[MBDyn-users] How to handle air drag force?

Hughe efx.ninenineone at gmail.com
Sat Oct 8 08:56:36 CEST 2011


Hi all,

I plan to run a numerical analysis of a simple pendulum. 

The shape of bob is major factor that would affect the T (period)
variation. 
I assume the shape of bob is a round sphere.  I have the following
formula that explains 
how the pendulum looses movement.

Fp - Fk - Fd

Fp: Inital Pendulum force which comes from the height of pendulum at
initial time t0.
Fk: Kinetic frictional force 
Fd: Drag force of pendulum bob

To get air drag force, I use
Fd = 0.5 x C x density x A x (v^2)
C: drag coefficient: 0.4 to 1.0
A: cross sectional area
density: air density
v: speed of the pendulum bob

Should I look into the relationship between C and A and calculate Fd? 
or 
MBDyn has built-in feature to handle C and A? 

Thanks in advance,
Hughe





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