[Kombinator]

Hello dear Foamers,
I have a following issue, may be somebody could help me.

I have a VolScalarField PotE
I am trying to calculate surface gradient for this variable. As I read in programmers guide, fvc:: snGrad(PotE) must help me with this. But when I try to create new variable

SurfaceVectorField A = fvc:: snGrad(PotE)*mesh.Sf() ;

I get an error and I don't understand why it happens. fvc:: snGrad(PotE) is a scalar, mesh.Sf() is a vector. Their multiplication must be a vector. Everything seems fine. Maybe is something wrong with my snGrad function?
Thanks in advance.

Best regards,
Artem

[EmadTandis]

Hello
Is it possible to show the error?

[Zeppo]

It should be surfaceVectorField not SurfaceVectorField. Check it carefully.

[Kombinator]

Hello all, thank you for your answers

Originally Posted by Zeppo

It should be surfaceVectorField not SurfaceVectorField. Check it carefully.

It is a misprint, in the code it was "surfaceVectorField" with small "s"

Originally Posted by EmadTandis

Hello
Is it possible to show the error?

Sure but is so huge, so I provide only the headline with the most important information (I guess)

mhdEpot2Foam.C: In function ‘int main(int, char**)’:
mhdEpot2Foam.C:148:66:  error: conversion from  ‘Foam::tmp<Foam::GeometricField<Foam::Vector<double>,  Foam::fvsPatchField, Foam::surfaceMesh> >’ to non-scalar type  ‘Foam::surfaceScalarField {aka Foam::GeometricField<double,  Foam::fvsPatchField, Foam::surfaceMesh>}’ requested
    surfaceScalarField jn = -sigma * fvc::snGrad(PotE)*mesh.Sf()  + psiub;  
                                                                  ^

[Zeppo]

If you want a dot-product of vector fields you should use

&

fvc::snGrad(PotE) & mesh.Sf()

It would give you a scalar field.

[Kombinator]

Originally Posted by Zeppo

If you want a dot-product of vector fields you should use

&

fvc::snGrad(PotE) & mesh.Sf()

It would give you a scalar field.

Hello, thank you for your answer. I have already tried &, unfortunately it didn't work, the same error:

mhdEpot2Foam.C: In function ‘int main(int, char**)’:
mhdEpot2Foam.C:148:55: error: no match for ‘operator&’ (operand types are ‘Foam::tmp<Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> >’ and ‘Foam::tmp<Foam::GeometricField<Foam::Vector<double>, Foam::fvsPatchField, Foam::surfaceMesh> >’)
    surfaceScalarField jn = -sigma * fvc::snGrad(PotE) & mesh.Sf()  + psiub;  
                                                       ^

[Zeppo]

My bad, fvc::snGrad results in a scalar field, you can't dot-product it with a vector field. Stick to your first option. Then fvc::snGrad(PotE)*mesh.Sf() is a vector field, what is psiub, how is it defined? It must be a vector field as well as summation fvc::snGrad(PotE) & mesh.Sf() + psiub only make sense over two vector fields.

[Alex21]

Originally Posted by Kombinator

Hello dear Foamers,
I have a following issue, may be somebody could help me.

I have a VolScalarField PotE
I am trying to calculate surface gradient for this variable. As I read in programmers guide, fvc:: snGrad(PotE) must help me with this. But when I try to create new variable

SurfaceVectorField A = fvc:: snGrad(PotE)*mesh.Sf() ;

I get an error and I don't understand why it happens. fvc:: snGrad(PotE) is a scalar, mesh.Sf() is a vector. Their multiplication must be a vector. Everything seems fine. Maybe is something wrong with my snGrad function?
Thanks in advance.

Best regards,
Artem

I propose you to use the alternative mesh.magSf() instead of mesh.Sf() using the operator "*" for scalars.

Since the snGrad isn't a tensor as you use the scalar "PotE" inside, it still a surfaceScalarField. Thus as you are already "speaking" in projections, use the magnitude of the surface because your snGrad is already oriented with it.

Even if its too late ...