bluuebunny/crossref_metadata_2025_split huggingface dataset:
Predictions of Tensile Strain Capacity for Strain-Based Pipelines With a Circumferential and Internal Surface Flaw
Authors: Jang Youn-Young , Kang Ju-Yeon , Huh Nam-Su , Kim Ik-Joong , Kim Cheol-Man , Kim Young-Pyo 
Published: November 2019

Abstract
Strain-based design assessment (SBDA) has been known for suitable assessment concept for pipelines subjected to displacement-controlled load and high plastic deformation rather than conventional stress-based design assessment. Tensile strain capacity (TSC) has been used for one of important factors to indicate limit state in strain-based design, so that it is main concern to predict accurate TSC to ensure the structural safety and integrity of pipelines. For the pipeline containing a flaw, especially a girth weld flaw, TSC based on fracture mechanics can be determined. Crack-tip opening displacement (CTOD) has been widely used for typical elastic-plastic fracture parameter, representing crack-driving force and crack-resistance curve, which are required to assess unstable crack propagation. The one of the main principles of crack assessment is that the definitions of crack-driving force and crack resistance curve should be coincident. However, there exist two kinds of the definitions of CTOD, which are based on 90° and original crack-tip concept, and these have been not unified in practical regions until now. Moreover, it is reported that the deviations of crack-resistance curve can occur in the same specimen and experiment, caused by the different definitions of CTOD. Therefore, CTOD solutions based on each of different definitions of CTOD should be highly required since inaccurate TSC would be assessed when using not the identical definition of that.
In the present study, CTOD solutions of pipelines with a circumferential and internal surface flaw are suggested by using two kinds of definitions of CTOD based on 90° and original crack-tip concept. For this purpose, FE analyses were systematically carried out considering various pipe geometries and material properties. And single-edge notched tension (SENT) specimen was used for representing resistance curve of API X70/X65 material. Moreover, the effect of the choice of each CTOD definitions on TSC was investigated through crack-driving force diagram (CDFD) assessment.
Effect of Coal Loading Conditions on Structural Characteristics of LFTS
Authors: Eto Hiroaki , Iizuka Koji , Nishigochi Ryo , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi 
Published: November 2019

Abstract
Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, Large-Scale Floating Coal Transshipment Station (LFTS) was proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. LFTS can store coal equivalent to five times the capacity of one bulk carrier (total 500,000T), and can accommodate 2 bulk carriers at the same time during offloading. The scale of LFTS is 590m × 160m. The LFTS has a flat spread and the elastic behavior becomes the dominant Structure. The upper part of the LFTS is different rigidity partly because the partition wall to be loaded by dividing the coal into each quality is provided. Loaded coal not only changes the draft of the LFTS but also greatly deforms the LFTS and is expected to cause local stress concentration on the structural members. Therefore, this paper investigates wave response characteristics and stress characteristics with the coal loading of the LFTS, and then evaluation of structural strength by limit state design method.
In this study, linear potential theory and the finite element method (FEM) were used to analyze the static hydroelastic motion under various coal loading condition and wave response of LFTS. And, to grasp the local stress concentration occurring inside the LFTS by using the response results, a detailed model modeling a complicated internal structure was prepared. Zooming analysis which is a method of giving the deformation result by the whole model of LFTS as forced displacement to the local detailed model was carried out. As a result, depending on the coal loading condition and wave conditions, it became clear that LFTS will be in a tough situation.
Dynamic Positioning Observer Design Using Exogenous Kalman Filter
Authors: An Song , Chen Dengshuo , Bai Yong 
Published: November 2019

Abstract
Observer of a dynamic positioning (DP) system utilizes DP’s measurement data, to predict vessel’s velocities, positions, and unknown environmental forces on the vessel, as well as to handle model uncertainties and errors. Stability and optimality of a DP observer is important for overall DP performance. Nonlinear observer (NLO) designs usually take global asymptotic or exponential stability as the primary goal, and discard the noise. On the other hand, linearized Kalman filter (KF) algorithm, e.g. the extended Kalman filter (EKF), is optimal in minimizing the covariance of observer states by taking both measurement and process noise into account. The applied exogenous Kalman filter (XKF) algorithm in this paper, is a two-stage cascade of NLO and linearized KF, which uses the first-stage NLO estimated states as exogenous inputs for the second-stage linearized KF. XKF approach is proved to have both the stability property inherited from NLO and optimality from linearized KF. Stability and optimality of XKF based observer is studied through DP station-keeping numerical simulations.
Asset Integrity Control: Prioritization of Offshore Topside Flange Openings During Preventive Maintenance Shutdowns
Authors: Ratnayake R. M. Chandima 
Published: November 2019

