bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of a Swarm of Autonomous Underwater Vehicles for High-Bandwidth Underwater Wireless Communication
Authors: Immas Alexandre , Alam Mohammad-Reza 
Published: November 2019

Abstract
High-bandwidth underwater wireless communication can be achieved over long-distance using a swarm of Autonomous Underwater Vehicles (AUVs) relaying an optical signal. The swarm behavior is of critical importance as it will determine the robustness and the autonomy of the communication link. Each vehicle must remain at a distance lower than the optical communication system range from each other while fighting against environmental disturbances such as ocean current. This technology could be a game changer in the deployment and supervision of future oil wells and of deep sea mining which will be deeper and deeper in the oceans. We developed an optimization program to maximize the communication link autonomy while assuring its robustness. The nonlinear optimization problem is transformed to a Second-Order Cone Problem (SOCP), a special case of convex problems that can be efficiently solved with Yalmip on Matlab. We show on two case studies that the autonomy of the swarm and thus the lifetime of the communication link is increased by more than 10% compared to a direct approach where the reference position of the vehicles is fixed.
Detection of Mooring Line Failure of a Spread-Moored FPSO: Part 1 — Development of an Artificial Neural Network Based Model
Authors: Sidarta Djoni E. , Lim Ho-Joon , Kyoung Johyun , Tcherniguin Nicolas , Lefebvre Timothee , O’Sullivan Jim 
Published: November 2019

Abstract
Artificial Intelligence (AI) has gained popularity in recent years for offshore engineering applications, and one such challenging application is detection of mooring line failure of a floating offshore platform. For most types of floating offshore platforms, accurately detecting any mooring line damage and/or failures is of great interest to their operators.
This paper demonstrates the use of an Artificial Neural Network (ANN) model for detecting mooring line failure for a spread-moored FPSO. The ANN model representation, in terms of its input variables, is based on assessing when changes in a platform’s motion characteristics are in-fact indicators of a mooring line failure. The output of the ANN model indicates the status condition for the mooring lines (intact or failed). This ANN model only requires GPS / DGPS monitoring data and does not require data on the environmental conditions at the platform. Since the mass of an FPSO changes with the stored volume of oil, the vessel’s mass is also an input variable.
The ANN training uses the results from numerical simulations of a spread-moored FPSO with fourteen mooring lines. The numerical simulations create the FPSO’s response to a range of metocean conditions for 360-degree directions, and they cover several levels of vessel draft (mass). Furthermore, the simulations cover both the intact mooring configuration and the full permutation where each of the fourteen mooring lines is modeled as broken at the top. The global performance analysis of the FPSO is presented in a different paper (Part 2 of these paper series).
The training of the ANN model employs a back-propagation learning algorithm and an automatic method for determining the size of ANN hidden layers. The trained ANN model can detect mooring line failure, even for vessel draft (mass), sea states and environmental directions that are not included in the training data. This demonstrates that the ANN model can recognize and classify patterns associated with mooring line failure and separate such patterns from those associated with intact mooring lines under conditions not included in the original training data.
This study reveals a great potential for using an ANN model to monitor the station keeping integrity of a floating offshore platform with changing storage, or mass status, and to detect mooring line failure using only the vessel’s mass and deviations in the platform’s motions derived from GPS / DGPS data.
Proposed Updates to the Buried-to-Surface Flaw Recharacterization Rules in Annex E of BS 7910
Authors: Bezensek Bostjan , Tkach Yuri , Sharples John , Coules Harry 
Published: November 2019

Abstract
BS 7910 “Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures” [1] is undergoing revision for the next edition. Updates are proposed for the Annex E flaw recharacterization guidance. The changes aim to make Annex E more applicable to real structures and to improve the synergy between the subcritical crack growth such as by fatigue and fracture of an embedded flaw. Several studies were done by WEE/37 fracture panel focusing on brittle and ductile material behaviour to support the proposed changes. These studies are summarised in the paper.
The main modifications in the proposed updated Ann ex E are in:
• Removal of use of Annex E for brittle fracture.
• Updated guidance on recharacterized surface flaw length for ductile fracture.
• Optional guidance on use of geometry-based criterion for embedded flaw break-through under ductile conditions.
• Alignment of fatigue crack growth in Section 8 with the flaw break-through in Annex E.
Large-Scale Resonant Fatigue Testing of Welded Tubular X-Joints for Offshore Jacket Foundations
Authors: Van Wittenberghe Jeroen , Thibaux Philippe , Van Poucke Maarten 
Published: November 2019

