Skip navigation
All Places > Simulation > Blog > 2009 > December
2009
Joe Galliera

Steps for Analysis

Posted by Joe Galliera Employee Dec 29, 2009
Back when I used to  do training, I would start off the course by going through the steps that I go  through for any and all analyses each and every time.  These steps are important  and just take some practice to get it used to doing it until it's like second  nature, so that's why I recommend at first writing them down until you do are doing them in your head unconsciously like I do  now.

Steps  for Analysis

1. What is the objective of the analysis?  This step here sets the tone for the  rest of the analysis steps so it is most important to identify all objectives  clearly.  Sometimes this is where your expectations have to come down to reality or feasibility within a given timeframe.
- Are you looking  for stress or displacement (or for another analysis any particular  quantity)?
- How accurate do the results need to be?
- Are you just comparing designs where accuracy takes second fiddle to  consistency?
2. How do I expect the model to move or what result is expected?  This may sound counter-intuituve such that you should already know what the answer is before you do the analysis, but in fact it is very important to be very familiar with the product design and how it behaves.  By knowing the answer to this question, it can help in both setting up the problem in later steps and as a check of the results.  The final results of the simulation are required for all the detailed numbers.
When someone asks me how long it takes to learn how to use SolidWorks Simulation, I typically tell them that: 1) by knowing SolidWorks you are already about 75% of the way there, since you're always working inside SW, and you can take training to learn the rest of the specific Simulation interface; and 2) how familiar you are with your products contributes a lot to the learning process and how to handle your particular analysis models.
3. What type of analysis do I need to perform?
- Can I make  certain assumptions to fit this problem into a linear static solution, or do I  need to do a transient, or dynamic, or nonlinear, or etc...
4. How can  I simplify the analysis?  I want to meet my objective as quickly as I  can, no matter how fast and how much RAM computers have these  days.
- Can I utilize symmetry?  Symmetry not only reduces the size of the geometry but also removes DOFs because of the need to define the natural boundary condisitons on the cut surfaces.
- Can I remove  extraneous geometry features, such as fillets or chamfers, which will not effect the result for what I am looking for?
- Can I use some type of connector to simplify the problem?
- How many parts in  the assembly do I need to include? The Rule of Thumb here is:
  • If Ea is the elasticity of part A (A  for that part you are doing the Analysis on) and  Eb is the elasticity of part B (the one that you could possibly replace with a Boundary condition), then if:
  • Ea ≈ Eb, you need to include part  B in the analysis model,
  • Ea » Eb, try using a remote load  condition for part B instead (as a displacement type  of remote load to allow rotations),
  • and finally Ea « Eb, you can replace part  B with a boundary condition because it is much stiffer than the part you are analyzing.
From here on you  follow the "recipe" set forth by the analysis tree:
5. What  material properties do I need, and where do I get them  from?
- Can I use the  properties that SW Simulation (SWS) provides or should I get them from somewhere  else?
- Remember that all  inputs should be evaluated so check the numbers that SWS reports because they  might be different from the actual material used.  For example from my  experience, the strengths that the SWS material library reports tends to be  on the conservative side.
(Note: I definitely  will need to expand on this topic with a later tip.  Besides boundary conditions, this is probably the next question that I get most often from  users.)
6. How do I  restrain and apply forces on the model (i.e. boundary  conditions)?
- The trick here is  that you don't want to impose a condition that would not have otherwise happened  without that boundary condition.
- Again I will have  to expand on this a little more in a separate tip, but I tend to try to stay away from fixed restraints because this condition does not exist in nature.
- Look for the Simulation Companion series for tips on applying loads & restraints, so for the time being I would refer you to those.  You can access this through the Customer Portal by clicking on the link for References > Webinars
7. How do  parts interact with one another (i.e.  contact/gaps)?
- Bonded? Free? No  penetration?
- If no penetration, then node-to-node, node-to-surface, or surface-to-surface?  Help (or the training manual) can aid in figuring out when one is better than others, so click on the ? to find out more.
8. What  element quality do I use? How do I mesh the model?
- Draft quality  is generally good for pure axial loads, or finding displacements, temperatures or frequencies, or lastly if you are just testing out your setup before  you launch a longer high-quality mesh run.
- If you have  meshing issues, have you tried meshing looping first; try manual mesh controls  next; mesh failure diagnostics can point you towards bad geometry that needs  a-fixin'; and lastly, go to the alternate (curvature-based) mesher after you switch to an incompatible mesh, and defined bonded contacts where  needed.
9. Which  solver do I use?
- Right now, all  I'll say about this is that the Automatic solver option for novice users will  choose the right solver for them.

 

10. View and  evaluate the results.  This is where the job of a design engineer comes in, because it's not just about viewing but also evaluating the results.
- Animate the results to see if it moves as one would expect it to move in real  life.  Going back to thinking about step 2, does it behave as you expected?
- Is von Mises  equivalent stress appropriate or do you also need to create other stress plots, like principal or shear stresses?  Cartesian or cylindrical coordinates? Is  strain more appropriate?
- Novice users can  use the Analysis Advisor for help in interpreting results.

 

11. Do I  need to go back to any previous step and rerun the  analysis?

 

______________________________________________________________
I hope that you get  a lot out of these steps as guidelines in what you should think about each and every time when performing any analysis.  Please comment if there's something that I might have missed or if you want to share something that you do every time?
Copyright © 2009 Dassault Systèmes SolidWorks Corp. All rights  reserved.
Do not distribute or reproduce without the written consent of  Dassault Systèmes SolidWorks Corp.

There are multiple benefits of using a Split Line (Insert > Curve > Split Line) feature for SW Simulation.  When you want to apply an attribute in Simulation, such as a fixture, load or mesh control, to only a portion of the face and not the entire face, a split line will break up that face to be able to do what you want.  New in 2010 is the ability to have many closed profiles in a sketch to use in a Split Line feature yielding multiple new faces.  But previously in 2009 or before, you could only do this for a single sketch profile.  And since I know that many of you are using 2009 or earlier, I will try to help out with a tip for multiple closed sketch profiles.  (I could go on about why for Simulation at least you should be using the latest version 2010, but I'll have to leave that until another blog post.)


In 2009 or earlier, have you ever gotten this error (see screenshot below): "Rebuild Errors: There should only be one profile in the sketch."  All you wanted to do was to project these four sketch circles onto the face of this plate.

image1.jpg


You could create a multitude of Split Line features to get the four breaks that you want (see screenshot).
image2.jpg
 
Go on a feature diet with a Wrap instead!  Create as many sketch profiles as you want, and then go to the Wrap feature (Insert > Features > Wrap) and choose Scribe as the Wrap Parameter as shown in the screenshot.
image3.jpg

This will break up the face for you with only one Wrap feature (see below), which now you can use in your Simulation studies.  The one down side is that you can only split a single face with a Wrap feature.  Did I happen to mention that with SW 2010, you can use a Split Line feature to split multiple faces with multiple closed sketch profiles!  SW 2010 is the real deal.

image4.jpg

 

Copyright © 2009 Dassault Systèmes SolidWorks Corp. All rights reserved.
Do not distribute or reproduce without the written consent of Dassault Systèmes SolidWorks Corp.