ansys solution summer04

8/12/2019 Ansys Solution Summer04

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Quickly vary geometry even

without parametric CAD

Chemical andProcessing

Industry Spotlight:

Researchers use ANSYS todevelop micron-sized, self-

powered mobile mechanisms

FEA is a valuable tool that

aids doctors in orthopedic

operations


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...a process that's more automated, more integrated,

more innovative and truer to life. Thats where ANSYSis taking engineering simulation. By combining technologies

like industry-leading meshing, nonlinear analysis and

computational fluid dynamics, you can reduce costs and

drive products to market quicker.

Bring your products and processes to life with ANSYS.

Visit www.ansys.com/secret/6 or call 1.866.ANSYS.AI.

Take a look at the future of

product development...


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ANSYS for VirtualSurgeryFEA is a valuable tool that

aids doctors in orthopedic

operations

FEA in Micro-RoboticsResearchers use ANSYS to

develop micron-sized, self-

powered mobile mechanisms

Design Insight forLegacy ModelsQuickly vary geometry even

without parametric CAD

Editorial -To Collaborate,You Need People

Simulation at Work -Analysis ofArtificial Knee Joints

Managing CAE Processes -UpfrontAnalysis in the Global Enterprise

Tech File -Demystifying ContactElements

Tips and Techniques-ContactDefaults in Workbench and ANSYS

For ANSYS, Inc. sales information, call 1.866.267.9724, or visit www.ansys.com on the Internet.

Go to www.ansyssolutions.com/subscribe to subscribe to ANSYS Solutions.

ANSYS Solutions is published for ANSYS, Inc. customers, partners, and others interested in the field of design and analysis applications.

Editorial DirectorJohn Krouse

[email protected]

Managing EditorJennifer L. Hucko

[email protected]

DesignersMiller Creative [email protected]

Art DirectorPaul DiMieri

[email protected]

Ad Sales ManagerAnn [email protected]

Circulation ManagerElaine Travers

[email protected]

ContentsDepartmentsIndustry Spotlight

Features

Chemical and ProcessingA continuing series on the value

of engineering simulation in

specific industries

There are many examples

of successful chemical and

processing companies using

ANSYS simulation technology

to improve products and

processes. Our cover article

describes how Twister BV

used ANSYS CFX to reduce

costs by 70% comparedto the conventional route

without CFD in developing

gas separator equipment.

About the cover

10

6

14

28

2

18

25

26

33

36

Industry News -Recent Announcementsand Upcoming Events 3

www.ansys.com ANSYS Solutions | Summer 2004

The content of ANSYS Solutions has been carefully reviewed and is deemed to be accurate and complete. However, neither ANSYS, Inc., nor Miller Creative Group guarantees orwarrants accuracy or completeness of the material contained in this publication. ANSYS, ANSYS DesignSpace, CFX, ANSYS DesignModeler, DesignXplorer, ANSYS WorkbenchEnvironment, AI*Environment, CADOE and any and all ANSYS, Inc. product names are registered trademarks or registered trademarks of subsidiaries of ANSYS, Inc. located in theUnited States or other countries. ICEM CFD is a trademark licensed by ANSYS, Inc. All other trademarks or registered trademarks are the property of their respective owners.POSTMASTER: Send change of address to ANSYS, Inc., Southpointe, 275 Technology Drive, Canonsburg, PA 15317, USA 2004 ANSYS, Inc. All rights reserved.

2004 ANSYS, Inc. All rights reserved.

Editorial AdvisorKelly [email protected]

CFD Update AdvisorChris Reeves

[email protected]

Want to continue receivingANSYS Solutions?Visit www.ansys.com/subscribe to update

your information. Plus, youll have the chanceto sign up to receive CFX eNews and email

alerts when the latest electronic version of

ANSYS Solutions becomes available!

Guest Commentary-Putting QualityAssurance in Finite Element Analysis 40

Software Profile -The New Face ofANSYS ICEM CFD 16

CFD Update -Simulation HelpsImprove Oil Refinery Operations


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Intellectual capital for creating innovative designs is lacking

at manufacturers that skimp on jobs.

To Collaborate, You Need People

Editorial

One of the most significant

and possibly least recognized

aspects of engineering

simulation is that the technol-

ogy can be a tremendously

effective communication

and collaboration tool inproduct development. By

using virtual prototyping,

what-if studies and a wide

range of other analyses

to show how proposed

products will perform,

engineering simulation can

give people in multi-functional

product development teams tremendous insight into

designs. The technology also provides an effective way

for team members to interact, with disciplines outside

engineering able to see the impact of their various ideas,

suggestions, feedback andinput. In this way, teams can

investigate even the most

unconventional ideas, some

of which can turn out to be

the basis of ground-breaking

new products.

Collaborative product

development is a growing

trend in manufacturing industries, getting engineers and

analysts working with others across the extended

enterprise: manufacturing, testing, quality assurance,

sales, marketing and service even those outside the

company such as suppliers, customers, consultants

and partners. These people typically dont know how to

build meshes, define boundary conditions, run analyses

or perform optimizations. But they can see the impact of

what simulations show, and they can provide valuable

feedback in spotting, evaluating and fixing potential

problems. Marketing could suggest a different contour

that would make a consumer product more saleable, for

example, or procurement might suggest alternate

suppliers for stronger and less expensive components

to reduce excess stress.

This multi-functional synergy is the basis for

the creativity necessary to develop innovative products

and processes that might not immediately occur to

individuals working separately. Collaboration taps into

the intellectual capital of the enterprise the combined

know-how and insight of workers about the companys

operation, its products and its customers.

Companies need people for multidisciplinary

collaboration. But, unfortunately, jobs at manufacturing

firms are in steady decline. According to the National

Association of Manufacturers, after peaking at 17.3 mil-

lion in mid-2000, manufacturing employment has fallen

by 2.8 million while employment in non-manufacturing

sectors of the economy rose by 671,000 to 115 million.Data from the U.S. Bureau of Labor Statistics indicates

there were 2,378 extended mass layoffs in

manufacturing during 2002 alone, resulting in 454,034

workers being removed from their jobs.

Meanwhile, the overall economy is rebounding,

with the Dow Jones Industrial Average undergoing

a strong sustained rally and corporate profits up.

Forecasters at the National Association for Business

Economics predict that the U.S. economy will show a

robust annual growth of 4.5% in 2004.

Despite this strong economic growth, payrolls in

manufacturing continue to go down as manufacturers

operate with as few peopleas possible. Running these

super-lean operations

pumps up short-term

profits. But manufacturers

cannot sustain long-term

growth based on savings

from a barely adequate

workforce being stretched

to the limit. Product quality, customer service and brand

image ultimately suffer, as do product innovations that

spring from collaborative design.

To collaborate, you need people: ones with enough

time in the workday to apply their knowledge on creative

projects. When manufacturers cut jobs indiscriminately,

theyre not just getting rid of salaried bodies, theyre

discarding the companys most valuable asset the

wealth of intellectual capital in its workforce. Companies

that fall into this trap risk being left behind in the market

by astute competitors with enough sense to invest in

their workers and the knowledge they bring to the

collaborative processes necessary to develop winning

products.

By John Krouse

Editorial Director

ANSYS Solutions

[email protected]

2


COLLABORATION TAPS INTO THE

INTELLECTUAL CAPITAL OF THE ENTERPRISE

THE COMBINED KNOW-HOW AND INSIGHT OF

WORKERS ABOUT THE COMPANYS OPERATION,

ITS PRODUCTS AND ITS CUSTOMERS.


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Recent Announcements

EASA 3.0 - The New Standard for Efficient

Application Development

EASA enables ultra-rapid creation and deployment

of Web-enabled applications that can drive most

applications, including ANSYS and CFX. EASA

also can be used to integrate several tools, thus

automating processes involving say CAD, FEA and

even in-house codes. EASA is available as a software

product to author and publish your own custom

applications. Alternatively, several ASDs are now using

EASA to create turnkey applications to your

specification as a service.

New features in EASA 3.0 include:

Connectivity to Relational Databases such as SQL

Server and Oracle, and with database applications

such as ERP, CRM and PLM systems.

Improved Security for Internet Use using Secure

Socket Layer (SSL) technology, enabling you to host

applications for use over the Internet.

