bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Hydrodynamic Performance of a Conceptional Sea-Train
Authors: Qin Yan , Yao Chaobang , Zheng Yi , Huang Jianghao
Published: October 2022

Multiple vessels sail together at sea through physical connection or non-physical connection attaching to each other to form a train, which is called “Sea-Train”. The “Sea-Train” is a new concept of multi-vessel navigation, which aims to minimize the collective resistance of its system. By reasonably optimizing the horizontal and vertical spacing of each ship, the “Sea-Train” uses the favorable wave interference between hulls to obtain drag reduction performance and increase its voyage. To investigate the resistance variation of formation “Sea-Train” with speed, transverse distance and longitudinal distance, Wigley ship is taken as the research object. Based on the STAR-CCM+ software platform, the VOF method and the K-Epsilon turbulence model are used to solve the Navier-Stokes equation to numerically simulate the motion of the “Sea-Train”. The total resistance and its components of the “Sea-Train” are calculated by CFD software, at different speeds and different formations, to analyze the characteristics and laws of hydrodynamic interference. Further analyzing the relationship between the resistance of the “Sea-Train” and the transverse and longitudinal distance, the wave patterns of the free surface and ship side are obtained by using the numerical simulation results. The mechanism of drag reduction is explored to provide theoretical basis for the layout optimization of “Sea-Train” at different speeds.
Model Experiments and Numerical Simulations on GPS Buoy With Steep Wave Mooring
Authors: Araki Motoki , Watanabe Mitsushi , Masanobu Sotaro , Omura Atsuo , Kaita Shouhei , Kunita Atsushi
Published: October 2022

Recent runout accidents of GPS buoy demand more robust mooring system in harsh environment. The mooring with steep wave configuration formed by intermediate buoys could be a candidate of the robust mooring system. However, the steep wave mooring (SWM) could have some risk of intersection problem in overlapped section of the mooring line, e.g., collision/contact and/or tangling. Therefore, the risks of the intersection problem of the SWM are identified with 1/20 scaled model experiment and numerical simulation of a GPS buoy with the SWM. In the model experiment, collision/contact and tangling of the mooring lines were observed and the top and bottom tensions were mainly analyzed. The numerical simulation corresponding to the model experiment was carried out using OrcaFlex. The simulation successfully reproduced the tangling phenomenon of the mooring line, and the spectra of computed top and bottom tensions show similar tendency with the model experimental results. Therefore, both the model experiment and the numerical simulation shows capability to identify the risks of the intersection problem of the SWM.
Evaluation of Nonlinear Fourier-Based Maximum Wave Height Predictors Under the Nonlinear Schrödinger Equation
Authors: Lee Yu-Chen , Wahls Sander , Brühl Markus
Published: October 2022

Rogue waves are extreme waves in the ocean that appear from nowhere and disappear without a trace. They are usually modelled by the nonlinear Schrödinger equation (NLS), which describes nonlinear phenomena such as modulational instability and solitons on finite backgrounds. In this study, the periodic nonlinear Fourier transform (NFT) for the NLS equation is applied to simulate ocean surface waves in deep water. The temporal and spatial structures of surface waves are obtained by evolving JONSWAP time series using the NLS equation. Several parameters extracted from the NFT spectra of the initial time series are investigated as predictors for the maximum wave height during evolution. We investigate several parameters from the literature, and find that with suitably optimized coefficients, a NFT-based parameter based on the largest unstable mode has a good correlation with the overall maximum wave amplitude. This new spectral criterion can contribute to rogue wave forecasting under extreme sea states.
Position Specific Monopile Fatigue Load in the Frequency Domain
Authors: Dahl Niels Christian , Larsen Richard Thyssen Nørby , Høgsberg Jan , Bjerre Nielsen Martin
Published: October 2022

This article presents a method for frequency domain calculations of fatigue loads for offshore wind turbines from wave loading on the monopile foundation. The method is used to estimate position-specific loads to lower the inherent conservatism to optimise the monopile design compared to the conventional approach where a conservative load envelope is applied for the whole or selected parts of the wind farm. The loads are calculated by transforming a wave spectrum into a stress spectrum, used for frequency domain rainflow counting. The remaining fatigue load is then determined by comparing the wave-only fatigue loads to the loads from an integrated loads analysis including all aero-dynamics associated with the turbine. The remaining contributions to fatigue loading are demonstrated to be nearly constant between positions and can thus be used to calibrate the wave-only load, estimated by frequency domain analysis, which subsequently enables the calculation of position-specific loads. When applying the method on site specific data, load reductions up to 12.5% are obtained on individual positions, while a 1–2% saving is achieved on the overall monopile mass.
Experimental Investigation of Flow Velocity Dispersion in Annuli
Authors: Lund Bjørnar , Ytrehus Jan David , Taghipour Ali , Saasen Arild
Published: October 2022

Deviated well sections are common in modern well construction. In mature areas like the North Sea region, practically all producers or injector wells will have highly deviated sections. These wells must be completed in an optimal manner including annular barrier integrity. This is important for zonal isolation through all stages of the well’s life cycle. Since all wells must be permanently plugged before abandonment it is important to ensure that annular barriers are designed with a long term perspective and not only to minimize construction time and cost. Controlled laboratory environments with various fluid compositions and flow parameters are important to develop, validate and improve models and practices. Cement displacement is normally the objective for such studies. Due to selection of fluids, data for casing cleaning operations are in reality derived.

