Cosmol News

8/18/2019 Cosmol News

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2 0 1 4

COMSOLNEWS

BOSTON SCIENTIFIC

ENGINEERS REVOLUTIONIZE

MEDICAL DEVICE DESIGN

BOEING MODELS

COMPOSITES

WITH LIGHTNING

PROTECTION

W W W . C O M S O L . C O M

P. 4

P. 10

P. 16

T H E M U L T I P H Y S I C S S I M U L A T I O N M A G A Z I N E

NASA OPTIMIZES MANNED

SPACECRAFT DEVICES USING

MULTIPHYSICS SIMULATION

mage suppl ied by Boeing. C opyright © Boeing


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ON THE COVER

”787-8 Flying Over Oregon Coast” fromwww.boeingimages.com.

We welcome your comments on COMSOLNEWS; contact us at [email protected].

© 2014,COMSOL. COMSOL News is published byCOMSOL, Inc. and its associated companies. COMSOL,COMSOL Multiphysics, Capture the Concept, COMSOLDesktop, and LiveLink are either registered trademarksor trademarks of COMSOL AB. All other trademarks are

the property of their respective owners, and COMSOLAB and its subsidiaries and products are not affiliatedwith, endorsed by, sponsored by, or supported by thosetrademark owners. For a list of such trademark owners,see www.comsol.com/trademarks

Verify, Optimize, Revolutionize:

Multiphysics Simulation DeliversInnovative Design Solutions

This year’s issue of COMSOL News providesyou with a front row seat to show how

multiphysics simulation is advancingproduct development. Engineers andresearchers strive to stay ahead of the gameby employing innovative design solutionsthat result in reduced cost and increasedrevenues while providing safer and betterproducts. But how do they do it?

You may have identified the familiarBoeing 787 Dreamliner featured on thecover. For this innovative jet airlinercomprised of more than 50 percent carbonfiber reinforced plastic, engineers atBoeing used multiphysics simulation toinvestigate and verify thermal expansion in

composite materials with expanded metalfoil for lightning strike protection. BostonScientific engineers are revolutionizingmedical device design by gaining theknowledge required to control theunderlying release mechanism of drug-eluting stents. Simulation provided vitaloptimization and design guidance to NASAengineers involved in the development oflife support systems providing breathableair and drinkable water for astronauts.

These are just a few highlights of themany successes achieved by the engineers

and researchers relying on the power andaccuracy of multiphysics simulation. Fromlab-on-a-chip to building physics, to MEMS& robotics and containerless processing,there are plenty of exciting projects youcan read about.

It’s been an honor to work with thetalented engineers, researchers, anddesigners featured in the articles and it is mypleasure to bring you this edition of COMSOLNews, the multiphysics simulation magazine.

Enjoy your reading,

Valerio Marra

TECHNICAL MARKETING MANAGER

COMSOL, Inc.

AEROSPACE4 Boeing Simulates Thermal

Expansion in Composites with

Expanded Metal Foil for LightningProtection of Aircraft Structures

STEELMAKING8 Continuous Casting: Optimizing

Both Machine and Process withSimulation

MEDICAL TECHNOLOGY10 Simulating the Release

Mechanism in Drug-Eluting Stents

IMAGING SPECTROMETRY13 Keeping Cool: SRON Develops

Thermal Calibration System forDeep-Space Telescope

SPACECRAFT ATMOSPHERE

REVITALIZATION16 Simulation Helps Improve

Atmosphere RevitalizationSystems for Manned Spacecraft

PASSIVE VACCINE STORAGE18 Innovative Thermal Insulation

Techniques Bring Vaccines to theDeveloping World

NUCLEAR WASTE STORAGE20 Battling Corrosion in Nuclear Waste

Storage Facilities

BUILDING PHYSICS22 Using Multiphysics Simulation to

Prevent Building Damage

BIOTECHNOLOGY24 Optimizing Hematology Analysis:

When Physical Prototypes Fail,Simulation Provides the Answers

AUTOMOTIVE28 Optimizing Built-in Tire Pressure

Monitoring Sensors

NUCLEAR ENGINEERING30 Researching a New Fuel for the

HFIR: Advancements at ORNLRequire Multiphysics Simulationto Support Safety and Reliability

ACOUSTIC STREAMING34 Gaining Insight into Piezoelectric

Materials for Acoustic Streaming

MATERIALS SCIENCE36 Simulation-Led Strategy for

Corrosion Prevention

BIOENGINEERING40 Patterning Cells with the Flip

of a Switch for BioengineeringApplications

COMPUTATIONALELECTROMAGNETICS

42 Scattering of ElectromagneticWaves by Particles

CONTAINERLESS PROCESSING44 Floating on Sound Waves with

Acoustic Levitation

MEMS & ROBOTICS46 Actuation Technique for

Miniature Robots Developedusing Multiphysics Simulation

GUEST EDITORIAL48 From Concept to Market:

Simulation Narrows the Oddsin Product Innovation

C O N T E N T S

INTERACT WITH THE COMSOL COMMUNITY

You can comment on this year’s stories via

BLOG comsol.com/blogs

FORUM comsol.com/community/forums

FACEBOOK facebook.com/multiphysics

TWITTER twitter.com/COMSOL_Inc

2 | COMSOL NEWS | 2014


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S P O N S O R E D B Y

C A T E G O R YS P O N S O R

P R I Z ES P O N S O R

She Created the Future.

Now it’s Your Turn. THE

DESIGN CONTEST 2014

Fluid-Screen (formerly Alpha-Screen) brings the functionality of a lab to a small portable device that fits in thepalm of your hand and detects bacteria from blood and water in less than 30 minutes. Fluid-Screen uses apatented electric field and biosensor technology to rapidly collect and detect bacteria.

“After being honored with the 2011 Create the Future Design Contest Grand Prize, the funding and publicity from the award was instrumental in helping us speed up the development of Fluid-Screen and make a working beta prototype,” says Monika Weber, Founder and CEO of Integrated Microfluidic Devices.

Monika Weber, Founder and CEO of Integrated Microfluidic Devices, was the Grand Prize Winner of the 2011Create the Future Design Contest.

www.createthefuturecontest.com

To enter, get details at

Fluid-Screen product test series will be launched in 2015 and enter the market in 2016.


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COMPOSITES | AEROSPACE Boeing, WA, USA

Boeing Simulates Thermal Expansionin Composites with Expanded

Metal Foil for Lightning Protectionof Aircraft StructuresModern aircraft such as the Boeing 787 Dreamliner are comprised of more than fifty percentcarbon fiber composite requiring the addition of expanded metal foil for lightning strikeprotection. Researchers at Boeing are using simulation to verify that protective coatings onthe metal foil will not fail due to thermal stress arising from a typical flight cycle.

BY JENNIFER A. SEGUI

The Boeing 787 Dreamliner isinnovative in that it is comprised ofmore than fifty percent carbon fiberreinforced plastic (CFRP) due to thematerial’s light weight and exceptionalstrength. Figure 1 shows the extensiveuse of composite materials throughoutthe aircraft. Although CFRP composites

inherently have many advantages,they cannot mitigate the potentiallydamaging electromagnetic effectsfrom a lightning strike. To solve thisproblem, electrically conductiveexpanded metal foil (EMF) can beadded to the composite structure layupto rapidly dissipate excessive current

and heat for lightning protection ofCFRP in aircraft.

Engineers at Boeing Researchand Technology (BR&T) are usingmultiphysics simulation and physicalmeasurements to investigate theeffect of the EMF design parameterson thermal stress and displacement

FIGURE 1. Advanced composites used throughout the Boeing 787 account for more than fifty percent of the aircraft body1.


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COMSOL NEWS | 2014 | 5

COMPOSITES | AEROSPACE

in each layer of the compositestructure layup shown at left in Figure

2. Stress accumulates in the protectivecoating of the composite structure asa result of thermal cycling due to thetypical ground-to-air flight cycle. Overtime, the protective coating may crackproviding an entrance for moistureand environmental species that cancause corrosion of the EMF, therebyreducing its electrical conductivityand ability to perform its protectivefunction.

Contributing to the research effortat BR&T are project lead Jeffrey Morgan

from Sealants and ElectromagneticMaterials, Associate Technical FellowRobert Greegor from AppliedPhysics leading the simulation, Dr.Patrice Ackerman from Sealants andElectromagnetic Materials leading thetesting, and Technical Fellow QuynhgiaoLe. Through their research, they aimto improve overall thermal stability inthe composite structure and thereforereduce the risks and maintenancecosts associated with damage to theprotective coating.

SIMULATING THERMAL EXPANSIONIN AIRCRAFT COMPOSITESIn the surface protection scheme shownat left in Figure 2, each layer includingthe paint, primer, corrosion isolationlayer, surfacer, EMF, and the underlyingcomposite structure contribute to thebuildup of mechanical stress in theprotective coatings over time as theyare subject to thermal cycling. Thegeometry in the figure is from thecoefficient of thermal expansion (CTE)model developed by Greegor2,3 and his

colleagues using COMSOL Multiphysics® in order to evaluate the thermal

stress and displacement in each layerof a one-inch square sample of thecomposite structure layup.

The structure of the EMF layeris shown at right in Figure 2. In thisstudy, the EMF height, width of themesh wire, aspect ratio, metalliccomposition, and surface layupstructure were varied to evaluatetheir impact on thermal performancethroughout the entire structure. Themetallic composition of the EMF waseither aluminum or copper where an

aluminum EMF requires additionalfiberglass between the EMF and

the composite to prevent galvaniccorrosion.

