bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Metallic Clamp for Flexible Risers
Authors: Doynov Krassimir , Iwicki Rachel , Henneke Brandon
Published: August 2024

A novel non-metallic clamp for flexible risers with breached outer sheath in the splash zone has been developed, qualified, and installed to restore annulus integrity and enable riser lifetime extension.

Flexible riser outer sheath breaches in the splash zone or aerial riser portion have been experienced by operators and reported to occur by Sureflex JIP, due to natural degradation (i.e., UV aging and fatigue), dropped objects, or blocked vent ports of riser end fittings terminated topside. An outer sheath breach in the splash zone or aerial riser portion exposes the structural carbon steel wires to rapid corrosion due to oxygen inflow at the breach location, and because existing cathodic protections are not effective above the mean seawater level. Rapid corrosion in turn decreases both riser strength resistance to pressure and tensile loads, and riser corrosion fatigue resistance, which over relatively short period of time may lead to loss of riser containment. Clamping of the breached outer sheath location has been historically used to mitigate that risk of loss of containment with the use of steel clamps of various design.

Three steel clamps were installed over a longitudinal-seam-weld-outer-sheath repair performed at riser installation over the course of a few years, with a new leakage discovered after each clamp installation. This experience has led to the realization the outer-sheath stiffness transition in the vicinity of the steel clamp edge and clamp tightening have driven initiation of new breaches nearby due to the degraded outer-sheath-seam-weld repair. This realization in turn inspired the development of a novel, cost effective non-metallic clamp that eliminates the sharp stiffness transition caused by metallic clamps.

This paper describes the development, qualification and installation of a novel non-metallic clamp to enable the lifetime extension of a flexible riser described in OMAE 2023-101167 [1]. The paper presents the transition from technology readiness level TRL-0 (basic research) to TRL-6 (system installation). It presents the logic of material and component functionality selection, failure mode identification, prototyping, validation testing, system integration, installation, and lessons learned. It concludes with recommendation on scalability of the non-metallic clamp use and further development on adding venting functionality.
Data-Driven Generation of Tailored Wave Sequences
Authors: Klein Marco , Wedler Mathies , Pick Marc-André , Seifried Robert , Ehlers Svenja , Stender Merten , Hoffmann Norbert
Published: August 2024

This paper explores the applicability of machine learning techniques for the generation of tailored wave sequences. For this purpose, a fully convolutional neural network was implemented for relating the target wave sequence at the target location in time domain to the respective control signal of the wave board. The database was generated by means of extensive wave tank tests. The experimental campaign focused on the generation of very steep wave groups including wave breaking which cannot be covered by the simplified wave generation methods. The extensive experimental campaign was performed in a small wave tank with an fully automated approach including determination and control of the wave maker motion as well as data measurement. The training data set features wave groups of short duration based on JONSWAP spectra, where the parameters wave steepness, peak wave period and enhancement factor were systematically varied. At the end of the training process, the trained models are able to predict the wave maker control signal based on time series of the target wave defined for a specific target location in the wave tank. The accuracy of the trained models are evaluated by means of unseen validation data. In addition, the predictive accuracy of the trained models is compared with the classical linear transformation approach.
Simulation Analysis of Critical Loads of Cylindrical Pressure Hulls With Initial Defects
Authors: Yuan Siming , Han Enquan , Han Husha
Published: August 2024

Pressure hull is an important part of underwater unmanned vehicle, which is the main provider of buoyancy force and withstands immense seawater pressure. Initial geometric defects will lead to the reduction of the ultimate strength of the structure, and the first-order mode is often used as the initial geometric defects in finite element analysis to study the ultimate strength of the structure. In this paper, based on ABAQUS finite element simulation software, an internal corrugated pressure hull model is established, and first, linear eigenvalue buckling analysis is performed on the internal corrugated pressure hull to obtain the first 30 order linear buckling modes of the pressure hull. Then, each order of buckling modes and the superposition of multi-order modes are respectively taken as the initial defects, and the nonlinear buckling analysis of the inner corrugated pressure hull is performed to obtain the critical buckling load. The results show that: for single-mode defects, the most unfavorable geometric defects are generally low-order modes. When considering the defects of the superposition of multi-order modes, with the increase of combined orders, the critical buckling load shows a decreasing tendency, and the decreasing amplitude changes from large to small and then large again. When the combination of orders from 1-8 to 1-24, the critical buckling load shows a slowly decreasing tendency, that the variation is within 3.28%.
Seabed Response Around a Partially Buried Pipeline Subjected to the Combined Ocean Waves and Currents Loads in a Trench Layer
Authors: Sun Ke , Gao Yuan , Zhang Jisheng
Published: August 2024

