bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Experimental Investigation of Cylindrical Floater VIM in Current and Waves
Authors: Saito Masakatsu , Fujiwara Toshifumi , Maeda Katsuya 
Published: September 2014

VIM (Vortex Induced Motion) is one of the important issues in the safety evaluation for cylindrical floating offshore structures. The VIM is basically placed as a phenomenon to occur in strong current, but that also appears in current and waves in the sea where offshore structures are installed.
The authors have recognized the phenomenon that the motion amplitude of a cylindrical floater in current and irregular waves together is larger than the sum of the motion amplitude in current and in irregular waves respectively in a VIM experiment. This VIM amplification phenomenon in the current and waves is remarkable when wave height is relatively low that has high occurrence frequency in the sea. It is, therefore, expected that the amplification phenomenon has large influence on the accumulative fatigue damages of the offshore structure’s mooring system.
In order to make clear this VIM amplification phenomenon, the authors have conducted detailed VIM experiment in waves using a circular cross sectional mono-column floater model. The results of the VIM experiment in current and waves are described in detail in this paper. The results of the experiment in irregular waves show different characteristics for VIM amplitude in current. The results in regular waves show the effect of wave height and wave period on VIM amplitude in waves. Using those results, the mechanisms of the VIM amplification in waves are investigated.
Physical and Numerical Modeling of the Performance of Dynamically Installed Anchors in Clay
Authors: Liu X. D. , Sun J. , Yi J. T. , Lee F. H. , Gu H. , Chow Y. K. 
Published: September 2014

Depletion of shallow-water hydrocarbons is increasingly forcing the oil and gas industry to explore in deeper water. Dynamically installed anchors (i.e. torpedo anchors and deep penetrating anchor) are increasingly used as a cost-effective solution for floating offshore structures in deep water environments because their installation cost is largely independent of water depth. In addition, dynamically installed anchors can be deployed accurately, and their performance is less dependent on accurate assessment of the soil shear strength since lower seabed strengths permit greater penetration depths. Despite of the economic advantages afforded by dynamically installed anchors, there remain significant uncertainties in the prediction of the embedment depth and verticality, which is likely to affect their long-term holding capacity. Currently, the holding capacity of the dynamically installed anchors is assessed using conventional pile capacity techniques, which neglect discrepancies in the rate of installation and failure mechanism between them.
This paper presents a series of model tests simulating dynamic installation and monotonic pull-out of dynamically installed anchors in normally consolidated clay. The model tests are carried out in a beam centrifuge at 100g, with varying penetration angles, extraction angles and model masses. A special designed apparatus allows model anchors to be penetrated and extracted with different penetration angles. The test results show that for models without fins, no matter by which angle the model penetrated the soil, the smallest value of holding capacity is obtained when the pullout and penetration directions are the same. Results also indicate that the penetration depth linearly increases with the anchor mass. This study also reported the results from finite element (FE) analyses. The Coupled Eulerian-Lagrangian (CEL) approach in the commercial FE package Abaqus/Explicit is carried out to simulate dynamic anchor installation.
The findings of this study points to a method of assessing the minimum holding capacity of the anchor and its depth of penetration. Further study is now on-going to study the behavior of finned anchors.
Full Scale Application of Thermal Ageing in Line Pipe Material Selection for Deepwater Pipelines
Authors: Kerstens Niels , Liu Ping , DeGeer Duane 
Published: September 2014

Comprising 4 pipelines over 900 km in length, with 32-in diameter and traversing water depths over 2200 m, the South Stream project requires a step-out in technology application. Following several years of preparation, the project is now approaching its implementation.
In order to document the reliability of the collapse resistance for South Stream, an extensive material development program was initiated and executed, including small scale, medium scale, and full scale testing on over one hundred purposely manufactured pipe joints by world’s 5 leading mills.
Testing performed included plate tests, full scale collapse tests on various combinations of plate sources, steel grades, and thermal ageing condition, pressure-bend tests, and reverse bending tests. A large number of medium and small scale tests were performed to allow the development of a suitably reliable statistical database for the probabilistic wall thickness design.
In addition, programs were developed and executed for weldability tests, performing over one hundred trial welds, and for H2S resistance tests.
This material development program was built on INTECSEA’s extensive experience with deep water large diameter pipelines (i.e. Oman-India, Blue Stream, Medgaz, Mardi Gras, IGI, etc.). Due to its extent and rigorous approach the South Stream material development program was able to conclusively prove the feasibility of the selected technological approach at an industrial scale.
This paper provides an overview of the key design issues that were successfully addressed and the major technological advances that have been implemented as part of the linepipe material development process for deepwater pipelines in an H2S containing environment.
The practical significance of this program is to optimize the wall thickness to a level that is manufacturable by the industry and hence enables the South Stream Project to proceed with its unprecedented depth and diameter combination.
Towing Tank Experiments on the Vortex-Induced Vibrations of a Flexible Cylinder With Wake Interference
Authors: Huera-Huarte Francisco J. , Bangash Zafar A. , Gonzalez Leo M. 
Published: September 2014