The material properties for eachlayer including the coefficient ofthermal expansion, heat capacity,density, thermal conductivity, Young’s

modulus, and Poisson’s ratio wereadded to the COMSOL model ascustom-defined values and aresummarized in Figure 3. The coefficientof thermal expansion of the paintlayer is defined by a step functionthat represents the abrupt changein thermal expansion at the glasstransition temperature of the material.

In the CTE model, the ThermalStress multiphysics interface couplessolid mechanics with heat transferto simulate thermal expansion andsolve for the displacement throughout

the structure. The simulations wereconfined to heating of the compositestructure layup as experiencedupon descent in an aircraft wherefinal and initial temperatures weredefined in the model to represent theground and altitude temperatures,respectively.

IMPACT OF EMF ON STRESSAND DISPLACEMENTThe results of the COMSOL simulationswere analyzed to quantitatively

determine the stress and displacementin each layer upon heating and for

FIGURE 3. Ratio of each material parameter relative to the paint layer. The paint layershows higher values of CTE, heat capacity, and Poisson’s ratio indicating that it will

undergo compressive stress and tensile strain upon heating and cooling.

FIGURE 2. At left is the composite structure layup from the COMSOL model and, at right,the geometry of the expanded metal foil. SWD and LWD correspond to short way of the

diamond and long way of the diamond. The mesh aspect ratio: SWD/LWD is one of theparameters varied in the simulations.


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varied properties of the expanded met-al foil. An example of the simulationresults is shown in Figure 4.

Through the paint layer at the topof Figure 4, it is possible to observe thedisplacement pattern of the underlying

EMF. The magnified cross-sectionalview clearly shows the variations indisplacement above the mesh andvoids in addition to the trend in stressreduction in the uppermost protectivelayers. Figure 5 shows the relative stressfor each layer in surface protectiveschemes that incorporate either copperor aluminum EMF. The fiberglasscorrosion isolation layer required by thealuminum EMF acts as a buffer, causingthe stress to be lower in the aluminumthan it is in the copper EMF.

Despite the lower stress in the

aluminum EMF, simulation resultsfrom the variation of the EMF designparameters reveal a consistent trendtoward higher displacements in thesurface protective scheme with thealuminum EMF when compared tocopper. The larger displacementsgenerally caused by the aluminumEMF can be attributed, in part, to therelatively higher CTE of aluminum.

Further analysis of the impact of theEMF design parameters was performedto confirm the effect of varying the

height, width, and mesh aspect ratio ondisplacement in the protective layers.When varying the mesh aspect ratio, itwas found that an increased ratio ledto a modest decrease in displacementof about 2 percent for both copperand aluminum EMF, where higher ratio

values correspond to a more openmesh structure. For any EMF designparameter, there is a trade-off betweencurrent carrying capacity, displacement,and weight. In the case of mesh aspect

ratio, while choosing an open meshstructure can reduce displacement andweight, the current carrying capacitythat is critical to the protective functionof the EMF is reduced as well and needsto be taken into account.

Similarly with regard to the meshwidth, varying the width by a factor ofthree led to a relatively minor increasein displacement of about 3 percentfor both copper and aluminum EMF.However, varying the height of the EMFby a factor of four led to an increase

in displacement of approximately 60percent for both aluminum and copper.Figure 6 shows the relative valuesfor displacement through each layerof the surface protection scheme forvaried height of copper and aluminumEMF. Due to the lower impact on

FIGURE 4. Top, middle: top-down andcross-sectional views of the von Mises

stress and displacement in a one-inchsquare sample of a composite structurelayup. At bottom, transparency was used

to show the high stress in the compositestructure and EMF. Stress was evaluated

along the vertical line extending throughthe depth of the sample.

FIGURE 5. Relative stress in arbitrary units was plotted through the depth of the composite structure layups containing either aluminum(left) or copper EMF (right).

“Increasing the mesh widthor decreasing the aspectratio are better strategies

for increasing the currentcarrying capacity of theEMF for lightning strikeprotection.”


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displacement, increasing the meshwidth or decreasing the aspect ratioare better strategies for increasing thecurrent carrying capacity of the EMF forlightning strike protection.

RELATING DISPLACEMENT WITHCRACK FORMATIONGreegor and his colleagues at BR&Tqualitatively regard any projectedincrease in displacement as an increasedrisk for developing cracks in the protectivelayers since mechanical stress due tothermal cycling accumulates over time.

Experimental evidence supportsthis logic as shown in Figure 7 in photomicrograph cross-sections of surfaceprotection schemes with aluminum andcopper EMF after prolonged exposureto moisture and thermal cycling in an

environmental test chamber. The layupwith the copper EMF shows no cracks,whereas the aluminum EMF led tocracking in the primer, visible edge andsurface cracks, and substantial crackingin mesh overlap regions.

Over the same temperature range,the experimental results correlate wellwith the results from the simulationsthat consistently show higherdisplacements in the protective layersfor the aluminum EMF. Both simulationand experiment indicate that the copper

EMF is a better choice for lightningstrike protection of aircraft compositestructures. Multiphysics simulation istherefore a reliable means to evaluatethe relative impact of the EMF designparameters on stress and displacementto better understand and reduce thelikelihood of crack formation. n

References

The information presented in this article is based on

the following publicly available sources:

1 The Boeing Company. 787 Advanced Composite

Design. 2008-2013. www.newairplane.com/787/

design_highlights/#/visionary-design/composites/

advanced-composite-use

2 J.D. Morgan, R.B. Greegor, P.K. Ackerman, Q.N.

Le, Thermal Simulation and Testing of Expanded

Metal Foils Used for Lightning Protection of

Composite Aircraft Structures, SAE Int. J. Aerospace

6(2):371-377, 2013, doi:10.4271/2013-01-2132.

3 R.B. Greegor, J.D. Morgan, Q.N. Le, P.K.

Ackerman,Finite Element Modeling and Testing

of Expanded Metal Foils Used for Lightning

Protection of Composite Aircraft Structures,

Proceedings of 2013 ICOLSE Conference;

Seattle, WA, September 18-20, 2013.18-20, 2013.

FIGURE 6. Effect of varying the EMF height on displacement in each layer of the surfaceprotection scheme. The graphs at top show displacement in arbitrary units; at bottom,the ratio is the displacement calculated for each height normalized by the displacement

for the smallest height.

FIGURE 7. Photo micrographs of the composite structure layups after exposure to moistureand thermal cycling. At left, the results for the copper EMF and at right, the aluminum.

Research team at Boeing Research and Technology, from left to right: Patrice Ackerman,

Jeffrey Morgan, Robert Greegor, and Quynhgiao Le.

BOEING, Dreamliner, and 787 Dreamliner are registered trademarks

of The Boeing Company Corporation in the U.S. and other countries.


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CONTINUOUS CASTING | STEELMAKING SMS Concast, Switzerland

Halfway through the twentiethcentury, the steelmaking processwas transformed when the batchprocess of ingot casting was replacedby continuous casting. With thistechnique, a constant stream of liquidsteel is transformed into endlessstrands of glowing, solid metal(see Figures 1 and 2).

In ingot casting, the head of eachingot must be cropped after it isremoved from the mold, producingwaste metal. In continuous casting,however, this cropping must onlybe done at the very start and veryend of each sequence during whichseveral hundred tons of steel arecast, meaning far less waste materialis produced. Additionally, the shapeof the cast strands is far closer to theshape of the final rolled product. This

results in improved yield, superiorquality, and better cost efficiency thanprevious methods. Not surprisingly,95 percent of steel is made usingcontinuous casting today.

SMS Concast has been a leader inthis field for 60 years, designing andbuilding technical equipment for steelmelting, refining, and continuouscasting. It has a worldwide marketshare of over 40 percent. “Continuous

casting presents a huge number ofvariables that we need to analyze aswe continue to improve the technologyand advance the boundaries ofwhat we know,” explains NicholasGrundy, Head of Metallurgy & ProcessContinuous Casting at SMS Concast.“We are constantly pushing the limitsand the only way to understandsomething that we have never donebefore is to simulate it.”

SIMULATION ACROSS ALL REALMSIn continuous casting, molten, refined

steel is typically brought to the caster inladles of 30 to 350-ton capacity. The steelis teemed into a tundish that distributesthe steel into one to eight strands. Thefirst solid steel is formed in the open-ended, water-cooled copper moldsand the formed strands are withdrawnout of the molds using driven rollers atspeeds of 0.1 to 6 meters per minute,depending on section size (see Figure2). After fully solidifying, the red-hotstrands are cut into 3 to 15 meter-longpieces and left to cool.

The process of continuous castingproduces a cast semifinished that isclose in shape to the final product,greatly reducing the cost of furtherprocessing by rolling or forging.Depending on the shape of the mold,square profiles called billets can becast for rolling into bars and wire forapplications ranging from concretereinforcement to piano wire. Larger,rectangular pieces called blooms can

also be forged, for example to form a

FIGURE 1. Discharge table of thecontinuous caster showing solidified

strands being cut and discharged.

FIGURE 2. Continuous casting diagram.Liquid steel is brought to the caster inladles. The tundish distributes the liquid

steel to the copper molds and the formedstrands are withdrawn out of the molds

using driven rollers.

CONTINUOUS CASTING: OPTIMIZING BOTHMACHINE AND PROCESS WITH SIMULATION

As manufacturing processes become more sophisticated, the demand for bigger and bettersteel products increases. SMS Concast uses simulation to ensure their customers can bringsteelmaking into new realms of size, quality, and complexity while simultaneously reducingenergy consumption.

BY JENNIFER HAND


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CONTINUOUS CASTING | STEELMAKING

crankshaft or to be rolled into bars orrails. Slabs are rolled into sheet metalout of which everything from cars tooil tankers are produced.

