bluuebunny/crossref_metadata_2025_split huggingface dataset:
UiS Subsea Freight-Glider: Controller Design and Analysis
Authors: Nawaz Ahmad Usman , Xing Yihan 
Published: October 2022

Abstract
The UiS subsea freight-glider (USFG) is a novel 785 DWT large cargo-carrying underwater autonomous vehicle. It uses variable buoyancy propulsion, i.e., it glides forwards using generated lift and drag forces at the hydrofoils while ascending and descending in water. This propulsion method is ultra-efficient and can transport cargo over long distances with minimal energy consumption. For USFG to operate with maximum speed and enhanced range, a robust, reliable, and accurate control is important as this results in a precise navigation system that would allow for its gliding motion to be extremely efficient. During long-distance voyages, a robust control system based on a feedback loop provides enhanced utility against any external uncertainties or environmental disturbances. The purpose of this work is to implement a control methodology that is based on feedback from the model. This approach removes the need for excessive tuning of controllers for any changes in operating conditions. Moreover, dynamic states, i.e., velocities, can be determined by designing an observer which can be used to predict the motion of the USFG in a planar axis. The gliding paths of USFG in the vertical plane are analyzed along with the observability and controllability of the steady equilibrium glides. For this purpose, the control system is designed with two different controllers, PID and LQR, which control the heave and pitch of the vehicle. Finally, a comprehensive comparison study is presented, which highlights the key differences for the controllers for tunning and rise time. This can also help in designing the ideal control for the required application.
Quantification of Pitting and Stress Concentration Factors on Steel Coupons Exposed to Seawater in the North Sea
Authors: Thibaux Philippe , Vanden Haute Cedric 
Published: October 2022

Abstract
Offshore structures are exposed to a harsh environment. Normally they are protected against corrosion by a combination of excess thickness, cathodic protection, paints and / or oxygen depletion. However, the corrosion protection system can also become ineffective leading to a thickness loss and a degradation of the surface, generally by pitting. The present investigation reports the characterization of the surface of corrosion coupons exposed to free corrosion inside monopiles. Three dimensional scans of the surfaces were performed, providing information about roughness data, identification of separate pits and their individual characteristics. The statistical distribution of the pits for a given coupon can then be extrapolated towards a complete structure and linked to an increased probability of failure by computing the stress concentration factor caused by the individual pits.
Derivation of Vessel Motions as Operational Limits and Motion Forecasting With 2D Wave Spectra: Case Study of Inter-Array Subsea Cable Installation in the North Sea
Authors: Riverola Calavia Javier , Paalvast Mark , Ledoux Bart , Kymmell Jelte 
Published: October 2022

Abstract
The conventional approach for estimating vessel operability for offshore installation operations relies on numerical results from discrete sea state simulations (tabulated operability) and wave forecasts simplified into a set of statistical parameters (Hs, Tp, direction, etc.), leading to an important loss of operability and reliability. Recently, the potential of using vessel motions as cable installation limits has been explored due to the evidence of strong correlations between the vessel motions and the dynamic response of the cable or pipe. This paper presents an end-to-end analysis methodology for calculating operational limits of cable installation operations based on vessel motion criteria using statistical modeling and estimating vessel operability using 2D wave spectra for motion forecasting. This response-based forecasting method mainly benefits from more accurate and realistic wave forecast input, more reliable probabilistic model of the system response (vessel and cable) and avoids the conservative sea state discretization. The method is then applied to the entire sequence of inter-array cable installation in a North Sea offshore windfarm using 2D wave spectral hindcast data, including a weather downtime comparison with the conventional method. Heave velocity was found to be a great and simple predictor of cable response in shallow water applications. Response-based method results showed a significant reduction in vessel weather downtime for array cable installation. This approach could help to reduce the cable installation costs in offshore windfarms considerably, while also increasing the confidence and understanding of the risks involved in the operations.
Real-Time Prediction of Incoming Wave Profile Surrounding Floating Offshore Wind Turbine Using Kalman Filter
Authors: Isnaini Rodhiatul , Toichi Kenta , Iijima Kazuhiro , Tatsumi Akira 
Published: October 2022

