bluuebunny/crossref_metadata_2025 huggingface dataset:
Leveraging Digital Twins for Hydrogen Loss Mitigation in Large Scale Salt Cavern Hydrogen Storage
Authors: Yilmaz Ayse , O’Brien Sally , Thies Philipp , Das Prodip , Oterkus Erkan
Published: August 2024

As hydrogen continues to emerge as a key solution to decarbonise the global energy sector, interest in efficient storage solutions increases to meet rising energy demands and to ensure energy security. Large scale hydrogen storage salt caverns look to be a promising solution for hydrogen storage due to their ability to store large volumes of gas safely, as proven when storing natural gas in underground salt caverns. Hydrogen stored in underground salt caverns exhibits losses due to reasons such as gas migration, and the active chemistry they possess in addition to leaks due to damage caused by the cyclic loading on the cavern. Understanding the hydrogen loss pathways could help reduce financial losses and mitigate any safety risks imposed. Using SSE’s Aldbrough Hydrogen Pathfinder project, based in the UK Humber region as a case study, this paper aims to demonstrate how a digital twin can be utilised to evaluate and forecast hydrogen leaks by incorporating real time and historical data from sensors, geological information, and environmental factors to provide a holistic view of the cavern’s dynamics. This research aims to facilitate early detection of failures and highlight possible intervention mechanisms and strategies for underground salt cavern storage used for green hydrogen.
Pipeline Lateral Buckling Mitigation With Combined Sleepers and Mattresses
Authors: Hayes Kevin , Qi Xinhai , Duan Gang , Ren Lan , Jin Joe , Sharma Akhilesh
Published: August 2024

Buckle initiation devices, such as sleepers and distributed buoyancy modules, are typically adopted to initiate lateral buckles at pre-determined locations to release thermal expansion in a controlled manner to ensure pipeline integrity. For pipelines installed by S-lay, sleepers are desired as it is difficult for buoyancy modules to pass over the stinger rollers. If the thermal cyclic fatigue is critical in the pipeline design, pipeline lateral buckling designs may result in small sleeper spacing. As such, buckle reliability of conventional sleepers may be inadequate in some cases.

In this paper, lateral buckling mitigation with sleepers is investigated using finite element (FE) models for a water injection pipeline. Sensitivity analyses are performed on key input parameters including single and dual sleepers, lower bound and upper bound friction factors between sleeper and pipeline, berm effects on soil lateral resistances, and sleeper heights.

Based on the sensitivity study results, a mitigation solution combining sleepers and mattresses under the pipeline touch down zones is proposed and evaluated. It is found that sleepers combined with reduced touch down point lateral friction can reduce the maximum longitudinal strain and thermal fatigue damage by more than 50% as compared to using sleepers alone as mitigation. Therefore, this design adds a new option to allow increases in the sleeper spacing and improved reliability of buckle initiation.
Gripping Methodology: A New Approach Towards Enhanced Reliability for the Installation of Flexible Pipes
Authors: Godefroy Elise , Delannoy Laurent , Machnik Adam , Deheeger Antoine , Micas Guillaume , Belamri Nabil
Published: August 2024

During offshore installation / retrieval with tensioners, the flexible pipe is submitted to an axial tension due to the suspended catenary weight. To sustain this downward axial force and avoid any slippage during installation, a suitable squeezing load must be radially applied to the flexible pipe by tensioner tracks to ensure a proper transmission of the tightening force, by friction, at every layer interface, to the core of the pipe without crushing the pipe inner structure.

This paper presents a novel design methodology for the determination of the specific squeezing load during flexible pipe installation with tensioners. Various challenges are faced when determining the proper squeezing load to safely install flexible pipe, due to the diversity of interfaces above the tensile armour layers. Indeed, flexible pipe cross-sections may contain different sheath and tape materials (for mechanical, chemical, thermal, or manufacturing purposes). Every interface may behave differently depending on the environment (when exposed to water, temperature, etc.), and the level of contact pressure.

Therefore, the design challenge was to build a comprehensive approach relying on the following main aspects:

- Friction interaction between flexible pipe layers addressing influent parameters, thanks to an extensive small-scale test campaign,

- Statistical treatment of these data and validation through testing with complete flexible pipes,

- Development of Finite Element Analysis (FEA) Abaqus models to validate the load transmission mechanisms from the tensioner to the core of the flexible pipe,

- Validation through a large full-scale test campaign including tensioner onboard an installation vessel,

- Certification of the full methodology with an Independent Verification Agent (IVA).

