periodic_load.cc

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//LIC// ====================================================================
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//LIC// multi-physics finite-element library, available 
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//LIC// Copyright (C) 2006-2025 Matthias Heil and Andrew Hazel
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//LIC// Lesser General Public License for more details.
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//LIC//====================================================================
// Driver for a periodically loaded elastic body
 
// The oomphlib headers
#include "generic.h"
#include "linear_elasticity.h"
 
// The mesh
#include "meshes/rectangular_quadmesh.h"
 
using namespace std;
 
using namespace oomph;
 
//===start_of_namespace=================================================
/// Namespace for global parameters
//======================================================================
namespace Global_Parameters
{
 /// Amplitude of traction applied
 double Amplitude = 1.0;
 
 /// Specify problem to be solved (boundary conditons for finite or
 /// infinite domain).
 bool Finite=false;
 
 /// Define Poisson coefficient Nu
 double Nu = 0.3;
 
 /// Length of domain in x direction
 double Lx = 1.0;
 
 /// Length of domain in y direction
 double Ly = 2.0;
 
 /// The elasticity tensor
 IsotropicElasticityTensor E(Nu);
 
 /// The exact solution for infinite depth case
 void exact_solution(const Vector<double> &x,
                     Vector<double> &u)
 {
  u[0] = -Amplitude*cos(2.0*MathematicalConstants::Pi*x[0]/Lx)*
        exp(2.0*MathematicalConstants::Pi*(x[1]-Ly))/
        (2.0/(1.0+Nu)*MathematicalConstants::Pi);
  u[1] = -Amplitude*sin(2.0*MathematicalConstants::Pi*x[0]/Lx)*
        exp(2.0*MathematicalConstants::Pi*(x[1]-Ly))/
        (2.0/(1.0+Nu)*MathematicalConstants::Pi);
 }
 
 /// The traction function
void periodic_traction(const double &time,
                       const Vector<double> &x,
                       const Vector<double> &n,
                       Vector<double> &result)
 {
  result[0] = -Amplitude*cos(2.0*MathematicalConstants::Pi*x[0]/Lx);
  result[1] = -Amplitude*sin(2.0*MathematicalConstants::Pi*x[0]/Lx);
 }
} // end_of_namespace
 
 
//===start_of_problem_class=============================================
/// Periodic loading problem
//======================================================================
template<class ELEMENT>
class PeriodicLoadProblem : public Problem
{
public:
 
 /// Constructor: Pass number of elements in x and y directions 
 /// and lengths
 PeriodicLoadProblem(const unsigned &nx, const unsigned &ny, 
                     const double &lx, const double &ly);
 
 /// Update before solve is empty
 void actions_before_newton_solve() {}
 
 /// Update after solve is empty
 void actions_after_newton_solve() {}
 
 /// Doc the solution
 void doc_solution(DocInfo& doc_info);
 
private:
 
 /// Allocate traction elements on the top surface
 void assign_traction_elements();
 
 /// Pointer to the bulk mesh
 Mesh* Bulk_mesh_pt;
 
 /// Pointer to the mesh of traction elements
 Mesh* Surface_mesh_pt;
 
}; // end_of_problem_class
 
 
//===start_of_constructor=============================================
/// Problem constructor: Pass number of elements in coordinate
/// directions and size of domain.
//====================================================================
template<class ELEMENT>
PeriodicLoadProblem<ELEMENT>::PeriodicLoadProblem
(const unsigned &nx, const unsigned &ny,
 const double &lx, const double& ly)
{
 //Now create the mesh with periodic boundary conditions in x direction
 bool periodic_in_x=true;
 Bulk_mesh_pt = 
  new RectangularQuadMesh<ELEMENT>(nx,ny,lx,ly,periodic_in_x);
 
 //Create the surface mesh of traction elements
 Surface_mesh_pt=new Mesh;
 assign_traction_elements();
 
 // Set the boundary conditions for this problem: All nodes are
 // free by default -- just pin & set the ones that have Dirichlet 
 // conditions here
 unsigned ibound=0;
 unsigned num_nod=Bulk_mesh_pt->nboundary_node(ibound);
 for (unsigned inod=0;inod<num_nod;inod++)
  {
   // Get pointer to node
   Node* nod_pt=Bulk_mesh_pt->boundary_node_pt(ibound,inod);
 
   // Pinned in x & y at the bottom and set value
   nod_pt->pin(0);
   nod_pt->pin(1);
 
   // Check which boundary conditions to set and set them
   if (Global_Parameters::Finite)
     {
      // Set the displacements to zero
      nod_pt->set_value(0,0);
      nod_pt->set_value(1,0);
     }
   else
     {
      // Extract nodal coordinates from node:
      Vector<double> x(2);
      x[0]=nod_pt->x(0);
      x[1]=nod_pt->x(1);
 
      // Compute the value of the exact solution at the nodal point
      Vector<double> u(2);
      Global_Parameters::exact_solution(x,u);
 
