bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Qualification of Heavy Wall Line Pipe and Girth Weld for High Pressure Applications
Authors: Darcis Philippe P. , Mota Noe , Garcia Enrique , Marines-Garcia Israel , Quintanilla Hector M. , Kan Wan C. , Visco Tyler , Ghosh Rupak
Published: November 2013

As the offshore oil & gas industry moves into deeper waters, more and more offshore projects, specifically the subsea, riser and flowline designs, rely on heavy wall line pipe materials. These pipe materials must be capable of operating in stringent working conditions such as high pressures, high temperatures, large deformations, fatigue loading, sour environments, etc.

Within this context, ExxonMobil Development Company and Tenaris have jointly conducted a detailed technical assessment of the mechanical and fatigue performance of the newly developed heavy wall X65 line pipe (LP) developed by Tenaris.

The main goal of such project is to evaluate and demonstrate via full-scale testing the fatigue performance of this new generation of heavy wall line pipe materials and the associated girth weld also recently developed by Tenaris. Although conclusive fatigue performance results at ID are not included in the present paper, the comprehensive test/qualification plan also includes a fatigue performance comparison at ID and OD.

The present work clearly demonstrates weldability of this Heavy Wall X65 (273 mm OD × 46 mm WT) line pipe. A narrow-groove bevel welding procedure utilizing the STT® process for the root pass and single torch GMAW process for hot-pass, fill, and cap has been successfully developed. Four full scale fatigue tests were also successfully conducted using a resonant fatigue test machine. The presented fatigue results help demonstrate a realistic level of fatigue performance achievable with this thick wall LP/girth weld technology which will help facilitate assessment of riser/flowline design feasibility in ultra-deep water applications and/or high pressures fields.
On the Generation of Spatially Periodic Breather in a Wave Tank
Authors: Waseda Takuji , Houtani Hidetaka , Tanizawa Katsuji
Published: November 2013

Spatially periodic modulational wave train was generated at the National Maritime Research Institute, Actual Sea Model Basin. The 76 m by 36 m basin of depth 4.5 m is surrounded by 382 paddle type wave generators with wave absorbing capacity. Taking advantage of this unique wave basin, we have compared two generation methods, first controlling the wave makers at both upwind and downwind sides and second controlling just the upwind side. The wave generator signal was computed a-priori by High-Order Spectral Method (HOSM hereafter). The HOSM provided temporally non-periodic time series of the unstable wave train as the wave-maker control signal. A number of wave wires located in the tank were used to compare the wave forms between two different generation methods. Our test result indicates that it is not necessary to provide signal at both ends, because the spatial evolution of the wave train remains periodic in space if the wave maker signal is appropriately controlled. The physical experiment and HOSM simulation seem to agree better with high order of nonlinearity.
Prediction and Screening of Truss Spar VIM With CFD
Authors: Constantinides Yiannis , Oakley Owen H.
Published: November 2013

The understanding and prediction of spar vortex induced motion (VIM) is an important area for the offshore industry as it affects the integrity of riser and mooring systems related to strength and fatigue loading. With exploration moving to deeper water, there is a desire not only to asses spar VIM early in the design cycle, but also to optimize the design. The methodology to model spar VIM with computational fluid dynamics (CFD) was pioneered by the authors and is utilized in this study to demonstrate how CFD can aid the design process, as well as conducting additional benchmark cases to improve confidence in CFD. Comparisons against experiments of a large scale hull at high Reynolds number are performed to validate CFD and establish an efficient methodology that is subsequently used for screening. This new method utilizes a boundary condition that allows simulation under arbitrary headings. As a result the overall computational cost and setup overhead is reduce by an order of magnitude enabling screening for VIM well within design cycle requirements. Simulations of spar geometries with increasing detail are performed starting from a hull with strakes, adding pipes and mooring components and finally incorporating the truss. The effects of each component are discussed with their impact on VIM response. Overall the computations show that high quality predictions are possible and it is practical to incorporate CFD into the design process. Screening and the generation of response curves can be done during initial design and more targeted assessments during detail design.
CFD Calculations for Free-Surface-Piercing Low Aspect Ratio Circular Cylinder With Solution Verification and Comparison With Experiments
Authors: Rosetti Guilherme F. , Vaz Guilherme , Hoekstra Martin , Gonçalves Rodolfo T. , Fujarra André L. C.
Published: November 2013

The flow around free-surface piercing, low aspect-ratio circular cylinder is investigated by means of unsteady Reynolds averaged Navier-Stokes (URANS) calculations together with verification procedures and comparison with small-scale experimental and Particle Image Velocimetry results. A two-phase interface capturing model is used to handle the free-surface flow, together with k-ω SST turbulence model. We investigate physical and modeling aspects of this problem in order to gain more knowledge about the interaction of free-surface and free-end effects so that this mechanism is better understood and taken into account when modeling the problem in engineering-applied situations, such as the vortex induced motion of spars, tension-leg platforms and semi-submersibles.

