may 21, 2007 the focus issue 57 - padtinc.com › blog › wp-content › uploads › ...cfx solve...

May 21, 2007 The Focus Issue 57

www.padtinc.com 1 1-800-293-PADT

By Doug OatisIf you're likeme, you've runinto your fairshare of"dirty" CAD

(specific CAD packages will not belisted due to fear of legal reprisals).One of the most common problems I'veencountered with "neutral" CAD files(.iges, .x_t, .stp, etc.) is missing surfac-es. These can either come from poor

tolerancing or an actual gap in the mod-el. This was something easily fixed inANSYS Classic by importing the areas,patching the hole, and creating a vol-ume from the areas. In WB v11, younow have this capability in DesignModeler thanks to the Sewing Opera-tion.

In DM V10, if you had a missing sur-face, the solid geometry import wouldfail and you would get an error messagesaying "No Valid Bodies Found".

Now, in V11, you can have DM importthe areas if the solid generation fails.DM also has a new option where it will

May 21, 2007 A Publication for ANSYS Users Issue 57

Part 2: DesignModeler and Simu-lationAs promised in last month's article, thismonth we will focus on the new develop-ments on the Workbench environmentfor ANSYS 11.0. Although the majorityof develops at ANSYS, Inc. work on the"core solver" technology, what we seeand deal with on a daily basis are thechanges made to the pre and post pro-

cessing tools, and especially Work-bench. This release has lots to payattention to.

A significant number of changes fit intothe "I'd use Workbench more if..." wish-es that many of us have. As with thechanges to the core ANSYS product,there are far too many new features andchanges to talk about in detail, instead,we will look at DesignModeler and Sim-ulation, and next month we will look atthe other Workbench modules.

DesignModelerAlready a mature tool, DM continues togrow in functionality, driven primarilyby user input. Besides the various newcapabilities and features, we have foundit to be more robust and a tad faster. The

top three changes are listed below, butlook for an article dedicated to DM en-hancements for more breadth and depth.

BooleansOne of the most requested additions to DMhas been the ability to do Boolean opera-tions. At V11 they are here, and added in aunique and powerful way. They work withsolids or surfaces/2D areas and give youpretty much the same functionality that youshould be used to from PREP7, but withsome different commands.

The basic operations are: Unite, Subtract orIntersect. To give users more control, whenyou are subtracting or intersecting, you cansay NO to "Preserve Tool Bodies." Thiskeeps what remains of the cutting geometryaround for future use. In addition, on the

This One Goes to 11

Table of ContentsThis one Goes to 11: DM and Simulation-----------------------------------------1Sewing in DesignModeler-------------------------------------------------------------1From /POST1 to Workbench---------------------------------------------------------5Advanced Search-----------------------------------------------------------------------4Gravity in Workbench------------------------------------------------------------------4

Sewing in DesignModelerFig. 1a: Starting

GeometryFig.1b: Union Fig.1c: Subtract Fig. 1d: Subtract,

Save ToolFig. 1e: Intersec-tion of all Bodies

Fig. 1f: Union ofAll Intersections

Fig. 1f: Intersec-tion, Save Tool

(Cont. on pg. 2)

Fig. 1: Bad Geometry

(Cont. on pg. 4)

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Intersect command, you can tell it to calcu-late the "intersection of all bodies" or the"union of all intersections." Figures 1a-1gshow what happens if a shark, a hook and atuna swim into DM and start playing withBoolean options.

Geometry Repair ToolsIn an ideal world, all CAD files are perfectand read into Workbench without any prob-lems. However, we don't live in that worldso the DM team has started adding tools andfeatures that let you import and repair realworld geometry. The first important stepthat they took is that you can now do a"partial import" of geometry. What thatmeans is that if your import fails, it reads inwhat it can and creates a surface body. Nowyou can go in and repair things.

The most important repair tool is the"patch" command that lets you click on aloop of edges, and the program sticks in asurface. Combine this with various deleteand slicing operations and you can repair alot of problems. Once you have all yourservices fixed up, you can then use the new"sew" command (a body operation option)to build a solid. Again, not all that differentfrom what you do in PREP7, just simpler,

more robust, and fully associative and re-peatable. Figures 2a-2c show a simple ap-plication.

Sketch ProjectionOne capability that exists in most CADtools that was previously missing in DMwas the ability to associatively project 3Dentities onto the sketch plane. You use it bycreating a plane that you want to projectonto, right click on the plane, then chooseInsert->Sketch Projection from the menu.Next, click the points, edges or faces youwant and regenerate to get your new 2Dsketch that projects the selected entitiesonto the plane you chose.

Figure 3 shows a good example- where bothsurfaces and edges are projected onto a newplane, ready to have new geometry associa-tively linked to it.

