bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling of Drilling Fluid Thixotropy
Authors: Cayeux Eric , Leulseged Amare 
Published: September 2018

Drilling fluids are visco-elastic materials, i.e. they behave as a viscous fluid when subject to a sufficient shear stress and like an elastic solid otherwise. Both their elastic and viscous properties are time-dependent, i.e. drilling fluids are thixotropic. Because of thixotropy, it takes a finite time before the effective viscosity of a drilling fluid attains an equilibrium when the fluid is subject to a change of shear rate. This effect is visible when one changes the applied shear rate in a rheometer, as the fluid will gradually adapt to the new shearing conditions.
When the velocity of a drilling fluid changes, for instance due to a change in pump flow rate, movement of the drill string, or change of flow geometry, the fluid will exhibit a time-dependent response to the new shearing conditions, requiring a certain time to reach the new equilibrium condition.
Unfortunately, the time-dependence of the rheological properties of drilling fluids are usually not measured during drilling operations and therefore it is difficult to estimate how thixotropy impacts pressure losses in drilling operations. For that reason, we have systematically measured the time-dependence of the rheological properties of several samples of water-based, oil-based and micronized drilling fluids with a scientific rheometer in order to capture how drilling fluids systems respond to variations of shear rates.
Based on these measurements, we propose to investigate how one existing thixotropic model manages to predict the shear stress as a function of the shear rate while accounting for the shear history and gelling conditions. Then we propose a modified model that fits better, overall, with the measurements even though there are still noticeable discrepancies, especially when switching back to low shear rates.
A Comparison of Fracture Toughness and Fatigue Crack Propagation Characteristics of High Manganese and Nickel Steels
Authors: Park Jeong-Yeol , Kim Myung-Hyun 
Published: September 2018

Recently, demands for liquefied natural gas (LNG) are increased by developing countries such as China, India and Middle East area. In addition, the International Maritime Organization (IMO) reinforced regulations to avoid the serious environmental pollution. This trend has led to manufacturing and operating various LNG vessels such as liquefied natural gas carrier (LNGC), floating liquefied natural gas (FLNG) and very large gas carrier (VLGC). In the design of LNG vessels, the structural integrity of LNG storage tank is of significant importance to satisfy the service conditions. In order to secure structural integrity, LNG storage tank is fabricated with low temperature materials. In general, low temperature materials such as SUS304L, Invar alloy, Al 5083-O, nickel alloy steel and high manganese steel exhibit excellent fatigue and fracture performances at cryogenic temperature. In particular, high manganese steel has attracted interest because they are potentially less expensive than the competing other low temperature materials.
This study compares the fracture toughness and fatigue crack growth characteristics of high manganese steel with those of nickel steels. In addition, fracture toughness and fatigue crack growth rate tests for various nickel steels are conducted according to BS 7448 and ASTM E647, respectively. In order to obtain less conservative design values, the results of high manganese steel and various nickel steels were compared to those of BS7910. As a result, the CTOD value of high manganese steel is higher than that of 9% nickel steel at cryogenic temperature. In case of FCGR, the high manganese steel and 9% nickel steel are found to be similar to each other.
Corrosion Assessment of Aluminium Conductor for Medium Voltage Cables for Subsea Umbilical System
Authors: Socariceanu M. , An X. , Deighton A. , Friday A. 
Published: September 2018

