
[Sponsors] 
November 8, 2010, 03:34 
(??) sinusoidal motion for DEFINE_CG_MOTION

#1 
New Member
jiho
Join Date: Mar 2010
Posts: 3
Rep Power: 9 
I'm testing with a simple UDF for sinusoidal angular velocity motion but it has a problem.
macro [DEFINE_CG_MOTION] presents [omega] for angular velocity variable and [time] to passes time variable, so try this to describe a pseudovibrating cantilever. omega is time dependant variable and displacement(angle) is intergation of the omega over the time passed. so I assumed if I put some intergand of the time into UDF, Fluent will reflect its integration to the moving boundary. Few graphs were ploted for investigation (http://yfrog.com/51graphbj) and equations are... w_1=sin(2*pi*t) F_1 = INTEGRAL(w_1, t) w_2=sin(2*pi*t + pi/2) F_2 = INTEGRAL(w_2, t) w_3=sin(2*pi*t  pi/2) F_3 = INTEGRAL(w_3, t) I choosed blue one(w_2) and its UDF code were... DEFINE_CG_MOTION(move, dt, vel, omega, time, dtime) { NV_S(vel, =, 0.0); NV_S(omega, =, 0.0); omega[2]=sin(2*M_PI*time + M_PI/2); } my desired output was correct y position of lever though, it only moves over y=0 but y>0 and vise versa (no alternation of +. just up and down under y=0 or over y=0). I have no idea for [dtime] and [accumulater+= valiable] form to the that situation. So I put integrand in the UDF and hope the Fluent updates position of that intergrand for the time, but it seemed not that explictly SO... It seems obiously there are stupid assumption or misunderstanding of UDF. Can I recieve a wise solution? Last edited by salzini; November 8, 2010 at 03:48. Reason: refine 

December 10, 2010, 05:47 

#2 
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
Rep Power: 13 
First of all, I don't see why F_1 is always positive in your picture (http://yfrog.com/51graphbj).
If angular velocity is: 1. then the integral of it should be: which alternates between 2. then the integral of it should be: which again alternates between My suggestion is to check around which origing you define this omega! 

Tags 
define_cg_motion, sinusoidal, udf 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
UDF for non sinusoidal or varying amplitude motion with respect to time  lalit kumar  FLUENT  1  November 13, 2010 17:58 
Sinusoidal motion udf  urmazda  Fluent UDF and Scheme Programming  6  July 30, 2010 11:44 
Convergence moving mesh  lr103476  OpenFOAM Running, Solving & CFD  30  November 19, 2007 15:09 
tank motion on boat  Tim  FLUENT  0  May 23, 2007 11:50 
Airfoil Sinusoidal Motion  How?  Andrew  FLUENT  1  April 8, 2005 19:42 