This novel methodology is a key enabler towards even safer offshore operations as it constructs clear installation domains which prevent slippage events considering multiple factors. The methodology was built in compliancy with DNV-ST-N001 that details how to derive the friction coefficients and select appropriate safety factors for flexible pipe industry.
Automatic Drone Landing on a Boat: Theory and Preliminary Experimental Results
Authors: Falang Martin , Hinostroza M. A. , Bull Hove Peter , Sundvoll Thomas , Lekkas Anastasios M.
Published: August 2024

Recent rapid advances within autonomy for unmanned aerial vehicles (UAVs) make it possible to consider deploying them for critical operations in challenging environments, such as the ocean. Going even further, the combined operation of UAVs and autonomous surface vessels (ASVs) could be a strong enabler for exploration and search and rescue missions at sea, to name a few examples. The main contribution of this paper involves designing the perception, planning and control modules for the fundamental phase of such a collaborative operation, that is, the automatic drone landing of an UAV on an ASV. The perception system utilizes an Extended Kalman Filter that fuses the estimates from two computer vision systems, one based on deep learning and one on traditional edge detection approaches. The control system is a cascaded structure of position, velocity, and attitude control. The high-level planning is based on the GraphPlan algorithm and generates action sequences to solve three missions of different complexity based on a set of defined domain variables. The efficiency of the proposed solution is demonstrated via field trials involving a Parrot Anafi quadcopter landing on a helipad installed on DNV’s Revolt ASV. Our preliminary experimental results demonstrate that the system is capable of landing the UAV on the Revolt at sea, in conditions that were almost stationary, or involved forced rolling motion.
Friendly FPSO Hull Structure for Robot Inspection
Authors: Torres Zuniga Waldy J. , Videiro Paulo Maurício , Mendes De Sousa José Renato , De Almeida Costa Newton Bruno , Sudati Sagrilo Luis Volnei , Dos Santos Rizzo Nicolau Antonio , De Souza Silva Rodrigo
Published: August 2024

The Floating Production Storage and Offload system (FPSO) is widely used in offshore oil and gas exploitation. Traditional FPSO hull structures are typically constructed employing stiffened steel panels consisting of steel plates and closely spaced stiffeners. Classification societies require periodic full inspections of the cargo tanks. Nevertheless, the structural impediments created by these stiffeners can pose challenges or even prevent using autonomous equipment for remote inspection of tank structures. Additionally, inspection surveys with people inside the tanks are time-consuming and risky. Hence, a steel-concrete-steel sandwich plate system to address this challenge is proposed as an alternative solution to the conventional stiffened plate composition. Using sandwich panels in the bottom of oil cargo tanks and their longitudinal and transverse bulkheads smooths the surfaces by eliminating the need to use stiffeners, thus facilitating remote inspections with autonomous equipment inside the tanks. Furthermore, this approach can potentially reduce the time needed for periodic inspections of tank structures, following the recommendations set by classification societies to mitigate operational risks. The article presents the results of numerical ultimate strength analyses of sandwich panels and the initial scantlings of an FPSO hull main structure built with the proposed technology. Also, a comparative analysis of the relative total weight is performed.
A Numerical Simulation Method for Prediction of Ice Resistance and Ship Motion in Level Ice
Authors: Song Ming , Tong Zhe , Yuan Wei , Tian Bokang
Published: August 2024

Estimating ice resistance and ship motion in ice-covered region is important for the planning of operations and transport routes. This paper proposes a numerical simulation method for predictions of ice loads and ship motions in level ice. The dynamic interaction between ship and level ice is considered on basis of nonlinear finite element method. Numerical simulations between level ice and a ship are carried out by LS-DYNA software. The ice material model which can simulate ice crushing and bending failure modes is used. To consider the net thrust during ship-ice interaction, the user-defined load subroutine LOADSETUD that provides a means to apply nodal loads as a function of velocity is used. In addition, the water effect on the level ice model is taken into account by using a nonlinear discrete spring model. The model tests of an icebreaker navigating in level ice is used to test the presented method. The predicted results including ice resistance, net thrust and attainable speeds for given ice conditions are compared with the model test data. The comparison shows a generally good agreement, which indicates that the presented method is able to give reasonable predictions. Furthermore, the comparison between the numerical results obtained by the rigid ship and the deformable ship is made. The ship structural response during ship-level ice interaction is investigated.
Active Control of Distributed Subs With Anti-Slip Logic for Torsional Vibration Damping in Drilling
Authors: Nüsse Pauline Marie , Ambrus Adrian , Aamo Ole Morten
Published: August 2024

Previous publications showed that torsional vibrations of the drill pipe can be attenuated by subs equipped with sleeves in which the pipe rotates and is subjected to passive or actively controlled magnetic damping. The damping force depends on the relative velocity between the pipe and the sleeve and an adjustable damping coefficient, but is limited by the friction between the sleeve and borehole wall. If the commanded damping coefficient is too large, the sleeve will slip, potentially harming the borehole wall or casing, and itself. In this paper, we combine a previously designed on-off controller with anti-slip logic which learns the maximum available damping force and prevents the on-off controller from commanding a damping coefficient that leads to slippage. Occasional slippage is allowed, however, in order to learn the maximum damping force under changing down-hole conditions. Simulations demonstrate that both reduction in slippage and improved vibration damping are achieved by the modified controller.
Study on Structural Design Scheme of Motion Suppression System
Authors: Yin Yan , Yuan Hongtao , Zhou Bo , Du Yuchun , Wang Yuhan , Wang Chao
Published: August 2024

In order to solve the problem of poor motion performance of cylindrical FPSO, a new motion suppression system scheme is proposed which can make the platform meet the requirements of dry tree operation. The structure design scheme has an impact on the structure safety, construction technology, construction cost and other factors, so it is very important to make clear the structure design scheme of the motion suppression system.

