bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid-Structure Interaction Vibration Characteristics of Flexible Riser Transporting High-Speed Spiral Flow in Deep-Sea Mining
Authors: Zhang Jiayu , Chen Nian-Zhong , Shen Cong
Published: September 2023

According to Hamilton’s principle and conservation law of mass and momentum, governing equations of fluid-structure interaction and structural dynamics of a flexible riser transporting high-speed spiral flow are developed for vortex-induced vibration (VIV) analysis for lifting pipe system in deep-sea mining. The bi-directional fluid-solid interaction between flexible riser and internal and external flows is achieved by data mapping and exchange among the flow field domain and the solid domain. where the radial basis function method is used for moving interpolation of the flow field grid boundaries and internal nodes. The governing equations are then discretized and solved by the finite element method. Based on the computational fluid dynamics (CFD) method, a three-dimensional flexible riser fluid-structure coupling numerical model is established, and the numerical accuracy of the model is verified. Furthermore, dynamic characteristics of VIV of the flexible riser transporting spiral flow are investigated and the effects of internal flow velocity of the spiral flow on VIV responses are evaluated. The results show that the variation of modal vibration pattern of the flexible riser under the combined excitation of internal and external flows is evident, and the flow velocity of internal flow have significant nonlinear effects on the inherent frequency and vibration deformation of the flexible riser.
Study on the Effect of Proof Load Test on Mooring Chain Wear for Floating Structures
Authors: Takeuchi Takaaki , Kurokawa Kazuki , Hironaka Masato
Published: September 2023

In order to ensure the long-term integrity of floating offshore wind turbines (FOWTs), reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues. For achieving that, although the effect of wear and corrosion on fatigue life has been studied, only a uniform decrease in chain diameter is considered without local dimeter loss due to the interlink wear caused between links. This can lead to the unexpected early failure of the mooring chain. In order to estimate the fatigue life accurately, it is necessary to reproduce the interlink wear in the long-term.

Prior to that, the author proposed the wear estimation method and validated with short-term measurements (about 1 year). In this method, two modeling methods for coupled dynamic analysis were investigated: the conventional lumped-mass model and the 3-D rigid-body link model which is assumed to be an ideal circular configuration. However, mooring chains generally have a plastic deformation (known as the impression) at the contact part caused by the proof load test which ensures the integrity and enhances the fatigue life by loading about 70% MBS (Minimum Breaking Strength). The impression can cause the change in the rolling motion to affect the wear amount. In this paper, the wear including the rolling motion with the impression is reproduced by three-dimensional finite element analysis. As a result, it is found that the impression significantly decreases the roll-up limit angle beyond which sliding causes. Additionally, there is no significant effect of the residual stress on the wear amount.
Evaluation of Parametric Modeling Method for Ship Maneuvering Motion With Experimental Data
Authors: Zhong Yu-Xuan , Wang Zi-Hao , Zou Zao-Jian
Published: September 2023

Experimental evaluation is essential to the identification modeling method for ship maneuvering motion. In previous work, the authors proposed and validated a nu-Support Vector Machine (nu-SVM)-based parametric modeling strategy under noisy simulation data. In this study, the method is further evaluated and test using free-running model test data of the KVLCC2. The training dataset is selected in principle to cover the input space. The pre-processing of data, selection of model structure, and algorithm hyperparameters are analyzed and discussed. The generalizability of the identified model is tested as adequately as possible with turning circle and zigzag maneuver data that are not involved in the training process. The results show that the models trained by informative data can achieve good generalization performance despite parameter drift. The effectiveness and superiority of the proposed method are demonstrated by comparing prediction results with other modeling methods from SIMMAN Workshop, including captive model tests, RANS computation, and empirical modular modeling, etc.
Hydrodynamic Damping of a Circular Cylinder in Current With High-Frequency In-Line Oscillation
Authors: Pang Dan , Cheng Liang , Jiang Hongyi , Tong Feifei , An Hongwei
Published: September 2023

This paper investigates the hydrodynamic damping of an oscillating circular cylinder in a steady current. The standard approach for estimating the hydrodynamic loads from combined wave and current conditions on structures employs linear superposition of the loads induced by each component separately. To validate the linear superposition assumption, two dimensional (2D) direct numerical simulations (DNS) of an oscillating circular cylinder in current have been carried out at Rec = 47–600, high Stokes number (β = 1000) and low Keulegan-Carpenter number (KC = 0.001–2).

