bluuebunny/crossref_metadata_2025_split huggingface dataset:
Research on Optimum Function and Utilization of Oceanic Architectures for Marine Space Use: Case Study on Kyushu Region, Japan
Authors: Sugahara Ryo , Kuroyanagi Akio 
Published: October 2017

Recently, the demanding for effective utilization of marine spaces in forms of oceanic architectures has been rising high by new social requirements as well as other constructions, and the like. Consequently, architecutural characteristics and structural effectiveness of them should be reevaluated accordingly.
Objects of this study are four architectures located in the shallow area of sea around Kyushu Region,namely Marizon, Genkai Sea Hot Spring Palea, Marine Aquarium Sea Doughnut, and Akasaki Elementary School.
Their functions, structures, setting forms, then conditions for situating buidings, processes of construction at sea, and challenges after construction had been clarified by our literature survey, the hearing investigation and the field research.
Our results are as following. Functionally, each above architectures has respective facilities to fully utlize regional marine resources and environment, etc.; Structurally, all of them had premeditated both the bad conditions of coastal environment and providing spaces for water activities. In terms of their construction processes at sea, factors blow had been carefully considered before being sited: limitations of local spatial scale, full utilization of local environmental conditions, measures against disadvantages of sites, the particularities of regional nature, environment, and society.
In conclusion, our findings suggest that planning of the oceanic architecuture should combine the usage, the fuction, and the understructures well with its marine conditions.
An Optimization Method for the Configuration of Inter Array Cables for Floating Offshore Wind Farm
Authors: Poirette Yann , Guiton Martin , Huwart Guillaume , Sinoquet Delphine , Leroy Jean Marc 
Published: October 2017

IFP Energies nouvelles (IFPEN) is involved for many years in various projects for the development of floating offshore wind turbines. The commercial deployment of such technologies is planned for 2020.
The present paper proposes a methodology for the numerical optimization of the inter array cable configuration. To illustrate the potential of such an optimization, results are presented for a case study with a specific floating foundation concept [1].
The optimization study performed aims to define the least expensive configuration satisfying mechanical constraints under extreme environmental conditions. The parameters to be optimized are the total length, the armoring, the stiffener geometry and the buoyancy modules. The insulated electrical conductors and overall sheath are not concerned by this optimization. The simulations are carried out using DeepLines™, a Finite Element software dedicated to simulate offshore floating structures in their marine environment. The optimization problem is solved using an IFPEN in-house tool, which integrates a state of the art derivative-free trust region optimization method extended to nonlinear constrained problems. The latter functionality is essential for this type of optimization problem where nonlinear constraints are introduced such as maximum tension, no compression, maximum curvature and elongation, and the aero-hydrodynamic simulation solver does not provide any gradient information.
The optimization tool is able to find various local feasible extrema thanks to a multi-start approach, which leads to several solutions of the cable configuration. The sensitivity to the choice of the initial point is demonstrated, illustrating the complexity of the feasible domain and the resulting difficulty in finding the global optimum configuration.
A Novel Approach to the Development of Squall Database for Mooring Response Based Analysis
Authors: Mariani Alessio , Elliott Grant , Wake Geoff , Whelan James , Jeans Gus 
Published: October 2017

This paper describes a novel approach to the characterisation of the winds associated with squall events. Squalls are short duration events during which wind speed increases rapidly and is often characterised by a substantial change in direction. Squalls are an important input for the design of offshore structures, particularly weather vaning facilities such as turret moored FPSO’s for which squalls may induce substantial mooring loads.
This paper presents the development of a synthetic squall database covering 63 years and combining direct high resolution wind measurements together with weather balloon observations of the lower atmosphere and historical daily maximum wind gusts. The squall database was a key input into a mooring Response Based Analysis (RBA) of a turret moored FPSO located offshore North Western Australia.
Details of the synthetic squall database development are presented including: regional squall regime characterization, direct measurements, identification of peak squall events from long term measured datasets, characterisation based on weather balloon observations, generation of representative synthetic time histories of squall events.
The squall database, coupled with a conventional hindcast metocean database including associated wave and currents parameters, allowed characterization of the weather vaning performance of the FPSO and identification of design loads for mooring design purposes.
Predicting the Changing Soil Response for Vertical Pipe-Seabed Interaction Accounting for Remoulding, Reconsolidation and Maintained Load
Authors: Zhou Zefeng , White David J. , O’Loughlin Conleth D. 
Published: October 2017

