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1
Lavasani, Seyed Mohammadreza Miri. "Advanced quantitative risk assessment of offshore gas pipeline systems". Thesis, Liverpool John Moores University, 2010. http://researchonline.ljmu.ac.uk/5976/.
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This research has reviewed the current status of offshore and marine safety. The major problems identified in the research are associated with risk modelling under circumstances where the lack of data or high level of uncertainty exists. This PhD research adopts an object-oriented approach, a natural and straightforward mechanism of organising information of the real world systems, to represent the Offshore Gas Supply Systems (OGSSs) at both the component and system levels. Then based on the object-oriented approach, frameworks of aggregative risk assessment and fault tree analysis are developed. Aggregative risk assessment is to evaluate the risk levels of components, subsystems, and the overall OGSS. Fault trees are then used to represent the cause-effect relationships for a specific risk in the system. Use of these two assessment frameworks can help decision makers to obtain comprehensive view of risks in the OGSS. In order to quantitatively evaluate the framework of aggregative risk, this thesis uses a fuzzy aggregative risk assessment method to determine the risk levels associated with components, subsystems, and the overall OGSS. The fuzzy aggregative risk assessment method is tailored to quantify the risk levels of components, subsystems, and the OGSS. The proposed method is able to identify the most critical subsystem in the OGSS. As soon as, the most critical subsystem is identified, Fuzzy Fault Tree Analysis (FFTA) is employed to quantitatively evaluate the cause-effect relationships for specific undesired event. These results can help risk analysts to select Risk Control Options (RCOs) for mitigating risks in an OGSS. It is not financially possible to employ all the selected RCOs. Therefore, it is necessary to rank and select the best RCO. A decision making method using the Fuzzy TOPSIS (FTOPSIS) is proposed to demonstrate the selection of the best RCOs to control the existing risks in the system. The developed models and frameworks can be integrated to formulate a platform which enables to facilitate risk assessment and safety management of OGSSs without jeopardising the efficiency of OGSSs operations in various situations where traditional risk assessment and safety management techniques cannot be effectively applied.
2
Snyman, M. F. "Numerical modelling of an offshore pipeline laid from a barge". Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/21804.
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Bibliography: pages 81-85.This thesis addresses some of the issues involved in using numerical methods to simulate the laying of an offshore pipeline, the objective being to contribute to the expertise of the South African offshore technology. Of particular interest is the prediction of the stresses in the pipe during such an event. The thesis concentrates on the use and suitability of the finite element method to simulate the important aspects of the pipelaying problem. ABAQUS, a nonlinear general purpose finite element code, was chosen as numerical tool, and nonlinear effects such as geometry and drag, as well as contact and lift-off at the boundaries, are included in the models. The analysis is performed in two parts: in the static analysis the displaced equilibrium position of the pipeline under self weight, buoyancy and barge tension is sought, whilst the response due to wave action and barge motion is of interest in the dynamic analysis. Numerical experiments show the suitability of ABAQUS to model the behaviour of slender structures under both static loads and dynamic excitations.
3
Mohamad, Basim I. "Thermal instability of infinitely-long structures". Thesis, University of Westminster, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386149.
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Laricchia, Francesco. "Study of offshore flexible pipelines with analytical and numerical methods". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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The work outlined presents three different analytical approaches for analyze a flexible pipelines, combined in one unified formulation.
Additionally, a finite element model of an unbonded flexible riser is presented.
Are reported results and discussion about a flexible pipeline subjected to a tensional load and internal pressure and
focus on Axial tension-elongation curves under different lay angles of helical tendons.
5
Givan, Daniel Rey. "Improved operational limits for offshore pipelay vessels". ScholarWorks@UNO, 2012. http://scholarworks.uno.edu/td/1439.
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Subsea pipelines are used extensively throughout the world’s oceans to transport oil and gas from offshore facilities to land, often hundreds of miles. These pipelines range in diameter from three to sixty inches and are installed in deeper depths every year, currently as deep as 2,900 meters. Pipeline construction and installation costs are a large percentage of offshore projects and thus, methods toward reducing costs is an imperative objective. With pipeline installation projects taking place in harsher environments, vessel operability is vital. This work presents an improved method for determining limiting criteria for pipelay operations to more effectively plan and execute offshore projects. This improvement is based on the consideration of total effective pipeline stresses as the limiting criterion rather than the traditionally used limiting pitch angle. Limiting sea curves based on a sample dynamic pipeline analysis are shown and their incorporation in workability planning is discussed.
6
Bakouros, Y. L. "Offshore pipeline reliability prediction : An assessment of the breakdown characteristics of offshore pipelines and the development of a statistical technique to improve their reliability prediction with particular reference". Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233657.
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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.
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Aris-Brosou, Margaux. "Soudage de polymères semi-cristallins utilisés dans l'isolation de pipeline offshore. Approches thermiques, rhéologiques et mécaniques". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM024/document.
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Cette étude porte sur la caractérisation des matériaux constituant le revêtement isolant de pipeline offshore ainsi que la soudure réalisée entre les deux polymères semi-cristallins du revêtement au niveau de la jonction entre deux tubes successifs.L’épaisseur très importante du revêtement induit, au cours du procédé de soudage, des vitesses hétérogènes de chauffe et de refroidissement des matériaux. Ces dernières ont été caractérisées grâce à une instrumentation du procédé en site industriel. Une modélisation numérique intégrant les phases successives du procédé est en bon accord avec les résultats expérimentaux. Cette modélisation permet de dresser une cartographie complète des champs de température dans l’ensemble du pipeline et plus précisément dans la zone de soudage.Cette étude nous a amené à réaliser une caractérisation des deux matériaux soudés au cours de leurs fusions et cristallisations qui représentent deux étapes cruciales lors du soudage. Une attention particulière a été portée au comportement rhéologique dans la zone de transition entre l’état fondu et l’état solide et inversement. Les données en refroidissement à différentes vitesses ont été corrélées avec le taux de transformation des matériaux.Les propriétés mécaniques des isolants ont été testées ainsi que celles des soudures en prélevant des éprouvettes sur les essais effectués en site industriel. Le peu de flexibilité du procédé industriel rend difficile une investigation de l’influence des paramètres de soudage. Une expérience « image », représentative des grandeurs industrielles, a donc été développée à l’échelle du laboratoire permettant de faire varier les paramètres de soudage. Il a été montré que le point de faiblesse de l’assemblage ne se situe pas au niveau de la soudure mais dans l’un des matériaux du revêtementThis PhD focuses on the characterization of the materials of the insulating coating of offshore pipelines as well as the welding made between the two semi-crystalline polymers of the coating at the junction of two consecutives pipes.The important thickness of the coating induces heterogeneous heating and cooling rates during the welding process. Those rates have been characterized through the implementation of thermal sensors during the industrial process. A simulation model of the different steps of the welding process is consistent with the experimental results. This simulation gives access to the thermal fields in the entire pipe and especially in the welding zone.This study allows us to characterize the two welded materials during their melting and crystallization which represent the two crucial steps during the welding. A particular attention has been drawn to their rheological behavior in the transition zone from the molten to the solid state and vice versa. The cooling data at different rates have been correlated with the transformation fraction of the materials.The mechanical properties of the insulating materials have been tested especially in the welding zone via the industrial process. However, the imposing infrastructure of the industrial process does not allow the study of the influence of welding parameters. To do so, a “mirror” experiment, representative of the industrial one, has been developed at a laboratory scale. Both the welding made via the industrial process and the “mirror” experiment have shown that the weak point of the structure is not the welding itself but one of the materials of the coating
9
Fu, Zhu. "Numerical simulation of a centrifuge test related to the interaction between an ice feature and an offshore pipeline". Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27844.
