Yes / Seabed consolidation state is one of important factors for evaluating the foundation stability of the marine structures. Most previous studies focused on the seabed consolidation around breakwaters standing on the seabed surface. In this study, a numerical model, based on Biot’s poro-elasticity theory, is developed to investigate the unsaturated seabed consolidation around a nearshore pile foundation, in which the pile inserted depth leads to a different stress distribution. Seabed instabilities of shear failure by the pile self-weight and the potential liquefaction under the dynamic wave loading are also examined. Results indicate that (1) the presence of the inserted pile foundation increases the effective stresses below the foundation, while increases and decreases the effective stresses around the pile foundation for small (de/R<=3.3) and large (de/R>3.3) inserted depths, respectively, after seabed consolidation, (2) the aforementioned effects are relatively more significant for small inserted depth, large external loading, and small Young’s modulus, (3) the shear failure mainly occurs around the inserted pile foundation, rather than below the foundation as previously found for the located marine structures, and (4) wave-induced momentary liquefaction near the inserted pile foundation significantly increases with the increase of inserted depth, due to the change of seabed consolidation state. / National Natural Science Foundation for Distinguished Young Scholars (51425901), the National Natural Science Foundation of China (51209082, 51209083), the Natural Science Foundation of Jiangsu Province (BK20161509), the Fundamental Research Funds for the Central Universities (2015B15514), Jiangsu Graduate Research and Innovation Plan Grant (#CXLX11_0450) and the 111 project (B12032).

Yes / An integrated Finite Element Method (FEM) model is proposed to investigate the dynamic seabed response for several specific pipeline layouts and to simulate the pipeline stability under waves loading. In the present model, the Reynolds-Averaged Navier-Stokes (RANS) equations are used to describe the wave motion in a fluid domain, while the seabed domain is described using the Biot’s poro-elastic theory. The interface between water and air is tracked by conservative Level Set method (LSM). The FEM and backward differentiation formula (BDF) are applied for spatial and temporal discretization respectively in the present model. One-way coupling is used to integrate flow and seabed models. The present model is firstly validated using several available laboratory experiments. It is then further extended to practical engineering applications, including the dynamic seabed response for the pipeline mounted on a flat seabed or inside a trench. The results show that the pipeline buried to a certain depth is better protected than that under partially buried in terms of transient liquefaction. / Energy Technology Partnership (ETP), Wood Group Kenny

A general framework is described for the solution of two-phase fluid-object interaction problems on the basis of coupling a distributed-Lagrange-multiplier fictitious domain method and a level-set method, intended for application to the problem of seabed scour by ice ridges. The resulting equations are discretized in space using stabilized finite-element methods and integrated in time using the generalized-α method. This approach is simple to implement and applicable to both structured and unstructured meshes in two and three dimensions. By means of examples, it is shown that despite the simplicity of the approach, good results are obtained in comparison with other more computationally demanding methods. A robust approach is utilized for constructing signed-distance functions on arbitrary meshes by introducing artificial numerical diffusivity to improve the robustness of classical signed-distance construction approaches without resorting to common pseudo-time relaxation. Under this approach, signed-distance functions can be rapidly constructed while preserving the numerical convergence properties and, generally, having minimal interfacial perturbation. The method is then applied with a modified deformation procedure for fast and efficient mesh adaptivity, including a discussion how it may be used in computational fluid dynamics. The two-phase fluid-object interaction approach is then customized for modeling of the seabed scour and soil-pipe interaction. In this approach, complex history-dependent soil constitutive models are replaced with a simple strain-rate dependent model. Utilization of this constitutive model along with the framework developed earlier leads to the treatment of seabed scour as a two-phase fluid-object interaction, and the soil-pipe interaction as a fluid-structure interaction problem without the need for remeshing. Good agreement with past experimental and numerical studies are obtained using our approach. The dissertation is concluded by conducting a parametric study of seabed scour in two- and three-dimensions. / text

