Compute the hyperbolic term of the governing equations. More...

#include <time.h>
#include <stdlib.h>
#include <basic.h>
#include <arrayfunctions.h>
#include <mpivars.h>
#include <hypar.h>

Functions
static int	ReconstructHyperbolic (double , double , double , double , int, void , void , double, int, int()(double , double , double , double , double , double , int, void , double))

static int	DefaultUpwinding (double , double , double , double , double , double , int, void *, double)

int	HyperbolicFunction (double hyp, double u, void s, void m, double t, int LimFlag, int(FluxFunction)(double , double , int, void , double), int(UpwindFunction)(double , double , double , double , double , double , int, void , double))

Detailed Description

Compute the hyperbolic term of the governing equations.

Author: Debojyoti Ghosh

Definition in file HyperbolicFunction.c.

Function Documentation

◆ ReconstructHyperbolic()

int ReconstructHyperbolic	(	double *	fluxI,
		double *	fluxC,
		double *	u,
		double *	x,
		int	dir,
		void *	s,
		void *	m,
		double	t,
		int	LimFlag,
		int()(double , double , double , double , double , double , int, void , double)	UpwindFunction
	)

static

This function computes the numerical flux \(\hat{\bf f}_{j+1/2}\) at the interface from the cell-centered flux function \({\bf f}_j\). This happens in two steps:-

Interpolation: High-order accurate approximations to the flux at the interface \(j+1/2\) are computed from the cell-centered flux with left- and right-biased interpolation methods. This is done by the HyPar::InterpolateInterfacesHyp function. This can be expressed as follows:

\begin{align} \hat{\bf f}^L_{j+1/2} &= \mathcal{I}\left({\bf f}_j,+1\right), \\ \hat{\bf f}^R_{j+1/2} &= \mathcal{I}\left({\bf f}_j,-1\right), \end{align}

where the \(\pm 1\) indicates the interpolation bias, and \(\mathcal{I}\) is the interpolation operator pointed to by HyPar::InterpolateInterfacesHyp (see src/InterpolationFunctions for all the available operators). The interface values of the solution are similarly computed:

\begin{align} \hat{\bf u}^L_{j+1/2} &= \mathcal{I}\left({\bf u}_j,+1\right), \\ \hat{\bf u}^R_{j+1/2} &= \mathcal{I}\left({\bf u}_j,-1\right), \end{align}

The specific choice of \(\mathcal{I}\) is set based on HyPar::spatial_scheme_hyp.

Upwinding: The final flux at the interface is computed as

\begin{equation} \hat{\bf f}_{j+1/2} = \mathcal{U}\left( \hat{\bf f}^L_{j+1/2}, \hat{\bf f}^R_{j+1/2}, \hat{\bf u}^L_{j+1/2}, \hat{\bf u}^R_{j+1/2} \right), \end{equation}

where \(\mathcal{U}\) denotes the upwinding function UpwindFunction() passed as an argument (if NULL, DefaultUpwinding() is used). The upwinding function is specified by the physical model.

Note: Solution-dependent, nonlinear interpolation methods (such as WENO, CRWENO) are implemented in a way that separates the calculation of the nonlinear interpolation weights (based on, say, the smoothness of the flux function), and the actual evaluation of the interpolant, into different functions. This allows the flexibility to choose if and when the nonlinear coefficients are evaluated (or previously computed values are reused). Some possible scenarios are:

For explicit time integration, they are computed every time the hyperbolic flux term is being computed.
For implicit time integration, consistency or linearization may require that they be computed and "frozen" at the beginning of a time step or stage.

The argument LimFlag controls this behavior:

LimFlag = 1 means recompute the nonlinear coefficients.
LimFlag = 0 means reuse the the previously computed coefficients.

Parameters

fluxI	Array to hold the computed interface fluxes. This array does not have ghost points. The dimensions are the same as those of u without ghost points in all dimensions, except along dir, where it is one more
fluxC	Array of the flux function computed at the cell centers (same layout as u)
u	Solution array
x	Array of spatial coordinates
dir	Spatial dimension along which to reconstruct the interface fluxes
s	Solver object of type HyPar
m	MPI object of type MPIVariables
t	Current solution time
LimFlag	Flag to indicate if the nonlinear coefficients for solution-dependent interpolation method should be recomputed
UpwindFunction	Function pointer to the upwinding function for the interface flux computation. If NULL, DefaultUpwinding() will be used.

Definition at line 167 of file HyperbolicFunction.c.

