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1
Adedipe, Oyewole. "Integrity of offshore structures". Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9692.
Testo completoAbstract (sommario):
Corrosion and fatigue have been dominant degradation mechanisms in offshore structures, with the combination of the two, known as corrosion fatigue, having amplified effects in structures in the harsh marine environments. Newer types of structure are now being developed for use in highly dynamic, harsh marine environments, particularly for renewable energy applications. However, they have significantly different structural details and design requirements compared to oil and gas structures, due to the magnitude and frequency of operational and environmental loadings acting on the support structures. Therefore, the extent of corrosion assisted fatigue crack growth in these structures needs to be better understood. In this research, fatigue crack growth in S355J2+N steel used for offshore wind monopile fabrications was investigated in air and free corrosion conditions. Tests were conducted on parent, HAZ and weld materials at cyclic load frequencies similar to what is experienced by offshore wind monopile support structures. The seawater used for testing was prepared according to ASTM D1141 specifications and was circulated past the specimens through a purpose designed and built corrosion rig at a rate of 3 l/min, at a temperature of 8-100C and at a pH of 7.78-8.1. A new crack propagation method accompanied by constant amplitude loading was used. Crack growth rates in parent, HAZ and weld materials were significantly accelerated under free corrosion conditions, at all the stress ratios used compared to in air environment. However, in free corrosion conditions, crack growth rates in the parent, HAZ and weld materials were similar, particularly at a lower stress ratio. The results are explained with respect to the interaction of the loading condition, environment and the rate of material removal by corrosion in the weldments. A new model was developed to account for mean stress effects on crack growth rates in air and in seawater, and was found to correlate well with experimental data as well as with the other mean stress models tested.
2
Richardson, Mark Damian. "Dynamically installed anchors for floating offshore structures". University of Western Australia. School of Civil and Resource Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0230.
Testo completoAbstract (sommario):
The gradual depletion of shallow water hydrocarbon deposits has forced the offshore oil and gas industry to develop reserves in deeper waters. Dynamically installed anchors have been proposed as a cost-effective anchoring solution for floating offshore structures in deep water environments. The rocket or torpedo shaped anchor is released from a designated drop height above the seafloor and allowed to penetrate the seabed via the kinetic energy gained during free-fall and the anchors self weight. Dynamic anchors can be deployed in any water depth and the relatively simple fabrication and installation procedures provide a significant cost saving over conventional deepwater anchoring systems. Despite use in a number of offshore applications, information regarding the geotechnical performance of dynamically installed anchors is scarce. Consequently, this research has focused on establishing an extensive test database through the modelling of the dynamic anchor installation process in the geotechnical centrifuge. The tests were aimed at assessing the embedment depth and subsequent dynamic anchor holding capacity under various loading conditions. Analytical design tools, verified against the experimental database, were developed for the prediction of the embedment depth and holding capacity.
3
Abdolmaleki, Kourosh. "Modelling of wave impact on offshore structures". University of Western Australia. School of Mechanical Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2008.0055.
Testo completoAbstract (sommario):
[Truncated abstract] The hydrodynamics of wave impact on offshore structures is not well understood. Wave impacts often involve large deformations of water free-surface. Therefore, a wave impact problem is usually combined with a free-surface problem. The complexity is expanded when the body exposed to a wave impact is allowed to move. The nonlinear interactions between a moving body and fluid is a complicated process that has been a dilemma in the engineering design of offshore and coastal structures for a long time. This thesis used experimental and numerical means to develop further understanding of the wave impact problems as well as to create a numerical tool suitable for simulation of such problems. The study included the consideration of moving boundaries in order to include the coupled interactions of the body and fluid. The thesis is organized into two experimental and numerical parts. There is a lack of benchmarking experimental data for studying fluid-structure interactions with moving boundaries. In the experimental part of this research, novel experiments were, therefore, designed and performed that were useful for validation of the numerical developments. By considering a dynamical system with only one degree of freedom, the complexity of the experiments performed was minimal. The setup included a plate that was attached to the bottom of a flume via a hinge and tethered by two springs from the top one at each side. The experiments modelled fluid-structure interactions in three subsets. The first subset studied a highly nonlinear decay test, which resembled a harsh wave impact (or slam) incident. The second subset included waves overtopping on the vertically restrained plate. In the third subset, the plate was free to oscillate and was excited by the same waves. The wave overtopping the plate resembled the physics of the green water on fixed and moving structures. An analytical solution based on linear potential theory was provided for comparison with experimental results. ... In simulation of the nonlinear decay test, the SPH results captured the frequency variation in plate oscillations, which indicated that the radiation forces (added mass and damping forces) were calculated satisfactorily. In simulation of the nonlinear waves, the waves progressed in the flume similar to the physical experiments and the total energy of the system was conserved with an error of 0.025% of the total initial energy. The wave-plate interactions were successfully modelled by SPH. The simulations included wave run-up and shipping of water for fixed and oscillating plate cases. The effects of the plate oscillations on the flow regime are also discussed in detail. The combination of experimental and numerical investigation provided further understanding of wave impact problems. The novel design of the experiments extended the study to moving boundaries in small scale. The use of SPH eliminated the difficulties of dealing with free-surface problems so that the focus of study could be placed on the impact forces on fixed and moving bodies.
