bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind/Wave Basin Verification of a Performance-Matched Scale-Model Wind Turbine on a Floating Offshore Wind Turbine Platform
Authors: Kimball Richard , Goupee Andrew J. , Fowler Matthew J. , de Ridder Erik-Jan , Helder Joop
Published: September 2014

In 2011, the DeepCwind Consortium performed 1/50th-scale model tests on three offshore floating wind platforms at the Maritime Research Institute Netherlands (MARIN) using a geometrically scaled model of the National Renewable Energy Laboratory (NREL) 5 MW reference turbine. However, due to the severe mismatch in Reynolds number between full scale and model scale, the strictly Froude-scaled, geometrically-similar (geo-sim) wind turbine underperformed greatly, which required significant modification of test wind speeds to match key wind turbine aerodynamic loads, such as thrust. The conclusion from these prior efforts was to abandon a geometrically similar model turbine and use a performance-matched turbine model in its place, keeping mass and inertia properties properly scaled, but utilizing modified blade geometries to achieve required performance at the lower Reynolds numbers of the Froude scaled model. To this end, the University of Maine and MARIN worked in parallel to develop performance-matched turbines designed to emulate the full scale performance of the NREL 5 MW reference turbine at model scale conditions. An overview of this performance-matched wind turbine design methodology is presented and examples of performance-matched turbines are provided.

The DeepCwind semi-submersible platform was retested at MARIN in 2013 using the MARIN Stock Wind Turbine (MSWT), which was designed to closely emulate the performance of the original NREL 5 MW turbine. This work compares the wind turbine performance of the MSWT to the previously used geometrically scaled NREL 5 MW turbine. Additionally, turbine performance testing of the 1/50th-scale MSWT was completed at MARIN and a 1/130th-scale model was tested at the University of Maine under Reynolds numbers corresponding to the Froude-scaled model test conditions. Results from these tests are provided to demonstrate effects on model test fidelity. Comparisons of the performance response of the geometrically matched turbine to the performance-matched turbines are also presented to illustrate the performance-matched turbine methodology. Lastly, examples of the fully dynamic floating system performance using the original geometrically scaled NREL 5 MW turbine and the MSWT are investigated to illustrate the implementation of the model test procedure as well as the effects of turbine performance on floater response. Using the procedures employed for the MARIN tests as a guide, the results of this work support the development of protocols for properly designing scale model wind turbines that emulate the full scale design for Froude-scale wind/wave basin tests of floating offshore wind turbines.
Ship Structural Design Support Methodology for the Reliability Based Design Optimization (RBDO)
Authors: Žanić Vedran , Pirić Karlo , Prebeg Pero
Published: September 2014

The objective of the paper is to present the structural design support system (DeSS) rationale for the reliability based design optimization (RBDO) in the concept design phase. Basic steps are as follows:

• Interactive identification of the design problem (design variables, constraints, objectives) as well as design problem variates and their distribution parameters. Safety related design criteria are used as objectives and as constraints in the presented procedure;

• Calculation of the cross section ultimate longitudinal strength criteria based on the extended Smith’s method; based on the Report SSC-398;

• Selection of non-dominated designs (Pareto-optimal, NDD points) for the given deterministic design criteria;

• Calculation of reliability/deterministic safety measures. Novel FASTREL code, based on the Dimension Reduction Method (DRM) is used for the reliability calculations;

• Generation of insight into the Multi Attribute Decision Making (MADM) process with 5D graphic presentation of designs in design and attribute spaces in the interactive OCTOPUS Designer (Demak/DeView) IT modules.

Practical application of the developed concept design methodology and of the design environment to the structural design of the verifiable test example corresponding to SSC-398 report. DeSS was used in fast generation of optimal designs using MODM (MOSLP) and MADM (MOPSO) techniques. To speed up the RBDO design process deterministic and probabilistic formulations of design problem were run concurrently and supporting each other are presented using the safety related design attributes (deterministic and reliability based) for the NDD supported decision-making technique.
Influence of Rigid Body Motions on Rotor Induced Velocities and Aerodynamic Loads of a Floating Horizontal Axis Wind Turbine
Authors: de Vaal Jacobus B. , Hansen Martin O. L. , Moan Torgeir
Published: September 2014

This paper discusses the influence of rigid body motions on rotor induced velocities and aerodynamic loads of a floating horizontal axis wind turbine. Analyses are performed with a simplified free wake vortex model specifically aimed at capturing the unsteady and non-uniform inflow typically experienced by a floating wind turbine. After discussing the simplified model in detail, comparisons are made to a state of the art free wake vortex code, using test cases with prescribed platform motion. It is found that the simplified model compares favourably with a more advanced numerical model, and captures the essential influences of rigid body motions on the rotor loads, induced velocities and wake influence.
Deepwater Production TTR Design
Authors: Blaquiere Andrew , Reagan Daniel , Thethi Ricky
Published: September 2014