The case herein presented is a captive, low aspect-ratio cylinder (L/D = 2.0) with flow velocity corresponding to Reynolds and Froude numbers (both based on diameter) of Re = 4.3 × 104 and FnD = 0.31, respectively. We will show that appreciable free-surface effects are perceived on the flow, but with dominance of free-end effects, at least in terms of forces. Furthermore, we investigate different boundary conditions that would represent this free-surface problem to show that the separation of viscous and free-surface effects is not valid in this instance. Therefore, the interaction between viscous and free-surface effects is also tangentially investigated. In order to support our conclusions, we will show forces with uncertainty estimation and field variables obtained with different modeling strategies, unveiling physical and numerical aspects of this problem.
Manage Tensioner Stroke for Dry Tree Semisubmersibles
Authors: Bian Sean , Xiang Sherry
Published: November 2013

The tensioner stroke range for a Dry Tree Semisubmersible (DTS) in a severe environment application is long and must be well defined for the concept to work. The range needs to be properly calculated and optimized. In this paper, the authors elaborate the design procedures for determining the tensioner stroke on a DTS, and demonstrate the design optimization of a conventional semisubmersible floater in the Center of Gulf of Mexico (GOM) 8000 feet water depth. The primary focus is on the design of the platform configuration to reduce the tensioner stroke by investigating each stroke component, while keeping the robustness of the design. A 4-Column ring pontoon conventional deep draft semisubmersible is re-configured considering the balance between the floater hull size and maximum tensioner stroke range. It is identified that the deck vertical layout, quayside /in-place stability and hull dynamic motions are the key parameters for DTS configuration design iterations. The hull principal particulars are first determined using a frequency domain screening approach to minimize dynamic motions for various loading combinations. Top Tensioned Riser (TTR) and export risers with Steel Catenary Configuration (SCRs) are modeled in the integrated screening process, and mooring line setups are optimized for the global motion analyses. For the governing design cases, riser pipe and tensioner details are modeled for various target tensioner characteristics in a dedicated riser design tool in time-domain. Sensitivity analyses including the tensioner stiffness curve, platform pitch and keel guide effects on the global performance are studied and presented. It can be concluded from the design example that when properly configured, a reasonable tensioner stroke is achievable for typical DTS applications in GOM environment.
Study on a Method for Estimating Fuel Consumption in a Seaway
Authors: Iseki Toshio , Nielsen Ulrik D.
Published: November 2013

On-board measurement of fuel consumption of a ship has been carried out in a relatively severe sea condition. In the full scale experiment, the ship traveled on several courses to investigate the change of fuel consumption relative to the encounter wave angle. The result shows that the wave direction has a great influence on the main engine horse power and fuel consumption, and also shows a possibility of fuel efficiency prediction. In order to develop an eco-friendly navigation support system, results of Bayesian wave estimation are applied to fuel efficiency prediction. The Bayesian method does not require wave measurements but needs only ship motion data as input and the method is suitable for on-site wave estimation.
A FE Model to Predict the Stress Concentration Factors in the Tensile Armor Wires of Flexible Pipes Inside End Fittings
Authors: de Sousa José Renato M. , Campello George C. , Bertoni Fabiano , Ellwanger Gilberto B.
Published: November 2013

In this work, a bidimensional finite element (FE) approach is proposed to estimate the stresses induced in the tensile armor wires inside end fittings (EF) of flexible pipes. This approach accounts for the residual stresses caused by the mounting procedure and the deformed configuration of the wire. The resin and its interaction with the wires are also addressed. A parametric study was performed aiming at investigating the influence of three parameters on the stress state along the wire, i. e., the contact conditions between the resin and the wire inside the EF, the stress levels induced during the factory acceptance test (FAT) or the offshore leak test (OLT) and the resin elastic properties. The study pointed that high stress concentration is induced in the transition between the flexible pipe’s body and the EF and the stress distribution along the wire may be significantly affected by these parameters. Moreover, the apparent axial stiffness of the wire is also modified by its anchoring conditions, which may lead to non-uniform stress distributions among the wires of the tensile armor layers.
Ultimate Strength Analysis of a River-Sea Ship Under Combined Action of Torsion and Bending
Authors: Wu Haochen , Wu Weiguo , Gan Jin , Sun Huanxiang
Published: November 2013

For a River-Sea ship hull with a relatively low torsional rigidity due to the large deck openings, the analysis of the effect of torsion induced warping stress[1] on the structural strength as well as the ultimate hull strength interaction relationships between the torsion and vertical bending is of significant importance. The present study deals with the ultimate strength of a River-Sea ship under combined action of bending and torsion by the means of numerical and experimental research.

