Sensor-Based Structural Health Monitoring and Control Group 01/27/2011NASA Grant URC NCC NNX08BA44A1 Research Team Members: Prof Helen Boussalis (CSULA)

Sensor-Based Structural Health Monitoring and Control Group

01/27/2011 NASA Grant URC NCC NNX08BA44A 1

Research Team Members:Prof Helen Boussalis (CSULA)

Prof Sami F Masri (USC)Jessica Alvarenga (CSULA)Armen Derkevorkian (USC)

Outline

• Background

• Objective

• Theory

• Modeling of 2D Beam and 3D Wing

• Future Work

• Timeline

01/27/2011 2NASA Grant URC NCC NNX08BA44A

Background

01/27/2011 3NASA Grant URC NCC NNX08BA44A

Helios Wing

01/27/2011 4NASA Grant URC NCC NNX08BA44A

Ultra-lightweight, unmanned, solar-powered flying wing aircraft

Long wingspan and high flexibility

Experienced large deformations during flight

Wing tip deflections could reach 40ft

Midair breakup at 3000ft altitude

Helios Wing In-flight breakup

In-flight Deformation Monitoring

• Need to develop method to monitor deformations of highly flexible

structures during flight

• As wingtip deflections approach limitations, emergency maneuvers

may be initiated

Ground-based pilots

Flight control system

01/27/2011 5NASA Grant URC NCC NNX08BA44A

Existing Methods of Inflight Monitoring

Electro-optical flight deflection detection

Requires onboard cameras and wing mounted targets

Heavy and requires lots of equipment

Strain gages

Requires a high number of sensors in order to observe higher deflection modes of

these flexible structures

The more strain sensing stations are used, the heavier the load on the wing

Too heavy and impractical for most weight conscious aircraft

01/27/2011 6NASA Grant URC NCC NNX08BA44A

Newly Proposed Method

• Fiber Optic Sensors with Fiber-Bragg Gratings

Immune to E&M/RF interference and radiation

Light weight and small (thin fibers)

Ability to multiplex 100’s of sensors onto a single fiber

Potential for embedment into structures

01/27/2011 7NASA Grant URC NCC NNX08BA44A

Laser Light

Reflected Light(IR)

ReflectorLoss Light

Application

• Validation of fiber optic sensor measurements and real-time wing shape sensing on NASA’s Ikhana Vehicle

01/27/2011 8NASA Grant URC NCC NNX08BA44A

In-Flight Shape Detection Algorithms

• Deflection Shape Algorithms based on strain data

• Validation with classical beam theory, and finite element analysis (FEA)

• Promising results, with much room for improvement

01/27/2011 9NASA Grant URC NCC NNX08BA44A

Structural Health Monitoring (SHM)

• Objectives System Identification Damage Detection

• Broad applications in civil, mechanical, and aerospace industries

• Special importance after natural disasters (earthquakes), during key flying missions (Helios)

01/27/2011 10NASA Grant URC NCC NNX08BA44A

Structural Health Monitoring (SHM)

• Destructive Evaluation (DE) Physical Decomposition to locate damage

• Non-Destructive Evaluation (NDE) Based on vibration signatures (Acc, Vel, Dsp) Enables real-time monitoring Involves sophisticated algorithms

01/27/2011 11NASA Grant URC NCC NNX08BA44A

Non-Destructive Evaluation (NDE)

• Parametric Techniques Involves major assumptions about the model Prior knowledge about the parameters

Advantages Well-Developed techniques, such as least-square, Kalman

Filter, Eigen Value Realization Algorithm (ERA) along with the Natural Excitation Technique (NExT), among others.

