Hydroacoustic Waves Research Articles

Well-posedness and potential-based formulation for the propagation of hydro-acoustic waves and tsunamis

Abstract We study a linear model for the propagation of acoustic and surface gravity waves in a stratified free-surface ocean. A formulation was previously obtained by linearizing the compressible Euler equations. In this paper, we introduce a new formulation written with a generalized potential. The new formulation is obtained by studying the functional spaces and operators associated to the model. The mathematical study of this new formulation is easier and the discretization is also more efficient than for the previous formulation. We prove that both formulations are well posed and show that the solution to the first formulation can be obtained from the solution to the second. Finally, the formulations are discretized using a spectral element method, and we simulate waves generation from submarine earthquakes and landslides. Résumé Nous étudions un modèle linéaire pour la propagation des ondes acoustiques et des vagues dans un océan stratifié à surface libre. Une première formulation, déduite des équations d’Euler compressible linéarisées, a été proposée dans un précédent article. Dans cet article, nous développons une nouvelle formulation écrite avec un potentiel généralisé. Cette nouvelle formulation est obtenue en étudiant les espaces fonctionnels et les opérateurs associés au modèle. L’étude mathématique et la discrétisation de cette nouvelle formulation sont plus simples que celles de la précédente formulation. Nous montrons que les deux formulations sont bien posées, et que la solution de la première formulation peut être calculée avec la solution de la seconde. Les deux formulations sont ensuite discrétisées avec une méthode d’éléments finis spectraux. Nous présentons des simulations d'ondes générés par des tremblement de terre et des glissements de terrain sous-marins.

An Open Source Hydroacoustic Benchmarking Framework for Geophonic Signal Detection

Passive hydroacoustic studies have underscored the efficiency and relevance of deploying autonomous hydrophones for the surveillance of underwater geophony. In particular, monitoring networks have been deployed for detecting SOFAR-propagating hydroacoustic waves generated by seismic events and locating their sources. The technique has been extended to study other hydroacoustic signals, such as P-waves from teleseismic events or impulsive waves generated by sea water-lava interactions. A significant challenge in this endeavor lies in the time required for the manual detection and annotation of these signals in long-term records. To address this issue, we tested the feasibility of implementing automated algorithms based on machine learning to detect and identify these various signals, and obtained satisfying classification and time picking accuracies. We incorporated those models in a benchmarking framework, proposing a training dataset, two evaluation datasets, two tasks to solve and the evaluations of the mentionned models on them. The goal of this framework is to foster the development of new models in the community, as it gives a clear way to evaluate them.

Steady-state triad resonance between a surface gravity wave and two hydroacoustic waves based on the homotopy analysis method

Under water compressibility, resonant triads can occur within the family of acoustic-gravity waves. This work investigates steady-state triad resonance between a surface gravity wave and two hydroacoustic waves. The water-wave equations are solved as a nonlinear boundary value problem using the homotopy analysis method (HAM). Within the HAM framework, a potential singularity resulting from exact triad resonance is avoided by appropriately choosing the auxiliary linear operator. The resonant hydroacoustic wave component, along with the two primary waves (one hydroacoustic wave and one gravity wave), is considered to determine an initial guess for the velocity potential. Additionally, by selecting an optimal “convergence-control parameter,” the steady-state resonance between a surface gravity wave and two hydroacoustic waves is successfully obtained. It is found that steady-state resonant acoustic-gravity waves are ubiquitous under certain circumstances. The two primary wave components and the resonant hydroacoustic wave component take up most of the energy in the steady-state resonant acoustic-gravity wave system. The amplitude of the resonant hydroacoustic wave component is mainly determined by the primary hydroacoustic wave component, and the amplitudes of both hydroacoustic waves are approximately equal in all cases considered. In addition, when the overall amplitude of the wave system increases, both dimensionless angular frequencies decrease, indicating that the nonlinearity of the entire wave system becomes stronger with an increase in the wave system amplitude. The amplitude of the primary hydroacoustic wave has a relatively large effect on the system's nonlinearity. This work will enrich and deepen our understanding of acoustic-gravity waves.