4
Segreti, John Michael. "Fatigue analysis methods in offshore structural engineering". Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/19287.
Testo completo
5
Pouliquen, Patricia. "La condition des travailleurs de l’off-shore". Brest, 1993. http://www.theses.fr/1993BRES5001.
Testo completoAbstract (sommario):
Le but de cette thèse a été de présenter la condition juridique et la protection sociale des travailleurs de l'offshore. Ainsi, dans une première partie, il a été examiné les protagonistes de la relation contractuelle à savoir l'employeur aux visages multiples et le salarié au statut ambivalent : certains personnels ont le statut de marin, d'autres sont des travailleurs terrestres, le plongeur connaît également un statut particulier. Ce statut particulier s'explique par le lieu de travail original de ces personnels : les structures offshore dont les variétés sont les plus diverses. Il a également été envisagé le droit applicable à la relation contractuelle dans la mesure où le départ du personnel offshore est régi par des normes matérielles internationales élaborées par les sociétés offshore. Mais cela n'exclut cependant pas les conflits de lois ou de juridiction susceptibles d'intervenir, d'autant plus que ce personnel peut évoluer dans les zones échappant à la souveraineté de l'état côtier. Dans une seconde partie, il a été examiné la protection sociale des travailleurs de l'offshore. Ce personnel travaillant dans la majorité des cas hors du territoire national, il a fallu relativiser le principe de territorialité de la protection sociale par des mesures nationales mais aussi communautaires, valables aussi bien pour les travailleurs terrestres que pour les marins. Quant à la réparation des risques professionnels, les marins connaissent un régime quelque peu différent de celui des travailleurs terrestresThe goal of this thesis has been to present the legal conditions and social welfare of off-shore workers. Therefore, the main players have been studied in their various roles; from the many-faced employeurs to the ambivalent nature and status of the personnel. Certain workers are considered to sailors, oters land-side workers and even divers have their own particular category. The enormous variety of jobs and job duties explains the creation of highly individual work categories. It has also been noted that in cases of resignation, the contract law applicable is based upon international norms which are then adapted by the off-shore companies. This however does not eliminate all conflicts of jurisdiction, particularly as the off-shore personnel can excluded from those under the jurisdiction of coastel law. Secondly, the social welfare of off-shore workers has been examined. As the large majority of off-shore personnel work outside national territories, the definition social welfare jurisdiction has had to be redefined by national and communal mesures which cover both land workers and sailors. As to the claims for professional risks. The sailors coverage differs very little from the land workers. The status of a salaried employee on detached service and that of an expatriate salaried employee must also be taken into account
6
Ghadimi, R. "Nonlinear dynamic analysis of offshore structures". Thesis, Cranfield University, 1986. http://hdl.handle.net/1826/3581.
Testo completoAbstract (sommario):
In this thesis consideration is given to a selection
of nonlinear dynamic problems in the field of offshore
engineering. Hydrodynamic loading on fixed horizontal and
vertical tubular members and the dynamic response of articulated
towers together with the distribution of shear force and
bending moment along the tower are investigated using various
wave theories. Effects of nonlinear convective acceleration
terms in the calculation of fluid inertia forces and moments
are examined and attention is given to integration of wave
forces up to the free surface for vertical members. Calculation
of fluid loading at the displaced position of the articulated
tower and any Mathieu type instabilities that may occur
have been considered. The dynamic analysis of a damaged
Single Anchor Leg Storage (SALS) system subject to loss
of buoyancy in the yoke chamber is studied. The equations
of motion of the yoke/riser system are derived assuming
large displacements and solved in the time domain. Time
histories of the response, variations of the riser tension,
velocities of riser top end and the time histories of pivot
reactions are given. Natural periods and mode shapes for
small displacements of the system are calculated. Two methods
of simulating random seas, both represented by a sum of
harmonic wave components, are used to simulate second order
low frequency (slow drift) force on a tanker in head seas
by Pinkster's time domain method. In one method the wave
amplitudes are generated randomly from a Rayleigh distribution
and in the other they are obtained deterministically via
the wave spectrum. Time histories of slow drift force and
response together with simulation results with various duration
lengths are presented and compared. Estimates of the extreme
vessel response and its relation to rms value are compared
with the result of a commonly used method of determining
peak/rms ratios. The results of these investigations highlight
the importance of accurately simulating nonlinear effects
in both fixed, floating and compliant offshore structures
from the point of view of safe design and operation of such-
systems.
7
Rodriguez-Sanchez, Jose Efrain. "Fatigue crack repair for offshore structures". Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313721.
Testo completo
8
Trim, A. D. "Probabilistic dynamic analysis of offshore structures". Thesis, Cranfield University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376215.
Testo completo
9
Klepsvik, Jonny. "Nonlinear wave loads on offshore structures". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36062.
Testo completo
10
Schulz, Karl Wayne. "Numerical prediction of the hydrodynamic loads and motions of offshore structures /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Testo completo
11
Fuglem, Mark. "Decision-making for offshore resource development". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34246.pdf.
