Kennedy and Pancu circle

Kennedy and Pancu circle

[¦ken·ə·dē ən ′pän·chü ‚sər·kəl]
(mechanics)
For a harmonic oscillator subject to hysteretic damping and subjected to a sinusoidally varying force, a plot of the in-phase and quadrature components of the displacement of the oscillator as the frequency of the applied vibration is varied.