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Effective State Awareness Information is
Enabling for System Prognosis
Mark M. Derriso
Advanced Structures Branch
Air Vehicles Directorate
Air Force Research LaboratoryWorkshop on Prognosis of Aircraft and Space
Devices, Components, and SystemsFebruary 19-20, 2008 – Cincinnati, OH
2
Overview
Workshop Topics: “…In the future, the USAF would like to develop
state awareness monitoring capabilities that could enable accurate prediction of the remaining service life and future performance capability of critical components as well as be used to take specific corrective actions to assure mission completion and minimize operating cost and risk.”
This is Integrated Systems Health Management!
Determine Ability to Perform MissionDetermine Ability to Perform Mission
Assess DamageAssess Damage
Detect DamageDetect Damage
4
Critical ComponentsMeasurands
Structural Health Management
Controls Health Management
Engine Health Management
Electronics Health Management
Sub-systems
HM Data
HM Data
HM Data
HM Data
Multiple 0.02 inchCracks in fuselage
Flight Control Actuator
Frozen at 20 degrees
Bearing Spalling
LRU is Malfunctioning
Data Analysis Damage
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System Performance
Multiple 0.02 inchCracks in fuselage
Flight Control Actuator
Frozen at 20 degrees
Bearing Spalling
LRU is Malfunctioning
Data Analysis Vehicle-Level Health Status
Alt
itu
de
Mach
CL max
T max
q max
System Performance Bounds
6
Airframe Design
MATERIAL STRUCTURE(Device, Component, or System)
Materials ProcessingManufacturing
Materials PropertiesLoads, Boundary Conditions,
Operational Environment
UNCERTAINTYassociated with each of these
areas that propagates through to the system level
Uncertainty_Total = U_material + U_manufacturing + U_operational
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Design for UncertaintySafe-life design
The Safe-life design technique is employed in critical systems which are either very difficult to repair or may cause severe damage to life and property. These systems are designed to work for years without requirement of any repairs.
Damage-tolerant design
Damage-tolerant is the property that enables a system to continue operating properly in the event of the failure of (or one or more faults within) some of its components. If its operating quality decreases at all, the decrease is proportional to the severity of the failure
F-4 F-16
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Failure Mode, Effects, & Criticality Analysis (FMECA)
FMECA The objective of FMECA is to
identify the components of products and systems most likely to cause failure, so that these potential failures can then be designed out.
FMECA allows the identification early in the product development process of potential problems or safety hazards which are inherent in a product design.
9
V&V of Airframe DesignStructural Design
Full- Scale Fatigue Testing
Problem Areas Identified
Front Spar
Main Spar
Rear Spar
Closure Spar
F-15 Wing
Conduit Hole (hot spot)
Inspection Schedule Constructed
Airframe Prognosis: No Failures Throughout Design Life
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Airframe Prognosis
However, requirements changes Vehicles asked to perform different missions Vehicles modified to fulfill new purposes Vehicles asked to serve past original design life
What is the prognosis then?
Vehicle prognosis based on airframe prognosis
1111
Operational UncertaintyOperational Uncertainty
External LoadingExternal Loading maneuvers, gusts, taxi-loadsmaneuvers, gusts, taxi-loads
Internal LoadingInternal Loading bending, torsion, shearbending, torsion, shear
Environmental ConditionsEnvironmental Conditions temperature, humiditytemperature, humidity
All are Factors the Effects Fatigue Life
12
State Awareness
State awareness refers to knowledge regarding the current condition or capability
For airframe subsystems, state awareness is from the diagnostic portions of the structural health monitoring (SHM) system which detect, localize and assess any damage
State awareness allows subsystem prognosis which enables overall system prognosis
13
Definition of SHM
SHM refers to automated methods for determining adverse changes in the integrity of mechanical systems
SHM system capability is typically broken into the following levels of increasing difficulty: damage detection damage localization damage assessment life prediction
diagnosis
prognosis
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SHM Development Process
Identify Item of Interest
Identify Relevant Failure Modes of Item– Dependent on operating environment
Characterize Failure Modes that Result in System Degradation
– Identify physics of degradation mechanisms – Identify precursors that indicate imminent degradation– Identify mechanisms which can be sensed and are
correlated to system degradation
Design Sensor System to Capture Degradation
Mechanisms– Direct, inferred, virtual– On-board, off-board
ComponentLevel
ReasonerObtain Initial Sensor Output
Real Time and
Updated Sensor Output
Assess Current State of Component
Predict Remaining Capability– Assumed operating conditions
Output to SystemLevel Reasoner
Identify Item of Interest
Identify Relevant Failure Modes of Item– Dependent on operating environment
Characterize Failure Modes that Result in System Degradation
– Identify physics of degradation mechanisms – Identify precursors that indicate imminent degradation– Identify mechanisms which can be sensed and are
correlated to system degradation
Design Sensor System to Capture Degradation
Mechanisms– Direct, inferred, virtual– On-board, off-board
ComponentLevel
ReasonerObtain Initial Sensor Output
Real Time and
Updated Sensor Output
Assess Current State of Component
Predict Remaining Capability– Assumed operating conditions
Output to SystemLevel Reasoner
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Understand the structure.
Understand available
technologies and methods.
Develop system-level SHM
requirements.
Develop candidate SHM system
designs.
Develop potential benefits for
applying SHM.
Compare each design to the requirements.
Understand the costs of the SHM
systems.
Does the design meet the
requirements?
Remove the design from
consideration.No
Yes
Implement the lowest cost SHM system design.
Structural design
SHM Development Framework
Requirements and knowledge of structural
behavior and loads
Sensing technology and sensing system design+
SHM System Design
Ultrasonic wave propagation model
Damage detection sensor
Maintenance Benefit
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State Awareness Architecture
MeasurandsData
AnalysisReasonin
gProcess
Experience&
Knowledge
Predictions(physics-based models,
trending)
Current State Information
The Real World
Based on Col Boyd’s OODA Loop
Loads, damage, etc..
17
The ISHM Goal
“I don't care about what anything was DESIGNED to do, I care about what it CAN
do”.
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