bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Service Buckling Assessment: The Correct Use of Engineering Analysis Tools
Authors: Bartolini Lorenzo , Marchionni Lorenzo , Tassetti Sara , Battistini Alberto , Vitali Luigino
Published: October 2015

There is consensus on the need for in-service buckling analyses to assess the integrity of both flowlines and long distance trunklines subject to HP/HT service condition. The extent of the analyses and supporting survey depends on the severity of the application.

In the last two decades, the pipeline industry has gained significant experience in both the design and operation of pipeline systems exposed to global buckling. Actually, the early 90s have been a watershed: before the phenomenon was just known (theoretically), then it was seen...as soon as pipeline integrity management programmes have been introduced in the offshore pipeline industry practices. Although, limited information have been documented in the open literature, now as then.

Several efforts have been dedicated to develop design methods and procedures suitable for operating pipeline safely as well as protecting the population, environmental resources and assets. At the beginning, there was a gap to be closed as specific mitigation measures were never designed. Nowadays, thanks to computational progress, it seems that the attention is addressed to face the uncertainties affecting the subject matter but, sometime, leading to overdesign.

The scope of the paper is to present aspects of global buckling design analyses that were performed in recent projects with the aim to highlight the challenges and the risks, the accuracy or the limitation of the methods, the feedback and the lesson learnt of real installed pipelines under operating conditions.
VIV Basics for Subsea Spool/Jumper Design
Authors: Bruschi Roberto , Bartolini Lorenzo , Molinari Caterina , Vignati Giulio C. , Vitali Luigino
Published: October 2015

Coming and future Deep and Ultra-Deep Water project developments involve the use of many Subsea Rigid Jumpers used to connect well heads, manifolds or riser base with Flowline End Terminations.

Generally, Subsea Rigid Jumpers are short and flexible pipe sections assembled in a variety of spatial configurations to accommodate the installation tolerances, the Flowline End Terminations translation and settlement guaranteeing the continuity and the flexibility needs of the subsea pipe layout. These Subsea Rigid Jumpers are critical components as they are subject to fatigue damage due to Vortex Induced Vibrations induced by the bottom currents and/or Flow Induced Vibrations induced by the high internal flow rate, often coupled with slugging flow conditions.

In this paper, a Subsea Rigid Jumper design approach based on basics of Vortex Induced Vibrations is presented, and outcomes on a few typical multi-planar Subsea Rigid Jumpers discussed.
Emission Reduction Technology and Cost Efficiency for Ships Operating on the Northern Sea Route: A Case Study
Authors: Skarbø Runa A. , Ehlers Sören , Æsøy Vilmar
Published: October 2015

The Northern Sea Route (NSR) has recently become an alternative route for seaborne transportation between Europe and Asia due to the decreasing ice conditions. The reduced sailing distance can provide great savings in time used and fuel consumption. However, there are environmental concerns regarding increased emissions in Arctic areas. Emission regulations in MARPOL’s Annex VI sets limits for emission of sulphur oxides (SOx) and nitrogen oxides (NOx) in special areas. The Arctic areas are potentially a candidate for a such status. There are several alternative technologies under development to comply with the new regulations, including exhaust gas cleaning systems, cleaner fuel and cleaner engines. However, the costs of complying are significant, and payback on investments depends on the overall operational profile. This paper addresses the decision of using either the NSR or the SCR between Europe and Asia, given a new Emission Control Area (ECA) in the Arctic Seas. The study quantifies the effects of introducing ECA regulations in these areas, and compares the costs of sailing the NSR to the costs of sailing the conventional route via the Suez Canal. The study considers one case ship and three different scenarios with different technology installed in order to comply with emission regulations. The results from the scenario simulations show significant reductions in fuel consumption and emission reductions for the NSR. However, with the present fuel cost and emission legislation, the NSR with an Arctic ECA will not be cost efficient compared to the SCR.
Spectral Strength Analysis of a Transportation Barge
Authors: Jedruszek Krzysztof , Meskers Geert
Published: October 2015

Heerema Marine Contractors has been awarded contracts for the transport and installation of two ultra-heavy platforms — Arkutun Dagi and Wheatstone. The total transportation weight including deck support frame is about 45,000 mT for both of these projects. It requires the largest transportation and float-over barge in the world (H-851) and pushes it to the limit of its strength. A detailed study has been performed to verify the structural integrity of the barge. The design stresses have been determined using a spectral analysis, based on stress RAOs for each of the elements in the FEM model. All elements are tested against relevant code, looking at requirements for strength as well as buckling capacity. The advantage of the spectral strength analysis is that no assumptions need to be made about the most critical acceleration and the associated design wave. The method focusses directly on finding the critical stresses.

