Design of paired column semisubmersible hull

There is a constant effort to reconfigure column stabilized semisubmersible unit to meet the challenging demands associated with deep water exploration. Paired column semisubmersible platform is one of the recent column stabilized semisubmersible hull configured to allow top-deck well head compatibility for oil reserves in deep waters. Its unique ability to maintain reduced vertical motion in extreme weather conditions despite its hull size and payload create a high payload to motion ratio, as compare to conventional semisubmersible hulls. This unique feature makes it recommendable for other hull applications in ocean engineering. A study has been carried out to harness this high payload to motion ratio offered by this new hull concept in the development of drilling and production platforms in deep waters, support and foundation systems. Numerical models were developed to understand the semisubmersible hull (dynamics of the reduced vertical motion and its ability to withstand bending and twisting behaviour from extreme wave conditions). Prior to this, a preliminary CFD model was developed in to understand the vortex shedding effect on the arrayed columns. An experimental setup was also put together to understand this motion behaviour, alongside a detailed review of the first model. The motion response of a scaled hull model was studied in a wave tank with a Digital Image Correlation (DIC) system known as Imetrum. To further investigate its application for other ocean depths and support systems, series of hydrodynamic models were developed in ANSYS AQWA with weather conditions as recommended by API, DNV, and ABS. The AQWA model was validated with results recorded by Imetrum system from the wave tank experimental test. The wave forces and moments were studied for different draft sizes and ocean conditions, and their response where checked in ORCAFLEX. A finite element model was finally developed in APDL to understand the nature and effect of stresses from wave, current and wind loads, alongside topside integration. The results obtained from the FE model was use to postulate reinforcement during scantling, for different hull applications. The results for motion response showed favourable heeling moment for smaller draft sizes as recommended by regulatory bodies, but a reconfiguration for heave displacement might be required for smaller draft size. In such case, an increase in pontoon area or an additional heave plate attachment has been recommended. Furthermore, the effect of wavecurrent interactions was observed to create unique motion behaviour for all draft sizes at resonance frequency range. A fluid-structure interaction model of multi-phase flow will be required to understand this behaviour. The stress concentration on the columns generated from hydrodynamic loads was observed to be higher on the inner columns, relative to the outer ones

A review of floating semisubmersible hull systems:Column stabilized unit

Abstract Column stabilized semisubmersible is one of the most commonly used hull systems for the design and development of drilling and production platforms used for offshore deep water operations. Recent reconfiguration and design alterations have improved its hydrodynamic behaviour in rough weather conditions and, thus, its application and functionality in ocean engineering. Semisubmersible dry-trees applications and large wind turbine foundation systems in ultra-deep waters require high payload integration for reduced motion responses in all degrees of freedom. This paper presents a review of recent industrial and academic contributions to the development of column stabilized semisubmersible hulls used for deep water operations. It also provides an overview of the motion and structural attachments of semisubmersibles. The type and formation of dry-trees semisubmersibles are discussed. The dynamic behaviour and comparative advantages of them are also explained

Wave induced stress profile on a paired column semisubmersible hull formation for column reinforcement

A study into reinforcing the hull of the recently developed paired column semisubmersible platform has been carried out by understanding the stress profile around its columns from hydrodynamic interaction during survival and extreme weather conditions in the Gulf of Mexico. The conceptualization of this hull system is to enable dry-tree technology on semisubmersibles for deep-sea exploration. Its hydrodynamic response behaviour has been confirmed to be compatible with this technology, although its size and high steel requirement are of major disadvantage. Preliminary CFD study has showed an unusual flow behaviour within and around the hull due to its unique column arrangement. This behaviour creates an unusual hydrodynamic pressure profile on the hull, dominated by the wave parameters. Numerical models were developed using ANSYS and AQWA to compute the stress distribution on the columns from this unique uneven hydrodynamic pressure. The boundary conditions for the FE-model were formulated using hydrostatic stiffness theories and hydrodynamic response plots developed in Orcaflex. The results have showed high stress concentration on the inner columns. For operating conditions (low wave amplitude), the wave propagating direction was observed to have little or no effect on the column stress distribution. Significant effect of the wave propagating angle was observed as its amplitude gradually increases. Results for topside and deck mass effect on the stress distribution on the columns also suggested high stress distribution around the joint area of the inner columns for extreme and survival weather conditions, irrespective of the flow orientation