The drag force and the inertia force are decomposed by assuming that the drag component is in phase with velocity profile, while the inertia force is out of phase by 90°. The performance of two hydrodynamic models in existing design guidelines, the relative velocity model and independent velocity model, have been examined under the parameter range in this work. The results show that the independent velocity model outperforms the relative velocity model in predicting hydrodynamic damping.
Experimentally Determined Response Behavior due to Waves for a Loitering Remotely Operated Vehicle Near the Surface
Authors: Marks Johnathan D. , Klamo Joseph T.
Published: September 2023

The objective of this research was to quantify the undesired pitch and heave motions caused by wave-induced loads on an ROV operating near the surface. An experimental study was conducted utilizing a towing tank with wave making capability and a commercially available ROV, the Blue Robotics BlueROV2. The ROV was tested in the tank, near the water surface, at zero forward speed in both single-component and two-component wave fields. Pitch, depth, and thrust data were collected from the ROV and compared against control runs to determine the effect of the wave-induced loads on the pitch response of the ROV and its ability to maintain depth. For pitch, the results showed that the response had components that were caused by linear wave loads and nonlinear wave loads. The linear loads resulted in a pitch response that increased with wavelength. Low-frequency nonlinear loads resulted in a measurable pitch response when the frequency difference was near the system natural frequency. For depth, little response was seen due to the control authority of the ROV. However, the vertical thrust response showed that wave-induced loads have the potential to affect depth if sufficient control authority is not present.
Subsea Processing Optimization Considering Reliability and Maintenance
Authors: Sales Leonardo , Stolpnes Thomas , Stanko Milan , Faanes Audun
Published: September 2023

Subsea technology often enables the low-cost development of small marginal fields with short production lifetimes and low profit margins. However, ensuring high levels of reliability and low maintenance requirements for these subsea systems is critical for success and can be difficult to achieve. The goal of this research is to use numerical programming and optimization as a decision-support tool for the design of subsea production systems, while taking reliability and maintenance into account.

The optimization was designed to determine the most suitable subsea equipment and production strategy while considering production constraints, system downtime, lost revenue from production losses, and operational expenses. The reliability and maintenance model was integrated in the optimization model to provide the best solution possible, avoiding the problem of using two separate models that may only provide suboptimal results. This paper also discusses some of the difficulties in offshore reliability and maintenance modelling, as well as the uncertainties, constraints, and calculations used to improve the model’s accuracy.

The method was tested on a synthetic field study case in the Norwegian Continental Shelf. When reliability and maintenance parameters were included in the model, a different optimal solution was discovered. When the two solutions were compared, the new optimal design had an increase in NPV of 11 million USD over the previous one. The methodology presented advances modelling and automated decision-making in subsea production system design.
Hydrodynamic Modelling of Membrane Floats Floating PV System in Offshore Environments
Authors: Taneli Marvin Ananda , Bakti Farid Putra
Published: September 2023

In this study, the hydrodynamic responses of Membrane Floats Floating PV System in offshore environments were studied. The structure is modelled based on previous experiment of multi-tori structure by Jonathan Winsvold in 2018. The experiment significantly simplifies a complex membrane structure into sets of tori and truss structures, which were much easier to handle in both experiment and in numerical settings. Just like the Winsvold (2018) experiment, the continuous membrane is modelled as five discrete elastic tori that are connected by elastic trusses in the radial direction. The elastic truss elements have negligible inertia properties and their tension are configured to mimic the actual membrane stiffness. The experimental scale numerical model is validated against the experiment and theoretical results from literatures. Then, the full-scale structural diameter of 50 metres and torus cross-sectional diameter of 1.6 metres is modelled in the numerical setup. In this study, the load from Solar PV Modules were inserted as additional mass per length on the tori to better represent the real-world condition. To obtain better understanding of the hydrodynamic behavior of the membrane floats, two configurations of wire rope mooring systems and various membrane pre-tensions were simulated in the time domain. The mooring response and elastic behavior of the structure under various environmental load such as current and wave were also investigated. The wind loading is neglected in the present study, considering that the FPV has almost zero elevation. The sensitivity study results were then presented in the frequency domain. The simulation results suggested that mooring configuration significantly affected the structural response of the outermost part of the membrane, while has little to no effect on the innermost part of the membrane. The membrane’s sensitivity to the change in elongation (i.e., pre-tension) shows that the model were also able to capture the increase of the membrane’s apparent bending stiffness. Based on the results, the model may be used to provide further insight to improve future design of the membrane floats floating PV systems. The approach also opens up the possibilities of using a typical, more accessible, off-the-shelf rod or beam element-based FEM software to be used for simulating membrane type FPVs.
Sloshing Loads Estimation Using a Genetic Programming
Authors: Ahn Yangjun
Published: September 2023

