bluuebunny/crossref_metadata_2025 huggingface dataset:
A Basic Investigation of Resonance Characteristics of Water Regions of PW-OWC WECs
Authors: Ikoma Tomoki , Kuwata Airi , Aida Yasuhiro , Masuda Koichi
Published: September 2023

This paper describes resonance characteristics of water regions of OWC (Oscillating Water Column) type WEC models installed with projecting-walls, which are called as PW (Projecting Wall)-OWC devices. We can easily improve PTO performance of an OWC type WEC device by installing projecting walls in front of it. One of the reasons is that such a device can have multi-resonance frequencies. Behaviors of the resonances are complex because we can change the resonance characteristic by varying a damping effect which decides a PTO characteristic. The thing would be that we can easily optimize the characteristic to a sea wave condition. However, the resonance characteristics have not been clarified yet. The paper shows the resonance behaviors of OWC and a water region surrounded by the projecting-walls.

The paper adopted a theoretical approach to predict the resonance characteristic as the primary conversion characteristic. The prediction method is a potential-theory-based model which can directly take into account a damping effect due to PTO in a boundary integral equation of the velocity potentials. As a result, there are two cases. One has two resonance frequencies and another has only one because of damper magnitude as PTO.
Methodology for the Integration of Experimental and Numerical Fluid Dynamics in the Study of a Floating Body Such As a Wind Turbine Subjected to Environmental Loads
Authors: Ducrozet Guillaume , Bouscasse Benjamin , Bonnefoy Félicien , Leroy Vincent
Published: September 2023

The decrease in the computational cost of high-fidelity solvers like Computational Fluid dynamics (CFD) has expanded its use in the design of marine structures. This is true among academics and industrial R&D departments. After a long debate about whether CFD would or not supplant traditional experimental methods, it is widely accepted that the two approaches need to be considered together. The present paper proposes a framework for the integration of both experiments and high-fidelity numerical simulations in the design procedures of offshore wind turbines. It makes use of the nonlinear potential flow software HOS-NWT for wave generation, together with the NREL OpenFast software for wind generation and calculation of aerodynamic loads acting on the structure. For the numerical simulation, the environment (wave field) and aerodynamic loads are fed into the high-fidelity software with adequate couplings in the resolution algorithm. For the experiments, the wavemaker motion is run based on the HOS-NWT result, and the aerodynamic loads are imposed thanks to an actuator controlled by software in the loop system. Different scenarios are considered, from the classical CFD validation with experimental results up to more complex situations where the numerics and the experiments are done in sequence one before the other or vice versa, in order to complement or verify the findings.
Calibration of Dynamic Riser Analysis Using Measured Motion Data
Authors: Bruun Mortensen Karina , Skjerve Håvard
Published: September 2023

For design and analysis of dynamic flexible riser motions, the common practice is to use tailor-made software to create an analysis model based on a large set of assumptions and simplifications regarding hydrodynamic loading and interaction between objects. Normally, most of the applied input values are based on theoretical considerations rather than tests and/or actual measured data, and it can be difficult to assess the overall level of conservatism.

When performing analyses on existing systems e.g., lifetime extensions, it is possible to reduce uncertainties by harvesting actual motion data and calibrate the analysis models to obtain a sound level of conservatism.

In the case described in this paper, dynamic motions of both the Åsgard B semi-submersible platform and the Mid Water Arch (MWA) were measured throughout an entire winter season and used to calibrate the analysis model.

The intention was to develop a method for improving accuracy in modelling of risers over the Åsgard B MWA structure in OrcaFlex.
Spatial and Temporal Evolution Characteristics of Water Quality in the Port Waters - A Case Study of Zhanjiang Port, China
Authors: Guo Jianqun , Jiang Zhonglian , Yu Zhen , Ying Jianglong
Published: September 2023

As an important part of the integrated transport system, ports contribute greatly to the prosperity and development of international shipping. Port construction, loading and unloading operations, incoming and outgoing of vessels, and sewage discharge have certain impact on the port water quality. Meanwhile, the deterioration of port water quality will inevitably affect the marine ecological environment. This paper utilizes the pollutant monitoring data of state-controlled cross-sections in the watershed of Zhanjiang Port area from 2015 to 2022, analyzes the characteristics and correlation of its temporal-spatial variations, and thus overviews its driving factors. The results present a positive correlation between total phosphorus (TP) and NH3N with a correlation coefficient r = 0.752, while a negative correlation is found between TP and dissolved oxygen (DO) with a correlation coefficient r = −0.638. The pH value of the water body has increased steadily while no significant variations have been found in the annual temporal-spatial distribution of DO and TP. The chemical oxygen demand (COD) has shown a fluctuating downward trend while the variation of total nitrogen (TN) appears a “U” shape pattern, reaching a minimum value between June to August each year. In general, the water quality of Zhanjiang Port is poor in summers and good in winters. Human activities and industrial production are the main drivers of water quality pollution. The increasing trend of major water quality parameters indicates that timely countermeasures should be taken to improve water quality of Zhanjiang Port.
Machine Learning Models for Predicting Cuttings Concentration in Annulus Based on Flowloop Experimental Data
Authors: Purwandari Sartika Dwi , Lund Bjørnar , Hovda Sigve
Published: September 2023

