Kajetan Dziedziech

Non-Linear Vibro-Acoustic Wave Modulations - Analysis of Different Types of Low-Frequency Excitation

Signal processing method based on wavelet transform used in non-linear acoustic test is presented in the paper. The method is applied for sidebands identification in response signal acquired during vibro-acoustic modulation test of impacted carbon fiber reinforced plate (CFRP). The plate was impacted with known energy using drop-weight testing machine. The modulation effect in investigated specimen results from the interaction of low and high frequency excitation with damage. The paper investigates different than mono-harmonic low-frequency excitation usually used in non-linear acoustics tests. Application of aperiodic low-frequency excitation signal allows to omit the modal test, where natural frequency of the structure are estimated. However, this requires the use of dedicated signal processing methods.

Wavelet-Based Frequency Response Function: Comparative Study of Input Excitation

Time-variant systems can be found in many areas of engineering. It is widely accepted that the classical Fourier-based methods are not suitable for the analysis and identification of such systems. The time-variant frequency response function—based on the continuous wavelet transform—is used in this paper for the analysis of time-variant systems. The focus is on the comparative study of various broadband input excitations. The performance of the method is tested using simulated data from a simple MDOF system and experimental data from a frame-like structure.

Efficient swept sine chirp excitation in the non-linear vibro-acoustic wave modulation technique used for damage detection

In this article, the non-linear vibro-acoustic modulation technique is used for structural damage detection. A new experimental configuration and data processing strategy are proposed to improve the damage detection capability of the technique. The swept sine chirp excitation is used for both low-frequency vibration/modal and high-frequency ultrasonic excitations. The adaptive resampling procedure is then applied to extract information about modulation intensity that relates to damage. The proposed method is illustrated using numerical simulations and experimental tests. The latter involves crack detection in an aluminium beam. The results of the proposed method are compared with the classical approach based on single harmonic excitation, demonstrating that similar damage detection information can be extracted. However, the major advantage of the proposed method is simplicity and robustness since no a priori selection of excitation frequencies is needed. As a result, crack detection is more reliable and unambiguous.

Enhanced nonlinear crack-wave interactions for structural damage detection based on Lamb waves

The paper presents a novel damage detection method that combines Lamb wave propagation with nonlinear acoustics. Low-frequency excitation is used to modulate Lamb waves in the presence of fatigue cracks. The work presented shows that the synchronization of the interrogating high-frequency Lamb wave with the low-frequency vibration is a key element of the proposed method. The main advantages of the proposed method are the lack of necessity for baseline measurements representing undamaged condition and lack of sensitivity to temperature variations. Numerical simulations and experimental measurements are performed to demonstrate the application of the proposed method to detect fatigue crack in aluminum beam.

Wavelet-based analysis of time-variant adaptive structures

Wavelet analysis is applied to identify the time-variant dynamics of adaptive structures. The wavelet-based power spectrum of the structural response, wavelet-based frequency response function (FRF) and wavelet-based coherence are used to identify continuously and abruptly varying natural frequencies. A cantilever plate with surface-bonded macro fibre composite—which alters the structural stiffness—is used to demonstrate the application of the methods. The results show that the wavelet-based input–output characteristics—i.e. the FRF and coherence—can identify correctly the dynamics of the analysed time-variant system and reveal the varying natural frequency. The wavelet-based coherence can be used not only for the assessment of the quality of the wavelet-based FRF but also for the identification. This article is part of the theme issue ‘Redundancy rules: the continuous wavelet transform comes of age’.

Structural Damage Detection Based on Nonlinear Acoustics: Application Examples

This chapter provides examples of recent application developments in the field of nonlinear acoustics and damage detection, highlighting future trends and challenges. The major focus is on nondestructive testing of engineering components. Examples of damage detection methods based on the vibro-acoustic wave modulation technique are presented.

