bluuebunny/crossref_metadata_2025_split huggingface dataset:
Full-Scale Validation of Stress Prediction Models for Flexible Pipe Foldless End Fitting Anchoring System
Authors: Gallina Alessandro , Rigon Henrique Chiaradia , Geusti Lucas Alban , Wallauer Frederico , Bertoni Fabiano , Clevelario Judimar de Assis 
Published: September 2023

Abstract
This article presents a validation analysis of analytical and numerical models that predict the stress distribution of flexible pipe tensile armor wires at the pipe body and inside the end fitting anchoring chamber when under axisymmetric loads. It validates the method and the properties of materials and interfaces obtained using standard and customized small-scale tests. Results from an analytical model and a simplified finite element model of a foldless end fitting are compared against stresses measured in the tensile armors of a full-scale flexible pipe sample submitted to internal pressure and axial tension loads. This analysis is part of an ongoing qualification program for a foldless end fitting for offshore flexible pipes that simplifies the assembly procedure by eliminating the folding process of wires and improving its performance when under dynamic loads by reducing the stress concentration factor at the end fitting anchoring entrance.
The stress profile induced on the tensile armor wires inside the end fitting differs from the one found in the pipe body due to the gradual load transfer from the wires to the epoxy resin as well as a change of the armor geometry inside the anchoring chamber. The tensile armor stress is often used as a critical parameter in design methodologies for the anchoring system, where validated models predict the stress distribution along the wire as a function of pipe layers geometry, disposition of wires embedded in resin inside the anchoring chamber, material, and interface properties. These models can predict the anchoring system maximum load capacity and stress concentration factors induced in the wires at end fitting entrance.
Comparative Study for Numerical Modelling and Analysis of Floating Offshore Wind Onsite Installation
Authors: Hong Sunghun , Yuan Shuai , Zhang Houxiang , Halse Karl Henning 
Published: September 2023

Abstract
This paper discusses an onsite installation method that involves the direct installation of a wind turbine at an offshore operating site. Since a fully assembled wind turbine is lifted and installed on a spar foundation at the operational site, complex responses are expected due to the multibody system of the installation vessel, the lifted wind turbine, and the spar foundation. To verify the reliability of the numerical results of the proposed alternative installation method and to gain a better understanding of the system dynamics, the installation system was modeled using SIMO and OrcaFlex, and the numerical results were compared. The comparative study was conducted in the following steps: 1) eigenvalue/modal analysis, 2) RAO verification and comparison, and 3) dynamic analysis and comparison. The results obtained in this study can be utilized in the design system components such as installation vessels, floating foundations, mooring systems, mechanical dampers, lifting devices, and control systems.
Simulations of Complex Offshore Problems Using GPU-Accelerated Near-Far Field Coupled Model
Authors: Lu Xin , Dao My Ha , Le Quang Tuyen 
Published: September 2023

Abstract
A fully nonlinear near- and far-field coupling numerical model is used for numerical simulations of the wave-current-structure interaction, with specific applications to the marine offshore floating structures. For a better efficiency, a GPU-accelerated high-order spectral (HOS-CUDA) solver is used to simulate the wave propagation and interaction with current in the large far field. In the small near field an incompressible multiphase flow solver with free surface capture scheme from the OpenFOAM library is adopted to solve the nonlinear wave loads and seakeeping response of the structure. The near and far field coupling model is applied to simulate the seakeeping response of a self-propulsive ship hull in head wave conditions. In addition, the model is used to simulate a more complex scenario where two moored floating offshore wind-turbines are considered.
To Improve the Orientation of a Jetty Exposed to Swell and Current to Minimise Operational Downtime
Authors: Eggermont Coen , van Deyzen Alex 
Published: September 2023

Abstract
For a jetty exposed to waves it is important to understand the behaviour of the moored ships and the operational downtime in early stages of the development to determine if the proposed terminal meets the downtime requirements. In case of steep depth contours, a breakwater is not a cost-effective solution to reduce the operational downtime. Other solutions to reduce the downtime to acceptable levels are required.
This paper shows, for a location with strong currents parallel to the coast but also with a predominant swell at a 45° angle with the coast, how numerical modelling of the moored ship response can be used in an early stage to optimize the orientation of the jetty with the aim to minimize the (annual average) downtime. The downtime has been determined based on the behaviour of moored tankers for five different jetty orientations.
The orientation which leads to the least amount of downtime, is an orientation more in line with the swell wave direction. For this location, the effect of current on the downtime is less dominant for the relevant sizes of tankers than the effect of swell waves.
This paper shows how numerical modelling of the moored ship response can provide the required insight in the operational downtime in an early stage of the development of a jetty exposed to waves, which in turn can be used minimize the operational costs.
A Practical Approach for Wave Loads on Bilge Keels in Irregular Seas
Authors: Xia Jinzhu , Liu Huaxing , Sukri Hilmi 
Published: September 2023