Abstract
Offshore wind turbines are being installed in deeper water and with more powerful generators resulting in more severe loading conditions on its foundations such as jacket structures. Because the main loading is due to wind and currents, the dominant design limit state is fatigue. The fatigue performance of the tubular joints used in jacket structures has been assessed several decades ago based on test results with limited component dimensions (diameter and wall thickness). In addition, improvements of welding methods and evolution of steel grades are not considered in the current design standards.
To provide experimental fatigue-life data on large-scale structures a test program has been carried out on 4 welded tubular X-joints. Each X-joint consists of two horizontal braces with a diameter of 711 mm welded to a central vertical tubular member with 806 mm diameter. The X-joint has a total length of 7.5 m and has two identical welds that are fatigue tested. The fatigue tests are carried out on an innovative resonant bending fatigue test rig that allows to load the specimen in in- and out-of-plane direction at a different amplitude to obtain an even stress distribution over the circumference of the welds. The tests are carried out at a speed close to the resonance frequency of the X-joint. During the test, hotspot strains are measured using strain gauges and a limited amount of water pressure is used to detect through-thickness cracks. The tests are carried out in two phases. During the crack initiation phase, the sample is loaded in both the in- and out-of-plane mode. Once cracks are detected, the test is continued in the crack propagation phase with loading in the plane where cracks had been initiated until through-thickness cracking appeared. During this phase the beach marking technique has been used to mark the shape of the fracture surface at different moments during the fatigue tests.
The testing program is part of the RFCS project JABACO that aims to reduce offshore wind cost by incrementing prefabrication of the jacket substructure.
Seismic Design Challenges of High Pressure Riser Systems on Gravity Based Structures
Authors: Sonawane Mahesh , Vaidya Rohit , Kadakia Ronak , Haeberle Hunter , Ward Phil 
Published: November 2019

Abstract
This paper presents two case studies of the seismic analysis of high pressure riser and conductor systems used on shallow water fixed platforms (approximately 120m water depth) offshore Newfoundland and Labrador, Canada. The case studies presented consider the Hebron and White Rose extension Husky gravity-based concrete platforms. A methodology is presented to assess the dynamic and resonant response of each conductor and riser system to seismic loading using a fully integrated conductor and platform interaction model. Seismic loading is an application of an earthquake-generated agitation to a structure. This occurs at contact surfaces either with the ground, or with adjacent structures, or with gravity waves. Nonlinear time history analyses of the riser system subjected to various ground motion records are performed to simulate the seismic load. Design considerations that drive the HP riser design are discussed.
The paper addresses the intricacies of the gravity base concrete platform-riser system interaction, initial configuration and dynamic seismic response. The riser and conductor system response is used to determine HP riser connector and centralization requirements. The learnings taken from the detailed modeling method are presented along with the advantages of this methodology.
An Improved Body-Exact Method to Predict the Maneuvering of Ships in a Seaway
Authors: Subramanian Rahul , Beck Robert F. 
Published: November 2019

Abstract
Over the last decade, the importance of considering the effects of waves on the maneuvering characteristics of ships has been widely recognized. This paper presents the application of a recently developed nonlinear body-exact scheme (Subramanian, Rakesh, and Beck (2018)) to directly simulate the maneuvering characteristics of a container ship in calm water and in regular waves. In the present body-exact scheme, the perturbation free surface boundary conditions are transferred to a representative incident wave surface at each station at each time. The hydrodynamic forces are computed on the exact instantaneous wetted surface formed by the intersection of the incident wave surface with the exact body position at each time. It is proposed that this model will not only improve first order sea loads but also the higher order drift force predictions which are critical for determining the trajectory of a maneuvering vessel in a seaway. The strip theory formulation has been found to be numerically stable, robust and computationally efficient, which are all critical aspects when performing long time maneuvering simulations. The hull maneuvering, rudder and propeller forces are adopted from standard systems-based approaches that are used to predict calm water maneuvers. Care is taken to ensure that ideal fluid effects are separated from viscous effects and not double counted. Results are presented for turning circle maneuvers in calm water and regular waves incident at various headings and wavelengths. The numerical results are compared with available experiments.
Numerical Modelling of a Relatively Small Floating Body’s Wave and Low Frequency Motion Response, Compared With Observational Data
Authors: Wright Christopher , Yoshimoto Haruki , Wada Ryota , Takagi Ken 
Published: November 2019

