Fundamentals of Vibrations

Concepts of analytical & approximate dynamics of SDOF/MDOF under excitations


Domain

Explanation

Phenomenon

Concepts

  • Newton’s laws: 1st inertia, 2nd momentum, 3rd action-reaction
  • Momentum: conservation, force-moment, angular momentum
  • Work, energy: conservation, dissipation
  • Types: potential energy, kinetic energy, mechanical/chemical/biological
  • Dynamics: 1) particles (SDOF), 2) rigid bodies (SDOF+continuity), 3) flexible bodies (MDOF+continuity)
  • Systems: 1) discrete, 2) continuous
  • Vibrations: 1) excitations, 2) self-induced, 3) about equilibrium points (stable)
  • Physical phenomenon: vibration modes, frequency, phase, periodic/non-periodic, random/arbitrary, (un)forced

SDOF

  • Angular oscillation, periods, frequency, single variable
  • Coulomb damping
  • Modeled after Meirovitch as well as Hart
  • System response to: 1) initial excitation, 2) harmonic & periodic, 3) non-periodic
  • Sensitivity analysis of response
  • Normal mode method

2DOF

  • Modal analysis: orthogonality, beat phenomenon, convolution sum
  • Rayleigh damping
  • Sensitivity analysis of response

MDOF

  • Eigenvalue problem
  • Coefficients of mass, stiffness & damping
  • Modal orthogonality, decomposition & analysis

Analytical dynamics

  • DOF & generalized coordinates
  • Principle of virtual work
  • Principle of D’Alembert
  • Extended Hamilton’s Principle
  • Lagrange’s equations
  • Exact solution to model as eigenvalue problem using wave equation

Approximate dynamics

  • Holzer’s method for torsional vibration
  • Myklestad’s method for bending vibration
  • Rayleigh’s principle
  • Galerkin’s method
  • Collocation method (numerical family: Newmark & Wilson part)

Nonlinear oscillations/response

  • Nonlinearity occurs w.r.t. oscillations (excitations), material properties, mass (rocket fuels), geometry (deformations) & uncertainties
  • Stability: w.r.t. equilibrium (critical) points, limit cycles, perturbation technique & stiffness criterion
  • Lindstedt’s method
  • Van der Pol oscillator

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