Tesi sul tema "Seabed"
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1
Russell, Peter. "Stormcloud to seabed". Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/1074.
Testo completo
2
Eiesland, Ole Wostryck. "Estimating seabed velocities from normal modes". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for petroleumsteknologi og anvendt geofysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18514.
Testo completoAbstract (sommario):
In this Master Thesis a method for estimating seabed p-wave velocities from normal mode seismic data is developed. This is done through forward modeling using two dimensional finite difference modeling to generate synthetic data based on a given parallel two layered laterally varying seabed velocity model and a constant two layered density model, with a common fixed water depth. A semblance inversion technique is developed in MATLAB using the period equation eqref{eq:period} and the resulting velocity profiles is plotted against the exact velocity model to check the validity of the estimates. The same method is extended to estimations of seabed densities. For analysis of the robustness of the method, analysis with added pseudo random noise is preformed.The results shows a good performance of the semblance method to reproduce the model velocity parameters. The introduction of noise is handled well and decent results are obtained for significantly low signal to noise ratios.It suggests that the semblance method is applicable to use for determination of other parameters influencing the normal mode response signal.
3
Caughey, David Arthur. "Seabed classification from acoustic echosounder returns". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ32738.pdf.
Testo completo
4
Paskin, Sandra. "The self-burial of seabed pipelines". Thesis, University College London (University of London), 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327090.
Testo completo
5
Krotov, Mikhael. "Water waves over a muddy seabed". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45283.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 199-200).
A generalized viscoelastic model is used to describe the rheological properties of mud and is fitted to the available experimental data, so that its constitutive coefficients are just material properties independent of the frequency of the external forcing. We integrate this model into a perturbation analysis to solve the interaction between a thin layer of viscoelastic mud and sinusoidal waves propagating on top of a water layer of intermediate depth. In contrast with the previous studies the analysis is done for decaying water waves and a rheological model with frequency independent coefficients. The leading order motion and the mean second order motion inside the mud layer is determined analytically together with the first two orders motion in water. The analysis is done in a fixed Eulerian frame and it is shown that both a mean horizontal displacement and a Eulerian mean horizontal velocity exists inside the mud layer at the second order. The effect of elasticity and viscosity on the damping of water waves and on the mean motion of the mud is studied. It is shown that a light mud with a high proportion of elasticity will significantly modify the leading order movement through damping. The results are applied to solve analytically the problem of the evolution of the narrow-banded waves propagating on top of a semi-infinite mud layer. It is shown that the presence of the mud layer gives rise to a negative mean current in water layer and to free waves generated at the edge of the mud layer and propagating at the dimensional velocity ....
by Mikhael Krotov.
S.M.
6
Cheuk, Chi Yin. "Soil-pipeline interaction at the seabed". Thesis, University of Cambridge, 2005. https://www.repository.cam.ac.uk/handle/1810/272147.
Testo completo
7
Li, Zhengxu. "Seabed Instability around a Submerged Breakwater due to Dynamic Loadings". Thesis, Griffith University, 2019. http://hdl.handle.net/10072/387387.
Testo completoAbstract (sommario):
A breakwater is one of common offshore structures for protecting ports and coastlines.
Dynamic response of a seabed around a breakwater caused by the interactions between waves
and currents is a critical aspect in evaluating the stability of the breakwater foundation. The
existence of breakwater does not only affect the propagation pattern of nearby waves but also
has a particular influence on the stability of the surrounding seabed. Under the interaction of
waves and currents, liquefaction of the seabed foundation is one of main causes of breakwater
damage, which must be fully considered in the design and construction of breakwaters. The
periodic motion of waves exerts a cyclical pressure on the interface between seawater and
seabed. Due to the effect of the cyclic wave pressures, the wave-induced residual pore
pressure will increase, and the effective stress will decrease in the seabed, which could cause
soil displacements and seabed deformation. Thus, under certain conditions, the shear failure
and liquefaction of the seabed will occur. Furthermore, under the action of cyclic wave
pressure, the normal stress and shear stress of the soil element in the seabed are cyclically
changed which will cause the principal stress axis continuously to rotate. As a consequence,
the plastic deformation of the soil is more significant, and the seabed is more prone to
liquefaction.
In this study, a one-way coupled two-dimensional numerical model is established integrating
the fluid model and the seabed model. The soil liquefaction caused by the excess
pore water pressure in the seabed is calculated by using the elasto-plastic porous medium
soil model. The feasibility of the model was verified by comparison with the laboratory
experiments, the centrifuge tests, and the previous numerical model data. It is shown that
the numerical model can simulate the dynamic response of the seabed under wave-current
interaction with high accuracy.
By adopting the integrated numerical model, the dynamic seabed response generated by
the rotation of the principal stress (PSR) axis is analysed under the cyclic wave loading. It is
found that the PSR will affect the seabed dynamic response significantly. The liquefaction
depth of the case considered PSR is much deeper than the results which did not consider the
PSR effects, since the plastic strain of the soil caused by the PSR is involved in. Secondly,
the dynamic response of seabed under different uniform current velocity and different wave conditions are solved. It is found that the following current accelerates the accumulation of
pore water pressure, increases the displacement of the soil, and makes the seabed easier to
liquefy, while the opposing current has an opposite effect. Also, the dynamic response of the
seabed under wave loading is calculated, and detailed parameter analysis of the liquefaction
potential of the seabed are carried out, including wave parameters (wave height, wave period),
and seabed parameters (soil permeability, degree of saturation).
In order to figure out the influence of the breakwater, a new-developed coupled model
is established to simulate wave-seabed-breakwater interactions under cyclic wave loading.
Firstly, the consolidation of the seabed under the effect of the self-weight of the breakwater
is calculated. The dynamic response of the seabed around the breakwater and the seabed
liquefaction depth are computed after consolidation process. Secondly, the interaction
between wave and submerged breakwater is studied by the coupled numerical model. The
influence of the height and crest width of the breakwater on the wave propagation is analysed.
The variations of wave height in front of and behind the breakwater are compared. At the
same time, the influence of breakwater height and crest width on liquefaction depth and
liquefaction potential of seabed under wave action is analysed.Thesis (Masters)
Master of Philosophy (MPhil)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
8
Jin, Xing. "Fatigue of Pipelines resting on Uneven Seabed". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15794.
Testo completoAbstract (sommario):
Subsea pipelines represent the most cost effective way of transporting oil and gas from the subsea field to the market. A large network of subsea pipelines has therefore been installed both at the Norwegian continental shelf an elsewhere. In the near-shore areas of Norway, the seabed is irregular and pipeline free-spans are unavoidable. This in combination with significant current action, may cause vortex induced vibration (VIV) and fatigue in the pipeline welds. This project focus on studying the fatigue performance of free-spanning pipelines using a combination of FEM analysis and the DnV recommended practices.
