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Volume 116 The COSMOS CompanSolidWorks for COSMOSWorks Par

Image courtesy of National Optical AstronomyObservatory, operated by the Association of Universitiesfor Research in Astronomy, under cooperativeagreement with the National Science Foundation.Image courtesy of Innovation Engineering Inc.

The COSMOS Companion

SolidWorks forCOSMOSWorks Part 2

Volume 115

Sponsored by:


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2 2006 SolidWorks Corp. Confidential.

What is the COSMOS Companion?

The COSMOS Companion is a series of short subjects to help design

engineers build better products with SolidWorks Analysis

Video presentations and accompanying exercises

A tool for Continuous Learning on your schedule

Pre-recorded videos are accompanied by a more detailed webcast withQ & A Download videos and review webcast schedule at:

http://www.cosmosm.com/pages/news/COSMOS_Companion.html

It is not an alternative to instructor-led introductory training We highly recommend you take a course with your local reseller to build a solidknowledge base

If you are new to the COSMOS Companion, a few comments on the program are warranted. The COSMOS

Companion series was developed in response to the request from many of our users for more detailedinformation on specific and/or new functionality within the COSMOS products. Additionally, many users have

been asking for clarification of common design analysis questions to enable them to make morerepresentative analysis models and make better decisions with the data. Whats more, users have asked for

this material to be made available in a variety of formats so they can review it how and when they wish. Toaddress this, each COSMOS Companion topic has been pre-recorded and made available thru the COSMOSCompanion homepage as a downloadable or streaming video with audio, as static PDF slides for printing, or

as a live webcast enabling attendees to ask questions and engage in additional discussion. We are trying toprovide continuous learning on your schedule so you can be as effective and efficient as possible when using

COSMOS for design analysis and validation.

It is important to note that this material is not developed as an alternative to instructor led training. We still

believe that the best introduction to any of the COSMOS products is in a class led by your resellers certified

instructor. In this program, we are hoping to build on the lessons learned in your initial training. In fact, we willmake the assumption that you have basic knowledge of the interface and workflow from intro training or

equivalent experience. We will try not to repeat what was taught in those classes or can be found in the on-line help but to augment that information.


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A Review of Part 1 Lessons

An accurate CAD model does not ensure an accurate

analysis

The COSMOS solver has no understanding ofgeometryonly nodes & elements

The geometry is only a template for the mesh - If it does notallow complete and accurate elements to be created, it mayhurt more than help

Great geometry cannot compensate for badengineeringGet the concept right before finishing off theCAD model.

In the first part of what will most likely be a several part topic, we discussed the philosophy

of good vs. bad CAD. This is with respect to building more efficient analysis models, notnecessarily in the same context you may have thought of it previously. One importantaspect of that discussion was that, in the end, the solver inside of COSMOS doesnt carehow pretty or precise your CAD model is. It only cares about the placement and quality ofnodes and elements. They are geometry to an FEA solver. Therefore, when analysis isimminent, you should make geometry decisions that facilitate a more effective and efficientvalidation of your design. Lets face it, if you need to do analysis, there are some doubtsabout the integrity of the structure. This is a healthy attitude for new or moderately changeddesigns. Therefore, it makes sense that the sooner you can determine you are on the rightcourse, the faster you can complete, or better yet, optimize a great design.

If you construct highly finished, detailed geometry or a design that isnt up to the structuralrequirements, you may have wasted precious hours or days in the project schedule.Remember, no matter how cool it looks on screen, the proof is in the validation and if youcan use your COSMOS tools to validate in a virtual environment sooner than later, you canavoid costly consequences.


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The Penalties of Poor Planning

Wasted Time / Cost of Adding Detail to A Design that

Doesnt Work

Cost of Rework to Fix Current Design

Emotional and or Concurrent Commitment Established

Cost of Less than Optimal Design Per unit Cost

Performance Cost

Market Share

Cost of Not Meeting Schedule (Market Share Loss)

As we discussed in Part 1, the consequences of poor planning range from lost time undoing

and redoing SolidWorks features all the way down to lost revenue because a projectrequired a complete redesign when it failed miserably in the prototype stage. As ananalysis consultant, I was brought in to too many scenarios where everyones best guesseswerent good enough and analysis was required to bail out a program vs. drive a qualitydesign from the beginning. If analysis can validate after a design is complete, it canobviously validate in the conceptual stage.