Track certain parameters in great detail which allows detecting changes “damages”

01/27/2011 12NASA Grant URC NCC NNX08BA44A

Non-Destructive Evaluation (NDE)

• Non-Parametric Techniques No knowledge about the model is required “Black-Box” or “Unknown-Structures”

approach Applicability on linear and non-linear systems Well-developed algorithms such the neural

networks

01/27/2011 13NASA Grant URC NCC NNX08BA44A

Objective

01/27/2011 14NASA Grant URC NCC NNX08BA44A

Vision

01/27/2011 15NASA Grant URC NCC NNX08BA44A

• Objectives: Develop and implement innovative methods for utilizing fiber-optic strain

sensors for structural health monitoring and control applications in aerospace

systems, with emphasis on using on-line aeroelastic shape estimation methods under

realistic flight conditions.

• Approach: Conduct analytical and experimental studies on a subset of challenging

research issues to develop and evaluate a variety of modeling, monitoring and control

strategies.

• Applicability: Results of the research will be useful in the monitoring and control of a

wide variety of current as well as future generations of aircraft and aerospace

structures.

Preliminary Tasks

Task 1: Development and validation of a NASTRAN model for a 2D beam and a 3D wing

Task 2: Computational studies with NASTRAN model for shape determination from strain

measurements under deterministic excitation

Task 3: Computational studies with NASTRAN model for shape determination from strain

measurements under stochastic aerodynamic loads

Task 4: Damage detection studies based on NASTRAN model to assess sensitivity of

strain measurements to damage type, severity, location, and orientation, under

uncertain conditions

01/27/2011 16NASA Grant URC NCC NNX08BA44A

In-flight deformation shape sensing theory

01/27/2011 17NASA Grant URC NCC NNX08BA44A

Development of Deflection Equations

01/27/2011 18NASA Grant URC NCC NNX08BA44A

Classical Beam Theory

• Classical Beam Differential Equation:

M(x): bending moment

E: Young modulus

I: moment of inertia

• By relating the bending moment to the associated bending strain at the top or bottom fiber:

σ(x): bending stress

c: half-beam depth

01/27/2011 19NASA Grant URC NCC NNX08BA44A

Cantilever Tubular Spar

Δl : spacing between sensing stations

c: half-beam depth

γi: torsion strain sensing station

xi: strain sensing station

01/27/2011 20NASA Grant URC NCC NNX08BA44A

M: bending moment

ε: bending strain

θ: slope angle

y: deflection

Bending: Slope Equations

• Slope Equation from Classical Beam Theory:

• Noting that at the built-in end, tan θ0=0, gives:

• Final Equation

01/27/2011 21NASA Grant URC NCC NNX08BA44A

θi+1

θi

θi-1

Bending:Deflection Equations

• Deflection equation from slope equation:

• Noting that at the built-in end, y0=tan θ 0=0.

• Final Equation

01/27/2011 22NASA Grant URC NCC NNX08BA44A

θi+1

θi

θi-1

yi-1

yi

yi+1

2D Beam

01/27/2011 23NASA Grant URC NCC NNX08BA44A

FEMAP Model

2D Beam Element

• 55 Nodes

• 40 Elements

• Aluminum

0.1 unit thickness

10 units in length

2unit deep

• Deterministic point load = 60 pounds

• Beam fixed in all 6 degree of freedom at root

• Deformation shows wing deflection

• Contour shows bending-strain measurements

01/27/2011 24NASA Grant URC NCC NNX08BA44A

Calculation of Strain• Case 1: Strain sensing station located in

the middle of an element

• Case 2: Strain sensing station located at the juncture of two elements

01/27/2011 25NASA Grant URC NCC NNX08BA44A

e

xi

e

xi

e

i- i+ δi: represents the displacement measurementse: represents the finite-element span-wise lengthxi:the i-th sensing station

Deformation of an infinitesimal rectangular material element [Sanpaz 2008]

2D Beam Results

01/27/2011 26NASA Grant URC NCC NNX08BA44A

2D Beam Results

01/27/2011 27NASA Grant URC NCC NNX08BA44A

2D Beam Results• Calculation of error:

e: errora: reference measurement (FEA)ã:analyzed measurement (Case1 and 2)|| . ||: norm