Improper drilling parameter values selection can result in a series of operational problems, such as stuck pipe, wellbore pack-off, reduced ROP, and increased equivalent circulation density. A large fraction of these problems occurs because the well is not sufficiently clean due to cuttings accumulation. Cuttings transport is a complex process that is influenced by drilling parameters such as flow rate, pipe rotation speed, fluid rheology, cuttings properties, and wellbore and drillpipe geometry. Numerous research projects have been conducted to study cuttings transport both using laboratory experiments and numerical approaches to build physics-based cuttings transport models. Yet, a model which can account for all relevant combinations of drilling parameter values with high predictive capability is still out of reach.

In this study, we investigated the use of various machine learning models on this very complex topic. In particular, we focused on the prediction of cuttings concentration based on flowloop experiments from three different research facilities. The data that were collected from the different research facilities have a total of 332 data points. Each data point consisted of these nine input variables: annular wellbore area, eccentricity, rate of penetration, pipe rotation, apparent viscosity, average flow rate, fluid density, cutting size and wellbore inclination. 61 data points were found as outliers from one input variable, namely ROP. Those outliers were decided to be kept due to those outliers were not occurred by error measurement. Therefore, a robust regression technique (Huber Regression) and two types of ensemble learning (Random Forest and Gradient Boosting) were chosen because those machine learning algorithms were not sensitive to the presence of outliers. The data were divided into two groups for training and testing, respectively with proportions 80% and 20%. Those models were trained using a training data group and evaluated using cross-validation to avoid over-fitting. Mean absolute error (MAE) and coefficient determination (R-squared) were used to analyze model performances when models were applied to data testing. The results showed that the two ensemble learning models both had lower mean absolute error and higher R-squared compared to the robust regression technique. Next, Larsen’s empirical approach which is based on the critical velocity concept was compared to the machine learning techniques. According to the performance evaluation results, machine learning models showed better predictions compared to an empirical approach and they had lower MAE and a higher value of R2. GB has the best performance by giving an error of the model prediction about 2.150 % and R2 0.920.
Modelling Hydrate Plug Capacity of Flexible Pipes
Authors: Schmidt Henrik Blicher , Solfeldt Thomas Iversen , Pedersen Tommy
Published: September 2023

Hydrate plug detection and removal in flexible pipe has gained increasing attention from operators and at the same time not much has been published on the subject. When operating flexible pipe for hydrocarbon applications there is a risk of hydrate formation. Hydrates can block the bore of the flexible pipe and differential pressure can form across the hydrate plug. This differential pressure can damage the inner layers of the flexible pipe.

The objective of the present study is to estimate the differential pressure capacity of the flexible pipe.

Hydrates most often form during production stop periods. When the well is started up the lack of flow can be used to detect a hydrate plug. Either during this detection or during the removal of a hydrate plug, the pipe can be subject to a differential pressure across the plug domain. The differential pressure can lead to excessive loading of the pipe layers, especially the carcass and pressure sheath layers.

A numerical model has been developed that can be performed with reasonable computational effort using an in-house pre/post-processor and FE solver. The model adopts the axisymmetrical framework, and the enmeshed domain is limited to the innermost layers, i.e. carcass, pressure sheath, and pressure armour.

The model simulates the hydrate plug by applying Boundary Conditions corresponding to the rigid body motion of the surrounding carcass windings and converting the reaction forces monitored in the model into a differential pressure.

The pressure sheath principal strain and carcass plastic strain are chosen as limiting criteria. The driving factor is the load transfer across each layer while the carcass windings are displaced axially (together with the plug) caused by the load from the differential pressure.

For a given plug length, the differential pressure capacity is evaluated at the “time-step” where the governing strain criteria is exceeded — the reaction forces acting on each carcass winding are integrated into a total reaction force. Finally, the total force is converted into a differential pressure, which is denoted the hydrate plug capacity of the pipe.

