bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mooring Optimization of Offshore Floating Systems Using an Improved Particle Swarm Optimization Method
Authors: da Fonseca Monteiro Bruno , de Lima Junior Mauro Henrique Alves , Albrecht Carl Horst , de Lima Beatriz de Souza Leite Pires , Jacob Breno Pinheiro 
Published: November 2013

The offshore oil production industry is currently expanding its activities in even deeper waters, using moored floating platforms submitted to extreme environmental conditions. Therefore, the design of mooring systems to keep the position of such platforms is of vital importance to assure safety and economical feasibility for offshore oil production.
In this context, this work presents optimization procedures to find the minimum offsets for floating platforms under environmental loads, taking radius, azimuth, pre-tension and material of the mooring lines as design variables.
Considering that such optimization procedures require high computational costs, due to the need of nonlinear static and dynamic analyses with Finite Element models for each candidate solution, among the various meta-heuristic algorithms the Particle Swarm Optimization method (PSO) was chosen due to its simplicity, efficiency and parallel capability.
Results of typical systems are presented, which indicate that the method is effective.
A Practical O(Δω) Approximation of Low Frequency Wave Loads
Authors: Monroy Charles , de Hauteclocque Guillaume , Chen Xiao-Bo 
Published: November 2013

The low-frequency quadratic transfer function (QTF) is defined as the second-order wave loads occurring at the frequency equal to the difference frequency (ω1 − ω2) of two wave frequencies (ω1, ω2) in bi-chromatic waves of unit amplitude. The exact formulation of the QTF which is recalled here is difficult to implement due to numerical convergence problems mainly related to the evaluation of an arduous free surface integral. This is why several approximations have been used for practical engineering studies. They have been the subject of a detailed review in [5]. Following this work, two closely-related formulations are investigated in this paper.
In [2], the classical formulations of QTF are examined by an analysis based on the Taylor development with respect to Δω for Δω ≪ 1 and an expansion of QTF in power of Δω is then obtained. It is shown that the zeroth-order term is a pure real function equal to the drift loads and that the term of order O(Δω) is a pure imaginary function.
The second-order low-frequency wave loading of order O(Δω) contains a free-surface integral representing the second-order corrective forcing on the free surface. Since the integrand is of order O(1/R4) with R as the radial coordinate, the free-surface integral converges rapidly with the radial distance. Unlike what has been assumed in previous studies of particular cases, this free-surface contribution is, in general, not negligible for high Δω compared to other components and the complete QTF.
Depending whether we use the O(Δω) approximation for the whole QTF or only for this free surface integral, it leads to two different approximations. The first one is called original O(Δω) approximation, because it is on this form that the O(Δω) approximation was first described in [2]. If we use the O(Δω) approximation only for the free surface integral, we call this approximation the practical O(Δω) approximation. It is shown in this paper that the original formulation fails to predict the behaviour of the QTF even for small O(Δω). Comparison for the O(Δω) approximation of the free surface integral is performed against the analytical solution and the exact numerical formulation. The results are improved compared to when we neglect this free surface integral for the range of Δω of interest, but still the agreement with the exact solution is not ideal. A path for further improvement is finally proposed.
Fatigue Performance of Submarine Pipeline Girth Welds Installed by S-Lay and Reeling
Authors: Hval Morten , Lamvik Trond 
Published: November 2013

Submarine pipelines installed on very uneven sea bottom usually results in many long free spans. If the free spans are above a certain length the pipeline will be subjected to vortex induced vibration (VIV) caused by sea currents or wave motions transverse to the pipeline direction. The onset and level of VIV will depend on several factors such as pipe dimensions and submerged weight, current velocity, seabed soil properties and span boundary condition. For uneven sea bottom, seabed intervention may be very costly if there are many high free spans that are longer than what is acceptable with respect to fatigue. There is obviously a possible economical benefit if longer free spans can be accepted due to improved fatigue performance, which may result in less intervention work by either excavation, trenching or rock/mechanical supports.
This paper will summarize results from a comprehensive full scale fatigue test program that has been performed in order to verify potential enhanced fatigue design parameters of high quality pipeline welds compared to standard fatigue design parameters according to DNV-RP-C203. The testing included pipe dimensions from 6 to 16 inch OD, and tests were performed on both as welded pipes and pipes subjected to simulated reeling strains. In addition to normal welds, also welds with deliberately introduced weld defects/weld indications, maximum acceptable axial misalignment and repaired welds were tested. The test results were compared with similar recommended design parameters for pipeline girth welds. Furthermore, the effect of reeling, weld residual stresses, weld defect and repair will be presented and discussed.
Minimizing Interference Between Top Tension Risers for Tension Leg Platforms
Authors: Koska Ryan , Kaculi Jim , Campbell Mike , Mills Darren 
Published: November 2013