SMS Concast uses simulation atevery stage of the casting process:

To analyze fluid flow in the tundish,primary solidification in the mold,solidification and mechanicaldeformation of the strand, andquenching or slow cooling of thecut blooms. “During solidification,we must minimize segregationof alloying elements towards thecenter of the strand, remove non-metallic inclusions, and improve themicrostructure of the solidifyingsteel,” describes Grundy.

“One way of achieving theseimprovements is by stirring the

liquid steel,” he says (see Figure 3).This is done using electromagneticstirrers that generate strong rotatingelectromagnetic fields around thestrands. This causes the liquid steelin the core of the strands to rotate.The field generated by the stirrersand the resulting flow pattern ofthe liquid steel is simulated usingCOMSOL Multiphysics®. Simulationis a crucial step in order to designthe electromagnetic stirrers correctlyand to achieve the best steel quality.

Stirring is particularly important forhighly-alloyed grades such as ballbearing steel, with high demands oncleanliness (with a minimal presence

of non-metals), even composition

(low segregation), and fine-grainedmicrostructure.

“Essentially, most of the problemswe face must be studied by combiningvarious realms of physics such aselectromagnetics, liquid or gas flow,mechanics and heat transfer. That’swhy we use COMSOL Multiphysics; weknow of no other tool that links allthese realms of physics into one singleplatform as seamlessly as COMSOL.”

PREDICTING SOLIDIFICATION

AND SHRINKAGEOne recent steelmaking trend is toroll strands of cast steel while theyare still hot, rather than cooling themdown and reheating them later in areheating furnace. This is called hotcharging, and avoids wasteful loss ofthermal energy but demands an evenmore accurate understanding of how astrand solidifies. Grundy explains, “Thecopper mold is at the heart of eachcontinuous caster. This is where thefirst solid steel skin is formed. A billetwill only be faultless if the internal

shape of the copper tube follows theshrinkage of the steel exactly, and abillet’s surface must be faultless if it’sto be hot-charged.”

The SMS Concast team used theirCOMSOL model to understand thecomplex heat exchange processestaking place during the firstsolidification of the steel in the mold.The results guided the design of anew type of mold to cast billets withlarge rounded corners (see Figure 4).These corners stay warm after casting,

resulting in a more even surfacetemperature. This makes it possibleto hot-charge the billets directly tothe rolling mill, without leaving themto cool down and then heating themagain in a reheating furnace fired with

fossil fuels, as is the practice ina conventional steel plant.The innovative mold design was

successfully implemented at Tung HoSteel in Taiwan in 2010, a steel plantthat runs completely without a gas-fired reheating furnace, resulting inhuge environmental and economicbenefits. This reduces yearly emissionsby 40,000 tons of CO

2, about the same

as the exhaust of 20,000 cars.

SIMULATE BUT ALSO VALIDATEGrundy concludes, “Whenever

possible, we like to validate oursimulations with results from thereal world or with physical models.For example, to validate our tundishflow simulation, one customer built aPlexiglas scaled water model and we

found excellent agreement betweenthe physical model and our flowsimulations. As trust in our modelsgrows, we gain the confidence toexplore allowable designs.” Thisapproach clearly works well for thecompany; the world’s widest beamblank (1150 x 490 x 130 mm) is alreadybeing cast on an SMS Concast casterin Germany, and the largest roundsection ever made (1000 mm indiameter) will go into productionin a South Korean mill in 2015. n

FIGURE 3. Model of a tundish using theCFD Module in COMSOL Multiphysics(top) and actual tundish during emptying

of molten steel (bottom).

Nicholas Grundy displaying the simulation

results of one of the CFD models of thecontinuous casting process.

FIGURE 4. The water-cooled copper moldtube where the first solid steel shell forms

is the heart of every continuous caster.Inset: Model of primary solidification and

shell growth in the copper mold.


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DRUG-ELUTING STENTS | MEDICAL TECHNOLOGY Boston Scientific Corporation, MN, USA

SIMULATING THE RELEASE MECHANISMIN DRUGELUTING STENTSEngineers at Boston Scientific are revolutionizing medical device designs. Teir recentsimulations of drug-eluting stents provide an understanding of the drug release mechanismby tying experimental findings to a computational model.

BY LEXI CARVER, COMSOL, INC.CONTRIBUTING AUTHORS: TRAVIS SCHAUER AND ISMAIL GULER, BOSTON SCIENTIFIC CORPORATION

FIGURE 1. A. Restricted blood flow in a vessel; B. Stent insertion and expansion; C. Normalized blood flow (left), arrangement inside ablood vessel (center), and cross-section of a stent strut (right).

Treating arteries in the heart that

have been blocked by plaque isa common challenge for medicalprofessionals. Known as stenosis, thiscondition restricts blood flow to theheart, resulting in symptoms such asshortness of breath and chest pain. It issometimes resolved using stents, whichare small, mesh-like tubular structuresdesigned to treat blocked arteries.They are usually placed in the coronaryartery and expanded with a balloon

catheter to keep the artery open, as

depicted in Figure 1.While stents are successful at

holding arteries open, an artery canre-narrow because of excessive tissuegrowth over the stent. This is calledrestenosis and is the body’s naturalhealing response, but it can actuallyimpede recovery. Thus, drug-elutingstents were developed to delivermedicine — which acts to reducecell proliferation and prevent the

unwanted growth — into the artery

tissue. These contain a coatingcomposed of medicine and a polymermatrix designed to provide acontrolled delivery; each strandof the stent mesh is surrounded bythis coating (see Figure 1C). Stentdesigns have improved dramaticallyin recent years in an effort toreduce restenosis rates, but muchremains unknown regarding therelease process.


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DRUG-ELUTING STENTS | MEDICAL TECHNOLOGY

DRUG RELEASE BEHAVIOR

Travis Schauer, Ismail Guler, and a teamof other engineers at Boston Scientific,a company that develops devices andtechnologies to diagnose and treat awide range of medical conditions,have sought to better understandthe mechanism of medicine releasewith computer simulation. UsingCOMSOL Multiphysics®, they havemodeled a stent coating to investigatethe release profile (the rate at whichthe medicine diffuses out of thecoating and into the vessel tissue) and

the influencing factors. They used theOptimization Module in COMSOL to fittheir simulation as closely as possibleto experimental data curves. Schauerexplained, “By gaining knowledge ofthe underlying mechanisms and

microstructure of the coating, we are

able to understand the release processand tailor it to achieve a desiredprofile.” Ultimately, this may lead to alevel of control over the release thathas until now been impossible.

The stent coating that Schauerand Guler modeled is a microstructurewith two phases: a medicine-rich,surface-connected phase and a phasewith drug molecules encapsulatedby a polymer. The development ofthis microstructure is affected by thesolubility of the drug, the drug-to-

polymer ratio, and the processingconditions during manufacturing.When the stent is inserted into anartery, the medicine-rich phase quicklydissolves and diffuses into the tissue,leaving behind interconnected cavities(pores) in the polymer coating, asdepicted in Figure 2. Meanwhile, themolecules encapsulated by the polymerdiffuse more slowly.

MODELING MEDICINE DELIVERYSchauer and Guler idealized thecomplex geometry of the coatingmicrostructure: in their model, thecoating consists of a pattern ofcylindrical pores filled with solid

medicine surrounded by a polymershell containing both the dissolveddrug and solid drug encapsulatedby the polymer. The moleculesdiffuse radially and axially, and themicrostructure geometry only changesradially — at the boundary betweenshell and pore. Therefore, a two-dimensional axisymmetric model(see Figure 3) was sufficient.

Using COMSOL has allowedSchauer and Guler to easilycustomize their model. “We focusedon understanding the transport

phenomena at hand instead ofspending time on cumbersomeprogramming,” Schauer remarked.“We customized the underlyingequations according to our needsdirectly through the user interface.”They performed simulations fortwo release profiles, in vitro andin vivo cases, seeking a descriptionof the cumulative release of themedicine. “We wanted to understandwhy certain release profiles wereobserved,” said Guler and Schauer.

“We compared experimental data tothe release profiles generated in oursimulations to confirm our findings.”

Schauer and Guler tracked boththe dissolution of solid drug and thediffusion of dissolved drug. As itdissolves within the pores, the poresfill with liquid media from thesurrounding tissue. The medicine hasa different solubility limit in the liquid

FIGURE 2. The coating microstructure prior to release (left) and the interconnected emptypores surrounded by the polymer matrix following the release from the coating (right).

FIGURE 3. Idealized microstructure of the stent coating. A single pore-shell was modeled(center). The labels R

pore and t

shell (right) refer to the pore radius and the shell thickness.

“By gaining knowledgeof the underlyingmechanisms andmicrostructure of thecoating, we are able tounderstand the releaseprocess and tailor itto achieve a desiredprofile.”


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DRUG-ELUTING STENTS | MEDICAL TECHNOLOGY

media than it does in the polymer,which results in a discontinuity in thedissolved medicine concentration atthe interface between pore and shell.As Guler explained, “The appropriateinterface conditions were easilyimplemented in COMSOL using astiff-spring method, which ensuredthe continuity of the diffusive flux.”The customizable boundary conditionsavailable in COMSOL Multiphysicsallowed Schauer and Guler to easilyadd the necessary terms.

