A review of the developments within the field of structural reliability theory shows that some gaps still exist in the reliability prediction process and hence there is an urgent desire for improvements such that the estimated structural reliability will be capable of expressing a physical property of the given structure. The current reliability prediction process involves the continuous estimation and use of reliability index as a way of estimating the safety of any given structure. The reliability index β depends on the Probability Density Function (PDF) distribution for the wave force and the corresponding PDF of resistance from respective structural members of the given structure. The PDF for the applied wave force will depend on the PDF of water depth, wave angular velocity and wave direction hence the reliability index as currently practiced is a statistical way of managing uncertainties based on a general probabilistic model. This research on Smart Offshore Structure for Reliability Prediction has proposed the design of a measurement based reliability prediction process as a way of closing the gap on structural reliability prediction process. Structural deflection and damping are some of the measurable properties of an offshore structure and this study aims at suggesting the use of these measurable properties for improvements in structural reliability prediction process. A design case study has shown that a typical offshore structure can deflect to a range of only a few fractions of a millimetre. This implies that if we have a way of monitoring this level of deflection, we could use the results from such measurement for the detection of a structural member failure. This advocated concept is based on the hypothesis that if the original dynamic characteristics of a structure is known, that measurement based modified dynamic properties can be used to determine the onset of failure or failure propagation of the given structure. This technology could reveal the location and magnitude of internal cracks or corrosion effects on any given structure which currently is outside the current probability based approach. A simple economic analysis shows that the recommended process shows a positive net present value and that some $74mln is the Value of Information for any life extension technology that could reveal the possibility of extending the life of a given 10,000bopd production platform from 2025 to 2028.

[Truncated abstract] The Arabian Gulf oil and gas production reserves have made it one of the world's strategic producers since early 1960s, with many of the existing platforms stretched beyond their original design life. Advances in drilling technology and reservoir assessments have extended the requirement for the service life of those existing platforms even further. Extension of the life span of an existing platform requires satisfactory reassessment of its various structural components, including piled foundations. The American Petroleum Institute Recommended Practice 2A (API RP2A) is commonly used in the Arabian Gulf for reassessment of existing platforms. The API guidelines have been developed for conditions in the Gulf of Mexico, the waters off Alaska and the Pacific and Atlantic seaboards of the USA. However, the Arabian Gulf conditions are fundamentally different to those encountered in US waters. Hence, there is a need to develop guidelines for reassessment of existing offshore structures to account for the specific conditions of the Arabian Gulf. This thesis performs statistical analyses on databases collected during this research from existing platforms to calibrate relevant load and resistance factors for the required guidelines. The developed guidelines are based on established approaches used in developing international codes and standards such as API RP2A-LRFD. The outcome of this research revolves around the following three main issues: 1. Calibration of resistance factors for axial capacity of piles driven in the carbonate soils API RP2A (1993, 2000) does not quantify limiting soil parameters for piles driven in carbonate soils and provides a single factor to predict the capacity of piled foundations. This research identifies a set of limiting engineering parameters and calibrates corresponding capacity reduction factors to predict axial capacity of driven piles in the carbonate soils of the Arabian Gulf. ... This contrasts with Section 'R' of API RP2A (1993, 2000), which focuses on extreme environmental conditions when performing reassessment. The probabilities of failure considered in this research do not include errors and omissions (controlled by quality assurance procedures) or material deterioration (controlled by choice of materials, detailing, protective devices, and inspection and repair procedures) or reliability-based maintenance. Addressing operating overload conditions requires attending to two issues, namely the capacity of piles driven in carbonate soils and OALL, which have been addressed in this research. The operational overload situation is likely to occur during shutdown condition or during drilling or work over activities where significant OALL are usually applied to platform decks. Such operational overload can be managed by placing signs at various open areas on the platform nominating the maximum load limits (kPa), introducing procedures that ensure that maximum load limits are not exceeded during operation and management of human behavior by reinforcing the importance of following the procedures. The outcomes of this research are expected to have a profound influence on reassessment of existing platforms in the Arabian Gulf.