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Beam Mesh

Shell Mesh

Solid Mesh

Choosing the Right Idealization Will

Help Improve Accuracy Speed Opportunity to Optimize

Build Geometry to Support Idealization

A key aspect of conceptual validation, and even final design validation, is to plan for the

proper idealization. Idealizations in FEA are conceptual representations of 3D geometry.Arguably, a solid mesh, the most commonly used by COSMOSWorks users, is anidealization in itself since it seeks to cature or represent all possible variations the finalmanufactured geometry might see. If you put tolerances on your drawings, your CADmodel is an idealization.

For parts that are very thin compared to the surface are of the smaller features, a shellmesh can provide a faster and more accurate solution than a solid mesh.

For parts that have a small cross section compared to their length, beam elements are themost efficient solution.

It is important to remember that as you progress further into a conceptual mesh, from solids

to shells to beams, the more detail gets lost at the mesh level. Therefore, as well discusslater, staying simplistic in your CAD is even more important since many of the details youmight be tempted to put in wont even show up in the analysis model.


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Build Geometry to Support Idealization

Clean Solids for Tet Mesh

Properly Connecting3D Sketch for Beam Mesh

Properly Oriented Surfaces forShell Mesh

For the three types of models mentioned, here are the guiding principles of geometry

creation:For solid models, keep the geometry clean and as simple as you can to validate macrolevel behavior before worrying about details.

For shell models, your best results come with properly positioned surfaces. These can beactual SolidWorks surfaces or outside faces of solids. However, remember that COSMOSassumes the surface chosen for the mesh is positioned at the mid-surface of the part andassigns half the defined wall thickness to each side. If your surface isnt properlypositioned, you may analyze a part thats smaller or larger than you intended.

For beam models, properly positioned and connected curves, preferably at the neutral axesof the structural members will give you the best start. Youll need to create Structural

Member Weldment entities using these curves but dont worry about the end conditionsuntil youve sized your beam layout and cross-sections.


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Clean Solids

Dont outrun your headlights!

Validate conceptual geometry before adding all the detail

The simpler the model is, the faster it will run & the less time you willhave wasted if you learn you are on the wrong track

Review face and edge interaction after adding features

Tweak dimensions if needed to:

Avoid Zero Degree corners

Avoid skinny, sliver surfaces & tiny edges

Review interaction of parts in an assembly for: Gaps and penetration

Slight misalignments


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Clean Solids

In this example, style was as pressing a reason as manufacturability to fillet nearly every

part of this casting. However, all this filleting created some questionable interactionsbetween edges as seen in the details on this slide. The designer also felt that since hedidnt know where the high stress would be, he should include all the fillets just to be safe.However, he didnt know if the part was even properly sized so all the time he spent puttingin variable radius fillets may have been wasted. Could he have validated the conceptwithout the fillets?


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Clean Solids

Complete Model Conceptual Model

These images show a typical part detail with all the fillets and without. The basic form is

clearly the same. The part without the fillets will analyze a little lighter, if gravity oraccelerations loads came into play. It should also analyze a little more flexible since thefillets do add to the cross-sectional area of the part legs.


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Clean Solids

From the images, you can see that the mesh on the conceptual model is much cleaner. If

you look at the Mesh Details, you can see that the percentage of low aspect ratio elements(low aspect ratio = better calculations) in the conceptual model was higher and that themesh time of 11 seconds was much more efficient than the almost 15 minutes of thecomplex model. The simpler model would also lend itself to h-adaptive meshing morereadily as the complex part could run into problems in the questionable faces.


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Clean Solids

< 10% Difference in Stress & Displacement

62,700 psi 67,800 psi

Looking at the stress and displacement plots, you can see that the results distribution

between the two models is identical for practical purposes. The magnitudes vary by lessthan 10% so it is reasonable to assume that any design decision that was valid based offone would be valid on the other. In this example the stress levels indicate the modelrequires some optimization to reduce stress levels so that can be done on the simple modelmuch more readily than the detailed one. Once the response has been brought toacceptable levels, the detailed fillets can be added and a check run on the final designcompleted. Since the additional fillets only improve the structure, you should expect that anacceptable simplified model will result in an acceptable complex model.


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Properly Positioned Surfaces

Solid features were the most expedient way to

develop the initial geometry based on stylingrequirements

For optimization and expected nonlinearities, ashell mesh is the way to go

For shell models, the most important aspect of geometry construction is properly placed

surfaces. Remembering that COSMOS assumes that half the assigned wall thickness willbe placed on each side of the selected surfaces, positioning the shell surfaces as close tothe midsurface of the part will usually pay off.