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Ice features present one of the major obstacles to offshore development in the Arctic and Atlantic regions of Canada. Ice features have been observed to interact with the see floor creating scour features (Clark et al., 1986). In particular, when an ice feature is driven by environmental forces into the shallow water, ice scouring of the seabed may cause a danger to bottom installations such as submarine pipelines.
In the present study, the ice-scour event in a centrifuge test is simulated by using PLAXIS and ADINA finite element programs. The centrifuge test data reported by (Lach et al., 1993; Yang and Poorooshasb, 1997) and the input data in their numerical study are utilized in the present work. In numerical analysis, geometric and material nonlinearities are considered. Two dimensional and three dimensional finite element models are used to calculate the stresses and deformations in the seabed soils, the deflections of the pipe, and the stresses acting on the pipe. In order to establish the validity of the finite element calculations, the experimental results and the numerical results are compared. The importance of using interface elements between the soil and the ice feature is also investigated.
The FE predictions are reasonably close to the centrifuge test data. The displacements of the pipe in 3-D model are smaller than those predicted by 2-D model due to the three dimensional effects. Bending and torsion of the pipe along its long axis can only be calculated in 3-D FE analysis. Using the interface elements in the numerical analysis helps to obtain a better agreement between the calculated and measured values. In addition, convergence problems are reduced.
10
Shabani, Behnam. "Wave-Associated Seabed Behaviour near Submarine Buried Pipelines". Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3532.
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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.
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Shabani, Behnam. "Wave-Associated Seabed Behaviour near Submarine Buried Pipelines". University of Sydney, 2008. http://hdl.handle.net/2123/3532.
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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.
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Nascimento, Lúcio Gomes. "Análise e estudo de estabilidade do padrão de escoamento golfadas severas num sistema pipeline-riser acoplado ao VASPS". reponame:Repositório Institucional da UnB, 2015. http://dx.doi.org/10.26512/2015.5.D.19176.
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2015.Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-01-05T15:01:51Z No. of bitstreams: 1 2015_LúcioGomesNascimento.pdf: 2249464 bytes, checksum: fafa46e2083c147b160da6586473ec64 (MD5)
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O padrão de escoamento das golfadas severas existentes em sistemas pipeline-riser acoplados a separadores submarinos do tipo VASPS, implementados na prospecção de petróleo offshore, é caracterizada por ser do tipo instável. Uma vez que este padrão apresenta flutuações na produção, o nível de líquido no interior do VASPS muda de acordo com a frequência de produção. Além disso, ele pode causar danos permanentes à bomba do tipo BCS (bomba centrífuga submersa) inserida no fluido, ou prejudicar a eficiência da separação, produção e ainda assim prejudicar o escoamento de gás derivado do escoamento multifásico do poço. São definidos dois critérios de estabilidade em função das transições nos padrões de escoamento característicos para a estabilidade ou não do sistema de separação e produção. São fixados valores constantes para a velocidade superficial de líquido (VSL) e para as razões de ar e água (RGO) a fim de serem analisados e estudados os padrões de escoamento de acordo com cada critério atendido (eliminação ou redução das golfadas severas) e, portanto, obter os pontos de operação ideais entre as vazões e as pressões características para a manutenção de escoamento permanente de acordo com o controle da válvula de estrangulamento e/ou controle na pressão do separador. Para cada valor fixado os resultados se comportam de maneira diferente em relação ao anterior, devido a mudança do escoamento ser significativa. A partir dos resultados podem ser obtidas as equações empíricas em função dos pontos de operação ideais para a estabilidade da separação e produção multifásica e finalmente poder acoplá-las ao controle do sistema através dos mecanismos existentes.
The flow pattern of the severe slugging in pipes coupled to subsea separators type VASPS, implemented on offshore oil drilling is unstable. Once this pattern features fluctuating flow in the production, the level of liquid within the present VASPS changes according to the frequency of production. Beyond this it may cause permanent damage to the pump type ESP (electrical submersible pump) inserted in the fluid, or impair the efficiency of production separation and yet it harm the derived gas of the multiphase flow from the well. Two criteria of stability are defined in terms of the transitions of the characteristics flow patterns in relation to the flow separation and the current production system. They are fixed constant values for the superficial liquid velocity (VSL) and the air-water ratios (RGO) to be analyzed and studied the flow patterns according to each criterion attended (elimination or reduction of severe slugging flow) and thus get optimum operating points between the characteristic pressures and the flow rates for maintaining permanent flow according to the control of the choke valve and/or through control the pressure in the separator. For each set values results behave differently in relation to the previous, because the change of the flow is significant. From the results one can obtain empirical equations as a function of the optimal operating points for the stability of the separation and the multiphase flow production, and finally to associate them to the control system via existing mechanisms.
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Phan, Van Trung. "Modelling of the in service behaviour of passive insulated structures for deep sea offshore applications". Thesis, Brest, 2012. http://www.theses.fr/2012BRES0098/document.
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L’étude se situe dans le cadre de la recherche de gains de performance de structures d’isolations passives pour l’offshore profond. Le travail proposé a pour support des analyses expérimentales et numériques de tubes revêtus par des matériaux isolants utilisés en eau profonde pour transporter du fluide chaud. Le raboutage des tubes en acier, préalablement revêtus en atelier, nécessite un dégagement du revêtement aux extrémités pour réaliser l'opération d'assemblage (généralement par soudure). La partie dégagée est ensuite recouverte par un nouveau matériau pouvant être appliqué sur site. Ainsi l’isolation de cette partie du tube (Field Joint), qui est soumise à des chargements thermomécaniques en service, doit être optimisée pour assurer une durée de vie compatible avec les contraintes de l’exploitation offshore en eau profonde. Le travail comporte principalement quatre parties : - la modélisation du comportement thermique pour analyser l’évolution en temps et en espace de la température du matériau au cours de la fabrication, de la pose et en service sachant que pour les matériaux d’isolation le comportement mécanique est fortement dépendant de la température,- une partie expérimentale pour l’analyse du comportement des matériaux isolants en fonction de la température et en fonction de la pression hydrostatique qui est le principal chargement mécanique de ces structures en service,- la modélisation du comportement mécanique des isolants,- et une partie modélisation et simulation du comportement en service d'assemblages multi-matériaux de type industriel, avec prise en compte du comportement non-linéaire des constituantsUltra deep offshore oil exploitation presents new challenges to offshore engineering and operating companies. Such applications require the use of pipelines with an efficient thermal protection. Passive insulation materials are commonly used to guarantee the thermal performance of the pipes, and syntactic foams are now the preferred material for this application. The mechanical behaviour of such insulation materials is quite complex, associating time-dependent behaviour of polymers with damage behaviour of glass microspheres. In order to allow an optimisation of such systems, while ensuring in-service durability, accurate numerical models of insulation materials are thus required. During the service life in deep water, hydrostatic pressure is the most important mechanical loading of the pipeline, so this study aims to describe the mechanical behaviour of the material under such loading. Using a hyperbaric chamber, the analysis of the evolution of the volumetric strain with time, with respect to the temperature, under different time-evolutions of the applied hydrostatic pressure is presented in this paper. Such experimental results associated with the mechanical response of the material under uniaxial tensile creep tests, allow the development of a thermo-mechanical model, so that representative loadings can be analysed
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Parks, David William. "Sub-sea gas processing". Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/2588.
