# Problems with system of PDE's

Posted 10 years ago
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 I'm working with a system of partial differential equations with Mathematica--the two linearized momentum equations below--and I'm having trouble figuring out how exactly to solve them. I've tried using DSolve and NDSolve, but I keep running into errors. u and w (velocities) are functions of [t,x] and [t,z] respectively. The problem I'm getting is that Fx, Fz, and p include powers of u and w terms in their definitions and DSolve and NDSolve don't seem to like that. The following definitions are straight from the above paper, consider just the u and x equation:Fx:=(\[Rho]*B*Cx*u[t,x]*Abs[u[t,x]])/2Cx:=0.4+(4600/Renx)^2.9Ren:=(u[t,x]*L)/vp:=(\[Rho]*u[t,x]^2)/2Where Rho, B, L, and v are constants:\[Rho]:=1000B:=200L:=.019v:=1.005*10^-6  Is there a better way to solve this? Ideally I'd like to include the boundary conditions:u[t,0]==tu[0,x]==1.3*E^(x)I've tried to find advice online and in person, but I've been unsuccessful. Any advice or code would be wicked much appreciated!
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Posted 10 years ago
 Also, your boundary conditions are inconsistent.  u[0,0] is 0 from one and 1.3 from the other.
Posted 10 years ago
 The definition of Cx contains Renx which isn't defined.  Ren is defined.
Posted 10 years ago
 I appologize for not clarifying about that. u[t,x] is a velocity that is dependent on functions of t and x. u[t,x]==T[t]*X[x]T[t]=tX[x]=E^xSo a stripped-down example Dsolve looks like:DSolve[{D[u[t,x],t]+2*u[t,x]D[u[t,x],x]==Fx,u[t,x]==T[t]X[x]},u[t,x],{t,x}]
Posted 10 years ago
 Your definitions of Fx, C, Ren, p don't include their dependence on x and t.  That may be the problem.