The widespread co-existence of the wave and ocean currents is a common phenomenon in coastal environment, nevertheless, the relevant work for seabed response was primarily restricted to either wave-alone or waves and a following/opposing co-directional current conditions. Unlike the previous studies, the oblique currents, ranging from perpendicular incidence to parallel incidence, are considered in the present study for fluid-pipeline-seabed interactions, which might be claimed that a two-dimension simulation was no longer applicable. An integrated model is proposed to examine the soil behavior from a three dimension prospective, in which the RANS equation is applied to govern the fluid domain, while the Biot’s poro-elastic theory is employed for the solid domain description. Results show that a fully/partially-backfilled pipeline in a trench layer has a remarkable resistance to the seabed momentary liquefaction in comparison with one positioned on the seabed surface. Under the presence of the counter-current waves, the transient pore pressure would be strengthened, whereas the co-current waves would weaken the pore pressure oscillation. The momentary liquefaction depth surrounding the undersea pipeline increases with the declination in the obliquity between the waves and current. Moreover, as the backfill thickness reduce and trench gradient decline, the instantaneous instability of the subsea pipeline and its underlying seabed would be compromised.
Experimental Assessment of Drilling Fluid and Wall Slippage for Wellbore Displacement
Authors: Johnson John , Wojtanowicz Andrew K.
Published: August 2024

In the ideal plug-flow mode Bingham-type drilling fluids display strong frontal displacement potential at a very low flowrate. The rate may be significantly increased with the fluid’s wall slippage so that maximum size of the fluid’s plug is maintained. Based on this concept the study qualifies the wall slippage effect as a rheological property to be used in fluid’s selection and evaluation for the purpose of wellbore displacement. The effect is analyzed using a conceptual model of fluid motion between two parallel plates to define the relationship between velocity of undisturbed fluid plug (slip velocity) and shearing rate for the maximum slippage effect. Applying the analysis to coaxial geometry gives practical formulas and a simplified procedure for fluid testing using either modified or conventional rotational viscometer. Also defined are new parameters of the fluid’s displacement performance: Maximum Slip Velocity and Plug Displacement Index. The study evaluates a variety of water-base drilling fluids such as high-molecular-weight polymer solutions, dispersed clay suspensions and suspensions flocculated with different electrolytes. The results show that the best-performing displacement fluid is a prehydrated bentonite suspension flocculated with sodium chloride.
Model Test of a Semi-Submersible Floating Wind Turbine: Hydrodynamic Motions and Internal Loads
Authors: Jiang Yucong , Zheng Xiang Yuan , Wang Shuaishuai , Zhao Mengyang , Zhang Sheng , Moan Torgeir , Gao Zhen , Li Wei
Published: August 2024

A semi-submersible floating wind turbine (FWT) similar to OO-STAR in geometry has been developed by the authors from the Department of Marine Technology of Norwegian University of Science and Technology (NTNU). This study is dedicated to experimentally fathoming its dynamic performance of motions and internal loads under wind and wave loads. Model tests are conducted in the ocean basin at Tsinghua Shenzhen International Graduate School. First, a physical model with a scale ratio of 1/28 is designed and fabricated, comprising an aluminum floating model, steel ballast, a small wind turbine, and a spread mooring system. A 6-axis force sensor is purposely placed at the root of central column for measuring the cross-sectional loads between the column and the floating foundation. Second, a series of model tests, including free-decay tests, wind-only tests, wave-only tests, and wind-wave tests, are carried out to investigate the primary dynamic performance of the floating system. The test results not only demonstrate the effectiveness and reliability of such an experimental method of measuring the internal loads, but also reveal important dynamic characteristics of this floating wind turbine. Under wave loads, the foundation exhibits low-frequency motion responses in pitch, heave, and surge, primarily concentrated at the corresponding natural frequencies. Moreover, there are both low-frequency and high-frequency responses induced by the natural vibrations of the tower in the cross-sectional loads, including the shear force, the axial fore and the bending moment. However, the contribution of the high-frequency component is relatively small. When wind loads are applied in combination of random wave loads, high-frequency responses induced by the natural vibrations of the tower could be observed in pitch, heave, and surge motion responses. Besides, the contribution of the high-frequency component in the section-crossing load becomes much more significant. Non-Gaussian effects are not significant for the shear force, the axial force and the bending moment in the tests.
Prevention of Flow-Induced Pulsations in Unbonded Flexible Pipes Using a Carcass Insert Technology
Authors: González Díez Néstor , Belfroid Stefan P. C.
Published: August 2024

Flow-induced pulsations (FLIP) originated from flexible pipes, when used in deepwater applications, can cause large vibrations and dynamic stress levels in the attached topside or subsea pipe systems. The pulsations are characterized by high frequencies that can cause fatigue failures within a short time, leading to loss of containment.

To prevent the appearance of FLIP, a new technology has been developed that involves manufacturing a T-shaped insert to cover the inner spiral cavity of the carcass, making the pipe bore relatively smooth. Smoothing the pipe bore with this insert delays and prevents the onset of flow-induced pulsations during dry gas transportation by minimizing the strength of pressure pulsations caused by local vortex flow and created in the spiral cavity. The use of this insert allows higher gas flow rates to be achieved in flexible pipes without introducing FLIP, thereby eliminating all FLIP-related structural integrity issues of the systems attached to the flexible. The smoothing of the pipe bore also reduces friction and improves flow assurance of pipe, reducing the pressure drop.