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To meet the demands of deeper and more remote reservoirs, subsea processing has been poised as one of the most potentially promising technology developments in the offshore development.Natural Gas usually contains significant quantities of water vapour, which must be removed for gas processing and transmission. A pipeline transporting natural gas at a pressure of 10 Mega Pascals at equilibrium with seawater at 4 C must have water content lower than around 144 parts per million (by volume) to ensure water will not condense within the pipeline. Failure to sufficiently reduce the water content can lead to condensation of liquid water and the formation and accumulation of gas hydrates into pipe blocking plugs. This is particularly important for subsea pipelines with the high pressure and low temperatures conditions that exposes the gas to hydrate formation conditions.This research investigates a novel dehydration solution that is applicable for subsea installation. The technique is based on technology that was trialled in an above ground implementation by Cool Energy with significant system modifications to make it applicable to a subsea environment. The ultimate objective of this research is to develop a sea bed dehydration solution that will reduce the water content of the gas to pipeline quality standard.The solution utilises the concepts of gas cooling through expansion and the controlled formation and management of gas hydrates to reduce the water content of a saturated gas stream to levels suitable for gas transport in subsea pipelines. A pilot plant was implemented to test the solution design at pressures up to 10 Mega Pascals and flow rates of 35 standard cubic meters per hour. The experiments successfully demonstrated gas dehydration to below -40 degrees C, performance that meets the pipeline water specification requirements for subsea transportation of natural gas.This thesis presents the current status of implemented subsea technology, reviews current dehydration technologies and discusses their applicability to subsea implementation. It describes the iterative dehydration process development and presents the achieved dehydration results. A production scenario is defined and a modelled solution presented together with novel approaches in management of the system.
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Yeow, Kervin. "Three dimensional scour along offshore pipelines". University of Western Australia. School of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0008.
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Three-dimensional scour propagation along offshore pipelines is a major reason to pipeline failures in an offshore environment. Although the research on scour in both numerical and experimental aspect has been extensive over the last three decades, the focus of the investigation has been limited to the two-dimensional aspect. The knowledge on three-dimensional scour is still limited. This dissertation presents the results of an experimental investigation on threedimensional scour along offshore pipelines in (1) steady currents (2) waves only and (3) combined waves and current. The major emphasis of the investigation is to investigate the propagation of the scour hole along the pipeline after the initiation of scour. Physical experiments conducted were used to quantify the effects of various parameters on scour propagation velocities along the pipeline. The problem of monitoring real time scour below a pipeline was solved by using specifically developed conductivity scour probes. Effects of various parameters such as pipeline embedment depth, incoming flow Shields parameter, Keuglegan- Carpenter (KC) number and flow incident angle to the pipeline on scour propagation velocities along the pipeline were investigated. The investigations clearly reveal that scour propagation velocities generally increase with the increase of flow but decrease with the increase of the pipeline embedment depth. A general predictive formula for scour propagation velocities is proposed and validated against the experimental results. There are still some common issues related to pipeline scour that is lacking in the literature to date. One of these issues is the effects of Reynolds number on two-dimensional scour beneath pipelines. A numerical approach was adopted to investigate the Reynolds-number dependence of two-dimensional scour beneath offshore pipelines in steady currents. A novel wall function is proposed in calculating the suspended sediment transport rate in the model. The effects of Reynolds number were investigated by simulating the same undisturbed Shields parameters in both model and prototype but with different values of Reynolds number in two separate calculations. The results revealed that scour depths for prototype pipelines are about 10~15% smaller than those for model pipelines. The normalized time scales was found to be approximately the same, and the simulated scour profiles for the model pipelines agree well with the experimental results from an independent study. The backfilling of pipeline trenches is also an important issue to the design and management of offshore pipelines. A numerical model is developed to simulate the self-burial of a pipeline trench. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-e turbulence closure, as well as the sediment transport equations, are solved using finite difference method in a curvilinear coordinate system. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development.
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Chen, Zhenxin. "The mechanical behaviour and fatigue analysis of flexible pipes". Thesis, Heriot-Watt University, 1990. http://hdl.handle.net/10399/1292.
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Aune, Vegard, i Morten Sagbakken Hovdelien. "Impact Against Offshore Pipelines : Experiments and Numerical Simulations". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18476.
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In the present thesis impact against offshore pipelines was studied. Incipient fracture in the pipes after impact was of special interest. The present work was a continuation of previous theses on the subject, and part of an ongoing research program between SIMLab (NTNU) and Statoil ASA.Component tests and numerical simulations using ABAQUS/Explicit and LS-DYNA were carried out to investigate the problem. Two pipes were impacted at different velocities in the pendulum accelerator at the Department of Structural Engineering, NTNU. The most exposed regions were investigated metallurgically to examine the material behavior at large deformations due to the impact.Pre-compressed notched tension tests at large compressive plastic strains (up to 40 %) were conducted. A material model with combined kinematic and isotropic work-hardening was calibrated based on the material tests. Inverse modeling was carried out with the optimization tool LS-OPT. In addition, the material model consisted of an uncoupled fracture criterion. The combined material model was used in the numerical simulations.The material tests revealed a distinct Bauschinger effect, transient and permanent softening, as well as a work-hardening stagnation during reversed loading. Simulations of the material tests in ABAQUS/Explicit corresponded well with the experiments. However, simulations of the pipe in ABAQUS/Explicit revealed little improvement regarding the global response compared to previous theses. Further, the volume element model in LS-DYNA revealed hydrostatic tension in the critical element during rebound, where incipient fracture was assumed to appear. This was supported by metallurgical investigations revealing a crack through 75 % of the thickness after impact at the highest velocity. It is clear that this decreases the strength of the pipes. Hence, cracks will propagate through the thickness earlier than expected during stretching in the simulations. This indicates that the single-parameter assumption regarding the fracture criterion used in this thesis ceases to be valid for the component test. To recreate the fracture in the impacted pipes an additional formulation must be included.
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Farrell, J. "Hyperbaric welding of duplex stainless steel pipelines offshore". Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/4513.
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Three duplex stainless steels (Avesta 2205, Sandvik SAF2507 and Zeron 100) were successfully welded automatically at a range of pressures from 1 to 32bar. The gas tungsten arc (GTA) welding process was chosen as it allows a high degree of control to be exercised during welding. Initial autogenous bead on plate welds established the effects of pressure on the welding process and allowed the process parameters to be determined for subsequent experiments. Analysis of the effects of pressure on the weld thermal cycle showed that at higher pressures the precipitation of phases deleterious to the weld quality was less likely than at ambient pressure. It was also found that the arc melting efficiency increased as the pressure increased, which was taken into account when the process parameters for the joints were selected. A V-butt design with a 'land' on each side was chosen for the joints to counteract any tendency for the welding arc to wander at higher welding pressures. The root welds were performed using pulsed current welding techniques to overcome the difficulties in achieving consistent penetration that were encountered when welding at lower pressures. It was found that by employing standard welding consumables commonly used for welding duplex steels at ambient pressure satisfactory austenite-ferrite phase balances could be achieved in the weld metal at all pressures. Metallographic examination of the welds showed that the joints did not have any microstructural complications that were related to pressure and mechanical testing revealed that, in terms of impact toughness, the weld metal and heat affected zone (HAZ) performed as well as, if not better than, the parent plate material. This work shows that welding of duplex stainless steels using the hyperbaric welding method is a viable option for subsea operations up to a depth of at least 320m, automated hyperbaric welding being advantageous at depths greater than 40m.
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Schupp, Jens. "Upheaval buckling and flotation of buried offshore pipelines". Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670004.
