ansys solution summer04
TRANSCRIPT
-
8/12/2019 Ansys Solution Summer04
1/44
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
-
8/12/2019 Ansys Solution Summer04
2/44
...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...
-
8/12/2019 Ansys Solution Summer04
3/44
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
Managing EditorJennifer L. Hucko
DesignersMiller Creative [email protected]
Art DirectorPaul DiMieri
Ad Sales ManagerAnn [email protected]
Circulation ManagerElaine Travers
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
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
-
8/12/2019 Ansys Solution Summer04
4/44
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
2
www.ansys.com ANSYS Solutions | Summer 2004
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.
-
8/12/2019 Ansys Solution Summer04
5/44
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
www.ansys.com ANSYS Solutions | Summer 2004
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.
-
8/12/2019 Ansys Solution Summer04
6/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
7/44
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.
www.ansys.com ANSYS Solutions | Summer 2004
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.
-
8/12/2019 Ansys Solution Summer04
8/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
9/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
10/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
Figure 5. Tetrahedron mesh for GL visualizationand FEA.
Figure 6. Different bar hole types and variablehelix paths to improve efficiency of lengthening.
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
18/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
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).
-
8/12/2019 Ansys Solution Summer04
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
21/44
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.
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
22/44
CFD Update: Whats New in Computational Fluid Dynamics
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.
www.ansys.com ANSYS Solutions | Summer 2004
20
-
8/12/2019 Ansys Solution Summer04
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.
www.ansys.com ANSYS Solutions | Summer 2004
21
5.0 secs
9.0 secs
13.0 secs
0.0 secs
16.5 secs
20 secs
-
8/12/2019 Ansys Solution Summer04
24/44
CFD Update: Whats New in Computational Fluid Dynamics
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
25/44
-
8/12/2019 Ansys Solution Summer04
26/44
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.
CFD Update: Whats New in Computational Fluid Dynamics
24
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
27/44
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
www.ansys.com ANSYS Solutions | Summer 2004
Managing CAE Processes
-
8/12/2019 Ansys Solution Summer04
28/44
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
www.ansys.com ANSYS Solutions | Summer 2004
-
8/12/2019 Ansys Solution Summer04
29/44
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