High tensile strength aluminum offers great potential as a conductor material for Medium Voltage power cables within subsea umbilicals. Its excellent fatigue performance makes it suitable for dynamic umbilicals and its high tensile strength and light weight make it an ideal candidate for deepwater dynamic umbilicals either as an independent load bearing member or as an electrical conductor taking load share in an armoured or steel tube umbilical.
Umbilicals, are the bundles of electrical and hydraulic components that connect and control elements of a subsea Oil and Gas production system.
6000 series aluminum conductors, commonly known as AAAC (All Aluminum Alloy) conductors are widely used on high voltage overhead transmission lines, primarily on long spans due to their increased tensile strength. They have been widely used in various environments and possess an excellent track record. However, the use of AAAC 6000 series in a subsea umbilical system is novel. The cable located inside an umbilical bundle is normally of a wet insulation design, and an area of concern is that the seawater may permeate through the cable insulation allowing the conductor material to be in contact with water throughout its design life. Hence the corrosion resistance of the AAAC 6000 series in a seawater environment is of paramount importance and therefore must be assessed.
This paper details the corrosion assessment of the 6000 series aluminum power cable conductor at RINA Consulting Ltd’s laboratories together with complimentary field testing. The presented test results are based on long term (6–12 months) laboratory testing. The test programme investigated permeation, impact of temperature, effect of hydrostatic pressure and galvanic corrosion, with the tests being performed on material coupons and cable samples in a simulated seawater environment. Also detailed is the outcome of a full-scale cable field immersion test, 6 months under 1000m depth at seabed temperature of 10°C.
The results demonstrated that there was no Cl− and Na+ ion permeation through the insulation layer. Also, there is no sign of aluminium conductor corrosion and no drop-in insulation resistance witnessed for all tested samples at temperatures up to 90°C and under a high pressure of 300bar after a one year test period, which is sufficient to qualify use in a subsea application.
Based on the results of the presented laboratory testing and field immersion testing, it can be concluded that 6000 series aluminium conductors within ‘wet design’ Medium Voltage power cables will not be susceptible to corrosion in a subsea environment and could be used in other applications such as renewables.
The Application of Caisson-Type Solutions to the Current Offshore Wind Energy Market
Authors: Abanades Javier , Ivars Javier , Molina Rafael , García Carlos 
Published: September 2018

The current offshore wind energy market is not only focused on the design of WTG foundations, but also on the design of offshore infrastructures that lead to an improvement in the current grid connection system, such as artificial islands. For all these type of projects, caisson-type solutions can be applied with numerous advantages. The present article present three different projects in which caisson-type solutions were used: the foundation of a WTG (Gravi3® patent) in the Portuguese Coast, the foundation of a meteorological mast installed in Scotland and the design of an artificial island in the North Sea.
The main advantage of this solution is the well-developed construction principle to build the caissons, which is based in the employ of a floating dock in a shelter area. As the caissons are cellular elements, the interior is empty; they float, so they are transported to the place in question to be deployed by means of filling with water the cells that comprised the caisson. This technology is rather used in Spain, being most of the kilometres of breakwater built using caissons thank to their high production rates. The three examples that will be presented in the article are proof of the versatility of this solution. Whereas the case of Gravi3® consists in a gravity based solution for WTG, which is comprised of 3 circular caissons connected by means of a steel tripod; the meteorological mast is formed by a rectangular caisson and a steel shaft. Finally, the artificial island is a mixed solution that uses caissons in the perimeter and hydraulic filling in the inner part. Furthermore, these solutions could be also applied in ports, integrating the WTG on the current or future dikes.
Safe Operation of Jacket Platforms in a Major Oil Field in the North Sea
Authors: Scherf Ingar , Hansen Trine , Sigurdsson Gudfinnur 
Published: September 2018

