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Beginner's Questions about Applying Symmetry Restraints

Question asked by John Willett on Sep 25, 2015
Latest reply on Oct 3, 2015 by John Willett

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These questions apply to planar symmetry of solid assemblies (multiple parts) in SW Premium 2015 SP4.0. For sake of argument, suppose I have an assembly (and its loads and restraints) that is symmetrical about two of the the three principal planes. One of the symmetrical quarters is illustrated here:

Question 1: I produced this quarter-solid from a previously designed full solid using an assembly extruded cut. Is there some more automated way to cut an assembly down to one symmetrical fragment, for example simply by referencing the planes of symmetry?

The easiest way to apply symmetry restraints for simulation in the above model seems to be to place a "Fixtures/Advanced Fixtures.../Symmetry" in the study tree and then list the planar surfaces to which symmetry should be applied. I presume that all six of the cut faces must be listed, although the yellow preview that I get suggests that a minimum of two (one on each symmetry plane) will do, as illustrated here:

Question 2: Is this preview deceptive in that all six cut faces must indeed be listed?

Question 3: Is there some automated way of checking that the symmetry restraints are valid in that they actually re-constitute the entire body? Is the yellow preview -- specifically the appearance of the fourth quarter opposite the original, in addition to the two quarters across their respective symmetry planes -- sufficient verification?

(I recall that, for cyclic symmetry applications, the approved test was to circular-pattern the segment and verify that the pattern could be merged into a single body. I suppose I might do something like that in this case too, although this is an assembly, not a single part...) -- John Willett

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Siavash Khajehhasani Sep 28, 2015 9:02 AM

Hi John,

Q1: There is an option in SOLIDWORKS to check the symmetry, in command manager of the Evaluate tab (see the figure below)

Q2: Yes, all six cut faces must be chosen in symmetry selection set of faces. It is a common mistake that as soon as you choose one face the yellow image of symmetry appears, which does not mean the sufficient faces are selected. User needs to be aware and select all faces that are cut through the symmetry plane.

Q3: There is no automated way to check if symmetry is correctly applied. However, user can check it after running simulation. The judgment method is as follows: displacement of the model perpendicular to plane of symmetry (at symmetry plane) has to be zero. This can be checked easily in post-processing stage of results.

By the way, another advanced method to apply symmetry is "Use Reference Geometry" or "On Flat Faces". To see how to also use this method see the the following link: 2013 SOLIDWORKS Help - Symmetry Restraints for Shell Models

Please let me know if it answers your questions.

Thanks,

- Siavash

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John Willett @ Siavash Khajehhasani on Sep 28, 2015 1:59 PM

>>Q1: There is an option in SOLIDWORKS to check the symmetry, in command manager of the Evaluate tab (see the figure below)<<

Siavash -- Thanks for the helpful responses. Regarding the above quote, however, I must be missing something. I created a simple assembly of two simple rectangular parallelepiped parts mated such that each of their front and right planes coincided with those planes in the assembly. Two problems:

1) If I apply Symmetry Check to each part individually, it agrees that they are symmetric about the front plane, but it gives me very limited options to split the part automatically -- not the ones I want, which are about the Front and Right Planes.

2) If I apply Symmetry Check to the assembly as a whole, there is no split option that I can find (automatic or otherwise), and the tool reports both parts asymmetric about the assembly Front Plane - see image:

What am I doing wrong? -- John Willett

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Siavash Khajehhasani @ John Willett on Sep 28, 2015 2:53 PM

Hi John,

No, you do not miss any point here. This is the fact that the symmetry check for part may not give the desired option, also for assembly there is no automatic symmetry check option. Let's put it this way, this is only a check tool to see if symmetry exists in the model or not. The splitting process should be done manually by user in part level is the desired symmetry section is not picked, as well as for the assembly level.

I am sorry if this is not that you expecting the software to do; nevertheless, I hope you find this information useful and maybe a correct answer to your question.

Thanks,

- Siavash

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John Willett @ Siavash Khajehhasani on Sep 28, 2015 3:02 PM

>>I am sorry if this is not that you expecting the software to do; nevertheless, I hope you find this information useful and maybe a correct answer to your question.<<

Thanks again, Siavash -- I guess the Symmetry Check just plain doesn't work on assemblies (SW Premium 2015 SP4.0). -- John Willett

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Siavash Khajehhasani @ John Willett on Sep 28, 2015 3:10 PM

Hi John,

Let's put it this way: in the assembly level, you can perform symmetry check to see if symmetry exists for all part with respect to the selected plane. Thereafter, split needs to be done in part level. Please let me know if it makes sense.

