${\omega }_n$	Natural frequency
n	Mode of vibration
L	Cable length
E	Modulus of elasticity
$I_p$	Polar moment of inertia
F	Cable tensile force
$\mu$	Linear mass density
$T_v$	Translational kinetic energy
$T_{\omega }$	Rotational kinetic energy
$U_g$	Gravitational potential energy
$U_K$	Linear elastic potential energy
$U_{K_t}$	Torsional elastic potential energy
$\mathcal{Q}$	External load
$v_{cg}$	Velocity of the tower’s center of gravity
$z_{cg}$	Height of the tower’s center of gravity
m	Mass of the tower structure
g	Gravitational acceleration
I	Moment of inertia referred to the center of gravity (in $x,y,z$ axes)
$\theta$	Tower angles (in $x,y,z$ axes)
k	Stay cable stiffness
$k_t$	Tower torsional stiffness at pivot base point
$L_c$	Stay cable instantaneous length
$L_{cn}$	Stay cable free length
${\widehat{x}}_k$	Estimated value at instant k
$P_{\overline{k}}$	Error covariance at instant k
A	State transition matrix
Q	Noise covariance matrix of the state transition
$K_k$	Kalman gain at instant k
R	Covariance matrix of the measurement noise
H	State matrix for the measurement
$z_k$	Measured signal at instant k