[TDi]

I'm having trouble getting DEFINE_GRID_MOTION to work. The example for grid motion in section 2.6.3 of the manual includes some macros for which I cannot find documentation but are important:
NV_VEC()
SET_DEFORMING_THREAD_FLAG()
NODE_POS_NEED_UPDATE()
NODE_POS_UPDATED()
I'm having trouble understanding how the node positions are updated. Where does the write occur? Is there are simple function for writing a new position to a node? Sample code from UDF manual 2.6.3 follows:

/**********************************************************
 node motion based on simple beam deflection equation
 compiled UDF
 **********************************************************/
#include "udf.h"

DEFINE_GRID_MOTION(beam,domain,dt,time,dtime)
{
  Thread *tf = DT_THREAD(dt);
  face_t f;
  Node *v;
  real NV_VEC(omega), NV_VEC(axis), NV_VEC(dx);
  real NV_VEC(origin), NV_VEC(rvec);
  real sign;
  int n;
  
  /* set deforming flag on adjacent cell zone */
  SET_DEFORMING_THREAD_FLAG(THREAD_T0(tf));

  sign = -5.0 * sin (26.178 * time);
  
  Message ("time = %f, omega = %f\n", time, sign);
  
  NV_S(omega, =, 0.0);
  NV_D(axis, =, 0.0, 1.0, 0.0);
  NV_D(origin, =, 0.0, 0.0, 0.152);
  
  begin_f_loop(f,tf)
    {
      f_node_loop(f,tf,n)
        {
          v = F_NODE(f,tf,n);

          /* update node if x position is greater than 0.02
             and that the current node has not been previously
             visited when looping through previous faces */
          if (NODE_X(v) > 0.020 && NODE_POS_NEED_UPDATE (v))
            {
              /* indicate that node position has been update
                 so that it's not updated more than once */
              NODE_POS_UPDATED(v);

              omega[1] = sign * pow (NODE_X(v)/0.230, 0.5);
              NV_VV(rvec, =, NODE_COORD(v), -, origin);
              NV_CROSS(dx, omega, rvec);
              NV_S(dx, *=, dtime);
              NV_V(NODE_COORD(v), +=, dx);
            }
        }
    }

  end_f_loop(f,tf);
}

[TDi]

I'll answer my own question since I'm certain someone else will have the same question.
Operations on node geometry happen using vectors declared as real NV_VEC.
Values are assigned with NV_S for scalars and NV_D for three component lists.
Thus NV_S(omega, =, 0.0) gives the omega NV_VEC a scalar value of 0.0 and NV_D(axis, =, 0.0, 1.0, 0.0) makes axis = [0,1,0].
The node value is changed later with NV_V(NODE_COORD(v),+=,dx) which has the effect of adding dx to the coordinates of node v.

Maybe this is obvious to other people, but it took some time for me to figure out.

[enry]

Hi TDi !

Have you understand how can you move the domain?
I have to deform a flat-plate to a given geometry, where deformation is imposed by user.
Can you help me?
Thanks a lot.

[TDi]

I didn't find cyl3d.msh in my tutorial files.

[TDi]

Here's how I did this:
In my geometry, there are multiple zones on the surface to be moved, so I keep track of the last time each was moved with a static global variable.
I have changed some of the variable names due to IP concerns and have not tested this code as shown below, so I can't promise that it's free of syntax errors.
In my application, the zones are moved automatically at a specified interval, but you can easily adapt this to other uses.
Hope this helps.

# include "udf.h"
# include "dynamesh_tools.h"

/********************** UDF Explanation Starts ***************************
         This udf is used to provide a moving boundary.

  Written by : Tim Diller (UT Austin)
  Last updated : 07/2010
********************** UDF Explanation Ends *****************************/

/*************************** User Input Starts *****************************/
# define INTERVAL 20      /* seconds - time between moves*/
# define START_TIME 20                /*time when the process starts*/
# define MOVE_THICKNESS 0.0005    /* meters */
# define ZONE1_ID 3                /*from Boundary Conditions panel*/
# define ZONE2_ID 6             /*from Boundary Conditions panel*/
# define NUM_ZONES 17    /*size array properly for tracking zone movement*/
/*************************** User Input Ends *******************************/

/*arrays initialized with a single value default to zero for all
  unspecified values*/
static float previous_move_time[2] = {0}; /*time of the last face move*/
static float previous_time[2] = {0};       /*time of the last execution*/

/*DEFINE_GRID_MOTION(move_layer, udf name*/
/*		   domain,      domain pointer - face to be moved*/
/*		   dt,             dynamic thread pointer*/
/*		   time,          current simulation time (s)*/
/*		   dtime,         time step (s)*/

DEFINE_GRID_MOTION(move_layer,domain,dt,time,dtime){
  real current_time = time;
  real NV_VEC(layer); /*real vector for offsetting the nodes*/
  Thread *tf = DT_THREAD(dt);
  face_t f;
  Node *node;
  int n;
  int zone_ID = THREAD_ID(tf);
  int zi=0;
 
  if (zone_ID == ZONE1_ID) {
    zi=0;
  }
  else if (zone_ID == ZONE2_ID) {
    zi=1;
  }
  else {
    printf("\nmove_layer: zone_ID %d not found",zone_ID);
    return;
  }
  
  /* Move the layer */
  if((current_time >= START_TIME) & \
     (current_time >= previous_move_time[zi]+INTERVAL)) {

     printf("\n***** Adjusting grid for zone %d at time %.1f.",zone_ID,current_time);
   /* write the layer offset direction to an NV_VEC variable 'layer'.*/
    NV_D(layer, =, 0.0, 0.0, LAYER_THICKNESS);
    SET_DEFORMING_THREAD_FLAG(THREAD_T0(tf));

    begin_f_loop(f,tf) { /* loop over all the faces in the domain (zone) to move */
      f_node_loop(f,tf,n) { /* loop over all the nodes of each face */
	node = F_NODE(f,tf,n);
	if(NODE_POS_NEED_UPDATE(node)){ /*add layer to the current node position*/
	  NV_V(NODE_COORD(node), +=, layer);
	  NODE_POS_UPDATED(node);
	}/* end if node pos needs update loop */
      }/* end_f_node_loop */
    } end_f_loop(t,tf);
    previous_move_time[zi] = current_time;
    printf("\n **** Z-position=%f.",NODE_Z(node));
  }/*end if - move layer*/

  previous_time[zi] = current_time;
  printf("\nDone with move_layer.");
}

[GeR]

Hi TDi,

I'm new to this area.
May I know this CG_MOTION is applicable for 3D problem ??
If I want to move a face, how should I proceed ?? Please advise !!

Thanks in advance.

[jahan53]

i want to write a udf that it can fluctuates a diaphragm but not as a piston(rigid body). two ends of diaphragm are fixed.
which of macros of dynamic mesh must be used? please advise.

[saas1y12@soton.as.uk]

Originally Posted by jahan53

i want to write a udf that it can fluctuates a diaphragm but not as a piston(rigid body). two ends of diaphragm are fixed.
which of macros of dynamic mesh must be used? please advise.

Hi,
Have u solve thos problem?