Certain model parameters had to beestimated because they were ‘effective’values that could not be measureddirectly, such as the polymer shell

thickness. Another was the retardationcoefficient that accounts for the twistedshape and constriction of the pores,steric effects, and other potentialinfluences on the diffusion throughthe pores. These parameters wererefined using the Optimization Module.Schauer and Guler made an initial guessfor the shell thickness and retardationcoefficient, based on experimentalkinetic drug release (KDR) data. Theycompared the model’s predicted releaseprofile to the KDR curves. Based on

the results, the Optimization Modulemodified the shell thickness andretardation coefficient to obtain thebest fit between the model results and

the experimental data. The releasecurves (see Figure 4) confirm that themedicine in the pores releases quickly,while the dispersed molecules inthe shell diffuse slowly through theencapsulating polymer. The results inFigure 5 depict the faster dissolutionand diffusion in the pore, compared tothe shell.

FUTURE STENT STUDIESReducing restenosis rates is anongoing goal for doctors and medical

professionals that is greatly aidedby drug-eluting stents. The modelingapproach employed by Schauer andGuler offers valuable insight intoone type of release mechanism.Although the simplified micro-structure model does not captureall the details of the release curves,the pore-shell simulation showedgood agreement, lending confidenceto the appropriateness of theiridealized model.

Researchers at the U.S. Foodand Drug Administration (FDA) are

developing even more comprehensivesimulations, based on diffuse-interface theory, to examine themicrostructure formation. Thesemodels aim to explain the relationshipbetween processing, microstructure,and release behavior in controlledsystems. Ultimately, simulationhas the potential to give medicaldevice designers more controlover the delivery process, andimprove treatment for patients withcardiovascular disease.n

FIGURE 4. Simulation results alongside experimental results showing release curves for the in vitro and in vivo cases.

FIGURE 5. Predicted medicine concentration for the in vitro case at time = 2 hours; C/Cs

= dissolved drug concentration/solubility limit (left), S/S0 = solid drug concentration/initial

solid drug concentration (right).


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SRON, Netherlands THERMAL DESIGN OPTIMIZATION | IMAGING SPECTROMETRY

Heat management takes on a uniquerole in outer space, especially forcryogenic systems that demandextremely low temperatures in orderto detect thermal radiation. This was

a challenge faced by the engineeringteam at SRON Netherlands Institute forSpace Research when designing theSpicA Far-InfraRed Instrument (SAFARI),an infrared camera that measures thecomplete far-infrared spectrum for eachimage pixel. SAFARI will fly aboard theJapanese Space Infrared Telescope forCosmology and Astrophysics (SPICA).

SPICA will look deeper into spacethan any space telescope has before.Because SAFARI has ultrasensitivedetectors, cooled to slightly aboveabsolute zero, it can pick up weaker

far-infrared radiation than previousspace cameras. Precise on-groundand in-space calibration is crucial tothe accuracy of the sensors and thesuccess of the mission. To design andoptimize these calibration systems,the team at SRON turned to aCOMSOL Multiphysics® simulationas their guide.

BEATING THE HEAT IN A TELESCOPECALIBRATION SYSTEMThe calibration source for SAFARIcontains a blackbody cavity orradiation source that provides

radiation with a spectrum dependingonly on the source temperature,making it a very reliable and accuratecalibrator. “However, SAFARI’sdetectors are so sensitive that thepower produced by the source isapproximately a million times toohigh and must be optically dilutedusing apertures and an integrating

KEEPING COOL: SRON DEVELOPS THERMALCALIBRATION SYSTEM FOR DEEPSPACE TELESCOPEObserving and analyzing regions in outer space where new stars and planets are bornrequires extremely sensitive detectors. Radiation and overheating can cause these detectorsto fail. Using multiphysics simulation, a team at SRON is developing a calibration sourcefor an imaging spectrometer that can operate with such vulnerable equipment.

BY LEXI CARVER

FIGURE 1. Left: Cross-section of the SAFARI calibration system. Right: Individual hardware components.


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sphere,” says Chris de Jonge, a designengineer at SRON. “After passingthrough the integrating sphere,radiation with the correct power andspectral distribution is then reimagedonto SAFARI’s detector arrays forcalibration.” Between the radiationsource and integrating sphere are amechanical shutter and iris mechanism(see Figure 1). The shutter opens andcloses the aperture to the radiationsource, while the iris fine-tunes and

modulates the output power.Thermal management is vital:the system is held in a “super-dark”environment at 4.5 kelvins (K) to

decrease the background radiationfrom the equipment itself. Variationin the base temperature of thedetectors, background radiation(affected by the orientation of thespacecraft), and power dissipated bythe iris and shutter mechanisms canall disrupt calibration.

“The radiation source temperaturecan be set between 95 and 300 K togenerate radiation — this createsa large temperature differential

between the source and the 4.5 Kenvironment, while available coolingpower at these temperatures islimited to just tens of milliwatts,”

de Jonge explained. “To account forthis, we needed to design a thermallyinsulating suspension system.” The

SRON team needed a stiff suspensionwith a high resonance frequency thatwould prevent heat transfer from thesource to the rest of the device whilealso protecting it from unwantedvibrations.

DESIGNING A THERMALLYINSULATING SUSPENSION SYSTEMUsing COMSOL simulations, de Jongeevaluated the heat load through thesuspension and performed modalanalyses on suspension concepts

with different geometries andmaterials, seeking a tradeoff betweenmechanical stiffness and thermalload. “COMSOL allowed us to quickly

THERMAL DESIGN OPTIMIZATION | IMAGING SPECTROMETRY

FIGURE 3. Left: Thermal model of the radiation source system with (1) stainless steel suspension strings, (2) the radiation source body,and (3) the interface between the suspension rig and the 4.5 K surrounding environment. Right: Modal analysis of the source, showing a

resonant frequency of 720 Hz.

FIGURE 2. Left: CAD drawing of the radiation source with stainless steel suspensionstrings (highlighted in red). Right: Actual hardware.

“COMSOL allowed

us to quickly studydifferent geometriesthat would otherwisebe difficult to analyze.”


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THERMAL DESIGN OPTIMIZATION | IMAGING SPECTROMETRY

study different geometries that wouldotherwise be difficult to analyze,”de Jonge remarked. “Because of thelarge temperature gradient over thebrackets and thermal properties thatchange very quickly as a function

of temperature, temperature-dependent material properties hadto be implemented. Ultimately, wechose the solution that had the bestcombination of mechanical stiffnessand thermal insulation.” Based onthe results, the team designed andoptimized a configuration of thin(100 µm) stainless steel wires to holdthe radiation source to a triangularframe (see Figure 2).

Because stainless steel has lowthermal conductivity at cryogenictemperatures and the cross-section of

the wires is very small, heat conductionthrough the wires was limited, whichthe simulation confirmed (see Figure 3).For a source temperature of 150 K,the experimental analysis showed10.17 mW of conducted heat. Thesimulation results were in closeagreement, accurate to within0.01 mW. The design also had aresonant frequency of 720 Hz, highenough to ensure proper functioningof the radiation source.

OPTIMIZING THE IRIS AND SHUTTERFOR MAXIMUM EFFICIENCYNext, de Jonge optimized the coil-driven iris and shutter mechanisms(see Figure 4). The iris is driven bya voice-coil actuator and containsfour stainless steel blades that rotatearound frictionless bearings. Theshutter is a magnetic latching device.

De Jonge used COMSOL tooptimize the iris coil and housing

geometry (his simulation resultsare shown in Figure 5), aiming tominimize the current and dissipatedheat during actuation. By performinga parametric sweep over the maindesign parameters on the air gap andnumber of coil windings, the teamdeveloped an optimal coil design thathas a low driving current of 38 mA

and a dissipation of just 1.6 mW.

SRON’S THERMALLY STABLEDEEP-SPACE SENSING SYSTEM ISON THE WAYBecause of SAFARI’s sensitivedetectors and the need for dissipativemechanisms in cryogenic systems,maintaining a controlled thermalenvironment is vital to the successof SPICA’s mission. COMSOL allowed

de Jonge and the team at SRON tooptimize their design for the bestthermal, material, and structuralconditions possible at extremely lowtemperatures. Their first tests of theSAFARI calibration source confirm theaccuracy of the COMSOL simulations.SPICA is scheduled to launch into orbitin 2022, when SAFARI will help us

unveil new mysteries of space beyondour solar system. n

FIGURE 4. Left: Components of the iris assembly, including the coil, wiring, and housing.The edges of the blades (internal) are visible through the center of the aperture. Right:

Shutter mechanism.

FIGURE 5. Left: Model of the iris mechanism showing the total displacement(surface plot) and magnetic flux density (arrows) of the blades and coil, respectively.

Simulation was performed using the Multibody Dynamics Module and AC/DC Module.The geometry was imported using the COMSOL LiveLink™ for Creo™ Parametric. Right:

Model of the shutter mechanism. Magnetic force was studied as a functionof coil current and anchor angle.

Chris de Jonge, Design Engineer at SRON,

working on the SAFARI calibration system.

PTC and Creo are trademarks or registered trademarks of PTC Inc.

or its subsidiaries in the U.S. and in other countries.


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EXOTHERMIC WATER ADSORPTION | SPACECRAFT ATMOSPHERE REVITALIZATION NASA Marshall Space Flight Center, AL, USA

The atmosphere in a manned spacecraftneeds to be regularly revitalized in orderto ensure the safety of the astronautsand the success of the space mission.For missions lasting a few months, thismeans air is continuously dehumidified,water collected for re-use, and carbondioxide (CO

2) ejected. One component

of the onboard atmosphere controlsystem is a water-saving device thatJim Knox, an aerospace engineer atNASA, is optimizing as part of the

Atmosphere Revitalization Recoveryand Environmental Monitoring(ARREM) project. He leads a team at theMarshall Space Flight Center (Huntsville,Alabama) that is aiming to make theassembly more cost-effective andefficient by reducing its power usageand maximizing the water saved; theirgoal is to save 80 to 90 percent of thewater in the air. They hope to offerflight system developers at NASA anintegrated approach to atmosphererevitalization and water collection thatwill ultimately increase the time and

distance space missions can travel.