Fundamental flow properties are investigated qualitatively. Water with and without viscosifiers is used to displace similar fluids from the annular section. The effects of inner pipe rotation are included. It is shown how this gives fundamental data providing a relevant background for understanding displacement processes.

The experiments have been performed in a flow loop that consists of a 10 meters long test section with 5″ OD transparent pipe inside a 6,5″ transparent pipe. Experiments were performed with concentric and eccentric horizontal annulus and both with rotating and non-rotating inner pipe. The applied flow loop dimensions are designed so that the results should be relevant for highly inclined sections in field operation.
Numerical Simulation Research About the Influence of Nozzle Parameters on the Quality of Ice-Core in Hot-Water Ice-Drilling
Authors: Liu An , Shan Zhigang , Shi Ting , Ni Weida
Published: October 2022

Ice sheets in the Arctic contain well-ordered accumulations of ancient ice that fell as snow years to millions of years ago. Ice-core data have become central to our understanding of climate change in the past, and to assessments of possible future climate change. Hot-water ice-coring drills are often used to recover ice-core samples from a desirable depth in conjunction with a full-scaled hot-water drilling systems. However, the recovered cores had the varying quality. In hot-water ice-coring drilling, many small nozzles are used to spray water out and melt out a cylindrical ice. Parameters of the nozzle, which mainly includes angle, diameter and quantity, are the most critical part of the drilling system. To improve the ice-core quality in hot-water ice-coring drilling, the influence mechanism of annular hot-water jets formed by nozzle with different parameters on ice-core quality was studied. Heat transfer law of annular jet on the ice-core was studied using the numerical simulation. Totally nine kinds of nozzle with different parameters were designed by using the orthogonal design method and the corresponding calculation domain model of ice was established. The ANSYS FLUENT software was used to analyze the heat flow field, variation trend of heat transfer to the ice-core with different nozzle parameters was researched. The result indicated that the heat transfer of hot water to ice core increased with the larger nozzle diameter while decreasing with the increase of nozzle quantity and nozzle angle. The result can help to give a reference for the design of hot-water ice-coring drill head used in the polar regions.
Research on Fatigue Load Analysis and Fatigue Strength Assessment of Stern Shaft Bracket of Large Ship
Authors: Xianyin Chen , Gaoxiang Wang , Qingchun Zhu
Published: October 2022

At present, the research on the fatigue strength characteristic of stern shaft bracket is almost in worldwide blank. Taking a large ship (displacement over 10000 tons) as an example, the fatigue loads and structural fatigue strength of the shaft bracket were studied. This paper studied the fatigue damage of shaft bracket separately under the action of high-frequency load (propeller excitation force) or low-frequency load (wave load and local fatigue hydrodynamic force). Based on the linear cumulative damage theory, the fatigue damage under the combined action of the three kinds of fatigue loads was calculated. According to the research results, this paper presented an effective calculation method for fatigue assessment of stern shaft bracket.
Development of Fire Integrity Matrix in Order to Achieve Type Approval for FRP Handrails Offshore
Authors: Eves Simon , Filho David , Jarreta Claudio , Byrne Tom
Published: October 2022

The objective of this project was to develop guidance for a Type Approval for FRP handrails in fire integrity applications offshore. BP, MODEC, PETROBRAS, ABS and NOV Fiber Glass Systems came together to form an FRP Industry Group which developed a Fire Integrity Matrix intended to be used as the basis for a Fire Integrity Type Approval for FRP handrails.

The notation R0, R3, R2 and R1 performance levels for FRP Handrails were adopted with the aim to correlate these levels as far as possible to already existing Service and Location definitions set out in the PFM 2-98 for FRP Grating. Heat flux and duration requirements for the R0, R3, R2 and R1 performance levels were proposed, based on industry practice and HSE guidance regarding heat flux levels.

An industry FRP handrail product (MARRS Offshore) was subsequently subjected to the Fire Integrity Matrix tests by Southwest Research Institute in Texas and found to meet all the test requirements. The data was subsequently assessed by ABS and the product was awarded a new Type Approval allowing, for the first time, use in fire integrity applications offshore.
Design and Demonstration of Autonomous Directional Drilling With a Miniature Scale Rig
Authors: Steinstø Magnus , Hånsnar Gaute , Gjersdal Benedicte , Skretting Trygve Mikal Viga , Pavlov Alexey , Florence Fred
Published: October 2022

