On Tue, Apr 7, 2015 at 9:45 PM, grandrabbit <[email protected]> wrote:
> I see. But is there a way to remove the nulspace explicitly in libmesh > other than forcing the presure value at one node, such as substraction the > average pressure value? > This is what we do in systems_of_equations_ex3. In that case we constrain the average value of the pressure, rather than pinning it at a single node. The constraint is imposed using a SCALAR variable as a Lagrange multiplier. David > > ------------------ Original ------------------ > From: "Roy Stogner";<[email protected]>; > Date: Apr 7, 2015 > To: "grandrabbit"<[email protected]>; > Cc: "libmesh-users"<[email protected]>; > Subject: Re: [Libmesh-users] Pin presure in lid-cavity case > > > > > On Tue, 7 Apr 2015, grandrabbit wrote: > > > Later I found in systems_of_equations_ex2, even I comment out the part > of pinning pressure, > > the code still can give a reasonable cavity flow, any body can show me > why? Thanks a lot. > > Without pinning the pressure, you have a non-invertible matrix. But > it's not an overconstrained system with no solutions, it's an > underconstrained system with an infinity of solutions, and in that > case many iterative linear solvers will still find some solution to > the system, one in which the final values of any underconstrained > modes are just indirectly determined by the initial iterate. > --- > Roy > > ------------------------------------------------------------------------------ > BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT > Develop your own process in accordance with the BPMN 2 standard > Learn Process modeling best practices with Bonita BPM through live > exercises > http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- > event?utm_ > source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF > _______________________________________________ > Libmesh-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/libmesh-users > ------------------------------------------------------------------------------ BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT Develop your own process in accordance with the BPMN 2 standard Learn Process modeling best practices with Bonita BPM through live exercises http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_ source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