Based on the limitations of the construction site, construction economy, weight control requirements and other factors, this paper proposes a structural design scheme. In the design process, the whole life service cycle of the platform is fully considered, and key parameters are optimized to save structural weight and construction cost. At the same time, the local strength analysis of the connected structure is carried out by finite element method and obtain the final structural design scheme. The scheme provides a reasonable structural optimization and a reference for the structural design of large structures.
Conceptual Design of Innovative Relocatable Wellhead Platform Using Multi-Column Structure “MCT” With Both Bottom Founded and Floating In-Place Capabilities
Authors: Bakti Farid Putra , Tahar Arcandra
Published: August 2024

This study addresses the design challenge of a relocatable wellhead platform that satisfies the complex operational and environmental requirements of both shallow and deeper water hydrocarbon extraction. A platform design capable of catering to three distinct fields: the shallow water A Field (∼20 m water depth) and the deeper waters B Field (∼40 m water depth) and C Field (∼65 m water depth), each with a production life expectancy of less than 10 years is shown in this study. Other requirements such as the use of dry-tree, simpler fabrication and decommissioning method, and cost effectiveness were also imposed on the proposed solution.

To answer these requirements, a Multi-Column Structure (referred to as “McT”) is proposed as the solution. In the initial stage, McT serve as a gravity-based substructure for the shallower water A Field. The McT’s fabrication and integration with the topside will take place in a dry dock. Subsequently, the integrated McT will be floated to the installation site, where it will be ballasted and placed on the seabed. This wet-tow option provided more flexible, economical, and simpler installation and fabrication method when compared to the jacket type structure. Furthermore, the size of the columns is designed with a dimension where a simple steel rolling devices may be utilized to fabricate the hull. Ring skirts and driven pile are incorporated into the McT’s foundation design to provide the in-place stability and to fulfill seismic requirement during its fixed mode utilization. Notably, well conductors and trees (up to 7 wells) will be situated alongside the McT, facilitating well drilling and production.

This study’s primary objective is to devise a single McT substructure capable of accommodating the operational needs of the A, B, and C Fields. The scope of the study includes the summary of Substructure (Hull) Configuration Design, Foundation Design, Wire Tendon and Suction Pile Design, Global Performance Analysis, Pre-Service stability Analyses, Flexible and Top-Tensioned Riser Design and qualitative cost comparison with jacket type offshore platform. This innovative platform design offers a versatile, relocatable wellhead platform solution, tailored to the specific needs of multiple fields, while satisfying stringent criteria for technology, operational feasibility, and cost-effectiveness.
On the Validity of Miner’s Rule for Pile Foundations in Sand
Authors: Hagemann Anne , Grabe Jürgen
Published: August 2024

The current design practice for offshore monopiles applies widely accepted simplifications of complex irregular loading scenarios. Highly cyclic loads from varying directions offshore are simplified by means of classification methods. This procedure involves reordering individual cycles in irregular loading scenarios by frequency, mean load, and amplitude. This approach is based on the assumption that the resulting accumulated deformation in the soil is independent of the ordering of the cycle packages, i.e. the validity of Miner’s rule. Different contributions in literature investigate the validity of Miner’s rule by evaluating the effect of the ordering of cycle packages on the resulting damage in the soil, i.e. the accumulated volumetric strain. This paper addresses the question of the validity of Miner’s rule from a different perspective. It investigates the load-displacement behaviour of sand in direct simple shear tests due to dynamic load scenarios. Hence, the load sequences during testing vary while the energy spectrum being employed to generate the irregular load signals remains constant. This method enables capturing natural conditions offshore during testing and allows for comparing individual loading scenarios as the wave spectrum in the frequency domain defines the distribution of wave amplitudes. The test program is carried out on medium dense fine silica sand. The test results are evaluated regarding the accumulated volumetric strain and relate to previous studies on the validity of Miner’s rule in sand.
Investigating Statistical Modelling of Excitation Forces in Inhomogeneous Waves
Authors: Laflèche Sébastien , Ommani Babak , Kristiansen Trygve , Fouques Sébastien
Published: August 2024

In coastal areas, and especially fjords, the wave field can present inhomogeneities that affect the responses of floating bridges among other very large floating structures. Recent studies have begun to include the effects of such inhomogeneities in the design phase. To that end, it is necessary to estimate not only the spectrum of the loads on the different pontoons, but also their coherence with each other. However, such information is usually not directly available everywhere, especially for coherence, as hindcast data does not contain phase information, and buoy data is sparse. Thus, assumptions need to be made for the coherence function.