Based on the results, a proposed equation defining the ultimate strength interaction relationship for this River-Sea ship is given.
The Wave Energy Converter Based on Helmholtz Mode, Inspired by Nature
Authors: Saadat Yalda , Fernandez Nelson , Ghorbani Reza
Published: November 2013

The present study examines a new concept of wave energy conversion inspired by geological tidal-bowls (i.e. toilet bowls) and blowholes in nature, capitalizing on the Helmholtz resonance phenomenon. Tidal-bowls are of interest because they concentrate ocean wave energy in a basin while in resonance with incoming waves. Tidal-bowls are formed as sea channels grow landwards into a water basin, which can result in a high pulsating current of water inside the channel in and out of the basin. The resonance of water inside the basin produced by asymmetry of its narrow water channel allows for the capture of Helmholtz mode, which is the most energetic mode of the ocean waves. Thus, the objective of this project is to experimentally investigate the geometry of tidal-bowls in a wave tank including the size of the basin and the channel in order to obtain Helmholtz resonance. The model in the wave tank is scaled using the Froude number. Preliminary experiments were carried out measuring the water surface, demonstrating a strong correlation of the model to the theoretical Helmholtz mode’s model, σH2 = gHB/A0L. Where a basin with maximum water depth, H, and horizontal area, A0, is connected to the sea by a narrow strait of width, B, and the strait length, L. The proposed geometry can be used to harvest wave energy through either pulsating current of the channel using a water-turbine or using an air-turbine on the top of the basin. This study aims to catalyze future works in effective applications of this model towards wave energy conversion device development. Thus, we investigated the effects of the device’s length, and the device’s winglet’s angle at the inlet of the channel on wave amplification inside the basin. In addition, we experimentally demonstrated that the flow dampening inside the channel has no effect on basin’s resonance frequency.
Gas Hydrate Deposition in Flowlines: A Challenging Problem in Flow Assurance
Authors: Grasso Giovanny A. , Vijayamohan Prithvi , Sloan E. Dendy , Koh Carolyn A. , Sum Amadeu K.
Published: November 2013

Gas hydrate deposition on the pipeline wall is one of the key processes leading to hydrate plug formation; however, this phenomenon is still poorly understood and missing in a full comprehensive model for simulating/predicting hydrate cold slurry flow (1). To gain a better understanding on hydrate deposition, we have performed several experiments of hydrate deposition on a solid surface for liquid systems (gas free). This preliminary investigation helps to better understand the challenges for further investigations of hydrate deposition in multiphase fluid flow. From this research, the importance of maintaining a constant concentration of the hydrate former and simulating a single pass system were identified; the challenges to control the temperature of the deposition surface, as well as the gradient of the temperature between the fluid and metal surface to promote deposition have also been identified.
Thruster-Interaction Effects on a DP Semi-Submersible and a Drill Ship: Measurement and Analysis of the Thruster Wake Flow
Authors: Cozijn J. L. , Hallmann R.
Published: November 2013

Thruster-interaction model tests were carried out in MARIN’s Deepwater Towing Tank. Detailed PIV measurements were performed of the wake flow behind the azimuthing thrusters on two different DP vessels, a Semi-submersible and a Drill Ship. The flow velocities were measured in a large number of cross sections at different distances from the thrusters. The PIV measurements provide a detailed image of the flow velocities in the thruster wake, showing the axial velocities, as well as the transverse and vertical velocity components.

First, measurements were carried out on a DP Semi-submersible (scale 1:40), which was equipped with 8 azimuthing thrusters. The results of the PIV measurements show the wake flow, interacting with nearby thrusters and the opposite pontoon of the semi-submersible. An example is shown in Figure 1 below. Deflection of the thruster wake, caused by the Coanda effect, was observed. The results for thrusters with a 7 deg downward tilt were compared with the results for thrusters with a horizontal propeller axis. Furthermore, the effect of ambient current was investigated.

Second, measurements were carried out on a DP Drill Ship (scale 1:40), which had 6 azimuthing thrusters. The results of these PIV measurements also gave insight in the wake flow behind the azimuthing thrusters and the interactions between neighbouring thrusters. An example is shown in Figure 2 below. In this case, special attention was paid to the development of the thruster wake along the vessel length, up to a distance of more than 40D downstream.

The results of the present research are used to further improve the understanding of the physics of thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations that are foreseen in the near future.
Effects of the Mooring Line Configuration on the Dynamics of a Point Absorber
Authors: Nava Vincenzo , Rajic Marin , Guedes Soares Carlos
Published: November 2013

The aim of this paper is to study the dynamics of a floating body with characteristics comparable to a point absorber wave energy converter with different mooring systems, in geometrical configuration or in the materials. To this purpose, the dynamics of a moored buoy is investigated. The point absorber is modeled as a spherical buoy in plane two-dimensional motion, and it is studied under the action of irregular unidirectional wind-generated waves, moored to the seabed by means of one, two or three mooring lines. Two different sets of moorings are considered, and typical wires and chains used in offshore technology are considered, leading to a total of 6 case studies.

