bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheological and Mechanical Properties of Rock-Based Geopolymers Developed for Well Abandonment: Effect of Chemical Admixtures at Elevated Temperatures
Authors: Chamssine Fawzi , Khalifeh Mahmoud , Saasen Arild
Published: October 2022

Examination of alternative cementitious material cured under elevated temperatures is essential to qualify their applicability in field operations. Geopolymers rise as an alternative for Ordinary Portland Cement in oil and gas applications due to its lower carbon footprint and raw material availability. Using chemical admixtures is crucial to engineer geopolymer material for displacement and to maintain well integrity and zonal isolation under elevated temperature and pressure. In this study, the rheological and mechanical properties of rock-based geopolymers, developed for utilization at elevated temperatures, have been examined with the addition of chemical admixtures to test their performance under operational conditions. Neat Class-G cement, by Dyckerhoff, was used as a reference sample for comparison at elevated conditions. The effect of Zn2+, K+, Na+ and Ca2+ species was examined on geopolymer properties. Samples were cured for 1,3, and 7 days at bottomhole static conditions. Properties examined in this study include workability, fluid loss, and viscosity for slurry properties. On the other hand, sonic strength, uniaxial compressive strength, and tensile strength were examined throughout the curing periods. The obtained results exhibited an enhancement in overall properties with an increase in workability and overall strength of the material while considering the poisoning effects from the usage of Zn2+ species. It was concluded that the combination of Na+ and Ca2+compensated the poisoning effect foreseen by the addition of Zn2+ species in geopolymer systems.
The Influence of Edge Treatment on Fatigue Behavior of Thermal Cut Edges
Authors: Grimm Jan-Hendrik , Diniz e Castro Juliana , von Selle Hubertus , Braun Moritz , von Bock und Polach Franz , Ehlers Sören , Hensel Jonas , Hesse Ann-Christin , Dilger Klaus
Published: October 2022

Thermal cut edges can be found in most maritime structures, e.g. in window openings or hatch corners on ships. It is very common to treat free plate edges by grinding or sandblasting due to fatigue and coating requirements. The aim of this study is to review the fatigue behavior of typical treatment methods. Within this study several fatigue tests are performed to outline the influence of treatment methods used for different steel grades, plate thicknesses and cutting processes. Especially the influence of the local edge geometry caused by treatment like grinding or milling is not covered by fatigue rules and guidelines like Eurocode or IIW. Also, the influence of yield strength is not considered by these regulations. Only in shipbuilding a fatigue bonus for high strength steels is given. However, these rules are based on older data and an update is requested by ship building industries. For the investigation shipyards and partners from other industries produced a big number of specimens for fatigue tests. Steel grades are from S235 to S460. Surface roughness as well as local treatment geometry are well documented. In addition, hardness as well as residual stress measurements were performed. Finally fatigue tests were done. Overall goal of the study is to present applicable FAT curves to be used for fatigue assessment.
Ice Basin Tests for Ice-Induced Vibrations of Offshore Structures in the SHIVER Project
Authors: Hendrikse Hayo , Hammer Tim C. , Owen Cody C. , van den Berg Marnix , van Beek Kees , Polojärvi Arttu , Puolakka Otto , Willems Tom
Published: October 2022

With the recent surge in development of offshore wind in the Baltic Sea, Bohai Sea and other ice-prone regions, a need has arisen for new basin tests to qualify the interaction between offshore wind turbines and sea ice. To this end, a series of model tests was performed at the Aalto ice basin as part of the SHIVER project. The tests were aimed at modeling the dynamic interaction between flexible, vertically-sided structures and ice failing in crushing. A real-time hybrid test setup was used which combines numerical and physical components to model the structure. This novel test setup enabled the testing of a wide range of structure types, including existing full-scale structures for which ice-induced vibrations have been documented, and a series of single-degree-of-freedom oscillators to obtain a better understanding of the fundamental processes during dynamic ice-structure interaction. The tests were primarily focused on the dynamic behavior of support structures for offshore wind turbines under ice crushing loads. First results of the campaign show that the combination of the use of cold model ice and not scaling time and deflection of the structure can yield representative ice-structure interaction in the basin. This is demonstrated with experiments during which a scaled model of the Norströmsgrund lighthouse and Molikpaq caisson were used. The offshore wind turbine tests resulted in multi-modal interaction which can be shown to be relevant for the design of the support structure. The dataset has been made publicly available for further analysis.
Physic Based Approach for Solid Transport in Deviated and Horizontal Well
Authors: Purwandari Sartika D. , Lund Bjørnar , Hovda Sigve
Published: October 2022