      // Assign these values to the nodal values at this node
      nod_pt->set_value(0,u[0]);
      nod_pt->set_value(1,u[1]);
     };
  } // end_loop_over_boundary_nodes
 
 // Complete the problem setup to make the elements fully functional
 
 // Loop over the elements
 unsigned n_el = Bulk_mesh_pt->nelement();
 for(unsigned e=0;e<n_el;e++)
  {
   // Cast to a bulk element
   ELEMENT *el_pt = dynamic_cast<ELEMENT*>(Bulk_mesh_pt->element_pt(e));
 
   // Set the elasticity tensor
   el_pt->elasticity_tensor_pt() = &Global_Parameters::E;
  }// end loop over elements
 
 // Loop over the traction elements
 unsigned n_traction =  Surface_mesh_pt->nelement();
 for(unsigned e=0;e<n_traction;e++)
  {
   // Cast to a surface element
   LinearElasticityTractionElement<ELEMENT> *el_pt = 
    dynamic_cast<LinearElasticityTractionElement<ELEMENT>* >
    (Surface_mesh_pt->element_pt(e));
   
   // Set the applied traction
   el_pt->traction_fct_pt() = &Global_Parameters::periodic_traction;
  }// end loop over traction elements
 
 // Add the submeshes to the problem
 add_sub_mesh(Bulk_mesh_pt);
 add_sub_mesh(Surface_mesh_pt);
 
 // Now build the global mesh
 build_global_mesh();
 
 // Assign equation numbers
 cout << assign_eqn_numbers() << " equations assigned" << std::endl; 
} // end of constructor
 
 
//===start_of_traction===============================================
/// Make traction elements along the top boundary of the bulk mesh
//===================================================================
template<class ELEMENT>
void PeriodicLoadProblem<ELEMENT>::assign_traction_elements()
{
 
 // How many bulk elements are next to boundary 2 (the top boundary)?
 unsigned bound=2;
 unsigned n_neigh = Bulk_mesh_pt->nboundary_element(bound); 
 
 // Now loop over bulk elements and create the face elements
 for(unsigned n=0;n<n_neigh;n++)
  {
   // Create the face element
   FiniteElement *traction_element_pt 
    = new LinearElasticityTractionElement<ELEMENT>
    (Bulk_mesh_pt->boundary_element_pt(bound,n),
     Bulk_mesh_pt->face_index_at_boundary(bound,n));
 
   // Add to mesh
   Surface_mesh_pt->add_element_pt(traction_element_pt);
  }
 
} // end of assign_traction_elements
 
//==start_of_doc_solution=================================================
/// Doc the solution
//========================================================================
template<class ELEMENT>
void PeriodicLoadProblem<ELEMENT>::doc_solution(DocInfo& doc_info)
{ 
 ofstream some_file;
 char filename[100];
 
 // Number of plot points
 unsigned npts=5; 
 
 // Output solution 
 snprintf(filename, sizeof(filename), "%s/soln.dat",doc_info.directory().c_str());
 some_file.open(filename);
 Bulk_mesh_pt->output(some_file,npts);
 some_file.close();
 
 // Output exact solution 
 snprintf(filename, sizeof(filename), "%s/exact_soln.dat",doc_info.directory().c_str());
 some_file.open(filename);
 Bulk_mesh_pt->output_fct(some_file,npts,
                          Global_Parameters::exact_solution); 
 some_file.close();
 
 // Doc error
 double error=0.0;
 double norm=0.0;
 snprintf(filename, sizeof(filename), "%s/error.dat",doc_info.directory().c_str());
 some_file.open(filename);
 Bulk_mesh_pt->compute_error(some_file,
                             Global_Parameters::exact_solution, 
                             error,norm);
 some_file.close();
 
// Doc error norm:
 cout << "\nNorm of error    " << sqrt(error) << std::endl; 
 cout << "Norm of solution : " << sqrt(norm) << std::endl << std::endl;
 cout << std::endl;
 
 
} // end_of_doc_solution   
 
 
//===start_of_main======================================================
/// Driver code for PeriodicLoad linearly elastic problem
//======================================================================
int main(int argc, char* argv[]) 
{
 // Number of elements in x-direction
 unsigned nx=5;
 
 // Number of elements in y-direction (for (approximately) square elements)
 unsigned ny=unsigned(double(nx)*Global_Parameters::Ly/Global_Parameters::Lx);
 
 // Set up doc info
 DocInfo doc_info;
 
 // Set output directory
 doc_info.set_directory("RESLT");
 
 // Set up problem
 PeriodicLoadProblem<QLinearElasticityElement<2,3> > 
  problem(nx,ny,Global_Parameters::Lx, Global_Parameters::Ly);
 
 // Solve
 problem.newton_solve();
 
 // Output the solution
 problem.doc_solution(doc_info);
  
} // end_of_main