Accuracy of instantaneous frequencies predicted by the Hilbert-Huang transform for a bridge subjected to a moving vehicle

2021 ◽  
pp. 361-361
Author(s):  
M. Casero ◽  
A. González ◽  
E. Covián
Keyword(s):  
Moving Vehicle ◽  
Hilbert Huang Transform ◽  
Instantaneous Frequencies

scholarly journals An acceleration-based approach for crack localisation in beams subjected to moving oscillators

2020 ◽  
pp. 107754632092982 ◽  
Author(s):  
Ali Nikkhoo ◽  
Hossein Karegar ◽  
Reza Karami Mohammadi ◽  
Iman Hajirasouliha
Keyword(s):  
Model Updating ◽  
Crack Depth ◽  
Arbitrary Point ◽  
Acceleration Sensor ◽  
Moving Vehicle ◽  
Hilbert Huang Transform ◽  
Small Depth ◽  
Bridge Type ◽  
Output Only ◽  
Moving Oscillator

In this study, an output-only crack localisation method based on the Hilbert–Huang transform is proposed for crack localisation in bridge-type structures subjected to a moving vehicle simulated by a moving oscillator. The proposed method can accurately identify the location of cracks without using the conventional computationally expensive model updating techniques. The new crack localisation method can be adopted using fixed sensor and moving sensor approaches. In the fixed sensor approach, an acceleration sensor is located on an arbitrary point of the bridge, whereas in the moving sensor approach, an acceleration sensor is attached to a moving vehicle. The efficiency of the fixed sensor and moving sensor approaches is assessed through several numerical examples. A comprehensive analytical study is also conducted to investigate the impacts of crack depth and moving vehicle characteristics (such as damping coefficient, natural frequency, and velocity) on the accuracy of the predictions. It is shown that the proposed crack localisation method using fixed sensor and moving sensor approaches could efficiently identify the location and localisation of the cracks in all cases. However, the results indicate that the accuracy of the fixed sensor approach is generally better than that of the moving sensor approach in the localisation of cracks with small depth.

scholarly journals On the nonstationarity of the decadal periodicities of the length of day

2013 ◽  
Vol 20 (6) ◽  
pp. 1127-1135 ◽  
Author(s):  
P. De Michelis ◽  
R. Tozzi ◽  
G. Consolini
Keyword(s):  
Measurement Techniques ◽  
Length Of Day ◽  
Intrinsic Mode Functions ◽  
Hilbert Spectrum ◽  
Hilbert Huang Transform ◽  
The Earth ◽  
Starting Point ◽  
Decadal Variations ◽  
Length Of The Day ◽  
Instantaneous Frequencies

Abstract. The Earth's rotation rate is not constant, but changes on all observable timescales, from subdaily to decadal and longer. These variations are usually discussed in terms of variations in the length of the day (LoD) and are caused by processes acting within the interior, at the surface and outside of the Earth. Here, we investigate the presence of long-standing decadal variations in yearly LoD data covering the period from 1832 to 2009 by applying the Hilbert–Huang transform (HHT). The HHT has been slightly modified here to take into account the uncertainty of LoD values that has changed greatly in time due to the use of different LoD measurement techniques. The LoD time series has been completely decomposed into five intrinsic mode functions (IMF) and a residual trend. The estimation of instantaneous frequencies and related amplitudes of the obtained IMFs has allowed us to compute the Hilbert spectrum that has been used as the starting point for studying and discussing the stationarity of typical LoD timescale stationarity. The obtained results while showing the presence of multiple periodicities also indicate the absence of really stationary periodicities. Therefore, rather than considering the processes taking place in the Earth's core as the result of a superposition of oscillations (i.e. stationary mechanisms) occurring on a discrete number of different timescales, it would be better to think of a superposition of fluctuations that are intermittent in both frequency and amplitude.

Instantaneous Frequencies of Continuous Blood Pressure a Comparison of the Power Spectrum, the Continuous Wavelet Transform and the Hilbert–Huang Transform

2017 ◽  
Vol 09 (04) ◽  
pp. 1750009
Author(s):  
Kathrine Knai ◽  
Geir Kulia ◽  
Marta Molinas ◽  
Nils Kristian Skjaervold
Keyword(s):  
Blood Pressure ◽  
Wavelet Transform ◽  
Power Spectrum ◽  
Continuous Wavelet Transform ◽  
Continuous Wavelet ◽  
Frequency Shifts ◽  
Hilbert Huang Transform ◽  
Frequency Components ◽  
Instantaneous Frequencies ◽  
Continuous Blood Pressure

Continuous biological signals, like blood pressure recordings, exhibit nonlinear and nonstationary properties which must be considered during their analysis. Heart rate variability analyses have identified several frequency components and their autonomic origin. There is need for more knowledge on the time-changing properties of these frequencies. The power spectrum, continuous wavelet transform and Hilbert–Huang transform are applied on a continuous blood pressure signal to investigate how the different methods compare to each other. The Hilbert–Huang transform shows high ability to analyze such data, and can, by identifying instantaneous frequency shifts, provide new insights into the nature of these kinds of data.

scholarly journals Green notes: The rhythms of cyanobacteria exoelectrogenesis as de-composed by the Hilbert-Huang transform

2021 ◽  
Author(s):  
Tonny Ipael Okedi ◽  
Kamran Yunus ◽  
Adrian Fisher
Keyword(s):  
Photosystem Ii ◽  
Current Density ◽  
Applied Research ◽  
State Of The Art ◽  
Circadian Period ◽  
Density Profiles ◽  
Glycogen Accumulation ◽  
Hilbert Huang Transform ◽  
Circadian Phase ◽  
Instantaneous Frequencies

