bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chain Out of Plane Bending (OPB) Fatigue Joint Industry Project (JIP) Static Test Program and OPB Interlink Stiffness
Authors: Rampi Lucile , Dewi Fata , Francois Michel , Gerthoffert Arnaud , Vargas Pedro 
Published: October 2016

In 2002, several mooring chains of a deepwater offloading buoy failed prematurely within a very small time frame. These chains were designed according to conventional offshore fatigue assessment using API recommendations. With this first deepwater buoy application, a new mooring chain fatigue mechanism was discovered. High pretension levels combined with significant mooring chain motions caused interlink rotations that generated significant Out of Plane Bending (OPB) fatigue loading. Traditionally, interlink rotations are relatively harmless and generate low bending stresses in the chain links. The intimate mating contact that occurs due to the plastic deformation during the proof loading and the high pretension of the more contemporary mooring designs have been identified as aggravating factors for this phenomenon.
A Joint Industry Project (JIP), gathering 26 different companies, was started in 2007 to better understand the Out of Plane Bending (OPB) mooring chain fatigue mechanism and to propose mooring chain fatigue design recommendations.
This paper summarizes the quasi static OPB stiffness measurement campaign and the post processing work to derive the OPB interlink stiffness.
A New User Defined Element for Nonlinear Riser-Soil Interaction Analysis of Steel Catenary Riser Systems
Authors: Liu Jiayue , Kimiaei Mehrdad , Randolph Mark 
Published: October 2016

Steel Catenary Risers (SCRs) provide a technically feasible and commercially efficient solution for the offshore field developments in deep waters. Fatigue design of SCRs in the touchdown zone (TDZ) is among the most complicated engineering challenges in riser design.
The cyclic interaction of the riser with seabed leads to a number of complex nonlinear behaviors including soil suction, separation of the riser from the soil, trench formation and degradation of soil resistance during cyclic loading. Accurate simulation of the riser-soil interaction has significant effects on the fatigue performance in the TDZ. Few hysteretic nonlinear riser-soil interaction models have recently been introduced and some of them have been implemented in commercial software packages for analysis and design of riser systems. Due to complexity of the models and also limited access to special software packages with in-built nonlinear soil models, traditional simple linear soil models are still being used widely for riser analysis, in particular for fatigue design.
In this paper, one of the existing nonlinear hysteretic seabed model, already been used in a commercial analysis program OrcaFlex [1], has been implemented into general finite element software Abaqus [2], through the coding of a user defined element (UEL) subroutine. The paper documents the implementation of UEL into Abaqus and the establishment of global riser model for both static and dynamic analysis on which the pipe is modelled efficiently as series of unidirectional beam elements from floater to seabed, resting on a bed of nonlinear springs. Longitudinal friction between pipe and seabed has also been considered.
A series of simulations are performed to illustrate the capabilities of the model. All these results have good agreement with those from OrcaFlex. Results indicate that the proposed UEL is capable of modelling nonlinear riser-soil interaction phenomena and has been verified to be a cost-effective alternative to OrcaFlex in terms of global analysis of SCRs. In addition, as an open source code, UEL provides the required tool for future development on nonlinear soil models. A new type of nonlinear soil with bilinear soil shear strength is modeled and its effect on structural performances of SCRs is investigated.
Applying CFD for In-Line Structure Hydrodynamics in Pipeline Installation Analysis
Authors: Hoekstra Carel , Smienk Henk , van Drunen Joris , Pistidda Alessio 
Published: October 2016

Over the last decade Heerema Marine Contractors (HMC) has successfully performed multiple installation campaigns of large sized in-line structures (ILS) with Deep Water Construction Vessels (DCV) Aegir and Balder. Nowadays steady increase in size and weight of ILS have made these special operations even more complex. Presence of large sized ILS and accompanying buoyancy modules in the catenary have proven to play a dominant role in pipeline integrity. Originally hydrodynamic force formulations in finite element analysis are solely designated for the pipeline itself. These computations comprehend the application of the Morison equation using constant hydrodynamic coefficients of basic shapes in steady flow.
Therefore hydrodynamic forces acting on the ILS, characterized by irregular relative motions of a complex shaped and perforated structure, are highly simplified while playing a dominant role in the analyses. Validity of applying the standard Morison equation is debatable, since large ILS cannot be assumed slender. Nonetheless Morison type formulations can provide reasonable results depending on the accuracy of the hydrodynamic coefficients. Deriving these coefficients for complex shaped structures using industry standards is a highly interpretive process involving an accumulation of assumptions. This approach yields varying coefficients, which are applied conservatively in installation analyses, resulting in an unnecessary reduction of DCV offshore workability.
To improve workability of these complex installations, HMC has implemented an ILS specific hydrodynamic profile from Computational Fluid Dynamics (CFD) analysis into the installation analyses. This is effectuated by the development of an enhanced methodology with a dedicated hydrodynamic formulation for large perforated ILS. Dependencies on Keulegan-Carpenter (KC) number and local angle of attack are addressed in this formulation to respectively cover the inertia dominated oscillating motions and complex geometric composition. The applied hydrodynamic formulation is based on work of Molin et al. which showed a good agreement to the CFD analysis performed for this study. Development and application of this methodology is initiated as a first assessment towards more accurate ILS installation analyses.
Analysis of a study case shows reductions up to 50% of maximum bending strain in a specific regular wave analysis. From the work presented it is concluded that the industry practice vastly overestimates hydrodynamic forcing on large sized ILS. Complementary research is needed on the topics of oscillations for low (<1.0) KC number, effects of relative fluid velocity and finally the implementation of irregular waves.
Assessment of Helicopter Emergency Response Capacity in the Barents Sea
Authors: Jakobsen Marion , Milaković Aleksandar-Saša , Ehlers Sören 
Published: October 2016