Selection of Suitable Method for Speed Recovery from Vibration Signal

Typically, if order analysis of vibration signal is expected, a speed sensor (phase marker) or an encoder are installed on the shaft. However, in some practical scenarios, the speed information recorded in parallel to the vibration signal acquisition is not available; yet, it is still required. In this case, one is forced to use a raw vibration signal to extract the information about so-called instantaneous phase or instantaneous frequency of a selected component, and—if required—scale to a selected shaft. In recent years, few different techniques for speed recovery have been proposed, each one with different assumptions and each implementing more or less complexed mathematical apparatus. The current paper proposes a guidance how to select a suitable method on the basis of the visual deduction about signal characteristics with the implication on selection of the easiest and most automatized method sufficient for analysed case.

Optimization of Calculations for Wireless Condition Monitoring Systems

Health Indicator for machine health monitoring are generally well-established. Regardless of the type of the Condition Monitoring System (stationary, remote, wireless) and the system’s manufacturer, the most commonly applied Health Indicators include wideband estimators (peak-to-peak, Root Mean Square, kurtosis, crest factor, velocity Root Mean Square), narrowband estimators (speed harmonics, gear meshing frequencies, rolling-element bearing characteristic frequencies), and simple spectral bands corresponding to a group of machine elements, e.g. 100–2000 Hz for gearboxes. In order to improve the reliability of Health Indicators, stationary Condition Monitoring System implement averaging and advanced data acquisition logic. In order to detect faults in very early stage, Condition Monitoring System implement resampling, order analysis, Deterministic Random Separation, and for instance auxiliary visualization. However, in case of wireless Condition Monitoring System without a speed sensor, improvement might concern only three aspect, namely hardware realization, data transmission, and power savings, where the latter one might be decomposed into data transfer power consumption, data acquisition power consumption, and data analysis power consumption. The current paper illustrates few recent ideas on how to minimize the power consumptions for data analysis. As it will be shown, it is possible to reduce the computational cycles by more than 60% comparing to stationary Condition Monitoring System while losing acceptable level of the quality of calculated Health Indicators.

On the Research of Extra Characteristic Frequencies in a Planetary Gearbox

Gearboxes have been investigated and monitored for decades since they present one of the important transmission power systems which have been used in navy, air and automotive sectors. One of the most adopted one is the planetary gearbox since it has an important reduction ratio within compact space. The dynamic behaviour of a such one is very complicated because it possesses several gears in mesh and differs from other types of gearboxes by the fact that planet gears can occupy different positions in one period carrier rotation which leads to an important influence on the overall vibration signal acquired by a transducer mounted one the external housing. Consequently, in a measured vibration spectrum, the pass planet frequency component is identified and its energy level is considered only as the pass planet energy. However, there is another phenomenon that increases the level of the pass planet frequency component which is the Open image in new window due to the rotation of planets. In this work, a comprehensive monitoring of a staged planetary gearbox is presented. The unbalance phenomenon is investigated in every stage. Then, an experimental validation is provided in order to support our hypothesis claiming that the Open image in new window phenomenon depends on the parity of the number of planets.

Damage detection in plate-like structures based on mode-conversion sensing with 3D laser vibrometer

Interpretation of Lamb waves signals raises serious difficulties due to their multi-modal nature. Various modes propagating with different velocities can be confused and erroneously treated as damage reflected components. Both S0 and A0 Lamb modes exhibit elliptical polarization, therefore, their in-plane and out-of plane motion components are shifted by ± 90°. Also, the ratios of in-plane and out-of-plane displacements between these components vary and the direction of particle motion is opposite for both modes. Using a 3D scanning laser vibrometer it is possible to capture the in-plane and out-of-plane motion. The modes differ not only in polarization parameters but also in group velocities, therefore, normally they are well separated in time. Two modes can occur simultaneously only close to the wave source or to a defect that leads to mode conversion. Since the in-plane and out-of plane motion components are generally out-of-phase, a comparison of these components permits detection of mode conversion, which leads to superior and reliable damage detection. Here, we present a damage imaging method based on mode-conversion indicator (MCI).