bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Flexible Pipes Under Compression
Authors: Malta Eduardo Ribeiro , Martins Clóvis de Arruda
Published: September 2014

Axial compressive loads can appear in several situations during the service life of a flexible pipe, due to pressure variations during installation or due to surface vessel heave. The tensile armor withstands well tension loads, but under compression, instability may occur. A Finite Element model is constructed using Abaqus in order to study a flexible pipe compound by external sheath, two layers of tensile armor, a high strength tape and a rigid nucleus. This model is fully tridimensional and takes into account all kinds of nonlinearities involved in this phenomenon, including contacts, gaps, friction, plasticity and large displacements. It also has no symmetry or periodical limitations, thus permitting each individual wire of the tensile armor do displace in any direction. Case studies were performed and their results discussed.
Progressive Collapse Analysis and Reliability of a Damaged Hull Girder
Authors: Ibekwe Achinike U. , Pu YongChang , Ham Wan L. , Dow Robert S.
Published: September 2014

With the expectation of hull girder asymmetry and corresponding shift in elastic neutral axis resulting from collision damages and other forms of structural deteriorations, the interaction of vertical and horizontal hull girder capacities become quite significant in the assessment of ship structural safety. This paper therefore extends the application of a previously proposed interactive-numerical probabilistic based methodology for structural safety to assess the hull girder ultimate strength reliability of a damaged ship by means of a user-defined numerical framework. Hull girder capacity is calculated using the NS94D ultimate strength code, which is based on the Smith’s progressive collapse method. The resulting deterministic responses have been interactively linked to the NESSUS probabilistic framework so that the reliability of the damaged hull girder is predicted using an implicit limit state function defined based on a transformation of coordinates to appropriately account for any shift in the neutral axis. Random deviations of the constituent variables are directly applied to calculate the ultimate strength deterministic responses, thereby circumventing the need to characterize any correlated strength variable, which is at best subjective. The conventional approach of characterizing ultimate strength by an assumed coefficient of variation and distribution type was found to be conservative in predicting structural safety of ships relative to the proposed method. Application of the interactive-numerical technique for structural reliability is therefore considered significant for problems involving correlated random variables with unknown statistical characteristics. The method is being considered to predict the safety of cracked hull girders by accounting for the residual strength and further load bearing capabilities of deteriorated and adjacent elements.
Numerical Modeling of Released Subsea Buoyancy Module for Reliable Prediction of its Trajectory and Velocity Using Transient CFD Analysis for Risk Assessment
Authors: Jia David , Agrawal Madhusuden , Malachowski Jim
Published: September 2014

Buoyancy modules are widely used in offshore and subsea fields, such as on pipelines, risers, umbilicals, and ROVs, etc. in operation and installation. Accidental release of subsea buoyancy modules due to broken or damaged parts may pose a potential risk and hazard to offshore vessels, floating platforms and risers & surrounding umbilicals. A released buoyancy module rises and may collide with any floating structures or pipes above it. For offshore and subsea field development, it is important to assess such potential risk to offshore vessels, floating platforms, and risers & umbilicals around them. Accurate prediction of the trajectory and the impact speed of the released buoyancy module is the key component for risk assessment in offshore and subsea field development. This paper presents a Computational Fluid Dynamics (CFD) solution for prediction of the trajectory and velocity of the released buoyancy modules from subsea. Six Degree of Freedom (DOF) rigid body motion of buoyancy module is modeled using an efficient moving mesh approach in transient CFD simulation. The effect of ocean currents at different water depths is considered in the motion of buoyancy modules.

This methodology has potential applications in many areas, such as, offshore vessel and floating platform protection, riser and umbilical protection, offshore and subsea field planning and layout, etc.

This transient CFD approach has been successfully implemented on typical buoyancy modules and demonstrated effect of ocean currents on the trajectory of the buoyancy modules. Hydrostatic forces, 6DOF motion and the velocities of the buoyancy module were predicted with different ocean current velocities.

The approach proposed in this paper captures the physics of released buoyance module in transient CFD and provides a practical tool for determining the trajectory and velocity of the released buoyancy modules from subsea and quantifying the risk for such an event. It can potentially be used for assessing the risk to offshore vessels and floating platforms, risers and umbilicals, as well as for offshore and subsea field planning and layout.
Numerical Simulation of an Ice Beam in Four-Point Bending Using SPH
Authors: Das Jitapriya , Polić Dražen , Ehlers Sören , Amdahl Jørgen
Published: September 2014