As the global demand for energy is increasing, oil and gas exploration is moving further north to more remote areas. Offshore activity in these areas is challenging. Arctic-specific environmental conditions, long distances from onshore facilities and general lack of infrastructure are some of the challenges faced. Therefore, new and more robust solutions — both on technological and operational side — are required before commencing operations safely in these areas.
In this paper, a helicopter emergency response capacity — with respect to prevailing wind conditions — for operations in the Barents Sea is studied and a method for mapping the rescue capacity in the given area is presented. The goal is to develop a method capable of assessing the probability of a successful rescue at different locations within given time requirements and under prevailing wind conditions. This is accomplished using a simulation model capable to determine how the wind speed and direction affect the search and rescue helicopter operations in the Barents Sea.
The simulation model uses historical wind data along a potential route as input for evaluating the flying time to different locations in an area under the given wind conditions. In addition to the wind conditions, the variation in recovery time, and mobilisation time is implemented into the simulation model. By running the simulation model multiple times, probability distributions of the number of personnel which can be recovered within the given time requirements are established. This information is then used to plot isocurves of equal rescue probability on top of a map of the Barents Sea.
Based on the results, it is concluded that wind conditions have significant effect on rescue capacity of a helicopter, and thus thorough weather observations should be made before establishing a search and rescue system for a given area.
Fatigue Considerations for Subsea Well Systems
Authors: Baker David A. , Walker Karen M. 
Published: October 2016

Fatigue assessments are a central component of subsea well system analysis and are essential in understanding overall well system performance. In recent years there has been an increased focus on understanding fatigue in well systems. This focus has taken on many forms — a broad industry JIP, technical studies by individual operators, development of a variety of technologies for subsea instrumentation and monitoring and case studies implementing this technology. An overarching objective of all these efforts is to clarify some of the complexity that is inherent to well system fatigue.
As with any analysis, well system fatigue analysis benefits from appropriately defined inputs. These inputs affect both sides of the analysis equation — loading considerations and resistance considerations. A majority of the efforts to date have examined loading considerations. Inputs such as metocean criteria and soil properties can have a dramatic impact on the analysis results. Accurate characterization of these inputs is desired, though often difficult to achieve. As a result, large safety factors are often employed to provide a margin against this uncertainty.
Often overlooked, however, is the resistance half of the assessment, particularly the accurate characterization of fatigue hotspots such as welds and connectors. Conservative analysis of hotspots is frequently employed as these components are not amenable to inspection, however the conservative assumptions can result in non-realistic assessment of fatigue performance.
This paper presents some additional considerations for minimizing the uncertainty in well system fatigue analysis, through thorough materials characterization and design analysis, focusing on connector hotspots. The information presented is representative of actual considerations utilized for ExxonMobil projects. Fatigue performance is improved through finite element characterization of the connector design and “hand picking” component match-ups to minimize the resulting stress amplification. Attention to the total life fatigue properties, including experimental assessment of the material used, is needed to provide an accurate representation of fatigue performance. Finally, in the absence of this information, mitigation of fatigue risks can be obtained by displacing fatigue hotspots.
Reliable Reservoir Characterization and History Matching Using a Pattern Recognition Based Distance
Authors: Lee Jiyoon , Choe Jonggeun 
Published: October 2016

