bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Efficient Importance Sampling Method for the Long-Term Mooring Lines Response Estimation Considering Wind Sea and Swell
Authors: Simão Marina Leivas , Videiro Paulo Maurício , de Oliveira Mauro Costa , Sagrilo Luis Volnei Sudati 
Published: December 2020

Abstract
Escalating demand in the oil and gas industry has led offshore structures to be installed in ever deeper waters and under severe environmental conditions. As the mooring system is a crucial element in floating offshore structures, a reliable estimation of its long-term response is a decisive step in any usual design procedure. In the long-term scenario, the environmental actions to which these structures are subjected to, such as waves, wind and current, are non-stationary processes. However, this long-term behavior is usually modeled as a series of short-term stationary conditions (typically 3-h). In a full long-term analysis approach, an estimate of the long-term N-year response can be obtained through a multidimensional integration over all these short-term environmental conditions. In this paper, this multidimensional integral is numerically evaluated by means of the Importance Sampling Monte Carlo Simulation (ISMCS) method, where the uniform distribution is used as the sampling function. Thus, all short-term environmental conditions have the same probability of being sampled, which assures that conditions with very low original probability of occurrence, but with knowingly higher contributions to the long-term response, are efficiently accounted for. The random variability of the short-term environmental parameters and their interdependencies are represented by a simplified joint probabilistic model which comprehends both wind sea and swell waves. The methodology is numerically validated for an idealized single-degree-of-freedom (SDOF) model and later investigated for a mooring line connected to an FPSO installed in Brazilian deep waters. It is shown that ISMCS provides good estimates for the long-term N-year response with a moderate amount of required simulations and can be a powerful tool in order to account for simultaneous occurrence of wind sea and swell waves in structural response evaluations.
Dynamic Ultimate Strength of a Container Ship Under Sagging Condition
Authors: Jagite George , le Sourne Hervé , Cartraud Patrice , Bigot Fabien , Derbanne Quentin , Malenica Šime 
Published: December 2020

Abstract
When technically specifying ships for the future, the following aspects are examples of what we will have even more focus on than today: bigger, lighter, and faster. Thereby, the hydro-elastic type of structural response will be more and more significant. In addition, some of the recent container ships’ designs are with very low values of the “minimum hogging still water bending moment.” Combined with high whipping induced sagging moments, it casts some doubts on the probability of buckling appearance in the upper structure. Therefore, the objective of the research work presented in this paper is to investigate the dynamic ultimate strength of the entire hull girder section, subjected to sagging bending moment associated with wave loads and whipping response. The dynamic ultimate strength is computed and compared with the quasi-static ultimate strength, in order to derive the dynamic load factors, which can be used as an estimator of the dynamic collapse effect.
A New Approach to Compute the Non-Linear Whipping Response Using Hydro-Elastoplastic Coupling
Authors: Jagite George , le Sourne Hervé , Cartraud Patrice , Malenica Šime , Bigot Fabien , de Lauzon Jérôme , Derbanne Quentin 
Published: December 2020

Abstract
In the last ten years, the importance of whipping on the extreme hull girder loads has received much attention, but its consequence on the hull girder’s collapse is still unclear. The most common practice is to consider the structural behavior as linear-elastic in the hydro-elastic coupling, and as non-linear elasto-plastic in the ultimate strength evaluation. In order to investigate the influence of the non-linear structural behavior on the hydro-structure interaction responses, a new hydro-elastoplastic model is proposed to compute the non-linear whipping response. The structural part is modeled as two beams connected by a non-linear hinge, which follows the collapse behavior of a ship’s hull girder. The hydrodynamic problem is solved using the three-dimensional boundary element method, and the exact coupling between the structural model and the hydrodynamic one is made by making use of the shape function approach. Finally, the fully-coupled hydro-elastoplastic problem is solved directly in time-domain by numerical integration.
Four-Phase Flow of Oil, Gas, Water, and Sand Mixtures in Pipelines
Authors: Odan Mohamed , Ben Rajeb Faraj , Rahman Mohammad Azizur , Aborig Amer , Imtiaz Syed , Zhang Yan , Awad Mohamed M. 
Published: December 2020