The flexural strength of sea ice is crucial for ice going vessels and hence the knowledge of mechanical properties of ice is very important for the design of such vessels. The primary objective of this investigation is the numerical simulation of sea ice in four-point bending using Smoothed Particle Hydrodynamics (SPH), which being a mesh free method offers a lot of advantages over traditional grid-based approaches. The numerical results will be compared to earlier simulations of in-situ four-point bending test results in terms of force, displacement and failure time. Further, the comparison of the SPH-based numerical simulations with the available literature will serve as a basis to discuss the potential advantages and shortcomings of the mesh free particle method used to model flexural failure of sea ice.
Influence of the Produced Fluids Properties and Flow Behavior on the Separation Efficiency of a Subsea Gas-Liquid Separator: A Sensitivity Analysis
Authors: Ramos Roberto Marcello Augustus , Estevam Valdir
Published: September 2014

The development of deep and ultra deep water fields, especially in marginal areas, always presents challenges related to profitability or associated flow assurance issues for subsea equipment.

Currently, Petrobras has a great number of production wells operating in deepwater, mainly in its mature fields (brown fields), therefore we are constantly motivated to improve production capacity and reduce operational costs (OPEX) in these scenarios.

In order to overcome this challenge (reduce OPEX and CAPEX) and keep focus in scenarios with high GOR, Petrobras has applied efforts in developing a high efficiency subsea gas-liquid separation system, particularly through PROCAP Technology Program - Future Vision [1]. The development of this technology is important to confirm whether is sound and reliable for use in large scale applications to increase oil production and, as well, improve both the flow assurance performance and recovery factor.

In the subsea gas-liquid separation technology one of the main challenges is related to variation in the design parameters and in the flowrate range expected during the life cycle of the project. The subsea separator has to be able to handle large flowrate variations since it can work with more than one production well connected.

The objective of this paper is to present the main results of the analysis carried out regarding the influence of the produced fluids properties and the flow behavior on the separation efficiency of a vertical annular subsea separator system (VASPS) [2]. The paper will present the subsea separator design and its performance when subjected to variations of fluid viscosity, fluid density, liquid and gas flowrates, bubble cut off diameter and water cut.
Fatigue of Risers: Calibrating Reliability Estimates From Full-Scale Data
Authors: Tognarelli Michael A. , Winterstein Steven R.
Published: September 2014

A number of measurement campaigns have sought to quantify fatigue damage on drilling and production risers in the field. The data from these campaigns have recently been used to test the accuracy of software predictions of riser motions and hence fatigue. It is often found that state-of-the-art software shows a conservative bias in predicting fatigue damage — conservative factors of 10 or more. At the same time, short-term damage estimates (e.g., over 10-minute intervals) show significant scatter: COV (coefficient of variation) values of 1.0–2.0 are typical.

We suggest methods here to better incorporate the information from these measurements into fatigue reliability predictions. We note that (1) software error statistics show markedly different behavior in different regimes; e.g., for different levels of predicted damage; and (2) our fatigue reliability concern lies with the variability not in individual 10-minute damage rates, but rather in the long-run damage rate over the entire structural life. These features suggest a non-parametric approach, in which software error statistics are binned and separately analyzed for different predicted damage levels. The sample means in each bin, together with their variabilities, then form the basis for our reliability assessment.

Because our interest lies with the average behavior in each bin, variability reduces notably: COVs of 1.0–2.0 (on individual 10-minute rates) are reduced by an order of magnitude or more. This variability is commonly dominated by the uncertainty in fatigue capacity (S–N curve, Miner’s rule, etc.) Thus, our measurement campaigns are of most interest in predicting only the mean bias in damage predictions; conventional methods are then available to propagate these into a standard fatigue reliability analysis. Results are shown for a number of applications, and implications considered for design (i.e., load factors).
Fatigue Damage to the Spar-Type Offshore Floating Wind Turbine Under Blade Pitch Controller Faults
Authors: Etemaddar Mahmoud , Vahidian Elaheh , Skjåstad Otto
Published: September 2014

