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helmholtz_square_transmission_problem_engine.py
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Sat, May 4, 22:04

helmholtz_square_transmission_problem_engine.py
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# Copyright (C) 2018 by the RROMPy authors
#
# This file is part of RROMPy.
#
# RROMPy is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# RROMPy is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with RROMPy. If not, see <http://www.gnu.org/licenses/>.
#
import numpy as np
import fenics as fen
import ufl
from rrompy.hfengines.base.helmholtz_problem_engine import \
HelmholtzProblemEngine
__all__ = ['HelmholtzSquareTransmissionProblemEngine']
class HelmholtzSquareTransmissionProblemEngine(HelmholtzProblemEngine):
"""
Solver for square transmission Helmholtz problems with parametric
wavenumber.
- \Delta u - omega^2 * n^2 * u = 0 in \Omega
u = 0 on \Gamma_D
with exact solution a transmitted plane wave.
"""
def __init__(self, nT:float, nB:float, kappa:float, theta:float, n:int,
degree_threshold : int = np.inf, verbosity : int = 10):
super().__init__(degree_threshold = degree_threshold,
verbosity = verbosity)
self.omega = kappa
mesh = fen.RectangleMesh(fen.Point(-np.pi/2, -np.pi/2),
fen.Point(np.pi/2, np.pi/2), n, n)
self.V = fen.FunctionSpace(mesh, "P", 3)
dx, dy = np.cos(theta), np.sin(theta)
Kx = kappa * nB * dx
Ky = kappa * (nT**2. - (nB * dx)**2. + 0.j)**.5
T = 2 * kappa * nB * dy / (Ky + kappa * nB * dy)
x, y = fen.SpatialCoordinate(mesh)[:]
TR, TI = np.real(T), np.imag(T)
if np.isclose(np.imag(Ky), 0.):
u0RT = (TR * fen.cos(Kx * x + np.real(Ky) * y)
- TI * fen.sin(Kx * x + np.real(Ky) * y))
u0IT = (TR * fen.sin(Kx * x + np.real(Ky) * y)
+ TI * fen.cos(Kx * x + np.real(Ky) * y))
else:
u0RT = fen.exp(- np.imag(Ky) * y) * (TR * fen.cos(Kx * x)
- TI * fen.sin(Kx * x))
u0IT = fen.exp(- np.imag(Ky) * y) * (TR * fen.sin(Kx * x)
+ TI * fen.cos(Kx * x))
u0RB = (fen.cos(kappa * nB * (dx * x + dy * y))
+ (TR - 1) * fen.cos(kappa * nB * (dx*x - dy*y))
- TI * fen.sin(kappa * nB * (dx*x - dy*y)))
u0IB = (fen.sin(kappa * nB * (dx * x + dy * y))
+ (TR - 1) * fen.sin(kappa * nB * (dx*x - dy*y))
+ TI * fen.cos(kappa * nB * (dx*x - dy*y)))
u0R = ufl.conditional(ufl.ge(y, 0.), u0RT, u0RB)
u0I = ufl.conditional(ufl.ge(y, 0.), u0IT, u0IB)
self.refractionIndex = ufl.conditional(ufl.ge(y, 0.),
fen.Constant(nT),
fen.Constant(nB))
self.DirichletDatum = [u0R, u0I]

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