SimulationThe road to full high-end mechanical simu-lation pre- and post-processing in Work-bench has been long and steep. Everyrelease takes us a lot closer to the top, andV11 may be one of the most ambitious inthis area so far. There is a lot of material,too much to detail, so the following is asummary of the changes that we feel willhave the biggest effect on user productivity:

Analysis TypesA big fundamental change was the intro-duction of "Analysis Types". This tells

Simulation whattype of analysis youare doing so that theuser interface canfilter and only showyou stuff you need.When you pick theanalysis type, it al-so inserts a settingand result branchinto your model.

We have found it more intuitive than the oldmethod and easier when you are doing mul-tiple types of analysis on the same model.Figure 4 shows the options.

ANSYS RST FileMany long time Simulation users will re-joice in the fact that V11 now reads theANSYS result file direction (insert soundclip of trumpet blaring?). This has severalpositive implications: 1) it allows access tomore complex result types, such as shellelement results, 2) it is much more compactwhen dealing with transient results, 3) youcan more easily use the results from one runas a boundary condition on another. 4) Itallows users to shuffle RST files around alittle.

All in all this is not a flashy change, but willhave major positive implications for com-plex simulation in the future.

Multibody DynamicsThe most significant effort from sheer de-velopment effort at V11 was the introduc-tion of Multibody Dynamics. This is amajor addition in capability that requiredchanges all across simulation and in AN-SYS as well. Most of the changes are subtleor behind the scenes, but some stand out andare deserving of special notice. Look forone or more future editions with detailedarticles on this subject.

The most obvious is that all bodies nowhave a new option in simulation: "StiffnessBehavior." The default is flexible, but if youchoose rigid the program will create a rigidmass, with properties based on your geome-try and material properties, connected toother parts through MPC's. This greatlysimplifies your model.

Another important change was a completeredo of what was the Contacts branch into anew branch called Connections used to de-fine joints, springs and contact areas. Thecontacts are still automatic, but the joints

(ANSYS 11.0, cont...)

(Cont. on pg. 3)



and springs are defined by hand. Of course,the solution options and post processinghave also changed to support this importantnew capability. Figure 5 shows a simplelatch model, and you can download an ani-mation and the model itself atftp.padtinc.com/public/downloads/latch2_wbmdl.zip

Meshing ImprovementsMeshing and meshing control are two areasexperienced users were always beating ondevelopment to improve. V10 saw someimportant steps in this area, and even moreare now available in V11. The most impor-tant is a new option called "Physics Prefer-ence." With this, you tell the mesher thetype of problem you are trying to solve andthe program changes the mesher defaultsand checking based upon what type of mesheach physics requires.

With the introduction of more non-linearcapabilities in Workbench, it was time totighten down the shape checking. So, underthe advanced meshing controls you can turnon aggressive checking, which is a lot likethe default checking in ANSYS PREP7.

Moving down the list, the next importantchange consisted of a lot of enhancementsto Sweeping, allowing you to hex mesh amuch larger number of geometries then inV10.

Newly exposed in V11, Inflation layermeshing is something that the CFD worldhas used for years to get a very refined meshon a surface of a tet mesh. You basicallymesh the surface with triangles then growwedges inward in thin layers to get refine-ment normal to the surface. Then you fill inthe rest of the volume with tets. In V11 youcan use this advanced feature for CFD,EMAG and stress meshes. Some prelimi-nary testing has shown it to be a powerful

way to get very good refinement in keyareas.

The last meshing change to really highlightmay be the simplest, but the most signifi-cant. You can now specify edge biasing onmesh controls on edges. For CFD and manystress models, this has been a long-neededfunctionality.

Tables and Functions for LoadsThere are certain capabilities in ANSYSthat are very powerful, but require a certainamount of skill and patience to use, andmastering them gives you a strong sense ofsuperiority. Unfortunately, those pesky de-velopers continue to take advanced capabil-ities and making them easier to use - andadding tables and function loads to Work-bench is a good example. You can nowspecify loads that vary with temperature ortime using functions or tables. And thetables can be stored in engineering data. Totop it off, the values are shown right in themain window as a graph to make sure youdid everything correctly. Look for spatialvariations in the next release. Figure 6shows a function and the table/graph it pro-duces

FSIAs PADT's sales team goes out with theircarpet bags beating on doors, we run acrosscustomer after customer looking for power-ful yet easy to set up Fluid-Solid Interaction(FSI) modeling. ANSYS has had this capa-bility for many years, but only with theintroduction of CFX and Workbench has itbecome accessible beyond the specialistuser. In V11 more functionality has beenadded in several ways. The one that will beused most is one-way load transfer from aCFX solve to an ANSYS solve. At V11Temperature and Convection join Pressureas the different types of surface loads thatyou can transfer.

For two-way FSI there has been a rewrite ofthe interface on both the Simulation andCFX side to make it even easier. Look forspecific articles on this in the focus as wellas tutorials on the ANSYS web site.