As the majority of “easy access” reservoirs have been discovered, deep water exploration and production is at the forefront of the Oil & Gas industry. Operators have utilized Top Tensioned Riser (TTR) systems in deepwater on Spar and TLP platforms and are now well established in the US Gulf of Mexico (GoM), West Africa and Asia. However, new reservoirs, particularly in the US Gulf, will be discovered in ultra-deep water (∼10,000 ft) with high pressure (HP) (>15 ksi) and high temperature (HT) (>284 °F). In such conditions, the criticality and complexity of a production TTR system is significantly increased. This paper addresses key design issues and considerations including wall thickness sizing, material selection, manufacturing capabilities, interface management and qualification testing.
Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy
Authors: Gravråkmo Halvar , Strömstedt Erland , Savin Andrej , Svensson Olle , Leijon Mats
Published: September 2014

A wave energy converter (WEC) of point absorber type is tested at the west coast of Sweden. The buoy is a vertical cylinder. The linear generator on the seabed has limited stroke length. Large waves cause the generator to reach its maximum stroke length. As this happen, a spring in the generator is compressed, causing the buoy to instantly come to rest. During this process the force between the buoy and the generator is measured. Also the acceleration of the buoy is measured. This process and the extreme forces on the generator hull is described and the study shows that the magnitude of this force is greatly influenced by the added mass of the buoy and thus the buoy geometry. The ratio between the extreme forces on the hull and the forces during normal operation will affect the dimensioning and economy of the WEC. Force acting between generator and buoy were measured during various events as the WEC was operating. Heave added mass was derived from the measurements and found to be greater than the theoretical value.
Scour Prediction Offshore and Soil Erosion Testing
Authors: Whitehouse Richard J. S. , Harris John M.
Published: September 2014

The analysis of the flow mechanisms causing scour in the marine environment combined with a conceptual model for scour in different seabed soils are applied to demonstrate how erosion testing can be used to support detailed assessments of scour. The important role of scour hazard assessment and scour monitoring in the life-cycle management of offshore assets is also assessed.
Development and Application of Trim Optimization and Parametric Study Using an Evaluation System (SoLuTion) Based on the RANS for Improvement of EEOI
Authors: Lee Jisun , Yoo Seonoh , Choi Sangkyu , Kim Heetaek , Hong Chunbeom , Seo Jongsoo
Published: September 2014

In general, the speed power performance of ships is optimized for design speed and draught in accordance with the contract condition. But, the contract condition may not be always the same as the actual operating condition. Therefore, in order to reduce the fuel consumption practically, it is necessary to optimize the performance under various conditions considering the actual voyage. This is the reason that the trim optimization covering various operating profiles becomes the main issue in reducing fuel oil consumption.

In this paper, a numerical study is carried out to optimize trim conditions through the computational evaluation system called SoLuTion developed by Samsung Heavy Industries Co. (SHI) with variation in draught, ship speed and voyage trim. In order to get more accurate results in resistance and self-propulsion performance, the Reynolds-Averaged Navier-Stokes (RANS) equations including Volume of the Fluid (VOF) method by Hirt and Nichols (1981) for free-surface boundary condition and moving mesh technique for propeller rotation effect are employed as governing equations. Reynolds Stresses Model (RSM) with the wall function is applied as a turbulence model for turbulent flow computation.

Through this study, the followings are the main three factors to be considered in evaluation of the quantitatively accurate speed performance by varying the draught, speed and voyage trim. First, the distance from hull surface to the first grid point should be adjusted to eliminate the effects of frictional resistance. Second, the grid system should be generated to avoid the grid dependency on variation of draught. Finally, the running trim and sinkage of the voyage conditions should be considered. The results of the trim optimization performed numerically are well-matched with the towing test results conducted at Samsung Ship Model Basin(SSMB). As the results of this study, it is confirmed that SoLuTion is a useful and efficient tool for trim optimization and the provided optimum trim will be able to contribute to fuel savings under the operating conditions. From trim optimization study, it is found that there is certain level of effects due to the bulb and transom immersion to find the optimum trim condition. Also SoLuTion is applicable not only to trim optimization but also to parametric studies in optimum shape of the ships considering the actual operating profile.
New Advances in Post-Installed Subsea Monitoring Systems for Structural and Flow Assurance Evaluation
Authors: Asgharzadeh Shishavan Reza , Brower David V. , Hedengren John D. , Brower Alexis D.
Published: September 2014

An overview of fiber optic sensors for temperature, pressure, strain, and fatigue of subsea structures is provided. Current progress details efforts to ensure proper installation and bonding to existing risers, flow-lines, mooring lines, trees, and other structures in actual subsea environments. Developments include clamp prototypes, bonding techniques, long-term fatigue analysis, sensor calibration, and temperature compensation.

