<div class="gmail_quote">2011/4/26 Alejandro Marcos Aragón <span dir="ltr"><<a href="mailto:alejandro.aragon@gmail.com">alejandro.aragon@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div>Hi Jed, thanks for replying. In fact, the problem I sent the results from is a dynamic problem of a simply supported beam subjected to a constant load at the center, so I'm integrating in time.</div></blockquote>
<div><br></div><div>I take it there is no buckling.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div> The material is linear elastic so the stiffness matrix doesn't change in non-zero structure. Of course the right hand side changes, but I don't think this is the problem because at some point it takes it goes back to just a few iterations to solve. The behavior is cyclic, but I don't understand the reason for this. I've noticed the same behavior of the solver also in quasi-static problems (increasing the load gradually but not integrating over time).</div>
<div></div></blockquote></div><br><div>Is the convergence relatively smooth? Are you losing a lot in GMRES restarts (every 30 iterations)? If you have a symmetric formulation (including boundary conditions), you can use -ksp_type cg, otherwise try -ksp_gmres_restart 500.</div>
<div><br></div><div>Also, try solving the system with a random right hand side.</div>