bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamics of an Array of Submersible Mussel Rafts in Waves and Current
Authors: Dewhurst Tobias , Hallowell Spencer T. , Newell Carter 
Published: November 2019

Abstract
A three-by-three grid of submersible mussel rafts was analyzed using an experimentally validated dynamic numerical modeling approach. When submerged, the rafts’ pontoons are flooded, and they are held vertically by lines attached to surface floats and horizontally by a mooring grid. The rafts’ decreased waterplane area and increased inertia reduce the heave and pitch natural frequencies so that they are below the frequencies associated with the greatest wave energy. This has been found to significantly reduce the motion of the rafts compared to the surfaced configuration.
The nine submersible rafts were anchored with 16 anchors and mooring lines. These mooring lines were connected to a grid of adjacent rectangular bays, with each corner (node) supported by a grid float. Each bay contains a raft connected to the submerged nodes of the grid by four bridle lines. The dynamics of the full system were modeled using a combined multibody and Finite Element Analysis (FEA) approach with dynamic loads computed using a modified Morison formulation. This model was implemented in the commercial code OrcaFlex. A similar model for a single submersible raft was previously validated with full-scale field experiments. The full dynamic system was simulated in the maximum expected waves and currents. Mean and maximum tensions in each grid line were quantified. Accelerations and velocities at the mussel rope attachment points were also examined, since these relate to mussel drop-off.
Shape Optimization of a Submerged Pressure Differential Wave Energy Converter for Load Reductions
Authors: Kelly Michael , Alam Mohammad-Reza 
Published: November 2019

Abstract
The ocean is full of untapped energy, however it is a wild place where harsh conditions can occur that can damage wave energy converters (WEC’s). During high load conditions, many WEC’s must go into survival mode to prevent damage or are overdesigned to continue operating in high sea states, which can increase capital costs. The authors propose a different approach, where geometry control is used to change to an absorber shape that experiences minimal hydrodynamic loads during high sea states. This could allow for a decrease in capital costs while increasing the operating range of WEC’s. This paper seeks an optimal geometry of a submerged planar pressure differential WEC that minimizes heave excitation force or motion magnitudes without using the power take-off system. Simple elliptical and circular absorbers as well as optimized absorbers are compared to quantify heave load reductions. Optimized absorbers are generated using a summation of Fourier terms with controllable weights and phases that are optimized with a genetic algorithm for two regular wave conditions. Heave load reductions are found to depend on wave frequency, orientation angle, and elongation. It is shown that peak loads can be reduced by up to 60% when comparing to a circular absorber.
Design of Steel Lazy Wave Riser for External Turret Moored FPSO
Authors: Cheng Jingyun , Cao Peimin 
Published: November 2019

Abstract
The external turret moored Floating Production Storage and Offloading system (FPSO) is one of the preferred solutions for deepwater fields in mild to moderate environments and far away from existing pipeline infrastructures. This paper presents a design of steel lazy wave riser (SLWR) system for an external turret moored FPSO in the water depth of 1,500 meter. The design challenges and feasibility are discussed. Due to the complexity of SLWR geometry, a systematic configuration approach is introduced to achieve the desired riser extreme and fatigue performance target, as well as external turret layout. The study includes the standardized FPSO, the selection of turret configuration, and riser design. The titanium taper stress joints and the interaction with turret structure are also studied. The study provides an optimal solution of the integrated turret, mooring and riser system. It concludes that external turret FPSO with SLWRs can be a feasible and cost effective solution for field development in mild to moderate environments.
Process-Structure-Property Fatigue Characterisation for Welding of X100 Steel Catenary Risers
Authors: Devaney Ronan J. , Connaire Adrian , O’Donoghue Padraic E. , Leen Sean B. 
Published: November 2019

