Relationships between ocean bottom noise and the environment

1994 ◽  
Vol 84 (6) ◽  
pp. 1991-2007 ◽  
Author(s):  
Jeffrey M. Babcock ◽  
Barry A. Kirkendall ◽  
John A. Orcutt
Keyword(s):  
Gravity Waves ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Environmental Data ◽  
Single Frequency ◽  
Frequency Noise ◽  
Ocean Bottom ◽  
Double Frequency ◽  
Frequency Peak ◽  
Northern Atlantic

Abstract Observations of ocean bottom low-frequency noise and surface environmental data over a period of 27 days in the northern Atlantic during the SAMSON and SWADE experiments reveal how closely related the noise is to meteorological conditions. Double-frequency microseisms produced by nonlinear interactions of storm-induced surface gravity waves are especially evident in the frequency band 0.16 to 0.3 Hz and show a high variability in both amplitude and peak frequencies. Bifurcated at times, the peak that characterizes the microseism band contains local and distant or “teleseismic” components, which are generated at different locations. Weather and storm fetch appear to be the major contributions to the size and shape of microseism spectra. Storm development on the sea surface is associated with progressively lower microseism frequencies along with a concurrent increase in amplitude. The single-frequency microseism peak is a continuous feature and is observed to portray the same time-dependent spectral characteristics as the portion of the double-frequency peak associated with distant storms. Coherence studies confirm that both peaks (single and teleseismic double) originate at a distant source. These peaks are generated at roughly the same location with some storm component over the coastline.

scholarly journals In Design of an Ocean Bottom Seismometer Sensor: Minimize Vibration Experienced by Underwater Low-Frequency Noise

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3446 ◽  
Author(s):  
Xiaohan Wang ◽  
Shangchun Piao ◽  
Yahui Lei ◽  
Nansong Li
Keyword(s):  
Seismic Waves ◽  
Low Frequency ◽  
Sound Field ◽  
Average Density ◽  
Vibration Velocity ◽  
Frequency Noise ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Underwater Noise ◽  
The Impact

Ocean Bottom Seismometers (OBS) placed on the seafloor surface are utilized for measuring the ocean bottom seismic waves. The vibration of OBS excited by underwater noise on its surface may interfere with its measured results of seismic waves. In this particular study, an OBS was placed on the seabed, while ray acoustic theory was used to deduce the sound field distribution around the OBS. Then using this information, the analytical expression for the OBS vibration velocity was obtained in order to find various factors affecting its amplitude. The finite element computing software COMSOL Multiphysics® (COMSOL) was used to obtain the vibration response model of the OBS which was exposed to underwater noise. The vibration velocity for the OBS calculated by COMSOL agreed with the theoretical result. Moreover, the vibration velocity of OBS with different densities, shapes, and characters were investigated as well. An OBS with hemispherical shape, consistent average density as that of the seafloor, and a physical structure of double tank has displayed minimum amplitude of vibration velocity. The proposed COMSOL model predicted the impact of underwater noise while detecting the ocean bottom seismic waves with the OBS. In addition, it provides significant help for the design and optimization of an appropriate OBS.

Low-frequency noise and impedance spectral characteristics of solid-state structures

2004 ◽  
Vol 49 (11) ◽  
pp. 617-621 ◽  
Author(s):  
I. V. Lebedev ◽  
I. N. Miroshnikova ◽  
D. V. Chuprov
Keyword(s):  
Solid State ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Solid State Structures

Self-synchronization theory of tri-motor excitation with double-frequency in far resonance system

2020 ◽  
Vol 234 (16) ◽  
pp. 3166-3184 ◽  
Author(s):  
Min Zou ◽  
Pan Fang ◽  
Yongjun Hou ◽  
Guodong Chai ◽  
Jinsong Chen
Keyword(s):  
Drilling Fluid ◽  
Structural Parameters ◽  
Rapid Development ◽  
Low Frequency ◽  
Single Frequency ◽  
Stable Phase ◽  
Resonance System ◽  
Double Frequency ◽  
Differential Motion ◽  
Motor Excitation

With the rapid development of petroleum exploitation industry, vibrating screen actuated with a single frequency is unsuitable to separate cuttings from drilling fluid, since it usually results in screen blocking. Hence, for solving the above-mentioned problem, tri-motor excitation with double-frequency in far resonance system is introduced. This paper aims to explore the self-synchronization mechanism of the proposed system. First, dynamic equation is established according to physical model of the system. Then, displacement response of the system in steady state is obtained with dynamic formulas. Subsequently, synchronous condition among the three exciters is determined by small parameters method, and criterion of synchronous stability among the three exciters is derived by Poincare-Lyapunov method. Finally, in light of the differential motion equation, Runge-Kutta principle is assigned to validate the reliability of self-synchronous theory and the stability of the double-frequency system. The results indicate that electromagnetic torques of low-frequency motors are dynamically antisymmetric in synchronous operation, and synchronous ability of the system is determined by the mass ratio among the rotors. In addition, stable phase difference among the rotors is significantly influenced by the structural parameters of the system. And this study will be helpful for the improvement of separation technology.

