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Type1civ
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Homework Statement
Stuck on two similar problems:
"State the normal stress boundary condition at an interface
[tex] x_3-h(x_1,x_2,t)=0[/tex]between an invisicid incompressible fluid and a vacuum. You may assume that the interface has a constant tension."
The second question in the same but the fluid is viscous.
2. The attempt at a solution
I worked out the normal to the surface to be:[tex]\mathbf{\hat n}=\frac{\partial h}{\partial t} -\mathbf{\hat x_3}+\frac{\partial h}{\partial x_1}\mathbf{\hat x_1}+\frac{\partial h}{\partial x_2}\mathbf{\hat x_2}[/tex]so then the normal stress at the boundary much be equal and opposite from both media? But since one of the medium is a vacuum the stress will be zero. so:
[tex]\frac{\partial h}{\partial t} -\frac{\partial w}{\partial x_3}+\frac{\partial h}{\partial x_1}\frac{\partial u}{\partial x_1}+\frac{\partial h}{\partial x_2}\frac{\partial v}{\partial x_2}=0[/tex]
where I am using the velocity of the fluid so that [itex]\mathbf{u}=(u,v,w)[/itex].
Not really sure how much of this is the correct line of thought, and also not sure how the viscosity should impact my result...
Thanks
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