Implementation of vibration and stability evaluation criteria for rotating machineries equipped with active magnetic bearings

Imbalance vibration is the main factor affecting the stability of rotating machineries equipped with active magnetic bearings (AMB). Accordingly, for safe and reliable operation, ISO 14839 standard sets out guidelines for measuring and evaluating the vibration and stability. However, technical approaches to realize fulfillment of the evaluation criteria have never been studied in theory. This paper presents insights of these criteria and proposes effective methods to simultaneously implement these evaluation criteria. Based on imbalance vibration model of AMB-rotor system, the theoretical connections between these evaluation indices are revealed. In order to obtain accurate vibration model of single-input single-output (SISO) AMB-rotor system, modal analysis is carried out and equivalent mass of SISO system is figured out. Afterwards, with the analysis of sensitivity function in theory, new indices of the evaluation criteria are proposed, which helps establish requirements of controller design and rotor balance quality. Finally, through experimental verification on a test rig, the limitations on the evaluation criteria can be negligible, and the proposed methods to simultaneously implement the evaluation criteria are validated.

Experimental Investigation of Vibration Damping Behavior of Magneto-Mechanical Coated AISI321 Stainless-Steel

High speed rotating machineries usually operate under severe conditions and enormous loadings and thus, are susceptible to several problems. One such problem that has caught the attention in recent decades is known as High Cycle Fatigue. More than 60 percent of rotating machinery failures has been attributed to this High cycle Fatigue. Along with High Cycle Fatigue, Vibration, an inherent phenomenon in machineries, also share its part in failure of rotating machineries. Rotating machinery components suffer from high amplitude vibrations when they pass through resonance. Stresses are developed as a result of these vibrations and fatigue in mechanical structures, providing a conducive environment for the development of cracks at Surface. When these surface cracks reach critical size, crack nucleation starts, which ultimately leads to catastrophic failures. So, in order to avoid the disastrous consequences, damping is needed. Damping keeps material’s integrity in case of impact forces, stresses due to thermal shocks in turbo machinery and earth quakes in huge structures. Thin layer of magneto elastic coating can be applied on substrate surface that acts as first line of defense. Large number of coating Processes are available around the globe. The optimized combination of coating material, substrate material and coating technique according to specific application is necessary. These coatings have the capability to combat the phenomenon of oxidation, wear and fatigue acting as a barrier between substrate and hostile environments. Further, they enhance the damping characteristics, and thus allows the highspeed rotating machinery to reach its operational speed without any failure at resonance. In this way, they not only enhance the performance of components in aggressive environments, but also improve the life cycle, saving assets of millions of dollars’ worth. This research is an endeavor to experimentally investigate effect of magneto mechanical coating on damping of AISI 321 Stainless steel. AISI 321 was selected as base material because of its wide applications in engine components of gas turbines, heat exchangers and in different chemical industries. Two types of Air plasma sprayed magneto-mechanical powder (NiAl & CoNiCrAlY) were coated on base material and thickness was maintained up to 250μm in both the cases. Experiments were designed and performed on cantilever beam specimens for dynamic response measurement. Dynamic response of the system was measured to investigate the modal parameters of natural frequencies, damping ratio and time of vibration decay. For damping ratio, vibration analyzer mode was adjusted in time domain and beam was excited by using a hammer. Vibration analyzer showed the vibration decay as a function of time. Logarithmic decrement method was used to calculate the damping ratio in both cases. Dynamic response of all the three cases (NiAl coating, CoNiCrAlY and uncoated AISI321) were compared. Results were very reassuring and showed a significant improvement in damping characteristics.

Control scheme of adaptive feedforward cancellation considering of Bode’s integral theorem for synchronous vibration suppression in rotating machineries

Synchronous vibration is a major obstacle to the stable operation of rotating machineries. In previous studies, active control methods were developed to compensate for synchronous vibration using actuators, such as an active magnetic bearing or a piezo actuator. Adaptive feedforward cancellation is another well-known control method and is used to compensate for the synchronous vibration in the actual system. The control methods can compensate for the synchronous vibration; however, the amplitude of the vibration in other frequency ranges can be increased by the waterbed effect due to Bode’s integral theorem. Therefore, there is a trade-off between the compensation of the synchronous vibration and the negative impact of other vibration. In this article, a novel control scheme for the adaptive feedforward cancellation is proposed to eliminate the negative impact due to the waterbed effect. The proposed method controlled the input signal of the adaptive algorithm in the adaptive feedforward cancellation and realized an ideal feedforward controller worked independently from the feedback loop. The effectiveness of this method was verified experimentally using a test rig.

Application of sensitive dimensionless parameters and PSO–SVM for fault classification in rotating machinery

Purpose Rotating machineries are widely used in manufacturing, petroleum, chemical, aircraft, and other industries. To accurately identify the operating conditions of such rotating machineries, this paper aims to propose a fault diagnosis method based on sensitive dimensionless parameters and particle swarm optimization (PSO)–support vector machine (SVM) for reducing the unexpected downtime and economic losses. Design/methodology/approach A relatively new hybrid intelligent fault classification approach is proposed by integrating multiple dimensionless parameters, the Fisher criterion and PSO–SVM. In terms of data pre-processing, a method based on wavelet packet decomposition (WPD), empirical mode decomposition (EMD) and dimensionless parameters is proposed for the extraction of the vibration signal features. The Fisher criterion is applied to reduce the redundant dimensionless parameters and search for the sensitive dimensionless parameters. Then, PSO is adapted to optimize the penalty parameter and kernel parameter for SVM. Finally, the sensitive dimensionless parameters are classified with the optimized model. Findings As two different time–frequency analysis methods, a method based on a combination of WPD and EMD used to extract multiple dimensionless parameters is presented. More vital diagnosis information can be obtained from the vibration signals than by only using a single time–frequency analysis method. Besides, a fault classification approach combining the sensitive dimensionless parameters and PSO-SVM classifier is proposed. The comparative experiment results show that the proposed method has a high classification accuracy and efficiency. Originality/value To the best of the authors’ knowledge, very few efforts have been performed for fault classification using multiple dimensionless parameters. In this paper, eighty dimensionless parameters have been studied intensively, which provides a new strategy in fault diagnosis field.

Design and development of a modular vibration test rig for combination types of fault in rotating machinery health diagnosis

As a basis to real application of rotating machineries operation, a test rig imitating the operation is designed for the research environment. The purpose of this study is to design a modular test rig which is able to facilitate different fault component combinations and evaluate the deformation pattern of the fabricated test rig. Rotating machineries face the probability of having simultaneous different faults and the study of this condition is limited. The designed test rig could be arranged into multiple configurations by adding or excluding desired components due to its modularity. This will be useful to study the response of each component during operation as well as the response of combinations of fault components. Included in this study is the analysis of the design, the components of the test rig and the final design as well as the experimental data results of the fabricated test rig. This test rig is beneficial for understanding the vibrational behavior of components especially in educational environment.