Interference Diagram plots the cyclic modal frequencies versus the harmonic index data as red rhombuses. The speed lines are also superimposed on the diagram for each speed multiplier. This is also known as a SAFE or ZZENF diagram and indicates potential frequencies where resonance may occur.
Note: Interference Diagram does not always guarantee the true resonance. It suggests that resonance occurs whenever the natural frequency of the block matches the excitation frequency. However, due to the cyclic nature of the structure, the mode shape may not match the Engine Order excitation shape coming out of the nozzles for the diagram's suggested critical speed. Hence, the SAFE or Interference Diagram, which relates the mode shapes with speed and natural frequency, predicts the true resonance and is used by industries for reliable design.
The Rotational Speed field is auto-populated from the Rotational Velocity value of the Static Structural system pre-stressing the Modal system and can be edited.
One or several engine orders may be plotted by setting values separated with commas (',).
Note: Only positive values are accepted.
The figure below illustrates an Interference Diagram with three speed lines. The speed lines follow this formula:
 | (3–1) |
where 
corresponds to the frequency, 
to the harmonic index, and 
to the rotational velocity.
