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From: David Knezevic <dknezevic@se...>  20120208 23:37:06

On 02/08/2012 06:09 PM, Mauro Werder wrote: > I've never done it but here my thoughts: It should be possible to > assemble the 1D system when looping over the boundary elements of the > 2D mesh (as is usually done for the BCs) as all the machinery is in > place to do this. All the machinery is there in the sense that you can already evaluate shape functions on boundaries (as in BC assembly), but you'd need to be able to add a "boundaryonly variable" to have the correct number of degrees of freedom for the 1D variable. Maybe this could be implemented similarly to the "subdomainonly variables"? > > At Wed, 8 Feb 2012 22:07:16 +0000, > Sylvain Vallaghe wrote: >> Hi, >> >> I'm trying to implement a 2d problem in libmesh where I have two scalar variables : one is 2d in the whole domain, the other is 1d and mapped on one of the boundaries of my domain. These two variables are coupled due to the global variational formulation. I don't know how to define my 1d variable so that it can be part of the equation_systems (since it is based on a 2d mesh). In the examples I've seen so far, problems with multiple variables all have the same dimension (e.g. Stokes). >> Any help would be much appreciated. >> Thanks, >> >> Sylvain >>  >> Keep Your Developer Skills Current with LearnDevNow! >> The most comprehensive online learning library for Microsoft developers >> is just $99.99! Visual Studio, SharePoint, SQL  plus HTML5, CSS3, MVC3, >> Metro Style Apps, more. Free future releases when you subscribe now! >> http://p.sf.net/sfu/learndevnowd2d >> _______________________________________________ >> Libmeshusers mailing list >> Libmeshusers@... >> https://lists.sourceforge.net/lists/listinfo/libmeshusers >  > Virtualization& Cloud Management Using Capacity Planning > Cloud computing makes use of virtualization  but cloud computing > also focuses on allowing computing to be delivered as a service. > http://www.accelacomm.com/jaw/sfnl/114/51521223/ > _______________________________________________ > Libmeshusers mailing list > Libmeshusers@... > https://lists.sourceforge.net/lists/listinfo/libmeshusers 
From: Mauro Werder <m_werder@sf...>  20120208 23:09:23

I've never done it but here my thoughts: It should be possible to assemble the 1D system when looping over the boundary elements of the 2D mesh (as is usually done for the BCs) as all the machinery is in place to do this. Mauro At Wed, 8 Feb 2012 22:07:16 +0000, Sylvain Vallaghe wrote: > > Hi, > > I'm trying to implement a 2d problem in libmesh where I have two scalar variables : one is 2d in the whole domain, the other is 1d and mapped on one of the boundaries of my domain. These two variables are coupled due to the global variational formulation. I don't know how to define my 1d variable so that it can be part of the equation_systems (since it is based on a 2d mesh). In the examples I've seen so far, problems with multiple variables all have the same dimension (e.g. Stokes). > Any help would be much appreciated. > Thanks, > > Sylvain >  > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL  plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnowd2d > _______________________________________________ > Libmeshusers mailing list > Libmeshusers@... > https://lists.sourceforge.net/lists/listinfo/libmeshusers 
From: Ali Roustaei <arousta@in...>  20120208 22:50:50

Thanks Jed! very nice explanations Best Regards, Ali 
From: David Knezevic <dknezevic@se...>  20120208 22:44:33

On 02/08/2012 05:07 PM, Sylvain Vallaghe wrote: > I'm trying to implement a 2d problem in libmesh where I have two scalar variables : one is 2d in the whole domain, the other is 1d and mapped on one of the boundaries of my domain. These two variables are coupled due to the global variational formulation. I don't know how to define my 1d variable so that it can be part of the equation_systems (since it is based on a 2d mesh). In the examples I've seen so far, problems with multiple variables all have the same dimension (e.g. Stokes). > Any help would be much appreciated. An EquationSystems object is tied to a Mesh, so it seems like you'd have to have two separate EquationSystems. But this would necessitate some sort of "loose coupling," which maybe you were hoping to avoid? Note that you can extract a boundary mesh using BoundaryMesh boundary_mesh(dim1); mesh.boundary_info>sync(requested_boundary_ids, boundary_mesh); David 
From: Sylvain Vallaghe <svallagh@MIT.EDU>  20120208 22:07:30

Hi, I'm trying to implement a 2d problem in libmesh where I have two scalar variables : one is 2d in the whole domain, the other is 1d and mapped on one of the boundaries of my domain. These two variables are coupled due to the global variational formulation. I don't know how to define my 1d variable so that it can be part of the equation_systems (since it is based on a 2d mesh). In the examples I've seen so far, problems with multiple variables all have the same dimension (e.g. Stokes). Any help would be much appreciated. Thanks, Sylvain 
From: Jed Brown <jed@59...>  20120208 21:11:44

