bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Approach for Environmental Contour and Multivariate De-Clustering
Authors: Derbanne Quentin , de Hauteclocque Guillaume 
Published: November 2019

Abstract
When the long term behaviour of a floating unit is assessed, the environmental contour concept is often applied together with IFORM (Inverse First Order Reliability Method). This approach avoids direct computation on all sea-states, which is computationally very demanding, and most often simply not feasible. Instead, only a few conditions (the contour) are assessed and results in an accurate estimate of the long term extreme. However, most of available methods to derive the contour require the knowledge of the joint distribution of the different random variables (waves, wind, current...), which is often difficult to derive accurately. In fact, some complex dependences exist and are attempted to be simplified in too few coefficients. Another limitation of current environmental contour is its difficulty to deal with the dependence issue. Indeed, extreme sea-states arise by groups (storms, hurricanes...) and are not independent. While de-clustering techniques exist and are quite straightforward in univariate problems, this becomes difficult when the number of dimension increases.
In an attempt to tackle those challenges, this paper presents a novel approach to derive IFORM contours. The method does not require any joint distribution and makes use of much more degrees of freedom to capture the dependence between variables. It also allows for an easy de-clustering. The approach is illustrated on two locations, using actual hindcast data of significant wave height and period; the resulting contours are compared to the ones obtained with more traditional methods.
Influence of Microstructural Variation in Thick Section Steels on the Characterisation of Fracture Toughness Using Sub-Size Specimens
Authors: Moore Philippa , Yordanova Borislava , Lu Yong , Janin Yin Jin 
Published: November 2019

Abstract
The challenges of performing full-thickness fracture toughness tests on steel plates of 100mm thickness and greater means that the use of sub-size specimens is desirable. In this work, 100mm thick parent plate of S690 high strength steel was characterised using SENB fracture toughness specimens with thickness of 12mm, 25mm, 50mm and 100mm. Sub-size specimens were extracted at two different locations through the plate thickness; mid-wall and quarter wall. Sufficient specimens were tested to apply the Master Curve method in ASTM E1921 to predict the behaviour of 100mm thick material from each set of sub-size specimens. The through-thickness microstructural variation in these heavy-wall steel plates meant that significantly different predictions of full-thickness fracture toughness were obtained from the two sampling locations. However, when sampled from the mid-wall location, sub-size specimens down to 25mm thick were able to conservatively predict full-thickness fracture toughness using Master Curve methods.
An Actuator Disc Analysis of a Ducted High-Solidity Tidal Turbine in Yawed Flow
Authors: Borg Mitchell G. , Xiao Qing , Incecik Atilla , Allsop Steven , Peyrard Christophe 
Published: November 2019

Abstract
This work elaborates a computational fluid dynamic model utilised in the investigation of the hydrodynamic performance concerning a ducted high-solidity tidal turbine in yawed inlet flows. Analysing the performance at distinct bearing angles with the axis of the turbine, increases in torque and mechanical rotational power were acknowledged to be induced within a limited angular range at distinct tip-speed ratio values. Through multiple yaw iterations, the peak attainment was found to fall between bearing angles of 15° and 30°, resulting in a maximum power increase of 3.22%, together with an extension of power development to higher tip-speed ratios. In confirmation, these outcomes were subsequently analysed by means of actuator disc theory, attaining a distinguishable relationship with blade-integrated outcomes.
Assessment of the Reliability of the Moorings of a Floating Structure Against the Extreme Cyclone Hazard
Authors: Manzocchi Mark , Kejriwal Vikas , Hoo Eric 
Published: November 2019

Abstract
This paper describes the methodology adopted for an analysis performed to assess the reliability of the moorings of a free weathervaning FPSO against the cyclone hazard. A joint distribution characterizing the long-term cyclone metocean conditions was fitted to a database of environmental conditions at the site of interest. A series of archetype cyclone histories were selected from the cyclone database to capture the evolving relationships between key environmental parameters during a cyclone. A response-surface model for extreme tension in the vessel moorings was developed for the short-term extreme vessel response as a function of environmental conditions by fitting the surface to an extensive series of time-domain vessel response analyses. The reliability of the mooring system was evaluated using Monte Carlo simulation by sampling from the fitted joint distribution of long-term cyclone characteristic and generating simulated cyclone time histories by scaling the archetype cyclones. The response model for short-term exceedance probability is used to develop the probability of exceedance within each simulated cyclone, and the probability of exceeding a given response is derived from the simulation.
Assessment of Latching Control for the Hemispheric Heaving Buoy Type Point Absorber With and Without Nonlinear Froude-Krylov Force Acting on the Buoy
Authors: Kim Sung-Jae , Koo Weoncheol , Jo Chul H. 
Published: November 2019

