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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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734.pdf
Description
Title
Simulation
of
Sound
Propagating
over
Soft
Surface
Using
the
Equivalent
Source
Method
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
the2
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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