On Wed, Feb 8, 2012 at 20:38, Roy Stogner <roystgnr@...> wrote: > > 3 Support for an Uzawa solver (stokes problem) > > This is doable in libMesh application code, but it wouldn't be as easy > as many other solvers, and it isn't built in to the library. > For simple Stokes problems, PETSc can construct this automatically (because there is 0 on the diagonal for the "pressure rows"). If you use stabilization or anything nonstandard, you would have to identify those rows corresponding to velocity and pressure (or whatever the split is). Also, if you want to use custom preconditioners for the Schur complement system (e.g. other than the Least Squares Commutator which we can construct a certain form of automatically), you would provide that too. These aren't libmesh native interfaces, but they are just a couple extra PETSc functions. > > 5 Support for mixed FEM, FVM. I want to use FEM for equation of fluid > motion and FVM for > > solving a pure convection problem (As I have a 2 fluids in my system > and want to handle it with VOF method). > > libMesh can do FVM with small flux stencils by using discontinuous > shape functions for those variables; for larger stencils you'd be out > of luck, since libMesh wouldn't be able to extend the parallel > ghosting or sparsity pattern as far as you'd like. You can do a second order TVD unstructured FVM in a slightly goofy way, but that isn't really bad. 1. Define a cellcentered P0 (discontinuous) space for averages of state variables and another P0 discontinuous space that holds cellcentered gradients. 2. Do a face traversal and add jumps in state (perhaps locally transformed to characteristic variables) into the gradients of the two cells. 3. Communicate the gradients. 4. Do a face traversal, evaluate the interface state using the gradients, then solve a Riemann problem using the reconstructed states, and contribute the fluxes (face area/cell volume weighted) into the residuals defined on the cells. 
From: Roy Stogner <roystgnr@ic...>  20120208 20:15:23

On Wed, 8 Feb 2012, water force wrote: > Yes this algorithm seems uncommon because the material properties > associated with these meshes are different. Is there any other > elegant way to do this? It should have been obvious from your code, but no  if your material properties affect the Jacobian and are changing dramatically then you're probably already doing things the most elegant way. Sorry if I got your hopes up. ;)  Roy 
From: Ali Roustaei <arousta@in...>  20120208 20:08:24

Thanks for info Best Wishes, Ali 
From: water force <wforce@gm...>  20120208 20:07:00

Thanks for your comments! A bug in my assemble function did result in the segfault. Actually I used attach_assemble_object in my code but made a mistake when passing the string sys_name to the constructor in the assembly class. Yes this algorithm seems uncommon because the material properties associated with these meshes are different. Is there any other elegant way to do this? Best Jingjing On Tue, Feb 7, 2012 at 5:29 PM, Roy Stogner <roystgnr@...>wrote: > > On Tue, 7 Feb 2012, water force wrote: > > I have a couple of meshes, each with the same linear equations and >> boundary >> conditions. Then I tried to solve them in a loop in the following way: >> >> for (int i = 0; i < number_of_meshes; i++) >> { >> EquationSystems es( mesh[i] ); >> es.add_system<**LinearImplicitSystem>(sys_**name); >> es.get_system(sys_name).add_**variable("u", FIRST); >> es.get_system(sys_name).**attach_assemble_function(**assemble_func); >> es.init(); >> es.get_system(sys_name).solve(**); >> } >> >> But it always gives a segmentation fault if the number of meshes is more >> than one. I guess it might be due to the declaration of an equation system >> in the loop. Could you give me any suggestions? Thanks! >> > > This is an uncommon sort of algorithm (and possibly very inefficient: > if you've got the same linear equations you shouldn't need to assemble > the same matrices and preconditioners over and over again just to > handle different forcing functions) but I don't see anything actually > *incorrect* here; there's either a bug in your assemble_func or in the > library. Have you run with METHOD=dbg or at least METHOD=devel to see > if you can hit an assertion failure before you hit a segmentation > fault? >  > Roy > 
From: Kirk, Benjamin (JSCEG311) <benjamin.kirk1@na...>  20120208 20:02:45

