bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automated Subsea Architecture Optimization Using Low-Dimensional Multiphase Flow Models
Authors: Khan Zurwa , Meziou Amine , Tafreshi Reza , Franchek Matthew , Grigoriadis Karolos 
Published: November 2019

Abstract
Due to the global increase in energy demand, the need for economic oil and gas production is rising more than ever. Therefore, it is necessary to ensure that subsea architecture designs are economical and safety oriented. While numerous challenges are encountered during subsea system’s installation and operation phases, most of these challenges can be avoided by ensuring an economical and reliable design. For a safe and cost-effective design and operating scenario, it is essential to predict the hydraulic and thermal behavior of multiphase fluid encountered in petroleum pipelines for a range of conditions. This cannot be accomplished by empirical models, which are dependent on limited data available. Consequently, mechanistic low-dimensional models have been used for two-phase gas-liquid steady-state flow. However, mechanistic low-dimensional models assume adiabatic conditions, which is rarely the case in subsea architectures, which encounter cold surroundings. Therefore, to predict the temperature-based characteristics of multiphase flow in environments with thermal gradients, a thermal model has been developed and validated with experimental data. 80% of the validation data was predicted by this developed thermal model with error difference of less than 30%. The developed two-phase gasliquid thermal model was merged with Beggs and Brill hydraulic multiphase flow model to predict the overall behavior of two-phase gas-liquid flow, and used to develop an optimal model-based multi-well subsea architecture design. A case study of a four-well subsea system was used to demonstrate the automated subsea architecture optimization technique. Through this case study, it was shown that approximately 23% of savings in pipelines procurement could be made relative to the conventional designing approach. Industry standards, safety factors, and multiphase flow models were used to design jumpers and place the manifold for a subsea multi-well system. Merging hydraulic and thermal multiphase flow models showed the effect of temperature on the flow, which led to an optimized design for the subsea insulation in which issues such as wax deposition can be prevented. The resulting optimized subsea architecture was then implemented in Simscape® environment to obtain the transient response. Along with optimized subsea architecture automated design, the developed thermal model has the potential to be used for real-time prediction of two-phase flow rate, pressure drop and void fraction as virtual sensors to provide economical alternative to expensive and impractical hardware sensors. Furthermore, the developed model can also be used to design effective control strategies for multiphase flow regulation in jumpers and prevention of backflow at the manifold.
CFD Simulation of Two-Phase Vertical Annular Flow in Both Upward and Downward Direction in a Small Pipe
Authors: Abobaker Ekhwaiter , Elsanoose Abadelhalim , Shirokoff John , Rahman Mohammad Azizur 
Published: November 2019

Abstract
Computational fluid dynamics (CFD) simulation is presented to investigate the annular flow behavior in the vertical pipe by using ANSYS Fluent platform 17.2. The study was analyzed complex behavior of annular flow in two cases (upward and downward flow) for different air superficial velocities and range of Reynolds number for water, in order to obtain the effect of orientation flow and increasing superficial gas and liquid velocities on the base film, mean disturbance wave thickness, the average longitudinal size of disturbance wave as well as pressure gradient. For multiphase flow model, the volume of fluid method (VOF) for two-phase flow modelling was used and coupled with RNG k-ε turbulence model to predict fully annular flow structures in the upward and downward flow direction. From CFD simulation results, it is clear to see how increases in air velocity result in reductions in film thickness and increase in pressure gradient. Additionally, the results showed monotonic enhancement of film thickness occurring in tandem with increases in the liquid flow rate. However, due to the effect of gravitational force and interfacial friction, the film thickness and pressure gradient are slightly larger for the upward flow than for the downward flow. The results agree with the recent experimental data that studied the annular flow behavior and pressure drop in the upward and downward flow direction. This study will be very helpful in understanding multiphase flow behavior in natural gas wells.
Experimental Validation of Towed Underwater Cable Model
Authors: Grindheim Jan Vidar , Fernandes Antonio Carlos , Sales Junior Joel Sena , Revhaug Inge 
Published: November 2019