9
Roos, Pieter Cornelis. "Seabed pattern dynamics and offshore sand extraction". Enschede : University of Twente [Host], 2004. http://doc.utwente.nl/50843.
Testo completo
10
Izedonmwen, Osaretin Ernest. "The environmental impact of deep seabed mining /". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59416.
Testo completoAbstract (sommario):
The deep seabed until the late sixties was a largely unknown part of the sea and represented nothing more than an academic curiosity. With technology making hitherto hidden depths of the ocean accessible for exploitation, it became known in the late sixties that the deep seabed contained precious minerals. In a world used to shrinking resources, this shot the deep seabed into the centre stage of world politics, becoming perhaps the most controversial issue in any United Nations Conference. The controversy centered around the legal status of the deep seabed. This work contends that there is not in place any viable international legal regime for supervising and regulating resource development in the deep seabed outside national jurisdiction; that whatever regulations there are, are geared towards facilitating exploitation of the area; that such lacunae would be at an environmental cost that could negate whatever short-term benefits are derivable therefrom.This work therefore examines the potential environmental impact of deep seabed mining and proposes a legal regime for preventing and minimizing same.
11
Ye, Jianhong. "Numerical analysis of Wave-Seabed-Breakwater interactions". Thesis, University of Dundee, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604579.
Testo completo
12
Swadi, Ghedhban. "A study of prediction in seabed mapping". Thesis, Cardiff Metropolitan University, 2010. http://hdl.handle.net/10369/2562.
Testo completoAbstract (sommario):
The aim of this research is to investigate the use of the modern prediction algorithms in seabed mapping. These prediction algorithms can be used in enhancing the quality of the measured bathymetric data to help in filtering the measured data and excluding noise from actual data to ensure higher seabed mapping accuracy for more secure navigation. The work involves the development of a general purpose sonar simulation platform to generate the required data for testing the different prediction algorithms. The simulation platform consists of a seabed simulator and an interferometric sonar simulator for bathymetric measurements. Two methods of building the seabed simulator have been investigated and applied; the fractal geometry based method and the random generator based method. The interferometric sonar simulator is based on SAS (Synthetic Aperture Sonar) which is a widely accepted modern technology. The predictors investigated in this work are based on KNN (K Nearest Neighbours) and dynamic ANN (Artificial Neural Networks). Both dynamic feedforward and dynamic recurrent networks are investigated. The comparison between the performances of these different predictors reveals that dynamic recurrent networks outperform the other types of predictors and the Nonlinear AutoRegressive eXogenous (NARX) Neural Network is the best.
13
Morrow, Damian. "Pipe-soil interaction on a clay seabed". Thesis, University of Dundee, 2016. https://discovery.dundee.ac.uk/en/studentTheses/a39e6fbb-c6f0-44cc-9419-4b018db357af.
Testo completoAbstract (sommario):
Subsea pipelines form an integral part of the infrastructure associated with offshore oil and gas developments. These pipelines fulfill a range of functions from linking extraction wells to other subsea infrastructure to transporting products onshore, or to a central processing facility. Ancillary pipelines may also be present for gas or water injection to the reservoir or transporting additives. Pipelines are typically installed directly onto the seabed and, in the absence of significant drivers to undertake burial operations, they may remain on the seabed for the remainder of their design life. This is typically the case for deepwater developments. Subsea pipelines are subjected to a wide range of load cases including, self weight, installation loads, thermal and pressure driven expansion and hydrodynamic loading. Design of pipeline systems to accommodate these load cases requires an understanding of pipe-soil interaction. This thesis reports the results of a research study investigating pipe-soil interaction on a clay seabed, as relevant to the design of subsea pipeline systems. This study has utilised numerical analysis techniques based on the finite difference code FLAC to investigate a range of problem definitions. These problem definitions include pipelines subject to both vertical loading (V) and combined vertical and horizontal (V-H) loading. Factors such as variation in interface conditions, large strain and large displacement effects, soil unit weight effects and variation in shear strength conditions were considered in these problem definitions. Reliability based analysis techniques have also been used to investigate both V and V-H loading problem definitions. The analyses and investigations undertaken as part of this study generally achieved the following; reproduction and validation of earlier research with additional interpretation, extension of problem definitions to deeper pipeline embedment depths and investigation of pipe-soil interaction problem definitions that have not previously been considered. Reliability based analysis techniques have also provided some interesting insights into the impact of soil shear strength variation as well as providing a fundamental link between safety factors and probability of failure. Application to design practice of this, and similar studies, has been considered as part of this thesis and potential areas for future research have also been suggested.
14
Stephenson, Fabrice. "Shellfisheries, seabed habitats and interactions in Northumberland". Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3482.
Testo completoAbstract (sommario):
A push for a more evidence based approach to management has resulted in the need for robust evidence of fisheries impacts (or lack thereof), including further research into fine-scale impacts of potting for which little evidence is available. The present work focusses on the inshore pot fishery in Northumberland, UK. Potting effort distribution maps - a combination of fishing vessel sightings recorded during routine patrols and fishing effort by the Northumberland Inshore Fisheries and Conservation Authority (NIFCA) – showed changes in potting effort across large sections of the study area between years (2004 – 2014). Temporal changes in fishers’ habitat selection were investigated using recently collected habitat data. Space-time clustering suggested fishers were actively targeting habitats of interest. Compositional analysis of habitat, showed that fishers preferred rocky habitats over sediment habitats when using both EUNIS level 3 and 6 habitat maps. Information on habitat use and fishing pressure provided the basis for investigation of long-term impacts of parlour potting on epibenthos and habitat within the Berwickshire & North Northumberland Coast European Marine Site (BNNC EMS) through analysis of historical videographic monitoring data between 2002 – 2011. Analysis of biotope change between years (a method recommended for monitoring purposes) showed that at the scales investigated here, change had not occurred. Weaknesses of this analysis for the use in robust ecological research are discussed. A more detailed analysis of community composition and diversity change between years showed that there was little evidence of change. However, changes in species composition and richness of ‘Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock’ were observed between years, in most models and between fishing pressures. Finally, quantification of direct impacts through in-situ experimental fishing was investigated using a BACI design. The high experimental fishing intensity, in small experimental areas, coupled with high levels of sampling and replication, provided iii robust evidence that current levels of potting are unlikely to have a direct physical impact on epibenthos in Faunal and algal crust, and Laminaria spp dominated habitats in Northumberland.
