Scholte wave inversion and passive source imaging with ocean-bottom DAS

2021 ◽  
Vol 40 (8) ◽  
pp. 576-583
Author(s):  
Ethan F. Williams ◽  
María R. Fernández-Ruiz ◽  
Regina Magalhaes ◽  
Roel Vanthillo ◽  
Zhongwen Zhan ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Power Cable ◽  
Offshore Platforms ◽  
Ocean Bottom ◽  
Foundation Design ◽  
Source Imaging ◽  
Offshore Area ◽  
Velocity Inversion ◽  
Geotechnical Characterization ◽  
Scholte Wave

Geotechnical characterization of marine sediments remains an outstanding challenge for offshore energy development, including foundation design and site selection of wind turbines and offshore platforms. We demonstrate that passive distributed acoustic sensing (DAS) surveys offer a new solution for shallow offshore geotechnical investigation where seafloor power or communications cables with fiber-optic links are available. We analyze Scholte waves recorded by DAS on a 42 km power cable in the Belgian offshore area of the southern North Sea. Ambient noise crosscorrelations converge acceptably with just over one hour of data, permitting multimodal Scholte wave dispersion measurement and shear-wave velocity inversion along the cable. We identify anomalous off-axis Scholte wave arrivals in noise crosscorrelations at high frequencies. Using a simple passive source imaging approach, we associate these arrivals with individual wind turbines, which suggests they are generated by structural vibrations. While many technological barriers must be overcome before ocean-bottom DAS can be applied to global seismic monitoring in the deep oceans, high-frequency passive surveys for high-resolution geotechnical characterization and monitoring in coastal regions are easily achievable today.

Scour protection assessment of monopile foundation design for offshore wind turbines

2021 ◽  
Vol 231 ◽  
pp. 109083
Author(s):  
Hongwang Ma ◽  
Chen Chen
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Foundation Design ◽  
Offshore Wind Turbines ◽  
Scour Protection

scholarly journals Physical Modelling of Offshore Wind Turbine Foundations for TRL (Technology Readiness Level) Studies

2021 ◽  
Vol 9 (6) ◽  
pp. 589
Author(s):  
Subhamoy Bhattacharya ◽  
Domenico Lombardi ◽  
Sadra Amani ◽  
Muhammad Aleem ◽  
Ganga Prakhya ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Prior Experience ◽  
Physical Modelling ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Foundation Design ◽  
Offshore Wind Turbines ◽  
Sea Bed ◽  
Geological Conditions

Offshore wind turbines are a complex, dynamically sensitive structure due to their irregular mass and stiffness distribution, and complexity of the loading conditions they need to withstand. There are other challenges in particular locations such as typhoons, hurricanes, earthquakes, sea-bed currents, and tsunami. Because offshore wind turbines have stringent Serviceability Limit State (SLS) requirements and need to be installed in variable and often complex ground conditions, their foundation design is challenging. Foundation design must be robust due to the enormous cost of retrofitting in a challenging environment should any problem occur during the design lifetime. Traditionally, engineers use conventional types of foundation systems, such as shallow gravity-based foundations (GBF), suction caissons, or slender piles or monopiles, based on prior experience with designing such foundations for the oil and gas industry. For offshore wind turbines, however, new types of foundations are being considered for which neither prior experience nor guidelines exist. One of the major challenges is to develop a method to de-risk the life cycle of offshore wind turbines in diverse metocean and geological conditions. The paper, therefore, has the following aims: (a) provide an overview of the complexities and the common SLS performance requirements for offshore wind turbine; (b) discuss the use of physical modelling for verification and validation of innovative design concepts, taking into account all possible angles to de-risk the project; and (c) provide examples of applications in scaled model tests.

scholarly journals Karhunen–Loeve representation of stochastic ocean waves

2012 ◽  
Vol 468 (2145) ◽  
pp. 2574-2594 ◽  
Author(s):  
Paul D. Sclavounos
Keyword(s):  
Wind Turbines ◽  
Ocean Waves ◽  
Offshore Wind ◽  
Yield Enhancement ◽  
Energy Yield ◽  
Offshore Platforms ◽  
Stochastic Representation ◽  
Nonlinear Loads ◽  
Floating Offshore Wind Turbines ◽  
Order Of Magnitude