Multi-Language EASAPs create your app in your

language, and users see it in their preferred

language. Character sets supported include

Roman, Chinese, Japanese, Russian and Arabic.

New parametric study and optimization capabilities

New API EASAs differentiator has always been toallow non-programmers to create professional-

grade Web-enabled applications around their

underlying software. Now an API allows EASA

authors who have programming skills to create

applications at the next level by using custom code.

For more information, visit www.ease.aeat.com.

2004 International ANSYS Conference Hailed

SuccessEngineering professionals from throughout the world

gathered at the Hilton Pittsburgh in May for the 2004

International ANSYS Conference to discover the true

meaning behind what it is to Profit from Simulation.

Industry News

3


Vis ion and strategy set the theme for the genera l

session. Kicking off the conference with a welcome

address, ANSYS president and CEO, Jim Cashman,

set the stage for keynote speaker, Brad Butterworth of

Team Alinghi. As the cunning strategist aboard the

Team Alinghi yachts, Brad shared his

experience and discussed how the Americas Cup

winner is using ANSYS integrated simulation

solutions to defend its title in the 2007 competition.

After the morning break, ANSYS presented its

Technology Roadmap, the companys successful,

ongoing strategy for integrating the power of the entire

ANSYS, Inc. family of products into the ult imate

engineering simulation solution. Then, Bruce Toal,

director of Marketing and Solutions, High Performance

Technical Computing Division at Hewlett-Packard

Company, spoke about the companys Adaptive

Enterprise for Design and Manufacturing.

Following a day of technical and general sessions,

and visiting exhibitor booths, attendees enjoyed a

conference social sponsored by Hewlett-Packard

Monday evening. Standing ovations and triumphant

applause echoed throughout the ballroom during the

social as ANSYS president and CEO, Jim Cashman,

presented Dr. John Swanson, ANSYS founder, with an

award for being the recipient of the 2004 AAES JohnFritz Medal.

ANSYS long-standing partners and its key customers

took to the podium for the Tuesday general session.

LMS Internationals Tom Curry, executive vice

president and chief marketing officer, spoke about the

product creation process. Tom guides the companys

growth in predictive computer-aided engineering,

physical prototyping and related services.

Herman Millers Larry Larder, director of engineering

services, discussed how they use ANSYS

simulation technologies to experiment and innovate in

the office furniture industry.


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Industry News

4

SGI s director of product marketing, Shawn

Underwood, presented future of high performance

computing followed by Dr. Paresh Pattani, director of

HPC and Workstation Applications at Intel

Corporation who focused on the paradigm shift in high

performance computing.

Jorivaldo Medeiros, technical consultant at

PETROBRAS, offered his ANSYS success story

on how the company drives development and

innovation in equipment technology.

In addition, ANSYS became the first engineering

simulation company to solve a 111 Million Degrees of

Freedom structural analysis model. After lunch, the

Management Track addressed strategies on how to

implement new technologies and explain the benefits

of engineering simulation to management.

ANSYS Breaks Engineering Simulation Solution

Barrier

ANSYS, Inc. has become the first engineering

simulation company to solve a structural analysis

model with more than 100 million degrees of freedom

(DOF), making it possible for ANSYS customers tosolve models of aircraft engines, automobiles,

construction equipment and other complete systems.

In a joint effort with Silicon Graphics, Inc. (SGI),

the 111 million DOF structural analysis problem was

completed in only a few hours using an SGI Altix

computer. DOF refers to the number of equations

being solved in an analysis giving an indication of a

models size.

ANSYSability to solve models this large opens thedoor to an entirely new simulation paradigm. Prior to

this capability, a simulation could be conducted only at

a less detailed level for a complete model or only

at the individual component level for a detailed model.

Now, it will be possible to simulate a detailed,

complete model directly; potentially shortening design

time from months to weeks. Equally important, having

a high fidelity comprehensive model can allow trouble

spots to be detected much earlier in the design

process. This may greatly reduce additional design

costs and can provide an even shorter time to

market,said Jin Qian, senior analyst at Deere &

Company Technical Center.

According to Marc Halpern, research director at

Gartner, although simulation accelerates the delivery

of quality products to market, users have faced major

challenges to realizing the full value. For example,

hardware and software limitations have historically

made realistic simulations elusive when realism

involves highly detailed models and complex physical

behavior.

Manufacturers are looking for more accurate, large

system simulations to improve their time-to-money,

said Charles Foundyller, CEO at Daratech, Inc. This

announcement means that users now have a clear

roadmap to improved productivity.

As hardware advances in speed and capacity, ANSYS

is committed to being the leader in developing CAE

software applications that take advantage of the latest

computing power. This leadership provides customers

with the best engineering simulation tools for their

product development process to help achieve better

cost, quality and time metrics.

This powerful new offering from ANSYS speaks to its

commitment to develop and deliver the best in

advanced engineering solutions. In turn, ANSYS has

entered into a three-year partnership with SGI

to advance the capabilities of ANSYS in parallelprocessing and large memory solutions.

Safe Technology Incorporates AFS Strain-Life

Cast Iron Database in fe-safe

Safe Technology Ltd has been granted a license to use

the AFS cast iron database from the research report

Strain-Life Fatigue Properties Database for Cast Iron

in its state-of-the-art durability analysis software suite

for finite element models, fe-safe. Safe Technology Ltdis a technical leader in the design and development

of durability analysis software that pushes the

boundaries of fatigue analysis software to ensure

greater accuracy and confidence in modern fatigue

analysis methods for industrial applications. The

availability of the AFS database within fe-safe ensures

that users will have access to the most up-to-date and

accurate cast-iron materials data for their durability

analyses.

The AFS Ductile Iron and the Gray Iron Research

Committees have developed a Strain-Life Fatigue

Properties Database for Cast Iron. This database

represents the capability of the domestic casting

industry and is available as a special AFS publication.

It is the culmination of a five-year effort in partnership



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5

Date Event Location

August 29-September 3 ICAS 2004 Yokohama, Japan

September 5-8 RoomVent 2004 Coimbra, Portugal

September 6-9 17th International Symposium Bonn, Germany

on Clean Room Technology

September 7-8 European UGM for Automotive Neu-Ulm, Germany

Applications Radtherm User Conference

September 19-20 German Aerospace Congress 2004 Dresden, Germany

September 21-22 Numerican Analysis and Simulation Troy, Michigan, USA

in Vehicle Engeineering

September 22-25 3rd International Symposium on Two-Phase Pisa, Italy

Flow Modeling and Experimentation

September 29-30 Calculation & Simulation in Vehicle Building Wurzburg, Germany

September 29-30 Pump Users Intarnational Forum 2004 Karlsruhe, Germany

September 28 - October 2 ASME DETC/CIE Conference Salt Lake City, Utah, USA

October 4 2004 PLM European Event UK

October 4-5 DaratechDPS Novi, MI

October 12 ANSYS Multiphysics Seminar Sweden

October 13 Construtec Conference Spain

October 20 ANSYS 9.0 Update Seminar Sweden

October 28-29 ANSYS User Conference Mexico

Upcoming Events

with the DOE Industrial Technology Program.

The scope of this information includes 22 carefully

specified and produced castings from ASTM/SAE

standard grades of irons, including Austempered Gray

Iron (AGI) (specification is under development). Each

grade is comprehensively characterized from an

authoritative source with chemical analysis,

microstructure analysis, hardness tests, monotonic

tension tests and compression tests. This information

is contained in user-friendly digital files on two

CD-ROMs for importing into computer aided design

software. AFS Publications are described online at

www.afsinc.org/estore/.

For more information, visit www.safetechnology.com

Product Development Platform Will Simulate

and Optimize Design Performance for Autodesk

Inventor Professional Customers

Autodesk will license ANSYS simulation technologies

and package them as an integral part of the Autodesk

Inventor Professional 9.0 product and future releases.

Powered by ANSYSpart-level stress and resonant

frequency simulation technologies, Autodesk Inventor

Professional 9.0 will enable design engineers to createmore cost-effective and robust designs, based on how

the products function in the real world, by facilitating

quick and easy what-ifstudies right within the

softwares graphical user interface.