Testo completo
12
Sadki, Nadia. "Faisabilité de modèles de terrain en offshore". Châtenay-Malabry, Ecole centrale de Paris, 2001. http://www.theses.fr/2001ECAP0711.
Testo completoAbstract (sommario):
On étudie la faisabilité d'une modélisation numérique de terrain en offshore. Cette modélisation sera basée sur les méthodes géostatistiques. Ces méthodes nécessitant un grand nombre de données, on va tout d'abord s'intéresser à l'échantillonnage des différentes mesures dont on dispose. On évaluera leurs supports (volume de mesure) et on se posera la question du passage d'un support à un autre. On étudiera ensuite la cohérence des données, par rapport à la profondeur, entre elles et par rapport aux paramètres de nature et de compacité. Cette étape sera suivie par une étude stratigraphique, basée sur la comparaison des profils de la résistance de pointe (CPTU), afin de confirmer ou d'infirmer l'homogénéité verticale et horizontale du site étudié. Pour cette étape de l'étude, on a développé un outil semi-automatique de nettoyage des artefacts du CPTU. On terminera notre étude par une comparaison des méthodes variographique et analyses factorielles; ainsi que par une étude variographique de la résistance de pointe.
13
Souissi, Ridha. "Fléxibilité des jonctions tubulaires dans les structures offshore". Paris 6, 1991. http://www.theses.fr/1991PA066640.
Testo completoAbstract (sommario):
En élasticité linéaire et dans le cadre de l'hypothèse de petites perturbations, on présente dans cette thèse une méthodologie générale permettant la prise en compte lors de l'analyse globale des structures offshore de type jacket du comportement des coques des zones de liaison entre tubes: jonctions tubulaires. Cela revient a prendre en compte la flexibilité ou semi-rigidite de la jonction, considérée comme nulle ou infinie dans une analyse conventionnelle. Une illustration de la méthodologie générale a été faite sur une jonction en t, en procédant de la manière suivante: définition d'un élément de jonction. Apres une analyse critique originale présentant les degrés d'approximation des modèles de coques cylindriques existants (flugge, timoshenko, sanders-koiter, koiter-morley-niordson) et montrant les mérites du modèle de koiter-morley-niordson, une analyse semi-analytique a permis de définir les frontières de l'élément de jonction; détermination de la matrice de rigidité de l'élément de jonction. En utilisant la méthode des éléments finis et en appliquant la technique de condensation statique, on a détermine la matrice de rigidité de 23 éléments de jonction choisis pour mesurer l'influence des paramètres géométriques sur la flexibilité de la jonction; détermination d'un modèle simplifie équivalent. Les matrices de rigidité obtenues ont permis de construire un modèle simplifie équivalent (modèle poutres ressorts), et l'on présente l'évolution des caractéristiques des ressorts en fonction des caractéristiques géométriques de la jonction tubulaire; introduction de la rigidité de la jonction dans l'analyse globale. Une illustration de l'influence de la semi-rigidite de la jonction sur le comportement de la structure a été faite en analysant une structure plane de 4 étages
14
Lubbad, Raed Khalil. "Some Aspects of Arctic Offshore Floating Structures". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12334.
Testo completoAbstract (sommario):
The present work highlights some aspects related to the analyses of Arctic offshore floating structures. This thesis consists of five papers, which can be divided into two main categories. One category deals with the dynamics of slender structures with an emphasis on the prediction and suppression of vortex induced vibrations (VIV), and the other category examines the process of interaction between sloping structures and sea ice with focus on developing a numerical model to simulate this process in real time. Slender structures, such as mooring lines and marine risers, are very important for the offshore petroleum industry, which is currently approaching deeper waters. Increasingly, attention has been focused on predicting the susceptibility of these structures to VIV. In this thesis, two asymptotic techniques namely, the local analysis and the WKB methods, were used to derive closed-form solutions for the natural frequencies and mode shapes of slender line-like structures. Both the top-tensioned nearly-vertical configuration and the catenary configuration were considered. The accuracy of the solutions derived was established through comparison with other analytic solution techniques and with results of numerical finite element solutions. The effects of the bending stiffness and the effects of approximating the tension variation as a linear function were discussed. Experimental data on the multi-modal in-line and cross-flow response behaviour of a towed catenary model were analysed to examine the usefulness of the solutions for predicting the response frequencies and envelopes due to VIV. Helical strakes are often used as a mitigating measure to suppress the VIV of slender structures. This thesis presented an innovative method to fit ropes helically to a riser in the installation phase. Such a procedure will help to overcome the handling problem associated with the use of conventional sharp-edged strakes. Experimental investigations were then performed to verify the efficiency of these ropes (round-sectioned helical strakes) in suppressing VIV. Systematic experimental investigations including twenty-eight configurations of round-sectioned helical strakes were tested in an attempt to find the most suitable strake configuration. The effects of varying pitch, the surface roughness and the ratio between the cross-flow and in-line natural frequencies on the efficiency of the proposed configuration of round-sectioned helical strakes were also investigated. The process of interaction between sea ice and offshore sloping structures (e.g., conical structures and ship-shaped structures) is quite complex. Modelling this process is very demanding and often computationally expensive, which typically hinders the chances for realtime simulations. This kind of simulation can be very useful for training personnel for Arctic offshore operations and procedures, for analysing the efficiency of various ice management concepts and as a part of the onboard support systems for station keeping. The challenge of meeting the real-time criterion was overcome in the present work. This thesis developed a numerical model to simulate the process of interaction between sea ice and sloping structures in real time. In this model, only level- and broken-ice features were studied. New analytical closed-form solutions were established and used to represent the ice breaking process. PhysX was used for the first time to solve the equations of rigid body motions with six degrees of freedom for all ice floes in the calculation domain. The results of the simulator were validated against experimental data from model-scale and full-scale tests. Accurate predictions of ice actions are also vital to optimise the design of the structures in the Arctic regions. A good understanding of the role of seawater in the process of interaction between the sloping structures and level ice will help to establish reliable models to estimate the ice forces. This work formulated both the static and dynamic bending problems for a floating wedge-shaped ice beam interacting with an offshore sloping structure. For the dynamic interaction, the effects of the water foundation on the bending failure of the ice were studied by comparing the results of an elastohydrodynamic approach with a model of a Winkler foundation. The thesis also investigated the breaking lengths of the ice wedges (i.e., the frequency of the ice loads) as a function of the ice thickness, the compression in the ice and the acceleration of the interaction.