Abstract
Welded connections are a fatigue sensitive location for offshore steel catenary risers. The susceptibility to fatigue is due to the notch effect of the weld and the gradient in microstructure and material properties across the weld which result from welding thermal cycles and differences in the composition of the parent material and weld metal.
In this work, a representative full-scale steel catenary riser girth weld is conducted using X100Q steel. The thermal and strain history in the weld zone are captured using a thermocouple and strain gauge array. A parallel programme of Gleeble thermomechanical simulation is implemented to develop microstructurally uniform heat affected zone (HAZ) test specimens. The parent material, weld metal, simulated HAZ and a cross-weld sample are characterised using a programme of nanoindentation, tensile and fatigue testing.
A softened region with microstructure corresponding to intercritical HAZ (ICHAZ) is identified in the girth weld. Tensile and fatigue failures are shown to occur in a representative microstructural region for simulated HAZ specimens, indicating a susceptibility to failure in the ICHAZ for matched or over-matched X100Q welds.
Lazy Wave Riser Design in High Current and Mild Sour Environment
Authors: Ghosh Rupak , Pellegrini Carlo , Visco Tyler J. 
Published: November 2019

Abstract
This paper presents an innovative design of Lazy Wave Steel Catenary Riser (LWSCR) associated with a major deepwater development in a new frontier and in very high current. The conventional LWSCR design with distributed buoyancy is not found acceptable considering fatigue design acceptance criteria in mild sour environment. The major design requirement is to meet acceptable design life of 20-yrs considering significant damage accumulated due to Vortex-induced-vibration (VIV) and motion fatigue. Further, other development basis including flow assurance requirements and reservoir souring are critical requirements for the design of the riser system.
The paper presents a very useful insight in how several qualified technologies can be leveraged to result in a workable riser design in a very aggressive execution schedule. The results from the analyses of a production LWSCR are presented in the paper.
Standardisation on Measurement and Interpretation of Residual Stress Data
Authors: Mirzaee-Sisan Ali , Bouchard P. John , Hosseinzadeh Foroogh 
Published: November 2019

Abstract
This paper highlights many unanswered questions relating to the characterisation of residual stresses in weldments and their treatment in engineering critical assessment and fitness for service assessment codes and standards. The need for an overarching standardisation framework is identified which goes beyond developing good practice guidelines for numerical prediction or measurement using a specific technique. The framework should cover all uncertainties and possible errors in measuring, simulating and interpreting residual stress in the context of structural integrity assessment.
The Increasing Prevalence of High Frequency Internal Waves in an Arctic Ocean With Declining Sea Ice Cover
Authors: Rippeth Tom , Vlasenko Vasyl , Stashchuk Nataliya , Kozlov Igor E. , Scannell Brian , Green Mattias , Lincoln Ben , Lenn Yueng-Djern 
Published: November 2019

Abstract
Receding seasonal sea ice extent over the Arctic Ocean is increasing access to what was a largely inaccessible region. At lower latitudes the complex vertical current structure associated with large amplitude, high frequency non-linear internal waves, sometimes referred to as solitons, present a significant challenge to the safe engineering design and operation of offshore infrastructure. In this paper we examine the prevalence this type of internal wave in the Arctic Ocean. To do so we will draw on both in situ and remotely sensed oceanographic data. This will be combined with state-of-the-art numerical modelling to demonstrate a link between the geographical occurrence of these waves and the tide. Whilst the link implies that these features are geographically limited, it is also likely that the geographical limits will change with declining sea ice cover. These results will then be used to provide a road map towards a methodology for forecasting the prevalence of these phenomena in a future Arctic Ocean.
Dynamic Response of Metallic Y-Frame Core Sandwich Panels Subjected to Air Blast Loading: Numerical Investigation
Authors: Liu Ting , Cheng Yuansheng , Liu Jun , Chen Ganchao , Chen Changhai , Zhang Pan 
Published: November 2019