An important finding is that the differential pressure capacity increases for longer plug length in a non-linear manner. The non-linear plug length dependence is in competition with the hydrate plug shear capacity assumed to scale linearly with the plug length. The applied differential pressure can then be compared to the hydrate shear capacity thereby establishing if the plug is removed by shearing. The applied differential pressure is subsequently compared to the pipe’s hydrate capacity, showing that the differential pressure is below the pipe capacity for the possible range of plug lengths.
Optimal Energy Management for Zero-Emission High-Speed Passenger Vessels
Authors: Najjaran Samieh , Skjetne Roger , Godø John Martin Kleven
Published: September 2023

To comply with IMO’s regulations on reduced emissions, the maritime industry is investigating various alternatives to achieve zero-emission high-speed passenger vessels (HSPVs). In this work, optimal loadsharing is studied for a given vessel with a zero-emission hybrid driveline with a fuel cell (FC) and a battery. The further aim is to include this as part of a computation model to assess feasibility of zero-emission solutions for passenger transport connections under study along the coast of Norway. A dynamic programming (DP) algorithm is derived to provide the global optimal solution of the loadsharing problem. This will serve as a benchmark for other and more computationally efficient optimization algorithms to be feasible for runtime applications. Here we formulate an alternative optimal loadsharing model based on a linear program (LP) and compare that to the DP. The proposed LP and DP are applied to a numerical model for an existing HSPV operating along a given route. AIS data is used to extract the route information and power load profile of the vessel. The results demonstrate a step towards an overall methodology for assessing the feasibility of a vessel and an onboard propulsion and power system to allow for zero-emission passenger transport.
Multiphase Seepage Flow Characteristics of Micro-Fractures in Subsurface Reservoirs Using the Lattice Boltzmann Method
Authors: Pu Dan , Shen Linfang , Wang Zhiliang , Li Miao , Li Zhenquan , Wang Pengyu
Published: September 2023

The traditional Shan-Chen pseudo-potential model has limitations, such as pseudo-velocity, density ratio limitation, and thermodynamic consistency defect. A method based on the improved Shan-Chen pseudo-potential model to study fluid flow in rock microfractures using the multiple-relaxation-time lattice Boltzmann method is proposed and validated using three arithmetic cases. The geometric characteristics (height and spacing) of the rough elements are varied to analyze the joint effects of rough elements and infiltration conditions on the multiphase seepage in microfractures. Rough microfractures are simulated using regular rough elements of different shapes, including rectangular, trapezoidal, and triangular rough elements. With the increase in the rough elements height, for the microfractures at the wall contact angle θ = 145.5°, 117.2°, and 67.0°, the flow velocity decreases and then increases; for the θ = 93.0° micro fissure, the fluid flow velocity decreases to stationary. With the increase in the rough element spacing, for the θ = 145.5° micro fissure, the liquid flow rate continuously increases; for the θ = 117.2°, 93.0°, and 67.0° micro fissures, the liquid flow rate continuously decreases. This study is expected to guide future researchers and engineering applications in terms of subsurface reservoirs.
As-Built Carcass Fatigue Modelling
Authors: Bonanni Michele , Nott Phil , McCormick Andrew , Bailey Trevor , Roberts Andrew
Published: September 2023

In rough bore flexibles, the carcass sustains external pressure loads. The design of the carcass section is such that displacements due to pipe bending do not significantly load the carcass. Cyclic loading is therefore typically avoided by design. Several decades of operational and dynamic testing experience indicate that these designs are indeed effective.

Nevertheless, an analytical methodology for the carcass is advisable in order to clear concerns regarding pipes with stiffer carcass layers or with tolerances close to the manufacturing limits. This work assesses the service life of as-built carcass and investigates sensitivities to carcass pitch and barrier intrusion.

For this purpose, a novel approach to carcass SN curves is presented. The use of these SN curves in the finite element simulations for the service life estimation improves the fatigue life prediction capability and allows the exploration of sensitivities in manufacturing tolerances — potentially leading to the relaxation of carcass tolerance limits, reducing the onus on the manufacturing of adjacent layers and thus improving the performance of the pipe overall.
Coupled Numerical Model for Residual Liquefaction With Partial Dynamic Approach
Authors: Cui Lin , Wan Zhipeng , Jeng Dong-Sheng
Published: September 2023

The evaluation of the seabed liquefaction is one of the key factors for the design of foundation of marine infrastructures. In this paper, a new numerical model developed within the framework of OpenFOAM® is proposed by two new features: (1) coupling oscillatory and residual mechanisms; and (2) adopting partially dynamic soil behavior in the existing models. The proposed numerical model predicts reasonable results comparing with the existing experimental data from wave flume tests. With the coupling model, a new liquefaction criterion is proposed to cover both oscillatory and residual liquefaction. Both wave and current loading are considered in the numerical example. Numerical examples conclude that the forward current can increase the maximum liquefaction depth by 23% after 35 wave cycles comparing to the wave only case.
Probable Ice Impact Locations and Magnitudes on a Naval Hull Form in Forward Transit Through Marginal Ice Zones
Authors: Bryson Edward , Quinton Bruce W. T. , Daley Claude
Published: September 2023

Operational capability assessment of ships in the Arctic have traditionally focused on icebreaking hull forms. The classification of these capabilities resulted in the development of the International Association of Classification Societies (IACS) Unified Requirements for Polar Ships, which requires the hull structure to withstand a predetermined glancing bow impact. The assumptions made when developing the Polar Class Rules, such as the collision with a thick and semi-infinite multiyear ice floe, slow speeds, and a glancing bow impact on an icebreaking bow shape, are not always valid when assessing the operational capabilities of non-icebreaking hull forms.

