bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of an Absorbing Boundary Condition in a Wave-Structure Interaction Problem
Authors: Duz Bulent , Huijsmans Rene H. M. , Borsboom Mart J. A. , Wellens Peter R. , Veldman Arthur E. P. 
Published: August 2013

For the design of offshore structures, an accurate assessment of the ability of the structure to survive in extreme sea conditions is of prime importance. Next to scaled model tests on the structure in waves, also CFD capabilities are at the disposal of the designer. However even with the fastest computers available, it is still a challenge to use CFD in the design stage because of the large computational resources they require.
In this study we focus our attention on the implementation of an absorbing boundary condition (ABC) in a wave-structure interaction problem. Unlike the traditional approach where the boundaries are located far from the object to avoid reflection, we gradually locate them closer while at the same time observing the influence of the absorbing boundary condition on the solution. Numerical calculations are performed using the CFD simulation tool ComFLOW which is a volume-of-fluid (VOF) based Navier-Stokes solver. Comparisons with experimental results are also provided and the performance of the ABC is discussed.
Modelling of Marine Riser Tensioner Load Variations and Implications for Minimum Top Tension Settings in Drilling Risers
Authors: Gallagher Conor , Williams Dara , Lang Donogh 
Published: August 2013

As the pace of deepwater oil and gas exploration continues to grow, so too does demand for modern drilling vessels with equipment capable of operating in water depths of 10,000ft or greater. These greater water depths place significant demands on the drilling riser and the riser tensioning system. Modern riser tensioners are complex hydro-pneumatic systems and far from applying a constant top tension, the stiffness and damping characteristics associated with the tensioner mean that the applied tension can vary substantially as the tensioner strokes in response to vessel heave. As a result it is critical that the riser tensioner system response be captured in sufficient detail when evaluating the loads on the drilling riser.
Riser tensioner systems for deepwater drilling must be capable of supplying the required tension to satisfy the minimum stability tension requirement, as per API RP 16Q; however this recommended practice does not adequately account for dynamic tensioner load variation, which can be up to 50% of the nominal tension. For deepwater drilling riser systems, where riser load limits are being approached, accurate modeling of the tensioner system load variation is required to ensure that the riser does not experience compression or excessive stresses. Furthermore, as the dynamic tension variations are largely velocity dependent, they can be relatively independent of water depth. Thus larger percentage variations in tension are experienced at low tensions when compared to higher tensions. This is an important consideration when calculating minimum top tensions for deepwater drilling rigs in shallower water depths.
This paper presents a comparison of the response of a direct-acting riser tensioner (DAT) system for a range of environments. The comparison is based on results from detailed tensioner models that include the individual hydraulic and pneumatic components of the tensioner system and that are fully integrated with a non-linear 3D structural FE analysis tool [1]. The FE model is based on a widely-validated-non-linear software tool [3]. The detailed tensioner model has been validated against manufacturer performance data for existing in-service tensioner systems. The detailed tensioner model has also been used as part of a drilling riser recoil analysis study [1] which provided a good comparison of recoil analysis results against a published recoil test case. The impact on the global riser response of accurately modeling the tensioner system behavior is demonstrated, while the implications for the calculation of minimum top tension are also discussed.
The Influence of Drilling Rig and Riser System Selection on Wellhead Fatigue Loading
Authors: Greene John F. , Williams Dara 
Published: August 2013

With drilling and exploration activity currently high in both deep and shallow water regions rig availability and selection is an issue for operators to consider in order to achieve the desired exploration schedule. At present the industry focus is on the development of 6th generation drilling rigs with the capacity to operate in increasing deep water. However despite the focus on deepwater exploration and the associated demand for deepwater drilling rigs there still exists demand for drilling rigs that can operate in shallow to moderate water depths (100m–500m). In addition, certain field development scenarios may exist where planned water depths for drilling activities vary significantly and therefore a drilling rig and riser system is required that can operate satisfactorily in both shallow and deep water depths.
For a given drill site, rig availability or well location, may be such that an operator may have to select a modern deepwater 6th generation rig for shallow water activities where a 3rd generation rig would appear to provide a better solution. Other considerations such as vessel station keeping requirements may lead to selection of a 6th generation rig over a 3rd generation rig, as the former tend to have improved DP thrusters capacity. However it is also important to note that while the 6th generation rigs may have been proven to be robust systems for operation in deep water, the response of a 6th generation drilling system in shallow water depths can be very different to that of an older 3rd generation rig and drilling riser system. Thus careful consideration must be made by the operator when considering the selection of drilling vessels for shallow to moderate water depths. Fatigue life of the wellhead is shown to be affected when one compares the response of the 6th generation and 3rd generation drilling systems in shallow to moderate depths. This also needs to be accounted for when selecting rigs for workover or intervention operations on older infrastructure.
This paper presents a discussion on the various parameters such as BOP stack size, riser, flex joint and vessel design that influence the response of the drilling system in shallow to moderate water depths (100m–500m). A number of case studies and parametric studies have been carried out and the results of these are presented in order to compare the wellhead fatigue damage from the older 3rd generation systems with the 6thgeneration systems and also to identify the critical drivers for this fatigue life reduction.
The Effects of Modelling Techniques and Data Uncertainty in Wellhead Fatigue Life Calculation
Authors: Williams Dara , Greene John 
Published: August 2013