15
Foroughi, Abdol Rahim. "Uncertainties in environmental loading on offshore structures". Thesis, University of Sunderland, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385010.
Testo completo
16
Monahan, Craig C. "Early fatigue crack growth in offshore structures". Thesis, University College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271908.
Testo completo
17
Kathiroli, S. "Optimisation of members of floating offshore structures". Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235703.
Testo completo
18
Emmerhoff, Ole Johannes. "The slow drift motions of offshore structures". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36503.
Testo completo
19
Latini, Corazzini Valentina. "Non-linear dynamic analysis of offshore structures". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amslaurea.unibo.it/359/.
Testo completo
20
Reyburn, Elizabeth Maury. "The design of offshore structures using load and resistance factor design". Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19978.
Testo completo
21
Chau, Fun-pang. "Numerical methods in wave loading of large offshore structures /". [Hong Kong] : University of Hong Kong, 1985. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12315916.
Testo completo
22
Jester, William Andrew. "Interactive numerical simulation of riser interference phenomena in offshore structures /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004297.
Testo completo
23
Venkataraman, Vijay. "Dynamic Response of a Mobile Offshore Base Hydroelastic Test Model". Fogler Library, University of Maine, 2001. http://www.library.umaine.edu/theses/pdf/VenkataramanV2001.pdf.
Testo completo
24
周奮鵬 e Fun-pang Chau. "Numerical methods in wave loading of large offshore structures". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1985. http://hub.hku.hk/bib/B31206797.
Testo completo
25
Coccon, Marco. "Structural Reliability Analysis of Complex Systems: Applications to Offshore and Composite Structures". Doctoral thesis, Università degli studi di Padova, 2015. http://hdl.handle.net/11577/3424201.
Testo completoAbstract (sommario):
This thesis aims at developing new methodologies for the reliability analysis of structural systems with applications to offshore and aeronautical fields. In general, sructures of practical interest are complex redundant systems, in which more than one element is required to fail in order to have catastrophic failure. Moreover, ramdomness inherently exists in both material properties and external loads. As a result, complex structural systems are typically characterised by a huge number of possible failure sequences, of which only some are most likely to occour. Therefore, for an efficient risk analysis, only the dominant failure modes need to be considered, so as to minimise the number of failure paths as well as the computational costs associated to their enumeration and evaluation. However, although several techniques have been developed for the identification of the critical failure sequences, these methods are still either time-demanding or prone to miss potential failure modes.
These challenges motivated the first part of the thesis, in which the merits of a risk assessment framework recently developed for truss and frame structures are here investigated in view of its extensive application to the offshore field. To this end, the case study of a jacket-type platform under an extreme sea state is considered. First, the dominant failure modes of the structure are rapidly identified by a multi-point parallel search employing a genetic algorithm. Then, a multi-scale system reliability analysis is performed, in which the statistical dependence among both structural elements and failure modes is fully considered through simple matrix operations. Finally, the accuracy and the efficiency of the proposed approach are successfully validated against crude Monte Carlo simulation.