This paper describes the merits of new insert technology using the FLIP prevention mechanism including the theoretical work related to analyzing flow and pressure pulsation. An acoustic energy balance framework is used to determine the onset velocity of pulsations originated at residual cavities left by the implementation of the insert. A shallow cavity is formed between two adjacent windings of the spiral insert. An aerodynamic analysis of these shallow cavities is described to determine whether self-sustained acoustic oscillations are possible. Other risks are introduced by the absence of the insert near end-fittings. Finally, in-situ conditions leading to non-uniformity such as bending of the flexible and pipe ovality are addressed. FLIP risks can be fully eliminated with the new insert technology in its nominal design and within its manufacturing tolerances.
Full-Scale Testing on Corrosion Resistant Alloy-Mechanically Lined Pipes (CRA-MLPs) for Submarine Pipeline Applications
Authors: Reda Ahmed , Kaspary Tiago , Montague Paul , A. Shahin Mohamed , Menezes Eduardo
Published: August 2024

Corrosion-resistant alloy (CRA) mechanically lined pipes (MLPs) have long been known as a cost-reduction alternative compared to CRA-clad (metallurgically bonded) pipes. Additional advantages also exist, including improved fit-up and installability, a wider choice of CRA materials, pipe dimensions and a lower carbon footprint. MLPs provide at least the same corrosion resistance as the CRA-clad pipes; however, as the liner is not metallurgically bonded to the carbon steel outer pipe, there is an additional failure mechanism of liner buckling during installation or strain associated with lateral buckling. Despite this, MLPs have been successfully installed in the subsea by reeling on several projects and many are currently in service without concerns. For any submarine pipeline, fatigue damage may be accrued from the loads incurred by fabrication, transportation, installation, pipeline spanning, thermal cyclic loading, instability, and interference loads such as fishing. As such, fatigue cracking can occur at both the girth weld and the triple point. Currently, the triple point is not classified in the fatigue design of many standards and there is limited data in the literature regarding the fatigue performance of the triple point. In this paper, full-scale bending testing was conducted on a 273.1 mm outside diameter MLP before a full-scale fatigue resonance testing. The full-scale bending testing was undertaken to replicate the through-life stresses experienced by the triple point, whereas the full-scale fatigue resonance testing was undertaken to understand the fatigue performance of the triple point. A periodic inspection of the liner was also performed during the full-scale fatigue testing as there is always a concern that the liner might crack before the back steel.
Research on USV Smooth Path Planning Method Based on IAC-QPSO Algorithm
Authors: Li Chengfeng , Wang Hongjian , Huang Yutong , Zhong Bo , Chi Zhikang , Tian Jinmu , Luo Naifu
Published: August 2024

Aiming at the problem of unmanned surface vehicle (USV) smooth path planning in complex obstacle environment, a USV smooth path planning method based on improved ant colony and quantum particle swarm optimization (IAC-QPSO) algorithm is proposed. An improved ant colony (IAC) algorithm is used to plan the global optimal polyline path, and the optimal turning regions are obtained by redundant optimization and merging strategies. The particle dimension is determined adaptively according to the number of optimal turning regions, which avoids the blindness and redundancy of size determination. To improve the quality of the initial solution, particle position initialization is carried out in the turning regions, so that it is easier to find the global optimal path. The boundary constraint is determined according to the extension of the optimal path turning regions, which greatly reduces the solution space, thus reducing the solution difficulty, and improving the search efficiency. Additionally, Levy flight, random particle and spiral search are introduced into quantum particle swarm optimization (QPSO) to enhance the optimization ability of the algorithm. Using the weighted sum of path length, safety degree and smoothness as fitness function, the optimal smooth path is obtained by the improved quantum particle swarm optimization (IQPSO) algorithm and cubic spline interpolation. Simulation results show the effectiveness of the proposed algorithm.
Experimental Investigation of Well Cement Integrity in Abandoned Oil and Gas Wells
Authors: Thaika Muhammad A. , Hu Ke , Kuru Ergun , Li Huazhou , Iremonger Simon , Lin Zichao , DeBruijn Gunnar
Published: August 2024

This research is focused on testing the limits of cement abandonment plugs, evaluating their isolating capabilities under severe conditions. The results will be used to understand possible failure modes and ensure long term effectiveness of wellbore abandonment operations of different cement systems.

In this study, small-scale bulk cement and abandonment plug (i.e. cement in casing) samples were optimally cured under 50°C and 1000 psi for a period of 7 days and tested for their permeability to understand the basic behavior of the cement. Water and Nitrogen permeability tests for all small-scale samples were conducted using a typical core flow setup.

