bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design and Performance Analysis of Anchor System for a Single-Body Wave Energy Converter
Authors: Banos Rodrigo L. , Lemu Hirpa G. 
Published: October 2016

The last couple of decades have observed an increasing interest in development of wave energy conversion technology for both research and commercial purposes. Though slow due to several reasons, the technology shows an evident progress. Because of the oil crisis facing the energy sector in particular, wave energy is currently seen as a good alternative to fossil fuel based power generation. This has marked its footprints on rising industrial ventures in wave energy based power generation and the search for new devices is gearing up. Among the latest invented models, point wave energy converters are attractive and low investment options. These devices are much smaller than the traditional oscillating water column devices and have good performance when combined in arrays of devices, thus placing the technology in the center of industrial and academic research.
This article reports the study conducted to understand the mechanics of the energy exchange in a single-body point wave energy converter device model Cape Verde, patented by the Norwegian company Euro Wave Energy. Furthermore, the article intends to give a practical solution for the design of the anchoring problem in the device. In general, the article attempts to present two completely different objectives: an academic part focusing on understanding the wave energy conversion mechanics, and the industrial development part that attempts to find a practical solution for a particular part of the device.
The first step involves establishing a model that describes the motion and potential of absorbance of a conic single-body absorber. The anchor system was designed in accordance with standards provided by Det Norske Veritas, the Norwegian regulatory framework. A quasi-static method is used to calculate the load that the absorber would suffer and a pulley and cable system is proposed to drive these loads to the anchor system. After a review of the different solutions offered for offshore facilities at the present time, the model of a suction anchor is chosen. As design verification through physical testing of prototypes of conversion devices is demanding and costly, various simulation tools are appearing in the field. The application range of some of these different simulation tools has been evaluated and reported in this article.
Experimental Investigation of Cuttings Transport With Oil Based Drilling Fluids
Authors: Sayindla Sneha , Lund Bjørnar , Taghipour Ali , Werner Benjamin , Saasen Arild , Gyland Knud Richard , Ibragimova Zalpato , Ytrehus Jan David 
Published: October 2016

Drilling fluids are very complex and are essential for safe and efficient drilling operations. It is vital for the drilling operator to be able to select an appropriate fluid for each individual well, including the decision of using oil-based or water-based fluids or “muds” (OBM or WBM). In this article we present results from a comparative study of three OBM’s which are based on the same fluid system (Versatec). This work is part of a larger investigation where the main objective is to identify and evaluate the difference in the hole cleaning capabilities of OBM’s and WBM’s with similar viscosity as measured by the API/ISO standards.
This paper describes an experimental investigation of cuttings transport using flow loop laboratory tests without and with injected cuttings size particles using various industrial oil based fluids with varying density and viscosity. The flow loop includes a 10 meter long test section with 2″ OD free whirling rotating steel drillstring inside a 4″ ID wellbore made of concrete elements positioned inside a steel tubing. Sand particles were injected while circulating the drilling fluid through the test section. Experiments are conducted at atmospheric conditions, but are otherwise designed to represent downhole conditions as closely as possible with respect to fluid and particle properties, flow rates and geometry.
Fluids are tested at different flow rates with and without rotation of drill string, with and without sand injection. This has allowed us to study the effects of flow rate and drill string rotation on hole cleaning capabilities of different fluids. The primary results are pressure drop, steady state sand bed height in a horizontal annulus versus fluid and cuttings rates for rotating and non-rotating drill string and in particular the critical rates for fully suspended flow. The results are interpreted in light of results from laboratory characterization of the same fluids, conducted as part of the same project.
The results will increase understanding of the relationship between drilling fluid properties and hole cleaning performance. This will enable the development of improved drilling fluids, both operationally and environmentally. Such know-how will also be important in order to develop more accurate transport models.
Hydrodynamic Performance Effect of Steel Catenary Risers on Wave Frequency Motions of a Semi Submersible
Authors: Gang Chen , Nan Zhao , Wei Zhang , Hongtao Yuan , Chunhui Li , Yong Yang 
Published: October 2016

The analysis of the influence of risers on the motions of a floating platform is often conducted and simplified by uncoupled method. As the number of risers and water depth increase, this method would not predict system motion accurately. Coupled analysis method in time domain becomes a very convenient approach in response calculation since it automatically includes the interaction among platform, mooring lines and risers.
This paper introduces a full coupled approach by AQWA-NAUT to include viscous damping of the semi submersible and effects of steel catenary risers on the wave frequency response of platform in time domain motion analysis.
The main conclusion of this paper is that full coupled method can accruately predict semi submersible Response Amplitude Operator (RAOs) comparing to the case without risers. Other conclusions are that risers have an important effect on the wave frequency motion of semi submersible and also lead to a phase lag with respect to platform motions.
CFD Driven Drillship Design
Authors: Krijger Jan Willem , Chalkias Dimitris 
Published: October 2016

