Inversion imaging based on point spreading function for viscoacoustic medium

2018 ◽  
Author(s):  
Xuejun Wang ◽  
Haoran Ren ◽  
Jinsheng Jiang
Keyword(s):  
Spreading Function

Geometrical spreading function for short-period S and coda waves recorded in southern Spain

1993 ◽  
Vol 80 (1-2) ◽  
pp. 25-36 ◽  
Author(s):  
J.M. Ibáñez ◽  
E. Del Pezzo ◽  
G. Alguacil ◽  
F. De Miguel ◽  
J. Morales ◽  
...  
Keyword(s):  
Southern Spain ◽  
Coda Waves ◽  
Geometrical Spreading ◽  
Short Period ◽  
Spreading Function

scholarly journals Monitoring and Analysis of Wave Characteristics during Pipeline End Termination Installation

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 569
Author(s):  
Duanfeng Han ◽  
Ting Cui ◽  
Lihao Yuan ◽  
Yingfei Zan ◽  
Zhaohui Wu
Keyword(s):  
Real Time ◽  
Wave Motion ◽  
Fourier Transforms ◽  
Classical Method ◽  
Suitable Model ◽  
Wave Data ◽  
Wave Characteristics ◽  
Environmental Monitoring System ◽  
Spreading Function ◽  
Marine Environmental

Pipeline end termination (PLET) installation is an essential part of offshore pipe-laying operation. Pipe-laying operations are sensitive to pipe-laying barge motion and marine environmental conditions. Monitoring the field environment can provide a reasonable basis for planning pipe-laying. Therefore, the measurement and analysis of sea wave motion is helpful for the control and operational safety of the pipeline and vessels. In this study, an environmental monitoring system was established to measure wave motion during PLET operation. Fourier transforms were used to process images that were acquired by ultra-high-frequency X-band marine radar to extract wave parameters. The resulting wave spectra, as measured each minute, were used to simulate real-time wave data and calculate wave characteristics and regressed wave frequency and direction spectrum throughout the PLET operation. The regressed frequency, spectral density, and direction spectra were compared with the theoretical spectra to evaluate their similarity and find the most similar spreading function in the operational area (the South China Sea). Gaussian fitting of real-time wave data was tested while using a classical method. The marginal distribution and joint density of the wave characteristics were estimated and then compared with theoretical distributions to find the most suitable model for improving marine environmental forecasting.

Three-Dimensional Ocean Wave Simulation Based on Directional Spectrum

2011 ◽  
Vol 94-96 ◽  
pp. 2074-2079 ◽  
Author(s):  
Qiu Ying Guo ◽  
Zun Yi Xu ◽  
Ying Jun Sun
Keyword(s):  
Navigation System ◽  
Three Dimensional ◽  
Ocean Waves ◽  
Directional Spectrum ◽  
Wind Speeds ◽  
Simulation Speed ◽  
Spreading Function ◽  
Interaction Simulation ◽  
Ocean Environment ◽  
Key Techniques

Simulating real virtual ocean environment is necessary for the research of interaction simulation of underwater gravity aided inertial navigation system. One of the key techniques of realizing virtual ocean environment is modeling and simulating three-dimensional ocean waves. Numerical simulation of three-dimensional ocean waves in the case of different wind speeds is realized using MATLAB based on directional spectrum composed of Pierson-Moscowitz frequency spectrum and directional spreading function. Experiments show that the simulation speed is fast and the simulation results are vivid if suitable simulation frequency band, interval of wave frequency and interval of direction angle are selected. The simulation can provide some technological supports for interaction simulation of gravity aided navigation system for underwater vehicles.

scholarly journals DIRECTIONAL GROWTH FOR NUMERICAL WIND WAVE MODELS

1986 ◽  
Vol 1 (20) ◽  
pp. 47
Author(s):  
W.L. Neu ◽  
S.H. Kwon
Keyword(s):  
Growth Mechanism ◽  
First Generation ◽  
Wind Wave ◽  
Point Spectrum ◽  
Wave Model ◽  
Directional Growth ◽  
Wave Fields ◽  
Ocean Wave Model ◽  
Spreading Function ◽  
Wave Models