Cuttings transport is one significant challenge during drilling especially in high deviated and horizontal wellbores. At high degree of inclination, cutting particles may settle to the low side of the wellbore. Below a threshold flow rate, the fluid forces on a particle at the wall will be insufficient to re-entrain the particle and a moving bed of particles will accumulate. The removal of cuttings bed could be difficult once it is formed. Cuttings bed accumulation can create operational problems with respect to drill time and drill cost. Therefore, a good strategy is needed to combine drilling parameters that influence the cuttings transport in efficient and economical ways.

In this study, bed shear stress from cuttings transport experiments in a 10 m annular flow loop is estimated using three different methods. The bed shear stress predicted using bedload transport model differed by less than 5% from the average wall shear stress calculated from experimental values for pressure drop and bed hold up. Calculation using a friction factor correlation gave significantly lower values than obtained with the other two methods. Inclination appears to have larger effect on particle transport properties to water based mud (WBM) than oil based mud (OBM) at low flow rate.
Development of Low Carbon Dioxide Intensive Rock-Based Geopolymers for Well Cementing Applications – One-Part Geopolymer
Authors: Omran Mohamed , Khalifeh Mahmoud
Published: October 2022

This study aims to reveal the development of short-term mechanical and chemical properties of one-part geopolymers for utilization in well construction and well abandonment activities. These geopolymers are heat-cured rock-based one-part products. The rock-based geopolymer precursor was activated by solid powders of potassium silicate. To enhance the setting time and early strength development of the geopolymers, a small portion of alkaline solution (KOH) was used as an accelerator. Properties of the slurry were characterized through investigating mechanical and chemical techniques. Sonic strength and uniaxial compressive strength of the specimens were studied. In addition, the mineralogy of the solidified samples was analyzed through crystallography to better understand their microstructure. Moderate compressive strength of ca. 7 to 10 MPa within 24 hours and up to 7 days were developed for the investigated one-part geopolymer mixes that have been activated by a solid activator with a modulus ratio of 2.4. One-part geopolymers not only could provide user-friendly slurries, but also can facilitate their commercialization and large-scale application in petroleum and civil engineering sectors.
A Single Cavitation Bubble Induced Damage
Authors: Sagar Hemant , el Moctar Ould
Published: October 2022

In the present work, we experimentally and numerically investigated the dynamics of a millimeter-sized cavitation bubble generated nearby a solid surface. In experiments, bubbles are induced by a focused Nd-YAG laser generating plasma. A specimen of the commercially pure aluminum surface was placed nearby a bubble at varying relative wall distances. Here, the relative wall distance is a ratio of the distance between the bubble center and specimen surface, and the maximum radius of the bubble. In experiments, we captured the bubble’s dynamics by back illumination method using a highspeed camera. Damage obtained was characterized by an optical microscope and profilometer. The surface profiles and damage patterns quantified the damage characteristics. The three-dimensional flow was captured numerically by solving the Navier-Stokes equations in an Euler-Euler approach with barotropic equations of state. The computations were performed assuming both water and vapor as compressible phases. The dynamics of a single bubble obtained in computations were compared with the experiments for shapes and collapsing times. The computed characteristics of flow around a bubble near the solid surface, e.g. impact velocities and pressures were also discussed. Additionally, the dynamics of a microscopic bubble collapse near the surface was also investigated to compute collapse-induced wall shear rate and flow around the collapsing bubble. The results of numerical simulations were compared with the existing experimental data. The comparisons showed, a good qualitative and quantitative agreement. Overall, the numerical method well reflected the dynamics bubble up to three collapses and resolved flow around the bubble. The statistical data of pits obtained are also useful in deriving loads induced by a single bubble collapse. Overall, this work extensively comprises the single cavitation bubble dynamics and induced damage. This article summarizes the investigations of Sagar (2018) and Sagar & el Moctar (2020).
The Effect of the Height of the Regular Wave on Seabed Liquefaction
Authors: Kazimierowicz-Frankowska Krystyna , Kulczykowski Marek , Majewski Dawid , Mierczyński Jacek , Smyczyński Marcin
Published: October 2022