A distance is defined as a measure of dissimilarity between two reservoir models. There have been many distances proposed for fast modeling. However, some distances cause distortion or loss in original permeability distribution of models. To avoid such problems, this study proposes a pattern recognition based distance.
The distance is defined by the difference of correlation coefficients between ensemble models. From multi-dimensional scaling, initial 400 ensembles are presented on 2D plane using the distance. Then 10 groups are made by K-medoids clustering. After comparing oil production from each centroid and that of the reference field, 100 models are selected around the best centroid.
We validate the clustering by comparing the uncertainty range of 100, 50, and 20 ensemble members sampled from the initial 400 models in box plots and cumulative distribution functions. For a history matching and reservoir characterization, ensemble smoother is applied to the 100 models selected. The proposed method takes only 25% time for simulation showing reliable results compared with the initial 400 models.
Statistical Method to Requalify Steel Grades During Conversion of Tankers to FPSO
Authors: Cambos Philippe , Parmentier Guy 
Published: October 2016

During ship life, operating conditions may change, tanker may be converted into FPSO, and flag requirements may be modified. Generally these modifications have few impacts on existing structures; flag requirements only rarely are to be applied retroactively. Nevertheless in some cases modifications of operating condition may induce considerable consequences, making in the worst cases impossible any reengineering. For example converting a common tanker, built with plain steel of grade A into an Offshore Floating Unit able operating in cold region, may require a grade change corresponding to a grade B. It is obviously meaningless to replace all material just because material certificates.
Steels used by shipyards have to fulfill Classification society’s requirements dealing with mechanical strength; generally shipbuilding corresponds to a small part of steelmaker’s production. For this reason steelmakers are reluctant to produce steels with mechanical properties corresponding exactly to the minima required. They generally deliver steels already in stock, with higher mechanical characteristics than required. In this case it can be taken advantage of this common practice. In order to demonstrate that the material fulfill the requirements of grade B it has been decided to adopt a statistic approach. At this stage there are two main issues, the first one is that it is needed to provide evidences that the actual material Charpy V characteristics fulfill the requirements of grade B; the second one is to provide these evidences with a minimum testing. To assess this assumption a random check has been carried out. Different probabilistic model have been tested in order to check common approaches and probabilistic model based on physical considerations. In the paper the main assumptions for estimating the minimum Charpy value main assumption in the probabilistic models are recalled, the behavior of empirical sample is examined, the parameters of probability laws fitting the empirical distribution and definitely as accuracy of probability law parameters determination is not perfect with a finite number of specimens the uncertainty in the determination of parameters is taken into account with confidence limits.
According to the selected probabilistic model the minimum value corresponds to an acceptable probability of failure, taking into account the target confidence level, or is independent of any acceptable probability of failure and is defined with the same confidence level. At the end it is concluded that a random check with a data treatment assuming a random distribution of Charpy V test results distributed according to a Weibull probability law of the minimum allows providing evidences that with a sufficient confidence level the steel used for the considered structure fulfill the requirements of the new operating conditions.
Evaluation of Wind Loads on FPSO Topsides Using a Numerical Wind Tunnel
Authors: Barcarolo Daniel , Andrillon Yann , Jacquin Erwan , Ledoux Alain 
Published: October 2016

The accurate evaluation of wind loads applied on floating offshore structures is extremely important as they are in specific conditions one of the dimensioning criteria for the mooring design. Nowadays these loads are mainly assessed through wind tunnel tests performed at model scale. Estimating realistic wind loads however, remains a big challenge. The complexity and associated simplification level of FPSO topside structures, the scale effects and the establishment of the atmospheric boundary layer imply that many simplifications are to be made. Typically, the FPSO topside is greatly simplified and equivalent blocs of wired frame are used. Today with the evolution of CFD software, and the increase of the meshing capacity, new scopes open to CFD. Aerodynamic simulations on complex FPSO structures are therefore now possible, but need specific developments and validations that are presented in this paper.
The main objective of the work presented is to investigate the ability of CFD to evaluate wind loads on complex FPSOs topsides and to provide information on the impact of model simplifications made in wind tunnels. In a first stage, the numerical model was intensively validated by comparing its results to a wind tunnel test case. The numerical model was developed in order to ensure the quality of the results and enable a relevant comparison that was obtained with grids density up to 30 million cells. For this purpose, the geometric model used corresponds to the one used in wind tunnel. The same Atmospheric Boundary Layer was simulated and a thorough effort was performed to ensure the mesh convergence. In a second stage, more physical aspects of the wind tunnel methodology were investigated. Typically the accuracy of the blockage effect correction was evaluated by performing computations with and without blockage, and results were compared with classical corrections applied in wind tunnel. The impacts of the Atmospheric Boundary Layer on wind loads have also been investigated. Finally, the wind load contribution of each component of the FPSO was evaluated.
Examination of Effect of Lateral Loads on the Hull Girder Ultimate Strength of Large Container Ships
Authors: Matsumoto Toshiyuki , Shigemi Toshiyuki , Kidogawa Mitsuhiko , Ishibashi Kinya , Sugimoto Kei 
Published: October 2016

