CFX expression language

mahdimazloom · October 8, 2014, 04:50

How can I solve an ordinary differential equation using CFX expression language?

ghorrocks · October 8, 2014, 06:23

You can't.

mahdimazloom · October 8, 2014, 12:48

Untitled.jpg

Menter, Florian, et al. "Overview of Fluid-structure coupling in ANSYS-CFX." 25th International Conference on Offshore Mechanics and Arctic Engineering. American Society of Mechanical Engineers, 2006.

singer1812 · October 8, 2014, 16:00

The motion of the cylindar is prescribed by the forces on it.
Weight is one = m_cylinder*g
Spring is one = k*dy_cylinder
damper is one = c*v_cylinder
Fluid force = F_fluid

All of those values are variables in CFX. You can sum those up to F_sum

Your cylinder wall motion will be dicretization of F_sum=ma. The resulting displacement (this is relative to previous mesh) is used for mesh motion of (assuming motion in one direction only):

(F_sum*tstep/m+v_cylinder)*tstep

That equation can be used in CEL to move the wall.

I leave it to you to derive that.

mahdimazloom · October 8, 2014, 17:49

Thanks Edmund. I think that's the answer

ghorrocks · October 8, 2014, 17:51

Nice work Edmund!

But in general you cannot solve an arbitrary ODE in CEL. It works in this specific case because it is using force as the variable and CFX has a lot of functions to calculate forces on bodies.

mahdimazloom · October 8, 2014, 18:09

I'v gotten my answer but is it possible to get access to the data from one or more steps before through CEL commands so one can solve the arbitrary ODE using finite difference method?

ghorrocks · October 8, 2014, 18:15

I thought my previous post was quite clear......

There is a messy way of accessing previous values. Do a search of the forum for "TRANS_LOOP".

October 8, 2014, 04:50	CFX expression language	#1
mahdimazloom New Member Mahdi Mazloom Join Date: Jul 2014 Location: Mashhad - Iran Posts: 12 Rep Power: 11	How can I solve an ordinary differential equation using CFX expression language?

October 8, 2014, 16:00		#4
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 20	The motion of the cylindar is prescribed by the forces on it. Weight is one = m_cylinderg Spring is one = kdy_cylinder damper is one = cv_cylinder Fluid force = F_fluid All of those values are variables in CFX. You can sum those up to F_sum Your cylinder wall motion will be dicretization of F_sum=ma. The resulting displacement (this is relative to previous mesh) is used for mesh motion of (assuming motion in one direction only): (F_sumtstep/m+v_cylinder)*tstep That equation can be used in CEL to move the wall. I leave it to you to derive that. mahdimazloom likes this.

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October 8, 2014, 06:23		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	You can't.

October 8, 2014, 12:48		#3
mahdimazloom New Member Mahdi Mazloom Join Date: Jul 2014 Location: Mashhad - Iran Posts: 12 Rep Power: 11	Untitled.jpg Menter, Florian, et al. "Overview of Fluid-structure coupling in ANSYS-CFX." 25th International Conference on Offshore Mechanics and Arctic Engineering. American Society of Mechanical Engineers, 2006.

October 8, 2014, 17:49		#5
mahdimazloom New Member Mahdi Mazloom Join Date: Jul 2014 Location: Mashhad - Iran Posts: 12 Rep Power: 11	Thanks Edmund. I think that's the answer

October 8, 2014, 17:51		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Nice work Edmund! But in general you cannot solve an arbitrary ODE in CEL. It works in this specific case because it is using force as the variable and CFX has a lot of functions to calculate forces on bodies.

October 8, 2014, 18:09		#7
mahdimazloom New Member Mahdi Mazloom Join Date: Jul 2014 Location: Mashhad - Iran Posts: 12 Rep Power: 11	I'v gotten my answer but is it possible to get access to the data from one or more steps before through CEL commands so one can solve the arbitrary ODE using finite difference method?

October 8, 2014, 18:15		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	I thought my previous post was quite clear...... There is a messy way of accessing previous values. Do a search of the forum for "TRANS_LOOP".