<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">There are definitely significant differences between how the two rheologies are done. You would need to look in the manual to see how to correlate the two. The power-law rheology is controlled by reference stress and reference strain rate values, rather than a viscosity coefficient. You can use the utility code powerlaw_gendb.py to convert the A-value for power-law to these values, but you will still need to watch out for factors of 2 and sqrt(3.0).<div><br></div><div>Charles</div><div><br></div><div>p.s. i'm at a workshop right now and don't have time to put together an example, but I may try to do that after the workshop.</div><div><br></div><div><br><div><div>On 13/10/2010, at 2:18 PM, Brad Aagaard wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Jeff-<br><br>Can you explain more specifically what differences you see in the <br>stresses? Please specify if this occurs for the elastic solution (first <br>time step) or at latter time steps. Is the displacement field the same <br>but only the stress fields are different? Are the strains different or <br>just the stresses?<br><br>When I use the pylith trunk, I get identical deformation (displacements, <br>strains, and stresses) for the elastic solution, but then the <br>deformation (all fields) seem to differ between the two problems.<br><br>Another issue to keep in mind is that the physical properties as well as <br>the initial state variables must be equivalent for the deformation to be <br>the same.<br><br>Charles- Is there anything tricky about differences in the state <br>variables between the MaxwellIsotropic3D model and the PowerLaw3D model <br>that could be responsible for this issue.<br><br>Brad<br><br><br>On 10/12/2010 01:58 PM, Jeffrey Thompson wrote:<br><blockquote type="cite">Dear CIG Developers,<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I've been running into difficulties with the magnitude of gravitational<br></blockquote><blockquote type="cite">stresses using a PowerLaw3D rheology. As a consistency check, I ran two<br></blockquote><blockquote type="cite">models with the same material parameters, using a MaxwellIsotropic3D<br></blockquote><blockquote type="cite">rheology first and a PowerLaw3D rheology (with n=1) second. I obtained<br></blockquote><blockquote type="cite">wildly different values of stress within the two model runs, with the<br></blockquote><blockquote type="cite">magnitudes of stresses varying by about 10 orders of magnitude. I've<br></blockquote><blockquote type="cite">attached a tarball with my model parameters for both cases, and was<br></blockquote><blockquote type="cite">wondering if you could take a look at this problem.<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">I'm currently running PyLith 1.5.1 using the tarballed version available off<br></blockquote><blockquote type="cite">of the CIG website (i.e. not an svn version).<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">Thanks,<br></blockquote><blockquote type="cite">Jeffrey Thompson<br></blockquote><blockquote type="cite">Seismolab<br></blockquote><blockquote type="cite">California Institute of Technology<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">_______________________________________________<br></blockquote><blockquote type="cite">CIG-SHORT mailing list<br></blockquote><blockquote type="cite"><a href="mailto:CIG-SHORT@geodynamics.org">CIG-SHORT@geodynamics.org</a><br></blockquote><blockquote type="cite"><a href="http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short">http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short</a><br></blockquote><br>_______________________________________________<br>CIG-SHORT mailing list<br><a href="mailto:CIG-SHORT@geodynamics.org">CIG-SHORT@geodynamics.org</a><br>http://geodynamics.org/cgi-bin/mailman/listinfo/cig-short<br></div></blockquote></div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Charles A. Williams</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Scientist<br>GNS Science<br>1 Fairway Drive, Avalon<br>PO Box 30368<br>Lower Hutt 5040<br>New Zealand<br>ph (office): 0064-4570-4566<br>fax (office): 0064-4570-4600</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="mailto:C.Williams@gns.cri.nz">C.Williams@gns.cri.nz</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">NOTE NEW E-MAIL ADDRESS</div></div></span>
</div>
<br></div></body></html>