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Alletto  2022  Comparison of overset mesh with morphing mesh 

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February 18, 2022, 17:22 

#21 
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Alvi Ahmmed
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Thank you very much. I can get the natural frequency(fn) from St=fnD/U equation right? And am I free to choose U and D for a fixed Re=100?


February 18, 2022, 18:14 

#22 
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Michael Alletto
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You can choose the parameters as you want as long all dimensional less parameters are the same. The frequency in the st number is the shedding frequency not the natural frequency


February 19, 2022, 02:54 

#23 
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Alvi Ahmmed
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How can I find the value of natural frequency (fn) ? From the FFT plot of the lift coff? Regards.


February 19, 2022, 03:05 

#24 
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Michael Alletto
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See https://en.m.wikipedia.org/wiki/Natural_frequency
For the natural frequency of a spring mass system. But I think I mentioned this also in the paper. Read it carefully. What is done in the python scripts is also explained in the paper. A fft of the lift signal is performed and the maximum amplitude is used to calculate the St number. Read the paper a few times if once is not enough. I usually need three or four times to fully understand a paper 

February 19, 2022, 03:08 

#25 
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Alvi Ahmmed
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Thanks very much for your guidence


March 22, 2022, 02:44 
How to set the density in the VIV case

#26 
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Mehdi Badri
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Hi,
According to the definition of nondimensional mass, , on page 18 of your paper, the density of the cylinder, , is calculated as . In your paper (and its corresponding git repo), you have used , whereas it seems that if we substitute , and , the density should be . Could you please clarify how you calculated it (and why my understanding is perhaps incorrect)? 

March 22, 2022, 04:16 

#27 
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Michael Alletto
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March 22, 2022, 20:58 
Thank you

#28  
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Mehdi Badri
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Quote:
That is a nice explanation and helpful note! Thanks 

March 23, 2022, 00:21 

#29 
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zink
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April 5, 2022, 12:12 
citation

#30 
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Wael Elorfi
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Is there a bibtex file available for citing this paper?


April 5, 2022, 12:34 

#31 
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Michael Alletto
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I usually copy the bibtex entry from Google scholar


April 5, 2022, 14:40 
citation

#32 
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Wael Elorfi
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Got it. Thanks a lot!
@article{alletto2022comparison, title={Comparison of overset mesh with morphing mesh: Flow over a forced oscillating and freely oscillating 2D cylinder}, author={Alletto, Michael}, journal={OpenFOAM{\textregistered} Journal}, volume={2}, pages={1330}, year={2022} } 

April 11, 2022, 06:15 
Doi

#33 
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Håkan Nilsson
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This paper has now been updated with the ISSN of the journal and its own DOI: https://doi.org/10.51560/ofj.v2.47


July 7, 2022, 13:42 

#34 
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zink
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Hi,
Can anyone explain the m in this equation? Is it only the mass of the cylinder? Does this include the added mass as well? 

July 8, 2022, 07:45 

#35 
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Michael Alletto
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It's only the mass of the cylinder


July 8, 2022, 14:46 

#36 
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zink
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I need some clarification regarding your paper
Q1: You have mentioned that density of the cylinder is set to 14817 kg/mˆ3. It should be called as the density of the fluid not the cylinder? Q2: In your calculations, in the case of Ur 4, you have used the k = m*(2*pi*f)ˆ2 that gives k value of 148.28. I want to ask about the f used in the calculation. We know that the reduced natural frequency of the system is given as Fr = I/Ur and Ur= Unif/f*D , here f is the frequency in the flow medium . It could be air, water or any medium used in the simulation. In the present case, it is the frequency in the fluid having density 14817 kg.m3. f= 0.0656/(4*0.0016) = 10.25 As you are using cylinder mass m=0.03575 ,then the k should be calculated as k=(m+m_added_mass)*(2*pi*f)ˆ2 m_added_mass= C_EA*(pi*Dˆ2*H*rhoInf/4) =0.003575 k=163.108 Please clarify? I just want to learn that how f is related with k when you are using medium other than air. Should it include the added mass or not? 

July 9, 2022, 04:35 

#37 
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Michael Alletto
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Q1: It is the density of the cylinder. If you fix the mass and the dimensions of the cylinder the density can be calculated
Q2: The added mass is not considered. It is actually not known in advance since it is solution dependent. What did you mean with added mass exactly. Can you specify it more precisely? The purpose of setting the constants in the paper in the way I did it, is to match all relevant nondimensional constants. This are U*, m* and Re. Actually you can choose all combination of dimensional quantities as you want as long as the nondimensional quantities remain the same. If the nondimensional quantities are the same you can compare the nondimensional solutions. Have a look at the pitheorem https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem Best Michael 

April 12, 2023, 12:12 

#38  
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Manchester
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Quote:
Many thanks for your contribution, one quick question is about overset mesh, for interpolation fringe, it's better to walk away from the cylinder boundary to avoid a huge gradient, is it right? When using overset mesh for your case, have you ever faced the issue at the interface between the overset component and background component? I mean the velocity and pressure field at this interface are not consistent, I think that's due to the issue about mass conservation, can we improve this phenomenon by adjusting the interpolation scheme? 

April 12, 2023, 16:07 

#39 
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Michael Alletto
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Hello,
yes better avoid regions of strong gradients where to place the overset boundary. Best Michael 

May 13, 2023, 14:41 
About fvSchemes

#40  
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Manchester
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Quote:
Thank you for your sharing, which helps me a lot. I noticed you used cubic for div(phi, U) term instead of other secondorder discretization schemes. I tried linearUpwind, QUICK, and cubic, and the results changed a lot, actually for the overset mesh, linearUpind predicts the highest frequency of lift coefficient, but the cubic returns the highest amplitude and reasonable frequency. Can you please explain why, is there any useful reference to support it? Best, Tian 

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