Configuration file
Introduction
nsfds3 usually use a configuration file to setup all simulation parameters. This file can contain the following entries.
[configuration]
version = 0.1.0
data dir = results/ # path to data file
data file = tmp # data filename
timings = True|False # Display timing detail
quiet = True|False # Quiet mode
cpu = 1 # Number of cpu used by the solver
[thermophysic]
norm = True|False # Normalize thermophysical values.
rho0 = 1.2 # Density of fluid (kg/m3)
t0 = 20.0 # Ambiant temperature (°C)
gamma = 1.4 # Heat capacity ratio
[geometry]
free = True|False # Free memory (ComputationDomain intermediate vars)
geofile = None|path # Path to .py file (for geoname/curvname and other functions)
geoname = None|func_name # Function name for geometry
curvname = None|func_name # Function name for curvilinear coordinates
bc = AWPP # Boundary conditions. Must be a mix of AWP
shape = (100, 80) # Grid points. Can be 2 or 3 elements tuple
origin = None|(10, 10) # Origin of the grid. Can be 2 or 3 elements tuple
steps = None|(1, 1) # spatial steps. Can be 2 or 3 elements tuple
flat = None|(ax, idx) # Make flat a 3d geometry along ax at idx location
bz grid points = 20 # Number of points of the buffer zone (BZ)
bz filter order = 3 # Order of the filtering in the BZ
bz stretch order = 3 # Order of the grid stretching in the BZ
bz stretch factor = 2 # Factor of the grid stretching in the BZ
[probes]
vars = () # field to get value from.
locs = () # Probe locations. Must be tuple of tuples
[sources]
on = True|False # Whether or not to setup sources
origins = (), # Origins of the sources (tuple of tuples)
amplitudes = () # Amplitudes of the sources
widths = () # widths of the sources
evolutions = () # time evolution of the sources
[flow]
type = None # Flow type (not supported for now)
components = (0, 0) # Components of the flow velocity [m/s]
[solver]
resume = True|False # Whether or not to resume a computation
nt = 500 # Number of time iterations
ns = 10 # Field saving frequency
cfl = 0.5 # Courant–Friedrichs–Lewy number
save fields = True|False # Whether or not to save fields
viscous fluxes = True|False # Compute viscous fluxes
vorticity = True|False # Compute vorticity
shock capture = True|False # Shock capture procedure
selective filter = True|False # Selective filter
selective filter n-strength = 0.7 # Strength of the filter
selective filter 0-strength = 0.1 # Strength on the nearest point from a wall
[figures]
show figures = True|False # Activate figures
show probes = True|False # Show probes in maps
show bz = True|False # Show PML in maps
show bc = True|False # Show bc profiles
fps = 24 # Framerate for movies
About [geometry] section
Grid
The geometrical parameters shape, origin, steps must have the same size if provided. The parameter bc represents the boundary conditions of the computational domain. Each boundary can be set to rigid wall (W), absorbing buffer zone (A), or periodic condition (P). They are declared in the following order:
left right front back [bottom top]
and must therefore have a length that is twice the dimension of the geometry (4 boundary conditions in 2d and 6 in 3d). If a periodic condition is specified on a side, it must also be specified on the opposite side.
For instance, for a 2d geometry, one can write:
[geometry]
bc = AWWW
shape = 512, 256
origin = 80, 80
steps = 1e-2, 2e-2
and for a 3d geometry:
[geometry]
bc = AWWWPP
shape = 512, 256, 96
origin = 80, 80, 50
steps = 1e-2, 2e-2, 3e-2
Buffer zones
The buffer zone parameters, i.e.:
bz grid points = 20
bz filter order = 3
bz stretch order = 3
bz stretch factor = 2
are used only when an absorbing condition (A) is specified. The grid is then stretched over bz grid points points by a factor bz stretch factor on each side where an absorbing condition is specified. All buffer zones in a simulation have the same parameters.
Note
The PMLs available under nsfds2 are replaced by buffer zones (which seem to be more efficient) under nsfds3. PMLs could potentially reappear in future nsfds3 releases.