On the effect of an ANC system towards the transient pressure fluctuations caused by smart-grid controlled centrifugal pumps

Smart-grid control aims to use current power converter technology of pump drives for grid stabilization. Hereby, fluctuations of the power grid frequency are transmitted to the pump drive resulting in pump speed changes. Along with the inherent impeller design these pump speed changes are resulting in pressure pulsations which propagate as hydro acoustic pressure waves throughout the pump system causing noise and vibration issues in the piping system. Therefor, in order to realize smart-grid control, a solution must be found to attenuate or counteract these hydro acoustic pressure waves. In an earlier work [1], an active noise control (ANC) system to reduce pressure pulsations at a pump’s blade passing frequency (BPF) was published with the focus on constant points of operation. However, utilizing smart-grid control will results in high gradients of the pump speed and constantly changing points of operation are to be expected. This paper aims to attack those kinds of operating conditions. Within this paper, moving frequencies of interest at different pump speed gradient with and without active attenuation are analyzed and extracted from time series data by means of Vold-Kalman order tracking filter. In relation to possible fluctuations in the power grids frequency, the active attenuation performance of the ANC system is evaluated.

Contrasting T-Phase and P-Wave Patterns from the 2015 and 2017 Eruptions of the Submarine Volcano Kick-‘em-Jenny: Influence of Cardinal Direction on Recorded First Phase Arrival

ABSTRACT Kick-‘em-Jenny (KeJ)—the most active volcano in the Lesser Antilles and located about 8 km north of Grenada—is the only known, live submarine volcano in the region. Unrest and eruption episodes are approximately decadal. Typically, a KeJ episode, which may consist of several eruptions, is short-lived and rapidly returns to quiescence, with virtually no background seismicity. Although two previous eruptions broke the surface of the sea, and some have had seismic effects felt in northern Grenada and sometimes Martinique, instrumental recordings of T phases were considered to provide firm evidence of eruptions. T phases are hydroacoustic waves that propagate efficiently in the Sound Fixing and Ranging channel allowing long-range recording. The most recent episodes occurred on 29 April 2017 and 23, 24 July 2015, with no reported surface evidence. The 2015 hr-long seismic signals, among the longest durations ever recorded, manifested differences in the first phase arrivals at some of the same recording stations suggesting a fundamental difference in T-phase wave trains’ generation at KeJ. The single eruption in the 2017 volcanic episode had a duration similar to those prior to the 2015 eruptions; however, except for the four stations in the immediate vicinity of KeJ, the detected signals propagated only as T waves. Real-time and posteruption deductions that the episodes occurred from different cardinal directions on the volcano were found to be supported by the findings from bathymetric analyses done shortly after the episodes. This characteristic enhances the KeJ profile, possibly improving real-time activity assessments in future KeJ episodes, with a view to strengthening hazard and risk communication.

Effects of oceanic ice cover and density stratification on the propagation of hydroacoustic waves

Effects of oceanic ice cover and density stratification on the propagation of hydroacoustic waves

Coherenceogram for leak detection in water pipes

A widely used technique for locating leaks in buried water distribution pipes is the cross-correlation between two measured acoustic signals at either side of a leak. The technique is not always effective in identifying leaks with high certainty due to the dispersion of the hydro-acoustic waves, unknown frequency characteristics of the leak signal and the potential presence of strong ambient noise. In this paper, a new method termed “coherenceogram” has been proposed for leak detection in water pipes. The frequency-dependent time delay of the leak signal at two measurement stations is estimated based on the principle that the coherence of the two signals will maximize when they are synchronized to contain the same segment of the leak signal. The effect of temporal windowing is investigated, along with the removal of uncertainty, to enhance the efficacy of the coherenceogram for leak detection. Field validations were then carried out on a water pipe (a part of a water distribution system in a busy city area) and a trunk main. The results of the field experiments in comparison with other methods (cross correlations and cross time-frequency spectrum) illustrate that: 1) the coherenceogram does not need any signal filtering and is easy to implement; 2) it can guide the selection of the signal filter for cross-correlation techniques; 3) it accommodates the frequency-dependent characteristics of the leak signals and can be also used in many other fields for time-delay estimation, such as processing acoustic waves and seismic waves which possess strong wave dispersion.

Quantitative demodulation of distributed low-frequency vibration based on phase-shifted dual-pulse phase-sensitive OTDR with direct detection.

Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has been proposed for distributed vibration sensing purpose over recent years. Emerging applications, including seismic and hydroacoustic wave detection, demand accurate low-frequency vibration reconstruction capability. We propose to use the direct-detection Φ-OTDR configuration to achieve quantitative demodulation of external low-frequency vibrations by phase-shifted dual-pulse probes. Simultaneous pulsing and phase shifting modulation is realized with a single acousto-optic modulator to generate such probes, relaxing the need for an additional optical phase modulator. In the experiments, vibrations with frequency as low as 0.5 Hz are successfully reconstructed with 10 m spatial resolution and 35 dB signal-to-noise ratio. Excellent linearity and repeatability are demonstrated between the optical phase demodulation results and the applied vibration amplitudes. The proposed method is capable of quantitative demodulation of low-frequency vibrations with a cost-effective system configuration and high computation efficiency, showing potential for commercial applications of distributed seismic or hydroacoustic wave acquisition.

Analysis of the engineering mathematical model of the physical properties of a three-layer hydroacoustic screen with anisotropic components

A numerical-analytical technique for analyzing the physical effects of the formation of fields of hydroacoustic waves in the area in front of a flat three-layer hydroacoustic screen and in the space behind the screen at normal incidence of a stationary hydroacoustic wave on it is presented. The engineering model of the screen uses the assumption that its components are made of anisotropic functional-gradient materials with exponential inhomogeneity in thickness, and thin, absolutely flexible, inextensible coatings can be applied to the outer and contact surfaces of the layers. The technique is based on the analytical integration of the equations of wave deformation of the screen components and obtaining complex amplitude characteristics for the reflected and generated hydroacoustic waves behind the screen when solving a system of algebraic equations with a functional matrix, which follows from the boundary conditions for the investigated problem. Parametric descriptions for the characteristics of the investigated physical fields are obtained and examples of numerical analysis of the considered engineering model are presented.

Noise Levels and Signals Observed on Submarine Fibers in the Canary Islands Using DAS

Abstract In this study, we investigate 70 days of distributed acoustic sensing (DAS) recordings in the Canary Islands using an undersea fiber-optic telecommunication cable that links the islands of Tenerife and Gran Canaria. Two DAS interrogators connected to both ends of the cable turned the fiber into an array of 11,968 strain sensors covering a total length of ∼120 km. We present the details of the experiment, noise analysis, and examples of recorded signals. Seismic ambient noise levels assessment indicates poor local coupling of the cable due to the irregular bathymetry that results in high-amplitude acoustic oscillations in some channels. The DAS array recorded several types of nonseismic (vehicles, surface gravity waves, ships) and seismic signals. Local and regional earthquakes were detected with magnitudes mbLg≥2. Surface waves from teleseismic events at a distance of ∼3000 km were also identified in the strain recordings. Here, we report the first observations with DAS of hydroacoustic T waves generated by oceanic earthquakes located at the Central Mid-Atlantic Ridge and the Cape St. Vincent region. Events had magnitudes from Mw 4.2 to 6.9, and the hydroacoustic waves were recorded at epicentral distances from 780 to 3400 km. Our findings show that submarine fiber-optic cables can effectively be used to assess the seismic activity in remote oceanic areas.

Investigation of dynamic pressure fluctuations in closed hydraulic circuits as a function of centrifugal pump speed gradients

Electrical consumers, such as pumps, contribute towards the stable operation of the electrical power grid due to active and reactive power consumption. If the consumers are indirectly connected to the grid via power electronic converters, the positive contribution is reduced or non-existent. Consequently, the ability to compensate imbalances within the power grid is greatly reduced. A research project founded by the European Union is focusing on investigations to utilize power converter technology of pump drives for grid stabilization. But in order to stabilize the fluctuating power grid frequency rapid adjustments of the pump speed are required, which can cause major troubles in the hydraulic system. For instance, rapid changes in pump speed are causing the emission of hydro acoustic pressure waves into the pipe system, which are exciting the structure of the hydraulic system and lead to undesirable vibrations and noise emissions. Most critical is the direct excitation of natural frequencies in the entire piping system based on the inherent pressure fluctuations caused by transient fluid flow and pump speed changes. Converter control for grid-adaptive speed adjustment is only possible as long as there is no significant increase in dynamic pressure fluctuations in the whole hydraulic system. For this purpose, a research pump is operated with different rotational speed gradients in a closed hydraulic circuit. Dynamic pressure sensors were used to record the resulting pressure fluctuations at various locations of the hydraulic system. Additionally, an outlook towards an active reduction of the dynamic pressure fluctuations by means of a specially developed hydrodynamic actuator is given. These results are an initial step but of particular interest towards the knowledge of permissible grid adaptive speed control regimes, which can be applied to a pump in a hydraulic piping system.