Abstract
In this study, a latching control strategy was utilized to increase the efficiency of a heaving buoy-type point absorber with a hydraulic Power take-off (PTO) system. For this purpose, the hydrodynamic performance of a floating buoy was analyzed based on the potential flow theory and Cummins equation. Nonlinear Froude-Krylov (FK) force according to instantaneous wetted surface of a buoy was calculated by a theoretical solution. The effect of the latching control on a point absorber was evaluated by considering PTO performance with hydrodynamic coefficients including nonlinear FK force. The hydraulic PTO system was modeled as an approximate coulomb damping force.
Optimal Control for Response Reduction of Single Hinged Articulated Tower Using MR-Damper
Authors: Solomon Kushal , Kumar Deepak 
Published: November 2019

Abstract
Articulated tower is a compliant offshore structure deployed in deep waters for oil and gas exploration. The base of the tower is connected to the sea bed through universal joint, which allows the tower to rotate about horizontal axis (pitch). Articulated towers attain stability due to large buoyancy forces acting on it. Under extreme wave loads, the response of ALP can exceed the design limit causing discomfort to the occupants and create unfavourable working conditions. Structural control systems can be implemented in order to reduce the response of ALP, thereby protecting the structure from damages and to increase its life span. In this paper, a semi-active optimal control strategy using Magneto-Rheological damper is adopted to reduce the responses of ALP. Bouc-Wen model is used to describe the force generated by MR-Damper. For achieving the optimal performance of the control system, the applied voltage is varied according to the measured feedback at any moment to change the damping force using linear quadratic regulator technique. Several parametric studies have been conducted and the performance of the controller is evaluated. It is observed that the response of ALP is reduced considerably by using MR-damper as a semi-active control device. However, the capacity of the damper required for achieving the desired control is huge.
Decisional Criteria for Off-Shore Operations Interruption due to Adverse Weather
Authors: Drago Michele , Vitali Luigino , Del Guzzo Andrea , Gaggiotti Federico 
Published: November 2019

Abstract
Off-shore operations and installations can be occasionally delayed or interrupted due to the arrival of severe metocean conditions which could put human safety or structural integrity of the work at risk. In particular, the motion and loads induced by wind, waves and current on the vessel and on the installing structure could exceed the allowable limit for a safe and correct installation.
Whatever the operation that is being carried out, it is necessary to have a favorable window with a duration longer than the time necessary to complete the job or to interrupt the operation in order to carry out the work safely, e.g. pipe abandonment for pipe laying.
Predicting when these windows will occur is not an easy task and the decision-making process shall be correctly managed by a reliable balance between safety, first of all, and efficiency, to not unduly increase time and the cost of operations. These two aspects, safety and efficiency, respectively, tend to cause unnecessary/anticipated interruptions to the work with consequent delays or to cause late interruptions of an operation with risks to assets integrity and/or human safety.
The available information for managing the decision-making process is the monitoring of the actual conditions, both weather and installation vessel motions, and the weather forecast bulletins. Valuable information can be found also in the metocean hindcasted time series, mainly wind and waves, nowadays available for any off-shore area which the oil&gas industry is interested in with a typical duration of 30 years, for the determination of the typical characteristics of the metocean conditions of the area of interest.
This paper presents a comparison between the performances of different criteria for interruptions of long duration operations based on monitoring and on forecast, proposing an improved method based on the combination of the two kinds of information. A preliminary analysis of the metocean conditions of the area based on hindcasted time series is considered as well.
It should be noted that the same principle can be adopted for short operations to be completed within favorable weather windows. In this case the time for completing the operation is equivalent to the time necessary to safely interrupt the operations.
Impact of Soil Modeling on Fatigue Design of Lazy Wave Riser Systems
Authors: Ghosh Rupak , Arslan Haydar 
Published: November 2019

Abstract
The Liza risers comprise production risers, water injection risers and gas injection risers, and a lazy wave configuration is selected considering FPSO motion, reservoir fluid and overall project execution requirements. During operation, the risers are expected to move cyclically with small vertical displacement amplitudes (e.g. 0.1% to 1% of the riser diameter), and a key design issue is the fatigue life of these risers at critical locations including the touch-down zone which will be governed by the seabed stiffness. The role of soil response on fatigue life of riser with buoyancy has been investigated through nonlinear finite element and comprehensive lab and field testing program. Published methodologies for determining seabed stiffness values for risers concentrate more on larger amplitude motions based on the design requirements of steel catenary risers.
The paper presents the sensitivity of the fatigue life at TDP to various soil model and provides insight in the results. Also included is the importance of site specific soil investigation in the context of design of riser.
A New Fully-Detailed Finite Element Model of Spiral Strand Wire Ropes for Fatigue Life Estimate of a Mooring Line
Authors: Bussolati Federico , Guiton Martin , Guidault Pierre-Alain , Poirette Yann , Martinez Michael , Allix Olivier 
Published: November 2019

