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LS-DYNA starter issues with *MAT_SPRING_ #1358

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SonSiont opened this issue Apr 12, 2023 · 1 comment
Open

LS-DYNA starter issues with *MAT_SPRING_ #1358

SonSiont opened this issue Apr 12, 2023 · 1 comment
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bug Something isn't working

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@SonSiont
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Describe the bug
The models contain springs of material *MAT_SPRING_NONLINEAR_ELASTIC, *MAT_SPRING_INELASTIC, *MAT_SPRING_GENERAL_NONLINEAR and *MAT_SPRING_ELASTIC with *SECTION_DISCRETE.

  1. In the output files ..._0000.out the SPRING VOLUME and INERTIA is zero.
  2. Sometimes the boundaries are not processed.
  3. sp4.k
    a) *MAT_SPRING_NONLINEAR_ELASTIC carry no load (IE is zero)
    b) SPC force not equal to the spring force e.g. Node 31 has a force of -10, the spring 31 reports -200
  4. sp4a.k springs are oriented in a general position in space. The reaction force is only in X-direction, e.g. Node 31 (-7.1, 0, 0)

To Reproduce
Run the attached models in a clean directory, watch the output for "IMPOSED VELOCITIES".
Evaluate the forces and energies from the TH file.

Expected behaviour

  1. Volume and inertia should be not zero, see Comment 1 from SECTION_DISCRETE: This keyword maps to /PROP/TYPE8 (SPR_GENE) spring using a default mass 2.0e-03 kg and inertia 2e-02 kgmm depending on the units.
  2. Each run should give the same results.
  3. The springs should carry loads and should have the same force in the spring.
  4. The springs should act when in a general position in space.

Output
A Comparison of a run with and without "IMPOSED VELOCITIES":
diff.out.gz
The input files:
sp4a.k.gz
sp4.k.gz

Desktop (please complete the following information):

  • Version [5c09e32]
  • Hardware [Linux: Intel(R) Core(TM) i7-5930K CPU @ 3.50GHz (x86_64), 3499 MHz, 64217 MB RAM]
  • Configuration [double precision SMP]

Additional context

@laurent-altr laurent-altr added the bug Something isn't working label Apr 12, 2023
@SonSiont
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A comparison between my solution and the direct run with the LS-DYNA file show:
grafik

  • Initial density is set to zero
  • DYNAMIC AMPLIFICATION FACTOR A = 1.0000000000000E-20 -> this is not the default, the spring cannot carry a load
  • FORCE-VELOCITY CURVE = 0 -> there should be the correct curve in
  • DYNAMIC AMPLIFICATION FACTOR GF3 -> In the manual is a different name
  • ...FAILURE DISPLACEMENT = 1.0000000200409E+20 -> this is at least ugly (single <-> double precision)

The difference in the spring force and the reaction force is still present.
Here is my solution:
conrad_0000.rad.gz

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