3.aerospace.applicaitons.part2

7/30/2019 3.Aerospace.applicaitons.part2

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Control of Smart Structure 3. Aerospace Applications of Control of Smart Structures --Part 21

Department of Mechanical Engineering

Dr. G. Song, Associate Professor

3. Aerospace Applications of Control of

Smart Structures -- Part 2


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Vibration Damping

Active Damping

Passive Damping Vibration Isolation

Applications in Aircraft and Spacecraft

Active Shape Control

Space applications Applications in fixed wing aircraft

Applications in rotary wing aircraft

Acoustic Control

Smart Skin for Aerospace Applications A New Smart Actuator for Aerospace Applications

Health Monitoring Using Smart Materials

Outline


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Passive Vibration Damping-SMAs

Passive Vibration Damping using SMAsSource: SPIE Smart Materials and Structures Conference, 2001


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The hysteresis between transformation to martensite andaustenite in a SMA is an intrinsic material property to beused to enhance damping.

The transformation process between martensite and

austenite is known for decades. Practical use of theresulting shape memory alloys (SMA) has been limited sofar to switching between these two phases only and hasresulted in clamps, switches or springs.

A large portion between these two phases is worthconsidering.

In terms of adaptive structures, where actuation comes intoplay, this portion of the material's constitutive behavior is

unfortunately complex, especially when compared to theeffort which has just been required to consider elastic-plastic behavior of materials instead of elastic behavioronly.



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Considering SMA constitutive behaviour may thereforerequire permanent sensing of the material's condition and acomplex multi-parametric control law.

This complexity may be one of the reasons why SMA

reinforced composites have been discussed for around adecade now but still have not achieved a stage of truepractical application.

A solution for tackling this complexity with SMAs can be to

concentrate on a few key elements and to clearly describethese elements in further depth; by looking at thepossibilities to enhance the damping characteristic ofcomposite materials by integrating SMA and specifically

avoiding any additional built-in sensing. SMAs show a clear hysteretic behavior in the higher

temperature austenitic stage, which allows for energydissipation and are thus very well suited to enhance

damping.



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To better understand this effect and potentialthus requires to:

Understand and analytically describe the SMA'sconstitutive behaviour regarding the differentparameters such as training, damping, temperature,strain rate, prestraining, etc.

Have a mechanical model which allows to performtrade-off studies regarding the material combinationsto be used in a SMA reinforced composite.

Identify the actions required and to be taken todetermine and manufacture promising SMAreinforced composites and composites in generalwith enhanced damping properties.



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The optimum damping is obtained when ED is maximized and thusthe hysteresis according to the applied loads fully falls into thestress-strain hysteresis of the SMA. In practical terms if one wantsto take full advantage of a 0.5 % strain amplitude one has at leastto prestrain the SMA up to 1.5 % in mean strain to take maximumadvantage of SDC.

A similar analysis can be made when considering the influence ofthe strain amplitude. Here again the bigger the strain amplitude

the more the SMA prestrain has to be set towards the centre ofthe full SMA hysteresis. (Details in the paper)



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SMA-Structure Coupling: To roughly understand the interactionbetween a host structure and an actuation device it is quitesufficient to select a relatively simple mechanical device in a firststep compared to the complexity being faced in a true composite

material. Such a simple device is shown , as the schematic of a beam

coupled with SMA-wires pinned to the end of the beam.



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Damping for beam model with SMA wires pinned perpendicular to the beamaxis considering different distances between the SMA transformation levels

(thickness of hysteresis)


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Comparison of beam tip deflections fora non reinforced and 15 vol % SMAreinforced beam with 8 MPa distancebetween the transformation levels


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Conclusions: Whenever SMA is considered as a means toenhance damping in a composite, the SMA has to beprestrained such that the starting point for any furtherloading is well positioned within the strain ranges wheretransformation occurs.

Heat transfer effects are an important issue wherever largequantities of energy are dissipated, being either with highvolume percentages of SMA and/or high strain rates beinggenerated through high vibration frequencies.

Under these conditions it is essential to use modelsdescribing the constitutive behavior of SMA which alsoinclude the effect of heat transfer and are therefore

thermodynamics based. Finally the damping characteristic of a SMA is proportional to

the distance in stress between the two transformation levelsof the SMA as well as the applied strain.



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Vibration Isolation

Vibration Isolation using Piezo Struts Recent Advances

Source: SPIE Smart Materials and Structures Conference, 2001

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The success of recent space experiments not only demonstratesthe feasibility of several new technologies, but also provides a

glimpse of the various future opportunities available for research

and development in the smart structures area.