Drillbotics, an international student competition hosted by SPE/DSATS, directed the 2020/2021 competitors to design, build and implement a 1.5″ (3.8cm) hole size, fully autonomous drilling rig capable of intersecting multiple pre-set targets within a rock sample with up to 30-degree inclination and 15-degree azimuth adjustments from the KOP. The Norwegian University of Science and Technology (NTNU) won the competition using a fixed bent Bottom Hole Assembly (BHA) and a simulated mud-motor stator with a rod inside the drillpipe transferring rotational torque from a top drive. The team designed and created a custom drill bit, bi-directional hydraulic swivel, and BHA. Trajectory control was achieved by changing the BHA bend orientation over time, rotating the drillpipe with inputs from a nonlinear Model Predictive Controller (nMPC) following a pre-planned Bezier-curve well path. Capabilities of the rig were demonstrated by drilling a 37-degree inclination well path in 6 minutes in a 60 cm sandstone replica.
On the Effect of Free-Surface Linearization on the Predicted Hydrodynamic Response of Underwater Vehicles Travelling Near the Free-Surface
Authors: Lambert William , Brizzolara Stefano , Woolsey Craig
Published: October 2022

This study presents a comparison of the hydrodynamic responses generated by a boundary element method with linear free-surface boundary conditions and a volume of fluid RANSE CFD method with nonlinear surface capturing for a shallowly submerged prolate spheroid travelling with constant forward velocity. Observing the effects of free-surface proximity and forward velocity on the hydrodynamic forces and wave disturbance between the two numerical methods reveals the influence and importance of considering a nonlinear free-surface. The forces and moments acting on the spheroid using the nonlinear method are generally larger than the linear method showing that nonlinear effects are important in the calculation of wave making resistance. The difference between the linear and nonlinear methods grows as submergence decreases or wave making increases. An additional phenomenon is shown where the difference between the methods displays a trend with respect to Froude number and depth that is similar to the values being compared. The physical response of these nonlinear effects is seen in the steepening of surface waves near the body, which breaks some of the assumptions made in the linear boundary element method.
Fatigue Assessment of Wind Assisted Propulsion Systems
Authors: Storhaug Gaute , Borzacchiello Guilherme R. , Hoffmeister Hasso
Published: October 2022

With the increasing focus on decarbonization, IMO has introduced a regime for rating ship emissions. Ship owners must adapt and utilize different strategies to reduce the fuel consumption to stay in compliance with regulations, but also to stay competitive. One solution is to utilize wind and set sails.

The new rapidly emerging technologies are not conventional sails, but wind assisted propulsion systems particularly developed for large vessels operating in harsh environments and designed for a long operational lifetime. They may be automatically adjusted by a sensor-based control system to achieve optimum performance. Associated safety risks may be high and one of the damage modes of concern is structural fatigue.

Fatigue accumulation may be driven by ship motions and wind gusts. The paper describes the process of how a pragmatic design formula has been derived to find a gust factor that is useful for combination with ship motions to predict fatigue damage in design. This factor depends on wind speed and ship roll or pitch period. Since fatigue assessment may result in requirements to increased strength, the new formula offers a less conservative design than gust factors used for extreme design, thereby saving material resources and installation costs.
Numerical and Empirical Based Fatigue Life Analyses of Submarine Cables Under Hydrodynamic Loads
Authors: Schütt Clemens , Otto Christoph , Kosleck Sascha
Published: October 2022

In order to perform meaningful fatigue life analyses and estimate the state of fatigue of existing submarine cables, detailed knowledge of the fluid-structure interaction for a variety of load cases as well as reliable data on the fatigue behaviour of the complex overall cable is required. To protect the conductor, submarine export cables consist of several layers. Here, a lead sheathing ensures complete radial water tightness. Regarding transient loads, due to the low fatigue resistance of lead this layer turnes out to be the weak point of the cable geometry. Accordingly, experimental investigations on full-scale cables are carried out in order to proof the cable’s stress-cycle curve.

Fully flexible, nonlinear time domain simulations are then used to determine transient stress distributions within the cable for defined load cases. Here, a non-linear model based on reduced finite element structures was developed and implemented. Finally, based on the fatigue data previously determined during the experiments, a damage analysis is carried out using rainflow-counting.
Geohazard Study of Mudslide Event at a Subsea Escarpment and Structural Response of Crossing Flowlines: Part II – CFD and FSI Analysis
Authors: Jang Hyunchul , Lai Lawrence S. H. , Hayes Kevin , Musto Anthony
Published: October 2022

Mudslides can occur on the seafloor due to subsea earthquakes. These extreme events have a significant impact on the structural integrity of subsea flowlines and equipment. A numerical geohazard study was performed on a subsea mudslide event occurring at an escarpment. The study objective was to determine the structural response of two flowlines and one umbilical crossing an escarpment area subject to the extreme mudslide event and to assess requirement for additional stabilization ancillaries.

The study utilized several numerical methodologies such as Computational-Fluid-Dynamics (CFD), Finite-Element-Analysis (FEA), and Fluid-Structure-Interaction (FSI). Different levels of CFD models were first considered (without flowlines) to show the effect of including additional physics with the final CFD model considering a viscous seawater column, viscoplastic multi-layered soil and high-mobility mud phases. The mudslide velocity field from this CFD simulation is extracted at every 1 s and applied to the Abaqus FEA simulation approach. This is presented in a separate paper [1].

