×F=(1rFzφFφz)er+(FrzFzr)eφ+(Fφr+Fφr1rFrφ)ez

si300_e  (Eq. 7.97)

×F=(1rFzφFφz)er+(FrzFzr)eφ+(r(rFφ)1rFzφ+Fφr)ez

si301_e  (Eq. 7.98)

Eq. 7.97 gives the curl in cylindrical coordinates. Again, Eq. 7.98 is a slightly more compact notation of the same equation.

7.6.1.4 Scalar Laplacian

The next conversion we require is the Laplace operator in cylindrical coordinates. Here, we can exploit a small trick due to the fact that

Δψ=(ψ)

si302_e

where we can use the gradient of ψ given by Eq. 7.90 as

ψ=ψrer+1rψφeφ+ψzez

si303_e

and the divergence by Eq. 7.93 as

Δψ=(ψ)=1rψr+r(ψr)+1rφ(1r,ψφ)+z(ψz)=2ψr2+12ψr+1r22ψφ2+2ψz2

si304_e  (Eq. 7.99)

=1rr(rψr)+1r22ψφ2+2ψz2

si305_e  (Eq. 7.100)

Eq. 7.99 is the Laplace operator in cylindrical coordinates. Eq. 7.100 is a commonly encountered, slightly more compact notation

7.6.1.5 Vector Laplacian

The second commonly encountered version of the Laplacian is the vector Laplacian of the vector Fsi1_e. For transferring into cylindrical coordinates we will make use of Eq. 7.6. For this equation we require the two terms (F)si307_e and ×(×F)si308_e. The first can be derived by first calculating the divergence Fsi309_e given by Eq. 7.93 as

F=Frr+Frr+1rFφφ+Fzz

si310_e

that we then use to form the gradient (F)si307_e given by Eq. 7.90 as

(F)=(r(Frr+Frr+1rFφφ+Fzz))er+(1rφ(Frr+Frr+1rFφφ+Fzz))eφ+(z(Frr+Frr+1rFφφ+Fzz))ez=(1r2Fr+1rFrr+Frr21r22Fφφ+1r2Fφφr+2Fzzr)er+(1r(1rFrφ+2Frrφ+1r2Fφφ2+2Fzzφ))eφ+(1rFrz+2Frrz+1r2Fφφz+2Fzz)ez

si312_e  (Eq. 7.101)

The second term we require for Eq. 7.6 is ×(×F)si308_e that can be obtained by applying Eq. 7.97 twice to the vector Fsi1_e finding

×(×F)=×((1rFzφFφz)er+(FrrFzr)eφ+(Fφr+Fφr1rFrφ)ez)=(1rφ(Fφr+Fφr1rFrφ)z(FrzFzr))er+(z(1rFzφFφz)r(Fφr+Fφr1rFrφ))eφ+(1r(FrzFzr)+r(FrzFzr)1rφ(1rFzφFφz))ez=(1r(1rFφφ+2Fφrφ1r2Frφ2)2Frφ22Fzrz)er+(1r2Fzφz2Fφz2+1r2Fφ1rFφr2Fφr21r2Frφ+1r2Frφr)eφ=(1r(FrzFzr)+2Frzr2Fzr21r(1r2Fzφ22Fφzφ))ez

si315_e  (Eq. 7.102)

Using Eq. 7.101 and Eq. 7.102 we can now reassemble Eq. 7.6 to

ΔFΔF=(F)×(×F)=(1r2Fr+1rFφr+2Fφr21r2Fφφ+1r2Fφφr+2Fzzr(1r(1rFφφ+2Fφrφ1r2Frφ2)2Frz2+2Fφrφ))er+(1r(1rFrφ+2Fφrφ+1r2Fφφ2+2Fφrφ)(1r2Fφφz2Fφz2+1r2Fφ1rFφr2Fφr21r2Frφ+1r2Frφr))eφ+(1rFrz+2Frrz+1r2Fφφz+2Fzz2(1r(FrzFzr)+2Frzr2Fzr21r(1r2Fzφ22Fφzφ)))ez=(2Frr2+1rFrr+1r22Frφ2+2Frz2Frr22r2Fφφ)er++(2Fφr2+1rFφr+1r22Fφφ2+2Fφz2Fφr2+2r2Frφ2)eφ+(2Fzz2+1rFzr+1r22Fzφ2+2Fzr2)ez

si316_e  (Eq. 7.103)

