Custom Use

Introduction

nsfds3 can also be used as a classical Python package. It provides several main objects to perform numerical simulations :

• cpgrid package provides objects related to the grid generation,

• solver package povides objects related to the solver itself,

• graphics module provides in particular nsfds3.graphics.MPLViewer for result inspection,

• utils package provides various utilities.

The following example gives the general philosophy to use nsfds3:

from nsfds3.solver import CfgSetup, FDTD
from nsfds3.cpgrid import build_mesh

# Initialize simulation parameter
cfg = CfgSetup()    # or cfg = CfgSetup('path_to_configfile.conf')

# Define the mesh
msh = build_mesh(cfg)

# Create and run simulation
fdtd = FDTD(msh, cfg)
fdtd.run()

# Figures
fdtd.show(view='p', nans=True, buffer=True, grid=False, obstacles=True)

Once the simulation is complete, you can access the acoustic field at the last iteration through the fdtd.fld object using the following attributes.

fdtd.fld attributes	description
r	density
ru	product of density and x component of velocity
rv	product of density and y component of velocity
rw	product of density and z component of velocity (for 3d computations)
re	product of density and energy
wx	x component of vorticity (for 3d computations, if vorticity is computed)
wy	y component of vorticity (for 3d computations, if vorticity is computed)
wz	z component of vorticity (if vorticity is computed)
Tk	Temperature (if viscous fluxes are computed)

nsfds3 files

As seen previously, each simulation can be configured using a .conf configuration file. nsfds3 creates also the additional following files:

• a .cfg file containing the nsfds3.solver.CfgSetup object used for the simulation,

• a .msh file containing the nsfds3.cpgrid.CartesianGrid or nsfds3.cpgrid.CurvilinearGrid object used for the simulation,

• a .hdf5 file containing, in particular, the fields computed during the simulation.

hdf5 files

If save fields option is True, hdf5 are created. They contain the following variables.

var	variable
r_itX	density
ru_itX	product of density and x component of velocity
rv_itX	product of density and y component of velocity
rw_itX	product of density and z component of velocity (for 3d computations)
re_itX	product of density and energy
wx_itX	x component of vorticity (for 3d computations, if vorticity is computed)
wy_itX	y component of vorticity (for 3d computations, if vorticity is computed)
wz_itX	z component of vorticity (if vorticity is computed)
x	x-grid
y	y-grid
z	z-grid
probe_locations	coordinates of probes
probe_values	pressure at probe locations

Also note that in curvilinear coordinates, additional variables are available :

var	variable
xp	physical x-grid
yp	physical y-grid
zp	physical z-grid (for 3d computations)
J	Jacobian matrix of transformation

The Y_itX quantities provide the field Y at the X-th time step.

The pressure is not directly provided. To access acoustic pressure, one can use the nsfds3.utils.get_pressure() function as follows:

from nsfds3.utils import get_pressure

    p = get_pressure(r=r, ru=ru, rv=rv, rw=rw, re=re, gamma=gamma)

gamma being the heat capacity ratio that can be accessed through the CfgSetup object (cfg.gamma).

cfg and msh pickle files

.cfg and .msh files are also automatically created for each simulation. They contain the configuration and grid objects relative to the simulation. One can use the nsfds3.utils.get_objects() function to load both files:

from nsfds3.utils import get_objects

cfg, msh = get_objects('path_to_cfg_and_msh_files', 'basename_of_these_files')

These objects contain in particular :

• msh.obstacles : the collection of obstacles

• cfg.dx, cfg.dy, cfg.dz, cfg.dt : spatial and time steps

• cfg.nx, cfg.ny, cfg.nz, cfg.nt, cfg.ns : Number of points (spatial and temporal)

• cfg.p0, cfg.rho0, cfg.T0, cfg.c0, cfg.gamma, cfg.prandtl, cfg.mu : Thermophysical parameters

• … and many other parameters.