Warning Messages

[pjuneja]

Hi,

I am simulating the deformation of breast under gravity. I initially have patent's breast images in one position (supine, with breast falling on the chest). I am applying gravity loading and simulate breast image in another position (prone, with breast falling away from the chest).

I am using C3D4H elements, in non-linear deformation using ABAQUS Static General analysis

In almost all cases am getting following warning messages:

C3d4h and c3d10i elements will enforce pressure continuity across material boundaries. In order to allow discontinuities in the volumetric field use *tie.

The gravity vector has changed for some elements. Only changes in magnitude will be ramped over the step, not changes in the vector.

Can someone please explain me these or their consequence on simulation results.

thanks
Prab

 

[mahsaa]

Hi Prab,
Regarding the magnitude of gravity force, it is better to take advantage of "body force" to represent the gravity force. However, to make the magnitude of a force constant you should create a table, such as t(0)= force, t(timestep)= force (Do not use ramp option).
Good luck,
-Mahsa Ghaffari

 

[IceBreakerSours]

Short answer: I do not know.

Long answer: I do not know but I can make guesses.

The gravity vector has changed for some elements. Only changes in magnitude will be ramped over the step, not changes in the vector.

This message seems benign. It seems to effectively suggest that the direction of the gravity vector is not going to change but the magnitude will simply be ramped up to the gravity constant provided by you. I don't see any reason for concern in the context of your particular model.

C3d4h and c3d10i elements will enforce pressure continuity across material boundaries. In order to allow discontinuities in the volumetric field use *tie.

Question: Are there any material boundaries? Is there any appreciable/significant interaction at the boundary? If so, how have you defined it? For example, does the breast touch the skin of the ribcage under gravity loading?

If you can, upload the inp/cae for folks to be able to best help you. If not, you could try and explain a little more about the model.

http://www.eng-tips.com/faqs.cfm?fid=376

 

[IceBreakerSours]

I forgot to add: Once you resolve your concerns, please let the rest of us know too.

http://www.eng-tips.com/faqs.cfm?fid=376

 

[pjuneja]

Thanks for the response and suggestions. Attached is CAE file (

https://lft.icr.ac.uk/

http://www/?a=d&i=4402636728)

@mahsa: I tried using tabular as suggested by you. I didn't get the magnitude of gravity force warning anymore. Given that am newbie at FEM I used the option of gravity force I will look into using "body force" as suggested by you.

@IceBreakerSours: I am taking bottom-up approach to increase complexity of breast model. Currently am not modeling skin and other regions of breast, am considering breast to be homogeneous tissue and applying fixed (encastre) BC to nodes at the chest wall and in addition applying gravity to recover reference state (ref_st step) and again gravity in direction of chest wall to nipple to simulate prone position (prone_st step).

Thanks
Prab

 

[IceBreakerSours]

The CAE was created in an older version. You might want to upload an INP.

http://www.eng-tips.com/faqs.cfm?fid=376

 

[mahsaa]

@Prab: you use student version of abaqus. Follow jobs> write input then attach .inp file.

@IceBreakerSource: Many thanks for your helpful suggestion in this forum. I'd be so grateful if you could take a look at my question in forum. I really need an expert to help me. TNXS

 

[pjuneja]

Attached is the input file.