This paper presents the results of an experimental study of seabed liquefaction under progressive waves. Firstly, during preliminary tests, the physical and mechanical parameters of the soil selected as the subgrade material were determined. A series of monotonic triaxial shear tests were carried out at different initial void ratios and mean effective stresses. The susceptibility of soil samples to liquefaction was estimated. The results were used to design experiments in a wave flume. Their main purpose was to study the effect of wave height on wave-induced liquefaction. The experiments were carried out in a wave flume that is 64.1 m long, 0.6 m wide, and 1.4 m high, in a specially built experimental stand located 5.0 m from the wave generator below the flume bottom. Wave propagation was conducted over constant water depth which was equal h = 0.5 m. The wave surface elevation was measured by resistance type wave gauges. The pore-water pressure was measured by transducers located in the middle of the sediment pit, at four different soil depths. Parametric studies were carried out to investigate the influence of wave height on the liquefaction process. The results of experiments shown that pressure buildup is a strong function of the wave height and increases with increasing its value.
Numerical Research on the Resistance Performance of a Ship Under Pack Ice Conditions
Authors: Tang Xiang-Jie , Zou Ming , Zou Lu , Zou Zao-Jian
Published: October 2022

For a ship navigating in waterways covered by pack ices, the ice load including resistance prediction is a critical issue at the design stage, which is directly related to the safety of the ship, and it is of great significance to the research of ship propulsion efficiency. This paper adopts a coupled numerical method to simulate the ship-ice interaction under pack-ice conditions: the fluid flow is solved by Computational Fluid Dynamics (CFD) method, while the governing equations of ice is solved and the ship-ice and ice-ice collisions are simulated by the Discrete Element Method (DEM). In addition, this method is also capable of building a random pack ice field. The DEM-based ice particles are established according to the model test conditions and the parameters in a published reference. The comparison between the present results with the model test data and the results in another study by the Finite Element Method (FEM) under the same conditions shows that the numerical model established in this paper has higher accuracy in predicting ice resistance. On this basis, the influence of ship speed on the ice resistance under different concentrations of pack ice is investigated.
Dynamic Simulation of an Offshore Aquaculture Structure Under Combined Wave and Current Conditions
Authors: Cheng Hui , Ong Muk Chen , Li Lin
Published: October 2022

The reliable design of offshore aquaculture structure (OAS) for fish farming in the open ocean is vital to the marine aquaculture industry in the future. However, the lack of easy-to-access numerical tools for the dynamic analysis of OAS challenges the development of marine aquaculture. This article presents a newly developed numerical library under an open-source, finite-element analysis code, Code_Aster, enabling the dynamic analysis of OAS. A numerical model of OAS is first developed using the present numerical library, and then validated against experiments. The validation shows a good agreement in terms of structural motions and tensions in mooring lines. After that, the dynamic responses of this model are analyzed under irregular waves and current conditions from field measurements on an offshore fish farm site. The results indicate that a negative mean pitch angle will occur when the current velocity is large.
Analysis of Welding Influences on Extruded Aluminum Panel Buckling
Authors: Wang Xintong , Amdahl Jørgen
Published: October 2022

Extruded aluminum panels are increasingly used in the marine industry, owing to the high strength-to-weight ratio and less welding paths. However, sensitivity to the welding makes it difficult to predict the structural resistance in the design stage with existed analytical formulations. It is therefore necessary to resort to numerical investigation. In this study, a previously developed numerical model that takes into account the welding effects is used to simulate the buckling behavior of extruded aluminum panels. Buckling of panels with two stiffener types, open (L-shaped) and closed (trapezoid), are investigated. The ultimate load sensitivity with respect to welding effects including different patterns, imperfection fields and amplitudes are discussed. Through comparison with design rules, the applicability of existed closed form methods is discussed. Regarding the ultimate load prediction of extruded aluminum panels, suggestions related to imperfection field introduction are addressed. The simulations can be further used as a foundation for development of improved analytical formulations.
Three-Dimensional Finite Element Models of a Flexible Pipe Interlocked Carcass Under Bending
Authors: Geremias Toni Fernando , de Arruda Martins Clóvis , Provasi Rodrigo
Published: October 2022