15
Kloser, Rudolf J. "Seabed biotope characterisation based on acoustic sensing". Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/524.
Testo completoAbstract (sommario):
The background to this thesis is Australia’s Oceans Policy, which aims to develop an integrated and ecosystem-based approach to planning and management. An important part of this approach is the identification of natural regions in regional marine planning, for example by establishing marine protected areas for biodiversity conservation. These natural regions will need to be identified on a range of scales for different planning and management actions. The scale of the investigation reported in this thesis is applicable to spatial management at 1 km to 10 km scale and monitoring impacts at the 10s of m to 1 km biotope scale. Seabed biotopes represent a combination of seabed physical attributes and related organisms. To map seabed biotopes in deep water, remote sensing using a combination of acoustic, optical and physical sensors is investigated. The hypothesis tested in this thesis is that acoustic bathymetry and backscatter data from a Simrad EM1002 multi-beam sonar (MBS) can be used to infer (act as a surrogate of) seabed biotopes. To establish a link between the acoustic data and seabed biotopes the acoustic metrics are compared to the physical attributes of the seabed in terms of its substrate and geomorphology at the 10s m to 1 km scale using optical and physical sensors. At this scale the relationship between the dominant faunal functional groups and both the physical attributes of the seabed and the acoustic data is also tested. These tests use data collected from 14 regions and 2 biomes to the south of Australia during a voyage in 2000. Based on 62 reference sites of acoustic, video and physical samples, a significant relationship between ecological seabed terrain types and acoustic backscatter and bathymetry was observed.These ecological terrain types of soft-smooth, soft-rough, hard-smooth and hard-rough were chosen as they were the most relevant to the biota in their ability to attach on or burrow into the seabed. A seabed scattering model supported this empirical relationship and the overall shape of backscatter to incidence angle relationship for soft and hard seabed types. The correlation between acoustic data (backscatter mean and standard deviation) and the visual and physical samples was most consistent between soft-smooth and hard-rough terrain types for a large range of incidence angles (16o to 70o). Using phenomenological backscatter features segmented into 10 common incidence angle bins from -70o to 70o the length resolution of the data decreased to 0.55 times depth. The decreased resolution was offset by improved near normal incidence (0o to 30o) seabed type discrimination with cross validation error reducing from 32% to 4%. A significant relationship was also established between the acoustic data and the dominant functional groups of fauna. Faunal functional groups were based on the ecological function, feeding mode and substrate preference, with 8 out of the 10 groups predicted with 70% correctness by the four acoustically derived ecological terrain types. Restricting the terrain classification to simple soft and hard using the acoustic backscatter data improved the prediction of three faunal functional groups to greater than 80%. Combining the acoustic bathymetry and backscatter data an example region, Everard Canyon, was interpreted at a range of spatial scales and the ability to predict the preferred habitat of a stalked crinoid demonstrated.Seabed terrain of soft and hard was predicted from the acoustic backscatter data referenced to a common seabed incidence angle of 40o. This method of analysis was selected due to its combined properties of high spatial resolution, consistent between terrain discrimination at the widest range of incidence angles and consistent data quality checking at varying ranges. Based in part on the research reported in this thesis a mid-depth Simrad EM300 multibeam sonar was purchased for use in Australian waters. A sampling strategy is outlined to map all offshore waters with priority within the 100 m to 1500 m depths.
16
Kloser, Rudolf J. "Seabed biotope characterisation based on acoustic sensing". Curtin University of Technology, Faculty of Science and Engineering, Department of Imaging and Applied Physics, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=18566.
Testo completoAbstract (sommario):
The background to this thesis is Australia’s Oceans Policy, which aims to develop an integrated and ecosystem-based approach to planning and management. An important part of this approach is the identification of natural regions in regional marine planning, for example by establishing marine protected areas for biodiversity conservation. These natural regions will need to be identified on a range of scales for different planning and management actions. The scale of the investigation reported in this thesis is applicable to spatial management at 1 km to 10 km scale and monitoring impacts at the 10s of m to 1 km biotope scale. Seabed biotopes represent a combination of seabed physical attributes and related organisms. To map seabed biotopes in deep water, remote sensing using a combination of acoustic, optical and physical sensors is investigated. The hypothesis tested in this thesis is that acoustic bathymetry and backscatter data from a Simrad EM1002 multi-beam sonar (MBS) can be used to infer (act as a surrogate of) seabed biotopes. To establish a link between the acoustic data and seabed biotopes the acoustic metrics are compared to the physical attributes of the seabed in terms of its substrate and geomorphology at the 10s m to 1 km scale using optical and physical sensors. At this scale the relationship between the dominant faunal functional groups and both the physical attributes of the seabed and the acoustic data is also tested. These tests use data collected from 14 regions and 2 biomes to the south of Australia during a voyage in 2000. Based on 62 reference sites of acoustic, video and physical samples, a significant relationship between ecological seabed terrain types and acoustic backscatter and bathymetry was observed.These ecological terrain types of soft-smooth, soft-rough, hard-smooth and hard-rough were chosen as they were the most relevant to the biota in their ability to attach on or burrow into the seabed. A seabed scattering model supported this empirical relationship and the overall shape of backscatter to incidence angle relationship for soft and hard seabed types. The correlation between acoustic data (backscatter mean and standard deviation) and the visual and physical samples was most consistent between soft-smooth and hard-rough terrain types for a large range of incidence angles (16o to 70o). Using phenomenological backscatter features segmented into 10 common incidence angle bins from -70o to 70o the length resolution of the data decreased to 0.55 times depth. The decreased resolution was offset by improved near normal incidence (0o to 30o) seabed type discrimination with cross validation error reducing from 32% to 4%. A significant relationship was also established between the acoustic data and the dominant functional groups of fauna. Faunal functional groups were based on the ecological function, feeding mode and substrate preference, with 8 out of the 10 groups predicted with 70% correctness by the four acoustically derived ecological terrain types. Restricting the terrain classification to simple soft and hard using the acoustic backscatter data improved the prediction of three faunal functional groups to greater than 80%. Combining the acoustic bathymetry and backscatter data an example region, Everard Canyon, was interpreted at a range of spatial scales and the ability to predict the preferred habitat of a stalked crinoid demonstrated.
Seabed terrain of soft and hard was predicted from the acoustic backscatter data referenced to a common seabed incidence angle of 40o. This method of analysis was selected due to its combined properties of high spatial resolution, consistent between terrain discrimination at the widest range of incidence angles and consistent data quality checking at varying ranges. Based in part on the research reported in this thesis a mid-depth Simrad EM300 multibeam sonar was purchased for use in Australian waters. A sampling strategy is outlined to map all offshore waters with priority within the 100 m to 1500 m depths.
