bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ship-Wave Impact Generated Sea Spray: Part 2 — Formulating Spray Frequency
Authors: Mintu Shafiul A. , Molyneux David , Colbourne Bruce 
Published: December 2020

Abstract
In certain, but not all, circumstances a cloud of spray forms after a wave impacts a ship. The frequency of spray events affects the icing process. Previous spray frequency formulas are derived empirically from field observations considering only the ship’s forward speed and oceanographic conditions. The significance of various degrees of ship motions on the spray frequency is ignored. However in reality, the interrelationships of heave and pitch motions under wave actions together with surge motion determine the number of spray events that a ship may experience in a given period of time.
This paper introduces a theoretical model for estimating the frequency of sea spray considering ship motions. Ship motions can be easily estimated by strip/panel methods. However, in this work, the aim was to develop a simple framework for a quick estimate of spray frequency. The model inputs are, therefore, restricted to ship’s principal particulars, its operating conditions, and the environmental conditions. The wave-induced motions are estimated by semi empirical analytical expressions. A novel spray threshold is developed to keep the deck wetness frequency separated from the spray frequency. The proposed spray frequency formula is validated against available full-scale field measurements from a Russian fishing vessel, MFV Narva, and reasonable agreement is found. Limitations of previous empirical formulas are also discussed.
A Comparative Study of Laminar-Turbulent Displacement in Eccentric Annulus Under Imposed Flow Rate Conditions
Authors: Foolad Yasaman , Bizhani Majid , Frigaard Ian 
Published: December 2020

Abstract
In this paper, we present and discuss an experimental study of fluid-fluid displacement in a fully eccentric horizontal annulus. Experiments were designed to simulate turbulent displacing flows, and the results are used to investigate the displacement processes in terms of interface dynamics and displacement efficiency. It is widely believed that turbulent flows are more efficient at displacement, but it is not always clear under what conditions this comparison is made. A set of experiments was conducted to investigate the role of flow regime under a constant imposed flow rate in the absence of any stabilizing buoyancy effect (i.e. iso-density fluids). Carbopol solutions are displaced with various concentrations of Xanthan gum, to simulate a drilling mud displaced by a spacer fluid. The flow regime of the displacing fluid spans from laminar to fully turbulent flow regimes. The displacement tests are all unsteady in a sense that wide-gap velocity is always faster than that of the narrow-gap. The displacement flows and interface dynamics are captured using optical techniques, and the images are post-processed to ascertain the displacement efficiency, interface velocity and elongation. We conclude with a discussion on the significance of outcomes achieved in this study, and also limitations of the experimental technique.
Numerical Simulation of the Domino Effect of Mooring System Failure for an Aquaculture Net Cage Under Waves and Currents
Authors: Tang Hung-Jie , Yang Ray-Yeng , Wen Tzu-Chieh , Yeh Po-Hung , Huang Chai-Cheng 
Published: December 2020

Abstract
Up to date, the mooring system failure of aquaculture net cage remains a continuing problem, especially the domino effect, which often leads to huge economic losses. Thus, this study aims to investigate the domino effect of a mooring system of a net cage under waves and currents. In this study, a time-domain numerical model based on the Morison equation and the lumped mass method is applied. A full-scale net cage system widely used in a local sea area is adopted. A 50 years return period waves with a strong following current is considered to be the design condition. It can be expected that the tension on the remaining upstream anchor increases dramatically when an upstream anchor is lost. Then, the domino effect occurs if the maximum tension on the remaining anchor exceeds its design condition. Therefore, in this simulation, the initial failure is considered to be a man-made event at a preset time, but the rest failures are resulted from exceeding the breaking strength of a rope. Both the current-only condition and the wave-current condition have been examined. The results including mooring line tension, volume reduction coefficient and rigid body motion are discussed. In addition, the results show that the failure sequence of anchor is different between the current-only condition and the wave-current condition.
Path Following Control of Autonomous Underwater Vehicle Using Nonlinear Model Predictive Control
Authors: Taniguchi Tomoki , Umeda Jun , Fujiwara Toshifumi , Kim Kangsoo , Sato Takumi , Inaba Shogo 
Published: December 2020

