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Poincare Map. Oscillator Motion. Harmonic motion has both a mathematical and geometric description. Equations of motion Phase portrait The motion is characterized by a natural period. Plane pendulum. E > 2. E = 2. E < 2.
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Oscillator Motion • Harmonic motion has both a mathematical and geometric description. • Equations of motion • Phase portrait • The motion is characterized by a natural period. Plane pendulum E > 2 E = 2 E < 2
The damped driven oscillator has both transient and steady-state behavior. Transient dies out Converges to steady state Convergence
Oscillators can be simulated by RLC circuits. Inductance as mass Resistance as damping Capacitance as inverse spring constant Equivalent Circuit L vin v C R
Devices can exhibit negative resistance. Negative slope current vs. voltage Examples: tunnel diode, vacuum tube These were described by Van der Pol. Negative Resistance R. V. Jones, Harvard University
Relaxation Oscillator • The Van der Pol oscillator shows slow charge build up followed by a sudden discharge. • Self sustaining without a driving force • The phase portraits show convergence to a steady state. • Defines a limit cycle. Wolfram Mathworld
The values of the motion may be sampled with each period. Exact period maps to a point. The point depends on the starting point for the system. Same energy, different point on E curve. This is a Poincare map Stroboscope Effect E > 2 E = 2 E < 2
Damped simple harmonic motion has a well-defined period. The phase portrait is a spiral. The Poincare map is a sequence of points converging on the origin. Damping Portrait Damped harmonic motion Undamped curves
Energetic Pendulum • A driven double pendulum exhibits chaotic behavior. • The Poincare map consists of points and orbits. • Orbits correspond to different energies • Motion stays on an orbit • Fixed points are non-chaotic l q m l f m pf f