Genetic programming (GP) is used to analyze the sloshing loads in a rectangular tank. The solution of the GP has been validated through a series of model tests of harmonic and horizontal excitations in a range covering all technically possible frequencies. The model tank scale is 1/40. The liquid depths are 70% and 95% of the tank height. 90 piezo-electric sensors are installed to measure pressure time signals for 200 cycles of excitation. Three different density ratios between the ambient air and liquid are considered. The genetic algorithm is to find an optimum solution for the average of the ten largest peak pressures for different frequencies. It considers the different loading conditions, density ratios of the ambient air and liquid, and excitation frequencies. The genetic algorithm is extensively validated for different population initialization, selection algorithms, crossover algorithms, mutation algorithms, and replacement algorithms. Good agreement is shown for the attributes leading to the optimum formulation of the sloshing loads. The solution of GP provides a simple and fast estimation of the sloshing loads. Furthermore, this application shows potential for practical application of analyzing general sloshing loads of various environmental conditions that the vessel would experience.
Effect of Axial Compression on Flexural Strength of Freshwater Ice
Authors: Anwar Taha , Taylor Rocky , Wang Jungyong
Published: September 2023

In the design of bridges, wind turbine towers, offshore structures and ice-class ships for operations in ice-prone regions, sloped structures may be employed to promote flexural failure of level ice to reduce loads on the structure. During such interactions, the ice sheet does not fail in pure bending since a component of the applied force at the sloped interface results in an axial load that induces a compressive stress in the ice. The net effect of this axial component is that the corresponding compressive stresses balance with flexure-induced tensile stresses in the outmost fibres of the ice. As a result, the apparent flexural strength of the ice is expected to increase with increasing axial compression, since larger bending forces would be required to generate sufficient tension to trigger fracture. In ice load prediction models for sloped structures, an in-plane compression (IPC) factor is applied to calculated loads to account for increased flexural strength which is empirically determined to be 1.5. While the method of superposition may be used to assess combined loading effects for elastic structures, assessing such effects in ice is more complex since the behaviour of ice is not purely elastic. In this paper, the relationship between axial compression and the flexural strength of freshwater ice is studied experimentally to assess how the flexural failure behaviour of the ice changes for different levels of in-plane compression factor. A series of experiments on freshwater ice have been conducted for compression levels at 75%, 135% and 185% of unconfined flexural strength for ram speeds of 0.1 mm/s, 1.0 mm/s and 10.0 mm/s. These results indicate that in-plane compression significantly increases the apparent flexural strength of the ice, highlighting the need for further work in this area to better understand this phenomenon and assess implications for design. This new testing approach provides a promising direction for further examination of these important effects, including extending this work to the analysis to sea ice and to consider lower IPC values.
Cross-Domain Knowledge Discovery and Sharing in Digital Subsurface Based on Federated Learning
Authors: Zhang Nan , Liu Ye , Geng Jiahui , Cui Boyu , Seo Jungwon , Cao Jie , Rong Chunming
Published: September 2023

The total volume of data in the subsurface is tremendous and grows exponentially each year. Sufficiently and effectively utilizing the subsurface data from multiple sites will advance the knowledge required for innovations that power the future growth of the energy industry. This research article explores the increasing needs and challenges for cross-domain knowledge discovery and sharing in the digital subsurface, and demonstrates the application of federated learning for improving the generalization ability and prediction accuracy of machine learning models using Rate of Penetration prediction as a field case study.

The lack of effective privacy and ownership protection solutions restricts the effective utilization of subsurface data across different organizations. However, due to the significant geological heterogeneity in reservoir formations and the severe long-tailed distribution, the machine learning models trained from a single data site suffer from overfitting and weak generalization ability. Federated learning provides a possible solution for this dilemma by training machine learning algorithms from multiple client datasets without exposing the data. Following the client-server architecture, clients train local models on their local datasets and exchange parameters with the central server at some frequency to generate and improve the global model.

In this paper, we demonstrate the application of federated learning for knowledge discovery and sharing across multiple sites using field data from multiple resources to train an advanced Long Short-Term Memory (LSTM) artificial neural network for drilling Rate of Penetration prediction. We discuss the learning and predictive performance of the global model, which outperforms local models in generalization ability and prediction accuracy due to the additional datasets contributing to revealing the actual data distribution. While this study provides promising results, potential limitations of this approach in the energy industry are also discussed.
Numerical Assessment of Novel Ice Breaking Technology
Authors: Tabri Kristjan , Saar Kalju , Aanensen Marie , Andersen Steiner
Published: September 2023

Paper deals with numerical assessment of a detachable icebreaking bow, that uses novel ice breaking technology. With the new technology, significantly smaller vessels are required for the ice breaking and the ice breaking capacity is exploited only when necessary. This is achieved by conceptually new ice breaking mechanism, where the ice is broken under 3-point bending mechanism. The focus is on ice fields with the maximum ice thickness up to 0.9 m.
Analytical and Finite Element Models for the Analysis of a Hybrid Flexible Pipe Under Combined Axisymmetric Loading
Authors: Freitas Inês S. G. , De Sousa Jose Renato Mendes
Published: September 2023