Offshore Structures operate for decades in extremely hostile environments. It is important during this period that the structural integrity is efficiently managed to ensure continuous and safe operation.
Increased use of enhanced oil and gas recovery means it is likely that many existing installations will remain operational for a significant period beyond the original design life.
The operator needs to capture, evaluate and, if necessary, mitigate design premise changes which inevitably occur during the life of a structure. Further, advances in knowledge and technology may imply changes in codes and standards as well as in analysis methodologies.
Changes in corporate structures, transfer of operator responsibility and retirement of experienced engineers call for reliable means to transfer historical data and experience to new stakeholders.
Effective emergency preparedness capabilities, structural integrity assessments and inspection planning presuppose that as-is analysis models and corresponding information are easily accessible.
This paper presents an implementation of the in-service integrity management process described in the new revision of NORSOK standard N-005 [1] for a large fleet of jackets at the Norwegian Continental Shelf.
The process, comprising management of design premise changes as well as state-of-the-art technical solutions over a range of disciplines, has enabled the operator to prolong the service life with decades at minimum investments.
A structure integrity management system (SIMS) has been developed and digitized over years and streamlined to meet the needs and challenges in the operation and management of the jacket platforms. SIMS enables a rather lean organization to control the structural integrity status of all load-bearing structures at any time.
Platform reinforcements and modifications along with other operational risk reducing measures like unman the platforms in severe storms enable continued use with the same level of safety as for new manned platforms. Advanced analyses are used to document regulatory compliance.
Modern fatigue and reliability based inspection planning analyses have reduced the costs needed for inspection of fatigue cracks significantly.
The benefits from the SIMS system are substantial and the resulting safety and productivity gains are apparent. The continuity of knowledge and experience is maintained, reducing risk to safety and regularity.
The digital transformation related to management of structural integrity status as described in NORSOK standard N-005 is realized through SIMS.
Bending Capacity of Corroded Pipeline Subjected to Internal Pressure and Axial Loadings
Authors: Gao Jie , Peng Zengli , Li Xin , Zhou Jing , Zhou Wenxing 
Published: September 2018

Offshore pipelines operating in a harsh environment are usually subjected to combinations of bending moment and axial loadings in addition to internal pressure. Due to the corrosive media transported in the pipelines and corrosive substances within seawater and soil outside the pipelines, local corrosion defects will generate on the pipeline’s inner and outer walls, reducing its ultimate bearing capacity.
This paper presents a series of full-scale failure tests and nonlinear finite element analysis (FEA) to study the bending capacity and failure mode of corroded pipelines with outside locally-thinned-areas (LTAs) subjected to combinations of internal pressure, axial compressive force and bending moment. The LTAs are loaded in compression to simulate corrosion. Material tests of API 5L X56 seamless pipe steel were conducted and the stress-strain relationship was obtained. FEA results of the moment versus curvature relation, bending capacity and local buckling behavior of each specimen model matched the experimental results very well, validating the accuracy of this simulation. Additional FEA is then performed to investigate the effect of corrosion geometric parameters, such as corrosion depth, corrosion width, and corrosion length, on the ultimate moment. Among them, the width is of the greatest impact, followed by is the depth, the length impact can be ignored.
Shutdowns Management: Changing Things Up by Only Applying Best Practices
Authors: Alonso Jose-Luis , Neal Bernie , Jolly Simon , Auld Steven , Adesanya Adetola 
Published: September 2018

Production efficiency is a key factor for oil & gas companies to have a good performance in a low oil prices environment, and planned shutdowns are events that impact crucially in this factor.
This technical paper objective is to explain how, starting from a point of high planned losses due to shutdowns bad performance (13%), the application during only one year of best practices compiled from oil & gas and other business experience is able to change things up to achieve an impressive outcome (3%).
Long term planning, meticulous preparation and efficient execution are achieved when best practices are applied with accountability, rigor and common sense.
Maintenance and Integrity shutdown plans compliance is also improved as they are considered inside a big picture that allows us to schedule them in the more efficient way to assure our HSE standards, and helped by some new technologies as the so called NII (Non-Intrusive Inspections).
Standards, procedures, deliverables, communication channels, materials control, organigrams… are the specific tools to be used and refed to implement the lessons we learn at the end of each shutdown.
Sharing regularly our experience with other operators is also a source of best practices and cross-pollination.
Maintaining this quality standard along the time and improving to the extent possible will drive us to excellence in the middle term. As our teams become more and more involved on this new method, they start to feel more comfortable and propose improvements, being more and more committed as they see good results arriving.
Finite Element Simulation of an Embedded Anchor Chain
Authors: Sun Chao , Feng Xiaowei , Gourvenec Susan , Neubecker Steven R. , Randolph Mark F. 
Published: September 2018