17
Gontz, Allen M. "Evolution of Seabed Pockmarks in Penobscot Bay, Maine". Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/GontzAM2002.pdf.
Testo completo
18
Rein, Henk B. van. "Monitoring methods for assessing change in seabed habitats". Thesis, University of Ulster, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553879.
Testo completoAbstract (sommario):
This research demonstrates the utility of repeat acoustic and photographic surveys for monitoring biotopes and hard-substratum communities in temperate waters. Kappa analysis of results derived from time-lapse backscatter surveys conducted at Church Bay, Rathlin Island (1999,2008 and 2009) indicate that the spatial distribution of biotopes is highly similar between each biotope map, possibly due to the stability of bedforms shaped by the local tidal regime. Maximum change is represented by seasonal and annual changes in the growth of Zostera marina. Changes induced by kelp harvesting are not detected in backscatter data. Low-cost photo-mosaics derived from stills and video imagery of fixed quadrats (1 OO-x-l 00 cm) are compared. Although video-collection is quicker, more species and less-conspicuous taxa are identified from stills imagery. Data extraction using point-intercepts proves efficient and generates data sensitive to 10% community change (N=16), but detects fewer species than the visual estimation measure. Frequency-of-occurrence extraction measures significantly over-estimate benthic cover. Seasonal growth, recruitment and mortality of Caryophyllia smithii, Hymeniacidon perleve and Plocamium cartilagineum are estimated to nearest 0.04 ern? month-l using digitisation. The presence of algal canopies reduce the accuracy of sessile-invertebrate cover estimates in spring and summer. Exploratory analysis of results from photoquadrat surveys conducted at Damicornis Bay, Rathlin Island (2009 and 2010), identifies six distinct sub-communities on a boulder slope. Community variability obscures detection of change. However, analysis of the most dominant sub-community indicates that boulder-slope community shifted, possibly due to local erosion of sediment. Optimal balance between precision, efficiency and species-detection ability for photoquadrats (25-x-25 cm) is 50 points-per-image. Functional groups retain structural relevance of communities, while improving precision, sensitivity and efficiency of data extraction and community-representation measures relative to full-species compositions. Continued monitoring of hard-substratum communities using high-resolution photoquadrats and fixed-photomosaics is recommended.
19
Bridge, Christopher. "Effects of seabed interaction on steel catenary risers". Thesis, University of Surrey, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431127.
Testo completo
20
Shabani, Behnam. "Wave-Associated Seabed Behaviour near Submarine Buried Pipelines". Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3532.
Testo completoAbstract (sommario):
Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.
21
Shabani, Behnam. "Wave-Associated Seabed Behaviour near Submarine Buried Pipelines". University of Sydney, 2008. http://hdl.handle.net/2123/3532.
Testo completoAbstract (sommario):
Master of Engineering (Research)Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.
22
Williams, Sally Jayne. "Wave-seabed interaction in a stratified coastal environment". Thesis, The University of Sydney, 2010. https://hdl.handle.net/2123/28910.
Testo completoAbstract (sommario):
The attenuation of non—breaking waves in shallow waters can be dominated by soft seabed
effects as opposed to water viscosity. Due to the complexity of natural systems, rheological
approaches can provide useful parameter constraints on natural behaviours.
In part I of this thesis a layered rheological model of the seabed is adopted. The upper part
of the seabed is considered to be in a state of dynamic liquefaction, whilst the lower portion
of the bed is more consolidated. It is demonstrated that in the absence of wave-induced
turbulence the magnitude of the surface wave damping due to the presence of the porous
bed is greater than that due to shear at the interface between the two fluids. For the case
of a shallow layer of fluidised bed material, it is shown that the maximum damping effect of
the porous elastic bed coincides with the maximum damping rates due to boundary layer
shear effects, thus accentuating wave damping when the dimensionless lower layer depth is
approximately 30—50% greater than the non—dimensionalised boundary—layer thickness.
In part II of this thesis a model for the interaction between interfacial waves with the
seabed is considered. A new wave dispersion equation is derived for waves on a two-layer
stratification above a porous seabed including free surface effects. Numerical results indicate
that the wavelength and wave amplitude are attenuated faster by a coarse seabed material
as opposed to a fine sandy bed. It is shown that the profile of an interfacial wave exhibits
properties similar to that of an interfacial wave propagating above a rigid bed and agrees
qualitatively with observations of interfacial waves in littoral waters. The effect of a porous
elastic bed is to increase the wave steepness, causing a narrower crest and a Wider trough.
Comparison of the numerical results with experimental results on the different mechanisms
for interfacial wave decay show that, in water of intermediate depth, the energy attenuation
caused by a coarse—grained sandy seabed is greater than that due to bottom boundary layer
damping, interfacial wave shear or interior Viscous damping.
23
Wang, Yuchen. "Stress Analysis of Seabed Using Finite Difference Modelling". Thesis, Griffith University, 2016. http://hdl.handle.net/10072/366693.
Testo completoAbstract (sommario):
Coastal structures are always facing the threat of damage caused by different wave actions. A better understanding of different seabed behaviours could effectively reduce the damage caused by waves. In this thesis, four different models (u-w-p, u-p, u and w-p) are developed to analyse the different behaviours of seabeds composed of fine granular soil (silt and normally consolidated clay) and coarse granular soil (loose sand, dense sand, and gravel). In relation to the u-w-p model, which is also the most important and comprehensive one used in this study, acceleration, velocity and displacement were considered, with the three important parameters being analysed: pore water pressure, effective stress, and shear stress.
The purpose of this research was to illustrate the general behaviour of various seabeds under wave actions, and to clarify the roles of different seabed soil parameters, then to identify the probability of liquefaction and shear failure for seabed composed of different materials. The research also sought to compare the different behaviour of fine granular soil and coarse granular soil, especially via a detailed description of the behaviour of fine granular soil, and giving a wider picture of seabed response under wave actions, which has not been studied in previous research and could become an important foundation in further analysis of fine grained seabed.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text
24
Wang, Xiaoxiao. "Numerical Studies for Seabed Response around Marine Structures". Thesis, Griffith University, 2020. http://hdl.handle.net/10072/394681.
Testo completoAbstract (sommario):
Seabed instability induced by flow fluctuations is of particular significance for coastal engineers involved in design the soil foundation of offshore infrastructures, such as pipelines, breakwaters, and anchors and piles. Soil liquefaction generally occurs under cyclic loading when the excess pore water pressure overcomes the effective stress. The liquefied foundation will be incapable of supporting marine constructions and consequently structure damage and destruction will be induced because the soil will behave like heavy fluid and the shear resistance will vanish. The present study provides a new numerical model to simulate the soil behaviour for the water-structure-soil interactions.