Abstract
The path following control of an AUV considering arrival times at waypoints is proposed in this paper. The temporal constraint is considered by adding the surge velocity and the nominal thrust force as reference trajectory in the objective function of the nonlinear model predictive control (NMPC). The proposed control strategy uses fewer reference variables than conventional trajectory tracking problems. The simulated results of the proposed control strategy are compared to the NMRI Cruising AUV#4 actual dive data. The simulated arrival times of waypoints were matched well to the measured data. Two guidance laws, the line of sight with lookahead-based steering law and the pure pursuit guidance law, are also applied to NMPC to determine reference yaw angle.
Numerical Study on the Slamming Impact of Stiffened Flat Panel Using ICFD Method: Effect of Structural Rigidity on the Slamming Impact
Authors: Yamada Yasuhira , Takamoto Kota , Nakanishi Toru , Chong Ma , Komoriyama Yusuke 
Published: December 2020

Abstract
In order to preliminary investigate structural response of stiffened panel due to slamming impact, two series of fluid structure coupling analysis is carried out using a new fluid structure interaction (FSI) methodology of Incompressible Fluid Dynamics (ICFD) [1]. ICFD is the method where structure and fluid are modeled as both Lagrange methods.
Firstly, slamming impact of a sphere is analyzed with ICFD and SPH methods respectively and compared with experimental and analytical results. Acceleration, slamming force and pressure are compared and discussed in detail.
Secondary a fixed stiffened flat panel of offshore structure subjected to slamming impact is investigated as a part of the ISSC II.1 benchmark study. Effect of mesh size is investigated. Analysis results are compared with existing ALE method [1] as well as other results within the framework of ISSC II.1 benchmark study.
In both studies, structure is modeled by elastic-plastic and by rigid respectively. By comparing these two results, effect of structural rigidity on the slamming pressure as well as slamming force is investigated.
Collapse Resistance Under Combined External Pressure and Bending Deformation of Coated Linepipe
Authors: Sakimoto Takahiro , Tajika Hisakazu , Handa Tsunehisa , Murakami Yoshiaki , Igi Satoshi , Kondo Joe 
Published: December 2020

Abstract
As offshore pipeline projects have expanded to deeper water regions with depths of more than 2 000 m, higher resistance against collapse by external pressure is now required in linepipe. Collapse resistance is mainly controlled by the pipe geometry and compressive yield strength. In UOE pipe, the compressive yield strength along the circumferential direction changes dramatically due to tensile pre-strain that occurs in pipe forming processes such as the expansion process. In order to improve the compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. As the mechanism of this effect, it is understood that internal stress is generated by the accumulation of dislocations, and this reduces reverse flow stress. Compressive yield strength is also changed by the thermal cycle associated with application of fusion-bond epoxy in pipe anti-corrosion coating by induction heating. In the typical thermal heat cycle of this coating process, the maximum heating temperature is from 200 °C to 250 °C. In this case, compressive yield strength increases as an effect of the thermal cycle, resulting in increased collapse resistance. Thus, for deep water application of UEO linepipe, it is important to clarify the conflicting effects of the Bauschinger effect and the thermal heat cycle on compressive yield strength. During installation of deep water pipelines by a method such as J-lay, curvature is imposed on the pipe axis, but the circumferential bending that leads to ovalization is determined by the interaction of the curvature of bending deformation. This bending deformation decreases collapse resistance. The interaction of external pressure and bending is also important when evaluating collapse.
Against this background, this study discusses the collapse criteria for coated linepipe and their bending interaction against collapse based on a full-scale collapse test under external pressure with and without bending loading. The effect of the thermal heat cycle on linepipe collapse criteria is also discussed based on the results of tensile pre-strain tests with simulation of the thermal cycle and a collapse calculation by FEA.
High-Fidelity Representation of Three-Hour Offshore Short-Crested Wave Field in the Fully Nonlinear Potential Flow Model REEF3D::FNPF
Authors: Wang Weizhi , Pakozdi Csaba , Kamath Arun , Bihs Hans 
Published: December 2020

Abstract
Stochastic wave properties are crucial for the design of offshore structures. Short-crested seas are commonly seen at the sites of offshore structures, especially during storm events. A long time duration is required in order to obtain the statistical properties, which is challenging for numerical simulations because of the high demand of computational resources. In this scenario, a potential flow solver is ideal due to its computational efficiency. A procedure of producing accurate representation of short-crested sea states using the open-source fully nonlinear potential flow model REEF3D::FNPF is presented in the paper. The procedure examines the sensitivity of the resolutions in space and time as well as the arrangements of wave gauge arrays. A narrow band power spectrum and a mildly spreading directional spreading function are simulated, and an equal energy method is used to generate input waves to avoid phase-locking. REEF3D::FNPF solves the Laplace equation together with the boundary conditions using a finite difference method. A sigma grid is used in the vertical direction and the vertical grid clustering follows the principle of constant truncation error. High-order discretisation methods are implemented in space and time. Message passing interface is used for high performance computation using multiple processors. Three-hour simulations are performed in full-scale at a hypothetic offshore site with constant water depth. The significant wave height, peak period, kurtosis, skewness and ergodicity are examined in the numerically generated wave field. The stochastic wave properties in the numerical wave tank (NWT) using REEF3D::FNPF match the input wave conditions with high fidelity.
Cost-Optimal Planning of Inspections and Maintenance of Production Tubings Subject to Scale Deterioration
Authors: Akinsanya Akinyemi O. , Qin Jianjun , Sørensen John D. , Faber Michael H. 
Published: December 2020