SEPARATING WATER AND CO2

THROUGH EFFICIENT ADSORPTIONRevitalizing the atmosphere inside aspacecraft requires separating water,removing CO

2, and returning the

water to the air before it is condensedinto liquid form. The water-savingsystem that the team developed (seeFigure 1A) is called an Isothermal BulkDesiccant (IBD). It consists of a chassiswith enclosed channels called packed

Simulation Helps Improve Atmosphere Revitalization Systemsfor Manned SpacecraftLife support systems for manned spacecraft must provide breathable air and drinkable waterfor the astronauts. Trough the Atmosphere Revitalization Recovery and EnvironmentalMonitoring project, engineers at NASA are developing atmosphere control devices for thesafety of the onboard crew.

BY LEXI CARVER

FIGURE 1. (A) Photograph of an IBD with four columns. (B) Meshed COMSOL model ofthe IBD. Purple regions indicate wet beds, red indicate dry.

FIGURE 2. Simulation results showing temperature (K) in each bed. The first and thirdcolumns contain wet air flowing downward, the second and fourth dry air flowing upward.

Image courtesy of NASA


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EXOTHERMIC WATER ADSORPTION | SPACECRAFT ATMOSPHERE REVITALIZATION

beds, each of which is lined with silicagel pellets to promote water adsorption(a “dry” bed to draw water out) ordesorption (a “wet” bed to returnwater to the air). Each pair of bedsstraddles an aluminum foam lattice

used for transferring heat.The water-saving process occursin simultaneous half-cycles, withsome air entering the dry beds whilesome leaves the wet beds. In a drybed, water in the air is exothermallyadsorbed onto the silica gel, dryingthe gas to save the water, beforethe air travels to a CO

2 removal

system. The CO2-free air flows back

to the wet bed. Meanwhile, the heatcaused by adsorption in the dry bedis transferred to the wet bed via thealuminum lattice, causing water to

desorb from the silica gel and returnto the air. This heat transfer hasthe added benefit of lowering thetemperature in the dry bed, allowingadsorption to continue longer. Thewater is pumped back into the cabin,and the CO

2 is expelled into space.

After flowing out of the IBD, thecabin air will enter a heat exchangerand centrifugal separator thattogether condense and separate theliquid water, collecting it for re-use.

SIMULATING GAS FLOW ANDOPTIMIZING BED CONDITIONSUsing COMSOL Multiphysics®, Knox’steam modeled a four-column IBD tocalculate the efficiency of the device (hismodel is shown in Figure 1B). The IBDgeometry was created in Pro/ENGINEER®

and imported using the LiveLink™ for Pro/ENGINEER®. “COMSOL let us performthis kind of multiphysics simulation on

intricate geometries,” Knox remarked.“We needed to simulate porous mediaflow in the beds and heat transferin multiple materials, input pressureboundaries, and find sorption rates.”They noted that dry beds gain heatas gas flows downward, due to theexothermic adsorption. Conversely, thewet beds lose heat as gas flows upward(see Figures 2 and 3).

One member of the team, RobCoker, calculated the efficiency of theIBD using a breakthrough test where

air was pumped through a dry bed.Initially, the air leaving the bed wascompletely dry; all the water vapor hadadsorbed onto the silica gel. As moreair flowed through, the water vaporconcentration in the air at the exitincreased; eventually, it had the same

humidity as the air entering since thesilica gel pellets could hold no morewater. Observing this process allowed

the team to gather parameter valuesfor the IBD model, and they comparedthe breakthrough and experimentalresults (see Figure 3). The capabilitiesof COMSOL let them track the waterconcentration, flow rates, and pressurewith the boundary conditions forinflow, outflow, and wet and dry airchanging for each half-cycle.

According to the simulation results,the IBD removed 85 percent of thewater in the air and returned it to theatmosphere for collection. The model

successfully predicted the efficiencyof the IBD; from here they will beable to further refine the design for athermally-linked bed.

OFFERING NASA A RELIABLE APPROACHTO ATMOSPHERE REGULATIONThe team’s COMSOL simulationprovided invaluable optimization anddesign guidance for the water-savingassembly. They are increasing theIBD efficiency by minimizing powerrequirements and maximizing thewater saved before CO

2 is ejected.

This is one of many important partsof a revitalization system that theyhope will extend the reach of spacemissions. They are also using COMSOLsimulations to design new systemssuited for longer missions, whichenable the separation of oxygen fromCO

2 and reduce the amount of O

2 that

must be carried onboard. With theseinnovative designs and the powerfulcapabilities of simulation, we’ll soonhave manned spacecraft travelingfarther than ever before.n

The atmosphere revitalization computer simulation team at the NASA MSFC. Left to right:

Rob Coker, Carlos Gomez, Greg Schunk, and Jim Knox.

FIGURE 3. Simulation results for air at the exit showing (A) gas temperature, (B) watervapor pressure.

PTC and Pro/ENGINEER are trademarks or registered trademarks of

PTC Inc. or its subsidiaries in the U.S. and in other countries.


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SUPER THERMAL INSULATION | PASSIVE VACCINE STORAGE Intellectual Ventures, WA, USA

In many areas of the developing world,there is extremely limited access toelectricity, and many places have neverhad any type of power infrastructure.This presents a huge challenge foraid workers and doctors. In the veryrecent past, vaccines that needed tobe stored at cold, relatively constanttemperatures could not be taken intothe remote areas where they wereneeded most. As part of the GlobalGood program at Intellectual Ventures(IV), a team of innovators invented

a thermos-like container called thePassive Vaccine Storage Device (PVSD)

that uses high performance insulationto completely change the way vaccinesare stored in areas with little or noelectricity (see Figure 1).

MEETING STRICT SAFETYREQUIREMENTSIf not kept within the necessarytemperature range at all times,vaccines can spoil and becomeunusable. Global Good’s researcherswere tasked with following theparameters dictated by the World

Health Organization. To be deliveredsafely, the vaccines are required to

stay within a narrow window of 0°and 10°C.

The first prototype that the researchersdesigned was based on a cryogenicdewar, a device that relies on vacuumand multilayer insulation technologyto store extremely cold liquids. Dewarsthat can normally hold liquid nitrogenor liquid oxygen for extended periodsof time were only able to hold ice for afew days before it melted.

Innovative Thermal InsulationTechniques Bring Vaccines tothe Developing WorldIntellectual Ventures’ Global Good program has been hard at work creating new technologyto bring vaccines to every corner of the world. Te Passive Vaccine Storage Device uses justa single batch of ice and requires no external power to store medicine at cold temperaturesfor an entire month.

BY LAURA BOWEN

FIGURE 1. The Intellectual Ventures team and aid workers with the PVSDs designed tocarry vaccines during a field study.

“Global Good’sresearchers usedexperimentationalong with thermaland vacuum systemmodeling withCOMSOL Multiphysicsin order to identifymaterials and designsthat would allow thePVSD to maintain highvacuum levels at hightemperatures.”


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SUPER THERMAL INSULATION | PASSIVE VACCINE STORAGE

Global Good’s researchers usedexperimentation along with thermaland vacuum system modeling withCOMSOL Multiphysics® in order toidentify materials and designs thatwould allow the PVSD to maintain highvacuum levels at high temperatures.Like a cryogenic dewar, the PVSD relieson multilayer insulation within a vacuum

space to minimize heat transfer. Thehigh quality vacuum virtually eliminatesconvective and gas conduction heattransfer, while the multilayer insulationdramatically cuts down on radiative heattransfer. The multilayer insulation, madeof reflective, extremely thin sheets ofaluminum and a low conductivity spacer,is similar to materials used in spacecraft.

SIMULATING VACCINE STORAGEIN EXTREME CONDITIONSResearchers for Intellectual Ventures’

Global Good program used anenvironmental chamber to recreateconditions similar to the climate inSub-Saharan Africa in order torigorously test and understand theperformance of their prototypes.However, building a quality prototypeof a vacuum dewar is an involvedeffort, so to explore different designdirections more efficiently beforebuilding prototypes, the team turnedto COMSOL Multiphysics and its HeatTransfer Module and Molecular FlowModule, among others. Their

challenges included optimizing theinternal geometry for maximum coldstorage time, maintaining highervacuum capacity, and managingoutgassing in the vacuum space. Theminimization of outgassing is critical,as even moderate amounts of residualoutgassing within the vacuum spaceover the life of the PVSD can cause thevacuum to lose its integrity, increasingheat transfer into the device.

The geometry of the deviceis optimized to maximize vaccine

hold time and to be as accessibleas possible for health workers inthe field. As a first line of defenseagainst the elements, the outsideof the device consists of a metalenclosure padded with protectiverubber bumpers, while the innerpart of the PVSD consists of a smallershell connected at the very top to the

outside with a cantilever neck (seeFigure 2). Because of this design,conductive heat transfer can onlyhappen at the connection point. Inaddition, a composite neck maintainsthe vacuum space so that there is nogas permeation from ambient air.According to David Gasperino, oneof the engineers deploying COMSOLto support the PVSD design effort,“COMSOL Multiphysics is great forreducing the amount of time spenton complex models.” He went on to

say that they especially appreciated“having everything flow together ina seamless, easy-to-access way, wherethe multiphysics couplings are spelledout very clearly.” The team found thebreadth of modules available helpfulfor capturing the complex physics theyneeded to explore with their models.

