# help for a simple student

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 January 5, 2006, 10:06 help for a simple student #1 harika Guest   Posts: n/a Hi! I'm a student of aerodynamics and I'm one of the first persons of my insitute who works with fluent. I want to work with dynamic mesh and UDFs to simulate a piston that moves back and forth. I wrote a UDF with F_PROFILE to move the piston, but it doesn't work. I'm sure, that it's not a big problem to write an UDF, that let a wall move with a sin-function. I have only the UDF manual, but it doesn't help. And as a simple student, I doesn't get a login for the Fluent user service center. Does anyone wants to make a good deed and send me an example with such an UDF? Thanks, and a happy new year!

 January 5, 2006, 16:30 Re: help for a simple student #2 manoj Guest   Posts: n/a send me your problem file and your f_profile for the piston. let me try to figure it out.

 January 6, 2006, 01:58 Re: help for a simple student #3 MANOJKUMAR Guest   Posts: n/a Hello Manoj Can y help me for setting injection setting. Manojkumar

 January 6, 2006, 04:59 Re: help for a simple student #4 Manoj Kumar Guest   Posts: n/a Hi You can use the following udf to move the piston (regid body). Compile and use the udf in dynamic mesh panel. ------------------ #include "udf.h" #define time 2 DEFINE_CG_MOTION(block,dt,vel,omega,time,dtime) { /* set x-component of velocity */ vel[0] = 0.0; /* set y-component of velocity */ vel[1] = 0.3*(2*3.14/2)*cos((2*3.14/2)*time); /* set z-component of velocity */ vel[2] = 0.0; } ----------------- If you want to move the piston in accordance with the pressure variation in the cylinder, you will have to extend this udf to calculate the total force acting on the cylinder and then set the vel[] vector accordingly. Good luck Manoj

 January 6, 2006, 20:53 Re: help for a simple student #5 manoj Guest   Posts: n/a hi manoj ( damn this sounds weird ) ! well yeah i can help ya settin the case....

 January 9, 2006, 09:45 Re: help for a simple student #6 harika Guest   Posts: n/a Hi Manoj, it works!!! It's so great! Thank you very munch! I'm so happy now...

 January 10, 2006, 01:18 Re: help for a simple student #7 MANOJKUMAR Guest   Posts: n/a Thanks a lot, I tried to set injection from help menu but not succes.There is lot of parameter to set so I confused.In my case There is a square furnace 5000-long,1500 height and 4800 width and all dimenstions are in mm. And all four corner there is a burner at right angle to each other.Now i am try to set injection. First i made a PDF file of LDO-light diesel oil. First solve laminar and tarbulent without energy and then on the energy with injection. but there is enthalpy divergence. If there is some sequence to set the injection then it is help ful for me. or give me ur e-mail id so i can send my full problem. my e-mail is : ms_project05@rediffmail.com Thanking you, MANOJKUMAR

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