The main function of an interlocked carcass is to provide radial stiffness to the flexible pipe, preventing failure modes such as collapse and crushing. The carcass is designed to withstand a specified collapse pressure while attaining minimum flexibility levels, the main parameter for its functionality. This combination of both high radial stiffness and flexibility arises from the interlocked profile and its associated clearances, which are also the main responsible for the highly nonlinear mechanical behavior of the carcass due to the wide range of self-contacts possibilities. In this way, given the complexities of modeling the interlocked carcass considering its exact geometry, most approaches available in the literature adopted simplifying hypotheses, the equivalent orthotropic layer being the most common one. However, with that, important effects from the interlocking are disregarded, such as stiffness variations and stress concentrations. For collapse problems in specific, three-dimensional carcass finite element models have already been developed, but there is nothing similar in the literature for bending loadings. Therefore, the present work proposes two full three-dimensional finite element models of an interlocked carcass, the last one also containing an inner polymeric sheath. For comparison, a third model was also developed, containing just a polymeric sheath. All models were meshed with second-order solid isoparametric finite elements, considering, therefore, all details of the interlocked profile and the self-contacts possibilities. The results are then presented in detail and comparison are carried out, allowing the evaluation of the interlocking effects during bending and how it influences the mechanical behavior of the carcass.
Application of Machine Learning for the Generation of Tailored Wave Sequences
Authors: Klein Marco , Stender Merten , Wedler Mathies , Ehlers Svenja , Hartmann Moritz , Desmars Nicolas , Pick Marc-André , Seifried Robert , Hoffmann Norbert
Published: October 2022

This paper explores the applicability of machine learning techniques for the generation of tailored wave sequences. For this purpose, a fully convolutional neural network was implemented for relating the target wave sequence at the target location in time domain to the respective wave sequence at the wave board. The synthetic training and validation data were acquired by applying the high-order spectral (HOS) method. The HOS method is a very accurate method for modeling non-linear wave propagation and its numerical efficiency allows the generation of large synthetic data sets. The training data featured wave groups of short duration based on JONSWAP spectra. The sea state parameters wave steepness, wave period and enhancement factor were systematically varied. At the end of the training process, the trained models were able to predict the wave sequences at the wave board based on the time series of the target wave defined for a specific target location in the wave tank. The accuracy of the trained models were evaluated by means of unseen validation data. In addition, the predictive accuracy of the trained models was compared with the classical linear transformation approach.
Assessment of Sea State Estimation With Convolutional Neural Networks Based on the Motion of a Moored FPSO Subjected to High-Frequency Wave Excitation
Authors: Bisinotto Gustavo A. , Cotrim Lucas P. , G. Cozman Fabio , A. Tannuri Eduardo
Published: October 2022

Motion-based wave inference has been extensively discussed over the past years to estimate sea state parameters from the measured motions of a vessel. Most of those methods rely on the linearity assumption between waves and ship response and present a limitation related to high-frequency waves, whose first-order excitation is mostly filtered by the vessel.

In a previous study in this project, the motion of a spread-moored FPSO platform, associated with a dataset of environmental conditions, was used to train convolutional neural networks models so as to estimate sea state parameters, displaying good results, even for high-frequency waves. This paper further explores this supervised learning inference method, focusing on the estimation of unimodal high-frequency waves along with an evaluation of particular features related to the approach.

The analysis is performed by training estimation models under different circumstances. First, models are obtained from the simulated platform response out of a dataset with synthetic sea state parameters, that are uniformly distributed. Then, a second dataset of metocean conditions, with unimodal waves observed at a Brazilian Offshore Basin, is considered to verify the behavior of the models with data that have different distributions of wave parameters. Next, the input time series are filtered to separate first-order response and slow drift motion, allowing the derivation of distinct models and the determination of the contribution of each motion component to the estimation. Finally, a comparison among the outcomes of the approach based on neural networks evaluated under those conditions and the results obtained by the traditional Bayesian modeling is carried out, to assess the performance presented by the proposed models and their applicability to face one of the classical issues on motion-based wave inference.
Estimation of Ocean’s Currents Acting on a Turret-Moored FPSO Using Machine Learning
Authors: Lavra Dias Pedro Felipe , Aoun Tannuri Eduardo , Costa Anna Helena Reali , Caurin Glauco Augusto De Paula , Bisinotto Gustavo Alencar
Published: October 2022