Fiber optic technology in subsea monitoring began over 20 years ago by migrating expertise from decommissioning of rocket motors. The first installations were on new installations of subsea pipelines, production risers, and drilling risers to measure strain and vibration for fatigue life monitoring. Of particular interest for these systems were detecting riser vortex induced vibration and strain throughout the touchdown zone. A prior limitation was that sensor installation was only performed top-side on new subsea equipment. This recent work demonstrates the capability to deploy on existing subsea equipment.

The novel contributions of this study are the developments that optimize the clamp design, bonding techniques, and factors that allow long-term service life. Button pull tests validate long term service life after the clamps are subjected to accelerated aging tests. Details on the subsea calibration also provide insight on the recent progress with post-installed sensors.

The purpose of reliable post-installed advanced sensors is not only to detect failures of subsea infrastructure but also to warn of signs of fatigue or hydrate formation that contribute to catastrophic failures. The calibration and testing mentioned in this paper are part of the Clear Gulf study, a collaboration formed in 2010 between the offshore energy industry and NASA. The study continues to make advances in highly sensitive monitoring systems that anticipate failures, catastrophic events, and flow assurance issues.
Preliminary Verification and Validation of WEC-Sim, an Open-Source Wave Energy Converter Design Tool
Authors: Ruehl Kelley , Michelen Carlos , Kanner Samuel , Lawson Michael , Yu Yi-Hsiang
Published: September 2014

To promote and support the wave energy industry, a wave energy converter (WEC) design tool, WEC-Sim, is being developed by Sandia National Laboratories and the National Renewable Energy Laboratory. In this paper, the WEC-Sim code is used to model a point absorber WEC designed by the U.S. Department of Energy’s reference model project. Preliminary verification was performed by comparing results of the WEC-Sim simulation through a code-to-code comparison, utilizing the commercial codes ANSYS-AQWA, WaveDyn, and OrcaFlex. A preliminary validation of the code was also performed by comparing WEC-Sim simulation results to experimental wave tank tests.
Ice Nonsimultaneous Failure, Bending and Floe Impact Modeling for Simulating Wind Turbine Dynamics Using FAST
Authors: Yu Bingbin , Karr Dale G. , Sirnivas Senu
Published: September 2014

Many promising locations for developing offshore wind energy are in cold regions. This type of environment introduces one important technological challenge for offshore wind turbine design: the impact of floating surface ice. Recent developments to add an ice-loading module to the wind turbine computer-aided-engineering tool FAST are described in this paper. These efforts enable FAST, developed and maintained by the National Renewable Energy Laboratory, to simulate the impact of ice on offshore wind turbines. The ice-loading module includes different ice mechanics models that address various ice properties, failure modes, and ice-structure interaction mechanisms. In a previous OMAE symposium paper, models for quasi-static crushing, transient dynamic ice breakage, and random forcing for the ice module were described.

In this paper, three new models are presented. One model evaluates the ice-loading effective pressure reduction caused by ice nonsimultaneous failure in discrete local zones across the contact area. The second model generates time-dependent ice forces on conical structures caused by bending failure. The third model is used to simulate large ice floe interaction with wind turbine support systems. This third model describes ice forces that are limited by momentum or splitting failure of ice floes. These models are integrated in the FAST modularization framework and allow for the simulation of coupled ice force, ice floe motion, and wind turbine structure response. This paper also presents example numerical simulation results of wind turbine dynamics using FAST coupled with these three new models.
Ocean City Planning in the Waters of Okinotorishima
Authors: Watanabe Yoshiyasu , Yoshida Koichiro , Nambara Takeshi
Published: September 2014

Okinotorishima is the Japanese southernmost tropical island and has the exclusive economic zone (EEZ) of about 430,000km2 area. It is located approximately 1,700km away from Tokyo and 1,100km away from Okinawa and consists of a coral reef of 7.6km2 area and two islands within the reef. In the waters of Okinotorishima, sea bottom mineral resources such as manganese nodule and cobalt rich manganese crust, biological resources such as fish and renewable energy resources such as ocean thermal energy conversion (OTEC), wind force and solar power are promising.

The objective of this research is to propose an OCEAN CITY Planning to administrate and utilize Okinotorishima and its surrounding waters (EEZ) and to report the development of mechanical connector, which is a key technology to construct the OCEAN CITY in its waters. In the OCEAN CITY, economic activity, research and development (R&D) activity and sightseeing/leisure activity are performed based on the resources mentioned above. The proposed OCEAN CITY consists of a semisubmersible floating ring structure and a semisubmersible floating rectangular runway. The ring structure and the runway are constructed with mechanically connected multiple floating units of about 300m length each. Both semisubmersible structures are also connected by mechanical connectors. In this paper, it is shown that the OCEAN CITY can produce electricity, water and food for the use in the city and for the sale outside the city. It is also shown that the mechanical connector, which is indispensable for very large floating structures such as the proposed OCEAN CITY used in open seas, has been promisingly developed.
Three-Dimensional Hydroelastic Dynamic Analyses Including Torsion for a Large Floating Platform in Frequency and Time Domains
Authors: Kang H. Y. , Kim M. H.
Published: September 2014