Nothing particularly tricky about the FVM interface so long as you are (i) cell centered and (ii) interested only in nearest face neighbors. In that sense it is a natural subset of the DG support. If you want a node centered scheme with dualmesh control volumes there will be many tricks  I would expect. On Feb 8, 2012, at 1:58 PM, "Ali Roustaei" <arousta@...> wrote: > Thanks you very much Roy, > > For periodic BC that's enough for me. For FVM computations do we have a clean interface? or it is done > with tricks? I guess this would be the more time consuming part > > Regards, > Ali > > >  > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL  plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnowd2d > _______________________________________________ > Libmeshusers mailing list > Libmeshusers@... > https://lists.sourceforge.net/lists/listinfo/libmeshusers 
From: Ali Roustaei <arousta@in...>  20120208 19:58:01

Thanks you very much Roy, For periodic BC that's enough for me. For FVM computations do we have a clean interface? or it is done with tricks? I guess this would be the more time consuming part Regards, Ali 
From: Roy Stogner <roystgnr@ic...>  20120208 17:53:12

On Wed, 8 Feb 2012, Derek Gaston wrote: > On Feb 8, 2012, at 10:38 AM, Roy Stogner wrote: > >> libMesh can do FVM with small flux stencils by using discontinuous >> shape functions for those variables; for larger stencils you'd be out >> of luck, since libMesh wouldn't be able to extend the parallel >> ghosting or sparsity pattern as far as you'd like. > > Well… you can compute those extra sparsity and ghosting entries > yourself and add them to what libMesh is computing… so it is > possible… just not automatically built into the library. I had forgotten you guys had added that in. Thanks for the correction.  Roy 
From: Derek Gaston <friedmud@gm...>  20120208 17:44:21

On Feb 8, 2012, at 10:38 AM, Roy Stogner wrote: > libMesh can do FVM with small flux stencils by using discontinuous > shape functions for those variables; for larger stencils you'd be out > of luck, since libMesh wouldn't be able to extend the parallel > ghosting or sparsity pattern as far as you'd like. Well… you can compute those extra sparsity and ghosting entries yourself and add them to what libMesh is computing… so it is possible… just not automatically built into the library. Derek 
From: Roy Stogner <roystgnr@ic...>  20120208 17:38:17

On Wed, 8 Feb 2012, Ali Roustaei wrote: > I'm looking for a flexible computational environment, currently my needs right now are: > > 1 Support for P1isoP2 elements, P0,P1,P2 and Q0,Q1,Q2 and Q0isoQ2 > 2 Support for discontinuous elements P1disc, Q1disc All of this is easy enough in libMesh. > 3 Support for an Uzawa solver (stokes problem) This is doable in libMesh application code, but it wouldn't be as easy as many other solvers, and it isn't built in to the library. > 4 Periodic Boundary Conditions The basics of periodic conditions are built in to libMesh  there are fancy things like angular periodicity, periodic conditions more complicated than u_side1 = u_side2, etc. that we don't support yet. > 5 Support for mixed FEM, FVM. I want to use FEM for equation of fluid motion and FVM for > solving a pure convection problem (As I have a 2 fluids in my system and want to handle it with VOF method). libMesh can do FVM with small flux stencils by using discontinuous shape functions for those variables; for larger stencils you'd be out of luck, since libMesh wouldn't be able to extend the parallel ghosting or sparsity pattern as far as you'd like.  Roy 
From: Ali Roustaei <arousta@in...>  20120208 17:30:52

Hi, I'm looking for a flexible computational environment, currently my needs right now are: 1 Support for P1isoP2 elements, P0,P1,P2 and Q0,Q1,Q2 and Q0isoQ2 2 Support for discontinuous elements P1disc, Q1disc 3 Support for an Uzawa solver (stokes problem) 4 Periodic Boundary Conditions 5 Support for mixed FEM, FVM. I want to use FEM for equation of fluid motion and FVM for solving a pure convection problem (As I have a 2 fluids in my system and want to handle it with VOF method). I read a bit about features of libMesh, but last I decided to ask question here from the experts so that I get the right info. Thank you very much, Ali 
From: John Peterson <jwpeterson@gm...>  20120208 00:18:56

On Tue, Feb 7, 2012 at 3:23 PM, water force <wforce@...> wrote: > Hello, > > I have a couple of meshes, each with the same linear equations and boundary > conditions. Then I tried to solve them in a loop in the following way: > > for (int i = 0; i < number_of_meshes; i++) > { > EquationSystems es( mesh[i] ); > es.add_system<LinearImplicitSystem>(sys_name); > es.get_system(sys_name).add_variable("u", FIRST); > es.get_system(sys_name).attach_assemble_function(assemble_func); > es.init(); > es.get_system(sys_name).solve(); > } > > But it always gives a segmentation fault if the number of meshes is more > than one. I guess it might be due to the declaration of an equation system > in the loop. Could you give me any suggestions? Thanks! How are you creating the vector/array of meshes?  John 