bluuebunny/crossref_metadata_2025_split huggingface dataset:
Method for Fatigue Testing of Subsea Wellhead Connector Segments
Authors: Barros Pedro , Horn Agnes Marie , Wormsen Anders , Osen Per , Macdonald Kenneth A. 
Published: December 2020

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 strong 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 connection is typically estimated by FE analysis. 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 a 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 a full-scale connector subject to bending loads. A secondary objective is to support the introduction of the practice of testing several segments cut from a single wellhead 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 text fixture, the connector locking dog, and wellhead segments designed to replicate the stress fields in a full-scale wellhead connector.
The test fixture and test specimens are designed to match conditions and fatigue stress of the full-scale connector. The test specimens are instrumented with strain gauges at fatigue hotspots. Digital image correlation (DIC) is used to measure the relative motion between the wellhead segment and the locking dog. The measured strains are compared with corresponding values from finite element analysis of the test. The DIC results are also used for estimating the coefficient of friction between wellhead profile and locking dog.
Very good agreement is found between measured hotspot strains and strains from the FE analyses for consistent load conditions. The test fixture is therefore considered suitable for segment fatigue testing, where the test results can be used to estimate the bending fatigue capacity of a full-scale wellhead connector.
Results from fatigue testing by this test method are presented in a separate OMAE2020 paper.
Horizontal and Torsional Modes of an Ultra Large Container Ship (ULCS)
Authors: Vijith P. P. , Rajendran Suresh 
Published: December 2020

Abstract
The hydro elastic responses of flexible structures under fluid loading is an important concern during the design of large ocean structures. The two-way coupling between the structural responses and the hydrodynamic loads is a complex problem in large flexible floating structures since the structures can vibrate in longitudinal, vertical, horizontal, or torsional modes. The antisymmetric distortion modes may be coupled depending on the location of the centroid and the shear centre. In the case of thin walled open structures, horizontal and torsional vibrations are usually coupled due to the asymmetry of cross section as well as eccentricity between centroid of the section and shear deformation centres. The acurate estimation of dry natural frequency and modes shapes of structure is indispensable since it helps to validate the accuracy of the structural modelling. A numerical method available from one of the existing literatures is used for the estimation of dry and wet natural frequencies, and mode shapes of horizontal and torsional vibrations of an ULCS. The natural frequency and modes are essential parameters for the analysis of interaction between structural responses and hydrodynamic loads. The numerical method is based on a 1D FEM beam model. Distortion due to warping is included in the numerical model since it is well known that containerships with large hatch opening are susceptible to warping. The numerical model is subdivided into 50 stations and the mass distribution and the sectional properties are calculated in order to match the bending, shear, torsion and warping moduli of the experimental model.
The dry and wet natural frequency and mode shapes for the horizontal and torsional vibrations of the ULCS is numerically calculated and compared with the experimental results.
Addressing Uncertainties Within Flow Induced Vibrations in Subsea Piping
Authors: Macchion Olivier , Stachyra Leszek , Hørte Torfinn , Renaud-Bezot Charles 
Published: December 2020

Abstract
The assessment of the risk arising from multiphase flow induced vibrations in subsea production systems is strongly affected by the accuracy of data and modelling for the production conditions, flow induced loading and estimate of the damping of the structure, both structural and flow induced. These uncertainties in the flow conditions and fluid structure interaction analyses are further compounded by uncertainties in the capacity of the structure to withstand vibration and fatigue damage.
As most calculation codes rely on deterministic analysis, these uncertainties are often addressed by their characteristic input and through safety factors, which are intended to ensure sufficient safety level. Subjective judgements, with unknown degree of conservatism, may be difficult to avoid. A need to address the associated uncertainties and provide a prediction of the accumulated probability of fatigue failure, using a consistent and sound methodology, has been expressed throughout the industry.
Structural Reliability Analysis (SRA) offers a framework to take into account, based on the same modelling basis as the deterministic approach, the uncertainties in all relevant parameters. Moreover, the framework allows for simultaneous consideration of these identified uncertainties when modelled by probability distributions and enables calculation of the probability of fatigue failure.
This article describes a general approach to implement reliability principles in the analysis of multiphase flow induced vibrations, discusses the use of the methodology, both in design and in operations. It also concludes on the feasibility of using Bayesian analysis, based on the results of subsea inspection, to update the probability assessment and provide updated input to the risk evaluations for future operations. The methodology may also be used to determine operational limitations for future production.
Numerical Investigation of the Physics of Higher Order Effects Generated by Wave Paddles
Authors: Law Yun Zhi , Liang Hui , Santo Harrif , Lim Kian Yew , Chan Eng Soon 
Published: December 2020