The safety and reliability margin of offshore floating wind turbines need to be higher than that of onshore wind turbines due to larger environmental loads and higher operational and maintenance costs for offshore wind turbines compared to onshore wind turbines. However rotor cyclic loads coupled with 6 DOFs motions of the substructure, amplifies the fatigue damage in offshore floating wind turbines. In general a lower fatigue design factor is used for offshore wind turbines compared to that of the stationary oil and gas platforms. This is because the consequence of a failure in offshore wind turbines in general is lower than that of the offshore oil and gas platforms. In offshore floating wind turbines a sub-system fault in the electrical system and blade pitch angle controller also induces additional fatigue loading on the wind turbine structure. In this paper effect of selected controller system faults on the fatigue damage of an offshore floating wind turbine is investigated, in a case which fault is not detected by a fault detection system due to a failure in the fault detection system or operator decided to continue operation under fault condition. Two fault cases in the blade pitch angle controller of the NREL 5MW offshore floating wind turbine are modeled and simulated. These faults include: bias error in the blade pitch angle rotary encoder and valve blockage or line disconnection in the blade pitch angle actuator. The short-term fatigue damage due to these faults on the composite blade root, steel low-speed shaft, tower bottom and hub are calculated and compared with the fatigue damage under normal operational conditions considering same environmental conditions for both cases. This comparison shows that how risky is to work under the fault conditions which could be useful for wind turbine operators. The servo-hydro-aeroelastic code HAWC2 is used to simulate the time domain responses of the spar-type offshore floating wind turbine under normal and faulty operational conditions. The rain-flow cycle counting method is used to calculate the load cycles under normal operational and fault conditions. The short term fatigue damage to the composite blade root and steel structures are calculated for 6-hour reference period. The bi-linear Goodman diagram and a linear SN curve are used to estimate the fatigue damage to the composite blade root and the steel structures respectively. Moreover the fatigue damage for different mean wind speeds, sea states and fault amplitudes are calculated to figure out the region of wind speeds operation with the highest risk of damage.
Brine Chemistry Effects in Waterflood and CO2 Injection in Carbonate Reservoirs
Authors: Sarma Hemanta K. , Zhang Yi
Published: September 2014

It has been reported that the waterflood performance in carbonate reservoirs could be significantly ameliorated by tuning the injected brine salinity and ionic composition. Also, it is noted that the brine salinity affects the CO2 injection process. This study looked into such possible effects of brine chemistry on waterflood and CO2 injection for typical UAE carbonate reservoir conditions of high temperature and pressure (T = 120°C and P = 20.68MPa).

Effects on waterflood performance were investigated experimentally by a series of flooding tests at temperatures of 70°C and 120°C. In addition, an imbibition test was conducted at 70°C, followed by wettability monitoring tests at 90°C to investigate the impact of brine salinity variations and ionic compositions on waterflood performance.

The impact of brine salinity on CO2-brine system properties including CO2 solubility in brine, interfacial tension between CO2 and CO2-saturated brine, and density and viscosity of CO2-saturated brine were evaluated through correlation-based studies in conjunction with some experimental data. A mathematical pore-scale model was developed to assess the brine salinity effect on water-isolated oil recovery by CO2 diffusion through water barrier. This study led to the following findings:

(1) Incremental oil recovery could be obtained by either reducing salinity or increasing sulfate concentration of the tertiary injected brine at both 70°C and 120°C. However, the incremental recovery was more remarkable at the higher temperature of 120°C.

(2) At 70°C, lowering the water salinity is more effective than raising the sulfate concentration in injected water in terms of incremental oil recovery. It also exhibited a similar potential for increased oil recovery at 120°C.

(3) Wettability monitoring tests showed that water-wetness of carbonate rock studied could be increased by either reducing the water salinity or increasing sulfate concentration of the surrounding water. This is consistent with the imbibition test, in which wettability alteration towards more water-wetness by low salinity water was noted.

(4) Under typical UAE reservoir conditions, reducing the brine salinity could significantly enhance CO2 dissolution in brine, consequently inducing significant variation to the CO2-brine system properties. This would undoubtedly impact CO2 injection performance.

(5) Under typical UAE reservoir conditions, the capacity and rate of CO2 diffusion through water barrier to oil phase could be significantly reinforced by lowering the brine salinity of the water barrier.
Coupling of Heave and Roll for High-Speed Planing Hulls
Authors: Judge Carolyn Q.
Published: September 2014

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. The dynamic lift forces acting on the bottom of a planing hull dominate the hydrodynamics and these lift forces are known to depend on speed and wetted surface. As a planing boat rolls the wetted surface changes, which affects the dynamic lift. A series of tests using a wooden prismatic planing hull model with a constant deadrise of 20 degrees were done at static heel and heave positions as well as oscillating heave conditions. This paper presents the results from these experiments, primarily looking at the hydrodynamic coefficients in heave as a function of heel angle and exploring the coupling between these motions for a prismatic high-speed planing hull.
Structural Analysis of Aquaculture Nets: Comparison and Validation of Different Numerical Modelling Approaches
Authors: Moe-Føre Heidi , Endresen Per Christian , Aarsæther Karl Gunnar , Jensen Jørgen , Føre Martin , Kristiansen David , Fredheim Arne , Lader Pål , Reite Karl-Johan
Published: September 2014