[Formulae and special characters can only be approximated here. Please see the pdf version of the abstract for an accurate reproduction.] Wave run-up is the vertical uprush of water when an incident wave impinges on a free- surface penetrating body. For large volume offshore structures the wave run-up on the weather side of the supporting columns is particularly important for air-gap design and ultimately the avoidance of pressure impulse loads on the underside of the deck structure. This investigation focuses on the limitations of conventional wave diffraction theory, where the free-surface boundary condition is treated by a Stokes expansion, in predicting the harmonic components of the wave run-up, and the presentation of a simplified procedure for the prediction of wave run-up. The wave run-up is studied on fixed vertical cylinders in plane progressive waves. These progressive waves are of a form suitable for description by Stokes' wave theory whereby the typical energy content of a wave train consists of one fundamental harmonic and corresponding phase locked Fourier components. The choice of monochromatic waves is indicative of ocean environments for large volume structures in the diffraction regime where the assumption of potential flow theory is applicable, or more formally A/a < Ο(1) (A and a being the wave amplitude and cylinder radius respectively). One of the unique aspects of this work is the investigation of column geometry effects - in terms of square cylinders with rounded edges - on the wave run-up. The rounded edges of each cylinder are described by the dimensionless parameter rc/a which denotes the ratio of edge corner radius to half-width of a typical column with longitudinal axis perpendicular to the quiescent free-surface. An experimental campaign was undertaken where the wave run-up on a fixed column in plane progressive waves was measured with wire probes located close to the cylinder. Based on an appropriate dimensional analysis, the wave environment was represented by a parametric variation of the scattering parameter ka and wave steepness kA (where k denotes the wave number). The effect of column geometry was investigated by varying the edge corner radius ratio within the domain 0 <=rc/a <= 1, where the upper and lower bounds correspond to a circular and square shaped cylinder respectively. The water depth is assumed infinite so that the wave run-up caused purely by wave-structure interaction is examined without the additional influence of a non-decaying horizontal fluid velocity and finite depth effects on wave dispersion. The zero-, first-, second- and third-harmonics of the wave run-up are examined to determine the importance of each with regard to local wave diffraction and incident wave non-linearities. The modulus and phase of these harmonics are compared to corresponding theoretical predictions from conventional diffraction theory to second-order in wave steepness. As a result, a basis is formed for the applicability of a Stokes expansion to the free-surface boundary condition of the diffraction problem, and its limitations in terms of local wave scattering and incident wave non-linearities. An analytical approach is pursued and solved in the long wavelength regime for the interaction of a plane progressive wave with a circular cylinder in an ideal fluid. The classical Stokesian assumption of infinitesimal wave amplitude is invoked to treat the free-surface boundary condition along with an unconventional requirement that the cylinder width is assumed much smaller than the incident wavelength. This additional assumption is justified because critical wavelengths for wave run-up on a fixed cylinder are typically much larger in magnitude than the cylinder's width. In the solution, two coupled perturbation schemes, incorporating a classical Stokes expansion and cylinder slenderness expansion, are invoked and the boundary value problem solved to third-order. The formulation of the diffraction problem in this manner allows for third-harmonic diffraction effects and higher-order effects operating at the first-harmonic to be found. In general, the complete wave run-up is not well accounted for by a second-order Stokes expansion of the free-surface boundary condition and wave elevation. This is however, dependent upon the coupling of ka and kA. In particular, whilst the modulus and phase of the second-harmonic are moderately predicted, the mean set-up is not well predicted by a second-order Stokes expansion scheme. This is thought to be caused by higher than second-order non-linear effects since experimental evidence has revealed higher-order diffraction effects operating at the first-harmonic in waves of moderate to large steepness when k < < 1. These higher-order effects, operating at the first-harmonic, can be partially accounted for by the proposed long wavelength formulation. For small ka and large kA, subsequent comparisons with measured results do indeed provide a better agreement than the classical linear diffraction solution of Havelock (1940). To account for the complete wave run-up, a unique approach has been adopted where a correction is applied to a first-harmonic analytical solution. The remaining non-linear portion is accounted for by two methods. The first method is based on regression analysis in terms of ka and kA and provides an additive correction to the first-harmonic solution. The second method involves an amplification correction of the first-harmonic. This utilises Bernoulli's equation applied at the mean free-surface position where the constant of proportionality is empirically determined and is inversely proportional to ka. The experimental and numerical results suggest that the wave run-up increases as rc/a--› 0, however this is most significant for short waves and long waves of large steepness. Of the harmonic components, experimental evidence suggests that the effect of a variation in rc/a on the wave run-up is particularly significant for the first-harmonic only. Furthermore, the corner radius effect on the first-harmonic wave run-up is well predicted by numerical calculations using the boundary element method. Given this, the proposed simplified wave run-up model includes an additional geometry correction which accounts for rc/a to first-order in local wave diffraction. From a practical view point, it is the simplified model that is most useful for platform designers to predict the wave run-up on a surface piercing column. It is computationally inexpensive and the comparison of this model with measured results has proved more promising than previously proposed schemes.

