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-   -   wave making resistance (http://www.cfd-online.com/Forums/cfx/98806-wave-making-resistance.html)

 leviathan March 19, 2012 18:42

wave making resistance

hi all, I'm trying to use ansys for evaluating wave making resistance on catamaran for my final assignment, but as I've done half of the work, I just know that ansys cfx would only calculate total resistance, not any spesific resistance. Is there any other way so that I could get the value of wave making resistance?
thx

 ghorrocks March 19, 2012 19:35

Splitting total drag into wave making and viscous is a little artifical anyway.

You might be able to something which looks like viscous drag by integrating the wall shear stress over the hull, and the wave resistance from the intergal of pressure.

 leviathan March 21, 2012 20:56

Could you give me some more explanations please? I mean, I don't really get it...Am I have to calculate shear stress and pressure instead resistance with cfx-post? does the integration would give valid value comparing to towing tank test results? and if I have to generate the wave, colud you give me some advice please?

thx

 ghorrocks March 21, 2012 22:12

My point is that you simply tow the model along and get a drag. You have to define something which splits it into wave and viscous and that split is a little artificial. And likewise, splitting the total drag in a CFD simulation into wave and viscous drag is a little artificial.

Integrating the wall shear over the body is a reasonable start, leaving the difference to total drag as the wave making resistance is one approach.

 leviathan March 25, 2012 06:38

that someting is the part that I don't understand....Does integrating the wall shear could give me valid result? and is that acceptable?

is it nothing I could do with CEL to solve it?

 ghorrocks March 25, 2012 06:56

I think you are missing my point. If you can mathematically define what wave drag is then you can do it in CFX and extract the number. If you have wishy-washy definitions like "it is the drag from the making the waves" you are not going to get anywhere. So yo uhave to define mathematically what it is, then it is usually fairly simple to calculate it from a CFX result.

 leviathan March 26, 2012 13:06

hi ghorrocks ,

I think I'm starting to understand your point...you're right, my previous definitions really2 something like "it is the drag from the making the waves" (that's what I've got from class)..then would you mind to tell me how it should be?

regards,
thx

 ghorrocks March 26, 2012 18:08

I do not know as this is not my field - and I do not have time to search for you. Google will help, also naval architecture textbooks. You need to find a solid definition of what it is then you consider implementing it.

 leviathan March 27, 2012 02:25

Well, I'll try to figure it out somehow, but then, would you mind to help me with the software afterwards? Cause I'm really newbie in CFD

regards

Thx

(ah one more thing, is it possible to see the wave spectrum? cause I guess I could figure something out if I could generate the wave...thx again)

 Cluain March 27, 2012 03:59

Leviathan, you can get a visual output in Post, Also if you record a time series of wave heights then you can do a spectral analysis on it

 ghorrocks March 27, 2012 05:46

If you have further questions feel free to start a new thread on the forum. I do not give out my email address for the forum.

 leviathan March 27, 2012 12:39

Quote:
 Originally Posted by Cluain (Post 351658) Leviathan, you can get a visual output in Post, Also if you record a time series of wave heights then you can do a spectral analysis on it
Where could I learn about it (making visual outpot and record time series) ? do you have links to any tutorial?

 leviathan March 27, 2012 12:39

Quote:
 Originally Posted by ghorrocks (Post 351697) If you have further questions feel free to start a new thread on the forum. I do not give out my email address for the forum.
okay...I'll try to learn about wave drag first...thx

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