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Lai version of DTijk v3
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Working notes by Phil dated 4.24.15, part of the May 2015 update to his curvilinear-coordinates tensor document. He restates Lai's (page 502-504) equations in his notation, using Christoffel-type coefficients G for the basis-vector derivatives. He rederives the derivative of a rank-2 tensor expanded in a curvilinear basis, and relates the rank-3 object M to the derivative of T under the x to x' transformation. The text ends mid-comparison with Lai's result.
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Lai's Version of (T)'ijk v3 PhL 4.24.15
I have never understood how they do this on page 503, but today I feel confident that I can translate their equations into my notation.
1. First, here is something I have shown. Here I choose to make x be the arg of en. This may be the wrong choice, but at least I am making a choice and displaying it. The other choice is en(ξ)
The whole idea here is that x-space is NOT Cartesian, it is the curvilinear coordinates!
dn = [Γ()]kjndxj k [Γ()]kjn ≡ hn-1 [hk Γkjn – (∂jhn) δk,n]
I can rewrite this as
∂jn(x) = [Γ()]kjnk(x)
To simplify, lets define
Gkjn ≡ [Γ()]kjn
Then I have
(∂jn(x)) = Gkjn(x)k(x)
dn = Gkjn dxj k
di = Gkji dxj k dei = Γijk dxj ek Lai p 502 dev notation I think
2. Next consider ( Lai notation equations are in blue)
Lai Me
ei i
Γijk Gkji
M = Mijk eiejej M = Σijk [M()]ijk ijk [M()]ijk = M'ijk
T = Tij eiej T = Σij [T()]ij ij [T()]ij = T'ij
Let's now install arguments as chosen above
M(x) = Σijk [M()(x)]ijk i(x)j(x)k(x) M = rank 3
M(x) = Σijk M'ijk(x) i(x)j(x)k(x)
T(x) = Σij [T()(x)]ij i(x)j(x) T = rank 2
T(x) = Σij T'ij(x) i(x)j(x)
3. Now look again at the dT and related objects: Here T is an abstract rank-2 tensor which I expand in a particular basis, assumed all functions of x.
(∂kT(x)) = Σij [(∂kT'ij(x)) + T'aj(x) Gika(x) + T'ia(x)Gjka(x) ] i(x)j(x)
dT(x) = (∂kT)dxk = Σij [(∂kT'ij(x)) + T'aj(x) Gika(x) + T'ia(x)Gjka(x) ] i(x)j(x) dxk
At this point T and M have no connection at all. Now I derived the above in some earlier document, so let's rederive right here to make sure it is done correctly. Start with
T(x) = Σij T'ij(x) i(x)j(x)
Then apply ∂k to get
∂kT(x) = (∂kT'ij(x)) i(x)j(x) + T'ij(x)(∂k i(x))j(x) + T'ij(x)i(x)(∂kj(x))
Now use the relation above that
(∂jn(x)) = Grjn(x)r(x)
so that
(∂k i(x)) = Grki(x)r(x)
(∂k j(x)) = Gskj(x)s(x)
and then
∂kT(x) = (∂kT'ij(x)) i(x)j(x) + T'ij(x)(∂k i(x))j(x) + T'ij(x)i(x)(∂kj(x))
= (∂kT'ij(x)) i(x)j(x) + T'ij(x) Grki(x)r(x)j(x) + T'ij(x)i(x)Gskj(x)s(x)
Now some index shuffling. In the middle term do i↔r and in the last term j↔s:
= (∂kT'ij(x)) i(x)j(x) + T'rj(x) Gikr(x)i(x)j(x) + T'is(x)i(x)Gjks(x)j(x
= [ ∂kT'ij(x) + T'rj(x) Gikr(x) + T'is(x)Gjks(x)] i(x)j(x)
and this verifies the result quoted above.
4. If we assume that in Picture C1 above the x-space is Cartesian, we may say
(∂kT)rs = ∂kTrs = Mrsk
and this is our first inkling of a connection between M and T. We are later going to invoke Picture C1' where x' is going to be non-Cartesian. The index ordering above I take from this quote
(T)ijk ≡ ∂kTij (J.1.3)
with the idea that somehow M = T in the abstract.
5. Question 1: What tensor transformation rules apply to the above line going from x to x'-space? First, we know that
M'rsk(x') =Rrb Rsc Rka Mbca(x) T'rs(x') = RrdRseTde(x) ∂'k = Rkd∂d
6. Going down a blind path, I could then evaluate, as in earlier appendices
∂'kT'rs(x') = ( Rkd∂d)(RrdRseTde)
= Rkd [RrdRse(∂dTde) + (∂dRrd)RseTde + Rrd(∂dRse)Tde ]
and this at least makes a connection between [ ∂'kT'rs(x')] and [∂dTde(x)] .
