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Old   October 13, 2015, 10:22
Default Issue with 6 dof solver
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Ludo
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Hi guys, i have a question for your gentle attention. I am implementing the SDOF solver to the canonical problem of the oscillating cylinder under current flow, and i continue to face negative mesh problems due to the cylinder going out of the 2D plane of the domain.
I will post here both screenshots of the behaviour and the UDF i wrote, i hope somebody may show me the way to correct what seems unbelievable to me. It is so simple that i must have missed something important i believe, but dunno what.
Many thanks in advance to those willing to help,
Ludo.

http://imageshack.com/a/img901/7654/Q6fSdy.jpg
http://imageshack.com/a/img901/2133/uA9LhU.jpg

the UDF is:

#include "udf.h"
DEFINE_SDOF_PROPERTIES(sdof_props, prop, dt, time, dtime)
{
real cgx;
real cgy;
real k = 1700;
cgx = DT_CG(dt)[0];
cgy = DT_CG(dt)[1];
prop[SDOF_MASS] = 170;
prop[SDOF_ZERO_ROT_X] = TRUE;
prop[SDOF_ZERO_ROT_Y] = TRUE;
prop[SDOF_ZERO_ROT_Z] = TRUE;
prop[SDOF_IXX] = 136;
prop[SDOF_IYY] = 136;
prop[SDOF_IZZ] = 136;
prop[SDOF_LOAD_F_Y] = -k*cgy;
prop[SDOF_LOAD_F_X] = -k*cgx;
}
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Old   October 14, 2015, 05:38
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Ludo
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-UPDATE for future readers-
Probably i solved my own issue with the implicit update option available on Fluent, near the SDOF option, since problems derived from the first transient part of the simulation when the pressure gains high peaks and gradients.
Setting mesh update to 100 solved partially this problem!
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Old   April 11, 2016, 18:00
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HI,
I am working on simulating in 2D, VIV of single cylinder at Re = 100000 using k-epsilon with enhanced wall conditions. I have used a similar UDF. except, k =718 and mass = 6146 kg. I keep getting the error dynamic mesh update failed-negative cell volume detected, my Cl value is very high , about 25. I tried refining the mesh and reducing the time step. I still can not solve this error.
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Old   March 6, 2017, 23:05
Default sdof problem
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betoche
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Hi.
can anyone explain simple example of SDOF function Please?
i coudnt solve any problem with this udf because of Dynamic mesh error.
can you clear it with for example one cylindrical (or any other shape) in water bowl?
i think i do something wrong in create dynamic mesh zone.
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Old   March 7, 2017, 08:56
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saurabh kumar gupta
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Hi,
Go through this link. May be it will help you.

https://www.sharcnet.ca/Software/Flu...udf/node79.htm

Regards
Saurabh
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Old   March 8, 2017, 14:22
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betoche
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thanks for Ur reply dear Saurabh
actually in simple sentence my model is a cylinder into another cylinder and small cylinder has angular velocity and big one must be fix completely.
i tried it again but outer cylinder move too
how can i say it inter cylinder must rotate and move but outer one be fix?
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Old   March 8, 2017, 15:04
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saurabh kumar gupta
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In define dynamic zones, make inside cylinder as rigid body and outer cylinder as fix. Use smoothing and remeshing. I think that's all you need to do.
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Saurabh
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oscillating_cylinder, out_of_plane_deformation, sdof

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