The principal objective of this investigation is to develop a nonlinear continuum based finite element formulation to examine dynamic response of flexible riser structures with large displacement and large rotation. Updated Lagrangian incremental approach together with the 2nd Piola-Kirchhoff stress tensor and the Green-Lagrange strain tensor is employed to derive the nonlinear finite element formulation. The 2nd Piola-Kirchhoff stress and the Green-Lagrange strain tensors are energy conjugates. These two Lagrangian tensors are not affected by rigid body rotations. Thus, they are used to describe the equilibrium equation of the body independent of rigid rotations. While the current configuration in Updated Lagrangian incremental approach is unknown, the resulting equation becomes strongly nonlinear and has to be modified to a linearized form. The main contribution of this work is to obtain a modified linearization method during development of incremental Updated Lagrangian formulation for large displacement and large rotation analysis of riser structures. For this purpose, the Green-Lagrange strain and the 2nd Piola-Kirchhoff stress tensors are decomposed into two second-order six termed functions of through-thethickness parameters. This decomposition makes it possible to explicitly account for the nonlinearities in the direction along the riser thickness, as well. It is noted that using this linearization scheme avoids inaccuracies normally associated with other linearization schemes. The effects of buoyancy force, riser-seabed interaction as well as steady-state current loading are considered in the finite element solution for riser structure response. An efficient riser problem fluid-solid interaction Algorithm is also developed to maintain the quality of the mesh in the vicinity of the riser surface during riser and fluid mesh movements. To avoid distortions in the fluid mesh two different approaches are proposed to modify fluid mesh movement governing elasticity equation matrices values; 1) taking the element volume into account 2) taking both element volume and distance between riser centre and element centre into account. The formulation has been implemented in a nonlinear finite element code and the results are compared with those obtained from other schemes reported in the literature.

Omni-directional acoustic wave source interactions with a rough seabed with a continuously varying density and sound speed in a fluid-like sediment layer. The acoustic properties in the sediment layer possess an exponential type of variation in density and one of the three classes of sound speed profiles, which are constant,~$k^2$-linear, or inverse-square variations. Analytical solution of mean field. The mean field reflection coefficients corresponding to the aforementioned density and sound speed profiles for various frequencies, roughness parameters, are numberically generated and analyzed. Physical interpretations are provided for various results. This simple model characterizes two important features of sea floor, including seabed roughness, sediment inhomogenieties, therefore, provide a canonical analysis in seabed acoustics.

This paper studies is considered the problem of coherent re ection of an acoustic plane wave from a rough seabed with a randomly inhomogeneous sediment layer overlying a uniform elastic basement. The randomness of the sound eld is attributable to the rough- ness of the seabed and the sound-speed perturbation in the sediment layer, resulting in a joint rough surface and volume scattering problem. An approach based upon perturbation theory, combined with a derived Green's function for a slab bounded above and below by a uid and an elastic half space, respectively, is employed to obtain an analytic solution for the coherent eld in the sediment layer. Furthermore, a boundary perturbation the- ory developed by Kuperman and Schmidt [22] is applied to treat the problem of rough surface scattering. A linear system is then established to facilitate the computation of the coherent re ection eld. The coherent re ection coe cients for various surface roughness, sediment randomness, frequency, sediment thickness, and basement elasticity have been generated numerically and analyzed. It was found that the higher/larger size of surface and/or medium randomness, frequency, thickness, and shear-wave speed, the lower the coherent re ection. Physical interpretations of the various results are provided.

