Fendering systems are widely used in offshore installations for attenuating the effects of the impact energy of ships and barges in berthing or moored conditions. This study focuses on investigating current design practices and, developing a rational and functional approach to address random loading effects exerted on fendering systems. These loadings are often a consequence of combined wind, wave and current excitation as well as more controlled vessel motions. Dimensional analysis is used to investigate the degree to which empirical design data can be collapsed and to provide an indication of the nonlinearity associated with the empirical data for fender sizing. In addition, model test data specifically measuring the normal fender force for a coupled mini-TLP/Tender Barge performed at the Offshore Technology Research Center (OTRC) model basin is used in this research investigation.. This data was characterized in terms of the typical statistical moments, which include the mean, standard deviation, skewness and kurtosis. The maxima and extreme values are extracted from the fender response data based upon a zero-crossing analysis and the results were studied in order to determine the underlying probability distribution function. Using selected parameter estimation techniques, coefficients of a best-fit two parameter model were determined. An illustrative example is presented and discussed that contrasts the deterministic and probabilistic models.

This study investigated Floating Production Storage and Offloading (FPSO) responses under wave and current interactions. A higher order boundary element method (HOBEM) was adopted to probe the behavior of an FPSO. Forces and moment of an FPSO were studied under wave and current interactions. The simulations of diffracted and radiated waves were performed in a time domain. Time marching schemes were used for this time domain calculation. The predictor-corrector(P-C) method was used. Boundary integral equations were used to solve each problem with Rankine sources and distributed over the entire calculation domain. For the far-field boundary condition, Orlanski’s truncated open boundary condition was used for an open truncated boundary condition to prevent reflected waves. The current effect was considered an explicit term due to being a moving coordinate. Various current heading angles were also studied. Truncated open boundary, maximum likelihood method, proper element size and shape, modulation function, and Chebyshev filtering were studied to avoid diverged solutions. From our findings, higher order elements fitted a complicated model such as an FPSO. We found that this method required considerably fewer elements than the constant panel method in order to obtain reasonable outcomes. Using our developed numerical method, we calculated wave forces and moment, mean drift forces, added mass, and damping coefficients. Conclusively, HOBEM was found to be more effective and more reliable in calculating and predicting wave and current influence on an FPSO. Future studies are needed to develop finer simulation tools for FPSO’s large horizontal behavior.

Hoje em dia, a maioria das operações de alívio é feita utilizando um sistema de posicionamento dinâmico (DP). O sistema DP permite controlar a posição relativa entre o navio aliviador e o FPSO (Floating Production Storage and Offloading), trazendo desta forma muitas vantagens à operação. Neste tipo de operação os dois corpos flutuantes precisam ficar muito próximos um do outro em alto-mar, aumentando de forma significativa a interação hidrodinâmica entre eles. Quando um corpo está no mar ele se torna uma barreira à propagação das ondas, distorcendo o campo de ondas ao redor. Este efeito é chamado de efeito de sombra de onda ou simplesmente efeito de sombra. O efeito de sombra depende do comprimento de onda, do tamanho do corpo que o está criando e da direção de propagação da onda. O efeito de sombra altera de forma significativa a distribuição de energia das ondas do mar na região do fenômeno, alterando desta forma, o comportamento do corpo que está sob a influência do mesmo. Com o comportamento do corpo alterado é esperado que o sistema DP se comporte de forma diferente quando sob influência do efeito de sombra. Este trabalho se propõe a estudar a influência que o efeito de sombra causa no sistema DP, visando obter dados para melhorar os projetos de sistema DP. / Nowadays, a great number of offloading operations is carried out using a dynamic positioning (DP) system. The DP system allows the position between the shuttle tanker (ST) and the FPSO platform (Floating Production Storage and Offloading) to be controlled, bringing several advantages to the operation. In this kind of operation the two vessels must be kept very close in the sea, increasing significantly the hydrodynamic interaction effects between them. When a body is floating at the sea, it turns into a barrier to the wave propagation, disturbing the wave field around it. This effect is called shielding effect or shielding area. The shielding area depends on the wave length, the size of the body and the wave direction. The shielding area significantly disturbs the energy of the wave field nearby the FPSO. Because of that, it is expected that the shuttle tanker presents a different hydrodynamic behavior. The purpose of this work is to study the influence of the shielding area on the DP system, trying to obtain data to improve DP systems design.

