Defining the problem #238

lokitkhemka · 2024-12-10T08:37:10Z

lokitkhemka
Dec 10, 2024

I am trying to create a plane-strain problem with quad-elements and monotonic loading. I have nodes that are fixed and nodes that allow only vertical displacements. How can I define the element-type, for the following element line, for example:

element 224 374 375 438 437

where 224 is the element id and 374, 375, 438 and 437 are the node ids. Is the element type CP4?

Also, how can I define the fixed and roller nodes (nodes that have only vertical displacements)?

I was going through triaxial_compression_of_sand example, but I don't understand the table given in the file monotonic

0 0
1 1
10 6

How can I create an equivalent table for increase of load factor from 0.0 to 1.0 from time 0 to 100, for example?

Thank you in advance for any help you can provide.

TLCFEM · 2024-12-10T15:26:08Z

TLCFEM
Dec 10, 2024
Maintainer

For CP4, you do element CP4 224 374 375 438 437 material_tag, leave the thickness as 1 is okay, plane strain is controlled by the material used.
Use PlaneStrain to wrap any 3D material into a plane strain one that can be used with membrane elements.
Define boundary conditions using fix and fix2, fixing both DoF 1 and DoF 2 to have a fixed node, fixing only DoF 1 to allow vertical displacement (if DoF 1 is horizontal axis).
A Tabular amplitude shall contain a table with two columns which defines the curve.

Check those pages and see which part still cannot be understood.

3 replies

lokitkhemka Dec 16, 2024
Author

Hi, I am still not clear about the boundary condition. For example, I have node ids 40 41 that are fixed in all three DoFs and suppose that I have node ids 175 176, that are free only to have vertical displacement, how would I write them in model scripts?

TLCFEM Dec 16, 2024
Maintainer

Why would it have 3 DOFs in a 2D problem using CP4?

fix 1 1 44 45 175 176 ! fix 1st DOF of nodes 44 45 175 176
fix 2 2 44 45 ! fix 2nd DOF of nodes 44 45

Assuming 2 DOFs $u_x$ and $u_y$, nodes 44 45 are fully fixed, nodes 175 176 are rollers.

lokitkhemka Dec 17, 2024
Author

Certain beam elements also have angular dofs, so I was thinking along that angle. Either way, thank you so much for this.

lokitkhemka · 2024-12-11T12:40:38Z

lokitkhemka
Dec 11, 2024
Author

Hi,

I have few questions regarding the Drucker Prager criterion as implemented in suanpan

In the cookbook the yield surface is defined as $\sqrt{J_2} + \eta p - \xi c $, where $\xi$ and $\eta$ are the parameters. The flow surface is defined $\sqrt{J_2} + \bar{\eta} p $. So, in the input file, if I set eta_y and eta_f, will I have the associative flow rule?

Also, comparing the yield equation with the equation in the wikipedia link: $\sqrt{J_2} - A - B I_1$, where $A = \frac{6 c \cos \phi}{\sqrt{3} (3 - \sin \phi)}$ and $B = \frac{2 \cos \phi}{\sqrt{3} (3 - \sin \phi)}$. I can use this equation to compute both $\xi$ and $\eta$ in the form of $\phi$ and $c$ (usually $c$ and $\phi$ are the parameters available to me). Is this approach appropriate? I don't know much about constitutive models, so that is why I am asking to you. However, both the equations need a reference pressure (or hydrostatic pressure) and I see a no way to define it in suanPan (link to the suanpan doc page. I am trying to define Drucker Prager material with no hardening and associative flow rule.

Thank you so much.

24 replies

TLCFEM Dec 21, 2024
Maintainer

I'd like to do so, but I have no time to draft an example based on the inputs.

Ideally, I'd like to have the following elements.

A markdown file that contains the example.
A zip file contains all input files, and one can unzip can run the main script with no additional setup, .txt files shall be renamed to .sp files so that syntax highlighting would work in Sublime Text and VS Code.
Present the context, explain how the model is established (selection of parameters, etc.), and discuss engineering practice implications (comparing with for example what Bishop's method gives).

I am able to do maybe 50% of the above tasks at most.
Are you interested in writing up something, as you clearly know more in this field?
Otherwise I presume it is not going to happen anytime soon.

lokitkhemka Dec 24, 2024
Author

I will spend some time writing it up and maybe you can check, if it works. I am hoping to write it, maybe after the new year, because I have some other work until new years or even until 8th of Jan (I have IELTS on 8th). But, I will try to get working on it as much as I can, in the meantime too.

lokitkhemka Dec 27, 2024
Author

Slope Stability Analysis in Geotechnical Engineering.zip
I have written the documentation for this. Can you please clean it up? It has been a while since I have had to write anything related to geotechnical engineering. I have put the folder in the Example of the docs and hence, the paths of the links are relative to that.

TLCFEM Dec 27, 2024
Maintainer

I made this available here: https://tlcfem.gitbook.io/suanpan-manual/example/geotechnical/slope-analysis
You can find the corresponding page in other deployments.
Revisions if any can be made later.

lokitkhemka Dec 28, 2024
Author

Thank you for allowing me to contributing.

TLCFEM · 2024-12-22T03:16:25Z

TLCFEM
Dec 22, 2024
Maintainer

BTW, feel free to revise the documentation you have read and clarify any existing confusion. I believe it can be improved, and feedback from a reader's perspective would be beneficial.

1 reply

lokitkhemka Dec 24, 2024
Author

I will go through the documentation to see if I can do that too.

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Defining the problem #238

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lokitkhemka Dec 10, 2024

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lokitkhemka
Dec 10, 2024

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