The ex-HMCS IROQUOIS was simulated in forward transit through marginal ice zones using the computer program “GEM” to study the location and magnitude of probable ice loads. The collision model was validated using the DDePS case 2a collision scenario (glancing collision on the bow). The model was simulated transiting forward at different speeds through ice regimes with varying identified parameters of interest, namely concentration, ice floe size distribution, and ice floe thickness.

The observed results show most of the high magnitude ice impacts for this naval hull form occurred at or near the stem, and only a few high magnitude impacts on the bow shoulder. This contrasts to an earlier study using GEM where an icebreaking hull form in forward transit through a marginal ice zone experienced a plurality of high magnitude impacts along the bow shoulder. The main reason for the difference is the shape of the bow, with the naval hull form being markedly slender with much lower normal frame angles. These results suggest that both stem and bow shoulder impacts are of importance when assessing the operational capability of naval hull forms in marginal ice zones.
Analytical and Finite Element Assessment of Thermoplastic Composite Pipes Subjected to Axisymmetric, Bending and Thermal Loading
Authors: Caire Marcelo , Luna Araújo Oliveira Pedro , He Yangye , Vinicius Da Cruz Marcus , Augusto Vaz Murilo
Published: September 2023

Thermoplastic Composite Pipes (TCPs) may be employed as an alternative to traditional unbonded flexible pipes for deep water developments. They are usually manufactured with PEEK or PVDF polymeric layers in the inner and outer layers and an intermediate carbon fiber composite laminate. The TCP composition leads to a lightweight pipe with high corrosion and fatigue resistance, but due to high bending stiffness, large drum diameters may be required for installation with the reel method. This paper presents an analytical formulation considering a carbon fiber/PEEK TCP subjected to pure bending. A previously presented analytical formulation for tension, internal and external pressures and thermal loading is employed to separately obtain the axisymmetric and thermal stresses. The temperature dependency of stiffness and strength material properties are considered for both models. The case study combines the axisymmetric and bending model results and compares the results against three-dimensional finite element models. The through thickness temperature profile for the TCP under different internal prescribed constant temperatures (60, 80 and 120°C) and subjected to outer pipe convection to the seawater at 4°C are presented followed by analytical formulation correlation with FEM stress distribution results. The temperature influence on the pipe bending stiffness is also shown. The Maximum Stress and von Mises failure criteria are respectively employed for the laminate and homogeneous layers and failure envelopes are presented for tension and bending loads for each prescribed internal temperature and fixed internal and external pressures.
Verification of Inverse Propeller Moment Estimation Using a Scale Laboratory Rig: Further Results and Discussion
Authors: Nickerson Brendon M. , Laas Jaco , Bekker Anriëtte
Published: September 2023

There has been increasing interest in the loads caused during interaction between ship propellers and ice. Recent research into propeller ice interaction has produced inverse models that can be used to estimate the propeller moment induced by ice impacts. These models rely on the measurement of the output response of the propulsion shaft, which is inverted to obtain the input propeller load. The particular model considered here makes use of modal superposition to invert the measured shaft response. Though the model has been validated numerically and used with full-scale response data, it has not been validated using simultaneous input and output measurements. Reliable full-scale simultaneous measurements can be difficult to obtain due to the harsh conditions experienced during propeller-ice interactions, and the cost involved with direct measurement of propeller loads. Thus, the use of a laboratory rig to verify the inverse method is investigated. An inverse model based on the use of modal superposition to represent the propulsion shaft as a continuous system has been implemented alongside a laboratory scale rig. The input loads and output responses are measured simultaneously during experiments with the scale model. These output responses are provided to the inverse model, and its estimation of the input load are compared to the measured loads. The comparison provides information about the accuracy of the estimations provided by the inverse model. A limitation in the inverse model, that spurious transients at the shaft natural frquency appear in the estimations, has been found and discussed.
Computational Fluid Dynamics Study of a Cross-Flow Marine Hydrokinetic Turbine and the Combined Influence of Struts and Helical Blades
Authors: Wiley Will , Tran Thanh Toan , Lawson Michael , Barrington Matthew
Published: September 2023