The current paper utilized a FSI simulation approach where the evolution of mudflow debris is directly coupled with the FEA flowline model. This allows the FEA model to continuously update loading created by the mudslide motion. The flowline structural responses were monitored and assessed in terms of displaced shapes and structural loading. This methodology reduces conservatism over conventional approaches by considering viscous effects of the seawater, multi-layer soil and mud layers.

Key findings from the study is that the mudslide event did not significantly displace flowlines over the escarpment. The two flowline responses were within structural design limits. It was also found anchoring did not significantly affect structural responses. The umbilical line, however, exceeded compression limits by four times the design limit. This is due to the high velocity mud-front interacting with an initially stationary umbilical and pushing it into compression during the initial stages of the mudslide event. The solution proposed was line rerouting which helped reduce compression levels to within design limits. This analysis assisted the project in CAPEX and installation cost reduction with no requirement of further umbilical compression mitigation components, and the omission of the pre-planned anchors.
The Impact of the Spectral Tail on the Kurtosis of Random Seas
Authors: Barratt Dylan , van den Bremer Ton S. , Adcock Thomas A. A.
Published: October 2022

We perform Modified Nonlinear Schrödinger (MNLS) simulations of random seas based on narrow-banded JONSWAP spectra (γ = 6) with directional spreading. Our wavefields are homogeneous in space and non-stationary in time, initialised with Gaussian statistics. We truncate the spectral tail for the initial conditions at different cut-off wavenumbers to assess the impact of the spectral tail on the kurtosis and spectral evolution. We consider two distinct cases based on truncation of the wavenumber tail at |k|/kp = 2.4 and |k|/kp = 6, where kp is the wavenumber of the spectral peak. A comparison of our results with previous experiments and simulations yields good agreement, supporting the findings of our study. Our simulations indicate that the peak kurtosis value increases if the tail is truncated at |k|/kp = 2.4 rather than |k|/kp = 6. For the case with a wavenumber cut-off at |k|/kp = 2.4, augmented kurtosis is accompanied by comparatively more aggressive spectral changes including redevelopment of the spectral tail, rapid broadening of the spectrum and downshifting of the spectral peak. Similar trends are observed for the case with a wavenumber cut-off at |k|/kp = 6, but the spectral changes are less rapid and less substantial. Thus, the spectral tail appears to play an important role in a form of spectral equilibrium that reduces spectral changes and decreases the peak kurtosis value. Our findings suggest that care should be taken when truncating the spectral tail for the purpose of simulations/experiments. We also find that the kurtosis evolution equation of Fedele (2015, J. Fluid Mech., vol. 782, pp. 25–36) provides an excellent estimate of the peak kurtosis value. However, the selected bandwidth parameter must account for the spectral tail to provide accurate estimates of the peak kurtosis.
A More Accurate Approach for the Design of Subsea Chemical Storage Systems Regarding Volume Requirements of Valve Leakage Tests
Authors: Sevillano Lucas Cantinelli , Sangesland Sigbjørn , Gjersvik Tor Berge , Faanes Audun
Published: October 2022

Subsea production systems require different chemicals to be injected into the wells, Xmas trees, manifolds, or flowlines to prevent or mitigate flow assurance issues, such as hydrate formation. Moving the chemical injection system subsea is one of the initiatives of the oil and gas industry to reduce field development costs and debottleneck topside facilities. Different studies present the potential benefits of adopting this technology, and the technological readiness level of the different concepts.

One premise for successfully adopting a subsea chemical storage and injection system is to have sufficient storage capacity and an efficient re-filling strategy. To achieve that, it is essential to have an accurate estimate of the required volume of injected chemicals during the service life of a well. One of the procedures which demands most of the injected volume of chemicals is the equalizing of pressures across a valve after a leak test has been performed. One single tree can easily have more than a dozen valves needed to be tested periodically.

The modelling of fluid behavior when equalizing the pressure across the valve to estimate the required volume of injected chemicals may be simplified, for instance, by employing an ideal gas law approach. However, a more sophisticated approach employing equations of state capable of determining properties based on fluid composition might be needed to properly simulate the behavior of reservoir fluids with changing composition and under different pressure and temperature conditions.

