[acasas]

Hi,

I need to generate a small udf code to apply forces and moment over a body C.G. that travels with initial velocity conditions. It´s a transient, VOF, 6 DOF, dynamic mesh type problem (all this settings are already established) . This forces will change its direction in time depending on C.G. rotation. Body mass, moments of inertia, force magnitude and other details needed will be provided. I'm willing to pay 50 $.
It´s a box with some thickness and some material. It´s CG its at 0,0,0 and I use symmetry respect the xy plane. The properties then are described in the following UDF

#include "udf.h"

DEFINE_SDOF_PROPERTIES(test_box, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 471;
prop[SDOF_IXX] = 130.83;
prop[SDOF_IYY] = 130.83;
prop[SDOF_IZZ] = 130.83;
prop[SDOF_SYMMETRY_X] = 0;
prop[SDOF_SYMMETRY_Y] = 0;
prop[SDOF_SYMMETRY_Z] = 1;

printf ("\n2d_test_box: Updated 6DOF properties");
}

I just need to include a moment and force with some magnitude, that of course will change due to the rotation of the body due to the external pressure from the flow. You can use for example a 1.5 Newtons in the x direction. Since this box is 1x1x1 m and I apply this force over one point , lets say at x=0.5, y=-0.5 and z=0, then over the cg, there will be a force and a moment. the force will be 1.5 N and the moment will be Mz=-1.5x0.5=-0.75 Mm .

here there is an example of what I believe should be something very similar, but I don´t know anything about udf so I´m not sure how this guy included the values and where. So I can´t trak the variables and I don´t know where to include them in thsi example

Below I attach info relevant on what I believe its necessary for this type of UDF which I don't have experience and programming knowledge.

thank´s a lot


2.6.4 DEFINE SDOF PROPERTIES
Description
You can use DEFINE SDOF PROPERTIES to specify custom properties of moving objects for
the six-degrees of freedom (SDOF) solver in FLUENT. These include mass, moment and
products of inertia, and external forces and moment properties. The properties of an object
which can consist of multiple zones can change in time, if desired. External load forces
and moments can either be specified as global coordinates or body coordinates. In addition,
you can specify custom transformation matrices using DEFINE SDOF PROPERTIES.
Usage
DEFINE SDOF PROPERTIES(name,properties,dt,time,dtime)
Argument Type Description
symbol name UDF name.
real *properties Pointer to the array that stores the SDOF properties.
Dynamic Thread *dt Pointer to structure that stores the dynamic mesh
attributes that you have specified (or that are calculated
by FLUENT).
real time Current time.
real dtime Time step.
Function returns
void
There are four arguments to DEFINE SDOF PROPERTIES: name, properties, dt, and
dtime. You provide the name of the UDF. properties, dt, and dtime are variables
that are passed by the FLUENT solver to your UDF. The property array pointer that
is passed to your function allows you to specify values for any of the following SDOF
properties:
SDOF_MASS /* mass */
SDOF_IXX, /* moment of inertia */
SDOF_IYY, /* moment of inertia */
SDOF_IZZ, /* moment of inertia */
SDOF_IXY, /* product of inertia */
SDOF_IXZ, /* product of inertia */
SDOF_IYZ, /* product of inertia */
SDOF_LOAD_LOCAL, /* boolean */
SDOF_LOAD_F_X, /* external force */
SDOF_LOAD_F_Y, /* external force */
SDOF_LOAD_F_Z, /* external force */
SDOF_LOAD_M_X, /* external moment */
SDOF_LOAD_M_Y, /* external moment */
SDOF_LOAD_M_Z, /* external moment */
The boolean prop[SDOF LOAD LOCAL] can be used to determine whether the forces and
moments are expressed in terms of global coordinates (FALSE) or body coordinates (TRUE).
The default value for prop[SDOF LOAD LOCAL] is FALSE.
Custom Transformation Variables
The default transformations used by FLUENT are typical for most aerospace and other
types of applications. However, if your model requires custom transformations, you can
specify these matrices in your SDOF UDF. First set the SDOF CUSTOM TRANS boolean
to TRUE. Then use the macros listed below to define custom coordination rotation and
derivative rotation matrices. CTRANS is the body-global coordinate rotation matrix and
DTRANS is the body-global derivative rotation matrix.
SDOF_CUSTOM_TRANS, /* boolean */
SDOF_CTRANS_11, /* coordinate rotation matrices */
SDOF_CTRANS_12,
SDOF_CTRANS_13,
SDOF_CTRANS_21,
SDOF_CTRANS_22,
SDOF_CTRANS_23,
SDOF_CTRANS_31,
SDOF_CTRANS_32,
SDOF_CTRANS_33,
SDOF_DTRANS_11, /* derivative rotation matrices */
SDOF_DTRANS_12,
SDOF_DTRANS_13,
SDOF_DTRANS_21,
SDOF_DTRANS_22,
SDOF_DTRANS_23,
SDOF_DTRANS_31,
SDOF_DTRANS_32,
SDOF_DTRANS_33,

Example 1
The following UDF, named stage, is a simple example of setting mass and moments of
inertia properties for a moving object. This UDF is typical for applications in which a
body is dropped and the SDOF solver computes the body’s motion in the flow field.
/************************************************** **********
Simple example of a SDOF property UDF for a moving body
************************************************** ************/
#include "udf.h"
DEFINE_SDOF_PROPERTIES(stage, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 800.0;
prop[SDOF_IXX] = 200.0;
prop[SDOF_IYY] = 100.0;
prop[SDOF_IZZ] = 100.0;
printf ("\nstage: updated 6DOF properties");
}
Example 2
The following UDF named delta missile specifies case injector forces and moments
that are time-dependent. Specifically, the external forces and moments depend on the
current angular orientation of the moving object. Note that this UDF must be executed
as a compiled UDF.
/************************************************** *****
SDOF property compiled UDF with external forces/moments
************************************************** *****/
#include "udf.h"
DEFINE_SDOF_PROPERTIES(delta_missile, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 907.185;
prop[SDOF_IXX] = 27.116;
prop[SDOF_IYY] = 488.094;
prop[SDOF_IZZ] = 488.094;
/* add injector forces, moments */
{
register real dfront = fabs (DT_CG (dt)[2] -
(0.179832*DT_THETA (dt)[1]));
register real dback = fabs (DT_CG (dt)[2] +
(0.329184*DT_THETA (dt)[1]));
if (dfront <= 0.100584)
{
prop[SDOF_LOAD_F_Z] = 10676.0;
prop[SDOF_LOAD_M_Y] = -1920.0;
}
if (dback <= 0.100584)
{
prop[SDOF_LOAD_F_Z] += 42703.0;
prop[SDOF_LOAD_M_Y] += 14057.0;
}
}
printf ("\ndelta_missile: updated 6DOF properties");
}

[Mehul Patel]

Hello,

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