Abstract
Global population growth and climate change are driving a need for increased clean renewable energy generation. One such resource is wind energy and while the onshore and fixed offshore wind energy industries are mature, the floating offshore wind energy industry is still at a demonstration phase. Floating wind turbine platforms are generally of a much smaller displacement than the typical offshore structures that have been used in the oil and gas industry. This difference results in changes to the platform dynamics, especially those resulting from second order wave forces. Existing research into low frequency drift motions of small body platforms has been mainly confined to numerical modelling with some experimental work. This work expands on this knowledge by validating numerical modelling with full scale observational data.
In this paper, a numerical time-domain model of a relatively small displacement platform is developed. The platform is installed in a relatively shallow water depth of about 110 m and station keeping is provided by four equally spaced catenary mooring chains. The required fidelity for the low frequency response is compared using first order forces only and either a full QTF (quadratic transfer equation) or Newman’s approximation. The model is compared with observation data from the Fukushima FORWARD project’s floating substation, an advanced spar type, which is composed of measurements of multidirectional wave spectra, wind and current as model inputs and six DOF platform motions as outputs. In addition to this the model computational expense is reduced by decreasing the number of wave directions simulated. The accuracy of such reductions is then described. Observation data is grouped according to sea-state data. An empirical drag coefficient formula is proposed. The 50 year return period design sea-state is also modelled using a JONSWAP spectrum and the various numerical models.
Experimental Study on Friction of Steel Wires of Dynamic Umbilical for Fatigue Life Analysis
Authors: Yin Yuanchao , Lu Qingzhen , Wu Shanghua , Yan Jun , Yue Qianjin , Chen Jinlong 
Published: November 2019

Abstract
Dynamic umbilicals are widely used in the wet tree development of deep-water field. In the application of dynamic umbilicals, fatigue is a key failure mode which may cause severe economic consequences. The fatigue behavior of dynamic umbilical is complicated by the mechanical properties of the material, the cross-section design and the interaction of different components. Published studies have shown that the interaction friction stress of steel wires is critical for fatigue analysis. Coefficient of friction were used as a constant during the fatigue life analysis. However, the friction stress and the coefficient of friction may change during the wear of the steel wire.
This paper presents a new experiment method and device to evaluate the change of the coefficient of friction of steel wire. Different cycles of reciprocating wear were carried out on samples to simulate interaction of the steel wires during the process of fatigue. The samples are pairs of steel wires which were cut on a dynamic umbilical. The interaction stress and friction stress were measured during the test. Micro morphology on the surface of steel wire at the contract zone were measured to investigate the wear of the sample.
The test result shows that the coefficient of friction and stress changes during the test. Worn marks were found on the contact zone of the steel wires. The change of the coefficient of friction may affect the accuracy of fatigue life analysis of dynamic umbilical. Conclusions were also presented on the coefficient of friction test and theoretical calculation method to approach a more accurate fatigue life for dynamic umbilical design.
Reduced Order Model for Unsteady Fluid Flows via Recurrent Neural Networks
Authors: Reddy Sandeep B. , Magee Allan Ross , Jaiman Rajeev K. , Liu J. , Xu W. , Choudhary A. , Hussain A. A. 
Published: November 2019

Abstract
In this paper, we present a data-driven approach to construct a reduced-order model (ROM) for the unsteady flow field and fluid-structure interaction. This proposed approach relies on (i) a projection of the high-dimensional data from the Navier-Stokes equations to a low-dimensional subspace using the proper orthogonal decomposition (POD) and (ii) integration of the low-dimensional model with the recurrent neural networks. For the hybrid ROM formulation, we consider long short term memory networks with encoder-decoder architecture, which is a special variant of recurrent neural networks. The mathematical structure of recurrent neural networks embodies a non-linear state space form of the underlying dynamical behavior. This particular attribute of an RNN makes it suitable for non-linear unsteady flow problems. In the proposed hybrid RNN method, the spatial and temporal features of the unsteady flow system are captured separately. Time-invariant modes obtained by low-order projection embodies the spatial features of the flow field, while the temporal behavior of the corresponding modal coefficients is learned via recurrent neural networks. The effectiveness of the proposed method is first demonstrated on a canonical problem of flow past a cylinder at low Reynolds number. With regard to a practical marine/offshore engineering demonstration, we have applied and examined the reliability of the proposed data-driven framework for the predictions of vortex-induced vibrations of a flexible offshore riser at high Reynolds number.
Squall Detection and Analysis From Historical Satellite Data
Authors: Renac L. , Hurdle D. P. , Enet F. J. M. , De Vroom J. 
Published: November 2019

Abstract
Thunderstorms and squalls (fronts of contiguous thunderstorms) are associated with short but intense local winds that have a great impact on operability or design conditions for moored ship operations in the coastal zone. The brevity and local scale of such events makes them difficult to capture using standard measurement data and usually requires dedicated long-term measurement campaigns. Because the standard measurements available are usually based on 10-minute averages taken once an hour, such data is often not available. In the absence of conventional measured data, the use of satellite data can provide useful design data if analyzed and applied with caution. We present two case studies (West Africa and Brazil) where squalls have been identified in satellite data and used for extreme value analysis (EVA) to support the design of intermediate water depth mooring systems. The detection of squalls is confirmed with satellite imagery and the handling of this data for the EVA is presented in detail with assumptions made and the sensitivity of the results to these assumptions. The impact on design values is also discussed for both geographic locations.
Experimental Evaluation of Hydrodynamic Loads on Marine Risers
Authors: Vileti Vinicius L. , Esperança Paulo de Tarso T. , Vitola Marcelo A. , Vignoles Mario A. 
Published: November 2019