Abstract
In this paper, the dynamic response of metallic Y-frame core sandwich plates subjected to air blast loading was investigated by employing the LS-DYNA software. The blast wave was generated by the directly detonation of TNT explosives. The deformation/failure modes and associated structural response were identified and analyzed in detail. Main attention was paid to explore the effects of face sheet thicknesses and core web thickness on the deformation response of Y-frame core sandwich plates. A comparison on the blast performance were drawn among the Y-frame core sandwich panel, corrugated core sandwich panel and solid plate in equal areal mass. Numerical results revealed that the Y-frame core sandwich panel experienced indent deformation in the front face, strut buckling in the core and large bending deformation in the back face under the stand-off distance of 100 mm. Increasing the face sheets and core web thicknesses could improve the blast performance of Y-frame core sandwich panels. The deflections of face sheets were sensitive to the variation of front face sheet and core thicknesses. Moreover, Y-frame sandwich panel has comparable anti-blast capacity with the corrugated counterparts and exhibits superior blast resistance than the solid plate.
Observation of Waves in Naru Strait, Goto, Nagasaki, a Tidal Current Test Site
Authors: Kyozuka Yusaku 
Published: November 2019

Abstract
Waves are primarily important for the tidal current power generation as they relate not only to the wave load acting on the tidal turbine but also to the installation/maintenance cost of the device through the workable day rate at the sea. Generally, the tidal current power site is in a narrow strait, and the wave characteristics are strongly dependent on the place. Also, there are few data itself. So, we conducted the wave observation in Naru Strait, Goto City, Nagasaki, where the tidal current power project by the Ministry of Environment is in progress.
An AWAC (Acoustic Wave and Current Meter) was deployed on the sea bottom of 20m depth in Naru Strait on 18 May and recovered on 12 November, 2017. The wave data obtained for about 6 months were analyzed as wave spectra and mean directions by the records of surface elevation together with tidal current velocity. In particular, the changes of wave amplitude by the tidal current and the storms including typhoon passing are presented.
Combined Wave-Current Induced Instantaneous Liquefaction of a Sandy Seabed
Authors: Yang Li-Jing , Li Chang-Fei , Wang Jun-Qin , Gao Fu-Ping 
Published: November 2019

Abstract
Accurate prediction for the liquefaction depth of a porous seabed is crucial to the design of shallow foundations; nevertheless most previous studies are predominantly limited to wave-only conditions. In this study, the combined wave-current induced instantaneous liquefaction of a sandy seabed is investigated analytically. The explicit expression of liquefaction depth under combined wave-current loading condition is derived, which can converge to that under the linear wave condition when the current velocity approaches zero. Parametric study indicates that the effects of imposing a current onto progressive waves on the distribution of excess pore pressures and the corresponding liquefaction depth are unneglectable, especially for the opposite current conditions.
Nonlinear Wave Loads on Offshore Wind Turbines: Extreme Statistics and Fatigue
Authors: Zhang Yu , Sclavounos Paul D. 
Published: November 2019

Abstract
The development is presented of an analytical model for the prediction of the stochastic nonlinear wave loads on the support structure of bottom mounted and floating offshore wind turbines. Explicit expressions are derived for the time-domain and frequency-domain nonlinear exciting forces in a seastate with significant wave height comparable to the diameter of the support structure based on the fluid impulse theory. The higher order moments of the nonlinear load are evaluated from simulated force records and the derivation of analytical expressions for the nonlinear load statistics for their efficient use in design is addressed.
Numerical Simulation of Fully Nonlinear Interaction Between Regular and Irregular Waves and a 2D Floating Body
Authors: Li Haoran , Bachynski Erin E. 
Published: November 2019