Abstract
Spiral strand wire ropes are commonly used in the mooring system of offshore structures. When dealing with the fatigue limit state, engineers have to consider many different load cases, according to the variability of the environmental state. This usually prevents the use of any detailed numerical model of the mooring lines. In this paper, we propose a new method to evaluate with an affordable computational cost the detailed mechanical stress state in different parts of the wire ropes used for mooring a floating offshore wind turbine. We first compute tension and bending history in the mooring, with the hydrodynamic software Deeplines™, assuming for simplification stationary aerodynamic loads on the floater. These time series are then accounted for in a novel Finite Element Model of the spiral strand, with small sliding among the wires. The obtained kinematics and stress state of the wires can then feed a fatigue law based on fretting fatigue, which has been experimentally evidenced to condition the fatigue life of spiral strand wire ropes. The potential of this method is illustrated with an application to a cylinder-like shape floater equipped with 3 pairs of catenary mooring lines. It is shown that bending and tension histories do not significantly depend on the wire rope bending stiffness.
Ship As a Wave Buoy: Estimating Relative Wave Direction From In-Service Ship Motion Measurements Using Machine Learning
Authors: Mak Bart , Düz Bülent 
Published: November 2019

Abstract
For operations at sea it is important to have a good estimate of the current local sea state. Often, sea state information comes from wave buoys or weather forecasts. Sometimes wave radars are used. These sources are not always available or reliable. Being able to reliably use ship motions to estimate sea state characteristics reduces the dependency on external and/or expensive sources.
In this paper, we present a method to estimate sea state characteristics from time series of 6-DOF ship motions using machine learning. The available data consists of ship motion and wave scanning radar measurements recorded for a period of two years on a frigate type vessel. The research focused on estimating the relative wave direction, since this is most difficult to estimate using traditional methods. Time series are well suited as input, since the phase differences between motion signals hold the information relevant for this case. This type of input data requires machine learning algorithms that can capture both the relation between the input channels and the time dependence. To this end, convolutional neural networks (CNN) and recurrent neural networks (RNN) are adopted in this study for multivariate time series regression.
The results show that the estimation of the relative wave direction is acceptable, assuming that the data set is large enough and covers enough sea states. Investigating the chronological properties of the data set, it turned out that this is not yet the case. The paper will include discussions on how to interpret the results and how to treat temporal data in a more general sense.
Analysis of the Coupled Dynamics of an Offshore Floating Multi-Purpose Platform: Part B — Hydro-Elastic Analysis With Flexible Support Platform
Authors: Ruzzo C. , Failla G. , Arena F. , Collu M. , Li L. , Mariotti A. 
Published: November 2019

Abstract
A multi-purpose platform (MPP) is an offshore system designed to serve the purposes of more than one offshore industry. Indeed, over the past decades, a number of industries have expanded, or are expanding, from onshore to offshore locations (renewables, aquaculture, tourism, mineral extractions, etc), and the research on these type of platform is increasing. In the present work, a MPP able to accommodate wind turbines, wave energy converters, and aquaculture systems is considered. For an overview of the MPP platform considered and its research context, please refer to the EU H2020 project overview (OMAE 2019-96104). This work presents the second part (Part B) of the analyses of the dynamics of the floating support structure for this MPP, focusing on the hydro-elastic analysis, while its complementary rigid-body hydrodynamic analysis is presented in Part A (OMAE2019-96212).
The aim here is to assess if the support platform structural elasticity has a substantial impact on the dynamic response of the platform. A beam model and a 3D solid model of the support structure have been developed, and the inertial forces, hydrodynamic added mass forces, hydrostatic and mooring restoring forces have been considered in the hydro-elastic analyses performed. The results show that the dynamic response to the wave loads is not substantially influenced by the elasticity of the support structure, and that, at first approximation, a rigid-body approach is acceptable.
Numerical and Mechanistic Modelling of Two-Phase Liquid-Gas Flow’s Pressure Drop Across Sharp-Edged Orifices
Authors: Khan Zurwa , Tafreshi Reza , Franchek Matthew , Grigoriadis Karolos 
Published: November 2019

