spine_two_layer_interface.cc

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//LIC// ====================================================================
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//LIC// multi-physics finite-element library, available 
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//LIC// Copyright (C) 2006-2023 Matthias Heil and Andrew Hazel
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//LIC//====================================================================
// Driver for two-dimensional two fluid interface problem, where
// the mesh is deformed using a spine-based node-update strategy
 
// Generic oomph-lib header
#include "generic.h"
 
// Navier-Stokes headers
#include "navier_stokes.h"
 
// Interface headers
#include "fluid_interface.h"
 
// The mesh
#include "meshes/two_layer_spine_mesh.h"
 
using namespace std;
 
using namespace oomph;
 
 
//==start_of_namespace====================================================
/// Namespace for physical parameters
//========================================================================
namespace Global_Physical_Variables
{
 
 /// Reynolds number
 double Re = 5.0;
 
 /// Strouhal number
 double St = 1.0;
 
 /// Womersley number (Reynolds x Strouhal, computed automatically)
 double ReSt;
 
 /// Product of Reynolds number and inverse of Froude number
 double ReInvFr = 5.0; // (Fr = 1)
 
 /// Ratio of viscosity in upper fluid to viscosity in lower
 /// fluid. Reynolds number etc. is based on viscosity in lower fluid.
 double Viscosity_Ratio = 0.1;
 
 /// Ratio of density in upper fluid to density in lower
 /// fluid. Reynolds number etc. is based on density in lower fluid.
 double Density_Ratio = 0.5;
 
 /// Capillary number
 double Ca = 0.01;
 
 /// Direction of gravity
 Vector<double> G(2);
 
} // End of namespace
 
 
/// ///////////////////////////////////////////////////////////////////////
/// ///////////////////////////////////////////////////////////////////////
/// ///////////////////////////////////////////////////////////////////////
 
 
//==start_of_problem_class================================================
/// Two fluid interface problem in a rectangular domain which is
/// periodic in the x direction
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
class InterfaceProblem : public Problem
{
 
public:
 
 /// Constructor: Pass the number of elements and the width of the
 /// domain in the x direction. Also pass the number of elements in
 /// the y direction of the bottom (fluid 1) and top (fluid 2) layers,
 /// along with the heights of both layers.
 InterfaceProblem(const unsigned &n_x, const unsigned &n_y1, 
                  const unsigned &n_y2, const double &l_x, 
                  const double &h1, const double &h2);
 
 /// Destructor (empty)
 ~InterfaceProblem() {}
 
 /// Set initial conditions
 void set_initial_condition();
 
 /// Set boundary conditions
 void set_boundary_conditions();
 
 /// Doc the solution
 void doc_solution(DocInfo &doc_info);
 
 /// Do unsteady run up to maximum time t_max with given timestep dt
 void unsteady_run(const double &t_max, const double &dt);
 
private:
 
 /// Spine heights/lengths are unknowns in the problem so their
 /// values get corrected during each Newton step. However, changing
 /// their value does not automatically change the nodal positions, so
 /// we need to update all of them here.
 void actions_before_newton_convergence_check()
  {
   Bulk_mesh_pt->node_update();
  }
 
 /// No actions required before solve step
 void actions_before_newton_solve() {}
 
 /// Update after solve can remain empty, because the update 
 /// is performed automatically after every Newton step.
 void actions_after_newton_solve() {}
 
 /// Deform the mesh/free surface to a prescribed function
 void deform_free_surface(const double &epsilon, const unsigned &n_periods);
 
 /// Fix pressure in element e at pressure dof pdof and set to pvalue
 void fix_pressure(const unsigned &e,
                   const unsigned &pdof, 
                   const double &pvalue)
  {
   // Fix the pressure at that element
   dynamic_cast<ELEMENT*>(Bulk_mesh_pt->element_pt(e))->
                          fix_pressure(pdof,pvalue);
  }
 
 /// Width of domain
 double Lx;
 
 /// Trace file
 ofstream Trace_file;
 
 /// Pointer to the specific bulk mesh
 TwoLayerSpineMesh<ELEMENT>* Bulk_mesh_pt; 
 
 /// Pointer to the surface mesh
 Mesh* Surface_mesh_pt;
 
}; // End of problem class
 
 
 
//==start_of_constructor==================================================
/// Constructor for two fluid interface problem
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
InterfaceProblem<ELEMENT,TIMESTEPPER>::
InterfaceProblem(const unsigned &n_x, const unsigned &n_y1,
                 const unsigned &n_y2, const double &l_x,
                 const double& h1, const double &h2) : Lx(l_x)
{
 