Offshore oil and gas exploration continues to move into deeper and more harsh environments and consequently the response of drilling riser systems and associated fatigue loading transmitted to the wellhead and conductor system are of key importance in the design of offshore wells. In addition the presence of ageing infrastructure in mature areas combined with requirements for future workover operations requires careful consideration of both past and future fatigue damage accumulation. In order to estimate remaining fatigue life for the wellhead and conductor the accumulation of damage from each stage of a drilling campaign and phase of operation of a well, including workover and completion operations, must be considered. Thus a detailed global finite element analysis of the impact of riser response, under wave and vortex induced vibration (VIV), on the conductor and wellhead structure is of critical importance.
Traditional engineering evaluation methods to estimate fatigue of wellhead systems in offshore regions with limited availability of environmental data may result in an over estimation of fatigue damage accumulated in the wellhead. Any assumptions regarding fatigue current profiles can also lead to over-prediction of fatigue damage in the wellhead. This can have implications for the planning of future workover operations and may also lead to unnecessary over-design of the system. A further limitation of traditional wellhead fatigue evaluation criteria lies in the assumptions regarding riser tensioner system load response. These methods do not account for the highly nonlinear load response of the tensioner system and can thus significantly underestimate fatigue damage contribution.
This paper presents a more detailed wellhead fatigue analysis methodology to incorporate new analysis techniques, as used for a number of recent applications, to assess with a greater level of refinement the impact of the riser motions on the wellhead fatigue. Specifically this methodology incorporates the generation of a detailed global finite element model of the riser and wellhead system to include detailed non-linear riser tensioner system models, accurate models of the wellhead and conductor, detailed non-linear soil response characteristics and the use of more refined current data as input to VIV calculations.
The details of the riser and wellhead system model are presented and the conservatisms associated with traditional modeling methods with regard to VIV and riser tensioner load variations are discussed. A number of case studies are presented to illustrate the effects of various data assumptions and simplifications on estimated wellhead fatigue.
Development of Corrosion Resistant Steel for Bottom Plates of Crude Oil Tankers and Onboard Evaluation Results
Authors: Ito Minoru , Kaneko Michio , Nishimura Seiji , Sato Hidehiko 
Published: August 2013

Pitting corrosion on the bottom plates of cargo oil tanks (COT) in very large crude carriers (VLCC) is very serious problem. Each tank may suffer up to 1,000 pits, with some reaching a depth of as much as 10 mm. As a result, the workload of repairing such pitting corrosions in periodical dock inspection is extremely heavy. Many studies have already been conducted to clarify the mechanism of pitting corrosion, but it has yet to be fully understood.
We have clarified the pitting corrosion mechanism through onboard research on some VLCCs and various corrosion tests, in addition to the findings obtained by previous studies. Based on our understanding of the mechanism, we developed a corrosion test method to simulate the corrosive environment within the pits. Furthermore, we developed a new corrosion resistant steel (CRS) with trace amounts of alloying elements. The corrosion rate for CRS is less than one-fifth of conventional steels. Due to its very low alloy content, the weldability and mechanical properties of CRS remain similar to conventional steels. This CRS has already been applied to several VLCCs and we have examined its corrosion resistance through onboard investigations of the two VLCCs. One was for all its uncoated COT bottom plates, which were built of CRS, at the first docking (after 2.5 years). No pits deeper than 4 mm were found in the bottom plates of any COTs. Also, only about twenty pits of 2∼4-mm depth were found. The other was for the bottom plates of six unpainted COTs built of CRS at her first and second dockings (after 2.3 and 5 years). At five years, tens of pits deeper than 4 mm were found in all, but the pit count was much lower than that of VLCCs constructed of conventional steel. Thus, the good corrosion resistance of CRS was confirmed. In addition, it was also revealed through onboard research during a dock inspection that pit growth halted on VLCCs with more than five years service.
SOLAS II-1 Cargo Oil Tank Corrosion Protection, which adopts the test method developed by us as the qualification test for bottom plates, comes into effect in 2013. In addition, CRS has already been certified by Class NK as corrosion resistant steel for COT bottom plates.
CRS is set to play its part in the safe navigation of oil tankers. Furthermore, CRS does not require a protective coating of paint, which also benefits the global environment by reducing the use of volatile organic compounds.
A Validation of Various Codes Using Hydrodynamic Wedge Impact Data
Authors: Jiang Minyee , Lien Van , Lesar Douglas , Engle Allen , Lewis Richard 
Published: August 2013

