Dynamic calculations serve to describe the behaviour of a structure on time-variable loads.
The natural frequency or eigenfrequency of a vibrating system is that at which it will vibrate after a nonrecurring excitation.
If you ignore the damping, eigenfrequency and resonance frequency are the same.
If a system is subjected to external excitation at a frequency coinciding with its natural frequency, the system will vibrate at a particularly high amplitude, which is known as resonance or, in case of damaging effects, as resonance catastrophe. Natural frequency measurement is determined computationally as eigenvalue problem.
The response of a system after excitation by a harmonic load can be determined as function of the frequency via a so-called Harmonic Response Analysis, corresponding computationally to a test on the vibrating table with a sine sweep.
The response of a structure to an impact or shock can be determined via impact analysis. Here, load is specified as a function of time (e.g. half sinus).
The response of a structure to any time-variable load can be specified via a spectral analysis. However, time information gets lost here. Energy density at a frequency band is the given input and response of the structure is being determined by a conservative superimposition of the single vibration modes.
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