Hoje em dia, a maioria das operações de alívio é feita utilizando um sistema de posicionamento dinâmico (DP). O sistema DP permite controlar a posição relativa entre o navio aliviador e o FPSO (Floating Production Storage and Offloading), trazendo desta forma muitas vantagens à operação. Neste tipo de operação os dois corpos flutuantes precisam ficar muito próximos um do outro em alto-mar, aumentando de forma significativa a interação hidrodinâmica entre eles. Quando um corpo está no mar ele se torna uma barreira à propagação das ondas, distorcendo o campo de ondas ao redor. Este efeito é chamado de efeito de sombra de onda ou simplesmente efeito de sombra. O efeito de sombra depende do comprimento de onda, do tamanho do corpo que o está criando e da direção de propagação da onda. O efeito de sombra altera de forma significativa a distribuição de energia das ondas do mar na região do fenômeno, alterando desta forma, o comportamento do corpo que está sob a influência do mesmo. Com o comportamento do corpo alterado é esperado que o sistema DP se comporte de forma diferente quando sob influência do efeito de sombra. Este trabalho se propõe a estudar a influência que o efeito de sombra causa no sistema DP, visando obter dados para melhorar os projetos de sistema DP. / Nowadays, a great number of offloading operations is carried out using a dynamic positioning (DP) system. The DP system allows the position between the shuttle tanker (ST) and the FPSO platform (Floating Production Storage and Offloading) to be controlled, bringing several advantages to the operation. In this kind of operation the two vessels must be kept very close in the sea, increasing significantly the hydrodynamic interaction effects between them. When a body is floating at the sea, it turns into a barrier to the wave propagation, disturbing the wave field around it. This effect is called shielding effect or shielding area. The shielding area depends on the wave length, the size of the body and the wave direction. The shielding area significantly disturbs the energy of the wave field nearby the FPSO. Because of that, it is expected that the shuttle tanker presents a different hydrodynamic behavior. The purpose of this work is to study the influence of the shielding area on the DP system, trying to obtain data to improve DP systems design.

Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The big research question is how the aeration of water and the elasticity of the structural section affect loading during severe environmental conditions. A further question is how the scattered waves from ships and offshore structures, the mooring line force and the structural response, which are known to affect local load and contribute to global load, will be affected by wave-structure interaction of a ship or offshore structure under non-breaking wave conditions. Three different experiments were undertaken in this study to try to answer these questions: (i) slamming impacts of a square flat rigid/elastic plate, which represents a plate section of the bottom or bow of ship structure, onto pure and aerated water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical rigid/elastic wall in pure and aerated water, where the wall represents a plate section of a hull; and (iii) wave-structure interactions of different FPSO-shaped models, where the models were fixed or taut moored. The experiments were carried out at Plymouth University’s COAST Laboratory. Spatial impact pressure distributions on the square plate have been characterised under different impact velocities. It was found that the impact pressures and force in pure water were proportional to the square of impact velocity. There was a significant reduction in both the maximum impact pressure and force for slamming in aerated water compared to that in pure water. An exponential relationship of the maximum force and the void fraction is proposed and its coefficients are found from drop test in this study. There was also a significant reduction in the first phase of the pressure and force impulse for slamming into aerated water compared with pure water. On the truncated wall, aeration also significantly reduced peak wave loads (both pressure and force) but impulses were not reduced by very much. For the case considered here, elasticity of the impact plate has a significant effect on the impact loads, though only at high impact velocities; here the impact loads were considerably reduced with increasing elasticity. Wave loading on the truncated wall was found to reduce with increasing elasticity of the wall for all investigated breaking wave types: high aeration, flip-through and slightly breaking wave impacts. In particular, impact pressure decreases with increasing elasticity of the wall under flip-through wave impact. As elasticity increases, the impulse of the first positive phase of pressure and force decreases significantly. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts. Scattered waves were generated from the interaction of focused wave groups with an FPSO model. The results show that close to the bow of the FPSO model, the highest amplitude scattered waves are observed with the most compact model, and the third- and fourth-harmonics are significantly larger than the incident bound harmonic components. At the locations close to the stern, the linear harmonic was found to increase as the model length was decreased, although the nonlinear harmonics were similar for all three tested lengths, and the second- and third-harmonics were strongest with the medium length model. The nonlinear scattered waves increased with increasing wave steepness and a second pulse was evident in the higher-order scattered wave fields for the fixed and free floating models. In addition, the higher harmonics of the mooring line force, and the heave and pitch motions all increased with increasing wave steepness. Incident wave angles of 0 (head-on), 10 and 20 degrees were experimentally investigated in this study. As the incident wave angle between the waves and the long axis of the vessel was increased from 0 to 20 degrees, the third- and fourth-harmonic scattered waves reduced on the upstream side. These third- and fourth-harmonic diffracted waves are important in assessing wave run-up and loading for offshore structure design and ringing-type structural response in fixed and taut moored structures. The second-, third- and fourth-harmonics of the mooring line force, and the heave and pitch motions decreased as the incident wave angle increased from 0 to 20 degrees.

