CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > STAR-CCM+

Error: Cycle detected in field function

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By abdul099

Reply
 
LinkBack Thread Tools Display Modes
Old   July 19, 2012, 06:15
Default Error: Cycle detected in field function
  #1
New Member
 
Rachit Prasad
Join Date: Jun 2011
Location: Blacksburg, Virginia
Posts: 29
Rep Power: 6
Rachit is on a distinguished road
Hi everyone,

I am carrying out a CFD analysis of a wind turbine. I want the turbine blades to rotating. The idea is to define a circular region around the blade which will be rotating at a certain angular velocity and will exchange data with the surrounding environment through a sliding mesh. Now, what I want is that angular velocity of the circular region be defined as:

w = 2.3559, for t <= 0.015s
w(t) = w(t - 1) + (Torque / Moment of Inertia)*TimeStep, for t > 0.015s

where Torque is the moment on the turbine blades.

for this i had defined a field function UserFieldFunction_1 defined as:

($Time <= 0.015) ? 2.3559 : $UserFieldFunction_1 + (($Torque/1.308)*0.005)
(moment of inertia is 1.308 kgm^2 and the time step is 0.005s)

however, following this i get the error message: "Warning: 1 cycle detected in function Turbine anglular velocity (UserFieldFunction_1)"

can anyone what am i doing wrong and how it can be rectified? i think its because of referencing the same field function in code, but then how else could such a function be defined?

Thanks in advance,
Regards,
Rachit
Rachit is offline   Reply With Quote

Old   July 19, 2012, 10:19
Default
  #2
Member
 
Ryan Coe
Join Date: Jun 2010
Location: Albuquerque, NM
Posts: 98
Rep Power: 7
ryancoe is on a distinguished road
If understand the logic that you're trying to use correctly, couldn't you use:

($Time <= 0.015) ? 2.3559 : 2.3559 + (($Torque/1.308)*0.005)

In your current implementation, when t > 0.015 the algorithm can never find a value of $UserFieldFunction_1 to use in the 2nd half of the statement.

Hope this helps,

Ryan
__________________
Ryan
ryancoe is offline   Reply With Quote

Old   July 24, 2012, 04:48
Default
  #3
New Member
 
Rachit Prasad
Join Date: Jun 2011
Location: Blacksburg, Virginia
Posts: 29
Rep Power: 6
Rachit is on a distinguished road
Hi Ryan,

Thanks for replying. I shall be more clear of what I wish to accomplish, and correct me if I am wrong. I want the turbine to rotate with an angular velocity which is directly obtained from the equation:

Torque = I*alpha, where I is moment of inertia and alpha is the angular acceleration

that gives, alpha = Torque/I

now applying, euler's first order integration, we have

[(w(t) - w(t - 1))/delta T] = Torque/I

that gives me the relation mentioned in the previous post:
w(t) = w(t -1) + (Torque/I)*TimeStep

that is why I have to use the angular velocity from the previous time step. I understand what error I am getting, any idea how I can bypass it?

Regards,
Rachit
Rachit is offline   Reply With Quote

Old   July 24, 2012, 08:26
Default
  #4
Member
 
Ryan Coe
Join Date: Jun 2010
Location: Albuquerque, NM
Posts: 98
Rep Power: 7
ryancoe is on a distinguished road
I see... Sorry I misunderstood you before. I think that the easiest way to do this within Star-CCM+ (that is without using macros), would be to assign the value of w(t) to a table value, and then reference that value as well. I've never done this myself, but I'm pretty sure its possible (there's a section describing this sort of thing in the Help manual: "Working With Table Values Through Field Functions").

Alternatively, if you want to stay away from tables and just use an algorithm, you could write a java macro containing a for loop which creates and references the array w(t). The macro can then reassign the new w(t) value to a field function at every time step.

Ryan
__________________
Ryan
ryancoe is offline   Reply With Quote

Old   July 27, 2012, 04:20
Default
  #5
New Member
 
Rachit Prasad
Join Date: Jun 2011
Location: Blacksburg, Virginia
Posts: 29
Rep Power: 6
Rachit is on a distinguished road
Dear Ryan,

I have been trying to figure out how to write a macro for this situation only to find myself extremely confused . This is my first macro so correct me if my approach is wrong. What I have been thinking is that I could record a macro in which I will change the field function definition as: [(2.3559 + (($Torque/1.308)*0.005))], following which I will run the simulation for 1 time step.
On recording this macro, I will change its java script by defining a variable temp which initially I will set it as 2.3559 and change the user field function definition as: [(temp + (($Torque/1.308)*0.005))], however, the value of temp has to be updated after every time step as temp = UserFieldFunction_1. I can then run the simulation for as many number of time steps by modifying simulation_0.getSimulationIterator().run().

Could you tell if this is possible or not? I have recorded the macro, but have little idea how to modify the java script. How can i update the term temp after every time step? Are there any guides available for scripting in Star CCM+? (There are very less examples in User Guide)
Rachit is offline   Reply With Quote

Old   July 27, 2012, 11:19
Default
  #6
Member
 
Ryan Coe
Join Date: Jun 2010
Location: Albuquerque, NM
Posts: 98
Rep Power: 7
ryancoe is on a distinguished road
If you've done any programming, editing and writing macros shouldn't be too hard. I would definitely suggest using an IDE like Netbeans or Eclipse. If you point theseIDEs to Star-CCM+'s packages, they can be really helpful.

There are 2 tutorials on Automation in the Help Manual that should give you a basic understanding of how things work.

I know this can be a bit daunting at first, but its worth your time.

Ryan
__________________
Ryan
ryancoe is offline   Reply With Quote

Old   July 28, 2012, 08:36
Default
  #7
Senior Member
 
Join Date: Oct 2009
Location: Germany
Posts: 637
Rep Power: 12
abdul099 is on a distinguished road
You don't even need to update the field function, you can try it with the attached macro. I couldn't upload a java file, so I renamed it to txt. Just change the file ending to java, and you can execute it in Star-CCM+.
I haven't tested the macro, but just try it and let us know when it doesn't work.
Attached Files
File Type: txt ChangeOmega.txt (1.6 KB, 102 views)
bluebase likes this.
__________________
We do three types of jobs here:
GOOD, FAST AND CHEAP
You may choose any two!
abdul099 is offline   Reply With Quote

Old   July 30, 2012, 06:42
Default
  #8
New Member
 
Rachit Prasad
Join Date: Jun 2011
Location: Blacksburg, Virginia
Posts: 29
Rep Power: 6
Rachit is on a distinguished road
@abdul099

Thanks a lot! Your macro works just fine. I am getting the expected results.

Regards,
Rachit
Rachit is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Field Function Question. Need help writing it :((( kj878 CD-adapco 1 February 14, 2012 19:30
LiencubiclowRemodel nzy102 OpenFOAM Bugs 14 January 10, 2012 09:53
problems after decomposing for running alessio.nz OpenFOAM 5 April 20, 2011 08:44
Force Report help~ or maybe Custom Field Function sailor FLUENT 0 April 13, 2011 03:45
time step size in Custom Field Function Tong FLUENT 0 May 2, 2008 15:51


All times are GMT -4. The time now is 19:47.