Interference between TTRs is a key design challenge. For spars, this is typically mitigated by having a large spacing between wellheads, thus increasing the distance between risers along the water depth. However, due to lower TTR tensioner stroke limits combined with larger vessel offsets, the feasibility of spacing out the wellheads for TTRs on a TLP is limited. The result is TTRs that are closer together through depth and therefore more likely to contact each other in extreme current conditions.
This paper presents the approach used to minimize the interference between the top tension risers on TLPs. Specific topics include considering current profiles with varying directions through the water depth, adjusting the top tension of the risers, and utilizing low-drag vortex-induced vibration (VIV) suppression strakes. The relative effect of each of these topics is also discussed.
The Development of a Fibre-Optic Based Breach Detection System for Flexible Pipe
Authors: Nott Phil , McNab John , Fernando Upul , Sheldrake Terry 
Published: November 2013

In service, flexible pipes are exposed to harsh environments and challenging conditions that subject the structure to demanding physical rigour that is largely unknown or unnoticed throughout the service life of the asset. Resistance to extremes and large fluctuations in strain, temperature and pressure are built into the pipe design, however the pipes are often breached due to accidental damage to the outer shield caused by external objects. Early knowledge of this damage is vital to limit the degradation of the metallic wires due to contact with seawater, and with the early knowledge of breach prompt remedial actions can be triggered to prevent further deterioration of the pipe that may lead to expensive repair or replacement. Using fibre optics as a distributed temperature sensor, the entire length of the asset can be continuously monitored, and the incidence of a breach in the outer shield of the pipe can be efficiently captured.
This paper describes a fibre optic-based breach detection system developed to monitor offshore flexible pipes. A brief outline of the development programme is presented. The work involved selection of fibre/monitoring equipment, physical encasement of the ‘harsh environment’ fibre optics in the pipe structure, subsequent termination in the pipe end-fitting, and the procedures for interrogation and interpretation of the Raman-based optical signals. A prototype system has been implemented on mid-scale pipe samples and the transient and steady state thermal behaviour of the pipe has been investigated under a simulated and wide range of controlled breach test conditions. A summary of the test results is presented.
Numerical models of the pipe geometry have been developed to predict the transient thermal behaviour of a shield breach. Good correlation of experimental results with the predictions shows the sound adaptation of fibre optic-based sensing technology in offshore flexible pipes.
Port Logistics Policy of Japanese Government for Strengthening Global Competitiveness of Industry in Case of Ocean Space Utilization
Authors: Takahashi Koji , Urabe Shinichi , Umeno Shuichi , Kozawa Keiji , Fukuda Isao , Kondo Takeo 
Published: November 2013

A port logistics is classified into two kinds, a container logistics and a bulk logistics.
In the field of a container logistics, a terminal operator pursues large-scale management of its container terminals by global M&A corresponding to the global growth of the container handling number, which resulted in container terminal operators’ oligopolization.
In the field of a bulk freight logistics, the private enterprises, which invest in and improve port equipment by themselves, are changing in the direction to reduce number of handling ports and to invest in port equipment intensively corresponding to the vigorous resource demand of the world.
The economic activities of the private enterprises are progressing on the basis of the management strategy which differs between “oligopolization” of a container logistics and “selection and concentration” of a bulk freight logistics.
On the other hand, since management of ports is the basis supporting a national logistics, each country of the world carries out various public participations, such as a legal support and a financial support.
For example, in Japan, although ‘a port authority system’ was brought to Japan almost 60 years ago by U.S.A. and the management right of main ports were transferred to local governments from national government, Japanese government has been taking the lead in implementation of many policies to strength global competitiveness of industry reflecting the flow of global privatization and concession.
Recently, many countries have been changing their public participation policies. A country has established the system which increases private investment and reduces public financial support since capital investment remaining power has decreased according to aggravation of the finances of national government and local governments. The other country has established the system which backs up logistics activity with public support.
This paper, to utilize ocean space, will show a port logistics policy of Japanese government, particularly the historical flow and the prospective view of the public participation to a port logistics based on the logistics trend of the world.
Neutron Diffraction Measurement of Weld Residual Stresses in an UOE Linepipe Subjected to Mechanical Expansion
Authors: Wen Shuwen , Dong Hongbiao , Zhang Shu Yan , Bannister Adam , Connelly Martin 
Published: November 2013

