bluuebunny/crossref_metadata_2025_split huggingface dataset:
Results From Fatigue Testing of Subsea Wellhead Connector Segments
Authors: Horn Agnes Marie , Barros Pedro , Wormsen Anders , Osen Per , Macdonald Kenneth A. 
Published: October 2021

Abstract
For subsea well drilling, the drilling rig is connected to the subsea well by a marine riser and subsea BOP equipped with a remotely controlled wellhead connector latched onto the subsea wellhead profile.
The level of cyclic loading on subsea wellheads is steadily increasing due to use of increasingly larger drilling rigs with larger BOPs, the drilling of wells in harsher environments characterized by high waves.
The remotely controlled wellhead connector forces a series of locking dogs into an externally machined profile on the wellhead. This external profile is generally referred to as a wellhead profile. The fatigue resistance of this safety-critical connector is typically estimated by finite element analyses (FEA). Due to the large size of the equipment, and high cost of testing, very limited fatigue testing, if any, has been carried out. A test method has therefore been developed, where a special test fixture is used to apply realistic boundary conditions and variable tensile loads to a small sector or segment of the wellhead connector. A primary objective is to generate fatigue-critical stress fields in the segments under tensile test load that closely replicates the stress fields in the full-scale wellhead connector. A secondary objective is to evaluate the possibility of using segment testing to determine the fatigue capacity of the full-scale connector. The testing of narrow sector segments allows the use of readily available test apparatus. It is thereby envisaged that the total cost of testing (specimens and test laboratory costs) can be substantially reduced in comparison with full-scale connector fatigue testing.
This paper describes the fatigue testing of wellhead connector segments, and the test results in terms of cycles to failure and the failure modes, i.e. crack initiation point, and final crack geometry. The test scope consists of nine segments tested in-air at ambient temperature (nominal 20 °C), at a frequency of approximately 2 Hz under axial load of R = 0.1. At the time of writing this paper, six out of these nine tests have been performed. These six fatigue tests are presented in this paper.
The test results are compared with estimates achieved by FEA of the test assembly and relevant S-N curves for the materials. It will be determined if the test results can be accurately predicted by the fatigue analysis methodology in Section 5.4 of DNVGL-RP-C203 (C203), including use of the new series of S-N curves for high strength materials in Appendix D.2 of C203. This design approach assumes that other failure modes (e.g. fretting or other local effects in the interface between components) do not govern the fatigue life, as this cannot be predicted by the fatigue analysis method applied here.
The fatigue test set-up and the finite element analysis of the segment test is presented in the OMAE2020-18652 paper.
Tangguh Project: In-Service Buckling Design of Offshore Pipelines With Major Uncertainties on Soil Characterization and Seabed Mobility
Authors: Bughi Sabrina , Foschi Luigi , Marchionni Lorenzo , Vichi Roberta , Zulkarnain Yansa 
Published: October 2021

Abstract
This paper is based on the experience made during the design and installation of an offshore pipeline recently completed in Indonesia, where a 24” subsea production pipeline (16km long in 70m water depth) was found susceptible during design to lateral buckling.
Buckling is a well understood phenomenon. However, this project was characterized by major uncertainties mainly driven by soil characterization, soil zonation, soil-pipe interaction, seabed mobility and seabed liquefaction. These uncertainties have played a key role in the in-service buckling design. In particular, extreme pipeline embedment scenarios ranging from fully exposed to fully covered (due to natural sand transportation) were accounted with a significant impact on soil-pipe interaction.
To limit the development of excessive strain within the acceptance criteria, a mitigation strategy based on interacting planned buckles has been adopted installing three Buckle Initiators (BI) along the pipeline route. During design great efforts have been spent with the aim to demonstrate the robustness of the proposed solution.
3-D FEM simulations with ABAQUS have been performed taking into account the pipeline route including route curves and the sea bottom profile and the buckle initiators with their main geometries. All uncertainties have been considered following a deterministic approach. The impact of environmental and accidental loads due to a potential trawl-gear interaction were assessed as well.
The pipeline susceptibility to lateral and/or upheaval buckling along the sandwave areas has been analyzed as well in order to evaluate the need of mitigation measures suitable to freeze the pipeline configuration during the operating life.
Finally, once the lateral buckling design philosophy was established, the cyclic expansion and walking behavior of the pipeline were assessed to verify the pipeline structural integrity at buckles, route curve pull-out and the accumulative pipeline expansion at spools.
This paper presents all main engineering aspects faced during design and first feedbacks from field after the pipeline installation.
Coupling of a Boundary Element Method With a Boundary Layer Method for Accurate Rudder Force Calculation Within the Early Design Stage
Authors: Carstensen Björn , Krüger Stefan 
Published: October 2021