Abstract
Pressure drop estimation across orifices for two-phase liquid-gas flow is essential to size valves and pipelines and decrease the probability of unsafe consequences or high costs in petroleum, chemical, and nuclear industries. While numerically modeling flow across orifices is a complex task, it can assess the effect of numerous orifice designs and operation parameters. In this paper, two-phase flow across orifices has been numerically modeled to investigate the effect of different fluid combinations and orifice geometries on pressure drop. The orifice is assumed to be located in a pipe with fully-developed upstream and downstream flow. Two liquid-gas fluid combinations, namely water-air, and gasoil liquid-gas mixture were investigated for different orifice to pipe area ratios ranging from 0.01 to 1 for the superficial velocity of 10 m/s. Volume of Fluid multiphase flow model along with k-epsilon turbulence model were used to estimate the pressure distribution of liquid-gas mixture along the pipe. The numerical model was validated for water-air with mean relative error less than 10.5%. As expected, a decrease in orifice to pipe area ratio resulted in larger pressure drops due to an increase in the contraction coefficients of the orifice assembly. It was also found that water-air had larger pressure drops relative to gasoil mixture due to larger vortex formation downstream of orifices. In parallel, a mechanistic model to directly estimate the local two-phase pressure drop across orifices was developed. The gas void fraction was predicted using a correlation by Woldesemayat and Ghajar, and applied to separated two-phase flow undergoing contraction and expansion due to an orifice. The model results were validated for different orifices and velocities, with the overall relative error of less than 40%, which is acceptable due to the uncertainties associated with measuring experimental pressure drop. Comparison of the developed numerical and mechanistic model showed that the numerical model is able to achieve a higher accuracy, while the mechanistic model requires minimal computation.
Operational Behaviour of Supersonic Separators for Real Gas Mixtures of Methane and Carbon Dioxide, From the Homogeneous Nucleation Point of View
Authors: Restrepo Julián , Simões-Moreira Jose R. 
Published: November 2019

Abstract
One of the several challenges of the oil and natural gas offshore extraction in pre-salt reserves in Brazil, is the high content of carbon dioxide inside the wells, reaching values close to 80% in a molar fraction. This issue has a big impact on the crude extraction, due to the necessity of further expensive equipment occupying considerable deck space in platforms.
Therefore, it is necessary to research and find new technologies, which allow separating high contents of carbon dioxide at low energy consumption and low maintenance. The supersonic separation concept fulfils all these requirements due to the absence of moving parts and simple operation, because its working principle is based on the strong temperature drop of gas mixtures at supersonic expansion as it occurs in de Laval nozzles. Eventually, at the right operating conditions, the mixture starts to nucleate and, therefore, it will drive the phase change.
Nevertheless, the physical phenomena involved in this device is complex, because it involves phase change at supersonic speeds, which comprise compressible, multispecies, and multiphase flow. This paper analyses the threshold of the phase change at supersonic speeds.
The objective of this work is to calculate the influence of operation conditions (pressure, temperature and composition) in the phase change performance in supersonic separators.
The phase change was modelled using the classical theory of homogeneous nucleation. In this approach allows to estimate the phase change inside the supersonic flow for different operating conditions and allows to establish operating strategies to ensure low Mach numbers (M &lt; 1.5) in the phase change region, allowing a further pressure recovery.
Development of Harsh Environment Field With Ice Loadings Using Concrete Spar: Variability of Options
Authors: Sablok Anil , Hovland Erlend , Stromme Svein , Blundon Andrew 
Published: November 2019

Abstract
A floating platform in deep water East Canada is required to withstand iceberg loads and/or be disconnected and towed away in the event of very large approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and in most cases, provide large quantities of oil storage in the hull. Concepts considered for deep water application in the area include ship shaped self-propelled disconnectable FPSO and disconnectable and permanently connected deep draft floaters. This paper presents the details of Concrete Spar platforms that have been configured to satisfy all the above requirements. Several variations in the functionality and configurations of the platforms were studied to understand the impact on the overall cost and risks. The case variations primarily included:
• Disconnectable options for hull, mooring and risers
• Non-disconnectable option able to handle the full iceberg load
• With and without crude oil storage in hull
• Sacrificial or non-sacrificial mooring or risers
• Steel riser configurations (freely hanging catenary, SCR vs. lazy wave, SLWR)
• Hull with and without riser support Buoy
• Location of mooring fairleads (on Upper hull or Buoy)
• Riser support configuration (Pull Tubes or Flex Joints)
The iceberg loads experienced by the hull depended on the disconnection philosophy. The Concrete Spar hull is a 6-cell structure with the risers located inside the open centerwell. The paper describes several key features of the hull, mooring and riser systems for each case that are specifically designed to withstand iceberg loads and other environment loads while maintaining the characteristic low motion response for all the options considered. Additionally, the system has been designed to minimize the disconnection and reconnection time for the disconnectable cases.
The platform dimensions and weights have been compared for the various options considered. The cases without oil storage in the hull have significantly smaller and lighter hull relative to similar cases with oil storage. The cases without hull disconnection option had similar hull dimensions but marginally higher concrete weight relative to the hull disconnection option. However, the cost of Buoy, required for the disconnection option, compensates for the concrete cost difference. The SCRs work for the inplace extreme environment and iceberg load cases. Depending on the hull offset required to avoid icebergs for the non-disconnection cases or the risers lowering depth for disconnection cases, SLWR may be needed.
Recommendations are made for the preferred option for field development.