The performance of three different numerical methods were compared and evaluated against data from physical model tests. A parameter study of a simplified net cage model subjected to a steady flow was performed by all methods, varying the net solidity and the flow velocity. The three numerical methods applied models based on springs, trusses or triangular finite elements. Hydrodynamic load calculations were based on the drag term in Morison’s equation and the cross-flow principle. Different approaches to account for wake effects were applied. In general, the presented numerical methods should be able to calculate loads and deformations within acceptable tolerance limits for low to intermediate current flow velocities and net solidities, while numerical analyses of high solidity nets subjected to high current velocities tend to overpredict the drag loads acting on the structure. To accurately estimate hydrodynamic loads and structural response of net structures with high projected solidity, new knowledge and methods are needed.
Numerical Study of Two Vessels Seakeeping in Waves
Authors: Zhan Dexin , Bass Don , Molyneux David
Published: September 2014

This paper presents a numerical study of seakeeping in regular waves for two vessels in close proximity using commercial seakeeping software HydroStar and an in-house code MOTSIM. The objective was to study the possible sheltering effect of the larger vessel (FPSO) on the smaller one (OSV) during personnel transfer between the two vessels, where one vessel was at some angle relative to the other vessel and there was no connection line between them. The study mainly focused on the OSV motion resulting from the interaction of the FPSO when the OSV was at different headings and wave directions. Initially the OSV motions close to the FPSO (and parallel) were compared with those for the OSV alone. For an un-parallel position of the two vessels, an objective function based on the OSV RAOs motion in roll, pitch and heave directions was used to optimize the OSV position. Finally comparisons between HydroStar and MOTSIM results are provided.

The main conclusions are:

1) When the FPSO and OSV are located in parallel, the OSV motions in sway, roll and yaw are larger than the single OSV motions in head waves while surge, heave and pitch are almost the same. The OSV motions in most of the six degrees of freedom are smaller than the single OSV motions when the waves are from other directions (always on the port side of the FPSO), which means that there is a sheltering effect.

2) The simulation results from different OSV rotation angles show that the hydrodynamic interaction between the FPSO and OSV e.g. the sheltering effect is related to the OSV angle and the wave heading. The objective function in roll, pitch and heave RAOs indicates that the OSV should maintain a close to parallel position with the FPSO to minimize motion when the waves come from the port side of the FPSO from 180 to 240 degrees. When the wave direction is around 240 degrees the OSV should have relatively small motion in waves for any OSV rotation angle.

3) A comparison of HydroStar and MOTSIM results shows that the MOTSIM results of a single vessel seakeeping simulation is in a good agreement with HydroStar. In two vessels situation more validation work needs to be done.
The Effect of the Boundary Layer and Liquid Viscosity and Vapor on Sloshing Characteristics
Authors: Zou Changfang , Wang Deyu
Published: September 2014

Using commercial code FLUENT and the volume-of-fluid (VOF) technique adopted to track free surface, numerical investigations for the numerical models including and excluding a second set of boundary layer grid, various liquid viscosity and vapor phase are carried out in this paper. The effect of relevant parameters (boundary layer grid, viscosity and vapor) on sloshing is investigated in detail. The numerical results show that the liquid viscosity effect in boundary layer influence on sloshing pressure for established a numerical model with a second set of boundary layer grid. Energy dissipation due to viscous friction within the boundary layer leads to reduction of sloshing pressure, especially when viscosity becomes bigger, the dissipation effect is more remarkable. The results are different from Lee’s [7]. Another factor influencing the sloshing pressure is vapor phase. Compared to incompressible air, the factor leads to pressure decrease. In addition, as a result of viscous damping effect within boundary layer, the rising time of impact pressure is larger and the wave amplitude of the free surface climbing up along the tank wall is smaller in bigger liquid viscosity. The boundary layer grid also has important influence on dynamic pressure distribution along the wall. Through comparison of computational results with experimental results, we found that a numerical model with boundary layer grid can predict the sloshing pressure more accurately.
Hydroelastic Analysis for Extended-Column of Extended Draft Semi-Submersible
Authors: Tay Zhi Yung , Popov Petyo Rumenov , Yordanov Vasil Zhivkov , Nguyen Hoang Dat
Published: September 2014

This paper presents a simplified model for assessing the hydroelasticity of the extended-column (e-column) for an extended-draft semi-submersible (E-SEMI) by using commercially available software. The E-SEMI comprises a second tier pontoon (STP) connected to a conventional semi-submersible by using extended-column (e-column). The purpose of attaching the STP is to increase the heave added mass, and as a result, could reduce the heaving motion and shift the natural period further away from the wave spectrum by increasing the natural period. One of the challenges of the E-SEMI is to obtain the hydroelastic response of the e-column when subjected to wave and current loadings. The simplified model models the e-column and STP using beam-column theory that has similar vibration frequencies and modes shapes of the complex model. The potential wave theory is used to model the waves and the Morrison equation is use to obtain the drag and inertia force acting on the e-column due to current loading. Hydroelasticity shall be performed on this simplified model to assess the strength performance as well as the deflection of the e-column. The bending moment obtained from the hydroelastic analysis is also significant in the connector design that keeps the e-column in place.
Predictive Simulation of Underwater Implosion: Coupling Multi-Material Compressible Fluids With Cracking Structures
Authors: Wang Kevin G. , Lea Patrick , Main Alex , McGarity Owen , Farhat Charbel
Published: September 2014