Recent increasing demands for more ocean energy and space utilization require larger scale of offshore structures, and the large scale leads to needs for comprehensive hydroelastic analysis to accurately account for the interaction of the floating body’s deformation with waves or other environmental loads. In this study, as generalization of the previous hydroelastic analyses by the present authors [4, 5], the three-dimensional hydroelastic analysis including torsion is achieved. Ocean wave is assumed to be potential flow. The example large-scale floating body studied here is 480 m long and 400 m wide with 8 m draft. It is modeled by 7857 elastic plate elements which have 6 degrees of freedom at each element. Modal analysis by finite element method (FEM) for all free boundary conditions is conducted and provides mode shapes, modal inertia/stiffness, and dry natural frequencies. The mode shapes are verified against experimental results by Leissa [10]. Using the mode expanded boundary element method (BEM), hydroelastic dynamics is first solved in frequency domain. Subsequently, the large flexible platform is applied to irregular waves in time domain. To investigate the three-dimensional dependency of dynamics, a series of oblique waves are applied as well as head waves, and the dynamic responses of the elastic system are systematically analyzed. Considering remarkable effect of added mass due to large submerged volume, its effects on elastic modes and resonance phenomena are also investigated. To validate the accuracy, pertinent verifications are carried out for both frequency and time domains.
Drifting Time of a Standard Drillship
Authors: Teixeira Fernando J. R. , Oshiro Anderson T. , Tannuri Eduardo A.
Published: September 2014

This paper presents a methodology in order to perform a drift off calculation for drillships according to given parameters such as: environmental conditions and water depth. Drift off occurs when there is insufficient thruster force so that the vessel is drifted away from the target position by the environmental forces. For a safe operational drillship it is expected that the drifting off will be resumed in due time when blackout recovery system starts running and, therefore, enough thrust takes place. Water depth plays an important role when considering the default maximum release of Lower Flex Joint (LFJ) angle for physically disconnecting, which is 10 degrees in the majority of suppliers. This methodology is intended to be applied to drillship design, by comparing the time to stop drifting and the distance from the reference point after a total blackout occurs.

Electrical generators sets installed in drillships are designed to work with extreme environmental conditions. Since there is an excess of installed power for the majority of the operational time, drillships often operate with all high voltage busbars connected to each other improving engine efficiency, decreasing levels of pollution emissions and reducing maintenance. The use of this electrical power configuration is possible because there is no need to turn on all generators at the same time, but only the ones that are needed on that particular moment. However, when a single failure such as a short circuit occurs and the system is not prepared to disable and segregate the failure, all electrical system will crash, causing a total blackout and the drillship will start to drift off.

The drifting off time was obtained by numerical simulations conducted by modeling a standard drillship using time domain software. The model took into consideration the vessel hydrodynamics under environmental conditions (wind, current and wave), the drag force in marine drilling riser, and the thrusters in Dynamic Positioning (DP) operation.

The simulation is divided into three steps: First, the behavior of the DP system in full operation is simulated until system is stable. After that, all thrusters are turned off to simulate a total blackout. Finally, since the ship will not stop immediately because of its inertia, a time range for the ship’s inertia was also considered and this time is added to the pre-established blackout duration.

The conclusion of the study shows how parameters as water depth, environmental conditions, and blackout recovery time affect the necessary time to stop drifting off, so as to foresee that after a total blackout the standard drillship will remain in safe limits.
Analysis of High Pressure Zone Attributes From Tactile Pressure Sensor Field Data
Authors: Richard Martin , Taylor Rocky S.
Published: September 2014

Tactile sensor data collected during the Japan Ocean Industries Association (JOIA) medium-scale field indentation test program provide detailed information about spatial and temporal distributions of contact pressures during ice crushing. The localization of contact into high pressure zones (hpzs) through which the majority of loads are transmitted to the structure is an important feature of these data. For all but the slowest interaction rates, non-simultaneous failure is observed, with linear distributions of hpzs comprising a total contact area on the order of 10% of the nominal interaction area (structure width × ice thickness). To improve understanding of the nature of individual hpzs during compressive ice failure, a new approach to analyzing tactile sensor data has been developed. Analysis algorithms developed for automatic hpz detection and tracking are discussed. Issues associated with pressure threshold value definition and selection are considered. Probabilistic descriptions of high pressure zone attributes based on analysis of JOIA field measurements are presented. The development of a probabilistic ice load model based on these hpz data is detailed in a companion paper.
Mooring System Monitoring Using DGPS
Authors: Minnebo Joerik , Aalberts Pieter , Duggal Arun
Published: September 2014

Over the recent years, the need for active monitoring of offshore production facilities has increased. Due to significant amount of mooring line failures in the recent past, permanent mooring systems for Floating Production Units such as FPSO’s, FSO’s and future FLNG’s are typically required to have active monitoring systems to provide feedback of the mooring system’s status, performance and integrity.