A computational fluid dynamics study was performed for a cross-flow marine hydrokinetic turbine. The analysis was done in three dimensions and used the unsteady Reynolds-averaged Navier-Stokes solver in the commercial code STAR-CCM+. The base turbine configuration is the RivGen® Turbine, designed by the Ocean Renewable Power Company. A convergence and uncertainty analysis was performed for both the spatial and temporal discretization; this was done using the base configuration, which features support struts and helical foils. Both struts and helical blades introduce three-dimensional flow effects, influencing the complex flow phenomenon of dynamic stall. The study compares the relative impact of struts on power performance and blade loading for both helical and straight blades, and found that for this turbine the relative loss in power from struts was lower with helical blades.
Time Domain Structural Analysis and Digital Twin Application for Floating Offshore Wind Turbine
Authors: Lim Ho-Joon , Samaria Sagar , Choi Sukjoo , Sablok Anil , Jang Hakun , Koo Bonjun
Published: September 2023

A response-based time domain structural analysis method for offshore floating platforms has been studied and validated. Compared to the conventional load-based and simplified method, the response base method can evaluate structural strength and fatigue damage with higher accuracy, taking into account irregular waves, non-linear environmental loadings, phasing between different loads, non-linear motion responses, and non-linear mooring and riser loadings.

The present study examines the structural assessment of the entire substructure and the turbine tower to substructure connection of a Floating Offshore Wind Turbine (FOWT) platform using a response-based time domain structural analysis. Finite Element (FE) models are constructed for the entire FOWT, and corresponding load components are mapped to the FE model. A fully coupled aero-hydro-servo-elastic analysis software, MLTSIM-OpenFAST, is used to calculate dynamic responses of a FOWT in the time domain. and used for the life cycle response analysis of a FOWT with 25 years of weather data.

All load components are synthesized at every instantaneous time step and converted to response-based stresses. This methodology efficiently and more accurately determines the stress distribution for different load cases which is useful for both new design and digital twin for integrity management to provide quick structural strength and fatigue damage assessment.
A Physical Model Approach to Mooring Forces and Motion Responses of a Closed Fish Tank Including Internal Free Water
Authors: Zhao Huaizhi , Dong Shuchuang , Zhou Jinxin , Li Qiao , Kitazawa Daisuke
Published: September 2023

In marine aquaculture farming, currently used flexible open-net cage systems face many problems and challenges, such as sea lice and other parasites, fish escape, and water pollution. The development of closed fish cage systems for fish farming has been driven by such problems. Closed fish cage systems interact with sea forces when subjected to waves and currents. The wave-induced motions of the closed fish cage would result in sloshing problems, i.e., internal fluid oscillations. Knowledge and experience on the internal sloshing issue are very limited, as closed fish cages are still a novel concept. In the present study, a series of physical model tests were performed to investigate the mooring forces and motion response characteristics of a circular closed fish cage. A decay test in calm water and regular wave experiments were performed for the closed fish cage in a wave basin. In addition, we set three different netting panels with different mesh sizes in the closed fish cage and investigated their inhibitory effects on internal sloshing flow under different configuration conditions. The results indicated that the general trend of maximum mooring forces was the same in both upstream and downstream mooring lines: first increased, then decreased, and finally increased again as the wave period continues to increase. The global motion responses of the fish cage system in the surge (pitch) directions exhibited similar trends with mooring forces. When the incident wave periods closed to the first mode of the sloshing period, the surge (pitch) response was almost zero. For internal water sloshing, it clearly showed that the second or higher harmonic components cannot be negligible, but had little effect on the global motion of the cage. Furthermore, the inhibition effect of the netting panels on the free water surface oscillation was confirmed, especially when the netting panel was horizontally placed on the inner free water surface, the most obvious inhibitory effect could be observed. Overall, these findings are expected to provide references for the design and operation of the closed fish cage system.
Numerical Modelling in the Development of the M4 Prototype for Albany, Western Australia
Authors: Kurniawan Adi , Wolgamot Hugh , Gaudin Christophe , Shearer Chris , Stansby Peter , Saunders Brad
Published: September 2023

A key step on the pathway to demonstrating wave energy converter (WEC) technology is ocean trials at a reduced scale. The Blue Economy Cooperative Research Centre and the Government of Western Australia (through the Department of Primary Industries and Regional Development) are funding the deployment of an M4 wave energy converter in King George Sound, Albany, Western Australia. The M4 WEC is an articulated device developed by M4 Wave Power Limited, which works best in waves comparable to the device’s length. At this location, strong easterly winds in the summer produce wind seas with wavelengths close to the length of the WEC, which is approximately 21 m. In order to determine the performance of the device at this site, a linear model of the M4 WEC has been developed using a generalised modes approach (not previously applied to the M4 WEC). Combined with local measurements of the wave field, this allows estimates of the power, motions, relative freeboard, etc. to be computed. The variant of M4 being analysed in this case is a ‘1-2-1’ version with a front triangular frame of 3 rigidly connected floats and one rear float on an articulated arm. This paper describes the model development, discusses reasons for choosing the scale of the device, the particular configuration, and the ongoing plan for the deployment.
Investigation of the Relation Between Coring Parameters and Formation Representation
Authors: Abugharara Abdelsalam , Butt Stephen
Published: September 2023