 {
   HyPar         *solver = (HyPar*)        s;
   MPIVariables  *mpi    = (MPIVariables*) m;
   _DECLARE_IERR_;
 
   double *uC     = NULL;
   double *uL     = solver->uL;
   double *uR     = solver->uR;
   double *fluxL  = solver->fL;
   double *fluxR  = solver->fR;
 
   /*
     precalculate the non-linear interpolation coefficients if required
     else reuse the weights previously calculated
   */
 
   if (LimFlag) IERR solver->SetInterpLimiterVar(fluxC,u,x,dir,solver,mpi);
 
   /* if defined, calculate the modified u-function to be used for upwinding
      e.g.: used in well-balanced schemes for Euler/Navier-Stokes with gravity
      otherwise, just copy u to uC */
   if (solver->UFunction) {
     uC = solver->uC;
     IERR solver->UFunction(uC,u,dir,solver,mpi,t); CHECKERR(ierr);
   } else uC = u;
 
   /* Interpolation -> to calculate left and right-biased interface flux and state variable*/
   IERR solver->InterpolateInterfacesHyp(uL   ,uC   ,u,x, 1,dir,solver,mpi,1); CHECKERR(ierr);
   IERR solver->InterpolateInterfacesHyp(uR   ,uC   ,u,x,-1,dir,solver,mpi,1); CHECKERR(ierr);
   IERR solver->InterpolateInterfacesHyp(fluxL,fluxC,u,x, 1,dir,solver,mpi,0); CHECKERR(ierr);
   IERR solver->InterpolateInterfacesHyp(fluxR,fluxC,u,x,-1,dir,solver,mpi,0); CHECKERR(ierr);
 
   /* Upwind -> to calculate the final interface flux */
   if (UpwindFunction) { IERR UpwindFunction   (fluxI,fluxL,fluxR,uL  ,uR  ,u   ,dir,solver,t); CHECKERR(ierr); }
   else                { IERR DefaultUpwinding (fluxI,fluxL,fluxR,NULL,NULL,NULL,dir,solver,t); CHECKERR(ierr); }
 
   return(0);
 }

◆ DefaultUpwinding()

int DefaultUpwinding	(	double *	fI,
		double *	fL,
		double *	fR,
		double *	uL,
		double *	uR,
		double *	u,
		int	dir,
		void *	s,
		double	t
	)

static

If no upwinding scheme is specified, this function defines the "upwind" flux as the arithmetic mean of the left- and right-biased fluxes.

Parameters

fI	Computed upwind interface flux
fL	Left-biased reconstructed interface flux
fR	Right-biased reconstructed interface flux
uL	Left-biased reconstructed interface solution
uR	Right-biased reconstructed interface solution
u	Cell-centered solution
dir	Spatial dimension
s	Solver object of type HyPar
t	Current solution time

Definition at line 226 of file HyperbolicFunction.c.

 {
   HyPar *solver = (HyPar*)    s;
   int   done;
 
   int *dim  = solver->dim_local;
   int ndims = solver->ndims;
   int nvars = solver->nvars;
 
   int bounds_outer[ndims], bounds_inter[ndims];
   _ArrayCopy1D_(dim,bounds_outer,ndims); bounds_outer[dir] =  1;
   _ArrayCopy1D_(dim,bounds_inter,ndims); bounds_inter[dir] += 1;
 
   done = 0; int index_outer[ndims], index_inter[ndims];
   _ArraySetValue_(index_outer,ndims,0);
   while (!done) {
     _ArrayCopy1D_(index_outer,index_inter,ndims);
     for (index_inter[dir] = 0; index_inter[dir] < bounds_inter[dir]; index_inter[dir]++) {
       int p; _ArrayIndex1D_(ndims,bounds_inter,index_inter,0,p);
       int v; for (v=0; v<nvars; v++) fI[nvars*p+v] = 0.5 * (fL[nvars*p+v]+fR[nvars*p+v]);
     }
     _ArrayIncrementIndex_(ndims,bounds_outer,index_outer,done);
   }
 
   return(0);
 }

◆ HyperbolicFunction()

int HyperbolicFunction	(	double *	hyp,
		double *	u,
		void *	s,
		void *	m,
		double	t,
		int	LimFlag,
		int()(double , double , int, void , double)	FluxFunction,
		int()(double , double , double , double , double , double , int, void , double)	UpwindFunction
	)

This function computes the hyperbolic term of the governing equations, expressed as follows:-

\begin{equation} {\bf F} \left({\bf u}\right) = \sum_{d=0}^{D-1} \frac {\partial {\bf f}_d\left({\bf u}\right)} {\partial x_d} \end{equation}

using a conservative finite-difference discretization is space:

\begin{equation} \hat{\bf F} \left({\bf u}\right) = \sum_{d=0}^{D-1} \frac {1} {\Delta x_d} \left[ \hat{\bf f}_{d,j+1/2} - \hat{\bf f}_{d,j-1/2} \right] \end{equation}

where \(d\) denotes the spatial dimension, \(D\) denotes the total number of spatial dimensions, the hat denotes the discretized quantity, and \(j\) is the grid coordinate along dimension \(d\). The approximation to the flux function \({\bf f}_d\) at the interfaces \(j\pm1/2\), denoted by \(\hat{\bf f}_{d,j\pm 1/2}\), are computed using the function ReconstructHyperbolic().

