SPINS User Guide

Welcome to the SPINS case setup page.

Getting SPINS and compiling

(Chris: Can we put it on GitHub or make a new repo?)

SPINS consists of a bunch of C++ source files and a bunch of case files, and it requires four libraries. UMFPack, AMD and Blitz++ are supplied with SPINS, and it uses the system-installed FFTW.

Directory structure:

• cpp/src - SPINS source files
• cpp/src/cases - a few dozen example case files
• cpp/AMD - AMD library
• cpp/UMFPack - UMFPack library
• cpp/UFconfig - Helper for compiling AMD/UMFPack

To compile, first ....

The basics

The SPINS model is a Navier-Stokes solver that gets parameters and initial/boundary conditions from calls to user-provided routines. The user-provided routines are encapsulated in the class BaseCase (see BaseCase.hpp).

Creating your own custom configuration involves building a derived class based on BaseCase. The case file cases/doc_minimal.cpp shows the structure of a case file. It makes sense to start with another similar case file and customise it.

Examples of common operations

Outputting the grid

At the top of your file include the global tensor indices:

// Tensor variables for indexing
blitz::firstIndex ii;
blitz::secondIndex jj;
blitz::thirdIndex kk;

Create array tmp and generate the grid, then write the array and the grid reader out:

tmp = xx(ii) + 0*jj + 0*kk;
write_array(tmp,"xgrid");
write_reader(tmp,"xgrid",false);

tmp = 0*ii + yy(jj) + 0*kk;
write_array(tmp,"ygrid");
write_reader(tmp,"ygrid",false);

tmp = 0*ii + 0*jj + zz(kk);
write_array(tmp,"zgrid");
write_reader(tmp,"zgrid",false);

Energy diagnostic

If you're on a periodic grid, use this for kinetic energy diagnostic

double ke = 0.5*rho_0*pssum(sum(u*u+v*v+w*w))/(Nx*Ny*Nz)*Lx*Ly*Lz; // KE
if (master()) {
  FILE * en_record = fopen("energy_record.txt","a");
  assert(en_record);
  fprintf(en_record,"%.8f %.14g\n",time,ke);
  fclose(en_record);
}

and if you're on a mapped chebyshev grid, you can use this for the KE computation

double ke = pssum(sum((*get_quad_x())(ii)*(*get_quad_y())(jj)*(*get_quad_z())(kk)*
                  (pow(u(ii,jj,kk),2)+pow(v(ii,jj,kk),2)+pow(w(ii,jj,kk),2))));

Initialising velocities

ToDo: More here!!