Abstract
When free-surface waves are generated using wave paddles to produce the desired waves, higher order effects might be inevitable for some cases. These can be due to the mismatch in the wave paddle displacement and non-linear free-surface wave kinematics, as well as the moving boundary of wave paddles. Such higher order effects are often manifested as higher harmonic waves, which can propagate independently (or free waves). The presence of such waves will contaminate the quality of the tank test, and together with effects due to scaling and finite size of tank, it is important to reduce or mitigate such effects as much as possible in a wave tank in order to simulate a more realistic scenario.
This study investigates the above problem in a systematic manner by using a fully-nonlinear numerical wave tank based on the three-dimensional time-domain Harmonic Polynomial Cell (HPC) method. Wave is generated by flap-type wave paddles on one end of the tank, and is damped on the other end. The paddle boundary conditions are satisfied on the instantaneous paddles surfaces, and the free surface is tracked by the generalized semi-Lagrangian scheme. In this study, first order paddle signal is used to generate regular waves, and the focus is on characterising the behaviour of the generated free higher harmonic waves.
We first look into a rectangular wave tank where the paddles are distributed at one side of the tank. Upon the generation of an oblique regular wave (primary wave), it is observed that the generated free waves propagate at a different angle/direction. An explicit analytical expression is derived for the direction of the free waves, which agrees with the numerical observation. Besides propagating at a different direction, the free waves also interact with the primary waves resulting in additional bound waves of the first and third harmonics. Next, we consider a circular wave tank, where paddles along half of the circumference are used to generate planar regular wave, while paddles at the other half are assumed to be able to fully absorb the wave. The generated free waves are observed to focus at a particular region in the tank due to constructive interference.
To eliminate or at least mitigate such undesired waves, correction to first order paddle signal is required. Second order correction scheme based on Schaffer (1996) is implemented for such purpose. Preliminary results seem to suggest that second order correction to the paddle signal can only mitigate but cannot completely eliminate the existence of free higher harmonic waves.
Case Study ROP Modeling Using Random Forest Regression and Gradient Boosting in the Hanover Region in Germany
Authors: Höhn Patrick , Odebrett Felix , Paz Carlos , Oppelt Joachim 
Published: December 2020

Abstract
Reduction of drilling costs in the oil and gas industry and the geothermal energy sector is the main driver for major investments in drilling optimization research. The best way to reduce drilling costs is to minimize the overall time needed for drilling a well. This can be accomplished by optimizing the non-productive time during an operation, and through increasing the rate of penetration (ROP) while actively drilling. ROP has already been modeled in the past using empirical correlations. However, nowadays, methods from data science can be applied to the large data sets obtained during drilling operations, both for real-time prediction of drilling performance and for analysis of historical data sets during the evaluation of previous drilling activities. In the current study, data from a geothermal well in the Hanover region in Lower Saxony (Germany) were used to train machine learning models using Random Forest™ regression and Gradient Boosting. Both techniques showed promising results for modeling ROP.
Friction Factor Equations Accuracy for Single and Two-Phase Flows
Authors: Assunção Germano Scarabeli Custódio , Marcelin Dykenlove , Von Hohendorff Filho João Carlos , Schiozer Denis José , De Castro Marcelo Souza 
Published: December 2020

Abstract
Estimate pressure drop throughout petroleum production and transport system has an important role to properly sizing the various parameters involved in those complex facilities. One of the most challenging variables used to calculate the pressure drop is the friction factor, also known as Darcy–Weisbach’s friction factor. In this context, Colebrook’ s equation is recognized by many engineers and scientists as the most accurate equation to estimate it. However, due to its computational cost, since it is an implicit equation, several explicit equations have been developed over the decades to accurately estimate friction factor in a straightforward way. This paper aims to investigate accuracy of 46 of those explicit equations and Colebrook implicit equation against 2397 experimental points from single-phase and two-phase flows, with Reynolds number between 3000 and 735000 and relative roughness between 0 and 1.40 × 10−3. Applying three different statistical metrics, we concluded that the best explicit equation, proposed by Achour et al. (2002), presented better accuracy to estimate friction factor than Colebrook’s equation. On the other hand, we also showed that equations developed by Wood (1966), Rao and Kumar (2007) and Brkić (2016) must be used in specifics conditions which were developed, otherwise can produce highly inaccurate results. The remaining equations presented good accuracy and can be applied, however, presented similar or lower accuracy than Colebrook’s equation.
Numerical Simulations of Turbulent Flow Through an Orifice Plate in a Pipe
Authors: Yin Guang , Nitter Bjørnar , Ong Muk Chen 
Published: December 2020