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current immersed in the wake of another cylinder, placed upstream in tandem configuration. Experiments were conducted at the E.T.S.I. Navales towing tank of the Technical University of Madrid during March 2012. The tank is 80 m long with a cross-section of 4 × 2.5 m. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 16 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. For these experiments, the upstream rigid cylinder was made stationary by fixing it at both ends, and it was located at different centre to centre distances.
More than 200 runs were conducted, with its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted with speeds up to 1.4 m/s. The cylinder had a low flexural stiffness of 6.04 Nm2 and low mass ratio of 2.7. Fundamental natural frequencies were in the range from about 2.3 to 6.2 Hz, and the cylinder responded in modes up to the third cross-flow.
Challenges for Using LNG Fueled Ships for Arctic Routes
Authors: Gaspar Henrique M. , Ehlers Sören , Æsøy Vilmar , Erceg Sandro , Balland Océane , Hildre Hans Petter 
Published: September 2014

The utilization of the Northern Sea Route by commercial ships is an official fact. Since 2009 the number of international cargo vessels using the passage has been increasing, and a continuous raise in these numbers is expected if the route establishes itself as reliable. The route saves vessels approximately two weeks’ time in summer over a route via the Suez channel, but the increase brings concerns, regarding environmental impact, safety, and operability on the route.
This paper investigates the current challenges of using LNG fueled ships for arctic transport routes. A panorama of the recent conditions and predictions for the arctic environment regarding ice concentration and seasonal route availability is presented. The current development of LNG as a commercial fuel is discussed based on this arctic panorama, approaching key topics such as infrastructure, economic viability, propulsion requirements, and environmental impact. Special attention is given to the performance of LNG propulsion systems under arctic conditions, focusing on powering and air emissions. We conclude the paper by proposing the implementation of a lifecycle model to predict economical and environmental performance indicators when simulating a fleet of LNG fueled ships operating under many possible future ice conditions scenarios.
Flexible Riser Carcass Collapse Analyses: Sensitivity on Radial Gaps and Bending
Authors: Axelsson Gunnar , Skjerve Håvard 
Published: September 2014

In the North Sea, carcass failures have over the last years been the largest failure category for flexible pipes, causing multiple riser replacements [1]. The carcass failures could be split into two groups: axial tear-off and collapse.
In order to determine the resistance to collapse, a 3D analysis model has been built using the explicit finite element (FE) program LS-Dyna.
In addition, the LS-Dyna results were compared with a simplified 2D FE approach, using the non-linear implicit solver MARC.
The 3D model allows for more complex sensitivities, such as curved pipe and carcass tension.
The FE analyses were based upon measured carcass profile geometries and material data from hardness measurements at several positions along the carcass profile, including effects of strain hardening during manufacturing.
Three different carcass profiles of three different risers were analysed. The study includes sensitivities on straight and curved pipe sections, axial preloaded carcass, carcass ovality, radial gap between carcass and pressure sheets and pressure increase velocity.
Collapse resistance of axial strained carcass and bent pipe is not well documented and this paper will highlight some of the observed effects.
The results from the FE analyses showed good correlation between the vendor data [2] both in shape of the buckling mode and capacity.
The Effect of Different Drilling Fluids on Borehole Mechanical Friction
Authors: Taghipour Ali , Ytrehus Jan David , Lund Bjørnar , Saasen Arild 
Published: September 2014