Abstract
Towed underwater cable models have been validated using experimental results performed in the current channel at Laboratório de Ondas e Correntes (LOC) at COPPE/UFRJ, Rio de Janeiro. The numerical simulators utilize a Finite Difference Method to solve the Partial Differential Equations describing the dynamics of a towed underwater cable under tension. A non-dimensional analysis of the system dynamics for the two-dimensional case has been performed, with non-dimensional governing equations being presented. The experimental setup consists of two cable sections of ∼1.5 m length each, the first having 3 mm diameter and slightly positive wet weight while the second section has 2.5 mm diameter and slight negative wet weight. With the cable in steady-state condition, the towpoint is moved 0.50 m sideways and the time for the cable to return to straight tow is measured. Further, the cable depths at midpoint and tail are measured in steady-state. Experiments are performed at currents ranging from 0.17 to 0.47 m/s. The presented experimental results are compared to the numerical results. Reasonable agreements are obtained.
Power Take-Off Selection for a U-Shaped OWC Wave Energy Converter
Authors: Romolo Alessandra , Henriques João C. C. , Gato Luís M. C. , Malara Giovanni , Laface Valentina , Gomes Rui P. F. , Portillo Juan C. C. , Falcão António F. de O. , Arena Felice 
Published: November 2019

Abstract
The REWEC3 (Resonant Wave Energy Converter) is a fixed oscillating water column (OWC) wave energy converter (WEC) incorporated in upright breakwaters. The device is composed by a chamber containing a water column in its lower part and an air pocket in its upper part. The air pocket is connected to the atmosphere via a duct hosting a self-rectifying air turbine. In addition, a REWEC3 includes a vertical U-shaped duct for connecting the water column to the open sea (for this reason it is known also as U-OWC). The working principle of the system is quite simple: by the action of the incident waves, the water inside the U-shaped duct is subject to a reciprocating motion, which induces alternately a compression and an expansion of the air pocket. The pressure difference between the air pocket and the atmosphere is used to drive an air turbine coupled to an off-the-shelf electrical generator connected to the grid.
The main feature of the REWEC3 is the possibility of tuning the natural period of the water column in order to match a desired wave period through the size of the U-duct. The REWEC3 technology has been theoretically developed by Boccotti, later tested at the natural basin of the Natural Ocean Engineering Laboratory (NOEL, Italy), and finally proved at full scale with REWEC3 prototype built in the Port of Civitavecchia (Rome, Italy).
The objective of this paper is to select and optimize a turbine/generator set of a U-shaped OWC installed in breakwaters located in the Mediterranean Sea, such as the Port of Civitavecchia, where the first prototype of REWEC3 has been realized, or the Port of Salerno or Marina delle Grazie of Roccella (Italy). The computations were performed using a time domain model based on the unsteady Bernoulli equation.
Based on the time-domain model of the power plant, the following data is computed for the turbines: i) the ideal turbine diameter; ii) the generator feedback control law aiming to maximize the turbine power output for turbine coupled to the REWEC3 device for Mediterranean applications.
Fatigue Approaches for Mooring Chains Subjected to Wear Degradation
Authors: Gemilang Gilang M. , Reed Philippa A. S. , Sobey Adam J. 
Published: November 2019