Coring is an essential operation for subsurface formation evaluation. It is a key to recover cores from formation and have them unaltered for best formation representation. Numerous reasons could influence core integrity that could produce data through core characterization that could misrepresent the formation. The aim of this paper is to investigate the influence of the (input vs. output) coring parameters and coring bit type on the coring performance and the cored formation property representation in high strength rocks. Such aim was investigated through coring operations applying Weight On Bit (WOB), rotary speed (revolution per minute - rpm), etc. In this research, high strength granite blocks were cored using a fully instrumented large-scale laboratory drilling simulator. Two main types of coring bits were utilized in the coring operations including a thick-wall coring bit and a thin-wall coring bit. The range of the applied WOB varied between a low weight (1kN) and a high weight (15kN) with increment increase of (2.5 kN). The applied rpm ranged between 60rpm and 300 rpm with increment increase of 60 rpm. Granite formation was characterized for rock property determination. The indirect Tensile (IT) Strength Test was conducted for the granite Material Characterization (MC). The analyzed and reported results of the overall coring performance, parameters (parameters vs. type of coring bit), and the IT for granite MC showed an influence of the un-optimized applied coring parameters and the random selection of the coring bit could remarkably impact the coring performance outcome and misrepresent rock property of the cored formation. Results recommend optimal selection of coring bit and applied coring parameters are essential for best coring performance.
Current Effect on Nonlinear Wave Height
Authors: Kumar Arun , Hayatdavoodi Masoud
Published: September 2023

Interaction of uniform and shear currents with nonlinear waves is studied by use of the computational fluid dynamics approach. A range of nonlinear waves are considered including shallow- and deep-water waves, and the effect of currents of variable speed and direction on the wave height is investigated. Uniform current consists of a fixed horizontal velocity across the water depth, while shear current imposes a linearly varying velocity from the seafloor to the still-water level. The current speeds are selected such that they remain comparable with the horizontal particle velocity under the wave crest and wave trough. A computational wave-current tank is developed for this purpose and the combined wave-current condition is obtained by developing a new wave-current maker in an open-source computational fluid dynamics package, namely OpenFOAM. The model is tested against laboratory measurements of various types of wave and currents and very good agreement is observed. The model is then used to investigate how currents of different profile, speed and direction modify the wave field. While the focus of the study is on the effect of these currents on the change of wave height, the surface elevation of the waves is also assessed in some cases. Discussion is provided on the differences between current effect on the wave height of shallow-water waves vs deep-water waves. The wave nonlinearity is found to play a remarkable role on how the wave changes under the ambient current. Shear currents are observed to have a stronger influence on the change of wave height than uniform currents.
Experimental Investigation on the Natural Frequency and Damping Coefficient of the Roll From Vessel Response in Random Seas
Authors: Javanmardi Mohammadreza , Mehr Javad A. , Heng Zi Hsiang
Published: September 2023

Autonomous shipping is inevitably the future of sea transportation which requires accurate decision-making systems. Analysis of big data as a key element to develop these decision-making systems is much easier than before. The precise prediction of vessel roll response, as a critical component of ship motions, by directly calculating hydrodynamic parameters from vessel response during the voyage, would tremendously aid in the real time adjustments to avoid dangerous situations the vessel would encounter.

This investigation aims to extract the natural period and damping coefficient of the roll from vessel response in random seas. Experimental tests were conducted to record the roll motions of vessel models, P&O Nedlloyd Hoorn container ship and Midi Mak Marad F bulk carrier, in random waves at Australian Maritime College Model Test Basin. The natural period obtained from the vessels’ roll response in random seas were in close agreement with the one obtained from the vessels’ roll decay test with negligible percentage error of under 1% for both models. Random Decrement Method (RDM) was used to produce roll decay from random vessel response and estimate the damping coefficient of the models. The estimated damping ratio from RDM show the good agreement with roll decay tests. This great achievement can help us to precisely predict the vessel roll response in random seas in order to avoid dangerous situation.
Impact of Chemical Impurities on the Integrity of Carbon Dioxide Transport Pipelines
Authors: Stokes Stephen , Haghighi Hooman , Mckay Craig
Published: September 2023

There are significant technical challenges to be addressed in the design of transportation pipelines for Carbon Capture and Storage (CCS) projects, not least of which is the management of non-carbon dioxide (CO2) components (impurities).