Ocean’s surface currents, although not easily measured by ship’s sensors, affect the movements of any vessel at sea. Especially when dealing with Turret-Moored FPSOs, due to its weathervaning property, there is an intrinsic relationship between the Platform’s motion and environmental conditions. In this sense, we propose using Machine Learning regression algorithms to estimate the surface currents that affect a Turret-Moored FPSO based on data commonly measured on board. These data are expressed by wind speed and direction (measured via anemometer and anemoscope); Platform’s heading (obtained by GPS or Magnetic/Gyro compass); and FPSO’s oscillating motion that is given by the standard deviation of pitch, roll, heave and yaw (measured by MRU sensors and considered as proxy variables of first-order waves’ forces). The prior dataset was composed by local environmental conditions at a specific offshore Basin (in Brazil), observed over ten years at a 3-hour time stamp. This corresponds to approximately 30,000 conditions, each used as input into numerical simulations for a partially loaded FPSO (length between perpendiculars: 257 m, beam: 52 m, draught: 15.6 m). Simulation results provide the Platform’s motion time-series used to generate the final dataset previously mentioned. After dividing this final dataset for train/validation/test into 70/20/10 proportion, a K-means algorithm was fitted to the training data, which grouped it into 3 clusters in which, for each one, 2 ‘specialized’ MultiLayer Perceptron (MLP) Neural Network (one for current’s velocity and another for direction) were implemented for. The mean measured value of current’s velocity of the test dataset is 0.33 m/s, whereas the mean prediction with the method proposed is 0.32 m/s. In current’s direction, the mean measured value is 220°, while the mean prediction is 225°.
Experimental Study of Displacement Flows in a Vertical Eccentric Annulus
Authors: Zhang Ruizi , Jung Heeseok , Renteria Alondra , Frigaard Ian
Published: October 2022

Primary cementing is an essential part in constructing an oil or gas well. Leakage occurs due to a poor seal of the cement in the annulus, which may be caused either during or after placement. Key in controlling leakage is to ensure the integrity of the surface casing, which is primarily vertical. This paper addresses the underlying fluid mechanics that may affect cement placement in vertical casings. We present results of miscible Newtonian displacement flow experiments carried out in a dimensionally scaled laboratory set-up. The experimental set-up has been described in detail (Renteria and Frigaard, J. Fluid Mech, 905, 2020) [1], and used previously in horizontal orientation. We use the same annular flow loop but in vertical configuration. The effects of density difference, viscosity ratio and eccentricity of the annulus have been studied. We find that the eccentricity is always dominant in affecting the displacement, and the narrow side view gives us more detail of residual layers. The buoyancy number and Reynolds number are key factors that affect the stability of the whole process. Large buoyancy number and small Reynolds number lead to stable interface and less dispersion. The residual layer at the narrow side can be removed out to a degree, under significant density difference and at lower flow rates. However, the viscosity ratio appears to play only a secondary role in vertical displacement flows. Our future directions will use the present experiments for comparison with 2D and 3D models, and we then aim to extend the experimental program to shear-thinning non-Newtonian fluids.
Order Reduction of a Transient Model of Viscous Pressure Loss Gradient in Laminar Flow for Non-Newtonian Fluid Flowing in Circular Pipes
Authors: Cayeux Eric
Published: October 2022

When circulating non-Newtonian fluids in pipes, the flowrate may vary because of inherent fluctuations of the mudpumps, swab and surge due to axial displacement of the drill-string, variations caused by a positive displacement motor (PDM) while drilling. Steady state estimations of viscous pressure loss gradients are not anymore valid under accelerated flowrate conditions. It is possible to precisely calculate the dynamic response in transient conditions, but such numerical calculations tend to be slow and incompatible with real-time constraints when used during a drilling operation. It is therefore desirable to derive a reduced order model that is fast, yet accurate.

Numerical schemes utilized to estimate viscous pressure gradients under fluctuating flowrate conditions need to solve a larger problem than just the evolution of the pressure drop. Indeed, they need to calculate the whole fluid velocity field in a cross-section. However, when only the pressure gradient is of interest, a reduced order model would be sufficient. To find a possible reduced order dynamic model that mimics the dynamic response of the advanced numerical model, the method of sparse identification of non-linear dynamic (SINDy) is used on synthetic datasets generated using the advanced model. The SINDy method allows to discover the non-linear ordinary differential equation (ODE) that models precisely the dynamic that is observable from the synthetic dataset. Nevertheless, the calibrated parameters of the discovered non-linear ODE are only valid for specific a fluid density and rheological behavior. Therefore, the method is applied multiple times on various combinations of fluid densities and fluid rheological behavior parameters, and an interpolator function is generated. The interpolator is built using radial basis functions. The interpolator can then be used to find the correct parameters of the non-linear ODE as a function of the current rheological behavior of the fluid that flows in a pipe section and the dynamic pressure gradients can be estimated as a function of the fluctuating flowrate by solving a simple ODE, for example by using the Runge-Kutta method.