The currently operating Vibration Isolation, Suppression, andSteering (VISS) space experiment and the Middeck Active Control

Experiment Reflight (MACE-II), as well as the upcoming Satellite

Ultra-quiet Isolation Technology Experiment (SUITE) are

discussed in terms of notable achievements and lessons learnedover the course of their execution.

As part of a joint program with the United Kingdom to build a

small experimental payload, the Space Test Research Vehicle-2

(STRV-2), The Ballistic Missile Defense Organization (BMDO) andAFRL funded a project with Honeywell, Trisys, and the Jet

Propulsion Laboratory (JPL) to design, fabricate, and test the

Vibration Isolation and Suppression System (VISS).

Vibration Isolation- VISS


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VISS, the first space demonstration of active vibrationisolation using a hexapod Stewart platform, utilizes six hybridisolation struts.

Passive isolation is provided by Honeywell's D-Strut, which is

very compliant at the six hexapod suspension frequencies inthe 2 to 5 Hz frequency range. The D-strut contains viscousfluid that is exchanged between metallic bellows throughnarrow orifices as the piston moves, providing damping.

Active isolation at lower frequencies is achieved through theuse of a voice coil mounted in parallel to the D-strut. Theactive system can effectively lower the hexapod suspension

frequencies by an order of magnitude so that isolation isachieved over a broader frequency range.

The active system may also be used for vibration suppressionand steering functions.


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Vibration suppression is needed to counteract disturbances from noisydevices, such as cryocoolers, that are directly attached to the opticalpayload. The steering function enables the VISS device to be used asa precision tracking gimbal for the optical payload. Accelerometersmounted to the payload side of each strut are used as feedback

sensors for all of the control functions.

The system reverts to its passive isolation performance in the eventof a power failure.

The success of VISS serves as jumping off point into several newtechnology development opportunities. The first possibility forcontinuing to explore the on-orbit isolation problem is to incorporateactive materials into future solutions.

Although a prior effort, the ACTEX-I2 flight experiment developedby TRW and sponsored by AFRL and BMDO, demonstrated the use ofpiezoelectric patches embedded in a composite strut for vibrationsuppression, active materials have not yet been demonstrated in anon-orbit isolation capacity.


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The increased power density of such materials offers thepossibility of power-efficient, low-weight devices that meet orexceed the performance of VISS.

The second avenue of opportunity in on-orbit isolation involvesminiaturizing the system. Such an approach would offer abenefit in terms of volume, and hence cost, and offer thepossibility of retrofitting an isolation solution late in a designcycle.

A third avenue exists in terms of developing tetheredcomponents, which by their very nature are isolated from thespacecraft bus.

On the path toward implementing active materials in isolationsolutions, the Satellite Ultra-quiet Isolation TechnologyExperiment (SUITE)3 was designed and fabricated.



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The Middeck Active Control Experiment (MACE), flown on STS-67in March 1995 as shown in Figure 4, was funded by NASALangley Research Center (NASA LaRC) and jointly developed by

the Massachusetts Institute of Technology (MIT) and PayloadSystems to demonstrate the effectiveness of structural control inimproving spacecraft stability and to assess the predictability ofcontroller performance based on analysis and 1-g testing.


ON-ORBIT ADAPTIVE STRUCTURAL CONTROL


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C t l f S t St t 3 A A li ti f C t l f S t St t P t 224


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The isolators are based on Honeywells patented three-parameterhermetically-sealed viscous D-Strut.

This isolator strut design demonstrates consistent linear dampingand isolation over several orders of magnitude of inputdisplacement and over a useful on-orbit temperature range

It supports and protects its payload during launch environments, andsubsequently provides micro-inch level jitter reduction on-orbit.

An elliptical hexapod provides six-degree-of-freedom support andisolation.

The fluid-damped D-Strut isolation system maintains its payloadoptical alignment after vibration and thermal exposure.

Vibration tests at one micro-inch input and at one- tenth of an inchinput show almost identical damping and isolation responses.

The 70-lb test payload was made from wood with an aluminumbackbone.

The payload provided accurate mounting geometries for the sixisolator struts, and precision locations for ten accelerometers and anoptical cube.

Vibration Isolation- Launch and On-orbit Isolator

C t l f S t St t 3 A A li ti f C t l f S t St t P t 225


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The modified elliptical

hexapod provides six-

degree-of-freedom

support and isolation forboth launch and on-orbit

environments.