Electrons from cyanobacteria photosynthetic and respiratory systems are implicated in current generated in biophotovoltaic (BPV) devices. However, the pathway that electrons follow to electrodes remains largely unknown, limiting progress of applied research. Here we use Hilbert-Huang transforms to decompose Synechococcus elongatus sp. PCC7942 BPV current density profiles into physically meaningful oscillatory components, and compute their instantaneous frequencies. We develop hypotheses for the genesis of the oscillations via repeat experiments with iron-depleted and 20% CO2 enriched biofilms. The oscillations exhibit rhythms that are consistent with the state of the art cyanobacteria circadian model, and putative exoelectrogenic pathways. In particular, we observe oscillations consistent with: rhythmic D1:1 (photosystem II core) expression; circadian-controlled glycogen accumulation; circadian phase shifts under modified intracellular %ATP; and circadian period shortening in the absence of the iron-sulphur protein LdpA. We suggest that the extracted oscillations may be used to reverse-identify proteins and/or metabolites responsible for cyanobacteria exoelectrogenesis.

Transform Operator Pair Assisted Hilbert–Huang Transform for Signals With Instantaneous Frequency Intersections

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Yuxin Sun ◽  
Chungang Zhuang ◽  
Zhenhua Xiong
Keyword(s):  
A Priori ◽  
Low Frequency ◽  
Ensemble Empirical Mode Decomposition ◽  
Frequency Resolution ◽  
Intrinsic Mode Functions ◽  
Hilbert Huang Transform ◽  
Time Frequency ◽  
Mode Decomposition ◽  
Start Up ◽  
Instantaneous Frequencies

Due to low frequency resolution for closely spaced spectral components, i.e., the instantaneous frequencies (IFs) lie within an octave or even have intersections, the Hilbert–Huang transform (HHT) fails to separate such signals and consequently generates inaccurate time–frequency distribution (TFD). In this paper, a transform operator pair assisted HHT is proposed to improve the capability of the HHT to separate signals, especially those with IF intersections. The two operators of a pair are constructed to remove the chosen component that is clearly observed in the TFD of the signal, and then recover it from intrinsic mode functions (IMFs). With this approach, the components can be clearly separated and the intersections can also be identified in the TFD. Since a priori knowledge of the transform operator is usually not available in real applications, an iterative algorithm is presented to obtain a global transform operator. The effectiveness of the proposed algorithm is demonstrated by analysis of numerical signals and a real signal collected from a cracked rotor–bearing system during the start-up process. Moreover, the proposed approach is shown to be superior to the normalized Hilbert transform (NHT) as well as the ensemble empirical mode decomposition (EEMD).

Periodic motions of a dual-disc rotor system with rub-impact at fixed limiter

2008 ◽  
Vol 222 (10) ◽  
pp. 1935-1946 ◽  
Author(s):  
Q Han ◽  
Z Zhang ◽  
B Wen
Keyword(s):  
Rotor System ◽  
Experimental Measurements ◽  
Fe Model ◽  
Intrinsic Mode Functions ◽  
Periodic Motions ◽  
Test Rig ◽  
Hilbert Huang Transform ◽  
Time Frequency ◽  
Transverse Vibrations ◽  
Instantaneous Frequencies

Periodic motions of a rotor system with two discs are investigated where rub-impacts occur at fixed limiter for a test rig with dual discs. First, a finite element (FE) model of the rotor system is developed. Then numerical simulations based on the FE model are conducted to study the rotor transverse vibrations of the rotor system under three typical cases with different rotating speeds, rub-impact clearances, rub-impact rod stiffness, and rub frictions. The results are further compared with typical multiperiodic characteristics by experimentally measured vibrations. The simulations demonstrate different rotor motions, including periodic, quasi-periodic or complex characteristics, which coincide with experimental measurements. Finally, the non-stationary time-frequency domain characteristics of rub-impact motions are investigated via the Hilbert—Huang transform, and intrinsic mode functions (IMFs) and instantaneous frequencies of the three typical cases are obtained. The research has revealed some of the inherent vibration features of the dual-disc rotor system with rub-impact only occurring at fixed limiters.

FREQUENCY VARIATION IN VEHICLE–BRIDGE INTERACTION SYSTEMS

2013 ◽  
Vol 13 (02) ◽  
pp. 1350019 ◽  
Author(s):  
Y. B. YANG ◽  
M. C. CHENG ◽  
K. C. CHANG
Keyword(s):  
Resonance Condition ◽  
Moving Load ◽  
Equations Of Motion ◽  
Frequency Variation ◽  
Variation Pattern ◽  
Moving Vehicle ◽  
Vehicle Mass ◽  
Moving Vehicles ◽  
Special Cases ◽  
Instantaneous Frequencies

The variation of the instantaneous frequencies of bridges under moving vehicles is a problem not well studied in the literature. A theoretical framework is presented for the problem, considering the variation in frequencies for both the bridge and moving vehicle. First, the equations of motion are written for the two sub-systems. By solving the eigenvalue problem, analytical solutions in closed-form are derived from the frequencies of the vehicle and bridge that are coupled with each other. Based on this, the variation pattern, range, and dominating factors involved are studied, along with the special cases of moving mass and moving load. The results reveal that, if a moving vehicle is to be used as a tool for measuring the bridge frequencies or for detecting the bridge damages, the frequency variation caused by moving vehicles should be taken into account. Such an effect will be crucial when the vehicle mass is not negligible compared with the bridge mass or when the resonance condition is approached.

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