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Old   January 25, 2012, 09:38
Default Force calculation help
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Tom Walker
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I have set up an SST flow to simulate the air flow around an underground train. With these settings I am trying to calculate the drag coefficient of the train but when I do an expression to calculate the force on the train then it keeps giving me a value of zero. The train is only moving at 15 m/s so i know the force will be low but zero seems a little extreme.

Is there a really obvious reason why it is doing this?

All help is highly appreciated

Thanks

Tom
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Old   January 25, 2012, 10:27
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Lance
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Could you post your expression for the drag coeff?
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Old   January 25, 2012, 10:30
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i was going to work out the drag coefficient in excel later i just needed ansys to measure the drag force so that I can incorporate it into my equation

Thanks
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Old   January 25, 2012, 10:34
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Quote:
Originally Posted by tomwalker View Post
... but when I do an expression to calculate the force...
so how does this expression look like? What do you want to export to Excel (and why?).
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Old   January 25, 2012, 10:37
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The only value i need out of ansys is the value for the force acting on the body in the same direction as the air flow (i.e. the drag force) using this value I can then use:

Cd = (2Fd)/(density*velocity*velocity*area)
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Old   January 25, 2012, 10:40
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Yes, that's the expression for the drag coeff, but I asked about your expression for the force (that apparently becomes zero...)

Is is something like:
force_x()@some_area?
Or its equivalent
areaInt_X(Pressure)@some_area+areaInt(Wall Shear X)@some_area

Last edited by Lance; January 25, 2012 at 10:54. Reason: typo
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Old   January 25, 2012, 10:42
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oh right sorry, miscommunication there

Yes that is what my equation looks like using x because that is the direction of flow and the area is front (because that is the domain that is on the front of my train)

Thanks
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Old   January 25, 2012, 10:56
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Quote:
Originally Posted by tomwalker View Post
oh right sorry, miscommunication there

Yes that is what my equation looks like using x because that is the direction of flow and the area is front (because that is the domain that is on the front of my train)

Thanks
Well, it shouldnt be zero (as you pointed out ). Is it the same for other surfaces? Is the pressure integral also zero?
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Old   January 25, 2012, 10:57
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I haven't checked the pressure integrals but looking at the force on the surface of the whole body it has given me a reasonable looking results

Thanks for your help

Tom Walker
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Old   February 14, 2012, 10:07
Default train moving in tunnel help
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hello
i am working on train moving in tunnel. i am getting floating error:invalid number. can any one help me. my email is sheikhnasir39@gmail.com
plz help me
thanks

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