Abstract
A fully nonlinear Navier-Stokes/VOF numerical wave tank, developed within the open-source CFD toolbox OpenFOAM, is used to investigate the response of a moored 2D floating body to nonlinear wave loads. The waveDyMFoam solver, developed by extending the interDyMFoam solver of the OpenFOAM library with the waves2Foam package, is applied. Furthermore, a simple linear spring is implemented to constrain the body motion. An efficient domain decomposition strategy is applied to reduce the computational time of irregular wave cases. The numerical results are compared against the results from potential flow theory. Numerical results highlight the coupling between surge and pitch motion and the presence of nonlinear loads and responses. Some minor numerical disturbance occurs when the maximum body motion response is achieved.
Environmental Assisted Cracking of High Strength Subsea Material due to CP
Authors: Horn Agnes Marie , Østby Erling , Røneid Viggo , Kirkemo Finn 
Published: November 2019

Abstract
Several of the offshore fields in the North Sea are approaching the end of their design life and a cost-effective solution to maximize production is to document that life extension is feasible for an asset. A trend the resent years [1] is that the BOP become larger, hence the required fatigue life increases. One way to meet the increased fatigue life and external loading is to use higher strength steel to meet the design requirements set by the operators. This has motivated research related to the fatigue performance of the base material connector material both for air and under sea water with cathodic protection (CP) [2,3,4] and possible degradation of ductility and toughness in seawater with CP. However, relevant test data for wellheads material that have been in service is not to the authors knowledge, available, nor recommendations in design guidelines related to possible material degradation to be safely applied for life extension of these assets.
To better evaluate life extension of subsea wellheads, a test campaign was initiated by Equinor on a retrieved wellhead in 2015. The wellhead had been in operation since 2000 in the North Sea. The general purpose of the test program was to evaluate if the low alloy steel AISI 8630 modified material had been substantial degraded during 15 years in service compared to design material properties and the materials susceptibility to hydrogen embrittlement.
The test program performed consisted of slow strain rate testing (SSRT) to document possible reduction of strength and ductility, CTOD testing to document possible reduction in toughness and S-N testing to establish the fatigue strength reduction due to seawater with CP.
The outline of the paper is as follows: first a summary of the latest research and trends within wellhead fatigue and materials are discussed. Next, a detailed description of the test program is given: SSRT, toughness testing and fatigue testing are presented. Finally, recommendations and proposal for further research work are given.
Triaxial Testing of Gas Shale Permeability Dependence on Heterogeneous Stress With Respect to Bedding
Authors: Chen Yufei , Jiang Changbao , Yin Guangzhi , Wojtanowicz Andrew K. , Zhang Dongming 
Published: November 2019

Abstract
Shale gas has recently become the most promising source of unconventional hydrocarbon energy. Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but is also controlled by in-situ stresses. Thus, prediction of well’s deliverability requires understanding permeability of a dipping shale with natural bedding under conditions of unequal stresses in-situ. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of Longmaxi shale in the Sichuan Basin, southwest China.
The study involved an analysis of the rock bedding structure, followed with triaxial testing of rock samples and theoretical modeling. We used SEM observation to identify existence of microfractures and numerous inter-particle pores along the shale bedding planes that provide dominant pathways for gas flow depending upon closing stress value. Stress-dependent permeability was tested with a newly-developed multi-functional true triaxial geophysical (TTG) apparatus providing for a steady state gas flow through the rock sample under conditions of normal stress and two unequal tangential stresses. Also simulated were the effects of stress-bedding and load cycling.
The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process for both normal and tangential stress loading cycles. A hysteresis of the permeability response to cyclic loading was the largest when normal stress cycling was dominant. Moreover, permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed — particularly when the tangential stresses were dominant. A theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results.
Assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5% and 14%, respectively, showing dominant effect of normal stress with clear contribution of tangential stresses. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for improvement in computing effective stress in permeability predictions of the Longmaxi shale. It also warrants testing other gas shales to specifically determine the effect.
Numerical Simulation of Ship-Ice Interaction
Authors: Huisman Michael , Erceg Sandro , von Bock und Polach Rüdiger U. Franz , Rung Thomas , Ehlers Sören 
Published: November 2019

