Introduction to Rotor Dynamics

Introduction to Rotor Dynamics

Introduction to Rotor Dynamics: Fundamentals

What is Rotor Dynamics?

Rotor dynamics is the study of dynamic characteristics related to rotating machinery components, with strong engineering applications in aerospace engines, gas turbines, steam turbines, compressors, hydro turbines, turbopumps, superchargers, diesel engines, pumps, and motors. Key research areas include:

• Vibration
• Dynamic response
• Stability
• Dynamic balancing
• Bearing/seal characteristics
• Strength, fatigue, and reliability
• Condition monitoring & fault diagnosis

It particularly addresses rotor behavior near or beyond critical speeds.
 

Turbine rotor model in DyRoBeS software

Core Concepts in Rotor Dynamics

1. Vibration Types (by Excitation Source)

Forced Vibration

• Caused by external periodic forces (e.g., rotor unbalance).
• Feature: Frequency matches excitation frequency (1X vibration for unbalance).

Forced vibration simulation in DyRoBeS

Self-Excited Vibration

• Triggered by internal cross-coupled stiffness (e.g., oil whip, seal whirl).
• Feature: Frequency depends on natural frequency, not rotation speed.

Self-excited vibration simulation in DyRoBeS

2. System Linearity

Linear Analysis

• Uses linearized bearings/damping (solved via linear ODEs).
• Covers 80%+ engineering cases (e.g., stability with 8-coefficient bearing models).

Nonlinear Analysis

• Required for cracks, severe unbalance, or nonlinear bearings (modeled via nonlinear ODEs).

3. Vibration Modes

• Lateral: Perpendicular to axis (most common).
• Torsional: Twisting about axis.
• Axial: Parallel to axis.

Learning Path for Rotor Dynamics

1. Start with linear lateral vibration – Solves most industrial problems.
2. Master fundamentals – Critical for transitioning to nonlinear cases (e.g., cracked rotors).
3. Use industry tools – DyRoBeS, ANSYS, or SAMCEF for simulations.

Rotor Dynamics vs. Structural Dynamics

Equation Notes:

• Rotor dynamics includes gyroscopic effects (GG) and cross-coupling (BB), critical for stability analysis.

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