[ystein]

Hi All,

I have been trying to deform a square into a rhombic shape such as the attached pure strain image and have been testing out a few UDFs to deform the boundaries.
purestrain.PNG


I start out with a simple mesh geometry like this:
mesh_square.PNG
and use DEFINE_GEOM to deform all four walls (labeling is wall12 top right wall and then going clockwise).
This is my dynamic mesh setup page:
dynamicmesh.PNG


Current issues with my UDF:
(1) Something that I am worried about is CURRENT_TIME, so I tried to output it as a message, but it always shows like 21 times? Should i put it outside the function? such as in my TUI:

"Updating mesh to time 3.00000e-02 (step = 00003)... time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
time = 0.020000
"


(2) my mesh is only moving in the y direction, but I know I need to be stretching all four "corners" so it should update x and y.
meshmotion.PNG

Any help is appreciated. I have also tried to use DEFINE_GRID_MOTION to move the walls at an angle, but to no avail.

I have attached my full UDF, but a snippet of it is as follows:

#include "udf.h"
#include "unsteady.h"

#define W 64 /* side wall of trough, mm */
#define gamma 0.2 /* desired strain */
#define vel_exp 5e-2 /* expansion velocity mm/s */
#define vel_comp 4.52267e-2 /* compression velocity mm/s */

DEFINE_GEOM(wall_12geom, domain, dt, position)
{ Message("time = %f\n ", CURRENT_TIME , '\n');
real D,R,L,l;
real hD,hL,hl;
real dlength_L, dlength_l;
real update_length_L, update_length_l;

/*constants */
D = sqrt(2)*W; /*diagnol of square, intial*/
R = sqrt((2+gamma)/(2-gamma));
L = R*D; /*expansion axis diagnol, final*/
l = pow(D,2)/L; /* compression axis diagnol, final*/
hD=D/2; /* use these variables to calculte angle*/

real t = CURRENT_TIME;
real slope12, intercept12; /* geometry line */

dlength_L = vel_exp*t; /*delta change in expansion axis from ORIGIN, lengthening x axis*/
dlength_l = -1*vel_comp*t; /*delta change in compression axis from ORIGIN, shortening y axis*/

update_length_L = hD + dlength_L; /* every time step length, L from ORIGIN to sharp corner*/
update_length_l = hD + dlength_l; /* every time step length,l from ORIGIN to sharp corner*/

/* set variables */
slope12 = dlength_l/dlength_L; /*neg */
intercept12 = update_length_l; /*pos*/

/* set y = mx + b dependent on time*/
position[0] = position[0] + dlength_L; /* START HERE */

position[1] = slope12*position[0] + intercept12;


}