Are you hoping to obtain symbolic expressions for Ana, Anm, Anr, Ans, Bna, Bnm, Bno and Bns in terms of n and theta ? Are you interested in numeric solutions for given n and theta ? For example:

sys:={eq1, eq2, eq3, eq4, eq5, eq6, eq7, eq8};
sys_sub:=subs({n=1,theta=0},sys);
fsolve(sys_sub, {Ana, Anm, Anr, Ans, Bna, Bnm, Bno, Bns});
      {Ana = 2.968328229*10^8, Anm = 1.395157953*10^9, Anr = -5.323482514*10^5, 
       Ans = -8.950727638*10^8, Bna = 0.7039319912e-2, Bnm = -0.3091044476e-2, 
       Bno = 1.269538296*10^(-8), Bns = 0.3530504109e-1}

T1 and T2 are functions of t, but you differentiate them with respect to x in the ODE definitions.

I'm afraid I've forgotten most of the mechanics I ever learned, so I can't advise on the model, but you might start by simply changing differentiation wrt x, to wrt t.

Normally when there is no result it means Maple didn't find any solutions.I can see a few problems in your code:

1. Z[0] = 377; should be Z[0] := 377;

2. It's generally not a good idea to use indexed variables such as Z[0] and then also use Z on it own.

3. subs(w = w[1], 2*Z[0]*(1-S[21])/S[21]) doesn't do anything

4. subs(w = w[2], 2*Z[0]*(1-S[21])/S[21]) also doesn't do anything

5. I counted 15 variables before I lost count, but there are only 10 equations

6. Generally, you may find it easier to assign a name to each of the equations on seperate lines, then call solve() with (solve({eq1,eq2,...}) etc 

I believe your problem is that Maple is case sensitive. Hence this should work:

dsolve({ODE,ics});

The problem seems to be that indrukking does not depend on s:

indrukking;
                   /                           2
           222.8 - \(152.5 - 108 cos(beta1[1])) 

                                            2\      
              + (-105.6 - 108 sin(beta1[1])) /^(1/2)

it seems to depend only on beta1[1] . So:

plot(indrukking, beta1[1] = 0 .. 180);

If you look at the output of solve(eq,{theta1,theta2}); it is giving you  θ1 =...... and θ2

Of course, as I mentioned above, there are two unknowns are only one equation so θ1 is given in terms of θ2 and vice versa.

If you give a value to one of θ1 or θ2 hen you can solve for the other. For example:

eq2:=subs(theta1=0,eq);

solve(eq2);

Now you have the problem that there are many solutions since the function is sinusoidal. so you can use fsolve, and restrict the range:

fsolve(eq2, theta2, 0..Pi);

2.431253757

You don't have any equations, only 4 assignments to variables. I *guess* you want the last assignment to be an equation, so

Lar := 416:
Iar := -45+158*cos(theta1)-416*cos(theta2):
Jar := 169+158*theta1-416*sin(theta2):
eq := Lar = sqrt(Iar^2-Jar^2):

However, now you have one equation and two unknowns. You can use solve, but you won't get a unique answer:

solve(eq,{theta1,theta2});

In your solve command, you seem to be solving for 10 unknown variables. However, you only have 4 equations: mf2, mf3, mf4 and mf5; while some of the "equations" in your solve command are actually just variable assignments (dm1, dm1A, dm1B, dm1C, dm2, dm2A,  dm2B , dm2C).  

I believe it is an instrument that measures the amplitude of a pulse/signal.

Here's a link that may help you get started (I found it from google, I'm not an expert)
http://www.universe.nasa.gov/xrays/programs/astroe/eng/pha-math.html 

I think it's normal behaviour by Maple.

For example, 

(a*c+c)/(b*c+c);
                            a c + c
                            -------
                            b c + c

The plot command is for curves. You have a surface. Does this do what you want ?

plot3d([x(eta,xi),y(eta,xi)],eta = -1..1, xi=-1..1);

Are you able to import it using the menu ?

Tools>Assistant>Import Data

?

The Search command in the DirectSearch package should be able to find the maximum and minimum

http://www.maplesoft.com/applications/view.aspx?SID=101333

As for the mean, you can find this by integration of the function over the volume, divided by the volume of integration.

Perhaps you need to use L[i] instead of L(i) inside the procedure ?

I'm not sure if there is an equivalent function in Maple, but I think this should work, if I've understood what you want to achieve

conv:=proc(f1::list,f2::list)
 # procedure computes the discrete convolution of two lists, returning a list
 local n, tmp, k, cv:
 cv:=[]:
 for n from 1 to nops(f1)+nops(f2)+1 do
   tmp:=0:
   for k from 1 to nops(f1) do
     if n>k and n-k<=nops(f2) then tmp:=tmp+f1[k]*f2[n-k]: end if
   end do;
   cv:=[op(cv),tmp]:
 end do:
end proc:

s1:=[1,2,1,2]:s2:=[1,3,1,2]:
conv(s1,s2);
                  [0, 1, 5, 8, 9, 11, 4, 4, 0]