Mais recentemente a exploração offshore de petróleo e gás tem se intensificado na costa brasileira. Uma das características da exploração offshore no Brasil está ligada ao fato de os hidrocarbonetos se situarem a grandes profundidades no mar, frequentemente abaixo de uma espessa camada de sal, exigindo o desenvolvimento de novas tecnologias para vencer os desafios para sua prospecção e extração. A profundidade dos poços pode variar entre dois mil e sete mil metros abaixo da superfície do mar. Um dos grandes desafios é garantir uma boa conexão dos equipamentos de extração com a unidade de produção na superfície, o que se faz com risers. Há distintas configurações de risers, entre as quais os verticais, em catenária, lazy waves ou steep waves, sendo que o riser em catenária e o vertical, em particular, serão estudados aqui. Este trabalho visa a estudar os efeitos dinâmicos não lineares no riser, que, por ser extremamente esbelto, exige a consideração da não linearidade geométrica. Entre eles, destaca-se a possibilidade de ocorrência da ressonância paramétrica. Os carregamentos dinâmicos podem ser provenientes da movimentação da unidade flutuante, correntezas ou escoamento interno. Neste trabalho serão elaborados modelos em elementos finitos, utilizando o software Abaqus, que possui mais recursos que a maioria dos softwares comerciais para as análises que se pretende realizar. Esses modelos simularão inicialmente a configuração de equilíbrio estático do riser e posteriormente serão adicionados os carregamentos dinâmicos. Na representação do encontro do riser com o solo no fundo do mar, serão utilizados elementos de contato elásticos. Pretende-se discutir a viabilidade e as limitações no uso de programas generalistas de análise estrutural pelo método dos elementos finitos, no confronto com programas dedicados, e ainda comparando os resultados obtidos com aqueles que decorrem de soluções analíticas, ou experimentais, quando disponíveis. / More recently the offshore oil and gas exploitation has being intensified on the Brazilian coast. One of the characteristics of offshore exploitation in Brazil is linked to the fact that hydrocarbons are located at great depths under the sea bed, often below a thick layer of salt, requiring the development of new technologies to meet these challenges. The depth of the wells can vary between 2,000 and 7,000 meters below the sea surface. A major challenge is to ensure a good connection between the extraction system and the production unit at the sea surface, which is provided by risers. There are different configurations of risers, including the vertical, catenary, lazy-wave or steep-wave; the catenary and vertical risers will be studied in this work. This work aims at studying the nonlinear dynamic effects on the riser, which, being extremely slender, requires consideration of the geometric nonlinearity. Among them, there is the possibility of occurrence of parametric resonance. The dynamic loads may come from the motion of the floating unit and external or internal fluid flow. This work will be developed using finite-element models in Abaqus, which has more resources than most commercial softwares to carry out the type of analyses of interest. Initially these models simulate the static equilibrium configuration of the catenary riser, which will be later disturbed by dynamic loads. The modeling of the so called touch-down zone (TDZ) will use elastic contact elements. It is intended to discuss the feasibility and limitations when using generalist codes for structural analysis by the finite-element method, in comparison with dedicated codes, and also to correlate these results with those from analytical and experimental studies, whenever available.