A new stochastic representation of a seastate is developed based on the Karhunen–Loeve spectral decomposition of stochastic signals and the use of Slepian prolate spheroidal wave functions with a tunable bandwidth parameter. The new representation allows the description of stochastic ocean waves in terms of a few independent sources of uncertainty when the traditional representation of a seastate in terms of Fourier series requires an order of magnitude more independent components. The new representation leads to parsimonious stochastic models of the ambient wave kinematics and of the nonlinear loads and responses of ships and offshore platforms. The use of the new representation is discussed for the derivation of critical wave episodes, the derivation of up-crossing rates of nonlinear loads and responses and the joint stochastic representation of correlated wave and wind profiles for use in the design of fixed or floating offshore wind turbines. The forecasting is also discussed of wave elevation records and vessel responses for use in energy yield enhancement of compliant floating wind turbines.

scholarly journals A Review of Recent Advancements in Offshore Wind Turbine Technology

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 579
Author(s):  
Taimoor Asim ◽  
Sheikh Zahidul Islam ◽  
Arman Hemmati ◽  
Muhammad Saif Ullah Khalid
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Offshore Wind ◽  
System Level ◽  
Offshore Wind Turbine ◽  
Component Level ◽  
Foundation Design ◽  
Offshore Wind Turbines

Offshore wind turbines are becoming increasingly popular due to their higher wind energy harnessing capabilities and lower visual pollution. Researchers around the globe have been reporting significant scientific advancements in offshore wind turbines technology, addressing key issues, such as aerodynamic characteristics of turbine blades, dynamic response of the turbine, structural integrity of the turbine foundation, design of the mooring cables, ground scouring and cost modelling for commercial viability. These investigations range from component-level design and analysis to system-level response and optimization using a multitude of analytical, empirical and numerical techniques. With such wide-ranging studies available in the public domain, there is a need to carry out an extensive yet critical literature review on the recent advancements in offshore wind turbine technology. Offshore wind turbine blades’ aerodynamics and the structural integrity of offshore wind turbines are of particular importance, which can lead towards system’s optimal design and operation, leading to reduced maintenance costs. Thus, in this study, our focus is to highlight key knowledge gaps in the scientific investigations on offshore wind turbines’ aerodynamic and structural response. It is envisaged that this study will pave the way for future concentrated efforts in better understanding the complex behavior of these machines.

Velocity inversion for the ocean bottom

1983 ◽  
Vol 73 (S1) ◽  
pp. S38-S38
Author(s):  
Frank G. Hagin
Keyword(s):  
Ocean Bottom ◽  
Velocity Inversion

scholarly journals A Method for Estimating the Distance of Near-Ocean-Bottom Sources by Combining VLF Underwater Acoustic Field and Scholte Wave Field

2018 ◽  
Vol 171 ◽  
pp. 012009
Author(s):  
Han Zhao ◽  
Guiqing Sun ◽  
Hanhao Zhu ◽  
Junxin Yuan
Keyword(s):  
Wave Field ◽  
Acoustic Field ◽  
Ocean Bottom ◽  
Underwater Acoustic ◽  
Scholte Wave

Probabilistic Investigation of Foundation Design for Offshore Gravity Structures

1976 ◽  
Vol 16 (02) ◽  
pp. 97-109 ◽  
Author(s):  
L.M. Kraft ◽  
J.D. Murff
Keyword(s):  
Prestressed Concrete ◽  
Soil Property ◽  
Probabilistic Method ◽  
Design Parameters ◽  
Ocean Bottom ◽  
Foundation Design ◽  
Sea Bed ◽  
Uncertainty Analyses ◽  
General Configuration ◽  
Important Design

