cbush methodology for rear axle-supension link

gopal_rathore

Hi,

I have attached an image for reference. The main objective is to convert a 3D rear axle suspension into a 1d element representation.

 

Kindly let ,me know about it.

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

Hi Gopal,

 

it is possible to have a zero length CBUSH element (GA1 and GA2 coincident) 

 

But you need to define CID in CBUSH card when GA and GB coincides to define axis of the 1D element.

' If GA and GB are coincident, or if GB is blank, CID must be specified. If GB is set to blank, the CBUSH simulates a grounded bushing element.'

 

Please refer to CBUSH card description for more details

 

 

gopal_rathore

Hi Prakash,

In this case, element is not of zero length. As CBUSH will be formed between GA and GB  and here both are at distance., You can refer image for it.

 

Thank you.

Altair Forum User

Gopal,

 

Sorry, I thought same element is on coincident nodes.

 

Yes, Please refer to the attached model where a single is shared by two CBUSH elements. 

Unable to find an attachment - read this blog

gopal_rathore

HI,

Thank you for the file.

You have also assigned a LCS for the spring element. If we give no CID then also will it take the Global coordinate system right.

Also have you gone through the methodology for it , any viewpoints you have on it.

Altair Forum User

Gopal,

 

I feel the FE realization matches.

 

The vector has to be defined either through GO ,or Xi or CID.

From help:

For noncoincident grids (GA ≠ GB), if neither GO or (X1, X2, X3) is specified and no CID is specified, the line AB is the element x-axis. This option is valid only when K1 or K4 or both on the PBUSH entry are specified (but K2, K3, K5, and K6 are not specified). If K2, K3, K5, or K6 are specified, the solver will terminate with an error. 

gopal_rathore

Hi,

Thank you for your response.

I was running the above file cbush.fem and there are certain doubts over it. I have attached the image for it.

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

Gopal,

 

I noticed it, If I give any stiffness along loading direction, I see results for both elements.

 

I am checking the same with experts and will get back to you soon. 

Altair Forum User

 

Gopal,

 

I think what we are seeing is correct. Element with zero stiffness will have zero deformation. ((Delta= Load*Length)/A*E). So you need to provide some stiffness to the element to see deformation.

gopal_rathore

Hi,

From above equation,

Delta = Load/Stiffness where stiffness =AE/l

so when stiffness tends tends to zero , delta tends to infinity. 

Correct me in case of any part missed.

Altair Forum User

Altair Forum User said:

so when stiffness tends tends to zero , delta tends to infinity. 

Gopal,

 

Yes, I think I messed up with the equation. Let me check and I will get back to you. 

Altair Forum User

Gopal,

 

Looks like a bug. But when I have stiffness the results matches with hand calculations. 

 

I will report this to devs.