I am trying solve the following two coupled PDE equations.
∂f/∂t=(∂^2 f)/(∂x^2 )+(∂^2 f)/(∂y^2 )-1/f^3 [(∂B/∂x)^2+(∂B/∂y)^2 ]-f+f^3
(∂^2 B)/(∂x^2 )+(∂^2 B)/(∂y^2 )-B*f^2+2/f [(∂B/∂x)(∂f/∂x)-(∂B/∂y)(∂f/∂y)]=0
The boundary conditions are
B(t,0,y)=const*t,B(t,x,0)=B(t,x,10),B(t,10,y)=0,
f(t,10,y)=1,f(t,x,0)=f(t,x,10),
Initial condition
f(0,x,y)=1 and B(0,x,y)=0
In order to solve I set up a square region {x=0,10 and y=0,10}.Left wall we don't know how f behaves.When time ramp up applied B increases so I need to know how B and f changes with time inside the box.
When I try to solve I get following errors:
1.NDSolve::pdord: Some of the functions have zero differential order, so the equations will be solved as a system of differential-algebraic equations.
2.NDSolve::bcart: Warning: an insufficient number of boundary conditions have been specified for the direction of independent variable x. Artificial boundary effects may be present in the solution.
I have following questions:
1.Is it possible to solve this type of coupled pde using ndsolve?
2.Is there any method I can use to over come this error? Please help..I am new to Mathematica.. Code is as follows.here u==f and v==B**
h = 0; inf = 10; k = 3;
pde = {D[u[t, x, y], t] ==
D[u[t, x, y], {x, 2}] +
D[u[t, x, y], {y,
2}] - (k^4/u[t, x, y])^3*(D[v[t, x, y], y]^2 +
D[v[t, x, y], x]^2) - u[t, x, y] + u[t, x, y]^3,
D[v[t, x, y], {x, 2}] +
D[v[t, x, y], {y, 2}] - (v[t, x, y]*u[t, x, y]^2)/k^2 +
(2/u[t, x, y])*(D[u[t, x, y], x]*D[v[t, x, y], x] -
D[u[t, x, y], y]*D[v[t, x, y], y]) == 0};
ic = {u[0, x, y] == 1, v[0, x, y] == 0};
bc = { u[t, inf, y] == 1, v[t, 0, y] == h + 0.1*t,
v[t, x, 0] == v[t, x, inf], u[t, x, 0] == u[t, x, inf],
v[t, inf, y] == 0};
NDSolve[{pde, bc, ic}, {u, v}, {x, 0, inf}, {y, 0, inf}, {t, 0, 15}];
Table[Plot3D[
Evaluate[u[t, x, y] /. First[%]], {x, 0, inf}, {y, 0, inf},
PlotRange -> All, PlotPoints -> 10, Mesh -> False], {t, 14, 15}]
+f-f^3part. BTW it's bad idea to name variables differently in code and text, this makes error checking painful. 2. Boundary atu[t, 0, y]is missing, this is a more serious problem, because we don't know what b.c. is added, for more information, check this post: https://mathematica.stackexchange.com/q/73961/1871 3. The equation causingpdordwarning is indeed troublesome, you can refer to this post as an example: https://mathematica.stackexchange.com/q/133731/1871u[t, 0, y]is necessary, or a hidden b.c. will be added (which we don't know what it represents at least for now. You may also want to read this). Also, notice the warningndszis easy to explain. If you check the solution ofuat0.0242, you'll see it hits0, which isn't allowed by the equation. – xzczd Nov 09 '17 at 03:07