
[Sponsors] 
How to speed up the simulation of a large amount of similar steady state cases 

LinkBack  Thread Tools  Search this Thread  Display Modes 
November 3, 2010, 12:33 
How to speed up the simulation of a large amount of similar steady state cases

#1 
New Member
PA
Join Date: Jan 2010
Posts: 6
Rep Power: 15 
Hi,
I need to simulate many (5000+) similar steady state cases with almost exact the same geometry/boundary conditions/meshing. The only thing different among these cases is the inlet and outlet velocity. Is it possible to speed up the simulation? Thanks. In our tests, even the slightest speed change (e.g., change from 0.6m/s to 0.7m/s) will result very different solutions so it is not possible to use one case's result as the initial iteration values of other cases. To my understanding, CFD will turn every case into a large linear system (Ax=b) using finite volume method and use CG method to solve the x. Will these cases have the same (or similar) A so I can solve A^1 for one time and use it for the 5000+ cases? 

November 5, 2010, 01:35 

#2 
New Member
PA
Join Date: Jan 2010
Posts: 6
Rep Power: 15 
anyone has an idea?


November 5, 2010, 02:35 

#3 
Member
Michiel
Join Date: Jul 2009
Location: The Netherlands
Posts: 42
Rep Power: 15 
Can you write some scripts?
I am familiar with a project working with scripts to run steady state pump analysis using ansys cfx. One case is used to set up the problem. After that a script is used to generate all the solver input files with different mass flow rates. The script also takes care of solving all the files. The scripts cannot change the mesh.. This sounds like an suitable approach for you when you are talking about changing inlet and outlet velocities. 

November 5, 2010, 03:23 

#4  
New Member
PA
Join Date: Jan 2010
Posts: 6
Rep Power: 15 
Quote:
Hi, Thanks for the reply. However, this is not what I want. automation is not a problem here  What I really need is "Speed Up" the simulation as the title mentioned since 5000+ simulations will take forever. My question is, if the cases are pretty similar, what are the similarities underneath the CFD simulation engine (at an algorithm level) so I can utilize some results instead of calculating them over and over. To be precise, when we apply the Finite Volume Method and turn the cases into linear equations, are there similarities among the matrixes? 

November 5, 2010, 14:36 

#5 
New Member
Join Date: Jun 2010
Posts: 16
Rep Power: 14 
If the discretized equaiton is linear in the discrete solution,
then the matrix A in Ax=b depends only on the geometry of the mesh. If the mesh is identical for each case, you can invert A just once, and reuse it for all cases. Each problem now becomes just a matrixvector multiplication. If the discretized equation is nonlinear (nonlinear governing equations or nonlinear schemes for linear governing equations), then the above procedure is not applicable. bjohn 

Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Calculation of the Governing Equations  Mihail  CFX  7  September 7, 2014 06:27 
Can I use Large Eddy Simulation like steady?  kdrbrk  FLUENT  2  June 7, 2010 17:08 
Rigid Body State Variables in Solid Immersed Simulation  Hamidreza  CFX  1  October 19, 2009 06:14 
Steady State 2 phase problem  fivos  FLUENT  0  April 27, 2009 16:34 
About the difference between steady and unsteady problems  Lisa  Main CFD Forum  11  July 5, 2000 14:37 