Learning Forum

[PedroFalcon]

Hi everyone,

I´m new in Ansys, and I’m modeling a buried pipe, so soil has the characteristics as shown in the picture, and I’m giving perpendicular force (15 Kpa) which is perpendicular to the soil block as show in the picture.

Which is the contact that I must use for the contact between the pipe and sand wich represents or described shear strength, through an elastic–perfectly plastic Mohr–Coulomb constitutive model?. Also the friction coefficient in pipe-soil interface is 0.3

 I´ve been using beam bonded (radius 0.457, OD/2 as in the picture 2) for soil, but this, isn't use a friction coefficient.

Regards

Pedro

[peteroznewman]

Hi Pedro,

Do you expect the pipe to not slip in the soil, but just apply shear stress to the soil? If that is the case, then does it matter if you use Bonded Contact or Frictional Contact?

You could certainly pull down on the Bonded setting for Type and change to Frictional and set the friction coefficient to 0.3, but if the pipe doesn't slip, the solution should be almost identical.

If the pipe does slip, then that is the point when the solution might stop converging. Shouldn't the model include Gravity?  If the pipe slipped, the unsupported soil would see a tension force, which Mohr-Coulomb cannot support and the solver would stop.

I'm new to soil modeling, so correct me if I am wrong.

Regards,
Peter

[PedroFalcon]

Hi Peter,

Thank you very much for you reply, well, the problem include gravity, and I would like see sliding soil phenomena that takes place when pipe is subjected to a pull out force, and I would like to see how this effect of soil resistance is dismissed and the magnitude of the pull out force decrease along the pipe length but increase the pipe stress in places near by the applied force .

But according what you´ve said, it means when the slip phenomena occurs, it might have a support condition in the contact region, so Mohr-Coulomb doesn’t works?, does it needs a Druker pragger yield criterion for this?, if so, which is the type of contact that I must have to use in this case???

Regards 

Pedro

 

[peteroznewman]

Hi Pedro,

There are many posts on people using Mohr-Coulomb materials on this site.

Open a browser tab to Google at paste this search request:

   site:studentcommunity.ansys.com mohr-coulomb

and you will get 24 results such as this one.

Regards,
Peter

[Ashish Khemka]

Hi Pedro,

Just a suggestion in addition to Peter's comment - if you are interested in the pipe sliding and frictional effects, then you can define orthotropic friction that is a function of sliding distance (see TBFIELD command).  This needs to be done with APDL Commands objects.

Regards,

Ashish Khemka