Autodesk is proud to be working with an industry

innovator like ANSYS, said Robert Kross, vice

president of the Manufacturing Solutions Division at

Autodesk. This reinforces our commitment to deliver

proven and robust technologies to manufacturers, in

order to help them deliver better quality products and

bring them to market faster. Inventor Pro 9.0 will make

simulation (CAE) functionality available to a broader

mechanical design community, while protecting

customers business investment by seamlessly

integrating with other high-end ANSYS offerings. Our

customers will surely benefit from this relationship.

The total solution will help product development

teams make more informed decisions earlier in the

design process, allowing them to reduce costs and

development time while designing better and more

innovative products.

This new offering from Autodesk will be viewed very

strategically by their customers. As they deploy

simulation tools throughout their product design

process, the Autodesk-ANSYS offering will be a

key component to a customers overall simulation

strategy,said Mike Wheeler, vice president and

general manager of the Mechanical Business Unit atANSYS. ANSYS is proud to be part of the design

effort to create this next generation tool as part of our

overall ANSYS Workbench development plan.


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6

Industry Spotlight

Industry Spotlight:Chemical and Processing

A continuing series on the value of engineering

simulation in specific industries.

The chemical and processing industries provide the building blocks for manyproducts. By using large amounts of heat and energy to physically or chemically

transform materials, these industries help meet the worlds most fundamental

needs for food, shelter and health, as well as products that are vital to such advanced

technologies as computing, telecommunications and biotechnology.

According to the American Chemical Society, chemical and processing industries account for 25% of

manufacturing energy use.

These industries consume fossil resources as both fuel and feedstock, and produce large amounts of

waste and emissions.

In turn, as exemplified by the U.S. Governments 2020 Vision, these industries face major challenges to

meet the needs of the present without compromising the needs of future generations in the face of

increasing industrial competitiveness. This translates into the need to make processes much more energy

efficient, safer and more flexible, and to reduce emissions to meet the many competitive challenges within

a global economy. As well as the need to reduce design cycle times and costs, major challenges where

simulation has an important role including:

Scale-up, to extrapolate a process from laboratory and pilot plant scale, to the industrial plant

scale, which may require many millions of dollars investment.

Process intensification, to combine different processes into smaller compact and efficient units,

instead of treating them as individual processes.

Retrofitting, to upgrade a plant to become more efficient, within the many constraints of the existing

footprint of the plant.

This issue ofANSYS Solutions provides examples of these, in offshore oil

production, waste water treatment and chemical processing, and many other

examples which highlight the benefits to be obtained are to be found on the

ANSYS CFX Website at www.ansys.com/cfx.

These problems are inherently multi-scale, with the combination of different

physical and chemical processes at the molecular level, and the macro-flow

processes transporting a reacting fluid around the complex geometries of a large

industrial chemical reactor. The recent advances in modeling capabilities,

combined with the scalable parallel performance of low cost hardware, and the

powerful geometrical and meshing tools in the ANSYS software modules open

up many new opportunities to achieve major new benefits in the complex anddemanding world of the chemical and process industries.

Offshore platform



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Integral Two-Phase Flow Modeling in

Natural Gas Processing

Customized version of CFX reduces costs 70%

compared to the conventional route without

CFD in developing gas separator equipment.

By Marco Betting, Team Leader Twister

Technology; Bart Lammers, FluidDynamics Specialist; and Bart Prast,

Fluid Dynamics Specialist, Twister BV

Natural gas processing involves dedicated systems

to remove water, heavy hydrocarbons and acidic

vapors from the gas stream to make it suitable for

transportation to the end-customer. From a process

engineering perspective, these systems are

combinations of flashes, phase separations, flow

splitters, and heat and mass exchangers exhaustively

designed to achieve required export specifications.

While the process engineer is concerned with

finding the optimal system configuration using

pre-defined process steps and equilibrium

thermodynamics, the flow-path designer tries to

optimize the performance of each individual process

step in the system based on an understanding of both

two-phase flow behavior and non-equilibrium

thermodynamics. The fluid dynamics interaction

between subsequent process steps is not always

7Case-in-point:

Twister separator

taken into account to its full extent, even though this

can strongly influence the total system performance.

Developing and designing new equipment for the

process industry is a time-consuming and expensive

exercise. Twister BV (www.twisterbv.com) offers

innovative gas processing solutions that can play

an essential role in meeting these challenges.

The team has been developing the Twister

Supersonic Separator, which is based on a

In Twister, the feed gas is expanded to supersonic velocity, thereby creating a homogeneous mist flow. During theexpansion, a strong swirl is generated via a delta wing, causing the droplets to drift toward the circumference of the tube.Finally a co-axial flow splitter (vortex finder) skims the liquid enriched flow from the dried flow in the core. The two flowsare recompressed in co-axial diffusers resulting in a final pressure being approximately 35% less than the feed pressure.

Normalized total C8 fraction in vortex section ofTwister Supersonic Separator

Uniform C8

distribution

C8 separation

Liquid

Vapor

Laval Nozzle

SaturatedFeed Gas

Cyclone Aeparator(300,000 g)

Liquids + Slip-Gas

Diffuser

Supersonic WingMach 1.3 (500 m/s)

CompressorCyclone SeparatorExpander

70 bar, 5C

Dry gas

70 bar, 5C

30 bar, -40C

100 bar, 20C



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Industry Spotlight

Multi-component gases with several

condensable species

A homogeneous nucleation model to

determine the droplet number density

A growth model, to allow for the change in size

of the particles, through condensation and

evaporation

Droplet coalescence models depending on

droplet size, number density and turbulence

intensities

Slip models to predict the separation of the

droplets from the continuous phase Accounts for turbulent dispersion

Aforementioned models are coupled via mass,

momentum and energy equations

Energy is affected by release of latent heat

during condensation/evaporation

The development and validation of the

customized CFX code was of paramount importance

in maturing the Twister separator for commercial

application in the oil & gas industry.

This custom version of CFX-5 includes all

first-order effects useful for determining the

performance of liquid/gas separators proceeded by an

expander or throttling valve.

unique combination of known physical processes,

combining aero-dynamics, thermo-dynamics and

fluid-dynamics to produce a revolutionary gas

conditioning process. The route from a new Twister

tube concept to marketable hardware via several

production field trials has been a major undertaking.

Reducing costs in the cycle of designing, testing and

redesigning of Twister prototypes for the challenging

conditions involved in high-pressure sour natural gas

processing is of great importance. The introduction

of computational fluid dynamics in the Twister

development four years ago resulted in a cost

reduction of approximately 70% compared to the

conventional route without CFD.

Customized Version of CFX

Twister BV and ANSYS CFX jointly have developed a

customized version of CFX 5.6*, capable of modeling

non-equilibrium phase transition in multi-component

real gas mixtures. The consulting team at ANSYS was

chosen to perform this work because of their

understanding of the needs of the industry and the

flexible nature of CFX-5, which made it suitable for

implementing the specialized features required. The

specific features of this customized two-phase CFD

code are:

Full equations of state, including the effects of

phase change

Twister and LTX separators

G + Lstratified

G + Ldispersed

L

G + Ldispersed

For a process engineer, the quality of the gas coming over thetop of the separator is determined with the phase equilibriumafter an isenthalpic flash, presuming a certain liquid carry-over.The flow-path designer is concerned with the reduction of thecarry-over by optimizing the flow variables of the separator,based on a feed with presumed droplet sizes.

8



11/44

Improving Facility Performance

Essential for the optimization of the separation

performance of Twister is the prediction of droplet

sizes. The droplet size is determined by both the vapor

diffusion rate toward the droplets and the mutual

agglomeration of these droplets. The size distribution

mainly depends on the time interval of the nucleation

pulse. The droplet size distribution determines the drift

velocity of the liquid phase and hence determines the

separation efficiency. Appropriate models for this have

been implemented.

LTX separator

Mach number

P, T, flow, LGR,composition

P, T, flow, LGR,droplet size,droplet number

P, T, flow,composition

Using the customized two-phase code, the flow path designer can study theinfluence of the geometry of a choke valve on the resulting droplet sizedistribution and better assess the performance of the separator based thereon.

This customized CFX code also enables the

process engineer to better understand the relationship

between the performance of subsequent process

steps, e.g., the operation of a Low Temperature

Separator (LTS) fed by a choke valve.

Twister BV and ANSYS CFX have completed a

powerful CFD code validated for natural gas processes.

This unique CFD capability enables process engineers

to optimize engineering practices, while increasing the

performance of gas processing facilities.