For this example, the shovel was modeled in solids initially for styling purposes but theproblem embodies several complex nonlinearities so a simpler, faster idealization isimportant to assess the stiffness and place ribs optimally. There may be 10-12 iterations inpursuit of the final design so every few minutes you can shave off the solution time isimportant.

Once the decision has been made to analyze this part as a shell mesh, you need toinvestigate ways to convert the model to a surface representation. Simply choosing outside

or inside surfaces is not an option in this problem for two reasons. First of all, the t-jointnature of the handle to scoop interface places a wall with thickness on the back of thescoop. If you selected the outer surface of the scoop, it would have slot-like cut-outs wherethe wall of the handle intersected. You couldnt choose the inside face of the scoopbecause it doesnt touch the handle. The other reason is that the features of the handle arenot significantly larger than the wall thickness. This geometry is on towards the thicker sideof shell modeling and as the wall thickness approaches feature size, it becomes all themore important that midsurfaces are used to get a proper geometric representation.Midsurfaces will be required.


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Insert : Surface : Midsurface wont resolve

this part

Insert : Surface : Offset gets you most of theway there

The Insert : Surface : Midsurface command didnt work for this model. It was too complex

for the automated tool to resolve. However, the Insert : Surface : Offset did the trick for themost part. Using the Select Tangency selection option, all the surfaces of the Handle wereoffset into the part the wall thickness and the same was done for the Scoop.


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The complex end conditions do not allow Surface Extend sothe handle needed to be trimmed to a plane before it wasextended.

Offset Surface : Delete Solid Body Insert : Surface : ExtendInsert : Surface :Trim

Once the surfaces were created, the solid body was no longer of any use so it can be

deleted from the Solid Body Folder using the Delete Solid Body option. This results in afeature on the tree called Delete Solid Body that can, itself, be deleted or suppressed laterto bring the solid back. When the solid is removed from the model, the surfaces can beexamined.

Unfortunately, this resulted in a wall thickness gap between the Handle surface and theScoop surface. These needed to be joined using surfacing techniques in SolidWorks. Youhave the option to extend existing surfaces but the end condition of the Handle was toocomplex for this technique. Therefore, the complex ends were trimmed back using Insert :Surface : Trim to a properly positioned plane. The squared off edges can then be easilyextended through the Scoop.


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The extended surfaces must be trimmed back to the shovelbody

The Handle surfaces can then be trimmed back using the Trim Surface option to force

positional correspondence of the Handle edges with the Scoop back face.


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Since the edges of the Handle meet the Shovel Body in the middle ofsurfaces, the Body surfaces need to be split to force edge compatibility

A Composite Curve used the edges of the Handle surfaces and a 3DSketch line to complete the Split Line

When a surface edge butts up to another face, COSMOSWorks will not force a continuous

mesh unless the face has been split to have matching edges. You can use bonded contactto join the two bodies together but that might create a fictitiously rigid joint on this otherwiseflexible plastic part so getting a continuous mesh in this area is important. For this example,I used the edges of the Handle surfaces to create a Composite Curve and then added aline joining the edges of the curve into a closed loop. This is required so that the resultingsplit line splits the faces of the scoop into distinct faces. You cant create a split line thatends in the middle of a face. As you can see from the image, the split line has created asplit face that is acceptable for getting a continuous mesh.


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A Split Line was added using Plane5below to provide a surface for Restraints

This restraint represents a simplifiedplunge into wet sand.

To complete the model, since theanticipated loading would be symmetrical,a final Surface Trim was made using theRight Plane to cut the part in half.

Remember that the Symmetry restraintdoesnt work for shells. You need torestrain all cut edges as follows: Translation Normal to Cut Plane: T=0

Rotation in the Cut Plane: R = 0

The last steps in preparing the model for analysis include a symmetry cut and a final split

line to provide faces to restrain to simulate the shovel in wet sand. Since we are trying tomake our model more efficient, and since our geometry, loads, and restraints are allsymmetric, symmetry will greatly reduce the solution resources for this problem.Remember that the Symmetry restraint type is only valid for solids. Youll need to manuallydefine symmetry restraints on the cut edges by remembering that a symmetry restraint,with respect to the cut plane, requires a 0 restraint on normal translations and in-planerotations.

This model is ready for analysis and optimization.


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Properly Connecting 3D Sketches

All features in this dunebuggy frame were sweeps

Top level document was anassembly

Obvious choice for analysisis Beam elements

Need 3D Sketch in a Part

Can we work with thismodel?