Drillships have specific features which make ship resistance and propulsion characteristics difficult to predict with simple empirical methods. In this paper, RANSE CFD was used to optimize the hull and appendages of a drillship for speed or fuel consumption. An innovative thruster arrangement was initially designed for dynamic positioning and its performance in transit was verified with the use of CFD. Furthermore a special hydrodynamically shaped moonpool has been developed to eliminate moonpool sloshing during transit, further reducing resistance and increasing safety on board.
CFD was also used to determine the propulsion efficiencies of the vessel. An innovative way to use an actuator disc approach was used to calculate effective wake factors.
The various CFD calculations and the resulting design modifications are verified and confirmed with calm water resistance and self-propulsion tests.
The bow shape modifications reduce the bare hull resistance by 12% and the headbox modifications reduce the added headbox resistance by 26% of the bare hull resistance. The Callirrhoe moonpool design reduces the added moonpool resistance by 37% compared to a conventional moonpool while at the same time eliminates sloshing in transit. The propulsion efficiency is above 60% when the aft thrusters are used, which is deemed high for such a vessel.
Computation of the Diffraction Transfer Matrix and the Radiation Characteristics in the Open-Source BEM Code NEMOH
Authors: Fàbregas Flavià Francesc , McNatt Cameron , Rongère François , Babarit Aurélien , Clément Alain H. 
Published: October 2016

Until now, widely available boundary element method (BEM) codes did not allow the calculation of two non-conventional hydrodynamic operators, which characterize the way a body diffracts and radiates waves, known as Diffraction Transfer Matrix and Radiation Characteristics respectively. When embedded into the finite-depth interaction theory developed by [1], they drastically speed up the computation of the added mass, damping and excitation force coefficients of a group (“farm”) of floating bodies.
This paper presents the implementation of their computation in the open source BEM solver NEMOH using the methodology proposed by [2]. Results for two different geometries, a cylinder and a square box, are presented and compared to an alternative computational approach developed by [3]. A very good agreement between them is found. In addition, the hydrodynamic operators of the cylinder are compared to a semi-analytical solution available in the literature showing a good match. Results obtained using the finite-depth interaction theory are shown for a generic multi-body wave energy converter (WEC) demonstrating how the capabilities added to the BEM software NEMOH can facilitate the numerical modeling of the hydrodynamic interactions in large arrays of bodies.
The Role of Software Quality in Maritime Safety and Security
Authors: Card David N. 
Published: October 2016

This article discusses the importance of achieving software quality to ensure the safety and security of maritime systems. Software controls the behaviour of many maritime and offshore systems, making it an essential component of such systems. Software defects have been the primary cause of several accidents and have contributed to many more. All the good work of mechanical engineers and marine architects can be undone by a simple programming error. Unfortunately, standards and risk analyses that address software currently are not part of standard industry practice.
This article reviews the motivation for addressing software as part of maritime systems assurance and summarizes the standards and risk analyses available to the industry. Both international standards and classification rules are beginning to be adopted, as part of an increasing recognition of the role of software in all complex systems.
This article introduces a framework for examination of software quality, including process product, operational, and customer perspectives. Important elements of this article were introduced in Card [1]. This article focuses on software process quality. Getting the software right the first time is much cheaper than testing and fixing it to reach acceptability. The cost of rework for a typical software development project ranges from 20% to 50% of total project costs. This article identifies some common software process reference models and explains how they help to achieve software quality. While, there is no specific national or international regulation addressing Software Quality Assurance (SQA) in the Maritime and Offshore industry, some recommendations and guidelines have emerged recently. Three classification societies (DNV GL, ABS, and LR) have published software process reference models (standards) as optional rules for offshore vessels. These standards are based on widely accepted ISO/IEC standards that have been endorsed by national standards bodies. Regulations and liability concerns will eventually force the maritime and offshore industry to accept greater requirements for software quality assurance, as has happened in other major industries. For now, if a customer wants quality, he/she must ask for it. These new optional standards make that easier.
Analysis of Clump-Weight Interference With Offshore Pipelines: Mechanisms and Actions
Authors: Alsos Hagbart S. , Wendel Åsta O. , Kvarme Stig Olav , Sævik Svein 
Published: October 2016