A quasi-static approach is used for modeling the restoring forces needed to keep buoy into station, using an innovative iterative procedure able to predict for each time instant and for each cable the lay down length of the cable, being each mooring line allowed to be taut or slack. Approaches in the time and frequency domains are used to obtain the system responses in intermediate waters, where these facilities are usually installed. Results for all case studies are compared both in terms of statistics of response and tensions on the top of the cable.
Swell Genesis, Modelling and Measurements in West Africa
Authors: Prevosto Marc , Ewans Kevin , Forristall George Z. , Olagnon Michel
Published: November 2013

Swell events show a large variety of configurations when they arrive at sites off West Africa after generation and propagation of waves across the Atlantic Ocean. Within the West Africa Swell Project (WASP JIP), these different configurations have been described and discussed and the ability of numerical models to reproduce faithfully their properties has been assessed from comparisons with in-situ measurements.

During the austral winter months, swells approach West African coast from the south to south-westerly direction. These swells are generated by storms in the South Atlantic mainly between 40°S and 60°S. But during austral summer, north-westerly swells are also observed coming from North Atlantic. Typical situations of superposition of these different swells are illustrated in the paper.

In spite of a poor overlapping between numerical and in-situ measurements databases at the time of the WASP project, and of reduced durations of measurement campaigns, comparisons between in situ measurements and hindcast models permitted identification of the limitations of the different numerical models available. Three sites have been used for this study, one in the Gulf of Guinea with directional Waverider and Wavescan buoys, a second one off Namibia with a directional Waverider and one last instrumented with two wavestaffs off Cabinda (Angola).

In addition, the existence of infra-gravity waves in shallow water measurements has been investigated.
Air Turbine and Primary Converter Matching in Spar-Buoy Oscillating Water Column Wave Energy Device
Authors: Henriques J. C. C. , Falcão A. F. O. , Gomes R. P. F. , Gato L. M. C.
Published: November 2013

The oscillating water column (OWC) equipped with an air turbine is possibly the most reliable type of wave energy converter. The OWC spar-buoy is a simple concept for a floating OWC. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends and fixed to a floater that moves essentially in heave. The air flow displaced by the motion of the OWC inner free-surface, relative to the buoy, drives an air turbine. The choice of air turbine type and size, the regulation of the turbine rotational speed and the rated power of the electrical equipment strongly affect the power performance of the device and also the equipment’s capital cost. Here, numerical procedures and results are presented for the power output from turbines of different sizes equipping a given OWC spar-buoy in a given offshore wave climate, the rotational speed being optimized for each of the sea states that, together with their frequency of occurrence, characterize the wave climate. The new biradial self-rectifying air turbine was chosen as appropriate to the relatively large amplitude of the pressure oscillations in the OWC air chamber. Since the turbine is strongly non-linear and a fully-nonlinear model of air compressibility was adopted, a time domain analysis was required. The boundary-element numerical code WAMIT was used to obtain the hydrodynamic coefficients of the buoy and OWC, whereas the non-dimensional performance curves of the turbine were obtained from model testing.
Non-Linear Model Predictive Control Applied to a Generic Ocean-Wave Energy Extractor
Authors: Tom Nathan , Yeung Ronald W.
Published: November 2013

This paper evaluates the theoretical application of nonlinear model predictive control (NMPC) to a model-scale point absorber for wave energy conversion. The NMPC strategy will be evaluated against a passive system, which utilizes no controller, using a performance metric based on the absorbed energy. The NMPC strategy was set up as a non-linear optimization problem utilizing IPOPT package to obtain a time varying optimal generator damping from the power-take-off (PTO) unit. This formulation is different from previous investigations in model predictive control, as the current methodology only allows the power-take-off unit to behave as a generator, thereby unable to return energy to the waves. Each strategy was simulated in the time domain for regular and irregular waves, the latter taken from a modified Pierson-Moskowitz spectrum. In regular waves, the performance advantages over a passive system appear at frequencies near resonance while at the lower and higher frequencies they become nearly equivalent. For irregular waves, the NMPC strategy lead to greater quantities of energy absorption than the passive system, though strongly dependent on the prediction horizon. It was found that the ideal NMPC strategy required a generator that could be turned on and off instantaneously, leading to sequences where the generator can be inactive for up to 50% of the wave period.
Residual Stresses Measurement in Various Joint Weldments
Authors: Ficquet Xavier , Hossain Sayeed , Kingston Ed J.
Published: November 2013

Published experimental data from residual stress measurements are generally limited or difficult to find. Experimental data in the offshore industry are even more scarce and difficult to access to. The oil and gas industry can benefit from research done in other industries. For example, the nuclear industry has published a multitude of residual stress measurements that could be beneficial to the offshore industry, gaining more understanding and confidence in the structural integrity of critical components.