[pt] Este trabalho apresenta um método para calcular a resistência à fadiga de uma torre de perfuração considerando a elevação da superfície do mar, a dinâmica da plataforma na qual a torre está instalada e a dinâmica da própria torre. Modelos de ordem reduzida são utilizados para obter a elevação da superfície do mar e a dinâmica torre, e as incertezas nos parâmetros dos componentes do sistema podem ser incluídas na análise também. As análises podem ser feitas para vários estados de mar, conforme sua distribuição de probabilidade, e nenhuma hipótese sobre a distribuição de probabilidade precisa ser feita inicialmente. O histograma de distribuição de ciclos de tensão para toda vida útil do equipamento é obtido usando um procedimento de contagem de ciclos Rainflow. Os resultados e as incertezas nos mesmos são discutidos. / [en] This work presents a method for evaluation of the fatigue resistance of a drilling tower considering the sea surface elevation, the dynamics of the platform on which the tower is installed and the dynamics of the tower itself. Reduced order models are used for obtaining the sea surface elevation and the dynamics of the tower, and the uncertainties on the parameters of the components of the system can be included in the analysis as well. The analysis can be done for several sea states, according its probability distribution, and no assumption about the probability distribution of the stress ranges has to be made previously. The histogram for the distribution of stress ranges for the entire working life of the equipment is obtained using a Rainflow technique. The results and the uncertainties on them are discussed.

Orientador: Celso Kazuyuki Morooka / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica e Instituto de Geociencias / Made available in DSpace on 2018-08-04T17:58:55Z (GMT). No. of bitstreams: 1 ChampiFarfan_David_M.pdf: 3228003 bytes, checksum: 8b3ed290e87307aa0cc1afcdd9c2ecf3 (MD5) Previous issue date: 2005 / Resumo: Na atualidade as descobertas de óleo a grandes profundidades no mar têm levado ao desenvolvimento de campos localizados numa profundidade aproximada de 3000m, sendo então o sistema de Riser Híbrido Auto-Sustentável uma alternativa atraente. O presente trabalho apresenta os modelos matemáticos que descrevem o comportamento estático e dinâmico de um riser vertical com bóia de sub-superfície nas direções in-line, que é a direção da onda e correnteza no mar, e a direção transversal, perpendicular à direção in-line. Apresentam-se também simulações numéricas em diferentes condições de onda e correnteza e o seu efeito combinado, assim como o estudo paramétrico para as principais variáveis que influenciam no comportamento dinâmico e estático / Abstract: Nowadays, the oil discoveries at big depths in the sea have taken to the development of fields located in an approach depth of 3000m, being the Self Standing Hybrid Riser an attractive alternative. The present work presents the mathematical models that describe the static and dynamic behavior of a Vertical riser with a subsurface buoy in the directions inline, that it is the direction of the wave and currents in the sea, and the transversal, that is perpendicular to the in-line direction. Numerical simulations in different conditions of wave and currents are also presented and its combined effect is studied, as well as the parametric study for the main variable that influences its dynamic and static behavior / Mestrado / Explotação / Mestre em Ciências e Engenharia de Petróleo

Deux points de vue sont souvent opposés dans le cadre de la modélisation des systèmes complexes.D’un côté, une modélisation microscopique cherche à reproduire précisément le comportement des nombreuses entités qui composent le système, ce qui impose des temps de calculs prohibitifs pour le passage à l’échelle de système réels. À l’inverse, l’approche phénoménologique consiste à nous concentrer sur le comportement global du système. Ces modèles macroscopiques reposent sur des lois descriptives qui autorisent des simulations plus rapides mais impliquent l’introduction de paramètres qui peuvent être difficilement identifiables dans le contexte. Pour répondre à ce problème, nous proposons de combiner les différents points de vue de modélisation et d’utiliser des simulations microscopiques pour nourrir un modèle macroscopique incomplet.L’objectif est d’obtenir une simulation descriptive rapide tout en profitant de la précision d’un modèle microscopique. Pour cela, nous proposons une architecture logicielle qui s’appuie sur la technique de la co-simulation pour généraliser la démarche de simulation redondante d’échelles de modélisation hétérogènes.Nous distinguons deux stratégies de co-simulation qui permettent de piloter un modèle