The article addresses challenges and actions from interference between trawl gear and offshore pipelines. Interaction from twin trawlers and their clump weights presents a particular challenge for offshore pipelines, especially in free-spans. The design loads are typically derived from DNV-RP-F111 and are of such magnitude that protection by rock installation is often required. This is especially the case for small and medium sized diameter pipelines, and has an obvious cost aspect tied to it.
The paper investigates the detailed behavior of clump weights interfering with pipelines by breaking down the kinematics of the clump weight and its interaction with an offshore pipeline to a set of differential equations. The system of equations is solved numerically and verified with tests. Next, the response of the clump weight and pipeline is assessed for various parametric variations. This involves assessing the sensitivity of the response for variations such as: interaction with free spans versus flat seabed, effect of varying the pipeline diameter, effect of contact friction, effect of trawl drag and warp line stiffness, effect of clump weight rigging, and the effect of lateral dragging resistance of the pipeline. Finally, the clump weight response solver is applied in case study to provide the trawl pullover design load for an FE pipeline model. The response and consequence for the pipeline is then finally compared with the equivalent scenario generated from the DNV-RP-F111 design pullover load.
Chain Out of Plane Bending (OPB) Fatigue Joint Industry Project (JIP) FEA Results and Multiaxiality Study Results
Authors: Rampi Lucile , Bignonnet Andre , Le Cunff Cedric , Bourgin Francois , Vargas Pedro 
Published: October 2016

In 2002, several mooring chains of a deepwater offloading buoy failed prematurely within a very small time frame. These chains were designed according to conventional offshore fatigue assessment using API recommendations. With this first deepwater buoy application, a new mooring chain fatigue mechanism was discovered. High pretension levels combined with significant mooring chain motions caused interlink rotations that generated significant Out of Plane Bending (OPB) fatigue loading. Traditionally, interlink rotations are relatively harmless and generate low bending stresses in the chain links. The intimate mating contact that occurs due to the plastic deformation during the proof loading and the high pretension of the more contemporary mooring designs have been identified as aggravating factors for this phenomenon.
A Joint Industry Project (JIP), gathering 26 different companies, was started in 2007 to better understand the Out of Plane Bending (OPB) mooring chain fatigue mechanism and to propose mooring chain fatigue design recommendations.
This paper summarizes the computational Finite Element Analysis (FEA) scope of work that provided the understanding and validation of the OPB mechanism through correlation with the test program results on chains. In addition, a multiaxial assessment of the fatigue stresses is studied and the main results are presented in this paper.
Chain Out of Plane Bending (OPB) Fatigue Joint Industry Project (JIP) Fatigue Test Program Results and Methodology
Authors: Rampi Lucile , Gerthoffert Arnaud , Francois Michel , Bignonnet Andre , Vargas Pedro 
Published: October 2016

In 2002, several mooring chains of a deepwater offloading buoy failed prematurely within a very small time frame. These chains were designed according to conventional offshore fatigue assessment using API recommendations. With this first deepwater buoy application, a new mooring chain fatigue mechanism was discovered. High pretension levels combined with significant mooring chain motions caused interlink rotations that generated significant Out of Plane Bending (OPB) fatigue loading. Traditionally, interlink rotations are relatively harmless and generate low bending stresses in the chain links. The intimate mating contact that occurs due to the plastic deformation during the proof loading and the high pretension of the more contemporary mooring designs have been identified as aggravating factors for this phenomenon.
A Joint Industry Project (JIP), gathering 26 different companies, was started in 2007 to better understand the OPB mooring chain fatigue mechanism and to propose mooring chain fatigue design recommendations.
This paper summarizes the full scale fatigue tests on chains and also the tests on small samples addressing the environmental influence on fatigue initiation and crack propagation stages. This paper also addresses the major step that was achieved: the implementation of a multiaxial fatigue criterion to address OPB hotspots as a standard practice in offshore industry. Moreover, the paper presents the first Industry OPB based S-N curves and its comparison to the existing industry fatigue S-N curve. Lastly, this paper provides a summary of the main steps in a framework for OPB fatigue calculation guidelines.
Fatigue Design and Analysis of Offshore Pipelines and Risers Subjected to Waves and Currents
Authors: Liu M. , Cross C. 
Published: October 2016

