Consider the turbine$-$generator system shown in Figure $3,$ consisting of

several interconnected components. Each component can be considered as a

rotating inertia, I, connected by a rotating spring, with the springs having a

rotational spring rate, $k.$ This system can be simply modeled as shown in

Figure $4.$

Figure $3-$ Diagram showing a turbine$-$generator system.

Figure $4-$ Block diagram of the turbine$-$generator system, represented as rotating inertia connected by

rotating springs.

Recall that the rotational equivalent of Newton's second law:

$F=ma$

is

$M=I{}^{\text{'}\text{'}}$

where I is the rotational equivalent of mass, called the mass moment of inertia

for a rotating disk, and ${}^{\text{'}\text{'}}$ is the rotational acceleration $($second derivative of

angular displacement$).$ Additionally, recall that a shaft in a rotating system has

rotational spring rate with units of $N\frac{m}{?}$ radian.