A set of permeability experiments were also carried out using a physical wellbore simulator, which allowed cement curing and subsequent permeability testing under elevated pressure and temperature. The setup is designed to simulate abandoned wellbore section with variable fluid injection pressure, confining pressure and temperature conditions. Cement shear bonding strength was also determined after each experiment.

From the small-scale experiments, it was observed that bulk cement on its own had exceptionally low permeability. The small-scale abandonment plug exhibited relatively higher permeability than the bulk cement. Nitrogen flow was observed in the small-scale abandonment plug experiments, possibly through the cement-casing interface.

Two different cement blends were tested using the wellbore simulator; Neat G cement without any additives and a Class G cement with additives that has been engineered to enhance its sealing performance.

The wellbore simulator experiments had shown that the Class G plus additives cement plug outperformed Neat G cement blend in every testing scenario. Although both cement systems were tested in severe conditions, both performed adequately.

The class G plus additives cement blend also resisted the formation of a micro annulus better than the Neat G cement. Results also indicate an inverse relationship between the shear bond strength of the cement plug and the permeability of the cement system, indicating that stronger mechanical bonding also delivered improved resistance to gas flow.

Data measured from these experiments will form the baseline for future experiments where other crucial parameters are to be investigated.
A Monte Carlo Based Model for Estimating the Reliability of Offshore Structures Exposed to Environmental Loading
Authors: Zeeberg Allan Rod , Tychsen Jesper , Nielsen Jørgen Svejgaard , Cholley Jean-Marc
Published: August 2024

In Denmark, as in many other countries, there is a legal requirement to ensure that risks related to health and safety and major environmental incidents in connection with offshore oil and gas operations have been identified, assessed, and reduced to a level as low as reasonably practicable (ALARP). One aspect of this involves determining the annual structural probability of failure for safety and environmental critical elements (SECEs) on offshore installations exposed to environmental loading. This is achieved by employing Structural Reliability Analysis (SRA). New knowledge about breaking waves has surfaced during the last decade which adds complexity to the SRA procedure. An SRA using crude Monte Carlo simulation considering breaking waves is described in this paper. The developed models are validated against physical model tests and other simulation methods. The process is complicated as numerous sources of uncertainty (both aleatoric and epistemic) are included. The aim has been to determine failure rates reflecting, as close as possible, the actual probability of failure (also denoted “actuarial”) by minimizing the epistemic uncertainties, as opposed to previous work, where, due to inadequacies in the various models, the failure rates were “notional”. The reader is provided a general overview only without going into details on the individual models due to the extent and complexity of the models.
Static and Fatigue Analysis of Wind Turbine Towers Made in Composite Materials
Authors: Petiteau Jean-Christophe , Paboeuf Stéphane , Al-Ghuwaidi Abdulelah
Published: August 2024

In the context of the increase of the energy demand, the offshore wind industry is developing larger floating platform to produce more electricity and to minimize the levelized cost of energy (LCOE). The target is to install 20MW power turbine and more at sea, but the size of the platform, of the tower and of the turbine will significantly increase. The change of scale will lead to huge dimensions and heavy weight that will contribute to an increase of the cost for the installation and for the mooring. A solution to reduce the weight of the structure of Floating Offshore Wind Turbine (FOWT) has been investigated within the European Research project FIBREGY and consists in replacing steel by composite materials. The overall objective of the FIBREGY project is to enable the extensive use of Fibre Reinforced Plastic (FRP) materials in the structure of the next generation of large Offshore Wind and Tidal Power (OWTP) platforms.

This paper aims to present the results obtained for FOWT towers made in carbon fibres. Firstly, the calculation methodology developed during the FIBREGY project to evaluate loads applied to a FOWT will be detailed. This methodology is based on Bureau Veritas software programs and particularly on OPERA, a hydro-aero-mooring coupled dynamic calculation tool. Then, numerical simulations performed with ultimate loads in static and cyclic loads for the fatigue analysis will be detailed. Stresses will be compared with criteria determined within the project for such application as well as the fatigue life. Finally, the design of tower will be optimised in considering the damage in fatigue, the static stresses, the maximal deflections and the buckling.
An Optimized Consideration for Catenary Mooring System Designs
Authors: Cao Jianchun , Bhandari Anil , Galagoda Mahi
Published: August 2024

Catenary mooring systems have been widely used in offshore industry when oil and gas exploration and production was conducted in shallow to deep water. To ensure a catenary mooring system arrives at the seabed horizontally, a very long seabed anchor chain is usually used. In actual applications, a substantial length of anchor chain could be saved if a small load angle at Touch-Down Point (TDP) can be considered in the design. This paper first reviews the chain-soil interaction analysis model from previous studies. Based on this, an excel spreadsheet tool to simulate the behavior of chain-soil interaction has been developed. Then, the chain’s configuration in soft clay is investigated using the developed tool. The influence of a small load angle at TDP on the embedded chain length in soil and the influence of a load angle at TDP on the padeye load or load components are checked. Finally, a recommendation is made to improve (or optimize) the traditional design concept of a catenary mooring system (i.e., no uplift load at TDP for any stage) by considering a small load angle at TDP (i.e., 1° – 5°) for the intact and damage conditions under the maximum design environment (i.e., extreme design loading cases).
The Coupling Mechanisms of Seepage and Heat Transfer in Rock Fractures in Enhanced Geothermal Systems Based on the Lattice Boltzmann Method
Authors: Su Wei , Wang Zhiliang , Li Miao , Shen Linfang
Published: August 2024