This study presents a benchmark of the various assumptions made in recent studies of fjord-crossing floating bridges, on the coherence of linear excitation forces on pontoons. Synthetic inhomogeneous wave fields were generated from an analytical solution, allowing to compare the forces obtained from the various assumptions to true values, not accessible otherwise at sea. This was done by placing “islands”, modelled by large circular cylinders, in an infinite ocean with incident homogeneous short-crested waves. It was found that most assumptions perform well for two pontoons either very close or far from each other. A new assumption is also proposed, adapted to measurements from heave-pitch-roll buoys. It performed systematically better than the historical assumptions for wavelengths larger than the pontoons, and for any distance between them.
Effects of Second-Order Hydrodynamic Loads on a Barge-Type Floating Wind Turbine Platform With Moonpools
Authors: Tan Lei , Liu Yingyi , Ikoma Tomoki
Published: August 2024

Barge-type floating wind turbines with moonpools have been shown to have reasonably good seakeeping performance in the literature. Following our previous studies, the main purpose of this work is to develop a time-domain numerical analysis tool implemented with the open-source hydrodynamic code NEMOH for conducting pre-hydrodynamic analysis in frequency domain. Special attention of this study is paid to quadratic transfer function (QTF), which is calculated by NEMOH and is included in time-domain simulations. To investigate the effect of second-order wave drift force on motion responses, we considered a barge-type floating foundation prototype under the available typhoon-induced wave condition and calculated the responses in frequency and time domains. It was found that the moonpool resonances may lead to considerable difference-frequency QTFs. The numerical results including difference-frequency QTF influence showed that the barge with moonpools had large-amplitude horizontal resonant motions at low frequencies, which dominated the total responses. This result indicates that the second-order wave drift loads play an important role in surge and sway responses. Regarding heave and roll (and pitch) motions, the wave drift loading can also cause the responses at low frequencies, but these low-frequency response amplitudes are generally small and non-dominant.
Global Dynamics of a Hang-Off Power Cable Immersed in the Flow Near a Fixed Offshore Wind Turbine
Authors: Liu Guojun , Yao Yong , Long Yi , Zhang Cheng
Published: August 2024

The hang-off power cable extending from the offshore wind turbine tower takes the significant responsibility of electric energy transportation. The scour, tide and wave have associated action in promoting the exposure and spanning of the hang-off power cable in the flow near fixed offshore wind turbine. The analysis of the global dynamics of the hang-off power cable is the basis for evaluating its safety. In the present study, a nonlinear dynamic model for the hang-off power cable is established based on the absolute nodal coordinate formulation (ANCF) and marine hydrodynamics. The absolute position and slope coordinates in the model can avoid the coordinate transformation, while the employed geometric relationships accurately describe the complex deformation of the cable. The hydrodynamic and seabed loads on the cable are evaluated by Morrison equation and linear pipe-soil interaction model, respectively. The flow velocity near the fixed offshore wind turbine is obtained through the numerical simulation of computational fluid dynamics (CFD), regarding as an external input of environmental condition for the hang-off power cable. By considering different incidence angles of inlet flow, the distributions of the dynamics along the cable are fully examined. This paper verifies that this model can reliably evaluate the motion characteristics of hang-off power cables, and simulates and calculates the overall dynamic response of the hang-off power cable under actual sea conditions. The study is expected to further support the wear and fatigue assessment of the hang-off power cable.
Statistical Validation of Surfaced Submarine Seakeeping Simulations Based on Open Water Tests
Authors: Büsken Wiebke , Krüger Stefan
Published: August 2024

Submarines are frequently required to operate in surfaced condition, partially in harsh seaways. Since diving is not always possible or permitted, an accurate prediction of a submarine’s seakeeping performance at the surface becomes essential for safe operation. The seakeeping of a surfaced submarine is a complicated problem of motions in all six degrees of freedom, which strongly depends on the respective parameter combination of seaway, forward speed, encounter angle, and surface stability. In this paper, time-domain seakeeping simulations are performed for a modern submarine hull form in short-crested irregular waves using the potential flow theory-based computation method E4-ROLLS. The simulation results of the roll, pitch and heave motions are compared with data obtained from open water model tests. These model tests were recently performed on a bay in Germany using free-running submarine models and specifically focused on the surface stability’s influence on the sea-keeping in natural seaways. The presented research contributed to the development of a novel surface stability regulation DMS 1030-2 for submarines of the German Navy.
A Novel Approach for Ship Digital Twin Optimisation: Principal Component Analysis-Driven Distortion Base Mode Selection and Utilisation
Authors: Song Seung Woo , Jin Chungkuk , Kim Do Kyun
Published: August 2024