This paper will address some of the offered solutions with regards to active mooring system monitoring. Some pros and cons are given for several techniques within the industry currently available, and then a simple but elegant alternative is proposed. With the use of position monitoring, for instance with GPS signals, qualitative and quantitative feedback can be provided on the status of the permanent mooring system. A detailed explanation is given backed up by a few real life examples in which such a system was used to quickly assess the status of the mooring system.
Structural Integrity Assessment of Independent Type ‘C’ LNG Carriers
Authors: Wang Bo , Shin Yung-Sup , Wang Xiaozhi
Published: September 2014

The objective of this paper is to present a complete procedure for strength evaluation of independent Type ‘C’ LNG carriers. This strength evaluation procedure includes two main parts, global finite element (FE) analysis mainly for hull structure evaluation and detailed FE analysis for tank and saddle supporting structures. A global FE model with three tanks including hull, tank and saddle supporting structures is used for structural analysis. Static and dynamic loads are applied to the global FE model as design load cases for the total strength assessment (TSA). FE analyses on the three tanks model have been performed and verified by the developed acceptance criteria to evaluate the safety adequacy of yielding, buckling, and fatigue of the hull and supporting structures. Additionally, a detailed FE model for a pressurized tank and its saddle supports is made, which consists of major components including tank shell, ring stiffeners, longitudinal central bulkhead, and saddle supports. An FE stress analysis of the pressurized bi-lobe tank with saddle supports considering the hull deflection effect has been carried out under internal pressure, dynamic loads due to ship motion, and thermal loads. Finally, an FE buckling analysis of the bi-lobe tank has been carried out under external pressure following gas carrier (IGC) code requirements. Meanwhile, acceptance criteria are developed for yielding and buckling strength evaluation of pressurized bi-lobe tanks according to the ASME Boiler and Pressure Vessel (BPV) Code. An independent Type ‘C’ bi-lobe LNG vessel has been utilized to implement the presented evaluation procedure. Finally, a complete procedure for evaluating the structural strength of cargo tank structures, supporting members and hull structures has been developed for an independent Type ‘C’ LNG carrier.
Multiscale Finite Element Analysis of Unbonded Flexible Risers
Authors: Edmans Ben , Pham Dinh Chi , Zhang Zhiqian , Guo Tianfu , Narayanaswamy Sridhar , Stewart Graham
Published: September 2014

Unbonded flexible risers are a key technology in existing and proposed offshore developments. With increasing water depth, the demands on risers increase and the design against hydrostatic and tension loads becomes more of a challenge. In addition, many existing subsea production systems are approaching the end of their design life and operators need to know if they can remain in-service.

To enable the benefits from deepwater production and life extension projects to be realized while minimizing risks to life, property and the environment, accurate modelling and analysis tools are required to improve the prediction of failure modes and to develop a better understanding of the conditions leading to progressive failure. In this work, a multi-scale approach is adopted whereby a global dynamic analysis model is employed to determine the overall displacements of the riser and this is linked with a local model that can provide accurate forces and stresses for the prediction of collapse, fatigue damage and buckling of tensile armour wires.

Firstly, we describe a nonlinear constitutive model for use in large-scale dynamic analysis of flexible risers based on an analytical homogenization of composite cylinders using the analogy between slip between pipe layers and plastic flow in continua. The model is able to reproduce the bending hysteresis behaviour observed in flexible pipes and its dependence on internal and external pressure. Secondly, we show a procedure for obtaining equivalent material parameters for this model from finite element local analyses of a flexible pipe. Finally, we show the implementation of this constitutive model in a riser system using two-dimensional co-rotational hybrid beam finite elements.
FloVAWT: Further Progresses on the Development of a Coupled Model of Dynamics for Floating Offshore VAWTS
Authors: Collu Maurizio , Borg Michael , Shires Andrew , Rizzo Francesco N. , Lupi Emilio
Published: September 2014

Interest in potential wind farm sites in deeper waters and further offshore has substantially increased recently, and in parallel an increased interest towards floating, rather than bottom-fixed, offshore wind turbines: the Energy Technologies Institute (UK) recently announced a plan to invest £25m in offshore floating wind turbine projects. Furthermore, a recent document by the UK LCICG (Low Carbon Innovation Coordination Group), demonstrated that the “Development and demonstration of new concepts such as floating foundations for water depths >60m”, has a value in meeting emissions targets at low cost of up to £13bn. The present article is a follow on with the previous article presented at OMAE 2013 [1], in which the progresses on the development of an aero-hydro-servo-elastic coupled model of dynamics for VAWT are illustrated, called FloVAWT. The further progresses presented consist in: a) the model, in particular the hydrodynamic module, has been now validated against experimental data provided by the DeepCwind project (see OC4) for the semi-submersible support structure configuration, b) the additional velocity component due to the 6 degree-of-freedom motion of the supporting floating structure are now taken into account within the aerodynamic module, while previously only the displacement imposed by the support structure was considered, c) a new module dedicated to the mooring system has been developed and validated, capable of modelling catenary mooring systems with a quasi-static, energy-based approach. Some of the new capabilities of the program are illustrated through a case study of a Darrieus-type VAWT rotor coupled with the OC4 semi-submersible support structure. Comparisons with the previous version of the program are presented, giving an insight on the relative importance of the additional aspects taken into account.
Application of CFD to Predict the Hydrodynamic Performance of Offshore Fairing Designs
Authors: Corson David , Cosgrove Steve , Constantinides Yiannis
Published: September 2014

