
[Sponsors] 
Data Produced From Fine Marine Cant Match with The Experimental Data 

LinkBack  Thread Tools  Display Modes 
August 21, 2014, 07:49 
Data Produced From Fine Marine Cant Match with The Experimental Data

#1 
New Member
Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 4 
Hi,
Question 1 I run the resistance simulation for my hull to compare with the experiment data. However, the data produced by fine marine is still not match with the experimental data. I already do my setting for my hull (1.372m) as listed below: In Hexpress; Global refinement = 8 Refinement for hull = 5 (tick target size cell) Refinement for transom = 6 (tick target size cell) Internal surface = 8 (target size cell is 0.2(for X&Y) and with aspect ratio of 200) y plus = 1 stretching ratio = 1.2 No. of layer = 10 In Flow Solver; Reference length = 1.372m Reference velocity = 0.32067m/s This parameters set to make a constant Reynold number (Laminar) Final velocity (body motion) = 1.029754m/s (1/2 sinusoidal ramp) The percentage of error is still big enough between the CFD and experimental data. Question 2 After that, as i increase froude number to run with my model, the percentage error of the data between the CFD and experimental become more bigger in value. Is it my setting for mesh or flow solver part wrong that lead to wrong data produced? ( I have already increase the mesh number to 3 million and increase the refinement number). Any suggestion or idea to solve the problem? Thanks. 

August 21, 2014, 09:57 

#2 
Member
Romain
Join Date: May 2009
Posts: 40
Rep Power: 9 
Hi,
1) What kind of boundary conditions did you use for the hull surfaces ? Also why did you use v=0.32067m/s as your reference velocity (to compute Reynolds number and then I assume the spacing to get a y+ of 1), while the hull is going at 1.029754m/s ? Check the y+ value on the hull in Cfview. Is your free surface resolution (in X and Y plane) good enough to capture the wake ? Check the free surface elevation in Cfview. 2) If you kept the very same mesh but for different velocities, it is likely that your original viscous layer spacing is off (and it might even be wrong in the first place). 

August 22, 2014, 07:18 

#3 
New Member
Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 4 
Hi Rombzh,
1) For hull surfaces (hull and transom), i set them to wallfunction while deck as slip. In flow model, i set v=0.32067m/s as my reference velocity because i want to make a constant reynold number in order to produce laminar flow. While, the hull is set to 1.029754m/s because i want my hull to going at this constant speed. Is that wrong where the reference velocity and the final velocity (hull speed) must be the same? If i put 1.029754m/s for reference velocity and the final velocity, the data is still have error but not have big value of error as i using difference value for those two velocity. While for y+ value, In Hexpress Viscous layers, i put the value as listed below to compute the first layer thickness; y+ = 1 reference length = 1.372 reference velocity = 0.32067m/s Kinematic viscosity = 1.1e006 2) The original viscous layer spacing is it corrected by increasing the number of layers Thanks 

August 23, 2014, 05:20 

#4 
Member
Romain
Join Date: May 2009
Posts: 40
Rep Power: 9 
Hi,
If you're targeting a y+ value of 1 you should not use Wall Functions but "No Slip Wall" for your hull boundary conditions. For the deck, free slip is fine. In Flow Model, the Reference Velocity is only used to compute the time step, that's basically it. But if you used v=0.32067m/s as a reference to compute your Reynolds number and then the spacing that will get y+=1, this is wrong. You need to specify the final velocity the hull will travel at, so here v=1.029754m/s. 

August 23, 2014, 05:33 

#5 
New Member
Lim Pei San
Join Date: Mar 2014
Posts: 25
Rep Power: 4 
Thanks Rombzh, i will try your suggestion.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
studying a valve case  mina.basta  OpenFOAM  33  August 30, 2013 04:46 
ABL simulation with experimental data: problems and doubts  Davide_sd  OpenFOAM Running, Solving & CFD  0  May 22, 2013 18:35 
Experimental data vs SimpleFoam sphere test case : Cd do not match  alsdia  OpenFOAM Verification & Validation  1  November 2, 2012 06:37 
Step Changes in Roughness Experimental Data  syler3321  Main CFD Forum  0  October 20, 2010 00:45 
Functions to import non grid associated experimental data  benk  OpenFOAM  1  June 30, 2010 05:11 