Method Of Mistuning Identification Research Articles

Mistuning identification and model updating approach for bladed disks based on blade tip timing

To solve the problem of online mistuning identification of bladed disks, this paper proposes a novel mistuning identification method based on proper orthogonal modes (POM-ID) and the response data. Firstly, the proposed method is analyzed by numerical simulation technology, and the influence of related parameters on the identification results is discussed. Compared with the traditional method, the effectiveness of the proposed method is verified. Secondly, the POM-ID method is applied to identify the mistuning parameters of an actual bladed disk based on the blade tip timing test data. Finally, the identification results of the rotating bladed disk are verified by using static test results, and the dynamic model of the bladed disk is updated. The accuracy of the updated model is confirmed by the aspects of natural frequency and vibration coupling effect. The results indicate that the natural frequency error of the modified model is less than 1%, and the vibration coupling law between blades is consistent with the test results. The mistuning identification method proposed in this paper is especially suitable for test data of the rotating bladed disk and is expected to be applicable for online dynamic updating of the bladed disk model.

Mistuning Identification of Blisks Using Mass Detuning and Influence Coefficients

Integrally bladed disks, also known as blisks, are important components in the operation of gas turbines. To study the dynamics of these structures, several computational techniques approximate blisks as tuned systems, where all blades have the same characteristics. In reality, manufactured blades have small variations from their intended design, thus creating so-called mistuned systems. Previous work has shown that such small variations can cause high response amplifications that can result in blisk structural failure. Therefore, it is essential to identify mistuning to ensure the safe operation of these systems. Several methods utilize cantilever blade frequencies in their procedure to model mistuning and calculate blisk vibration response. A previously developed mistuning identification method uses mass detuning to isolate the cantilever blade frequencies and a set of influence coefficients to quantify the blade-to-blade couplings. However, the mistuning is calculated with respect to an arbitrary mistuning value that later needs to be identified through a trial-and-error procedure that can affect the accuracy of the final mistuning values. This paper focuses on updating the method to eliminate this additive error that cannot precisely be determined. Furthermore, the updated procedure is applied to an as-manufactured blisk using experimental ping test results. An additional analysis is performed on the effect of adding multiple sets of influence coefficients to capture the blade-to-blade couplings more accurately.

An improved mistuning identification and dynamic strain prediction method for rotating blades with application of blade tip timing technology

Blade tip timing (BTT) is the most effective technique for vibration monitoring of rotating blades. The research of dynamic characteristics and forced responses of the blisk is crucial to the matters of blade vibration with far-reaching significance. The general mistuning identification techniques require experimental tests and numerical solutions of the whole bladed disk. Since the feature of the BTT technique can identify the modal properties of blades, this paper proposed a blade natural frequency deviation-based mistuning identification method, which achieves the mistuning quantitative evaluation and the model online update of mistuned blisk. Numerical analysis and experimental investigations prove that the improved mistuning identification method can reach accurate and reasonable results, especially in the mode dominated by blade vibration. Furthermore, based on the three assumptions of the fundamental mistuning model (FMM), an additional condition was defined: The mode strain energy proportions of the blade in the isolated modal family can be believed identical. This study revealed the relationship between blade strain and blade vibration, and an improved dynamic strain prediction method for the implementation of non-contact measurement of blade strain was proposed. The numerical analysis shows the prediction error of dynamic strain is less than 3%. Two experimental tests reported that the prediction results of dynamic strain are consistent with the FMM and BTT-based non-contact dynamic stress measurement (FB-NDSM) method, and the maximum error of prediction results is less than 2% about a FB-NDSM method reference, which is acceptable in practical applications. Improved mistuning identification and dynamic strain prediction method with the application of BTT technology are attractive for the dynamic characteristic study and health management of the bladed disk, which significantly promotes the application of BTT technology in blade vibration monitoring of large-scale rotating machinery.

Exploration of blade detuning tests for mistuning identification of blisks

This paper presents a novel blade mistuning identification method based on blade detuning tests. Blade detuning tests consist of blade-by-blade impact testing in a blisk with detuning masses purposefully attached on all the blades except the one currently under test. Due to the quite simple test setup and implementation, the detuning tests enable to estimate the blade frequency mistuning pattern of the blisk with low experimental effort. However, it was proved that non-negligible residual inter-blade coupling is responsible for an inaccurate identification of the truly ‘blade-alone’ mistuning pattern from the blade detuning test results. Therefore, a novel mistuning identification method is herein proposed in order to improve the accuracy of the estimated mistuning pattern. This method fully exploits the blade detuning test results and includes the residual inter-blade coupling due to the mass detuning mechanism. The quantification and the introduction of the residual inter-blade coupling into the identification procedure leads to the determination of a more accurate ‘blade-alone’ frequency mistuning pattern. This novel mistuning identification method is firstly validated in a numerical test case and then applied to a real blisk test piece.