Abstract
A probabilistic approach is proposed to derive the design wave loads on bilge keel structures in irregular seas. An equivalent drag coefficient is introduced to account for both drag and inertia contributions in the wave loads. For each irregular sea state, the most probable maximum (MPM) value of the wave load is expressed in terms of the equivalent drag coefficient and the MPM value of the relative flow velocity. A generalized Keulegan-Carpenter (KC) number is also introduced in terms of the MPM value of the relative flow velocity and the associated mean up-crossing period of the relative velocity, which can be directly obtained from 3D diffraction analysis. The KC-dependent equivalent drag coefficient is determined by fitting a modified hyperbolic relation to the values derived based on the total wave load measurement from the model tests in irregular sea states of a Floating Production Storage and Offloading (FPSO) system design. The proposed new approach involves the application of an equivalent drag coefficient for each irregular sea state specified in the metocean report for FPSO design. The wave load formula is directly applicable for calculating short-term extreme wave loads for ultimate strength design. A 2-parameter Weibull distribution is found to fit well the measured short-term wave load distribution. The long-term probabilistic load distribution for fatigue design can be developed by summing the short-term distribution of each sea state weighted by the probability of occurrence. Thus, efficient, frequency-domain wave load calculations can be performed for both ultimate and fatigue state designs of the bilge keels. A practical application is presented of the proposed approach to a deep water Brazilian FPSO project.
Simulation and Characterization of Low-Frequency Flow Oscillations Over a Symmetrical Sail at Large Attack Angles for an Unmanned Sailboat
Authors: Zeng Qingsong , Cai Wei 
Published: September 2023

Abstract
Unmanned sailboats harvest wind energy as their main thrust power. This ability makes them outstanding for continuous marine hydrometeorological research on open seas. Different from airplanes, where small attack angles are generally used to avoid a stall, sailboats typically sail with large attack angles (more than 20 degrees) in downwind conditions. Although stall happens and the lift drops dramatically, the drag now acts as the main contributor to thrust. However, at low Reynolds numbers (around 10^5) and large attack angles, low-frequency flow oscillations would be easily triggered by vortex shedding. Such periodic or quasi-periodic aerodynamic forces would cause an undesirable change at the moment, which would result in large force fluctuations and random behaviors of the sail. In this study, LES simulations are carried out at Reynolds number 3.6E5, with the attack angle varying from 5 to 90 degrees for a 3D NACA0012 sail. Validation is performed at the same Reynolds number using experimental data. The influence of turbulence intensity is also explored. The results show that the wiggles of both lift and drag coefficients increase with the attack angle. The fully separated flow will form a recirculating flow region on the low-pressure surface of the sail, which triggers vortices at different scales. The flow lacks enough energy to keep a fixed shape, and the vortex shedding causes variations in the pressure leading to oscillations in the lift and drag. The dominant frequency locates in the range of 0.5–10Hz, which straightforwardly indicates a low-frequency oscillation. It also shows that a change in attack angle will alter the frequency of the low-frequency oscillations. Designers of the unmanned sailboat should keep this information in mind when determining the attack angle in a specific condition.
Buoyant Miscible Jets in a Viscoplastic Medium With Applications in Plug and Abandonment of Oil and Gas Wells
Authors: Hassanzadeh Hossein , Joshi Saptarshi , Akbari Soheil , Taghavi Seyed Mohammad 
Published: September 2023

Abstract
Plug and abandonment (P&A) is the final stage in the lifetime of oil and gas wells, during which the well is properly sealed to prevent fluid movements between different layers. The main steps of P&A include accessing the annulus section, cleaning the target area, and installing the cement plug barrier. Jet cleaning is an efficient technique for the second step of P&A, in which a heavy fluid is injected to displace lighter undesirable fluids. It is crucial to understand the effects of fluid properties on the jet cleaning process to achieve efficient cleaning. This study focuses on the jet flow dynamics in a miscible buoyant jet, where a Newtonian fluid is discharged through a circular nozzle into a viscoplastic ambient fluid. The effects of different parameters on the jet flow behaviour are analyzed, including the injection velocity and the yield stress of the ambient fluid. The buoyant jet flow behaviour is characterized using various jet features, including the laminar length and the penetration length. Our results show that the yield stress of the ambient fluid resists the jet evolution, decreases the jet penetration length, and changes the laminar length variation.
Environmental Loading on a Concrete Gravity-Based Offshore Structure in the Presence of Freak Waves and Currents
Authors: Zaman M. Hasanat , Akinturk Ayhan 
Published: September 2023

