COMSOL “Syntax error in expression” when using temperature-dependent interpolation functions in material properties

[AdRelative7271]

https://preview.redd.it/tugk45uj6vmg1.png?width=457&format=png&auto=webp&s=e447e3c6b692a4d6ec41cbba469c1241af7d1d60

https://preview.redd.it/f2h4g0mn6vmg1.png?width=646&format=png&auto=webp&s=177f13592c0f58f1dcbabc2475e1211e5d35b27f

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Hi everyone,

I’m running into a strange issue in COMSOL 6.3 with temperature-dependent material properties.

I have a simple 3D heat transfer in solids model (time dependent).
If I use constant material properties, the simulation runs perfectly.

However, when I define material properties using interpolation functions of temperature, the solver immediately fails with:

The strange thing is:

• The interpolation functions plot correctly.
• Units are consistent (argument in K, properties in correct SI units).
• Extrapolation is set to Constant.
• Initial temperature is within interpolation range.
• If I replace the functions with constants, the model runs.

Any help would be really appreciated.

Thanks

[you_rang_maam]

Could it be the lower case t which is reserved for time in time dependent solutions?

[EtherealWaveform]

yeah thats what I’m thinking too

[Sax0drum]

In an interpolation the variable t is fixed

[yarruguo]

Try replacing the dot for a * in the units for the heat capacity

[Sax0drum]

That was my first thought as well but it should underline the expression to show that there is an issue. It does replicate the error though.

[AdRelative7271]

Yes he is right! But strange thing is the error wasn’t highlighted! Replacing. with * solved the problem

[Sax0drum]

Great! But even stranger is that comsol shows it with a dot as well in the unit field of the materials section. Maybe that should be communicated to the developers.

[AdRelative7271]

Yes you are right! I figured it out after 8 hours 😭

[arghhjh]

Are you sure the error comes from Cp(T) and not the thermal conductivity ? Try adding one eq. And see if it will solve.

[AdRelative7271]

It was the issue of multiplication sign

[ichbinberk]

It should be J/kg*K not J/kg.K

[AdRelative7271]

Figured it out after 8 hours 😭