In this dune buggy frame example, the parts are long compared to their cross-section. A

solid mesh of this would require the end conditions of each tube to be cleaned up and aconsiderable amount of resources to mesh and solve. It is more appropriate to solve thismodel with a beam mesh, new to v2007.

A couple of notes regarding this geometry. First of all, the top level document was anassembly and all the components were swept solids. The nature of the sweep provided acurve at the neutral axis of each member. This will be useful when creating the beams.

To use beam elements in COSMOSWorks, the model needs to be rebuilt using StructuralMember weldment entities and to get those, a 3D sketch entities need to be placed at theneutral axis of the tubes. Since we have those in the sweep features, they can be copied toa more complete 3D Sketch.


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All the solid bodies were hidden in the assembly using the right mouse click option in the

Solid Bodies folder for each part. This exposed the driving curves. In some cases, thosecurves were hidden and needed to be shown.


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A new part was added to the assembly called Beams although the name is unimportant. A

3D sketch was then added to the new part and all the existing sweep curves wereconverted to sketch entities in the new 3D sketch. This is similar to the technique youmight use to create a Joined part in an assembly that merges all the solids. Once all theneeded sketch entities were converted, well close the assembly and work directly with the3D Sketch in the new part.


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Create Library

Feature sketchesfor the StructuralMember Profiles

Modify an existingsketch

Weldment ProfileLibrary folders

must haveStandard Folderand Type Folder

StandardSize

Since Structural Members are required, we needed to develop the profiles that are used in

this model. Ive found that it is more reliable to copy and modify the default profiles than totry to create new reference features. You can leave the new profiles in the existing foldersor create a new folder for them. Remember that the folder structure is important if you wantSolidWorks to see the profiles. Under the folder you add to the library folder in theSolidWorks options, you need to have a subfolder that corresponds to the Standarddesignation and then the Size designation. While the names and content of these foldersdont need to be based on standards and sizes, failing to copy this folder tree structure willblock access to the profiles in the Structural Member dialog.


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Curve Replaced withLine Segments

Not shown in the image are some intermediate steps where the 3D curves are cleaned up.

The Solid-to-Beam converter works best when all the driving curves meet at their ends. Aquick scan of the model should point you to the ends that need to be merged. Youll needto remove restraints that tie back to the original assembly in some cases and in others, itmay be easier to simply delete the curve and add a line back into the 3D Curve.Additionally, the Solid-to-Beam converter doesnt currently support curved StructuralMembers so the curves need to replaced with line segments. For short shallow curves,simply replacing the curve with a line may be sufficient. For others, you may want to create2-3 segments per curve as shown in the image.

Once the curves have been cleaned up, you must create your Structural Members.COSMOSWorks doesnt currently support the use of multi-segment, non-collinearStructural Members so to be safe, it is best to simply pick one segment per solid. If you areworking with previously created models containing Structural Members, you may want toreview your part in light of this restriction.


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When all the solids have been created, jump into COSMOSWorks, create a Beam Mesh

study, new to v2007, and youre nearly there. Youll note that a Beams folder has beenadded to the Feature Tree. Right Mouse Click on this folder and choose the option toTreat All Structural Members as Beams. This will automatically convert your solids tobeam elements using the cross-sections defined in the profiles that created the StructuralMembers. Its that easy


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If you zoom in on the joints, youll see that they ends are rather messy looking. While you

may want to clean these up later for the final design, they are OK for the analysis. TheBeam idealization uses virtual geometry that is, internally, a line at the neutral axis of thebeam member. Therefore, end conditions as shown dont enter into the calculations. Onelimitation of the beam element is that these local results are not reliable. You can use theforces generated at these joints however to properly size welds or other connectionmethods.


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To highlight the importance of clean 3D sketches, well look at this example of a container

frame. Unlike the Dune Buggy frame, the members in this model vary greatly in size anddepth. They dont all meet at endpoints as in the previous model so joint creation may be aproblem.


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As this model was originally constructed, the designer chose to create the fewest sketch

entities possible and took advantage of patterning and mirroring to complete the solidmodel. This is not the best way to proceed if beam elements are to be used inCOSMOSWorks. The Solid-to-Beam converter is more reliable when the StructuralMember entities are created directly on an underlying sketch. Another technique thisdesigner used was to place the sketch entities where they were most convenient for hisprofiles, not necessarily at the neutral axis or where the joined with each other. Thisresulted in gaps between curve endpoint that were often larger than the profile dimensions.These gaps make resolving a joined beam model in COSMOSWorks difficult.


