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-   -   CFD of water waves phenomena-sawteeth at the free surface + slow execution time (http://www.cfd-online.com/Forums/main/117561-cfd-water-waves-phenomena-sawteeth-free-surface-slow-execution-time.html)

nore5 May 10, 2013 12:45

CFD of water waves phenomena-sawteeth at the free surface + slow execution time
 
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Dear all,

I am quite new to CFD of water waves related phenomena. Many questions are actually puzzling at the moment and I can t get answers on my own. :(

Let me start with the most disturbing one however :) This is in fact a question that may be extended to other CFD softwares. What is the reason behing having a free surface profile with some saw teeth like in the third crest of the picture attached?

I read somewhere that it might be linked to the time or space discretisation, but my step step is extremely small 0.02s for a mesh resolution of 0.01 and 0.0125 in the horizontal and vertical directions respectively around the free surface region (to fulfil the reauirement needed to resolve wave height and length by the way). The simulated wave here is a 2nd order Stokes waves of wave height 0.15 and wave period of 2.31, the water depth is 0.82s. The simulation is done using OpenFOAM.

What level of control a CFD user can have to avoid such a phenomenon?

Second big interrogation :), what level of control a user have to avoid execution time that gets larger and larger? I know it is a very vague question but generally speaking what level of control one has to run a simulation in optimal time?

I am asking these questions because there are few documentation when it comes to CFD of water waves so the best practices and choices regarding time stepping, shemes, solvers, spatial discretisation are rare, CFL number choice.... Thus for a beginner it is very hard to understand why things go wrong and how they should work

I have found this link on CFX but to what extent can it be extended to openFOAM or more complicated wave simulation cases...

http://www.ipen.org.br/Artigos-congr...NA2010-141.pdf


Thank you in advance for sharing your experience and shedding some light on the topic of CFD simulations of waves transformation, propagation and interaction with strutures.

Best regards,

Nore


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