Abstract
Top side flange inspection on offshore production and process facilities (P&PFs) has been a challenging task, due to complex geometries, produced crude oil and gas quality changes over the production well’s maturity, as well as the stringent regulatory requirements that need to be followed to assure the anticipated integrity of the operating assets. The complex geometries hinder the use of non-destructive testing (NDT) testing approaches and necessitate shutting down the system or subsystem in order to disassemble the flange to perform close visual inspection (CVI). Using risk-based asset integrity (AI) assessment and control (RBAIA&C) approaches, it is possible to classify the flanges into different classes, according to probability of failure (PoF). The PoF is estimated by considering the last inspection date, past inspection data, findings from similar locations/systems in the same offshore facility, etc. Together with consequence of potential failures (CoF), it is possible to estimate the risk of a potential failure due to the loss of integrity of a selected flange. Although several flanges are qualified to be disassembled, based on RBAIA&C activities, it is not possible to take all of them off during a certain preventive maintenance (PM) shutdown. Currently, ad hoc approaches have been used to further prioritize the flanges that have been recommended for inspection during a PM shutdown, based on RBAIA&C activities. The aforementioned jeopardizes the integrity of flanges and subsequently the overall system, possibly leading to catastrophic accidents. This manuscript demonstrates a methodology for the systematic further prioritization of flanges that need routine CVI. The flange inspection related system analytics have been incorporated with the analytic hierarchy process (AHP) to make logical further prioritization with sufficient transparency. The approach has been demonstrated with an illustrative case study that has been chosen from an offshore P&PF. A sensitivity analysis has also been performed and is presented to demonstrate how to carry out trade-off evaluations between different factors in the flange prioritization in a PM shutdown.
Analysis of Subsea Umbilical Mechanical Behavior Under Simultaneous Bending, Tension and Torsion
Authors: Saneian Mohsen , Gao Yifan , Bai Yong , Liu Ting 
Published: November 2019

Abstract
One of the major failure modes of an umbilical is found to occur under simultaneous bending, tension and torsion. Umbilical cables are compatible in bending but have a rigid response to tension and torsion, hence validation the axisymmetric performance of it, is a significant matter. This paper has applied theoretical models to analyze umbilical cables mechanical behavior under combined loading. Lanteigne (1985) theoretical model, which its feature is a large-diameter central pipe umbilical cross section with homogeneous materials that a number of wires helically wrapped around it, is developed in this article. The equilibrium equations are presented and showed the helical elements effects on bending, tension and torsion of the umbilical cable.
A Conjoint Analysis of the Stability and Time-Domain Analysis on Floating Platform During Mooring Line Breaking
Authors: Feng Jiaguo , Yu Yi , Qu Yan , Xie Wenhui , Wu Min , Zhao Jingrui 
Published: November 2019

Abstract
The stability of platform is important to ensure the platforms are safe, especially during the mooring line breaking process in typhoon condition. The paper presents a stability analysis method for floating platforms of the mooring line breaking process based on the time-domain analysis. The time-domain simulation during the mooring line breaking is provided. The time of the mooring line break, the max tilt angle of platform and the amended equivalent overturning moment are calculated for the stability analysis. The results show that the platform would have a serious tilt when the mooring line breaks, this increases the overturning moments and may cause the platform not meets the stability requirements during this process. It is necessary to pay attention to the stability problem during the mooring line breaking process in typhoon condition. And properly locating the down-flooding points is recommended to avoide the stability problem.
Multiobjective Reliability-Based Design of Ship Structures Subjected to Fatigue Damage and Compressive Collapse
Authors: Garbatov Yordan , Huang Ying Cai 
Published: November 2019

Abstract
This work deals with reliability-based design and optimization of ship structures subjected to stochastic loads and accounting for the local fatigue damage and ultimate global strength. The reliability multi-objective structural optimization is performed in minimizing the structural component net-section area, lateral deflection and fatigue damage. The probability of compressive collapse and fatigue damage of the ship hull is used to define the minimum risk of structural collapse and best design solution. The Pareto frontier solutions calculated by the Non-Dominated Sorting Genetic Algorithm (NSGA-II) is employed in defining the feasible solutions of the design variables. The first order reliability method is employed to estimate the beta reliability index based on the topology of the structural component as a part of the Pareto frontier solutions. Comparing with the original design solution, the optimized section area decreased by 9%.
Synergistic Flow Induced Oscillation of Multiple Cylinders in Harvesting Marine Hydrokinetic Energy
Authors: Hai Sun , Bernitsas Michael M. , Zhiyun Chen 
Published: November 2019

