Lateral Vibration Attenuation Research Articles

Lateral vibration attenuation of a rotor system using an axial control mechanism with resonance detuning

This work is aimed to develop a lateral vibration attenuation mechanism for a rotor system using an axial control strategy with resonance detuning, allowing the rotor to operate through its critical speeds without exciting its resonances. An efficient control mechanism via controllable tensile axial loads applied using linear actuators and thrust bearings, was proposed to suppress rotor vibration without unnecessary continuous control force applications, in contrast to active vibration control strategies. The control strategy using resonance detuning caused the shifting of resonance to a higher frequency by regulating the rotor lateral stiffness using the axial control mechanism. The efficacy of the actuation mechanism in mitigating rotor lateral vibration was investigated through simulation and experimental studies, demonstrating the effectiveness of the control mechanism in allowing a rotor to operate over a wide operational working range over its first critical speed without a continuous application of control forces. It was experimentally demonstrated that the proposed control strategy allowed the rotor system to bypass its critical speed without exciting its resonance. The control mechanism has shown high-responsiveness to an immediate change in axial load to suppress rotor vibration, while achieving a degree of robustness in ensuring the worst-case vibration suppression performance against the variation in rotor disc offset, mass, and eccentricity by selecting an appropriate level of axial load.

Estimation of an improved surrogate model in uncertainty quantification by neural networks

Quantification of uncertainty of a technical system is often based on a surrogate model of a corresponding simulation model. In any application, the simulation model will not describe the reality perfectly, and consequently the surrogate model will be imperfect. In this article, we combine observed data from the technical system with simulated data from the imperfect simulation model in order to estimate an improved surrogate model consisting of multilayer feedforward neural networks, and we show that under suitable assumptions, this estimate is able to circumvent the curse of dimensionality. Based on this improved surrogate model, we show a rate of the convergence result for density estimates. The finite sample size performance of the estimates is illustrated by applying them to simulated data. The practical usefulness of the newly proposed estimates is demonstrated by using them to predict the uncertainty of a lateral vibration attenuation system with piezo-elastic supports.

Estimation of Uncertainty in the Lateral Vibration Attenuation of a Beam with Piezo-Elastic Supports by Neural Networks

Quantification of uncertainty in technical systems is often based on surrogate models of corresponding simulation models. Usually, the underlying simulation model does not describe the reality perfectly, and consequently the surrogate model will be imperfect.In this article we propose an improved surrogate model of the vibration attenuation of a beam with shunted piezoelectric transducers. Therefore, experimentally observed and simulated variations in the vibration attenuation are combined in the model estimation process, by using multi--layer feedforward neural networks. Based on this improved surrogate model, we construct a density estimate of the maximal amplitude in the vibration attenuation.The density estimate is used to analyze the uncertainty in the vibration attenuation, resulting from manufacturing variations.

Reducing Uncertainty in Shunt Damping by Model-Predictive Product Stiffness Control in a Single Point Incremental Forming Process

The stiffness of metal formed products strongly affects the dynamic behavior of structures in which they are integrated. Forming processes underlie short and long-term variations which cause the stiffness to be uncertain.In the application of resonant shunted piezoelectric transducers for vibration attenuation, uncertain stiffness may cause significant reduction in the vibration attenuation performance due to imprecise tuning. In the past, large efforts were made to control one or more geometrical feature of products while weightier features that cause uncertainty have not been addressed.In this paper, a single point incremental forming process of a membrane-like spring element on a servo press with a 3 degrees of freedom drive system is investigated. This spring element is used in a beam support for lateral vibration attenuation with resonant shunted transducers as well as axial buckling stabilization.To reduce uncertainty caused by process variations, an offline closed-loop control of product stiffness is presented. Different product and forming criteria are integrated into a control approach based on an optimization routine. By making use of a model-based prediction of the product properties, the approach shows how to realize a multi-objective control.

Effect of static axial loads on the lateral vibration attenuation of a beam with piezo-elastic supports

In this paper, vibration attenuation of a beam with circular cross-section by resonantly shunted piezo-elastic supports is experimentally investigated for varying axial tensile and compressive beam loads. The beam's first mode resonance frequency, the general electromechanical coupling coefficient and static transducer capacitance are analyzed for varying axial loads. All three parameter values are obtained from transducer impedance measurements on an experimental test setup. Varying axial beam loads manipulate the beam's lateral bending stiffness and, thus, lead to a detuning of the resonance frequencies. Furthermore, they affect the general electromechanical coupling coefficient of transducer and beam, an important modal quantity for shunt-damping, whereas the static transducer capacitance is nearly unaffected. Frequency transfer functions of the beam with one piezoe-elastic support either shunted to an RL-shunt or to an RL-shunt with negative capacitance, the RLC-shunt, are compared for varying axial loads. It is shown that the beam vibration attenuation with the RLC-shunt is less influenced by varying axial beam loads and, therefore, is more robust against detuning.