Wave induced stress profile on a paired column semisubmersible hull formation for column reinforcement

A study into reinforcing the hull of the recently developed paired column semisubmersible platform has been carried out by understanding the stress profile around its columns from hydrodynamic interaction during survival and extreme weather conditions in the Gulf of Mexico. The conceptualization of this hull system is to enable dry-tree technology on semisubmersibles for deep-sea exploration. Its hydrodynamic response behaviour has been confirmed to be compatible with this technology, although its size and high steel requirement are of major disadvantage. Preliminary CFD study has showed an unusual flow behaviour within and around the hull due to its unique column arrangement. This behaviour creates an unusual hydrodynamic pressure profile on the hull, dominated by the wave parameters. Numerical models were developed using ANSYS and AQWA to compute the stress distribution on the columns from this unique uneven hydrodynamic pressure. The boundary conditions for the FE-model were formulated using hydrostatic stiffness theories and hydrodynamic response plots developed in Orcaflex. The results have showed high stress concentration on the inner columns. For operating conditions (low wave amplitude), the wave propagating direction was observed to have little or no effect on the column stress distribution. Significant effect of the wave propagating angle was observed as its amplitude gradually increases. Results for topside and deck mass effect on the stress distribution on the columns also suggested high stress distribution around the joint area of the inner columns for extreme and survival weather conditions, irrespective of the flow orientation

Numerical Modelling on the Local Design of a Marine Bonded Composite Hose (MBCH) and Its Helix Reinforcement

With the exploration of oil trending deeper, from shallow waters to deep waters, there is a corresponding increase in the need for more sustainable conduit materials for production purposes. Secondly, there is an increasing demand for more energy from fossil fuels that are excavated with less expensive technologies. As such, short-service hoses are applied in the offshore industry. The industry has utilised composites to improve the material and solve different offshore issues. This study analyses a current problem facing the oil and gas industry at present regarding hose usage. This paper presents results from the local design and analyses of a marine bonded composite hose (MBCH), to present its result visualisations and nephographs. In this paper, the local design of a 1 m section of an MBCH was carried out in ANSYS under different loading conditions. Some design criteria were set, and other load conditions were used to simulate the model using the finite element model (FEM) approach. From this study, composites could be considered to improve conventional marine hoses. The findings of the study include the identification of linear wrinkling and damage sites on the helix reinforcement. An experimental investigation and proper content test are recommended for the bonded hose. Additionally, highly reinforced hose ends are recommended in the ends of the MBCH, as they had maximum stress and strain values. It is recommended that hose operations like reeling must be conducted under operational pressure and not design pressure, as the study shows that the design pressure could be high on the hose model

Local and Global Design of Composite Risers on Truss SPAR Platform in Deep waters

The application of risers in offshore deep waters have been necessitated due to the increase in the water depths. Thus, the number of marine riser segments increase, which also increase the weight of the offshore platform. To reduce the weight of the risers, composite risers are proposed. The material property of composites can be harnessed to develop composite marine risers, which will reduce the weight on the offshore platform. Numerical tools are employed and the system is coupled using ANSYS 19.2 System Coupling tool, ANSYS ACP and ANSYS AQWA. The local design of the composite risers involved 18 layers and an inner liner. Composite materials used include AS4/PEEK, AS4/Epoxy and different configurations were investigated. Other liner materials on the composite risers were also looked at in the study. Hydrodynamic investigations were also carried out using environmental conditions. Results of the local analysis of the riser were applied in the global design on a Truss SPAR Platform in a deep water condition of 2000m water depth. Comparative studies of the composite risers and the steel risers were carried out. From the results of the study, the composite risers local and global designs applied in deep water conditions were satisfactory. Recommendations too were given in line with the industry standards