Typical impurities such as glycols (diethylene glycol (DEG) and triethylene glycol (TEG)), amines (ethanolamine (MEA), diethanolamine (DEA), methyl diethanolamine (MDEA)) and alcohols (methanol) could be potentially carried over during transient or upset operations from gas processing units to the CO2 pipelines. Furthermore, impurities (for example monoethylene glycol (MEG)) could remain in the system following pre-commissioning depending on the approach to pipeline dewatering and conditioning.

These chemical impurities, though in very low amounts, can trigger water dropout and lead to the presence of a free aqueous phase. CO2 and reactive components such as hydrogen sulphide (H2S), sulphur dioxide SO2, nitrogen dioxide (NO2) and oxygen (O2) can dissolve in free water and form stronger acids such as carbonic or sulphuric acids that can influence the operation and material integrity of CO2 pipelines. Particularly, the heavier corrosive acidic liquids can be stagnant at low points and increase the risk of localised corrosion.

This paper reviews the research that has been conducted to date on chemical carry-over, risks of acid formation and component solubility limits in CO2 streams. The research is applied to a practical example of a post-combustion CO2 gas gathering pipeline to demonstrate the importance of controlling minor impurities to a tight specification in the CO2-rich fluid.
A Numerical Study of Wave Impacts on a Semi-Submersible
Authors: Deng Yanfei , Li He , Wang Zixuan
Published: September 2023

A fully nonlinear numerical wave tank (NWT) is set up for extreme wave modelling and wave impact simulation. As a first step, a focused wave train was model and the focal location where the steep focused wave is close to breaking was determined. Subsequently, an in-depth investigation is performed on the wave impact loads on the wave-ward side of a deck box of a semi-submersible subject to this extreme wave. The numerical results are also compared with the predictions in accordance to the DNVGL technical guide. It is concluded that the severe horizontal impact loads are caused by the “strike” action of the rushing water mass from near-breaking waves rather than the run-up jets. The predictions based on the technical guide are conservative and in general overestimate the impact loads. These findings could contribute to a more comprehensive understanding and a more accurate algorithm with respect to the horizontal impact loads.
Development of Numerical Model of Floating Body With Air Chamber for the OWC-WEC Using Two-Phase Flow MPS Method
Authors: Sasahara Yutaro , Masuda Mitsuhiro
Published: September 2023

The floating oscillating water column type wave energy converter (OWC-WEC) is highly maintainable and safe because it has no moving parts underwater. For the commercialization of the floating OWC-WEC, a method is required to analyze, indepth, its response to waves over a wide range of wave conditions, from operational to survival conditions. In this study, the authors have developed a floating body model with an air chamber for expressing the floating oscillating water column by extending the high accuracy two-phase flow moving particle simulation (MPS) method. The MPS method is one of the particle methods used for computational fluid dynamics (CFD) simulations which can easily solve problems related to large free surface deformation and nonlinear fluid and structure interaction. Numerical and experimental investigations using the free heave decay test were conducted to confirm the validity of the developed model. A comparison of the numerical and experimental results showed that although a numerical pressure oscillation of particles increases as the power take-off (PTO) damping increased, both results generally agreed on the heave motion of the floating body, water mass height and air pressure in the air chamber, and the applicability of the proposed method was verified.
SHANSEP-Based Approach to Account for Consolidation Induced Strength Gain in Capacity Assessment of Shallow Foundations
Authors: Zhou Hongjie , Sun Chao , Krisdani Henry , Dias Helena
Published: September 2023

It is well recognised that soil strength increases with time due to consolidation under sustained foundation load. This is typically termed ‘consolidation strength gain’. Quantification of such beneficial effect on the foundation capacity, however, is not straightforward for design. In this paper a practical approach is described to account for this effect in the design of shallow foundations on seabed dominated by fine-grained sediments. This approach is based on the relationship of Stress History and Normalised Soil Engineering Properties (SHANSEP), and featured by a consistent procedure throughout the processes from soil characterisation to foundation capacity assessments. The SHANSEP relationship can be parameterised during the site characterisation stage and is used in the numerical modelling to estimate strength increase due to consolidation effects, which in turn is used in the capacity calculations of a mudmat foundation.

Data from a deepwater project is used to demonstrate the entire process. The beneficial effect of consolidation on the foundation capacity is illustrated through the expansion of the failure envelopes in the horizontal-vertical-moment load space. The magnitude of such effect is expected to vary between soils and interface conditions and be affected by the consolidation load and consolidation period. However, in general the horizontal and torsional capacities are expected to increase more significantly than the vertical and moment capacities.
Slope Effect on the Evolution of Kurtosis Over a Shoal
Authors: Mendes Saulo , Kasparian Jérôme
Published: September 2023