For the past year VEQTER Ltd has been developing a web access database for storing and comparing residual stress measurement and modelling results. This paper presents a comparison of through thickness residual stress measurement results that are published. The first case will show numerous measurements using different techniques on girth welded joints. Then, measurements on the temper bead welding processes which have been developed to simulate the tempering effect of post-weld heat treatment will be presented and compared with cladding. Finally, comparison of residual stress measurements on T-section plate fillet weld will be made.
Single-Step Measurement of Elastic Modulus and Adhesion Mapping of Surface of Carbonate Reservoir Rocks
Authors: Kalfagiannis Nikolaos , Gupta Anuj
Published: November 2013

The surface of a carbonate rock, representing the surface of a natural oil reservoir, has been characterized with a new atomic force microscopy mode, namely the PeakForceTM tapping. Employing this technique it was possible to map the mechanical properties and adhesion forces simultaneously with the topography of the sample. While mechanical properties find great utility in drilling operations and fluid dynamics, adhesion forces give an indication of the sample’s surface energy which in turn can provide an understanding of the behavior of the surface and the adsorption mechanisms of water or oil components.
Semi-Coupled Scheme for the Analysis of Floating Production Systems
Authors: Corrêa Fabrício Nogueira , Jacob Breno Pinheiro
Published: November 2013

Traditionally, the design practice of floating production systems (FPS) employed uncoupled numerical tools where firstly the hydrodynamic analysis of the hull is performed with the lines represented by scalar models (leading to the hull motions); subsequently, these motions are prescribed at Finite Element (FE) models of the lines. Nowadays, it is widely acknowledged that coupled analysis tools should be employed for deep-water applications, considering that the overall behavior is dictated by the interaction between the hydrodynamic behavior of the hull and the structural behavior of the lines.

In this context, considering that in some situations the use of coupled formulations can lead to excessive computing times, this work presents a formulation for the analysis of FPS, referred here as the semi-coupled (S-C) strategy. Its goal is to attain faster simulations than a coupled formulation, with better accuracy than usually provided by the classical uncoupled scheme. In this strategy, for each load case a coupled static simulation is performed. From this simulation a global 6-DOF stiffness matrix that represents the array of lines is automatically calculated and added to the global matrix for the subsequent dynamic analysis to solve the equations of motion of the hull. Therefore, this dynamic analysis will adequately consider the nonlinear stiffness contribution of the lines, as well as the effect of the current profile acting on them, all evaluated at the static mean position for each load case. Case studies are presented to compare the computational costs and accuracy of this S-C strategy with coupled formulations.
Turbine Floater-Tether Coupled Dynamic Analysis Including Second-Order Sum-Frequency Wave Loads for a TLP-Type FOWT (Floating Offshore Wind Turbine)
Authors: Bae Y. H. , Kim M. H.
Published: November 2013

In the present study, a numerical simulation tool has been applied for the time-domain turbine-floater-tether fully-coupled dynamic analysis of a FOWT. The fully coupled dynamic analysis includes aero-blade-tower dynamics and control, mooring dynamics, and platform motions. In particular, the effects of second-order sum-frequency wave excitations on the coupled dynamic analysis are investigated. The fully coupled simulations with full blade operation are compared with those with parked condition (without blade rotation). For this purpose, a mono-column TLP with 5MW turbine in 200m water depth is selected as an example. The time histories and spectra of the FOWT motions and accelerations as well as tether top-tensions are presented for the given random collinear wind-wave condition. The shift of original floater natural frequencies due to the inclusion of tower flexural modes is demonstrated. The increase of aero damping in the case of rotating blades is also explained. The second-order sum-frequency wave loading introduces high-frequency excitations near pitch-roll resonance frequencies or lowest tower flexural modes. Its effects are more clearly seen in the blade-parked condition than the blade-fully-operational condition. The increased high-frequency responses may significantly increase tower-top accelerations and accumulated fatigue.
VIV Excitation Competition Between Bare and Buoyant Segments of Flexible Cylinders
Authors: Rao Zhibiao , Vandiver J. Kim , Jhingran Vikas
Published: November 2013

This paper addresses a practical problem: “Under which coverage of buoyancy modules, would the Vortex Induced Vibration (VIV) excitation on buoyant segments dominate the response?” This paper explores the excitation competition between bare and buoyant segments of a 38 meter long model riser. The source of data is a recent model test, conducted by SHELL Exploration and Production at the MARINTEK Ocean Basin in Trondheim Norway. A pipe model with five buoyancy configurations was tested.

