Vibration Control Of Rotor Research Articles

Self-Powered Eddy Current Damper for Rotordynamic Applications

The vibration control of rotors is often performed using elastomeric or fluid dampers together with rolling element or hydrodynamic type bearings. Electromagnetic dampers seem a valid alternative to conventional solutions and also to active magnetic bearings (AMBs) because their simpler architecture, size and, if of transformer type, also for the absence of power electronics, position sensors, and any fast feedback loop. However, transformer eddy current dampers require a constant voltage power supply than can be provided by an embedded generator to reduce cost and improve the reliability. The present paper proposes a self-powered damper to fulfill these requirements. A three-phase permanent magnet electric generator (connected to the rotating shaft) generates the required power for the damping device. The generator is connected to the damping circuit by means of tuned impedance and a three-phase rectifier.

Vibration Control and Experimental Study of Flexible Rotor in Magnetically Suspended Motor

Vibration Control and Experimental Study of Flexible Rotor in Magnetically Suspended Motor

Rotor Mass Eccentricity Vibration Compensation Control in Bearingless Induction Motor

In the process of motor rotation, the vibration caused by the rotor mass eccentricity seriously affects the dynamic characteristics and safety operation of system. So rotor mass eccentricity vibration compensation control on rotating machine has great significance, especially for the high speed bearing less induction motor (BIM). A rotor mass eccentricity compensation control strategy was presented to restrain the vibration of suspended rotor for BIM. Firstly, the suspension rotor dynamical model was deduced and unbalanced vibration mechanism was analyzed. Secondly, based on decoupling control between electromagnetic torque and radial force, the obtained vibration signal from the displacement sensor was put into the original radial force control system. Then, a feedforward compensator was set up to increase the same period component of the given radial force signal and enlarge the stiffness of the vibration signal. Finally, the compensation control of rotor vibration was realized by forcing the rotor shaft rotation around its geometric center. The simulation results show that the presented feedforward compensator can suppress the vibration of rotor under different speed and improve the precision of rotor suspension. The further experimental results also show that the control method can obviously reduce the peak-peak value of rotor radial displacement and effectively restrain rotor vibration.

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

A concise review of the active control approaches for vibration reduction in rotorcraft is presented. Next, the evolution and status of higher harmonic control and pitch link actuated individual blade control is presented since these serve as the foundations of on blade control. Despite the success of these approaches, demonstrated by both full-scale wind tunnel and flight tests, higher harmonic control and pitch link actuated individual blade control have not managed to earn their way onto a production helicopter. An alternative, on blade control, is defined as a special implementation of individual blade control, where the control surfaces are located on the rotating blade and each blade has its own controller. A concise description of four on blade devices: (1) the actively controlled flap, (2) the active twist rotor, (3) the active tip rotor, and the (4) deployable Gurney flap, or microflap, is presented. An outline of an aeroelastic response modeling capability used to simulate active vibration and noise reduction using flaps or microflaps is presented. The simulation is a thread that links the various parts of the paper. Next, selected results from simulations and scale wind tunnel model tests on active flaps are used to provide insight on the operational and modeling aspects of these systems. Full-scale wind tunnel and flight tests are presented as culmination of the research effort invested in active flap rotors. Then, the evolution and application of the active twist rotor, and deployable Gurney flaps, or microflaps, is presented. The paper concludes with lessons learned and speculation about the potential implementation of on blade control on production rotorcraft.

Static mass imbalance identification and vibration control for rotor of magnetically suspended control moment gyro with active-passive magnetic bearings

Identification of the static mass imbalance is critical to the control of magnetically suspended rotors. A static mass imbalance identification method without using the closed-loop transfer function is proposed in this paper. Then the null displacement control of the magnetically suspended rotor is realized by using the identified static mass imbalance. Because null vibration is the control target for the rotor of a magnetically suspended control moment gyro (MSCMG) with active-passive magnetic bearings, a null vibration control method depending on the displacement stiffness is introduced. However, the displacement stiffness of the passive magnetic bearing is hard to obtain accurately. Therefore, the least mean square method is utilized to adjust the uncertain displacement stiffness adaptively according to the centroid acceleration. Simulation results show that adaptive null vibration control based on the static mass imbalance identification can remove the synchronous magnetic bearing force effectively, thus enabling the rotor of the MSCMG with active-passive magnetic bearings to rotate about its initial axis.