The conventional approaches for the wave-induced soil response, such as finite element method, finite volume method and finite difference method, have been reported in the literature. These techniques have been evolved and matured over the past decades and reliable results can be accessed. However, meshing is a time-consuming procedure during establishing a model. Moreover, mesh singularity is a challenging issue although it appears easily for the computational domain with a large deformation. In contrast to that, meshless methods attracted growing attentions from researchers because of its strong features, such as handling cases with a complex boundary or large deformation precisely. Furthermore, the continuity problem of interpolation can be improved. The adoption of meshless methods will reduce data storage and computational time. In the present study, a meshless approach is applied to establish fluid-seabed-structure models for marine pipelines or breakwaters.
The present numerical modelling framework involves two sub-models associated with the fluid and soil field. The first is developed within OpenFOAM, in which the VARANS equations are solved. Finite difference two-step projection method and the forward time difference method are used for the space and temporal discretization, respectively. Biot’s equations are used to governing the behaviour of soil sediments, meanwhile local radial basis function collocation method and Crank-Nickson method are employed for space and temporal discretization, respectively. A one-way coupling algorithm is implemented on the interface between the flow water and solid domain.The dynamic wave pressure simulated in the hydrodynamic process will be exerted on the seabed and structure surface as a boundary condition based on the grid nodes of geotechnical model.
The geotechnical model including marine structures in this study is a new meshfree model. Numerical simulations are implemented and validated with a series of analytical solutions and experimental results. After the accuracy and capability of the integrated model is confirmed, it is used to obtain the dynamic soil behaviour around marine structures, especially evaluating the potential failure risks for structures induced by liquefaction occurring in loosely deposited sand foundations.
Computational outcomes illustrate that the newly proposed meshless geotechnical model is reliable to estimate wave-induced dynamic soil response, such as pore water pressure, effective stresses and shear stress, as well as the development of liquefaction depth from the seafloor or under the bottom of structures. It can be found that wave characteristics, soil properties and configuration of offshore pipeline or breakwater affect the distribution of liquefaction zone in the vicinity of marine structures considerably. The influence of wave randomness on the soil behaviour is presented, which demonstrates that random wave is a significant component during the design phase of offshore structure foundation.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
25
Schmidt, M. "Common heritage or common burden? : The United States position on the development of a regime for deep seabed mining in the Law of the Sea Convention". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376001.
Testo completo
26
Condon, Patrick J. "Seismic stratigraphy and distribution of Palaeogene sediments west and east of Shetland". Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/13452.
Testo completo
27
Ludvigsen, Martin. "An ROV toolbox for optical and acoustical seabed investigations". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for marin teknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14121.
Testo completoAbstract (sommario):
This thesis describes a set of optical and acoustical methods for documenting a research site using underwater vehicles. The need for observations in cold-water coral research has formed the design problem in this work. A common survey protocol template is developed to describe video-, bathymetry-, photo mosaic- and photogrammetry surveys. For photogrammetry, the body of knowledge is small, and it was necessary to develop a new method rather than adapting existing methods. Axiomatic design methodology is applied to create the protocol template. Functional requirements for documenting these biological communities have been established and matched with solutions found in academic literature, industry standards and established best practice from hydrography, offshore subsea sector and related research disciplines. The protocols provide guidelines for design of all phases of scientific surveys from planning to survey reporting. The first step in the survey design is to evaluate the practical constraints, the purpose of the operation and to establish requirements for the desired data products. Step two is to choose and configure the survey instruments using the information from step one. To create a plan for the operation containing a description of central parameters like survey lines, line spacing and necessary vehicle velocity the results from step one and two are applied. Step four is the final step in the survey design process where the data processing pipeline is compiled based on the previous design steps. The survey protocols presented are followed by data examples collected by the candidate to show their relevance and application. The survey methods presented are complimentary with different levels of coverage and data resolution to cover a range of scales to address subjects like target confirmation, search, coral reef mapping and detailed documentation of individual specimen. Sonar surveys represent high coverage and low data resolution, while photogrammetry on the contrary provides high data resolution and low coverage. This thesis may contribute to the establishment of a common practise for marine science using ROV for data acquisition. This can enhance the value of ROV-based surveys. The efficiency in data acquisition operations will increase and the value of the collected data increases if one succeeds standardizing operations.
28
Harrison, Mark James. "P-wave AVAz analysis from noisy seabed seismic recordings". Thesis, Birkbeck (University of London), 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504740.
Testo completoAbstract (sommario):
In this thesis, I assess the impact of data quality on the use of P-wave seabed seismic recordings for fracture characterisation. A noise removal technique for removing refracted noise from dual-sensor OBC records was developed and tested on 2D data. A practical correlation based approach to dual-sensor summation was devised, tested on real and synthetic data, and compared with existing approaches. A North Sea seafloor seismic dataset was processed into azimuth sector stacks which were used to map amplitude differences between azimuths, highlighting regions of anisotropic variation. Subsequent azimuthal amplitude analysis (AVAz) used the concept of the effective angle of incidence of a stacked reflection to implement surface fitting. The AVOA fits and subsequent fracture interpretation were constrained by modelling a range of fluid-fill and crack properties using information from a nearby well. Maps of fits to the orientation and magnitude of anisotropy produced at each CMP, proved to be biased due to poor signal-tonoise ratios (SIN). To improve the fits analysis was performed over groups of CMPs where the AVOA parameters were expected to be stable, improving the SIN ratio. Testing these AVAz fits against no variation with azimuth showed them to be insignificant, due to the low SIN (3.5) of this data. The impact of different levels of noise on AVAz fitting was determined for the rock properties of this North Sea data, highlighting a requirement for a SIN greater than 10 for meaningful fracture orientation estimates. This was extended to the general case of AVO classes I and III, for a range of azimuth sampling, showing the level of SIN required to reliably fit an AVAz signature. Variations in fold associated with creating restricted azimuth stacks were assessed, as were variations in the effective angle of incidence. Maps of timing errors between azimuth stacks associated with centring on the peak everit were also created. These maps aid interpretation of the AVAz showing regions of low fold, unreliable picks and changes in the vent position with azimuth.
29
Wong, Yat Seng. "A beach and seabed crawling UUV for oceanographic measurements". Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399321.
Testo completo
30
Giuliani, Giorgio. "Experimental study of ice gouging in a sand seabed". Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=201897.
