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Theses and Dissertations
Simulation of Sound Propagating over Soft Surface Using the Equivalent Source Method
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Simulation of Sound Propagating over Soft Surface Using the Equivalent Source Method
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514.pdf
Description
Title
Simulation
of
Sound
Propagating
over
Soft
Surface
Using
the
Equivalent
Source
Method
Subject
Simulation
methods
(acoustics)
;
Noise
control
;
Military
bases
;
Noise
barriers;Wave
equation
;
Description
Noise
generated
by
large
explosions
at
military
bases
causes
discomfort
to
residents
living
in the
vicinity
, for
up
to
20km
away
. This
noise
explosion
has
strong
lowfrequency
content
and
can
travel
over
long
distances
.
Most
of the
theoretical
and
experimental
work
that has been
done
to
study
and
reduce
this
type
of
noise
involved
the
use
of
barriers
and
sound
proofing
the
residential
houses
. In this
thesis
,
we
consider
the
application
of
reducing
the
acoustic
noise
by
shaping
the
landscape
. The
solution
of this
problem
is
difficult
due
to the
semiinfinite
domain
,
especially
in the
case
of
soft
ground
. To
overcome
the
difficulty
of
calculating
a
faraway
acoustic
field
for an
undulating
soft
surface
,
we
use
the
Equivalent
Source
Method
(ESM)
as a
generalization
of the
image
source
method
which
is
applicable
to
flat
surfaces
only
.
Additional
sources
are
used
to
account
for the
undulation
, and their
amplitudes
and
phases
and
locations
are
determined
by
solving
a
leastsquare
problem
derived
from the
boundary
conditions
. The
method
then
estimates
the
pressure
field
using
superposition
of the
effect
of the
equivalent
sources
. In
short
, the
acoustic
field
caused
by a
source
above
an
impedance
plane
is
computed
by
using
a
superposition
of
equivalent
point
sources
located
below
the
surface
. A
special
notation
is
derived
to
simplify
this
formulation
. To
account
for
finite
impedance
,
we
incorporate
an
integral
introduced
by
Ochmann
[31]
which
represents
additional
sources
located
at
complex
locations
paraxial
to the
image
source
. This
integral
is
known
to be
convergent
for
acceptable
impedance
. The
boundary
conditions
are then
updated
as to
reflect
the
influence
of the
Ochamann
term
, and the
matrices
involved
in the
leastsquares
solution
now
have
six
additional
terms
. The
proposed
method
is
then
applied
to a
sinusoidally
varying
surface
. To
simplify
the
calculation
, the
positions
of the
equivalent
sources
are
postulated
to be a
small
distance
below
the
surface
to
avoid
unnecessary
complications
due
to
singularity
within
the
domain
.
Subsequently
the
complex
amplitudes
are
derived
by
enforcing
the
boundary
conditions
at a
number
of
test
points
chosen
along
the
flat
and the
undulating
parts
of the
surface
. The
resulting
equivalent
sources
presented
inversely
decaying
amplitudes
as
expected
and their
phases
presented
an
expected
pattern
.
Subsequently
,
we
computed
the
pressure
at the
far
field
and
both
the
undulation
and the
impedance
were
shown
to
contribute
to the
suppression
of the
acoustic
field
faraway
.
Creator
Ocansey
,
Daniel
Teye
Publisher
North Carolina Agricultural and Technical State University
Date
2014
Type
TEXT
Format
PDF
Language
English
Major Professor
Bikdash
,
Marwan
Academic Department
Computational
Science
and
Engineering
Degree
MASTER
OF
SCIENCE
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