For the gas-producer wells modelled in the study cases of this paper, the results obtained indicate a clear difference in estimated chemical injection volumes when using the proposed equations of state approach instead of the simplified ideal gas approach. This equation of state method may be used to design more accurately the volume capacity of a subsea chemical storage and injection system, in particularly as the subsea production system’s demands evolve with time.
A Numerical Study on the Thrust and Interaction of a Three-Sail Wind-Assisted Propulsion System
Authors: Chen Zhengqiao , Cai Wei , Zeng Qingsong
Published: October 2022

Wind-assisted propulsion is deemed to be a potential way to effectively reduce CO2 emissions in ship navigation. Some studies are discussing the characteristics of different sail types and their thrust performance, but a systematic investigation on the features of a multiple-sail system is insufficient, especially the effects of sail geometry and position on lift and drag. In this study, three arc-shaped sails are selected, and the geometric and spacing parameters are chosen as variables. The Computational Fluid Dynamics (CFD) method is applied to perform the simulations. The 2D overset mesh technique is applied to allow convenient mesh rotations. One sail alone is first investigated to find the best attack angle, and three sails with consistent attack angles and even mast distance are studied afterward. Finally, the Design of Experiment (DOE) is implemented to evaluate the significance level of the variables. Based on the results, it shows that the sails interaction can provide both positive and negative effects on the thrust performance. The distance between Sail 1 and Sail 2, the attack angle of Sail 1 and Sail 2 are significant factors impacting the thrust of the three-sail propulsion system. The mechanism of the interaction effects on the lift is also addressed. This study helps to find the predominant parameters affecting sail thrust performance and contributes to an intelligent manipulation of a multiple-sail propulsion system.
Feasibility of Riser Emergency Disconnections During Drilling MPD Operations With Surface Back Pressure
Authors: Richa Luan , Venero Germain , Carvalho Roberto
Published: October 2022

Managed-Pressure Drilling (MPD) techniques are used by operators to reduce the non-productive time associated with kicks, losses and well-control events. There are different MPD techniques applied to work reservoirs where fluid loss are common, or where the fracture gradient and the pore pressure are close [1].

MPD techniques on deep water drilling operations can lead to extreme scenarios for the riser integrity, with low effective tension scenarios for Floating Mud Cap Drilling (FMCD) up to high effective tension for Pressurized Mud Cap Drilling (PMCD) and Surface Back Pressure (SBP). Feasibility of drilling operations using MPD techniques will depend, among other factors, on the feasibility of the riser disconnection on an emergency scenario, which present restrictions due to the distribution of effective tension and axial forces along the riser. Recoil analysis is required to define safe windows for emergency disconnection during MPD operations.

The critical parameters during emergency disconnection of a riser with MPD have been studied based on recoil analyses, which were performed for ultra-deep water for a range of SBP scenarios and for a non-pressurized operation with equivalent bottomhole pressure. Numerical simulations are applied for solving the transient problem of the riser disconnection in the time domain, considering the mud outflow, the riser dynamics, the vessel response and detailed tensioning system model to properly capture the system behaviour during the disconnection.

Individual and comparative results are presented, and conclusions describes the influence of the SBP usage for the riser integrity during an emergence disconnection.
Port Plans to Reduce Disaster Damages of High Tide and Tsunamis
Authors: Takahashi Koji , Sugiyama Asami , Nakamura Shuichi , Shibata Daisuke
Published: October 2022

Japan’s major ports must be reorganized as part of the changes in the country’s industrial structure. The Port Management Bodies of the major ports intend to formulate or revise the Port Plan due to these changes.

On the other hand, in Japan, the occurrence of large-scale tsunamis or high tide that exceeds H.H.W.L are expected in the future. When port facilities are damaged by these natural disasters and port functions are paralyzed, the logistics base of the bulk cargo (crude oil, iron ore, coal etc.) which is not suitable for transport by land is more likely to suffer damage because the logistics base is located near the port. The logistics base of the bulk cargo (cereals, automobiles, etc.) and the container cargo which are suitable for long-distance transport by land suffers less damage. The reason for such less damage is that the logistics base is generally located a long way from the port. Port logistics can be restored early with non-damaged ports.

In recent years, Japan also saw increasing damages caused by rising sea levels and growing scale of typhoons due to the influence of climate change.

Today, it is necessary to verify that tsunamis and high tide occur at the same time.

The authors points out the importance of the backup ports using the sacrifice model considering the characteristics of such port logistics, and then, the importance of formulating or revising the port plans to reduce disaster damage from overtopping volumes caused by rising sea levels using Takayama’s method and CADMAS-SURF.

Finally, the authors propose the importance of formulating or revising the port plans to reduce disaster damage to realize these points and to prepare for large-scale natural disasters.
Restoration Models for Quantifying Resilience of FPS Under Mooring Failure
Authors: Wu Jingyi , Yu Yang , Yu Jianxing , Xu Lixin , Wu Fanlei , Chang Xueying
Published: October 2022

During its service life, floating production system (FPS) is exposed to various risks, with mooring failure being one of the catastrophic events. Based on the recorded failure data, it is definitely not a single event. Resilience investigation would improve the performance of FPS under adverse events. In order to assess and quantify the resilience of a FPS under mooring failure, it is essential to use reliable capacity restoration metrics and models. So far, there are no restoration models available for FPS under mooring failure, which help quantify the pace of post-failure capacity and functionality gain to facilitate well-informed decision making for reliable prioritization and efficient allocation of resources in restoration work. This paper proposed a reliable restoration model based on the schedule of restoration tasks for mooring repair. The restoration tasks are carefully analyzed and the key influence factor, damage extent is categorized. Proposed restoration models are then illustrated and validated by traditional FPS under mooring failure.
A Numerical Macro Model to Simulate the Whole Life Response of Anchors for Floating Offshore Renewable Energy Systems
Authors: Kwa Katherine A. , Sivasithamparam Nallathamby , Deeks Andrew , White David J.
Published: October 2022

The offshore renewable energy (ORE) industry is developing new solutions to enable floating facilities that can operate further from shore where more ocean space is available and stronger wind resources can be harnessed. Future ORE facilities will involve arrays of devices that connect and will transmit loads to the seafloor via mooring and anchoring systems. Therefore, it is essential to have a reliable estimation of the capacity that the anchoring system can provide for the variety of loads that are transmitted via the mooring lines.