IMPROVING STORAGE DEVICE DESIGNFOR FUTURE GENERATIONSAs a result of the experimental andtheoretical work that went into thePVSD, the device is capable of making

a significant impact on the vaccine coldchain in the developing world, allowingvaccines to travel into more remoteregions and to be stored for longerperiods of time without the need forpower. Down the road, IntellectualVentures will improve their storagedevice designs to keep vaccines coldfor extended periods with even moreefficiency. The team will continueworking to create groundbreakingtools with the ability to save livesaround the world. n

FIGURE 2. Top: Thermal simulation ofthe PVSD shortly after loading; the

process of melting ice blocks is modeledusing the phase change feature in

COMSOL Multiphysics. Bottom: The PVSDuses similar temperature control storage

methods to a cryogenic dewar. With asingle batch of ice, it can store vaccines

for extended periods of time.

“COMSOL Multiphysics is great for reducingthe amount of time spent on complex models ...having everything flow together in a seamless,

easy-to-access way, where the multiphysicscouplings are spelled out very clearly.”


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ENERGY-EFFICIENT DEHUMIDIFICATION | NUCLEAR WASTE STORAGE Sogin, Italy

Corrosion is a relentless andunforgiving enemy of metal, and thebattle against it simply cannot be lostwhen steel drums full of nuclear wasteare involved.

Such is the situation in Italy, wheredomestic nuclear power production hasbeen halted, yet the need is ongoing tosafely store low-level radioactive wasteproduced as a byproduct of powergeneration, research, medical, and

industrial activities.Sogin S.p.A. is the Italian state-owned company responsible for thedecommissioning of Italy's nuclearsites and the management ofradioactive waste.

NUCLEAR WASTE STORAGE REQUIRESACCURATE HUMIDITY CONTROLOne Sogin project is the ongoingrenovation of a building at a formernuclear power plant located in thecenter of Italy. The goal is to meetItalian and international requirements

for temporary storage of low-levelradioactive waste until the wastecan be delivered to the NationalPermanent Repository.

The temporary facility is anapproximately 30 m x 15 m single-floor rectangular space divided intotwo rooms. The waste is stored insteel drums encased in concrete forradiological reasons. The drums havean external diameter of 0.8 meters,while the overpack is one meter indiameter. Relative humidity of 65

percent or lower must be maintained

to prevent corrosion.Gianluca Barbella is a Sogin

structural engineer and Team Leaderfor the project. “The need to controlair humidity is due to the non-stainlesssteel drums that are used. The concreteoverpacks mean the drums aren’tinspectable without first extractingthem, which makes it difficult toconstantly monitor the corrosionprocess. Also, the site is exposed to highlevels of relative humidity. Therefore,humidity control is critical,” he explains.

However, the cost of operating

a heating, ventilating, and air-conditioning (HVAC) system tomaintain optimum conditionsover the anticipated 25-year lifeof the facility is substantial. Inaddition, because the facility can’tbe expanded, an HVAC system’sspace requirements would resultin less space available for wastestorage. Moreover, HVAC systemdowntime is inevitable because ofboth equipment malfunctions andscheduled maintenance.

BATTLING CORROSIONIN NUCLEAR WASTESTORAGE FACILITIES

BY GARY DAGASTINE

FIGURE 1. Floor plan for a space divided into two rooms and used as a temporary storagefacility for low-level radioactive waste. The waste is stored in the rooms in non-stainless

steel drums with a concrete overpack.

Multiphysics simulations

helped Sogin S.p.A. designa simple, energy-effi cientdehumidification system toprevent corrosion in drumsof radioactive waste.


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ENERGY-EFFICIENT DEHUMIDIFICATION | NUCLEAR WASTE STORAGE

A potential alternative is to useindustrial isothermal dehumidifiersinstead, which are relatively small,mobile, require less maintenance, andhave substantially lower operatingcosts. These units are based on thereverse Carnot thermal cycle: A fandraws air into the unit, where it passes

over an evaporator and is cooled.Excess moisture from the air condensesinto drops of water that fall into atank. The air then passes througha condenser where it is warmed byseveral degrees. It is then recycled intothe environment as drier, warmer air.

The Sogin project relied onnumerical simulation to studythe impacts of various sizes andconfigurations of two differentindustrial isothermal dehumidifiers.The analyses were carried out byPiergianni Geraldini, from the

mechanical design department. Thegoals were to identify equipmentrequirements and also to determineoptimum placement of the units in therooms (see Figure 1).

SIMULATIONS HELPED DETERMINEOPTIMUM LAYOUTThe team first studied turbulentair flow in the room by performingstationary fluid-flow studies based ona single-phase incompressible k-epsilonturbulence model. Its purpose was

to reproduce the air velocity fieldin the storage area assuming thedehumidifiers were in use.

Then they used the results fromthose studies in time-dependent,fully-coupled simulations to studyheat and moisture transfer within theroom’s atmosphere (see Figure 2). The

overall results were used to develop anoptimum layout for the dehumidifiers.

All simulations were conductedusing COMSOL Multiphysics® and theHeat Transfer Module. “Without such arefined simulation tool, we would havehad to model the dehumidificationprocess using simplified approximationscoupled with dehumidifier performancecurves supplied by the units’manufacturers. But the simulationsshowed us that COMSOL has a

powerful capability to solve 3D heatand moisture transfer problems,” saysPiergianni. “COMSOL Multiphysicsmakes it easy to couple differentphysics, has an intuitive interface, andopens up the possibility of managingthe entire modeling process within thesame interface.

“The simulations helped us todesign a layout based on the use

of two dehumidifiers that providesthe same dehumidification capacityas other configurations, but theyrequired four units,” concludesBarbella. “The system we designedwill limit stagnant air pockets, enablethe units to operate at peak efficiency,and help us reduce the risk of drumcorrosion once the facility is finalizedand commissioned.” n

FIGURE 2. For a room designed to store radioactive waste for up to 25 years, Italy’s Sogin S.p.A. used COMSOL simulations to study air

flow velocities in the room (left) and surface relative humidity throughout the room (right) that would result from various dehumidifiertypes and locations within the space. The results helped engineers design a dehumidification system that minimizes stagnant air,

enables maximum operating efficiency, and optimizes relative humidity.

“COMSOL Multiphysics makes it easy to coupledifferent physics, has an intuitive interface, andopens up the possibility of managing the entiremodeling process within the same interface.”


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FROST DAMAGE PREVENTION | BUILDING PHYSICS Vahanen Group, Finland

Though they often go unnoticed,underground insulation and heatingsystems prevent critical damageto concrete building foundations,and keep occupants safe and warm

indoors. Since concrete is porous,water and contaminants can enterthe foundation. When the foundationor the soil underneath freezes, thiscan cause structural damage such ascracking. Some older buildings areprotected from this by insulation,while others are protected by heatedpipes that travel from the boiler to thebuilding’s indoor heating units.

Ongoing damage can lead toserious risks, such as the bucklingor collapse of a building. To address

the challenges of cold and moisture,Vahanen Group (Espoo, Finland),a company specializing in buildingservices such as quality assessmentsand construction recommendations,analyzes the potential for frostdamage in buildings being consideredfor renovation. Their work is especiallyvital in cases where renovations arenecessary due to existing damage, forinstance, where heating systems andpipes need to be replaced.

WHAT’S THE BEST WAY TO INSULATE

A BUILDING?Pauli Sekki, building specialist atVahanen, is using the simulationcapabilities of COMSOL Multiphysics® to perform risk assessments — hisgoal is to discern whether certainrenovations to foundations or heatingsystems would require adding externalfrost insulation. If added unnecessarily,this would waste valuable money,time, and work.

For one project, Sekki’s COMSOLmodel (see Figure 1) includes the

foundation, levels of loose soiland packed earth, several types ofinsulation, lightweight concrete walls,

and a pipe from a heating systempassing underneath a building nearthe wall and foundation.

First Sekki simulated temperaturechanges based on local climate datafor Helsinki, Finland. Governmentfrost table data provides annualtotal freezing degree hours (FDH),a quantity representing the numberof degrees that the daily meantemperature is below 0°C. (Forexample, for a day with an averagetemperature of -5°C, the FDH is 5

degrees x 24 hours = 120.) An annualtotal sums the FDH from each day ina year (the annual freezing index),

typically about 14,000 FDH for Helsinki.From the existing data, Sekki

generated a “critical freezing”quantity to account for abnormallycold winters that occur, on average,every fifty years (with about 40,000FDH). Given the importance ofbuilding strength and longevity, anyrenovations would have to withstandnot only a typical winter climate, butalso these rarer, harsher conditions.“Design and construction teamsturn to Vahanen to verify that their

Using Multiphysics Simulation toPrevent Building DamageIn extreme climates, moisture and temperature changes can damage building foundations.Vahanen Group is using multiphysics simulation to equip construction teams withassessments that help prevent frost damage and maintain safe building structures.

BY LEXI CARVER

FIGURE 1. Schematic of the building model geometry. The heating pipe runs from theboiler to the indoor heating units, and keeps the foundation warm at the same time.


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FROST DAMAGE PREVENTION | BUILDING PHYSICS

renovation plans are safe, will last,and are the best use of the availablematerials and resources,” Sekkiexplained. “And we turn to COMSOLfor that information.”

In this example, he needed to

determine whether renovationsincluding the complete removal of adamaged heating pipe would endangerthe building. Was the existing insulationsufficient? To answer this question, hemodeled heat transfer in the pipe, theinsulation, and the foundation. “Tools inCOMSOL Multiphysics are very easy touse for this kind of complex model,” hecommented. “The almost unlimitedpossibilities for setting boundaryconditions were a huge advantage.”