Abstract
The increasing activities in arctic sea areas over the last years have led to a rising demand for numerical tools to design and evaluate ice-going ships. Numerical simulation of ship-ice interaction can be a suitable method for engineers to evaluate ship designs in early development phases. We present an efficient method to evaluate local and global loads on ships in level ice at moderate computational effort. The objective of this contribution is the holistic simulation of the icebreaking process along with the hydrodynamic interplay of the broken ice cups with the surrounding level ice and the hull. For this purpose, a free surface flow solver based upon the Lattice Boltzmann method is coupled to an icebreaking model and a contact-dynamic physics engine. Overall, the approach seeks to compute both local loads, acting on the ship hull, as well as the total resistance in ice. The direct simulation approach makes it possible to consider the load contributions of icebreaking and displacement separately and to analyze their contribution to the total resistance more precisely. Simulation results for a tanker in various ice conditions show significant differences in load distribution and can provide valuable information for the designer of ice-going ships.
Cement Bond Strength Measurements
Authors: Opedal Nils , Cerasi Pierre , Vrålstad Torbjørn 
Published: November 2019

Abstract
Cement is an important component to ensure safe and economic sustainable operations of wells. To optimize the performance of cement in a well, and to achieve an adequate level of well integrity, experimental testing of cement under realistic and relevant conditions is vital. This paper reviews three different types of cement bond strengths relevant for the petroleum industry and gives an evaluation of the methodologies used to study these bond strengths. Although the term “Bond strength” should at first be assessed and discussed as an easy-to-understand parameter, the review shows that it is important to understand the fundamental differences between the three-bond strengths. In terms of how they are measured, and in terms of what the information can be used for.
Effects of Cap Bottom Elevation on Wave Loads on the Piles Under the Cap
Authors: Zhou Jifu , Wang Xu 
Published: November 2019

Abstract
High-rise pile cap foundations are generally used to support offshore wind turbines or sea-crossing bridges. They endure complex wave loads due to the interaction of free surface and the cap. An additional pressure increment has been found under the cap when free surface impinges the cap bottom. This additional pressure changes the wave loads on the piles under the cap compared with the case without the cap. In the present paper, we investigate the effects of the cap bottom elevation on the wave loads of the piles under the cap by using fully nonlinear numerical simulations. Based on parameters of waves and the structure used in Donghai Bridge Wind Farm, China, we simulate a number of cases with different cap bottom elevation to explore its influence on wave loads of the piles under the cap. We find that the influence is of significance and requires enough attention.
A Preliminary Study on the Modeling and Analysis of Nonlinear Effects of Ocean Waves and Power-Take-Off Control on Wave Energy Conversion System Dynamics
Authors: Yim S. C. , Adami N. , Bosma B. , Brekken T. , Chen M. , Ghorban Zadeh L. , Glennon D. N. , Lian Y.-S. , Lomonaco P. , Mohtat A. , Ozkan-Haller T. , Thomson J. 
Published: November 2019

Abstract
This article describes the model development and preliminary progress of an on-going research study on the effects of nonlinearities in ocean wave input and power-take-off (PTO) control on wave energy conversion system dynamics and efficiency. The model system employed and progress on recent developments are: (1) nonlinear wave modeling in the ocean, generation and propagation in a wave basin, and (2) nonlinear PTO control algorithm. An overview of the holistic analytical, numerical and experimental research approach/work plan is presented. To provide a simple means for analysis, comparison and performance evaluation, the WEC-Sim numerical platform is used for model implementation and system dynamic simulation. Analytical and numerical predictions of the nonlinear wave fields in a wave basin using the nonlinear Fourier analysis (NLFA) technique and corresponding nonlinear wavemaker theory and a plan for future validation using a comprehensive series of experimental test data as well as ocean wave measurements are described. Efficiency of the nonlinear PTO control and a future evaluation work plan by comparing numerical simulations with results of WEC model test data under corresponding wave conditions of the experimental studies without the presence of the WEC system are also presented.