The results of these tests show that (1) the excitation on the bare and buoyant regions could be identified by frequency, because the bare and buoyant regions are associated with two different frequencies due to the different diameters; (2) a new phenomenon was observed; A third frequency in the spectrum is found not to be a multiple of the frequency associated with either bare or buoyancy regions, but the sum of the frequency associated with bare region and twice of the frequency associated with buoyancy region; (3) the contribution of the response at this third frequency to the total amplitude is small; (4) the power dissipated by damping at each excitation frequency is the metric used to determine the winner of excitation competition. For most buoyancy configurations, the excitation on buoyancy regions dominates the VIV response; (5) a formula is proposed to predict the winner of the excitation competition between bare and buoyant segments for a given buoyancy coverage.
The Drift on Top of Waves
Authors: Bratland Anne Katrine
Published: November 2013

Wave particles move in circles, and for steep waves they also move with a drift in the wave direction. This drift can be found by second order Stokes theory. In this document it is questioned if Stokes’ theory gives reliable drift on the free surface, or if an extra term should be introduced in the equations. The CFD program COMFLOW is used to show that classic Stokes theory may be insufficient for calculating drift on the free surface.
An Offshore Platform Selection Approach for the Black Sea Region
Authors: Mentes Ayhan , Helvacioglu Ismail Hakki
Published: November 2013

This paper identifies and evaluates various offshore platforms which could be feasible for the deep sea operations in the Turkish Black Sea. The aim of this study is to propose a fuzzy based decision making model for selecting an optimum production system by using effective and major criteria at the same time. The model incorporates fuzzy linguistic variables in place of numbers. The conventional methods for production system selection are inadequate for dealing with the imprecise or vague nature of linguistic assessment. To overcome this difficulty, a fuzzy based multi-criteria decision-making method is proposed. Proposed approach is based on the combination of fuzzy analytic hierarchy process (FAHP) and the fuzzy TOPSIS methods. The application could be interpreted as demonstrating the effectiveness and feasibility of the proposed model.
A Classification of Shallow Water Resonant Sloshing in a Rectangular Tank
Authors: Bouscasse Benjamin , Colagrossi Andrea , Antuono Matteo , Lugni Claudio
Published: November 2013

A numerical and experimental analysis of sloshing phenomena (i.e. violent fluid motions inside a tank) has been conducted in shallow water regimes. A large range of experimental data from moderate to large amplitude sway motions has been considered for different filling heights. The numerical simulations, performed through a δ-SPH model, aim to cover the configurations where no experiments were available and provide an exhaustive description of the shallow-water sloshing motion.

A convergence analysis for non breaking and breaking cases has also been presented.
Bend Over Sheave Durability of Fibre Ropes for Deep Sea Handling Operations
Authors: Davies P. , Lacotte N. , Kibsgaard G. , Craig R. , Cannell D. , François S. , Lodeho O. , Konate K. , Mills S. , François M. , Defoy A.-L. , Durville D. , Vu D. , Gilmore J. , Sherman D.
Published: November 2013

This paper describes work performed within a Joint Industry Project aiming to evaluate the lifetime of deep sea handling ropes. Various HMPE (High Modulus Polyethylene) fiber ropes, with and without coatings, have been studied under both tensile and cyclic bend over sheave (CBOS) loading. A large test program has enabled both tension-cycle to failure relationships and empirical expressions for residual strength after cycling to be determined. A special device was then developed to apply a known couple to the sheave, allowing both dynamic friction measurements to be made and the influence of applied couple on cycles to failure to be measured. These experimental data were used in the development of a numerical model which can be used to study the influence of rope and sheave parameters.
Review of Hydrodynamic and Nautical Studies for Offshore LNG Operations
Authors: de Wilde Jaap , Dekker Johan
Published: November 2013

In this paper we review hydrodynamic and nautical studies for offshore LNG operations. Based on full mission bridge simulations, model tests campaigns, time domain simulations, fast time maneuvering simulations and downtime assessments, we address the major findings in terms of weather limitations, tugboat requirements and other critical aspects for the berthing and offloading operation.
Boundaries Influence on the Flow Field Around an Oscillating Sphere
Authors: Mirauda Domenica , Plantamura Antonio Volpe , Malavasi Stefano
Published: November 2013

This work analyzes the effects of the interaction between an oscillating sphere and free surface flows through the reconstruction of the flow field around the body and the analysis of the displacements.

The experiments were performed in an open water channel, where the sphere had three different boundary conditions in respect to the flow, defined as h* (the ratio between the distance of the sphere upper surface from the free surface and the sphere diameter). A quasi-symmetric condition at h* = 2, with the sphere equally distant from the free surface and the channel bottom, and two conditions of asymmetric bounded flow, one with the sphere located at a distance of 0.003m from the bottom at h* = 3.97 and the other with the sphere close to the free surface at h* = 0, were considered. The sphere was free to move in two directions, streamwise (x) and transverse to the flow (y), and was characterized by values of mass ratio, m* = 1.34 (ratio between the system mass and the displaced fluid mass), and damping ratio, ζ = 0.004. The comparison between the results of the analyzed boundary conditions has shown the strong influence of the free surface on the evolution of the vortex structures downstream the obstacle.
Application of Markov Chain to Determine the Electric Energy Supply System Reliability for the Cargo Control System of LNG Carriers
Authors: Hidalgo Erick Miguel Portugal , Silva Dennis Wilfredo Roldán , de Souza Gilberto Francisco Martha
Published: November 2013

The natural gas industry, as well as other industrial activities, is not free from accidents, which can cause serious consequences to the integrity of people and properties. For this reason, it is necessary to develop studies to determine what are the possible causes of LNG leakage during the loading or unloading operation. This paper aims to determine the reliability of the Cargo control system electric power supply system applying Markov Chain technique. This reliability modeling tool is used because the system consists of several components in passive parallel. Based on the reliability analysis maintenance recommendations are proposed aiming at reducing system failure probability.

