Problems:
1 Determine the material derivative of the flux of any vector property Q*i through the spatial area S. Specifically, show that
d/dt ∫S Q*inidS = ∫S (Q.*i + Qi*Vk,k - Q*Vi,k) nidS
2. Let the property P*ij..... be the scalar 1 so that the integral in that equation represents the instantaneous volume V. Show that in this case
P.ij.. = d/dt ∫v dV = ∫v vi,jdV
3 Verify the identity
εijk = 2 (w.i + wivj,j - wj vi,j
and, by using this identity as well as the result of Problem 1, prove that the material derivative of the vorticity flux equals one half the flux of the curl of the acceleration; that is, show that
d/dt ∫s winidS = 1/2 ∫s εijk, αk,jnidS
4 Making use of the divergence theorem of Gauss together with the identity
∂wi/ ∂t = 1/2 εijkαk,j - εijk εkmq (wmvq),j
5 Show that the material derivative of the vorticity of the material contained in a volume V is given by
d/dt ∫v widV = ∫s(1/2 εijkαk + wjvi)njdS
6 Given the velocity field
v1 = ax1 - bx2, v2 = bx1 + ax2, v3 = c√(x21 + x22)
7 For a certain contiuum at rest, the stress is given by
σij = - poδij
where po is a constant. Use the continuity equation to show that for this case the stress power may be expressed as
σijDij = p0ρ./ρ
8 Consider the motion xi = (1 + t/k)Xi where k is a constant. From the conservation of mass and the initial condition ρ = ρo at t = 0, determine ρ as a function of ρo, t, and k.
9. Using the identity
εijkαk,j = 2(w.i + wivj,j - wjvi,j)
as well as the continuity equation, show that
d/dt (wi/ρ) = (εijkαk,j + 2 wjvi,j )/ 2ρ