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Old   August 30, 2015, 03:12
Exclamation Conductivity as a vector value
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Nurzhan
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Hi Guys,

I am trying to set a thermal conductivity as a full tensor so it varies based on one of the directions (X, Y, and Z). In order to set a magnitude of the conductivity, I looked at material properties and changed the magnitude there. However, my conductivity is described by three functions of temperature, each function per direction.

I believe there is an easy way to do it, but I am failing to find the solution.

Could you please help me?

Cheers,
Nurzhan

Last edited by Nurzhan; August 31, 2015 at 04:50.
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Old   August 30, 2015, 06:27
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Use a CEL expression, interpolation function or junction box rountine.
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Old   August 30, 2015, 15:28
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Based on the mathematical formalism for heat conduction, thermal conductivity cannot be a vector. It is a second order tensor, that for isotropic materials reduces to scalar.

In the case of anisotropic thermal conduction, ANSYS CFX has a hidden feature to input the orthotropic conductivities (principal values on a specific orientation of the material) , or the full tensor.

You can search this forum for "Thermal Conductivity X".. Otherwise, you should probably contact ANSYS CFX support for help.

Either of those values can be set using CEL expression, interpolation functions or via user Fortran junction boxes.
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Old   August 30, 2015, 17:50
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Thank you very much for your responses!

Cheers,
Nurzhan
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Old   August 31, 2015, 03:05
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Hi Glenn/Opaque,

I managed to set thermal conductivity as a full tensor using CEL as you advised me. However, the same way does not work for electrical conductivity.

The error looks like that:

ERROR
CCL validation failed with message:
Error: Invalid Option parameter 'Orthotropic Cartesian Components'

Any ideas how to get over this problem?

The feeling is like ANSYS intentionally stopping people to use electrical conductivity as a vector value. What do you think?

Thank you in advance!
Nurzhan

Last edited by Nurzhan; August 31, 2015 at 04:50.
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Old   August 31, 2015, 03:23
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Thermal conductivity is not a vector. Opaque explained that very well.

As the anisotropic thermal conductivity is a hidden feature that means it is not a supported feature. This means it has not completed all testing, may not be accurate or correctly implemented. For many of these cases it is because the introduction of this additional flexibility introduces additional terms into the modelled equations which CFX does not model. It is then user beware when you decide to use them.

So no, it is unlikely that ANSYS has removed anisotropic electrical conductivity. Why would they develop it then remove it? What is far more likely is that it can introduce additional difficulties into the modelled equations and CFX has not got a model to handle that yet.
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Old   September 3, 2015, 00:06
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Quote:
Originally Posted by Opaque View Post
Based on the mathematical formalism for heat conduction, thermal conductivity cannot be a vector. It is a second order tensor, that for isotropic materials reduces to scalar.

In the case of anisotropic thermal conduction, ANSYS CFX has a hidden feature to input the orthotropic conductivities (principal values on a specific orientation of the material) , or the full tensor.

You can search this forum for "Thermal Conductivity X".. Otherwise, you should probably contact ANSYS CFX support for help.

Either of those values can be set using CEL expression, interpolation functions or via user Fortran junction boxes.
Hi Opaque,

I used your suggestion to set thermal conductivity for an anisotropic material, using an orthotropic coordinates option (shown below), it worked for me. Thanks!

THERMAL CONDUCTIVITY:
Option = Orthotropic Cartesian Components
Thermal Conductivity X Component= # [W m^-1 K^-1]
Thermal Conductivity Y Component= # [W m^-1 K^-1]
Thermal Conductivity Z Component= # [W m^-1 K^-1]
END

However, I tried to use the same method to set electrical conductivity for an anisotropic material, and it didn't work. Do you have any idea how to handle this problem?