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Netto, Theodoro Antoun. "On the dynamics and arrest of propagating buckles in offshore pipelines /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Kimura, Fumiaki. "Probabilistic Design of Steel Structures Applied to Offshore Pipelines". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511814.
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Helgaker, Jan Fredrik. "Modeling Transient Flow in Long Distance Offshore Natural Gas Pipelines". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23660.
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The objective of this thesis is to improve flow modeling through offshore natural gas pipelines. Gassco is a state owned Norwegian company responsible for the operation of 7800 km offshore natural gas pipelines located in the North Sea. The pipelines have a diameter of 1 m and can be up to 1000 km in length. Measurements of the state of the gas, such as pressure, mass flow, temperature and composition are available only at the inlet and outlet. To know the state of the gas between these two points one has to rely on computer models. Gassco uses commercial tools to model the flow of gas through their pipelines. These have previously given inaccurate results, especially during transient conditions. The flow of natural gas through long distance offshore pipelines is modeled by numerically solving the governing equations for one-dimensional compressible viscous heat conducting flow. An implicit finite difference scheme is used to solve the governing equations. Both spatial and temporal discretization errors are computed. The implemented flow model is validated by running simulations on one of Gassco’s offshore pipelines. Modeled results show good agreement with measured values, however some discrepancies are present, especially in the modeled outlet gas temperature. These discrepancies are determined to be caused by physical approximation errors, and not because of numerical errors or model simplifications. The sensitivity of the selection of the equation of state for high pressure natural gas pipelines is investigated by comparing the SRK, Peng-Robinson, BWRS, GERG 88 and GERG 2004 equations of state. Gassco currently uses a BWRS equation of state which is especially tuned for hydrocarbons. In a typical offshore natural gas pipeline, the difference in computed inlet pressure between using the tuned BWRS and the GERG 2004 equation of state was determined to be approximately 0.1 MPa (1 bar). Although GERG 2004 is believed to be the most accurate equation of state, it is computationally demanding compared to BWRS, resulting in BWRS being the preferred choice. Although there is a difference in computed inlet pressure between GERG 2004 and BWRS, this difference is relatively constant during both steady state and transient conditions. By tuning the equivalent sand grain roughness, the computed inlet pressure using both GERG 2004 and BWRS can be matched in order to compensate for differences in the equation of state. The heat exchange between the gas and the surrounding environment is modeled using two different approaches. The steady external heat transfer model currently used by Gassco is compared to an unsteady external heat transfer model which includes heat accumulation in the ground. It is shown by example that the steady heat transfer model over predicts the amplitude of temperature changes in the flow compared to the unsteady heat transfer model. The unsteady heat transfer model also improves the modeled inlet pressure and outlet mass flow during transient conditions. Although the modeled temperature is improved using the unsteady heat transfer model, there is still a discrepancy between modeled and measured outlet gas temperature. The most important parameters which can account for this deviation are the ambient sea bottom temperature, soil thermal conductivity and pipe burial length.
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Antunes, Felipe da Silva. "Alternativas técnico produtivas para o aproveitamento do gás natural da camada pré-sal". Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=4602.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoAs reservas brasileiras de petróleo e gás natural apresentarão um significativo crescimento a partir do desenvolvimento das reservas da camada do pré-sal. Segundo estimativas elaboradas pela EPE e pela EIA, nos próximos vinte anos, haverá um quadro de grande oferta de gás natural no país, com a oferta excedendo a demanda. Como o segmento de transporte do gás natural tem grande importância na formação do custo desse energético, uma tecnologia de transporte menos onerosa irá proporcionar um cenário mais vantajoso para a entrada do gás no mercado. A presente dissertação analisa duas tecnologias disponíveis para escoamento do gás natural da camada pré-sal gasoduto submarino e gás natural liquefeito embarcado e as possibilidades de utilização no mercado interno ou para ser exportado. De acordo com dados da Petrobras, foram utilizadas três rotas para escoar o gás do pré-sal. A metodologia Valor Presente Líquido (VPL) foi utilizada para analisar qual dos investimentos em transporte é mais viável economicamente. Os resultados mostraram que de acordo com as perspectivas de produção do gás natural no horizonte de tempo analisado as duas tecnologias serão viáveis, com o transporte por gasodutos a alternativa mais viável economicamente.
The Brazilian reserves of oil and natural gas will present a significant growth from the development of the reserves of the pre-salt layer. According to estimates prepared by the EPE and the EIA, the next twenty years, the supply of natural gas will exceed demand. As the transportation sector natural gas has great importance in the formation of the cost of energy, a less costly transport technology will provide a more advantageous to enter the gas market. This dissertation examines two technologies available to transport the gas from the pre-salt layer - offshore pipeline and liquefied natural gas shipped - and the possibilities of using the domestic market or for export. According to data from Petrobras, three routes were used to drain the gas from the pre-salt. The methodology Net Present Value (NPV) was used to analyze which of the investments in transport is more economically viable. The results showed that according to the outlook for natural gas production in the time horizon analyzed the two technologies will be feasible to transport by pipeline economically the most viable alternative.
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Yahaya, Nordin. "The use of inspection data in the structural assessment of corroding pipelines". Thesis, Heriot-Watt University, 1999. http://hdl.handle.net/10399/1150.
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Williams, Elizabeth S. "Upheaval buckling of offshore pipelines buried in loose and liquefiable soils". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:10c2cf4d-ab26-4f2c-82d9-35e15cfa03bc.
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Pipelines used for the transportation of oil and gas products offshore are often buried beneath the seabed for protection from mechanical damage and for thermal insulation. During high temperature and high pressure operations, these pipelines are susceptible to resurfacing behaviour known as upheaval buckling, a structural response that is strongly influenced by the resistance of the surrounding soil. Despite much previous research on pipe uplift, the influence of the initial soil state – particularly in loose and liquefiable soil conditions – on the uplift resistance and corresponding buckling behaviour of the pipe is not well understood. This thesis presents research that examines the implications of these backfill conditions in the context of the global behaviour of the pipeline. The work consists of plane-strain monotonic uplift experiments focusing on density, rate, and stress level effects on the initial pipe-soil response. This is followed by numerical modelling of the global buckling behaviour using the experimental data as inputs. Finally, plane-strain cyclic experiments examine the possibility of progressive upward displacements over a number of cycles causing eventual upheaval buckling. A key finding from the uplift tests is that very loose backfill conditions may result in a localised flow-around failure mechanism, associated with lower peak resistance and a softer force-displacement response than with the sliding block mechanism that is typically assumed. This leads to lower peak buckling loads/temperatures than those predicted by current design guidelines. High quality data from both the monotonic and cyclic experiments was used to assess and suggest improvements to design guidance for these conditions.
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Baumgard, Alexander James. "Monotonic and cyclic soil responses to upheaval buckling in offshore buried pipelines". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621210.
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Macaro, Giulia. "Distinct element modelling of pipe-soil interaction for offshore pipelines on granular soils". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:cf38c129-502f-4d7d-aa8c-fea5d95ad2d2.
