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Angle two vectors.

Good morning,

I am looking to calculate the angle between two 3D vectors in my CFD results. I can do this mathematically, but I don't know how to implement it in code for a general coordinate system. Has anyone any ideas were I can learn how to use standard CFD code to calculate such quantities??

Re: Angle two vectors.

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<p class=MsoNormal>This actually is just basic vector analysis. The scalar product of two vectors, a and b <span class=GramE>is<span style='mso-spacerun:yes'>* </span>a</span> · b = |a| |b| <span class=SpellE>cos<span style='font-family:Symbol'>f , </span>from</span> which <span style='font-family:Symbol'>f</span> – the angle between a and b – may be solved.

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Re: Angle two vectors.

I know that, but how do I implement it numerically. How do I implement it numerically? How do I calculate that angle using code?

Re: Angle two vectors.

Fortran implementation:

real a(3), b(3)

AdotA = a(1)*a(1) + a(2)*a(2) + a(3)*a(3)

BdotB = b(1)*b(1) + b(2)*b(2) + b(3)*b(3)

den = AdotA*BdotB

if(den .gt. 0.) then

AdotB = a(1)*b(1) + a(2)*b(2) + a(3)*b(3)

cosphi = AdotB / sqrt(den)

phi = acos(cosphi)

endif

Re: Angle two vectors.

Thank you.

If I have two grid lines, which are not orthogonal, how can I find the angle between them? What term do I use to describe their direction? Also, how is this done in a general curvilinear coordinate system? How can I find the angle between a grid line and a velocity field for example.

Re: Angle two vectors.

give me ur email i will drop u an email how to calculate what u need. (i understood that u want to use that in calculation for CFD, say for angle between the faces etc.)

Re: Angle two vectors.

Hi zxaar,

This is my email account address as requested: cfd_user_uk@yahoo.co.uk

I would appreciate any help you can give me for this problem.

Thank you.

"give me ur email i will drop u an email how to calculate what u need. (i understood that u want to use that in calculation for CFD, say for angle between the faces etc.) "