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Old   September 22, 2005, 05:01
Default 6 DOF simulation
Manoj Kumar
Posts: n/a

I am trying to simulate a wooden block fall in water using a udf. The simulation can be viewed at

The problem is that during the initial phase of the fall, the simulation looks fine, but once it hits the water surface, the block undergoes an unnatural movement. The block rebounds from the water surface and hits one of the wall of the rectangular domain.

I am using following loop to calculate the force and the moment acting in the block.

begin_f_loop (f, t)





/* x,y,z - components of Force x-component of force = Pressure on the face * x-component of Area vector */

Fx += F_P(f,t)*A[0];

Fy += F_P(f,t)*A[1];

Fz += F_P(f,t)*A[2];

node = F_NODE(f,t,n);

/* Moment (M) = vector product of Force and Displacement vector (F X r);

F = Fx i + Fy j +Fz k

r = (x - cg_x)i + (y- cg_y)j + (z - cg_z)k


Mx += F_P(f,t)*(A[1]*(NODE_Z(node) - loc_z)-A[2]*(NODE_Y(node) - loc_y));

My += F_P(f,t)*(A[2]*(NODE_X(node) - loc_x)-A[0]*(NODE_Z(node) - loc_z));

Mz += F_P(f,t)*(A[0]*(NODE_Y(node) - loc_y)-A[1]*(NODE_X(node) - loc_x));



end_f_loop (f, t)

Can anyone let me know if there is any problem with force and moment calculation ?

Thanks in advance.

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Old   September 22, 2005, 08:08
Default Re: 6 DOF simulation
Manoj Kumar
Posts: n/a
The force on the body reported though Fluent's Force panal and the one calculated though my udf are different. Can anyone help me out?

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