Weld residual stresses in double submerged arc welded (DSAW) UOE linepipes can have significant implications on the integrity and in-service performance of the pipeline from which it is normally constructed, often for deep and ultra-deep water applications. Therefore they have to be considered as a crucial data input for accurate Engineering Critical Assessments (ECAs) of offshore pipelines. This has so far been based on the assumption that the residual stresses in the UOE pipe seam weld are equal to the yield strength of the parent material: an assumption that is likely to cause over-conservatism in conventional pipeline design.
In the current study neutron diffraction technique was used to quantify the weld residual stresses of an UOE linepipe (18″ OD × 25.4mm WT, grade X65) in post-expansion condition. The UOE linepipe manufacturing process is briefly introduced first, which involves forming steel plate into pipe, followed by DSAW seam welding and then pipe mechanical expansion. The sample preparation for neutron diffraction measurement of lattice parameters is described next in detail. Neutron diffraction was used to measure the residual elastic strain within the pipe through the precise characterisation of the interplanar crystal lattice spacing and the atomic lattice itself was used as a strain gauge. The measurements were mainly taken in and near the seam weld area of the pipe along the pre-defined lines in through-thickness and cross-weld orientations. The weld residual stresses in three primary directions, namely axial, hoop and radial, were calculated from the measured lattice parameters in as-supplied (welded and expanded) and stress-free conditions using Hooke’s law of linear elasticity, and are systematically presented in the paper. It was found that weld residual stresses of the UOE linepipe in post-expansion condition were significantly lower than the yield strength of the parent material, and in most cases these were less than 50% of the actual yield strength of the parent material. The mechanism of weld residual stress formation and the influence of post-weld expansion on the reduction and through-thickness normalisation of weld residual stresses were studied through finite element (FE) modelling analysis.
Finally an example ECA analysis was carried out for the current linepipe under an assumed service loading condition. The degree of over-conservatism that could result by assuming weld residual stresses to be equal to the yield strength of the parent material was demonstrated, as compared to the situation where the values of the required residual stresses were taken from the neutron diffraction measurement. It was therefore shown by the current study that the combined approach of neutron diffraction measurement and FE modelling could greatly enhance the understanding of performance of seam-welded UOE pipes.
Comparison of Simulation and Tank Test Results of a Semi-Submersible Floating Wind Turbine Under Wind and Wave Loads
Authors: Philippe Maxime , Courbois Adrien , Babarit Aurélien , Bonnefoy Félicien , Rousset Jean-Marc , Ferrant Pierre 
Published: November 2013

A model of the Dutch Tri-floater semi-submersible platform equipped with the NREL 5MW wind turbine has been tested in the hydrodynamic and ocean engineering tank of École Centrale Nantes under wind and wave loads. This paper aims at comparing the results obtained with numerical simulations with these experimental results. The numerical model is based on the FAST design code from NREL and a user defined platform load model for calculating hydrodynamic and mooring loads. This hydrodynamic model includes non linear hydrostatic and Froude-Krylov forces, diffraction/radiation forces obtained from linear potential theory and Morison forces to take into account viscous effects on the braces and heave plates.
First the hydrodynamic model is calibrated against the results of free decay tests without wind. A good agreement is achieved by calibrating mooring properties and heave plates properties of the numerical model. Then a comparison of regular wave cases without wind is realised, and a fair agreement is observed for surge, heave and pitch motions of the floating system. Finally comparisons are realised for regular wave cases with a constant wind speed. A good agreement is observed for the steady state surge and pitch offset. Surge and heave motions also shown a good agreement, these degrees of freedom are not being strongly influenced by wind loading. For pitch motion, numerical simulations show differences around 0.4 rad/s wave frequency, for which model tests have shown a significant influence of wind loading on system motion.
Methodology for Performance Assessment of a Two-Body Heave Wave Energy Converter
Authors: de Andrés Adrian , Guanche Raúl , Armesto José A. , del Jésus Fernando , Vidal César , Losada Íñigo J. 
Published: November 2013

