The Synchrosqueezing transform for instantaneous spectral analysis

The Synchrosqueezing transform is a time-frequency analysis method that can decompose complex signals into time-varying oscillatory components. It is a form of time-frequency reassignment that is both sparse and invertible, allowing for the recovery of the signal. This article presents an overview of the theory and stability properties of Synchrosqueezing, as well as applications of the technique to topics in cardiology, climate science and economics

Synchrosqueezed Wave Packet Transforms and Diffeomorphism Based Spectral Analysis for 1D General Mode Decompositions

This paper develops new theory and algorithms for 1D general mode decompositions. First, we introduce the 1D synchrosqueezed wave packet transform and prove that it is able to estimate the instantaneous information of well-separated modes from their superposition accurately. The synchrosqueezed wave packet transform has a better resolution than the synchrosqueezed wavelet transform in the time-frequency domain for separating high frequency modes. Second, we present a new approach based on diffeomorphisms for the spectral analysis of general shape functions. These two methods lead to a framework for general mode decompositions under a weak well-separation condition and a well different condition. Numerical examples of synthetic and real data are provided to demonstrate the fruitful applications of these methods.Comment: 39 page

Study on the seismic damage and dynamic support of roadway surrounding rock based on reconstructive transverse and longitudinal waves

The magnitude and frequency of induced seismicity increase as mining excavation reaches greater depth, leading to the increasingly severe damage to roadways caused by high-energy seismic waves. To comprehensively simulate the damage caused by dynamic loads, a synchrosqueezing transform and empirical mode decomposition method was developed, which effectively decomposed raw seismic wave signals into transverse and longitudinal components. This novel method produced more accurate results in terms of velocity, displacement, rock yielding patterns, and reflecting theoretically orthogonal oscillating directions of transverse and longitudinal waves compared to using raw mixed waves at the seismic source. Under the disturbance of transverse and longitudinal waves, the vertical displacement was much higher than horizontal displacement at the top position of the roadway, while the horizontal displacement was greater at the sidewalls. The particle vibration velocity, displacement and yielding zone of the surrounding rock of roadway were proportional to the energy level of seismic, while inversely proportional to the source-roadway distance. The proportion of damage attributed to transverse waves increased with the energy level, ranging from 75.8% to 85.8%. Eventually, a roadway dynamic support design was optimized based on the proposed seismic wave processing and modeling methodology. The methodology offers guidance for roadway dynamic support design, with the goal of averting excessive or insufficient support strength.Document Type: Original articleCited as: He, S., Shen, F., Chen, T., Mitri, H., Ren, T., Song, D. Study on the seismic damage and dynamic support of roadway surrounding rock based on reconstructive transverse and longitudinal waves. Advances in Geo-Energy Research, 2023, 9(3): 156-171. https://doi.org/10.46690/ager.2023.09.0

Post-Earthquake Damage Identification of Buildings with LMSST

Copyright © 2023 by the authors.. The structure is said to be damaged if there is a permanent shift in the post-event natural frequency of a structure as compared with the pre-event frequency. To assess the damage to the structure, a time-frequency approach that can capture the pre-event and post-event frequency of the structure is required. In this study, to determine these frequencies, a local maximum synchrosqueezing transform (LMSST) method is employed. Through the simulation results, we have shown that the traditional methods such as the Wigner distribution, Wigner–Ville distributions, pseudo-Wigner–Ville distributions, smoothed pseudo-Wigner–Ville distribution, and synchrosqueezing transforms are not capable of capturing the pre-event and post-event frequency of the structure. The amplitude of the signal captured by sensors during those events is very small compared with the signal captured during the seismic event. Thus, traditional methods cannot capture the frequency of pre-event and post-event, whereas LMSST employed in this work can easily identify these frequencies. This attribute of LMSST makes it a very attractive method for post-earthquake damage detection. In this study, these claims are qualitatively and quantitatively substantiated by comprehensive numerical analysis.The APC was funded by Manipal Academy of Higher Education

Mining Safety and Sustainability I

Safety and sustainability are becoming ever bigger challenges for the mining industry with the increasing depth of mining. It is of great significance to reduce the disaster risk of mining accidents, enhance the safety of mining operations, and improve the efficiency and sustainability of development of mineral resource. This book provides a platform to present new research and recent advances in the safety and sustainability of mining. More specifically, Mining Safety and Sustainability presents recent theoretical and experimental studies with a focus on safety mining, green mining, intelligent mining and mines, sustainable development, risk management of mines, ecological restoration of mines, mining methods and technologies, and damage monitoring and prediction. It will be further helpful to provide theoretical support and technical support for guiding the normative, green, safe, and sustainable development of the mining industry

