# Accuracy problem

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

 March 22, 2011, 14:21 Accuracy problem #1 New Member   Ivan Join Date: Sep 2010 Location: Russia , Moscow. Posts: 14 Rep Power: 8 Sponsored Links Hello everyone ! I have a quite strange problem with solving of two equations: Code: ```fvVectorMatrix uEqn ( fvm::ddt(U) == (fvc::div(sigma) - fvc::grad(p))/rho ); uEqn.solve() ; pU = p*U ; fvScalarMatrix EEqn ( fvm::ddt(E) == -fvc::div(pU)/rho ); EEqn.solve() ;``` initial condition for U is uniform (0 0 0) for E uniform 215250, for p i made a step-like distribution with funkySetFields : Code: ```gap { field p; expression "2e05"; condition "(pos().x)<=(pi)"; keepPatches 1; }``` Solution domain is one-dimensional with 10000 cells. The problem is that second equation gives that E changes throughout all solution domain with a small fluctuations about e-12, and after each time step this errors accumulates. Here 1st 100 values of E : Code: ```215250 215250 215250 215249.999999999971 215250 215250 215250 215249.999999999971 215250 215249.999999999971 215250 215250 215250 215249.999999999971 215250.000000000029 215250 215250 215250 215249.999999999971 215249.999999999971 215249.999999999971 215250 215249.999999999971 215250 215250 215250 215250 215250 215249.999999999971 215250.000000000029 215249.999999999971 215250 215250 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215250 215250 215250 215249.999999999971 215250 215250 215249.999999999971 215250 215249.999999999971 215250 215250 215249.999999999971 215249.999999999971 215250 215250 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215250 215249.999999999971 215250 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215249.999999999971 215250 215250 215250 215250 215249.999999999971 215249.999999999971 215250 215250 215250 215250 215249.999999999971 215250 215250 215249.999999999971 215249.999999999971 215250 215250 215250 215250 215249.999999999971 215249.999999999971 215250 215250 215250 215250 215249.999999999971 215250 215250 215249.999999999971 215250 215249.999999999971``` I use Gauss linear scheme for div(pU) term. I've tried various linear solvers with difference tolerance values, but it doesn't help.

 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 Wouter Fluent UDF and Scheme Programming 6 June 6, 2012 04:43 Paolo Lampitella FLUENT 0 June 12, 2008 06:25 Gianni FLUENT 0 April 5, 2008 10:33 Jack Main CFD Forum 0 December 15, 2002 01:15 Gauthier Lambert Main CFD Forum 1 August 3, 2000 09:22