01/27/2011 28NASA Grant URC NCC NNX08BA44A

3D Wing

01/27/2011 29NASA Grant URC NCC NNX08BA44A

FEMAP Wing Model• 138 Nodes

• 284 Elements

• 6 deterministic point loads each 250 lbs

• Pressure distribution along upper and lower wing skins

• Varying half-beam depth and width along span

01/27/2011 30NASA Grant URC NCC NNX08BA44A

3D Wing Details

01/27/2011 31NASA Grant URC NCC NNX08BA44A

3D Wing Details

01/27/2011 32NASA Grant URC NCC NNX08BA44A

Potential Placement of Fiber Sensors

01/27/2011 33NASA Grant URC NCC NNX08BA44A

Wing Deflection

01/27/2011 34NASA Grant URC NCC NNX08BA44A

Contour shows deflection values in y-direction

Future Work

01/27/2011 35NASA Grant URC NCC NNX08BA44A

Future Tasks

• Validation of: Combined Bending and Torsion (CBT) Theory Perturbation Method Stepwise Method

• Modeling artificial damage in 3D model

• Error analysis and classification

01/27/2011 36NASA Grant URC NCC NNX08BA44A

Timeline

01/27/2011 37NASA Grant URC NCC NNX08BA44A

USC-CSULA-Dryden Team Timeline: November 2010 - January 2011

2010 2011

Student Name November December January

ArmenDerkevorkian

Learn NASTRAN/FEMAP Continue Simple Wing Element [3D]

Implement algorithm on strain data obtained from beam, simple wing, and UAV Elements as they become

available

Beam Element [2D] Simple Wing Element [3D]

Start Modeling the UAV Wing Element [3D]

Learn about obtaining deformation shapes from strain, as time allows

Begin Coding the algorithm for obtaining deformation shape

JessicaAlvarenga

Learn NASTRAN/FEMAP Continue Simple Wing Element [3D]

Implement algorithm on strain data obtained from beam, simple wing, and UAV Elements as they become

available

Beam Element [2D] Simple Wing Element [3D]

Start Modeling the UAV Wing Element [3D]

Learn about obtaining deformation shapes from strain, as time allows

Begin Coding the algorithm for obtaining deformation shape

Timeline

01/27/2011 38NASA Grant URC NCC NNX08BA44A

USC-CSULA-Dryden Team Timeline: February 2011 – Month Year

Student Name February March April

ArmenDerkevorkian

• Modeling artificial damage on 3D Wing Element.

• Creating Damage Scenarios.• Implementing theory on

proposed damage conditions.• Error Analysis of results.

• Possible review of health monitoring techniques, including parametric and non-parametric methods.

• Application of Health-Monitoring algorithms on the computational models.

JessicaAlvarenga

• Modeling artificial damage on 3D Wing Element.

• Creating Damage Scenarios.• Implementing theory on

proposed damage conditions.• Error Analysis of results.

• Possible review of health monitoring techniques, including parametric and non-parametric methods.

• Application of Health-Monitoring algorithms on the computational models.

ReferencesEmmons, M., Karnani, S., Trono, S., Mohanchandra, K., Richards, W., and Carman, G. 2010. Strain

Measurement Validation Of Embedded Fiber Bragg Gratings. International Journal of Optomechatronics, 4(1):22-33.

Ko, W. and Richards, W. 2009. Method for real-time structure shape-sensing.

Ko, W., Richards, W., and Tran, V. 2007. Displacement Theories for In-Flight Deformed Shape Predictions of Aerospace Structures.

Sanpaz. 2008. Deformation of an infinitesimal rectangular material element. Wikepedia, Accessed January 27, 2011. http://en.wikipedia.org/wiki/File:2D_geometric_strain.png

01/27/2011 39NASA Grant URC NCC NNX08BA44A

Questions?

Thank You

01/27/2011 40NASA Grant URC NCC NNX08BA44A