Abstract
There has been a rise in oil and gas industry activity in the offshore area of the North Seas as well as in other parts of the world. Operating offshore fixed and floating structures in such areas come with additional menaces due to the coexistence of large waves and strong currents and their consequent interactions. The effects of strong currents and large waves that move through the area may seriously impair the functionality and safety of these offshore structures, particularly when a large wave travels against a strong current since this could produce extremely high waves. In this study, the loadings of such a strong wave-current coexistence field on a concrete gravity based structure (GBS) are described both on its shaft and topside. The simulations use a 3D mass, momentum, and energy balanced model as numerical tools for predicting loads on the structure. Using mass, momentum, and energy flux conservation equations, the proposed 3D numerical model is formulated that describes the characteristics of the wave-current coexistence field. To study a variety of scenarios, incident wave and current conditions are systematically changed in the simulations. The local still water depth and the geometry of the GBS were maintained constant. The shaft has a diameter of 30m, and a length of 95m and the topside has a dimension of 50m towards incident wave direction, 75m in length, and 2m in depth. The still water depth is taken as 80m, and the estimated air gap is 15m. In each situation, the simulation lasts for three hours.
The new data and information that would be generated as a result of this effort may be vital for potential inclusion in the GBS design process and hence improve structural and operational safety in the severe and wave-current coexistence environment.
Erosion-Corrosion of Steel Structure Caused by Friction of Sea Ice Based on Simple Experiment and Theory
Authors: Kioka Shinji , Takeuchi Takahiro 
Published: September 2023

Abstract
In this study, we focused on the corrosive wear, assuming that the frequent removal of rust layers by sea ice friction may accelerate corrosion. We performed simple experiments on repeated removal of rust layers on a metal material surface by an artificial method to simulate the rust removal caused by friction with sea ice, and developed a simple calculation model for corrosion progression based on diffusion-controlled process of oxygen under the formation of corrosion film. We found that structural steel further corroded with an increase of the removal frequency of corrosion film, and that corrosion progression did not depend on hysteresis and previous removal frequencies of corrosion film, provided each exposure time under the formation of corrosion film is the same. The calculation model showed that corrosion progresses linearly with a square root of time, and also agreed with such experimental trends. Tangent line of the progress curve of corrosion at the time of zero by the model also agreed well with the experimental results with high removal frequencies, which indicates the validity of the model. We demonstrated conceptually corrosion processes depending on contact frequencies of sea ice with steel structure, and added considerations for practical applications.
Lüders Induced Localization in Tubes Under Cyclic Bending
Authors: Zhang Weihan , Kyriakides Stelios 
Published: September 2023

Abstract
Preceding experiments and analyses revealed that bending of tubes whose material exhibits Lüders banding leads to the progressive nucleation of inclined bands of higher strain organized into periodic diamond clusters. The clusters cover both the tensioned and compressed sides of the tube with the affected length developing a higher curvature than the unaffected section. Between the diamond patterns are elastic zones required for each periodic domain to conform to the curvature of the tube. The present work examines how this non-uniformly deformed structure behaves under curvature symmetric cycling. A combined isotropic/kinematic hardening constitutive model that incorporates partial softening over the extent of the Lüders strain is adopted. A tube is first bent until the diamond patterns cover the whole length and in uniform curvature. During unloading and reverse bending the curvature remains uniform. The diamond patterns are gradually erased but simultaneously local secondary patterns of higher strain develop in the hitherto elastic zones between the original diamonds. When completing the cycle, the pattern evolution follows the reverse order with the secondary patterns being erased and the diamond patterns reappearing. The curvature remains uniform throughout and the evolution of local patterns develops simultaneously along the length. The paper demonstrates that the main effects of the extent of the Lüders strain and of the material yield strength are captured under monotonic bending. The behavior under curvature symmetric cycling follows broadly those of the base case outlined above.
Testing to Reveal Vertical Soil Stiffness and Damping at Pipeline Free-Span ‘Shoulders’
Authors: Papavasileiou Vasileios , Bransby Fraser , Watson Phil , O’Neill Michael 
Published: September 2023