Abstract
There are currently 365 FPSOs in service around the world. These vessels all use mooring lines to maintain position and provide stability, keeping the vessel and cargo safe. However, more than 21 failures have occurred between 2001 and 2011 and approximately 50% of the reported failures occurred in the first 3 years of 20-year design life. Each mooring line failure represents the potential for serious environmental and economic consequences. Based on industry surveys, the most common failure mode is fatigue failure. In the current offshore standards, the surface degradation due to wear and corrosion is modelled as a diameter loss at a standards rate. To assess whether the uniform reduction in chain diameter suggested in the offshore standards is able to explain the early chain failures seen in service, this paper incorporates two wear rates into a fatigue life calculation; one wear rate is taken from DNV-OS-E301 and is compared against one taken from NORSOK M-001. Three fatigue life estimation approaches: tension, nominal stress and hotspot, are used to compare the differences in fatigue method. The stress in the chain is calculated using an analytical model, which is verified against an FE model. The effect of wear degradation on the ultimate strength of the chain is calculated based on the minimum breaking load. The results show that the diameter loss rates suggested in the offshore standards are not able to explain the early mooring chain failures seen in the past and that the reduction of diameter cannot solely explain the early failures seen in service. The hotspot approach, not often used in mooring line predictions, is best able to predict these shorter lives, as it offers more accurate fatigue predictions by considering high peak stresses compared to standard methods such as tension and nominal stress approaches.
Methodology Proposal for Corrosion-Fatigue Assessment for Flexible Pipes Tensile Armour in Aggressive Environments
Authors: Favaro Borges Marcelo , dos Reis Tagliari Mariana , Gonçalves Rafaela , Fortis Kwietniewski Carlos Eduardo 
Published: November 2019

Abstract
Flexible risers are the main way to connect wells and floaters for petroleum and gas applications on the Brazilian coast. The failure of those risers in operation can generate huge irreversible economic and environmental expenses. Statistics indicate that there is a predominance of premature failure associated with the flooding of the annular space. When cyclic loads are present, this condition will introduce corrosion-fatigue of the metallic reinforcements. Therefore, to ensure the operational safety, their design should consider the combined action of fatigue and corrosion phenomena. The experimental test procedure to be applied for generating S-N curves and qualifying the steel materials with respect to corrosion-fatigue face different challenges. One of the important ones is to introduce representative surface defects that reflects the exposure time of the real life corrosion process as this will have a strong influence of the slope parameter of the S-N curves. The aim of this work is to propose a new methodology to obtain S-N design curves allowing for the samples to be pre corroded to obtain realistic surface defects. The pre corrosion procedure is made to ensure that all samples have the same defects caused by localized corrosion and that those defects are representative of those presented in real risers with flooded annulus. Considering the effect of the defects aspect on fatigue evaluation allows a better prediction of the remaining life of pipes operating in flooded annulus conditions. Two S-N curves were compared allowing for proving the potential of the methodology and promising results were obtained, giving more reliable S-N curves. Furthermore, it was possible to conclude that under the assessed conditions the fatigue in air tests of pre-corroded wire during 60 days showed the same performance as the new one (non-pre-corroded) wires tested in corrosion-fatigue.
The Impact of Second-Order FPSO Motions on the Fatigue Performance of Large Diameter SCRs
Authors: Hejazi Rasoul , Grime Andrew , Randolph Mark , Efthymiou Mike 
Published: November 2019

Abstract
Large diameter steel catenary risers (SCRs) are considered a cost efficient export riser solution for gas field developments at deep-water sites. However, SCRs are prone to fatigue damage at their interface with the seabed (the touchdown zone, TDZ) and hence accurate estimation of their fatigue life is crucial. The major source of TDZ fatigue damage is the motions of the host vessel subjected to irregular ocean waves. The first-order interaction between the host vessel and the ocean causes oscillations in all degrees of freedom at the same frequencies as the incident waves. The second-order interactions result in a mean-drift offset from the static equilibrium position in the horizontal plane and slowly-varying cyclic motions about that offset position. This paper investigates the effects of second order motions on the fatigue life of a 26” SCR connected to a representative Floating Production Storage and Offload vessel (FPSO), using realistic environmental conditions relevant for a deep-water site on the Australian Northwest Shelf. A diffraction analysis was performed to obtain the hydrodynamic characteristics of the ship-shaped vessel which was subsequently used as the input into a fully coupled response model consisting of the floater, mooring lines and the SCR. A realistic fatigue wave scatter diagram was adopted, consisting of 100 sea-states combining irregular seas, swell, current and winds. This was combined with dynamic time-domain motion analysis and a rainflow cycle counting algorithm in order to determine the fatigue damage within the SCR TDZ due to the host FPSO motions. The results shows that for this representative system the second-order cyclic low frequency (LF) motions have beneficial impacts on fatigue life of the large diameter SCR. Similarly, mean-offsets of the FPSO have a beneficial effect due to changes in the fatigue hotspot location along the SCR within the TDZ for each sea-state. Finally, a simplified method is presented to capture these beneficial effects at the early design stages.
The Analysis of the Joint Limitation Condition of Wave Height-Period on the Floating Crane Lifting Operation
Authors: Wang Xue-gang , Ying Zong-quan , Chen Ze-cong 
Published: November 2019