Abstract This paper lays the groundwork for establishing foundation safety criteria for offshore gravity structures. The concepts are explained in terms of first- and second-order uncertainty analyses. Various uncertainties associated with foundation analyses are identified and applications are illustrated with examples. Introduction Gravity structures play a prominent role today in North Sea oil development. These structures are not supported by piles, as are most ocean structures, but rather sit directly on the ocean bottom and depend on their foundation geometries and large weights m resist severe environmental loadings. A number of structural and foundation configurations have been proposed; however, attention is restricted here to a general configuration typical of the most prominent structures presently being constructed. prominent structures presently being constructed. An example of a gravity structure is illustrated in Fig. 1. The structure foundation consists of a large caisson placed directly on the unprepared sea-bed surface. The deck is supported by large columns extending from the caisson. Various combinations of steel and reinforced concrete have been proposed, but most structures are being constructed almost entirely of reinforced and prestressed concrete. prestressed concrete. One of the primary engineering concerns with these structures is foundation design. Because of the variability associated with the environmental forces, as well as the basic soil properties, this problem lends itself well to modem probabilistic problem lends itself well to modem probabilistic procedures. Such procedures provide a rational, procedures. Such procedures provide a rational, quantitative means for evaluating uncertainties affecting appropriate design, even though a degree of subjectivity will always remain in any such evaluation. The probabilistic method requires the engineer to formally and consistently recognize die variability of many of the important design parameters. The method gives management and parameters. The method gives management and others responsible for setting design criteria an opportunity to appraise cost/benefits of design levels required for given reliability levels. It also quantifies reliability to permit direct comparison with other options. This paper presents a method for analyzing the reliability of gravity-structure foundations in terms of simple loading and resistance models. The sources of variability in estimating resistance to loads are discussed, with particular emphasis on the nature of soil-property variability and uncertainty. These concepts are illustrated through an analysis of a typical gravity-structure foundation. SPEJ P. 97

Probabilistic Analysis of Live Loads on Offshore Platform Piles

2005 ◽  
Author(s):  
Hassan Zaghloul ◽  
Beverley Ronalds ◽  
Geoff Cole
Keyword(s):  
Probabilistic Analysis ◽  
Field Measurements ◽  
Weather Conditions ◽  
Load Resistance ◽  
Live Load ◽  
Offshore Platforms ◽  
Open Area ◽  
Foundation Design ◽  
Live Loads ◽  
Load Intensity

Relatively accurate techniques are available to assess structural behavior under given loads, yet the loads themselves remain an estimate based in part on field measurements, in part on professional logic and experience, and in part on trial and error. The design of piled foundations for fixed offshore platforms must consider operating and extreme weather conditions. In the operating condition, the magnitude of live loads on open areas of topside structure is an important consideration. Unfortunately, the design live load intensity that applies to open areas on offshore platforms is not identified in international codes and standards. There does not appear to be any consensus on the value to be adopted in the industry. Some operators suggest the open area live loads need not be considered for pile foundation design, while others stipulate values such as 10 kPa. This is partly due to the variability associated with the different live loads sources. The objective of this study is to obtain a better understanding of open area live loads on offshore platforms and develop a methodology to obtain the long-term and extreme open area live load. A load survey was conducted for the purpose of this study, and a probabilistic analysis was carried out to derive the maximum axial load on piles that is expected during platform lifetime. The results of this study indicate that the use of a single value for the open area live load (OALL) may not be appropriate and suggest appropriate values for Load Resistance Factor Design (LRFD) or Working Stress Design (WSD) methods.

2-D velocity inversion/imaging of large offset seismic data via the tau‐p domain

Geophysics ◽  
1993 ◽  
Vol 58 (7) ◽  
pp. 1002-1016 ◽  
Author(s):  
Edmund C. Reiter ◽  
G. Michael Purdy ◽  
M. Nafi Toksöz
Keyword(s):  
Velocity Field ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Velocity Model ◽  
Intermediate Step ◽  
Ocean Bottom ◽  
Velocity Inversion ◽  
Best Fitting ◽  
Ray Parameter ◽  
Refraction Data

We describe a method for determining a two‐dimensional (2-D) velocity field from refraction data that has been decomposed into some function of slowness. The most common decomposition, intercept time‐slowness or [Formula: see text], is used as an intermediate step in an iterative wave field continuation procedure previously applied to one‐dimensional (1-D) velocity inversions. We extend the 1-D approach to 2-D by performing the downward continuation along numerically computed raypaths. This allows a correction to be made for the change in ray parameter induced by 2-D velocity fields. A best fitting velocity model is chosen as a surface defined by critically reflected and refracted energy that has been downward continued into a three dimensional (3-D) space of velocity, offset, and depth. Synthetic data are used to demonstrate how this approach can compensate for the effects of known lateral inhomogeneities while determining an underlying 1-D velocity field. We also use synthetic data to show how multiple refraction lines may be used to determine a general 2-D velocity model. Large offset field data collected with an Ocean Bottom Hydrophone are used to illustrate this technique in an area of significant lateral heterogeneity caused by a sloping seafloor.

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