In this work, the hydrodynamic performance of various fairing designs have been investigated using Computational Fluid Dynamics (CFD). This paper is divided into two primary sections. The first section involves a thorough sensitivity study to investigate the parameters that are vital in establishing an accurate and robust CFD modeling approach for fairings. The parameters that were investigated during this phase of the work include the mesh density used in the simulations, the blockage ratio (i.e. physical size of the domain that is modeled), the Reynolds Number, and the geometric detail included in the simulations. Upon completion of the sensitivity studies, CFD “best practices” were established. These practices were then applied to a baseline fairing design, and the results were compared against available test data. The CFD approach was shown to predict drag coefficients that agreed with test data within 10% for all cases that were investigated.

The second section of this paper focuses on application of the CFD techniques to evaluate 3 candidate fairing designs. The designs differed in the length and taper angle of the fins. The effect of shortening the fins on straight fin cases had a minor impact on the resulting drag. However, a significant reduction in the drag on the fairings was observed when the fins were tapered inward.
The Maximum Entropy Estimation of Structural Reliability Based on Monte Carlo Simulation
Authors: Huang Wenbo , Mao Jiangang , Zhang Zhiyong
Published: September 2014

Taking the advantage of the high efficiency of Monte Carlo simulation for events of high failure probability, it is adopted to estimate the probabilities of failure of the reduced safe margins of structures. By assuming that the low tail of the probabilistic distribution of the safe margin to follow a Weibull distribution, the failure probabilities simulated are taken as empirical data to extrapolate the Weibull parameters. Among the candidate Weibull distributions, the maximum entropy is used to identify the optimum one which is used to predict the truth probabilities of failure of structures. Two typical numerical examples are carried out to demonstrate the method developed.
Analytical Approach for Mechanical Responses of Spanning Pipelines
Authors: Bai Qiang , Duffy Brian
Published: September 2014

An analytical analysis method for spanning pipelines with vertical imperfections under different loading conditions is presented. Analytical solutions for the pipe configuration, stress distributions, and contact reaction load to the crossed object are obtained under tensile or compressive axial loads by solving the governing differential equations. A comparison of this analytical method with the finite element method is carried out to evaluate the accuracy and consistency of the solutions. This analytical approach may be very helpful for obtaining preliminary results in a limited time without using the more time-consuming and expensive finite element method.

The analytical model accounts for the vertical pipe-soil interaction and drives the solution for the mechanical response of pipeline at the touchdown points of the spanning pipeline. Parametric analyses of the spanning pipeline are carried out to investigate the influences of the span length, vertical imperfection magnitude, and soil stiffness on the mechanical response of the pipeline.

A simplified analytical method for the span segment only is given to compare with finite element analysis. A correlation of dimensionless span length and dimensionless effective axial force is obtained based on the simplified analytical method for different vertical offsets and axial force (tensile or compressive load). The comparison results show that the simplified analytical method may be used as for a quick engineering calculation when the pipe soil-interaction is not clear.
Performance Predictions and Validation of a Two Coaxial-Cylinder System as a Wave-Energy Extractor
Authors: Son Daewoong , Yeung Ronald W.
Published: September 2014

Experiments were conducted to investigate the performance of two newly designed coaxial cylinders as a wave-energy extractor system in regular waves. The coaxial-cylinder design as a point-absorber consists of a tension-tethered vertical inner cylinder and a heaving outer or toroidal cylinder moving in the vertical direction. The relative heave motion between the two cylinders is used to convert the wave-induced response to electrical energy. The first-order heave response of the outer cylinder is used as the mathematical model in the frequency domain and the predicted results are compared with experimental measurements taken in a wave basin. The analytical solutions for the hydrodynamic added mass, damping, and wave-exciting force of the heaving floater are obtained from Chau and Yeung (2012, OMAE2012-# 83987). Experimentally determined hydrodynamic coefficients from free-decay tests at the resonance frequency are obtained to account for the effects of viscosity. Experimental results first reported include the wave-exciting force on the outer cylinder and its free response induced by the incident waves. The permanent magnet linear generator (PMLG) developed in Tom and Yeung (2012, OMAE2012-# 83736) is next installed as a passive power take-off (PTO) system. The electrical power output from the linear generator is measured with the resistance load as a parameter. The measured performances of the coaxial cylinders with and without the PTO are compared with the theoretical predictions. Excellent agreement is found, confirming the effectiveness of guiding theoretical model and of the engineering design.
Real-Time Software to Estimate Friction Coefficient and Downhole Weight on Bit During Drilling of Horizontal Wells
Authors: Tahmeen Mazeda , Hareland Geir , Aadnoy Bernt S.
Published: September 2014

