Acronym Definition
PIVV Particle Image Velocimetry Verification
PIVV Peak Inverse Voltage Verification
PIVV Pentium 4 Voltage
PIVV Peripheral IVV
PIVV Personal Identification Verification Validation
PIVV Personal Identity Verification Validation
PIVV Phase IV Validation
PIVV Physical Inventory Verification Validation
PIVV Pontoon Implantment Various Vehicle
PIVV Positively Infinitely Variable Validation
PIVV Post Implementation Verification Validation
PIVV Post Indicator Valve Validation
PIVV Pre-Inventory Visit Validation
PIVV Product Improvement Verification Validation
PIVV Propellant Isolation Valve Validation
PIVV Physical Independent Verification and Validation
PIVV Phase Inertial Vertical Velocity
PIVV P Instituto da Vinha e do Vinho (Portugal)
PIVV P Internationale Vereinigung der Vermessungsingenieure
PIVV stands for:
Pinnacle Internet Viewer Vision an online grading system for schools
Plena Ilustrita Vortaro, an extensive, monolingual dictionary of Esperanto
Particle image velocimetry optical method to measure velocities
Pentium 4 microprocessor produced by Intel
Peak Inverse Voltage in electronics
Personal Identity Verification as specified by FIPS 201
Project InVision a Web-based project management software package
Particle image velocimetry
Particle image velocimetry (PIV) is an optical method used to measure velocities
and related properties in fluids. The fluid is seeded with particles which, for
the purposes of PIV, are generally assumed to faithfully follow the flow
dynamics. It is the motion of these seeding particles that is used to calculate
velocity information.
History
For a recent overview of the history of PIV technique see: Adrian, R.J., "Twenty
years of particle image velocimetry". Experiments in Fluids 39:159169 (2005).
Technique
Typical PIV apparatus consists of a camera (normally a digital camera in modern
systems), a high power laser, for example a double-pulsed Nd-YAG laser laser or
a copper vapour laser, an optical arrangement to convert the laser output light
to a light sheet (normally using a cylindrical lens), and the fluid/gas under
investigation. A fibre optic cable often connects the laser to the cylindrical
lens setup. The laser acts as a photographic flash for the digital camera, and
the particles in the fluid scatter the light. It is this scattered light that is
detected by the camera.
In order to measure the velocity at least two exposures are needed. They can be
recorded on one or several frames.
The frames are split in a large number of interrogation areas, often called
tiles. It is then possible to calculate a displacement vector for each tile with
help of signal processing (auto-correlation/cross-correlation). This is
converted to a velocity using the time between image exposures.
Timing electronics allows one to control the spacing between image exposures.
The electronics also permits image pairs to be acquired at various times along
the flow. These digital delay and pulse generators provide several outputs that
can be delayed and referenced to each other.
Advantages
The method is to a large degree nonintrusive. The added tracers (if they are
properly chosen, see for the reference Melling, 1997 ) generally cause
negligible distortion of the fluid flow.
Optical measurement avoids the need for Pitot tubes, hotwires or other intrusive
Flow measurement probes. Additionally the method is capable of measuring an
entire two-dimensional cross section (geometry) of the flow field
simultaneously.
High speed data processing allows the generation of large numbers of image pairs
which, on a modern personal computer may be analysed in real time or at a later
time. Thus a high quantity of near continuous information may be gained.
Sub pixel displacement values allow a high degree of accuracy, since each vector
is the statistical average for many particles within a particular tile.
Displacement can typically be accurate down to 10% of one pixel on the image
plane.
Drawbacks
The particles will, due to their higher density, not exactly follow the motion
of the fluid (gas/liquid).
Particle image velocimetry methods will in general not be able to measure
components along the z-axis (towards to/away from the camera). These components
might not only be missed, they might also introduce an interference in the data
for the x/y-components.
The size of the recordable flow field is limited by the size of the tracer
particles. The scattered light from each particle should be in the region of 2
to 4 pixels across on the image. If too large an area is recorded, particle
image size drops and peak locking will occur with loss of sub pixel resolution.
The typical maximum size of the recordable plane is in the region of 10cm to
50cm square, depending on the technology and complexity of the analysis
algorithms used.