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Joints are found automatically using a tool called the Pinball. The Pinball Radius essentially

defines a sphere at each beam end. If more than one beam end falls within any givenPinball, they are assumed rigidly connected. It is important to choose the Preview Pinballoption and adjust the size based on your typical end-to-end clearance so that the mostefficient joint selection occurs.


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If Pinball radius is too small, it cant bridge the larger gaps

If the Pinball radius is set to bridge the larger gaps, it joins too manystructural members

Due to the varies section size and the different gaps between the curves, a small pinball

radius fails to connect some of the smaller floor braces to the side channels but a largerpinball radius that captures joins those also joins more members than desired. While youhave the option to manually reconfigure your joints, this can be very tedious for largemodels. Trust meits better to have the automatic joint detection work correctly the firsttime.


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Rebuilding sketch entities took less time than attempting to resolve evena few of the Joints in the mesh

Sketch entities can be 3D Sketches or a group of 2D sketches

A better way to create this model is to explicitly define all the frame members with

underlying curves. This takes less time than cleaning up the joints in the previousattempt and gives you a more robust model. Note that even though the StructuralMembers use sketch entities in 3D space, this frame sketch was made with a combinationof 2D sketches. The repeating members were easily created using the Offset Entity curvecreation option in Sketch mode. Note that all the curves either join at end points or their endpoints are coincident with another curve.


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When the beam model is created in COSMOSWorks, all the beams are converted

flawlessly and the members are joined without any manual correction. The resulting modelis ready for validation and optimization.


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Presentation Summary

Use Design Analysis to get the concept right FIRST

Consider the best idealization option & build SolidWorksfeatures to facilitate that meshing method

Review your geometry as you create it to ensure thatfeatures dont cause meshing problems.

After validation, you can tweak the dims back for manufacturing

Consider the Needs of Nonlinear & Optimization

Focus on the Big Picture (A Working Design) - Not LocalEfficiencies or Successes (Drawings)

To summarize this session, it is important to remember that Design Analysis is most

effective when you use it to drive your decisions at the conceptual stage. You have thebest chance of success if you build geometry that facilitates the idealization inCOSMOSWorks which is most efficient for the problem. Remember that beam elementsare driven by curves and Structural Members, Shells are best represented by properlyplaced midsurfaces and even though you can mesh the most complex, detailed solid, thismay not be the fastest path to design validation and optimization.

Always check your model as you are building it for sliver surfaces, short edges and otherfeatures that can give the mesher headaches. If you have to tweak dimensions a little tomake the analysis more efficient, do so in a Configuration or change them back when youknow the design will work.

Also remember that even thought static models of even the most complex geometries solvepretty fast in COSMOSWorks, when you need to use a Nonlinear study or you know youllbe analyzing several iterations in pursuit of an optimal design, keep model sizes small willpay off in the end.

Finally, remember that it is your job to develop a working and cost-effective design asquickly as possible. As much as we may feel like it sometimes, a drawing is not the endproduct of a design department so take the time at the beginning of the process to workthrough some of the driving decisions using conceptual geometry and analysis techniquesbefore you put in all the detail for manufacturing.


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Conclusion

For more information

Contact your local reseller for more in-depth training or support ontechniques within SolidWorks to make your COSMOS simulationmore effective in your design process

Review the on-line help for a more detailed description of the featuresdiscussed

Attend, or better yet, present at a local COSMOS or SolidWorks usergroup.

See http://www.swugn.org/ for a user group near you

Id like to thank you for taking to the time to sit thru this edition of the COSMOS

Companion. These concepts will be revisited using different examples with new techniquesin subsequent units. If you walk away with one lesson, I hope its that a little thought aboutthe analysis at the time geometry is started can lead to major gains in efficiency forconceptual analysis later on.

If some of the SolidWorks or COSMOSWorks techniques reviewed in this session are notfamiliar to you , I highly encourage you to work with your reseller support team tounderstand them better. Having a good relationship with these engineers can help you thrumany design challenges down the road.

As always, I also encourage you to look for local COSMOS or SolidWorks users groupsand get involved. These are excellent resources for networking and learning from the

experiences of others. If the local SolidWorks group hasnt had any design analysispresentations in awhile, volunteer and talk about your modeling challenges. Youd besurprised at how much feedback you can get from your peers, even if they arent experts inanalysis. You can find your local groups on the SolidWorks User Group Network website atwww.swugn.org.

Thanks again for your time and I look forward to seeing you again on the COSMOSCompanion.

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115_SWforCW_Part2