[CIG-SHORT] Maxwell bulk rheology behavior in v1.3.1 versus v1.4.2
Ikuo Cho
ikuo-chou at aist.go.jp
Thu Apr 1 14:16:31 PDT 2010
Brad,
> This is consistent with the
> stable time step for MaxwellIsotropic3D of 0.028 years (0.2 times the
> Maxwell time of 0.14 years). Increasing the viscosity to 7.1e+19 results
> in the stresses relaxing over a much longer time scale.
I see.
By the way, the most important problem I wanted to solve when I ran
PyLith1.4.2 is:
>*info.vtk indicates that medium properties have been read correctly, but
>the way stresses attenuate apparently doesn't reflect the given
>inhomogeneities and absolute values of the viscosity coefficients.
I provide some figures of the calculation results by PyLith1.4.2 to
illustrate this (FIG.pdf). I solved the example problem dislocation.cfg
in pylith-1.4.2/examples/3d/hex8, where the medium was changed to have
two values of viscosity coefficients, 10**18 and 10**20.
Here is what I did.
1) Place eight files (one cfg file and seven spatialdb files) in the
exercise directory pylith-1.4.2/examples/3d/hex8.
2) Execute PyLith1.4.2 by typing:
cd pylith-1.4.2/examples/3d/hex8
pylith dislocation_1.4.2.cfg
3) Repeat running PyLith with changing the parameter "db_properties.iohandler.filename"
in dislocation_1.4.2.cfg (by 3d_*1.4.2.spatialdb or mat_*1.4.2.spatialdb).
The calculation results reflect the influences of viscosity coefficient
10**20 everywhere when I used 3d_x1.4.2.spatialdb and 3d_y1.4.2.spatialdb, while the
calculation results
reflect the influences of viscosity coefficient 10**18 everywhere when I
used 3d_xi1.4.2.spatialdb and 3d_yi1.4.2.spatialdb. They look
intuitively correct only when I gave variations of the viscosity
coefficients in the z direction (mat_*1.4.2.spatialdb and
3d_z1.4.2.spatialdb).
I'd like to know the reason why I cannot obtain reasonable results by
PyLith1.4.2. Could you tell me where I mistook the description of the
parameters for pylith (if any)?
Ikuo
On Thu, 01 Apr 2010 08:20:21 -0700
Brad Aagaard <baagaard at usgs.gov> wrote:
> Ikuo-
>
> The test problem you provided had viscosities as low as 1e+17, which
> corresponds to Maxwell times of 0.14 years. This is consistent with the
> stable time step for MaxwellIsotropic3D of 0.028 years (0.2 times the
> Maxwell time of 0.14 years). Increasing the viscosity to 7.1e+19 results
> in the stresses relaxing over a much longer time scale.
>
> Brad
>
>
>
>
> Ikuo Cho wrote:
> > Dear Brad
> >
> >> Because the Maxwell time in your problem is so short, the stresses relax
> >> very quickly. In using a time step of 1.0*year with v1.3.1 the stresses
> >> are relaxing artificially slowly because the time step is so large.
> >
> >> instead of the elastic constants. The elastic solution at the first time
> >> step (-dt to 0) should match the solution for a purely elastic material.
> >> In v1.4.2 this is true, but in v1.3.1 it is not. This is subtle in most
> >
> > Thank you for your comments. I ran PyLith1.3.1 with a short time step,
> > dt=0.028 year, which is the value requested by PyLith 1.4.2. All other
> > parameters are the same as those used in the previous calculation (I
> > used the cfg file and the spatial database attached to the previous
> > email I sent). The calculation results didn't show visible differences,
> > however (See the figure). The only exception is the elastic solution at t=0. The elastic
> > solution is influenced by some viscoelastic parameters when the time
> > step is set to 0.028 year.
> >
> > Although I don't fully understand your comments for PyLith1.3.1, I will
> > concentrate myself to PyLith1.4.2 from now on because I want to apply
> > PyLith 1.4.2 or later to some problems of power-law fluids.
> >
> > You said "v1.4.2 looks correct", but it looks incorrect for me. The
> > calculation results from v1.4.2 (Figures are attached to my previous
> > email) showed that stresses fell two orders of magnitude everywhere in
> > just one year. I gave viscosity coefficients ranging from 7.1*10**19 to
> > 7.1*10**20 [Pa*s] (relaxation times from 100 to 1000 years) at the rear
> > part of the volume (y > 0), and so the stress relaxation seems too short .
> >
> > Perhaps I mistook the use of some important parameters for PyLith1.4.2.
> > But it is also possible that some problem arises when PyLith1.4.2 reads
> > three-dimensional data using a spatial database. I want to solve this
> > problem anyway and will write another email soon for the illustration.