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Offshore on-bottom pipelines are subjected to cycles of thermal and pressure-induced axial expansion, which can cause them to buckle laterally. For an elegant and cost-effective solution, lateral buckling is allowed in a controlled manner. Of the various design parameters, the soil resistance has the greatest associated uncertainty. Previous studies of lateral pipe-soil interaction have used laboratory model tests and continuum-based numerical methods. However, they are economically and computationally expensive, and have mostly been restricted to pipes on undrained clay. To overcome this limitation, this thesis introduces the distinct element method (DEM) as a novel numerical tool for the study of lateral pipe-soil interaction for partially embedded offshore pipelines on sandy seabeds. The DEM directly models the particulate nature of sandy soils, allowing large displacements of discrete bodies and providing insights into the mechanics of the soil at a particle level. Pipe{soil interaction is studied by DEM analyses through four separate research stages: (i) mechanical characterisation of the soil, (ii) specimen preparation and pipeline implementation, (iii) small displacement pipe loading tests and (iv) large displacement pipe loading tests. The soil is modelled as an assembly of spherical particles exchanging contact forces, energy and momentum when they interact. At the microscopic scale, a novel moment-relative rotation contact law is introduced to account for the irregular shape of real sand grains. At a macroscopic scale, the mechanical behaviour of the sand is calibrated using experimental triaxial test data. Additional work includes the numerical preparation of a soil assembly and the implementation of a pipeline object in the open-source DEM code Yade. A novel specimen preparation technique is developed to assemble a homogeneous sample at a desired relative density. The pipeline is implemented as a cylindrical body with a continuously curved surface and a specific mass. Small displacement loading tests are performed, with a segment of the pipeline interacting with a 3D prismatic soil domain, replicating plane strain conditions. The influence of particle size, domain thickness, loading velocity and damping are investigated. The findings provide valuable recommendations for performing DEM simulations of this problem, balancing numerical accuracy and computational effort. Large displacement loading tests are performed to validate the DEM approach and to obtain detailed insights into the nature of the pipe-soil interaction. Monotonic vertical and lateral loading simulations are quantitatively compared with laboratory results. To replicate realistic loading conditions of the pipeline on the seabed, cyclic large displacement tests are also performed. Both the monotonic and the cyclic tests show a good level of agreement with experimental results obtained in previous research. Moreover, the numerical analyses provide insights into the evolution of particle motion and the failure mechanism within the soil.
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Alam, Muhammad Shafiqul. "Lattice Boltzmann modelling of two and three-dimensional flow and scour around offshore pipelines". University of Western Australia. School of Civil and Resource Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0161.
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[Truncated abstract] The hydrodynamic forces on a marine pipeline and the local scour around it are the most serious and important issues in designing and maintaining pipelines. This thesis explores the vortex shedding phenomena for the flow over smooth surface and rough surface isolated cylinders. This thesis also explores the two-dimensional and three-dimensional scour process beneath offshore pipelines numerically. A series of numerical models are proposed in this dissertation for the prediction of flow characteristics and the time development of local scour around pipelines. All the models presented in this thesis are deliberately developed based on novel lattice Boltzmann method (LBM), because in recent years it has been considered as a serious alternative to standard computational fluid dynamics (CFD) as it is ideally suited to massively parallel computations. The lattice Boltzmann method is described in details to reveal how it recovers the Navier- Stokes equations. Various grid refinement schemes available in literature are discussed and a slightly modified new scheme is proposed to remove oscillatory solutions at high velocity change regime. The proposed scheme is then validated against bench mark tests for low Reynolds number flow. A turbulent model based on LBM is developed in order to predict the vortex shedding flow around an isolated square smooth surface cylinder. The various local and global flow parameters and structure of vortices are validated against experimental and numerical data available in literature. The model is then extended to investigate the vortex shedding flow over an isolated rough surface cylinder as it has an engineering significance in the design process of pipelines. The model is employed to investigate the influence of pipe roughness on various local and global parameters of flow. ... Significant part of this thesis is aimed at modelling flow and local scour around pipelines employing LBM and cellular automata (CA) methods. The erosion mechanism of the CA method available in literature for sand particles is improved by defining the threshold of sediment entrainment on bed in a similar manner to that employed in the traditional scour models. The predicted scour profiles for various incoming flow conditions are found to compare well with the experimental results reported in the literature. The existence of lee wake erosion due to continuous generation of vortex shedding in the lee of the pipelines is revealed. The time development of the maximum scour depth below the pipe is also found to be in good agreement with the experimental measurements reported in literature Finally, a three-dimensional flow and scour model is developed in order to explore the scour process beneath pipelines. It is revealed that the three-dimensionality effects are more pronounced near the span shoulder. On the other hand, there exists a two-dimensional scour regime in the vicinity of the middle section of the suspended pipe. It is found that the propagation speed of the scour hole in the sapnwise direction remains almost constant at all stages of scour process.
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Ayoade, Adedayo. "Addressing the decommissioning problem : towards a theory of 'sustainable decommissioning' for disused offshore installations/pipelines". Thesis, University of Dundee, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398311.
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Liang, Zuodong. "Three-Dimensional Model for Seabed Instability around Offshore Pipelines under Combined Wave and Current Loadings". Thesis, Griffith University, 2020. http://hdl.handle.net/10072/391522.
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Seabed stability near offshore pipelines is one of the main concerns in engineering practice, being potentially affected by waves and ocean currents. The traditional model used to analyse soil behaviour near the pipeline assumes a two-dimensional interaction between the seabed and the marine structure. In other words, it is generally believed that the waves travel in the direction of the pipe. However, the actual marine environment is three-dimensional, with waves and currents approaching the structure from all directions. Based on a wide review of the literature, it may be claimed that the simplified 2D model no longer simulates the complex layouts of environment where offshore pipelines can be built, which should be represented as an integrated system. Therefore, the main objective of this project is to study the mechanism of soil response and liquefaction caused by waves and currents in the porous seabed near the offshore pipeline from a three-dimensional perspective.
A three-dimensional numerical model is developed based on the Finite Volume Method (FVM) to analyse the instantaneous soil behaviour under the combined loads from both ocean waves and currents. In this integrated model, the hydrodynamic model is governed by the VARANS (Volume-Averaged Reynods Averaged Navier-Stokes) equation for simulating the two-phase incompressible flow motion outside and inside the porous media. The Biot’s consolidation equations are then solved for the soil responses by linking the dynamic wave pressure on the interface between the wave and seabed. The seabed behaviour is considered to be linear elastic with inversely small deformations. Overall good agreement with laboratory experimental measurements validates this newly proposed 3-D model. The numerical results reveal that the flow obliquity between the incident waves and the ocean currents has a non-negligible effect on the instantaneous pore-water pressure around the submarine pipeline, a phenomenon that cannot be observed in two dimensional numerical model. Further, a parametric study is conducted to show that the instantaneous pore-water pressure around the pipeline increases with decreasing flow obliquity; such influence can significantly increase with the increasing current velocity. Moreover, the liquefaction zone is more easily observed near the inlet of the ocean currents.
By adopting the established FVM model, a numerical study on the soil response caused by waves and ocean currents near the trench structure has been conducted. The numerical results show that an offshore pipeline positioned in a trench layer is more stable than one directly laid on the seafloor. The following ocean currents can increase the liquefaction depth below the pipeline, while the opposing ocean currents can reduce the liquefaction depth near the pipeline. Moreover, the lee-wake vortex can be avoided with enough backfill thickness, which also decreases the occurrence of the onset of scour around the pipeline. Also, the nonlinear wave-current-induced seabed response around a pipe-protective cover system was investigated using the 3-D integrated model developed in OpenFOAM®. It was shown that, with sufficient quantity of stone covers and protective mattresses, the stability of the system can be maintained even with large current velocities. At this point, valuable suggestions can be drawn from the numerical results and then applied to engineering applications: (i) different backfill materials can be used to maintain the stability of a trenched pipeline with critical backfill thickness;(ii) pipelines laid directly on the surface of the seabed can be protected by a full stone cover or protective mattress under the environmental loadings from both ocean waves and currents with different directions; (iii) the protective mattress can be economically constructed over the pipeline with critical spacing to avoid an increase in the engineering budget.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Giaccobi, Stéphane. "Méthode de conception de multimatériaux à architecture multicouche : application à la conception d’une canalisation sous-marine". Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13829/document.