Eq. 7.103 is the vector Laplacian in cylindrical coordinates. If you look very carefully, you will see that the first four terms of each of the vector components are nothing other than the scalar Laplacians ΔFr, ΔFφ and ΔFz which allows a slightly more compact notation in the form of

ΔF=(ΔFrFrr22r2Fφφ)er+(ΔFφFφr2+2r2Frφ)eφ+(ΔFz)ez

si317_e  (Eq. 7.104)

7.6.1.6 Material Derivative

The last operator we will convert is the material derivative (see section 7.1.3.10) which we will require, e.g., for the Navier–Stokes equation (see Eq. 11.40). For this we will first require the scalar product Fsi318_e of the vector

F=FrFφFz=cosφFrsinφFφsinφFr+cosφFφFz

si319_e

that we converted to Cartesian coordinates according to Eq. 7.32. We now carry out the scalar product in Cartesian coordinates finding

F=cosφFrsinφFφsinφFr+cosφFφFzxyz

si320_e  (Eq. 7.105)

where we now require the partial differentials x,y,andzsi321_e that we can simply copy from Eq. 7.86, Eq. 7.87, and Eq. 7.88 by simply omitting ψ. Using these equations, Eq. 7.86 becomes

FF====cosφFrsinφFφsinφFr+cosφFφFzcosφrsinφrφsinφr+cosφrφz(cosφFrsinφFφ)(cosφrsinφrφ)+(sinφFr+cosφFφ)(sinφr+cosφrφ)+FzzFr(cosφ(cosφrsinφrφ)+sinφ(sinφr+cosφrφ))+Fφ(sinφ(cosφrsinφrφ)+cosφ(sinφr+cosφrφ))+FzzFrr+Fφrφ+Fzz

si322_e

Please note that the result is a scalar. It is the intuitive result of the scalar multiplication of Fr,φ,zr,φ,zsi323_e. In the next step we multiply this expression with the vector Gsi56_e that we again convert to Cartesian coordinates finding

(F)G====(Frr+Fφrφ+Fzz)cosφGrsinφGφsinφGr+cosφGφGz((Frr+Fφrφ+Fzz)(cosφGrsinφGφ))ex+((Frr+Fφrφ+Fzz)(sinφGr+cosφGφ))ey+(Frr+Fφrφ+Fzz)Gzez(Frr(cosφGrsinφGφ)+Fφrφ(cosφGrsinφGφ)+Fzz(cosφGrsinφGφ))ex+(Frr(sinφGr+cosφGφ)+Fφrφ(sinφGr+cosφGφ)+Fzz(sinφGr+cosφGφ))ey+(FrGzr+FφrGzφ+FzGzz)ez(Fr(cosφGzrsinφGφr)+Fφr(sinφGr+cosφGrφ)cosφGφsinφGφφ)+Fz(cosφGrzsinφGφz))ex+(Fr(sinφGrr+cosφGφr)+Fφr(cosφGr+sinφGrφsinφGφ+cosφGφφ)+Fz(sinφGrr+cosφGφz))ey+(FrGzr+FφrGzφ+FzGzz)ez

si325_e

where we reconvert the result into cylindrical coordinates using Eq. 7.28, Eq. 7.29, and Eq. 7.30 to find

