Chladni patterns Simulation

Hey, so I developed this code to try a simulation on chladni patterns and the wave equation of vibrating plates.

So here’s my code so far

X = 1;
Y = 1;
k1 = n*\[Pi]/X;
k2 = m*\[Pi]/Y;
k = c*\[Pi]*Sqrt[(n/X)^2 + (m/Y)^2];
nmax = 10;
mmax = 10;
Manipulate[
 Plot3D[Sum[
   Sin[k1*x]*Sin[k2*y]*Cos[k * t], {n, 1, nmax}, {m, 1, mmax}], {x, -X/
    2, X/2}, {y, -Y/2, Y/2}], {t, 0, 20}]



edit: i forgot to put a value to constant "c"
now i put "c=1;" and the part of Cos[k*t] now only has values of {1;-1} somehow

The problem is that it doesn’t work for t>0 somehow.
I know there’s probably some bug there, but I can’t see where.

The argument of your Plot3D does not have any dependence on t. And this may be because you have not given an argument to your Cos that is multiplying your Sin functions on their right.

You should take a look at this Demonstration: Chladni Figures