Realistic predictions of service life of steel catenary risers (SCR) require an accurate characterization of seafloor stiffness in the zone where the riser contacts the seafloor, the so- called touchdown area (TDA). This paper describes the key features of a seafloor-riser interaction model based on the previous experimental model tests. The seafloor is represented in terms of non-linear load-deflection (P-y) relationships, which are also able to account for soil stiffness degradation due to vertical cyclic loading. The P-y approach has some limitations, but simulations show good agreement with experimental data. Hence, stiffness degradation and rate effects during penetration and uplift motion (suction force increase) of the riser are well captured through comparison with previous experimental tests carried out at the Centre for Offshore Foundation Systems (COFS) and Norwegian Geotechnical Institute (NGI). The analytical framework considers the riser-seafloor interaction problem in terms of a pipe resting on a bed of springs, and requires the iterative solution of a fourth-order ordinary differential equation. A series of simulations is used to illustrate the capabilities of the model. Due to the non-linear soil springs with stiffness degradation it is possible to simulate the trench formation process and estimate deflections and moments along the riser length. The seabed model is used to perform parametric studies to assess the effects of stiffness, soil strength, amplitude of pipe displacements, and riser tension on pipe deflections and bending stresses. The input parameters include the material properties (usually pipe and soil), model parameters, and loading conditions such as the amplitude of imposed dis- placements, tension, and moment. Primary outputs from this model include the deflected shape of the riser pipe and bending moments along riser length. The code also provides the location of maximum trench depth and the position where the maximum bending moment occurs and any point where user is interested in.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2010. / Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-12-16T02:03:18Z No. of bitstreams: 1 Paloma Lumi Costa.pdf: 5921417 bytes, checksum: f675464f8e1a0f393d83b8cfc5e4ed76 (MD5) / Approved for entry into archive by Sabrina Andrade (sabrinabeatriz@ibest.com.br) on 2013-12-18T18:15:15Z (GMT) No. of bitstreams: 1 Paloma Lumi Costa.pdf: 5921417 bytes, checksum: f675464f8e1a0f393d83b8cfc5e4ed76 (MD5) / Made available in DSpace on 2013-12-18T18:15:15Z (GMT). No. of bitstreams: 1 Paloma Lumi Costa.pdf: 5921417 bytes, checksum: f675464f8e1a0f393d83b8cfc5e4ed76 (MD5) Previous issue date: 2010 / O presente estudo teve como objetivo principal a realização de um mapeamento de fundo, através de metodologia acústica, para a região da Bacia de Pelotas e, de correlacionar tipos de substratos à diversidade e abundância de teleósteos demersais. O mapeamento foi realizado utilizando o parâmetro de refletividade da superfície do fundo, definido como a razão entre a intensidade acústica que atinge o leito marinho e é refletida pelo mesmo, registrando dessa forma características de fundo associadas a impedância do substrato. Os dados referentes a peixes foram obtidos na bibliografia ou disponibilizados por pesquisadores. Inicialmente foi realizado um estudo piloto em um setor costeiro da Bacia de Pelotas, Banco do Capela (RS), onde foram adquiridos dados de BSBS, posteriormente separados em quatro classes de valores: -5 a -10dB; -10 a -15dB; - 15 a -20dB e < -20dB. Um mapa com estas classes foi gerado por meio da interpolação dos valores BSBS e comparado a um mapa sedimentológico. Os resultados indicaram coerência para a classe de -15 a -20 dB, a qual foi predominante em áreas com a presença de sedimentos arenosos. No entanto, altos valores de refletividade foram encontrados nos setores mais costeiros onde o mapa sedimentológico apontou a predominância de sedimentos lamosos. Interpreta-se este resultado à presença de beach rocks presentes em sub-superfície. O passo seguinte foi a elaboração de um mapa de classes de BSBS utilizando dados referentes a quatro cruzeiros realizados em uma área da Bacia de Pelotas, em profundidades entre 100 e 1000 m, mapa este que apresentou coerência quando comparado a mapas sedimentológicos. Quatro feições com altos valore de BSBS foram identificadas entre as profundidades de 100 e 200m, a maior delas na altura do Cabo de Santa Marta e atribuídas principalmente a fundos consolidados ou com presença de material biodetrítico. Acima dos 500 m predominaram fundos com baixa refletividade acústica, atribuídos a presença de sedimento lamoso. Ao mapa acústico foram sobrepostas as ocorrências de nove espécies de teleósteos demersais cujas distribuições mostraram-se não aleatórias em relação às classes de refletividade acústica de fundo. Mullus argentinae, Nemadactylus bergi, Prionotus punctatus, Genypterus brasiliensis, Cynoscion guatucupa e Lopholatilus villarii ocorreram com mais freqüência e abundancia nas classes com menores valores de refletividade. Já o Pagrus pagrus teve maior abundancia e ocorrência em fundos com maiores valores de refletividade acústica, atribuídos a presença de sedimentos consolidados e biodetríticos. Posteriormente, o mapa foi analisado frente a informações de ocorrência de corais de profundidade, disponíveis na literatura. A comparação dos mapas gerados com base em informações dos corais de profundidade apresentou forte relação com áreas alta refletividade. / The main aim of this study was conduct a seabed mapping, using acoustic methods, in the region of Pelotas Basin and to correlate different types of substratum to the occurrence and abundance of demersal bonefishes. The map was created using the parameter BSBS, defined as the ratio between the acoustic intensity which reaches the ocean bottom and is backscattered and it is a function of the seabed surface acoustic impedande. Fish data were gathered from the literature or made available by researchers and overlaid to the map. Initially an experiment study was conducted in a coastal sector of the Pelotas Basin, Banco do Capela (RS) where BSBS data were acquired, post processed and grouped in four classes of values, namely: -5 to -10dB, -10 to -15 dB, -15 to -20dB and < -20dB. A map was created with these classes and compared with a sedimentological map. The results were consistent with in the class of - 15 to -20 dB, which was dominant and coincident with the presence of sandy sediments. However, high values of reflectivity were found in the most coastal sectors where the sedimentological map indicated the presence of muddy sediments. It is suggested that these results might be associated with the presence of beack rocks in the subbottom. Next was generated a map using BSBS data from four large scales cruises in the Pelotas Basin area, between 100 and 1000 m deep. This map was consistent when compared to sedimentological maps of the region. Four features with high acoustic reflectivity were identified between depths of 100 and 200 m, the largest in the Cabo de Santa Marta area. These features were attributed mainly to consolidated sediments or to the presence of biodetritus. Deeper than 500 m the map showed bottoms with low reflectivity associated to the presence of muddy sediments. To the BSBS map was overlayed the occurrences of nine species of demersal bonyfishes which showed not to be randomly distributed with relation to the BSBS classes. Mullus argentinae, Nemadactylus bergi, Prionotus punctatus, Genypterus brasiliensis, Cynoscion guatucupa and Lopholatilus villarii occurred more often and in higher abundances in classes with low values of reflectivity. In addition, Pagrus pagrus showed greater abundances and occurrences in higher acoustic reflectivity bottoms, related to the presence of biodetritus and consolidated bottoms. The acoustic map was also compared with the presence of deep sea corals as obtained from the literature. The comparison showed strong similarities among areas with high reflectivity identified in this work.