Infrasonic Earthquake Detectability Investigated in Southern Part of Japan, 2019.

The Kochi University of Technology (KUT) Infrasound Sensor Network contains 30 infrasound sensors which are distributed all over Japan especially in Shikoku Island. At all infrasound stations installed with three-axis accelerometers to measure the peak ground acceleration (PGA). Many earthquakes were detected by our system after establishing of the network since 2016. In this study we will focus on all the possibilities for infrasound detection generated from earthquakes using KUT sensor network and International Monitoring system (IMS) stations for the earthquakes which were detected in southern part of Japan during 2019. As for earthquakes with strike-slip mechanisms the P-waves could not be detected by our sensors. In addition, The conversion from seismic to acoustic waves can be happened through the generating of the T-phase from oceanic earthquakes. On 9 May 2019, progressive multi-channel cross correlation (PMCC) method applied infrasound and hydroacoustic waves from two earthquakes happened in west of Kyushu Island as the T-phase was well-recorded at H11N station near Wake Island. Moreover, infrasound propagation modeling is applied to the reconstructed atmosphere profile by Ground to Space Model (AVO-G2S) to confirm the infrasound arrivals, furthermore the 3D ray tracing process and the calculations by using the transmission loss equation with normal modes and parabolic equation methods are investigated. The study confirmed the infrasound generation scenario from the T-phase of oceanic propagation.

Scientific Basis of Excitation of High-Intensity Hydroacoustic Waves Using Detonation of a Hydrogen and Oxygen Mixture

In this paper, we establish the scientific basis for the generation of intense hydroacoustic waves in a liquid as a result of the detonation of a stoichiometric mixture of hydrogen and oxygen. The idea of the possibility of carrying out this process with the help of a deep-water electrolyzer, which was confirmed experimentally, is expressed. The processes of combustion and detonation of a stoichiometric mixture of hydrogen and oxygen surrounded by a liquid medium and the initial conditions for an increase in pressure and temperature at the interface between detonation products and a liquid medium at the moment of explosion decay, providing the emergence and propagation of a hydroacoustic wave in a liquid medium, were studied using mathematical modeling methods. The dependence of the peak pressure of the resulting wave, the duration of its positive phase, and the duration of the first wave period on the volume of hydrogen and oxygen, pressure, and other parameters is estimated. The possibility of using the established effect to enhance oil production in oil and gas production is shown.

Seadrome: Multi-Frequency Hydro Acoustic Wave Recorder for Measurement of Hydro Conditions in the Water Area

Seadrome: Multi-Frequency Hydro Acoustic Wave Recorder for Measurement of Hydro Conditions in the Water Area

Investigation of acoustic fields in the arctic zone with uneven ice cover

A mathematical model for elastic wave propagation in an ice cover with uneven relief (hummock) has been developed. The theoretical model is based on the application of “directed” Green’s functions. We obtained numerical results for different distances between radiating and receiving antennas installed inside the ice layer and in water medium. An information-measuring system was created to investigate elastic acoustic waves along ice surface based on electo-hydraulic generator. Experiments of high-frequency acoustic signal propagation from electro-hydraulic generator in water-ice-air system were carried out. We illustrated the model validity for the investigation of hydroacoustic wave propagation in real ice conditions.