The increasing complexity and higher drilling cost of horizontal wells demand extensive research on software development for the analysis of drilling data in real-time. In extended reach drilling, the downhole weight on bit (WOB) differs from the surface seen WOB (obtained from on an off bottom hookload difference reading) due to the friction caused by drill string movement and rotation in the wellbore. The torque and drag analysis module of a user-friendly real-time software, Intelligent Drilling Advisory system (IDAs) can estimate friction coefficient and the effective downhole WOB while drilling. IDAs uses a 3-dimensional wellbore friction model for the analysis. Based on this model the forces applied on a drill string element are buoyed weight, axial tension, friction force and normal force perpendicular to the contact surface of the wellbore. The industry standard protocol, WITSML (Wellsite Information Transfer Standard Markup Language) is used to conduct transfer of drilling data between IDAs and the onsite or remote WITSML drilling data server.

IDAs retrieves real-time drilling data such as surface hookload, pump pressure, rotary RPM and surface WOB from the data servers. The survey data measurement for azimuth and inclination versus depth along with the retrieved drilling data, are used to do the analysis in different drilling modes, such as lowering or tripping in and drilling. For extensive analysis the software can investigate the sensitivity of friction coefficient and downhole WOB on user-defined drill string element lengths. The torque and drag analysis module, as well as the real-time software, IDAs has been successfully tested and verified with field data from horizontal wells drilled in Western Canada. In the lowering mode of drilling process, the software estimates the overall friction coefficient when the drill bit is off bottom. The downhole WOB estimated by the software is less than the surface measurement that the drillers used during drilling. The study revealed verification of the software by comparing the estimated downhole WOB with the downhole WOB recorded using a downhole measuring tool.
Viability of Fixed Riser Support Structures for Lazy S Riser Configuration in Shallow Waters
Authors: Labanca Edson L. , Ribeiro Elton J. B. , Medeiros Cipriano J. , Ferreira José A. N. , Gomes Victor P. , Amaral Renato D. C. , Mejia Oscar J. P. R. , Basilio Leandro P. , Noronha Neto Celso C.
Published: September 2014

When in shallow waters, not only the risers, but also the structures and equipment are submitted to different conditions from the ones related to deepwater applications. OGX has developed offshore applications in shallow waters in Campos Basin, Brazil, using a FPSO with Lazy S riser configuration, based on the Midwater Arch systems (MWA).

MWA systems are feasible due to OGX application scenario, but they present some disadvantages, such as: high compliance of the buoyant section to the FPSO, large static offset (common issue in shallow waters applications), which makes the MWA carry the risers that are clamped at the top; high manufacturing and installation costs, associated to the high weight of the structure, which includes large and heavy buoys; limitation regarding transportation, sometimes requiring heavy duty trucks, and consequently, more expensive ones. These disadvantages could be avoided by using another type of support structure, but it depends on the application conditions.

Aiming to optimize the Lazy S configuration for new applications in shallow waters, a viability study of a most simplified concept of support, fixed and less compliant, was carried out considering as a standard scenario the Waimea field (under development), located in Campos Basin, Brazil. As a result of this study, OGX and Wood Group Kenny developed the conceptual project of an innovative design of Riser Support Structure (RSS).

Therefore, this paper addresses the technical challenges that were faced during the design of this new concept of Riser Support Structure for shallow waters in offshore applications, including issues regarding the required structural safe response and aspects comprising installation and some decommissioning considerations.

Regarding the design, this paper discusses the structural analyses performed to validate the RSS, which include VIV and Finite Element Analyses, presenting its main results, and the critical issues encountered during these analyses. They include issues such as: Overstress due to combined loads; stress concentration in important structural components; and stress concentration due to impact load (issue recognized during dynamic analysis to simulate the pile driving operation).
Application of CFD Based Wave Loads in Aeroelastic Calculations
Authors: Schløer Signe , Paulsen Bo Terp , Bredmose Henrik
Published: September 2014

Two fully nonlinear irregular wave realizations with different significant wave heights are considered. The wave realizations are both calculated in the potential flow solver Ocean-Wave3D and in a coupled domain decomposed potential-flow CFD solver. The surface elevations of the calculated wave realizations compare well with corresponding surface elevations from laboratory experiments.

In aeroelastic calculations of an offshore wind turbine on a monopile foundation the hydrodynamic loads due to the potential flow solver and Morison’s equation and the hydrodynamic loads calculated by the coupled domain decomposed potential-flow CFD solver result in different dynamic forces in the tower and monopile, despite that the static forces on a fixed monopile are similar. The changes are due to differences in the force profiles and wave steepness in the two solvers.

