dynamic meshing UDF motion coding issue!
 

Hello!

I am trying to simulate a 2D moving piston to analyse the pressure flow field in a closed system. I currently have a rectangular mesh and am trying to write a Define_GEOM macro to define the motion of one moving boundary to simulate the movement piston.

I do not have much experience with coding, but have been looking at various tutorials and examples and have so far come up with the following code:


#include "udf.h"

DEFINE_GEOM(moving_boundary,domain,dt,position)

int position;
for (int position=0; position<=230.5; position++)
{
nextposition = position+1;
if (position<230.5)
{
nextposition = - 138399*position*position + 2716.6*position - 0.7678;
}
position = nextposition;
}


The code contains a simple sin function: y = -138399x^2 + 2716.6x - 0.7678 which should allow the piston to accelerate and decelerate. The code is designed to move the piston wall from position 0mm to position 230.5mm and then stop. So I want the position to increment at 1mm every iteration from 0mm to 230.5mm at a rate of the sin function shown.
I am getting a lot of errors with this though and was hoping someone might be able to help!:confused:

Originally I used this code: { position[1] = - 138399*position[0]*position[0] + 2716.6*position[0] - 0.7678; }
and managed to hook it to my model, however as there is no loop function, the wall only moves slightly once.

Any help would be massively appreciated.

Thanks!

Lisa