Hybrid flexible pipes, consisting of typical flexible pipes with composite layers replacing steel armors, are an alternative to traditional flexible pipes because they are lighter and insensitive to Stress Corrosion Cracking (SCC). Hence, the present work proposes analytical and finite element (FE) models for analyzing the behavior of offshore hybrid flexible pipes under combined axisymmetric loads, such as axial force, torsion, and internal and external pressure. The analytical models were implemented in Matlab and relied on equilibrium and compatibility equations combined with the Classical Laminate Theory (CLT) and the Lamé theory, representing the composite and the other non-composite polymeric layers. In contrast, the FE models were constructed in ANSYS®, where three-dimensional solid elements modeled the layers of the pipe, and contact elements ensured their interaction. Finally, a case study compared their responses, revealing an excellent adherence between the proposed models. Moreover, some insights concerning the orientation of the plies in the composite layer are presented and indicate the importance of associating different fiber orientations because risers are subject to complex load combinations.
Dual Shear Gun for Efficient Drilling Fluid Shearing – Laboratory Experiments
Authors: Taghipour Ali , Lund Bjørnar , Ytrehus Jan David , Saasen Arild , Ånesbug Geir Olav , Pallin Jan Egil
Published: September 2023

A dual shear gun prototype was produced to provide an efficient, low noise shear gun for rig site shearing of oil-based drilling fluids. At the same time this shear gun shall not produce metallic debris to the drilling fluid as such debris alters logging results. In this shear gun, two opposite directed jets collide inside a silencer chamber. Improved efficiency of the shear gun reduces the need for drilling fluid circulation to maintain drilling fluid properties.

Initial series of laboratory experiments are conducted. During the experiments a pumping unit was connected to a fluid tank and a divided flow is lead through a model shear gun device with adjustable nozzles. The viscosity and electric stability were measured as a function of time for the mixture. The experiments were conducted in an acrylic model of the planned tool. It is also possible to implement camera recordings of the experiments, including borescope view from the centre of the mixing unit.

Within the accuracy of measurements, also following API specifications, the viscosity profile developed rapidly. No significant noise was observed from the shear gun. These two properties are showing that the shear gun will be efficient in practical application. An analysis shows how the dual jet mixing chamber flow appears and how this flow will provide proper mixing.
Wave Effects on Vortex-Induced Motions of a Floating Offshore Wind Turbine
Authors: Passano Elizabeth , Yin Decao
Published: September 2023

Vortex-induced motions (VIM) of a spar type floating offshore wind turbine (FOWT) are studied. Wave effects on VIM responses are discussed and investigated using nonlinear time domain numerical simulations with typical combinations of current and waves.

VIM displacement orbits are sensitive to the ratio between the in-line and cross-flow natural frequencies, which is determined by the nonlinear stiffness introduced by the mooring system.

The simulations show that the waves reduce the VIM responses. This is in agreement with findings from VIM model test of other systems. The reduction is larger when the waves are in the cross-flow direction than when the waves and current are in the same direction.

Mean and dynamic tension forces are checked and cross-compared.
Latching Control of Wave Energy Converters Using Tunable Electrical Load
Authors: Tahir Uzair Bin , Zhang Jingxin , Manasseh Richard
Published: September 2023

Frequency of ocean waves varies over the time, and maximum power generation is only possible when wave energy converters (WECs) and incoming waves are at resonance. Adaptive control strategy is required for an optimal power absorption, which is impractical using available mechanical models. Electrical load control strategy can help to achieve the resonance condition without any structural change. WEC studied in this paper is a heaving bouy connected to the electrical power take off (PTO) having tunable passive load at the output. Electrical load based compensation has been presented to achieve the resonance during varying ocean wave frequencies. Many control strategies have been investigated in the past, but always required complex mechanical and electrical implementation. The only notable electrical control strategy is complex conjugate match, which is misleading as it requires external power to be implemented. Mechanical latching control is known for decades that can provide optimal tuning of excitation wave with WEC device for maximum power absorption. Electrical load based latching control has been used which regulates movement of the bouy according to the input wave force. An electromechanical mathematical model has been presented for the control conditions, and MATLAB/Simulink is used for the simulation of WEC’s operation under regular input waves. Results shows the use of passive electrical damping can control velocity, displacement, and improve power absorption compared to conventional latching control.
Preliminary Assessment of the Effect of Bottom Warp on the Dynamics of Planing Hulls Using OpenFOAM
Authors: Paredes Rubén J. , Plaza David , Marin-Lopez Jose R. , Begovic Ermina , Datla Raju
Published: September 2023

