yade-dev team mailing list archive

[Christian Jakob <1362090@xxxxxxxxxxxxxxxxxx>]

i send you a "small" version of my script. step 1 took around 8 minutes to prepare the sample.
the final calc. is unfortunately running for ca. 2 hours. i hope this is ok for testing ...

what i see is, that for small increase or decrease of porosity, the
pressure is ok (like in the beginning of the calc.):

p: 0.0785083522065 /poro: 48.1453194129
p: 0.0861023388763 /poro: 48.1453043476
p: 0.0870515283585 /poro: 48.1452806796
p: 0.124337357905 /poro: 48.1452662981
p: 0.134103911243 /poro: 48.1452555768
p: 0.134944854374 /poro: 48.1452507787
p: 0.13938079395 /poro: 48.1452458346
p: 0.141438612959 /poro: 48.145242923
p: 0.152935808325 /poro: 48.1452409334

...

but when the grain structure collapses, pressure calculation does not
work correctly anymore:

p: 11.42792547 /poro: 48.1451353243
p: 11.4313053052 /poro: 48.1451358473
p: 11.4343726311 /poro: 48.1451363719
p: 11.4371363766 /poro: 48.1451368869
p: 11.4392032959 /poro: 48.1451373207
p: 11.4424940715 /poro: 48.145137852
p: 8.11778479291 /poro: 48.1448508288
p: 9.8711045028 /poro: 48.1447914659
p: 10.7528636056 /poro: 48.1450854371
p: 10.5477578602 /poro: 48.1447098899
p: 8.11642447213 /poro: 48.1465865647
p: 6.99041462318 /poro: 48.1486620985
p: 8.99533593814 /poro: 48.1506954255
p: 7.83218662093 /poro: 48.1531095185
p: 8.69203259997 /poro: 48.154684897
p: 11.6359525072 /poro: 48.1548101512
p: 12.2310464532 /poro: 48.1519503998
p: 11.8209039334 /poro: 48.1508466024
p: 10.41266522 /poro: 48.1496083854
p: 13.8113509815 /poro: 48.1501534546
p: 11.7659257219 /poro: 48.1449743123
p: 11.3078736187 /poro: 48.1416428342
p: 11.7379254629 /poro: 48.1358210037
p: 7.75968666335 /poro: 48.1314928616
p: 9.11740236569 /poro: 48.1293477162
p: 9.30441402016 /poro: 48.1290937942
p: 10.6806525624 /poro: 48.1307995448
p: 10.256471075 /poro: 48.1334583699
p: 11.1890787209 /poro: 48.1358109485

...

p: 27.3255613877 /poro: 48.1124053232
p: 18.8932169787 /poro: 48.0921313593
p: 25.0517632071 /poro: 48.0918358101
p: 30.6684972931 /poro: 48.0860760522
p: 24.5449112901 /poro: 48.0819263772
p: 22.9203772051 /poro: 48.081861069
p: 23.4897854262 /poro: 48.0809934653
p: 30.0214400989 /poro: 48.0765479153
p: 28.6346694789 /poro: 48.0705626027
p: 30.475391 /poro: 48.0628890719
p: 27.1475228671 /poro: 48.0583210558
p: 29.2405442094 /poro: 48.0497216434
p: 25.9130183935 /poro: 48.0443911735
p: 20.737201863 /poro: 48.0378116206
p: 27.6899778636 /poro: 48.035147687
p: 27.2237453694 /poro: 48.0277675295
p: 29.6125202476 /poro: 48.0245254687
p: 27.7152319951 /poro: 48.018681696
p: 27.2864857718 /poro: 48.0154804492
p: 24.0510331304 /poro: 48.0148798888
p: 23.9897576147 /poro: 48.0158389365
p: 23.9914264679 /poro: 48.0165658403
p: 26.6901780408 /poro: 48.0155119429
p: 24.9508433898 /poro: 48.0144790611
p: 28.3914458976 /poro: 48.0112270994
p: 26.2457685113 /poro: 48.0033967489
p: 28.4702987162 /poro: 47.9955400221
p: 30.7188956685 /poro: 47.9883818643
p: 28.8575853606 /poro: 47.9814830293

...

p: 106.320892489 /poro: 46.75595998
p: 106.306309536 /poro: 46.7559601475
p: 106.294913322 /poro: 46.7559601918
p: 106.285210065 /poro: 46.7559603014
p: 106.273826458 /poro: 46.7559605049
p: 106.263787039 /poro: 46.7559605891
p: 106.251639788 /poro: 46.7559606068 (end)

so there is a porosity decrease around 1.35 %, but it is not reflected
in increase of p.


regards,

c

** Attachment added: "reproduce bug (takes around 2 hours)"
   https://bugs.launchpad.net/yade/+bug/1362090/+attachment/4188766/+files/pfv-bug-cell-pressure-too-low.py

-- 
You received this bug notification because you are a member of Yade
developers, which is subscribed to Yade.
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.

To manage notifications about this bug go to:
https://bugs.launchpad.net/yade/+bug/1362090/+subscriptions