The implosive collapse of a gas-filled underwater structure can lead to strong pressure pulses and high-speed fragments that form a potential threat to adjacent structures. In this work, a high-fidelity, fluid-structure coupled computational approach is developed to simulate such an event. It allows quantitative prediction of the dynamics of acoustic and shock waves in water and the initiation and propagation of cracks in the structure. This computational approach features an extended finite element method (XFEM) for the highly-nonlinear structural dynamics characterized by large plastic deformation and fracture. It also features a finite volume method with exact two-phase Riemann solvers (FIVER) for the solution of the multi-material flow problem arising from the contact of gas and water after the structure fractures. The Eulerian computational fluid dynamics (CFD) solver and the Lagrangian computational structural dynamics (CSD) solver are coupled by means of an embedded boundary method of second-order accuracy in space. The capabilities and performance of this computational approach are explored and discussed in the full-scale simulations of a laboratory implosion experiment with hydrostatic loading and a three-dimensional manufactured implosion problem with explosion loading.
Experimental Determination of Roll Damping Coefficient for FPSO
Authors: Seelis Oliver A. , Tao Longbin
Published: September 2014

The roll damping coefficient is a crucial parameter for several design and operational aspects of FPSOs. The accurate prediction of the coefficient is not a trivial task and generally performed experimentally. A polynomial linearization of the decay test data has been widely applied in the offshore industry. However, research has indicated that for FPSOs with rectangular cross section and attached bilge keels, this methodology may lead to inaccurate damping coefficients.

This paper presents a study on the experimental determination of roll damping coefficients for FPSOs, obtained by free decay tests. For this purpose model tests are executed in the towing tank of the Marine Hydrodynamic Laboratory at Newcastle University. The model is based on the design of a purposely build FPSO, as typically applied in the central North Sea sector. The cross section of the FPSO is boxed shaped with a characteristic knuckle shaped bilge. The tests are conducted using three different bilge keel arrangements. The parametric change in bilge keel size results in the variation of the flow characteristics around the bilge knuckle. The damping coefficients are then established from the decay test data using a polynomial approach, a bi-linear approach and a hyperbolic approach.

A comparison between the damping evolutions obtained with the different methodologies is performed for each bilge keel configuration. Further, a numerical model of the FPSO is created using DNVs Sesam software. With the established damping coefficients, damping matrices are manually defined as an input to Sesam and roll transfer functions are numerically established. The computational determined transfer functions are then compared against the RAOs obtained from the model tests in regular waves to determine the most appropriate methodology.

The damping coefficient for the bare hull is well established by all three proposed methodologies. However, with the attached bilge keels the bi-linear and the hyperbolic methodologies produce damping coefficients reflecting the experimental results more accurately than the polynomial approach, indicating that the recently developed hyperbolic method is a valid alternative, and in certain cases, is more suitable to determine the roll damping coefficient. The experimental measurements could serve as a benchmark for further research and contribute to the practical application of FPSO roll damping determination.
On the Challenges With Pipeline Free Spans in Operational Phase
Authors: Raposo Celso , Fyrileiv Olav , Pereira Antonio
Published: September 2014

Free span assessment has more and more become an important part of modern pipeline design. The reason for this is partly that the remaining hydrocarbon reservoirs are located in more challenging places, e.g. with very uneven seabed. Another explanation is that the pipeline design codes a few decades ago did not allow for vibrating free spans, while the modern, state-of-the-art pipeline codes, such as DNV-OS-F101 “Submarine Pipeline Systems” (2013) and its Recommended Practices, opens for long spans that are allowed to vibrate as long as the structural integrity is ensured.

In presence of non-cohesive soils and high on-bottom flow velocities significant free span development may occur over the design life, e.g. due to scouring. Such spans may be associated with a fatigue life capacity less than the design life if the spans are assumed stationary. For non-stationary spans with occasional long span lengths this may not be true since the criticality is strongly linked to the persistence of long spans and the prevailing environmental condition. A realistic fatigue assessment must account for the history of the span (i.e. stress cycles encountered for a critical weld) including predictions into the future development.