In the second part of the thesis, system reliability theory is applied to the uncertainty quantification of the longitudinal tensile strength of UniDirectional (UD) composites, a structural component very common in aircraft structures. Predictive models for size effects in this class of materials are paramount for scaling small-coupon experimental results to the design of large composite structures. In this respect, a Monte Carlo progressive failure analysis is proposed to calculate the strength distributions of hierarchical fibre bundles, which are formed by grouping a predefined number of smaller-order bundles into a larger-order one. The present approach is firstly validated against a recent analytical model to be later applied to more complex load-sharing configurations. The resulting distributions are finally used to analyse the damage accumulation process and the formation of clusters of broken fibres during progressive failure.Lo scopo principale di questa tesi è lo sviluppo di nuove metodologie per determinare l’affidabilità dei sistemi strutturali con applicazioni sia in campo offshore che aeronautico. In generale, strutture di interesse pratico sono caratterizzate da un elevato grado di ridondanza, per cui il collasso globale richiede la rottura simulatanea e/o progressiva di più elementi. Inoltre, i sistemi fisici sono influenzati da diverse fonti di incertezza, quali le prorietà dei materiali e le condizioni ambientali e operative. Pertanto, il collasso strutturale può avvenire con diverse modalità (modi di guasto), di cui solo alcune possiedono una probabilità di accadimento significativa (modi di guasto dominanti). Per una valutazione efficiente del rischio risulta dunque indispensabile limitare l’analisi ai soli modi dominanti, così da ridurre il costo computazionale associato alle fasi di identificazione e di valutazione dei modi stessi. Tuttavia, nonostante in letteratura vi siano numerose soluzioni per l’analisi del rischio, tali metodi richiedono ancora tempi di calcolo notevoli e sono inclini a tralasciare potenziali modi di guasto. Queste motivazioni conducono alla prima parte delle tesi, in cui si ripropone un metodo recentemente sviluppato per l’analisi del rischio di strutture discrete (reticolari e telai) in previsione di una sua applicazione al campo offshore. A tale scopo si considera il caso di studio di una piattaforma di tipo jacket in condizioni di mare estremo. Dapprima, i modi di guasto dominanti vengono rapidamente identificati per mezzo di un algoritmo genetico. In seguito, l’affidabilità del sistema viene calcolata mediante un approccio multi-scala che fa uso di semplici operazioni matriciali, in cui la dipendenza statistica viene considerata sia tra le componenti strutturali che tra i modi di guasto dominanti. Infine, l’accuratezza e l’efficienza del metodo vengono testate con successo tramite comparazione con Monte Carlo. Nella seconda parte della tesi, la teoria dell’affidabilità dei sistemi viene applicata per la quantificazione dell’incertezza nella resistenza a trazione di compositi UniDirezionali (UD), problema di notevole interesse per l’ambito aeronautico e non solo. Infatti, il comportamento aletorio di questi materiali è fortemente influenzato da effetti di scala, che limitano la progettazione di strutture in composito di grandi dimensioni sulla base dei dati sperimentali ricavati da provini. In quest’ottica, si propone di modellare fasci di fibre secondo una legge di scala gerarchica, ossia raggruppando un numero prestabilito di fasci più piccoli in un fascio di ordine superiore. La distribuzione di resistenza di tali fasci viene quindi simulata attraverso un’analisi di collasso progressivo. Questo approccio, dapprima validato rispetto ad un modello analitico recentemente sviluppato per disposizioni semplici di fasci, viene poi esteso a configurazioni più realistiche. I risultati così ottenuti sono infine processati per l’analisi statistica del danno.
26
Sarkar, Abhijit. "Dynamics of moored offshore structures in random seas". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284464.
Testo completo
27
Walker, Daniel Anthony Guy. "Interaction of extreme ocean waves with offshore structures". Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:6858dc08-1bd4-4195-8893-1af98d5e68e3.
Testo completoAbstract (sommario):
With most of the world's untouched oil and gas resources offshore and the possibility that hurricanes are becoming more frequent and more intense, the risks associated with offshore oil and gas production are increasing. Therefore, there is an urgent need to improve current understanding of extreme ocean waves and their interaction with structures. This thesis is concerned with the modelling of extreme ocean waves and their diffraction by offshore structures, with the ultimate aim of proposing improved tools for guiding airgap design. The feasibility of using linear and second order diffraction solutions with a suitable incident wave field to predict extreme green water levels beneath multi-column structures is investigated. Such tools, when fully validated, could replace the need to carry out model tests during preliminary design. When contemplating airgap design it is crucially important that consideration is given to the largest waves in a sea state, the so-called freak or rogue waves. This thesis studies the nature of one specific freak wave for which field data is available, namely the Draupner New Year wave. Unique features of this wave are identified, distinguishing it from a typical large wave, and an estimate of the probability of occurrence of the wave is given. Furthermore, a design wave, called NewWave, is proposed as a good model for large ocean waves and is validated against field and experimental data. The diffraction of regular waves and NewWaves by a number of structural configurations is studied. In order to assess the validity of using diffraction solutions for the purposes of airgap design, comparisons are made with measured wave data from a programme of wave tank experiments. Wave data for a real platform configuration are examined to highlight the key issues complicating the validation of diffraction based design tools for real structures. The ability of diffraction theory to reproduce real wave measurements is discussed. The phenomenon of near-trapping is also investigated, allowing guidelines for airgap design to be established.
28
Aritenang, Wendy. "Behaviour of composite tubular connections in offshore structures". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47336.
Testo completo
29
Kountouris, Ioannis Savvas. "The assessment of weld defects in offshore structures". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47520.
Testo completo
30
Liang, Yibo. "Vortex-induced motions of multiple cylindrical offshore structures". Thesis, University of Newcastle upon Tyne, 2018. http://hdl.handle.net/10443/4014.
