Examples for Linear Gaps modelling.

Dear all,

I would like to study some examples with linear gap elements. We don`t have SOL400 available and to have a work around for i.e. objects touching or near eachother.

Could you provide wtih some examples or give location of study material? Thanks.

0 Prafulla Kulkarni over 7 years ago

There is a chapter in MSC Nastran linear static Analysis user guide "Contact in Linear Static Analysis" in which linear gap capability has been explained with an example.

In addition, you can refer this article which shows demo about linear gaps creation in Patran. simcompanion.mscsoftware.com/.../index
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0 Ken Walker over 7 years ago

You don't need SOL 400 to model contact. Linear Contact (for general contact modeling) has been part of MSC Nastran since 2010. It uses the same input and iterative solution method from SOL 400 in SOL 101. The only limitation is small sliding assumptions (consistent with linear analysis/small deflection assumptions - linear gaps have them too). In addition, you can use Touching or Glued contact (or a combination of them). Compared to linear gaps, this method is easier to setup, easier to visualize (and understand) and has fewer limitations.

I strongly encourage you to investigate Linear Contact before spending time on 'linear gaps'.

Check out these SimAcademy Webinars:

Nastran Contact Analysis - New Features and Tips

simcompanion.mscsoftware.com/.../index

Contact Pair Modeling: New Approach to Contact Modeling Setup in Patran 2013 with MSC Nastran 2013.1

simcompanion.mscsoftware.com/.../index
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0 ron.kunz over 7 years ago

Thanks Ken,

An additional question regarding the topic of Linear Contacts:

If one has two parts seperated by a component (a plastic part). One is not interested in this plastic part. So the top part lays on the bottom plate resting on this plastic part. Is it then possible to use a linear contact? I have seen an example where a RBE3 element is used to have these 2 parts connected (touching each other) however no stiffness is added.

Thanks in advance.
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0 Ken Walker over 7 years ago

Hi Ron,

If you're running Nastran 2016++, you can maintain an initial gap (aka a "virtual shim"). The initial gap (or overlap) is defined as a BCONPRG option (clearance option is invoked with the OGINGP parameter). There is an example in the 2016 Release Guide.
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0 ron.kunz over 7 years ago

Thanks again Ken.

Where can I find this release guide documentation (and others as well)?
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0 Ken Walker over 7 years ago

All MSC product documentation is available on the SimCompanion site:

simcompanion.mscsoftware.com/.../index

You can get MSC Nastran documents here:

simcompanion.mscsoftware.com/.../index
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0 ron.kunz over 7 years ago

Regarding the topic of Linear Gaps, I was also wondering how this will influence your model with respect to boltforces. In fact I have two identical models. One model is modelled with linear gaps and the other one with contacts. The output for the boltforces seems to be completely different. Of course the modelling of the bolts could be incorrect, but I was wondering if one models this in a correct way, if it is then possible to compare a model with contacts with a model with linear gaps (of course non-linear behavior is not included in both models)?
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0 Ken Walker over 7 years ago

Choice of contact model (linear gaps or linear contact bodies) should not affect calculated bolt forces, assuming all other model details are the same. In the end both methods are comparing nodal displacements, and preventing them from moving into the opposing body.

If you are getting different results, start by comparing deformations. If those are different, figure out why. If they are the same, then compare the contact force distribution. Again they should be similar.
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0 ron.kunz over 7 years ago

Linear Contact is not limited to surfaces? It can also be used for lines to surfaces?

Thanks.
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0 ron.kunz over 7 years ago

Dear all,

I would like to know if one can say something about the disc space needed for linear contacts. Is there a "handcalculation" for this? At the moment I have a model of 860000 elements and 740000 nodes. I still have to create a lot of contacts. But I would like to know if it is possible on my current desktop.

Thanks.
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