The results indicate that an accurate description of the wave loads is very important in aeroelastic calculations especially in cases where the aerodynamic loads and damping are insignificant.
Fatigue Precracking Methodology for HDPE
Authors: de Sequeira Thais Pereira , da Costa Marysilvia Ferreira , da Costa Neto Celio Albano
Published: September 2014

With the discovery of new reservoirs of petroleum and gas in ultra deep-water, the offshore exploration conditions are becoming tougher. Structural polymers applied in these conditions may be resisted because of the high offshore/subsea exigencies. As an example, the application of High Density Polyethylene (HDPE) as a thermoplastic jacket in subsea umbilicals which the existence of cracks can impair its performance. The long-term behavior of this material is not well established and it is not known how the fracture behavior and fatigue crack opening and growth are. This knowledge is quite important because it enables to determine safer conditions of operation. Therefore, the crack opening and growth of HDPE will be evaluated using Tension Tests and Dynamical-Mechanical Analysis (DMA) to find relevant mechanical parameters. In addition, a crack opening and growth methodology is formulated and used to calculate KIC value of HDPE considering the Linear Elastic Fracture Mechanics.
Dissimilar Metal Welding of Nitronic 50 HS® and 25% Cr Super Duplex Stainless Steel
Authors: Nissley Nathan , Anderson Timothy D. , Noecker Fredrick F. , Roepke Caleb , Gallagher Morgan , Hukle Martin
Published: September 2014

High pressure tubing and associated tubing couplers are critical components required for the operational control of subsea oil and gas production equipment. Tubing couplers used in subsea oil and gas developments are commonly made from Nitronic 50 HS® (N50HS) due to its high strength, corrosion resistance, and resistance to galling. Nitronic couplers are typically welded to several dissimilar metals including super duplex stainless steel (SDSS) control tubing using SDSS filler metals such as AWS A5.9 ER2594.

Recent evaluations have found that sigma (σ) phase forms in N50HS weldments and its effect is not broadly understood by industry. During N50HS solidification, Scheil solidification conditions establish compositional gradients in the unmixed zone located along the fusion line adjacent to the N50HS base metal. This solidification-induced segregation promotes compositions that are susceptible to interdendritic intermetallic compound formation when they are reheated by subsequent weld passes such as in multipass welding or at weld start-stop locations.

Decreasing heat input is a common approach to reduce or eliminate the formation of intermetallic compounds in SDSS. Although decreasing heat input can reduce the amount of energy available to drive the solid state transformation from ferrite to σ, it does not change the solidification mode (AF) or solidification conditions from Scheil to para-equilibrium within the range of cooling rates possible with arc welding processes. As such, the compositional gradients that promote intermetallic compound formation along the N50HS fusion line can only be minimized through heat input control and cannot be eliminated in arc welds regardless of the heat input used.

The effects of σ on toughness and corrosion resistance of Nitronic weldments were evaluated. N50HS solidified samples with up to 2 volume percent σ were found to have CVN of >40J at −40°C, and no evidence of pitting at 25°C in the ASTM G48 test.
Experimental and Numerical Investigation of BOP Shear Ram Performance
Authors: Tulimilli Bhaskar Rao , Naik Pramod , Chakraborty Arindam , Sawant Sourabh , Whooley Alan , Weiss Robert
Published: September 2014

A Blowout Preventer (BOP) consists of several sets of shear rams stacked together out of which Blind Shear Rams (BSR) is a very critical component to achieve complete shearing of drill pipe. The current study focusses on developing a methodology to model the shearing process and validate it with the shop test. Shop tests were conducted to shear a drill pipe using a surface BOP to obtain the maximum shearing force, shape of sheared drill pipes, shearing time etc. The shear rams used in the test are laser scanned and used in FEA simulations. The FEA model is developed such that it replicates the shop test and simulations are performed using Abaqus Explicit finite element solver. The output from simulations and shop test are compared and found to be in good agreement. The developed methodology is further verified by applying it for shearing different drill pipe sizes and the output is compared with the available data and found to be comparative which proves that the methodology can be implemented for various shearing studies.

Original Equipment Manufacturer (OEM) formulas are currently being used in industry to compute the maximum shearing force required to shear the drill pipe under various scenarios. The OEM shearing force is computed for the model under consideration and compared with the shop test and simulation and is found to be conservative. The validated model can be used for conducting studies that provide information on the governing parameters in terms of loading or positioning of the drill pipe to be considered in shear ram designs. This study provides a tool for optimizing the preliminary design of new shear rams and can contribute to more reliable and efficient shear ram design. The study is conducted as part of a Technology Assessment Programs (TAP) for the Bureau of Safety and Environmental Enforcement (BSEE) in the areas of BOP stack sequencing, monitoring and kick detection.