This paper explains the steps taken to perform a spectral strength assessment of a transportation vessel. It shows how stress RAOs are determined by combining results of a hydrodynamic analysis with a full scale FEM model. The stress RAOs are used to perform a strength and buckling verification using a full wave spectrum and results are related to the outcome of a design wave analysis performed by a third party. Explanations are provided based on Arkutun Dagi project.
Seakeeping of a Research Vessel With Azimuthing Propellers
Authors: McTaggart Kevin , Marly Jean-François
Published: October 2015

This paper gives comparisons of numerical predictions with seakeeping model tests for R/V Melville, an oceanographic research vessel that is propelled by two ducted azimuthing propellers. The model tests were conducted on a 1/23 scale model that was controlled by a human pilot using a remote control. The ship motions were predicted using the ShipMo3D ship motion library, which uses potential flow theory to determine hull radiation and diffraction forces. Predicted roll and pitch motions give good agreement with model tests. Predicted yaw motions and azimuthing propeller deflection angles are much less than values observed during the model tests. Challenges with prediction of yaw and azimuthing propeller deflection are likely due to approximation of the human model pilot with a simple proportional-derivative (PD) autopilot. The comparisons between numerical predictions and model tests suggest that the azimuthing propellers have minimal influence on roll for R/V Melville.
New Extreme Model Applied to Mooring System Design Load Case Assessment
Authors: del Jesus Fernando , Guanche Raúl , Losada Íñigo J. , Vidal César
Published: October 2015

Offshore wind energy turbines are being deployed massively in the North Sea. Most of the latest developments are monopile based due to the local bathymetry. However, future offshore wind farms will be located at larger water depths. Mainly because the nearest sites to the shoreline will be already occupied, future wind farms will be in 60 m water depth at least. This is, approximately, the limit for fixed support structures, such as monopiles, tripods and jackets. Some developers have already identified this need and some prototypes are under testing, such as WindFloat and Hywind.

Floating wind technology will face some challenges. One of the most important ones is how to moderate the cost of the platform and the mooring system. Consequently, it is necessary to reduce the uncertainty during design steps.

In this paper, new extreme mixed model will be applied to mooring system design. This extreme model combines instrumental and reanalysis data in order to obtain more accurate design parameters, reducing the uncertainty and improving the input that is required for the structural design of these concepts.
Vertical Wave Impact Loading on a Fixed Platform Deck
Authors: Scharnke Jule , Hennig Janou
Published: October 2015

The TLP model tests in CresT [1] showed that there is a significant difference in the maximum load events due to long-crested and short-crested waves of same peak period and significant wave height. This decrease in load amplitudes for increasing spreading was not dominated by the reduction in crest heights, but related to a change in wave excitation. In ShorT-CresT wave-in-deck model tests were carried out with the focus on the physics of impact loading. The primary objective of the platform tests was to link crest height and wave impact with local and global loading on the deck. The model test results showed that the global vertical loads in short-crested waves can be similar to long-crested events, if the wetted deck area is comparable. In other words, the platform deck loading corresponds to the relative short-crestedness of the sea state: if the crest length is at least as large as the characteristic deck dimension, the loads are significantly larger than for lower crest lengths (step change). In this paper the results of the wave-in-deck model tests are presented and discussed. The analysis of the model tests is focused on a comparison between short-crested and long-crested impacts and a comparison of the measurements to a simplified loading model.
Achieving Competence in Offshore Emergency Egress Using Virtual Environment Training
Authors: Smith Jennifer , Veitch Brian , MacKinnon Scott
Published: October 2015

As a precursor to simulation transfer studies, this research assessed the level of competence in basic offshore safety gained through a virtual environment training program and investigated the training time required to reach competence. The experiment demonstrated that the offshore egress learning objectives can be taught using the All-hands Virtual Emergency Response Trainer (AVERT) training program with some limitations. The two main findings were: 1. due to individual differences in spatial learning, some individuals required more exposure to the virtual setting to ensure knowledge retention; and 2. the procedural learning objectives required reinforcement during training scenarios to ensure knowledge acquisition. Overall, this research recommends modifications to the training and technology design in order to prepare for future transfer studies and offshore applications.
Viscoelastic Large Strain Model of Bitumen Used for Corrosion Protection in Subsea Cables and Umbilicals
Authors: Komperød Magnus , Konradsen Bjørn , Slora Roger
Published: October 2015

Bitumen is used as anticorrosion material to protect armor wires in subsea cables and umbilicals. Establishing bitumen’s viscoelastic properties is essential for developing analytical models of how bitumen influences the cable’s mechanical properties, in particular the bending stiffness. A new laboratory instrument has been developed for establishing the viscoelastic properties of bitumen subject to equally large strains as in real-life cables. This paper presents the basic principle of the new instrument and derives how to calculate bitumen’s viscoelastic properties from the measurements logged by the instrument. The paper also models bitumen’s viscoelastic properties as function of strain amplitude, strain frequency, and bitumen temperature, using multi-variable data analysis. These models show that the viscoelastic properties are highly temperature dependent. Bitumen’s shear stress / shear strain amplitude ratio grows with increasing rate as the temperature decreases.
Preliminary Hazard Analysis of the Activities of Inspection and Repair in a Cargo Tank of an Operating FPSO
Authors: Van Loon Karoline De Carli Loureiro , Orsolini Ana Luisa , Ysla Karla , Martins Marcelo Ramos
Published: October 2015

