the arrangement of the components gradU

zikou55 · September 29, 2020, 18:36

Hello,
gradU is a 9 components tensor, I want to know the arrangement of the components
gradU.compoent(0)=dudx
gradU.compoent(1)=dudy
gradU.compoent(2)=dudz
gradU.compoent(3)=dvdx
gradU.compoent(4)=dvdy
gradU.compoent(5)=dvdz
gradU.compoent(6)=dwdx
gradU.compoent(7)=dwdy
gradU.compoent(8)=dwdz

please am I right ?

jackjiang1989@gmail.com · September 17, 2021, 08:54

Hi,
I got the same question, after some search found it should be like below,
gradU.compoent(0)=dudx
gradU.compoent(1)=dvdx
gradU.compoent(2)=dwdx
gradU.compoent(3)=dudy
gradU.compoent(4)=dvdy
gradU.compoent(5)=dwdy
gradU.compoent(6)=dudz
gradU.compoent(7)=dvdz
gradU.compoent(8)=dwdz

check below link,
discrepancy in fvc::grad(U)

BR/Jack

Tobermory · September 17, 2021, 11:30

Yep - for confirmation, check out Tensor.H (https://cpp.openfoam.org/v8/Tensor_8H_source.html):

Code:

     //- Component labeling enumeration
     enum components { XX, XY, XZ, YX, YY, YZ, ZX, ZY, ZZ };

but remember that for partial derivatives, the derivative is the first index. So for the second component in the list above, XY, this is $\partial /\partial x (V) = \partial V/\partial x$ . Take a look at the link that Jack quotes for more discussion.

Redrakham · February 6, 2025, 08:00

Quote:

Originally Posted by Tobermory

Yep - for confirmation, check out Tensor.H (https://cpp.openfoam.org/v8/Tensor_8H_source.html):

Code:

     //- Component labeling enumeration
     enum components { XX, XY, XZ, YX, YY, YZ, ZX, ZY, ZZ };

but remember that for partial derivatives, the derivative is the first index. So for the second component in the list above, XY, this is $\partial /\partial x (V) = \partial V/\partial x$ . Take a look at the link that Jack quotes for more discussion.

Is there a way to calculate tangential component of velocity in normal direction to a curved surface in OpenFOAM?

Tobermory · February 6, 2025, 08:05

Yes - with some simple vector arithmetic. Start with the unit normal vector to the surface, n, then the component of f that is normal to the surface is

$(f \cdot n) n$

and therefore the tangential part is:

$f - (f \cdot n)n$

Dot product in OpenFOAM is done with the & operator.

September 29, 2020, 18:36	the arrangement of the components gradU	#1
zikou55 New Member zaki Join Date: Nov 2018 Posts: 17 Rep Power: 8	Hello, gradU is a 9 components tensor, I want to know the arrangement of the components gradU.compoent(0)=dudx gradU.compoent(1)=dudy gradU.compoent(2)=dudz gradU.compoent(3)=dvdx gradU.compoent(4)=dvdy gradU.compoent(5)=dvdz gradU.compoent(6)=dwdx gradU.compoent(7)=dwdy gradU.compoent(8)=dwdz please am I right ?

September 17, 2021, 08:54		#2
jackjiang1989@gmail.com New Member jackjiang Join Date: Feb 2020 Posts: 10 Rep Power: 7	Hi, I got the same question, after some search found it should be like below, gradU.compoent(0)=dudx gradU.compoent(1)=dvdx gradU.compoent(2)=dwdx gradU.compoent(3)=dudy gradU.compoent(4)=dvdy gradU.compoent(5)=dwdy gradU.compoent(6)=dudz gradU.compoent(7)=dvdz gradU.compoent(8)=dwdz check below link, discrepancy in fvc::grad(U) BR/Jack fly_light likes this.

September 17, 2021, 11:30		#3
Tobermory Senior Member Join Date: Apr 2020 Location: UK Posts: 825 Rep Power: 16	Yep - for confirmation, check out Tensor.H (https://cpp.openfoam.org/v8/Tensor_8H_source.html): Code: //- Component labeling enumeration enum components { XX, XY, XZ, YX, YY, YZ, ZX, ZY, ZZ }; but remember that for partial derivatives, the derivative is the first index. So for the second component in the list above, XY, this is $\partial /\partial x (V) = \partial V/\partial x$ . Take a look at the link that Jack quotes for more discussion.

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February 6, 2025, 08:05		#5
Tobermory Senior Member Join Date: Apr 2020 Location: UK Posts: 825 Rep Power: 16	Yes - with some simple vector arithmetic. Start with the unit normal vector to the surface, n, then the component of f that is normal to the surface is $(f \cdot n) n$ and therefore the tangential part is: $f - (f \cdot n)n$ Dot product in OpenFOAM is done with the & operator.