It is known that the hull girder ultimate strength with consideration of lateral loads such as bottom sea pressures and/or cargo loads generally decreases than that without consideration of the lateral loads (i.e. the effect of lateral loads).
In this study a series of elasto-plastic analyses of three cargo holds models, which can reproduce the collapse behavior of the hold structures subjected to both vertical bending moment and lateral loads such as bottom sea pressures, container cargo loads etc., were carried out on a number of container ships with various sizes, and the hull girder ultimate strength obtained through the analyses were comparatively examined focusing on the effect of the lateral loads.
As results of the examination, it has been concluded that local strength of the double bottom structure against the lateral loads is closely related to the hull girder ultimate strength in the case of container ships, the effect of the lateral loads on the hull girder ultimate strength varies among container ships due to the difference of construction of the double bottom structure and it is important to assess the hull girder ultimate strength explicitly taking into consideration the effect of the lateral loads for large container ships such as Post-Panamax sizes.
Numerical and Experimental Study of a Multi-Use Platform
Authors: Armesto José A. , Sarmiento Javier , Ayllón Víctor , Iturrioz Arantza , Jurado Alfonso , Guanche Raúl , Losada Iñigo J. 
Published: October 2016

A complete hydrodynamic study of a Multi Use Platform designed to harvest energy from waves and wind is presented. The steps given in the study, and presented in this paper are: (i) the design of the platform, (ii) the laboratory tests performed at the Cantabria Coastal and Ocean Basin, (iii) the development of a new in-house time domain numerical model that integrates all components and (iv) the first validation cases of the numerical model.
The development of time domain numerical model that coupled the behaviour of the platform and the OWCs based in Cummins equation is presented. The model includes nonlinear friction forces and a quasi-static approach to model the mooring system. The obtained system is extended to include the variation of the pressure inside each chamber. The effect of the wind turbine in the movements and power production of the platform is studied using also a quasi-static approach.
Real-Time Hybrid Model Testing of a Braceless Semi-Submersible Wind Turbine: Part II — Experimental Results
Authors: Bachynski Erin E. , Thys Maxime , Sauder Thomas , Chabaud Valentin , Sæther Lars Ove 
Published: October 2016

Real-Time Hybrid Model (ReaTHM) tests of a braceless semi-submersible wind turbine were carried out at MARINTEK’s Ocean Basin in 2015. The tests sought to evaluate the performance of the floating wind turbine (FWT) structure in environmental conditions representative of the Northern North Sea. In order to do so, the tests employed a new hybrid testing method, wherein simulated aerodynamic loads were applied to the physical structure in the laboratory. The test method was found to work well, and is documented in [1].
The present work describes some of the experimental results. The test results showed a high level of repeatability, and permitted accurate investigation of the coupled responses of a FWT, including unique conditions such as blade pitch faults. For example, the influence of the wind turbine controller can be seen in decay tests in pitch and surge. In regular waves, aerodynamic loads due to constant wind had little influence on the structure motions (except for the mean offsets). Tests in irregular waves with and without turbulent wind are compared directly, and the influence of the wave-frequency motions on the aerodynamic damping of wind-induced low-frequency motions can be observed.
Numerical Modelling of Breaking Wave Interaction With a Group of Four Vertical Slender Cylinders in Square Arrangements
Authors: Alagan Chella Mayilvahanan , Bihs Hans , Kamath Arun , Myrhaug Dag , Arnsten Øivind Asgeir 
Published: October 2016

The main purpose of the study is to investigate the breaking wave interaction with a group of four circular cylinders. The physical process of wave breaking involves many parameters and an accurate numerical modelling of breaking waves and the interaction with a structure remain a challenge. In the present study, the open-source (Computational Fluid Dynamics) CFD model REEF3D is used to simulate the breaking wave interaction with the multiple cylinders. The numerical model is based on the incompressible Reynolds Averaged Navier-Stokes (RANS) equations, the level set method for the free surface and the k–ω model for turbulence. The model uses a 5th-order conservative finite difference WENO scheme for the convective discretization and a 3rd-order Runge-Kutta scheme for time discretization.
The numerical model is validated with experimental data of large-scale experiments for the free surface elevation and the breaking wave force on a single cylinder. A good agreement is seen between the numerical results and experimental data. Two different configurations with four cylinders are examined: in-line square configuration and diamond square configuration. The breaking wave forces on each cylinder in the group are computed for the two cases and the results are compared with the breaking wave force on a single isolated cylinder. Further, the study investigates the water surface elevations and the free surface flow features around the cylinders. In general, the cylinders in both configurations experience the maximum forces lower than the maximum force on a single cylinder. The results of the present study show that the interference effects from the neighbouring cylinders in a group strongly influence the kinematics around and the breaking wave forces on them.