Since the resulting velocity vectors are based on cross-correlating the
intensity distributions over small areas of the flow, the resulting velocity
field is a spatially averaged representation of the actual velocity field. This
obviously has consequences for the accuracy of spatial derivatives of the
velocity field, vorticity, and spatial correlation functions that are often
derived from PIV velocity fields.
Improvements to basic PIV
Each of the above limitations have been addressed by specialist techniques. For
example, a similar velocimetry method known as molecular tagging velocimetry, or
MTV, uses molecule sized tags, which are often already a part of the flow. Small
molecules being much closer to the size and density of a flow minimize the error
of particles not following the flow. One example used in humid air flows uses a
laser to dissociate the water (H2O) in the flow into H + OH. The hydroxyl (OH)
molecule serves as the tag. This method is known as hydroxyl tagging velocimetry
(HTV).
Stereoscopic PIV utilises two cameras with separate viewing angles to extract
the z-axis velocity component. Holographic PIV similarly extracts the third
component. However Both these techniques drastically increase cost and
complexity of the system.
Recent research has outlined the possibility of treating the flow images as a
continuous system of flow structures, instead of a system of quasi-random
points. This allows the imaging of a limitless size of flow field, provided
appropriate seeding is ensured.
The molecules used as tracers in MTV are subject to Brownian motion. This limits
the method to ultra-high speed flows. A typical example of the successful
application of MTV is the investigation the intake flow in engines. Here the
spray is very dense and flow speeds are high enough to allow accurate results
for MTV.
The effect of the spatial averaging can be reduced by the use of more
complicated algorithms based on deforming the interrogation areas or based on
Particle tracking velocimetry using PIV as an initial estimate for the position
where individual particles are advected.
Applications
PIV has been applied to a wide range of flow problems, varying from the flow
over an aircraft wing in a wind tunnel to vortex formation in prosthetic heart
valves. Though less common, PIV can also be used for quantifying the deformation
and motion of solid materials and tissues that have embedded markers or are in
some other way visually heterogeneous (e.g. using fluorescent speckles or
particle grains).
Rudimentary PIV algorithms based on cross-correlation can be implemented in a
matter of hours, while more sophisticated algorithms may require a significant
investment of time. Several open source implementations are available including
URAPIV (a Matlab Toolbox), PyPIV (an implementation in Python), OSIV and Gpiv
(both implementations in C).
Personal Identification Verification and Validation
FIPS 201 incorporates three technical publications specifying several aspects of
the required administrative procedures and technical specifications that may
change as the standard is implemented and used. NIST Special Publication 800-73,
"Interfaces for Personal Identity Verification" specifies the interface and data
elements of the PIV card; NIST Special Publication 800-76, Biometric Data
Specification for Personal Identity Verification" specifies the technical
acquisition and formatting requirements for biometric data of the PIV system;
and NIST Special Publication 800-78, "Cryptographic Algorithms and Key Sizes for
Personal Identity Verification" specifies the acceptable cryptographic
algorithms and key sizes to be implemented and used for the PIV system.
In addition, a number of guidelines, reference implementations, and conformance
tests have been identified as being needed to: implement and use the PIV system;
protect the personal privacy of all subscribers of the PIV system; authenticate
identity source documents to obtain the correct legal name of the person
applying for a PIV "card"; electronically obtain and store required biometric
data (e.g., fingerprints, facial images) from the PIV system subscriber; create
a PIV "card" that is "personalized" with data needed by the PIV system to later
grant access to the subscriber to Federal facilities and information systems;
assure appropriate levels of security for all applicable Federal applications;
and provide interoperability among Federal organizations using the standards.
These activities will be pursued as resources permit.
FIPS 201 (Federal Information Processing Standards Publication 201) is a United
States federal government standard that specifies Personal Identity Verification
(PIV) requirements for Federal employees and contractors.
In response to HSPD-12 , the NIST Computer Security Division initiated a new
program for improving the identification and authentication of Federal employees
and contractors for access to Federal facilities and information systems. FIPS
201 was developed to satisfy the technical requirements of HSPD 12, approved by
the Secretary of Commerce, and issued on February 25, 2005.
FIPS 201 together with NIST SP 800-78 (Cryptographic Algorithms and Key Sizes
for PIV) are required for U.S. Federal Agencies but do not apply to US national
security systems.
The SmartCard Interagency Advisory Board has indicated that to comply with FIPS
201 PIV II US government agencies should use Smart card technology.
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