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Simulation Using IMSL C Numerical Libraries Software
in Submarine Acoustics
Even the smallest noise can make the crew of a submarine extremely
vulnerable. Therefore, the acoustic profile of modern submarines
is taken into account right from the design phase. Nevertheless,
for various reasons (wear and tear, ageing, poor assembly) an
unacceptable level of sound may still arise. That being the
case, to be able to remedy this, there must be tools available
that enable these sounds to be attributed to one or more devices
operating in the vessel.
In this context, LABRADOR software (LArge Bande Recherche Analyse
et Détermination des ORigines [Wide Band Search Analysis
 and
Determination of Sources]) has been developed on Sun and HP
workstations. This software is based on three main modules,
which the user sees as three graphics windows, designed to be
as user-friendly and therefore as simple to use as possible.
The bulk of the software has been written in C, using IMSL C
Numerical Library routines, while the user interface is based
on X-Motif and Exponent Graphics. Via an X-Motif-based user
interface, the first window allows the user to define the problem
that he or she wishes to resolve by specifying first the location
of measurement sensors near potential noise sources and those
measuring radiated noise and second, the signal processing parameters
that are going to be used for the analysis.
In the second window, known as standard analysis, the user
can select from menus the display of standard values for acoustic
and vibration analysis (auto spectrum, transfer and coherence).
The calculation of these quantities relies heavily on the routines
contained in the C Numerical Library, in particular with regard
to Fourier transforms and all operations on complex vectors.
The display itself is produced using Exponent Graphics. In addition
to very careful presentation of the graphics, Exponent Graphics
ensures interaction between the user and the graphics, allowing
customized presentation using menus and buttons (colors, character
sets, marker type, line thickness, etc.) Exponent Graphics also
allows the generation of output files in HPGL and PostScript,
in particular guaranteeing a faithful and careful reproduction
of the window graphics, facilitating incorporation into reports.
In the third window -- known as identification of sources --
and after the program has made all the necessary calculations,
users can select the display of different graphics allowing
them to diagnose the responsibility for the radiated noise.
Here also, the majority of operations rely heavily on the contents
of the C Numerical Library, in particular the formation of a
spectral matrix for each discrete frequency using the FFT routine,
its breakdown into distinct values and vectors and a set of
product and addition calculations on the complex vectors resulting
from this breakdown. This set of complex operations has the
aim of constructing imaginary sensors independent of one another
(i.e., representing exclusively one source), based on real sensors,
of which each is a linear combination of all the sources in
operation.
 The
most important of the various graphical outputs in this attribution
phase is the spectral synthesis, allowing a simple glance to
identify the device(s) responsible for the radiated noise output.
In effect, on this representation, each of the devices is allocated
a color; the area covered between the background noise is measured
and the auto spectrum of radiated noise is colored proportionately
according to the influence of each of the devices with the color
that has been attributed to it.
Another graphics output enables a comparison to be made between
the measurement of spectral density of radiated noise for all
the devices in operation and that calculated by the software
for the noise radiated by just one of these devices. This function
is particularly interesting, because for the majority of the
time, it is not possible for a device to function independently
of the others, and a signal-processing algorithm combined with
linear algebra enables simulation of this operating mode.
A LABRADOR software function makes it possible to eliminate
the contribution of one or more of the sources identified in
the signals measured by each sensor. This enables a display
of the spectral density of radiated noise when one or more incriminated
devices are not in operation. The use of IMSL, C Numerical and
Exponent Graphics libraries has made it possible to reduce the
cost of development by exploiting tried and tested graph-plotting
calculation routines, with interactive possibilities and formatted
print outputs, while concentrating efforts on the specific processes.
PV-WAVE Helps Determine Cell Shapes at the State University of New York at Stony Brook
Shuttle astronauts spending large amounts of time
in space, persons experiencing osteoporosis, the bedridden and
the elderly -- all may have tremendous bone loss from not using
the body's joints.
"We analyze the various mechanical and other physical
factors involved in the regulation of bone and cartilage growth,"
said Farshid Guilak, assistant professor of orthopedic surgery
at the State University of New York at Stony Brook.
Guilak's research is a subset of biomedical engineering.
Known as biomechanics, it is the science of applying mechanical
engineering principles to the study of the human body. "Biomechanics
is a very interesting multidisciplinary field that draws upon
mechanical and electrical engineering, cell and molecular biology,
anatomy, biochemistry and many other related fields to solve
the problems in medicine and physiology," he said. In fact,
the research group at Stony Brook is asking basic questions
about how biological systems run and operate. Guilak hypothesizes
that the "mechanical environment" controls the basic mechanism
behind which the human body can regulate its growth.