*I.P. Jones et. al, The use of coupled solvers for multiphase and reacting flows; 3rd international conference of CSIRO, 1012 December 2003, Melbourne, Australia.

P, T, flow, LGR composition

9


1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0


12/44

Analysis, imaging and visualization technologies

are being applied increasingly in medical applications,

particularly in evaluating different approaches to

surgery and determining the best ways to proceed in

the operation. In this growing field, one of the primaryfocuses of our work applies finite element analysis to

orthopedic surgery: specifically, the specialized area of

osteotomy, where bones are surgically segmented

and repositioned to correct various deformities. We

chose ANSYS for this work because of the reliability

and flexibility of the software in handling the irregular

geometries and nonlinear properties inherent in these

materials.

Medical imaging technologies such as CT, MRI,

PET or SPECT deliver slice or projection images

of internal areas of the human body. These tools are

generally used to visualize configurations of bones,

organs and tissue, but they also have the ability

to export image data and additional information in

commonly known medical file formats like DICOM.

These files then can be processed by third-party

computer programs for assessing and diagnosing

the condition of the patient and planning surgical

intervention, that is, how the surgical procedure will be

performed. Other very promising fields includetelesurgery, virtual environments in medical school

education and prototype modeling of artificial joints.

The goal of the research is to develop computer

applications in the field of orthopedic surgery,

especially osteotomy intervention procedures based

on CT images. the team at the Institute of Informatics

uses this simulation technology to examine theories

underlying new types of surgeries as well as to aid

doctors in treating individual patients undergoing hip

joint correction. These two approaches have many

common tasks: extracting image data from diverse

medical image exchange format files, enhancing

images, choosing the appropriate segmentation

techniques, CAD-oriented volume reconstruction,

data exchange with FEM/FEA tools, and geometric

description of virtual surgery.

ANSYS for Virtual SurgeryFEA is a valuable tool that aids doctors in orthopedic operations.

By Andrs Hajdu and Zoltn Zrg

Institute of InformaticsUniversity of Debrecen, Hungary

10



13/44

Figure 1. Steps of volume (bone) reconstruction in ANSYS.

Building Orthopedic Models

CT data files. The first step in building an

orthopedic model is extracting an image file from

medical data exchange formats. As CT images

represent the X-ray absorption of a given cross-

section, the intensity values of their pixels represent

this 12-bit absorption rate, rather than common color

ranges. Since the slice density is usually reduced to

a minimum for in-vivo scanning, considerable

information often is lost, especially in complex regions

of the human body. For visualization purposes, this

deficiency can be compensated with interpolation

techniques, but no lost anatomical data can be

recovered in this way. Using these files for FEA work

thus often requires further enhancement.

Image enhancement and segmentation.As

given tissue structures have their own absorption rate

intervals, a windowing technique might be sufficient

for a simple visualization. However, because these

intervals can overlap, other tissue parts that differ from

our VOI (Volume Of Interest) remain in the image, after

applying the intensity window. Some conventional

procedures like morphological or spectral-space

filtering must be applied, as well as specific

techniques for CT segmentation. We found that other

methods, such as region growing and gradient-based

segmentation, achieved excellent results for bone

structures.

Volume reconstruction. The final goal of the

project is to develop an application to be used in

surgery planning on a routine basis by medical staff

without experience in using CAD-related software. We

wanted this application to be able to transfer structural

data into a finite element modeling and analysis

software. Thus, volumetric information must be

represented in a geometrically appropriate way. There

is a difference between simple surface rendering and

geometrical volume reconstruction in CAD systems.

Volumetric data has to be represented using solid

modeling primitives, and reconstructed using related

concepts: keypoints, parametric splines, line loops,

ruled and planar surfaces, volumes and solids.

When extracting contour points of ROIs (Regions

Of Interest), we need to reduce the number of points

to approximately 10-15% by keeping only points with

rapidly changing surroundings. These points then can

be interpolated with splines, splines assembled to

surfaces and surfaces to solids. The major difficulty is

that CAD-related systems are designed to work with

regular-shaped objects, and bone structures are not

like that. However, to be able to execute FEA, it is

necessary to use this approach. Moreover, virtual

surgery interventions have to be carried out on

this representation, or in such a way that propergeometrical representation of the modified bone

structure remains easy to regain. As is often the case,

conversion problems may occur when exchanging

data between CAD systems, so we perform the above

volume reconstruction procedure directly in the FEM

software using built-in tools provided in the package.

After testing many FEM programs, we chose ANSYS

software for this task. Figure 1 illustrates how they

11



14/44

reconstructed in ANSYS an 8-inch part of a femur

(pipe-like bone) using the mentioned procedure. The

entire reconstruction procedure was implemented in a

simple ANSYS script file.

A natural extension of this method seems to be

suitable also for bones containing more parts, holes,

etc. In this case, Boolean operations between solids

provided by ANSYS gives us a powerful tool. Another

challenging problem currently being investigated is the

reconstruction of those parts of the bones where the

CT slices contain varying topology (e.g., when

reaching a junction in some special bones).

Figure 2. Part of theoretical path and planar

intersection of the cutting tool.

12

Figure 3. Subtraction of the cutting tool from a

bone section profile in 2-D, and the 3-D outcome.

Figure 4. Subtracting a helix from the diaphysis.

Approaches to Virtual SurgeryPlanar approach. There are some cases when

information from 2-D slices is sufficient for performing

virtual surgery instead of 3-D solids. For example,

the first subject of our project human femur

lengthening using helical incision provided a good

opportunity for experimenting with 3-D interventions

performed in 2-D. By taking the intersection (dark

section on Figure 2) of the theoretical cutting tool path

(Figure 2 left) with the planes of the individual

CT slices, we subtracted these profiles from the bone

section profile (Figure 3).

After the volume reconstruct ion using thistechnique, we obtained the modified bone structure

without the need for further intervention. Another

possibility is to use ANSYS to build up the geometric

model of the bone and the cutting tool from their

boundary lines, then to remove the solid defined by

the path of the cutting tool. The team wrote an ANSYS

script to obtain fast and automatic model creation.

In the case of the hip joint correction, some

intervention also might be simulated in 2-D, but

designating and registering ROIs on the slice set is

more difficult. However, handling volumes as a set of

unsorted 3-D points with additional attributes serves

as an intermediate solution.

Three-dimensional approach. In the first subject,

the 3-D approach adopted by us was the combination

of the volume reconstruction technique and

conventional CAD modeling. We reconstructed the

middle part (diaphysis) of the human femur, and, in the

same coordinate system, using the axis of the actual

bone, we constructed the solid object representing the

path of the cutting tool. This was achieved by applying

helical extrusion along this axis on a rectangle,

using the parameters of the actual osteotomy. By

subtracting these solids from each other, they



15/44

References and Resources for Further Reading

H. Ab, K. Hayashi and M. Sato (Eds.): Data Book on

Mechanical Properties of Living Cells, Tissues, and

Organs, Springer-Verlag, Tokyo, 1996.

Z. Cserntony, L. Kiss, S. Man, L. Gspr and K.

Szepesi: Multilevel callus distraction. A novel idea to

shorten the lengthening time, Medical Hypotheses,

2002, accepted.

R. C. Gonzalez and R. E. Woods: Digital image

processing, Addison-Wesley, Reading,

Massachusetts, 1992.

A. L. Marsan: Solid model construction from 3-D

images (PDF, PhD dissertation), The University of

Michigan, 1999.

K. Radermacher, C. V. Pichler, S. Fischer and G. Rau:

3-D Visualization in Surgery, Helmholtz-Institute

Aachen, 1998.

L. A. Ritter, M. A. Livin, R. B. Sader, H-F. B. Zeilhofer

and E. A. Keeve: Fast Generation of 3-D Bone Mod-

els for Craniofacial Surgical Planning: An Interactive

Approach, CARS/Springer, 2002.

M. Sonka, V. Hlavac and R. Boyle: Image processing,

analysis, and machine vision, Brooks/Cole Publishing

Company, Pacific Grove, California, 1999.

Tsai Ming-Dar, Shyan-Bin Jou and Ming-Shium Hsieh:

An Orthopedic Virtual Reality Surgical Simulator

(PDF), ICAT 2000.

