Where, i
α and i
ω are the damping coefficient (the real part) and damped natural frequency (the imaginary part) describing
damped sinusoidal motion. The motion for each mode can be described in terms of the complex conjugate eigenvalue and
eigenvector. A positive damping coefficient causes the amplitude of oscillations to increase with time. Therefore the system is not
stable when the damping coefficient is positive. By examining the real part of the system eigenvalues the modes that are unstable
and likely to produce squeal are revealed. An extra term, damping ratio, is defined as − 2α /ω . If the damping ratio is negative,
the system becomes unstable, and vice versa.