Abstract
This paper investigates issues around four-phase (Oil/CO2/water/sand) flows occurring within pipelines. Multiphase flows are the norm, as production fluid from reservoirs typically include sand with water. However, these multi-phase flow mixtures, whether three- or four-phase, are at risk of forming slug flows. The inclusion of sand in this mixture is concerning, as it not only leads to increased levels of pipeline erosion but it also has the potential, to accumulate sand at the bottom of the pipe, blocking the pipe or at the very least hindering the flow. This latter impact can prove problematic, as a minimum fluid velocity must be maintained to ensure the safe and regulated flow of particles along a pipeline. The presence of low amounts of sand particles in oil/gas/water flow mixtures can serve to reduce the pressure exerted on bends. The sand volume fraction must in this case, be relatively low such that the particles’ resistance causes only a moderate loss in pressure. Therefore, the study aims to gauge the impact of oil/gas/water/sand mixtures on various pipeline structures as well as to further investigate the phenomenon of flow-induced vibration to determine the optimal flow variables which can be applied predicting the structural responses of pipelines.
Research on Lateral Buckling Mechanism of Tensile Armor Wires in Unbonded Flexible Pipe
Authors: Yang Zhixun , Yan Jun , Zhang Liang , Shi Dongyan , Lu Qingzhen 
Published: December 2020

Abstract
The buckling behavior and critical value are analyzed to explain the mechanism of the lateral buckling. Moreover, a 3D numerical model of four tensile armor wires with symmetrical arrangement is established with the interaction between armor wires and inner structure. The lateral buckling is discussed through a relationship between critical value and axial displacement. Then the sensitivity of critical value on friction coefficient is figured out. The results show that the lateral buckling resistance of tensile armor wires performs better with the friction coefficient in the range of 0.25 to 0.3. Finally, this research provides mechanical support for the lateral buckling resistance design of the unbonded flexible pipe.
Research on Intelligent Loading of Bulk Carriers
Authors: Fang Sheng , Chen Shunhuai 
Published: December 2020

Abstract
With the rapid development of computer technology in recent years, the shipbuilding industry is accelerating its intelligent process. Intelligent cargo management is an important functional module of intelligent ships, and intelligent loading is an important part of intelligent cargo management. Cargo loading is an important link in the process of cargo transportation. The loading effect affects the sailing performance, safety performance and loading efficiency of the ship, so it is necessary to improve the intelligence of ship loading. Based on the calculation and research of the floating state, stability, structural strength and loading efficiency of the bulk carrier during loading, a general mathematical model for the intelligent loading of bulk carriers is established. The model comprehensively considers the influence of loading rounds, loading capacity and loading order. It is solved using an improved genetic algorithm to obtain optimized loading results. The loading case calculation was carried out using a 20000t bulk carrier as an example, and an optimized solution was obtained, which proved the effectiveness of the algorithm. The results show that the method can effectively improve the loading efficiency of the ship while ensuring that the ship has sufficient strength and suitable floating state.
Convolutional Neural Networks Applied to Flexible Pipes for Fatigue Calculations
Authors: Ribeiro Machado da Silva Vinicius , Serrano de Araujo Breno 
Published: December 2020

Abstract
The industry standard approach for the design of flexible pipes makes use of non-linear finite element analysis (FEA) in time domain to simulate the physical responses of the structure in different environmental conditions. Wave dynamics can be represented either by an irregular wave (IW) or an equivalent regular wave (RW) approach, which simplifies the analysis. Irregular wave modeling approximates better the structural responses, due to the stochastic nature of the environmental loading, having the drawback of being more computationally expensive. The computer processing time of IW-FEA often becomes intractable due to the large number of scenarios that need to be simulated, for different values of Hs (significant height), Tp (peak period) and different wave directions. Reducing the time needed to simulate each scenario would reduce significantly the total processing time. In order to achieve this, alternative hybrid methods have been proposed in the literature, combining FEA with machine learning models. This paper proposes the use of nonlinear autoregressive exogeneous convolutional neural networks (NARX-CNN) to predict tension and curvature responses along the length of a flexible riser. Experimental results show that the proposed model can generate more accurate responses than previous models. This work also extends the region analyzed by forecasting responses beyond the bending stiffener level, going down to the end-fitting and touch down zone locations. It is the first time that such regions, prone to fatigue issues, are evaluated with these types of algorithms for flexible pipes, as per authors’ knowledge.
A Numerical Investigation of Steep Irregular Wave Properties With a Mixed-Eulerian Lagrangian HOS Method
Authors: Fouques Sébastien , Pákozdi Csaba 
Published: December 2020