The prediction of the dynamics of High-Speed Craft (HSC) with prismatic hulls is commonly performed by designers using semi-empirical formulations based on Savitsky’s classic method. However, the accuracy of this prediction decreases with the presence of warp, when the deadrise of the hull change along its length, which is typical for small passenger ferries, even when considering the effective deadrise and trim angle concept proposed by Savitsky in 2012. The present work assessed the dynamics of three planing warped hulls and one prismatic monohull developed by the University of Naples, using a morphing grid approach implemented in OpenFOAM to capture the motion of the vessel. Numerical results on resistance, wetted area, dynamic trim angle, wall shear stress, and pressure distribution were compared with the method proposed by Savitsky, and previously published results where possible. Results suggested that it is possible to improve Savitsky prediction by changing the location where the equivalent deadrise angle is evaluated. This single modification will allow to extend the application of Savitsky method for a wider range of warp rates.
The Coupling Effects of Bubble Collapse, Ice Breaking and Structural Response
Authors: Chen Qiyang , Xiong Chengwang , Dong Qianqian
Published: September 2023

This study is concerned with the coupling effects between the fracture of an ice plate floating on the water surface induced by the pulsation of a high-pressure bubble and the corresponding deformation of an aluminium plate that is obliquely connected to the horizontal plate. The dynamic behaviours of bubbles and fractured ice were captured by high-speed cameras, and the transient plastic deformation of the aluminium plate was analysed with a digital image correlation (DIC) system. Our experimental observations revealed that the jet direction of the collapsed bubble strongly depends on the thickness of the ice, since the fractured ice causes an abrupt change in the boundary condition. It is notable that the jet direction was also influenced by the angle of the two walls and the standoff distances of the bubble. The angle of the ice and aluminium plates determines whether the jet points towards the corner or the walls. The location with the smallest bubble-ice distance and the largest bubble-plate distance generally provided the strongest ice-breaking capability due to the vertical jet impact by bubble collapse. However, a small bubble-plate distance should be avoided to prevent the deformation of the aluminum plate. The study can shed light on the efficient and safe ice-breaking strategy by understanding the dynamics of bubble collapse near floating ice and structures.
Lateral Buckling of Tensile Armor Wires in Flexible Pipe Subject to Axial Compressive and Cyclic Bending Load
Authors: Ye Naiquan , Ji Guomin , Sævik Svein
Published: September 2023

Flexible pipes and subsea cables are often manufactured with a number of helically wound armor wire layers. Lateral buckling of tensile armor wire may occur when the flexible pipe is exposed to combined axial compressive load and cyclic bending. During installation and operation in hash offshore environments, the touch down section of the flexible pipe may subjected to compressive axial load together with cyclic bending, which can lead to severe damage to the flexible pipe due to the lateral buckling failure mode. The present study investigates the lateral buckling capacity of one 8” flexible riser using Repeated Unit Cell (RUC) modelling technique. The RUC model has been proven to be valid in predicting the onset of the material yield in the most vulnerable tensile layer by comparing the results with a full-scale test data. Development of the stress components in the tensile amor wires as a function of cyclic bending, distribution of gaps between tensile armor wires around circular position are discussed. Lateral buckling is assumed to occur when the total axial stress exceeds yield stress of the armor material. Lateral buckling capacity is defined as the ability of the cross section to withstand certain amount of axial compression when it is exposed to a certain number of cyclic bending.
Retrieval of Ocean Wave Spectra From X-Band Marine Radar Images Using Inversion Schemes Based on Auto-Spectral Analysis
Authors: Radhakrishnan Gowtham , Leira Bernt J. , Gao Zhen , Sævik Svein , Christakos Konstantinos
Published: September 2023

Estimation of ocean wave conditions is extremely crucial for the planning and execution of demanding marine operations. Further, the Response Based Decision-Making requires accurate wave inputs to derive the responses using a numerical model. The X-band marine radars, installed on top of the vessels, are cost-effective means to assess the incoming wave field. Dedicated full-scale measurements were conducted using the research vessel Gunnerus in the Breisundet field, located on the west coast of Norway. After interaction with the ocean waves, the electromagnetic waves from the radar are backscattered based on the Bragg scattering mechanism. The radar digitizes the backscattered signal in the form of intensity images. 3-Dimensional (3-D) Fast Fourier Transform (FFT) was adopted to convert the temporal sequence of backscattered images to the wavenumber-frequency representations. The current velocity components estimated using the least-squares approach showed better agreement with the buoy-based current measurements. Then the wave-related components were extracted based on the linear wave dispersion relationship. Subsequently, the spectra were corrected for the shadowing effect using modulation transfer functions. Finally, the radar-based wave measurements were scaled using the nearby wave buoy records. The estimation of wave spectra improved considerably after the application of the Modulation Transfer Function (MTF). The spectra at the mid-range gave the best results when studying the effects due to range dependency. The spectra processed from radar images were validated using wave buoy measurements.
Visibility Enhancement in Turbid Water Based on Polarization and CLAHE
Authors: Liu Luping , Li Xin , Zhang Xiantao , Zhang Fan
Published: September 2023

