FUNDAMENTALS OF DYNAMIC ANALYSIS
Damping
Damping is not important in static analysis.
Damping is difficult to model accurately because it is caused by many different mechanisms.
Viscous: Force proportional to velocity. Viscous damping has more influence al low frequencies.
Structural: Force proportional to displacement.
Modal: It has no physical meaning. Modal damping includes the global damping in the structure, due to all mechanisms. Modal damping can be easily derived from experimental measurements, and allows decoupling the system of equations.
Modelling problems
A single degree of freedom (dof) system has 1 resonant frequency. A continuous body has infinite dof, so it has infinite resonance frequencies.
Modelling and numeric errors increase with increasing frequencies. To solve high frequency problems (high modal density) statistical methods are used.
Stiffness has more influence at low frequency, while a variation in mass will affect the high frequency region.
Supports and joints are often idealised, an adequate modelling of their stiffness and damping is very important in the dynamic results.