Abstract
During the early design stage, it is essential to produce quick and reliable results. Regarding the calculation of forces acting on a rudder in the propeller slipstream, potential flow solvers are often used for this purpose due to their low computational effort. The drawback of these solvers is that viscous effects as drag or flow separation cannot be calculated. To overcome this drawback, the coupling of an inviscid three dimensional boundary element method with a viscous two dimensional boundary layer method is presented. The inflow from the propeller and the propeller rudder interaction is calculated using a lifting line approach. The inviscid calculation of the rudder forces is done with a boundary element method and the viscous rudder forces are calculated with the boundary layer method. Two different approaches are presented for the coupling. The results calculated with the implemented methods are compared to reverse open water model tests.
A Study on Performance Evaluation of Non-Reflective Boundary for Progressive Waves Reproduction Introduced in Numerical Wave Tank With MPS Method
Authors: Aida Yasuhiro , Takeo Tomotaka , Ikoma Tomoki , Masuda Koichi 
Published: October 2021

Abstract
Numerical simulation based on the moving particle semi-implicit (MPS) method is effective for the analysis of floating motion in stormy waves in both coastal and offshore areas. However, when the outer circumference of the calculation area is composed of wall boundaries, superimposed waves are generated by the reflected waves, which makes it difficult to reproduce wave fields in offshore areas. Therefore, in this study, we developed two types of non-reflective boundary that can be applied to a numerical wave tank with the MPS method. One type is an attenuation zone in which a high-viscosity region with a finite width is set from the end of the water tank. The other type is a wave absorption control boundary that detects the amount of water surface fluctuation in front of the boundary and prevents reflection via position control. Regular and irregular waves were created in a numerical wave tank with these boundaries and the wave dissipation performance was quantitatively evaluated by comparing the estimates for incident and reflected waves, the time-series waveform, and the wave spectrum.
Hydrodynamic Response of Buoy Form Spar With Heave Plate Near Free Surface
Authors: Hegde Pooja , Nallayarasu S. 
Published: October 2021

Abstract
Hydrodynamic response of spar with appendages such as heave plate has been investigated in the past, mostly attached at the bottom of the spar. The effect of geometry and appendages on the hydrodynamic response of spar has been investigated in this article. A curved neck form with a heave plate near the free surface is proposed as an energy dissipation device for both heave and pitch responses. Numerical simulation using Computational Fluid Dynamics (CFD) is used for capturing the flow around the curved neck with heave plate and corresponding damping characteristics. CFD free decay simulations have been carried out to obtain heave and pitch damping and were noted to be higher than the conventional spar with heave plate at the bottom. Comparison of the proposed geometry and heave plate at the free surface with a conventional heave plate at the bottom of the spar has been made, and significant changes to the response and hydrodynamic characteristics have been noted. It is observed that the buoy form spar combined with the heave plate located near the surface (within 10% of the draft) helps dissipate energy and thus reduce the heave response.
Neural Network Optimization for Lifetime Structural Adaptation to Evolving Natural Events
Authors: Wang Xiaowei , Heo YeongAe 
Published: October 2021

Abstract
Recent advances in data analytics, numerical modeling, and structural health monitoring (SHM) boost the application of machine learning methods in the field of structural engineering. Among them, the multi-layer neural network (MLNN) is one of the most popular ones. However, mathematical details of MLNN have yet to be well understood for structural problems. This study aims to identify optimal MLNN parameters for regression modeling of structural response estimates. SHM data-validated finite element models considering stochastic uncertainties in the natural events and structural properties are used to prepare a large dataset for regression modeling. The efficacy and accuracy of regression modeling are optimized by extensive sensitivity analyses for key MLNN parameters (e.g., numbers of hidden layers and neurons, activation functions and learning rates) via a k-fold cross-validation process. The optimized regression modeling is incorporated into a conceptual smart framework for lifetime structural performance assessment adapting to evolving natural events. The presented optimization process and smart framework is applicable to marine and offshore structures by characterizing the offshore hazards and structural responses.
Development and Verification of Modeling Practice for CFD Decay Calculations to Obtain Roll Damping of FPSO
Authors: Koop Arjen , Crepier Pierre , Loubeyre Sebastien , Dobral Corentin , Yu Kai , Xu Haihua , Zheng Yingying , Kim Jang , Huang Jerry 
Published: October 2021