Mechanical friction is one of the most important aspects in highly inclined wellbores such as extended reach drilling (ERD) and through tubing extended reach drilling (TTERD). Friction caused by the contact between the drill string and the well casing or borehole is dependent to the drilling weight and fluid properties. Drilling fluids play an important role on mechanical friction and using oil based drilling fluids with higher lubricity can reduce torque and drag and minimize stick and slip concerns. Reducing mechanical friction will improve drilling efficiency in general, and will in particular enable longer reach for ERD wells.
This paper presents results from experimental laboratory tests where mechanical friction has been investigated in non-circular wellbore geometry. The experiments have been conducted as part of a research project in the tribology lab in Technical University of Luleå. The project was sponsored by the Research Council of Norway and four oil companies.
Friction behavior has been investigated for two different drilling fluids; water based and oil based drilling fluids both with and without solid particles. A pin on disc setup was used for these experiments where a spherical steel pin was sliding on a rotational disc made of granite. Friction force has been measured in constant sliding speed and in presence of particles in wet condition. The test results show that mechanical friction is smaller with oil based than water based drilling fluids in the presence of solid particles. In addition, the friction coefficient depends to the particle types and is higher when solid particles were added to the lubricants.
Such experiments in a tribology laboratory are important to identify the effect of drilling fluid on mechanical friction from a basic point of view isolated from the other wellbore parameters. Test results and the experimental approach could therefore be of value for any one working with drilling and well construction.
Assessment of Stabilized Phase-Field Lattice Boltzmann Method for Two-Phase Flows
Authors: Raman K. Ashoke , Lee T. S. , Jaiman Rajeev K. , Low H. T. 
Published: September 2014

The simulations of many offshore flow problems are currently facing the physics of complex mixtures of moving fluids. Typical situations where two-phase flow should be taken into account are slamming, wave breaking, slug flows, water entry, LNG sloshing and green water loading.
In the present paper, a recent approach based on phase-field Lattice Boltzmann for high density ratios is examined. This scheme uses two distribution functions, one for pressure and momentum and the other distribution function for density with a compact isotropic differencing scheme to discretize the intermolecular forcing terms. Stress form of the intermolecular forcing terms is used to model pressure and momentum distribution function for its momentum conserving properties while potential form of the intermolecular forcing term is used for order parameter. We discuss the numerical method and implement it by solving various benchmark problems and compare with analytical solutions and results from previous literature. The method alleviates the issue of spurious currents which is investigated through the verification of convergence of Laplace law for a stationary bubble followed by oscillating droplet problem. Then we analyse a case of rising bubble under buoyancy for different Eotvos and Morton numbers and compare it with results from previous literature. To assess the capability of the method to solve complex problems the case of droplet impact on thin film has been performed. This problem studied for different Reynolds Number to examine the phenomenon of splashing and deposition of the droplet on thin films. Finally the capability of the method to simulate offshore problems is demonstrated by studying the ocean wave breaking problem with the periodicity in the flow direction.
Deriving Robust Design Parameters and Design Criteria for the First Offshore Artificial Island for Electricity Conversion in the Northern North Sea
Authors: Haerens Piet , Vandenbroucke Tim , Mercelis Peter , De Wit Kathleen , Sas Marc , Steensels Marc 
Published: September 2014

In support of future wind farm developments and to anticipate the intentions to create a European wide smart electricity grid, an offshore high voltage grid in the Belgian North Sea is under development to connect several wind farms to the Belgian onshore electricity grid, called Belgian Offshore Grid (BOG). This grid will contain the first artificial island (AI) to support electricity conversion and transport in the North Sea. The AI will be part of an offshore high voltage grid that shall connect a number of offshore wind farms to an onshore high voltage station.
An accurate definition of site conditions and design criteria is of utmost importance for the design, operability and exploitation of the island and is the main driver for the cost of such islands. Deriving robust, but not over conservative site conditions and appropriate design criteria was one of the first challenges for the project. Based on in-situ measurements of geotechnical, geophysical and met-ocean conditions design parameters have been derived together with design criteria. This paper focuses on the methods and numerical models used to define the appropriate design input and the sensitivity analysis of the design criteria.
In order to derive robust but not over conservative design parameters not only in-situ measurements are required, but also a combination of statistical analysis, numerical models and sensitivity analysis of design criteria and functional requirements. One of the driving design criteria for such works is the allowable overtopping discharge and related hydrodynamic forces on the infrastructure on the island, which largely influences the cost.
A Bond Graph Approach to Improve the Energy Efficiency of Ships
Authors: Jafarzadeh Sepideh , Pedersen Eilif , Notti Emilio , Sala Antonello , Ellingsen Harald 
Published: September 2014