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Les méthodes de sélection de matériaux monolithiques peuvent conduire à des impasses lorsque les exigences fonctionnelles sont très élevées ou contradictoires. Le passage aux multimatériaux peut alors être envisagé. L’objectif de la thèse est de proposer une méthode de conception de multimatériaux à architecture fixée, avec en perspective une application à la conception de conduites offshore pour le génie pétrolier. Seuls les multimatériaux à architecture multicouche sont considérés et la méthode de conception est redéfinie comme une méthode de sélection des constituants du multimatériau et de dimensionnement. Une adaptation des étapes classiques de sélection des matériaux conduit à présenter la méthode en détail sur des exemples simples. Les techniques de programmation par satisfaction de contraintes s’avèrent nécessaires pour la résolution de cas réels de conception multimatériaux. L’application à la conception de conduites offshore permet de valider la méthode et de démontrer sa pertinenceWhen the design requirements are either too stringent or are conflicting, no monolithic material solution exists. In such cases the selection of a multimaterial could be considered. The primary aim of this thesis is to provide a methodology for designing multi-materials with a prescribed arrangement of the constituent materials. The second objective is to apply this new methodology to the design of a submarine pipeline. From amongst the huge variety of multi-material arrangements available, this study focusses on multilayered stackings and therefore the design methodology becomes a method for selecting the materials of the stack and sizing the layers. This original approach is presented in detail using basic examples in order to match the steps of classical methods for selecting engineering materials. The constraints programming techniques were very useful for solving real multimaterial design problems. Applying this new method to the design of a submarine pipeline permits its validation and provides proof of its relevance
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Santos, Marcus Vinicius Franchi dos 1983. "Um estudo comparativo de dutos em vãos livres através de simulações numéricas". [s.n.], 2015. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265806.
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Orientador: Celso Kazuyuki MorookaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências
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Resumo: Vibrações Induzidas por Vórtices em dutos com vãos livres sujeitos a corrente marítima é um problema presente na indústria offshore. Embora significativos esforços tenham sido feitos para entender este complicado problema de interação fluido estrutura, a modelagem numérica para cálculo é ainda um grande desafio. O presente trabalho tem como objetivo principal caracterizar o comportamento dinâmico dos dutos em vãos livres sob os efeitos do fenômeno da vibração induzida por vórtices (VIV). A disponibilidade de diversos programas de cálculo de VIV para estruturas offshore esbeltas facilita a avaliação da vida útil dessas estruturas e reduz o custo de projetos. No entanto, um bom domínio das metodologias adotadas por programas utilizados na indústria e a consciência das limitações correspondentes a diferentes técnicas são fundamentais para que o analista faça uso adequado dessas ferramentas computacionais. Neste sentido, este trabalho faz uma revisão dos diferentes modelos para estimar as forças de VIV devidas à corrente marinha. Para isto, diferentes programas de computador foram utilizados para calcular as vibrações na direção transversal de incidência de corrente, provocadas pelo desprendimento de vórtices em um duto com vão livre. As simulações do comportamento dinâmico da parcela em vão livre do duto foram realizadas utilizando três abordagens, respectivamente: modelos hidrodinâmicos de força de VIV semi-empíricos, no domínio da frequência; modelos hidrodinâmicos de força de VIV semi-empíricos, baseados nos coeficientes de sustentação e número de Strouhal, no domínio do tempo e um modelo hidrodinâmico de wakeoscillator, no domínio do tempo. Os resultados das simulações são analisados através de comparações com dados experimentais. Além disso, as limitações da cada modelo são discutidas
Abstract: Vortex induced vibration (VIV) of free span pipeline subjecting to ocean current is a present problem in the offshore industry. Although significant efforts have done to understand this complicated fluid structure interaction problem, the numerical modeling and predicting is still a big challenge. The primary objective of this work is to characterize the dynamic behavior of pipelines with free span under the effects of the Vortex-Induced Vibration (VIV) phenomenon. Different models to estimate VIV forces due to sea current are discussed. For this purpose, different computer programs were used to predict vibrations in the transverse direction of the current incidence direction, caused by the vortex shedding in a free span of the pipeline. Simulations of the dynamic behavior of a free span portion of the pipeline were carried out by two approaches, respectively: semi-empirical hydrodynamic VIV force model, in frequency domain and, semi-empirical VIV force model based on the lift coefficient and Strouhal number, in time domain and a wake oscillator in time domain. Simulations results are analyzed through comparisons with experimental data and also limitations of the each model are discussed
Mestrado
Explotação
Mestre em Ciências e Engenharia de Petróleo
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Krupiński, Szymon. "Suivi des structures offshore par commande référencée vision et multi-capteurs". Thesis, Nice, 2014. http://www.theses.fr/2014NICE4051.
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Cette thèse vise à rendre possible l’utilisation des véhicules sous-marins autonomes (AUVs) dans l’inspection visuelle des structures offshore. Deux tâches sont identifiées: le suivi des structures rectilignes et la stabilisation devant les cibles planaires. Les AUVs complétement actionnés et équipés d'une centrale inertielle, un DVL, un altimètre et une caméra vidéo sont visés. La dynamique en 6 d.d.l. d'un AUV est rappelée. L'architecture de contrôle reflétant la structure en cascade de la dynamique est choisie. Une boucle interne asservie la vitesse du véhicule à la consigne et une boucle externe calcule la vitesse de référence à partir des informations visuelles. Le suivi de pipe est assuré par l'asservissement visuel 2D qui calcule la vitesse de référence à partir des bords du pipeline détectés dans l’image. La convergence globale asymptotique et localement exponentielle de la position, de l’orientation et de la vitesse sont obtenues. Le contrôleur de stabilisation utilise la matrice d’homographie. Seule la connaissance imprécise de l’orientation de la cible est nécessaire. L’information cartésienne de la profondeur de la cible est estimée à l’aide d’un observateur. La convergence quasi-globale et localement exponentielle de ce contrôleur est démontrée. Afin de tester ces méthodes un simulateur a été développé. Des images de synthèse de haute-fidélité sont générées à partir de simulateur Morse. Elles sont traitées en temps réel à l’aide de la bibliothèque OpenCV. Un modèle Simulink calcule la dynamique complète des 6 d.d.l. du véhicule simulé. Des résultats détaillés sont présentés et mettent en avant les résultats théoriques obtenusThis thesis deals with a control system for a underwater autonomous vehicle given a two consequent tasks: following a linear object and stabilisation with respect to a planar target using an on-board camera. The proposed solution of this control problem takes advantage of a cascading nature of the system and divides it into a velocity pilot control and two visual servoing schemes. The serving controllers generate the reference velocity on the basis of visual information; line following is based on binormalized Pluecker coordinates of parallel lines corresponding to the pipe contours detected in the image, while the stabilisation relies on the planar homography matrix of observed object features, w.r.t. the image of the same object observed at the desired pose. The pilot, constructed on the full 6 d.o.f. nonlinear model of the AUV, assures that the vehicle’s linear and angular velocities converge to their respective setpoints. Both image servoing schemes are based on minimal assumptions and knowledge of the environment. Validation is provided by a high-fidelity 6 d.o.f. dynamics simulation coupled with a challenging 3D visual environment, which generates images for automatic processing and visual servoing. A custom simulator is built that consist of a Simulink model for dynamics simulation and the MORSE robot and sensor simulator, bound together by ROS message passing libraries. The OpenCV library is used for real-time image processing. Methods of visual data filtering are described. Thus generated experimental data is provided that confirms the desired properties of the control scheme presented earlier
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Woodson, Ross D. "Offshore pipeline failures". Thesis, 1990. http://hdl.handle.net/10945/28420.