Development of a Python Library for Processing Seismic Time Series

Earthquakes occur around the world every day. This natural phenomena can result in enormous destruction and loss of life. However, at the same time, it is the primary source for studying Earth, the active planet. The seismic waves generated by earthquakes propagate deep into the Earth, carrying considerable information about the Earth’s structure, from the shallow depths in the crust to the core. The information transferred by seismic waves needs advanced signal processing and inversion tools to be converted into useful information about the Earths inner structures, from local to global scales. The ever­evolving interest for investigating more accurately the terrestrial system led to the development of advanced signal processing algorithms to extract optimal information from the recorded seismic waveforms. These algorithms use advanced numerical modeling to extract optimal information from the different seismic phases generated by earthquakes. The development of algorithms from a mathematical­physical point of view is of great interest; on the other hand, developing a platform for their implementation is also significant. This research aims to build a bridge between the development of purely theoretical ideas in seismology and their functional implementation. In this dissertation SeisPolPy, a high quality Python­based library for processing seismic waveforms is developed. It consists of the latest polarization analysis and filter algorithms to extract different seismic phases in the recorded seismograms. The algorithms range from the most common algorithms in the literature to a newly developed method, sparsity­promoting time­frequency filtering. In addition, the focus of the work is on the generation of high­quality synthetic seismic data for testing and evaluating the algorithms. SeisPolPy library, aims to provide seismology community a tool for separation of seismic phases by using high­resolution polarization analysis and filtering techniques. The research work is carried out within the framework of the Seismicity and HAzards of the sub­saharian Atlantic Margin (SHAZAM) project that requires high quality algorithms able to process the limited seismic data available in the Gulf of Guinea, the study area of the SHAZAM project.Terramotos ocorrem todos os dias em todo o mundo. Esta fenomeno natural pode vir a resultar numa enorme destruição e perda de vidas. No entanto, ao mesmo tempo, é a principal fonte para o estudo da Terra, o planeta activo. As ondas sísmicas geradas pelos terramotos propagam­se profundamente na Terra, levando informação considerável sobre a estrutura da Terra, desde as zonas de menor profundidade da crosta até ao núcleo. A informação transferida por ondas sísmicas necessita de processamento avançado de sinais e ferramentas de inversão para ser convertida em informação util sobre a estrutura interna da Terra, desde escalas locais a globais. O interesse sempre crescente em investigar com maior precisão o sistema terrestre levou ao desenvolvimento de algoritmos avançados de processamento de sinais para extrair informação óptima das formas de ondas sísmicas registadas. Estes algoritmos fazem uso de modelos numéricos avançados para extrair informação óptima das diferentes fases sísmicas geradas pelos terramotos. O desenvolvimento de algoritmos de um ponto de vista matemático­físico é de grande interesse; por outro lado, o desenvolvimento de uma plataforma para a sua implementação é também significativo. Esta investigação visa construir uma ponte entre o desenvolvimento de ideias puramente teóricas em sismologia e a sua implementação funcional. Com o decorrer desta dissertação foi desenvolvido o SeisPolPy, uma biblioteca de alta qualidade baseada em Python para o processamento de formas de ondas sísmicas. Consiste na mais recente análise de polarização e algoritmos de filtragem para extrair diferentes fases sísmicas nos sismogramas registados. Os algoritmos variam desde os algoritmos mais comuns na literatura até um método recentemente desenvolvido, que promove a frequência de filtragem por tempo e frequência. Além disso, o foco do trabalho é a geração de dados sísmicos sintéticos de alta qualidade para testar e avaliar os algoritmos. A biblioteca SeisPolPy, visa fornecer à comunidade sismológica uma ferramenta para a separação das fases sísmicas, utilizando técnicas de análise de polarização e filtragem de alta resolução. O trabalho de investigação é realizado no âmbito do projecto SHAZAM que requer algoritmos de alta qualidade que possuam a capacidade de processar os dados sísmicos, limitados, disponíveis no Golfo da Guiné, a área de estudo do projecto