Thanks in advance,
Nurzhan
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Old   September 3, 2015, 17:45
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I do not think CFX can handle anisotropic electrical conductivity. Don't forget the anisotropic thermal conductivity is just a beta feature so is not fully supported.
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Old   September 3, 2015, 19:41
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There are hidden ways to access the anisotropic diffusion model for several equations. If you contact ANSYS CFX, they can provide you with the following beta re-configuration of the electrical conductivity settings:


Code:
RULES:
  SINGLETON: ELECTRICAL CONDUCTIVITY
    Description = Hold the details for an advanced description of \
                  Electrical Conductivity.
    Solver Name = CONELEC
    Context Rule = Option
    Essential Parameter List = Option
    Allowed Option List = \
      Value, \
      Orthotropic Cartesian Components
    CONTEXT: Value
      Essential Parameter List = \
       Electrical Conductivity
    END
    CONTEXT: Orthotropic Cartesian Components
      Essential Parameter List = \
        Electrical Conductivity X Component, \
        Electrical Conductivity Y Component, \
        Electrical Conductivity Z Component
    END
  END
  PARAMETER: Electrical Conductivity X Component
    Parameter Type        = Real
    Quantity Type         = Electrical Conductivity
    Dynamic Reread Item   = Yes
    Solver Name           = CONELEC-1
    Group Membership      = VECTOR, CONELEC, 1
  END
  PARAMETER: Electrical Conductivity Y Component
    Parameter Type        = Real
    Quantity Type         = Electrical Conductivity
    Dynamic Reread Item   = Yes
    Solver Name           = CONELEC-2
    Group Membership      = VECTOR, CONELEC, 2
  END
  PARAMETER: Electrical Conductivity Z Component
    Parameter Type        = Real
    Quantity Type         = Electrical Conductivity
    Dynamic Reread Item   = Yes
    Solver Name           = CONELEC-3
    Group Membership      = VECTOR, CONELEC, 3
  END
END
If you copy the rules above into a, say, aniso_eleccon.ccl, you can use along the cfx5solve command line as

Code:
cfx5solve -def MyAnisoCase.def -ccl aniso_eleccon.ccl .....
Keep in mind that is not even beta, so you may have to validate the results carefully.
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Old   September 3, 2015, 23:50
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Thank you, guys! I do not know how to express my feelings right now - I really appreciate your help.

Regards,
Nurzhan
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Old   September 30, 2015, 20:58
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Hi Opaque,

I have been trying to apply the additional rules, written above to my simple simulation. However, I get an error saying that there is an "Error reading Command Language data from memory". I tried my simulation without the additional rules and the simulation worked fine. I decided to describe the procedure of my simulation below.

1) Setting all paramters in cfx pre (electrical conductivity specified as isotropic) and cube.def file is created:

Quote:
# State file created: 2015/10/01 13:39:12
# CFX-14.5 build 2012.09.19-21.47

LIBRARY:
ADDITIONAL VARIABLE: Electric Power
Option = Definition
Tensor Type = SCALAR
Units = [W m^-3]
Variable Type = Volumetric
END
MATERIAL: Solid
Material Description = Aluminium
Material Group = User
Option = Pure Substance
Thermodynamic State = Solid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 2700 [kg m^-3]
Molar Mass = 1.0 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 0.91 [J kg^-1 K^-1]
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 237 [W m^-1 K^-1]
END
ELECTRICAL CONDUCTIVITY:
Electrical Conductivity = 5 [S m^-1]
Option = Value
END
END
END
END
FLOW: Flow Analysis 1
SOLUTION UNITS:
Angle Units = [rad]
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
Option = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 100 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.1 [s]
END
END
DOMAIN: Cube
Coord Frame = Coord 0
Domain Type = Solid
Location = solid
BOUNDARY: Ground
Boundary Type = WALL
Location = ground
BOUNDARY CONDITIONS:
ELECTRIC FIELD:
Option = Ground
END
HEAT TRANSFER:
Option = Adiabatic
END
END
END
BOUNDARY: High Voltage
Boundary Type = WALL
Location = highvoltage
BOUNDARY CONDITIONS:
ELECTRIC FIELD:
Option = Voltage
Voltage = 10 [V]
END
HEAT TRANSFER:
Option = Adiabatic
END
END
END
BOUNDARY: Insulated Surfaces
Boundary Type = WALL
Location = externalsurfaces
BOUNDARY CONDITIONS:
ELECTRIC FIELD:
Option = Zero Flux
END
HEAT TRANSFER:
Option = Adiabatic
END
END
END
DOMAIN MODELS:
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
END
SOLID DEFINITION: Solid 1
Material = Solid
Option = Material Library
MORPHOLOGY:
Option = Continuous Solid
END
END
SOLID MODELS:
ADDITIONAL VARIABLE: Electric Power
Additional Variable Value = Current Density X *Electric Field X + \
Current Density Y *Electric Field Y + Current Density Z *Electric \
Field Z
Option = Algebraic Equation
END
ELECTROMAGNETIC MODEL:
ELECTRIC FIELD MODEL:
Option = Electric Potential
END
MAGNETIC FIELD MODEL:
Option = None
END
END
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
THERMAL RADIATION MODEL:
Option = None
END
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
ELECTRIC POTENTIAL:
Electric Potential = 0 [V]
Option = Automatic with Value
END
TEMPERATURE:
Option = Automatic with Value
Temperature = 0 [C]
END
END
END
OUTPUT CONTROL:
MONITOR OBJECTS:
Monitor Coefficient Loop Convergence = On
MONITOR BALANCES:
Option = Full
END
MONITOR FORCES:
Option = Full
END
MONITOR PARTICLES:
Option = Full
END
MONITOR RESIDUALS:
Option = Full
END
MONITOR TOTALS:
Option = Full
END
END
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = Electric Power,Electric Field,Electrical \
Conductivity,Current Density,Temperature
OUTPUT FREQUENCY:
Option = Timestep Interval
Timestep Interval = 50
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 40
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 0.000001
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 14.5
END
(If I run the above code alone, I get an accurate result.)

