What are Active Magnetic Bearings (AMBs) and what happens when they fail?

Active Magnetic Bearings, or AMBs, are used in turbomachinery to provide frictionless operation and minimize energy loss. They rely on a consistent power supply to maintain the rotor's position. However, if there's a power failure, the rotor drops onto Touch-Down Bearings. Predicting this behavior is vital to prevent significant damage.

What are Touch-Down Bearings (TDBs) and what role does the ribbon damper play during a rotor drop?

Touch-Down Bearings, or TDBs, are emergency bearings designed to protect AMBs during a power failure. A ribbon damper, often a corrugated steel foil around the TDB, absorbs energy and controls the rotor's motion. The effectiveness of the ribbon damper directly impacts the rotor's trajectory and the overall system's integrity.

How do traditional damping models differ from dry-friction models in predicting rotor drop dynamics?

Traditional models often use simple viscous dampers to represent TDBs and ribbon dampers. However, experimental data shows that dry-friction models, like macroslip and microslip models, are more accurate. Macroslip models assume the entire contact surface sticks or slips, while microslip models allow for mixed configurations. These advanced models provide a better understanding of the energy dissipation during a rotor drop.

Can you describe the specific dry-friction models, such as the Masing model and the Generalized Dahl model, and how they compare to the Kelvin-Voigt model?

The Masing model is a macroslip model that uses stick stiffness to represent the ribbon being stuck. Once the slipping threshold is reached, all bumps slip, and a change of slope occurs. The Generalized Dahl model is a dry-friction restoring force model that uses a non-linear first-order differential equation, allowing the model to adopt any shape of loop. The Kelvin-Voigt model is a linear spring-damper model. The Masing and Generalized Dahl models offer a more realistic representation of stick-slip phenomena.

How do advanced models for ribbon dampers enhance the reliability of turbomachinery with Active Magnetic Bearing systems?

Dry-friction models like the Masing and Generalized Dahl models more accurately predict the dynamic behavior during rotor drop events compared to the Kelvin-Voigt model. These models capture the stick-slip phenomenon, providing a better understanding of energy dissipation. By using these models, engineers can design more robust AMB systems and minimize the risk of damage and downtime, enhancing the reliability of turbomachinery.

Stylized rotor drop with glowing touch-down bearings and energy dissipation waves.

Rotor Drop Dynamics: Enhancing Turbomachinery Reliability

Jordan Keane in Tech & Innovation December 2025 • 5 min read.

"Unveiling Advanced Models for Predicting and Preventing Failures in Active Magnetic Bearing Systems"

Turbomachinery supported by Active Magnetic Bearings (AMBs) represents a pinnacle of engineering, promising frictionless operation and minimized energy losses. However, the reliance on a consistent power supply introduces a critical vulnerability. In the event of an AMB power failure, the rotor, the rotating component, faces a non-linear transient behavior dictated by mass imbalance, contact forces, and gravity. Understanding and predicting this behavior is paramount to preventing catastrophic failures.

When an AMB system fails, the rotor inevitably drops onto Touch-Down Bearings (TDBs). These emergency bearings, often rolling-element types, are designed to act as a safety net, mitigating the impact of the fall and protecting the AMBs from permanent damage. Crucially, a ribbon damper, a corrugated steel foil fitted around the TDB, plays a vital role in absorbing energy and controlling the rotor's motion during this critical event. The effectiveness of this damping directly influences the trajectory of the rotor and the overall integrity of the system.

This article investigates advanced modeling techniques to predict the dynamic behavior of turbomachinery during rotor drop events. We'll delve into innovative dry-friction models for the ribbon damper, benchmarked against experimental data, and compare their performance against traditional viscous damping models. By understanding the nuances of these models, engineers can design more robust and reliable AMB systems, minimizing the risk of damage and downtime.

Dry-Friction Models: A New Approach to Damper Dynamics

Stylized rotor drop with glowing touch-down bearings and energy dissipation waves.

Traditional models often represent the TDB and ribbon damper as simple viscous dampers. However, experimental data reveals that the ribbon damper's behavior is more accurately described by dry-friction phenomena. Dry friction introduces a highly non-linear force, capable of flattening the frequency response of dynamic systems, a crucial characteristic for managing the chaotic energy release during a rotor drop.

To capture this behavior, researchers have explored two primary categories of friction models: macroslip and microslip. Macroslip models assume that the entire contact surface either sticks or slips simultaneously, while microslip models allow for mixed configurations where some areas stick while others slip. The choice of model depends on the scale of displacement; large displacements tend to generate brutal stick-slip transitions, making macroslip models more suitable.

Masing Model: A macroslip model combined with an elastic restitution force. It uses a stick stiffness (k₁) representing the point where the ribbon is stuck along the inner-race and housing surfaces, resulting in a high global stiffness. Once the slipping threshold (µFN) is reached, all bumps slip and a change of slope occurs.
Generalized Dahl Model: A dry-friction restoring force model that uses a non-linear first Order Differential Equation (ODE), allowing the model to adopt any shape of loop.
Kelvin-Voigt Model: A linear spring-damper model.

These advanced models, particularly the Masing and generalized Dahl models, offer a more nuanced representation of the ribbon damper's behavior. By accurately capturing the stick-slip phenomenon, they provide valuable insights into the energy dissipation mechanisms at play during a rotor drop event. This improved understanding allows engineers to optimize the design of ribbon dampers for enhanced performance and reliability.

Enhancing Reliability Through Advanced Modeling

The investigation into rotor drop dynamics using advanced ribbon damper models has yielded promising results. The dry-friction models, Masing and generalized Dahl, demonstrate a superior ability to predict the dynamic behavior of the system compared to the traditional Kelvin-Voigt model. By accurately capturing the stick-slip phenomenon, these models provide a more realistic representation of energy dissipation during rotor drop events.

The findings suggest that incorporating dry-friction models into the design and analysis of AMB systems can lead to significant improvements in reliability. By optimizing the ribbon damper's performance based on these models, engineers can minimize the risk of damage to the rotor and bearings during a power failure. This translates to reduced downtime, lower maintenance costs, and increased overall system lifespan.

While the harmonic tests used to validate these models provide valuable insights, future research should focus on shock tests to further refine the understanding of ribbon damper behavior under sudden impact conditions. This will pave the way for even more robust and reliable AMB systems, ensuring the continued advancement of turbomachinery technology.