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-   -   Convert transient case to steady state case (https://www.cfd-online.com/Forums/fluent-udf/237662-convert-transient-case-steady-state-case.html)

zeefar July 29, 2021 04:44

Convert transient case to steady state case
 
Hello,
I'm working on simulating kinematics of insect wing flapping and I wrote a UDF for its transient kinematics which works fairly well. The problem is that I need to actually rework the simulation as a steady state case for my final results. My current code has a time component which does not get processed by Fluent as the case is steady state, as you may see below:

/* flap.c */
/* UDF for specifying a simple harmonic motion*/
/* */
/**********************************************/

#include "udf.h"
#define Freq 0.1
#define angular_freq 2.0*M_PI*Freq
#define tetmax -45.0*M_PI/180

DEFINE_CG_MOTION(shm, dt, cg_vel, cg_omega, time, dtime)
{
real omega;
omega = tetmax*angular_freq*cos(angular_freq*time); /* rotational speed about axis*/

cg_vel[0] = 0.0075 * sin(3.1415927 * time / 5.);
cg_vel[1] = 0.0;
cg_vel[2] = 0.0;

cg_omega[0] = 0.0;
cg_omega[1] = 0.0;
cg_omega[2] = omega;
}


I need to know how I can change this code so it works in a steady state case as well.

AlexanderZ July 29, 2021 05:41

motion itself implies something transient, isn't it?

if you need steady state simulation on specific configuration of domain, you may :
1. prepare this mesh from the very beginning and run it as steady state
2. or stop your transient simulation at specific moment

probably you have special knd of problem, which I don't fully understand


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