
//
#ifndef TRANSIENT_DIFFUSION_EQUATION_H
#define TRANSIENT_DIFFUSION_EQUATION_H
#include <vector>
#include <iomanip>
#include <petsc.h>
#include "grid.h"
template <typename T>
union Neighbours {
struct Names {
T center;
T west;
T east;
T north;
T south;
T top;
T bottom;
T rhs;
void report() {
std::cout << "\nCoefficients:" << "\n";
std::cout << " center: " << center << "\n";
std::cout << " west: " << west << "\n";
std::cout << " east: " << east << "\n";
std::cout << " north: " << north << "\n";
std::cout << " south: " << south << "\n";
std::cout << " top: " << top << "\n";
std::cout << " bottom: " << bottom << "\n";
std::cout << " rhs: " << rhs << "\n";
}
} name;
T data[8] = { };
};
class Coefficients {
public:
Coefficients() {
value.data[0] = value.data[1] = value.data[2]
= value.data[3] = value.data[4] = value.data[5]
= value.data[6] = value.data[7] = 0.;
exist.data[0] = exist.data[1] = exist.data[2]
= exist.data[3] = exist.data[4] = exist.data[5]
= exist.data[6] = exist.data[7] = false;
}
~Coefficients() { }
Neighbours<double> value;
Neighbours<bool> exist;
void report() {
std::cout << "\nCoefficients:" << "\n";
std::cout << " center: " << value.name.center << "\n";
std::cout << " west: " << value.name.west << "\n";
std::cout << " east: " << value.name.east << "\n";
std::cout << " north: " << value.name.north << "\n";
std::cout << " south: " << value.name.south << "\n";
std::cout << " top: " << value.name.top << "\n";
std::cout << " bottom: " << value.name.bottom << "\n";
std::cout << " rhs: " << value.name.rhs << "\n";
}
};
class Index {
public:
Index() { }
Index(int _i, int _j) : i(_i), j(_j), k(0) { }
Index(int _i, int _j, int _k) : i(_i), j(_j), k(_k) { }
int i;
int j;
int k;
int get_id(const int NJ) const {
return j + i * NJ;
}
int get_id(const int NJ, const int NK) const {
return k + NK * (j + i * NJ);
}
void set_ind(const int id, const int NJ) {
i = floor(id / NJ);
j = id - i * NJ;
}
void set_ind(const int id, const int NJ, const int NK) {
i = floor(id / (NJ * NK));
j = floor((id - i * NJ * NK) / NK);
k = id - j * NK - i * NJ * NK;
}
};
class Equation {
public:
/*!
* @brief Steady state problem setup
* @param _grid Object of Grid
* @param T0 Initial temperature
*/
Equation(Grid *_grid, double T0);
/*!
* @brief Transient problem setup
* @param _grid Object of Grid
* @param _dt Time step
* @param T0 Initial temperature
*/
Equation(Grid *_grid, double _dt, double T0);
~Equation() {
destroy_field();
destroy_linear_sys();
}
void solve();
private:
/*!
* @brief General problem setup
* @param _grid Object of Grid
* @param _dt Time step
* @param T0 Initial temperature
*/
void general_setup(Grid *_grid, double _dt, double T0);
/*!
* @brief Populate matrix coefficients using spatial derivatives.
* @param ind Global indices of the current cell
* @param coeff Structure of coefficients
*/
void spatial_contrib(const Index ind, Coefficients &coeff);
/*!
* @param id Local index of the current cell
* @param coeff Structure of coefficients
*/
void transient_contrib(const int id, Coefficients &coeff);
/*!
* @brief Assemble linear system
*/
void assemble();
/*!
* @brief Write solution to the file
* @param file_name File name
*/
void write_field_to_file(const std::string file_name);
/*!
* @brief Copy new field to the old one
*/
void copy_field_to_old();
/*!
* @brief Copy solution of the linear system to the field
*/
void copy_solution_to_field();
/*!
* @brief Allocate memory for new and old fields
* Should be called after the @e create_linear_sys() function
* @param T0 Initial temperature
*/
void create_field(double T0);
/*!
* @brief Deallocate memory used by new and old fields
*/
void destroy_field();
/*!
* @brief Allocate memory for linear system (A, x, b)
*/
void create_linear_sys();
/*!
* @brief Deallocate memory used by liner system (A, x, b)
*/
void destroy_linear_sys();
private:
typedef std::vector<double> Field;
Field field; // field from the new time step
Field field_old; // field from the old time step
Grid *grid; // numerical Grid
double dt; // time step
double max_t; // max simulation time (s)
double T_e, T_w; // boundary conditions on the west and east walls respectively (C)
double T_s, T_n; // boundary conditions on the south and north walls respectively (C)
double T_t, T_b; // boundary conditions on the top and bottom walls respectively (C)
double alpha; // thermal diffusivity (m2/s)
bool is_transient; // "true" if problem is transient, "false" otherwise
int freq_file_writing; // frequency of writing files with the field (ignored for steady state problem)
// linear system
Mat A;
Vec x, b;
std::string solver_name; // name of the PETSc solver
std::string precond_name; // name of the PETSc solver
};
#endif //TRANSIENT_DIFFUSION_EQUATION_H