The number of Floating Production Storage and Offloading units (FPSOs) operating worldwide has been increasing due to the fact that they are well recognized as one of the most economical systems to develop offshore (ultra) deep water areas lacking infrastructure. In order to comply with the regulations, especially the Classification Society rules, and to monitor the hull integrity, all the cargo tanks must be submitted to periodical surveys on a continuous base. Eventually during this survey, some anomalies may be found, such as cracks and thickness loss in structural elements that will require repairs.

This study provides a brief review of the methodology provided by the Guidelines for Formal Safety Assessment (FSA) proposed by IMO (2002) and its application to the activities performed to survey and repair a cargo tank of an operating FPSO. A detailed description of these activities is provided in order to define the scope and frontiers of this study. Special attention is paid to the first step of the FSA methodology and the “Preliminary Hazard Analysis” technique is applied to the mentioned activities.
Slamming Loads on a Wedge Elastically Suspended on a Marine Structure
Authors: Sun Hui , Helmers Jens B.
Published: October 2015

Slamming loads on a two-dimensional wedge elastically suspended on a marine structure are analyzed by using either a combined Wagner and von Karman method (W-vK) or a boundary element method (BEM). Fully nonlinear free surface conditions are satisfied in the BEM. Hydroelasticity effects are considered in both methods. A sinusoidal free surface motion relative to the marine structure is specified for the slamming event. Both the water entry phase and the water exit phase are simulated. The numerical results by the two different methods are compared. The W-vK method can generally predict the same trend of the variation of the body motions and the water forces, although the predicted maximum forces are larger than those by the BEM. The influence of the stiffness and damping of the elastic connection on the water impact force are discussed.
Estimation of Force Reduction on Ocean Structures With Perforated Members
Authors: Chandrasekaran Srinivasan , Natarajan Madhavi , Sreeramulu Lognath Radhakrishnan
Published: October 2015

While retrofitting and rehabilitation are usually related to strengthening of members, the presented concept is a novel attempt as it addresses decrease in the encountered forces on the members. Presence of perforated members in ocean structures reduces the wave-structure interaction significantly; breakwaters with perforated members are classical examples of such kind. This concept of encompassing the perforated outer cylinder with inner existing structure is found to be most feasible rehabilitation concept as it does not demand replacement of any damaged members. The presence of outer perforated cover alters the water particle kinematics significantly and eventually this remains the reason for the force reduction mechanism. In this study, the variation of water particle kinematics along the depth of the cylinder is estimated on the cylindrical structure with and without perforated outer cover. Forces on the inner cylinder are quantified numerically and experimentally; experimental results show a close agreement with that of the numerical ones. Velocity variations along the water depth are quantified in the form of design charts, which shall be helpful for the practicing professionals while attempting for retrofitting or re-design. Force variations derived through numerical analyses, which are functions of the water particle kinematics along the depth shall be useful in the design offices for cylindrical members encompassed with perforated outer cover. Introduction of perforated member over the existing cylindrical structure showed a significant force reduction around 60% on an average for all the wave steepness indexes considered for the study, when compared to the force on the member without perforated cover.
Wettability Alteration in Limestone and Dolomite With Brines and CO2
Authors: Muñoz Eddy Ruidiaz , Winter Alessandra , Trevisan Osvair Vidal
Published: October 2015

Wettability test is one of the most used tools for evaluating rock/fluid interaction in oils reservoir. In the present paper two carbonate outcrop rocks are evaluated for wettability alterations when subjected to brine injections of varying salinities and content of dissolved CO2. The evaluation included a qualitative appraisal via spontaneous imbibition tests and a quantitative assessment by the Amott-Harvey procedure. Rocks refer to limestone and dolomite samples with petro-physical properties similar to the Brazilian pre-salt reservoirs. Testing fluids are a medium gravity crude oil, seawater concentration brine, formation equivalent brine and the carbonated version of these brines. Results show additional oil recovery directly associated with wettability alteration provoked by brine concentration changes. Increments in recovery were observed independently if the brine concentration decreased or increased in the replacement process. For dolomites and limestone wettability changed in the direction of turning the rock from oil-wet to neutral wet. Tests carried out with equivalent carbonated brines show that similar alteration in the wetting properties also occur. Alterations were as well independent of the increase or decrease of the salt concentration in the brine changed. However, CO2 or its derived ions dissolved in the brines seem to inhibit the mechanism of wettability change when rocks are subject to changes in brine salt concentrations.
ShorTCresT: Directional Wave Measurements at MARIN
Authors: Hennig Janou , Scharnke Jule , Schmittner Christian E. , van den Berg Joris
Published: October 2015

