Dynamic characteristic analysis of rotating blade with breathing crack

Crack is the most common failure mode of the pipeline system, which may lead to high-speed and high-pressure hydraulic oil leakage. In this paper, the dynamic modeling and model order reduction methods for the fluid-delivering cracked pipeline (FDCP) considering the breathing effect are proposed, and the structural intensity method (SIM) is introduced to visualize the vibration transmission and breathing effect of FDCP. The fluid, solid, and coupling elements are constructed to establish the dynamic model of FDCP, the spring element is used to simulate the breathing effect, the dynamic substructure method is extended to perform the model order reduction of FDCP, and the rationality of the modeling method is verified by experiments. SIM and energy principles are used to visualize and analyze the vibration transmission of FDCP. The analysis results show that the natural frequencies are sensitive to the cracks in the maximum modal displacement and stress regions, and the fluid velocity and pressure (FVAP) will enhance the breathing effect of FDCP. In addition, the vibration transmission analysis can accurately detect the crack with different damage degrees, and FVAP do not influence the vibration transmission laws. The modeling and analysis method in this paper can provide a theoretical reference for fault diagnosis of FDCP. 

Dynamic modeling and analysis of fluid-delivering cracked pipeline considering breathing effect

The seismic response is a critical aspect of structural engineering, as it directly influences the design and safety evaluation of such systems. Structural seismic response becomes more complicated when unavoidable uncertainties in the structure are considered. Therefore, solving and analyzing the stochastic dynamic response of structures efficiently and accurately is of great significance. Various uncertainty quantification methods such as the stochastic finite element method, Monte Carlo method, and polynomial chaos expansion method have made significant progress in this field. However, these methods do not provide a comprehensive study of the seismic response of stochastic structures and efficiency problems rapidly emerge as the number of random variables increases. This paper delivers a comprehensive study of the seismic dynamic response of space truss and reticulated shell structure considering uncertainties in material properties, geometry, and loading. To this end, the finite element model of the structure was first modeled and the deterministic solutions were obtained. Then, polynomial surrogates are modeled for the natural frequency, mode participation factor, mode superposition response, and transient response of the structure under stochastic uncertainties. The sparse grid technique is used to select sparse quadrature points, which overcomes the curse of dimensionality caused by full grid integration. The results demonstrate that the sparse grid-based polynomial chaos expansion is more efficient. Uncertainty quantification reveals the uncertainty of modal analysis, response spectrum analysis, and transient response analysis of space truss and reticulated shell under seismic excitation. In summary, this study provides valuable insights and an efficient and accurate uncertainty quantification tool for the seismic dynamic analysis of stochastic structures, ultimately contributing to safer and more robust structural designs. 

A comprehensive study on seismic dynamic responses of stochastic structures using sparse grid-based polynomial chaos expansion

In this study, a hybrid finite element and extended transfer matrix method (FEM-ETMM) is formulated to simulate the breathing effect and fluid disturbances of a fluid-conveying cracked pipeline (FCCP). Furthermore, the frequency spectra of structural intensity (SI) responses and the normalized displacement-structural intensity (D-SI) curves are used to detect cracks. In this FEM-ETMM, the finite element method (FEM) is adopted to determine the contact state and establish the equivalent contact model, and the extended transfer matrix method (ETMM) is obtained by constructing the state transfer matrix in the crack region. Based on ETMM, the time-varying fluid disturbances are obtained. Furthermore, the model modal reduction and parametric modeling methods are used to improve solution efficiency. Finally, the effects of the crack parameters on vibration responses with and without considering fluid disturbances are analyzed. The results show that SI responses can amplify the odd-mode harmonics, thereby accurately detecting cracks at different depths and locations. In addition, the fluid disturbances change the contact states and enhance the damping effect. The proposed modeling and analysis method will provide valuable insights for crack detection of pipelines. 

A hybrid finite element and extended transfer matrix method for the dynamic modeling of fluid-conveying pipeline with breathing cracks

The branching structure is commonly utilized in the rotor system due to several merits, such as enabling a more compact structure and achieving a higher power-weight ratio, and also usually omitted or concentrated on a disk in the form of lumped mass during modeling, resulting in an inability to achieve the desired modeling accuracy. The aim of this paper is to investigate the nonlinear dynamic characteristics of a power-turbine rotor system with branching structure in turbo-shaft engine. Considering the branching structure and the effect of nonlinear oil-film force due to the squeeze film damper (SFD), the dynamic model of the power-turbine rotor system with branching structure is developed by means of finite element method. Meanwhile the critical speeds and mode shapes of the power-turbine rotor system are achieved by numerical calculation, simulation and experiment. The results reveal that the calculation results of the critical speeds and mode shapes are in good agreement with the simulation and experimental results. Moreover, the detailed comparison of vibration responses of the power-turbine rotor system with and without SFD is conducted, and the effects of oil-film clearance, length and viscosity on vibration responses are further investigated, respectively. The numerical results reveal that when the oil-film clearance goes up, the vibration amplitude at resonance goes down and the opposite is also true, moreover, increasing the oil-film length or decreasing the oil-film viscosity will improve the vibration-reduction performance of SFD. 

Nonlinear dynamic characteristics of a power-turbine rotor system with branching structure

Novel energy identification method for shallow cracked rotor system

Rotor machinery supports are susceptible to fracture arising from multi-period or irregular transient vibration and even the inconspicuous fatigue phenomenon. The novel dynamic model of a rotor mounted on the floating ring squeeze film damper (SFD) was developed. The proposed SFD implements low stiffness and small scale to overcome the deficiency. Based on the theory of hydrodynamic lubrication, the Reynolds equations on the working principle of the floating ring are established. Then, the dynamic characteristics of the rotor system during maneuvers, with the floating ring SFD supports, are subsequently examined by adopting the finite difference method. In addition, the oil film whirl mechanism of the floating ring SFD is demonstrated according to the transient analysis of the fluid–structure interaction model. The results of the SFD simulation reveal that, with increasing eccentricity ratio, both the inner and outer oil film pressure tend to be larger due to the shrinkage of the effective coverage of oil film. The maximum oil film pressure and bearing capacity increase nonlinearly within a certain eccentricity ratio range. Through the comparisons of the results, the vibration suppression effects of the proposed SFD are analyzed. This work will provide the practical reference for the dynamic design of the rotor support system.

https://www.mdpi.com/2076-3417/12/14/7167/pdf?version=1658138888

Analysis of Dynamic Characteristics of Small-Scale and Low-Stiffness Ring Squeeze Film Damper-Rotor System

Investigation of Vibration Energy and Transfer State in a High-Speed Rotor System with Crack Fault

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Papers

Novel energy identification method for shallow cracked rotor system

Analysis of Dynamic Characteristics of Small-Scale and Low-Stiffness Ring Squeeze Film Damper-Rotor System

Investigation of Vibration Energy and Transfer State in a High-Speed Rotor System with Crack Fault