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pls. help : life-drag coefficient in dynamic mesh

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Old   November 30, 2007, 13:20
Default pls. help : life-drag coefficient in dynamic mesh
  #1
loogtaan
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Hello,

I solve flapping motion by using dynamic mesh but I don't know hoe to define force vector for cl,cd plot in force monitor.Have anyone can suggest me.

thanks.
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Old   December 1, 2007, 03:16
Default Re: pls. help : life-drag coefficient in dynamic m
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zhang
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firt,you can't define the foce vector, there are only three options you can choose:x_axis,y-axis and z-axis. but you can rotate the mesh to get different vector

second, force monitor just plots the force coefficient.you must know how to change the reference value to get the real forces
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Old   December 1, 2007, 09:32
Default Re: pls. help : life-drag coefficient in dynamic m
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loogtaan
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Thank you Zhang,

But I don't know how to change the reference value because I use only DEFINE_CG_MOTION to predict airfoil motion. Please explain me.

loogtaan
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Old   December 1, 2007, 09:42
Default Re: pls. help : life-drag coefficient in dynamic m
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loogtaan
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This is my udf code

#include <udf.h> #define PI 3.141592654

DEFINE_CG_MOTION(airfoil, dt, cg_vel, cg_omega, time, dtime) {

real freq = 1.707;

real amp = 1.4;

cg_vel[0] = 2*PI*freq*amp*sin(2.0*PI*freq*time); /* x-velocity*/

cg_omega[2] = 2*PI*freq*0.78534*(sin((2.0*PI*freq*time)+1.5708)) ;/*angular-velocity*/

}
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Old   December 8, 2007, 23:15
Default Re: pls. help : life-drag coefficient in dynamic m
  #5
zhang
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Sorry loogtaan, I'm being busy on my job thess days. Beyond the report menu, you can see the reference values.Once you change denstity 1.225 to 2. The forces in the "Force Monitors" become the real forces
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Old   December 20, 2007, 21:54
Default Re: pls. help : life-drag coefficient in dynamic m
  #6
loogtaan
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Thank you Zhang,

could you told me how about the velocity that I must use in the reference menu because I give same result for different Renolds Number.
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