This study aims to improve the efficiency of distortion base mode selection using Principal Component Analysis (PCA) and enhance structural response estimation techniques for digital twin applications in the maritime structures. Real-time determination of loads on a structure is essential for digitalisation in the maritime sector. Methods such as modal superposition and inverse finite element methods have been investigated to calculate loads at arbitrary points from a limited number of sensors. The objective of this study is to estimate loads by using a conversion matrix constructed by distortion base modes. In this study, modes are selected based on the response to regular waves. To achieve this, a distinct algorithm has been developed to select orthogonal modes. This study proposes a novel mode selection method by implementing PCA, which enables obtaining the most representative direction. Wave load case with responses which is most parallel to this direction is determined to be the first mode. To validate our methodology, we estimate hotspot stresses on an FPSO. This method reduces computation time while maintaining high accuracy of estimation. These findings show potential for application to other offshore structures. Further research using actual measurement data is expected to enhance the validity and reliability of these techniques, making a significant contribution to the field of maritime structural analysis and digital twin technology.
An Ecology Friendly, Closed-Cage Fish Farm. Computational Model Validation Against Results From Field Measurements
Authors: Iwanowski Bogdan , Myrholt Jim-Roger , Ovesen Glenn , Hanssen Finn-Christian W. , Brask Annette Kristin , Latif Adil
Published: August 2024

A closed-cage fish farm was built at a rather sheltered location in northern Norway. The closed-cage solution is more ecology friendly than the frequently used net cage fish farms, since the fish breeding water is separated from the outside ocean space, thus preventing entry of the parasitic sea lice. Moreover, the fish food, waste, applied chemicals and medicines are under control and do not contaminate the outside sea water.

The fish farm structure was designed to be sound mechanically under local environmental loads occurring at the installation site. To verify initial estimates of the environmental loads due to current and waves, two sensors that measure vertical current speed profile and directional wave parameters were placed in the fish farm neighborhood.

The structural response was measured as well. Sensors that recorded forces in mooring lines, internal structural forces and motions (accelerations) of the fish farm moving components were placed at critical positions, based on foreknowledge obtained from numerical simulations.

The measurement campaign lasted for one year, thus covering all weather seasons. The acquired large data sets were analyzed statistically, but also an effort was made to find individual extreme environmental load occurrences. It is underlined that the measurements were made in full scale conditions (geometry and environment), and not on the geometrically scaled model as in a laboratory or experimental tank.

A detailed hydro-mechanical model of the fish farm was created. Numerical calculations of the structure’s response were performed with the OrcaFlex software. The detected individual extreme environmental load events were reproduced numerically, and the corresponding structural response was simulated in time domain. Acomparison of the field-measured data with the computational results is presented in the paper, followed by a discussion and conclusions.
Hydrodynamic and Dynamic Analysis of a Multi-Module Semi-Submersible Photovoltaic Platform Considering Tidal Variation
Authors: Tang Yichang , Chen Mingsheng , Jiang Yanlin , Li Tingqiu , Zhang Kai , Zhou Hao
Published: August 2024

Floating Photovoltaic (FPV) systems are considered a novel method to generate electricity. The semi-submersible platform which has been studied mature to exploit renewable energy in the deep sea was built for generating power by photovoltaic systems in recent years. With the development of multi-module designation and various arrangements of mooring systems, the motion response with correcting viscous damping of the semi-submersible platform and the stiffness of the mooring system in the deep sea are significant problems. This paper presents an efficient multi-module coupled hydrodynamic and structural based on the Cummins equation to study the nonlinear multi-body hydrodynamic interference of the semi-submersible platform of FPV systems. Connections between modules are modeled as linear springs with certain stiffness to release all Degrees of Freedom (DoF) of the module. Furthermore, supporting members of modules are modeled as Morison bars. The motion response with hydrodynamic interference of every module is calculated accurately and different design types of mooring systems are studied in this paper, discussing vibration behaviors in low frequency. The diverse layout scenarios are obtained by altering the spacing of the FPV system when deployed adjacent to each other as well as the configurations of the mooring systems. The results suggest that arranging the layout scenario of the mooring system to increase the global stability and the FPV system built as a rectangle with four semi-submersible modules has a lower motion response.
Experimental Study on the Slamming Loads on Inclination Bulwark of a Cylindrical FPSO
Authors: Hu Haifeng , Deng Shi , Cai Yuanlang , Qiao Xiaoguo , Zhang Wenbo
Published: August 2024

Slamming loads on the inclined bulwark of a cylindrical floating production storage and offloading (CFPSO) unit are studied experimentally with respect to sea states and distances from mean sea level. From model test result, the maximum load is obtained at the lower part, and the load decreases with the height increasing. Lasting period of load is short at the lower and upper positions but it is a little longer at the medium position due to wave surface properties. Empirical mode decomposition method is an alternative to remove sensor resonance and dynamic amplification effect in the test result postprocessing in addition to the conventional statistical analysis. Moreover, from pure wave test cases, larger slamming loads are obtained coincidently with the larger vertical motions (heave and roll/pitch). However, in coupled wave-current cases, smaller slamming loads are observed even though the vertical motions are amplified. Findings in the paper provide basic understandings on slamming loads distribution on a CFPSO in extreme sea state and propose an alternative method in the slamming loads design at the same time.
Unlocking the Flow: A Comparison of Off-Bottom Plug Placement Techniques in Well Abandonment
Authors: Shakeri Amin , Ghazal Abdallah , Karimfazli Ida
Published: August 2024

Plug and abandonment (P&A) of oil and gas wells are essential for the protection of the environment and public safety. In Western Canada, a common abandonment technique involves placing cement plugs along the wellbore, utilizing either the balanced-plug or the dump-bailing methods. The balanced-plug technique employs a constant injection flow rate, whereas the dump-bailing method relies on gravity to release cement slurry above a mechanical barrier. Ensuring minimal mixing of cement slurry with wellbore fluids is critical for the integrity of the abandonment process.