Parameters

hyp	Array to hold the computed hyperbolic term (shares the same layout as u
u	Solution array
s	Solver object of type HyPar
m	MPI object of type MPIVariables
t	Current simulation time
LimFlag	Flag to indicate if the nonlinear coefficients for solution-dependent interpolation method should be recomputed (see ReconstructHyperbolic() for an explanation on why this is needed)
FluxFunction	Function pointer to the flux function for the hyperbolic term
UpwindFunction	Function pointer to the upwinding function for the hyperbolic term

Definition at line 31 of file HyperbolicFunction.c.

 {
   HyPar         *solver = (HyPar*)        s;
   MPIVariables  *mpi    = (MPIVariables*) m;
   int           d, v, i, done;
   double        *FluxI  = solver->fluxI; /* interface flux     */
   double        *FluxC  = solver->fluxC; /* cell centered flux */
   _DECLARE_IERR_;
 
   int     ndims  = solver->ndims;
   int     nvars  = solver->nvars;
   int     ghosts = solver->ghosts;
   int     *dim   = solver->dim_local;
   int     size   = solver->npoints_local_wghosts;
   double  *x     = solver->x;
   double  *dxinv = solver->dxinv;
   int     index[ndims], index1[ndims], index2[ndims], dim_interface[ndims];
 
   LimFlag = (LimFlag && solver->flag_nonlinearinterp && solver->SetInterpLimiterVar);
 
   _ArraySetValue_(hyp,size*nvars,0.0);
   _ArraySetValue_(solver->StageBoundaryIntegral,2*ndims*nvars,0.0);
   if (!FluxFunction) return(0); /* zero hyperbolic term */
   solver->count_hyp++;
 
 #if defined(CPU_STAT)
   double cpu_time = 0.0;
   clock_t cpu_start, cpu_end;
 #endif
 
   int offset = 0;
   for (d = 0; d < ndims; d++) {
     _ArrayCopy1D_(dim,dim_interface,ndims); dim_interface[d]++;
     int size_cellcenter = 1; for (i = 0; i < ndims; i++) size_cellcenter *= (dim[i] + 2*ghosts);
     int size_interface = 1; for (i = 0; i < ndims; i++) size_interface *= dim_interface[i];
 
     /* evaluate cell-centered flux */
     IERR FluxFunction(FluxC,u,d,solver,t); CHECKERR(ierr);
     /* compute interface fluxes */
     IERR ReconstructHyperbolic(FluxI,FluxC,u,x+offset,d,solver,mpi,t,LimFlag,UpwindFunction);
     CHECKERR(ierr);
 
     /* calculate the first derivative */
     done = 0; _ArraySetValue_(index,ndims,0);
     int p, p1, p2;
 
 #if defined(CPU_STAT)
     cpu_start = clock();
 #endif
 
     while (!done) {
       _ArrayCopy1D_(index,index1,ndims);
       _ArrayCopy1D_(index,index2,ndims); index2[d]++;
       _ArrayIndex1D_(ndims,dim          ,index ,ghosts,p);
       _ArrayIndex1D_(ndims,dim_interface,index1,0     ,p1);
       _ArrayIndex1D_(ndims,dim_interface,index2,0     ,p2);
       for (v=0; v<nvars; v++) hyp[nvars*p+v] += dxinv[offset+ghosts+index[d]]
                                               * (FluxI[nvars*p2+v]-FluxI[nvars*p1+v]);
       /* boundary flux integral */
       if (index[d] == 0)
         for (v=0; v<nvars; v++) solver->StageBoundaryIntegral[(2*d+0)*nvars+v] -= FluxI[nvars*p1+v];
       if (index[d] == dim[d]-1)
         for (v=0; v<nvars; v++) solver->StageBoundaryIntegral[(2*d+1)*nvars+v] += FluxI[nvars*p2+v];
 
       _ArrayIncrementIndex_(ndims,dim,index,done);
     }
 
 #if defined(CPU_STAT)
     cpu_end = clock();
     cpu_time += (double)(cpu_end - cpu_start) / CLOCKS_PER_SEC;
 #endif
 
     offset += dim[d] + 2*ghosts;
   }
 
 #if defined(CPU_STAT)
   printf("HyperbolicFunction CPU time = %8.6lf\n", cpu_time);
 #endif
 
   if (solver->flag_ib) _ArrayBlockMultiply_(hyp,solver->iblank,size,nvars);
 
   return(0);
 }