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 hasim January 12, 2009 09:01

hello

i would like to ask some things about boat simulations, firstly if the software is good enought for the user to calculate the hydrodynamic drag and the results if there are good enought, it would be very good if i can have the advice of a boat expert analist to tell me if he made the simulation and then the real expiriment and how much % different have the results.

i also would like to ask if the people of the shipyards are using simulation software for the design of the hull, or using tables???

i would like to have answers from people that already have expirience, we are going to spent a loto of money on this .

best regards hasim

 Stefano January 14, 2009 05:00

hello hasim, we do boat simulations, and recently we are performing calculations comparing the numerical FLOW-3D results with experiments on sailboat and motor-planning hulls too. I can tell you that with a good setup and making simulations of 2 dof coupled motion hulls, you can reach an accuracy of the 0.1° on the pitch angle, less than the 0.1% (about the lenght of the hull) on the heave, and less than the 4% on the total force vs the experiment. You can ask whatever you want, we'll be glad to help you.

 hasim January 14, 2009 08:38

less than 4% !!!!!! thats a great number.

can i ask some more questions?

you said sailboats!! so in sailboat are you using vof with two fluids? i mean that we can calculate the aerodynamic and hydrodynamic at the same time? with 6 DOF???

thanks

 Stefano January 14, 2009 08:58

yes, you could, but it will be very computationally expansive and with some limitations. (in the end probably it will not be convenient to you such simulation) When I spoke about sailboat I mean that we simulate just the hydrodynamic part, in bare hull configuration. Where are you from?

 hasim January 14, 2009 19:02

turkey

 hasim January 14, 2009 19:07

i have also a qustion in the main forum about the hydrodynamic of the ships, please take a look of it and tell me your opinion since you are more exprt on the flow 3d software ( we do not know this software)

 Stefano January 15, 2009 03:58

sorry hasim, but I can't find your previous message in the main forum. If you want you can reply here the question.

 hasim January 15, 2009 05:38

hello

there is been a spam attack to the main forum, you will see them after the restore of the messages.

hasim

 Alex January 19, 2009 23:18

Stefano,If simulate the wave generated by ship, how should I set the F3D?I set the Gravity, Moving and deforming objects, Viscocity and turbulence in physics tab, and in Meshing_Geometry, set a Gmo moving from left to right.

Is it enough for simulating ship wave?

 Stefano January 22, 2009 11:52

what do you mean by ship wave? If you want to simulate the ship when hits a wave, then you have also to set up the "wave" boundary condition at the inflow boundary.

 Alex January 24, 2009 03:45

Noï¼Œ I mean that wave generated by a ship in the river. So tell me how should I set the Inputfile.

Thanks.

 Stefano January 26, 2009 04:16

then the setup that you wrote should be enough to see the wave pattern generated by a moving boat. What do you see? The boat moves without generating waves?

 kkh March 29, 2010 09:34

Regarding accuracy in ship resistance calculations

Quote:
 Originally Posted by Stefano I can tell you that with a good setup and making simulations of 2 dof coupled motion hulls, you can reach an accuracy of the 0.1° on the pitch angle, less than the 0.1% (about the lenght of the hull) on the heave, and less than the 4% on the total force vs the experiment. You can ask whatever you want, we'll be glad to help you.
Hi Stefano

Your results sound quite impressive. Maybe you aware that there is a tech paper on validation of Flow-3d for flow around a ship hull posted on Flow Science's web page, dating back to 2006. Here, the frictional resistance is severely overestimated. I would like to think that this is partly due to poor setup, but I fear that Flow-3d's meshing strategy can make it dfficult to predict the aft ship separation for a conventional displacement hull with sufficient accuracy - unless you use an excessive amount of grid cells. Do you have any comments? I would really like to see a benchmark computation of Flow-3d for this type of problem that disproves the poor results reported in the paper mentioned above.

Regards,
Kjetil

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