A simple example :
A beam on side full restraint.
D = 88,9 mm
t = 6,0 mm
E-Modul 210 000 N/mm2
rho 7,85 kg/dm3
L 2000 mm

At Euler Beam Theorie
first eigenvalue:

f = 0,56 * (1/L*L) * sqrt (E*I/rho*A)
Theoretical f = 21,28 Hz

Now calculat the first eigenvalues with Caesars eigensolver
with 1,2,4,8 Elements.
You can see the Tendenz.
This show : More elements higher first eigenvalue and approach to theoretical f = 21,28 Hz.
So much the better your mass discretation ==> exacter the frequency by the solver.