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Shock Response Anaylsis and Transient Analysis

Hi Dear,
I would like to apply a response spectrum analyses and transient shock analysis for same structure.
I have both frequency dependent SRS datas and time dependent Trasnsient Shock datas. ( For example MIL-STD 20g 11ms)

I'm asking two questions:

1) When I make a frequency dependent Shock Response Analysis which structure exciteid by only one axis, the stress results so high. (Like 1990 MPa)
However we know that the ultimate stress values of structures under Shock Loadings is more high, I just want to ensure with my application. You can find it in

2) When I try to compare SRS results with time dependent transient shock analysis, I just a confused with gravitation multiplier in shock datas. Normally, If I have 20g acceleration datas to
excite the structure, I have to multiply each 20 g acceleration datas with 9810 mm/s**2 values. Then, my results will go up so high values.

Input deck includes two loadsteps which one of them has transient datas multiplied 9810 mm/s2 and another one has no multiplied with gravitation value.

I need to MPa result for both analysis. So, could you please evaluate my applications and just let me know if you see wrong application.

Best Regards.

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Altair Forum User

Hi @Omer Faruk

if you apply acceleration(20g =20x9810=190000) in OS Analysis then you get the displacement very high which is the issue with Optistruct.

For that you have to define the value of Accln is 20 only in Tabled1.And in control cards –Parm-ENFOMTM-REAL for the real displacement values in FRF. Then you will get the correct displacement, Stress values.

Altair Forum User

Dear Prakash,

But I wonder about that if I apply the MIL-STD standards how can I represent 20 g. When I input only 20 in Tabled1, where would be the 'g multiplier' applied in Transient Analysis.

Altair Forum User

Hi @Omer Faruk

if you apply acceleration(20g =20x9810=190000) in OS Analysis then you get the displacement very high which is the issue with Optistruct.

For that you have to define the value of Accln is 20 only in Tabled1.And in control cards –Parm-ENFOMTM-REAL for the real displacement values in FRF. Then you will get the correct displacement, Stress values.

An also when I define the transient acceleration shock load as 20 in Tabled1, how would I expect the results form. ( g, mm/s^2, ..) . Normally, results should be 'g' if I input the only 20 in Tabled1.

Altair Forum User

Hi Omer Faruk,

Sorry for a late reply. I will get back to you soon on this.

Altair Forum User

@Omer Faruk

Please ignore my last comment.

When running modal transient, the results calculated are absolute to the applied enforced loads that is why you see such high values.

Converting to REAL values is done using ENFMOTN>>REAL

Altair Forum User

Thank you for your efforts,

I got your recommendations. But my other questions are still remain non-answered .

1) I wonder about that if I apply the acceleration from MIL-STD standards how can I represent 20 g. When I input only 20 in Tabled1, where would be the 'g multiplier' applied in Transient Analysis.

2) When I define the transient acceleration shock load as 20 in Tabled1, how would I expect the results form. ( g, mm/s^2, ..) . Normally, results should be 'g' if I input the only 20 in Tabled1.

Altair Forum User

Hi Omer,

1) You can apply a dynamic scale factor through SPCD

2) HyperMesh is unit neutral. So maintain unit consistency. Acceleration will be used as parameter based on load type defined on TLAOD1

mpvnaresh

@ Omer Faruk you got any solution for your question of giving acceleration input asper MIL-STD and getting real displacements in Direct Transient analysis.?

If so please help , I am struggling with the same question.