Lateral Vibration Attenuation by the Dynamic Adjustment of Bias Currents in Magnetic Suspension System

Switching stiffness control is applied to attenuate vibration in the lateral directions in an active magnetic suspension system with electromagnets operated in differential mode. The magnetic suspension system using the attractive force between magnetized bodies is inherently unstable in the normal direction so that feedback control is necessary to achieve stable suspension. In contrast, it can be stable in the lateral directions due to the edge effects in the magnetic circuits. In several applications, such passive suspension is used in combination with the active one to reduce cost and space. However, damping in the lateral directions is generally small. As a result, induced vibrations in these directions are hardly attenuated. To suppress such vibration without any additional actuator (electromagnet), switching stiffness control is applied to an magnetic suspension system operated in the differential mode. The stiffness in the lateral direction is adjusted by varying the bias currents of an opposed pair of electromagnets located in the normal direction simultaneously according to the motion of the suspended object. When the varied bias currents are adjusted for the additive normal forces cancel each other, such control does not affect the suspension in the normal direction. The effectiveness of the proposed control methods is confirmed experimentally.

Lateral vibration attenuation of a beam with circular cross-section by a support with integrated piezoelectric transducers shunted to negative capacitances

Undesired vibration may occur in lightweight structures due to excitation and low damping. For the purpose of lateral vibration attenuation in beam structures, piezoelectric transducers shunted to negative capacitances can be an appropriate measure. In this paper, a new concept for lateral vibration attenuation by integrated piezoelectric stack transducers in the elastic support of a beam with circular cross-section is presented. In the piezoelastic support, bending of the beam in an arbitrary direction is transformed into a significant axial deformation of three stack transducers and, thus, the beam’s surface may remain free from transducers. For multimodal vibration attenuation, each piezoelectric transducer is shunted to a negative capacitance. It is shown by numerical simulation and experiment that the concept of an elastic beam support with integrated shunted piezoelectric stack transducers is capable of reducing the lateral vibration of the beam in an arbitrary direction.

Lateral Vibration Attenuation of Shafts Supported by Tilting-Pad Journal Bearing With Embedded Electromagnetic Actuators

Hydrodynamic tilting-pad bearings with electromagnetic actuators are designed to take advantage of the load-carrying capacity of the hydrodynamic bearing together with the actuation capacity of the electromagnets. Hence, actuators can be downsized because they do not work as bearings as it is the case of magnetic bearings. In this work, one presents the numerical and experimental analysis of rotor vibration attenuation using a tilting-pad journal bearing with embedded electromagnetic actuators when proportional-derivative (PD) control is implemented. Experimental results in the frequency domain show reductions in shaft-vibration amplitude of 11% for the rotating speed of 600 rpm and 18% for the rotating speed of 1100 rpm, with good agreement of the mathematical model. The actuation capacity of the bearing in study is compared to the capacity of other active bearings in literature, showing that the present bearing is competitive in terms of specific control capacity.

Investigation of Vibration Mitigation of Flexibly Support Rigid Rotors Equipped with Controlled Elements

Abstract The subject of investigations presented in this article is achieving the optimum attenuation of lateral vibration of rotors by means of two design variants of constraint elements: semiactive magnetorheological squeeze film dampers and actively controlled hydrodynamic bearings. The damping effect of magnetorheological dampers is controlled by the change of magnetic flux generated in electric coils and of the hydrodynamic bearings by the change of magnitude of the proportional gain of a feedback controller exciting movement of the bearing housings. In the developed mathematical models the rotor is considered as absolutely rigid and the controllable constraint elements are represented by force couplings. The rotor turns at constant angular speed, is loaded by its weight and in addition it is excited by a centrifugal force caused by the disc unbalance. In both design cases its lateral vibration is governed by a nonlinear equation of motion. The pressure distribution in the lubricating film in the magnetorheological squeeze film damper is described by a Reynolds equation modified for Bingham fluid whose yield shear stress depends on magnetic induction. The hydraulic forces acting in the hydrodynamic bearings are determined for the case of π-film cavitation and position of the bearing housings is adjusted by actuators activated by a proportional feedback controller. The aim of the analysis is to deal with approaches leading to minimizing amplitude of the rotor steady state vibration and magnitude of the force transmitted into the rotor casing and to compare efficiency of both design variants. The performed computer simulations show that the arrangement with the magnetorheological squeeze film damper gives better results in reducing magnitude of the transmitted force than those when the rotor is supported by hydrodynamic bearings with actively controlled position of the bearing housings.

Active Control of Lateral Vibrations of a Railway Carriage

As trains are continually designed for higher and higher speeds the problems of railway carriage vibration are on the increase. Lateral vibrations in a railway carriage are noticeable to passengers if the vibration frequencies are lower than approximately 20 Hz. Below this frequency discomfort is a common problem for the passengers and below approximately 1 Hz motion sickness is a problem. The passive solution of stiffening the carriage chassis to shift the vibrational frequencies higher up results in inflated manufacturing and running costs, and opposes higher travel speeds due to increased weight. Semi-passive solutions such as modifying the structural dynamics of the carriage body by decoupling heavy underfloor equipment do not reduce the vibrations sufficiently. However, by appending a multi-reference feedforward active vibration control system, one way expect a substantial reduction in the lateral vibration level. Using a dynamic computer model of a railway carriage simulating the lateral vibration, and using as input bogie acceleration data measured on a running train, multiple-input/single-output coherence spectra were shown to constitute a suitable set of reference signals for an active control system. Control simulations based on the Feedforward Multiple-Input/Single-Output Filtered-x LMS Algorithm are carried out using different reference signal combinations. The control results indicate lateral vibration attenuation on the order of 15dB at the objective frequency of 10Hz.