Testo completoAbstract (sommario):
Vortex-induced motions (VIM) has been receiving continuous attention in the field of offshore exploration and exploitation as an increasing number of deep-draft floating structures have been operating in different regions around world. Deep-draft floating structures are well known for their favourable vertical motions behaviour compared with other types of floating offshore structures. However, the increases in the structure’s draft can also lead to more severe VIM, which may lead to potential damage particularly causing fatigue to the mooring and riser systems. This research is to carry out an in-depth study on the fundamental fluid physics and the associated hydrodynamic characteristics of a multi-column structure, i.e. the deep-draft semi-submersible (DDS). A comprehensive set of numerical simulations has been conducted and experimentally validated in physical models. Good correlation has been demonstrated among the vortex shedding patterns, the fluctuation forces on the structures, and the VIM trajectory in the present work. The “lock-in” phenomenon was found to have the most striking effect on the vortex shedding processes, the force and the VIM trajectories. Analysis of the drag and lift force coefficients on and the work done by different members of the DDS revealed that the portside and starboard side columns are the key structure members responsible for amplifying the VIM responses while the pontoons are acting to restrain VIM responses. Additionally, based on the analysis of flow over a stationary structure, it is revealed that adding the pontoons into the structures can significantly alter the flow patterns around the structure. The vortex street tends to be more tidy and structured. Hence, the vortex shedding period and the lift force coefficient for the overall structure are increased.
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Cofer, William Franklin. "An analytical determination of ultimate strength of tubular joints for offshore structures". Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/21494.
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Salgado, Francisco Manuel Goncalves Alves. "Analysis procedures for caisson-retained island type structures". Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30845.
Testo completoAbstract (sommario):
This thesis is concerned with the analysis of large offshore gravity structures used for oil exploration and recovery in the Beaufort Sea. Because of the high ice loads and the water depths involved, these structures comprise a large steel box infilled with a sand core for stability. One such structure was subjected to severe ice loading in April 1986 causing portions of the sand core to liquefy and bring the structure to a near failure condition. This structure was heavily monitored and thus serves as a case study against which the proposed analysis procedure can be checked.
The behaviour of these soil-structure systems is highly complex depending upon the characteristics of the soil, the structural elements and the soil-structure interface. In this thesis a three-dimensional Finite Element computer program with soil, interface and structural elements is developed.
Emphasis is placed on the three-dimensional stress-strain constitutive law both in terms of its ability to model observed laboratory response as well as the determination of the constitutive law parameters from in situ testing.
The results obtained in terms of displacement, acceleration and zones of liquefaction by the analysis were then compared with the field measurements obtained during the April 1986 ice load event. The good agreement obtained between predicted and observed response is a validation of the proposed procedure.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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McGowan, David. "Ultimate capacity of offshore platform conductor strings". Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41703.
Testo completoAbstract (sommario):
The ultimate capacity of offshore platform conductor strings is studied. The unique way in which conductors are loaded is described and the various design methods that exist are presented. Previous research in the field of tubular member behavior is also reviewed.
The results of seven experimental tests are evaluated and compared with the existing conductor design criteria. The test matrix calls for various amounts of lateral loading to be imposed on the conductor system. Axial load, applied to simulate the weight of inner casings, is then applied until failure.
Results indicate that internally applied axial loads do not induce stability related failure in the outer conductor. Additionally, the design internal moment, which is based on an inner casing being as eccentric as possible, accurately represents the upper limit for the bending moment observed in the experimental tests. The flexural stiffness of the inner casing serves to strengthen the conductor system. Therefore, a design method that considers the strength of the outer conductor and the inner casings is recommended.Master of Science
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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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Cheung, Kwok Fai. "Hydrodynamic interactions between ice masses and large offshore structures". Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26686.
Testo completoAbstract (sommario):
The objective of the work described in this thesis is to evaluate the significance of the ambient fluid on the motion of an ice mass in the vicinity of an offshore structure and during the subsequent impact mechanism.
Models for iceberg drift are first reviewed. The changes in flow field around an ice mass drifting in a current near an offshore structure are investigated by potential flow theory. The proximity effects and current interactions are generalized by introducing the added mass and convective force coefficients for the ice mass. A two-dimensional numerical model based on the boundary element method is developed to calculate these coefficients over a range of separation distances up to the point of contact.
A numerical model based on ice properties and geometry is developed to simulate the impact force acting on the structure. Both the 'contact-point' added masses estimated in this thesis and the traditionally assumed far-field added masses are used in the impact model separately. The results from the two cases are compared and the crucial roles played by the ambient fluid during impact are discussed.
Finally, a number of related topics is proposed for further studies.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Sakamoto, Takashi. "Nonlinear static and dynamic analysis of flexible risers subjected to vortex excitation". Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309379.
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Tang, Zifan. "One-dimensional mechanistic modelling of gas-liquid two phase flow in pipes". Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284815.
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Hardy, Noel. "Parallel computing in marine technology". Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357632.
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Batt, C. "Optimising cathodic protection requirements for high strength steels in the marine environment". Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323886.