macroscopique en cours de simulation. La première consiste à estimer dynamiquement, et de manière explicite, de nouvelles valeurs pour un paramètre critique donné à l’aide d’un simulateur microscopique dédié. La seconde stratégie permet de déterminer implicitement un jeu de paramètres interdépendants sur la base d’une sortie commune des différents niveaux de description simulés. Nous appliquons nos travaux au problème concret du design de structures offshore pour des conditions polaires. Nous détaillons dans un premier temps l’implémentation d’un simulateur phénoménologique d’interactions glace-structure. Dans un second temps, nous illustrons l’intérêt et l’intégration de nos stratégies de co-simulation pour, d’une part améliorer la précision des simulations des phénomènes hydrodynamiques, et d’autre part guider un modèle de plus haut niveau à des fins de prototypage rapide. / There are usually two opposite points of view for the modelling of complex systems. First, microscopical models aim at reproducing precisely the behavior of each entity of the system. In general, their great number is a major obstacle both to simulate the model in a reasonable time and to identify global behaviors. By contrast, the phenomenological approach allows the construction of efficient models from a macroscopic point of view as a superposition of phenomena. A drawback is that we often have to set empirical parameters in these descriptive models. To respond to this problem, we want to make joint use of different levels of description and to use microscopical simulations to feed incomplete macroscopical models.We would then obtain enhanced descriptive simulations with the precision of microscopical models in this way. To this end, we propose a redundant multiscale architecture which is based on the co-simulation methodology in order to generalize the redundant multiscale approach. We suggest two specific co-simulation strategies to guide a macroscopical simulation.The first one consists in dynamically and explicitly estimating critical parameters of a macroscopical model thanks to a dedicated microscopical simulator The second one allows to implicitly determine a full set of dependant parameters on the basis of an output shared by the different levels of description. Then we apply our works to the effective problem of the design offshore structures for arctic conditions. We first describe the implementation of an ice-structure simulation tool by means of a phenomenological and multi-model approach. In a second phase, we show the benefits of our co-simulation strategies to improve the precision of hydrodynamics simulations on the one hand, and on the other to pilot a more macroscopical model for the purpose of fast prototyping.

The need to protect marine structures from the high-intensity impulsive loads created by underwater explosions has stimulated renewed interest in the mechanical response of sandwich structures. The objective of this combined numerical and experimental study is to analyze the dynamic response of composite sandwich structures and develop material-structure-property relations and design criteria for improving the blast-resistance of marine structures. Configurations analyzed include polymer foam core structures with planar geometries. A novel experimental facility to generate high-intensity underwater impulsive loads and carry out in-situ measurements of dynamic deformations in marine structures is developed. Experiments are supported by fully dynamic finite-element simulations which account for the effects of fluid-structure interaction, and the constitutive and damage response of E-glass/polyester composites and PVC foams. Results indicate that the core-density has a significant influence on dynamic deformations and failure modes. Polymeric foams experience considerable rate-effects and exhibit extensive shear cracking and collapse under high-magnitude multi-axial underwater impulsive loads. In structures with identical masses, low-density foam cores consistently outperform high-density foam cores, undergoing lesser deflections and transmitting smaller impulses. Calculations reveal a significant difference between the response of air-backed and water-backed structures. Water-backed structures undergo much greater damage and consequently need to absorb a much larger amount of energy than air-backed structures. The impulses transmitted through water-backed structures have significant implications for structural design. The thickness of the facesheets is varied under the conditions of constant material properties and core dimensions. The results reveal an optimal thickness of the facesheets which maximizes energy absorption in the core and minimizes the overall deflection of the structure.