 // Allocate the timestepper (this constructs the time object as well)
 add_time_stepper_pt(new TIMESTEPPER); 
 
 // Build and assign mesh (the "true" boolean flag tells the mesh
 // constructor that the domain is periodic in x)
 Bulk_mesh_pt = new TwoLayerSpineMesh<ELEMENT>
  (n_x,n_y1,n_y2,l_x,h1,h2,true,time_stepper_pt());
 
 Surface_mesh_pt = new Mesh;
 
 //Loop over the horizontal elements
 for(unsigned i=0;i<n_x;i++)
  {
   //Construct a new 1D line element on the face on which the local
   //coordinate 1 is fixed at its max. value (1) -- Face 2
   FiniteElement *interface_element_pt =  new 
    SpineLineFluidInterfaceElement<ELEMENT>(
     Bulk_mesh_pt->finite_element_pt(n_x*(n_y1-1)+i),2);
   
   this->Surface_mesh_pt->add_element_pt(interface_element_pt);
  }
 
 
 // --------------------------------------------
 // Set the boundary conditions for this problem
 // --------------------------------------------
 
 // All nodes are free by default -- just pin the ones that have
 // Dirichlet conditions here
 
 // Loop over mesh boundaries
 for(unsigned b=0;b<5;b++)
  {
   // Determine number of nodes on boundary b
   const unsigned n_node = Bulk_mesh_pt->nboundary_node(b);
 
   // Loop over nodes on boundary b
   for (unsigned n=0;n<n_node;n++)
    {
     // Pin x-component of velocity on all boundaries (no slip/penetration)
     Bulk_mesh_pt->boundary_node_pt(b,n)->pin(0);
 
     // Pin y-component of velocity on both solid boundaries (no penetration)
     if(b==0 || b==3) { Bulk_mesh_pt->boundary_node_pt(b,n)->pin(1); }
    }
  }
 
 // ----------------------------------------------------------------
 // Complete the problem setup to make the elements fully functional
 // ----------------------------------------------------------------
 
 // Determine number of bulk elements in lower/upper fluids
 const unsigned n_lower = Bulk_mesh_pt->nlower();
 const unsigned n_upper = Bulk_mesh_pt->nupper();
 
 // Loop over bulk elements in lower fluid
 for(unsigned e=0;e<n_lower;e++)
  {
   // Upcast from GeneralisedElement to the present element
   ELEMENT *el_pt = dynamic_cast<ELEMENT*>(Bulk_mesh_pt->
                                           lower_layer_element_pt(e));
 
   // Set the Reynolds number
   el_pt->re_pt() = &Global_Physical_Variables::Re;
 
   // Set the Womersley number
   el_pt->re_st_pt() = &Global_Physical_Variables::ReSt;
 
   // Set the product of the Reynolds number and the inverse of the
   // Froude number
   el_pt->re_invfr_pt() = &Global_Physical_Variables::ReInvFr;
 
   // Set the direction of gravity
   el_pt->g_pt() = &Global_Physical_Variables::G;
 
  } // End of loop over bulk elements in lower fluid
 
 // Loop over bulk elements in upper fluid 
 for(unsigned e=0;e<n_upper;e++)
  {
   // Upcast from GeneralisedElement to the present element
   ELEMENT *el_pt = dynamic_cast<ELEMENT*>(Bulk_mesh_pt->
                                           upper_layer_element_pt(e));
 
   // Set the Reynolds number
   el_pt->re_pt() = &Global_Physical_Variables::Re;
 
   // Set the Womersley number
   el_pt->re_st_pt() = &Global_Physical_Variables::ReSt;
 
   // Set the product of the Reynolds number and the inverse of the
   // Froude number
   el_pt->re_invfr_pt() = &Global_Physical_Variables::ReInvFr;
 
   // Set the viscosity ratio
   el_pt->viscosity_ratio_pt() = &Global_Physical_Variables::Viscosity_Ratio;
 
   // Set the density ratio
   el_pt->density_ratio_pt() = &Global_Physical_Variables::Density_Ratio;
 
   // Set the direction of gravity
   el_pt->g_pt() = &Global_Physical_Variables::G;
 
  } // End of loop over bulk elements in upper fluid
 
 // Set the pressure in the first element at 'node' 0 to 0.0
 fix_pressure(0,0,0.0);
 