A exploração de bacias petrolíferas do pré-sal, principalmente campos gigantes como o campo de Libra, na bacia de Santos, traz consigo demandas por sistemas capazes de operar com poços de alta capacidade de produção e em grandes profundidades. Nesse cenário, linhas de produção ou injeção (risers) rígidas em catenária livre apresentam a forma mais simples de solução para essas demandas. A utilização de risers rígidos em catenária livre, como já sabido, permite uma maior produtividade por linha devido a possibilidade de utilização de dutos de maiores diâmetros, ao mesmo tempo em que resistem a maiores pressões, possibilitando a exploração de forma mais eficiente de poços em grandes profundidades. No entanto, este tipo de solução, devido a sua natureza de maior rigidez quando comparado com dutos flexíveis, é submetida a esforços dinâmicos elevados impostos no topo do riser pela grande movimentação da embarcação, principalmente em operações em águas profundas, inviabilizando sua aplicação em unidades do tipo FPSOs convencionais, construídos a partir da conversão de um navio petroleiro. Este problema dinâmico é agravado pelas condições ambientais da região, que são mais severas do que as observadas na Bacia de Campos, tornando difícil a aplicação das tecnologias existentes. A alta produtividade dos poços do pré-sal da Bacia de Santos também estimula a utilização de plantas de processo de alta capacidade de processamento de óleo, maiores do que as utilizadas até hoje no offshore brasileiro. Estimativas iniciais mostram que estas plantas gigantes demandam uma área de convés muito maior do que as plataformas convencionais, e, mais do que isso, de uma maior largura (boca) da embarcação. Para atender requisitos tão conflitantes, foi desenvolvido o conceito ULFPSO (Unidade Flutuante de Produção, Armazenamento e Alívio Ultra-Larga), que se caracteriza por sua proa e popa circulares e pela presença do moonpool, de forma a viabilizar a conexão dos risers mais próximos ao centro de gravidade da plataforma, reduzindo assim o esforço dinâmico. Adicionalmente a forma do casco é otimizada para redução do nível de movimentos verticais, reduzindo os esforços dinâmicos nos risers. Nesta dissertação de mestrado serão apresentados os estudos relativos à comprovação de viabilidade do conceito, dividido em três etapas: A primeira com foco no entendimento do problema e dimensionamento preliminar da unidade; A segunda focada na avaliação experimental do conceito; E finalmente, a terceira, com objetivo de avaliar o modelo de síntese para otimização do projeto do casco, com base nos resultados obtidos nas fases anteriores. / The offshore exploitation of oil fields in the pre-salt, especially giant fields such as Libra, in the Santos basin, brings with it demands for systems capable of operating with high capacity production wells and at ultra-deep waters. In this scenario production or injection steel catenary risers present the simplest solution for these demands. As known in industry, the use of steel catenary risers in free-hanging configuration allows greater productivity per line due to the possibility of using pipes of larger diameters, at the same time withstand higher pressures, allowing for more efficient wells operation at great depths. However, due to its nature more rigid compared to flexible pipe, this kind of solution is subjected to high dynamic forces imposed on the top of the riser by the large movement of the vessel, especially in deepwater operations, impeding their application in FPSO conventional units, constructed from the conversion of an oil