"Our research examines this process at the cellular
level because cells control everything. They cause more tissue
to be put down, to grow or to be resorbed. In order to find
the very basic mechanism the cell is using, you have to see
what is happening to the cell under various environments. When
a cell is compressed, there are stresses and strains within
it and around it. These forces and deformations are what we
refer to as the mechanical environment," he said.
Guilak uses PV-WAVE, the software industry's leading
Visual Data Analysis (VDA) solution, in several different ways.
The first application allows him to grid a random array of points
and then plot contours from it. PV-WAVE is used as a post-processor
for the process labeled the Finite Element Method.
 "The
Finite Element Method is a mathematical technique for determining
solutions to various engineering problems. These methods allow
us to calculate the stresses, strains and fluid flow within
a tissue model. We use PV-WAVE to display these massive amounts
of information (such as stress contours and streamlines of flow)
in three dimensions and in color," Guilak said.
Measuring with Light at NASA Lewis Advanced Research Center
Mention the word "NASA" today, and most people think of the space
shuttle and the search for distant sources of light. But starlight
is not the only light important to NASA scientists and engineers.
At the NASA Lewis Advanced Research Center, light is a fundamental
tool for probing the secrets of the physical world.
 Nancy
Piltch and Carolyn Mercer work in the Center's Optical Measurements
Systems Branch. They and their colleagues are researching methods
for using light as a powerful and precise tool for measuring the
engineering properties of NASA hardware. "All our measurements
take advantage of the properties of light or involve the interaction
of light with a physical object," says Piltch. Their methods typically
include various types of laser spectroscopy and interferometry.
Piltch's experiments focus on using light to discover the properties
of arc jet thrusters, which are small engines used to stabilize
the movement of satellites in orbit. The gas discharge from an
arc jet thruster can be hotter than a typical acetylene welding
torch. "You can't exactly put a thermometer or any other kind
of probe in there," says Piltch. "It would melt." She views the
properties of the gas by measuring the amount of laser light absorbed
and reemitted by atoms and molecules in the exhaust gas.
The process is called laser-induced planar fluorescence. Piltch
captures the fluorescence image data with a photodiode detector
attached to a solid-state video camera. Data from the camera are
loaded into Visual Numerics' PV-WAVE visual data analysis (VDA)
software, where the resulting image is processed interactively.
"Before we had PV-WAVE, I used to try to make sense of the data
by taking black and white photographs of the video screen," says
Piltch. "Now we have numerical data that we can process in simple
ways and the data just jump out at us. We don't have to spend
half our time convincing ourselves that something is really there."
Piltch uses the data to determine various parameters of the exhaust
plume: temperature, types of particles present, how the thrusters'
chemical energy is converted to other kinds of energy and the
extent and pattern of ionization. For example, Piltch's analysis
reveals that design changes can maximize the conversion of fuel
into kinetic energy or minimize the number of ionized species
present that would otherwise damage satellite electronic systems.
Carolyn Mercer's experiments also provide important data to NASA
engineers. She uses a process called phase-stepping interferometry
to probe the surface and subsurface of physical objects. The process
is based on the interference pattern produced when two coherent
laser light beams are recombined after traveling slightly different
paths.
The recombined light produces an interference fringe pattern
that is used to illuminate the object under study. By collecting
the light reflected off the object with a video camera, Mercer
records an intensity image. Next she steps the relative phase
difference between the two beams by 90 degrees, taking advantage
of a novel feedback loop for very accurate stepping. If four such
images are recorded, with relative phase differences of 0, 90,
180, and 270 degrees, then the images are related by a simple
mathematical formula that is used to calculate the phase of interference
pattern at each point on the object.
 The
phase map can be displayed on a computer either as an image, a
contour map or a surface. According to Mercer, "The interactive
nature of the PV-WAVE software makes it easy to work with these
maps. You can display them as a surface or as an image or as both
at the same time, and PV-WAVE is fast! My entire calculation takes
less than a minute, and we're talking about almost 64 kilobytes
of data in each of the four images." No matter how it is displayed,
the phase map is exquisitely sensitive to slight differences in
the shape of an object. Mercer has used phase-stepping interferometry
to look for cracks in the space shuttle main engine turbine blades
and has been able to find and measure minuscule fissures with
this method. This application also can reveal subsurface cracks
and other material defects. By subtracting the phase map of an
unstressed object from the phase map of the same mechanically
stressed object, the resulting phase map, Mercer says, "shows
a sharp discontinuity that dramatically displays the defect."
The same procedure can be used to reveal how an object deforms
as it is heated or is stressed in some other way. "The beauty
of phase-stepping interferometry is that it can be used to look
at something as small as a micron-sized crack or as large as an
automobile."
Both scientists stress the importance of interacting directly
with their data in the visualization and analysis steps of their
process. According to Mercer, "I wrote 75 to 100 lines of code
to do the same thing I did in PV-WAVE in 17 lines. It was much
easier to use PV-WAVE."
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