(F)G=(Fr(cosφGrrsinGφr))+Fφr(sinφGr+cosGrφcosφGφsinφGφφ)+Fz(cosφGrzsinφGφz))(cosφersinφeφ)sinφGφ+cosφGφφ(Fr(sinφGrr+cosφGφr)+Fφr(cosφGr+sinφGrφsinφGφ+cosφGφφ+Fz(sinφGrzcosφGφz))(sinφercosφeφ)+(FzGrr+Fφr+FzGrz)ez=(Fr(cosφGrrsinφGφr)+Fφr(sinφcosφGr+cos2φGrφcos2φGφsinφcosφGφφ)+Fz(cos2φGrzsinφcosφGφz)+Fr(sin2φGrr+sinφcosφGφr)+Fφr(sinφcosφGr+sin2φGφrsin2φGφ+sinφcosφGφr)+Fz(sin2φGrz+sinφcosφGφz)er+(Fr(sinφcosφGrr+sin2φGφr)+Fφr(sin2φGrsinφcosφGrφ+sinφcosφ+sin2Gφφ)+Fz(sinφcosφGrz+sin2φGφz)+Fr(sinφcosφGrr+cos2φGφr)+

si326_e

(F)GFφr(cos2φGr+sinφcosφGrφsinφcosφGφ+cos2φGφφ)+Fz(sinφcosφGrz+cos2φGφz)eφ+(FrGzr+FφrGzφ+FzGzz)ez=(FrGrr+FφrGrφ+FzGrzFφGφr)er+(FrGφr+FφrGφφ+FzGφzFφGrr)eφ+(FrGzr+FφrGzφ+FzGzz)ez

si505_e  (Eq. 7.106)

Eq. 7.106 is the sought material derivative in cylindrical coordinates.

7.6.2 Polar Coordinates

We can skip the derivations in polar coordinates again, due to the fact that we can simply insert the operators in cylindrical coordinates while ignoring the contribution along the z-axis.

7.6.2.1 Gradient

The gradient in polar coordinates according to the simplified version of Eq. 7.90 is given by

Δψ=ψrer+1rψφeφ

si327_e  (Eq. 7.107)

7.6.2.2 Divergence

Likewise, the divergence can be derived from Eq. 7.93 as

F=Frr+Fr+1rFφφ

si328_e  (Eq. 7.108)

7.6.2.3 Curl

In analogy, the curl is given by simplifying Eq. 7.97 as

×F=(1rFzφFφz)er+(FrzFzr)eφ

si329_e  (Eq. 7.109)

7.6.2.4 Scalar Laplacian

The scalar Laplacian is derived from Eq. 7.99 as

Δψ=2ψr2+1rψr+1r22ψφ2

si330_e  (Eq. 7.110)

7.6.2.5 Vector Laplacian

Likewise, the vector Laplacian can be derived from Eq. 7.104 as

ΔF=(ΔFrFrr22r2Fφφ)er+(ΔFφFφr2+2r2Frφ)eφ

si331_e  (Eq. 7.111)

7.6.2.6 Material Derivative

Finally, the material derivative is given from simplifying Eq. 7.106 to

(F)G=(FrGrr+FφrGrφFφGφr)er+(FrGφr+FφrGφφ+FφGrr)eφ

si332_e  (Eq. 7.112)

7.6.3 Spherical Coordinates

7.6.3.1 Gradient

Finally, we will derive the operators in spherical coordinates (see Fig. 7.4d). Again, we will begin with the gradient of the scalar ψ defined as

ψ=ψxex+ψyey+ψzez

si273_e  (Eq. 7.113)

where we again require the total differentials in order to express ψ(x, y, z) which is a function of x, y, and z in Cartesian coordinates as a function of ρ, θ, and φ in spherical coordinates. We find

ψx=ψρρx+ψθθx+ψφφx

si334_e  (Eq. 7.114)

ψy=ψρρy+ψθθy+ψφφy

si335_e  (Eq. 7.115)

ψz=ψρρz+ψθθz+ψφφz

si336_e  (Eq. 7.116)

where we take the partial derivatives from the inverse Jacobian (see Eq. 7.72) from which we find