Abstract
The present research discusses the possibility of employing a Kalman filter algorithm to predict a real-time data of the incoming wave elevations over a floating offshore wind turbine (FOWT). This is suggested to address some problems in the existing safety management system of FOWT’s operation and maintenance, from the perspective of personnel safety. In this case, knowing immediate wave elevation from a couple cycle ahead is very beneficial to elevate the safety factor during the crew transfer process from the boat to the FOWT. This can be done when the incoming waves are able to be predicted. This time, the prediction is carried out centering around the elementary wave coefficients estimation. Hence, these coefficients are prescribed to be the state variables in the Kalman filter. Meanwhile, two types of observation data are introduced. The first one retrieved its values from numerically generated data, while the other one is data from experiment. Transfer functions that are particular over some specific measurements are used as the bridge between the state model and observation model. Filter capability to predict wave profiles from unidirectional and bidirectional spectrum is explored. Overall, prediction results obtained through numerically generated data show a good agreement with its references. Experiment-based prediction results however, exhibit less favorable results.
Introducing Observation-Based Physics Into the WAM Wave Model
Authors: Kousal Joshua , Liu Qingxiang , Staneva Joanna , Behrens Arno , Günther Heinz , Bidlot Jean-Raymond , Babanin Alexander V. 
Published: October 2022

Abstract
Third generation spectral wave models predict the growth, decay and transformation of wind-generated waves. WAM is one of the two dominant third-generation spectral wave models covering the global ocean. The standard representation of deep-water wave physics in WAM is the semi-empirical approach of Ardhuin et al. (2010; hereafter ARD). The other modern package of wave physics for spectral models, available in WAVEWATCH-III and SWAN, but not in WAM, is the observation-based approach developed by A. V. Babanin, I. R. Young, M. A. Donelan, M. L. Banner and W. E. Rogers (hereafter BYDBR). Its source functions were measured and therefore are not subject to tuning (within confidence limits of the measurements). Furthermore, the observations revealed and/or quantified physical phenomena missing or neglected in other source packages for spectral wave models such as non-linear airflow separation (hence relative reduction of wind input at strong winds), steepness-dependent wave growth (making the wind input a weakly non-linear function of the wave spectrum), negative wind input under adverse winds, two-part wave dissipation consisting of a local in wavenumber space term and a cumulative term (which is an integral of the spectrum), a wave breaking threshold below which no breaking occurs, and swell decay due to interaction with and production of oceanic turbulence. This work documents the implementation of BYDBR physics into WAM. We find that the performance of WAM using BYDBR physics is comparable to the standard with respect to the mean-based metrics. The mean differences between BYDBR and ARD are most prominent in Boreal winter, with widespread reductions in the N. H. of ∼10cm and ∼0.2s for significant wave height and mean wave period respectively.
Discretization Challenges in Crash Simulations: Mesh, Geometry and Failure Criterion Effects From the Energy Perspective
Authors: Coppejans Okko , Werter Noud 
Published: October 2022

Abstract
The simulation of collisions of ships using FEA has a long history of rules and guidelines to which such simulations should conform. Nevertheless, there are still subjects that lack thorough understanding in literature and standards. With the rise in popularity of stress state dependent failure criteria and the ability to simulate with smaller element sizes, new questions arise. This paper is part of an ongoing sensitivity study of the effect parameters such as element size, choice of failure criterion, geometric placement of the striking vessel and friction have on the dissipated energy in a collision simulation. It is shown that the use of different mesh sizes and different failure criteria results in different failure mechanisms and deformation patterns and have a great effect on dissipated energy. The stress states in which most of the plastic work is performed (and therefore energy is dissipated) are shown to be in the triaxiality range of 0.27–0.35. The energy contributions of the regions above that, towards equi-biaxial tension, and below that, towards pure shear, are very significant on first contact and shape the initial deformation mechanism. Furthermore it is shown that the placement of the incoming V-bow with respect to element boundaries significantly influences the energy absorption. The parameters influencing energy dissipation are numerous and just a very small selection is discussed in this paper. No perfect deterministic approach is presented in this paper, but a base for a probabilistic approach is given.
A Physical-Based Damping Model of Gap and Moonpool Resonance in WAMIT
Authors: Ravinthrakumar Senthuran , Ommani Babak , Kristiansen Trygve , Olimb Idunn , Lyngvær Bernt Karsten 
Published: October 2022

