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-   -   how to see the hydrodynamic drag (http://www.cfd-online.com/Forums/flow-3d/27271-how-see-hydrodynamic-drag.html)

 Eleazar October 30, 2008 05:26

how to see the hydrodynamic drag

hello

i am working on the version 9.2 , import an stl ship and make a simulation to calculate the hydrodynamic forces, but i do not know how to see them.

can anyone help me???????

thanks eleazar

 George October 30, 2008 15:13

Re: how to see the hydrodynamic drag

You go to Analyze > Prob, select General history and Text or Graphical. From the list for Data Variables, you will find all the output data for GMO. Select Component # x (or y, z) comp. of GMO hydraulic force. Then click Render.

George

 Eleazar October 30, 2008 17:58

Re: how to see the hydrodynamic drag

is this possible to have for a 60 meters yacht a number of 5*1e-13 drag force????????????????

what id i make wrong??? what are the units?????

thanks eleazar

 George October 31, 2008 10:16

Re: how to see the hydrodynamic drag

You can use either SI or CGS unit. I have never met any case with so small drag force. Make sure you selected the correct item in the history data list. If it is still wrong, you may contact Flow Science if you have support.

 Michael Barkhudarov October 31, 2008 11:36

Re: how to see the hydrodynamic drag

Hi Eleazar,

If the yacht is modeled as a stationary object, not a GMO component, then to get the fluid forces on it you need to define a force window in the input file (a 3d shoe-box around the object). Then run the simulation, and look for the force and moment components in Probe>General history data catalogue.

If the yacht is a moving (GMO) compnent, then these forces will be automatically computed and stored.

 Eleazar October 31, 2008 16:38

Re: how to see the hydrodynamic drag

hello

i just take the example of the sphere from the flow 3d examples and delete the sphere with a stl file a yacht. this is one fluid free surface simulation where the yacht is 60 meters. two thing i did not understand yet....

1) the units are meter N sec etc... but the box is 300 000 units at Y , 400 000 units in X and 200 000 units in z , so if the units are in meters them the model is a little bit wrong because the box could not be 300 000 meters..... so what the box units are???

2) the correct way is the one flid and free surface or two fluids (to also include air?????

thanks a lot for the help i really have to see that as soon as possible.

eleazar

 aginor December 8, 2008 20:17

Re: how to see the hydrodynamic drag

what did you do?? i have the same problem! i can see the correct force only in the direction that is coupled motion (free to move) i need the force in the not moving axis. i try the force window also but the same problem

 eleazar January 9, 2009 04:34

Re: how to see the hydrodynamic drag

i found it !!!!!!!!!!!!!!!!!!!!!!!!!!!!

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