Underwater visual distance is usually limited due to absorption and scattering of light, particularly in turbid water scenes. Currently, most underwater optical image processing algorithms are developed for the post-processing of static single-frame images taken in shallow water environments to achieve clear, color restoration images. Moreover, in turbid water scenes without ambient light, relying solely on post-processing algorithms to obtain ideal image quality can be challenging. In this study, we seek for underwater image quality recovery solution that can be applied during underwater vehicle operations. Polarization technology is used to remove the veiling light, which is the main cause of image degradation. The optical devices are fitted by polarizing filters through simple modifications. Additionally, a contrast limited adaptive histogram equalization (CLAHE) algorithm is employed to improve contrast and modify the color cast of images caused by direct signal attenuation. The proposed solution is tested and evaluated on underwater images acquired in laboratory experiments and the results are compared against other underwater post-processing methods. The study expects this approach will enhance the clarity and visual range of underwater targets, thereby improving target recognition in underwater operations.
New Developments and Capabilities Within WEC-Sim
Authors: Tom Nathan , Ruehl Kelley , Keester Adam , Forbush Dominic , Ogden David , Leon Jorge , Husain Salman , Grasberger Jeff , Topper Mathew B. R. , Yu Yi-Hsiang
Published: September 2023

WEC-Sim is an open-source software for simulating wave energy converters and has been actively developed and applied since its initial release in 2014 to simulate a wide variety of device archetypes. WEC-Sim is developed jointly by the National Renewable Energy Laboratory and Sandia National Laboratories within the MATLAB/SIMULINK environment. A general wave-to-wire model begins with a deployment site resource characterization, which is used to complete the hydrodynamic simulation of wave energy converters (WEC), with the power generation profile imported to a grid simulator to understand the influence on the local electrical network. While modeling the entire wave-to-wire is difficult and encompasses multiple time scales and physics, WEC-Sim is focused on the hydrodynamics simulation to predict, analyze, and optimize WEC dynamics and power performance. WEC-Sim simulations are performed in the time domain based on the radiation and diffraction method using hydrodynamics coefficients derived from boundary element method (BEM)-based frequency-domain potential flow solvers (e.g., WAMIT, NEMOH, Capytaine, or ANSYS-AQWA). With this level of modeling fidelity, WEC-Sim can handle floating body hydrodynamics, mechanical and electrical power generation methods, advanced control implementation, mooring systems, and other unique applications such as desalination. Additional WEC-Sim functionalities include pre-built Simulink blocks and MATLAB scripts that can simulate a wide range of floating systems and the corresponding auxiliary subsystems. The developers of WEC-Sim continue to release new versions of the software, at least annually, with the latest release in September 2022. These releases include bug fixes, updates to software documentation, as well as new features to expand WEC-Sim’s capabilities to model a wide range of WEC concepts. This publication will highlight the new features added to WEC-Sim between versions 4.1.0 to 5.0.1, which spans a 2-year period from June 2020 to September 2022. New features described here include topics such as continuous integration checks, revised Morison Element and nonlinear hydro implementations, run directly from Simulink (required for hardware-in-the-loop execution), BEMIO updates to import Capytaine BEM hydrodynamics, addition of cable blocks, and new wave visualization features.
Preliminary Investigation Into the Dynamic of Planing Hulls In Regular Waves Using the Smoothed Particle Hydrodynamics Method
Authors: Capasso Salvatore , Tagliafierro Bonaventura , Mancini Simone , De Luca Fabio , Martínez-Estévez Iván , Domínguez José Manuel , Altomare Corrado , Crespo Alejandro J. C. , Pensa Claudio , Viccione Giacomo
Published: September 2023