Testo completoAbstract (sommario):
This thesis aims to investigate ice gouging processes in general and the influence of geotechnical parameters on subgouge deformation. A sand channel has been built up at the University of Aberdeen where a number of scaled models of iceberg have been tested. A number of scaled models were manufactured with a base 150 x150mm and different shapes (specifically with the front face angle of 90°, 75º, 60° and 30°) to represent the part of the iceberg below the water line as a rigid body. During the tests several parameters were varied such as: the velocity at which the iceberg models were towed/moved, their mass and shape, and the soil density. All tests were performed in cohesionless soil, dry silica sand placed in a wooden channel. At this stage two different types of tests were carried out: tests at free penetration and tests at fixed penetration. The effects of the iceberg geometry under these various conditions were explored using an instrumented model gouge, with particular attention paid to the resulting tow force and penetration. Tests at free penetration showed that the penetration (P) of the object into the seabed is influenced by its weight and shape as it increased with an increase of the mass and the front face angle (P90º > P75º > P60º > P30º). The drag force (F) is also considered and it increases with an increase in penetration and mass of the object due to the mound of sand formed at front. For tests at fixed penetration (20mm and 30mm depth from the top surface) the attention was on the drag force which was influenced by the shape of the ice models (F90º < F60º < F30º). Pressure sensors were positioned inside the tank from the start point aligned long the same vertical. The purpose was to measure the stress within the seabed during the ice gouging event exerted by the front mound formed on the front of the object. Results showed that the pressure induced by the object decreased with the depth. The test results were compared to an empirical model developed by Kioka (2006) and Barrette (2011). A burial depth of pipeline has been proposed based on the physical gouge model which may allow trenching contractors to make better predictions of ice gouging performance in sands.
31
Merxhani, Andi. "Analytical and numerical study of poroelastic wave-seabed interactions". Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648743.
Testo completo
32
Hadden, Scott Duncan. "Remote geotechnical classification of seabed sediments using acoustic techniques". Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/13953.
Testo completoAbstract (sommario):
Although the sonar amplitude of return is undoubtedly determined by the acoustic-sediment interaction at the seabed, the raw amplitude of return is of little practical use to geotechnical engineers. By focusing upon the relationships between the strength of the acoustic scattering and the roughness of the surficial seabed sediments, this research aims to derive a remote acoustic methodology that can be used to predict the geotechnical characteristics of the seabed sediment. The main field survey areas selected were Loch Earn, Scotland, and the Portsmouth coastal waters in the Solent, England, with the precise location of the field sites being determined by the distribution of differing sediment types. The sonar data was acquired by a 234kHz Interferometric Seabed Inspection Sonar system, which provided not only high precision and high resolution, but also extensive and very dense data coverage. These sonar datasets were then complemented by a sediment ground-truthing programme within the same area. Using trigonometry and the 'sonar equation' parameters, the complex post-processing of the bathymetric and acoustic data resulted in the generation of an acoustic roughness measurement. The sediment grain size analysis then followed standard techniques to derive values for the statistical roughness parameters of the sediment. The correlation between the acoustic and sediment roughness uncovered a good correlation between the mean grain size and also the finest modal value, with an increase in acoustic scattering strength reflecting an increase in the mean and finest modal grain sizes. The reversal of this correlation therefore enables a prediction of mean or finest modal grain size, thereby demonstrating an approach towards an 'unsupervised' acoustic sediment classification scheme. This study was carried out over a very narrow grain size range, from muds to fine sands, and therefore the addition of sonar datasets recorded over coarser sediments are required to complete the classification scheme.
33
Teh, Thiam Chuan. "Stability of marine pipelines on unstable and liquefied seabed". Thesis, University of Cambridge, 2003. https://www.repository.cam.ac.uk/handle/1810/272024.
Testo completo
34
Varayudej, Same. "The international deep seabed mining regime and third states". Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26618.
Testo completoAbstract (sommario):
This thesis analyses the legal effects on third States of the deep seabed mining regime embodied in the 1982 Law of the Sea Convention. As a general rule, a treaty can neither impose obligations, nor confer rights, upon a third State without its consent. However, the thesis argues that the legal position of the third States could be affected by the Convention's regime in one or more of the following ways: namely, the objective legal personality of the International Seabed Authority, the customary status of the common heritage principle, the concept of an "objective regime" and the concept of an obligation erga omnes. The thesis examines these concepts in turn, relying on the assumption that the Convention (including Part XI) will come into force in its present form with widespread acceptance from many States including some major industrialized States, and that some States, particularly the US, will remain non-parties to the Convention. Finally, the thesis examines the interim obligations of certain industrialized States which are signatories to the Convention in the context of the compatibility of the reciprocating States regime with the Convention's regime.
35
Ainsworth, Stephen E. "The reflection and scattering of sound from the seabed". Thesis, University of Bath, 2001. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340931.
Testo completo
36
Granli, Petter. "Semantic segmentation of seabed sonar imagery using deep learning". Thesis, Linköpings universitet, Programvara och system, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-160561.
Testo completoAbstract (sommario):
For investigating the large parts of the ocean which have yet to be mapped, there is a need for autonomous underwater vehicles. Current state-of-the-art underwater positioning often relies on external data from other vessels or beacons. Processing seabed image data could potentially improve autonomy for underwater vehicles. In this thesis, image data from a synthetic aperture sonar (SAS) was manually segmented into two classes: sand and gravel. Two different convolutional neural networks (CNN) were trained using different loss functions, and the results were examined. The best performing network, U-Net trained with the IoU loss function, achieved dice coefficient and IoU scores of 0.645 and 0.476, respectively. It was concluded that CNNs are a viable approach for segmenting SAS image data, but there is much room for improvement.
37
Lau, Ryan. "A 3D finite-element modelling investigation into optimal survey parameters and direct imaging for marine controlled-source electromagnetic surveys". Texas A&M University, 2003. http://hdl.handle.net/1969.1/5790.
Testo completoAbstract (sommario):
Relatively little is known about marine controlled-source electromagnetic
surveys (MCSEM) used to detect hydrocarbon reservoirs. Typical MCSEM require the
use of inversion to generate a model of the subsurface. We utilize a 3D finite-element
forward model to simulate a MCSEM survey. With the results we were able to
determine the strengths and weaknesses of each transmitter and receiver configuration
that would best detect a shallow hydrocarbon target. Careful selection of the correct
configuration is important as we have found that incorrect transmitter orientation, offset
and receiver measurement component can yield misleading results. Using the ideal
configuration we were able to directly image the hydrocarbon target without the use of
inversion modeling. The direct image is able to show the hydrocarbon target's shape
and edges without any ambiguity. The direct image of the target can potentially be used
to refine 3D inversion modeling, or be used in conjunction with seismic profiles to refine
seismic picks.
