{"id":292168,"date":"2023-07-09T17:19:53","date_gmt":"2023-07-09T17:19:53","guid":{"rendered":"\/forum\/forums\/topic\/a-rigid-body-being-moved-by-water-within-a-dynamic-mesh\/"},"modified":"2023-07-09T17:19:53","modified_gmt":"2023-07-09T17:19:53","slug":"a-rigid-body-being-moved-by-water-within-a-dynamic-mesh","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/a-rigid-body-being-moved-by-water-within-a-dynamic-mesh\/","title":{"rendered":"A rigid body being moved by water within a dynamic mesh."},"content":{"rendered":"

Dear all, I have a cylinder involving a piston being moved by water, as depicted in Figure 1. The water exerts a force on the piston, pushing the water located behind the piston towards the outlet. The mesh employed has an element size of 0.15 mm. I have compiled a User-Defined Function (UDF) in ANSYS Fluent for the properties of water density, water sound speed, and the motion of the piston as a “rigid body” as in the corresponding TXT File. Most simulation settings are in figures 2 through 9. The time step is 0.001 sec.
In my attempts to solve this problem, I have explored three different solution methods: SIMPLE, PISO, and Coupled. Unfortunately, all three methods have yielded the same result – convergence has not been achieved.
I kindly request assistance from anyone who can identify the errors in my work. Furthermore, I would appreciate guidance on how to correctly implement this simulation.
Thank you in advance for your support.<\/p>\n

=================================
TXT File
=================================
#include<\/a> “udf.h”<\/p>\n

#define<\/a> Bulk_Modulus 2.2e09
#define<\/a> rho_ref 997.0<\/p>\n

DEFINE_PROPERTY(water_density, c, t)
{
real rho;
real p, dp, p_operating;<\/p>\n

p_operating = RP_Get_Real(“operating-pressure”);
p = C_P(c, t);
dp = p – p_operating;
rho = rho_ref \/ (1.0 – dp \/ Bulk_Modulus);<\/p>\n

return rho;
}<\/p>\n

DEFINE_PROPERTY(water_speed_of_sound, c, t)
{
real a_soundspeed;
real p, dp, p_operating;
p_operating = RP_Get_Real(“operating-pressure”);
p = C_P(c, t);
dp = p – p_operating;
a_soundspeed = (1.0 – dp \/ Bulk_Modulus)*sqrt(Bulk_Modulus \/ rho_ref);<\/p>\n

return a_soundspeed;
}<\/p>\n

DEFINE_SDOF_PROPERTIES(piston_rec, prop, dt, time, dtime)
{
prop[SDOF_MASS] = 0.094488;
prop[SDOF_IXX] = 0.0000291338;
prop[SDOF_IYY] = 0.000003937;
prop[SDOF_IZZ] = 0.000031496;
prop[SDOF_ZERO_TRANS_X] = FALSE;
prop[SDOF_ZERO_TRANS_Y] = TRUE;
prop[SDOF_ZERO_TRANS_Z] = TRUE;
prop[SDOF_ZERO_ROT_X] = TRUE;
prop[SDOF_ZERO_ROT_Y] = TRUE;
prop[SDOF_ZERO_ROT_Z] = TRUE;
}<\/span>\"\"<\/p>\n

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