Abstract
An engineering model to estimate and incorporate quadratic damping of the piston-mode moonpool responses in the proximity of the piston mode period is proposed. The model provides a physical-based equivalent linearized damping coefficient. The method is not limited to forced motion, but applicable to freely floating moonpool vessels. Further, it is not limited to moonopools, but can be generalized to gap resonance problems, such as side-by-side operations. The soundness of the proposed physical-based method is demonstrated using the panel code WAMIT with a linear damping term in the free-surface boundary condition inside the moonpool using two existing moonpool experiments as case studies; (1) a two-dimensional rectangular box with a moonpool subject to forced heave, and (2) a freely floating offshore vessel in incident waves. The WAMIT computations using the proposed method reconstructs the experimentally obtained piston-mode and vessel responses well. We suggest that the proposed method can be used with fair degree of confidence in an early design or operational analysis phase, in the (often) case that the quadratic damping is not known from either experiments or CFD. To our knowledge, this is the first general, physical-based piston-mode damping model that does not require any tuning from experiments.
A Bayesian Networks Approach for Safety Barriers Analysis: A Case Study on Cryogenic Hydrogen Leakage
Authors: Lenti Manuel , Balestra Lorenzo , Schjølberg Ingrid 
Published: October 2022

Abstract
One of the main concerns, when considering hydrogen storage systems, is the possibility of an unwanted leak, which can result in potential fire, explosions, or detonation, potentially affecting both structures and passengers safety. Safety barriers can be implemented with respect to the storage system design to prevent, mitigate and control unwanted events or accidents. After the identification of the relevant failures, and hazards inherent in the system, a quantitative safety barrier analysis can be performed to assess the safety barriers reliability and quantify with numerical values the overall risk. Typically, the SB’s performances can be quantified using recorded historical failure data, applying well-known modeling tools (e.g. fault tree and event tree). This paper illustrates how the use of Bayesian networks can overcome the limitations of conventional static-structured techniques improving the flexibility in the cause-consequences representation and evaluation of potential accident scenarios. The aim of this work is to test the application of Bayesian networks for a quantitative risk analysis considering a leakage of cryogenic hydrogen from a storage tank installed on a fuel cell powered maritime vessel. A case study for liquid hydrogen release inside the tank connection space of a maritime storage vessel has been proposed. The safety barrier performances have been evaluated calculating their failure probability and assessing the possible consequences. The results indicate the advantages of Bayesian networks for quantitative assessment of safety barriers in critical accident scenarios, increasing the confidence towards hydrogen as a safe energy carrier for maritime applications.
Numerical Simulation of Nonlinear Wave Interaction With Floating Solar Platforms With Double Tubular Floaters Using Viscous Flow Model
Authors: Baruah Gautam , Karimirad Madjid , Abbasnia Arash , MacKinnon Pauline , Sarmah Nabin , Moghtadaei Abdolmajid 
Published: October 2022