38
Kay, Robert Charles. "An integrated approach into modern and ancient wave ripple morphology and ridge/runnel dynamics". Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327789.
Testo completo
39
Lepper, Paul Andrew. "The development and testing of a parametric sonar system for use in sediment classification and the detection of buried objects". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/32977.
Testo completoAbstract (sommario):
This thesis describes the work carried out in the development and testing of parametric sonar systems for application in the fields of seabed sediment characterisation and classification, and the detection of seabed embedded objects. Parametric sonar systems offer a number of advantages over conventional sonar systems. This is especially true of the conflicting requirements of both seabed delineation and penetration required for a practical sub-seabed profiling system. Echoes from sub-bottom layers vary in strength dependent on both the boundary acoustic reflectivity and the absorption characteristics of the layer above. Absorption effects are usually frequency dependent, allowing better penetration to lower frequency signals.
40
Veen, Hennie Henriët van der. "Natural and human induced seabed evolution the occurrence of large-scale bad patterns and the effects of human activities on the North Sea seabed /". Enschede : University of Twente [Host], 2008. http://doc.utwente.nl/58721.
Testo completo
41
Evans, Gareth. "Seabed protection systems to prevent scour from high-speed ships". Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4648.
Testo completoAbstract (sommario):
This document reviews the scour protection systems required around port structures where these are to be used for the berthing of vessels powered by water jet systems. The development of a scour protection system at Poole Harbour in Dorset has been documented and reviewed and a series of laboratory investigations were then undertaken. This has enabled a greater understanding of the scour mechanisms from the water jet propulsion systems of High Speed Ships. This work has shown that current design guidance on scour protection is not appropriate for use on berths used by High Speed Ships, that failure of these systems can occur rapidly and catastrophically, and secondary effects from water jets may promote the failure of quay walls. The scour protection system should comprise two individual elements, a filter layer and an armour layer. It has been found that systems involving individual isolated armour units are inappropriate and prone to failure and that shaped linked armour blocks need to be used. The loads on the armour layer were also found to be oscillatory and the materials used for both the armour and filter layers need to be designed for cyclic fatigue loading and fretting. Water jets are also capable of reducing the strength of permeable, seabed strata.
42
Heald, Gary J. "An analysis of normal incidence acoustic backscatter for seabed discrimination". Thesis, University of Bath, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341149.
Testo completo
43
Casullo, Caterina. "Japan and seabed mining : policy in a changing global context". Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308488.
Testo completo
44
Garnier, Erell-Isis. "Long waves in water over a visco-elastic muddy seabed". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67613.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 289-290).
The propagation of surface waves over a flat muddy seabed are studied. Mud is first considered as a Newtonian fluid. Water and mud equations are derived in order to obtain governing equation for surface and interface waves. By the method of multiple scales. nonlinear evolution equations are derived for the harmonic amplitudes. These equations are numerically solved for a finite number of harmonics to show the behavior of surface and interface motions. A drift current in mud is found at the second order., meaning that surface waves induce mud motion. Equation governing the total wave energy variation is derived and used to verify the accuracy of numerical solutions. The model is extended to viscoelastic mud, using the results of four experiments carried on different types of muds. These muds range from very elastic to rather viscous, allowing us to compare hie differences in behavior. Surface and interface variations. mud drift current and energy variations are plotted and compared to the results with Newtonian muds. A sloping muddy seabed is then considered. Mud is modeled as viscoelastic to avoid a constant static current that would happen with Newtonian mud. By the method of multiple scales and by introducing a space-dependent wavenumber, mud drift current and energy variation equations are derived again, taking into account the effect of the slope. An analytic stud v of the surface variations demonstrates that surface and interface waves, as well as drift current, exponentially decay to reach a zero value at the shore.
by Erell-Isis Garnier.
S.M.
45
Harrison, Richard John Patrick. "Machine learning methods for discriminating natural targets in seabed imagery". Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/48800/.
Testo completoAbstract (sommario):
The research in this thesis concerns feature-based machine learning processes and methods for discriminating qualitative natural targets in seabed imagery. The applications considered, typically involve time-consuming manual processing stages in an industrial setting. An aim of the research is to facilitate a means of assisting human analysts by expediting the tedious interpretative tasks, using machine methods. Some novel approaches are devised and investigated for solving the application problems. These investigations are compartmentalised in four coherent case studies linked by common underlying technical themes and methods. The first study addresses pockmark discrimination in a digital bathymetry model. Manual identification and mapping of even a relatively small number of these landform objects is an expensive process. A novel, supervised machine learning approach to automating the task is presented. The process maps the boundaries of ≈ 2000 pockmarks in seconds - a task that would take days for a human analyst to complete. The second case study investigates different feature creation methods for automatically discriminating sidescan sonar image textures characteristic of Sabellaria spinulosa colonisation. Results from a comparison of several textural feature creation methods on sonar waterfall imagery show that Gabor filter banks yield some of the best results. A further empirical investigation into the filter bank features created on sonar mosaic imagery leads to the identification of a useful configuration and filter parameter ranges for discriminating the target textures in the imagery. Feature saliency estimation is a vital stage in the machine process. Case study three concerns distance measures for the evaluation and ranking of features on sonar imagery. Two novel consensus methods for creating a more robust ranking are proposed. Experimental results show that the consensus methods can improve robustness over a range of feature parameterisations and various seabed texture classification tasks. The final case study is more qualitative in nature and brings together a number of ideas, applied to the classification of target regions in real-world sonar mosaic imagery. A number of technical challenges arose and these were surmounted by devising a novel, hybrid unsupervised method. This fully automated machine approach was compared with a supervised approach in an application to the problem of image-based sediment type discrimination. The hybrid unsupervised method produces a plausible class map in a few minutes of processing time. It is concluded that the versatile, novel process should be generalisable to the discrimination of other subjective natural targets in real-world seabed imagery, such as Sabellaria textures and pockmarks (with appropriate features and feature tuning.) Further, the full automation of pockmark and Sabellaria discrimination is feasible within this framework.
46
Ong, Paul Pang Awn. "Modelling seabed interaction in frequency domain analysis of mooring cables". Thesis, University of Cambridge, 2004. https://www.repository.cam.ac.uk/handle/1810/272080.
Testo completo
47
Van, Komen David Franklin. "Deep Learning to Predict Ocean Seabed Type and Source Parameters". BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9213.
