Wave equation with inhomogeneous boundary conditions

[josh146]

I'm reposting this because there was a problem with the title/LaTeX last time.

Homework Statement

Solve the wave equation (1) on the region 0<x<2 subject to the boundary conditions (2) and the initial condition (3) by separation of variables.

Homework Equations

(1) \frac{\partial^2 u}{\partial t^2}=c^2\frac{\partial^2 u}{\partial x^2}

(2) \frac{\partial u}{\partial x}(0,t)=1 ; \frac{\partial u }{\partial x}(2,t)=1

(3) \frac{\partial u}{\partial t}(x,0)=0

The Attempt at a Solution

I've defined \theta(x,t)=u(x,t)-u_{st}(x) = u(x,t)-x-h(t) where u_st is the steady state solution (4). I've used this to create a new PDE with homogeneous boundary conditions.

The PDE is:

\frac{\partial^2 \theta}{\partial t^2} + h&#039;&#039;(t)=c^2 \frac{\partial^2 \theta}{\partial x^2}.

By subbing in \theta=f(t)g(x) I get:

f&#039;&#039;(t)g(x)+h&#039;&#039;(t)=c^2 f(t) g&#039;&#039;(x)

I'm not sure how to transform this into two ODEs. Can someone help?

(4): The solution to \frac{\partial^2 u}{\partial x^2} = 0 subject to (2).

 

[quZz]

I think you just need to introduce new function v: u(x,t) = v(x,t) + x. The equation for v(x,t) will be the same but boundary conditions will become homogeneous =) and btw, you are missing one more initial condition like u(x,t=0) = ...

 

[Spoony]

Im also stuck on this one, for me its the initial conditions and boundary conditions being partial derivitives that throws me.

 

[Spoony]

I think you just need to introduce new function v: u(x,t) = v(x,t) + x. The equation for v(x,t) will be the same but boundary conditions will become homogeneous =) and btw, you are missing one more initial condition like u(x,t=0) = ...

The eqn. given for boundary conditions is a partial derivative so do i intergrate it to find u(x,t)
in which case is it that; u(o,t) = x and u(2,t) = x. so that.
u(x,t) = v(x,t) + x so that in both cases... umm then i get stuck.

 

[Spoony]

No-one at all?

 

[Spoony]

So far I've got that:
U_{st} (x) = x
(a) Find the steady state solution, ust(x), by solving \frac{\delta ^{2} U_{st} }{\delta x^{2}} = 0 and applying the boundary
conditions. (You will only be able to determine one of the two arbitrary constants).

confused here, surely U_{st} (x) = x + c (as boundary conditions given are derivitives)

then initial condition:

<br /> \frac{\partial u}{\partial t}(x,0)=0<br />

given means that c = 0? :S

 

[Spoony]

Latex is fail :(

So far I've got that:
U_st (x) = x
(a) Find the steady state solution, u_st(x), by solving (partial second derivative u by x = 0) and applying the boundary
conditions. (You will only be able to determine one of the two arbitrary constants).

confused here, surely U_st (x) = x + c (as boundary conditions given are derivitives)

then initial condition:

(as above... in first post)

given means that c = 0? :S

 

[Spoony]

Can no one point me in the right direction?

 

[guhan]

Instead of integrating the BC, you may differentiate the solution you get and then apply the BC.