Reduction Methods with CMSMETH

Altair Forum User

Hello,

I finally solved the problem with creating MNF Files for ADAMS with CB and CC Method.

But I wanted to analyse the reduction methods, without creating MNF, with the Guyan, GM and CBN Method. What cards I have to activate and which settings I have to use in CMSMETH Card to get modes and frequenzies out of the these reduction methods? For example i have to set a starting node with SPID but it still don't work.

 

An other problem is to find something about the reduction method CBG? I didn't find anything in the help? Is it similar to CB or CC or what are the differences?

Altair Forum User

Hi ErikBa,

 

Maybe you should look at Direct Matrix Input  in help.

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Altair Forum User

Hello,

 

Yes I aready tried all of these help files and tutorials, but I didn't get it work.

Can you have a short look at my model?

Altair Forum User

Erik,

 

Please share the model using the dropbox link in my signature.

Altair Forum User

Hi Erik,

 

thanks for sharing the file. I will check and update to you ASAP!!

Altair Forum User

Hi Erik,

 

FLex body generation is limited to CC and CB methods and frequencies are only calculated for these methods.

Altair Forum User

Altair Forum User said:

Hi Erik,

 

FLex body generation is limited to CC and CB methods and frequencies are only calculated for these methods.

Hello,

Yes I know but i wanted to analyse these reduction methods to see the differences in frequenzies and eigenmodes. I don't want to build up a flex body for use in multi body tools.

So please can u help me to see the values for these already mentioned parameters?

Altair Forum User

Hi Erik,

 

Unfortunaltely, Normal modes are ignored when using GUYAN method in CMS, but the frquencies can be seen in H3D file.Let me try with CBN method.

Altair Forum User

Hello,

Yeah with Guyan Method I get some Frequenzies which I can not get a defined sequence.

By using GM or CBN I get a fatal error message. I hope you can send me back a working file.

Altair Forum User

Hi Erik,

 

Yeah, with GUYAN there is no way to output normal mode frequencies. I will check with experts on this.

Altair Forum User

Altair Forum User said:

Hi Erik,

 

Yeah, with GUYAN there is no way to output normal mode frequencies. I will check with experts on this.

I found another Problem by using Craig-Chang method.

When I read the basics about CC Mehtod there is no need to add any constraints, because it is an free-free method. So without any constraints I get the same frequencies when I use the craig-bampton method without any constraint. Why is it possible to use CB Method without constraints or does he automatically switch to CC-method?

 

Maybe I have to use an other load collector for CC method? I know that I must use ASET for CB method and define the constraint where i attache my body. In help I found that I have to use CSET or BNDFREE for CC method but then I get an error message that these two load types are not allowed for CMS methods.

 

So my question is how to use the Craig-Chang method in a right way?

 

The other questions, mentioned in my posts before, are still up to date ;-)

Altair Forum User

Hi ErikBa,

 

I will check with experts on how to get mode numbers with GUYAN method.

 

I will try rh CC and CB method as you have done and will update the results with you.

Altair Forum User

Hi Erik,

 

CB method has two approaches. One is free-free mode and the other is constrained mode..

 

Where as CC has  free-interface modes, i.e. the component is considered un-constrained at its interface DoF.

 

So there is no difference in frequencies when using CC or CB without constraints, I assume

 

The better way to use CC is again without any constraints. Even though if you have constraints, it will treated as a rigid body mode, I guess.

Altair Forum User

Hello Prakash,

Thank you very much. So there is only one problem left. How to get frequencies form Guyan (CBN) and GM reduction methods? I hope you can surf the problem.

Altair Forum User

Hi Erik,

 

I checked with experts about this. 

 

For GUYAN, GM and CBN, the usage of these methods are FEA purpose. which means there is no way to output frequencies for now.

Altair Forum User

Altair Forum User said:

Hi Erik,

 

I checked with experts about this. 

 

For GUYAN, GM and CBN, the usage of these methods are FEA purpose. which means there is no way to output frequencies for now.

Hello Prakash,

Thank you very much for all your efforts.

But know I'am interested how to use these methods for FEA purpose. That's because I need a good explanation why I can't compare these methods with CB or CC. So how can I use them with CMSMETH card, or isn't it possible?

 

Another question was about the CBG method. What are the differents between CBG and CBN?

Altair Forum User

Hi Erik,

 

GUYAN, CBN methods can be used to reduce the model matrix. You can either write the matrix to a nastran punch file or to h3d file.

 

Imagine you have huge automotive structure which is very large and dont want to include everything for your analysis. Using Dynamic reduction methods you can simplify the model.

Altair Forum User

Ok Thank you,

Now there is only the question about the CBG Method left. I can't find anything in the help files. So what are the differents between CBG and CB or CC

LOKESH KATARI

Hello sir 

 

can you exactly tell me what is the use of SPID_INT in creation of FBI files?

 

Altair Forum User

 It is useful when you have CMSOUT which takes the starting point used in CMS matrix.