Shoaling surface gravity waves induce rogue wave formation, but are reduced to water waves passing over a step. We show that non-equilibrium physics allows finite slopes to be considered in this problem. A spatially varying energy density describes the dependence of the rogue wave amplification as a function of the slope steepness. Increasing the slope increases the amplification of rogue wave probability, until this amplification saturates at steep slopes. In contrast, the increase of the down slope of a subsequent de-shoal zone leads to a monotonic decrease in the rogue wave probability. In view of the central role played by the excess kurtosis in estimating rare event probabilities, we find an effective theory for the excess kurtosis evolving over a shoal.
The Sidetracking Configuration Optimization and Detailed Scheme Design in a Oilfield Middle East
Authors: Nie Zhen , Shi Shuzhe , Du Zhengxue , Huang Xueqin , Wu Bohong , Wang Chunpeng , Zhang Yanna
Published: September 2023

Sidetracking horizontal wells is a significant technology in the oilfield development industry. It can be applied in repairing abandoned wells, low production wells, casing damaged wells, and severe water breakthrough wells. This technology has advantages for the developed reservoir, for example, re-boost the production of the existing shut-off wells, prolonging the life of oil wells, and achieving the purpose of reducing costs and increasing efficiency. The recovery rate of the A oilfield main reservoir is about 10%, the producing water has fully broken through in A oilfield. The water cut in some areas is higher than 80%, and more than 55% of the production wells have a water cut higher than 70%. The overall water cut rises rapidly, which makes water control difficult.

Therefore, the sidetracking horizontal well technology is urgently needed in this A oilfield middle east, and a well-designed sidetrack configuration needs to be studied for the purpose of reducing water cut and re-boost oil production. In this work, reserves of each candidate layer of the reservoir have been evaluated to determine the best layer. Then, investigate the kick-off point locations and the specific sidetracking point locations to better design the sidetrack parameters, which is the most crucial section for oil production improvement and cost efficiency. One sidetracking well case is selected by applying the optimized parameters, and the detailed sidetrack plan was also designed, the numerical simulation was done to predict the production performance and complete the economic evaluation.

This work can add value to re-boosting the oil production of the poor-performance wells in A oilfield, and also provides theoretical support for future sidetrack drilling wells in other oilfields Middle East.
Ultrasonic Well Integrity Logging Using Phased Array Technology
Authors: Johansen Tonni Franke , Buschmann Philip Erik , Røsberg Knut Marius , Diez Anja , Viggen Erlend Magnus
Published: September 2023

Ultrasonic well integrity logging is an important and common procedure for well completion and plug-and-abandonment operations. Typical logging tools employ single-element ultrasound transducers. In medical ultrasound imaging, however, more flexible phased arrays are the standard. This paper presents a first set of experimental results obtained with up to two linear 32-element phased arrays that are specifically designed for plug-and-abandonment operations in terms of their centre frequency. The experiments encompass pulse-echo and pitch-catch studies for different incidence angles and aperture sizes on plates and pipes with wall thickness as encountered in the offshore industry. The pulse-echo experiment is backed up by simulations, and shows that effect of the incidence angle on the pipe resonance’s frequency and strength is weak and more strong, respectively, and that the effect depends on the frequency response and directivity of the transducer. The pitch-catch experiment demonstrates the importance of carefully choosing the right angle of incidence to excite the intended wave modes.
Well Integrity Operations Experience Transfer Using Long Short-Term Memory (LSTM) Recurrent Neural Network
Authors: Semwogerere David , Pavlov Alexey , Sangesland Sigbjørn
Published: September 2023

Well integrity is critical throughout the lifecycle of a well. During well operations especially for new fields, inexperienced engineers encounter many well integrity challenges which require a fast-learning curve. This ranges from downhole problems such as lost circulation and kicks to equipment damage due to lack of experience during installation, etc. The success of well integrity as a criterion in wells operations therefore heavily depends in the experience of the humans involved. For offshore operations this lack of experience can translate into very expensive consequences in case of loss of well integrity. Damaged equipment, lost time, injury to personnel and contamination of the environment are some of the consequences of blowouts. In oil and gas well construction and service operations petabytes of data in form of logs, reports and other sensor data are generated which contain vast information. By using machine learning and other statistical data analytic techniques on the data, insights on well integrity can be generated.

While yet most well data analytics focuses more on the numerical indicators of well integrity for example pressure, temperature, and casing thickness, text in well integrity reports gives elaborate description on the nature, context and experience applied in well integrity problems encountered. It’s important to transfer this experience in a faster way to the next well operation without laboring through the unstructured data repositories by using advanced text analysis. This smoothens the learning curve for the engineers, saving costs and improving well integrity.

In this paper, a language model for experience transfer using the Long Short-Term Memory (LSTM) recurrent neural network that reads well integrity problem description text from a report and classifies it into a root cause is proposed. It is benchmarked against the state-of the art Bidirectional Encoder Representation from Transformer (BERT) model. The pitfalls of current state of the art language models in processing datasets of oil and gas well operations text are discussed using the Volve end of well reports as an example.