Hydraulic boundary conditions

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angelo.lambrughi
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Joined: Fri Mar 04, 2011 3:48 am
Location: SOIL srl

Hydraulic boundary conditions

Post by angelo.lambrughi » Tue May 24, 2011 12:00 am

Dear all,

I've been studying/using OPENSEES in the past few weeks, with the intention of performing a dynamic analysis of a 2D model of a submerged slope.

I found OPENSEES a very powerful tool for this purpose. In addition, the example contained in the "Example Manual" is very similar to my case and help me a lot in the make up of my numerical model.

However, I can't find a straightforward way to assign non-null fixed values of the pore-pressure variable along the upper "wet" boundary of my slope. At these nodes, I'd like to assign a constant, hydrostatic value of the pore pressure, so that this value won't change during the analysis.

Anyone can help?

Thank you and regards,

Angelo Lambrughi

P.S. after a few hours of tests and manual reading, it looks like that the best way to assign fixed values of the pore pressure variable at the boundary is by means of the "pattern + sp" commands. I tried this option with a very basic model (2 elements) and it works well with the assignment of fixed values for displacements. However, it doesn't work properly when it comes to pore pressures. Any clue?

hsafti
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Location: Braunschweig

Re: Hydraulic boundary conditions

Post by hsafti » Wed Jun 15, 2011 12:02 am

Hi Angelo

I have the same problem. I confirm that the (sp) command does not work for the 3rd DOF for the quadUP element. I hope for advise on that matter as well.

I add that ... introducing pore pressure as a load works well but through (sp) command (at the same point) causes the dynamic analysis to "halt" ... OpenSees uses a lot of computer resources but the solution does not advance and no messages what so ever.

Introducing the sp command for the pore pressure at a point on a null hydraulic boundary causes no problem in solution (However, of course, the point pore pressure is set to zero at all time)

What I want to do is to be able to define pore pressure at soil surface through a PathTimeSeries instead of having a constant or null value.

Best regards,
Hisham El Safti

fmk
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Re: Hydraulic boundary conditions

Post by fmk » Wed Jun 15, 2011 8:28 pm

the sp command should be able to set a non-homogeneous time-varying value when used inside a LoadPattern for the 3'rd dof when ndf >= 3 .. if this happens to be the pore pressure, so be it .. if the resulting boundary condition shows a 0 value for this quantity it means you used the Plain constraint handler which cannot handle no-homo constraints .. if the analysis is failing, the problem lies in your model or the elements not being able to handle this .. looking at the update method in the fourNodeQuadUP it should
be able to use it .. the question is can the material take this strain.

i might suggest using the new SSPQuadUP element in the newest release 2.3.0 . if it fails then post a message and i can get the author of that element to help you better.

hsafti
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Re: Hydraulic boundary conditions

Post by hsafti » Fri Jun 17, 2011 11:58 am

Hi Frank

From the code of the SSPquadUP element:

SSPquadUP::SSPquadUP(int tag, int Nd1, int Nd2, int Nd3, int Nd4, NDMaterial &theMat, double thick, double Kf, double Rf, double k1, double k2, double eVoid, double alpha, double b1, double b2)

It is hard to figure out what some of these parameters mean. Is there an update for the manual? An example would be real handy in such situation.

Thanks a lot for your effort and time.

Best regards,
Hisham El Safti

hsafti
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Location: Braunschweig

Re: Hydraulic boundary conditions

Post by hsafti » Fri Jun 17, 2011 12:05 pm

Does this element support Template Elasto-Plastic Material of UC Davis?
Hisham El Safti

fmk
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Re: Hydraulic boundary conditions

Post by fmk » Fri Jun 17, 2011 12:36 pm

they should .. you could write a simple experiment to test .. have you tried one of the other materials to see if your problem is not elated to the Template material!

hsafti
Posts: 68
Joined: Thu Apr 22, 2010 5:38 am
Location: Braunschweig

Re: Hydraulic boundary conditions

Post by hsafti » Fri Jun 17, 2011 12:48 pm

I am using the nDmaterial model by San Diago ... The Template Elasto-plastic material is only supported by the block elements as far as I understand (not the quadUP) that's why I ask


I cannot form the SSPquadUP element command. Therefore, I need an example or a manual entry on the element


OpenSees halts when I use nDpressuredependent. When using nDpressure independent the analysis completes and it seems correct. HOWEVER, the first 170 steps (3.45 sec) the solution gives radical displacements and pore pressures that are not supposed to happen because I applied only slight pore pressure change. After that time the problem seems to be OK. All in all, something is wrong with both material models.

Nevertheless, I need a pressure dependent soil model because I'm modelling sand.
Hisham El Safti

hsafti
Posts: 68
Joined: Thu Apr 22, 2010 5:38 am
Location: Braunschweig

Re: Hydraulic boundary conditions

Post by hsafti » Sat Jun 18, 2011 6:46 am

I've tried the BrickUP element (imposing zero displacement out of plane). The nD materials gave identical behavior as for the case of the quadUP element (OpenSees 2.2). OpenSees 2.3 have trouble running the brickUP element ... even the example (24) provided in the website (http://cyclic.ucsd.edu/opensees/).

I tried to define a Template3Dep material model for the BrickUP elements (I obtained the definition of elements from a presentation of Prof. Boris Jeremić [no modifications]) ..... Neither 2.2 nor 2.3 ran ... They just halt as the material model is defined (consuming computer resources infinitely until process is manually terminated)....

I need help on this ... I invested a lot of time in OpenSees and I really wish to go forward with my research using OpenSees!

I cannot formulate the command for the new SSPquadUP element (provide information please).

Thanks for your time (I can provide the tcl files)
Hisham El Safti

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