Zoltn Zrg, Andrs Hajdu, Sndor Man, Zoltn

Cserntony and Szabolcs Molnr: Analysis of a

new femur- lengthening surgery, IEEE IASTED

International Conference on Biomechanics (BioMech

2003) (2003), Rhodes, Greece, Biomechanics/34-38.

obtained the wanted solid object (Figure 4). This

Boolean subtraction was also executed by ANSYS.As previously mentioned, they also work on

pre-operative analysis and comparison of hip joint

osteotomy. The 3-D reconstruction of this region

is more difficult because of the information loss

during the CT scanning procedure. There are many

consecutive slice pairs with large differences. In this

case, interpolation gives no satisfying results, and we

specialize in general methods to reduce the level of

user action required.

Our interface for virtual surgery is GLUT-based,

containing I/O tools for importing existing meshes and

exporting the model into a FEM/FEA environment.Besides using similar scripts for building up the

geometry as described above, we also take advantage

of the mesh generator and manager capabilities of

ANSYS in data exchange. That way, we can import a

tetrahedron mesh used in OpenGL technology into

ANSYS for FEA analysis, for example, and ANSYS

geometry also can be exported as a tetrahedron mesh

for visualizing purposes. Figure 5 shows an example of

a tetrahedron mesh visualization in OpenGL.

FEM/FEA results. Using the volume

reconstruction approach, we needed only to translate

our internal representation to the scripting language.Material types and parameters also can be defined

using scripts. The bone material model we used is a

linear isotropic one. After applying constraints and

forces on the nodes of the solids, they have tested

stress and displacement of the bone structure. Using

the obtained results, a comparison can be made for

the known osteotomy interventions of a certain type.

For femur lengthening, our experience indicated that

the highest stress values occurred around the starting

and ending boreholes of the cut, so we also

considered the usability of different borehole types

and helix with variable pitches, as shown in Figure 6.

Dr. Andrs Hajdu is an ins tructor with the Institute of

Informatics at the University of Debrecen in Hungary and

can be contacted at [email protected]. His research is

supported by OTKA grants T032361, F043090 and IKTA

6/2001. Zoltn Zrg([email protected]) is in PhD studies

at the Institute.

Web Links to More Information

http://graphics.stanford.edu/data/3-Dscanrep/

http://image.soongsil.ac.kr/software.htmlhttp://medical.nema.org

http://www.ablesw.com/3-D-doctor/

http://wwwr.kanazawa-it.ac.jp/ael/imaging/synapse

http://www.materialise.com

http://www.nist.gov/iges

13


Figure 5. Tetrahedron mesh for GL visualizationand FEA.

Figure 6. Different bar hole types and variablehelix paths to improve efficiency of lengthening.


16/44

The anticipated applications for mobile

micro-robots are numerous: manipulation of biological

cells in fighting cancer, for example, or stealth

surveillance technology where clouds of flying

micro-robots could monitor sites relatively undetected

by sight or radar. Micrometer-sized robots could

actively participate in the self-assembly of higher-

order structures, linking to form complex assemblies

analogous to biological systems. One could envisionsuch self-assembly to take place inside a human

body, growing prosthetic devices at their destination,

for example, thus alleviating the need for intrusive

surgery.

Targeting these types of potential future

micro-robotic applications, the Micro-Robotics Group

at Dartmouth College has been developing a new

class of untethered micro-actuators. Measuring less

than 80 mm in length, these actuators are powered

through a novel capacitive-coupled power delivery

mechanism, allowing actuation without a physical

connection to the power source. Finite element

analysis using ANSYS allowed us to test the feasibility

of the power delivery mechanism prior to actual

fabrication of the device.

The micro-actuators are designed to move in

stepwise manner utilizing the concept of scratch-drive

actuation (SDA). The functionality of a scratch-drive

Researchers use ANSYS to develop micron-sized, self-powered

mobile mechanisms.

actuator is shown in Figure 1. The actuation cycle

begins when an electrical potential is applied between

the back-plate and an underlying substrate. The

back-plate bends downward, storing strain energy,

while the edge of a bushing is pushed forward. When

the potential is removed, the strain energy is released

and the back-plate snaps back to its original shape.

The actuation-cycle is now completed, and the

actuator has taken a step forward.

In contrast to traditional SDA power delivery

schemes (such as using rails or spring tethers), our

designs induce the potential onto the back-plate using

Figure 1. Concept behind scratch-drive actuation, whichmoves the micro-actuators in a stepwise manner. An elec-trical potential applied between the back-plate (1) and anunderlying substrate (2) causes the back-plate to benddown, storing strain energy, while the edge of a bushing(3) is pushed forward. When the potential is removed fromthe back-plate, the strain energy is released and the back-plate snaps back to its original shape, causing the actuatorto move forward.

Mobile robots with dimensions in

the millimeter to centimeter range

have been developed, but the

problem of constructing such

systems at micron scales remains

largely unsolved.

FEA in Micro-Robotics

14

By Bruce Donald, Craig McGray, and Igor Paprotny of the Micro-Robotics Group, Computer Science Department,Dartmouth College; Daniela Rus, Department of Electrical Engineering and Computer Science, MassachusettsInstitute of Technology; and Chris Levey, Dartmouth Thayer School of Engineering



17/44

a capacitive circuit formed between underlying

interdigitated electrodes and the back-plate of the

actuator. A circuit representation of the system as

shown in Figure 2 indicated that the back-plate

potential should be approximately midway between

the potentials of the underlying electrodes. We

validated the power delivery concept for the specific

geometry of our design by modeling the systemthrough electro-static analysis in ANSYS. Figure 3

shows the volume model of the actuator and the

electrode field.

The results of the analysis are shown in Figure 4,

indicating the electrical potentials of the conductive

elements in the model. Additionally, a cut through the

air element shows the electrical potential from the field

propagating through it. The potential of the electrodes

in this example was set to 0 V (blue) and 100 V (red),

which represented the model boundary conditions.

The required potential of the back-plate was solved to

be approximately 50 V, validating the circuit-modelapproximation. We also discovered that the potential

of the back-plate changes only slightly as a function of

the orientation of the drive in relation to the electrode

field. This indicates that the actuator can be powered

regardless of its orientation, so long as the device

remains inside the electrode field.

Additionally, we used the ANSYS model to

visualize the intensity of the electric field propagating

through the bottom layer of the insulation material, as

shown in Figure 5. We suspect charging of the device

due to charge-migration in the direction of the field,

and charges embedding in the insulating layer

underneath the drive. We anticipate that these charges

will cluster along the areas where the electric field is

the strongest. In future experiments, attempt will be

made to image this pattern using a scanning electron

microscope.

Following the finite element analysis, we have

successfully fabricated and actuated an untethered

scratch-drive actuator capable of motion at speeds of

up to 1.5mm/sgood pace for such a tiny device.

Our current work is focused on how to apply these

actuators to create steerable autonomous

micro-robotic systems. We anticipate further use of

ANSYS to model the electrostat ic and mechanicalinteraction of the system components to further

shorten our development cycle. In particular, we plan

to use the ANSYS coupled-physics solver to

determine the snap-down and operational

characteristics of our actuators.

Figure 5. Intensity of the electric field propagating throughthe bottom insulation layer of the actuator.

Figure 2. Simplified capacitive-circuit representationof the system.

Figure 3. Volume model of the actuator and the electrodefield, prior to solving the model in ANSYS.

Figure 4. Results of the electrostatic analysis, indicating thecalculated potentials of the different model componentsafter applying the boundary conditions.

15



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16

V5.0 represents a significant redesign for

the market leader in mesh generation.

The New Face ofANSYS ICEM CFD

The new user interface for ANSYS ICEM CFD brings

important benefits to all users and has undergone

extensive testing, with earlier releases of

AI*Environment and ANSYS ICEM CFD 4.CFX utilizing

essentially the same interface.

The learning curve for new users can be

dramatically shortened by way of an updated layout

consisting of tabbed panels, a hierarchical model tree

and intuitive icons.

Existing users can look forward to enhanced

meshing technology in a single

unified environment for shell,

tet, prism, hex and hybrid mesh

generation. Performance improve-

ment highlights for these users

include hotkeys (which provide

one-click access to the most com-

monly used functions), selection

filters and support for the Spaceball

3-D motion controller.