Subsurface intake systems are known to improve the feed water quality for SWRO plants. However, a little is known about the feasibility of implementation in coastal settings, the degree of water quality improvements provided by these systems, and the internal mechanisms of potential fouling compounds removal within subsurface intake systems. A new method was developed to assess the feasibility of using different subsurface intake systems in coastal areas and was applied to Red Sea coastline of Saudi Arabia. The methodology demonstrated that five specific coastal environments could support well intake systems use for small-capacity SWRO plants, whereas large-capacity SWRO facilities could use seabed gallery intake systems. It was also found that seabed intake system could run with no operational constraints based on the high evaporation rates and associated diurnal salinity changes along the coast line. Performance of well intake systems in several SWRO facilities along the Red Sea coast showed that the concentrations of organic compounds were reduced in the feed water, similar or better than traditional pretreatment methodologies. Nearly all algae, up to 99% of bacteria, between 84 and 100% of the biopolymer fraction of NOM, and a high percentage of TEP were removed during transport through the aquifer. These organics cause membrane biofouling and using well intakes showed a 50-75% lower need to clean the SWRO membranes compared to conventional open-ocean intakes. An assessment of the effectiveness of seabed gallery intake systems was conducted through a long-term bench-scale column experiment. The simulation of the active layer (upper 1 m) showed that it is highly effective at producing feed water quality improvements and acts totally different compared to slow sand filtration systems treating freshwater. No development of a “schmutzdecke” layer occurred and treatment was not limited to the top 10 cm, but throughout the full column thickness. Algae and bacteria were removed in a manner similar to slow sand filtration, but it took many months to produce consistent reductions in NOM fractions and TEP. The data suggested that a thicker active layer (2m) is needed to facilitate a more rapid reduction in the main potential fouling organics.

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.