In this study we develop three-dimensional hydrodynamic models of the two placement methods to compare the flow dynamics and mixing of the slurry and wellbore fluids. The primary difference between the placement methods is the slurry flow rate during the placement process. Our results reveal that the dump bailing approach leads to more extensive mixing of the slurry and wellbore fluids, especially as the distance between the cement release level and the barrier increases. The balanced plug method typically leads to the accumulation of a cement slurry with water content close to target specifications, contrasting with the dump bailing method, where the water content can vary significantly from the intended design.
Preparation of Transparent Soil and its Application in Model Tests for Offshore Geotechnical Engineering
Authors: Zhang Chunhui , Zheng Xiaoming , Tian Yinghui , Wang Le , Zhang Wenlong , Zhang Bowei
Published: August 2024

The characteristics and mechanism of the interaction between seabed foundations and seabed soil are crucial for comprehending the bearing capacity mechanism of seabed foundations. To observe the movement of foundations in seabed soil and the deformation mechanisms of seabed soil, transparent clay and transparent sand with similar mechanical properties to seabed soft clay and sand were prepared in this paper. A transparent soil-PIV model test system was developed to investigate the interaction between seabed foundations and seabed soil. The test system comprises an actuator, a charge-coupled device camera, a control system and two laser devices. The T-bar penetration test and the plate anchor keying test were conducted in transparent clay and transparent sand, respectively, using the developed model test system. The soil flow mechanism during T-bar penetration and the keying behavior of the plate anchor were observed. Results indicated that during the penetration of T-bar, a trapped cavity is formed above the T-bar. The trapped cavity hinders the soil flow and prevents it from entering the full-flow mechanism. The peak load is reached when the anchor rotates to an angle of 24 ° from the horizontal plane during the keying process. The soil deformation is classified as a shallow failure mechanism, with the affected area extending from the anchor to the sand surface. This study provides a novel approach to investigate the interaction mechanism between seabed foundations and seabed soil.
Mooring Anchor Radius and Spread-Angle Optimization for a 2 MW Semi-Submersible Floating Wind Turbine in Taiwan Strait
Authors: Lai Zhao-Yu , Ivanov Glib , Chen Jui-Chen , Chen DongHui , Ma Kai-Tung
Published: August 2024

Floating Offshore Wind Turbines (FOWTs), especially the semi-submersible type, have gained significant attention due to their potential to produce energy in deeper water. Nevertheless, the design of such floaters in the typhoon-prone and shallow water environmental conditions of the Taiwan Strait poses some challenges, particularly concerning their mooring systems, which are pivotal to the FOWT’s reliability and cost-effectiveness. The study focuses on the method to find the best combination of anchor radii and spreading angles, which directly impact the behavior of mooring lines, using a 2MW semi-submersible FOWT, TaidaFloat Demo. Critical factors such as mooring line tension and platform motion are investigated to ensure the robustness of the design. The study is conducted by applying optimization techniques to minimize mooring line costs while meeting Class Rules required for the specific environmental conditions of the Taiwan Strait. The result shows that the combination of a spreading angle of 10 degrees and an anchor radius of 17.5 times of water depth is the most cost-effective considering material usage in Taiwan Strait condition. This research contributes insights into the method of design and optimization of semi-submersible floating offshore wind turbines under challenging environmental conditions.
Standardizing Second-Order Roll Analyses for FPSOs in Brazilian Deep and Ultra-Deep Waters: Approximations and Damping Evaluation
Authors: C. Oliveira Allan , P. Carvalho Luiz Felipe , G. T. Menezes Fabio
Published: August 2024

Evolution in the design of FPSOs for Brazilian deep and ultra-deep waters has resulted in larger platforms with increased weight and footprint. Consequently, the dynamics of FPSOs, particularly in terms of rolling motions, have been affected, leading to an observed increase in the natural periods of rolling motion in recent years. While the increase in the natural period of roll motion significantly reduces the observed first-order motion, platforms are still subject to second-order excitations, resulting in responses at their resonance periods.

The analysis of second-order motions is more complex and typically requires substantial computational power for accurate assessment. Approximations are often used to evaluate second-order loads and motions, with the level of approximation complexity depending on the natural period being assessed. To meet design schedules, a tradeoff between computational cost and the quality of the approximation may be necessary since second-order motions are input for riser and structural analyses.