The coupling mechanism of seepage and heat transfer in high-temperature rock fractures controls the heat extraction ability of enhanced geothermal systems. Utilising the lattice Boltzmann method, a numerical model is proposed to capture this coupling, accounting for fluid temperature’s influence on kinematic viscosity and thermal diffusion coefficient in rough fractures. The model’s validity is confirmed through a classic example. The effect of rough fracture surface on the coupling mechanism of seepage and heat transfer was analysed. The relationship between the roughness of the fracture surface and the performance indicators of geothermal extraction was discussed. The results show that neglecting the roughness of the fracture surface would lead to a severe underestimation of water temperatures within the fractures. As the roughness of the fracture surface intensified, its thermal breakthrough time gradually increased while the heat recovery rate and heat production power decreased.
Forced Vibrations of Cold-Water Pipe for OTEC Based on Generalized Integral Transformation Technique
Authors: Tan Jian , Zhang Yu , Zhang Yulong , An Chen , Duan Menglan , Sun Le
Published: August 2024

This paper investigates the forced vibration and stability performance of cold-water pipe (CWP) for Ocean Thermal Energy Conversion (OTEC) under different types of loads and boundary conditions. The vibration control equation of the pipe is derived considering viscoelastic dissipation, damping ratio of surrounding environment, mass ratio, and gravity parameter. The generalized integral transform technique (GITT) is applied to solve the vibration control equation and obtain the critical flow velocity and mode shapes of the pipe. The effects of damping ratio, viscoelastic coefficient, mass ratio, gravity parameter, and load types on the vibrational characteristics of the pipe are analyzed. The results show that the critical flow velocity of the pipe is sensitive to the boundary conditions and the parameters of the pipe and the fluid. The damping ratio and the viscoelastic coefficient can effectively change the stability of the pipe. The mass ratio and the gravity parameter have complex influences on the critical flow velocity, depending on the boundary conditions and the load types. The proposed method and results can provide guidance for the preliminary design and optimization of CWP for OTEC systems.
Basic Research on Seabed Visualization Technology Applying UV-Laser
Authors: Ishibashi Shojiro , Okada Takamitsu
Published: August 2024

Recently, in order to efficiently explore seabed resources using underwater vehicles, researches on effective technologies to visualize the seabed have been conducted. Underwater laser scanners have been proposed as one of effective methods that combine good measurement range and accuracy. An underwater vehicle equipped with an underwater laser scanner emits a laser and detects the reflection on the seabed to visualize the seabed topography with high precision. The characteristics of seabed reflection is difference depending on laser wavelength. Conventionally, visible lasers of blue to green wavelengths, which have good underwater propagation properties, have been used. Currently, we are currently working on a new underwater laser scanner that applies an invisible ultraviolet (UV) laser. It is expected that by understanding the underwater propagation properties of invisible laser and effectively detecting the laser reflections from the seabed, some unique state quantities of the seabed might be extracted. The new underwater laser scanner that uses UV wavelengths laser has been developing and its basic performance and effectiveness were verified in an actual deep seabed environment.
Offshore Wind-To-Hydrogen: the Impact of Intermittency on Hydrogen Production and Transport
Authors: Summers Eoghan , Race Julia , Mignard Dimitri , Tian Mi , Almoghayer Mohammed Alaa
Published: August 2024

Offshore wind is a promising renewable energy source for green hydrogen production, providing a versatile solution for energy storage and power-to gas concepts. This research investigates how the intermittent nature of offshore wind impacts the components of an offshore wind-to-hydrogen system. Proton exchange membrane electrolysers are frequently identified as being best suited to integration with intermittent renewables. However, stop-start cycling of current from a variable power supply can damage electrodes and reduce electrolyser lifetime. Therefore, a small current is required during no wind periods to prevent electrolyser degradation. An intermittent offshore wind resource can also impact pipeline transport of hydrogen. Variable hydrogen production leads to fluctuating hydrogen flow in pipelines. The resulting pressure variations, combined with the potential occurrence of hydrogen embrittlement in steel pipelines can increase the potential and severity of fatigue crack growth, thereby impacting pipeline integrity. Careful selection of pipeline materials and buffer storage to smoothen gas flows, can mitigate these potential impacts. This research proposes a configuration for hydrogen production on an offshore platform from a floating wind farm. It uses battery and hydrogen storage offshore to provide buffers, mitigating the potential impacts of intermittency on each component of the offshore wind to hydrogen system.
Vibration and Fatigue Mitigation of a 5 MW Barge-Type Floating Offshore Wind Turbine Under Misaligned Wind and Wave Loadings
Authors: El Hamoud Riad , Alkhoury Philip , Aït-Ahmed Mourad , Soubra Abdul-Hamid , Schoefs Franck , Dib Rabih
Published: August 2024