The D-Strut. isolation

system maintains its

payload optical alignment

after vibration and

thermal-cycle testing, with

no stiction, low thermal

pointing, and with

controlled, repeatable

isolation performance.



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Control of Smart Structure 3 Aerospace Applications of Control of Smart Structures Part 229


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Shock testing, launch-level random vibration, andlaunch sine vibration were also conducted.

The system was also subjected to thermal cycling.Functional transmissibility tests were performed before,midway, and after launch environments, at 0.25-g and2.5-g sine input levels.

In summary, a single passive isolation system canperform well both during launch and during on-orbitflight.


Control of Smart Structure 3 Aerospace Applications of Control of Smart Structures --Part 230


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A Miniature Vibration Isolator

Source: SPIE Smart Materials and Structures Conference, 2001

Vibration Isolation- Miniature Isolation system



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Introduction: Space-based optical sensors demand maneuvers withexacting motion. They can stand very little unsettling movement such

as vibration or jitter and still perform optimally.

Major sources of jitter for most satellites include momentum/reaction

wheels, solar array drive mechanisms, and specialized devices with a

moving or rotating mass such as cryogenic coolers.

As optical satellites evolve their structures are becoming larger and

more flexible. This makes their payloads more susceptible to jitter than

ever before.

The Miniature Vibration Isolation System (MVIS) can be utilized at either

or both locations, with minimal envelope and mass impact.

The MVIS program was sponsored by the U.S Air Force ResearchLaboratory to develop technology that performed isolation functions and

flight demonstrate a reliable, application-flexible, low-cost miniature

alternative to the larger Vibration Isolation Steering, and Suppression

system.




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Control of Smart Structure 3. Aerospace Applications of Control of Smart Structures Part 2






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Control of Smart Structure 3. Aerospace Applications of Control of Smart Structures Part 2



MVIS SPECIFICATION: MVIS system active stage attenuates

low frequency jitter, and the passive stage removes high

frequency disturbances.

The active stage strut level requirements stem from the worst

case disturbance. Worst case disturbance values were

determined to be around 2000 micro-inches (with the

exception of Space Station). The active stage was designed

using these performance goals while utilizing minimal real

estate.

A few observations can be made about the performance

requirements for MVIS.

Displacement-sensitive Space Station Applications will be left

to the larger size, longer-stroke, VISS hybrid technology or

soft passive isolation, for now.



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Co o o S S uc u e 3. e osp ce pp c o s o Co o o S S uc u es



Comparative performance shows that for payloads requiringlarge strokes VISS is an optimal solution whereas MVISbecomes a more attractive solution for payloads requiring lessstroke.




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p pp



Best candidate hardware architecture was a deterministichexapod, or Stewart Platform, mount because six identicalelements could be utilized, lowering cost and maximizing6-degree-of-freedom isolation performance.


MVIS SYSTEM ARCHITECTURE


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p pp



Figure illustrates how MVIS performs itsvibration isolation function. Basedisturbances are sensed and rejected bythe active stage over a prescribedfrequency bandwidth.

The passive stage damps isolatorresonance and removes high frequencydisturbance components easing theactive stage performance burden.

The launch lock system shunts thehybrid isolator during launch and isremoved once the system is system iscalled into operation.

The one-dimensional schematic ofFigure can be easily expanded to a full6 degree of freedom system byconfiguring 6 hybrid elements into a

hexapod or Stewart Platform.



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Two hybrid struts were developed and the hybrid element wasmade up of an active and passive stage.

The active stage accomplishes actuation using a proprietarypiezoelectric based actuator. The active stage is complementedby the addition of a serially mounted miniature D-Strut.

This combination allows the hybrid element to behave as akinematic link improving the linearity and predictability of theMVIS hexapod.

The addition of an integrally mounted miniature accelerometercompletes the element and provides the feedback sensenecessary for active control.

Each completed element weighs 0.2 lb. The Hybrid Strutelement measures just over 1 inch in diameter and 2 inches

long making it easily packaged within most payload envelopes.


HYBRID STRUT PERFORMANCE


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An open-loop test wasconducted to determine if theactuator section would perform

both statically and dynamically.The MVIS strut was designed foran active stroke of 0.003-inch(+/-0.0015).

A Micro-sense non-contactingdisplacement probe was used tomeasure displacement.

The actuator is located wherethe red wire enters the base ofthe MVIS strut. A stand andcylindrical adapter (the blackwire crosses the adapter) arebelow the MVIS active element.