Assessment of roll damping in second-order motions is also crucial due to its impact on roll motion levels. The use of roll damping devices remains important in controlling and reducing second-order platform response. This paper discusses different approaches to assess second-order loads and responses, aiming to establish the minimum requirements for a reliable assessment of second-order roll motion.
Experimental and Numerical Investigation of the Inlet Effect on the Dynamics of a Water Intake Pipe
Authors: Hisamatsu Ryoya , Yamaguchi Yusei , Riveros-Jerez Carlos A. , Utsunomiya Tomoaki
Published: August 2024

A water intake pipe/riser is an important component in deep seawater utilization technologies. Regarding the issue of flow-induced vibration, the concern of instability due to the internal flow has received considerable interest. A key question, particularly in the water-aspirating pipes, is the effect of the inlet flow on the dynamics. This study experimentally investigates the internal flow and inlet effects on the dynamics of a hang-off water intake pipe under top-end excitations. The results indicate that the internal flow effect increases inline response. In particular, it suggests the existence of a bifurcation phenomenon, where the amplitude significantly increases under excitation at slightly shorter periods than the natural period. The experiments further compare different inlet shapes: bellmouth, T-shape and L-shape; however, no significant differences in their response characteristics are observed. The second part of this paper provides a discussion based on CFD simulations stressing the contribution of the contracted jet formed inside the pipe and the sink flow in the vicinity outside the inlet to the dynamics of the water intake pipes.
Experimental Investigation on Stress Components of the Sealing Structure of Subsea Connectors Under Axial Preloads
Authors: Zhang Kang , An Weizheng , Wei Pengyu , Yi Qi , Wang Haining
Published: August 2024

The sealing performance of subsea connectors plays a vital role in the safe operation of subsea oil and gas production systems, which is directly determined by compression deformations of the gasket of the subsea connector. Therefore, the changing rules of the sealing structural deformations under various axial loads are key problems when designing subsea connector products. In this paper, experimental measurements are performed in order to investigate the structural stresses of the sealing structure of the subsea connector, i.e. the hub and the gasket. As for the real products of the hub and gasket structures, test solutions are designed. Structural stress components of some representative points are observed when the axial preloads are loaded. Test results show the maximum tensile stress of the outer wall is more than that of the inner wall, which indicates the weak point of the hub is on the outer wall surface nearby the joint region between the hub’s shoulder and the thick-walled cylinder. The maximum tensile stress of the outer wall is less than that of the inner wall, which indicates the weak point of the hub is on the inner wall surface.
Numerical Simulation of Pulsating Slurry Flow in a Jumper for Subsea Mining
Authors: Masanobu Sotaro , Takano Satoru , Yamamoto Marcio
Published: August 2024

For the design and operation of a subsea mining system, it is important to predict pressure loss due to the hydraulic transport of solid particles in the lifting system.

The lifting system has a short flexible jumper to connect the seafloor mining tool to the lifting pump and a vertical riser pipe connecting this pump to the production support vessel. The configuration of the flexible jumper shall have an inclined part so that the mining tool can move freely on the seafloor.

In the actual mining system, the slurry flow in the pipe system is expected to be unsteady. Then, the time-domain simulation is required for safe and reliable ore lifting. In the present paper, we develop the numerical model for the time-domain simulation for pulsating slurry flow in a jumper. The model is validated by comparison with the experimental results we carried out in the previous work using alumina beads, of which densities are almost the same as those of seafloor polymetallic sulphides ore, as solid particles. Next, we investigate the slurry flow in a jumper with steep wave configuration using the model developed. We assume the 100 m long flexible jumper of which outer and inner diameters are 0.254 m and 0.200 m, respectively. Seafloor polymetallic sulphides ore, whose density and diameter are 3,440 kg/m3 and 0.03 m respectively, are assumed as the solid particles. We vary the pulsating conditions of slurry flow and jumper configuration, and discuss the effects of slurry parameters, such as slurry flow pulsation on water velocity, solid velocity, solid concentration and pressure loss in the jumper system. As a result, the total time-averaged pressure loss increases as the top end of jumper is away from the neutral position. The amplitude of pressure loss pulsation is almost uniformly distributed along the jumper although the amplitude of solid concentration pulsation is ununiformly distributed. The slurry parameters should not be estimated using straight pipe simulation results for the neutral or near position of the jumper system.
SPH Simulation of Hydrodynamic Response of a Semi-Submersible Aquaculture Platform
Authors: Liu Jiaming , Wang Kai , Han Ruolang , Huang Shuo , Xiao Yue
Published: August 2024