The reduced order model is very efficient, yet accurate, and can therefore be used in a real-time context. This is possible because many high-quality simulations are made upfront and used by machine learning methods (SINDy and radial basis functions) to discover a non-linear ODE and its associated parameter interpolator. The application of these two machine learning methods results in a solution that has good generalization capabilities. The reason for providing good estimation of the dynamic response outside the domain of the training examples is due to the ability of the SINDy method to extract ODEs that represent a good approximation of the real physical behavior of the system.
Modified Environmental Contours Approach for Long-Term Extreme Response Prediction of Marine Risers
Authors: Miao Qingqing , Low Ying Min
Published: October 2022

Accurate prediction of the long-term extreme response of offshore structures is challenging for complex systems under varying marine environments. The long-term uncertainties come from the varying environmental parameters such as significant wave height and spectral peak period, while the short-term uncertainties are due to the random wave amplitudes and phases. The conventional environmental contour lines method provides a fast approximate way to estimate the extreme response by performing simulations along the environmental contours. However, the method is unconservative if the short-term uncertainties are neglected. Current methods to account for the short-term uncertainties are approximate and require an empirical parameter that is case-dependent. This paper presents a modified environmental contour line approach, based on introducing an additional multiplicative random variable to account for the short-term variability. It is efficient as additional simulations are performed only in the critical direction determined by the conventional approach. The method is first tested on a single-degree-of-freedom model representing the surge motion of a floating offshore structure. Subsequently, it is applied on the top riser stress of a catenary moored floating production system. Monte Carlo simulation is impractical here as a validation tool due to the extensive simulation time. Hence, the results are compared with subset simulation, which is known to be asymptotically unbiased.
Importance of the Inertial Components in Modal State Covariances
Authors: Geuzaine Margaux , Fenerci Aksel , Øiseth Ole , Denoël Vincent
Published: October 2022

The modal state responses of very large floating structures subjected to sea waves are addressed in this paper. Semi-analytical approximations for their second order statistics are first provided. They are derived by using the multiple timescale spectral analysis and they aim at calculating the variances of the nodal state responses much more rapidly than with the traditional time and frequency domain methods. Based on these approximate formulas, such expressions are developed for the correlation coefficients in this paper. They allow to understand in which cases the covariances between two modal state responses are significant and cannot legitimately be neglected. They are for instance important to consider when the natural frequencies of the corresponding modes are close to one another or when their shapes are similar. The accuracy of the proposed expressions is then verified on a realistic example inspired by an actual floating pontoon bridge. The results are shown to be less precise, although still acceptable, when the peak frequency of the loading and the natural frequencies of the structure are of the same order of magnitude. This is to be expected since the validity of the proposed approximations is conditioned upon the separation of these timescales.
A Reliable Multilevel Method for Simulation-Based Load Determination on Deck Cell Guides
Authors: Detlefsen Ole , Reiner Carl , Abdel-Maksoud Moustafa
Published: October 2022

The loss of containers at sea endangers ships and crew and causes environmental pollution. Within the Joint Research Project RetroLadung, weight-optimized container cell guides with integrated motion sensors and AI-based decision support (DSS) are developed as a technical solution for increased safety in marine transportation. Therefore, the authors developed an efficient simulation-based approach to determine the motion-induced loads acting on the containers. For the validation of the applied numerical methods, model tests have been performed in the towing tank operated by the Institute for Fluid Dynamics and Ship Theory (FDS). The paper describes the applied numerical methods for the load determination and first preliminary results from the ongoing experimental validation work. Finally, the application of the developed method is demonstrated by calculating the loads for the structural design and optimization of the cell guides for a towed container barge operated at the US east coast.
Experimental Investigation of Methane Absorption for Offshore Gas Influx Management
Authors: Mahmud Shahriar , Chen Yuanhang
Published: October 2022