Abstract
The development of a numerical model for the simulation of wave interaction with floating solar structures is presented in this paper. A twin-cylinder platform representing the floating structure of the floating solar is used in the simulation. To evaluate the response of the structure under waves that affects the integrity of solar panels, a numerical model is developed. Taking account of the viscous effects is essential for reliable estimation of the exciting loads and structural responses of the platform. Hence, the RANS (Reynolds-averaged Navier-Stokes equations) model is established to simulate this structure under a range of wave frequencies. The viscous model takes advantage of the finite volume solver to accomplish computational fluid dynamic (CFD) analysis. Convergence and stability of the model are evaluated for different mesh resolutions and correspondingly the computational cost is demonstrated. Numerical solutions are compared with experimental data for verification and validation. Therefore, the range of validity of the viscous model is evaluated for strong nonlinear incident waves.
A Deep Learning Approach for Underwater Leak Detection
Authors: da Silva Viviane F. , Netto Theodoro A. , Ribeiro Bessie A. 
Published: October 2022

Abstract
The increase in costs in the exploration and production of oil and gas in deep waters has led companies in the sector to invest in innovative technologies to detect, locate and correct faults in their production systems.
This research aims to develop a methodology for monitoring and detecting leaks in subsea structures based on deep neural networks, allowing automated, efficient, and less costly monitoring than conventional monitoring methodologies.
A set of monitoring data will be pre-processed for noise elimination, resolution improvement and resizing, to obtain a better performance of the algorithm. The next step consists of extracting relevant characteristics from the dataset to clearly identify the leak.
The results show the metrics used to evaluate the performance of the neural network as the accuracy and efficiency of the algorithm to detect leaks in the underwater structures and equipment.
Images of the Gulf of Mexico oil spill were used to test the methodology and the successful detection of the leak demonstrates the potential of the methodology for underwater leak detection.
Influence of Sail Design Parameters on Unsteady Propeller Thrust for Underwater Vehicles
Authors: Takahashi Kenshiro , Arai Jun , Mori Takayuki 
Published: October 2022

Abstract
To realize covert missions, submarines and other underwater vehicles must satisfy strict requirements pertaining to their acoustic signatures. However, marine propellers produce unsteady forces, resulting in undesirable noise. In this work, a parametric study was performed on the sail design under unsteady propeller thrusts by using computational fluid dynamics (CFD). The CFD procedure was validated for multiple propeller models and wake profiles and used to compute the unsteady propeller thrust of an underwater vehicle. The DARPA SUBOFF submarine and INSEAN E1619 propeller were adopted as benchmarks. The axial location of the sail and the sail width were varied, and the unsteady propeller thrusts were determined. Dominant harmonics of the computed propeller thrusts were analyzed via Fourier series. Furthermore, a correlation analysis was performed between the harmonics of the unsteady propeller thrust and inflow wake. The amplitude of the thrust fluctuation for the aft-fitted sail model was nearly two times that for the original fore-fitted sail model. The dominant 7th harmonic was significantly lowered by altering the sail width. Positive correlation coefficients were obtained at several harmonics that did not match the number of blades.
Low Cycle Fatigue Evaluation for High Strength Welded T-Joint Based on Structural Strain Method
Authors: Kim Ji Hoon , Kim Myung Hyun , Moon Won Ki , Lim Jong Il , Kim Seong Min , Yun Kwang Hee 
Published: October 2022

Abstract
In design process of welded structures, fatigue failure is one of the main issues to be carefully considered in the assessment of the structural integrity. In general, fatigue failure typically occurs at locations structural discontinuities. In particular, welded structures inevitably contain structural discontinuities during manufacturing process and those locations are vulnerable to fatigue loads. The 2007 ASME Div.2 Code suggests a master S-N curve approach based on structural stress that is insensitive to the size of element with improved accuracy in stress calculation [1]. Structural stress method has been validated based on numerous experimental data and studies in the high-cycle fatigue regime. However, these methods cannot be applied in low-cycle fatigue regime, and validations of the structural stress method in the low-cycle regime are insufficient so far. In this regard, an extension to the master S-N curve, structural strain method was introduced to evaluate the low-cycle fatigue performance by Dong et. al [2].
The target of this study is to validate the structural strain method in low-cycle fatigue regime of welded joints. For that purpose, low-cycle fatigue test was performed on high strength steel welded T-joints. Pseudo structural stress can be calculated through the derived structural strain, and the equivalent structural stress is expressed in consideration of the shape and thickness effects. Fatigue life evaluation using structural strain method exhibited a good correlation with the master S-N curve not only in the elastic region but also in the low-cycle regime accompanied by plastic deformation. By using structural strain method, it is possible to comprehensively evaluate the fatigue life both in high and low-cycle fatigue regime.
Study on Hydrodynamic Performance of a Conceptional Sea-Train
Authors: Qin Yan , Yao Chaobang , Zheng Yi , Huang Jianghao 
Published: October 2022