Abstract
The design of structures at sea requires knowledge on how large and steep waves can be. Although extreme waves are very rare, their consequences in terms of structural loads, such as wave impact or ringing, are critical. However, modelling the physical properties of steep waves along with their probability of occurrence in given sea states has remained a challenge. On the one hand, standard linear and weakly nonlinear wave theories are computationally efficient, but since they assume that the steepness parameter is small, they are unable to capture extreme waves. On the other hand, recent simulation methods based on CFD or fully nonlinear potential solvers are able to capture the physics of steep waves up to the onset on breaking, but their large computational cost makes it difficult to investigate rare events. Between these two extremes, the High-Order Spectral (HOS) method, which solves surface equations, is both efficient and able to capture highly nonlinear effects. It may then represent a good compromise for long simulations of steep waves. Unfortunately, it is based on a perturbation expansion where the small parameter is the wave steepness, and consequently, simulations tend to become unstable when steep wave events occur.
In this work, we investigate the properties of irregular waves simulated with a modified HOS method, in which the sea surface is described with a Lagrangian representation, i.e. by computing the position and the velocity potential of individual surface particles. By doing so, nonlinear properties of the surface elevation are simply captured by the modulation of the horizontal and vertical particle motion. The same steep wave is then described more linearly with a Lagrangian representation, which reduces the instabilities of the HOS method. The paper focuses on bi-chromatic waves and irregular waves simulated from a JONSWAP spectrum. We compare simulations performed with the standard HOS and the modified Lagrangian methods for various HOS-orders.
State of the Art in Determination of Crack Direction in Shell Structures
Authors: Heidari Hossein , Walters Carey L. 
Published: December 2020

Abstract
Considerable work has been done on the modelling of fracture and necking for accidents in the maritime and offshore industry, but very little has been done to find the crack orientation during this failure. Such information will be required in future analyses which use the eXtended Finite Element Method (XFEM), rather than the element deletion approach which is typically used. It also offers a more realistic portrayal of the extents of damage, which will be useful in assessments of salvageability and residual strength analysis in maritime structures. This paper reviews the current state of the art on the direction of necking and fracture relative to the main in-plane loading axes. It was found that necking and fracture can both evolve under different angles relative to the first principal stress, depending on the ratio of inplane strains, material anisotropy, and other effects. Traditional analysis has given an easy relationship between necking orientation and strain ratio for negative second principal strains. Anisotropy is found to have a very important role for the necking angle for strain ratios (ε2/ε1) greater than 0.5. Fracture theory predicts a fracture angle perpendicular to the first principal stress for states of stress between uniaxial tension and equi-biaxial tension, but it predicts in-plane slant fracture for strain ratios less than −0.5.
Computational Fluid Dynamics Simulation of the Transient Behavior of Liquid Loading in Gas Wells
Authors: Khaled Mohamed , Rahman Mohammad Azizur , Hassan Ibrahim , Sultan Rasel A. , Hasan Rashid 
Published: December 2020

Abstract
Liquid loading is one of the major flow assurance challenges in gas wells, causing production problems and reducing the ultimate recovery. Liquid loading is defined as the inability of a well to carry all the co-produced liquid up the tubing. This leads to liquid accumulation in the well resulting in increased bottomhole pressure and decline of gas flow rate. Although many studies have been performed on liquid loading phenomena, available models generally lack the ability to capture transient behavior of liquid loading in gas wells. We have developed a computational fluid dynamics (CFD) model using Ansys Fluent 19.1 R3 version to model the transient features of liquid loading.
In this study, the CFD model is developed and validated with data from 42 meter long vertical pipe lab at Texas A&M University. The Eulerian multiphase approach combined with volume of fluid approach (VOF) - Multi-fluid VOF model with realizable k-Є turbulence closure is used to study the flow behavior. In addition, hexahedral mesh is utilized and compared to tetrahedron mesh to test accuracy and computational time.
The developed CFD model has unique parameters combinations that shows an acceptable agreement with the experimental work. Model accuracy and computational time is improved by using hexahedral mesh. Liquid film flow reversal mechanism is expected to be the root cause of liquid loading in gas wells rather than droplet fall back mechanism. The CFD model captures the transition from one phase to another that is crucial for determining well end life. Model novelty is based on the ability to be a reliable predictive tool that can help in the remediation of liquid loading and give a precise representation of liquid loading transient behavior in gas wells.
Investigations Into Tidal Current Turbine System Faults and Fault Tolerant Control Strategies
Authors: Yan Xuhua , Norman Rosemary , Elgendy Mohammed A. 
Published: December 2020

Abstract
In recent years, there has been a growing interest in tidal current energy as it is a potential source for green electricity generation and the most predictable form of ocean renewable energy. Due to the harsh marine environment, the Tidal Current Turbine (TCT) system has to be designed to be robust and to work reliably with high availability to minimize the need for intervention. Thus, fault tolerant control strategies are needed to enable the system to continue operating under some fault conditions, this will reduce the power generation cost and also increase the system robustness. This paper introduces some of the different fault conditions that may occur in TCT systems such as sensor faults, especially tidal current sensors. Potential solutions for these faults are then introduced. The paper then presents a standalone TCT generation system model with perturb and observe (P&O) control; this control aims to solve the tidal current speed sensor fault problem, ensuring that the system operates near the maximum power point (MPP) without the tidal current speed sensor. The control system is simulated using MATLAB/Simulink, for a TCT, utilizing a permanent synchronous generator (PMSG) and a boost converter.
Structural Connection Fatigue Evaluation Methodology Using Time Domain Approach
Authors: Samaria Sagar , Zhang Bob , Tallavajhula Sudhakar , Kyoung Johyun 
Published: December 2020