This study is concerned with the operation of spectral wind wave models. Many spectral wind wave models use a growth mechanism which operates on the point spectrum with directionality being introduced after the fact by the use of a spreading function. It is recognized here that this approach leads to errors whenever the wind and wave fields are not aligned. This is demonstrated by comparing the performance of two first generation models under various conditions. One makes use of a point spectral growth mechanism and follows the operation of the Spectral Ocean Wave Model (SOWM). The other uses a directional growth mechanism but is otherwise the same as the first. A large difference between the models is noted for swell corrupted seas.

A Generic Method to Model Frequency-Direction Wave Spectra for FPSO Motions

2008 ◽  
Author(s):  
Hermione J. van Zutphen ◽  
Philip Jonathan ◽  
Kevin C. Ewans
Keyword(s):  
Frequency Spectrum ◽  
Two Dimensions ◽  
Wind Forcing ◽  
Wave Spectra ◽  
Spectral Form ◽  
New Approach ◽  
Spreading Function ◽  
Wind Sea ◽  
Model Frequency ◽  
Sea Wave

We report a new approach to model the frequency-direction spectrum, in which the frequency-direction spectra from measurements or hindcast studies are fitted simultaneously in two dimensions, frequency and direction. Depending on the amount of wind forcing on the partition, either a unimodal (swell) or bimodal (wind-sea) wave spreading function is adopted together with the spectral form which best fits the frequency spectrum. This paper describes the new method and presents the results on a measured dataset.

Geometrical spreading and Q of Pn waves: An investigative study in eastern Canada

1991 ◽  
Vol 81 (3) ◽  
pp. 882-896 ◽  
Author(s):  
Tianfei Zhu ◽  
Kin-Yip Chun ◽  
Gordon F. West
Keyword(s):  
Velocity Gradient ◽  
Geometrical Spreading ◽  
Eastern Canada ◽  
Frequency Dependent ◽  
Study Region ◽  
Amplitude Data ◽  
Short Period ◽  
Head Waves ◽  
Geometric Spreading ◽  
Spreading Function

Abstract Station site effects, uncertainties in seismic source spectrum, and instrument response errors are among the well-known frequency-dependent contaminating factors that limit the reliability of short-period Q measurements of regional phases. For the Pn wave, a regional phase of importance for both magnitude determination and nuclear test ban verification, the problem is made worse by the added uncertainty of its geometric spreading function. For realistic earth models, the Pn geometric spreading function is likely to depart drastically from that expected of canonical head waves. The extent of this departure is sensitively dependent upon the regional crust/mantle structure, making geometric spreading assumption a conspicuous source of disagreement among the published Pn attenuation (QPn) estimates. We describe a technique, referred to here as the extended reversed two-station method (RTSM), for simultaneous determination of QPn and geometrical spreading function. The formulation, being designed to bring about direct cancellation of the contaminating source, station and instrument effects, is a reliable tool for mapping the Pn propagation characteristics over continental paths, long and short. The extended RTSM has been tested using Pn spectral amplitude data derived from seismic records of the Eastern Canada Telemetered Network (ECTN). We find the spreading rate coefficient n in the power-law representation of the geometric spreading (d−n, d being epicentral distance) to be frequency dependent, increasing from 1.11 at 1 Hz to 1.77 at 20 Hz. Our QPn model in eastern Canada takes the form of QPn = 189f0.87. The results from eastern Canada suggest that: (a) there exists a significant positive velocity gradient in the uppermost mantle (≧ 0.0037 sec−1); (b) the regionally recorded Pn waves are dominated by the superposition of a series of interfering diving waves bent by the velocity gradient and internally reflected at the underside of the Moho discontinuity; and (c) the very strong frequency-dependence of QPn we found in this study region may not be unique among low-attenuating shield and platform regions.

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