Abstract
Considering the influence of wave period on the motion of ship, the hydrodynamic model of the floating crane-lifting objects coupling system is built. This model can calculate the motion response of floating crane and lifting object under wave conditions with different wave heights and periods. And it takes stability and sea-keeping of ship, personnel comfort as well as safety of equipment into full account. By comparing swing amplitude and acceleration amplitude of the floating crane and the lifting object, the limit working condition including both wave height and period for hoisting operation of the floating crane is determined. The method for limitation operation condition analysis of the floating crane not only offers calculating foundation for the construction operating adaptability of the engineering ship and the allowable working time window of the construction sea area, but also provides a new technical approach to the arrangement for the construction plan.
REEF3D::FNPF: A Flexible Fully Nonlinear Potential Flow Solver
Authors: Bihs Hans , Wang Weizhi , Martin Tobias , Kamath Arun 
Published: November 2019

Abstract
In situations where the calculation of ocean wave propagation and impact on offshore structures is required, fast numerical solvers are desired in order to find relevant wave events in a first step. After the identification of the relevant events, Computational Fluid Dynamics (CFD) based Numerical Wave Tanks (NWT) with an interface capturing two-phase flow approach can be used to resolve the complex wave structure interaction, including breaking wave kinematics. CFD models emphasize detail of the hydrodynamic physics, which makes them not the ideal candidate for the event identification due to the large computational resources involved. In the current paper a new numerical wave model is represented that solves the Laplace equation for the flow potential and the nonlinear kinematic and dynamics free surface boundary conditions. This approach requires reduced computational resources compared to CFD based NWTs. In contrast to existing approaches, the resulting fully nonlinear potential flow solver REEF3D::FNPF uses a σ-coordinate grid for the computations. Solid boundaries are incorporated through a ghost cell immersed boundary method. The free surface boundary conditions are discretized using fifth-order WENO finite difference methods and the third-order TVD Runge-Kutta scheme for time stepping. The Laplace equation for the potential is solved with Hypres stabilized bi-conjugated gradient solver preconditioned with geometric multi-grid. REEF3D::FNPF is fully parallelized following the domain decomposition strategy and the MPI communication protocol. The model is successfully tested for wave propagation benchmark cases for shallow water conditions with variable bottom as well as deep water.
Efficient Anchoring System for FPSO in Arbitrary Waters
Authors: de Araujo Jairo B. , Fernandes Antonio C. , Sales Joel S. , dos Santos Mario Jorge C. , Thurler Ana Clara S. 
Published: November 2019

Abstract
Oil offshore Brazil, as well as in other continents, has demanded floating units for oil production. Typical anchored production units are the semi-submersible platforms, FPSO, Spar Buoys and TLPs. All of them use several anchoring lines for station keeping.
In the offshore Brazil scenario, the last twelve years the FPSOs adopts the torpedo piles and polyester ropes in the anchoring lines in deep and ultra-deep waters. The FPSO “Cidade de Angra dos Reis” was the first to operate in pre-salt area in October 2010. From then on, it became common the production units with VLCC size, oil production of 150,000 barrels per day and 24 anchoring lines. The reason for such large number of anchors is the 1,200 tonnes torpedo piles holding power restriction.
The proposition developed in this paper reduces the number of anchor lines using well know offshore equipment such as: driven piles, mooring chains, polyester ropes and conventional anchoring deck equipment. The main difference is the use of driven piles with holding power above 1,800 tonnes and anchor lines with a breaking strength of more than 2,000 tonnes. It is shown that a decrease of number of anchoring lines from 24 to 12 can be achieved. Consequently, it will decrease also the space occupied by the anchoring lines in the seabed by reducing the subsea layout of risers, flow lines and well head. This allows a technical and economical scenario more feasible when compared with the currently used on the Brazilian oil & gas market.
Dynamic Response of a Gangway Between Two Floating Bodies in a Side-by-Side Configuration
Authors: Dong Qing , Yang Jianmin , Lu Haining , Li Xin , Lu Wenyue , Liu Lei 
Published: November 2019