Abstract
Orifice flow meters are widely used in industries to measure the flow rate in pipelines. The flow rate inside the pipe can be calculated using the relationship between the flow velocity and the pressure drop across the orifice plate. In the present study, numerical simulations have been carried out using three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations combined with the k-ω SST turbulence model to thoroughly investigate the turbulent flow through a circular square-edged orifice with various orifice plate thicknesses and orifice diameters inside a pipe at different Reynolds numbers ranging from 2500 to 40000. The orifice thickness to pipe diameter ratio (t) varies between 0.125 and 2 and the orifice diameter to pipe diameter (β) varies between 0.25 and 0.75. The resulting centerline profiles of the streamwise velocity and pressure of the present study are compared with the previous published numerical results and experimental data as the validation study. The effects of Reynolds numbers and orifice geometries on the pressure, the flow velocity and vorticity distribution in the orifice are discussed in detail.
Annular Frictional Pressure Losses for Drilling Fluids
Authors: Saasen Arild , Ytrehus Jan David , Lund Bjørnar 
Published: December 2020

Abstract
The most common viscosity models used in the drilling industry are the Bingham, the Power-Law and the Herschel-Bulkley models. In addition, it is common to refer to the low-shear yield-point. The scope of the present paper is to discuss numerical methods applicable for calculating annular frictional pressure losses.
The topic of annular frictional pressure loss modelling has been treated in textbooks. None of these couple their models with the selection of viscosity data from measurements at the relevant shear rates.
It is earlier shown how rotation of the inner string in an annulus can complicate the flow due to establishment of Taylor vortices. There are currently no analytical methods to handle such flow. The effect of the vortices depends strongly on the fluid’s composition in addition to the flow conditions. The practical way to handle these situations are by “fingerprinting” during circulation.
In the paper examples will be presented showing how the Herschel-Bulkley fluid can be transferred to simple models for axial flow in an annulus where the inner cylinder does not rotate. It is common to use the narrow slot approximation. This method was used by Founargiotakis et al. In this paper both the modified Herschel-Bulkley model with dimensionless shear rates and the traditional model where the consistency depends on the shear rate will be presented. The dimensionless shear rate model can easily be translated back to the traditional form and vice-versa. Mathematical models will be presented. Hence a framework is given that is easier to use for digitalization and automation and in correlations including pressure, temperature and composition.
Peridynamic Analysis of Fragmentation of Ice Plate Under Explosive Loading With Thermal Effects
Authors: Zhang Yuan , Wang Chao , Guo Chunyu , Tao Longbin 
Published: December 2020

Abstract
Along with the development in arctic region, the icebreaking technologies are gradually becoming the focus. As one of the most powerful and effective way to breaking ice, especially in the ability to solve ice jams, the study of the behaviour of the sea and river ice under dynamic loads is an urgent subject of scientific research and it attracts extensive attention. In addition, the temperature change in the process of ice failure cannot be neglected since that temperature plays an important role in the mechanical properties of the ice. In this study, a fully coupled thermoelastic ordinary state-based Peridynamic model is employed to investigate fragmentation of ice cover subjected to an underwater explosion. Both the deformation effect on the thermal effects and the thermal effects on deformation are taken into consideration. The pressure shocks generated by the underwater explosion are applied to the bottom surface of the ice cover for non-uniform load distributions. Crack propagation paths are investigated, the damage is predicted and compared with existing experimental results. The corresponding temperature distributions are also examined. Furthermore, the ice failure mode in both the top surface and the bottom surface of the ice sheet is investigated.
Local Buckling of Dented Subsea Pipelines Under the Combined Loadings
Authors: Chen Yanfei , Hou Fuheng , Dong Shaohua , He Guoyan , Zhang Qi , Liu Hao , Li LuLu 
Published: December 2020

Abstract
Dents has long been regarded as a potential hazard for integrity of subsea pipelines in the oil and gas industry. The dents in subsea pipeline are usually caused by the collision and extrusion with other objects resulting in permanent plastic deformation in pipe wall. Meanwhile, seabed deformation or motion due to subsidence, mudslides, and seismic activities may load the pipeline to an ultimate state, where the pipeline is under combined external pressure and bending moment. It is of great importance to carry out the research on the buckling failure and bending capacity of dented subsea pipelines under these combined loads.
Nonlinear finite element method is adopted to investigate the local buckling failure of the dented subsea pipeline under combined loads. The numerical results show that the buckling behavior and bending capacity of the pipeline can be largely reduced due to the existence of external pressure and axial force. Based on numerical results, a formula for predicting the bending capacity of dented subsea pipelines is proposed. Finally, the accuracy of propose solution is validated.
An Uncertainty Evaluation of Different Fidelity Methods to Predict Ship Motions and Structural Loading in Waves
Authors: Husser Nicholas , Brizzolara Stefano 
Published: December 2020