Abstract
Multiple vessels sail together at sea through physical connection or non-physical connection attaching to each other to form a train, which is called “Sea-Train”. The “Sea-Train” is a new concept of multi-vessel navigation, which aims to minimize the collective resistance of its system. By reasonably optimizing the horizontal and vertical spacing of each ship, the “Sea-Train” uses the favorable wave interference between hulls to obtain drag reduction performance and increase its voyage. To investigate the resistance variation of formation “Sea-Train” with speed, transverse distance and longitudinal distance, Wigley ship is taken as the research object. Based on the STAR-CCM+ software platform, the VOF method and the K-Epsilon turbulence model are used to solve the Navier-Stokes equation to numerically simulate the motion of the “Sea-Train”. The total resistance and its components of the “Sea-Train” are calculated by CFD software, at different speeds and different formations, to analyze the characteristics and laws of hydrodynamic interference. Further analyzing the relationship between the resistance of the “Sea-Train” and the transverse and longitudinal distance, the wave patterns of the free surface and ship side are obtained by using the numerical simulation results. The mechanism of drag reduction is explored to provide theoretical basis for the layout optimization of “Sea-Train” at different speeds.
Model Experiments and Numerical Simulations on GPS Buoy With Steep Wave Mooring
Authors: Araki Motoki , Watanabe Mitsushi , Masanobu Sotaro , Omura Atsuo , Kaita Shouhei , Kunita Atsushi 
Published: October 2022

Abstract
Recent runout accidents of GPS buoy demand more robust mooring system in harsh environment. The mooring with steep wave configuration formed by intermediate buoys could be a candidate of the robust mooring system. However, the steep wave mooring (SWM) could have some risk of intersection problem in overlapped section of the mooring line, e.g., collision/contact and/or tangling. Therefore, the risks of the intersection problem of the SWM are identified with 1/20 scaled model experiment and numerical simulation of a GPS buoy with the SWM. In the model experiment, collision/contact and tangling of the mooring lines were observed and the top and bottom tensions were mainly analyzed. The numerical simulation corresponding to the model experiment was carried out using OrcaFlex. The simulation successfully reproduced the tangling phenomenon of the mooring line, and the spectra of computed top and bottom tensions show similar tendency with the model experimental results. Therefore, both the model experiment and the numerical simulation shows capability to identify the risks of the intersection problem of the SWM.
Evaluation of Nonlinear Fourier-Based Maximum Wave Height Predictors Under the Nonlinear Schrödinger Equation
Authors: Lee Yu-Chen , Wahls Sander , Brühl Markus 
Published: October 2022

Abstract
Rogue waves are extreme waves in the ocean that appear from nowhere and disappear without a trace. They are usually modelled by the nonlinear Schrödinger equation (NLS), which describes nonlinear phenomena such as modulational instability and solitons on finite backgrounds. In this study, the periodic nonlinear Fourier transform (NFT) for the NLS equation is applied to simulate ocean surface waves in deep water. The temporal and spatial structures of surface waves are obtained by evolving JONSWAP time series using the NLS equation. Several parameters extracted from the NFT spectra of the initial time series are investigated as predictors for the maximum wave height during evolution. We investigate several parameters from the literature, and find that with suitably optimized coefficients, a NFT-based parameter based on the largest unstable mode has a good correlation with the overall maximum wave amplitude. This new spectral criterion can contribute to rogue wave forecasting under extreme sea states.