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[Christian Jakob <1362090@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Hi,

I want to get the pore pressure of a saturated soil sample in an
undrained triaxial test when the sample volume is decreasing.

...
TriaxialStressController(thickness=0,stressMask=7,internalCompaction=False,label='triax')
...

	triax.goal1 = 35000
	triax.goal2 = 35000
	triax.goal3 = 70000
	triax.wall_back_activated = False
...
	flow.viscosity = 1.3e-3
	flow.fluidBulkModulus = 2e9
	flow.bndCondValue=[0,0,0,0,0,0]
	flow.bndCondIsPressure=[0,0,0,0,0,0]
...

For one of my simulations a decrease of ca. 1,8 % in porosity (=-dV/V)
is obtained. When I calculate corresponding pressure increase I get

dp = K*(-dV/V) = 2e9*0.018 = 36000000 Pa

But the output from PFV shows maximum average pressures around of 16 Pa
(not MPa!). As long as I use SI units the output of
flow.averagePressure() should be Pa, right?

So is there a problem in the code or did I miss something in the
compressibility option of PFV?

regards,

christian


###additional info:

I double-checked my script and did not see anything wrong. So I think it
is on C++ side. So I was going on testing PFV method:

I also tested a drained situation with incompressible fluid. The porosity is decreasing due to a triggered collapse of the grain structure, but the pore pressure gets negative (see attachment).
So I think it is a bug in pressure calculation of PFV method.

** Affects: yade
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1362090

Title:
  problem with pressure calculation in PFV cells

Status in Yet Another Dynamic Engine:
  New

Bug description:
  Hi,

  I want to get the pore pressure of a saturated soil sample in an
  undrained triaxial test when the sample volume is decreasing.

  ...
  TriaxialStressController(thickness=0,stressMask=7,internalCompaction=False,label='triax')
  ...

  	triax.goal1 = 35000
  	triax.goal2 = 35000
  	triax.goal3 = 70000
  	triax.wall_back_activated = False
  ...
  	flow.viscosity = 1.3e-3
  	flow.fluidBulkModulus = 2e9
  	flow.bndCondValue=[0,0,0,0,0,0]
  	flow.bndCondIsPressure=[0,0,0,0,0,0]
  ...

  For one of my simulations a decrease of ca. 1,8 % in porosity (=-dV/V)
  is obtained. When I calculate corresponding pressure increase I get

  dp = K*(-dV/V) = 2e9*0.018 = 36000000 Pa

  But the output from PFV shows maximum average pressures around of 16
  Pa (not MPa!). As long as I use SI units the output of
  flow.averagePressure() should be Pa, right?

  So is there a problem in the code or did I miss something in the
  compressibility option of PFV?

  regards,

  christian

  
  ###additional info:

  I double-checked my script and did not see anything wrong. So I think
  it is on C++ side. So I was going on testing PFV method:

  I also tested a drained situation with incompressible fluid. The porosity is decreasing due to a triggered collapse of the grain structure, but the pore pressure gets negative (see attachment).
  So I think it is a bug in pressure calculation of PFV method.

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