Sensor based structural health monitoring and control group
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S P A C E Structures, Propulsion, And Control Engineering C e n t e r. Sensor-Based Structural Health Monitoring and Control Group. Research Team Members: Prof Helen Boussalis (CSULA) Prof Sami F Masri (USC) Jessica Alvarenga (CSULA) Armen Derkevorkian (USC). Outline.

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Sensor-Based Structural Health Monitoring and Control Group

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Sensor based structural health monitoring and control group

S P A C E

Structures, Propulsion, And Control Engineering

C e n t e r

Sensor-Based Structural Health Monitoring and Control Group

Research Team Members:

Prof Helen Boussalis (CSULA)

Prof Sami F Masri (USC)

Jessica Alvarenga (CSULA)

Armen Derkevorkian (USC)

NASA Grant URC NCC NNX08BA44A


Outline

Outline

  • Background

  • Objective

  • Theory

  • Modeling of 2D Beam and 3D Wing

  • Future Work

  • Timeline

NASA Grant URC NCC NNX08BA44A


Background

Background

NASA Grant URC NCC NNX08BA44A


Helios wing

Helios Wing

  • 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

NASA Grant URC NCC NNX08BA44A


In flight deformation monitoring

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

NASA Grant URC NCC NNX08BA44A


Existing methods of inflight monitoring

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

NASA Grant URC NCC NNX08BA44A


Newly proposed method

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

Reflector

Laser Light

Loss Light

Reflected Light

(IR)

NASA Grant URC NCC NNX08BA44A


Application

Application

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

NASA Grant URC NCC NNX08BA44A


In flight shape detection algorithms

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

NASA Grant URC NCC NNX08BA44A


Structural health monitoring shm

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)

NASA Grant URC NCC NNX08BA44A


Structural health monitoring shm1

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

NASA Grant URC NCC NNX08BA44A


Non destructive evaluation nde

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”

NASA Grant URC NCC NNX08BA44A


Non destructive evaluation nde1

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

NASA Grant URC NCC NNX08BA44A


Objective

Objective

NASA Grant URC NCC NNX08BA44A


Vision

Vision

  • 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.

NASA Grant URC NCC NNX08BA44A


Preliminary tasks

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

NASA Grant URC NCC NNX08BA44A


In flight deformation shape sensing theory

In-flight deformation shape sensing theory

NASA Grant URC NCC NNX08BA44A


Development of deflection equations

Development of Deflection Equations

NASA Grant URC NCC NNX08BA44A


Classical beam theory

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

NASA Grant URC NCC NNX08BA44A


Cantilever tubular spar

Cantilever Tubular Spar

Δl : spacing between sensing stations

c: half-beam depth

γi: torsion strain sensing station

xi: strain sensing station

M: bending moment

ε: bending strain

θ: slope angle

y: deflection

NASA Grant URC NCC NNX08BA44A


Bending slope equations

Bending: Slope Equations

  • Slope Equation from Classical Beam Theory:

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

  • Final Equation

θi+1

θi

θi-1

NASA Grant URC NCC NNX08BA44A


Bending deflection equations

Bending:Deflection Equations

  • Deflection equation from slope equation:

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

  • Final Equation

θi+1

yi+1

θi

yi

yi-1

θi-1

NASA Grant URC NCC NNX08BA44A


2d beam

2D Beam

NASA Grant URC NCC NNX08BA44A


Femap model

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

NASA Grant URC NCC NNX08BA44A


Calculation of strain

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

xi

e

xi

Deformation of an infinitesimal rectangular material element [Sanpaz 2008]

i-

i+

e

e

δi: represents the displacement measurements

e: represents the finite-element span-wise length

xi:the i-th sensing station

NASA Grant URC NCC NNX08BA44A


2d beam results

2D Beam Results

NASA Grant URC NCC NNX08BA44A


2d beam results1

2D Beam Results

NASA Grant URC NCC NNX08BA44A


2d beam results2

2D Beam Results

  • Calculation of error:

    e: error

    a: reference measurement (FEA)

    ã:analyzed measurement (Case1 and 2)

    || . ||: norm

NASA Grant URC NCC NNX08BA44A


3d wing

3D Wing

NASA Grant URC NCC NNX08BA44A


Femap wing model

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

NASA Grant URC NCC NNX08BA44A


3d wing details

3D Wing Details

NASA Grant URC NCC NNX08BA44A


3d wing details1

3D Wing Details

NASA Grant URC NCC NNX08BA44A


Potential placement of fiber sensors

Potential Placement of Fiber Sensors

NASA Grant URC NCC NNX08BA44A


Wing deflection

Wing Deflection

Contour shows deflection values in y-direction

NASA Grant URC NCC NNX08BA44A


Future work

Future Work

NASA Grant URC NCC NNX08BA44A


Future tasks

Future Tasks

  • Validation of:

    • Combined Bending and Torsion (CBT) Theory

    • Perturbation Method

    • Stepwise Method

  • Modeling artificial damage in 3D model

  • Error analysis and classification

NASA Grant URC NCC NNX08BA44A


Timeline

Timeline

NASA Grant URC NCC NNX08BA44A


Timeline1

Timeline

NASA Grant URC NCC NNX08BA44A


References

References

Emmons, 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

NASA Grant URC NCC NNX08BA44A


Questions

Questions?

Thank You

NASA Grant URC NCC NNX08BA44A


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