The objective of the ShortCresT JIP Joint Industry Project was to take into account short-crestedness in the design of offshore structures against extreme waves based on a good description of their spectral characteristics, statistics, kinematics, breaking and loading and to deliver a concrete (empirical) design methodology. The second order wave crest distribution showed to be a good basis for the estimation of a design wave crest. However, depending on sea state steepness and directional spreading, crests may exceed the second order distribution in some severe seas by around 10 %. On the other hand, the very highest crests may be limited by breaking and even fall below the second order model. This paper addresses experimental results from the MARIN where directional wave measurements were carried out in two dimensions. Conclusions with respect to evolution of wave spectra in the basin, directional analysis and calibration, sampling variability, local variability of measured crest heights and measured crest height distributions due to different types of spreading are evaluated. Furthermore, the influence of the type of instrumentation and the effect of the spectral high frequency tail on the crest distributions are assessed.
Drained Breakout Resistance of a Pipeline on a Mobile Seabed
Authors: Tom Joe G. , Leckie Simon H. F. , White David J. , Draper Scott
Published: October 2015

This paper describes a numerical study investigating the effect of sediment transport and associated changes in the local seabed profile on the drained breakout resistance of subsea pipelines. Limit analyses were conducted assessing the breakout response of a pipeline placed on a cohesionless Mohr-Coulomb material considering different seabed profiles around the pipeline. These profiles were determined from surveys of a pipeline on an erodible seabed. The parametric study shows the relative importance of various parameters describing the seabed profile geometry, including the local pipe embedment and the adjacent slope of the seabed. Significant changes in drained resistance occur due to changes in local pipeline embedment resulting from scour induced pipeline lowering and/or sedimentation. The seabed slope local to the pipeline also has a strong impact. The assumption of a flat seabed can lead to predicted seabed resistance that differs significantly from the actual value, accounting for a more natural seabed profile.
Development of Alternative Drive Concepts for Down-the-Hole Hammer in Deep Drilling
Authors: Lehmann Franziska , Reich Matthias
Published: October 2015

Hard rock drilling is facing increasing importance by using geothermal energy as a new energy source. Percussive drilling methods are generally well suited for drilling hard rocks. However, until now there is no drilling tool available on the market that uses percussive drilling methods and can be applied in deep boreholes in combination with common drilling muds. The aim of the DGMK project 733 is to develop a hammer drill which generates the impact energy downhole and works with conventional drilling mud. Seven different drive concepts were developed during the feasibility study. Demonstrators were manufactured for four of the seven drive concepts. The evaluation of the drive concepts showed that two of them have a high potential for the implementation in the field. These two concepts will be developed further to laboratory prototypes and were investigated at a test facility.
Investigation on Effect of Downhole Vibration Force on Drilling Performance With a Dynamic BHA Model
Authors: Wang Lei , Yang Jianming , Butt Stephen , Qiu Hongyuan
Published: October 2015

A dynamic bottom hole assembly (BHA) model is built with finite element method (FEM) in this paper. This model is used for evaluation the influence of externally added vibration to the BHA system. With this dynamic model along with a general bit-rock interaction formula, the BHA’s motion in axial and torsional directions are examined. Parametric study is carried out by varying the parameters of the applied vibration force, including the mean value, amplitude, angular frequency, and the location of this force excitation. The simulation results indicate that externally applied vibration force is indeed able to improve drilling performance. In particular, the mean value and amplitude of the applied force have a almost linear relation with ROP and WOB. The stresses distributions along BHA are investigated as well.
Parameter Identification of a Steel Catenary Riser Using Hilbert and Wavelet Transforms
Authors: Torres Lizeth , Verde Cristina , Borges Flavia , Magluta Carlos , Roitman Ney
Published: October 2015

This article presents a methodology — for Multiple Degree of Freedom (MDOF) systems — to identify the modal parameters of a steel catenary riser (SCR) by employing both the Hilbert and the wavelet transforms. To validate the proposed approach, a set of experiments were performed in a small scale model of a real SCR that is installed in the P18 platform operating in Campos Basin, Brazil. During the experiments, the damping factor along the SCR was modified by adding viscoelastic sandwich layers on its structure. Each change was recorded with two accelerometers mounted at the bottom of the riser; one of them was set to get measurements in the catenary plane and the other one to get measurements out of the plane. Then, in order to obtain the impulse response of the structure — from which is possible to obtain the modal parameters — some hammer impacts were applied at locations close to these accelerometers.
Gas Filled Pipelines Monitoring Using Multipoint Vibroacoustic Sensing
Authors: Bernasconi Giancarlo , Giunta Giuseppe , Chiappa Fabio
Published: October 2015

eni S.p.A. has promoted and supported a research project (DIONISIO) for the design of a proprietary pipeline monitoring system, exploiting negative pressure waves and statistical analysis principles. A discrete network of pressure and vibration sensors are installed on the pipeline, at relative distances of tens of kilometers. The acoustic and elastic waves produced by third party interference and by flow variations (leaks, spills, valve regulations, pig operations, etc.), propagate along the pipeline, and they are recorded at the monitoring stations. Multichannel processing of the collected signals enables the real time detection, localization and classification of the triggering event.

