Results at final load factor for nonlinear static analysis are inconsistent from load factors 0.1 through 0.9

Aleksandr Breit_21922
Aleksandr Breit_21922 New Altair Community Member
edited July 2023 in Community Q&A

Hello,

I am comparing the results from two studies:

1. A nonlinear static analysis with a preload using CNTNLSUB

2. A nonlinear static analysis with NO preload

(The cases are identical with one using a preload case)

My problem is that the results from the two cases are different for all load factors 0.1 through 0.9 (as expected), but on the final load factor (100%), the results become identical. Or in other words, the final load factor the Case 1 matches the final load factor for Case 2 which should not be true.

Would anybody happen to know why this is happening? Thank you for the help.

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Answers

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2023

    would you mind sharing more details and pictures on your setup?

    they should be different. Maybe checking the reaction forces (SPCF) and contact forces (CONTF) would help you investigate.

    Also there's an output for the pretension, written by OS that should help as well.

  • Aleksandr Breit_21922
    Aleksandr Breit_21922 New Altair Community Member
    edited July 2023
    Adriano A. Koga_21884 said:

    would you mind sharing more details and pictures on your setup?

    they should be different. Maybe checking the reaction forces (SPCF) and contact forces (CONTF) would help you investigate.

    Also there's an output for the pretension, written by OS that should help as well.

    Hello Adriano,

    Thank you for your response. Here's a picture of my setup for the nonlinear analysis using CNTNLSUB (the other case is identical except for no CNTNLSUB to start from the pre-load results). Please let me know if you need the setup details for the "Pre-Tension" case.

    image

    image

    image

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited July 2023
    Aleksandr Breit_21922 said:

    Hello Adriano,

    Thank you for your response. Here's a picture of my setup for the nonlinear analysis using CNTNLSUB (the other case is identical except for no CNTNLSUB to start from the pre-load results). Please let me know if you need the setup details for the "Pre-Tension" case.

    image

    image

    image

    is it a bolt pretension case?

    If so, you should include Statsub(Pretens) in the second loadstep as well.

    And add Pretension to loadstep #1.

     

    If it is just a sequential loading (no pretension). the you should keep the loads from preload in the second case + new loads.

  • Aleksandr Breit_21922
    Aleksandr Breit_21922 New Altair Community Member
    edited July 2023
    Adriano A. Koga_21884 said:

    is it a bolt pretension case?

    If so, you should include Statsub(Pretens) in the second loadstep as well.

    And add Pretension to loadstep #1.

     

    If it is just a sequential loading (no pretension). the you should keep the loads from preload in the second case + new loads.

    It is not bolt pretension, just sequential loading. I am first applying load to a cross-bracing structure to "tighten it" before I apply the second load step. 

    I want to make sure the full (100% load factor) tightening load is applied before the second load step begins. I am concerned that if I combine the "preload" with the second load case into a single load collector that both loads would be increasing from zero during the nonlinear analysis instead of the preload being 100% applied before the second load case begins. 

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