The industry consensus would appear that the effect of currents on wave induced fatigue damage accumulation is assumed as insignificant and can be ignored. Only when dealing with stability, ultimate limit state design and vortex induced vibration, the recommended industry practice is to consider both currents and waves simultaneously, but except for fatigue design.
This paper presents a study on how environmental loads should be considered in terms of currents and waves for the fatigue life design of offshore pipelines and risers. The study is intended as a spur to redress the misapprehension by focusing on the coupling effect of direct waves and currents in the context of fatigue damage assessment.
It is demonstrated unequivocally that waves and currents cannot be decoupled for fatigue design assessments. Wave induced fatigue with the inclusion of currents is manifested twofold, not only the increased mean stress correction effect but also higher total damage accumulation due to elevated stress ranges. The practice of using wave histograms while ignoring currents is shown to result in an unacceptable non-conservative fatigue design. Both effects should be accounted for in the engineering assessment. A first order correction factor involving the ratio of current and wave velocities is introduced to evaluating the environmental load coupling effect. It is recognized that fatigue associated specifically with VIV phenomena is well understood and documented elsewhere, its discussion is thus outwith the aims of this paper.
Life Extension and Management of Ageing FPSOs
Authors: Salleh Hilman 
Published: October 2016

FPSOs have been a popular choice for deep water oil and gas production with many installations worldwide. Many of these floating production systems were tanker conversions and they are now approaching their mid-life or end of life hence, facing ageing issues relating to asset integrity.
Concurrently, there are also requirements for these floating production systems to operate to operate beyond the design life. As most of this maintenance and refurbishment work is to be done while on station, there needs to be a structured process to ensure that all key areas of concerns are reviewed.
This paper outlines the strategy available and addresses the issues and possible solutions to manage the life extension and ageing of FPSOs.
VIM Model Test and Assessment on a Semi-Submersible Type Floater With Different Column Intervals
Authors: Fujiwara Toshifumi , Nimura Tadashi , Shimozato Kohei , Matsui Ryosuke 
Published: October 2016

Semi-submersible type offshore floating structures are expected to be used in the Japanese coastal area and at sea off Japan for promoting resource exploitation and development in near future. As a moored offshore floating structure may be suffered from current, Vortex-induced Motion (VIM) effect should be assessed in an appropriate manner since the VIM may cause fatigue damage of the floating structure’s mooring lines. VIM phenomenon on semi-submersible type floating structures, however, is not clear, and its comprehension is insufficient since there are only small number of open research papers with lack specifications of the structures. Moreover, a standardized assessment method for the VIM on them has not ever been proposed.
At first in this paper, the results of VIM measurement test using some large semi-submersible floating structure models in relatively high Reynolds number flow are presented, and afterwards simplified estimation method, that is useful in the design stage for a semi-submersible type offshore floating structure, is introduced as one trial.
The Fracture Resistance Approach in Order to Prevent Brittle Failure of Offshore Structures Under Arctic Environments
Authors: Horn Agnes Marie , Østby Erling , Moslet Per Olav , Hauge Mons 
Published: October 2016

This paper is concerned with the challenges related to steel design under Arctic conditions where both loading and temperature have been discussed in relation to material requirements. Today there is a lack of rules and standards for selecting steel materials for bulk engineering for a lower design temperature than −10°C (NORSOK N-004 [1] allows down to −14°C). Both ISO 19902 Steel Structures [2] and NORSOK N-004 Design of steel structures make reference to EN10225 “Weldable structural steels for fixed offshore structures technical delivery conditions [5]” where steel materials are Charpy tested at a lowest test temperature of −40°C and proven for a design of −10°C. Hence, one major challenge for designers are to specify adequate toughness requirements at an early stage of the design process for low temperature applications.
Both NORSOK N-004[1] and ISO 19902[2] provide requirements to load combinations that need to be fulfilled, however the relationship between various load types and temperature is not mentioned in any of these standards. Thus, in the design stage the material needs to demonstrate adequate toughness where loading and temperature are treated independently. For the offshore industry, the main question is the balance between materials requirements and cost-effective solutions, and how to address this within an overall design perspective in order to avoid brittle failure. This paper discusses some of these challenges with the aim of starting a focused process leading up to a clear interpretation of the implications of overall design philosophies, necessary in order to define consistent materials requirements ensuring that brittle fracture is not going to represent a significant threat to the structural integrity. The material recommendations provided in the paper are based on the latest research results from the Arctic Materials project (2008–2017) managed by SINTEF and supported by the industry.
Equivalent Model for Interlocked Carcass Under Axial Loads
Authors: Provasi Rodrigo , Geremias Toni Fernando , de Arruda Martins Clóvis 
Published: October 2016

The modelling of flexible pipe interlocked carcasses is complicated when considering all the geometric complexity of their profile. A possible approach is to model them as cylindrical equivalent layers. To follow this path several alternatives can be considered in changing the geometrical and material properties. However, the thickness and the mean radius of those layers must not be changed to not interfere with the diameter of the other flexible pipe layers.
In this paper, a model of an orthotropic cylindrical layer, with the same thickness and mean diameter of the original carcass layer is constructed and its material parameters are adjusted for axial loads using a finite element model of the real carcass profile.