7. I don't really see any connection between this last item and the expansions in 2. Well there is this;
Define
Q'ijk ≡ [(∂kT'ij(x)) + T'aj(x) Gika(x) + T'ia(x)Gjka(x) ]
I arbitrarily put Q in script with a prime but it means nothing right now, just a definition. Then from 3 above
(∂kT(x)) = Σij Q'ijk i(x)j(x)
dT(x) = (∂kT)dxk = Σij Q'ijkdxk i(x)j(x)
So OK, the first line above does make some kind of connection between an expansion and ∂kT. However, I don't really know what (∂kT(x)) means having no indices. It is a vector in direct product space. Probably I could dot both sides with ua(x)ub(x) and use ua(x) i(x) = [i(x)]a = [i(x)]a . Then maybe this is true
∂kTab(x) = Σij Q'ijk [i(x)]a [j(x)]b
and then I have connected Qkij with something which at least has a meaning. Suppose I then multiply both sides of this by [r(x)]a [s(x)]b and sum on a and b. I end up then with things like
Σa [i(x)]a [r(x)]a = i(x) r(x)
Now comes a confusion. These vectors are in ξ-space of Picture C1. Therefore i(x) hi = ei(x) where there is no prime on the hi. Then continue the above
Σa [i(x)]a [r(x)]a = i(x) r(x) = (hihr)-1 ei(x) er(x) = (hihr)-1 gir(x)
where g is for x-space in Picture C1. For Cartesian x-space, we know that hi = 1 and g = δ, wo then
Σa [i(x)]a [r(x)]a = (hihr)-1 gir(x) = δi,r
which is what your intuition suggests in Cartesian space. So carrrying out this process we get
[r(x)]a [s(x)]b ∂kTab(x) = Σij Q'ijk δi,r δj,s = Q'krs(x)
so we have now an expression for Qkrs, for what it is worth. At least I now know this:
∂kTab(x) = Mabk = Σij Q'ijk [i(x)]a [j(x)]b
8. What I am really interested in is M'abk = h'ah'bh'k M'abk. So I can write
M'abk = h'ah'bh'k M'abk // Picture A,B notation
M'abk = h'ah'bh'k RaARbB RkK MABK = h'ah'bh'k RaARbB RkK ∂KMAB
But x-space is Cartesian, so ∂KMAB = ∂KMAB and I know that
∂KTAB(x) = Σij Q'ijK [i(x)]A [j(x)]B
so I then have
M'abk = [ h'kh'ah'b RkKRaARbB [i(x)]A [j(x)]B ] Q'ijK
Now this last statement is valuable. It relates [M()]abk = M'abk to QijK . So now the question is this: Can this last line be simplified? I first quote
Mab ≡ h'a Rab (E.8.7)
and then I can write
M'abk = [ MaAMbB h'kRkK [i(x)]A [j(x)]B ] QijK
I quote again.
Nin = h'n-1Rni = h'n-1(en)i = (n)i , // (7.13.1) (E.8.12)
Then I can further simplify
M'abk = [ MaAMbB h'kRkK [i(x)]A [j(x)]B ] Q'ijK
NAi NBj
or
M'abk = [ MaAMbBNAiNBjh'kRkK] Q'ijK
= [ MaANAiMbBNBjh'kRkK] Q'ijK
= [ (MaANAi)(MbBNBj)h'kRkK] Q'ijK
= [ δaiδbj)h'kRkK] Q'ijK
= h'kRkK Q'abK
= h'kRkK [(∂KT'ab(x)) + T'rb(x) GaKr(x) + T'as(x)GbKs(x) ]
This is similar to something I found before, and it seems very close to the answer I seek which is shown on Lai page 504 top.
9. Now how would I convert this to Lai notation? From above I already have
Mijk = M'ijk Tij = T'ij Γijk = Gkji
Then in Lai notation I have shown that
Mijk = h'kRkK [(∂KTij(x)) + Trj GiKr(x) + TisGjKs(x) ]
ΓrKi ΓsKj
or
Mijk = h'kRkK [∂KTij + TrjΓrKi + TisΓsKj ]
or
Mijk = h'kRkK [∂KTij + TqjΓqKi + TiqΓqKj ]
or
But here is what appears in