Abstract
Pipeline (or cable) engineers routinely have to manage free-spans — i.e. sections of the pipeline which are or which may become unsupported by the seabed — during their operational lifetime. Free-spans can make the pipeline susceptible to Vortex-Induced-Vibration (VIV), with associated potential of fatigue failure, leading to the requirement for regular pipeline inspections and expensive free-span mitigation for critical spans. VIV can lead to significant dynamic movement of the pipelines in the free-span and requires consideration of the metocean inputs, the local hydrodynamics, seabed changes due to scour, the structural response of the pipeline and the seabed support conditions (‘pipe-soil interaction’).
Although recommended practice guidelines exist for pipe-soil-interaction of submarine pipelines, there is a knowledge gap in the realistic selection of non-linear vertical soil springs and dashpots at the free-span shoulders (i.e. sections of continuous pipeline support on either side of a free-span), which may lead to increased conservatism and potentially unnecessary remediation. This paper reports an experimental investigation into the variation of soil stiffness and damping ratio for a pipeline section on the seabed that can be idealised as a segment (representing part of the free-span shoulder) when subject to different cyclic vertical loading conditions.
Results from the tests are compared with state-of-practice guidelines, and show that both the load history and amplitude of the cyclic loading have a significant impact on the soil response. The reported results will contribute to better understanding of pipe-soil-interaction for free-span shoulders and improved selection of non-linear soil springs and dampers.
Toward Environmental and Structural Digital Twin of Offshore Wind Turbine
Authors: Zhao Xiang , Dao My Ha , Le Quang Tuyen 
Published: September 2023

Abstract
In the wind energy industry, a digital twin (DT) is very useful for managing the operation of a wind turbine and predicting structural health conditions in real-time as well as projections in the near future. A real-time surrogate model is a very crucial part in building a DT. Towards that end, we employ a Reduced-Order Modelling (ROM) approach to construct a surrogate model for the environment-structure system of a bottom-fixed offshore wind turbine (OWT). The entire environment-structure system is broken down into major sub-systems of wind, wave, and structure. Based on the high-fidelity Computational Fluid Dynamics (CFD) data, the wind ROM model can quickly provide the loadings on the components above water level in the parameter space spanned by the incoming wind speed, the rotational speed of the rotor, the pitch and tilt angles of the turbine. The hydro loadings on the underwater components of the OWT are solved by the empirical Morison formula. The OWT structural ROM model is component-based consisting of blades, hub, nacelle, tower, and monopile. The structural ROM model takes the loading data feeds from the wind and wave models to predict the structure responses of the OWT system, including stress. Since the DT is constructed via the component-based, it can also be used to play out “what if” scenarios when there are component level changes. For instance, the model can predict the system response of OWT when certain parts undergo structure failures. Benefiting from the cost-efficient ROM models, the DT is over two orders of magnitude faster than high-fidelity simulations while maintaining good accuracy.
Design Drivers for Pre-Lay and Recovery Installation of Deep-Water Steel Lazy Wave Riser Systems
Authors: Sebastian Abhilash A. , Jeon Jaehyeuk , Patel Vikas , Lal Mayank 
Published: September 2023

Abstract
Wet storage of risers prior to installation on the vessel is generally done to make the installation schedule more flexible, especially in harsh environments with a small weather window. The wet storage of flexible, umbilical, or traditional steel catenary configuration has become quite common. However, more steel lazy wave riser systems (SLWRs) are increasingly being wet stored in recent projects.
This paper will present an installation and wet park example study of an SLWR riser system at 7000 ft water depth. The major design drivers and technical challenges involving wet park configuration, laydown, recovery, and transfer during installation are discussed. The steel lazy wave riser wet park stability and fatigue and transient response of wet-parked risers during flooding and dewatering are evaluated from an analytical aspect. The riser wet park stability and fatigue, consist of clashing checks, extreme strength, and vortex-induced vibrations (VIV) fatigue during the duration of wet park.
Hydrodynamic Damping of a Riser Oscillating in an In-Line Steady Current at Low Keulegan-Carpenter Numbers
Authors: Peng Peng , Liu Kun , Wang Jiaxia , Gao Zhenguo 
Published: September 2023

Abstract
Hydrodynamic damping is key to the fatigue design of risers whose dynamic responses are controlled by the wave induced vessel motions. The effect of in-line steady current on the hydrodynamic damping is not fully understood and the prediction of hydrodynamic damping of a riser at low KC with the relative velocity Morison equation raises concerning for overestimation, which may result in overestimation of fatigue life in design. In this paper, the hydrodynamic damping of a circular cylinder oscillating in an in-line steady current is investigated based on the 2D direct numerical simulation (DNS). The Stokes number is 20950 while the KC is in the range of 0.4 ∼ 4.9 in the numerical simulation. The drag and added mass coefficients from the numerical simulations agree well with those from the experimental measurements at the same Stokes number and KC values. Different steady current velocities are considered in numerical simulations to demonstrate the effect of in-line current on the hydrodynamic damping of the oscillating cylinder. The appropriateness of using relative velocity Morison model for prediction of hydrodynamic damping with an-line steady current is examined by analyzing the in-line hydrodynamic force. The effect of the steady current on the vortex shedding of the oscillating cylinder is investigated to give an insight of the flow field characteristics.