Abstract
As the exploration of oceans for oil and gas goes to deeper depths, understanding the riser dynamics is fast becoming a key aspect of such systems’ design. The hydrodynamic loads acting on marine risers such as inertial and drag forces due to the relative motions between the riser and fluid, is of great concern for researchers and exploration systems’ designers.
The lack of information regarding some conditions applied on risers systems nowadays, led to an experimental approach to understand the hydrodynamic loads on these conditions, to extract those information, and complement the available literature on this subject.
This study provides new insights into the inertial and drag hydrodynamic coefficients (Cm and Cd respectively), how they evolve for higher KCs. These findings should make an important contribution expanding the understanding of the hydrodynamic loads on a circular cylinder.
This paper first gives a brief overview of the recent research history of this subject and the theoretical background used, followed by the description of test setup and analysis method. Lastly, the results are presented and discussed in comparison with literature data.
On Environmental Contours for Marine and Coastal Design
Authors: Ross Emma , Astrup Ole Christian , Bitner-Gregersen Elzbieta , Bunn Nigel , Feld Graham , Gouldby Ben , Huseby Arne , Liu Ye , Randell David , Vanem Erik , Jonathan Philip 
Published: November 2019

Abstract
Environmental contours are used in structural reliability analysis of marine and coastal structures as an approximate means to locate the boundary of the distribution of environmental variables, and to identify environmental conditions giving rise to extreme structural loads and responses. There are different approaches to estimating environmental contours, some directly linked to methods of structural reliability. Each contouring approach has its pros and cons. Although procedures for applying contours in design have been reported in articles and standards, there is still ambiguity about detail, and the practitioner has considerable flexibility in applying contours. It is not always clear how to estimate environmental contours well. Over four years, DNV-GL, Shell, the University of Oslo and HR Walling-ford worked together to review current practice regarding the use of design contours. In this paper, we present a summary of our findings. We overview the motivations for different approaches to contours, and their resulting characteristics. Using different marine applications, we also explore the various sources of uncertainty present, their impact on contour estimates and the estimation of extreme environmental loads and responses.
A Fatigue Assessment Procedure for Drilling Pipes of Scientific Vessels
Authors: Aguiari Martina , Rizzo Cesare Mario , Inoue Tomoya 
Published: November 2019

Abstract
In recent years, many disasters due to earthquakes and tsunamis occurred in various countries, including Japan. Two triple junctions exist below the Japanese archipelago and around Japan, where three plates meet to form a complicated crustal structure. To conduct research on the Tohoku earthquake, which accompanied the tsunami that devastated northern Japan in March 2011, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) constructed the scientific deep-sea drilling vessel Chikyu. To understand the mechanism of the earthquakes, a direct access to the fault zone is necessary. During drilling operations, the drill pipes are stressed by different forces and the occurrence of drill-string failures is high, which causes significant loss of money and time. This study focused on the definition of a practical fatigue assessment procedure useful to avoid failures during drilling operations. In this paper the proposed procedure is outlined, and the sensitivity analysis carried out to highlight most influencing parameters is presented.
An Experimental Investigation of Filtercake Reinforced Wellbore Strengthening and Fracture Sealing
Authors: Yang Mingzheng , Chen Yuanhang , Growcock Frederick B. , Zhang Feifei 
Published: November 2019

Abstract
Drilling-induced lost circulation should be managed before and during fracture initiation rather than after they propagate to form large fractures and losses become uncontrollable. Recent studies indicated the potentially critical role of filtercake in strengthening the wellbore through formation of a pressure-isolating barrier, as well as plugging microfractures during fracture initiation. In this study, an experimental investigation was conducted to understand the role played by filtercake in the presence of lost circulation materials (LCMs). A modified permeability plugging apparatus (PPA) with slotted discs was used to simulate whole mud loss through fractures of known width behind filtercake. Cumulative fluid loss upon achieving a complete seal and the maximum sealing pressure were measured to evaluate the combined effects of filtercake and LCMs in preventing and reducing fluid losses. The effects of some filtercake properties (along with LCM type, concentration and particle size distribution) on filtercake rupture and fracture sealing were investigated. The results indicate that filtercake can accelerate fracture sealing and reduce total mud loss. Efficiently depositing filtercake while drilling can reduce the concentration of LCM that is required to plug and isolate incipient fractures.