However, when I apply the additional rules (a ccl file, named aniso_eleccon.ccl)

Quote:
RULES:
SINGLETON: ELECTRICAL CONDUCTIVITY
Description = Hold the details for an advanced description of \
Electrical Conductivity.
Solver Name = CONELEC
Context Rule = Option
Essential Parameter List = Option
Allowed Option List = \
Value, \
Orthotropic Cartesian Components
CONTEXT: Value
Essential Parameter List = \
Electrical Conductivity
END
CONTEXT: Orthotropic Cartesian Components
Essential Parameter List = \
Electrical Conductivity X Component, \
Electrical Conductivity Y Component, \
Electrical Conductivity Z Component
END
END
PARAMETER: Electrical Conductivity X Component
Parameter Type = Real
Quantity Type = Electrical Conductivity
Dynamic Reread Item = Yes
Solver Name = CONELEC-1
Group Membership = VECTOR, CONELEC, 1
END
PARAMETER: Electrical Conductivity Y Component
Parameter Type = Real
Quantity Type = Electrical Conductivity
Dynamic Reread Item = Yes
Solver Name = CONELEC-2
Group Membership = VECTOR, CONELEC, 2
END
PARAMETER: Electrical Conductivity Z Component
Parameter Type = Real
Quantity Type = Electrical Conductivity
Dynamic Reread Item = Yes
Solver Name = CONELEC-3
Group Membership = VECTOR, CONELEC, 3
END
END
and change the electrical conductivity using the following code (a ccl file, named solid.ccl):

Quote:
LIBRARY:
&replace MATERIAL: Solid
Material Description = Aluminium
Material Group = User
Option = Pure Substance
Thermodynamic State = Solid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 2700 [kg m^-3]
Molar Mass = 1.0 [kg kmol^-1]
Option = Value
END
SPECIFIC HEAT CAPACITY:
Option = Value
Specific Heat Capacity = 0.91 [J kg^-1 K^-1]
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 237 [W m^-1 K^-1]
END
ELECTRICAL CONDUCTIVITY:
Option = Orthotropic Cartesian Components
Electrical Conductivity X Component = 5 [S m^-1]
Electrical Conductivity Y Component = 0 [S m^-1]
Electrical Conductivity Z Component = 0 [S m^-1]
END
END
END
END
Then I get the error.

I run all three codes using through the command line

Quote:
cfx5solve -def cube.def -ccl aniso_eleccon.ccl -ccl solid.ccl
I checked the RULES file, where written that

Quote:
The solver supports anisotropic electric conductivity as well, additional rules are needed. Translation in tt.txt is ready.
I did not want to bother you again and tried to figure out the problem myself. However, I cannot find a clue. I also do not have a direct access to ANSYS commercial portal and support, as I am a student.

Thanks for taking your time to read this.

Regards,
Nurzhan
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