Steel catenary risers (SCRs) are subjected to fatigue in the touchdown zone (TDZ) where the pipe interacts with the seabed. In this zone the seabed is subjected to intermittent episodes of cyclic loading and reconsolidation during long-term operation. Cyclic loading, reconsolidation and maintained load can cause variations in the soil strength and stiffness, which has a significant influence on the fatigue life of the riser in the TDZ.
The weakening effect of cyclic loading on soil strength is well recognized throughout design practice, and methodologies for determining the cyclic ‘fatigue’ of clay during undrained cyclic loading are well established (e.g. Andersen et al. 1988; Andersen 2015). However, traditional undrained assessments neglect the effects of drainage and consolidation that inevitably occur in pipe-seabed interaction during long-term operational stages, and can lead to changes in stiffness by a factor of up to 5 or 10. This overlooked effect of consolidation on soil resistance and stiffness can be very important for SCR fatigue analysis.
In this paper, a new analytical framework considering these effects has been used to analyze vertical pipe-seabed interaction. This framework is developed using a critical-state concept with effective stresses, and by discretizing the soil domain as a one-dimensional column of soil elements. The model can accurately capture the changing soil resistance and stiffness to account for the effects of remoulding, reconsolidation and maintained load. The framework is used to back-analysis the pipe-soil interaction response during small and large amplitude vertical cycles. The simulation prediction compares well with the measured results from the laboratory (Aubeny et al., 2008), and can accurately capture the observed changes in stiffness of up to a factor of 5.
Prediction of Combined IL and CF VIV Response of Deepwater Risers
Authors: Wu Jie , Lekkala Malakonda Reddy , Ong Muk Chen , Passano Elizabeth , Voie Per Erlend 
Published: October 2017

Deepwater risers are susceptible to Vortex Induced Vibrations (VIV) when subjected to currents. When responding at high modes, fatigue damage the in in-line (IL) direction may become equally important as the cross-flow (CF) components. If a riser experiences directional currents, fatigue damage must be evaluated at several locations on the cross-section’s circumference. Accurate calculation of both IL and CF responses are therefore needed.
Empirical VIV prediction programs, such as VIVANA, SHEAR7 and VIVA, are the most common tools used by the offshore industry to design against VIV loads. Progress has been seen in the prediction of CF responses. Efforts have also been made to include an IL load model in VIVANA. A set of excitation coefficient parameters were obtained from rigid cylinder test and adjusted using measured responses of one of the flexible cylinder VIV tests. This set of excitation coefficient parameters is still considered preliminary and further validation is required. Without an accurate IL response prediction, a conservative approach in VIV analysis has to be followed, i.e. all current profiles have to assumed to be uni-directional or acting in the same direction.
The purpose of the present paper is to provide a reliable combined IL and CF load model for the empirical VIV prediction programs. VIV prediction using the existing combined IL and CF load model in VIVANA is validated against selected flexible cylinder test data. A case study of a deepwater top tension riser (TTR) has been carried out. The results indicate VIV fatigue damage 1 using 2D directional current profiles is less conservative compared to the traditional way of using unidirectional current profiles.
Learning From Riser Analyses and Predicting Results With Artificial Neural Networks
Authors: Authén Kristian 
Published: October 2017

Subsea wellheads are subjected to fatigue loading from semi-submersible drilling vessels in harsh and relatively shallow waters like in the North Sea. Dynamic finite element riser simulations are run to ensure safe operations. These simulations calculate loads and fatigue damage on the subsea wellheads, and are run in large numbers, often with only small alterations in input. Building and running all these models for each new well are both time consuming and costly.
By storing and structuring the results from such analyses, machine learning algorithms can be trained, and used to predict new results, without the need of running simulations for every new well. If there are insufficient simulation data available, data with inconsistent modeling, or little variety in the input of the data, it is also possible to use model builders to generate a sparse but sufficient set of simulation data to train the model.
A trained model can predict simulation results instantly, and gains accuracy as more analysis data becomes available for training.
The trained model is efficient for estimating fatigue status on oil fields with large numbers of subsea wells, since it is unnecessary with separate simulations for each well. It can also be used for early phase concept studies and as a QA tool for verifying results of other simulations.
Projected Changes in the Occurrence of Extreme and Rogue Waves in Future Climate in the North Atlantic
Authors: Gramstad Odin , Bitner-Gregersen Elzbieta , Vanem Erik 
Published: October 2017