The embedded portion of a mooring line plays an important role for efficient and economic design of an overall mooring system. This paper presents a methodology for numerical simulation of the behaviour of an embedded anchor chain as it cuts through the soil, focusing on the tensioning of a catenary mooring. The Coupled Eulerian–Lagrangian (CEL) approach within ABAQUS is used to capture the interaction between the embedded chain (Lagrangian structure) and the soil (Eulerian material). The anchor chain is simulated by a series of rigid cylindrical segments connected together by LINK connectors.
Before analysing the global behaviour of an embedded chain, a calibration exercise is undertaken where a straight multi-link portion of the chain is displaced normally and axially in soil. The resulting normal and frictional resistances (per unit length) are compared with those adopted in general practice, in order to calibrate the relationship between the diameter of the cylindrical segments and the bar diameter of the chain. After that, the tensioning process of an anchor chain is simulated, starting from an initial configuration with a 9 m length embedded vertically (attached to a fixed padeye), with the remaining length lying on the seabed. Horizontal tensioning of the chain causes it to cut through the soil until it forms an inverse catenary with an angle of just under 35 degrees to the horizontal at the padeye (and zero degrees at the mudline).
The loading curve, and also the inverse catenary profile of the chain for different angles at the padeye, are shown to agree well with the Neubecker-Randolph closed-form analytical solution. However, the ratio of the tensions at the padeye and the mudline from the CEL results differs significantly from the analytical solution. Insights from the CEL results indicate that this is because the frictional soil resistance is not fully mobilised, particularly for the portion of the chain in the stronger soil at depth, near the padeye, where the axial displacements are small. This result has significant implications for the geotechnical design of anchoring systems that involve a (nominally) fixed padeye. The simulation methodology also has considerable potential for exploring the creation of an open trench adjacent to a fixed anchor due to monotonic and cyclic perturbations of the anchor chain.
Boom Overtopping Assessment Based on a Coupled Hydrodynamic - CFD Analysis
Authors: Limburg Hans , Sainte-Rose Bruno , Verjut Jean-Sébastien 
Published: September 2018

Plastic pollution in the marine environment is an increasing problem with severe impacts on ecosystems and economies around the globe. The Ocean Cleanup (TOC) Foundation develops a floating barrier able to intercept, concentrate and extract plastic from the marine environment.
TOC has conducted several experiments and numerical studies to determine the capture efficiency of its system. One of the phenomena leading to its decrease is wave overtopping or under-flowing when the system cannot properly follow the waves, this issue is amplified by the use of a stiffer barrier than the original deep-water moored concept. When such events occur, plastic debris won’t be captured by the system and will escape into the open ocean. Such an event will therefore be decreasing the capture efficiency.
To model and quantify plastic loss due to wave overtopping and under-flowing, the ideal approach would be to use a nonlinear 3D CFD method including hydro-elasticity of the barrier structure. Given the size of the problem and the number of conditions that need to be simulated to characterize the design space of the system, the use of such a method is computationally very expensive and therefore unrealistic. Therefore, the objective of this work is to propose an alternative method.
This paper presents a method of quantifying plastic loss by coupling a hydrodynamic solver to a 2D CFD solver. A hydrodynamic model is set up to predict the dynamics of the boom. A 2D CFD model with imposed motion is used to analyze the local effects of wave overtopping. From there, wave overtopping events along the barrier system are analyzed and quantified using the results found in the 2D CFD study.
A Fundamental Study on Collision of a Tsunami Drifting Objects Against Structures Using MPS Method and FEM
Authors: Masuda Koichi , Ikoma Tomoki , Murata Daichi , Eto Hiroaki , Matsuoka Akihiro , Aida Yasuhiro , Ikegami Masaharu 
Published: September 2018