Getting Geometry In

ANSYS ICEM CFD is well-known

for its ability to get geometry from

virtually any source: native CAD

packages, IGES, ACIS or other

formats. The package continues to

be unique among mesh generators

in its ability to use geometry in both CAD and faceted

representations. Faceted geometry is commonly used

for rapid prototyping (stereo lithography, STL), reverse

engineering (where the STL geometry comes from

techniques such as digital photo scan) and biomedicalapplications (where the geometry can come

from techniques such as magnetic resonance

imaging [MRI]).

One major development is that V5.0 is the first

version of ANSYS ICEM CFD capable of running

within the ANSYS Workbench Environment. As the

common platform for all ANSYS products, Workbench

provides a common desktop for a wide range of CAE

applications. With ANSYS Workbench V8.1 and

ANSYS ICEM CFD V5.0 installed, ANSYS ICEM CFD

meshing is exposed as the Advanced Meshing tab.

Geometry can be transferred seamlessly from

DesignModeler to ANSYS ICEM CFD.

Fault-Tolerant Meshing

Having the geometry in hand doesnt do you any good

if you cant create a mesh. Fault-tolerant meshing

algorithms remain the heart of the

ANSYS ICEM CFD meshing suite.

Using an octree-based meshing

algorithm, ANSYS ICEM CFD Tetra

generates a volumetric mesh of

tetrahedral elements that are projected

to the underlying surface model. This

methodology renders the mesh

independent of the CAD surface patch

structure. This makes the meshing

algorithm highly fault-tolerant sliversurfaces, small gaps and surface

overlaps cause no problem. The mesh

has the ability to walk over small

details in the model. Control is in the

hands of the user, who has the flexibility

to define which geometric details are

ignored and which are represented

accurately by the mesh. Tetras computation speed

has been improved with V5.0. As an example, a test

model of 250,000 elements and moderate geometry

complexity required 32% less CPU time during

meshing when compared with the previous version.The Delaunay tet meshing algorithm was added

to the meshing suite in the previous version and has

undergone numerous improvements, including

support for density volumetric mesh controls.

For viscous CFD applications, tet meshes can be

improved by adding a layer of prism elements for

improved near-wall resolution for boundary layer

ANSYS ICEM CFD remains the clearchoice for meshing complex geometry.Shown is a tet/prism mesh for a racecar wheel and suspension.

Software Profile

Judd Kaiser, Technical Solution Specialist



19/44

17

efficient. Most operations now take advantage of

multi-selection methods, such as box and polygon

select. The addition of blocking hotkeys is a real

time-saver, giving the user single-keystroke access to

the most frequently used operations.

For shell meshing, V5.0 offers unstructured 2-D

blocks, combining the best of ANSYS ICEM CFD

Hexa and the patch-based mesher formerly known as

Quad. The creation of blocks for 2-D shell meshing

has been automated, so that blocks can be created

automatically for all selected surfaces.

Mesh Editing

ANSYS ICEM CFD offers maximum flexibility in its

mesh editing tools, whether its via global smoothing

algorithms or techniques to repair or recreate individ-

ual problem elements. These tools provide one last

place to work around any bottlenecks.

Noteworthy are new unstructured hex mesh

smoothing algorithms, which strive for mesh smooth-

ness and near-wall orthogonality while preservingmesh spacing normal to the wall. Two new quality

metrics have been added in order to help quantify

mesh smoothness: adjacent cell volume ratio and

opposite face area ratio.

Scripting Tools

ANSYS ICEM CFD provides a powerful suite of tools

for geometry creation, model diagnosis and repair,

meshing and mesh editing. All of these tools

are exposed at a command line level, providing a

formidable toolbox for the development of vertical

applications. Every operation performed can be storedin a script for replay on model variants. This power can

be extended by using the Tcl/Tk scripting language,

enabling the development of entire applications.

These tools enable users to get around virtually

any geometry or meshing bottleneck, getting the mesh

you need using the geometry you have.

flows. ANSYS ICEM CFD Prism also has been

improved for this release. Prism layers can now be

grown from surface mesh without the need for an

attached volume tet mesh. Perhaps more significant,

prism layers can now be grown from both tri and quad

elements. This means that it is now possible to grow a

prism layer in a combined hybrid hex/tet mesh.

Integrated Hex Meshing

ANSYS ICEM CFD Hexa remains a leader in getting

high-quality, all-hex element meshes on geometries,

which most competitors wouldnt even attempt a hex

mesh. The key to the approach is a block structure

that is generated independent of the underlying

arrangement of CAD (or faceted) surfaces. Think of the

block structure as an extremely coarse all-hex mesh

that captures the basic shape of the domain. Each

block is then a parametric space in which the mesh

can be refined. For CFD meshes, the ability of this

parametric space to be distorted to follow anisotropic

physics makes it very efficient at capturingkey features of the flow with the lowest possible

element count.

Dassault Systemes recognized the power and

promise of this methodology, selecting ANSYS ICEM

CFD technology as the only hex meshing solution to

be offered integrated into CATIA V5. CAA V-5based

ANSYS ICEM CFD Hexa offers hex meshing that

maintains parametric associativity to the native CATIA

Design Analysis Model.

New in V5.0, Hexa has been fully integrated into

the new user interface. Hex meshing functions are

housed in the blocking tab, and block structure

entities are organized on the blocking branch of the

model tree. In addition to reworking the user interface,

several operations have been significantly streamlined.

New methods of creating grid blocks have been

added. The process of grouping curves and defining

edge-to-curve projections has been made more

Prism before Prism after


Images showing a cut through a hybrid hex/tet mesh of a wind tunnel/missile configuration before and after adding a layer of prism elementson the wind tunnel walls. Note that the prism layer is included for both the hex and tet zones (new feature in V5.0).


20/44

CFD Update: Whats New in Computational Fluid Dynamics

Coupled ANSYS and CFX fluid structure simulations help

researchers develop optimal surgical recommendations,

improved stent designs and proper stent placement.

18

Blood Flow Analysis Improves Stent-Grafts

By Dr. Clement Kleinstreuer, Professor and Director of

the Computational Fluid-Particle Dynamics Laboratoryand Zhonghua Li, Doctoral Student, Biomechanical

Engineering Research Group, North Carolina StateUniversity

One of the more intriguing challenges in modern

medicine is the repair of abdominal aortic aneurysms

using stent-grafts: tubular wire mesh stents

interwoven with a synthetic graft material. The device

is guided into place through a small incision in the

groin and then propped open in the aorta, thus

reinforcing the damaged area of the artery. For

reasons that were not well understood until recently,

however, some stent-grafts move out of place. This

migration may again expose the weakened aortic wall

to relatively high blood pressure, potentially leading to

sudden aneurysm rupture and death.Developing an understanding of stent-graft

migration and finding suitable solutions is our current

work at the Biomechanical Engineering Research

Group (BERG) of North Carolina State University in

Raleigh. We are using a pairing of computational

fluid dynamics (CFD) interactively coupled with

computational structure analysis. Using coupled CFX

and ANSYS Structural models in these fluid structure

interactions (FSI), we are learning what goes on inside

the aorta before and after a stent-graft is surgically

inserted, and how the stent-graft might migrate or

dislodge.

Most studies assume that artery walls are stiff

with regard to the pressure changes that come with

each heartbeat, and that arterial wall thicknesses

are constant both axially and circumferentially. Neither

is usually true, especially for older patients with

hypertension, a group that suffers most from

aneurysms.

Studying Stent Migration

The stent migration problem in abdominal aortic

aneurysm (AAA) repairs is critical to the patients

survival. When the stented graft slides out of place

axially, the weakened or diseased artery wall is

re-exposed to the high blood pressure of pulsating

blood flow. That greatly increases the possibility of

AAA-rupture, which is usually fatal. Easily overlooked,

aortic aneurysms are the 13th leading cause of death

in the United States.

LEFT: Representation of a cross-section of an abdominal aortic aneurysm(AAA) with a bifurcating stent-graft. RIGHT: Representation of an aortic arteryaneurysm (bulge on left) between the renal artery (to the kidneys, top) and theiliac bifurcation (to the legs). Aside from the color shading chosen, this iswhat the surgeon would see before starting to implant the stent-graft.