The system has been tested in single phase and multiphase transportation lines during several field campaigns. This paper collects the results for gas transportation pipelines.

The field experience has been used to upgrade the prototypal version of the system to an industrial version, that is currently operative, or in an advanced installation phase, on several pipelines in Italy and in Nigeria, and it has detected tens of bunkering activities with a localization accuracy of about 25 m, from a distance up to 35 km from the sensing point.
Flexible Pipe Hysteretic Bending Behavior: Comparison With Experimental Characterization and Finite Element Method
Authors: Péronne Simon , Izarn Cécile , Estrier Pascal , Caro Olivier , Leroy Jean-Marc , Charliac David
Published: October 2015

The flexible riser global behavior is of major importance during the design phase of a flexible riser system configuration.

Flexible riser design is an optimization loop involving several iterations. The flexible riser main mechanical characteristics are used as inputs into the global dynamic analysis. The dynamic analysis is performed to derive global loads that are then used for the flexible riser design. At each step of the riser design optimization loop, from the global configuration to flexible pipe cross-section, accurate knowledge of the flexible pipe mechanical characteristics is essential.

One of the main mechanical characteristics of a flexible riser that drives its global behavior is its bending stiffness. Considering the flexible riser composition, the bending stiffness is much lower than its torsional and axial stiffnesses and therefore has a larger influence on its static and dynamic behavior.

In order to simplify the global analysis, the first approach considered uses a linear bending stiffness. In this case, only the contribution of the polymer layers of the flexible is accounted for. The linear bending stiffness is therefore only impacted by thermal loads.

In reality, because of the friction that can occur between the armor layers, the bending behavior is non-linear and the relation between bending moment versus curvature is hysteretic. This hysteretic behavior induces energy dissipation and therefore, when accounted in the global modeling of the riser, reduces the curvature response of the flexible riser.

Technip and IFPEN previously developed a model to describe mechanical flexible pipe characteristics. This model is based on the finite difference method. To ensure the accuracy of stress prediction of this method in response to external loads (tension, curvature, internal pressure and external pressure), results are validated with both experimental and finite element methods.

This paper presents the theory of bending behavior of a flexible riser and explains how the model is used to derive a hysteric bending model. The matrix of experimental tests campaigns performed on flexible pipe to characterize bending behavior of flexible risers, and comparisons with hysteretic behavior predictions from the FEA and finite difference models are presented.

Finally results from experimental tests, FEA and calculated hysteretic bending models are implemented into the dynamic analysis model of a flexible riser system. Then the global behaviors of the flexible pipe configuration, with the different properties, are compared.
Basic Design Considerations for Arctic Submarine Concepts
Authors: Frühling Christian
Published: October 2015

The paper discusses basic design considerations for civil submarines which are supposed to be applied in ice covered waters. The vessels taken into consideration are in the range of 4000 t displacement with lengths of approx. 60–100 m. Main mission scenarios relate to installation, maintenance and repair of subsea equipment, sub-ice oil spill response, and sub-ice seismic. Topics covered in this paper are related to geographic boundary conditions, the basic hull layout, hydrodynamics in shallow ice covered waters, hydrodynamics under surfaced conditions, and cargo transportation. The paper closes with a conceptual design example for a multi-purpose submarine.
Efficient Probabilistic Fatigue Analysis of a Riser Suspended and Moored by Chains
Authors: Giraldo Juan S. M. , Sagrilo Luis V. S. , Dantas Claudio M. S.
Published: October 2015

Fatigue analysis of an offshore structure usually requires the numerical simulation of a huge number of loading cases to compute the long-term integral associated to the accumulated fatigue damage. Papadimitriou et al. [1] and Low and Cheung [2] proposed two distinct approaches to solve the long-term fatigue damage more efficiently. These methods are known as Asymptotic Approximation Method and Perturbation Method, respectively. This paper investigates the efficiency of these two methods in the fatigue analysis of the steel pipe of a riser suspended and moored by chains (RSAA). Since there is an analytical solution for the stress spectrum of this riser, both time and frequency domain fatigue assessments approaches are considered. The accuracy and computational efficiency of the aforementioned methods are compared with the “brute force” direct integration methodology.
Applying Risk-Based Design to Arctic Ships
Authors: Bergström Martin , Erikstad Stein Ove , Ehlers Sören
Published: October 2015