Rotor Vibration Control of Active Magnetic Bearing System Using Adaptive Forced Balancing Method

The adaptive forced balancing (AFB) method was used to estimate and eliminate the rotor vibration with unknown amplitudes and frequencies in active magnetic bearing (AMB) feedback control systems. Firstly, the rotor vibration producing mechanisms of AMB were analyzed. Then, the AFB under the assumption of unknown rotational frequency and amplitude are designed. Finally the simulation results show that the AFB method proposed in this paper makes it possible to completely reject unknown sinusoidal disturbance in a closed loop control system

Experiments on the Vibration Control of Flexible Rotor Using Shear Mode MR Elastomer Damper

A shear mode magnetorheological (MR) elastomer damper is designed and manufactured, in which the MR elastomer is made by mixing RTV silicone, carbonyl iron particles and silicone oil, and solidifying under magnetic field. A flexible cantilever rotor system with single disk is constructed, and the controllability, effectiveness and stability of vibration control for the imbalance response of the rotor system using the MR damper are experimentally studied. From the test, it is found that as the strength of applied magnetic field increases, the damping and stiffness of the damper are increased; the critical speeds of the rotor system supported on the MR damper is increased distinctly, and the vibration at two critical speeds are restrained; the on-off control method may be used to control the rotor vibration while passing through the two critical speeds. The study shows that the shear mode MR elastomer damper is suitable for active vibration control of flexible rotor.

Resonant Vibration Control of Three-Bladed Wind Turbine Rotors

Rotors with blades, as in wind turbines, are prone to vibrations due to the flexibility of the blades and the support. In the present paper a theory is developed for active control of a combined set of vibration modes in three-bladed rotors. The control systemconsists of identical collocated actuator-sensor pairs on each of theblades, and targets a set of three modes constituting a collective mode with identical motion of all the blades, and two independent whirling modes, in which a relative motion pattern moves forward or backward over the rotor. The natural frequency of the collective mode is typically lower than the frequency of the whirling modes due to support flexibility. The control signals from the blades are combined into amean signal, addressing the collective mode, and three components from which the mean signal has be subtracted, addressing the pair of whirling modes. The response of the actuators is tuned to provide resonant damping of the collective mode and the whirling modes by using the separate resonance characteristics of the collective and the whirlingmodes. In the calibration of the control parameters it is important to account for the added flexibility of the structure due to influence of other nonresonant modes. The efficiency of the method is demonstrated by application to a rotor with 42mblades, where the sensor/actuator system is implemented in the form of an axial extensible strut near the root of each blade. The load is provided by a simple but fully threedimensional correlated wind velocity field. It is shown by numerical simulations that the active damping system can provide a significant reduction in the response amplitude of the targeted modes, while applying control moments to the blades that are about 1 order of magnitude smaller than the moments from the external load.

Active Control of Rotor Vibration in an Electric Machine by Cascaded Optimal and Convergent Control Methods

This paper presents a method for suppressing radial rotor vibrations in an electric machine by the means of active vibration control. The required control forces are generated by an electro-magnetic actuator implemented as extra windings in the stator slots of the machine. A generic modified optimal LQ-based controller cascaded with a convergent controller is introduced to tackle the problem. The test results obtained by the implementation of the designed control algorithms in a 30 kW squirrel-cage induction motor are presented. The results show that the proposed control strategy is capable of significant vibration suppression.

