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1d elements with varying cross section

Hi everyone,

I have a question about 1d element with varying cross section. Is it possible to use such elements with optistruct?

I have tried CBEAM as an element and property PBEAML, I ve tried everything and I cant figure it out.

I ve tried using the PBEAML card option 'pbeamlintstationslen' for dividing element into different cross sections but it doenst work.

Can anyone guide me on this subject?

Thank you very much for your time,

Gonçalo

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Altair Forum User

Hi,

OptiStruct has predefined beam shapes and varying cross section beam is not one of them.

You can create generic shapes using HyperBeam module.

Altair Forum User

Hi Prakash,

Thank you very much for your answer.

But is it possible to have 1d elements with varying cross section?

I've read in 'Practical Aspects of Finite Element Simulation' that this is possible using taper elements. I've read aswell in the internet that there is possible to make this in hypermesh, but never explain how it's done.

Thank you again,

Best regards,

Gonçalo

tinh

Hi Prakash,

Thank you very much for your answer.

But is it possible to have 1d elements with varying cross section?

I've read in 'Practical Aspects of Finite Element Simulation' that this is possible using taper elements. I've read aswell in the internet that there is possible to make this in hypermesh, but never explain how it's done.

Thank you again,

Best regards,

Gonçalo

It is possible and right method you used pbeamlstationslen

what do you mean by 'it doesn't work'?

You have to specify cross section DIMs at distance X/XB from A

Visualization may not show varying cross section.

Altair Forum User

Tinh thank you very much for your answer,

I've used that method, but it's not possible to visualize so I assumed it wasn't working.

Using PBEAML element prop, Beam Section is unspecified and pbeamlstationslen = 2.

Then I will define 2 sections (equal HyperBeam pre-defined shape, diferent DIM), first in x/xb=0 and next x/xb=1.

Is this correct?

is it possible then to assign a size variable to each section used and optimize a varying section beam?

Thank you very much,

Best regards,

Gonçalo

Rahul Rajan_21763

Hi Prakash,

Thank you very much for your answer.

But is it possible to have 1d elements with varying cross section?

I've read in 'Practical Aspects of Finite Element Simulation' that this is possible using taper elements. I've read aswell in the internet that there is possible to make this in hypermesh, but never explain how it's done.

Thank you again,

Best regards,

Gonçalo

Hypermesh is a pre processor for major finite element solver.Looks like that option of varying cross section was wrt to Ideas solver.I believe that they have stopped development for Ideas solver 5-6 yrs back.As Prakash said try for generic shapes using Optistruct.

Altair Forum User

Rahul thank you for your answer,

I dont know if I'm making myself clear on explaining my doubt. What I want is a varying cross section across the length of the element, with the same generic shape of HyperBeam, only changing DIM's.

As Tinh said, i can use PBEAML 'pbeamlstationslen' option. But there is some missing steps as i mentioned in my last comment above.

Thank you for your time,

Best regards,

Gonçalo

Rahul Rajan_21763

PBEAML card and defined different section .As far as I know, tapered beam sections cannot be rendered in 3D for visulaztion.Check user guide for detailed information.Also if possible you can share hm or fem file for better understanding.

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

Altair Forum User

Rahul thank you for your answer,

Yes, it's exactly what I'm looking for. I wanted to know if this is possible because I'll model a structure using this for the next step of my project.

I've already achieved this point.

But i do have three questions:

1-Do I have to use a Beam section outside of the 'pbeamlstationslen' option? (I see that you are using, defined as DIM1A)

2- Shouldnt the Xi_Xb(1) be 0? (it's the ratio of x coordinate of the element to place section/ element length rigth?)

3- Or, it's enough to use DIM1A as a starting section of the element and a pbeamlstationslen = 1 and use a different section in Xi_Xb(1)=1 to define the ending section of the element?

Thank you very much for the help,

Best regards,

Gonçalo

tinh

DIMA is cross section' size at node A and X/XB is distance from A/length

so you dont need to set x/xb=0 , just set x/xb=1 for tapered beam

visualization will not show tapered shape, as Rahul commented

Altair Forum User

Ok, that answers my question. Thank you very much for your answers, helped a lot.

Best regards,

Gonçalo

Altair Forum User

Hi everyone,

Sorry to bring this topic back up.

I already know how to do it and it works fine.

But when I request CBEAM element stress in the DCEF points of the section, what the program uses to calculate tensions in element nodes are the element center section.

The loads used are correct the only problem is that i get bad Stress readings in the nodes because it does not use the correct section properties.

I've confirmed this by hand.

Is there a way to make the program use the A and B section props when calculating stresses? It's not a big problem, but it's time consuming to check stresses with real properties.

Best regards,

Gonçalo

tinh

hi,

try setting field SO(i) in pbeaml card, it is for stress output

Altair Forum User

Hi tinh,

Thank you for your answer.

The SO (stress output) is on.

When the software makes the rigidity matrix, does it use an section variable element formulation or does it simplify by using the element middle cross section?

Because this first option has a very high computanional cost and by the result I'm getting, I'm thinking the software simplifies by using element mid section.

Please correct me if I'm wrong.

In this case I need to use a lot of elements to model it and create properties for each element?

Best regards,

Gonçalo

Altair Forum User

Hi,

I've been looking into the reference guide and I found this statement:

6 - For tapered beams, a single prismatic beam is created with dimensions obtained by

weighted averaging of all station dimensions.

So I guess this element will not be very helpfull for my need.

Sorry for re-opening the topic.

Best regards,

Gonçalo

tinh

yes, i think you should use 3d mesh if you need to capture detail your structure