It is well known that slamming and whipping can significantly contribute to a ship’s structural loading which can severely impact a ship’s operational safety. Therefore, a method of predicting severe transient structural loads is needed, especially for the design of future high-speed patrol boats and high-speed ferries. A number of computational fluid dynamics (CFD) codes have demonstrated the ability to cope with complex body shapes and to numerically capture the nonlinear effect of hydro-elasticity. However, validation is scarce both due to a lack of experimental data and the computational intensity of the problem.
This paper describes a validation study of a Reynolds averaged Navier-Stokes (RANS) code (STAR-CCM+) and a Lagrangian-Eulerian fluid structure interaction (FSI) code (DYSMAS) using 10 degree wedge drop test experimental data obtained at the Naval Warfare Center, Carderock Division, December 2010.
Strength and Reliability of Ships ‘As-Built’
Authors: Žiha Kalman , Kodvanj Janoš , Ljubenkov Boris , Dupor Nikola , Bakić Ante 
Published: August 2013

This report firstly presents the rule based scantlings and sectional properties of the example ship defined by using the nominal properties of mild shipbuilding steel. It also describes the way of collection of characteristic material specimens of rolled steel plates and bars delivered by the steel manufacturer to the shipyard for to the example ship.
Secondly it summarizes the results of tensile testing in the Laboratory for experimental mechanics of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb of plates and bars denoted here as ‘in-built’ material properties for the example ship according to the production plans.
The report then reminds on the rule based material properties for acceptance purposes. Next it considers the influence of ‘in-built’ mechanical properties with respect to the rule requirements on local, global and ultimate strength of ships. The report discusses material properties other than yield strength, which participate in the assessment of the overall ship safety such as the weld strength, buckling and fatigue strength, low temperature behavior, corrosion and reliability.
The results of the tensile testing of ‘in-built’ materials are then applied to checking of the local, global and ultimate ‘as-built’ strength of the example ship’s hull instead of the ‘as-designed’ strength defined by the nominal material properties.
The report at the end discusses the differences between the ‘as-designed’ and the ‘as-built’ hull strength, fatigue life and reliability. It suggests minimization of the hull strength uncertainties by adopting the mechanical properties of ‘inbuilt’ materials. The conclusion supports the stirring idea of this report that in addition to the ‘as-designed’ strength, a ship deserves individualized assessment of the “as-built” ship hull strength based on the measured realistic ‘in-built’ properties.
Risk Mitigation Through the Application of New Power Umbilical Technology
Authors: Dobson Alan , Frazer Steven 
Published: August 2013

This paper describes the substantial service life improvements that can be achieved through a new, high technology solution developed for deep water electrical power umbilical and cable applications. The new design represents an enabling technology for power cable projects in the deepest and most dynamic waters, provides a lower risk solution for risers in highly stressed conditions and can give a technically improved solution for the range of electrical power umbilical application.
The significant advantages of aluminum alloy cable bundles over traditional copper cable bundles under static and dynamic loading associated with a typical deep water floating installation are presented. A design case study is used to illustrate improvements in structural response and fatigue life associated with the aluminum alloy cable cores against conventional technologies. The paper concludes with an overview of the associated risk reduction through the implementation of the aluminum alloy cables in the form of a failure mode and effect analysis.
Full Scale Sour Fatigue Testing With Dense Phase Gases
Authors: Vargas Pedro M. , Crowder Ben , Yu Weiwei , Mishael Sam , Armstrong Keith 
Published: August 2013

The petrochemical industry is very interested in the sour service fatigue performance of girth welded steel pipes. As a result several papers are published every year addressing this issue, and several Joint Industry Projects (JIP) are currently underway addressing different aspects of sour service performance of steel pipelines. To date research work has focused on quantifying the fatigue performance via small scale specimens due to the difficult and danger in dealing with H2S. Currently a JIP is underway that promises to provide full scale fatigue performance of pipeline welds under sour service.
This paper documents the knockdown-factor-on-life (KD) determination for full scale sour service testing. In an industry first, a very difficult full scale sour service test was performed: 1) High Pressure, 2) High content of H2S, 3) Dense phase gases with ultra low water content (less than 400 ppm), and 4) Loading rate of 0.01 Hz. The loading was applied in full longitudinal tension. The full scale sour tests are compared with full scale in-air tests to obtain the knockdown factor. Resource constraint limited the number of full scale tests to 3.
The main objective of the tests for the practical application was to ensure that the usage of crack growth based knock-down factors, i.e. the use of Fatigue-Crack-Growth-Acceleration-Factor (FCGAR) from small scale fracture mechanics specimens, was reasonable and conservative.
Some additional comparisons are done with crack-growth based knockdown factors that may help explain the effect of the ultra-low water concentration. Knockdown factors from small scale crack growth specimens, Fatigue-Crack-Growth-Acceleration-Factor = 60 (FCGAR), are significantly higher than the full scale results, KD = 7. The ultra-low-water dense phase gases do not pit the surface, thus leaving the initiation life relatively intact. The knockdown factor for the full scale test is then mostly the result of the accelerated crack growth that occurs once a macro-crack nucleates.
Analysis of the Physics of Bilge Keel Vortex Generation
Authors: Minnick Lisa , Bassler Christopher , Percival Scott 
Published: August 2013

