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A novel low-pass filtering self-adaptive (LPFA) denoising method combining complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and a wavelet threshold (WT) strategy is proposed to solve the problem of the aero-engine gas-path electrostatic signal noise, which challenges the gas-path component condition monitoring and feature extraction techniques. Firstly, the integration of CEEMDAN addresses modal aliasing and intermittent signal challenges, while the proposed low-pass filtering method autonomously selects valuable signal components. Additionally, the application of the WT in the unselected components enhances the extraction of useful information, presenting a unique and advanced approach to electrostatic signal denoising. Moreover, the proposed method is applied to simulated signals with different input signal-to-noise ratios and experimental fault electrostatic signals of a micro-turbojet engine. The comparison with several traditional approaches in a denoising test for the simulated signals and experimental signals reveals that the proposed method performs better in extracting the effective components of the signal and eliminating noise. [ABSTRACT FROM AUTHOR]

A passive tuned mass damper can only be designed to have a good damping effect near the resonance frequency of the primary structure. To overcome this limitation, a novel semi-active tuned mass damper with continuously tunable stiffness is proposed in this paper. The proposed design features a compact mechanism that can vary its stiffness by changing the number of active coils in parallel and series configurations of helical springs. The real-time control of the stiffness is achieved by designing and implementing a driving system for this mechanism. The motion characteristics and required driving torque for the designed prototype are also examined during the stiffness tuning process. It is demonstrated that the novel semi-active tuned mass damper can tune its stiffness over a wide range, and consequently tune its working frequency band to a desirable region with a proper control law. The effectiveness of the proposed prototype was investigated numerically and experimentally with respect to one-degree-of-freedom harmonic excitations in the frequency ratio range of 0.8–1.2. The results indicate that the prototype preserves optimal vibration suppression performance across a broad frequency range. Thus, the proposed semi-active tuned mass damper can provide a simple and effective in-situ tunable tool for suppressing primary structure vibration in the presence of non-stationary vibratory excitations. [ABSTRACT FROM AUTHOR]