A wave energy farm composed by several two-body heaving wave energy converters is being developed by IH Cantabria. This study presents a methodology to obtain the power performance of an isolated two-body heaving wave energy converter, previously presented and analyzed by [1]. The methodology relies on a numerical model which represents the motion of the two bodies in the time domain. This time domain model has been built substituting the entire Cummins equation system with a state-space system, thereby avoiding the convolution integral of the radiation force term with a state-space subsystem, previously used in [2] and [3].
The performance of the device along its life cycle has been estimated based on a proposed new methodology. The new method is proposed in order to obtain the long term power production of a device with the same computational effort than the classical method based on the power matrix. The proposed method is able to estimate long term power production time series. This long time series is obtained using the MaxDiss selection technique from [4] in order to compute only the power of the most representative sea states and the Radial Basis Function interpolation technique (RBF) to obtain the complete power series.
Experimental Study of Hydraulics and Cuttings Transport in Circular and Non-Circular Wellbores
Authors: Taghipour Ali , Lund Bjørnar , Ytrehus Jan David , Skalle Pål 
Published: November 2013

Cuttings transport is one of the most important aspects to control during drilling operations, but the effect of wellbore geometry on hole cleaning is not fully understood. This paper presents results from experimental laboratory tests where hydraulics and hole cleaning have been investigated for two different wellbore geometries; circular and a non-circular, where spiral grooves have been deliberately added to the wellbore wall in order to improve cuttings transport. Improving hole cleaning will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells.
The experiments have been conducted as part of a research project where friction and hydraulics in non-circular wellbores for more efficient drilling and well construction is the aim. The experiments have been performed under realistic conditions. The flow loop includes a 12 meter long test section with 2″ diameter freely rotating drillstring inside a 4″ diameter wellbore made of concrete. Sand particles were injected while circulating the drilling fluid through the test section in horizontal and 30° inclined positions. The test results show that borehole hydraulics and cuttings transport can be significantly improved in a non-circular wellbore relative to a circular wellbore.
Investigating the cutting transport in non-circular wellbores with available models is even more complex than for circular wellbores. Most drilling models assume circular wellbores, but in reality the situation is often different. Also, it may be possible to create non-circular wellbores on purpose, as in the present study. Such a comparative, experimental study of hole cleaning in different wellbore geometries has to our knowledge previously never been performed, and the results were obtained in a custom-made and unique experimental flow loop. The results and the experimental approach could therefore be of value for any one working with drilling.
Geology-Based Reservoir Model Building for Carbonate Reservoirs
Authors: Lagkaditi Lydia , Srivastava Ashok , Gupta Anuj 
Published: November 2013

Environment in which carbonate reservoir rocks are deposited was studied by visiting and collecting rock samples from a carbonate reservoir analog located at Jabal Fuwairit in the Northeastern coast of Qatar. The primary objective of this study is to develop methods to characterize carbonate reservoirs.
The experimental procedure included collecting samples based on geology, mapping the location and altitudes of the samples using a high-resolution Global Positioning System (GPS) with an altimeter, permeability measurements at selected locations, conducting petrophysical measurements on the samples, Conventional and Micro-X-ray Computed Tomography Scanning (CT Scanning), Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Spectroscopy (EDS) and Atomic Force Microscopy (AFM) imaging.
It is observed that the permeability measurements show an alternating pattern as a function of height above sea level. The cyclicity is probably representative of repeating sequences of sea level changes over geological time. CT Scanner and Micro-CT Scanner measurements were employed to obtain vital information about the flow pathways in the rock, thus assisting in calculating the porosity to compare with values measured in the lab. SEM results gave direct visualization of the pore network and information about grain size (500 microns) and intergranular porosity, mineralogy, compared with the EDS results, and lithotype. EDS results showed that reservoir rocks directly exposed to environment had significant alteration due to weathering. However, it is encouraging to learn that samples even few inches away from the surface had minimal environmental influence.
Evaluation of Loads During a Free-Fall Lifeboat Drop
Authors: Califano Andrea , Brinchmann Kristoffer 
Published: November 2013

A new Offshore Standard (DNV-OS-E406) [1] has been developed for the design of Free Fall Lifeboats (FFLB) used for emergency evacuation from offshore structures. This standard aims at ensuring safe evacuation, focusing on the design at an early stage. Load (CFD) and structural (FE) analyses are used to assist in determining whether or not the free fall lifeboats comply with the Target Safety requirements as set forth by the Standard.
The present paper describes the methodology used when assessing the structural capacity of FFLB. The structural integrity is established throughout every phase of a lifeboat drop, linking computational fluid dynamics (CFD) and finite element analysis (FEA). Loads computed from CFD on a finite volume mesh are interpolated to a finite element model where the structural analysis can be performed in order to obtain stresses, strains and deflections, and finally assess the structural capacity of the lifeboat.
Emphasis in this work is given to the hydrodynamic model and loads, while structural analyses are discussed more in depth by Brinchmann et al. [2].