A reduced rotor model using modified SEREP approach for vibration control of rotors

For analysis and control of dynamic behaviour of continua, equations of motion are usually obtained after discretizing the continuum into finite elements. Thus discretization gives rise to a set of simultaneous differential equations, the number of which increases with the fineness of discretization. As an associated effect, increasing fineness increases the number of states, many of which are difficult to measure and feedback, due to impracticability of location of measurement or non-availability of proper sensor, in addition to the constraint on the cost of sensors and computation. Solution to the above problem calls for a suitable scheme to reduce the problem size, however, keeping the modal information unspoilt as far as possible. For a vibratory system, a reduced model is built by retaining modes with higher participation factor and also choosing conveniently within the retained modes, a number of pre-decided measurable states. Fewer state equations are thus found helpful for formulating suitable control law, applicable for improving the system dynamic performance over uncontrolled condition. This paper attempts first to obtain a reduced model for a rotor–shaft system, generally a non-self-adjoint system, and next uses the reduced model to implement active vibration control action using a single, stator-mounted electromagnetic actuator suitably located at a section along the rotor–shaft.

An Adaptive Multi-Objective Controller for Flexible Rotor and Magnetic Bearing Systems

This paper considers two issues in the vibration of rotating machines, namely, control of rotor vibration and control of the forces transmitted to the base. An adaptive multi-objective method is developed to tackle these issues simultaneously using magnetic bearings. A two-stage weighting strategy is developed, involving base weightings calculated by using a singular value decomposition of the system’s receptance matrices and an adjustable single weighting parameter tuned automatically to shift the balance between the two objective functions in accordance with performance specifications. This new real-time controller does not require measurements in addition to those required for the open-loop adaptive strategy. Frequency and time domain simulations of an existing experimental rig are used to assess the effectiveness of the proposed multi-objective adaptive controller as a precursor to an experimental study.

Active Control of Vibrations in a Rolling Process by Nonlinear Optimal Controller

In this paper a method of suppressing vibrations in an industrial rolling process with varying rotational frequency is presented. The vibrations in a rolling process are problematic as they do not only cause structural fatigue on the machinery, but also deteriorate the quality of the end product. The traditional approach for this type of a problem would be to avoid the critical frequencies of the process by changing the rotation speed of the reel, thus decreasing the vibrations. However, in practice this is hard to achieve as the radial velocity of the reel should be constant, while rotation speed of the reel varies depending on the diameter of the reel. The changes in radial velocity are typically not allowed as the rolling process is usually part of a larger process, where change in rotation speed affects the whole process. This paper introduces a generic modified LQ-control law to tackle the problem. This control design was designed in a previous ACRVEM-project (Active Control of Radial Rotor Vibrations in Electric Machines) and has been successfully used in suppression of radial rotor vibrations in electric drives, resulting in 90% damping of the vibrations. The major drawback of the controller has been the limitations due to its linear nature; the control is applicable only at a certain predefined rotational frequency, and outside this frequency the controller becomes unstable. In order to resolve this problem, a nonlinear optimal state-feedback controller based on continuous gain scheduling is introduced. This modification of the original controller is capable of suppressing the vibrations over the whole operational frequency range. In this paper the modelling and identification of the rolling process is first discussed. After the model has been obtained the control design procedures for both linear and nonlinear controllers are presented in detail. The performances of both controllers are analyzed in extensive simulations. Finally the simulation results are validated by implementing the designed controllers in the actual rolling process. It will be shown that this control methodology is highly effective for this type of vibration damping problems resulting in over 90% decrease in the vibrations over the whole frequency range of rotation.

