# Multi step transient UDF velocity profile problem

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 January 31, 2008, 09:47 Multi step transient UDF velocity profile problem #1 William177 Guest   Posts: n/a Hello, Could anyone please offer some advice on perfecting this UDF. The model is a 2D axi-symmetric with fluid flow over a disc. I am trying to have various combinations of velocity function across the inlet to the domain. I am attempting to simulate a disc being pushed and pulled through the fluid. Here's my source code: /************************************************** ******************** unsteady.c UDF for specifying a transient velocity profile boundary condition ************************************************** *********************/ #include "udf.h" DEFINE_PROFILE(unsteady_velocity3, thread, position) { face_t f; real t = CURRENT_TIME;begin_f_loop(f, thread) if (t<=1) { F_PROFILE(f, thread, position) = 10*t; } else if(t>1 && t<=2) { F_PROFILE(f, thread, position) = 10; } else { F_PROFILE(f, thread, position) = 30-(10*t); } end_f_loop(f, thread) } --------------------------------------------------- The velocity profile should take the form of an initial steady increase in velocity to 10m/s @ t=1s followed by a constant velocity of 10m/s until t=2s. I then want the velocity to profile to have a negative gradient from t=2s. Unfortunately the velocity gradient remains positive, even with the negative sign. Can anyone spot anything wrong with my UDF or offer any solutions? I am fairly new to writing UDFs so any help is much appreciated. Thanks very much. William

 February 3, 2008, 06:47 Re: Multi step transient UDF velocity profile prob #2 William177 Guest   Posts: n/a Any hope on attaining a negative gradient for the velocity profile folks?