Abstract
A number of tender assisted drilling platforms (TAD) are built to offer comfortable accommodation for crew, onsite construction and maintenance for production platforms. The two platforms are usually connected by a telescopic gangway. The safety and feasibility of gangway are essential during personnel transfer operation. In this paper, a TLP-TAD coupled system was investigated numerically and experimentally to study the gangway motion responses. The numerical model was established in frequency domain using 3D multi-body diffraction/radiation wave theory. Then time domain simulation was performed to consider the second-order drift loads and nonlinearity of mooring lines and hawsers. A systematic model test was also conducted for the coupled system. The connection point between gangway and platform was regarded as a joint, so gangway motion could be derived by global motions of TLP and TAD. Both single-body and multi-body cases were studied for comparison. The differences of global responses between two cases were relatively small, indicating that multi-body hydrodynamic interaction was not quite significant. The interaction aroused sway-surge and sway-heave coupling, and shielding effect also existed. Based on the above, gangway extension was investigated to analyze which degree of freedom (DOF) of global motion governed it.
Fatigue Assessment of SLWR Riser in Brazilian Pre-Salt: The Impact of Slope Changing Point in SN Curve
Authors: F. Senra Stael , Aguiar Ludimar L. , Hippert Eduardo , Garmbis Alexandre G. , Dos Santos Marcelo , D. Martins Marcos André , P. Nunes Luis Manoel 
Published: November 2019

Abstract
One of the main challenges in rigid riser design for Brazilian Pre-salt is the fatigue limit state. At this new production frontier, some key points are imposed as a challenge for riser designers, mainly due to the high level of motions imposed by the FPSO at the riser top in a coupled system with water depth around 2200 meters, and thicker riser’s thermal insulation demanded for flow assurance (which worsens the dynamic response of production risers). Additionally, high contaminant levels in the fluid (CO2 & H2S) demands CRA materials. Within this context, Petrobras has been considering Steel Lazy Wave Riser (SLWR) configuration as a base case scenario for rigid riser projects, since this configuration is able to absorb part of the FPSO motions that would reach the touch down zone (TDZ) and, consequently, making this region much less demanded when compared against Steel Catenary Risers (SCR). In its pioneer deepwater SLWR [1], Petrobras adopted a conservative approach for fatigue assessment that involved degenerated SN curves from DNV-RP-C203, i.e. D curve in cathodic protection with the slope changing point (SCP) shifted to 5 × 106 for external wall and F1 curve in air with SCP at 5 × 107 for internal wall. More recently, both DNVGL and BSI have reviewed their fatigue assessment codes and no longer holds parity between SN curves. BS-7608 Ed. 2014 introduced different SCPs in order to account for a possible non-conservativeness in the assessment of low stresses under variable amplitude in the loading spectra. DNVGL-RP-C203 Ed. 2016 now presents three different bilinear SN curves for the internal wall of pipelines and risers that depends on weld misalignment, while it keeps SCP unchanged. This paper presents a recent case study for a typical SLWR configuration in pre-salt, in order to evaluate the impact of the changes proposed by the new versions of these design codes in the fatigue life of riser girth welds. Results of this work showed that the impact of different positioning of slope changing points in SN curves can have a great importance for riser design, since typical load spectrum lies around this region. Fatigue life could be increased up to twice or three times if one of these codes are adopted instead of the Shifted SN curves. However, the effect of low stresses under variable amplitude loading spectra is still a concern and it should be further investigated.