We investigate the future wave climate in the North Atlantic with respect to extreme events as well as on wave parameters that have previously not been considered in much details in the perspective of wave climate change, such as those associated with occurrence of rogue waves. A number of future wave projections is obtained by running the third generation wave model WAM with wind input derived from several global circulation models. In each case the wave model has been run for the 30-year historical period 1971–2000 and the future period 2071–2100 assuming the two different future climate scenarios RCP 4.5 and RCP 8.5. The wave model runs have been carried out by the Norwegian Meteorological Institute in Bergen, and the climate model result are taken from The Coupled Model Intercomparison Project phase 5 - CMIP5.
In addition to the standard wave parameters such as significant wave height and peak period the wave model runs provided the full two-dimensional wave spectrum. This has enabled the study of a larger set of wave parameters. The focus of the present study is the projected future changes in occurrence of extreme sea states and extreme and rogue waves. The investigations are limited to parameters related to this in a few selected locations in the North Atlantic.
Our results show that there are large uncertainties in many of the parameters considered in this study, and in many cases the different climate models and different model scenarios provide contradicting results with respect to the predicted change from past to future climate. There are, however, some situations for which a clearer tendency is observed.
An Experimental and Numerical Investigation of the Effect of Axial Thermal Gradients in Flexible Pipes
Authors: Fergestad Dag , Klæbo Frank , Muren Jan , Hylland Pål , Grøv Tom Are , Lange Hans , Gjøsteen Janne K. Ø. , Gjendal Andreas , Melve Bjørn , Kristensen Claus Egebjerg 
Published: October 2017

This paper discusses the structural challenges associated with high axial temperature gradients and the corresponding internal cross section forces. A representative flexible pipe section designed for high operational temperature has been subject to full scale testing with temperature profiles obtained by external heating and cooling. The test is providing detailed insight in onset and magnitude of relative layer movements and layer forces. As part of the full-scale testing, novel methods for temperature gradient testing of unbonded flexible pipes have been developed, along with layer force- and deflection-measurement techniques. The full-scale test set-up has been subject to numerous temperature cycles of various magnitudes, gradients, absolute temperatures, as well as tension cycling to investigate possible couplings to dynamics.
Extensive use of finite element analysis has efficiently supported test planning, instrumentation and execution, as well as enabling increased understanding of the structural interaction within the unbonded flexible pipe cross section. When exploiting the problem by finite element analysis, key inputs will be correct material models for the polymeric layers, and as-built dimensions/thicknesses. Finding the balance between reasonable simplification and model complexity is also a challenge, where access to high quality full-scale tests and dissected pipes coming back from operation provides good support for these decisions.
Considering the extensive full scale testing, supported by advanced finite element analysis, it is evident that increased attention will be needed to document reliable operation in the most demanding high temperature flexible pipe applications.
Consistent Free Span VIV Fatigue Analysis of Flexibles
Authors: Caruso Mário , Han Xu , Sødahl Nils 
Published: October 2017

The fatigue life assessment of free spanning flexible products, such as subsea cables and umbilicals, due VIV requires special attention to the structural properties due to the stick/slip behaviour of helix elements in bending. Essential parameters for assessment of stick/slip effects in free span VIV response are the structural damping in the stick regime (i.e. umbilical behaves as a solid cross section due to friction between the helix elements) as well as the additional damping introduced by the hysteretic damping due to the stick/slip behaviour in bending. Furthermore, consistent fatigue stress recovery considering the stick/slip behaviour in bending is essential for fatigue life predictions.
The consistent evaluation of stick/slip behaviour requires more sophisticated calculation procedures due to the non-linearity it introduces. Hence, industry practice has been to consider simplified, linear calculation procedures. However, future flexibles utilization may be much benefitted by a consistent stick/slip treatment in free spanning VIV fatigue assessments, as it may allow for longer allowable free span lengths or longer fatigue life.
The overall objective of the paper is to establish a consistent free span VIV analysis methodology for flexibles in compliance with requirements given in ISO 13628-5 ‘Subsea Umbilicals’ and the overall philosophy of DNV-RP-F105 ‘Free Spanning Pipelines’.
A consistent fatigue analysis scheme for VIV in free spans is outlined using commercially available state-of-the-art computer programs for free span VIV response analysis (FatFree) and cross section stress analysis (Helica). The performance of the calculation scheme is demonstrated by case studies in a complex long-term current loading environment. It is shown that consistent treatment of the mechanical properties of flexibles is essential for VIV fatigue life assessments of free spans.
Seismic Design of Jumpers: The Coupling Conundrum
Authors: Cademartori Marcello , Zanoli Omar , Parker Eric J. 
Published: October 2017