Abstract
In this study, four approaches are investigated to predict the motions and structural loads on a containership in waves. The Flockstra (1974) containership model is used as the benchmark for this study as extensive experimental data is available to compare to the predictions. The hydrodynamic loads and motions are predicted using strip theory, a zero speed Green’s functions panel method with forward speed correction, a fully unsteady 3D panel method and unsteady RANSE simulations for limited cases. Simulations are performed at Fn = 0.245 in head, stern quartering, and bow quartering seas for wave length to ship length ration λ/L of 0.35–1.40. The accuracy of each method, relative to experimental results, in predicting the amplitudes of heave, pitch, and roll are investigated. Vertical and horizontal bending moments, shear forces, and the torsional moment on the hull at midships and 0.25LBP forward and aft of midships are also calculated and compared with the measured values. Through comparison with experimental data, the relative uncertainty of all four methodologies in predicting both motions and structural loads are assessed and discussed. Overall, all linearized potential flow methods show a large discrepancy with the experimental loads, motivating the need for further studies on non-linear effects for this particular ship type. This paper has been prepared in the framework of the ISSC-ITTC special joint committee on uncertainty quantification in wave load estimation.
Hydrodynamic Analysis of Floating Docks With Alternative Geometries for Floating Wind Turbine Installation
Authors: Gran Viktor A. , Jiang Zhiyu , Pan Zhiyuan 
Published: December 2020

Abstract
Installation of spar floating wind turbine offshore is a challenging task. Usually, the spar platform is upended first, and mating of the tower assembly with the spar platform is assisted by a crane vessel. Due to motions of the spar platforms and of the crane vessel, such an operation often takes place in shielded areas with relatively small wave heights and wind speed. The floating dock concept has been recently proposed to expand the weather window for installing spar floating wind turbines. The idea is to use a cylindrical dock to shield the spar platform from wave excitations. However, because of the trapped internal fluid, the cylindrical geometry is subjected to piston mode and sloshing mode excitations, and these modes may fall in the wave periods and cause unfavourable response characteristics. This paper investigates the influence of floating dock geometries on the piston and sloshing modes. We assumed a homogeneous mass distribution of the floating dock and changed the geometry of the cylindrical dock by expanding or reducing the neck area. Then, hydrodynamic analysis of the alternative geometries was carried out using a potential flow code. By comparing the system’s piston modes and sloshing modes, we identified the trend of variation and found that an expanded neck area can lead to increased sloshing period and piston mode. This indicates a potential improvement of the dock responses in operating sea states. The results of this analysis can be used in the shape design optimisation in a future work.
Time Domain VIV Analysis Tool VIVANA-TD: Validations and Improvements
Authors: Wu Jie , Jin Jingzhe , Yin Decao , Lie Halvor , Passano Elizabeth , Sævik Svein , Tognarelli Michael A. , Grytøyr Guttorm , Andersen Torgrim , Karunakaran Daniel , Igland Ragnar 
Published: December 2020

Abstract
An empirical time-domain (TD) vortex-induced vibration (VIV) prediction model has been implemented in a software called VIVANA-TD based on its earlier development by Thorsen at NTNU. It models the synchronization of VIV loads and structural responses with a set of empirical parameters generalized from model tests. Combining this time domain hydrodynamic load model with a non-linear finite element structural model makes it possible to account for structural non-linearities and time-varying flow.
A joint industry project (JIP), i.e., Lazy Wave Riser JIP has been organized to improve the design basis for SLWRs. This JIP is executed by SINTEF Ocean with support from NTNU. The industry participants are Equinor, BP, Subsea7, Kongsberg Maritime and Aker Solutions. The overall objective of this JIP is to systematically validate VIVANA-TD, in order to establish it as an industrial tool for VIV prediction. It is also aimed to improve the empirical basis and methods for calculation of VIV of deep-water steel lazy wave risers (SLWRs).
In the present paper, the validation study is presented for selected model tests in constant flow conditions with uniform and sheared profiles. The test model includes bare pipe, pipe with partial strake coverage and riser model with staggered buoyancy elements. The empirical parameters have been generalized based on extensive model test data. Limitations and improvement of the model have been also been explored. The results show that the present TD model can represent reasonably the VIV loads and that the prediction has good agreement with measurements in general.