The drastic dynamic response of a floating aquaculture platform serving in the deep sea would endanger the safety and integrity of the system due to the extreme environments. Therefore, it is essential to simulate and analyze the motion of a semi-submersible deep-sea aquaculture platform in real sea states. This study introduced a new concept of a semi-submersible aquaculture platform named Zhuhaiqin, and the computational domain was built for numerical simulations via the open-source code DualSPHysics. The interaction between the platform and the waves was discretized by the smoothed particle hydrodynamics (SPH) method, while information on the net structures and the mooring system was obtained based on the lumped-mass approach. Moored floating box and flexible net deformation tests were used to demonstrate the reliability and validity of the numerical model used in this work. Subsequently, the dynamic response of the simplified real-scale model based on “Zhuhaiqin “ was analyzed under different wave conditions. The results indicate that wave heights and net structures significantly affect the motion response of the aquaculture platform. In particular, the mooring forces on the fairleads on the waveward side of the platform are more sensitive to wave height than on the other side. In addition, the nets significantly increase the forces on the fairleads. It is recommended to optimize the platform profile and mooring strength concerning the results presented in this work to avoid accidents.
Pipe-Soil Interaction for VIV of Free Spans in Carbonate Silty Sand
Authors: Papavasileiou Vasileios , Bransby Fraser , Hou Zhechen , O’Neill Michael , Watson Phil , Low Han Eng , Peek Ralf , Rathbone Andrew
Published: August 2024

Pipeline free-spans are sections of the pipeline that are not supported by the seabed, and can occur either due to natural processes such as seabed undulations and scour, or exist as engineered sections including pipeline crossings or buckle initiators. Free-spans can leave the pipeline susceptible to inline (horizontal) or cross-flow (vertical) Vortex-Induced-Vibrations (VIV) that could potentially result in fatigue failure. For spans deemed to have a high probability of failure, i.e. critical spans, or for spans evolving over time due to seabed mobility, expensive mitigation can be required. To assess the remaining fatigue life of a free-span, the system response must be quantified, including interactions with the seabed at the span shoulders, which are usually defined in terms of dynamic soil spring stiffness and soil damping values.

The paper presents findings from an experimental study to determine soil stiffness and damping during simulated VIV motions for pipeline ‘elements’ (representing parts of the free-span ‘shoulder’) at varied pipeline vertical pressures and installation modelling scenarios. Testing was performed in a carbonate silty sand sample. The paper focuses on in-line VIV, although selected results for cross-flow VIV are also presented.

The results indicate that the initial embedment, amplitude of the cyclic motion and pipeline self-weight significantly affect the soil response. These findings will improve understanding of Pipe-Soil-Interaction (PSI) for free-span shoulder sections, resulting in increased confidence in the selection of non-linear soil springs and dashpots, and contributing to more informed assessment of free-span behavior.
Fatigue Assessment and Resonance Effects in an Inter Array Cable due to Global Dynamic Deflections in a Bottom Fixed Monopile Wind Turbine Foundation
Authors: Li Henan , Arnholm Carsten , Siddiqui Mohd Atif , Farnes Knut-Aril , Midttveit Steinar , Rolland Louise Ankerstjerne , Nordheim Knut
Published: August 2024

Inter Array Cable (IAC) hanging through the Monopile (MP) are critical components for fixed offshore wind turbines. Here, fatigue analysis for IAC is performed with focus on resonance modes of the IAC. The IAC is modelled using a specialized time-domain solver for offshore marine systems (OrcaFlex) with imposed motion time-series at IAC hang-off location. The IAC responses (tension and curvature time series) are extracted for further computation of component stress time series. The IAC cross-section is further modelled in detail considering friction between components using a tailor-made cross-section analysis tool (Uflex2D) for extracting stresses under various tension and curvature combinations. Finally, cable fatigue is calculated using an in-house tool, Flexstress for Umbilicals (FFU). FFU allows both non-linear stress calculations and processing a relatively large amount of load cases with significant computational efficiency. FFU further calculates fatigue damage based on Rainflow counting using appropriate SN curves. It is found for the current cable configuration that the most critical component with regards to fatigue damage is the copper tape screen with fatigue service life of 31 years considering a safety factor of 10. During fatigue assessment it is also observed that IAC resonance modes can be excited. The resonance effect is further investigated, and mitigation methods are discussed.
Impacts of Small Gaps and Embedment Depths on Forces of a Circular Cylinder Near a Plane Wall
Authors: Liu Zinan , Cheng Liang , Ren Chengjiao , Tong Feifei
Published: August 2024

Numerical simulations of a cylinder placed on or near a plane wall are often required in engineering design of offshore structures to determine hydrodynamic forces, such as a power cable laid directly on the seabed. Generation of computational mesh around such a configuration has been a challenge of conducting simulations, primarily due to the narrow gaps formed between the cylinder and the plane wall. Extremely fine meshes are often required around the narrow gaps to achieve reliable numerical results, leading to additional computational costs. To alleviate this problem, this study examines the hydrodynamic features of two alternative geometric configurations, namely (1) a near-wall cylinder with sealed gap and (2) a cylinder shallowly embedded in the plane wall, whose meshing and simulation are less challenging than that would otherwise be needed for a cylinder placed on the wall. A series of three-dimensional numerical simulations for a constant Reynolds number 3900 and a range of narrow gap distances / embedment depths from 0.001 to 0.1 cylinder diameters are conducted. The possibility of employing the three configurations to determine the hydrodynamic forces on a cylinder placed on a wall is examined in this study.