PREDICTING THE POTENTIAL

FOR FROST DAMAGESekki used his simulation to predicttemperatures at the two lowestcorners of the concrete foundation(points A and B in Figure 1). He

investigated three cases: the originalstructure, the structure after heating

system renovations (where heattransfer from a pipe would nolonger occur), and the structure afterrenovations that additionally replaceddamaged wood wool cement board(WWCB) with expanded polystyrene(EPS) insulation.

For a typical year in Helsinki,the ground stayed warm enough toprevent damages to the building inits original state as well as afterheating system renovations. However,after the WWCB insulation was

replaced with EPS, the ground near thefoundation dipped to 0.5°C (see Figure2), low enough to be a concern. “Thenew EPS-insulated structure wouldhave been at risk for frost damage,”Sekki said. “Thankfully, multiphysicssimulations are helping us avoid that.”

KEEPING STRUCTURES STRONGFOR THE WORST WINTERSAfter simulating the building duringa longer winter, he found thatonly the foundation of the originalstructure stayed safely above freezing

temperatures (see Figure 3).The ground around the

foundation of the renovatedstructure with WWCB dipped to -2°Cin the simulation. The foundationof the renovated structure with thereplacement-EPS insulation dippedeven farther, to -4°C. This meantremoving the heating pipe wouldrisk serious damage to the buildingfoundation (see Figure 4). It wouldbe necessary to install additionalinsulation at the same time.

PRESERVING STRUCTURALINTEGRITY THROUGH SOUND

RECOMMENDATIONSSekki is using his findings to ensuresafe building renovations in climateslike Helsinki. Using simulation, heis able to assess the heating needsof structures with complicatedgeometries, and can test differentinsulation materials and thicknessesto make sure the techniques herecommends are safe and sufficient.To further their aims of providingstrong support to construction teams,Vahanen is also using COMSOL to

model transient heat and moisturetransport, and indoor air flow. “Thanksto simulation, we can make goodrecommendations to our customers,”Sekki remarked, “and prevent changesthat would ultimately cause structuraldamage.” n

FIGURE 2. Simulation results showingtemperatures over a typical year (14,000FDH) for the renovated building with EPS

insulation added.

FIGURE 3. Temperature distribution forthe unrenovated building for extremewinter conditions (40,000 FDH) occurring

every 50 years.

FIGURE 4. Temperature results (40,000 FDH case) for the building after renovations andadditional EPS insulation. The orange line (line graph) and vertical contour (surface plot)indicate 0°C.

Pauli Sekki, building physics specialist for

Vahanen Group.


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CYTOMETRY | BIOTECHNOLOGY HORIBA Medical, France

Laboratory tests, such as hematologyanalysis, influence up to 70 percentof critical decisions includinghospital admittance, discharge, andtreatment. The accuracy of these

tests, therefore, is of the utmostimportance to the bottom line —curing a patient’s ailment or saving alife. At HORIBA Medical, a worldwidesupplier of medical diagnostic

equipment, simulation softwareplays an important role in theresearch and development process,helping to ensure that these testsare as accurate and encompassingas possible.

At the center of HORIBA Medical’scutting-edge hematology analysisequipment is a well-known approach toblood analysis that uses a combinationof optical measurement and electricalimpedance to analyze a sample. Theimpedance measurement device utilizes

a micro aperture-electrode systemthrough which blood passes (seeFigure 1). Electrical impedance is thenused to count the number of cells andmeasure the size and distribution oferythrocytes (red blood cells), platelets,and leukocytes (white blood cells). Afterimpedance measurement, a laser andoptical detector are used to sort thedifferent types of leukocytes.

Considerations for theproduction of HORIBA Medical’sline of hematology and clinicalchemistry equipment include speed,

accuracy, size, and ease of use fortheir customers. “Today, in vitrodiagnostics specialists have to designsystems that are capable of carryingout increasingly complex tests, whilesimultaneously making results easierto interpret,” describes DamienIsèbe, Scientific Computing Engineerat HORIBA Medical. “Numericalsimulation allows us to design devicesthat meet these goals.” HORIBAplaces numerical simulation at thecenter of its research activities and

In order to take measurements that are inaccessible using just physical prototyping,HORIBA Medical turned to simulation to optimize and improve their line of leadinghematology analysis equipment.

BY ALEXANDRA FOLEY

OPTIMIZING HEMATOLOGY ANALYSIS:WHEN PHYSICAL PROTOTYPES FAIL,SIMULATION PROVIDES THE ANSWERS

FIGURE 1. Diagram of the aperture-electrode system present in the ABX Pentra Series Analyzers.


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CYTOMETRY | BIOTECHNOLOGY

10 percent of its revenues areinvested directly in research anddevelopment activities.

SIMULATION OF THE MICRO

APERTURE-ELECTRODE SYSTEMIsèbe uses COMSOL Multiphysics® toimprove the electrical impedancesystem in the Pentra Series (see Figure 2),one of HORIBA Medical’s mostadvanced hematology analyzers. Thefully-automatic process begins withthe placement of a blood sample in ananalysis chamber, where it travelsthrough a hydraulic channel and isthen diluted with reagents. Afterdilution, the sample is sent into acounting and measurement chamberthat consists of a micro-aperture

flanked by a pair of electrodes(see Figure 3).

The electrodes generate a strongelectric field inside the countingchamber, and as the particles withinthe blood sample pass through

the micro-aperture, the electricalimpedance of the medium induces achange in voltage between the twoelectrodes. This voltage differenceis then used to count the number ofparticles and determine the particle’ssize, with a greater voltage difference

corresponding to a larger molecule(see Figure 3).

“Inside the counting chamberthere are a lot of complex physicalprocesses: high fluid velocity, pressuredrop through the aperture, heattransfer, intense electric field, and alsoa risk of pollution due to mechanical

design issues,” describes Isèbe. “Weuse COMSOL to develop a betterunderstanding of how these physicsinteract within the device.” One ofthe key advantages that Isèbe foundwith COMSOL Multiphysics was theability to import CAD models directly

into the software environment.“Importing the CAD model of the

measurement chamber allowed us toextract the computational domain,”he explains. “In this case, if we wantto compute fluid flow in the system,the simulation software automaticallycreates the fluid domain directlyfrom the CAD model.” Once theaperture-electrode system geometry(see Figure 4) was imported intoCOMSOL, analysis and optimizationscould then be performed using theactual geometry of the device beingmanufactured.

COMPLICATIONS AFFECTINGACCURATE MEASUREMENTThe main goal of Isèbe’s work was tooptimize the impedance measurementsystem by analyzing and controlling forfactors that can negatively influencethe accuracy of the device. Thisincludes the particle trajectory throughthe aperture as well as its orientation,both factors that affect the measureddifference in voltage.

“Due to advancements in computational analysisand supercomputing capabilities, numericalsimulation has become the third pillar of science,next to theory and experimentation.”

FIGURE 2. The ABX Pentra 60C+ (left) and Pentra 80 XLR (right), two hematologyanalyzers of the Pentra Series, use an aperture-electrode system for counting and sizingblood particles by impedance measurement.

FIGURE 3. Principle of impedance measurement.


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For example, when a particlepasses close to the edges of theaperture where the electric fieldexhibits high gradients (see trajectory

T2 in Figure 5), the particle is exposedto higher electric fields than onethat passes through the center of theaperture (see trajectory T1 in Figure5). Such a phenomenon is known asedge effect. Due to this effect, theresulting electrical pulse is distortedand computation of the particle’ssize results in overestimation.

This is further complicated bythe particle’s orientation throughthe aperture. The electric fielddistribution changes depending on

a particle that passes horizontally orvertically through the aperture, again

resulting in an overestimation of theparticle’s size (see Figure 6).

A REAL IMPROVEMENT FOR

DIAGNOSTIC EFFICIENCYIsèbe used simulation techniquesto develop a way to account forvarying particle trajectories and

orientations. “Since this is a verysmall system, it’s very difficult to takeany measurements experimentally,”describes Isèbe. “Simulation allowsus to improve processes that areinaccessible with just physicalprototypes.”

Historically, counting andsizing of biological particles in anaperture-electrode system have beencompleted with the assumptionthat a sample is evenly distributedwithin the micro-aperture. The mean

particle size was then determinedstatistically to compensate forerrors due to particle trajectoryand orientation. This compensationignores the electrical pulsesgenerated by the particles that passclose to the edge, but in practice it isdifficult to differentiate the alteredpulses from the normal ones due tothe high speed of counting.

In order to improve the accuracyof the device, Isèbe developednumerical models to prove thathydrodynamic focusing could be used

to reduce analysis error (see Figures 7and 8). “Hydrodynamic focusing usessheath flow to control the samplerate inside the aperture and to direct

the sample flow along the centralaxis of the aperture,” says Isèbe.“The simulations of this system usea multiphysics approach that modelsthe electrical pulses resulting fromthe impedance variation combinedwith particle fluid flow analysis.”

FIGURE 5. Electric field contour plot insidethe electrode-aperture. Two possible

particle trajectories, T1 and T2, are shown.

FIGURE 6. Effect of particle orientation on the electric field distribution within theelectrode-aperture system and the resulting difference in voltage.

FIGURE 4. CAD model of the micro aperture-electrode system, which was imported intoCOMSOL Multiphysics using the CAD Import Module.

“Simulation allows us to improve processes thatare inaccessible with just physical prototypes.”