Abstract
Integrity tests, inspections (caliper log) and maintenance activities are critical to the integrity management of the production tubing and are important to ensure that loss of production — due to e.g. excessive reduction in the wells cross-section and numerous unplanned shut-ins, is reduced over the service life while maintaining safety and availability. The progressive loss of integrity of production resulting from deterioration processes such as scaling, are time variant with large uncertainties. The time variability together with large uncertainties is one main driver of increasing need of rational tools for cost-optimal planning of inspections and maintenance. Optimal planning of inspections and maintenance is therefore necessary to achieve timely and risk-efficient management of the production wells by finding a trade-off between the cost of inspection and maintenance, and the benefit of increased production amongst others.
This paper presents a framework for identifying cost-optimal planning of inspections and maintenance of the production tubing of sub-surface oil and gas wells subject to time dependent scale degradation. The proposed framework is based on a risk-based approach, which allows uncertainties to be accounted for. By adopting this approach, the strategies which give the minimum expected value of the total cost of inspection and maintenance are identified. In this paper, the approach uses categorization of the sizes of scale thickness characterized by damage sizes, and inspection results into damage states, and takes into account imperfection in the inspection results in terms of the probability of detection and damage sizing accuracy. For each of the damage states, a certain damage cost and maintenance decision rules, stating the next line of action, are established. The inspection and maintenance decision problems are therefore modeled based on the pre-defined decision rules while the optimization parameters are the intervals of inspections and the maintenance alternatives. The probabilistic model, accounting for uncertainties, scale propagation proposed by Guan et. al. (2019) is used to describe the scale growth or damage evolution. Bayesian pre-posterior decision theory is the basis for the decision making. All costs — including damage, inspections and maintenance costs, through the lifetime of the production tubing are evaluated and included in the decision model and the expected value of the life cycle costs are estimated and compared for different maintenance alternatives. An example in the paper demonstrates the framework and the implementation of the decision rules for one sub-surface production well subject to calcite scales.
Aerodynamic Roll-Yaw Instabilities of Floating Offshore Wind Turbines
Authors: Haslum Herbjørn , Marley Mathias , Navalkar Sachin Tejwant , Skaare Bjørn , Maljaars Nico , Andersen Håkon 
Published: December 2020

Abstract
This paper presents an investigation of a newly discovered motion instability phenomenon for floating wind turbines. The instability is due to anti-symmetric coupling terms in roll and yaw caused by the turbine thrust force. For floaters with small separation between the uncoupled roll and yaw natural periods these coupling forces may result in rigid body roll and yaw oscillations. The paper explains the theory and the physics of the instability phenomenon, and analytical expressions for these stiffness coupling terms (K46 and K64) are derived.
The instability phenomenon is demonstrated using several points of attack, by using time domain simulations, conservation of energy flow and eigenvalue stability analysis. The problem is stripped down to a simplified two degree of freedom roll-yaw model where analytical stability criteria are developed. The instability is also demonstrated in tailor made six degree of freedom time domain simulations, and in simulations using a fully coupled aero-hydro-servo elastic simulation tool including a BEM model.
An important finding is that damping forces are needed to fully understand the observed instability. It is demonstrated, quite counter-intuitively, that damping reduces the stability margin. This is explained by considering the effect damping forces has on roll-yaw phasing, for the typical damping values relevant for a floating offshore wind turbine.
Distributed Potential Theory and its Application for Spar-Type Floating Offshore Wind Turbines
Authors: Engebretsen Espen , Haslum Herbjørn , Aagaard Olav 
Published: December 2020