Abstract
There is an ever-increasing demand for life extension of existing floating platforms worldwide. To adequately support these life extension projects there is a need to predict fatigue life of floating structures more accurately using a time domain approach. However, structural fatigue damage calculations using time domain response analysis can be very time consuming and challenging. An efficient and effective structural analysis methodology is developed to calculate accumulated fatigue damage for structural connections in a floating offshore platform using a response-based time domain routine. The methodology discussed in this paper can be applied to estimate fatigue life for hull critical connections in floaters such as Spars, TLPs or Semis as well as local structural supports such as mooring foundations and riser foundations. It also provides the option to generate stress histograms that can be utilized for Fracture Mechanics Evaluation (FME) of welds in structural connections.
To calculate the accumulated fatigue damage at desired locations on a floating platform, the time domain analysis employs a Stress Intensification Factor (SIF) which correlates global loads with local stresses. In cases where a crack initiation is observed on a structural connection, fracture mechanics is used to evaluate the structural integrity of the weld. The FME requires fatigue stress range histograms as one of the input parameters. The stress ranges and cycles that are calculated and used to compute the fatigue damage using this methodology can be converted to stress range histograms which can then be used in the FME. The standard method to compute fatigue damage for a structural connection is by using an S-N fatigue approach under the assumption of linear cumulative damage (Palmgren-Miner rule). The methodology discussed in this paper uses a rainflow counting algorithm to effectively calculate the stress range and cycles which are then utilized for computing the fatigue damage.
This methodology can be applied to green field projects involving a new design or for life of field studies of an existing platform requiring life extensions. It is particularly beneficial for brownfield projects where more accurate re-evaluation of fatigue life is needed. It can also provide Clients with reliable Engineering Criticality Assessments (ECA) and enable them to plan in-service inspections and repair work. As an application, a typical truss connection for a Spar platform is used to evaluate structural fatigue damage and generate the stress range histogram for FME. Also, a comparative study is performed for a typical truss connection fatigue damage result between the traditional approach used and the method discussed in this paper.
RANS Simulation of the Flow Around a Ship Advancing in Shallow Water
Authors: Zhang Yan-Yun , Zou Zao-Jian , Yao Jian-Xi 
Published: December 2020

Abstract
This paper simulates the viscous flow about a ship advancing in calm water of different water depths using Reynolds-Averaged Naiver-Stokes (RANS) method. A Wigley hull is taken as the study object, and the hull is free in sinkage and trim in the simulations. The fluid domain is discretized into hexahedral structured grids. The overset grid method and the deforming grid method are applied in different cases to capture the ship’s sinkage and trim motion. The grid independence analysis and validation of numerical method are carried out under deep water condition. Then, systematic simulations are carried out under shallow water condition at different ship speeds. The resistance performance and the wave pattern characteristics are compared with deep water condition to demonstrate the shallow water effect. Furthermore, resistance coefficient results under water depth-to-draft ratios of 2.0 and 1.5 are presented and compared. All simulations show great consistency with the theoretical and other potential theory based numerical results.
Study on the Consideration Method of Damage Stability Criteria Corresponding to IEC 61400-3-2 for Floating Offshore Wind Turbine
Authors: Chujo Toshiki , Haneda Ken , Komoriyama Yusuke , Kokubun Kentaroh , Yamada Yasuhira , Fujiwara Toshifumi , Inoue Shunji 
Published: December 2020

Abstract
The development of FOWTs (Floating Offshore Wind Turbines) is going into the commercial stage from the demonstration one. One of the subjects for success in the commercial stage is how to reduce the construction cost. For example, watertight bulkheads in narrow space of FOWTs are obstacles for the cost reduction from the perspective of structural complexity and manufacturing. On the other hand, new IEC 61400-3-2 standard describes the unnecessity of the damage stability requirement under certain conditions. To satisfy enough safety without the damage stability requirement according to the IEC 61400-3-2, an examination method with a probability theory and the FEM analysis is proposed in this paper. The collision probability with cruising ships, P1, around a FOWT is decided to use by the AIS data, and the probability of structural total loss, P2, due to the ship collision is indicated according to the total loss curve which is delivered from the FEM collision analysis. The joint probability which is represented by the product of P1 and P2 is compared to the target damage probability, 10−4 per year. The detailed information about this method and the results of trial analyses for a FOWT off the coast of Nagasaki Prefecture are also introduced in this paper.