This paper provides a model for soft soils (i.e. soft clays, loose-medium silts and sand), where the capacity can evolve with time due to the sustained loads and variable components of the cyclic loads, which vary due to environmental conditions and the characteristics of the floating system. The model is referred to as a ‘macro-model’, meaning that the response of all soil elements around the anchor are defined by a representative value of strength and other properties at a single node. The model captures ‘hidden’ anchor capacity enhancements from (i) ‘whole-life’ changing soil strength, (ii) viscous effects on soil strength and (iii) added soil mass effects, which are usually absent in geotechnical foundation design.

It is shown that these effects can be efficiently modelled and integrated into existing numerical analysis packages to provide a new basis for assessing through-life changes in geotechnical anchor capacity. This enables a better understanding of the fully coupled soil-anchoring-mooring behaviour of floating infrastructure over its operational lifetime.
Expanded Vermiculite Blended Foamed Cement Composite for Geothermal Wells Cementing and Its High Temperature Adaptability
Authors: Zhou Wei , Wang Chengwen , Lu Haoxin
Published: October 2022

Geothermal resource is a clean and efficient unconventional energy source. It is crucial to reduce heat loss along shallow interval around non-net for efficient use of geothermal energy. One potential method is to create a cement sheath with good mechanical and insulation properties through well cementing. However, there are few relevant studies. In this paper, the foamed cement slurry with good thermal insulation performance was prepared by a new nitrogen gas generating reactant, and the properties of cement slurry were further optimized by nano oxide and expanded vermiculite. The results show that: the foam distribution in self-generating nitrogen foamed cement is uniform and stable, which is beneficial to ensure the mechanical strength and thermal insulation ability of cement stone; The thermal conductivity of the cement stone with 5–8% expanded vermiculite can be reduced to 0.3719 W/m·k after curing for 48 h at 120 °C, and there is no adverse effects on the compressive strength of cement stone; Nano oxide can improve the mechanical properties and temperature resistance of the cement stone; The compressive strength of foamed cement composite remains above 18 MPa after curing for 48 h at 120 °C, without obvious deterioration of the cement performance. This research can provide reliable technical means for efficient exploration of geothermal energy.
Observations on Horizontal Velocities Under Waves in Shallow Water at a Wave Energy Site
Authors: Vogler Arne , Miguez Diego , Pepper Ben
Published: October 2022

Based on a two-year dataset from a bottom mounted ADCP in shallow water the horizontal particle velocities under waves are analysed in this paper. The sensor was deployed at one of the most exposed coastlines of the UK at a prospective wave energy site and good data returns were obtained throughout the deployment period. The distributions of wave heights, periods, and particle velocities are analysed for all observed individual waves. Waves were binned into combinations of a range of wave heights and periods and the average values of the measured peak horizontal velocities per bin are compared against wave theory. Results show that the average of the measured values per bin compares reasonably well against theory, with measured values slightly exceeding the calculated results. Good similarity was observed between shorewards and seawards setting velocities under the waves, with higher values observed for shorewards facing velocities. Distributions of shorewards setting velocities in each bin were analysed with Kernel and Burr distributions providing good estimations of them. The maximum observed velocities for all bins were more than twice of either the average value per bin or the theoretically derived values. Results described here are relevant to stress or fatigue calculations of coastal structures, moorings and cables, aquaculture, wave surge energy converters, or sediment transport studies.
Nonlinear Moment-Based Optimal Control of Wave Energy Converters With Non-Ideal Power Take-Off Systems
Authors: Faedo Nicolás , Giorgi Giuseppe , Ringwood John V. , Mattiazzo Giuliana
Published: October 2022

The mechanical-to-electrical energy conversion stage in wave energy devices is commonly affected by losses associated with the power take-off (PTO) system, inevitably leading to non-ideal conversion in practical scenarios. Such behaviour needs to be incorporated within the wave energy converter (WEC) energy-maximising control design procedure, so as to guarantee optimal operation of the device under these non-ideal conditions. Motivated by this requirement, we present, in this paper, a nonlinear moment-based energy-maximising control solution for WECs under non-ideal PTO behaviour. We show that the mathematical formalism proposed always admits a globally optimal energy-maximising solution, facilitating the application of state-of-the-art numerical routines, leading to real-time performance. Numerical results are presented for a heaving point absorber WEC system, illustrating the capabilities of the proposed controller in a non-ideal PTO conversion scenario, including a comparison with a benchmark control strategy.
Smooth Carcass for Flexible Pipe –Field Case Study
Authors: Barbier Jérémie , Holyst Cyril , Phelut Renaud , Tran Eric
Published: October 2022