> >
> > Ikuo
> >
> >
> > On Tue, 30 Mar 2010 09:33:34 -0700
> > Brad Aagaard <baagaard at usgs.gov> wrote:
> >
> >> Ikuo-
> >>
> >> We found a couple issues related to the test problem you supplied.
> >>
> >> (1) The time step in your simulation using v1.3.1 is too large so the
> >> simulation isn't accurately modeling the viscoelastic deformation.
> >>
> >> PyLith v1.3.1 did not have a check to make sure the time step is
> >> sufficiently small relative to the shortest Maxwell time. This was added
> >> in v1.4, which is why if you try to run v1.4.2 with a time step of
> >> 1.0*year you will get an error message, but not in v1.3.1.
> >>
> >> Because the Maxwell time in your problem is so short, the stresses relax
> >> very quickly. In using a time step of 1.0*year with v1.3.1 the stresses
> >> are relaxing artificially slowly because the time step is so large.
> >>
> >> (2) The elastic solution in v1.3.1 for the Maxwell bulk rheology is
> >> incorrect.
> >>
> >> It appears that v1.3.1 is using the viscoelastic elastic constants
> >> instead of the elastic constants. The elastic solution at the first time
> >> step (-dt to 0) should match the solution for a purely elastic material.
> >> In v1.4.2 this is true, but in v1.3.1 it is not. This is subtle in most
> >> problems with large Maxwell times, but your test problem has such a
> >> short Maxwell time that this bug shows up. I don't know the precise
> >> location in the code where this bug occurs in v1.3.1, but v1.4.2 looks
> >> correct.
> >>
> >> Regards,
> >> Brad
> >>
> >>
> >> Ikuo Cho wrote:
> >>> Dear PyLith developers
> >>>
> >>> I calculated linear viscoelastic responses of a medium, under the
> >>> setting MaxwellIsotropic3D, while giving three-dimensional
> >>> inhomogeneities to its viscosities using the SimpleDB spatial database.
> >>> *info.vtk indicates that medium properties have been read correctly, but
> >>> the way stresses attenuate apparently doesn't reflect the given
> >>> inhomogeneities and absolute values of the viscosity coefficients. An
> >>> earlier version (PyLith 1.3.1) produced intuitively expected results,
> >>> but PyLith 1.4.2 gave counter intuitive outputs, no matter which one I
> >>> used--binary for XP, binary for Linux or the source code to be compiled
> >>> by the user (see attached figures).
> >>>
> >>> You can validate what I am saying using the setting files attached to
> >>> this email: Here is what I did.
> >>> 1) Place four files (dislocation_3d_mat1.4.2.cfg,
> >>> dislocation_3d_mat1.4.2.cfg, 3d_mat1.3.1.spatialdb and
> >>> 3d_mat1.4.2.spatialdb) in the exercise directory
> >>> pylith-1.4.2/examples/3d/hex8.
> >>>
> >>> 2) Execute PyLith1.4.2 by typing:
> >>> cd pylith-1.4.2/examples/3d/hex8
> >>> pylith dislocation_3d_mat1.4.2.cfg
> >>>
> >>> 3) Execute PyLith1.3.1 by typing:
> >>> mv pylithapp.cfg pylithapp.cfg.org
> >>> pylith dislocation_3d_mat1.3.1.cfg
> >>>
> >>> The following is the only difference in "spatialdata" that describes material properties.
> >>> < value-units = kg/m^3 m/s m/s Pa^s // units
> >>> ---
> >>>> value-units = kg/m**3 m/s m/s Pa*s // units
> >>> I have no idea what the problem is. Did I miss any important changes in
> >>> the way input should be given?
> >>> I'd be happy to receive any advise.
> >>>
> >>> ----------------------------------------------------------
> >>> Ikuo Cho ( ikuo-chou at aist.go.jp )
> >>> Geological Survey of Japan,
> >>> National Institute of Advanced Industrial Science and Technology
> >>> Tsukuba Central 7, Tsukuba 305-8567 Japan
> >>> Tel +81-29-861-3891, Fax +81-29-861-3682
> >>> ----------------------------------------------------------
> >>>
> >>>
> >>> ------------------------------------------------------------------------
> >>>
> >>> _______________________________________________
> >>> CIG-SHORT mailing list
> >>> CIG-SHORT at geodynamics.org
> >>> http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short
> >> _______________________________________________
> >> CIG-SHORT mailing list
> >> CIG-SHORT at geodynamics.org
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> >
>
長 郁夫 (Ikuo Cho)
----------------------------------------------------------
独立行政法人 産業技術総合研究所
活断層・地震研究センター 地震発生機構研究チーム
〒305-8567 つくば市東1-1-1 つくば中央第七
Tel 029-861-3891
029-861-3688,3534(つながらない場合はこちら迄)
Fax 029-861-3682, e-mail ikuo-chou at aist.go.jp
Homepage http://staff.aist.go.jp/ikuo-chou
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