Testo completoAbstract (sommario):
In the ocean, light from the surface dissipates quickly leaving sound the only way to see at a distance. Different sediment types on the ocean floor and water properties like salinity, temperature, and ocean depth all change how sound travels across long distances. Hard sediment types, such as sand and bedrock, are highly reflective while softer sediment types, such as mud, are more absorptive and change the received sound upon arrival. Unfortunately, the vast majority of the ocean floor is not mapped and the expenses involved in creating such a map are far too great. Traditional signal processing methods in underwater acoustics attempt to localize sources and estimate seabed properties, but require a priori decisions and fall victim to ill conditioning and non-linear relationships between the unknowns and are computationally expensive. To address these problems, a deep learning method is proposed to distinguish between seabed types while also predicting source parameters such as source-receiver range from simulated training data. In this thesis, several studies are presented that explore the effectiveness of convolutional neural networks to make predictions from two types of sounds that propagated through the ocean: impulsive explosions and ship noise. These studies show that time-series signals and spectrograms contain sufficient information for deep learning, and additional preprocessing for feature extraction is not necessary. Training data considerations, such as randomness in the network weights and inclusion of representative variability are also explored. In all, this study shows that deep learning is a useful tool in underwater acoustics and has significant potential for seabed parameter estimation.
48
Evans, G. "Seabed Protection Systems to prevent Scour from High-Speed Ships". Thesis, Department of Engineering Systems and Management, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4648.
Testo completoAbstract (sommario):
This document reviews the scour protection systems required around port structures
where these are to be used for the berthing of vessels powered by water jet systems.
The development of a scour protection system at Poole Harbour in Dorset has been
documented and reviewed and a series of laboratory investigations were then
undertaken. This has enabled a greater understanding of the scour mechanisms from
the water jet propulsion systems of High Speed Ships. This work has shown that
current design guidance on scour protection is not appropriate for use on berths used
by High Speed Ships, that failure of these systems can occur rapidly and
catastrophically, and secondary effects from water jets may promote the failure of
quay walls. The scour protection system should comprise two individual elements, a
filter layer and an armour layer. It has been found that systems involving individual
isolated armour units are inappropriate and prone to failure and that shaped linked
armour blocks need to be used. The loads on the armour layer were also found to be
oscillatory and the materials used for both the armour and filter layers need to be
designed for cyclic fatigue loading and fretting. Water jets are also capable of
reducing the strength of permeable, seabed strata.
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Margelowsky, Gary R. "Characterization of seabed geometry in a free surface wave environment". Connect to resource, 2008. http://hdl.handle.net/1811/35767.
Testo completo
50
Cui, Lin. "Three-dimensional Numerical Model for Seabed Foundation Stability around Breakwaters". Thesis, Griffith University, 2020. http://hdl.handle.net/10072/395539.
Testo completoAbstract (sommario):
With the increasing demand for coastal zones from human activities, a growing number of breakwaters have been constructed around the main beach and major estuaries to defend against wave erosion and damage. The vulnerability of the breakwater foundation can be associated with dynamic soil responses in the vicinity of structure when subjects to the consecutive ocean wave loading. For the severe situations, soil liquefaction may occur around the breakwater foundation, which is considered as a significant cause of catastrophic failures of many marine structures. Therefore, understanding and predicting soil responses and liquefaction potential around breakwaters have become one of the main concerns when design and maintain these marine structures.
The traditional models used to analyse the soil responses and liquefaction potential in the neighbourhood of breakwaters were mostly limited to two-dimensional (2D) frameworks, in which only the middle cross-section of the breakwaters under perpendicular waves can be investigated. However, the natural environment is three-dimensional (3D) that involves much more complicated fluid-seabed-structure interactions, which requires a 3D model. What’s more, most of the existing models assumed the seabed foundation as poro-elastic medium, which only the oscillatory soil responses and momentary liquefaction can be studied. Nevertheless, the residual soil responses and liquefaction within the poro-elastoplastic soil are more significant and can cause more severe damage to the marine structure foundations. Another deficiency of the traditional models is the lack of advanced Computational Fluid Dynamic (CFD) model to accurately simulate more realistic conditions, for example, including the interactions of ocean currents.
According to the gaps in previous literature, the main objective of this thesis is defined as numerically predicting the soil responses and examining the breakwater foundation stability (i.e., liquefaction potential) under combined waves and currents loading within both poroelastic and poro-elastoplastic seabed foundation from both two- and three-dimensional perspectives for different engineering conditions. One of the main novel contributions of this study is to develop the integrated numerical model that make up for the deficiency of the fluid-seabed-structure interactions problems mentioned above: the wider application ranges including complicated 3D situations; the consideration of poro-elastoplastic soil behaviour and corresponding soil liquefaction; the inclusion of an advanced flow model to precisely predict the hydrodynamic behaviour around the structures. In the future, the models can be further developed and applied to practical engineering analyses, providing preliminary results for the design of the projects.
The integrated numerical model consists of the flow sub-model, the seabed sub-model and the coupling module between two sub-models. The flow model is developed based on the Finite Volume Method (FVM) by solving the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations for simulating the two incompressible phases (i.e., water and air) inside and outside the porous medium. The seabed model is governed by the dynamic Biot’s equations known as the u− p approximations, in which the relative displacements of pore fluid to soil particles are ignored and the acceleration of pore fluid and solid particles is included. Two constitutive models: poro-elastic model for oscillatory soil responses and momentary liquefaction; and poro-elastoplastic model for residual soil responses and residual liquefaction, are incorporated into the seabed model. An integration module is developed between flow sub-model and seabed sub-model through pressure continuity on the common faces. A set of validation works have been done to prove the capability of simulating the fluid-seabed-breakwater interactions in an accurate way.
By adopting the integrated numerical model, three numerical studies have been conducted in this thesis, including one 2D study (soil responses around submerged breakwaters with Bragg reflection) and two 3D studies (seabed foundation stability around breakwaters at river mouth; seabed foundation stability around offshore detached breakwaters). A series of results, including the hydrodynamic properties of flow domain, variation of pore pressure, effective stresses and soil displacements, and characteristics of soil liquefaction within both poro-elastic and poro-elastoplastic seabed foundation have been obtained. Numerical results revealed that the construction of breakwaters can dramatically change the flow pattern and stress state in the vicinity, which will further affect the assessment of foundation stability. Besides, compared to the poro-elastic seabed foundation, the liquefaction is much easier to occur in the poro-elastoplastic seabed foundation and usually will develop to a much more significant level, which can cause critical failure of the structures. Furthermore, the effects of wave characteristics and soil properties on the breakwater foundation stability have been examined through parametric studies: the soil liquefaction is more serious within the loosely deposited seabed with poor drainage conditions under large wave height and wave period. It was also found that the currents have remarkable effects on foundation stability that aggravate with the increase of currents velocity.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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