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An overview of current concerns in the regulation of offshore pipelines is presented along with tabulated summaries of pipeline failure causes, failure prevention techniques, and pipeline monitoring and early intervention techniques. A database of over 1000 offshore pipeline failures in the Gulf of Mexico Offshore waters has been compiled from combined records of the Department of Transportation Office of pipeline Safety, U.S. Coast Guard National Response Center, and the Department of Interior Minerals Management Service. The data has been analyzed to identify trends and initial recommendations for future data collection have been suggested
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Arjomandi, Kaveh. "MECHANICAL RESPONSE OF SANDWICH PIPES SUBJECT TO HYDROSTATIC PRESSURE AND BENDING". Thesis, 2010. http://hdl.handle.net/10222/13156.
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The recent substantial increase in world demand for energy and raw material resources has accelerated oil and gas exploration and production. At the same time, the depletion of onshore and shallow water oil resources presents a challenge to engineers to develop new means of harvesting and transporting oil and gas from harsh and remote areas. Sandwich Pipe (SP) is a relatively new design concept developed to address the transportation of oil in deep and ultra-deep waters as well as in cold environments. The main focus of this thesis is on the characterization of the structural performance of these novel systems.
Deep and ultra-deep water offshore pipelines are subjected to excessive hydrostatic external pressure during installation and operation. In this research, an innovative analytical solution was developed to evaluate the external pressure capacity of SPs by calculating the linear eigenvalues of the characteristic equations of the system. In the proposed solution, the interface condition between the layers of the system is accounted for in the governing equations. As well, a set of comprehensive parametric studies using the Finite Element (FE) method was developed to investigate both the elastic and plastic buckling response of SPs. The influence of various structural parameters such as the material, geometrical and intra-layer interaction properties on the characteristic behavior and the buckling pressure of SPs was examined. In addition to the proposed analytical solution, two sets of semi-empirical equations based on the FE analysis results were recommended in calculating the elastic and plastic buckling pressure of SPs.
As bending represents an important loading state in the installation and service life of SPs, it should be considered a governing loading scenario. In this thesis, the behavior of SPs under bending was investigated using a comprehensive set of parametric studies. SP systems with a wide practical range of physical parameters were analyzed using the FE method, and the influence of various structural parameters on the characteristic response and bending capacity of the system was explored, including pipe geometry, core layer properties, material yield anisotropy of high-grade steel pipes, and various intra-layer adhesion configurations.
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Lee, Liang-hai 1973. "On the design of slip-on buckle arrestors for offshore pipelines". Thesis, 2007. http://hdl.handle.net/2152/3734.
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Offshore pipelines are susceptible to the damage that leads to local collapse. If the ambient pressure is sufficiently high, local collapse can initiate a buckle that propagates at high velocity catastrophically destroying the pipeline. Buckle arrestors are circumferential local stiffeners that are placed periodically along the length of the pipeline. When properly designed, they arrest an incoming buckle thus limiting the damage to the structure to the distance between two adjacent arrestors. Slip-on type buckle arrestors are tight-fitting rings placed over the pipe. They are relatively easy to install and do not require welding. As a result they have been widely used in shallow waters. It has been known that such devices often cannot reach higher levels of arresting efficiency. The somewhat deficient performance is due to the fact that a buckle can penetrate such devices via a folded-up U-mode at pressures that are lower than the collapse pressure of the intact pipe. Because of this they have not seen extensive use in deeper waters. The aim of this study is to quantify the limits in arresting performance of slip-on buckle arrestors in order to enable expanded use in pipelines installed in moderately deep and deep waters. The performance of slip-on buckle arrestors is studied through a combination of experiments and analysis. The study concentrates on pipes with lower D/t values (18-35) suitable for moderately deep and deep waters. The arresting efficiency is studied parametrically through experiments and full scale numerical simulations. The results are used to generate an empirical design formula for the efficiency as a function of the pipe and arrestor geometric and mechanical properties. The performance of slip-on arrestors is shown to be bounded by the socalled the confined propagation pressure. That is the lowest pressure that U-mode pipe collapse propagates inside a rigid circular cavity. Therefore, a quantitative study of this critical pressure is undertaken using experiments and numerical simulations. A new expression relating this critical pressure to the material and geometric parameters of the liner pipe is developed. This in turn is used to develop quantitative limits for the efficiency of slip-on buckle arrestors.
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Huang, John Chih-Ming. "On the arresting efficiency of spiral buckle arrestors for offshore pipelines". Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-05-5490.
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Buckle arrestors are devices placed along an offshore pipeline for the purpose of arresting an incoming propagating buckle. Typically, buckle arrestors locally increase the pipe’s bending rigidity in the hoop direction. Spiral buckle arrestors are rods closely wound around the pipe for a number of turns and then welded at the ends to secure it in place. Spiral buckle arrestor have some key advantages to other designs in that they provide limited resistance to axial bending of the pipeline, and they can be wound on a continuous line away from free ends. This thesis uses a combination of experiments and modeling to study the effectiveness of spiral buckle arrestors.
A series of experiments are conducted using 1.25-inch diameter SS-304 tubes with diameter-to-thickness ratios of 19 and 25. Stainless steel rods of four diameters are wound on tubes for a chosen number of turns and secured in place. A propagating buckle is subsequently initiated in the tube, engages the arrestor quasi-statically, is temporarily arrested, and eventually crosses the arrestor at a pressure defined as the crossover pressure. The crossover pressure was found to depend on the tube D/t and mechanical properties; and the rod diameter, number of turns, and mechanical properties.
Finite element models are developed that enable the simulation of rod winding, buckle propagation, and buckle crossover. Local collapse is induced by external pressure and is propagated quasi-statically until it engages the arrestor. The pressure is increased until the buckle crosses the arrestor. The model is shown to reproduce the experimental observations and a large number of the measured crossover pressures with sufficient accuracy. Additional simulations were performed varying the rod diameter, numbers of turns, and tube D/t in order to enrich the database developed. This database was subsequently used to develop an empirical design formula for the arresting efficiency based on key nondimensional parameters of the problem. As was the case for the slip-on buckle arrestor, the arresting efficiency is bounded by the confined propagation pressure of the pipe.text
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Iranpour, Mohammad. "FATIGUE CHARACTERIZATION OF RISERS AND PIPELINES UNDER REALISTIC VARIABLE AMPLITUDE LOADING AND THE INFLUENCE OF COMPRESSIVE STRESS CYCLES". Thesis, 2013. http://hdl.handle.net/10222/50472.
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One of the most prominent factors affecting the performance and longevity of risers is vortex induced vibration (VIV), which can cause severe fatigue damage, especially in risers used in deep waters. The available approaches for analyzing VIV induced fatigue in risers mainly focus on the VIV aspect of the problem; indeed less attention has been paid on the effect of VIV on a riser’s fatigue life and in prediction of fatigue life using various models.