Wall displacements and pressure/stress levels for Resteady=1200, using CFX and ANSYS: (left) axisymmetric AAA,and (right) stented AAA, where the stent-graft clearly shields the weakened aneurysm wall from the blood flow



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19

Using five case histories, CFX and ANSYS

Structural were used to compute the incipient

migration forces of a stented graft under different

placement conditions. In the process, we modeleddifferent artery neck configurations, variable arterial

wall thicknesses, transient hemodynamics and

multi-structure interactions.

The actual stented AAA model in ANSYS

consisted of a lumen or bulge in the artery wall, an

endovascular graft shell, a cavity of stagnant blood

and the AAA wall.

Using iterative fluid structure interaction was an

intense computational problem as ANSYS Structural

and CFX exchanged coupled variations in wall flex and

geometry, requiring several new flow and structure

results at each time step. The ANSYS Structuralproblem centered around nonlinear, large deformation,

contact and dynamic analyses.

Insight into Physical Processes

The CFX post-processor in conjunction with our

programs gives us a great deal of insight into the

physical processes. It helps us to spot critical areas

where platelets or low-density lipoproteins (LDLs) may

clump together, and, ultimately, it helps us with design

optimization of stent-grafts and secure stent-graft

placements.

The coupled CFX and ANSYS results werevalidated with experimental data sets and with clinical

observations.

Surgeons and scientists know that forces

triggering stented graft migration include blood

momentum changes, blood pressure and artery wall

Velocity distribution in non-stentedaxisymmetric AAA model

Wall stress and velocity distribution in stentedaxisymmetric AAA model

Cardiac cycle (time level ofinterest: t/T=0.32, Re=550)

Schematic representationof an axisymmetric AAA,including implanted stent-graftwith relevant analytical data.

For this study, CFX-4 was linked to ANSYS withFortran to perform fluid-structure interaction.

Presently, generalized, fully representative stented

abdominal aortic aneurysm configurations are being

analyzed, employing ANSYS and CFX-5.

shear stress, inappropriate configurations of the

healthy aortic neck section, tissue problems in the

aortic neck segment and biomechanical degradation

of the prosthetic material.To set the model stent-graft into motion, an

increasing pull force was applied with an APDL

subroutine. Coulombs Law was used for each contact

elements friction coefficients, but the simulations

revealed a nonlinear correlation in large displacements

between the migration force needed to move the stent

and the friction coefficients. The simulation also

revealed that the risk of displacement rises sharply in

patients with high blood pressure.

Coupled ANSYS and CFX fluid structure

simulations verified that a stent-graft can significantly

reduce the risk of an aneurysm rupture even whenhigh blood pressure is the fundamental cause. Clearly,

these tools for blood-flow-stent-artery interactions are

valid, predictive and powerful for opt imal surgical

recommendations, improved stent designs and proper

stent placement.



22/44


Simulation Helps Improve OilRefinery Operations

Analysis assists in reducing coke deposits while improving

hydrocarbon stripping.

Syncrude Canada Ltd. is the worlds largest

producer of crude oil from oil sands and the largest

single-source producer in Canada. CSIRO (Australias

Commonwealth Scientific and Industrial Research

Organisation) is one of the worlds largest and most

diverse scientific global research organizations.

CSIRO Minerals is a long time user of CFX and in

collaboration with the Clean Power from Lignite CRC

developed the fluidized bed model in CFX-4. Because

of its robust multiphase capability and its ability to be

extended into new application areas, CFX is used

extensively by CSIRO Minerals in undertaking

complex CFD modeling of multiphase, combustion

and reacting processes in the mineral processing,

chemical and petrochemical industries.

In the past, physical modeling had been used to

understand the flow of solids and gas in the stripper.

This modeling is performed at ambient conditions, so

scaling of both the physical size and materials is

required to approximate the actual high temperature

and pressure in the stripper. This scaling process can

introduce some uncertainty in understanding the

actual stripper operation.

By Dr. Peter Witt

Research ScientistCSIRO Minerals

Maintenance work on a coker unit at Syncrudesoil sands plant in Alberta, Canada.

During oil processing, heavier products are broken down by high

temperatures into lighter products in cokers. This crackingprocess strips off lighter liquid hydrocarbon products such as

naphtha and gas oils, leaving heavier coke behind. The challenge

that CSIRO Minerals has been helping Syncrude resolve is how to

best reduce coke deposits that build-up in their fluid coker stripper

while maintaining or improving hydrocarbon stripping.


20


23/44

Three-dimensional fluidized bed model of the Syncrude fluidcoker stripper. The model predicts the motion of bubbles (inpurple) rising from injectors in the lower part of the bed andthe complex flow behavior of coke particles. Flow simulationsprovide insights into the stripperoperation, which are then used to

improve the design. Gas VolumeFraction

0.750.680.600.520.45

By using CFD modeling to complement the

physical modeling programs, scaling is eliminated and

the actual dimensions and operating conditions are

used. Furthermore, CFX simulation provides much

greater detail of the flows and forces in the stripper

than can be obtained from physical models or from

the plant. This is due to the difficulty in making

measurements and visualizing the flow in complex

multiphase systems.

Syncrude senior research associates Dr. Larry

Hackman and Mr. Craig McKnight explain that

extensive cold flow modeling (but not CFD modeling)had previously been used to investigate the operation

of the fluid bed coker stripper and the gas and solids

behavior in the unit. McKnight notes this project with

CSIRO Minerals resulted in detailed, high quality

reports, which provide a new understanding of the

fluid coker stripper operation.Hackman indicated,

By using CFX to gain a better understanding, it is

anticipated that design changes will be identified to

improve stripping efficiency, reduce shed fouling and

optimize stripper operation.

To most efficiently perform the simulations andutilize the results, the two companies are leveraging

the distance separating their facilities. When it is night

in Edmonton, Alberta, Canada where Syncrude

Research is located, CSIRO Minerals staff is hard at

work in Australia performing analyses and posting

results (including pictures and animations) on their

extranet. The next morning, the group in Canada can

view progress of the modeling work and provide

feedback for a quick turnaround.

In this way, CSIRO is utilizing CFX technology to

assist Syncrude in determining how best to utilize their

current plant to get maximum throughput and thus

make the most of their capital investment.


21

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22 CFX-5.7 Brings Powerful IntegratedTools to Engineering Design

Latest release enhances core CFD features and givesusers greater access to ANSYS tools.

By Michael Raw

Vice President, Product DevelopmentANSYS Fluids Business

bi-directional associative CAD interfaces to all major

CAD packages. The CFX-5 mesher, called CFX-Mesh

and based on the advancing front inflation tetra/prism

meshing technology, has been implemented in

Workbench as a native GUI application that is easy to

use and closely integrated with DesignModeler.

ANSYS ICEM CFD meshers, including the unique

hexahedral element meshing tools, are also now

available in Workbench. They provide meshes for the

most demanding CFD applications and are well

known for their robustness when applied to very large

or complex industrial CAD models. The combination

of ANSYS DesignModeler, CFX-Mesh and ICEM

CFX data can be interpolateddirectly onto ANSYS CBDfiles, providing a flexible routeto transfer CFX results to anexisting ANSYS mesh.

Released in April 2004, CFX-5.7 demonstrates

the continuing development of core CFD technologies,

plus leverages ANSYS technologies to provide

an exciting new series of capabilities for CFX users.

This latest version contains the most advanced

CFD features available, representing a powerful

combination of proven, leading-edge technologies

that provide the accuracy, reliability, speed and

flexibility companies trust in their demanding fluid

simulation applications.

ANSYS Integration

CFX customers are now gaining access

to state-of-the-art geometry modelingsoftware with ANSYS DesignModeler, a

Workbench-based product that is our

new geometry creation tool providing



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Improving Water Treatment SystemsEngineers design compact,

more efficient secondary

clarifiers with the aid of CFX.

By David J. Burt

Senior EngineerMMI Engineering

A secondary clarifier is the final treatment stage of a traditional

activated sludge sewage works. It separates solid precipitate

material from effluent water prior to discharge. Because of recent

changes in environmental legislation, many treatment works in

the UK are required to carry increased throughput or meet more

stringent effluent quality limits. This means that more clarification

capacity is needed. But with land in urban areas scarce and

construction costs high, there is an increasing need to maximize

the performance of existing units rather than build new ones.