A literature review on the technologies of bonded hoses for marine applications

Marine bonded hoses are conduit-tubular structures used for loading, discharging, transferring and transporting fluid products like oil, gas, and water. These marine conduits are applied in the offshore industry by utilising novel marine materials and sustainable technologies. Based on sustainability, there are advances made as solutions for challenging environments. These challenges include scouring gases, deep water regions, changing sea water temperatures, platform loads and vessel motions. These environments also require sustainable materials like marine composites. This paper reviews historical timeline and patent development of hoses in the marine environment. It highlights key developments on marine hoses and their configurations. These configurations include FPSO-FSO with hose attachments in catenary configurations and CALM buoy-PLEM in Lazy-S configurations. The review also discusses the evolutions in the hose designs, potentials of the hoses, and recent state-of-the-art developments in the industry. Comprehensive discussions with necessary recommendations are made for fluid applications in the offshore industry

Numerical Study on Plastic Strain Distributions and Mechanical Behaviour of a Tube under Bending

Tubular pipe structures have been used in various applications—domestic, aviation, marine, manufacturing and material testing. The applications of tubular pipes have been considered greatly in the installation of tubular pipes, marine risers and pipe bending. For the investigation of plastic strains and the mechanical behaviour of a tube under bending, considerations were made utilising an exponent model with assumptions on the plane strain. The bending moment, wall thickness effect, cross-sectional distribution, stresses during bending and neutral layer boundaries were all presented as necessary theoretical formulations on the physics of tubular pipe bending. This model was based on the analytical and numerical investigation. In principle, the application can be observed as the spooling of pipes, bending of pipes and reeling. Comparisons were made on two models developed on the finite element analysis in Simscale OpenFEA, namely the linear-elastic and the elasto-plastic models. This study presents visualization profiles using plastic strain to assess its effect on the tubular pipes. This can increase due to the limitation of plastic deformation on the composite materials selected

Finite element modelling on the mechanical behaviour of Marine Bonded Composite Hose (MBCH) under burst and collapse

Currently, the properties of composites have been harnessed on pipelines in the marine offshore industry. In this study, Marine Bonded Composite Hose (MBCH) has been presented. It is aimed at understanding the stress/strain distribution on marine bonded hoses using local design pressure under burst and collapse cases. This study also investigates on composite material modelling, hose modelling, liner wrinkling, helical spring deformation and two MBCH models- with and without ovalisation. The ovalized model is considered the simplified model in this research. Mesh study was carried out on meshing the hose layers. In this study, local design pressure was considered and not operational pressure. This finite element model was adopted to predict the deformation and mechanical response behaviour of MBCH. From this study, composites could be considered to improve conventional marine hoses. The study findings include identification of buckled sections on the hose, and stressed zones on the helix reinforcement. Highly reinforced hose ends are recommended in ends of the MBCH as they had maximum stress and strain values

Review of Composite Marine Risers for Deep-Water Applications: Design, Development and Mechanics

In recent times, the utilisation of marine composites in tubular structures has grown in popularity. These applications include composite risers and related SURF (subsea umbilicals, risers and flowlines) units. The composite industry has evolved in the development of advanced composites, such as thermoplastic composite pipes (TCP) and hybrid composite structures. However, there are gaps in the understanding of its performance in composite risers, hence the need for this review on the design, hydrodynamics and mechanics of composite risers. The review covers both the structure of the composite production riser (CPR) and its end-fittings for offshore marine applications. It also reviews the mechanical behaviour of composite risers, their microstructure and strength/stress profiles. In principle, designers now have a greater grasp of composite materials. It was concluded that composites differ from standard materials such as steel. Basically, composites have weight savings and a comparative stiffness-to-strength ratio, which are advantageous in marine composites. Also, the offshore sector has grown in response to newer innovations in composite structures such as composite risers, thereby providing new cost-effective techniques. This comprehensive review shows the necessity of optimising existing designs of composite risers. Conclusions drawn portray issues facing composite riser research. Recommendations were made to encourage composite riser developments, including elaboration of necessary standards and specifications