 // Determine number of 1D interface elements in mesh
 unsigned n_interface_element = Surface_mesh_pt->nelement();
 
 // Loop over interface elements
 for(unsigned e=0;e<n_interface_element;e++)
  {
   // Upcast from GeneralisedElement to the present element
   SpineLineFluidInterfaceElement<ELEMENT>* el_pt = 
    dynamic_cast<SpineLineFluidInterfaceElement<ELEMENT>*>
    (Surface_mesh_pt->element_pt(e));
 
   // Set the Strouhal number
   el_pt->st_pt() = &Global_Physical_Variables::St;
 
   // Set the Capillary number
   el_pt->ca_pt() = &Global_Physical_Variables::Ca;
 
  } // End of loop over interface elements
 
 // Apply the boundary conditions
 set_boundary_conditions();
 
 this->add_sub_mesh(Bulk_mesh_pt);
 this->add_sub_mesh(Surface_mesh_pt);
 
 this->build_global_mesh();
 
 
 // Setup equation numbering scheme
 cout << "Number of equations: " << assign_eqn_numbers() << std::endl;
 
} // End of constructor
 
 
 
//==start_of_set_initial_condition========================================
/// Set initial conditions: Set all nodal velocities to zero and
/// initialise the previous velocities and nodal positions to correspond
/// to an impulsive start
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
void InterfaceProblem<ELEMENT,TIMESTEPPER>::set_initial_condition()
{
 // Determine number of nodes in mesh
 const unsigned n_node = Bulk_mesh_pt->nnode();
 
 // Loop over all nodes in mesh
 for(unsigned n=0;n<n_node;n++)
  {
   // Loop over the two velocity components
   for(unsigned i=0;i<2;i++)
    {
     // Set velocity component i of node n to zero
     Bulk_mesh_pt->node_pt(n)->set_value(i,0.0);
    }
  }
 
 // Initialise the previous velocity values for timestepping
 // corresponding to an impulsive start
 assign_initial_values_impulsive();
 
} // End of set_initial_condition
 
 
 
//==start_of_set_boundary_conditions======================================
/// Set boundary conditions: Set both velocity components
/// to zero on the top and bottom (solid) walls and the horizontal
/// component only to zero on the side (periodic) boundaries
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
void InterfaceProblem<ELEMENT,TIMESTEPPER>::set_boundary_conditions()
{
 
 // Loop over mesh boundaries
 for(unsigned b=0;b<5;b++)
  {
   // Determine number of nodes on boundary b
   const unsigned n_node = Bulk_mesh_pt->nboundary_node(b);
   
   // Loop over nodes on boundary b
   for(unsigned n=0;n<n_node;n++)
    {
     // Set x-component of the velocity to zero on all boundaries
     Bulk_mesh_pt->boundary_node_pt(b,n)->set_value(0,0.0);
     
     // Set y-component of the velocity to zero on both solid
     // boundaries (top and bottom)
     if(b==0 || b==3)
      {
       Bulk_mesh_pt->boundary_node_pt(b,n)->set_value(1,0.0);
      }
    } // End of loop over nodes on boundary b
  } // End of loop over mesh boundaries
 
} // End of set_boundary_conditions
 
 
 
//==start_of_deform_free_surface==========================================
/// Deform the mesh/free surface to a prescribed function
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
void InterfaceProblem<ELEMENT,TIMESTEPPER>::
deform_free_surface(const double &epsilon,const unsigned &n_periods)
{
 // Determine number of spines in mesh
 const unsigned n_spine = Bulk_mesh_pt->nspine();
 
 // Loop over spines in mesh
 for(unsigned i=0;i<n_spine;i++)
  {
   // Determine x coordinate of spine
   double x_value = Bulk_mesh_pt->boundary_node_pt(0,i)->x(0);
   
   // Set spine height
   Bulk_mesh_pt->spine_pt(i)->height() = 
    1.0 + epsilon*(cos(2.0*n_periods*MathematicalConstants::Pi*x_value/Lx));
  }
 
 // Update nodes in bulk mesh
 Bulk_mesh_pt->node_update();
 
} // End of deform_free_surface
 
 
 
//==start_of_doc_solution=================================================
/// Doc the solution
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
void InterfaceProblem<ELEMENT,TIMESTEPPER>::doc_solution(DocInfo &doc_info)
{ 
 
 // Output the time
 cout << "Time is now " << time_pt()->time() << std::endl;
 