Abstract
Flow Induced Oscillations (FIO) of cylinders in tandem can be enhanced by proper spacing to increase hydrokinetic energy harnessing. In a farm of multiple cylinders in tandem, the issue of the effect of interference on harnessing efficiency arises. Over the course of three years of development in the Marine Renewable Laboratory of the University of Michigan, systematic experiments on an isolated cylinder, and two and three cylinders in tandem have revealed that synergistic FIO can actually enhance oscillations of cylinders in close proximity. Two cylinders in tandem can harness 2.5–13.5 times the hydrokinetic power of one isolated cylinder. Three cylinders in tandem can harness 3.4–26.4 times the hydrokinetic power of one isolated cylinder.
Quantification of the Effects of Filtercake on Wellbore Strengthening: Filtercake Rupture Resistance and Fracture Sealing Time
Authors: Yang Mingzheng , Chen Yuanhang , Growcock Frederick B. 
Published: November 2019

Abstract
Wellbore strengthening (WBS) has proven to be an effective method for expanding the pressure windows of drilling operations. Recent research on WBS disclosed the critical role of filtercake in sealing microfractures during the initial stages of fracture initiation and propagation. In this study, a new parameter — “filtercake rupture resistance” — is proposed to simplify the quantitation of the filtercake’s potential to withstand pressure over a small fracture. A modified permeability plugging apparatus (PPA) was used to experimentally simulate the processes of filtercake rupture over a fracture on the wellbore wall and fracture sealing. The effects of filtercake thickness (permeability), filtercake yield strength in shear, and concentration of bentonite and a fine fibrous LCM on filtercake rupture resistance were investigated, along with the effects of these parameters on the effectiveness of filtercake in reducing fracture sealing time. Pressure spikes and fluctuations were observed when applying differential pressure across the filtercakes after formation of the cake. Filtercake of lower permeability and higher shear yield strength produce greater filtercake rupture resistance and shorter fracture sealing time. These results can be used to guide drilling fluids design for improved control of fluid loss.
Structural Safety Assessment of Marine Operations From a Long-Term Perspective: A Case Study of Offshore Wind Turbine Blade Installation
Authors: Verma Amrit Shankar , Gao Zhen , Jiang Zhiyu , Ren Zhengru , Vedvik Nils Petter 
Published: November 2019

Abstract
A marine operation is a complex non-routine activity of limited duration carried out in offshore environment. Due to safety reasons, these operations are normally performed within specific sea state limits, which are derived from numerical modelling and analysis of hazardous events. In view of the uncertainties in the assessment of structural responses under stochastic environmental conditions, these limiting curves correspond to a target structural failure probability recommended in offshore standards (for example, 10−4 per operation as specified by DNV-GL). However, one of the main limitations is that these curves do not reflect site-specific safety assessment. The current paper presents a novel methodology for assessing the structural safety level of marine operations from a long-term perspective. The methodology includes estimation of extreme response distribution under all possible operational sea states (i.e. the operational domain under the limiting sea states) for a given offshore site and is compared to the response limit to obtain an average failure probability. A case study is also presented for a blade root mating process onto preassembled hub using a jack-up crane vessel and risk of impact between root and hub is considered critical. Global time-domain simulations are performed using multibody dynamics, and extreme value distributions for impact velocities are derived for different wind-wave conditions. The allowable impact velocity between the blade root and the hub is determined by an explicit finite element analysis of the damage at the blade root. Finally, the average failure probabilities considering the operational domain are obtained for four different European offshore sites and are compared to the target level of structural failure probability considered for the limiting sea states.
Nonlinear Analysis of an Oscillating Water Column Wave Energy Device in Frequency Domain via Statistical Linearization
Authors: S. P. da Silva Leandro , Pesce Celso P. , Morishita Helio M. , Gonçalves Rodolfo T. 
Published: November 2019

Abstract
Wave energy converters (WECs) are often subject to large displacements during operating conditions. Hence, nonlinearities present in numerical methods to estimate the performance of WECs must be considered for realistic predictions. These large displacements occur when the device operates on resonant conditions, which results in maximum energy conversion. The system dynamics are usually simulated via time domain models in order to being able to capture nonlinearities. However, a high computational cost is associated with those simulations. Alternatively, the present work treats the nonlinearities in the frequency domain via Statistical Linearization (SL). The SL results are compared to the Power Spectrum Density (PSD) of time domain simulations to verify the reliability of the proposed method. In this regard, the work initiates with the derivation of the governing equations of the air-chamber and the Oscillating Water Column (OWC). Then, the SL technique is presented and applied. The SL results show a satisfactory agreement for the system dynamics, mean surface elevation, mean pressure, and mean power compared to time domain simulations. Also, the SL technique produces a rapid estimation of the response, which is an effective approach for the evaluation of numerous environmental conditions and design, and further optimization procedures.
Gaining Insight in Wind Turbine Drivetrain Dynamics by Means of Automatic Operational Modal Analysis Combined With Machine Learning Algorithms
Authors: Gioia Nicoletta , Daems P. J. , Peeters C. , Guillaume P. , Helsen J. , Medico Roberto , Deschrijver Dirk , Dhaene Tom 
Published: November 2019