The large-scale tsunami generated by the Great East Japan Earthquake on March 11, 2011 caused a great deal of damage. In addition to tsunami hydrodynamic forces, loads generated by drifting objects such as ships and cars can cause destruction in coastal areas. As such, impact forces due to collisions of drifting objects are an important consideration in the design and planning of structures in coastal areas.
Depending on the size of the drifting object, it is difficult to evaluate the effect of the impact force at the time of collision through tank experiments. Therefore, it is necessary to develop a numerical simulation method that can reasonably evaluate such effects. Such a method must consider the nonlinear interactions among drifting objects, a fluid, and fixed structures.
In the present study, we used the moving particle semi-implicit (MPS) and finite element methods to calculate the effect of collisions between drifting objects and structures, and then verified the results experimentally. The MPS method was applied to calculate the loads and pressures due to the collisions. These results were then used to simulate the deformation of the structure using the finite element method. A tank experiment was then conducted in order to confirm the accuracy of the numerical calculations. The deformation of a rod-shaped steel structure was measured following collision with a floating acrylic plate. The experimental results confirmed the accuracy of the numerical calculations.
Coupled Dynamics of a Vertical Axis Wind Turbine (VAWT) With Active Blade Pitch Control on a Semi-Submersible Floater
Authors: Vlasveld Ebert , Huijs Fons , Savenije Feike , Paillard Benoît 
Published: September 2018

A vertical axis wind turbine (VAWT) typically has a low position of the center of gravity and a large allowable tilt angle, which could allow for a relatively small floating support structure. Normally however, the drawback of large loads on the VAWT rotor during parked survival conditions limits the extent to which the floater size can be reduced. If active blade pitch control is applied to the VAWT, this drawback can be mitigated and the benefits can be fully utilized.
The coupled dynamics of a 6 MW VAWT with active blade pitch control supported by a GustoMSC Tri-Floater semi-submersible floater have been simulated using coupled aero-hydro-servo-elastic software. The applied blade pitch control during power production results in a steady-state thrust curve which is more comparable to a HAWT, with the maximum thrust occurring at rated wind velocity.
During power production, floater motions occur predominantly at low frequencies. These low frequency motions are caused by variations in the wind velocity and consequently the rotor thrust and torque. For the parked survival condition, it is illustrated that active blade pitch control can be used to effectively reduce dynamic load variations on the rotor and minimize floater motions and mooring line tensions.
Large Scale Earthquake Analysis of Integrated Subsea Facilities
Authors: Hesar Majid 
Published: September 2018

Subsea facilities located in earthquake-prone regions of the world can be subjected to severe excitation and have to be designed in a two-tier manner against both ELE and ALE level earthquakes. The return period of these earthquake levels can be 100–300 years and greater than 1000 years, respectively. These facilities may typically consist of rigid pipelines, sliding PLET structures on skirted or hybrid mudmat foundations, connected via rigid spools or jumpers to manifolds on suction pile foundations, with flexible flowlines hanging off goosenecks.
In recent practice Subsea 7 have developed a novel methodology for modelling and simulating the seismic response of such complex clusters in which the so called “system effects” are intractable and dominate the response of certain critical components. Chief amongst the latter are rigid spools and jumpers that span large distances between PLEM, PLET and X-Tree structures without touching the seabed.
In the nonlinear implicit direct integration dynamic FE analyses in Abaqus each of the cluster models in a project is subjected to time history accelerations of seven representative earthquakes, as per ISO 19901-2 requirements. Hysteretic damping characteristics of soil-structure interfaces are modelled with special kinematically hardening elements, calibrated to the site-specific seabed geotechnical properties. Specially developed post processing scripts are used to automatically extract the vital information from the large amount of data produced and perform the unity checks of various components to their respective codes of practice.