High costs related to span intervention puts focus on minimizing these costs while still ensuring integrity of the pipeline with respect to vortex induced vibrations (VIV) and associated fatigue damage. On the other hand the potential costs related to fatigue failure of a pipeline (recovery costs, economical loss and environmental consequences) are enormous. Therefore it is essential to ensure that the probability of failure for free spans is within acceptable limits.

One frequent challenge faced with old pipelines in operations survey reports are that they report several free spans. Old pipelines were not designed to allow any vibration and usually there is scanty information about different parameters such as soil conditions, operational parameters, lay tension, environmental data, etc., thus it’s difficult to determine whether it’s necessary to intervene the span or not.

State-of-the-art free span codes are deterministic in their nature. If the new codes are used to evaluate such old pipeline spans, considering all the before mentioned uncertainties in the input parameters, this would eventually lead to over conservative very low time to failures. The outcome will be that many spans need to be fixed immediately or should have failed already. Such a situation leads to a mistaken conclusion about the conservatism of the codes and not on the way they were applied.

This paper discusses some of the challenges often seen with free spans during the operational phase. The objective of the paper is to demonstrate that for in-service pipelines the lack of reliable information about the free spans is the main source of commonly low life encountered and not the methodology used to evaluate the free span. Some of these challenges are discussed in detail and potential ways forward are outlined.
Numerical Simulation of Fatigue Crack Growth of a Welded Structural Component Under Block Program Fatigue Test
Authors: Gotoh Koji , Takuno Masao , Okada Koichi , Kusuba Sadaharu
Published: September 2014

Numerical simulations of fatigue crack growth of welded structural component were performed under fatigue testing conditions with block loading and constant stress range and the fatigue crack growth profiles were measured under the same loading conditions. In the experiments, fatigue cracks developed at the boxing fillet welded toe and grew toward the top flange plates of the specimens.

An advanced fracture mechanics approach based on the improved effective stress intensity factor range, which is the RPG (Re-tensile Plastic zone Generating) stress criterion, was applied to perform the numerical simulations of fatigue crack growth in the modeled components. A comparison of estimated fatigue crack growth profiles with measured ones verified that a reasonable estimation of fatigue crack growth can be estimated by applying the proposed numerical method.
Experimental Investigation on the Suppression Device of VIV of a Flexible Riser
Authors: Gao Yun , Fu Shixiao , Song Leijian , Peng Tao , Lei Runpei
Published: September 2014

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.
Improvement of Shallow-Water Basin Wave Generation Using ‘Anti-Waves’
Authors: van Essen Sanne , Pauw Willemijn , Schmittner Christian
Published: September 2014

The demand for hydrodynamic research facilities to correctly model shallow-water effects associated with low-frequency (LF) waves increases. Modelling such shallow-water waves in a basin introduces extra challenges, on top of the issues such projects are associated with at full scale. Various unwanted LF wave contributions are introduced by the geometry of the basin and the wave generators. Measurements show significantly more LF wave energy than expected based on second-order bound wave theory, where certain basin modes can generally be identified. This paper describes a method to minimize the unwanted part of this LF wave energy, by creating an ‘anti-wave’ and choosing an appropriate location in the basin. A wave-splitting tool was used to separate the original wave field into bound and LF free wave components in incident and reflected directions. The resulting LF free wave travelling from the wave generator was used to define a deterministic ‘anti-wave’, which was designed to cancel this LF free wave. Some first tests of this theory in MARIN’s Offshore Basin showed that it is possible to reduce the amount of unwanted LF spurious wave energy in shallow water by generating an anti-wave at the wave generator. This is promising for further development, although phasing of the anti-wave is difficult for basin oscillation modes. A procedure to follow for future shallow-water basin projects was identified.
Selection of an Offshore Petroleum Production System by Evaluating an Environmental Impact Index
Authors: Gonçalves Maiara Moreira , Morooka Celso Kazuyuki , Guilherme Ivan Rizzo
Published: September 2014

The development of an offshore petroleum production system corresponds to define a set of equipment to make possible oil and gas extraction from an underwater petroleum reservoir. To better comprehension of the process, definition of this production system can be divided into phases. Phase I corresponds to the selection of number of wells and type of the well. Then, following the previous work (Franco, 2003), in the Phase II, the layout arrangement of wells and the set of the stationary Floating Production Unit (FPU) are selected. And, in the Phase III, storage and offloading alternatives for the produced oil and gas are selected.