In this work a numerical investigation on a planing hull in regular waves is carried out by means of the Smoothed Particle Hydrodynamics (SPH) meshfree method. The simulation of the interaction of such vessels with wave trains features several challenging characteristics, from the complex physical interaction, due to large dynamic responses, to the likewise heavy numerical effort. A novel numerical wave flume implemented within the SPH-based DualSPHysics open-source solver fulfills both demands, guaranteeing comparable accuracy with established proprietary CFD code without sharpening the computational load. The numerical wave flume uses ad-hoc open boundary conditions to reproduce the flow characteristics encountered by the hull during its motion, combining current and waves while adjusting their characteristics with respect to the vessel experimental towing speed. It follows a relatively small three-dimensional domain, where the potentiality of the SPH method in modeling free-surface flows interacting with moving structures is unleashed. This novel application of the SPH method shows its feasibility proving an overall good agreement with the experiments; it is established, hence, an interesting alternative procedure to simulate seakeeping test in several marine conditions with reasonable effort and accuracy.
Slamming Effects on FPSO Balconies: Numerical and Experimental Analysis of Alternative Configurations for Impact Attenuation
Authors: e Silva Daniel Fonseca de Carvalho , Menezes Fabio Gouveia Telles de , Schmidt Dilnei , Mello Pedro Cardozo de
Published: September 2023

Wave slamming is a very complex physical phenomena that must be evaluated and analyzed during offshore structures design. Ship type offshore platforms like FPSOs (Floating, Production Storage and Offloading) take slamming effects into consideration by traditional standard recommendations and safety factors. However, FPSO may require additional deck area by using riser and mooring balconies and the slamming effects in such structures are not straightforward to be considered based on traditional approaches. This paper describes the analysis of a balcony structure that was found to be subjected to extreme impact loads and presents the numerical and experimental investigation of alternative configurations that may lead to impact loads attenuation. The alternatives include modifying the balcony flat-platted bottom by using wedge type elements, installation of cylindrical shape fender like structures and perforations on the balcony structure itself. The numerical analysis was carried out by prescribed motion short duration CFD (Computational Fluid Dynamics) calculations and the experiments were executed in USP (University of São Paulo) ocean basin considering the most relevant sea states expected. The balcony modifications were evaluated in several configurations by a single impact CFD simulations, and the most promising ones were tested for sea states realization in the ocean basin. The results, presented as impact force time series and as probability of exceedance curves, demonstrate the most promising balcony shape design alternatives to minimize wave impact loads and its effects on the hull structure.
Evaluation of Granite Deformation Through Non-Compliant Versus Compliant Indirect Tensile Strength Application
Authors: Abugharara Abdelsalam , Butt Stephen
Published: September 2023

Rock deformation evaluation as an essential approach for rock characterization and property determination has been examined via several methods through experimental and simulation studies. Such methods are reported to be conventional techniques applied to define the rock stress-strain relationship that consists of several regions including elastic and plastic regions. The load-displacement relationship also determines the yield and the breakage limits and shows the overall rock deformation behavior. The focus of this research is to evaluate the rock deformation behaviour through the implementation of compliant loading versus non-compliant. In this new approach and unconventional testing technique, the ultimate rock strength through rigid compression and the trend of the load-displacement curve were firstly determined. Secondly, Belleville springs were utilized in various stacks as per their full compression loads to determine the compression levels of 50% and 100% compression ranges of the non-compliant loading application. Results of testing about 150 samples of granite as high strength formation by indirect tensile tests, the compliant loading using Belleville conical disc springs compared with the non-compliant “rigid” loading was observed to influence the load-displacement curve to shift and the ultimate rock main failure to delay in the favor of compliant loading. Results also showed changes in granite fracture mode from pure and clean tensile in the case of non-compliant to a combination of tensile with rupture fractures in the 50% and the 100 compliant application. Such curve shift, rock failure delay, fracture modes, and overall deformation behaviour allow providing valuable data for controlling and predicting rock failure. This could also be used in optimally applying drilling parameters to evaluate rock fragmentation, improve the rate of penetration, and for safely designing civil structures.
Life Extension of Risers and Engineering Criticality Assessment
Authors: Mansour Ghiath (Guy)
Published: September 2023

Extending the service life of existing oil and gas offshore production structures beyond their original design life is on the rise as opposed to investing billions of dollars building new structures. Such structures typically include the floating platforms, topsides, subsurface and subsea equipment, moorings, risers, flowlines, pipelines, and umbilicals. As far as risers are concerned, industry codes and standards and government regulations for the official requirements of life extension are yet to be issued, albeit some are in the works. The general requirements for risers are essentially to be fit for service for the intended period of life extension utilizing the latest available codes, standards, and Metocean criteria at the time life extension is considered. This also includes taking into account the actual conditions of the risers as verified by inspection and the history of the risers as documented through the integrity management program. The fitness for service assessment of Steel catenary risers (SCRs) consists typically of assessment of strength, S-N fatigue from all contributing sources, interference with other risers, umbilicals, or objects, flow assurance, cathodic protection, etc. A less straight forward issue of life extension of is engineering criticality assessment (ECA). This paper discusses the different aspects of life extension of SCRs and perspectives on ECA in particular and provides strictly recommendations absent official requirements for life extension as noted earlier. The experts assessing life extension should evaluate these recommendations and determine whether to follow them.
Stochastic Vortex-Induced Vibration in Free-Stream Turbulence Using a Phenomenological Model
Authors: Badhurshah Rameez , Srinil Narakorn , Chaplin John R. , Thies Philipp , Johanning Lars , Borthwick Alistair G. L. , Venugopal Vengatesan
Published: September 2023