A 2D forced roll oscillation experiment was performed to examine and characterize the physics of vortex generation from ship bilge keels. Measurements included ship model motions, normal force on the bilge keels, and flow field visualizations using Particle Image Velocimetry (PIV). Data was collected for a range of roll oscillation amplitudes, including large amplitudes where the bilge keels interacted with the free surface and for three roll oscillation frequencies.
This paper presents analysis and description of the observed phenomena, and examines whether a functional relationship can be established between the force measured on the bilge keel and the flow field generated by the bilge keel. A qualitative discussion of the observed flow characteristics, including the vortex generation at the tip of the bilge keel, detachment, and interaction with the free-surface, is presented. In addition, the circulation in front and behind the bilge keel was calculated, analyzed, and compared to the measured bilge keel force. The analysis conducted was intended to provide improved understanding of the phenomena which occur during bilge keel vortex generation and aid in the development of improved roll damping and bilge keel force models for the prediction of ship motions.
Fatigue Life Analysis for a Steel Catenary Riser in Ultra-Deep Waters
Authors: Rodrigues Marcos V. , Ferraz Caroline , da Silva Danilo Machado L. , Nabuco Bruna 
Published: August 2013

With new discoveries in the Brazilian Pre-Salt area, the oil industry is facing huge challenges for exploration in ultra-deep waters. The riser system, to be used for the oil transportation from seabed to the production unit, is one of them. The definition of riser configurations for ultra-deep waters is a real challenge. Problems have being identified for flexible risers, hybrid risers and steel catenary risers (SCR) configurations to comply with rules requirements and criteria in water depths of 2000m.
The objective of this work is to present a study on the fatigue behavior of a Steel Catenary Riser in 1800m of water depth. One of the main challenges for SCRs in ultra-deep waters is the fatigue, due to platform 1st order motions, at the touch down zone (TDZ).
A case study is presented for a Steel Catenary Riser connected to a semi-submersible platform. The influence of some design and analysis parameters is studied in order to evaluate their impact on the SCR fatigue life. The main parameters to be evaluated in this work are: The mesh refinement, in the global analysis, at the Touch Down Zone; The internal fluid density variation along the riser, and; The 1st order platform motions applied to the top of riser; In addition to the results of this paper, some highlights are presented for SCR analysis in similar conditions.
Drill String Strength Evaluation for Deep Earthquake Zone Drilling
Authors: Inoue Tomoya , Kyo Masanori , Sakura Koji , Fukui Toshihiko 
Published: August 2013

The scientific drilling vessel Chikyu was designed to have the deep drilling capability to reach the deep earthquake zone. To realize such deep drilling, a drill pipe with higher than ever strength and reliability is of necessity. A strength evaluation of such high strength drill pipe is also necessary.
Around Japan, the earthquake zones are widely located under the seabed in deep water. For example, the Nankai Trough located beneath the ocean off the southwest coast of Japan is one of the most active earthquake zones where large-scale earthquakes have occurred repeatedly throughout history. Thus, the Chikyu has started the first scientific drilling at the Nankai Trough as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). NanTroSEIZE targets the megasplay fault zone at 3500 m below the seafloor and finally 6000m deep drilling into the seismogenic zone and across the plate interface into the subducting crust at water depths of around 2500m. In addition, a huge earthquake zone is expected to be located about 1000m below the seafloor at water depths of around 7000m. For this drilling task, the riserless drilling technique should be applied.
To realize such deep drilling with both riser and riserless techniques, a S150 drill pipe was developed during the construction phase and has been used in the past scientific drillings of the Chikyu. For deeper drillings in the future and drilling operations in harsh environments, we are developing superior high strength drill pipes, S155 and S160, possessing high reliability including corrosion resistance to achieve high toughness and reduction of stress concentration. An evaluation of the maximum possible stress was conducted. In the maximum strength evaluation, we considered dynamic stress and bending stress due to the current and the vessel inclination.
This paper describes the development of superior high strength drill pipes and the strength evaluation of such drill pipes for deep earthquake zone drilling.