2 Vector derivatives in orthogonal coordinates

Given an orthogonal coordinate system u , v , w with unit vectors û ̲ , v ̂ ̲ and ŵ ̲ and scale factors, h u , h v and h w , it is possible to find the derivatives ̲ f , ̲ F ̲ and ̲ × F ̲ .

It is found that

grad f = ̲ f = 1 h u f u û ̲ + 1 h v f v v ̂ ̲ + 1 h w f w ŵ ̲

If F ̲ = F u û ̲ + F v v ̂ ̲ + F w ŵ ̲ then

div F ̲ = ̲ F ̲ = 1 h u h v h w u ( F u h v h w ) + v ( F v h u h w ) + w ( F w h u h v )

Also if F ̲ = F u û ̲ + F v v ̂ ̲ + F w ŵ ̲ then

curl F ̲ = ̲ × F ̲ = 1 h u h v h w h u û ̲ h v v ̂ ̲ h w ŵ ̲ u v w h u F u h v F v h w F w

Key Point 6

In orthogonal curvilinear coordinates, the vector derivatives ̲ f , ̲ F ̲ and ̲ × F ̲ include the scale factors h u , h v and h w .