tanker. This dynamic problem is compounded by environmental conditions of the region, which are harsher than those observed in the Campos Basin, making it difficult to apply other extant technologies. The high productivity of the pre-salt of Santos Basin wells stimulate the use of plants to high-capacity oil processing process, larger than those used today in the Brazilian offshore. Initial estimates show that these plants require a much larger deck area than conventional platforms and, more than that, a greatest width (breadth) of the vessel. To satisfy such conflicting requirements, the ULFPSO (Ultra Large Floating Production, Storage and Offloading) concept was developed, which is characterized by its circular bow and stern and the presence of the moonpool, to enable the connection of the risers closest to the platform\'s center of gravity, thereby reducing the dynamic tension. Additionally, the hull shape is optimized to reduce vertical movements, reducing dynamic stresses on the riser. In this master\'s thesis will be presented studies on the proof of concept viability, divided into three stages: The first focused on understanding the problem and preliminary sizing of the unit; The second focused on the experimental evaluation of the concept; And finally, the third, to evaluate the synthesis model for optimizing hull design, based on the results obtained in the previous phases.

To reduce large motion responses of moored platforms in a harsh environment in deep waters, a thruster-assisted position mooring system can be applied. By applying the system, global dynamic responses can be improved in terms of the mooring line/riser top tensions, operational radii, and the top and bottom angle of the production risers. Kalman filtering as an optimum observer and estimator for stochastic disturbances is implemented in the developed control algorithm to filter out wave frequency responses. Investigation of the performance of thruster-assisted moored offshore platforms was conducted in terms of six-degree-of-freedom motions and mooring line/riser top tensions by means of a fully coupled hull/mooring/riser dynamic analysis program in the time domain and a spectral analysis. The two cases, motion analyses of a platform with thrusters and without thrusters, are extensively compared. The numerical examples illustrate that for deepwater position-keeping of platforms a thruster-assisted moored platform can be an effective solution compared to a conventionally moored platform.

To reduce large motion responses of moored platforms in a harsh environment in deep waters, a thruster-assisted position mooring system can be applied. By applying the system, global dynamic responses can be improved in terms of the mooring line/riser top tensions, operational radii, and the top and bottom angle of the production risers. Kalman filtering as an optimum observer and estimator for stochastic disturbances is implemented in the developed control algorithm to filter out wave frequency responses. Investigation of the performance of thruster-assisted moored offshore platforms was conducted in terms of six-degree-of-freedom motions and mooring line/riser top tensions by means of a fully coupled hull/mooring/riser dynamic analysis program in the time domain and a spectral analysis. The two cases, motion analyses of a platform with thrusters and without thrusters, are extensively compared. The numerical examples illustrate that for deepwater position-keeping of platforms a thruster-assisted moored platform can be an effective solution compared to a conventionally moored platform.