Subsea developments in seismically active areas present a number of engineering challenges. One such item, which is frequently underestimated, is design of jumpers to resist earthquake loading. Jumpers connect quite dissimilar pieces of subsea equipment, for example heavy manifolds on deep foundations, PLETs on mudmats and wellheads supported on slender well casings. If the structures connected have a different dynamic response (e.g. manifold, PLET and wellheads with different fundamental periods), the jumpers receive additional loads from the out of phase structure movements. Such “seismic coupling” is particularly an issue for high pressure high temperature (HPHT) fields, where stiff heavy jumpers are combined with large manifolds. This paper discusses possible approach to evaluate coupling, and provides practical advice for subsea designers. Specifically we address coupling from a point of view of the fundamental period of the connected structures and jumpers, making reference to results of dynamic modeling and codified experience from nuclear power plant design. Differentiation between cases which require fully coupled treatment, and those in which a more straightforward separation and analysis of the individual subsystems is very important to producing an efficient design in reasonable time frame. These aspects are illustrated using a case history from our project files.
Coupled dynamic analysis of primary (supporting) and secondary (supported) systems may not be always feasible or desirable. The number of supported structures may be such that a coupled analysis may create computational difficulties. In addition to this, data regarding the secondary system may be not available at the time of the analysis of the primary system with the result that development of a coupled model would be not applicable.
In cases where an attempt is made to develop complex coupled systems, sanity checks of such a system may be not an easy task. For these and other reasons, complete analysis of complex coupled systems is rarely performed. The objective of this paper is to explore the conditions under which an uncoupled analysis is justified and to give simplified indication to check the results of coupled models.
The paper presents a case study of a manifold-jumper-PLET. The system is evaluated using a standard uncoupled approach in which seismic actions are computed for the manifold, jumper and PLET considered as separate structures. The resulting actions are compared to those from a “coupled analysis” in which the full system is analyzed. The standard uncoupled analysis is found to be unconservative in cases where the jumper’s natural period of vibration is similar to that of the manifold or PLET. This approach shows promise as a means of identifying cases where coupled analysis is required to correctly assess seismic forces.
Experimental Study of Hydrodynamic Responses of a Single Floating Storage Tank With Internal Fluid
Authors: Chi Zhang , Magee Allan R. , Ling Wan , Wang Chien Ming , Hellan Øyvind 
Published: October 2017

When floating structure with internal fluid compartment is close to other structures, the multibody interaction problem needs to be addressed in addition to the internal fluid influence. Furthermore, shallow water effects become important, especially when the gap between the floating structure and the sea floor is small. These issues are encountered when designing a novel floating oil storage facilities in nearshore area. To investigate these issues, floating models under 1:50 scale are built to perform model tests.
The test set-up uses a set of flexible constraints working as fenders placed on frames to restrain the motions of the models in the horizontal plane. Various tests in waves are carried out to measure motion responses of single model in waves with different filling levels and stiffness of “fenders”. The reaction forces on the “fenders” are also measured. Several regular wave conditions are selected to perform tests on double model system to investigate multibody interactions under the influence of internal fluid and effects of waves between the tanks. The drag forces for both single model and double models are measured by performing model tests under constant current from different directions, to check the shielding effects. The tests are performed in shallow-water wave basin, and the constant currents tests are performed by towing the models in a flume tank. Both facilities are located at National University of Singapore (NUS).
This paper presents the detailed setting of the model tests. The single model’s RAOs with 20% filling level of internal fluid are given to demonstrate the influence of internal fluid on the motions. The performances of a single tank, including six DOF motions are shown. The results will be used for validation of numerical analysis results in the near future.
Verification Scheme for Unbonded Flexible Pipes: Definition, Implementation and Reflection of API 17J
Authors: Conti Fabien , Migeon François , David Aymeric 
Published: October 2017

The present paper is related to the verification of unbonded flexible pipes designed and manufactured as per API 17J [1].
Back in the early nineties, in response to the needs of the industry for better quality, reliability and safety in unbonded flexible pipe products, Bureau Veritas established an innovative verification scheme relying not only on qualification testing, but also on the assessment of design methods, materials as well as manufacturing processes. This approach has proven particularly relevant considering several specificities of the flexible pipe industry: no ‘on-the-shelf’ design (each pipe being designed for project specific conditions), manufacturer specific local design methodologies, specific materials and manufacturing methods, high complexity and cost of testing.
This paper presents the verification methodology, its application as well as its ability to embody the latest normative requirements given in [1]. The specificity of the verification scheme, which consists in a breakdown between a Type Approval phase and a project phase, is also presented.