Analysis and decomposition of frequency modulated multicomponent signals

Frequency modulated (FM) signals are studied in many research fields, including seismology, astrophysics, biology, acoustics, animal echolocation, radar and sonar. They are referred as multicomponent signals (MCS), as they are generally composed of multiple waveforms, with specific time-dependent frequencies, known as instantaneous frequencies (IFs). Many applications require the extraction of signal characteristics (i.e. amplitudes and IFs). that is why MCS decomposition is an important topic in signal processing. It consists of the recovery of each individual mode and it is often performed by IFs separation. The task becomes very challenging if the signal modes overlap in the TF domain, i.e. they interfere with each other, at the so-called non-separability region. For this reason, a general solution to MCS decomposition is not available yet. As a matter of fact, the existing methods addressing overlapping modes share the same limitations: they are parametric, therefore they adapt only to the assumed signal class, or they rely on signal-dependent and parametric TF representations; otherwise, they are interpolation techniques, i.e. they almost ignore the information corrupted by interference and they recover IF curve by some fitting procedures, resulting in high computational cost and bad performances against noise. This thesis aims at overcoming these drawbacks, providing efficient tools for dealing with MCS with interfering modes. An extended state-of-the-art revision is provided, as well as the mathematical tools and the main definitions needed to introduce the topic. Then, the problem is addressed following two main strategies: the former is an iterative approach that aims at enhancing MCS' resolution in the TF domain; the latter is a transform-based approach, that combines TF analysis and Radon Transform for separating individual modes. As main advantage, the methods derived from both the iterative and the transform-based approaches are non-parametric, as they do not require specific assumptions on the signal class. As confirmed by the experimental results and the comparative studies, the proposed approach contributes to the current state of the-art improvement

Développement d’une procédure non intrusive basée sur la propagation des ondes élastiques pour l’évaluation de l’état des structures en béton enfouies du réseau de distribution d’Hydro-Québec

Depuis l’automne 2011, des travaux de recherches ont été réalisés par le groupe de recherche en géotechnique de l’Université de Sherbrooke afin de développer une méthode d’inspection non-destructive permettant l’évaluation de l’état de dégradation du toit des structures enfouies du réseau de distribution d’Hydro-Québec (chambre de raccordement). En plus d’être non-destructive, la méthode développée se doit d’être réalisable depuis la surface du sol et donc ne pas nécessiter d’accès direct à la structure. Cette thèse explique en détail le processus de recherche réalisé depuis l’automne 2013 qui a mené au développement d’un outil permettant de faire l’inspection d’une structure souterraine à l’aide de l’étude de la propagation des ondes élastiques dans le sol. Premièrement, un survol de l’état des connaissances montre que les méthodes géophysiques peuvent offrir une alternative intéressante aux méthodes d’inspections traditionnelles. Cette revue montre également que la propagation des ondes élastiques peut être simulée à l’aide de différentes méthodes analytiques, semi-analytiques et numériques. Deuxièmement, il est montré que les algorithmes utilisés dans cette thèse permettent l’identification et la séparation dans le domaine vitesse-fréquence de différents groupes d’ondes présents dans divers types de signaux sismiques. Ces algorithmes permettent également le calcul de l’énergie et des vitesses de groupe et de phase des différents groupes d’ondes identifiés. Troisièmement, la méthode de la matrice de propagation et des simulations numériques en 2D montrent que l’énergie et les vitesses de propagation du mode fondamental des ondes de Rayleigh varient en fonction de la profondeur d’une structure souterraine. Il est notamment montré que la présence d’une structure souterraine agit comme un guide d’onde entrainant une variation importante de la vitesse de groupe près d’une fréquence nommée phase d’Airy. Des simulations numériques en 2D réalisées sur des structures dont la surface comporte des anomalies permet de montrer que la présence de ces dernières entraîne des variations importantes de l’énergie et des vitesses de propagations des ondes élastiques calculées à partir de la variation de l’accélération verticale mesurée à la surface du modèle. Ces observations ont mené à l’élaboration d’un protocole d’inspection qui a par la suite été testée sur de vraies structures construites sur le site expérimental de l’IREQ. Ces essais sur le site expérimental ont permis de confirmer que la profondeur et l’état de dégradation de la surface du toit d’une structure souterraine affectent l’énergie et la vitesse de propagation des ondes élastiques. Quatrièmement, des simulations numériques en 3D ont été réalisées afin d’améliorer le protocole d’inspection et d’évaluer l’effet de la présence du puits d’accès reliant la structure à la surface du terrain. Ces simulations ont permis de développer un nouveau protocole d’inspection et de montrer que la présence du puits d’accès n’empêche pas la détection d’anomalies présentes à la surface d’une structure. L’efficacité de ce nouveau protocole a également été validée en réalisant de nouveaux essais sur le site expérimental de l’IREQ. Finalement, il est montré que la présence d’un revêtement rigide à la surface du sol n’empêche pas la caractérisation du profil souterrain se trouvant sous un revêtement rigide lorsque la source se trouve directement en contact avec le sol