Active Stage Performance:


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Whole-Spacecraft Vibration Isolation (Passive)

Source: CSA Engineering

Passive Isolation for payloads (PIP)


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Except the restrictive considerations of mass, bandwidth, hysteresis andenvironmental stability , the performances in terms of maximal freedeformation and of mass energy density are important parameters for thechoice of materials.

The ultimate and decisive criteria are related to the toughness and damagetolerance capability.

The deformation of parts induces high stress levels which are necessarilysupported by the active material. So the polymeric piezoelectric films, tooflexible are quite unsuited.

Piezocomposites are dedicated to applications requiring a complex andrapid shaping of the surfaces but the deformations which can be generatedare small and the carried efforts are low.

Piezoelectric fibers and even ribbons are promising on the two aspects ofcapable maximal deformation and mass energy density with thecomplementary benefits ofcomplex shape warping, possible control of theanisotropy and the possibility to cover large surfaces with a relative safety.

Ceramic embedded in resin becomes less brittle.

Active Shape Control-Materials and Actuators

MATERIALS


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Electrostrictive ceramics present at ambient temperature,deformations slighter higher than those of piezoelectricmaterials (from 10 to 20% highest).

This information is to be taken with care because it dependson the thickness and the sintering conditions of the product.

Bulk electrostrictive ceramics are in fact very delicate toelaborate at an industrial scale and properties are very

sensitive to temperature, particularly around 0C, and to thefrequency of actuation.

Another advantage lies in the absence of polarity.



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Compared to piezoelectric materials, electrostrictive materialshave very high capacitances and loss factors and changessignificantly with frequency and temperature.

Other types of actuators such as moonies, cymbals, thundersand bi or multi-morphs presenting intermediate force-displacement diagrams show gradually larger runs anddevelop low forces.




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The linear actuators incorporate quasi exclusively soft PZTceramics because for their primary purpose (micro positioning).

Polytec P.I proposes a large array of low voltage (100V) and

high voltage (1000V) actuators. The stacks of these actuatorsare contained in a protective cylindrical stainless housing andare pre-stressed during assembly by a stack of Bellevillewashers.

This prestress allows to work in the two directions but oftendissymmetrical and more in compression than in tension.

The effective mechanical power available for the external workis then reduced compared to a pure induced strain stack by theinternal work absorbed by the whole elastic element (i.ewashers and housing).

Low voltage elliptic amplified actuators developed for micropositioning present large strokes while keeping quitesatisfactory force transmission capability.


Actuators in Pre Stressed Casings



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Flap Deflection: The control of the deflection of a flap located on arotor blade, based on a 1/3rd scale model , has been studied byaddressing several principles using commercial actuators coupled toinnovative linkages or the bending of beams realized by the action ofcouples of bonded electroactive ceramics.

Flap Deflection by Actuators: The first system uses a linear P.Iactuator, centered on the pitch axis of the blade and coupled to aroller screw which clutches the axis to the flap through a fork.

Another variant of the motion transforming device consists of a lever

arm with an orthogonal angle reverse which have some judiciousflexible knee-joints.

The resistant hinge moment, representative of the action of theaerodynamic moment which applies on the flap and which isassumed to be linear with the deflection angle, is done by severalsets of two stiff calibrated flexible strips.

The drawback of this first solution is the great inertia of moving partsand friction in the bearings.



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The new idea consists of embedding ribbons instead of fibers and touse the d31 as well the d33 mode which needs lower voltages.

The use of ribbons, enables having round corners to avoid electricalarcs and also to reduce the cracking sensitivity.

It also removes a more dense material in favor of a higher d33, ahigher stiffness exempting from the use of additional fiberglass, abetter piezoelectric coupling exempting from the introduction of PZTpowder in the resin, a higher force generation capability and abetter energy efficiency. Another benefits is easier implementation.




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Swelling of aerodynamic profile: The aim is to modify theaerodynamic profile of a relatively flexible wing model destined tolow speed wing tunnel testing by a combining controlled increaseof the relative thickness and of the twist of the wing tip.

An experiment inflating the small length of elliptic constantsection (long axis : 300 mm, short axis : 53 mm, spanwise100mm) made up of 1.4mm of fiberglass fabric plies 21 wasconducted.

A 0.8 mm Nitinol wire, which is simpleeffect treated and whose transitiontemperature have been measured(As=54C, Af=79C, Ms=40C and

Mf=28C), is set in the martensitic stateand preloaded.

A voltage of 1.86 V and 3 A were appliedfor a 45 s to modify the thickness asshown.


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