{"id":354943,"date":"2024-03-02T15:03:27","date_gmt":"2024-03-02T15:03:27","guid":{"rendered":"\/forum\/forums\/topic\/external-forces-udf-for-store-separation-6dof\/"},"modified":"2024-03-02T15:03:27","modified_gmt":"2024-03-02T15:03:27","slug":"external-forces-udf-for-store-separation-6dof","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/external-forces-udf-for-store-separation-6dof\/","title":{"rendered":"external forces UDF for store separation 6DOF"},"content":{"rendered":"

Hello,<\/p>\n

 <\/p>\n

I am using a UDF for a simple store separation case, where external forces should be applied to the CG while it is less than a certain Z displacement (0.1m). The reference frame is oriented at the CG, with axes consistent with the body frame orientation (Z down, X Fwd). From what I can tell, the UDF I am using  (which is from the udf guide) is not applying these external forces but is applying the physical properties (Ixx, Iyy, Izz) to the body which then experiences a gravity drop. I was hoping someone could look at this UDF and provide insight into why the external forces are not being applied. My time step is 0.01. It appears that the Z displacement that I want the external forces to be acting before is not met until appx. 9 time steps. Below is a copy of the UDF I am trying to use:<\/p>\n

\n
\/*******************************************************<\/div>\n
SDOF property compiled UDF with external forces\/moments<\/div>\n
*******************************************************\/<\/div>\n
#include “udf.h”<\/div>\n

<\/p>\n

DEFINE_SDOF_PROPERTIES(delta_missile, prop, dt, time, dtime)<\/div>\n
{<\/div>\n
   prop[SDOF_MASS]       = 907.185;<\/div>\n
   prop[SDOF_IXX]        = 27.116;<\/div>\n
   prop[SDOF_IYY]        = 488.094;<\/div>\n
   prop[SDOF_IZZ]        = 488.094;<\/div>\n

<\/p>\n

   \/* add injector forces, moments *\/<\/div>\n
   {<\/div>\n
     register real dfront = fabs (DT_CG (dt)[2] –<\/div>\n
                            (0.179832*DT_THETA (dt)[1]));<\/div>\n
     register real dback  = fabs (DT_CG (dt)[2] +<\/div>\n
                            (0.329184*DT_THETA (dt)[1]));<\/div>\n

<\/p>\n

     if (dfront <= 0.100584)<\/div>\n
       {<\/div>\n
         prop[SDOF_LOAD_F_Z] = 10676.0;<\/div>\n
         prop[SDOF_LOAD_M_Y] = -1920.0;<\/div>\n
       }<\/div>\n

<\/p>\n

     if (dback <= 0.100584)<\/div>\n
       {<\/div>\n
         prop[SDOF_LOAD_F_Z] += 42703.0;<\/div>\n
         prop[SDOF_LOAD_M_Y] += 14057.0;<\/div>\n
       }<\/div>\n
   }<\/div>\n

<\/p>\n

   printf (“\\ndelta_missile: updated 6DOF properties”);<\/div>\n
}<\/div>\n<\/div>\n","protected":false},"template":"","class_list":["post-354943","topic","type-topic","status-closed","hentry","topic-tag-dynamic-mesh","topic-tag-udf"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t