 // Document time and vertical position of left hand side of interface
 // in trace file
 Trace_file << time_pt()->time() << " "
            << Bulk_mesh_pt->spine_pt(0)->height() << " " << std::endl;
 
 ofstream some_file;
 char filename[100];
 
 // Set number of plot points (in each coordinate direction)
 const unsigned npts = 5;
 
 // Open solution output file
 sprintf(filename,"%s/soln%i.dat",doc_info.directory().c_str(),
         doc_info.number());
 some_file.open(filename);
 
 // Output solution to file
 Bulk_mesh_pt->output(some_file,npts);
 Surface_mesh_pt->output(some_file,npts);
 
 // Close solution output file
 some_file.close();
 
} // End of doc_solution
 
 
 
//==start_of_unsteady_run=================================================
/// Perform run up to specified time t_max with given timestep dt
//========================================================================
template <class ELEMENT, class TIMESTEPPER>
void InterfaceProblem<ELEMENT,TIMESTEPPER>::
unsteady_run(const double &t_max, const double &dt)
{
 
 // Set value of epsilon
 const double epsilon = 0.1;
 
 // Set number of periods for cosine term
 const unsigned n_periods = 1;
 
 // Deform the mesh/free surface
 deform_free_surface(epsilon,n_periods);
 
 // Initialise DocInfo object
 DocInfo doc_info;
 
 // Set output directory
 doc_info.set_directory("RESLT");
 
 // Initialise counter for solutions
 doc_info.number()=0;
 
 // Open trace file
 char filename[100];   
 sprintf(filename,"%s/trace.dat",doc_info.directory().c_str());
 Trace_file.open(filename);
 
 // Initialise trace file
 Trace_file << "time, free surface height" << std::endl;
 
 // Initialise timestep
 initialise_dt(dt);
 
 // Set initial conditions
 set_initial_condition();
 
 // Determine number of timesteps
 const unsigned n_timestep = unsigned(t_max/dt);
 
 // Doc initial solution
 doc_solution(doc_info);
 
 // Increment counter for solutions 
 doc_info.number()++;
 
 // Timestepping loop
 for(unsigned t=1;t<=n_timestep;t++)
  {
   // Output current timestep to screen
   cout << "\nTimestep " << t << " of " << n_timestep << std::endl;
   
   // Take one fixed timestep
   unsteady_newton_solve(dt);
 
   // Doc solution
   doc_solution(doc_info);
 
   // Increment counter for solutions 
   doc_info.number()++;
 
  } // End of timestepping loop
 
} // End of unsteady_run
 
 
/// ///////////////////////////////////////////////////////////////////////
/// ///////////////////////////////////////////////////////////////////////
/// ///////////////////////////////////////////////////////////////////////
 
 
//==start_of_main======================================================
/// Driver code for two-dimensional two fluid interface problem
//=====================================================================
int main(int argc, char* argv[]) 
{
 // Store command line arguments
 CommandLineArgs::setup(argc,argv);
 
 // Compute the Womersley number
 Global_Physical_Variables::ReSt =
  Global_Physical_Variables::Re*Global_Physical_Variables::St;
 
 /// Maximum time
 double t_max = 0.6;
 
 /// Duration of timestep
 const double dt = 0.0025;
 
 // If we are doing validation run, use smaller number of timesteps
 if(CommandLineArgs::Argc>1) { t_max = 0.005; }
 
 // Number of elements in x direction
 const unsigned n_x = 12;
   
 // Number of elements in y direction in lower fluid (fluid 1)
 const unsigned n_y1 = 12;
   
 // Number of elements in y direction in upper fluid (fluid 2)
 const unsigned n_y2 = 12;
 
 // Width of domain
 const double l_x = 1.0;
 
 // Height of lower fluid layer
 const double h1 = 1.0;
   
 // Height of upper fluid layer
 const double h2 = 1.0;
 
 // Set direction of gravity (vertically downwards)
 Global_Physical_Variables::G[0] = 0.0;
 Global_Physical_Variables::G[1] = -1.0;
 
 // Set up the spine test problem with QCrouzeixRaviartElements,
 // using the BDF<2> timestepper
 InterfaceProblem<SpineElement<QCrouzeixRaviartElement<2> >,BDF<2> >
  problem(n_x,n_y1,n_y2,l_x,h1,h2);
   
 // Run the unsteady simulation
 problem.unsteady_run(t_max,dt);
 
} // End of main