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<font size="2"><span style="font-size:11pt">Dear Petsc Users<br>
I wrote a code in 2D solving PF equations for solidification of alloys. <font size="2">
<span>I have two variables in the equations 1-non-dimensional concentration (U) 2- order parameter (p)</span></font>. Everything is fine with this code.<br>
When I change the code to 3D, the code has convergence problems which I cannot solve it.</span></font><font size="2"><span style="font-size:11pt">
<div style="font-size:12pt"><font size="2"><span style="font-size:11pt">I know the term which is causing problem is a term in the equation for U:</span></font></div>
</span></font><font size="2"><span style="font-size:11pt"></span></font><font size="2"><span style="font-size:11pt"></span></font><font size="2"><span style="font-size:11pt"></span></font><font size="2"><span style="font-size:11pt"></span></font><font size="2"><span style="font-size:11pt">
<div style="font-size:12pt"><font size="2"><span style="font-size:11pt">(dp/dt)*(Pxx+Pyy+Pzz)<br>
</span></font></div>
<div style="font-size:12pt"><font size="2"><span style="font-size:11pt">where Pxx,Pyy,Pzz are the second derivative of order parameter in x,y,z, respectively.
</span></font></div>
<br>
</span></font></div>
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<font size="2"><span style="font-size:11pt">When I eliminate this term, the results of 2D and 3D are close to each other. But adding that term the time step should be reduced a lot to obtain convergence, otherwise the timestep does not converge. I have no idea
how I should solve this problem.</span></font></div>
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<font size="2"><span style="font-size:11pt"></span></font><font size="2"><span style="font-size:11pt"> I solve the equations considering (I chose based on suggestions of Moose for solving Cahn-hillard)</span></font><br>
<font size="2"><span style="font-size:11pt"></span></font></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)">
<font size="2"><span style="font-size:11pt"> -ts_type bdf -ts_bdf_adapt -pc_type bjacobi -snes_linesearch_type l2 -snes_type newtontr -ksp_type gmres -ksp_gmres_restart 1001 -sub_pc_type ilu -sub_ksp_type preonly
<br>
</span></font></div>
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<font size="2"><span style="font-size:11pt"><br>
</span></font></div>
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<font size="2"><span style="font-size:11pt">Would you please help me solve this issue?<br>
Best,<br>
sepideh</span></font></div>
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