ОБОСНОВАНИЕ МАСШТАБОВ ПОДОБИЯ АКУСТИЧЕСКИХ ВЕЛИЧИН В УСТАНОВКАХ ДЛЯ ВЫРАЩИВАНИЯ ГИДРОБИОНТОВ

The article is devoted to studying the problems of physical modeling of acoustic and hydroacoustic waves, which are reflected from hydrobionts in recirculation aquatic systems (RAS), as well as open aquaculture cages (OAC). The behavior of aquatic organisms in RAS and OAC is so complex that it is difficult to be described mathematically because it is necessary to determine the temporal and spatial parameters of hydrobionts and to provide favourable conditions for aquatic organisms in RAS and OAC close to the natural habitat, including the acoustic regime. The use of simulation and physical modeling for calculating the acoustic quantities will make it possible to use machine vision to and optimize technological processes, to increase the productivity of the ultrasonic and ultrasonic treatment pools, to raise productivity and to reduce costs. The aim of acoustic quantities similarity in RAS and OAC is to determine the parameters of sound sources, the reflecting ability of hydrobionts with different characteristics (length, volume, density and others). In the problems of acoustic quantities it is required to ensure the coincidence of mechanical and acoustic processes. It is necessary to reduce the quantities dependent on the dimensional attributes of the object (length of a sound wave, sound power, sound energy, sound intensity, speed of sound, frequency, etc.) to their independent dimensionless form. When studying the behavior of aquatic organisms in RAS and OAC it is important to take into account mechanical, hydrodynamic, electrodynamic, optical and light similarities. There have been proposed the additional similarity scales for acoustic values, the methods for their calculation and the graphs of their dependence on the geometric scale Cl. Knowing the scale of Cl, it is possible to determine the scale effect

Calculation of Hydroacoustic Propagation and Conversion to Seismic Phases at T-Stations

The International Monitoring System (IMS) hydroacoustic network consists of six hydrophone stations and 5 T-stations. The IMS T-stations are high-frequency seismic stations (sample rates of 100 Hz) situated on islands or coastal stations and intended primarily to capture impulsive signals from in-water explosions. However, while there are numerous recordings of impulsive-like signals from in-water explosions at the hydrophone stations, recordings of this type of signal at the T-stations are rare. This is because the conversion of the hydroacoustic to a seismic signal as it propagates from ocean to land is inefficient, characterized both by complex geologic and topographic features and by strong attenuation. To improve the understanding of this signal conversion at T-stations, we performed numerical calculations using the spectral element code SPECFEM2D, modelling the acoustic signal as it propagates from the deep ocean through the ocean/land interface and finally, as an elastic signal, to the T-station. Environmental information from a variety of sources was gathered to construct the earth and ocean models used in the calculations. The goal of this work is to provide a set of calculated waveforms to complement the limited set of observed waveforms and to assist in the characterization of arrivals from explosion-generated hydroacoustic waves recorded at the T-stations.

Tomography of the Marine Crust, Based on the Use of Coastal Laser Strainmeters and Underwater Acoustic Projectors

Features of the tomography of the marine crust are described, based on the use of coastal laser strainmeters and broadband low-frequency underwater acoustic projectors. This approach is useful in studying the structure and composition of the marine crust in shelf areas, including ones covered with ice without destroying it. Numerous experimental studies have established that at sea depths equal to or less than half the length of a hydroacoustic wave generated by low-frequency underwater acoustic projectors, the hydroacoustic energy is mainly transformed into Rayleigh-type surface waves that radiate through the bottom on the hydroacoustic source–coast path.

Study of Low-Frequency Hydroacoustic Waves’ Behavior at the Shelf of Decreasing Depth

In research into various hydrophysical and hydroacoustic wave processes, it is extremely important to know the regularities of their propagation in the sea at decreasing depths, especially in the shelf areas, and also to know the regularities of their transformation into seismoacoustic processes in the earth crust. In the course of the processing and analysis of the experimental data of our complex experiment, in this paper we investigate these regularities. In our experiment, we used a low-frequency hydroacoustic transmitter that generated harmonic oscillations at the frequency of 22 Hz and received hydroacoustic systems with a shore laser strainmeter. It was established that hydroacoustic waves, propagating at the shelf of decreasing depth, transform into seismoacoustic waves at the depth of the sea equal to or less than a half-length of the hydroacoustic wave. A comparison of the results of this work with earlier-obtained results allows us to state that such regularities should be inherent to all hydrophysical and hydroacoustic processes.

Effects of the sound speed vertical profile on the evolution of hydroacoustic waves

We present a novel analytical model for the evolution of hydroacoustic waves in weakly compressible fluids characterised by depth variations of the sound speed profile. Using a perturbation expansion in terms of the small vertical variation of the sound speed, we derive a novel expression for the second-order velocity potential and show that this solution does not exist in the case of homogeneous sound speed. At the third order, we derive a linear Schr¨odinger equation governing the evolution of the wave envelope for large length and time scales, which features new terms depending on the sound speed distribution. We show that for generalised sound speed vertical profiles the frequency of the hydroacoustic signal can increase or decrease with respect to the constant sound speed case, depending on the profile. This has substantial implications on the speed of the wavetrain envelope. Our findings suggest the need to extend existing models that neglect the sound speed vertical variation, especially in view of applications to tsunami early warning.