One of the challenges related to the design of arctic cargo ships is that their transport capacity is dependent on a number of arctic specific design parameters (e.g., ice conditions and the availability of icebreaker support) in which there typically is a significant level of uncertainty and stochasticity. This paper addresses that challenge by presenting a design method that deals with the parameter uncertainty by integrating method of risk assessment in to the design process, i.e., by utilising the principles of Risk-Based Design (RBD). In order to obtain a holistic approach, the design method treats a ship as an arctic sea transport system that might include multiple ships, icebreakers, and port-based facilities such as cargo storages. Using the method it is possible to design an arctic sea transport system that provides a desired level of operational reliability. This provides the means to minimise costs and financial losses due to over- or undercapacity, and thereby to improve the resource-efficiency of the system as a whole.
Stochastic Linearization of the Morison Equation Applied to an Offshore Wind Turbine
Authors: Housseine Charaf Ouled , Monroy Charles , de Hauteclocque Guillaume
Published: October 2015

This paper aims at comparing different implementations of the Morison equation for seakeeping analysis in frequency domain. For more consistency, different wave models are considered and the total wave field (incoming wave, the diffracted and the radiated wave field) is included in the Morison equation.

A state-of-the-art of theMorison equation and the drag force linearized forms are presented. The implementation procedure, based on an iterative frequency domain scheme, is developed for the regular and the irregular wave cases.

Seakeeping analysis of an offshore wind turbine is considered as an application case. A comparison between numerical simulations and measured responses is presented.

For the floater’s numerical model, skirts damping effect and hydrodynamic loads applied on cylindrical bracings are modeled using the Morison equation. The drag and inertia coefficients are considered constant for all sea states and calibrated using the experimental results.

Response amplitude operators (RAOs) and short-termstatistics of motions show a good agreement between experimental and numerical results. The influence of different calculation parameters including the wave model (regular/irregular) and the wave fields (incident/total) are investigated.
Whitening Generation in PVDF Under Cyclic Loading
Authors: Silva Marlon Demauir Cozine , Laurentino Daniele Alves , da Costa Marysilvia Ferreira , Costa Neto Celio Albano da
Published: October 2015

Whitening is defined as the change in the opacity of a polymeric material due to microvoid nucleation and/or grow, resulting in volume increase and possible modification of the mechanical properties. Its formation may arise from processing conditions or mechanical stresses acting in the polymers. The understanding of the whitening phenomenon and its effect on mechanical behavior is of great importance for engineering application; for instance, poly (vinylidene fluoride) (PVDF) is widely used as pressure barrier in flexible raisers, where high pressure and aggressive media are presents and the presence of whitening may increase the gas permeation rate.

The present study, cyclic loading experiments were performed on PVDF to generate whitening in a controlled manner. Subsequently, the whitening effect on the mechanical properties were evaluated using tensile tests and the structure was evaluated using X-ray diffraction, while the fracture surface was analyzed via scanning electron microscopy. It was observed that cyclic load was able to nucleated the voids and there was an increase in the crystallinity and in the mechanical properties of the material.
Effect of Line Integral on the Computation of Forward-Speed Ship Motions
Authors: Peng Heather , Wang Junshi , Qiu Wei
Published: October 2015

Computations have been performed to predict motions ships at forward speeds. The radiation and diffraction problems of a ship with forward speed are solved with the panel-free method in the frequency domain. In this paper, the effect of the line integral on the solutions are investigated using three ships, including a Series 60 ship, the S175 ship and the DTMB 5512 hull. Computed motions were compared with experimental data and those by other numerical methods.
Fatigue Life Assessment of Single Layer 60512 PVDF Barrier in Unbonded Flexible Risers
Authors: Fernando Upul S. , Davidson Michelle
Published: October 2015

The polymeric barrier is one of the key components in a flexible pipe, the sound function of which is essential for the containment of the transported medium, ensuring no leakage to the environment which could result in undesired consequences. According to API 17J the barrier design must be able to sustain certain static and dynamic strain conditions however; the actual design or the fatigue assessment of the barrier is not covered within the standard. Since the barrier is subjected to the same dynamic loading as the pipe the durability and integrity of the barrier is a key issue that needs to be addressed during barrier design for dynamic risers. This paper discusses a fatigue life assessment procedure for a barrier made of copolymer Grade 60512 PVDF.

A flexible pipe barrier is manufactured by continuous extrusion of polymer onto a metallic carcass. The carcass has a spiral structure with an irregular outer profile. As such, the extruded polymer on this irregular surface inevitably gives non-uniform thickness and geometric anomalies where the polymer has flowed into gaps in the carcass. During pipe loading such anomalies act as stress concentrations and become critical locations for fatigue crack formation. The evaluation of the effect of the barrier profile shape on the fatigue durability of the barrier is therefore an essential requirement, in particular, in cases where the barrier consists of a single extruded polymer layer.