This paper presents the complete qualification of the TechnipFMC flexible pipe Anti-FLIP solution termed Smooth-Carcass and uses a case study to show how this technology is a versatile and cost-effective solution to improve hydraulic performances of tie-back developments. The first commercial project for Smooth Carcass technology consists of 2 subsea wells gas tie-back to an existing facility connected by a total of 24 kms of flexible flowlines. Hydraulic modelling has been used to demonstrate the benefit of Smooth Carcass flexible pipe compared to a conventional rough bore flowline, reducing pressure losses in the production system. Hydraulic performance results are presented for different internal flowline diameters and roughness values considering the bathymetry of the field (180m to 1000m water depth) and tie-back distance to existing facility (∼20km). It is found that Smooth Carcass technology reduces pressure loss when benchmarked to a conventional carcass flexible pipe with a positive cost impact on procurement and installation by reducing flowline diameter size requirements.

Beyond the primary anti FLIP properties (Flow Induced Pulsation); Smooth Carcass is an evolution of the conventional carcass reducing pressure losses and optimizing bore size as well as upper flexible pipe layers. This paper demonstrates that Smooth Carcass is a smart, versatile and cost-effective solution which can add significant value to the customer and be a key enabler for future field developments.
Rationale for NORSOK U-001 5th Edition Revision of Static and Cyclic Subsea Wellhead Loads
Authors: Holden Harald , Muff Anthony , Reinås Lorents
Published: October 2022

NORSOK U-001 is a Norwegian national standard with requirements and recommendations that are supplementary to the ISO 13628 series of standards. NORSOK U-001 4th edition was issued in 2015 and carried a significant revision of design drilling riser loads applicable to subsea structures and well equipment. These maximum wellhead design loads were based on an analytical study followed by verification efforts indicating a shallow water under estimation bias of ULS and ALS design loads and overestimation bias of FLS design loads. As for cyclic design wellhead loads the NORSOK U-001 4th edition included informative design load histograms classified by BOP weight and water depth classes. As a part of development of NORSOK U-001 5th edition, a new wellhead load study has been performed to establish normative maximum and cyclic design loads for subsea wells.

The objective of this paper is threefold; first to present the analysis methodology employed and explain how loads have been established. The analysis work included more than 60 000 dynamic global riser simulations of marine risers from 5 different semi-submersible drilling rigs at water depths from 80 to 1000 m. Secondly, to explain how design loads have been extracted from these results for the upcoming 5th edition. A water depth reclassification was carried out with the intent to better cater for the shallow water bias from the 4th edition. Normative cyclic loads are based on a normalized load histogram scalable by a cyclic design load value (ΔMo) determined by water depth and operational mode. Finally, to outline quantified advice on maximum and cyclic load reduction potential that can be extracted from the underlying studies.
Ship Path Following Control via Output Redefinition Method in Restricted Waters
Authors: Zhou Xueqian , Xin Ping , Jia Dezheng , Huang Jin , Xu Donghao
Published: October 2022

Due to the advances in shipbuilding technology and the needs in the shipping industry, the ship dimensions have kept increasing, and so is the traffic in the ports, approach channels, and harbors. Increase in ship dimensions and traffic in restricted waterways results in challenges in waterway transportation safety. Safe maneuver of ships of overtaking and encounter is one of them. This paper addresses the problem of the path control of ships in parallel motion in restricted waters accounting for the hydrodynamic effects, in which, the path control with nonminimum phase zero dynamics is a major concern. A new output redefinition method has been developed to solve the nonminimum phase zero dynamics. With the assumption of low-frequency ship motion in restricted waters and the use of the output redefinition method, a new ship response equation is proposed. Based on the new ship response equation, a feedforward + PID control law has been developed to control ship parallel motion in restricted waters. Simulation results show good control effect in medium hydrodynamic interaction, the control law and ship response equation can enhance the safety of ships moving in restricted waters.
Activation of Local Bentonite for Oil and Gas Industry Application
Authors: Al-Yami Abdullah , Al-Safran Ali
Published: October 2022

Magzoub, et al 20171 have proposed a method of converting calcium bentonite to sodium bentonite. The method will require a reactor for upscaling. The method involves preparation of soda ash solution, heating, mixing for at least 24 hours and finally removing impurities and drying out. Besun et al. 19972 have proposed a method that will require also a reactor facility to upscale. Starch has to be added in water then bentonite is added in a separate water solution. Both were mixed and heated to form a structure of bentonite-starch gel. The formed gel has 20% starch and 80% bentonite. Bentonite is used in different applications such as drilling fluid, leaching earth, and animal feed additive.3 Sodium bentonite is more attractive in applications such as drilling due to its high swelling and good fluid loss control which makes it always in high demand. 4 & 5 The objectives of this study are to investigate and characterize local calcium bentonite in Saudi Arabia and to find optimum method to activate it for application in drilling fluids and cementing.