The present paper aims to identify environmental impacts associated with the each component of an offshore system for oil and gas production, and quantify each of them through indexes. It is expected to support the decision makers to select the best fitted system for a given offshore petroleum field. The increasing needs of petroleum to fulfill the energy matrix demanded in Brazil, the growing concern of the society for keeping the environment clean and the inclusion of an index related to the environment besides the technical and technological indexes usually taken makes it an important contribution to improve the process for selection and decision about the offshore production system. Particularly, it will be fundamental in the adverse condition of the Pre-salt scenario of petroleum production, in ultra-deep water depth and oil and gas with more aggressive contaminants to the system.

The proposed methodology follows a similar procedure for the assessment of environmental impacts through the use of environmental sensitivity index (ESI) and the use of impact matrix (NOOA, 1997; Patin, 1999; Mariano and La Rovere, 2006). For the estimation of environmental impacts, it was defined the ESI of the area to be developed, and it was constructed an impact matrix based on the activities involved in the installation of platform, operational phase and decommissioning of a FPU and the elements from environment. Therefore, this systematic and structured approach allowed incorporating to the process of selection of the offshore production system for an oil and gas field the selection of alternative which combines the best technical and technological characteristics with better aspects from the environment.
Examining the Effects of Scale, Mass Ratios and Column Shapes on the Vortex Induced Motion Response of a Semisubmersible Through CFD Analyses
Authors: Rijken Oriol
Published: September 2014

The phenomenon of vortex induced motions (VIM) of a semisubmersible has been observed in the field and in model tests. The VIM response can be onerous to the fatigue live of SCR’s that are supported from the semisubmersible. Field observations indicate significantly smaller VIM amplitude than what present day model tests predict. The Scruton number is a parameter which affects the magnitude of the VIM response; the Scruton number includes the effect of mass ratio and damping. The effect of damping on VIM response has been examined in model test scale, and this analysis indicated that damping has a minimal effect on the VIM response amplitudes. The effect of the mass ratio and the effect of performing physical experiments at model scale are examined through CFD analyses. The objectives of the CFD analyses are to focus on the VIM phenomenon itself and to compare response magnitudes, while giving less importance to semisubmersible hull details and absolute response magnitudes. Hence, most of the CFD work is done in a 2D environment. Responses for various column cross-sectional shapes are examined; the column cross-sectional shapes include square, rectangular and five-sided. The VIM response is the result of pressures acting on the semisubmersible columns. The CFD analyses provide means to obtain the pressures at various locations at the various columns, and therefore can be used as a way to describe the phenomenon. These pressure data sets are evaluated to show where the majority of the excitation occurs and phase relationships between excitation forces acting on each individual column are presented.
Sandwich Pipes With Strain Hardening Cementitious Composites (SHCC): Numerical Analyses
Authors: Fu Guangming , Moura Paz Claudio , Hernández Chujutalli John Alex , Lourenço Marcelo Igor , de Lima Dirney Bessa , Li Yong , Toledo Filho Romildo , Estefen Segen F.
Published: September 2014

Sandwich pipes (SP) combining high structural resistance with thermal insulation have been considered as an effective solution for using in ultra deepwater pipelines. Research has been conducted at COPPE/UFRJ with different core materials aiming to develop qualified pipes to transport deepwater oil and gas, especially for the pre-salt reservoirs in offshore Brazil. SPs using SHCC material are easy to manufacture and cost-effective. Moreover, the composition of the SHCC material can be controlled to achieve structural requirements along with good thermal insulation. Investigation on the buckling under external pressure and feasibility of installation by reel-lay method is required. This study presents numerical analysis of the collapse, collapse propagation and bending of sandwich pipes with different geometries. The Drucker-Prager formulation is employed for SHCC constitutive model and it is calibrated through small-scale tests. Model geometries match full scale specimens manufactured and tested in bending apparatus and hyperbaric chamber. Numerical/experimental correlation is also presented.
Extending the Capabilities of the Mooring Analysis Program: A Survey of Dynamic Mooring Line Theories for Integration Into FAST
Authors: Masciola Marco , Jonkman Jason , Robertson Amy
Published: September 2014

Techniques to model dynamic mooring lines take various forms. The most widely used models include a heuristic representation of the physics (such as a lumped-mass system), a finite-element analysis discretization of the lines (discretized in space), or a finite-difference model (which is discretized in both space and time). In this paper, the authors explore the features of the various models, weigh the advantages of each, and propose a plan for implementing one dynamic mooring line model into the open-source Mooring Analysis Program (MAP). MAP is currently used as a module for the FAST offshore wind turbine computer-aided engineering (CAE) tool to model mooring systems quasi-statically, although dynamic mooring capabilities are desired. Based on the exploration in this paper, the lumped-mass representation is selected for implementation in MAP based on its simplicity, low computational cost, and ability to provide physics similar to those captured by higher-order models.