Within the procedure outlined in this paper, the fatigue assessment of the barrier is made using the local plastic strain behaviour. The maximum stress concentration factor and the acceptable profile for the extruded barrier are selected to provide adequate safety margins for the project specific loading conditions. A procedure has been proposed to predict the local plastic strain of the barrier using global service loading data.
Effect of Epoxy Filling in End Fitting on the Integrity of Flexible Pipes: With Reference to Suncor Terra Nova Flowlines
Authors: Fernando Upul S. , Roberts Andrew , Karabelas George
Published: October 2015

Two flowlines installed in the Suncor Terra Nova riser replacement programme were found to leak during leak tests performed after site installation. No hydrocarbon loss was suffered nor was there any pollution incident; however the scheduled production start-up for the pipes was delayed. Investigations confirmed that the leaks in both pipes occurred due to a crack in the polymer (PVDF) barrier within the end fitting region of the pipe. It was also concluded that the crack in the barrier in these pipes occurred either during the transportation or installation of the pipes in the field due to thermo-mechanical loading on the pipe during this period. Both failures were found to have initiated from a void in the epoxy which was used to fill small clearances within the end fitting.

This paper describes the finite element stress/stain analyses performed to investigate the effects on the PVDF barrier and epoxy within the end fitting due to the thermal and mechanical loading encountered during pipe installation. A multi-scale modelling approach has been used where a full pipe with detailed end fitting components was modelled in a coarse mesh model whilst the stress-strain behaviour near epoxy void was analysed using a macroscopic sub-model. A brief description of the models and the results are presented.

The analyses involved predicting the barrier deformation response at the failure location under the anticipated thermo-mechanical loading exerted on the pipe. The results have shown that the failure occurred due to the presence of the void in the epoxy at a critical location; cooling of the pipe during its transportation was considered to have created the thermo-mechanical loading to drive the crack from the epoxy into the PVDF. It was concluded that the failure in the pipes would not have occurred if either the void was not present in that critical region in the epoxy, or if it had not been subjected to the thermo-mechanical loading. A design change removing the filling of epoxy in the end fitting process is being implemented to prevent this failure in the future.
A Fluid-Structure Coupled Computational Framework for Fluid-Induced Failure and Fracture
Authors: Lea Patrick D. , Farhat Charbel , Wang Kevin G.
Published: October 2015

This work extends and generalizes a recently developed fluid-structure coupled computational framework to model and simulate fluid-induced failure and fracture. In particular, a novel surface representation approach is proposed to represent a fractured fluid-structure interface in the context of embedded boundary method. This approach is generic in the sense that it is applicable to many different computational fracture models and methods, including the element deletion (ED) technique and the extended finite element method (XFEM). Two three-dimensional model problems are presented to demonstrate the salient features of the computational framework, and to compare the performance of ED and XFEM in the context of fluid-induced failure and fracture.
Risk Based Structural Integrity Assessment of LNG FPSO
Authors: Yeun Dong-Yun , Jang Chang-Hwan , Jun Seock-Hee , Oh Yeong-Tae
Published: October 2015

As the importance of the risk based structural integrity assessment for offshore installations against the accidental loads is more emphasized, the structural engineering activities are essential for shipyards. Especially, in case of EPC (Engineering, Procurement and Construction) being performed by shipyards, more attention should be paid to the risk based structural integrity assessment in case that the results may have an unexpected impact on design and the associated procurement.

This paper introduces a procedure for the risk based structural integrity assessment which is established by DSME and the actual application to the world’s first LNG FPSO project for ship collision, dropped objects and explosion.
Hydrodynamic Evaluation of a Generic Sail Used in an Innovative Prawn-Trawl Otter Board
Authors: Balash Cheslav , Sterling David , Broadhurst Matt , Dubois Arno , Behrel Morgan
Published: October 2015

In prawn-trawling operations, otter boards provide the horizontal force required to maintain net openings, and are typically low aspect ratio (∼0.5) flat plates operating on the seabed at high angles of attack (AOA; 35–40°). Such characteristics cause otter boards to account for up to 30% of the total trawling resistance, including that from the vessel. A recent innovation is the batwing otter board, which is designed to spread trawls with substantially less towing resistance and benthic impacts. A key design feature is the use of a sail, instead of a flat plate, as the hydrodynamic foil. The superior drag and benthic performance of the batwing is achieved by (i) successful operation at an AOA of ∼20° and (ii) having the heavy sea floor contact shoe in line with the direction of tow. This study investigated the hydrodynamic characteristics of a generic sail by varying its twist and camber, to identify optimal settings for maximum spreading efficiency and stability. Loads in six degrees of freedom were measured at AOAs between 0 and 40° in a flume tank at a constant flow velocity, and with five combinations of twist and camber. The results showed that for the studied sail, the design AOA (20°) provides a suitable compromise between greater efficiency (occurring at lower AOAs) and greater effectiveness (occurring at higher AOAs). At optimum settings (20°, medium camber and twist), a lift-to-drag ratio >3 was achieved, which is ∼3 times more than that of contemporary prawn-trawling otter boards. Such a result implies relative drag reductions of 10–20% for trawling systems, depending on the rig configuration.
Optimization of OSV Fleet for an Offshore Oil and Gas Field in the Russian Arctic
Authors: Milaković Aleksandar-Saša , Ulstein Mads , Bambulyak Alexei , Ehlers Sören
Published: October 2015