The method used in this paper is divided in three steps. The first step consists in carrying out a study to identify what are the components that are part of electric power supply system. The second step involves the reliability analysis of the electric energy supply system. Finally some maintenance recommendations are presented aiming at reducing system failure rate. This analysis is used for the analysis of a LNG carrier operating in a Brazilian harbor indicating the most probability failure modes of this system and the most suitable maintenance actions to avoid them.
Experimental Validation of a New Shallow Water CALM Buoy Design
Authors: Williams A. Neil , McDougal Williams G.
Published: November 2013

This paper presents an overview of the model testing of a new turret-type CALM buoy concept developed by WISON for shallow water (20m–80m) applications. In the WISON design the outer body of the buoy is hexagonal, a geometry that allows for ease of fabrication while retaining hydrodynamic efficiency. The overall objective of the model tests was to demonstrate the performance of this new design for a typical shallow water environment under both operating and survival conditions. Additionally, the model tests were intended to provide data to calibrate the numerical models for buoy motions and line tensions used in the design, and to give guidance regarding the suitability of the buoy freeboard and deckhouse arrangement.
Simulation-Length Requirements in the Loads Analysis of Offshore Floating Wind Turbines
Authors: Haid Lorenz , Stewart Gordon , Jonkman Jason , Robertson Amy , Lackner Matthew , Matha Denis
Published: November 2013

The design standard typically used for offshore wind system development, the International Electrotechnical Commission (IEC) 61400-3 fixed-bottom offshore design standard, explicitly states that “the design requirements specified in this standard are not necessarily sufficient to ensure the engineering integrity of floating offshore wind turbines” [1]. One major concern is the prescribed simulation length time of 10 minutes for a loads-analysis procedure, which is also typically used for land-based turbines. Because floating platforms have lower natural frequencies, which lead to fewer load cycles over a given period of time, and ocean waves have lower characteristic frequencies than wind turbulence, the 10-min simulation length recommended by the current standards for land-based and offshore turbines may be too short for combined wind and wave loading of floating offshore wind turbines (FOWTs). Therefore, the goal of this paper is to examine the appropriate length of a FOWT simulation — a fundamental question that needs to be answered to develop design requirements.

To examine this issue, we performed a loads analysis of an example FOWT with varying simulation lengths, using FAST, the National Renewable Energy Laboratory’s (NREL’s) nonlinear aero-hydro-servo-elastic simulation tool. The offshore wind system used was the OC3-Hywind spar buoy, which was developed for use in the International Energy Agency (IEA) Offshore Code Comparison Collaborative (OC3) project, and supports NREL’s offshore 5-MW baseline turbine. Realistic metocean data from the National Oceanic and Atmospheric Administration (NOAA) and repeated periodic wind files were used to excite the structure. The results of the analysis clearly show that loads do not increase for longer simulations. In regard to fatigue, a sensitivity analysis shows that the procedure used for counting half cycles is more important than the simulation length itself. Based on these results, neither the simulation length nor the periodic wind files affect response statistics and loads for FOWTs (at least for the spar studied here); a result in contrast to the offshore oil and gas (O&G) industry, where running simulations of at least 3 hours in length is common practice.
Module and Vessel Interaction Analysis for Module Ocean Transportation
Authors: Liu Zhonghui , Hai Xin , Ji Andy , Liang Chun , Cheng Yinguo
Published: November 2013

Bechtel has been contracted for and is in the process of executing multiple onshore Liquefied Natural Gas (LNG) Engineering, Procurement, and Construction (EPC) projects utilizing the modular construction strategy. Modules and associated pieces of equipment have to be shipped to the job site from various manufacturing and fabrication facilities across open oceans.

Naval Architects play a key role to assure safe and effective module ocean transportation. Primary naval architectural work consists of a routing study, module design criteria definition, ballasting and stability analysis, grillage and seafastening design, transportation vessel selection and support for module load out and load in.

The main challenge is to make the modules, which are originally designed for onshore assembly, sound for ocean transportation. Therefore, module design criteria related to ocean transportation become crucial. Among these criteria, the wave induced inertia loads and vessel deflection have great impact on designed module structure integrity. In order to define inertia loads and deflection appropriately, the interface between vessel and module becomes a main concern. It raises the question of whether the transport vessel and module should be fully integrated. It also increases complexity of the hydrodynamic interaction, which has been demonstrated by widely divergent methods used to address the interface issue in offshore industry. More importantly, whether or not the interface is thoroughly taken into account is critical to successful module design and fully meeting the Marine Warranty requirements. In order to achieve safe and economic module design, a direct method of integrating vessel and module is considered preferable in analysis and design when the inertia effects and structure hydrodynamic response are significant.