Abstract
Coupled aero-hydro-servo-elastic time-domain analysis is required for robust design and engineering of Floating Offshore Wind Turbines (FOWTs). For spar-type FOWTs, it is convenient to adopt a nonlinear beam finite element formulation in order to capture the coupled structural response of substructure, tower, blades and mooring lines accurately.
The Distributed Potential Theory (DPT) approach applies first-order frequency-dependent added mass, radiation damping and excitation loads distributed over all submerged beam elements in the coupled time-domain simulation, as obtained from diffraction/radiation analysis. This approach therefore includes frequency-dependent diffraction effects for all wavelengths, while keeping the substructure flexible, thus enabling hydro-elastic coupling and extraction of internal sectional loads along the substructure.
This paper demonstrates the use of DPT in coupled aero-hydro-servo-elastic time-domain analysis of a spar-type FOWT and illustrates the effect on tower and substructure fatigue life compared to using the classical Morison approach.
Cabin Noise Prediction and Acoustic Optimization Design of a Cruise Ship
Authors: Ni Yue , Li Xiaobin 
Published: December 2020

Abstract
The cabin noise level is an important criterion in high-performance ships, and the noise prediction is the premise of the ship noise control and low noise design. Taking a cruise ship as the research object, a comprehensive application of the statistical energy analysis (SEA) and the finite element-statistical energy analysis hybrid method (FE-SEA) is used to predict the full-frequency noise of typical cabins. The structure-borne noise and air-borne noise, caused by the external excitation from the main engine, propellers and auxiliary machinery, are obtained with the empirical formula. The primary noise sources of typical cabins are analyzed. The noise reduction scheme of sound package is adopted and optimized for the cabin with excessive noise.
Study on Vertical Bearing Capacity of the Wide-Shallow Bucket Foundation in Two Layered Sand
Authors: Sun Guodong , Liu Run , Lian Jijian , Cai Runbo , Yang Xu , Fu Dengfeng , Chen Guangsi 
Published: December 2020

Abstract
The wide-shallow bucket foundation proposed by Tianjin University of China is a new type of offshore wind turbine foundation. In this paper, the vertical bearing capacity of wide-shallow bucket foundation embedded in two layered sand that contains an underlying medium strength sand layer and a weaker or stronger overlaying sand layer is studied. A parametric study for bearing capacity is carried out with the ratio of unit weight γ1/γ2 (where γ1 and γ2 are the unit weight of the upper and lower sand layers respectively), the ratio of internal friction angle φ1/φ2 (where φ1 and φ2 are the internal friction angle of the upper and lower sand layers respectively) and relative thickness of the top sand layer H1/B (where H1 and B are the thickness of the top sand layer and the bucket foundation diameter). All of the presents were performed by the Finite Element Method and the results show that the thickness of the top layer has a great influence on the vertical bearing capacity of the foundation. Specifically, the upper sand layer is stronger, the bearing capacity ascends with the increase of the thickness of the top layer, and on the contrary, the upper layer is weaker, and the bearing capacity decreases with the increase of the top layer thickness. In addition, the bearing capacity of the foundation also increases with the ratios of the effective unit weight and the internal friction angle.
Validation of Numerical Wave Tank Simulations Using REEF3D With JONSWAP Spectra in Intermediate Water Depth
Authors: Pakozdi Csaba , Fouques Sebastien , Thys Maxime , Kamath Arun , Wang Weizhi , Dadmarzi Fatemeh Hoseini , Bachynski Erin , Bihs Hans 
Published: December 2020

Abstract
As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data.
In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.
A KNN Based Collapse Methodology and Recent Qualification of Flexible Pipes in Deepwater Application
Authors: Zhu Linfa , Nogueira Victor Pinheiro Pupo , Tan Zhimin 
Published: December 2020

Abstract
As the flexible pipe industry targets more on deepwater applications, collapse performance of flexible pipes becomes a key challenge due to the huge hydrostatic pressure during installation and service. The collapse strength of flexible pipes largely depends on the structural characteristics of carcass, pressure sheath and pressure armor layers. Therefore, the collapse prediction methodology involving a sound modeling of these layers is essential. Over the years, Baker Hughes have collected a large amount of collapse testing data. The prediction tool needs to be validated and calibrated against all the collapse tests for best accuracy. In this paper, the latest progress of the collapse prediction methodology and qualification tests are presented. A generalized collapse model was developed to predict the collapse pressure of flexible pipes. This model incorporates the advantages of both the weighted kNN regression technique and an analytical collapse model. It is able to reproduce the exact collapse pressure on the pipes tested and can predict the collapse pressure of other pipe designs not tested. As part of the qualification process, the capacity to prevent collapse must be demonstrated. Several flexible pipes were designed based on this generalized prediction methodology for deep water application, and pipe samples were manufactured using industrial production facilities for collapse tests. The results show that flexible pipes following current design guidelines are suitable for deepwater applications.