PSDAnother core ANSYS capability moves toworkbench with Power Spectral Density(PSD) simulation. In the electronics andaerospace industries, as well as many civilengineering applications, you use PSD toget the statistical response of a structure toa random vibration input. The implementa-tion is pretty complete and includes supportfor pre-stressed modal, different units, scal-ing to get 2, 3, N sigma, and the all-impor-tant Segalman-Reese method forcalculating accurate 1-sigma EquivalentStresses.

Shell Element Result SupportYet another core functionality showing up atV11 is the ability to plot shell results on thetop, bottom or middle of shells. Nothingreally that fancy but if you need it, you haveto have it and now you don't have to post-process in POST1 to get your bending stresses.

Chart ToolThe last enhancement we are going to talkabout is the first tool in Simulation for whatcan be called advanced post-processing. TheChart Tool makes nice X-Y graphs of resultsinformation from any multi-step simulation.This may be another relatively simple addi-tion to the program, but one that is needed toallow users to stay in Simulation for a com-plete analysis.

(ANSYS 11.0, cont...)

ftp://ftp.padtinc.com/public/downloads/latch2_wbmdl.zipftp://ftp.padtinc.com/public/downloads/latch2_wbmdl.zip



try and stitch the surfaces together auto-matically. This feature (on by default)will cause the model with the missingcorner fillet to import as shown in Fig-ure 1.

As you can see, it created a solid andsurface body. This isn't quite what wewanted, so you can turn off the auto-mated stitching in the details window(Fig. 2) of the import object. You willthen get the quiltwork of surface areasimported.

Next, use the 'Surface Patch' under-neath "Tools", and select the three edg-

es that define the gap. Finally, insert abody operation, and change the 'Type'to "Sew". Select all the surfaces, makesure to set 'Create Solids' to "Yes".Click Generate and you'll see you nowhave a solid body ready for meshing inSimulation.

In case you're curious about what hap-pens if 'Create Solids' is set to "No", itsimply joins all the surface bodies to-gether. In the parts list you will just seea single surface body (think of it asunfreezing multiple surface bodies to-gether).

Not my finest mesh ever…but it's betterthan fighting a surface model to repair

(Sewing, cont...)

Fig. 2: Turn off Stitching on Import

Fig. 4: Bad Geometry

Fig. 5: The MeshFig. 3: Surface Bodies Ready for Repair

Your Search forAdvanced Searching is

OverMany of us spend much of the day roam-ing around the ANSYS help files. Evenafter learning how to use Booleans in thesearch(http://www.padtinc.com/epubs/focus/common/focus.asp?I=40&P=article3.htm), we still wanted more advanced search-ing capabilities. The often unnoticedfolks in documentation have come to ourrescue with an modern web-based searchengine on the ANSYS, Inc. customerportal:

http://expert.ansys.com/ExpertHelp/

Some of the great features are:

Choose which manual to search Search within results Search titles or content Match on similar words Advanced search building tools with

controls like “must/must not contain,”“case sensitive,” “Match Synonyms”

You can also save common searchesto come back to later. There is even adecent “help” manual for the ExpertSearch Capability.

As an example, we got a question on howto define the normal direction of a pre-tensioned entity. If I simply search allfor “pretension normal” I get 576 refer-ences. If I do “pretension” I get 51.Doing a search within results on“normal” I get 16. Doing one more“search within” on direction gets medown to 14. If I cut that down to just theANSYS Basic Analysis Guide I get only1 listing. I could of done the same thingon the AdvancedSearch page with evenfewer steps

So next time you find yourself lookingfor something in the help, don’t bring upthe old interface. Go to the customerportal (you will need a login) and use thenew advanced help.

Einstein is Spinning in His Grave: Gravity in WorkbenchEveryone should be aware of a simple little change in Simulation for V11.0. InANSYS and Simulation prior to V11 you specified gravity as an acceleration actingon your geometry. The whole point of general relativity was that there is no way foran observer to tell the difference between being accelerated at 32.2 ft/sec^2 orstanding on the earth. In fact, gravity is the acceleration caused on an object as ittravels through time, duo to the warping of the space-time fabric by the mass of alarge object. Therefore gravity was defined as an “up” acceleration. But this confuseda lot of people so bowing to public pressure, and ignoring the equations that governthe universe, Simulation V11 specifies gravity in the direction of the force, or down.We shall see if the International Physics Congress lodges an official protest, but untilthen remember that it is different in Simulation than ANSYS. (Is it obvious that we don’tagree with this change?)



By Rod SchollWith release 11.0, you can now take your ANSYS results and post-process them in Simulation!