To begin, the underlying theories defining the three classes of dynamic mooring line models are identified and explored. This leads to insight into the capabilities of each representation. These capabilities are weighed against the current needs of the FAST wind turbine CAE tool, to which MAP will be coupled. Based on the assessment, a plan for integrating the dynamic mooring line theory into the current MAP structure is developed. Common problems arising from the determination of the model static equilibrium and known issues with numerical stability are addressed. Because MAP is a module that FAST can call, a plan consistent with the FAST modularization framework principles is described. Adding dynamic mooring line capabilities extends the features in MAP and also allows uncoupled analysis to be performed through MAP’s native Python bindings.
Optimal Design of the Linkage Between Two Downhole Hydrocyclones in Series
Authors: Zhang Yong , Wang Yang , Li Feng , Zhao Lixin , Jiang Minghu , Zhang Yan , Wang Fengshan , Zheng Guoxing
Published: September 2014

Downhole Oil/Water Separating System is the key technology to bring the produced fluid with 90% water cut or more from reservoir to the ground. Hydrocyclone is widely used as the downhole separator to separate oil from the produced fluid before water’s reinjection into the reservoir. Hydrocyclone can obtain high separating efficiency with a simple structure. Two hydrocyclones used in series is the new hot spot about the technology of downhole separation but it is limited for wildly use by the relatively small wellbore diameter. Two hydrocylones used in series can assure perfect separation of the oil outlet and the water outlet. The design and its optimal improvement are presented in this paper of the linkage between the water outlet of the first hydrocyclone and the inlet of the second one. Some experiments based on CFD would show its function is presented in this paper as the path between the two hydrocyclones and as the rotary of the second separator.
Flexible Pipe Modeling Using Finite Macro-Elements
Authors: Provasi Rodrigo , Martins Clóvis de Arruda
Published: September 2014

Modeling flexible pipes in the local level is not a trivial task and many authors have employed a great amount of time in such task. The non-triviality arises from the various layers and their interaction, which are pretty tough to correctly model. The possible approaches to solve the problem are divided in to major categories: analytical models and numerical models. The analytical ones rely on a great number of hypotheses and, after a great effort, result in a system of algebraic equations. The numerical ones can be further differentiated in the ones developed using commercial software and the other ones using proprietary models.

The authors choose the second way to approach the problem and presented in previous works a group of elements called macro-elements, including a cylindrical element for orthotropic layers, a three dimensional curved beam for helical elements, a rigid connection and a contact element, both dealing with different node displacement natures. These elements take into account the physical and geometrical characteristics of the components. In this paper a pipe model, with a flexible internal core, two tensile armors and an external sheath, will be simulated and its the results will be checked against commercial software and commented.
3D Numerical Wave Basin Based on Parallelized SPH Method
Authors: Wen Hongjie , Ren Bing
Published: September 2014

A viscous 3D numerical wave basin for high nonlinear waves was developed based on Smoothed Particle Hydrodynamics (SPH) method. The computational accuracy of SPH method is mainly improved by introducing the Corrective Smoothed Particle Hydrodynamics Method (CSPM) and a novel pressure correction scheme. The incident waves are generated from the inflow boundary by prescribing a velocity profile of the flap-type wavemaker motions, and the outgoing waves are numerically dissipated inside an artificial damping zone located at the end of the basin. Moreover, the parallelization of the improved 3D SPH scheme has been carried out using a hybrid MPI-OpenMP programming, together with a dynamic load balancing strategy to improve the computational efficiency. The generation and propagation of regular wave and solitary wave have been simulated. Wave forces induced by regular wave acting on a large-diameter circular cylinder and solitary wave passing over a submerged breakwater are also presented to verify the accuracy of SPH model. In addition, several computing cases of different particle resolutions are investigated and a high parallel efficiency is obtained.
Response Control of TLP Using Tuned Mass Dampers
Authors: Chandrasekaran Srinivasan , Kumar Deepak , Ramanathan Ranjani
Published: September 2014

Offshore tension leg platform (TLP) is a compliant type offshore structure where the tendons are deployed under initial pretension to counteract the excessive buoyancy. TLPs show large amplitude response under environmental loads due to their compliancy, which poses threat under extreme loads. Use of passive dampers like Tuned Mass Damper (TMD) is common to control such large amplitude motion, however their deployment in offshore structures is relatively new. Response control of a scaled model of TLP is attempted using tuned mass damper of pendulum type under regular waves. Based on the experimental studies carried out, it is seen that there is a significant reduction in the surge response under the folded pendulum type damper. Results also show that there is a reduction in the heave response due to the control envisaged in the surge motion. The discussed method of response control is one of the effective methods of retrofitting offshore platforms whose operability at rough sea states is a serious concern.