This paper aims at investigating vibration suppression and fatigue mitigation of a 5 MW barge-type floating offshore wind turbine (FOWT) under misaligned wind and wave loadings. A passive omnidirectional tuned mass damper (TMD) installed in the floating platform was employed. The aero-hydro-servo-elastic coupled simulation program for wind turbines, OpenFAST, was used to perform the numerical simulations. The omnidirectional TMD was tuned to the platform pitch and roll natural frequencies in order to mitigate the vibration and fatigue loads in fore-aft and side-side directions respectively. The TMD damping ratios in fore-aft and side-side directions were obtained from two minimization procedures where the objective functions are the standard deviations of platform pitch and platform roll motion respectively. The effectiveness of the omnidirectional TMD was checked for one load case under three misalignment angles (0° ; 45° ; 90°). The percentage change of the standard deviation (SD) and damage equivalent moment (DEM) between the controlled and the uncontrolled cases were used as indicators of vibration suppression and fatigue mitigation respectively. The obtained results have shown that the omnidirectional TMD can effectively mitigate vibrations and fatigue of the FOWT under misaligned wind and wave loadings. For instance, the reduction in SD of platform pitch and DEM of tower base fore-aft moment could attain 47% and 31% respectively in the case of a misalignment angle between wind and wave of 90°. Moreover, a comparison with an equivalent dual TMD was carried out. It was found that the omnidirectional TMD provides better bidirectional vibration and fatigue mitigation when compared to the dual TMD.
The Proposed Long Island Project in Singapore, is there a More Sustainable Way?
Authors: Lim Soon Heng
Published: August 2024

The Singapore Government recently announced plans for an 800-hectare reclamation on Long Island, south of East Coast Park. The announcement came under the scrutiny from city planners, and the academia as well environmental scientists, and NGOs. The government is seeking inputs from those who have interests. The multi-year in-depth feasibility study will commence in 2024.

Several alternatives are possible. The government’s proposal is essentially an 800-hectare polder. Between the existing shoreline and the landward side of the reclaimed land a large strip serves as a catchment for freshwater fed by monsoon rain.

This paper proffers a solution using a series of gravity-based caisson (GBC) modules to form a lagoon separating the freshwater from the seawater. They can be manufactured offsite, launched and towed to its final position where it is aligned and ballasted with seawater. Some of the GBCs are designed to accommodate floating gates which when partially raised by deballasting allows excess water in the lagoon to be discharged into the sea. The top deck of the GBC is designed as a roadway for light vehicles.

Within the lagoon, floating platforms serve as foundations for residential and commercial buildings and for recreation parks or as dormitories for students in nearby institutions of higher learning. Transportation may be by ferries, flying taxis (such as the EH216-S) or buses similar to Vaporetto in Venice. Floating electric bicycles would be a personal mobility option. There will not be any roads or drains to build or maintain. Floating bridges link key points to the mainland or the caisson roadways. Small barges ply the lagoon to collect garbage and floating debris which are mechanically transferred to a larger barge outside the lagoon for transport to incinerators. There will not be any roads or drains to build or maintain.

Why would a government consider this proposal when a major source of its income is leasing land? First, it is a greener option. Second, the capital outlay will be a fraction of the cost of land reclamation (estimated at SGD 6.4 billion). Third, the seaspace can also generate a source of revenue. At the end of the lease the plot can be freed up in a short time frame (by the owner), freeing up the plot for another investor to lease.

Maintenance of reclaimed land is costly as experience at the Kansai Airport and Jumeirah Island has shown. Foundations for land-based buildings take more money and time to complete. Buoyancy is a principle of physics independent of the soil properties below.
Extreme Value Analysis - Statistical Inference Method for the Identification of Most Probable Extremes in Highly Nonlinear Systems. Case Study: Green Water Loads on FPSO
Authors: Gkikas Georgios
Published: August 2024

This work aims at deriving the most probable extreme response of highly nonlinear systems under random excitations based on a collection (ensemble) of small size samples by using order statistics in combination with non-parametric statistical inference methods (SIMs). The resulting scheme essentially consists of the r-largest Order Statistics (r-LOS) model and the (Delete-d) Jackknife or Bootstrap non-parametric, resampling methods. Using the r-LOS model when dealing with relatively small size samples, more information from the collected set of extremes per sample can be accrued as opposed to the common engineering practice of employing just the single highest extreme per sample, i.e., Block-Maxima approach.