Testo completo
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Zhang, Yahui. "Response statistics of a floating vessel in spreading seas". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609145.
Testo completo
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Olowe, Adedayo Christianah. "Corrosion assessment and cathodic protection design parameters for steel structures in deep and ultra deep offshore waters". Thesis, University of Aberdeen, 2013. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=201965.
Testo completoAbstract (sommario):
Carbon steel finds much application for use in industries including civil; manufacturing; oil and gas; as well as, renewable energy. Common examples for usage of steel include water pipelines; oil pipelines; bridges; etc. The main advantages of steel over other engineering materials are its strength and affordability. However, steel undergoes corrosion which is a degradation mechanism that occurs as a result of the electrochemical interaction between steel and its environment. There are two main options to control corrosion, aside from material selection techniques, namely, the use of protective coating systems to isolate the steel from the environment; or the use of cathodic protection. Cathodic protection involves the use of galvanic anodes or impressed current system to prevent steel corrosion. Currently the oil and gas industry accounts for the major share of consumption of galvanic anodes for the protection of steel in engineering applications. Recent incursions into deep water depths by the Oil and Gas industry in the last decade or so has brought to the fore the need to understand better the performance of steel at deep and ultra deep water depths; as well as to develop an understanding of how cathodic protection works at these water depths. So far, the bulk of industry experience lies in shallow waters and current international cathodic protection design guidelines are based on data collated at these shallow water depths. It is the objective of this research work to assess the corrosion properties of steel with deep seawater parameters and determine design current density requirements for effective cathodic protection of steel at deep and ultra deep water depths offshore.
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Rguig, Mustapha. "Méthodologie des surfaces de réponse pour l'analyse en fiabilité des plates-formes pétrolières offshore fissurées". Nantes, 2005. http://www.theses.fr/2005NANT2044.
Testo completoAbstract (sommario):
Durant les années 70, un grand nombre de structures offshore de type jacket, treillis, composées de joints tubulaires soudés, ont été implantées. Certaines d'entre elles présentent une réserve importante de résistance malgré les défaillances locales observées. L'objectif de ce travail de recherche est l'examen de l'impact des fissures traversantes. L'idée est de développer des surfaces de réponse physiques introduisant le chargement aléatoire de la houle et la géométrie aléatoire de la fissure. On choisit de modéliser au niveau global l'effet d'une fissure traversante en utilisant un critère de type évolution de l'énergie potentielle totale ou évolution du déplacement d'un nœud stratégique de la structure. On s'appuie pour cela sur la méthode des surfaces de réponse en couplant l'analyse mécanique (Rouhan 1999) généralisée en 3D et les sollicitations (Schoefs 1996). Des illustrations sont présentées en s'appuyant sur des structures usuelles de l'industrie pétrolière offshoreThe structures built during the Seventies present a significant reserve of resistance in spite of the local failures observed. The objective of this research task is the examination of the impact of the through cracks on metal offshore structures made up of welded tubes. The idea is to model at the total level the effect of a through crack using a criterion of the type evolution of total potential energy or evolution of the displacement of a strategic node of the structure. Indeed, these structures, conceived in the Seventies, are very redundant and profit from a reserve of significant integrity. All the dubious or random sizes, length of crack, loading of swell. . . , are modelled and integrated by approaches of the probabilistic types. One use for that the method of response surfaces by coupling the mechanical analysis (Rouhan 1999) and the requests (Schoefs 1996)
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El-Gharbawy, Sherif Lotfy. "The pullout capacity of suction caisson foundations /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Amundsen, Morten. "Dynamic Analysis of Offshore Concrete Structures subjected to Earthquake". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19005.
Testo completoAbstract (sommario):
This thesis attempts to study the dynamic response of offshore concrete structures by sequentially introducing physical phenomena which are related to those types of analyses. This is done by modelling a simplified part of a typical offshore concrete structure, with the purpose of establishing a reference case, on which more advanced analyses can be based, as well as evaluate simplified approaches that serve to shorten the analysis time.To establish characteristic earthquakes for the selected return periods of 475, 1000, 3000 and 10 000 years, a seismic hazard analysis is performed for an area slightly off the southwest coast of Norway. Here, information from 964 earthquakes was collected, such that the Gutenberg-Richter relationship could be established. Based on this, 50 000 earthquakes were generated based on Monte Carlo simulations, which served as an extrapolation from which order statistics could be performed. The determined characteristic earthquake parameters for the different return periods were found to have a remarkable similarity with the seismic zonation maps used in most design codes. Finally, the applied accelerogram for a given return period was simulated from a response spectrum which was chosen to be similar to the mean response spectrum for that return period.A comparison was made between the time history and response spectrum analysis, where three modal combination methods were evaluated. It was found that the results were either impractically conservative, or dangerously unconservative for all return periods, suggesting that the response spectrum analysis is not applicable for the investigated structure.A material model which included plasticity was evaluated, which resulted in margin-ally lower stresses, slightly reduced eigenfrequencies and small changes displacements of the top of the shaft. With the inclusion of elastic stiffness degradation, the results were similar, leading to the conclusion that plasticity is an unnecessary complication, as the large dimensions of the structure combined with the low seismicity of the North Sea results in a structural behaviour which is approximately elastic for all return periods.Two methods for the modelling of surrounding water was tested. The first was the added mass method, where the stresses mostly increased, except for the 10 000-year earthquake. The second method was an acoustic-structural interaction, where the fluid around the structure was modelled. This resulted in similar stresses for all return periods, and gives credibility to the simplified method. For either methods, the eigenfrequencies were reduced significantly.The soil upon which the structure rests was included into the analysis by two methods. The first method involved the use of springs and dashpots which were made to represent the stiffness and damping of the soil. The other method was a finite element analysis of the soil layer. Both soft and hard soil was tested, and for the soft soil, the stresses were radically reduced, as the structure became almost fully isolated from the earthquake. The stiffer soil resulted in higher stresses. The two methods agreed for the soft soil, but not for the hard soil. This was found to be caused by the spring method being overly simplistic.
