COMSOL News

MULTIPHYSICS
NAVAL UNDERSEA WARFARE CENTER DIVISION NEWPORT, NEWPORT, RI
Better, Faster Sonar Development with Multiphysics Simulation
BY GARY DAGASTINE, CONTRIBUTING EDITOR, TECH BRIEFS MEDIA GROUP
As any dolphin could tell us, sound
travels well in water. While water
absorbs electromagnetic radiation and
light waves over relatively short distances,
sound travels widely and even faster
in water than in air. That’s why we use
sonar (SOund NAvigation Ranging), the
acoustic equivalent of radar, to detect and
locate underwater objects.
Sonar system developers continually
seek to increase performance while
also reducing size, weight, and cost,
but this is easier said than done. Factors
that must be taken into account
include the characteristics of acousticwave
propagation in water of varying
densities, the vibrations and elastic
waves that come into play with respect
to the sonar system’s materials and
components, electrical considerations,
and many others.
Building and testing a series of physical
prototypes on a trial-and-error basis
is one way to conduct system development,
but this tedious approach is timeconsuming,
costly, and makes it difficult
to achieve real-world performance close to
the theoretical best case.
In contrast, the use of tightly coupled
multiphysics modeling, simulation, and
visualization capabilities, such as those
provided by the COMSOL software environment,
can speed up system development
exponentially and lead to a better
end result as well.
A case in point is the development of a
new type of sonar acoustic projector, designed
to provide improved performance
Projectors
at half the size and weight of existing
projectors. Stephen Butler, an Acoustical
Engineer and Principal Investigator at
the U.S. Navy’s Naval Undersea Warfare
Center Division Newport in Newport, RI,
used COMSOL Multiphysics with the
Acoustics Module to accelerate the development
of the new projector.
The Naval Undersea Warfare Center
Division Newport provides research,
“ The use of tightly coupled multiphysics modeling,
simulation, and visualization capabilities,
such as those provided by the COMSOL software
environment, can speed up system development
exponentially and lead to a better end result as well.”
Transmitted
Wave
Figure 1. Sonar uses transmitted and reflected sound waves to locate underwater objects.
development, test and evaluation, engineering,
analysis and assessment, and
fleet support capabilities for submarines,
autonomous underwater systems, and offensive
and defensive undersea weapon
systems. The Center also stewards existing
and emerging technologies in support
of undersea warfare.
Hydrophones
Reflected
Wave
Object
Sonar Basics
A sonar system consists of a projector
to transmit acoustic energy and an array
of hydrophones to receive the reflected
sound waves from underwater objects.
Sound waves are not generally unidirectional,
though, so one key design goal is to
increase the strength of the acoustic beam
in one direction and to null it in the other.
This will result in a more precise acoustic
beam, which increases the sonar system’s
capability to detect objects (Figure 1).
Some acoustic projectors are based
on flextensional transducer technology.
These are rugged, high-power, and compact
devices, with an actuator such as
a piezoelectric ceramic stack positioned
between curved metal shells or staves
made from aluminum, steel, or fiberglass.
The staves may be either convex
or concave, but are usually convex in
conventional devices (Figure 2). The actuator
is fixed to each end of the curved
shells so that as it expands and contracts
with an applied electric field, that motion
is converted into flexure of the shells
with an approximately 3:1 amplification
in motion. These flexures produce acoustic
energy in a manner similar to that of
an acoustic loudspeaker’s cone.
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