High fuel consumption coupled with increasing fuel prices, emission regulations and increasing concern about the environment, act as incentives to reduce the energy consumption of ships. However, different barriers hinder the adoption of cost-effective energy saving measures by ship owners and operators. These barriers are the reason for the existence of an ‘energy efficiency gap’ between the current level of energy efficiency and the potential for development of higher order efficiency. Imperfect information regarding the current level of energy consumption of vessels, availability and application of energy saving measures, and the impact of adopting these measures, form a group of so called ‘information barriers’.
The main objective of this article is to reduce those information barriers, as faced in shipping and more specifically in the fishing sector. The bond graph methodology is presented as a potential solution to these issues. It is utilized as a modeling and simulation method by which to visualize energy flow in a fishing vessel. The bond graph method is employed to estimate the fuel consumption of the vessel under different operational conditions: steaming, trawling and hauling of the fishing gear. It is also applied in pinpointing the major energy consuming apparatuses onboard the vessel. In this way knowledge regarding the current levels of energy consumption can be increased. The main energy consumers can then be studied to further improve energy efficiency knowledge and subsequently reduce the energy efficiency gap of the fishing vessel. Finally, the effectiveness of implementing a slow steaming strategy as a possible energy saving mechanism is studied.
Simulation-Based Analysis of Arctic LNG Transport Capacity, Cost and System Integrity
Authors: Erikstad Stein Ove , Ehlers Sören 
Published: September 2014

This paper presents a design case for arctic LNG transport, where liquefied gas is shipped from the Kharasevey terminal in Northern Russia to markets in US and Europe. Based on a fleet simulation model, the trade-off between the two main performance issues related to arctic transport are investigated; namely how to maintain transport system integrity in the harsh ice conditions, while maximizing the capacity utilization in a situation with considerable seasonal variations.
The fixed contract, single destination base case shows that meeting the requirements for a robust solution implies a low degree of utilization in the summer season. To improve upon this situation, several mitigating strategies are evaluated, including vessel speed and size changes, fixed and seasonally varying contract and market mix schedules, revision stop rescheduling, storage capacity extensions and backhauling.
The results indicate a high payoff from renegotiating the initial fixed schedule contract to allow for a higher degree of seasonal variations in the LNG deliveries. Further, increased storage capacity in loading port, combined with winter revision stops will have a significant impact on both fleet utilization and total system integrity. Flexible contracts that implies seasonal deliveries to the UK will help ensure continuous production and deliveries in winter season. Finally, surplus capacity gives opportunities for seasonal spot cargoes that could be exploited to increase fleet utilization rate.
Reel-Lay Method to Control Global Pipeline Buckling Under Operating Loads
Authors: Endal Geir , Giske Stein R. , Moen Kjetil , Sande Stian 
Published: September 2014

This paper presents a simple and cost effective method to control pipeline thermal buckling in the operational phase. The method is based on active use of the straightener system during reel-lay installation in order to create intermittent residual curvature sections in the pipeline. These residual curvature sections form ‘expansion loops’, in which deflection of the pipeline appears, and the result is controlled pipeline deflection and acceptable utilization at these locations under operational loads.
The method was first applied on Statoil’s Skuld project in 2012, using Subsea 7’s reel ship “Seven Oceans” for installation of a 26 km long 14″–16″ dual diameter pipeline in the Norwegian Sea. Implementation was performed at a small cost related to making the straightener adjustments and the effect on vessel time, and eliminated the need for other measures to control thermal buckling of the pipeline. For the Skuld project, engineering analysis demonstrated that the method would be superior to other methods with regards to both robustness and load controlled utilization in the pipeline under operating loads. Inspection survey during operation has verified the suitability of the method. The technique therefore has the potential to become a vitally important reel-lay method to control global pipeline buckling under operating loads.
Findings From Dissection and Testing of Used Flexible Risers
Authors: Skjerve Håvard , Kristensen Claus , Muren Jan , Søfferud Mario , Engelbreth Knut Inge 
Published: September 2014

During Statoil’s recent riser replacement project more than 30 used risers have been dissected onshore [1]. The main objective has been to reveal the root cause of carcass axial tearing failures. However, this also gave the opportunity to investigate details of other carcass damages, armor corrosion, annulus environment, external sheath breaches and polymer ageing as described in [5], [6] and [7]. This paper discusses some of the new knowledge obtained from the dissections.
New tools and methods have been developed for carcass pitch measurements in order to determine axial movements, maximum load level seen by the carcass and determine the utilization against tearing.
Offshore free-volume annulus testing and gas sampling is compared to liquid sampling and actual liquid found when dissecting, with significant deviations observed. Expected annulus environment is assessed in light of actual observed corrosion, with generally less corrosion than expected, however at some few selected areas significant corrosion attacks are found. Residual stresses and condition of polymer layers is quantified, with generally more degeneration and larger changes than anticipated before riser recovery.