[sg.lee]

hello.
I am wondering how to set up feedback control in terms of heat src as shown in figure and expression.
I'm not sure how to set "Src_old". I don't know how to set the volumetric heat source value used for the current iteration as a variable.


<figure>
|temp_sensor|<~~~heat~~~~|_heater_|
|_(T_current)|<~~~heat~~~~|_(Src)__|
|___[K]____ |<~~~heat~~~~|[W/m^3]|


<named expression>
T_target = 3000 [K]
T_current = AreaAve(T, ['temp_sensor'])
damp = 0.2
Src_new = Src_old*(1+damp*(T_target - T_current)/T_target))*1[W/m^3]
Src_old = ???????

regards
CFD user

[AlexanderZ]

as you've used Src_old to calculate Src_new probably you don;t need it anymore so Src_old = Src_new

show the whole UDF to get meaningfull answer, people cant read your mind
if you are using DEFINE_SOURCE macro, then you probably need UDMs to store source values for the next timestep

[sg.lee]

Originally Posted by AlexanderZ

as you've used Src_old to calculate Src_new probably you don;t need it anymore so Src_old = Src_new

show the whole UDF to get meaningfull answer, people cant read your mind
if you are using DEFINE_SOURCE macro, then you probably need UDMs to store source values for the next timestep

====================================

I do not mean 'UDF', but 'named expression'.
I need how to define src_old using 'named expression'.

There is a variable called 'User Volumetric Energy Source', so I tried to set Src_current = VolumeAve(User Volumetric Energy Source, ,['heater']), but a message saying 'User Volumetric Energy Source could not be defined' appeared.

I don't know how to define the heat source [W/m^3] used in the 'named expression', not 'UDF'.

Thank you for your answer.

[AlexanderZ]

so you may try this approach

Src_new =  VolumeAve(User Volumetric Energy Source, ,['heater'])*(1+damp*(T_target - T_current)/T_target))*1[W/m^3]
 VolumeAve(User Volumetric Energy Source, ,['heater']) = Src_new

however, this is valid starting from the second timestep, as User Volumetric Energy Source is not difed to the initial timestep

so you should check if "IF" condition is avaliable in expression:
1. yes -> you should check the time , if time ==0 -> apply some value to user columetric source, else expression above
2. no -> probably you may try to change expression manually -> apply some value to user columetric source on initial timestep, then manually change expression

[sg.lee]

Originally Posted by AlexanderZ

so you may try this approach

Src_new =  VolumeAve(User Volumetric Energy Source, ,['heater'])*(1+damp*(T_target - T_current)/T_target))*1[W/m^3]
 VolumeAve(User Volumetric Energy Source, ,['heater']) = Src_new

however, this is valid starting from the second timestep, as User Volumetric Energy Source is not difed to the initial timestep

so you should check if "IF" condition is avaliable in expression:
1. yes -> you should check the time , if time ==0 -> apply some value to user columetric source, else expression above
2. no -> probably you may try to change expression manually -> apply some value to user columetric source on initial timestep, then manually change expression

thank you
I've already used 'User Volumetric Energy Source', but a error message 'Cannot define User Volumetric Energy Source..?' appeared.
Initialization was necessary with 'IF'.
Thank you very much.

[sg.lee]

Originally Posted by AlexanderZ

so you may try this approach

Src_new =  VolumeAve(User Volumetric Energy Source, ,['heater'])*(1+damp*(T_target - T_current)/T_target))*1[W/m^3]
 VolumeAve(User Volumetric Energy Source, ,['heater']) = Src_new

however, this is valid starting from the second timestep, as User Volumetric Energy Source is not difed to the initial timestep

so you should check if "IF" condition is avaliable in expression:
1. yes -> you should check the time , if time ==0 -> apply some value to user columetric source, else expression above
2. no -> probably you may try to change expression manually -> apply some value to user columetric source on initial timestep, then manually change expression

So what about cfx?
Do you know what variable corresponds to 'User Volumetric Energy Source' in CFX instead of fluent?? I would like to recalculate the same interpretation with CFX. If you know, please let me know.