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Shetty, Navilkumar. "System reliability of fixed offshore structures under fatigue deterioration". Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/7581.
Testo completo
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Helmy, Amr Ibrahim I. "Behaviour of offshore reinforced concrete structures under hydrostatic pressure". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq35181.pdf.
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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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Santa, Maria Paulo Eduardo Lima de. "Behaviour of footings for offshore structures under combined loads". Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:50fb3d35-90b3-4685-9ace-0ec5a50014df.
Testo completoAbstract (sommario):
The lack of knowledge about the behaviour of footings for jack-up rigs under storm loads poses a design problem which can be tackled by model testing. The areas of prime concern are the ultimate loads on footings under combined loading, which affects the safety of the rig, and the rotational stiffness, which affects the interaction between the foundation and the structure. A programme of loading tests was performed on model footings on clay, and was divided into two stages: monotonic loading and cyclic loading. The clay samples were obtained by consolidating Speswhite kaolin slurry in cylindrical tanks 450mm in diameter. The strength and compressibility characteristics of the samples were verified by means of standard laboratory tests. The model footings were 50mm and 100mm in diameter and several shapes were tested: circular flat plate, cones of various angles and model spud-cans. Loads and displacements were monitored using appropriate instrumentation and a data logger. A series of central vertical loading tests provided data for comparison with existing bearing capacity theories. Combined loading tests were performed applying a displacement controlled horizontal load at a fixed height above the footing which was also subjected to a fixed vertical load. The main series of tests involved a parametric study of the relevant variables. Special tests allowed the assessment of the effect of embedment of the footing and the interaction of a flexible leg with the foundation. Cyclic loading tests were carried out using a load controlled system which applied a sinusoidal load simulating wave action. Effects of currents were investigated by introducing an offset to the loading cycle. The influence of amplitude and period of loading as well as the influence of vertical load were also investigated. Special tests were carried out to cover some peculiarities of real loading conditions. Fitting of a three-parameter hyperbola to the test results provided a systematic and accurate method of analysis of monotonic loading tests, leading to valuable information involving stiffness and ultimate loads. Analysis of cyclic loading tests yielded useful qualitative information regarding the progress of settlement and the variation of rotational stiffness and damping ratio with the number of cycles.
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Ohl, Clifford Owen Groome. "Free surface disturbances and nonlinear runup around offshore structures". Thesis, University of Oxford, 2000. http://ora.ox.ac.uk/objects/uuid:320ff8da-c225-40da-a7dd-d6cf55c97b51.
Testo completoAbstract (sommario):
Diffraction of regular waves, focused wave groups, and random seas by arrays of vertical bottom mounted circular cylinders is investigated using theoretical, computational, and experimental methods. Free surface elevation η is the defining variable used to test the potential theory developed. In addition, the nonlinearity of focused wave groups is investigated through the Creamer nonlinear transform and analysis of numerical wave tank data. Linear focused wave group theory is reviewed as a method for predicting the probable shape of extreme events from random wave spectra. The Creamer nonlinear transform, a realistic model for steep waves on deep water, is applied in integral form to simulate nonlinear focused wave groups. In addition, the transform is used to facilitate analysis of nonlinear wave-wave interactions within focused wave groups from a uni-directional numerical wave tank developed at Imperial College London. Experiments in an offshore wave basin at HR Wallingford are designed to measure free surface elevation at multiple locations in the vicinity of a multicolumn structure subjected to regular and irregular waves for a range of frequencies and steepness. Results from regular wave data analysis for first order amplitudes are compared to analytical linear diffraction theory, which is shown to be accurate for predicting incident waves of low steepness. However, second and third order responses are also computed, and the effects in the vicinity of a second order near trapping frequency are compared to semi-analytical second order diffraction theory. Analytical linear diffraction theory is extended for application to focused wave groups and random seas. Experimental irregular wave data are analysed for comparison with this theory. Linear diffraction theory for random seas is shown to give an excellent prediction of incident wave spectral diffraction, while linear diffraction theory for focused wave groups works well for linearised extreme events.
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Janardhanan, K. "The dynamics of flexible offshore structures in irregular seaways". Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385096.
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