Abstract
Estimates for roll damping are important input parameters for simulation studies on vessels operating at sea, e.g. FPSO mooring in waves, wind and current, workability and operability investigations, Dynamic Position studies, ship-to-ship operations and safety studies of vessels. To accurately predict the motions of vessels this quantity should be determined with confidence in the values. Traditionally, model experiments in water basins using so-called decay tests are carried out to determine the roll damping. With recent advancements in CFD modelling, the offshore industry has started using CFD as an alternative tool to compute the roll damping of FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD modelling practice is developed within the Reproducible CFD JIP for roll decay CFD simulations. The Modelling Practice describes the geometry modelling, computational mesh, model set-up and post-processing for these type of CFD calculations. This modelling practice is verified and validated by three independent verifiers against available model test data.
This paper provides an overview of the developed modelling practice and the calculated CFD results from the verifiers. The CFD modelling practice is benchmarked against available model test results for a tanker-shaped FPSO. By following this modelling practice, the CFD predictions for the equivalent linear damping coefficient and natural period of the roll motions are within 10% for all verifiers and within 10% from the model test results. Therefore, we conclude that when following the developed modelling practice for roll decay simulations, reliable, accurate and reproducible results can be obtained for the roll damping of tanker-shaped FPSOs.
Effect of the Simplified Superstructure and Soil-Structure Interaction Models on the Natural Frequencies of an Offshore Wind Turbine
Authors: Alkhoury Philip , Soubra Abdul-Hamid , Rey Valentine , Aït-Ahmed Mourad 
Published: October 2021

Abstract
Monopile-supported offshore wind turbines (OWTs) are dynamically sensitive structures, in which their design is principally based on a dimensioning criterion related to its fundamental frequencies. Therefore, an accurate estimation of the natural frequency is essential to assess the working lifetime of the OWT.
For the calculation of the OWT natural frequency, several studies exist but few of them simultaneously consider both the real geometrical configuration of the OWT superstructure (blades, nacelle, tower, and transition piece) and the three-dimensional (3D) soil domain and its interaction with the foundation. The aim of this paper is to investigate the suitability of (i) the different simplifying assumptions used in literature for the superstructure and (ii) the recently proposed PISA soil-foundation interaction model, when calculating the natural frequency. This is performed by comparing the results obtained using a rigorous three-dimensional (3D) finite element-based model recently developed by the authors of this paper with those obtained based on these simplifications. The comparison results have shown that both the simplified superstructure models and the newly developed soil reaction curves of the PISA project provide very good results of the OWT natural frequency.
Numerical Simulation of 5th-Order Stokes Wave in Finite Water Depth Based on Momentum Source Method
Authors: Wang Wenjie , Gao Zhiliang 
Published: October 2021

Abstract
For numerical simulation of structure-wave interaction, the wave generation with high accuracy is prime to analyze the wave loads and motions of the structure. Based on the fifth-order Stokes theory, a two-dimensional viscous wave flume, which was modeled using the commercial CFD solver ANSYS-FLUENT, was applied to the generation and propagation of regular waves in finite water depth. With the user-defined function provided by the solver, the momentum source term and boundary condition, which are used for the wave generation and dissipation, were developed to ensure the accuracy of wave simulation with large steepness. In addition, the wave flume was separated into two regions, which are governed by the laminar model and turbulent model, respectively. The separation of laminar and turbulent regions can alleviate the side effect of turbulence on the accuracy of wave generation. In order to validate the present method, the regular wave propagating with different steepness in finite water depth were simulated. The numerical results were in good agreement with the theoretical ones. The study showed that the present method was effective for the simulation of Stokes wave in finite water depth, especially effective to improve the numerical accuracy in case of large wave steepness.
Response of Multiple Bend System to Multi Phase Flow
Authors: Pereboom H. , Belfroid S. P. C. , Gonzalez-Diez N. , Reijtenbagh J. 
Published: October 2021

Abstract
Multiphase flow can induce high amplitude vibrations in piping systems. Several experimental campaigns focused on the force spectrum on a single bend. To evaluate the evolution of the forces from bend to bend, experiments have been done on an air-water, one inch pipe system consisting of six bends at near-atmospheric conditions. In a first phase, all individual bends were clamped to measure the phase relation and correlation of the flow-induced forces on the subsequent bends. In a second phase, all clamps were removed to measure the free vibrations. In this paper which focusses on the phase 2 results, the vibration measurements were compared to the calculated vibrations. For the excitation forces and phase relations, the measured force spectra from phase 1 are used. Damping values are based on experimental results from phase 2. The results show a good match between modeled and measured vibrations levels. Including the measured correlation between forces at multiple bends, improves the modeled results for slug flow cases. It is possible to directly use extract damping values from the measured signals, however, robustness of the damping estimation needs to be improved. Using average damping values currently leads to the best match.
Evaluation Study on Integration of Comfort and Energy Efficiency Models in Cruise Ship
Authors: Cai Wei , Liu Wushuai , Wan Shuqiao , Zeng Qingsong 
Published: October 2021

