FPDualReal in Fluid Properties UO

[joe61vette]

Hi:

Very basic question. Trying to code a UO for a fluid property that would use AD system. In the header file I have:

class ConstantFluidProperties : public SinglePhaseFluidProperties
...
virtual FPDualReal rho_from_p_T(const FPDualReal & pressure, const FPDualReal & temperature) const override;

and in the corresponding C file:

FPDualReal
ConstantFluidProperties::rho_from_p_T(const FPDualReal & pressure, const FPDualReal & temperature) const
{
...
}

I get a compile error:

ConstantFluidProperties.h:23:23: error: 'rho_from_p_T' marked 'override' but does not override any member functions
virtual FPDualReal rho_from_p_T(const FPDualReal & pressure, const FPDualReal & temperature) const override;

It seems like it should be overriding propfuncAD. Is there something obvious that I am doing wrong?

Thanks,
Joe K

[GiudGiud]

Hi Joe

I think it's because propfuncAD is using DualReal for its arguments and return types. Going to check now.

Guillaume

[joe61vette]

THANKS! I finally got it. So, the "approved" way is to follow the normal

Real rho_from_p_T(Real p, Real T)

type of coding and let the macro handle it. I tested it and it does work for my case where rho is an AD Material Property and p & T are adCoupledValues. One only implements the extra FPDualReal coding (as in your example) if the normal way is simply too slow. Which for Water/Steam properties would be the case.

I'll mark this as answered. Thanks again,
Joe

[joe61vette]

Well, I would have marked it as answered if I could figure out how. Joe

[lindsayad]

Unfortunately you can only mark the beginning of the thread as the answer.

FWIW with the new sparse AD default configuration of MOOSE, DualReal should not be so slow any more because it keeps track of the number of derivative entries automatically and consequently dual number operations only happen over the sparsity entries (which can be a small number, less than 5 for example, in these fluid property contexts) and not over the entire underlying container size of 50.

[cpgr]

Thanks for the info @lindsayad. I'll do some comparisons when I get the time and swap those instances of FPDualReal to normal DualReal if there isn't much of a difference.

[lindsayad]

You would definitely pay a memory penalty though because derivative vector is still statically sized

[joe61vette]

Just want to thank everyone for the help. It is great that I can simply use the old style property fns and have them magically return the value with derivatives. Also, using the AD system as Chris did to get derivatives for properties that return them will save me time later.