C. R. Burrows

Vibration control of multi-mode rotor-bearing systems

This paper presents a computationally fast and efficient least-squares method to minimize the vibration of any general rotor-bearing system by the application of external control forces. The D-optimality concept is used to optimize the force locations. The proposed method provides a wide range of statistical information, and the sensitivity of the optimum response to changes in the control forces. Magnetic bearings can be applied to implement the open-loop adaptive vibration control strategies outlined in the paper. These components can also be used to inject a multi-frequency test signal as required for identification studies.

Active vibration control of flexible rotors: an experimental and theoretical study

This paper develops the authors’ earlier work on vibration control of multi-mode rotor-bearing systems. It shows how a single magnetic actuator can be used to estimate system characteristics and apply the optimum control force needed to minimize synchronous vibration. In the application considered here, a rotor is supported on oil-film bearings. The algorithm determines the optimum control force without prior knowledge of the bearing or rotor characteristics or the distribution of out-of-balance forces. A rig is described and used to illustrate the application of the theoretical work.

Multiple Sliding and Rolling Contact Dynamics for a Flexible Rotor/Magnetic Bearing System

Active magnetic bearings (AMBs) offer contact-free and frictionless support of rotating machinery. However, because of their limited force capacity, they have to incorporate retainer bearings to protect the rotor and stator laminations against high-amplitude vibration levels. Efficient modeling of contact dynamics is important for the design of adaptive controllers to prevent contact. If, however, contact does occur, it is necessary to recover the rotor position with minimum damage and without shutting down the system. This paper utilizes constrained Lagrangian equations of motion to develop a computationally efficient method to model contact dynamics. The method does not require a direct physical modeling of contact forces, although the contact forces are automatically evaluated from the constraint conditions, and it can be applied to multicontact cases. Furthermore, the technique is capable of detecting and simulating the destructive backward whirl rolling motion. A model reduction technique is introduced to improve the computational efficiency. This is demonstrated by comparing numerical predictions with experimental results, obtained for a 2-m-long flexible rotor supported by two magnetic bearings

Towards fault-tolerant active control of rotor-magnetic bearing systems

Abstract This paper considers a control system design for a rotor–magnetic bearing system that integrates a number of fault-tolerant control methods. A survey is undertaken of possible system failure modes which are classified according to whether they are internal or external to the magnetic bearing control system. Improved tolerance to specific external faults is achieved through multivariable controller design with H ∞ optimised disturbance rejection criteria. Tolerance to internal faults requires the integration of additional control sub-systems, including a fault detection algorithm and a supervisory algorithm to reconfigure control on occurrence of a fault. Experimental results obtained from a flexible rotor system are used to demonstrate the effectiveness of the control implementations.

Fault diagnosis of a hydraulic actuator circuit using neural networks—an output vector space classification approach

Abstract This paper presents a neural network approach to fault diagnosis of dynamic engineering systems based on the classification of surfaces in system output vector space. A simple second-order system is used to illustrate graphically the nature of the diagnosis problem and to develop theory. The approach is then applied to the diagnosis of a laboratory-based hydraulic actuator circuit. Results are presented for networks trained on both simulation and experimental data. An important achievement is the diagnosis of experimental faults using a network trained only on simulation data.

The Dynamic Behavior of a Rolling Element Auxiliary Bearing Following Rotor Impact

The dynamic behavior of a rolling element bearing under auxiliary operation in rotor/ magnetic bearing systems is analyzed. When contact with the rotor occurs, the inner race experiences high impact forces and rapid angular acceleration. A finite element model is used to account for flexibility of the inner race in series with non-linear ball stiffnesses arising from the ball-race contact zones. The dynamic conditions during rotor/inner race contact, including ball/race creep, are deduced from a non-linear matrix equation. The influences of bearing parameters are considered together with implications for energy dissipation in the bearing.

An Appraisal of a Proposed Active Squeeze Film Damper

A theoretical model for an active squeeze film damper (SFD) is introduced. The design makes it possible to change the radial clearance and land length of the SFD by adjusting the position of the damper ring. Expressions for the oil film forces are obtained. The vibration control of a flexible rotor is taken as an example of the application of the new design. The possibility of controlling rotor vibrations is demonstrated by means of numerical experiments.

Fault detection and tolerance in synchronous vibration control of rotor-magnetic bearing systems

Abstract The use of magnetic bearings in rotating machinery provides contact-free rotor support, and allows vibration control using both closed-loop and open-loop strategies. One of the simplest and most effective methods to reduce synchronous lateral vibration when using magnetic bearings is through an open-loop adaptive control technique, in which the amplitude and phase of synchronous magnetic control forces are adjusted automatically to minimize the measured vibrations along the rotor. However, transducer malfunction, or faults in the signal-processing channels, may cause the controller to adapt incorrectly, with unwanted and possibly catastrophic effects. It is shown that an extension to the control strategy, which utilizes the variances of the measured system response and identified parameters, enables the faults to be detected and accounted for so that a modified control action can achieve continued and effective control of the synchronous vibration. The approach is extended further to identify changes in external factors, such as unbalance and rotor dynamics. Various faults and perturbations are examined experimentally, and the ability of the controller to detect and compensate for these changes is demonstrated.

An adaptive squeeze-film bearing

This paper examines the effect of controlling the oil supply pressure to squeeze-film bearings in applications where these elements are used to provide damping for a light flexible transmission shaft having an arbitrary unbalance mass distribution. The shaft length and diameter selected for the study are typical of those used for helicopter tail rotor transmissions. A computer simulation is undertaken to study the effect of a squeeze-film damper located at: 1) The end supports. 2) Mid-span with undamped end supports. 3) Mid-span with damped end supports. The simulation shows that in this type of application, good vibration control can be achieved by using a squeeze-film damper which is capable of switching between two levels of damping. The feasibility of attaining such a characteristic is examined experimentally.

Modeling Requirements for the Parallel Simulation of Hydraulic Systems

Parallel simulation of systems offers the benefit of increased speed of execution, but requires the system model to be partitioned to enable numerical tasks to be performed concurrently. Hydraulic systems are characterised by a transport delay in the pipelines connecting physical components, which is due to the propagation of waves at the speed of sound through the fluid medium. The transmission delay allows component models to be decoupled for the current time step, enabling a parallel solution; the inputs to each component model are delayed outputs from connected models. This paper describes a simulation environment suitable for the simulation of hydraulic system performance, using the transmission line modelling approach for the pipelines, decoupling the component models in a hydraulic circuit simulation. Computationally efficient models for cavitation and friction are developed and evaluated. In addition, partitioning strategies for parallel operation are outlined, although these have yet to be implemented