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burgers_time_viscous.py
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burgers_time_viscous.py
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#! /usr/bin/env python
#
from dolfin import *
def burgers_time_viscous ( e_num, nu ):
#*****************************************************************************80
#
## burgers_time_viscous, 1D time-dependent viscous Burgers equation.
#
# Discussion:
#
# dudt - nu u" + u del u = 0,
# -1 < x < 1, 0 < t
# u(-1,t) = -1, u(1,t) = 1
# u(x,0) = x
#
# This equation is nonlinear in U.
#
# Licensing:
#
# This code is distributed under the MIT license.
#
# Modified:
#
# 21 October 2018
#
# Author:
#
# Sourangshu Ghosh
#
# Parameters:
#
# Input, integer E_NUM, the number of elements to use.
#
# Input, real NU, the viscosity, which should be positive.
# The larger it is, the smoother the solution will be.
#
import matplotlib.pyplot as plt
print ( '' )
print ( ' Number of elements is %d' % ( e_num ) )
print ( ' Viscosity set to %g' % ( nu ) )
#
# Create a mesh on the interval [0,+1].
#
x_left = -1.0
x_right = +1.0
mesh = IntervalMesh ( e_num, x_left, x_right )
#
# Define the function space to be of Lagrange type
# using piecewise linear basis functions.
#
V = FunctionSpace ( mesh, "CG", 1 )
#
# Define the boundary conditions.
# if X <= XLEFT + eps, then U = U_LEFT
# if X_RIGHT - eps <= X, then U = U_RIGHT
#
u_left = -1.0
def on_left ( x, on_boundary ):
return ( on_boundary and near ( x[0], x_left ) )
bc_left = DirichletBC ( V, u_left, on_left )
u_right = +1.0
def on_right ( x, on_boundary ):
return ( on_boundary and near ( x[0], x_right ) )
bc_right = DirichletBC ( V, u_right, on_right )
bc = [ bc_left, bc_right ]
#
# Define the initial condition.
#
u_init = Expression ( "x[0]", degree = 1 )
#
# Define the trial functions (u) and test functions (v).
#
u = Function ( V )
u_old = Function ( V )
v = TestFunction ( V )
#
# Set U and U0 by interpolation.
#
u.interpolate ( u_init )
u_old.assign ( u )
#
# Set the time step.
# We need a UFL version "DT" for the function F,
# and a Python version "dt" to do a conditional in the time loop.
#
DT = Constant ( 0.01 )
dt = 0.01
#
# Set the source term.
#
f = Expression ( "0.0", degree = 0 )
#
# Write the function to be satisfied.
#
n = FacetNormal ( mesh )
#
# Write the function F.
#
F = \
( \
dot ( u - u_old, v ) / DT \
+ nu * inner ( grad ( u ), grad ( v ) ) \
+ inner ( u * u.dx(0), v ) \
- dot ( f, v ) \
) * dx
#
# Specify the jacobian.
#
J = derivative ( F, u )
#
# Do the time integration.
#
k = 0
t = 0.0
t_plot = 0.0
t_final = 1.0
while ( True ):
if ( k % 10 == 0 ):
plot ( u, title = ( 'burgers time viscous %g' % ( t ) ) )
plt.grid ( True )
filename = ( 'burgers_time_viscous_%d.png' % ( k ) )
plt.savefig ( filename )
print ( 'Graphics saved as "%s"' % ( filename ) )
plt.close ( )
t_plot = t_plot + 0.1
if ( t_final <= t ):
print ( '' )
print ( 'Reached final time.' )
break
k = k + 1
t = t + dt
solve ( F == 0, u, bc, J = J )
u_old.assign ( u )
return
def burgers_time_viscous_test ( ):
#*****************************************************************************80
#
## burgers_time_viscous_test tests burgers_time_viscous.
#
# Licensing:
#
# This code is distributed under the GNU LGPL license.
#
# Modified:
#
# 21 October 2018
#
# Author:
#
# John Burkardt
#
import dolfin
import platform
import time
print ( time.ctime ( time.time() ) )
#
# Report level = only warnings or higher.
#
level = 30
set_log_level ( level )
print ( '' )
print ( 'burgers_time_viscous_test:' )
print ( ' Python version: %s' % ( platform.python_version ( ) ) )
print ( ' FENICS version %s'% ( dolfin.__version__ ) )
print ( ' Solve the time-dependent 1d viscous Burgers equation.' )
e_num = 32
nu = 0.05
burgers_time_viscous ( e_num, nu )
#
# Terminate.
#
print ( "" )
print ( "burgers_time_viscous_test:" )
print ( " Normal end of execution." )
print ( '' )
print ( time.ctime ( time.time() ) )
return
if ( __name__ == '__main__' ):
burgers_time_viscous_test ( )