The standard technique for designing a final clarifier is mass

flux theory. However, this method uses a one-dimensional settling

model and cannot account for the density currentflow typical in

a clarifier. Even if the clarifier external design satisfies mass flux

theory it may still fail, or perform badly in practice because of theinternal flow features. Often designers are forced to allow a for

a 20% factor of safety in tank surface area to allow for the

shortcomings of mass flux theory. With CFD modeling, it

is possible to capture all of the flow processes to show

short-circuiting, scouring of the sludge blanket and solids

re-entrainment to effluent. This means it is possible to design

more compact units or retrofit existing units with internal baffling

to allow for higher loading.

By augmenting the standard drift flux models in CFX,

engineers at MMI have established a set of validated and verified

models for clarifier performance. These models include settling

algorithms and rheological functions for activated sludgemixtures. The models have recently been used at a number of

UK sites to optimize final effluent quality for increased load.

MMI Engineering is a wholly owned subsidiary of GeoSyntec Consultants

and provides a range of env ironmenta l, geotechnical , hydrological

and civ il eng ineering services. Fur ther detail s can be found at

www.mmiengineering.com and www.geosyntec.com.

How many holes do we needto dig? Construction costscan exceed $1 million for anew 22m diameter tank at awater treatment plant.

A useful post-processing idea is to track stream

lines for the solid phase velocity field. In thiscase colored with G scalar to show where flocmay experience greatest shear.

Concentration profiles through a cross section ofthe clarifier approaching 8000 mg/l solids in theblanket. This tank features an Energy DissipationInfluent EDI, optimized stilling well diameter andadditional Stamford baffling below the effluentweir.


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Two important side effects of the continuing pressure

to reduce product development time and developmentcosts have been the increased use of analysis in the

early stages of design and the development and

manufacturing of many products at overseas sites.

Upfront analysis has been identified by many

companies as a critical stage of product development

due to the many benefits it provides. Done properly,

upfront analysis can shorten the design cycle of a

product drastically by identifying problems early

before substantial investment of time and material has

been made in the product. In the earlier stages of

design, engineers have more options at their disposal

when changing a design to address problems

uncovered by analysis. As a products design

approaches completion, many design modification

options are eliminated due to a variety of reasons

such as manufacturability, cost, system integration,

packaging etc. Therefore, problems that are

discovered later in the process are generally more

expensive to implement. Once a problem is

discovered using upfront analysis, all the viable design

options can also be evaluated by employing the same

analysis techniques. As a result, when a prototype is

finally built and tested, it is much more likely to pass

the tests than if upfront analysis had not been used.

Another fact of todays global economic

environment is that many companies have moved

beyond establishing manufacturing-only facilities

overseas to performing some of their product

development activities at the overseas locations

as well.This global footprint can lead to situations

where a product is conceived and its performance

requirements specified in country A, it is then designed

and tested in country B and mass produced in country

C. Therefore, development centers have to be flexible

enough to respond to the needs of their local market

as well as be able to develop products for

different, distant markets. Once again, the shorteneddesign schedules makes the use of CAE mandatory,

especially in the early stages. Because of the

distributed product development process, it is

important that all the engineers and designers use the

same processes

and techniques.Using analysis as an

integrated part of product

development enables engineers

from around the world to collaborate

in unprecedented ways.

Many of Delphi Corporations customers are

global companies which market and sell their products

around the world. It is therefore important for all of

Delphis resources to be used to satisfy our customers

needs regardless of where the need arises. Recent

programs at Delphi Electronics and Safety (Formerly

Delphi Delco Electronics Systems) have involved just

such a scenario. Engineers from three different

countries have been involved in the design process

from the moment contracts are awarded. Even while

some the system features are being finalized,

the resources of the company around the world are

mobilized to analyze and evaluate the component

designs. Finite element analysis is used extensively to

evaluate component performance. In many cases

the early analysis indicates that modifications

are necessary. The modifications are made and

assessed until all problems are eliminated. Engineers

responsible for making design modifications can use

the local resources as well as those abroad to ensure

the viability of their design. For example, many

engineers at Delphi Electronics and Safetys design

centers around the world have been trained to use

first-order analysis tools. These engineers are usually

able to use analysis to eliminate many design flaws.

However, often they need help in completing the

picture, either because of shortage of time and other

resources, or because they lack the specialty skills

that are available at other sites.

Finally, one of the most important reasons for

performing upfront CAE is simply that many of

our customers require it. In many cases, customershave developed extensive validation requirements

that use simulation extensively in the concept

approval phase.

Early simulation is especially important when engineers atdispersed locations must collaborate in product development.

By Fereydoon DadkhahMechanical Analysis and Simulation

Delphi Electronics and Safety

Upfront Analysisin the Global

Enterprise25


Managing CAE Processes


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Simulation at Work

26

Founded in 1895, DePuy is the oldest manufacturer

of orthopedic implants in the United States, with a

reputation for innovation in new product development.

The company has patented a wide range of

replacement knee systems, the first of which was

developed more than 20 years ago. One of these

types incorporates a state-of-the-art mobile bearing,

which offers a wide range of options to allow the

surgeon to match the implant to the patients anatomy.

Figure 1 illustrates a typical replacement knee.

In one recent application, two sizes of areplacement knee design were analyzed at different

angles of articulation using ANSYS. Initially, finite

element results were compared with known

experimental measurements obtained on one of the

two sizes at three angles of articulation. Once

correlation had been achieved, the same methodology

was used to analyze the other design at various angles.

Meshing Critical Components

The replacement knee design is composed of two

components: the femoral component and the bearing.

Figure 2 shows the solid geometry of the designin ANSYS after importation of the CAD model in

Parasolid format.

Both the femoral component and the bearing

were meshed with 3-D higher order tetrahedral

elements. The meshing of the two parts was made

fully parameterized. The mesh on the underside of the

femoral component was made sufficiently fine to

ensure minimal loss of accuracy in the geometry of the

curved contact surfaces.

A coarser mesh was used in the interior and on

the upper side of the femoral component, since

its material was significantly stiffer than that of the

bearing, and, consequently, very little structuraldeformation was expected. Another option was to

mesh the contact surfaces of the femoral component

with rigid target and the load applied to a pilot node.

A similar approach was used for the bearing,

as the size of the elements was more critical in the

contact region than other non-contacting surfaces.

However, a mesh density even finer than that on the

contact surfaces of the femoral component was

desirable in the bearing to ensure a good resolution of

the contact area and stresses.

An indiscriminate refinement of the mesh on all

the upper surfaces of the bearing proved to be

computationally too expensive, and a new meshing

procedure was developed and tested by IDAC, a finite

element analysis and computer-aided engineering

consulting firm and the leading UK provider of ANSYS

and DesignSpace software.

ANSYS provides fast, accurate feedbackon new orthopedic implant designs.

Analysis of ArtificialKnee Joints

X

Y

Z



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27

Running the Analysis

A preliminary contact analysis was first run with the

original mesh density prescribed to the bearing, then

the elements that were in contact with the femoral

component were further refined for the subsequent

solution. An example of this mesh is depicted in Figure

3. The image illustrates the stress distribution in the

contact area between the bearing and the femoral

component. These stress distribution plots can be

created in the ANSYS program for any point in time

during the nonlinear solution.

It was found that excessive geometricpenetration at setup produced stress singularities and

that, therefore, the contact pair should be checked

prior to the solution. Localized peak contact stresses

also could be produced by the discretization of

the otherwise smooth contact surfaces. The mesh

refinement level for the elements in the vicinity of

contact after the preliminary contact analysis may be

increased, but at the expense of a longer solution time.

Apart from contact stresses, the total contact

area was also an important aspect of the design being

studied. The total contact area was obtained from

summing the areas of all contact elements showing

partial or full contact. This generally leads to an

overestimation of the actual contact area (although it

was considered insignificant given the high mesh

density in the contact area).

All analysis work described in this project was

performed on Intel-based personal computers running

the ANSYS program. DePuy are users of ANSYS and

the parametric models created by IDAC have been

supplied to DePuy for their engineers to perform

further analyses and modifications in-house.

Benefits: Speed and Accuracy

Following on from this study, and working with IDAC,

a number of our own engineers have been able to do

further comparisons of a new design against an

existing product in various loading conditions,says

James Brooks, a senior mechanical design engineer at

DePuy. This has rapidly allowed us to get a good

indication of the performance of the product before

testing.

Fiona Hai

ansys solution summer04

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