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gash789
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Homework Statement
I am trying to show the shallow wave equations (Pg 35 Ockendon). For a shallow channel of water, with one free surface h(x,t) that runs parallel to the x-axis, the fluid has a constant density and the pressure is nearly hydrostatic and equal to P(x,t)=ρg(h-y)
Homework Equations
I have already shown that
[itex]
h_{t}+[hu]_{x}=0
[/itex]
But I am struggling to show
[itex]
\rho\left(u_{t}+u u_{x}\right)=-P_{x}=-\rho g h_{x}
[/itex]
The Attempt at a Solution
I have begun by trying to show using the Navier Stokes equation that
[itex]
\rho\left(u_{t}+u u_{x}\right)=b
[/itex]
where b is a "sink or source of momentum". This implied to me that it is a rate of change of momentum such as
[itex]
P_{t}
[/itex]
of which could be solved using the original equation for the pressure, but the equation the book has suggests it should be a spatial derivative. This does not make sense to me?
Just to be clear
[itex]h_{x}=\frac{\partial h}{\partial x} [/itex]