A exploração de bacias petrolíferas do pré-sal, principalmente campos gigantes como o campo de Libra, na bacia de Santos, traz consigo demandas por sistemas capazes de operar com poços de alta capacidade de produção e em grandes profundidades. Nesse cenário, linhas de produção ou injeção (risers) rígidas em catenária livre apresentam a forma mais simples de solução para essas demandas. A utilização de risers rígidos em catenária livre, como já sabido, permite uma maior produtividade por linha devido a possibilidade de utilização de dutos de maiores diâmetros, ao mesmo tempo em que resistem a maiores pressões, possibilitando a exploração de forma mais eficiente de poços em grandes profundidades. No entanto, este tipo de solução, devido a sua natureza de maior rigidez quando comparado com dutos flexíveis, é submetida a esforços dinâmicos elevados impostos no topo do riser pela grande movimentação da embarcação, principalmente em operações em águas profundas, inviabilizando sua aplicação em unidades do tipo FPSOs convencionais, construídos a partir da conversão de um navio petroleiro. Este problema dinâmico é agravado pelas condições ambientais da região, que são mais severas do que as observadas na Bacia de Campos, tornando difícil a aplicação das tecnologias existentes. A alta produtividade dos poços do pré-sal da Bacia de Santos também estimula a utilização de plantas de processo de alta capacidade de processamento de óleo, maiores do que as utilizadas até hoje no offshore brasileiro. Estimativas iniciais mostram que estas plantas gigantes demandam uma área de convés muito maior do que as plataformas convencionais, e, mais do que isso, de uma maior largura (boca) da embarcação. Para atender requisitos tão conflitantes, foi desenvolvido o conceito ULFPSO (Unidade Flutuante de Produção, Armazenamento e Alívio Ultra-Larga), que se caracteriza por sua proa e popa circulares e pela presença do moonpool, de forma a viabilizar a conexão dos risers mais próximos ao centro de gravidade da plataforma, reduzindo assim o esforço dinâmico. Adicionalmente a forma do casco é otimizada para redução do nível de movimentos verticais, reduzindo os esforços dinâmicos nos risers. Nesta dissertação de mestrado serão apresentados os estudos relativos à comprovação de viabilidade do conceito, dividido em três etapas: A primeira com foco no entendimento do problema e dimensionamento preliminar da unidade; A segunda focada na avaliação experimental do conceito; E finalmente, a terceira, com objetivo de avaliar o modelo de síntese para otimização do projeto do casco, com base nos resultados obtidos nas fases anteriores. / The offshore exploitation of oil fields in the pre-salt, especially giant fields such as Libra, in the Santos basin, brings with it demands for systems capable of operating with high capacity production wells and at ultra-deep waters. In this scenario production or injection steel catenary risers present the simplest solution for these demands. As known in industry, the use of steel catenary risers in free-hanging configuration allows greater productivity per line due to the possibility of using pipes of larger diameters, at the same time withstand higher pressures, allowing for more efficient wells operation at great depths. However, due to its nature more rigid compared to flexible pipe, this kind of solution is subjected to high dynamic forces imposed on the top of the riser by the large movement of the vessel, especially in deepwater operations, impeding their application in FPSO conventional units, constructed from the conversion of an oil tanker. This dynamic problem is compounded by environmental conditions of the region, which are harsher than those observed in the Campos Basin, making it difficult to apply other extant technologies. The high productivity of the pre-salt of Santos Basin wells stimulate the use of plants to high-capacity oil processing process, larger than those used today in the Brazilian offshore. Initial estimates show that these plants require a much larger deck area than conventional platforms and, more than that, a greatest width (breadth) of the vessel. To satisfy such conflicting requirements, the ULFPSO (Ultra Large Floating Production, Storage and Offloading) concept was developed, which is characterized by its circular bow and stern and the presence of the moonpool, to enable the connection of the risers closest to the platform\'s center of gravity, thereby reducing the dynamic tension. Additionally, the hull shape is optimized to reduce vertical movements, reducing dynamic stresses on the riser. In this master\'s thesis will be presented studies on the proof of concept viability, divided into three stages: The first focused on understanding the problem and preliminary sizing of the unit; The second focused on the experimental evaluation of the concept; And finally, the third, to evaluate the synthesis model for optimizing hull design, based on the results obtained in the previous phases.