Study on Effect of Rotor Vibration on Tip Clearance Variation and Fast Active Control of Tip Clearance

The tip clearance flow of axial turbomachines is important for their aerodynamic and maneuver performance. And the tip clearance gap leakage flow is of continuing concern in reducing efficiency losses that occur within turbines. In order to gain significant reductions in emissions and specific fuel consumption as well as dramatic improvements in operating efficiency and increased service life of aero-engine, variation mechanism of blade tip clearance was analyzed and the equation of dynamic clearance was shown firstly, then the effect of rotor vibration in clearance variation which include flight loads and engine loads was studied in this paper; based on the dynamic measurements of blade tip clearance, a method that ensure tip clearance at optimal state in given mission profile through active rotor vibration control and active tip clearance control was presented. Besides, fuzzy control theory was used to solve the high nonlinear variation of tip clearance. The analysis result shows that this technique is useful.

A Multiobjective Adaptive Controller for Magnetic Bearing Systems

The paper considers three issues in flexible rotor and magnetic bearing systems, namely, the control of rotor vibration, control of transmitted forces, and prevention of rotor contact with auxiliary bearings. An adaptive multiobjective optimization method is developed to tackle these issues simultaneously using a modified recursive adaptive controller. The proposed method involves automatic tuning of the weighting parameters in accordance with performance specifications. A two-stage weighting strategy is implemented, involving base weightings, calculated from a singular value decomposition of the system’s receptance matrices, and two adjustable weighting parameters to shift the balance between the three objective functions. The receptance matrices are functions of rotational speed and they are estimated in situ. The whole process does not require prior knowledge of the system parameters. Real-time implementation of the proposed controller is explained and tested by using an experimental flexible rotor magnetic bearing system. The rotor displacements were measured relative to the base frame using four pairs of eddy current displacement transducers. System stability is ensured through local PID controllers. The proposed adaptive controller is implemented in parallel, and the effectiveness of the weighting parameters in changing the balance between the transmitted forces and rotor vibrations is demonstrated experimentally.

Design of Electromagnetic Dampers for Aero-Engine Applications

The vibration control of rotors for gas or steam turbines is usually performed using passive dampers when hydrodynamic bearings are not used. In layouts where the rotating parts are supported by rolling bearings, the damping is usually provided by squeeze film dampers. Their passive nature and the variability of their performances with temperature and frequency represent the main disadvantages. Dampers with magnetorheological and electrorheological fluid allow solving only a part of the abovementioned drawbacks. Active magnetic bearings (AMBs) are promising since they are very effective in controlling the vibration of the rotor and offering the possibility of monitoring the rotor’s behavior using their displacement sensors. However they show serious drawbacks related to their stiffness. Electromagnetic dampers seem to be a valid alternative to visco-elastic, hydraulic dampers due to, among the others, the absence of all fatigue and tribology issues resulting from the absence of contact, the small sensitivity to the working environment, the wide possibility of tuning even during operation, the predictability of the behavior, the smaller mass compared with AMBs, and the failsafe capability. The aim of the present paper is to describe a design methodology adopted to develop electromagnetic dampers to be installed in aero-engines. The procedure has been validated using a reduced scale laboratory test rig. The same approach has then been adopted to design the electromagnetic dampers for real civil aircraft engines. The results in terms of achievable vibration reductions, mass, and overall dimensions are hence presented. A trade-off between the various proposed solutions has been carried out evaluating quantitative performance parameters together with qualitative aspects that this “more electric” technology implies.

Optimum Control of Gyroscopic Systems

The problem of optimal control of transverse rotor vibrations with gyroscopic interactions has been described and solved in the paper. An integral performance index has been defined for such system in order to minimize vibration level of a chosen rotor point. For this reason, an efficient way of establishing weight coefficients of integral performance index for multi-degree-of-freedom system with gyroscopic interactions has been described. Presented method enables to determine such weighing coefficients that selected modal forms would be assumed before dynamics properties and a performance index would took the minimum value. Computation results demonstrate that the proposed method is efficient and may be applied for complex mechatronic systems.