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Isèbe ran simulations to analyzehow hydrodynamic focusing improvesimpedance measurement, and todetermine the optimal configurationof the device. “Using these models,we can precisely compute the velocity

field within the device and analyze theacceleration phase at the entrance ofthe micro-aperture. We can then use thisinformation to determine which designsproduce the most accurate results.” Thesimulation results demonstrated thathydrodynamic focusing greatly improvesthe accuracy of particle measurement(see Figure 8, top).

Next, these analyses were comparedto the experimental results. “Whenwe compared the simulation andexperimental results for the two cases,we estimated that the hydrofocused

device is about twice as accurate as thenon-hydrofocused one,” explains Isèbereferring to Figure 8, bottom.

SIMULATION JUSTIFIESTECHNOLOGICAL INNOVATIONThe design and optimization ofthis system of electrical impedancemeasurement for hematology analysiswas truly a multiphysics application,involving the coupling of mechanical,fluid, chemical, and electrical analyses.The resulting devices, the ABX Pentra

Series, are among the most accurate

fully-automatic analyzers on themarket today. “Using simulation, I wasable to justify the implementationof this technique for hematologyanalysis into the diagnostic equipmentat HORIBA,” says Isèbe. Currently,Isèbe is working on improvements tothe particle fluid flow analysis, andplans for future research include 3Dprocessing and the deformability

of particles under hydrodynamic

stresses. “Due to advancementsin computational analysis andsupercomputing capabilities,numerical simulation has become thethird pillar of science, next to theoryand experimentation,” says Isèbe.“Simulation is now a critical tool forresearch and development at HORIBAMedical, and it’s a key resource usedfor decision-making in technological

innovation.”n

FIGURE 7. Hydrodynamic focusing simulation, showing how sheath flow is used todirect the sample along the central axis of the electrode aperture (sample flow in red and

sheath flow in blue).

FIGURE 8. Top: Simulation results of the static particle size distribution without hydrofocusing (left) and with hydrofocusing (right).Bottom: Experimental validation without hydrofocusing (left) and with hydrofocusing (right).


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TIRE PRESSURE SENSORS | AUTOMOTIVE Schrader Electronics, Northern Ireland, UK

Tire pressure is the unsung heroof automobile performance. Wheninflated to the proper pressure,

tires are the exact shape that thedesigners intended. As air pressuredecreases, the tires need more energyto move. Drivers can easily forget tomaintain their tire pressure in theday-to-day routine of moving fromone place to another. Punctures cantake place and go completelyunnoticed. That is why having anonboard sensor that alerts the driverwhen it’s time to add more air makesall the difference. Creating thesesensors requires careful consideration

of all the fine details, and simulationprovides the tools for finding just theright design.

TIRE PRESSURE SENSORS SHAPEDRIVING EXPERIENCEOne consequence of low tirepressure is a significant reductionin fuel economy. Additionally,vehicles running on low tires canadd tons of greenhouse gases tothe atmosphere over time. Low tirepressure can also make it hard forthe vehicle to stop, or cause the car

to slip on wet surfaces. Automakersare generally required to attachpressure monitoring sensors to wheelsthat inform drivers if a tire fallsbelow the intended pressure, andSchrader Electronics is currently theglobal market leader in tire pressuremonitoring technology.

Schrader Electronics manufactures45 million sensors annually andprovides sensors to leadingautomotive companies including GM,Ford, and Mercedes. For a sensor to

survive road conditions throughoutthe life of a vehicle, reliability anddurability are key. Consideration isgiven to shock, vibration, pressure,humidity, temperature, and variousdynamic forces when designing forthe necessary functions, geometry,

and materials. Christabel Evans, anengineer with the Schrader Electronicsmechanical design team, has beenusing finite element analysis (FEA)and multiphysics simulation to buildsuccessful, efficient tire sensors for allkinds of vehicles.

Optimizing Built-in Tire PressureMonitoring SensorsMiniature sensors that regulate automobile performance are designed in a very particular

way to operate properly while housed directly on moving automobile tires. Tey needto have the sensitivity to pick up measurements while in motion and the durability to

withstand the elements.

BY LAURA BOWEN

FIGURE 1. Top: A Hi-Speed Snap-In Tire Pressure Monitoring Sensor (TPMS) used tomonitor tire pressure and send measurement info. Bottom: 10x amplification of stress and

deformation on the transmitter housing as a result of centrifugal loading produced by thewheel’s rotation.


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TIRE PRESSURE SENSORS | AUTOMOTIVE

DESIGNING BETTER SENSORSWITH FEAThe Hi-Speed Snap-In Tire PressureMonitoring Sensor, shown in Figure 1,

is a frequently-used product atSchrader that mounts directly onthe wheel assembly and measurestire pressure — even when the caris in motion. When the tire pressuredecreases too much, a warning goesoff, alerting the driver that it is timeto stop and re-inflate the tire.

Schrader Electronics has beencreating sensors for almost 20 years,but Christabel Evans and hercolleagues wanted a more efficientapproach for product design and

testing. They simulated theirdesigns using FEA and iterated theprocess — this allowed them tominimize experimental cost and toevaluate design performance duringdevelopment. Schrader Electronicsfound that the existing FEA softwareoptions were expensive if they wantedto deploy it to their entire team.They turned to using the StructuralMechanics Module and the CAD ImportModule of COMSOL Multiphysics®.They started with a series of tests,comparing standardized samples with

simulations to validate the softwareand build confidence in the results.

IMPROVING SENSITIVITY ANDDURABILITY WITH BETTERSIMULATION TOOLSOver time, the researchers beganincorporating more natural parametersinto their simulations, from dynamicloads such as centrifugal force,to environmental stresses such astemperature change, to static factorssuch as pressure and crush load. The

Hi-Speed Snap-In TPMS consists ofa transmitter made up of a circuithoused in an enclosure and attachedto a valve stem with a cap. The valvestem connects to the tire rim andallows air to pass through. On theHi-Speed TPMS, the valve geometryincludes a rib that helps retain theassembly in the rim hole.

In Figure 1, Schrader Electronicsmeasured the stress on the enclosure

from outside forces like tire fitment,shock, or vibration from the road

conditions, and the deformation thatoccurs when the device is loadedunder these conditions. Figure 2shows a component designed for aspin test machine that rotates the partat high speed. This component was

analyzed to verify that the materialchoice would be able to handle therequired loads.

By analyzing several modelssimultaneously, Evans and her teamwere able to find the one that worksbest and improve upon their design.They focused on testing differentgeometries, materials, and loadscenarios.

The researchers at Schrader wereable to learn COMSOL Multiphysicssoftware much faster than similarsimulation packages, and deployment

through the organization was easierbecause of flexible licensing options.According to Evans, “COMSOL is user-friendly and it is fast to learn — theengineers picked it up right away.”

At the moment, Schrader plans tospend most of their focus on designand growth, with some emphasison failure analysis, but they hope toimprove their development-focusedapproach with the aid of simulationtools. They are working hard toimprove driver comfort, environmental

impact, and road safety with eachnew design. n

FIGURE 2. A spin test simulated on thecollar of the device shows stress induced

by the centrifugal force concentrated atthe bolt locations.

COMSOL is used by many engineers across multiple teams within the MechanicalEngineering Department at Schrader Electronics. From left to right: Andrew Herron, Sam

Guist, Adam Wright, Christabel Evans, and Russell McKee.

“COMSOL is user-friendly and it is fast

to learn — theengineers picked itup right away.”


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In simple terms, when a beam ofneutrons is aimed at a sample, someneutrons pass through the material,while others scatter away at an angle,similar to balls colliding in a game ofpool. The final deflection patterns andenergies of the neutrons can then be

interpreted, allowing scientists to gaininformation about the fundamentalproperties of studied matter. Thisenables neutron-scattering scientiststo determine the atomic and magneticstructures of materials and ultimatelyto achieve a deeper understanding ofthe world around us.

The High Flux Isotope Reactor orHFIR (pronounced High-FIR) at theOak Ridge National Laboratory (ORNL)includes a neutron scattering facilitythat is used by over 500 researchersfrom around the world each year. The

HFIR is a multi-purpose research reactorthat also provides stable and radioisotopes to customers in academia,industry, and the medical field. Inaddition, the HFIR offers uniqueirradiation experiment facilities andneutron-activation analysis capabilities.The high power production of the HFIR(85 MW) likewise produces a high fluxof neutrons to the targets, therebyproviding one of the highest steady-state neutron fluxes of any researchreactor in the world (see Figure 1).

The HFIR was designed to usehighly enriched uranium (93 percentU-235 or HEU), which is similar to aweapons-grade uranium. However, inresponse to the increasing awarenessof the risks caused by the proliferationof nuclear materials, the Global

Threat Reduction Initiative has calledfor the conversion of research reactorsusing HEU fuel to low-enricheduranium (LEU) fuel.

While many of the world’snuclear reactors have already beenconverted, a few high-performance

HEU reactors still remain. Amongthese is the HFIR, which, due to itsunique fuel and core design (seeFigure 2) as well as the high powerdensity of the reactor, presents acomplex and challenging task forfuel conversion. Researchers at ORNLare using COMSOL Multiphysics® simulation software to explore theimpact that the fuel change will haveon the HFIR’s performance and on

neutron scattering initiatives, isotopeproduction, irradiation experiments,and neutron activation analyses.

“Successful conversion of the HFIRwill preserve reactor performance,minimize negative effects on operationefficiency, and help to ensure safety,”

says Franklin Curtis, PhD graduatestudent at ORNL. “We have foundthat COMSOL is a superior tool forachieving these goals because of itsmultiphysics capabilities, its use of thefinite-element method, and the abili

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