[vga67]

hi everybody,

I have simulated a 3 dimensional problem with SDOF solver and Dynamic mesh of Fluent V.6.3.26. the problem is about the sinking of a solid spherical particle with 5 mm diameter and 1010 kg/m3 density in water. I used the same UDF that exists in Fluent tutorial "falling box" but have changed it so that it can be used in my problem.
the following text is the desired UDF:

DEFINE_SDOF_PROPERTIES(test_box, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 1.55e-5;
prop[SDOF_IXX] = 2.5e-11;
prop[SDOF_IYY] = 2.5e-11;
prop[SDOF_IZZ] = 2.5e-11;
prop[SDOF_IXZ] = 2.5e-11;
prop[SDOF_IXY] = 2.5e-11;
prop[SDOF_IYZ] = 2.5e-11;
(all of the above units are of SI units "kg and meter")
after 0.2 second with 0.001 time step, the particle moves 50 mm which i think is not logical and it should last longer, since the density difference between the particle and the water is very low. in each time step a message is written which is "the program can not calculate the angular velocity". i know the problem with this message and that is because of the fact that second moment of inertia is less than 1e-6. with the situation i described above, my question is that " why does the particle sink too fast?"

thanks