The characterization performed utilized XRF, XRD, and ESEM backscattered electron images along with EDS spectra for samples collected from different depths (5 meter and 7-meter samples). API testing including viscosity and fluid loss measurements were also conducted in the characterization phase. Activation was done utilizing cost effective additives such as soda ash. The activated bentonite was testing using standard testing procedures for drilling fluids and cementing such as rheology, fluid loss control, settling, compressive strength and thickening time tests.

The characterization concluded that the samples consisted mainly of Na-montmorillonite with appreciable amounts of impurities of quartz, kaolinite, illite, albite, calcite, and hematite. Compared to API reference sample, the local bentonite samples had less Na-montmorillonite contents, which probably needs some treatments to improve their quality. From this characterization, we can tell that activation of the 7 meter will be easier than the 5-meter bentonite because the Sodium Montmorillonite content is higher. The activation effort was focused on the 7-meter local bentonite sample since it showed better properties in terms of viscosity build up and fluid loss control. A new cost-effective activation method was conducted compared to the previous methods in the literature. Soda ash is an important step to convert or to increase the Na/Ca ratio to ensure higher swelling capacity.
Establishing New Guidelines for Stability Testing of Cementing Mix Fluids
Authors: Al-Yami Abdullah , Wagle Vikrant
Published: October 2022

American Petroleum Institute (API) has led for more than 85 years the development of equipment and operating standards in petroleum and petrochemical industries. API maintains 685 standards and recommended practices which have been also followed by international organization for standardization (ISO). Currently, there are no established guidelines in the industry to evaluate stability of cementing-mix fluids with time prior to mixing and pumping with cement.

API specification is not the same as API recommended practice. Specifications apply to pure materials while recommended practices are used on daily basis for cement slurries. Recommended practices can be modified and altered to be more suitable to field cementing operations and this is the main topic of this paper, to establish guidelines addressing stability of mix fluid in terms of thickening time, fluid loss, and most importantly the stability of latex and polymers within the mix fluid to ensure proper resistance against temperature and pressure cycling. To the best of the authors’ knowledge this is the first study to establish such guidelines.

API objective is to have a group of tests that produce consistent, reproducible results from test to test and from one lab to another. API only consider small part of testing so we should not be disqualifying additional tests because they are not API.

In addition to standard tests such as thickening time, rheology, and fluid loss. New and quick tests were designed to evaluate polymer and latex stability within the mix fluid that can be performed in a quick and an effective way to support the operator decision of dumping or maintaining the mix fluids with time for the cementing operations. Such a critical decision can not only be achieved by the standard API testing such as thickening time, rheology, fluid loss, etc. The consequence can definitely affect wellbore isolation and well performance. If the stability is not tested properly, then the cementing pumping operations can be achieved however we might end up with improper zonal isolation when changing mud weight or conducing fracturing operations.
Machine Learning in Fatigue Analysis for an Unbonded Flexible Riser
Authors: Yuan Jiabei , Zhu Linfa , Hou Yucheng , Tan Zhimin
Published: October 2022

Flexible pipelines are widely used in the offshore oil and gas projects. Comparing to steel pipes, flexible risers consist of multiple components layers, with each layer serving designated functions. For example, the helical tensile layers are used to work against axial tension from static pipe weight and amplification from the dynamic motions. As the risers are constantly experiencing stress variations due to different loadings, the fatigue performance of the tensile layers is essential to the design and operation of the flexible pipe system. Global and local fatigue analyses are usually performed in the design stage to estimate the fatigue life of tensile layers. Various parameters like vessel characteristic, pressure and temperature, environmental loadings affect the riser long-term performance. Also, multiple locations like top end fitting, bend stiffener region, touch-down zone are all potential fatigue hot-spots. To evaluate the fatigue damage at these locations, the industry standard practice is to run fatigue analysis in time domain with irregular wave. This approach is however time and resource consuming, especially when the designers have to consider thousands of load cases with long duration for numerous combinations of sea-states and operating conditions.

Baker Hughes developed a frequency domain technique for fatigue assessment on tensile layers of flexible risers. The approach builds transfer functions based on chosen time domain simulation and predict the total stress spectrum for other cases. Dirlik’s approximation method is used to estimate the fatigue damage based on the stress spectrum. Comparing to time domain approach, this approach is considerably more efficient in implementation. Since frequency domain technique simplifies the riser response as a linear system, the discrepancy must be addressed by calibration factors. To improve accuracy, more transfer functions are required to be built prior to the damage calculation.

In this paper, Baker Hughes introduces artificial neural network (ANN) technique to the developed frequency domain fatigue damage methodology. The ANN model is built between the wave spectrum and stress spectrum. Unlike the general AI technique, the type of neuron at each layer is carefully selected to represent the dynamic behavior of the riser system to improve the model efficiency. The ANN model is trained based on selected sea states. The trained model is used to predict riser damage and compared to that calculated from the time domain approach.