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, 2010. / Submitted by Lilian M. Silva (lilianmadeirasilva@hotmail.com) on 2013-04-23T00:25:38Z No. of bitstreams: 1 Monitoramento de Deformações e Deslocamentos Relativos nas Estruturas de Suporte de Plantas de Processo Modulares em Unidades Flutuantes de Produção de Petróleo do Tipo FPSO.pdf: 3764587 bytes, checksum: 70312a121e0f141c7936b32ac56e47c2 (MD5) / Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2013-06-03T19:38:06Z (GMT) No. of bitstreams: 1 Monitoramento de Deformações e Deslocamentos Relativos nas Estruturas de Suporte de Plantas de Processo Modulares em Unidades Flutuantes de Produção de Petróleo do Tipo FPSO.pdf: 3764587 bytes, checksum: 70312a121e0f141c7936b32ac56e47c2 (MD5) / Made available in DSpace on 2013-06-03T19:38:06Z (GMT). No. of bitstreams: 1 Monitoramento de Deformações e Deslocamentos Relativos nas Estruturas de Suporte de Plantas de Processo Modulares em Unidades Flutuantes de Produção de Petróleo do Tipo FPSO.pdf: 3764587 bytes, checksum: 70312a121e0f141c7936b32ac56e47c2 (MD5) Previous issue date: 2010 / Os projetos mais recentes de plataformas do tipo FPSO da PETROBRAS utilizam plantas modulares sobre cascos convertidos de mais de 300m de comprimento. Os módulos podem atingir 2.000t (peso seco) e mais de 3.000t em operação, sendo suportados em quatro pontos por estruturas chamadas stools. No projeto da P-53, para cada módulo há dois stools deslizantes (os quais permitem deslocamentos longitudinais, paralelos ao eixo da embarcação), e dois fixos (com restrição de movimentos em todas as direções), cada par em transversais distintas. Teoricamente, os stools deslizantes são empregados para evitar que os efeitos das deflexões do casco da plataforma induzam esforços nas estruturas dos módulos. As dúvidas a respeito da eficiência deste mecanismo para essa configuração de suportação de módulos motivaram a realização deste trabalho, cujo objetivo é analisar e compreender o comportamento estrutural dos apoios dos módulos (stools) da plataforma P-53. Para se obter estas respostas, foi desenvolvido um projeto de pesquisa na FURG com apoio da PETROBRAS, o qual mobilizou três pesquisadores e dez bolsistas, durante 3 anos e meio. Um sistema de aquisição de dados foi especialmente implementado, e através deste foram monitoradas deformações e deslocamentos relativos sobre esses stools. No total foram instalados na plataforma 75 sensores (entre extensômetros, transdutores de deslocamento e acelerômetros). Foram realizadas medições durante o assentamento dos módulos sobre a embarcação ainda no estaleiro, e na locação final, submetida às condições ambientais da Bacia de Campos. Nas condições em que foi realizado o monitoramento, não foram registrados deslocamentos relativos entre os stools deslizantes e os pés dos módulos durante todo o período de observação. A não ocorrência de deslizamento pode ser justificada pelo elevado peso dos módulos, alto coeficiente de atrito, e as características das ondas sob as quais a embarcação foi submetida. Nestas condições, a ocorrência de deslocamentos relativos é mais provável para módulos mais leves, e improvável, ou até impossível, para módulos mais pesados. Mesmo assim não foram registrados níveis de deformações que pudessem indicar um incremento relevante de carga sobre as estruturas dos stools e dos módulos. / The most recent PETROBRAS FPSO projects used modular process plants on converted vessels with more than 300m length. The modules may reach 2,000t (dry) and more than 3,000t on operation, being supported by four points on structures called stools. In the P-53 design, there are two sliding stools (that allow longitudinal displacements, parallel to vessel axis), and two fixed stools (that restrict the displacement in all directions), each pair is at different transversal frames on the hull. In theory, the sliding stools are employed to avoid that the hull deflections induce deformation on the module’s structures. The doubts about the efficiency of this apparatus for this support configuration of modules motivated the development of this research, which aim is analyze and understand the structural behavior of the module’s supports. To get these answers, it was developed a research in FURG with support of PETROBRAS, which mobilized three researchers and ten students, during three and a half year. A data acquisition system was specially implemented to attend this goal, through that was monitored strain and relative displacements on these stools. A total of 75 sensors (among them strain gages, displacement transducer and accelerometers) was installed on the platform. It was taken measurements during the installation of the modules upon the hull at the shipyard, and at the final location, under the environmental conditions of Campos Basin. In these conditions where the monitoring was done, no relative displacement among the sliding stools and module’s pads was recorded throughout the observation period. The non-occurrence of sliding can be justified by the high weight of the modules and high coefficient of friction, and by the environmental conditions under that the vessel was subjected. On these conditions, the occurrence of relative displacements is more probable to lighter modules, and improbable, even impossible to heavier ones. Despite that, it was not recorded strain levels that could indicate a relevant load increasing on the structures of modules or stools.