On the other hand, SIMs, with the aid of resampling with or without replacement, can further enhance this information using artificially created ensembles. As a result, from the ensembles produced via resampling, quantile levels and distribution parameters such as shape, scale and location become new random variables. With the aid of these new distributions, the probability of extremes can be explained better in terms of both sample size, i.e., number of realizations and number of largest extremes per sample.

Due to data availability, a direct application-example for the illustration of the merits of this novel approach is the determination of the most-probable maximum of experimental green water related extreme loads. Using the proposed approach, the statistical attributes of recorded extremes and distribution-fit parameters can be assessed w.r.t:

a. the number of realizations,

b. the number of largest extremes per realization,

c. all possible combinations of a and b.
An Innovative Testing Method to Qualify Deep-Water 66kV Power and Hydraulic Combined Umbilical
Authors: Zhou Ying , Wang Xu , Chen Kai , Shi Luhao , Yuan Yanyan , Zhang Dayu
Published: August 2024

With the development of deep-water offshore oil & gas and the extensive application of subsea high-voltage equipment, integration of 66kV power cable into umbilical will become a trend. With the increasing water depth of oil & gas field development, how to verify the reliability and safety of the 66kV power and hydraulic combined umbilical for deep-water application is a topic worthy of discussion. An innovative testing method is proposed, which incorporates mechanical tests in API 17E and type test in IEC 63026 on a single testing sample. The main purpose of the test is to verify the performance of the umbilical taking into account high voltage and deep water characteristics.

An innovative 66kV power and hydraulic combined umbilical was designed and manufactured, and subjected to a series of tests based on the testing method proposed in this paper. The results show that the designed umbilical performs well and the testing results are more conservative. The proposed testing method can provide a reference for the validation of high voltage power cable integration umbilical for deep water applications in the future.
Wind Turbines and Hydrogen-Based Energy Storage Hub Concept for Offshore Oil and Gas Platforms in the Norwegian Continental Shelf
Authors: Damaceno Daniela S. , Treider Thomas , Svendsen Harald
Published: August 2024

The Norwegian government has the ambition to decarbonize the offshore petroleum sector while retaining its international competitiveness. Considering that individual electrification of platforms from shore is both inefficient and expensive, the centralization of the heat and power generation at an offshore hub is thought to have the potential to be an energy and cost-efficient solution. This paper aims to develop an innovative cost-efficient concept for a clean offshore energy hub for supplying low-carbon heat and power to existing offshore oil and gas cluster. The simulations were performed using Oogeso, an optimization tool used to study the optimal operation of offshore energy systems. In summary, the concept is based on an offshore wind farm supplying a cluster of offshore platforms, with energy storage, electrolyzer, and fuel cells added to smooth out fluctuations in wind power. Two different variations of this concept are analyzed and compared by evaluating metrics such as wind power curtailment and hydrogen usage. The results have shown that a hybrid system using renewable energy sources can successfully power a cluster of offshore oil and gas platforms.
Non-Destructive Measurement of Residual Stress in the Carcass Layer of Marine Non-Bonded Flexible Risers Using X-Ray Diffraction Method
Authors: Li Wenbo , Wang Xinyue , Lu Hailong , Yan Jun
Published: August 2024

The carcass layer is the innermost structure of marine non-bonded flexible risers, primarily responsible for withstanding external hydrostatic pressure to prevent the risers from collapsing and failing. The carcass layer is formed by repeatedly bending metal strips through multiple rolling processes. This unique processing method results in significant non-uniform residual stresses within the carcass layer. The impact of these residual stresses on the mechanical performance of the carcass layer is currently not well understood. Therefore, determining the magnitude and distribution of residual stresses within the carcass layer is of great importance for the design and analysis of flexible risers. To address the issue of traditional measurement methods being unable to measure residual stresses within the unique structure of the carcass layer, this study employed X-ray diffraction techniques with a discrete stress analyzer. The axial and circumferential distribution of residual stresses for three different sizes of carcass layers were measured. The experimental results indicate that the axial residual stresses in the carcass layer are predominantly tensile stresses. The circumferential residual stresses are uniformly distributed along the circumferential direction, with the maximum circumferential residual tensile stress located at the outer bend and the maximum circumferential residual compressive stress located at the inner bend radius.
Numerical Investigation on Uplift Capacity and Failure Mode of Inclined Circular Plate/Helical Anchor in Sand
Authors: Hao Dongxue , Chen Xichao , Chen Rong , Yuan Chi
Published: August 2024

