Resonance & Structural Analysis Flashcards

What is the anti-resonance in a frequency response function?

Answer: A local minimum in the FRF magnitude that occurs between two resonant peaks

Anti-resonances appear as sharp dips (minima) in the FRF between resonant peaks; they represent frequencies at which the response at a specific measurement location is very small due to destructive interference from different mode contributions.

In vibration isolation, the ratio of excitation frequency to the isolator natural frequency must exceed what value for effective isolation?

Answer: 1.414 (√2)

For transmissibility to be less than 1.0 (effective isolation region), the excitation frequency must exceed √2 times the isolator natural frequency; below this ratio, the isolator actually amplifies the vibration.

What is a node point in a structural mode shape?

Answer: A location of zero or near-zero displacement in the mode shape

A node is a point in a mode shape that remains stationary (has zero displacement) while the rest of the structure oscillates; its location is determined by the boundary conditions and geometry of the structure.

What does 'critical damping' mean for a mechanical system?

Answer: The damping level (cc = 2√km) at which the system returns to equilibrium without oscillating after a disturbance

Critical damping (cc = 2√km) is the minimum damping required for a system to return to equilibrium without overshooting or oscillating; it represents the boundary between overdamped and underdamped behavior.

Which of the following best describes acoustic resonance as it relates to machinery vibration?

Answer: Resonance of fluid columns in pipes or cavities excited by machinery vibration or pulsation

Acoustic resonance occurs when pressure pulsations from pumps, compressors, or fans excite natural frequencies of piping systems or cavities, causing excessive vibration, noise, and potential fatigue failures in the piping.

What is the purpose of performing a 'bump test' (impact test) on machinery structure while it is NOT running?

Answer: To identify structural natural frequencies and assess whether they coincide with machine operating speeds

A bump test excites the structure with an impulse while it is stationary, and the resulting free-vibration response reveals the structural natural frequencies, allowing the analyst to assess potential resonance risks with operating harmonics.