Underwater dynamic power cables connected to offshore floating energy devices are subject to ocean flow turbulence and, through eddy shedding, may experience vortex-induced vibration (VIV). A high level of turbulence intensity may cause fatigue damage to cables during the operation. The present preliminary study investigates the VIV response of a rigid circular cylinder in free-stream turbulence. A phenomenological reduced-order wake oscillator model is coupled with a stochastic differential equation that represents flow turbulence. The model consists of two coupled ordinary differential equations: a structure oscillator forced by the wake vortex shedding and a van der Pol oscillator coupled with the structural acceleration. Wake oscillator models have been extensively used in the past, with several application-specific versions having been developed. The stochastic differential equation accounts for random fluctuations in the fluid flow velocity. Here, we vary the turbulence intensity in the model up to a maximum of 20%. The cylinder response is not significantly affected by very low levels of turbulence, but amplitude modulations and beating phenomena are observed in a strongly turbulent flow. Lock-in, whereby the structure oscillation frequency synchronizes with the vortex shedding frequency, is also explored to study how the resonant frequencies differ in cases with and without the present turbulence. We also investigate the stochastic VIV response subject to the mass ratio variation. The model validation with selected empirical coefficients of the prediction model is also presented. The findings should be of benefit to researchers and design engineers who are concerned with the development of floating energy systems by better characterizing operational load conditions for new installations.
Finite Element Analysis of Composite Mooring Tensioner Springs in Wave Energy Converters
Authors: Cai Yuanzhen , Heitzmann Michael T.
Published: September 2023

Floating structures are widely used in the offshore oil and gas industry, in deep-sea wind farms, and ocean wave energy converters, where fixed-bottom designs are often uneconomical due to the water depth. The traditional way of positioning a floating platform is using a catenary mooring system. The mooring tensioner is a critical component of a mooring system and is responsible for station-keeping during different ocean wave conditions. Statistically, a disproportionate amount of offshore floating structure incidents can be attributed to premature mooring failures [1]. Therefore, a new concept of a taut leg mooring system that utilises a fibre-reinforced polymer (FRP) mooring tensioner will be introduced in this paper. FRP mooring tensioners not only can be used for station-keeping of offshore structures but also can be used for wave energy harvesting. This is due to its advantages compared to metal tensioners, such as corrosion resistance, high specific strain energy, and the ability to tailor the spring constant without changing the overall dimensions. In this paper, the operation envelope of the FRP mooring tensioner in a Wave Energy Converter (WEC) will be investigated through simulation. By doing a simulation, this paper will discuss the estimated amount of energy stored by the mooring tensioners made with different materials at the same torque. The analysis shows that UD S2 glass/epoxy mooring tensioners can store significantly more energy than a metal spring made with spring steel at the same wave conditions, and therefore generators inside the Power Take-Off (PTO) unities can convert more stored mechanical energy into electricity. This FRP mooring tensioner not only can be used in WECs, but also can be used in offshore oil, gas, offshore wind, and aquaculture industries. The generated electricity can power auxiliary equipment, such as feeding barges in the aquaculture industry. In the case of the wind farm industry, the FRP mooring tensioners integrated PTO systems can be the wave energy converter component of wind-wave multi-purpose renewable energy generation systems.
Minimum Operating Pressure to Prevent the Onset of Wrinkling Tendency in MLP During Transient Shutdown Condition
Authors: Rao Venu , Fernandez-Vega Jens
Published: September 2023

The use of mechanically bonded lined pipes (MLP) is a cost-effective option for sour service applications. It has been shown that reel-lay installation of MLPs with 30 bar nominal internal pressure would ensure the wrinkle-free installation of the MLP on the seabed. The internal pressure during the remaining phases of design life such as hydrotest, leak test, and operating conditions is relatively much higher than the internal pressure used in reel lay installation and hence, provides adequate constraint to disallow liner wrinkling for these conditions.

This paper presents the findings of a finite element based analysis study to see whether minimum threshold internal pressure is required during the cycling of transient operational loading of the MLP line to prevent the onset of wrinkling of the liner. It should be noted that the experimental work to back up FE analyses cannot be undertaken due to time and cost constraints related to the simulation of transient operating conditions.