This paper will provide an overview of integrated vessel and module interaction analysis for the module ocean transportation and focus on the method and procedure of how Bechtel performs analyses: i) spectral motion analysis with a fully coupled constitutive model and ii) vessel and module interaction analysis utilizing an integrated 3D model with fully hydrodynamic loads transferred. In order to determine realistic extreme load case, the equivalent design wave selection will be addressed as well.
VIV Response of a Subsea Jumper in Uniform Current
Authors: Wang Howard , Huang Jerry , Lee Sungho , Gioielli Paulo , Kan Wan , Spencer Don , Islam Mohammed
Published: November 2013

Subsea jumpers are susceptible to in-line and/or cross-flow vortex induced vibration (VIV) fatigue damage due to sea bottom currents. However, there is no proven industry standard design analysis methodology currently available specifically for assessing subsea jumper VIV response.

In 2012, ExxonMobil conducted a jumper VIV model test to assess the validity of potential jumper VIV prediction approaches. A towing test rig was used to expose a small scale jumper model to flow conditions simulating uniform bottom currents. The jumper model was instrumented to acquire acceleration, bending strain and end connection load data. Several accelerometers and strain gauges were installed to enable reconstruction of static and dynamic deformations and bending deflections along the jumper model. Towing tests at different orientations and tow speeds were performed on both a bare pipe model and a straked pipe model. The data were analyzed to examine the frequencies and amplitudes of the jumper vibration. The data from these experiments provide a benchmark for validating jumper VIV prediction approaches.

In this paper, the model test program is presented including model testing philosophy, jumper design and fabrication, and high level model test results.
Estimation of Critical Platform Integrity Parameters in the Absence of Direct Measurements in the Context of Integrated Marine Monitoring Systems
Authors: Maroju Soma , Delaney Kevin , Leon Christopher , Prislin Igor
Published: November 2013

Integrated Marine Monitoring Systems (IMMS) are designed to help operators to reduce operational risk by providing information about the environment and the platform responses in real time. In spite of efforts to keep monitoring systems in working condition by following planned maintenance and upgrades, some sensors may fail intermittently or may generate spurious data. Quite often, intervention to repair or to replace a faulty sensor is either difficult, or even not feasible.

This paper discusses various methods to estimate critical platform integrity parameters with satisfactory confidence in the cases when direct measurements are temporarily unavailable or questionable. Methods such as Artificial Neural Network and Extended Kalman Filter have been employed and specifically tuned to particular challenges.

Estimated results for the missing data, such as platform position or riser loads, are reliable as they have been validated against historically good data.

The merit of the paper is to present the methods that can increase reliability of the IMMS, enhance safety, reduce operational risk and decrease cost in maintaining expensive offshore systems.
Hydrodynamic Issues of FLNG Systems
Authors: Chen Xiao-Bo , Diebold Louis , de-Hautecloque Guillaume
Published: November 2013

Advanced hydrodynamic analyses of floating LNG terminals are presented in the paper. They consist of the complex interaction of multiple bodies and the coupling effect of seakeeping (wave diffraction and radiation around bodies) and sloshing (liquid motions in tanks). Based on the recent development to introduce the dissipation in potential flows and new formulations of boundary element method, the seakeeping analysis is enhanced to be able to make accurate predictions of gap resonances and major dynamic effect of liquid motion in tanks.
Carbon Dioxide Uptake by Concrete Modified With Carbon Nanotube
Authors: Escobar Mariano Martin , Di Paolo Adrián , Vazquez Analía
Published: November 2013

CO2 emission from fossil fuel fired power plants contributed 30% of global emissions in 1990. In the same year, the cement industry contributed about 5% of the total. According to Kyoto Protocol, a tremendous effort is required to reduce the carbon dioxide emission. One potential technology in CO2 mitigation responses is the use of concrete products as carbon sink through the early age fast curing. The cement compounds C3S and C2S are instantaneously carbonized into calcium carbonate and silica gel, once cement is mixed with water and exposed to the carbon dioxide gas. The objective of this work is to evaluate the effect of adding carbon nanotubes in cement paste matrix on the capacity as CO2 sink. Adiabatic temperature was determined for different carbon nanotubos content on the cement paste. The microstructure was studied by scanning electronic microscopy. The calcium carbonate and calcium hydroxide content were determined by a thermogravimetric analysis. The storage modulus was measured for the specimens of cement paste before and after the immersion in CO2. Carbon nanotubes act as nuclear agent of the calcium carbonate and increase the maximum temperature and decrease the time of hydration. The incorporation of carbon nanotubes to Portland cement paste could modify the transport properties of the matrix. In fact, it was shown that interfacial interactions between the hydration products and multi-walled carbon nanotubes occur; and it was observed the insertion of multi-walled carbon nanotubes between the hydration products.