Inclined circular plate or helical anchor has been extensively used as tensile foundations with certain horizontal forces, such as transmission tower and offshore structure foundations. The studies on the influences of inclination angle on the bearing characteristics under different sand compactness and embedment depth are insufficient. Therefore, this research carried out FEM analysis using a modified Mohr-Coulomb model considering the variation of mobilized sand strength, and the coupled Eulerian-Lagrangian technique to investigate the influence of inclined angle and embedment depth of circular anchors for different sand densities on uplift capacity and failure mode. Numerical results show that the influences of embedment ratio and density on uplift capacity are particularly important. The uplift breakout factor of the anchor plate increases rapidly at first and then slowly with the increase of the embedment ratio, until it approaches a stable value, and deep failure mode occurs. The critical embedment ratio increases with the sand compactness. The uplift capacity increases with the increase of inclination angle for shallow embedment depth, but the influence of inclination angle gradually decreases for deep embedment depth. Also, the influence of the inclination angle of the anchor plate becomes more pronounced with the increase of compactness.
A Nesting Boundary Approach in ISPH Model for Wave Impact Computation
Authors: Yang Xiaoxiao , Xu Haihua , Zheng Jiapeng , Chan Eng Soon
Published: August 2024

Given the intricate nature of wave impact, encompassing phenomena like air entrapment and turbulent mixing, laboratory measurement techniques have struggled to fully capture the flow field without constraints. In the past twenty years, numerical modeling has emerged as a valuable tool for researchers to surmount the challenges faced in experimental investigations. Nonetheless, due to the highly localized and exceptionally sensitive nature of wave impact, effective modeling necessitates substantial high-performance computing resources and entails lengthy computation times. Recognizing that higher resolution is only needed in a local zone where wave impact occurs, in this paper, we deploy a nesting boundary method based on incompressible smooth particle hydrodynamics (ISPH) model, which concentrates the computation resource on the truncated domain where the essential wave transformation and wave-structure interaction occurs. The scheme is then applied to simulate a flip through impact condition and results are compared with those attained using paddle and wall boundaries. It has been demonstrated that the nesting boundary scheme is proficient and successful in capturing essential flow field particulars, leading to significant savings in computational resources. This is particularly advantageous for wave propagation simulations conducted in very long flumes. Discussions are made on comparisons between different nesting schemes including nesting boundary and periodic boundary.
Contribution of Waves to Horizontal Low Frequency Motions of Floating Offshore Wind Turbines
Authors: H. Dadmarzi Fatemeh , Fonseca Nuno , Berthelsen Petter Andreas
Published: August 2024

The dynamic responses of INO WINDMOOR Floating Wind Turbine (FWT) in low frequency surge motion is investigated as a case study. A set of environmental conditions is selected to represent operational conditions with aligned wind and waves. The relative contribution of waves, as well as wind, low frequency excitations to the low frequency horizontal motion of the floating wind turbine is investigated. Simulations are conducted for turbulent wind and irregular waves with an aero-hydro-servo-elastic computational tool with the state-of-the-art force models. The effect of increasing wind speed in turbine’s operational range, in presence of low and moderate sea states, is studied in terms of low frequency surge motion of the platform. A detailed comparison for a moderate sea-state and rated wind speed is presented, where the effect of waves on slowly varying surge motion is discussed. The combined wind and wave contributions to the turbine aerodynamic damping is considered. The additional low frequency damping in surge due to wave frequency motions of hull and mooring lines are investigated. It is shown that the aforementioned damping could contribute to reduction of the response spectrum in the vicinity of the surge natural frequency. Further investigations are proposed to form a better understanding of wave and wind relative contributions to slowly varying motions.
Evaluation of Offshore Wind Power Production in Extreme Wind Conditions
Authors: Liu Xuan , Zhang Xiaoqin , Xing Xiuqing , Kang Chang Wei , S. G. Raghavan Venugopalan , Nguyen Vinh Tan , Li Jichao
Published: August 2024

Offshore wind energy plays a key role in the transition to renewable energy sources. With the growing interest and installations of offshore wind farms, a deeper understanding of how extreme wind conditions in the coastal area impact power production becomes essential. According to the working regimes of a wind turbine, wind energy production can be affected or disrupted by extreme atmospheric events particularly when facing specific thresholds such as below the cut-in wind speed, reaching the rated output speed and exceeding the cut-off wind speed. Given that these wind thresholds might all occur during extreme wind events, accurately calculating power production capacity during a coastal extreme atmospheric event becomes critical to assess wind farm availability.

In order to evaluate the power production at a proposed offshore wind farm site during an extreme wind event, this study utilized a coupled atmosphere-wave-ocean modelling system (COAWST) comprising fully coupled configuration (ROMS-SWAN-WRF) to represent the complex meteo-oceanographic conditions along US east coast area: Gulf of Maine. The selection of the fully coupled configuration was based on its superior performance, validated through comparison with various buoy observations. Subsequently, the study compared the gridded wind power production from different wind turbine configurations during an extreme winter storm event. Power production was computed separately based on each turbine model’s power curve and thrust curve. Assessing the spatial and temporal variations in power production capacity among different turbine model configurations during this extreme winter event in this study not only advances the understanding of wind assessment over the Gulf of Maine but also provides invaluable insights for researchers into advantages of employing more advanced meteo-oceanographic modelling system, such as COAWST, in offshore wind farm industry.