Learning Forum

[yasser1987]

 

Dera All 

 

 

 

i have found a paper that describes how to model a soil with mohr coulomb  and its Boundary condition, but i cannot understand how to apply this kind of boundary condition to my model in Ansys, i mean which options and icons must be used in order to apply and define  the BC and etc

could you please help and guide me to apply the BC to my model?

 

 

Regards

[jj77]

This paper seems to be referring to dynamic analysis including transient waves in soils, where they apply absorbing boundaries, in order to avoid the waves being reflected back into the model.

 

As far as I remember you model was static so you do not need this. You need to go as far as needed from your main area of interest (cap/bucket structure) so that the boundaries do not have any influence on your results.

 

Boundaries are typically perpendicular on a face of the soil domain. At the bottom if you have problems with rigid body movement you could fix the bottom face completely.

An example to show what I mean. So say we have soil in 2D space (xy), y is the gravity direction, then for the two sides of the soil domain, fix x (x is perpendicular to the left and right edges of the model), and for the bottom edge of the soil fix y (y is perpendicular to the bottom edge of the model).

 

Another example for the model shown in your image.

[yasser1987]

Dear jj77

 

 

This is my model with big boundary condition (the real one should have been 24.5 meter but this one is 100meter ) in order to dissipate the effect of  defined failure criteria  with fixed support around the boundary 

 

 

but as you explained me in the previous post 

i have tried to use others supports such as cylindrical and compression only support beside fixed support but more or less i got the same respond and error as well 

this picture shows the available support for the model, could you please suggest me which one of them should be used in order to define the boundary condition that you have already introduced me in the previous post,

 

actually, i do not know how i can apply this restriction that you defined to my model, which icons or options , i just followed the support icon to  apply the boundary 

is there another way to apply the BC  ?

 

Best regards

 

[jj77]

I hope you understood the theory I described with regards to BC.

 

As for your domain size normally you will do a sensitivity study, to see how big it needs to be, so you can start up with smaller one an increase gradually.

 

As for the BC, normal to a face below is shown how you can do it for the cylindrical outer face of the domain (as for the bottom face I would just fix it).

[yasser1987]

Many thanks 

 

i made the changes as you mentioned and i have run it , i got these messages 

Any idea about it?

[jj77]

It means that the model is not converging, could be due to many reasons (contacts, soil,..).

 Again since we are now moving in to another area (we are almost there now), could you again close this one (Is solution), and start a new post/one for the convergence problem.

 

In the new post please include your model (please make sure it is not too large because I have only a student licence which is node limited), and I will have a look for you.,

[yasser1987]

Many thanks

[Huan19Han]

You should use APDL-Snippets with the element combin14.  

[yasser1987]

Dear Huan19han 

 

could you explain it a little bit more, since i am struggling with it and Not solved yet

[Huan19Han]

First you should use named selection to choose the surface.

Then use the snippet to create the spring. 

The snippet looks like this:

/prep7

! Define the material parameter and coefficient.

! define the array to store the coefficient for each spring.

! select node of the surface which you chose (use ndnext)

! calculate the area attached to the each node of the surface which you chose (use ARNODE).

! calculate coefficients for each spring

! store the coefficients in the array.

! define 3 new points for each node in x, y, z direction respectively

! create spring (combin14)

 

[shiv]

Many thanks 

 

i made the changes as you mentioned and i have run it , i got these messages 

Any idea about it?

 

This is possible because of the element type you are using. As I remember, your model is using Mohr-Coulomb which means your model is brittle in nature. So I recommend you to use SOLID65 as the element type in your model. You can call it in using APDL Macros inside Mechanical workbench. 

 

And since you are trying to execute a seismic analysis( look like that from the image(model) you shared). Please use transient analysis system and instead of modelling the large boundary as cylindrical, model it as a cubical shape, then define symmetric boundary on the outside surface of the large boundary. This will give you a perfect result. I once validated using this modelling technique for a seismic analysis. 

[SriVin]

Huan19Han

Can you please describe the procedure to create such a boundary in workbench !

Right now I can use damper along anyone of axis and set the damping. I can't put dampers along 3 axes as per requirement. Ansys shows a warning and in solution information it says, few of constraints will be ignored.

[ali.ismail]

I'm using a student version of Ansys workbench and I have the problem of "The solver engine was unable to converge on a solution" while using Mohr-Coulomb to define a soil with very low cohesion. I will be very grateful if anyone tells me what to do asap