Due to a constantly increasing global energy demand on one side, and depletion of available hydrocarbon resources on another, a continuous search for new reserves of hydrocarbons is required (BP Energy Outlook 2035 [1]). Having in mind that estimated 22% of the world’s undiscovered petroleum is located in the Arctic, 84% of which is projected to be offshore (US Geology Survey [2]), the Arctic becomes a logical region of activities expansion for the oil and gas industry. Opposing large expected quantities of hydrocarbons that are to be found in the Arctic, there are also numerous challenges that need to be overcome in order to make production economically feasible. One of the segments of offshore production process that is expected to be influenced by Arctic conditions is upstream supply chain, or chain of delivery of products and services that are necessary for unhindered operation of an offshore field. Within upstream supply chain, it is expected that the configuration of Offshore Supply Vessel (OSV) fleet will be significantly affected by specific Arctic conditions, mainly by large distances to supply base as well as by environmental conditions. Therefore, this paper seeks to identify an optimal composition of OSV fleet taking into consideration specific Arctic conditions. A simulation model describes an upstream supply chain taking into consideration stochastic nature of environmental conditions in the Arctic. An optimization model is built on top of the simulation model in order to assess optimal configuration of the fleet with respect to operational costs. Simulation and optimization are run for a case of an offshore oil and gas field development in the Russian Arctic.
A Simulation-Based Decision Support Tool for Arctic Transit Transport
Authors: Schartmüller Bernhard , Milaković Aleksandar-Saša , Bergström Martin , Ehlers Sören
Published: October 2015

The Russian Federation attempts to foster the Northern Sea Route (NSR) as a transport alternative to the current Suez Canal Route (SCR). Therefore, this paper seeks to identify under which conditions the use of the NSR is economically feasible. To evaluate this in a realistic way it is essential to take the significant uncertainty of input variables like ice data predictions into account. For that reason a simulation-based decision-support (SBDS)-tool based on a discrete-event simulation model is developed.

The SBDS-tool requires as input vessel dimensions, available power and information about the route(s) including waypoints and ice data. It calculates then the general performance of the vessel in both open water and ice. Next it generates day-specific ice conditions according to a probability distribution between lower and upper limit obtained from satellite measurements. Based on this and the previously calculated vessels’ performance the SBDS-tool calculates day-specific transit times and fuel consumptions for examined time period. This is then used as input for a discrete-event simulation to assess the number of roundtrips, transported cargo and fuel consumption for joint use of different routes, dependent on the predefined operational days along the routes. The obtained results are then used to calculate the cost per transported cargo unit between two ports and to assess the sensitivity in order to determine if an economically advantageous and robust transport system can be achieved. In addition, possible economy of scale effects using larger vessels can be evaluated.

In order to show the applicability of the developed model a comparative case study for three container vessels operating between Rotterdam (NL) and Yokohama (JP) is carried out.
Dynamic Response Behaviour of Stiffened Triceratops Under Regular Waves: Experimental Investigations
Authors: Chandrasekaran Srinivasan , Mayank Senger , Jain Arvind
Published: October 2015

Among the various compliant type offshore structures, offshore triceratops is one of the recent innovative designs that is developed for exploration and production of oil and gas fields in deep and ultra-deep waters. Triceratops consists of a deck, which is supported by the Buoyant Leg Structures (BLS). Buoyant legs are connected to the deck by ball joints and held down in position by taut-moored tethering system. As buoyant legs are independently flexible, they need to be stiffened with the intermediate stiffeners to integrate them for counteracting the encountered lateral loads. Presence of ball joints restrains the transfer of rotational response from the BLS to the deck and vice-versa; only translational motion is transferred to the deck. Stiffened buoyant legs impose sufficient rigidity in the vertical plane, making it similar to that of a taut-moored Tension Leg Platform (TLP). The objective of present study is to show the reduction in transverse motions of offshore stiffened triceratops in operational sea state by increase in tethers stiffness (pretension). Hence, the study is focused on experimental investigations of a scaled model of a triceratops with stiffened buoyant legs under regular waves. Results show that the free-oscillation characteristics conform to a stable behavior of the platform under calm sea state. Deck exhibits lesser roll response under the chosen sea states, highlighting the advantage of ball joint between the deck and BLS units. However, the surge response is relatively high, which is controlled by stiffening the buoyant legs. This type of behavior is advantageous to upkeep more facilities on the deck and ensure comfortable operation during moderate sea states.