Identification and influence factors analysis of blade crack mistuning in hard-coated blisk based on modified component mode mistuning reduced-order model

Blade crack will cause severe mistuning of hard-coated blisks, which will lead to vibration localization. To identify crack mistuning and analyze influence factors, in this study, a mistuning identification method of blade cracks in hard-coated blisks is presented based on modified component mode mistuning reduced-order model, in which the hard-coated blisk with blade crack is decomposed into a substructure of tuned hard-coated blisk and a substructure of coated blade with cracks. Crack mistuning of each coated blade can be obtained by a single identification calculation. After verifying the rationality of this identification method, the influence factors of blade crack mistuning are analyzed. The influence factors include the crack location on the coated blade (cracks occurring only in coating or only in blade substrate or both in blade substrate and coating), crack length, crack position in the radial direction of the blisk, and modal data type of coated blisk used for mistuning identification calculation. The research results show that, with the increase of crack length, the mistuning of crack occurring only in the coating does not increase continuously but decreases firstly and then increases. For the first bending modes, the closer the blade crack is to the blade root, the larger the mistuning is. For the second bending modes, the blade crack located at the position of maximum modal displacement will produce large mistuning. For hard-coated blisk with blade crack, these crack mistuning variation rules are of great significance to the dynamic analysis and the determination of the crack location.

Mistuning identification for coated blisks using small amount of experimental data

Because the coatings are likely to produce new mistuning which aggravates the vibration failure of coated blades, it is particularly important to study the mistuning identification for coated blades. In this study, the degrees of freedom of the whole disk of the coated blisk is completely constrained, and the orders of the dynamic model of the coated blisk based on component mode mistuning (CMM) method is further reduced. Based on this model, a novel mistuning identification method for the coated blade of the coated blisk by small amount of experimental data is proposed, which can identify the mass, stiffness and damping mistuning of the blade substrates and coatings. The input parameters with high amount of data, such as modal shape matrix, are removed from identification formulas, thus, both the amount of data for identification calculation and the workload of vibration testing are reduced. The mistuning identifications of the numerical case and actual case are carried out respectively, and the identification process of the mistuning identification method in this paper is compared with the one based on the classical CMM model. It is shown that the mistuning identification method is effective and feasible, and the identification efficiency is higher than the classical CMM identification method.

Effective Mistuning Identification Method of Integrated Bladed Discs of Marine Engine Turbochargers

Radial turbine and compressor wheels form essential cornerstones of modern internal combustion engines in terms of economy, efficiency and, in particular, environmental compatibility. As a result of the introduction of exhaust gas turbochargers in the extremely important global market for diesel engines, higher engine efficiencies are possible, which in turn reduce fuel consumption. The associated reduced exhaust emissions can answer questions that results from environmentally relevant aspects of the engine development. In shipping, the international Maritime Organisation (IMO) prescribes the step-by-step reduction of nitrogen oxide and other types of emissions. To reduce these emissions, various systems are being developed, in which turbochargers are an important part. The requirements for the reliability and service life of turbochargers are constantly increasing. Turbocharger blade vibration is one of the most important problems to be solved when designing the rotors. In the case of real rotors, so-called mistuning arises, which is a slight deviation of the properties of the individual blades from the design parameters. The article deals with an effective method of mistuning identification for cases of integrated bladed discs of marine engine turbochargers. Unlike approaches that use costly scanning laser Doppler vibrometers, this method is based on using only a simple laser vibrometer in combination with a computational model of the integrated bladed disc. The added value of this method is, in particular, a significant reduction in the cost of laboratory equipment and a reduction in the time required to obtain the results.

A New Mistuning Identification Method Based on the Subset of Nominal System Modes Method

Abstract The mistuning problem of quasi-periodic structures has been the subject of numerous scientific investigations for more than 50 years. Researchers developed reduced-order models to reduce the computational costs of mistuning investigations including finite element models. One question which has also high practical relevance is the identification of mistuning based on modal properties. In this work, a new identification method based on the subset of nominal system modes method (SNM) is presented. Different to existing identification methods where usually the blade stiffness of each sector is scaled by a scalar value, N identification parameters are used to adapt the modal blade stiffness of each sector. The input data for the identification procedure consist solely of the mistuned natural frequencies of the investigated mode family as well as of the corresponding mistuned mode shapes in the form of one degree-of-freedom per sector. The reduction basis consists of the tuned mode shapes of the investigated mode family. Furthermore, the proposed identification method allows for the inclusion of centrifugal effects like stress stiffening and spin softening without additional computational effort. From this point of view, the presented method is also appropriate to handle centrifugal effects in reduced-order models using a minimum set of input data compared to existing methods. The power of the new identification method is demonstrated on the example of an axial compressor blisk. Finite element calculations including geometrical mistuning provide the database for the identification procedure. The correct functioning of the identification method including measurement noise is also validated to show the applicability to a case of application where real measurement data are available.

Mistuning identification and model updating of coating blisk based on modal test

Abstract Compared with a single material structure, the coating blisk contains at least two kinds of materials, thus the mistuning modeling and identification are more challenging than the usual bladed disk structure. In this study, on the basis of the component mode mistuning (CMM) and modal test, a method of mistuning identification was proposed for the coating blisk. The CMM model of the coating blisk was described firstly. Considering the mass and stiffness mistuning of the blisk substrate and coating materials simultaneously, the mistuning identification formula of the coating blisk was derived. Then, a novel method for the mistuning identification of coating blisk by measuring only two point modal coordinates of the blades was proposed. For the simplified numerical model and the relevant actual structure of coating blisk, the mistuning identifications were performed respectively, it was shown that the identification results are basically consistent with the predefined mistuning, which proved the rationality of the proposed mistuning identification method. Finally, based on the identification result of actual coating blisk, the original finite element model (FEM) of coating blisk was updated, and the simulation precision of FEM was improved.