This dissertation first demonstrates how one can characterize fatigue of pipes and risers using an equivalent plate specimen as opposed to using a pipe specimen, thereby simplifying the task, yet obtaining good accuracy. Actual variable amplitude loadings (VAL) are used to study the fatigue crack growth in risers’ material with a focus on the various influencing parameters. Extensive experimental investigations are performed, followed by analytical and computational nonlinear finite element analyses. It is shown that the higher harmonics do cause significant fatigue damage, thus their influence should not be ignored. The influence of load interaction effects is also investigated, focusing on the fatigue crack growth retardation effects due to tension overloads, as well as the acceleration effects due to compression underloads. The crack closure concept is then used to explore into both the fatigue retardation and acceleration effects within a VAL scenario. An effective method for calculation of the stress intensity factor is proposed, which considers only the tensile portion of the stress range, while proposing another effective approach for accounting for the influence of compressive stress cycles.
Moreover, a two-parameter approach is used in this dissertation, relating the fatigue crack growth rate (FCGR) to the crack tip opening displacement (CTOD). It is shown that the CTOD provides adequate information for calculating the FCGR under VAL, and it can be effectively used to account for the influence of the compressive stress cycles. The experimental investigation also considers the retardation effect resulting from the applied peak tensile overload cycles (TOLC) and the influence of various so-called “clipping” levels, demonstrating the significant influence of the TOLC on crack growth retardation in VAL.
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Nourpanah, Nikzad. "Integrity and Fracture Response of Offshore Pipelines Subject to Large Plastic Strains". 2011. http://hdl.handle.net/10222/13299.
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Steel pipelines are widely used in offshore oil/gas facilities. To achieve economically feasible designs, regulatory codes permit utilization of the pipelines well past their elastic response limit. This requires thorough integrity check of the pipeline subject to large scale yielding (LSY). Engineering criticality assessments (ECA) are used to justify the integrity of a cracked pipeline against fracture failure. The currently used ECA crack driving force equation was developed for load-controlled components subject to very limited crack-tip plasticity. Moreover, fracture toughness data are extracted from deeply-cracked laboratory specimens that produce the lowest margin of toughness values. Therefore, the current framework can be overly conservative (or include non-uniform inaccuracies) for ECA of modern pipelines that undergo LSY and ductile crack growth prior to failure. The two main goals of this thesis are: (i) Development of an alternative crack driving force estimation scheme, (ii) Justification of the use of use of shallow-cracked single edge notch tensile (SENT) specimens for the ECA. Strain concentration in concrete coated pipelines, and effect of Lüders plateau on the fracture response are also investigated.
A new reference strain J-estimation scheme is proposed and calibrated to 300 nonlinear parametric FE models, which takes advantage of the linear evolution of the J with LSY bending strains. The scheme is hence strain-based and needless of limit load solutions, providing additional accuracy and robustness.
The near-tip stress and strain fields of cracked pipelines were also investigated and compared to those obtained from a K-T type formulation. It is shown that the J-Q constraint theory can satisfactorily characterize these fields up to extreme plastic bending levels. Similar J-Q trajectories were also observed in the SENT and pipeline models. Subsequently, FE models utilizing a voided plasticity material were used to parametrically investigate ductile crack growth and subsequent failure of pipelines subject to a biaxial stress state. Plastic strain and stress triaxiality fields ahead of the propagating crack, along with R-curves, were compared among SENT and pipeline models. It is concluded that the SENT specimen could be a viable option for ECA of such pipes based on the observed crack tip constraint similarity.
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Razi, Pejman. "DEVELOPMENT OF A VIBRATION-BASED HEALTH MONITORING STRATEGY FOR ONSHORE AND OFFSHORE PIPELINES". 2013. http://hdl.handle.net/10222/42699.
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Ageing mechanical, civil, aerospace, marine and offshore structures require continuous and accurate assessment on their integrity to avoid potentially hazardous failures. To further facilitate this crucial demand, a new technical terminology, generally referred to as structural health monitoring (SHM) has been coined in three past decades. SHM involves deployment of a sensory network on such structures in order to gather useful data, such that processing and interpreting the data through specific algorithms would enable one to detect defects and anomalies within the structures.
This dissertation presents the results of a series of efforts expended towards the refinement and enhancement of a vibration-based SHM technique, which was originated within our research group. In the adopted damage detection scheme, vibration data are gathered from structures via piezoelectric sensors. Data are processed by a robust signal processing approach, known as the empirical mode decomposition (EMD) in order to establish energy-based damage indices (EMD_EDIs). Interpretation of the damage indices enables detection of onset, location and advancement of defects within structures.
A series of adjustments and modifications were devised and implemented to the application of the originally developed methodology, such that, besides increasing the methodology’s robustness and accuracy, they also facilitate a remote vibration-based SHM targeting onshore and offshore pipelines.
The integrity of the method in detection of bolt-loosening in a bolted flange joint of a full-scale pipeline was verified through numerical simulations and experimental investigations. The source of a significant inconsistency reported in the previous trials was identified and resolved. Also, for the first time, the remote application of the technique was facilitated by incorporating an advanced wireless data acquisition system. Moreover, the application of the methodology was extended to detection of cracks in girth-welds of offshore pipelines. In this regard, a comprehensive discussion is first provided, which identifies the role of parameters that influence the accuracy of numerical modeling of the dynamic response of submerged structures. The experimental and numerical investigation following the aforementioned modeling efforts presents encouraging results in detection of an advancing notch in the girth-weld of a submerged pipe. The use of a piezoelectric-based excitation technique, incorporated for the first time in the application of the methodology would evidence the enhanced practicality and robustness of the approach. The study concludes with a successful detection of a real-life sharp propagating crack in a beam due to cyclic loadings.
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Mullan, Sean. "Tidal sedimentology and geomorphology in the central Salish Sea straits, British Columbia and Washington State". Thesis, 2017. https://dspace.library.uvic.ca//handle/1828/8943.
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Intra-archipelago waterways, including tidal strait networks, present a complex set of barriers to, and conduits for sediment transport between marine basins. Tidal straits may also be the least well understood tide-dominated sedimentary environment. To address these issues, currents, sediment transport pathways, and seabed sedimentology & geomorphology were studied in the central Salish Sea (Gulf and San Juan Islands region) of British Columbia, Canada and Washington State, USA. A variety of data types were integrated: 3D & 2D tidal models, multibeam bathymetry & backscatter, seabed video, grab samples, cores and seismic reflection. This dissertation included the first regional sediment transport modelling study of the central Salish Sea. Lagrangian particle dispersal simulations were driven by 2D tidal hydrodynamics (~59-days). It was found that flood-tide dominance through narrow intra-archipelago connecting straits resulted in the transfer of sediment into the inland Strait of Georgia, an apparent sediment sink. The formative/maintenance processes at a variety of seabed landforms, including a banner bank with giant dunes, were explained with modelled tides and sediment transport. Deglacial history and modern lateral sedimentological and morphological transitions were also considered. Based on this modern environment, adjustments to the tidal strait facies model were identified. In addition, erosion and deposition patterns across the banner bank (dune complex) were monitored with 8-repeat multibeam sonar surveys (~10 years). With these data, spatially variable bathymetric change detection techniques were explored: A) a cell-by-cell probabilistic depth uncertainty-based threshold (t-test); and B) coherent clusters of change pixels identified with the local Moran's Ii spatial autocorrelation statistic. Uncertainty about volumetric change is a considerable challenge in seabed change research, compared to terrestrial studies. Consideration of volumetric change confidence intervals tempers interpretations and communicates metadata. Techniques A & B may both be used to restrict volumetric change calculations in area, to exclude low relative bathymetric change signal areas.Graduate
2018-12-07