# Implicit equation solving

 Register Blogs Members List Search Today's Posts Mark Forums Read

 December 9, 2004, 16:50 When I want to have a solver #1 Dr B.M. Smith (Smith) Guest   Posts: n/a When I want to have a solver that must solve for a vector implicitly defined, but which can be written explicitly by matrix inversion, is this possible? Can I write an implicit equation and request foam to solve for a particular vector field within the equation? Or rather must one write all equations to be solved in explicit form, and if so, when using the expression "inv(M)" to invert a matrix M, if M is a complicated sum of products of tensors, say "M=A+div(nu, U)" for example, can one write combined expressions as equation terms such as "inv(A+div(nu, U))", or must one separate such operations by first solving the field eqn for M on the mesh and then later solve the eqn involving the inverse? (I'd like to get some hints before committing to writing solver before I commit to trial and error testing.) Thanks in advance for any help, Blair.

 December 10, 2004, 06:20 The latter, you must separate #2 Mattijs Janssens (Mattijs) Guest   Posts: n/a The latter, you must separate the operations. You create an equation for a single variable (can be a vector or tensor) using explicit terms (e.g. fvc::div) or implicit terms (e.g. fvm::laplacian) where the implicitness is only in the variable solved for. You can then call 'solve' on it which does your 'inv'. Have a look at a simple solver, e.g. icoFoam (\$FOAM_SOLVERS/incompressible/icoFoam/icoFoam/C) Hope this answers some of your questions. Mattijs

 December 10, 2004, 06:36 Here as an example, is the mem #3 Eugene de Villiers (Eugene) Guest   Posts: n/a Here as an example, is the mementum predictor step from icoFoam: fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) ); solve(UEqn == -fvc::grad(p)); As Mattijs said the elements prefaced by fvm are implicit terms in the Ueqn matrix, while the fvc term will be treated explicitly by the solver. (U = velocity, phi = face flux, nu = viscosity, p = pressure) Eugene

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post sek OpenFOAM Running, Solving & CFD 38 July 11, 2015 04:59 felixrieper OpenFOAM Running, Solving & CFD 1 February 9, 2014 01:58 srinath OpenFOAM 2 October 13, 2008 00:50 cfd-beginner Main CFD Forum 0 August 9, 2005 13:32 Venkatesh Main CFD Forum 2 September 26, 2003 04:26

All times are GMT -4. The time now is 16:43.