Abstract
In the design of cruise ships, it is necessary to make them have an excellent level of energy efficiency and at the same time provide tourists with a good comfort experience. Therefore, it is urgent to explore the balance between cruise comfort and energy efficiency. Based on Maslow’s hierarchy of needs theory, a cruise comfort evaluation system was established combined with the “Cruise Leisure Design Index” issued by China Classification Society; according to the characteristics of cruise ships, a specific “Energy Efficiency Design Index” (EEDI) for cruise ships was proposed. From the perspective of a life cycle, the “Life Cycle Assessment” (LCA) was applied to the cruise design. Meanwhile, the EEDI-LCA cruise ship energy efficiency model was established, and the baseline fitting and comparative analysis were carried out. The combination weighting method combines comfort index and energy efficiency index to establish a cruise ship comfort and energy efficiency evaluation system. The model was verified with a 60,000-ton MSC Sinfonia cruise ship. The results show that the model can find a comparatively good balance between comfort and energy efficiency so that the cruise ship’s energy can be reduced without sacrificing comfort. The balance is a good guide on the selection of cruise design parameters.
Void Fraction, Pressure Drop, and Flow Pattern Behavior for Two-Phase Non-Newtonian Slug Flow
Authors: Ben Rajeb Faraj , Imtiaz Syed , Zhang Yan , Aborig Amer , Awad Mohamed M. , Rahman Mohammad Azizur 
Published: October 2021

Abstract
Slug flow is one of the most common flow patterns in non-Newtonian two-phase flow in pipes. It is a very common occurrence in gas-liquid two-phase flow in the pipe. Usually, it is an unfavorable flow pattern due to its unsteady nature, intermittency as well as high pressure drop. The differences between slug flow and elongated bubble flow are not clear because usually these two types of flow combined under one flow category. In general, these two-phase flow regimes are commonly defined as intermittent flow. In the present study, pressure gradient, and wave behavior in slug flow have been investigated depending on experimental work. In addition, void fraction has been estimated regarding available superficial liquid and gas velocities. The experimental records of superficial velocities of gas and liquid for slug flow and other flow patterns is used to create flow regime map for the gas non-Newtonian flow system. The effect of investigated flow regime velocities for non-Newtonian/gas flow on pressure drop and void fraction is reported. Pressure drop has been discovered to be reduced in slug flow more than other flow patterns due to high shear thinning behavior.
Advancing the Performance of Wave Forecast Models Under Low Wind Conditions
Authors: Yasrab Muhammad , Babanin Alexander V. 
Published: October 2021

Abstract
Ocean surface is complex and difficult to predict accurately due to its random nature. Ocean surface waves in strong wind conditions have been widely studied for last few decades. Almost half of world’s winds are below 7.5 m/s and the physics of such winds contains a lot of uncertainties. The simulation of ocean waves is largely dependent on the driving winds force accuracy and source term parameterizations. However, low winds are often ignored on the perception of their lesser effect on overall results of existing models. It is important to understand the relative strength/ weaknesses of wave forecast models under low wind conditions from scientific perspective which should lead to improved wave forecast and wave-ocean-weather coupling capabilities. There are many critical thresholds involved in the initial generation and growth of wind waves whereas current parameterizations of wave models are mostly based on moderate – high wind conditions. Wave model’s performance, although not very prominent, contains bias under low winds conditions and these thresholds need to be embedded in current physics of wave forecast models for more accurate simulations. In this study, WAVEWATCH III (v6.07) wave forecast model with observation based source terms parameterizations (ST6 package) is used to simulate waves on a global scale. The model’s output is analyzed with a globally calibrated and cross validated global dataset of 13 altimeters to analyze its performance under low wind conditions. A relative error of −1 to 6 is observed in global significant wave heights simulated by WAVEWATCH III model compared to altimeter’s measured wave heights for wind speeds less than 5ms−1.
Numerical Simulation of Microscopic Formation of Carbon Dioxide Hydrate in Two-Phase Flow
Authors: Yamaguchi Alan Junji , Kobayashi Kaito , Sato Toru , Tobase Takaomi 
Published: October 2021

Abstract
The global warming is an important environmental concern and the carbon capture and storage (CCS) emerges as a very promising technology. Captured carbon dioxide (CO2) can be stored onshore or offshore in the aquifers. There is, however, a risk that stored CO2 will leak due to natural disasters. One possible solution to this is the natural formation of CO2 hydrates. Gas hydrate has an ice-like structure in which small gas molecules are trapped within cages of water molecules. Hydrate formation occurs under high pressure and low temperature conditions. Its stability under these conditions acts like a cap rock to prevent CO2 leaks. The main objective of this study is to understand how hydrate formation affects the permeability of leaked CO2 flows. The phase field method was used to simulate microscopic hydrate growth within the pore space of sand grains, while the lattice Boltzmann method was used to simulate two-phase flow. The results showed that the hydrate morphology within the pore space changes with the flow, and the permeability is significantly reduced as compared with the case without the flow.