Abstract
Detailed knowledge about the modal model is essential to enhance the NVH behavior of (rotating) machines. To have more realistic insight in the modal behavior of the machines, observation of modal parameters must be extended to a significant amount of time, in which all the significant operating conditions of the turbine can be investigated, together with the transition events from one operating condition to another. To allow the processing of a large amount of data, automated OMA techniques are used: once frequency and damping values can be characterized for the important resonances, it becomes possible to gain insights in their changes. This paper will focus on processing experimental data of an offshore wind turbine gearbox and investigate the changes in resonance frequency and damping over time.
Effect of Reynolds Number on Local Scour Around a Monopile in Steady Current
Authors: Lou Xiaofan , Zhang Kaibing , Chen Zhenhong 
Published: November 2019

Abstract
The effect of Reynolds number (Re) on the local scour around a monopile encountering steady current was investigated experimentally in a water flume. The experiment was performed using circular cylinders with different diameters under two different freestream velocities, covering both clear-water and live-bed scours and a Reynolds number range of approximately 9,000–60,000. The time-series of the scour depth was recorded during the whole scour process and the scour pit was scanned after the scour process reached equilibrium. Results are presented in terms of the equilibrium scour depth, the time-scale of the scour process and the three-dimensional scour profile at different Reynolds numbers. For both clear-water and live-bed scours, the time history of the scour process indicate that the time-scale becomes larger as Re increases. It is also found that the normalized equilibrium scour depth, as well as the normalized scour radius, decrease with the increasing Re. An empirical equation of the equilibrium scour depth is derived as a function of Reynolds number based on the experimental results so as to better account for Re effect in the scour design.
Experimental and Numerical Study on the Hydrodynamic Properties of a Simplified Floating Hydrocarbon Storage Facility
Authors: Zhang Chi , Fonseca Nuno , Magee Allan R. , Ren Nianxin 
Published: November 2019

Abstract
A compliant modular floating hydrocarbon storage facility (FHSF) has been proposed for ocean space utilization. The FHSF consists of many floating hydrocarbon storage tanks (FHST) and several surrounding barges. These modules are connected in proximity through soft mooring system which reduces the environmental loads significantly. However, there are concerns on the potential resonance in the narrow gaps and the strong hydrodynamic interactions. This paper focuses on the hydrodynamic properties of a simplified subsystem which qualitatively represents part of the behavior of the entire FHSF but with reduced complexity. This subsystem consists of two FHSTs and a barge frame and is suitable for evaluating numerical analysis tools. Experimental studies on the subsystem and the complete system were performed in the ocean basin in SINTEF Ocean. A series of random, wide-band and realistic random wave tests were carried out to generate benchmark data to verify numerical analysis tools. Empty, partially loaded and fully loaded conditions were tested. The free surface elevations in the narrow gap and in the internal tank were obtained. A frequency domain numerical model of the subsystem was established in WAMIT based on linear potential theory. Higher order boundary element method (HOBEM) has been utilized to improve the accuracy and convergence. The influence of internal liquid (sloshing) inside the tanks is also considered in the linear range. The mooring system is simplified as linear springs. Linearized damping is introduced. The response amplitude operators (RAOs) of 6 degrees of freedom (D.O.F) and free surface elevations from numerical and experimental studies under the head sea conditions are compared. Good agreement on the motion RAOs are found, but significant differences are found on the RAOs of the elevation of the free surface. Finally, the influence of significant gap resonances is used to generate insight into how these problems might be mitigated.
Effect of Special Outermost Module Designs on the Hydrodynamic Responses of a Modular Multi-Purpose Floating Structure System
Authors: Ren Nianxin , Zhang Chi , Magee Allan Ross , Liu Xiao , Hellan Øyvind , Ang Kok Keng 
Published: November 2019

Abstract
The present work investigates the effect of different outermost module designs on the hydrodynamic responses of a modular multi-purpose floating structure (MMFS) system. The MMFS system is initially designed for a mild sea zone. As the entire system consists of more than 20 bodies, a simplified system with seven interconnected standardized modules is proposed for numerical and experimental study. In this simplified system, each module is assumed as a rigid body. Both hydrodynamic interactions and mechanical coupling among modules are taken into consideration in the time-domain numerical analysis. The structural deformation of the MMFS system mainly occurs in the connectors among adjacent modules. The maximum deformation appears at the connectors between outermost modules with the internal modules. To reduce the deformation and improve the concept, two special design, outermost module of deeper draft and outermost module with additional heave plate are proposed and investigated for the MMFS system. The numerical results indicate that the two proposed designs for the outermost module can significantly reduce the hydrodynamic responses of the MMFS system, especially the motion of the outermost module and the vertical bending moment on the connector. The extreme responses of the MMFS system with different outermost module designs are also studied and compared.