Thanks,

- Siavash

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John Willett @ Siavash Khajehhasani on Sep 28, 2015 3:54 PM

>>Let's put it this way: in the assembly level, you can perform symmetry check to see if symmetry exists for all part with respect to the selected plane. Thereafter, split needs to be done in part level. Please let me know if it makes sense.<<

Siavash -- I guess I'm still missing it. Please examine the figure and point (2) in my previous message more closely. For me at the assembly level Symmetry Check finds both parts asymmetric, even though at the part level it finds them symmetric. Perhaps I'm doing it wrong, but I don't see how. -- John Willett

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John Willett @ John Willett on Oct 3, 2015 1:42 PM

>>Please examine the figure and point (2) in my [response of Sep 28, 2015 1:59 PM] more closely. For me at the assembly level Symmetry Check finds both parts asymmetric, even though at the part level it finds them symmetric.<<

Can anybody tell me what I'm doing wrong on this last detail? (Siavash has fully answered the others.) -- John Willett

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7 Replies

Siavash Khajehhasani Sep 28, 2015 9:02 AM
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Hi John,
Q1: There is an option in SOLIDWORKS to check the symmetry, in command manager of the Evaluate tab (see the figure below)
Q2: Yes, all six cut faces must be chosen in symmetry selection set of faces. It is a common mistake that as soon as you choose one face the yellow image of symmetry appears, which does not mean the sufficient faces are selected. User needs to be aware and select all faces that are cut through the symmetry plane.

Q3: There is no automated way to check if symmetry is correctly applied. However, user can check it after running simulation. The judgment method is as follows: displacement of the model perpendicular to plane of symmetry (at symmetry plane) has to be zero. This can be checked easily in post-processing stage of results.

By the way, another advanced method to apply symmetry is "Use Reference Geometry" or "On Flat Faces". To see how to also use this method see the the following link: 2013 SOLIDWORKS Help - Symmetry Restraints for Shell Models

Please let me know if it answers your questions.
Thanks,
- Siavash
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- John Willett @ Siavash Khajehhasani on Sep 28, 2015 1:59 PM
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  Correct Answer
  >>Q1: There is an option in SOLIDWORKS to check the symmetry, in command manager of the Evaluate tab (see the figure below)<<
  
  Siavash -- Thanks for the helpful responses. Regarding the above quote, however, I must be missing something. I created a simple assembly of two simple rectangular parallelepiped parts mated such that each of their front and right planes coincided with those planes in the assembly. Two problems:
  
  1) If I apply Symmetry Check to each part individually, it agrees that they are symmetric about the front plane, but it gives me very limited options to split the part automatically -- not the ones I want, which are about the Front and Right Planes.
  
  2) If I apply Symmetry Check to the assembly as a whole, there is no split option that I can find (automatic or otherwise), and the tool reports both parts asymmetric about the assembly Front Plane - see image:
  What am I doing wrong? -- John Willett
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  - Siavash Khajehhasani @ John Willett on Sep 28, 2015 2:53 PM
    Mark Correct
    Correct Answer
    Hi John,
    No, you do not miss any point here. This is the fact that the symmetry check for part may not give the desired option, also for assembly there is no automatic symmetry check option. Let's put it this way, this is only a check tool to see if symmetry exists in the model or not. The splitting process should be done manually by user in part level is the desired symmetry section is not picked, as well as for the assembly level.
    I am sorry if this is not that you expecting the software to do; nevertheless, I hope you find this information useful and maybe a correct answer to your question.
    Thanks,
    - Siavash
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    - John Willett @ Siavash Khajehhasani on Sep 28, 2015 3:02 PM
      Mark Correct
      Correct Answer
      >>I am sorry if this is not that you expecting the software to do; nevertheless, I hope you find this information useful and maybe a correct answer to your question.<<
      
      Thanks again, Siavash -- I guess the Symmetry Check just plain doesn't work on assemblies (SW Premium 2015 SP4.0). -- John Willett
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      - Siavash Khajehhasani @ John Willett on Sep 28, 2015 3:10 PM
        Mark Correct
        Correct Answer
        Hi John,
        Let's put it this way: in the assembly level, you can perform symmetry check to see if symmetry exists for all part with respect to the selected plane. Thereafter, split needs to be done in part level. Please let me know if it makes sense.
        Thanks,
        - Siavash
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        John Willett @ Siavash Khajehhasani on Sep 28, 2015 3:54 PM
        Mark Correct
        Correct Answer
        >>Let's put it this way: in the assembly level, you can perform symmetry check to see if symmetry exists for all part with respect to the selected plane. Thereafter, split needs to be done in part level. Please let me know if it makes sense.<<
        
        Siavash -- I guess I'm still missing it. Please examine the figure and point (2) in my previous message more closely. For me at the assembly level Symmetry Check finds both parts asymmetric, even though at the part level it finds them symmetric. Perhaps I'm doing it wrong, but I don't see how. -- John Willett
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        John Willett @ John Willett on Oct 3, 2015 1:42 PM
        Mark Correct
        Correct Answer
        >>Please examine the figure and point (2) in my [response of Sep 28, 2015 1:59 PM] more closely. For me at the assembly level Symmetry Check finds both parts asymmetric, even though at the part level it finds them symmetric.<<
        
        Can anybody tell me what I'm doing wrong on this last detail? (Siavash has fully answered the others.) -- John Willett
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Beginner's Questions about Applying Symmetry Restraints

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