ρx=sinθcosφ

si337_e

ρy=sinθsinφ

si338_e

ρz=cosθ

si339_e

θx=cosθcosφρ

si340_e

θy=cosθsinφρ

si341_e

θz=sinθρ

si342_e

φx=1ρsinφsinθ

si343_e

φy=1ρcosφsinθ

si344_e

φz=0

si345_e

Reinserting these into Eq. 7.113 yields

ψ=(ψρρx+ψθθx+ψφφx)ex+(ψρρy+ψθθy+ψφφy)ey+(ψρρz+ψθθz+ψφφz)ez=(ψρsinθcosφ+ψθcosθsinφρψφ1ρsinφsinθ)ex+(ψρsinθsinφ+ψθcosθsinφρ+ψφ1ρcosφsinθ)ey+(ψρcosθψθsinθρ)ez

si346_e  (Eq. 7.117)

where we now convert the basis vectors exsi138_e, eysi139_e, and ezsi118_e of the Cartesian coordinate system to functions of the basis vectors ersi116_e, eθsi123_e, and eφsi117_e, of the cylindrical coordinate system using Eq. 7.50, Eq. 7.51, and Eq. 7.52 finding

ψ=(ψρρx+ψθθx+ψφφx)ex+(ψρρy+ψθθy+ψφφy)ey+(ψρρz+ψθθz+ψφφz)ez=(ψρsinθcosφ+ψθcosθcosφρψφ1ρsinφsinθ)(sinθcosφeρ+cosθcosφeθsinφeφ)+(ψρsinθsinφ+ψθcosθsinφρ+ψφ1ρcosφsinθ)(sinθsinφeρ+sinφcosθeθcosφeφ)+(ψρcosθψθsinθρ)(cosθeρsinθeθ)=(sinθcosφ(ψρsinθcosφ+ψθcosθcosφρψφ1ρsinφsinθ)+sinθsinφ(ψρsinθsinφ+ψθcosθsinφρ+ψφ1ρcosφsinθ)+cosθ(ψρcosθψθsinθρ))eρ+(cosθcosφ(ψρsinθcosφ+ψθcosθcosφρψφ1ρsinφsinθ)+sinφcosθ(ψρsinθsinφ+ψθcosθsinφρ+ψφ1ρcosφsinθ)sinθ(ψρcosθψθsinθρ))eθ+(sinφ(ψρsinθcosφ+ψθcosθcosφρψφ1ρsinφsinθ)+cosφ(ψρsinθsinφ+ψθcosθsinφρ+ψφ1ρcosφsinθ))eφ=(ψρsin2θcos2φ+ψθsinθcosθcos2φρψφsinφcosφρ)+ψρsin2θsin2φ+ψθsinθcosθsin2φρ+ψφsinφcosφρ+ψρcos2θψθsinθcosθρ)eρ+(ψρsinθcosθcos2φ+ψθcos2θcos2φρψφcosθsinφcosφρsinθ+ψρsinθcosθsin2φ+ψθcos2θsin2φρ+ψφcosθsinφcosφρsinθψρsinθcosθ+ψθsin2φρ)eθ+(ψρsinθsinφcosφψθcosθsinφcosφρ+ψφsin2φρsinθ+ψρsinθsinφcosφ+ψθcosθsinφcosφρ+ψφcos2φρsinθ)eφ=(ψρ(sin2θcos2φ+sin2θsin2φ+cos2θ)+ψθ(sinθcosφcos2φρ+sinθcosθsin2φρsinθcosθρ)+ψθ(sinφcosφρ+sinφcosφρ))eρ

si353_e

ψ+(ψρ(sinθcosθcos2φ+sinθcosθsin2φsinθcosθ)+ψθ(cos2θcos2φρ+cos2θsin2φρ+sin2θρ)+ψθ(cosθsinφcosφρsinθ+cosθsinφcosφρsinθ))eθ+(ψρ(sinθsinφcosφ+sinθsinφcosφ)+ψθ(cosθsinφcosφρ+cosθsinφcosφρ)+ψφ(sin2φρsinθ+cos2φρsinθ))eφ=ψρeρ+1ρψθeθ+1ρsinθψφeφ

si504_e  (Eq. 7.118)

Eq. 7.118 gives the gradient in spherical coordinates.