Vibration Control of a Flexible Rotor Supported on Cavitated Squeeze Film Dampers

Vibration Control of a Flexible Rotor Supported on Cavitated Squeeze Film Dampers

Active vibration control of unbalanced flexible rotor–shaft systems parametrically excited due to base motion

Rotor vibrations caused by large time-varying base motion are of considerable importance as there are a good number of rotors, e.g., the ship and aircraft turbine rotors, which are often subject to excitations, as the rotor base, i.e. the vehicle, undergoes large time varying linear and angular displacements as a result of different maneuvers. Due to such motions of the base, the equations of vibratory motion of a flexible rotor–shaft relative to the base (which forms a non-inertial reference frame) contains terms due to Coriolis effect as well as inertial excitations (generally asynchronous to rotor spin) generated by different system parameters. Such equations of motion are linear but time-varying in nature, invoking the possibility of parametric instability under certain frequency–amplitude combinations of the base motion. An investigation of active vibration control of an unbalanced rotor–shaft system on moving bases is attempted in this work with electromagnetic control force provided by an actuator consisting of four electromagnetic exciters, placed on the stator in a suitable plane around the rotor–shaft. The actuator does not levitate the rotor or facilitate any bearing action, which is provided by the conventional suspension system. The equations of motion of the rotor–shaft continuum are first written with respect to the non-inertial reference frame (the moving base in this case) including the effect of rotor internal damping. A conventional model for the electromagnetic exciter is used. Numerical simulations performed on the flexible rotor–shaft modelled using beam finite elements shows that the control action is successful in avoiding the parametric instability, postponing the instability due to internal material damping and reducing the rotor response relative to the rigid base significantly, with sufficiently low demand of control current in comparison with the bias current in the actuator coils.

Self-Sensing Active Magnetic Dampers for Vibration Control

The aim of this paper is to investigate the potential of a self-sensing strategy in the case of an electromagnetic damper for the vibration control of flexible structures and rotors. The study has been performed in the case of a single degree of freedom mechanical oscillator actuated by a couple of electromagnets. The self-sensing system is based on a Luenberger observer. Two sets of parameters have been used: nominal ones (based on simplifications on the actuator model) and identified ones. In the latter case, the parameters of the electromechanical model used in the observer are identified starting from the open-loop system response. The observed states are used to close a state-feedback loop with the objective of increasing the damping of the system. The results show that the damping performance are good in both cases, although much better in the second one. Furthermore, the good correlation between the closed-loop model response and the experimental results validates the modeling, the identification procedure, the control design, and its implementation. The paper concludes on a sensitivity analysis, in which the influence of the model parameters on the closed-loop response is shown.

Active Control of Rotor Vibrations by Two Feedforward Control Algorithms

Resonance vibrations (critical speeds) play a significant role in rotor vibration control. Active vibration control methods for rotors are studied to develop solutions to enhance machines’ dynamic behavior, durability, and operating range. This paper reports rotor vibration attenuation with a supplementary electromagnetic actuator located outside the rotor bearing span. Feedback and feedforward control system design are shown, and comparative experiments on two active vibration control methods for mass unbalance compensation are reported. The methods compared are adaptive FIR filter with the least mean squares (LMS) algorithm and convergent control (CC) method with a frequency-domain adaptation algorithm. The methods were experimentally validated on the rotor test rig (rotor weight 2.7 kg, length 560 mm, and first critical speed about 50 Hz). The feedback system provided wideband damping in the sub- and supercritical regions. The feedforward systems attenuated vibratory responses at the speed of rotation and its harmonic. The attenuation achieved was about 20 dB depending on the rotor speed. Also, discrete-time CC algorithm is shown to have a feedback equivalent circuit. The significance of feedback control lies in making the system phase-characteristics sufficiently smooth for feedforward control methods. Then, feedforward algorithms provided a good vibration damping performance over the operating range. CC was found to be a more effective and simpler algorithm for the purpose than the adaptive FIR filter with the LMS algorithm. The equivalent feedback circuit derived for CC, and systems similar to CC, facilitates their stability and robustness analysis.