Every time I rotate an image in Workbench's Simulation I am freshlyamazed. After years of waiting for redraws in ANSYS, it just seemstoo good to be true. And when I turn on something slick like Simula-tion's sliced section abilities (a dynamically updating capped-hiddendisplay) and can drag the slice plane back and forth through resultcontours in real time… it really makes for better understanding of astate of stress…

But hopefully I don't have to sell you on some of the great and fastpost-processing features of Simulation - rather let's detail the processof getting your ANSYS created and solved model in to Workbench --its not just a push of a button:

1. In ANSYS write out your mesh as a .cdb file. Use CDWRITE,DB,,-- the (CDWRITE,GEOM option will not work properly.)

2. In Workbench, launch FEModeler specifying the .cdb file from step1.

3. Create the geometry. Because Simulation expects a solid model onwhich to apply BC's there must be some present. Do this byhighlighting the Geometry Synthesis branch and select Initial Geom-etry. Save the file.

4. If you are still in the same probject database, you can simply clickon "New Simulation". If you are reopening WB and specifying an

existing FE Model session, then on the project page select (or browseto) the desired .fedb file which you preciously created. Then on theWorkbench project page, you can click on New Simulation.

5. Okay, now we have the geometry in Simulation. Catch your breath.(I didn't say this would be easy, hehe.)

6. To read in the results, we have to prep Simulation for the incominginformation. So we will create a dummy branch (of the same

physics). Also, you have tospecify a type of result (similarto Simulation behavior beforerelease 11.0) such as a singleEquivalent Stress plot. Finally,there must be a force of somesort applied under the environ-ment branch. For our structuralmodel, I applied a dummy forceof 5 lbs to an arbitrary surface.

7. Now, along the top menu underTools, the “Read ANSYS .rst” file is no longer grayed out. Note thatyou will be only specifying the folder, and a jobname in the unitsystem dialog box (may haveto scroll down to find the job-name specifier). Also, thisfolder is going to get duplicat-ed on your harddrive, so youmight want to stick the .rst in aempty folder to avoid delaysand wasted space. Simulationnow begins converting the .rstto the format which Simulationuses.

8. Once complete… you can save the Simulation database, and yourresults can be operated on normally. Well, relatively normally. Youwill notice that the lightening bolt color scheme doesn't match - butadd postprocessing items and retrieve results for them and theplotting works fine.

As easy as 1,2,…8! (Expect it to get more streamlined in futurereleases.)

From /POST1 toWorkbench



The Focus is a periodic publication of Phoenix Analysis & Design Technologies (PADT). Its goal is to educate and entertain the worldwideANSYS user community. More information on this publication can be found at: http://www.padtinc.com/epubs/focus/about

Upcoming Training ClassesMonth Start End # Title Location

May ‘07 5/21 5/22 105 ANSYS WB Sim Struct. Nonlin. Tempe, AZJune ‘07 6/4 6/6 101 Intro. To ANSYS, Part I Tempe, AZ

6/11 6/12 201 Basic Structural Nonlinearities Tempe, AZ6/13 6/14 204 Adv. Contact & Fasteners Tempe, AZ6/21 6/22 301 Heat Transfer Tempe, AZ6/25 6/26 107 ANSYS WB DesignModeler Tempe, AZ

July ‘07 7/9 7/10 104 ANSYS WB Simulation - Intro. Albq, NM7/12 7/13 105 ANSYS WB Sim Struct. Nonlin Albq, NM7/19 7/20 801 ANSYS Customization w/ APDL Tempe, AZ7/23 7/24 203 Dynamics Tempe, AZ7/26 7/27 102 Intro. To ANSYS, Part II Tempe, AZ

Aug. ‘07 8/1 8/2 104 ANSYS WB Simulation - Intro Tempe, AZ8/6 8/7 152 ICEM CFD/AI*Environment Tempe, AZ8/9 8/10 202 Adv. Structural Nonlinearities Tempe, AZ

8/13 8/14 501 ANSYS/LS-DYNA Tempe, AZ8/16 8/17 604 Intro to CFX Tempe, AZ

News - Links - InfoANSYS, Inc. does a 2-1 Stock Split [story]

ANSYS, Inc. Recognized on list of Top R&D Spend-ers [story]

FLUENT for CATIA V5 Released [story]

Not using the customer portal? You should. Thereis a ton of useful information and a growing on-linecommunity: www1.ansys.com/customer/

ANSYS, Inc. has combined their ANSYS and FLU-ENT magazines into a new pub-lication: ADVANTAGEThis first issue has lots of techni-cal content and a special supple-ment with examples on howpeople use simulation in thesports and leisure business.Subscribe to the print version orview the on-line version at:www.ansys.com/magazine

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V11: DM and SimulationSewing in Design ModelerGravity in WorkbenchAdvanced Search/POST1 to WorkbenchNews-Links-InfoTrainingAdvertising

may 21, 2007 the focus issue 57 - padtinc.com › blog › wp-content › uploads › ...cfx solve...

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