7.6.3.2 Divergence

Next we derive the divergence Fsi2_e of the vector

F=Fρeρ+Fθeθ+Fφeφ=(Fρsinθcosφ+FθcosθcosφFφsinφ)ex+(Fρsinθsinφ+FθcosθsinφFφcosφ)ey+(FρcosθFθsinθ)ez

si355_e  (Eq. 7.119)

in spherical coordinates where we have used Eq. 7.53 to convert the basis vectors. According to Eq. 7.3 the divergence is given by

F=x(Fρsinθcosφ+FθcosθcosφFφsinφ)+y(Fρsinθsinφ+FθcosθsinφFφcosφ)+z(FρcosθFθsinθ)=Fρxsinθcosφ+Fρ(sinθxcosφsinθcosφx)+Fθxcosθcosφ+Fθ(cosθxcosφ+cosθcosφx)(Fφxsinφ+Fφsinφx)+Fρysinθsinφ+Fρ(sinθysinφ+sinθsinφy)+Fθycosθsinφ+Fθ(cosθysinφ+cosθsinφy)+Fφycosφ+Fφcosφy+Fρzcosθ+FρcosθzFθzsinθFθsinθz

si356_e  (Eq. 7.120)

where we now again need to convert the partial differentials with respect to x, y, and z to partial differentials of ρ, θ, and φ for which we find

Fρx=Fρρρx+Fρθθx+Fρφφx=Fρρsinθcosφ+Fρθ1ρcosθcosφFρθ1ρsinφsinθ

si357_e

FρyFρzFθxFθyFθzFφxFφyFφzsinθxsinθysinθzcosθxcosθy=Fρρρy+Fρθθy+Fρφφy=Fρρsinθsinφ+Fρθ1ρcosθsinφ+Fρφ1ρcosφsinθ=Fρρρz+Fρθθz+Fρφφz=FρρcosθFρθ1ρsinθ=Fθρρx+Fθθθx+Fθφφx=Fθρsinθcosφ+Fθθ1ρcosθcosφFθφ1ρsinφsinθ=Fθρρy+Fθθθy+Fθφφy=Fθρsinθsinφ+Fθθ1ρcosθsinφ+Fθφ1ρcosφsinθ=Fθρρz+Fθθθz+Fθφφz=FθρcosθFθθ1ρsinθ=Fφρρx+Fφθθx+Fφφφx=Fφρsinθcosφ+Fφθ1ρcosθcosφFφφ1ρsinφsinθ=Fφρρy+Fφθθy+Fφφφy=Fφρsinθsinφ+Fφθ1ρcosθsinφ+Fφφ1ρcosφsinθ=Fφρρz+Fφθθz+Fφφφz=FφρcosθFφθ1ρsinθ=sinθρρx+sinθθθx+sinθφφx=cos2θcosρρ=sinθρρy+sinθθθy+sinθφφy=cos2θsinφρ=sinθρρz+sinθθθz+sinθφφz=sinθcosθρ=cosθρρx+cosθθθx+cosθφφx=sinθcosθcosφρ=cosθρρy+cosθθθy+cosθφφy=sinθcosθsinφρ

si657_e

cosθzsinφxsinφysinzcosφxcosφycosφz=cosθρρz+cosθθθz+cosθφφz=sin2θρ=sinφρρx+sinφθθx+sinφφφx=1ρcosφsinφsinθ=sinφρρy+sinφθθy+sinφφφy=1ρcos2φsinθ=sinφρρz+sinφθθz+sinφφφz=0=cosφρρx+cosφθθx+cosφφφx=1ρsin2φsinθ=cosφρρy+cosφθθy+cosφφφy=1ρsinφcosφsinθ=cosφρρz+cosφθθz+cosφφφz=0

si358_e

Inserting the partial differentials into Eq. 7.120 yields

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