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helmholtz_cavity_scattering_problem_engine.py
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Tue, May 7, 16:50

helmholtz_cavity_scattering_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
from rrompy.hfengines.fenics_engines import ScatteringProblemEngine
class HelmholtzCavityScatteringProblemEngine(ScatteringProblemEngine):
"""
Solver for scattering problem inside a cavity with parametric wavenumber.
- \Delta u - omega^2 * n^2 * u = 0 in \Omega
u = 0 on \Gamma_D
\partial_nu - i k u = 0 on \Gamma_R
with exact solution a transmitted plane wave.
"""
def __init__(self, kappa:float, n:int, gamma : float = 0.,
signR : int = -1, *args, **kwargs):
super().__init__(kappa, *args, **kwargs)
self.signR = signR
pi = np.pi
mesh = fen.RectangleMesh(fen.Point(0, 0), fen.Point(pi, pi),
3 * n, 3 * n)
self.V = fen.FunctionSpace(mesh, "P", 1)
self.RobinBoundary = (lambda x, on_boundary: on_boundary
and np.isclose(x[1], np.pi))
self.DirichletBoundary = "REST"
x, y = fen.SpatialCoordinate(mesh)[:]
C = 4. / pi ** 4.
bR = C * (2 * (x * (pi - x) + y * (2 * pi - y))
+ (kappa * gamma) ** 2. * x * (pi - x) * y * (2 * pi - y))
bI = C * signR * 2 * kappa * (gamma * (pi - 2 * x) * y * (pi - y)
+ 2 * x * (pi - x) * (pi - y))
wR = fen.cos(kappa * signR * (gamma * x + y))
wI = fen.sin(kappa * signR * (gamma * x + y))
self.forcingTerm = [bR * wR + bI * wI, bI * wR - bR * wI]

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