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Why? Penetration VS Initial Penetration

Sebastian Yang

Hi all!

I have a question regarding the initial penetration in explicit analysis (crash)

As far as I know, initial penetration detection in Radioss is ONLY dependent of the value of the minimum gap.

I am using TYPE 7 by the way.

For example:

Those two shells are at a distance of 2 mm, so if the minimum gap = 2 or larger, there will be initial penetration.

Now my question is:

What does thickness do here if I set a minimum gap = 1.5 manually?

I could set the thickness of the shells to 5 mm,

and the program won´t say anything, isn´t this counter-intuitive? In "normal" penetration check you have two shell thickness penetrating each other,

but for crash analysis initial penetration check, there is actually NO initial penetration and the check is independent of the thickness (in this case)?

Thank you!

Community-Pasted-Attachment-1713658464220.png

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Accepted answers

Polyvios Romanidis

Hi Sebastian,

The initial penetration is dependent on the Gap value, which generally depends on the Gap_min value you insert and the thickness and dimensioning of the elements you use. The Gap calculation is done with different formulas based on the Igap formulation you use.

For the specific situation you describe here I can assume that you used Igap = 0 when you set up the /INTER/TYPE7, or left the Igap entity empty. This formulation made the Gap value equal to the Gap_min you inserted. By that, Radioss searched for potential contacts in the distance of 1.5 mm without taking into account the thickness of the parts. Because the distance between the parts is 2 mm not penetration detected.

If you change the formulation to Igap=1 the penetration should be detected, because now the thickness of the shell elements is considered.

I attach some slides that explain the penalty method, the calculation of the Gap and the penetrations theory.

In the following link you can find the exact formulas used for the calculation of the Gap value (note 11).

https://help.altair.com/hwsolvers/rad/topics/solvers/rad/inter_type7_starter_r.htm?zoom_highlight=%2FINTER%2FTYPE7#inter_type7_starter_r__inter_type7_starter_r_fn_yth_wfp_tz

You can also learn more about contacts in the following video:

https://www.youtube.com/watch?v=kQnMhFM9iAE

Or by following a Radioss Basic Training (more info in the link):

https://learn.altair.com/course/view.php?id=4

Polyvios

1 Penalty Method.png

2 Contact Gap.png

3 Initial Intersections.png

4 Initial Penetrations.png

All comments

Pohan28

Hi which type of contact do you use?

Sebastian Yang

Hi which type of contact do you use?

Hi, it´s type 7, I have added it to the thread text.

Polyvios Romanidis

Hi Sebastian,

If you change the formulation to Igap=1 the penetration should be detected, because now the thickness of the shell elements is considered.

I attach some slides that explain the penalty method, the calculation of the Gap and the penetrations theory.

In the following link you can find the exact formulas used for the calculation of the Gap value (note 11).

https://help.altair.com/hwsolvers/rad/topics/solvers/rad/inter_type7_starter_r.htm?zoom_highlight=%2FINTER%2FTYPE7#inter_type7_starter_r__inter_type7_starter_r_fn_yth_wfp_tz

You can also learn more about contacts in the following video:

https://www.youtube.com/watch?v=kQnMhFM9iAE

Or by following a Radioss Basic Training (more info in the link):

https://learn.altair.com/course/view.php?id=4

Polyvios

1 Penalty Method.png

2 Contact Gap.png

3 Initial Intersections.png

4 Initial Penetrations.png

Sebastian Yang

Hi Sebastian,

The initial penetration is dependent on the Gap value, which generally depends on the Gap_min value you insert and the thickness and dimensioning of the elements you use. The Gap calculation is done with different formulas based on the Igap formulation you use.

For the specific situation you describe here I can assume that you used Igap = 0 when you set up the /INTER/TYPE7, or left the Igap entity empty. This formulation made the Gap value equal to the Gap_min you inserted. By that, Radioss searched for potential contacts in the distance of 1.5 mm without taking into account the thickness of the parts. Because the distance between the parts is 2 mm not penetration detected.

If you change the formulation to Igap=1 the penetration should be detected, because now the thickness of the shell elements is considered.

I attach some slides that explain the penalty method, the calculation of the Gap and the penetrations theory.

In the following link you can find the exact formulas used for the calculation of the Gap value (note 11).

https://help.altair.com/hwsolvers/rad/topics/solvers/rad/inter_type7_starter_r.htm?zoom_highlight=%2FINTER%2FTYPE7#inter_type7_starter_r__inter_type7_starter_r_fn_yth_wfp_tz

You can also learn more about contacts in the following video:

https://www.youtube.com/watch?v=kQnMhFM9iAE

Or by following a Radioss Basic Training (more info in the link):

https://learn.altair.com/course/view.php?id=4

Polyvios

Hi Polyvios,

Thank you. Sorry for late replay.

I actually used igap = 1000, which is basically the same as you explained, only gapmin value is considered.

I will go through the learning materials you passed! By the way, it is possible to ask you whether it is a standard practice to check initial penetrations using only gapmin value without taking into account the thickness? Or it is more common to consider the thickness when checking initial penetrations? I believe the latter option make it much more complicated to get rid of initial penetrations.

Thank you again.

Polyvios Romanidis

Hi Polyvios,

Thank you. Sorry for late replay.

I actually used igap = 1000, which is basically the same as you explained, only gapmin value is considered.

I will go through the learning materials you passed! By the way, it is possible to ask you whether it is a standard practice to check initial penetrations using only gapmin value without taking into account the thickness? Or it is more common to consider the thickness when checking initial penetrations? I believe the latter option make it much more complicated to get rid of initial penetrations.

Thank you again.

Hi Sebastian,

I would say that the standard practice is to use Igap = 2, which if you don't set up Fscale_gap and Gap_max is equivalent to Igap = 1.

Both of the above formulations are consider the thickness of the parts to detect penetrations.

This is the best practice because you consider the thickness and not only a value you insert manually and can showcase some penetration not easily seen by the user initially.

Polyvios

Sebastian Yang

Hi Sebastian,

I would say that the standard practice is to use Igap = 2, which if you don't set up Fscale_gap and Gap_max is equivalent to Igap = 1.

Both of the above formulations are consider the thickness of the parts to detect penetrations.

This is the best practice because you consider the thickness and not only a value you insert manually and can showcase some penetration not easily seen by the user initially.

Polyvios

Hi Polyvios,

Understood, thank you very much!