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AATAS Offline Analysis of Vibrations Software Components Core Module - Part 1 Core Module - Part 2 Traveling Wave LSMF Analysis Individual Blade FFT Analysis

Analysis of Vibrations There are two general types of Vibrations which can be analyzed by AATAS Software: . Synchronous Vibration Non-Synchronous Vibration

Synchronous Vibration Also referred to as Integral vibration. Synchronous vibrations are excited by drivers which are stationary to an engine case and typically located in the flow field. The frequencies of these vibrations are locked in phase with engine speed. Their deflections reach maximum peaks at points of resonance. Hardware transmitted synchronous energy can drive responses which appear to be non-stationary relative to the case but remain synchronous to rotation.

Non-Synchronous Vibration Also referred to as non-Integral vibration. This vibration is excited by drivers which are typically not stationary and are therefore not tied to engine speed. Energy that enters the system causes rotor blades to vibrate along their natural frequency modes. There are two sub-categories for non-synchronous vibration: Forced Non-Synchronous Vibration and Vibrations induced by aerodynamically unstable conditions.   Forced non-synchronous responses can come in many forms; vortex shedding, acoustic excitation, periodic flow disturbances. Typically, these responses are limit cycle meaning that the amplitude reaches a maximum and levels out. This is due to the damping present in the mechanical system. Stall and surge can also be grouped in forced non-synchronous vibrations. Rotating stall acts like a low frequency impact typically at approximately ½ the rotational rate. Surge acts on the blades like a single impact.   Non-synchronous vibrations induced by unstable aerodynamic conditions are known as flutter. These responses occur because the aero and mechanical damping of a system reaches a negative value. It this scenario energy is added to the vibration from the flow field after each cycle. If left unchecked, this type of vibration will continue to increase in amplitude with each cycle until failure occurs.