Element Stresses Optimization (Linear Static)

Keonkim1991

My model is a simple 1D PBEAML element structure (BOX beam sections) assigned for linear static analysis.

I was able to assign design variables and property relationships for beam thickness 1 & 2.

Then I assigned the optimization response for all nodes and constrainted them by lower/upper bounds ±25.4 mm under the objective of minimizing mass.

With these steps, I was able to reduce the weight of the structure as well as meeting my displacement design criteria as closest as possible.

 

However, the issue is now the stress increased beyond the yield strength. So I went back to my model and added the optimization reponse for static stress for all properties and constrained them with lower/upper bounds -234.4 MPa and 289.6 MPa (compressive and tensile yield strength). I made sure the response and loadsteps are assigned to the optimization constrain properly. After running the optimization, I checked the results in Hyperview, but it doesn't seem like the stress part hasn't been assigned correctly.

 

I'm specifically looking for constrainting Element Stresses (1D) (s) - CBAR/CBEAM Axial Stress. It seems like there are other types of stress you can assign besides the static stress, such as frf stress and psd stress? Please help me.

Altair Forum User

Hi,

 

Can you please share the .out files?

 

Also, For CBAR, CBEAM, stresses are normal (axial) stresses for the element.

Keonkim1991

Hi Prakash, 

 

I'm not allowed to distribute any of my files due to company's confidentiality.

I know the definition of CBAR/CBEAM axial stress, but my question is to know how to properly assign optimization response/constraint for this matter, just like how I was able to optimize the minimized mass with the displacement criteria.

 

Below are optimization reponse and constrain that I've assigned to the model. 

 

Altair Forum User

HI,

 

Constrain looks fine. 

 

Apart from beam elements do you have anything else in your model?

If yes, can you only contour beam elements and check the stress range?

 

 

Keonkim1991

it's 100% beam elements with 1 RBE3 element that was used for attached object's CG where assign axial load.

Below figure is a contour plot for element stresses (1D) (CBAR/CBEAM Axial Stress). It's within the criteria I've assigned, but still, way too low (tension = 40.1 MPa, compression = 98.8 MPa). I understand displacement response/variables play a role to determine the stress results. But I want it to be as close as possible to my criteria (tension = 289.6 MPa, compression = -234.4 MPa).

 

 

 

 

Altair Forum User

HI @Keonkim1991

 

I will try on a sample model with your approach and I will share my feedback soon. 

Keonkim1991

Thank you Prakash. Please let me know. Have a great week.

Altair Forum User

HI,

 

I am unable to reproduce a similar case. 

 

Is there any design and non-design space in your model with 1D elements?

 

What are all responses you have on your model?

Keonkim1991

High Prakash,

 

Sorry for late reply. What do you mean by design and non-design space? 

 

My model is consist of 1D elements (PBEAM) with the cross section area (BOX: 50.8 x 25.4 x 5.0 x 5.0 mm).

I have optimization responses of total mass, total displacement, and static stress. Displacement and stress were constrainted under the objective of minimizing the mass.