Optimal Stiffener Design for Interior Sound Reduction Using a Topology Optimization Based Approach

2003 ◽  
Vol 125 (3) ◽  
pp. 267-273 ◽  
Author(s):  
Jianhui Luo ◽  
Hae Chang Gea
Keyword(s):  
Topology Optimization ◽  
Optimization Problem ◽  
Low Frequency ◽  
Coupled System ◽  
Conservative System ◽  
Sound Level ◽  
Single Frequency ◽  
Frequency Noise ◽  
Topology Optimization Problem ◽  
Sound Reduction

A topology optimization based approach is proposed to study the optimal configuration of stiffeners for the interior sound reduction. Since our design target is aimed at reducing the low frequency noise, a coupled acoustic-structural conservative system without damping effect is considered. Modal analysis method is used to evaluate the interior sound level for this coupled system. To formulate the topology optimization problem, a recently introduced Microstructure-based Design Domain Method (MDDM) is employed. Using the MDDM, the optimal stiffener configurations problem is treated as a material distribution problem and sensitivity analysis of the coupled system is derived analytically. The norm of acoustic excitation is used as the indicator of the interior sound level. The optimal stiffener design is obtained by solving this topology optimization problem using a sequential convex approximation method. Examples of acoustic box under single frequency excitation and a band of low frequency excitations are presented and discussed.

scholarly journals Distributed sensing of microseisms and teleseisms with submarine dark fibers

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Ethan F. Williams ◽  
María R. Fernández-Ruiz ◽  
Regina Magalhaes ◽  
Roel Vanthillo ◽  
Zhongwen Zhan ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Surface Gravity ◽  
Ocean Bottom ◽  
S Wave ◽  
Deep Earthquake ◽  
Double Frequency ◽  
Surface Gravity Waves ◽  
Seismic Sensors ◽  
Submarine Earthquakes ◽  
Seismic Networks

AbstractSparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. Here we report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We observe in-situ how opposing groups of ocean surface gravity waves generate double-frequency seismic Scholte waves, as described by the Longuet-Higgins theory of microseism generation. We also extract P- and S-wave phases from the 2018-08-19 $${M}_{w}8.2$$Mw8.2 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies. These results suggest significant potential of DAS in next-generation submarine seismic networks.

scholarly journals Application Study of Adaptive Tracking Algorithm in Active Noise Control System of Transformer

2019 ◽  
Vol 9 (13) ◽  
pp. 2693 ◽  
Author(s):  
Liming Ying ◽  
Jinwei Wang ◽  
Qin Liu ◽  
Donghui Wang
Keyword(s):  
Noise Reduction ◽  
Noise Control ◽  
Spectral Characteristics ◽  
Active Noise Control ◽  
Low Frequency ◽  
Cost Effective ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Active Noise ◽  
Reduction Methods

Active noise control (ANC) technology can be able to reduce the low frequency noise effectively, and has been widely applied in limited enclosed equipment, such as cars, aircraft cockpits, and headphones, etc. Compared with the traditional noise reduction methods, ANC technology is a cost-effective method in handling the low-frequency noise of transformers. An experimental ANC system in a virtual substation is designed and constructed. An adaptive signal tracking ANC algorithm is proposed, and a set of ANC experimental prototypes applied to a virtual substation is designed. Based on the proposed algorithm, the distributions of the acoustics and spectral characteristics of transformer noise in substations are analyzed. Experimental results show that the effective noise reduction can be achieved an average of 5 dB(A) in a given region with respect to the absence of the ANC system.

scholarly journals Two-frequency acoustic-gravitational waves, simulation of satellite measurements

2020 ◽  
Vol 36 (6) ◽  
pp. 22-36
Author(s):  
E.I. Kryuchkov ◽  
I.T. Zhuk ◽  
O.K. Cheremnykh
Keyword(s):  
Gravity Waves ◽  
Natural Frequencies ◽  
Initial Conditions ◽  
Spectral Characteristics ◽  
Single Frequency ◽  
Center Frequency ◽  
Dual Frequency ◽  
Satellite Measurements ◽  
Acoustic Gravity Waves ◽  
Isothermal Atmosphere

The theory of acoustic gravity waves (AGW) considers free disturbances of the atmosphere within the framework of a single-frequency approach. In this case, the theory implies the existence of two separate types of waves with different natural frequencies - acoustic and gravitational. In the single-frequency approach, wave fluctuations of density, temperature, and velocity are related to each other through the spectral characteristics of the wave, and these relationships are unchanged. However, satellite observations of AGW parameters cannot always be explained within the framework of a single-frequency approach. This paper presents a two-frequency approach to the study of AGWs using the model of two coupled oscillators. It is shown that the perturbed movements of the elementary volume of the medium occur simultaneously at two natural frequencies. In this case, the connections between the wave fluctuations of the parameters are determined by the initial conditions, which can be arbitrary. Solutions in real functions for an isothermal atmosphere are obtained. The conditions under which single-frequency AGWs are obtained from the general two-frequency solution are investigated. The AGW waveforms measured from the satellite for velocities and displacements in single-frequency and dual-frequency modes are numerically simulated. The results of simulating two-frequency AGWs agree with the data of satellite measurements. Two-frequency AGWs are not always implemented at two different frequencies. It is shown that when the frequencies approach each other, the beat effect occurs and two closely related modes become indistinguishable. At the same wavelength, they have one center frequency and one phase velocity. The main feature of the two-frequency approach to the study of AGW is the expansion of the relationships between the wave parameters of the medium. This makes it possible to achieve satisfactory agreement of the model waveforms with the data of satellite measurements. Thus, the use of a two-frequency AGW treatment opens up new possibilities in the interpretation of experimental data.

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