Obstacles and transformations
To customize the geometry, one can provide a set of custom obstacles to the
nsfds3.cpgrid.CartesianGrid or
nsfds3.cpgrid.CurvilinearGrid constructors. This can
be done directly in the configuration file by providing a geofile containing a
python function called geoname that setup a custom geometry. In the same way,
a curvilinear transformation can be provided to the solver by setting up a
python function curvname:
[geometry]
geofile = path_to_my_file/my_file.py
geoname = squares
curvname = mountain
The parameter geofile specifies the path to a python file that can contain
function (or class) definitions. The solver will then search this file for
geoname and/or curvname attributes and use them for the simulation. If these
attributes are not found in the specified geofile, nsfds3 will search for
them in nsfds3.cpgrid.TestCases. If no attributes are found, they
will be automatically set to None.
The geoname function must take the shape of the grid as input argument and
return a list of nsfds3.cpgrid.Obstacle objects. For example:
from nsfds3.cpgrid import Obstacle
def squares(shape):
"""Obstacle arangment example."""
obs1 = Obstacle(origin=(10, 10), size=(15, 15), env=shape, bc='WWWW')
obs2 = Obstacle(origin=(80, 70), size=(20, 20), env=shape, bc='WWWW')
return [obs1, obs2, ]
In the same way, a curvilinear transformation can be provided to the solver by providing a python function curvname that must takes as input arguments the numerical axes (xn, yn[, zn]) and returns the transformed axes (xp, yp[, zp]). For example:
import numpy as np
def mountain(x, y):
"""Curvilinear function example."""
xs = np.linspace(-np.pi, np.pi, x.shape[0])
s = np.sin(xs / 0.1)
profile = np.zeros_like(x)
for i in range(x.shape[1]):
profile[:, i] = (2 / (i / 50 + 1)) * (s - xs**2)
return x.copy(), y + profile
About wall sources
As mentioned previously, obstacles can be defined with
nsfds3.cpgrid.Obstacle. It is possible to specify one or more faces
on each obstacle, which will be treated as a wall whose velocity can be set.
To do this, the parameter bc of the obstacle have to be set to V for the
desired side and the set_source method inherited by each obstacle face has to
be called.
The set_source method takes as input argument a function describing the time evolution of the wall velocity. This function must take the time physical time t defined as:
import numpy as np
from nsfds3.solver import CfgSetup
cfg = CfgSetup()
time = np.linspace(0, cfg.nt * cfg.dt, cfg.nt + 1)
and must return a 1d numpy.array of the same dimension as time.
The set_source method also takes the profile keyword argument that specifies the spatial profile of the boundary that can be a sine (profile=’sine’) or a tappered cosine (profile=’tukey’). For example:
import numpy as np
def sine(t):
"""Sinusoïdal time evolution."""
f = 1 / (50 * t[1])
amp = 1
return amp * np.sin(2 * np.pi * f * t)
def single_source(shape):
"""Single obstacle with wall source on right face."""
obs = Obstacle(origin=(20, 20), size=(30, 40), env=shape, bc='WVWW')
obs.face_right.set_source(func=sine, profile='sine')
return [obs, ]
About [sources] and [initial pulses] sections
It is possible to declare sources or initial pulse as follows:
[sources]
on = True
origins = (50, 40), (120, 80)
amplitudes = 1e4, 2e4
widths = 5, 4
evolutions = 14, sine
In this example, two sources are specified for a 2d configuration:
the first one is located at (50, 40) with an amplitude of 1e4 Pa, a width of 5 times de spacial step, and a sinusoïdal time evolution at 14 Hz,
the second one is located at (120, 80) with an amplitude of 2e4 Pa, a width of 4 times the spacial step. and a time evolution specified by the sine function that must be defined in geofile.
Note on the use of .wav files as sources
Important: When using a Monopole or a wall source whose time evolution is specified from a .wav file, you will have to resample it at the sampling frequency of the simulation, i.e. 1/dt. Then, pay attention to the spatial steps (dx, dy, dz) used for the simulation. To resolve frequencies until 20 kHz, dx, dy, dz must be < 0.017 m.
Examples
Here are some configuration examples.
To run the solver with one of these configuration:
nsfds3 solve -c reference.conf