During oil and gas drilling operations, formation gas (mostly methane) may enter the wellbore annulus or the drilling riser. This gas influx may get absorbed into the surrounding mud causing complexity for kick detection. Absorption mass transfer experiments of methane into four different fluid systems were performed. The continuous phase for all these fluids was Internal olefins (IO) which is widely used within the drilling industry as a base fluid. Two of the fluids were emulsions (Water as the second phase) and the other fluid comprised of Internal Olefins with Suspentone. Ultrahigh purity methane was used as the absorbing gas phase. The system pressure was kept at 100psi (0.689MPa) with a superficial velocity of 0.009 m/s. Volumetric mass transfer coefficients (kLa) from these experiments were individually determined using a bubble column with an internal diameter of 0.0381m. The volume of the liquid was kept constant during each of the tests. It was observed that methane in pure IO has the highest kLa value while its value is the lowest when it was flown through the IO/Water/suspentone fluid system. The reduction of kLa values was attributed to the increase of viscosity of the fluid and reduction of interfacial area of the IO due to the addition of water.
On the Influence of Hull-Shape on the Location of Roll-Axis
Authors: Johnsen Lars , Krüger Stefan
Published: October 2022

The location of the average roll axis of a ship in water is around the combined center of mass of the ship itself and the so-called added mass of the fluid surrounding it. The location of this combined center is often assumed to be somewhere in the middle between the waterline and the center of mass of the ship, as e.g. in the interim guidelines of the second generation intact stability criteria. These assumptions are approximately valid for deeply submerged ships with low B/T ratios and small bilge radius, but not necessarily for the hull forms of fast, modern roro- or ropax-ferries or other ship types with equal properties. For these ships, the center of added mass and thus the average roll-axis can be located way above the waterline, leading to different accelerations and loads on cargo and personnel on the ship. The paper shows systematically how section wise added mass behaves for certain trends in frame shape and compares numerical results based on strip theory for the location of the roll axis of two different ships with full-scale measurements.
Dynamic Reservoir Behaviour and Production Due to Periodic Supply of Wind Power
Authors: Bergmo Per E. S. , Holt Torleif , Skogestad Jan Ole
Published: October 2022

Wind power can replace power from gas turbines and thus reduce the CO2 emissions related to oil production. However, a main challenge with wind power is the variability in power production due to weather variations. The water injection pumps are often major power consuming units. The water pumps were therefore identified as possible non-critical loads in an isolated power system with variable power supply. The power to a non-critical load can be varied and even stopped depending on the power supply. The objective of the present work was to study how variable water injection rates affects oil production.

Using simulated wind power curves, water injection profiles for a model oil field were constructed. Reservoir simulations show that the oil production is almost insensitive to variable injection rates if the injected volumes were the same. Lower injected rates and volumes resulted in lower oil production. This was most pronounced in the plateau phase of the production, but later the differences become gradually smaller. Thus, reducing the water injection volumes with 30 % decreased the total oil recovery by less than 5 % after 28 years.

If constant water injection rates are needed thermal power can supply wind power. This will increase the CO2 emissions. However, if wind power not used by the water injection pumps can be utilised for other unit operations significant reductions in CO2 emission can still be obtained.
Investigation of Eccentricity on Cuttings Transport With Oil-Based Drilling Fluids
Authors: Ytrehus Jan David , Lund Bjørnar , Taghipour Ali , Pedrosa Camilo , 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 drilled and completed in an optimal manner with respect to drill time, cost, risk and functionality. Most cuttings transport and hydraulic models are developed based on tests with model fluids and often in small diameter test sections. Hole cleaning and hydraulics with field fluids are different than the properties considered with most model fluids. Furthermore, results from small diameter tests with model fluids may not always be relevant for, nor scalable to, field applications due to time, length, and other scales. Hence, there is a need for studies in controlled laboratory environments with various field application designed drilling fluids to improve engineering models and practices.

This paper presents results from laboratory studies with geometries that permits comparison with field operations when oil-based drilling fluids from Norwegian offshore operations are applied. The oil-based drilling fluids have densities and viscosities within the relevant shear rate range applied during drilling operations and in the tests.

The experiments have been performed in a flow loop that consists of a 10 meters long test section with 2″ OD freely rotating steel drill string inside a 4″ ID wellbore made of cement. Sand particles were injected while circulating the drilling fluids through the test section. Experiments were performed at different wellbore inclinations. The applied flow loop dimensions are designed so that the results are scalable to field applications; especially for the 12,25″ and 8,5″ sections. The selected setup is designed to provide correct shear rate ranges and equal Reynolds number to the field application when the same fluids are applied.

Results show that hole cleaning is significantly better in fully eccentric annulus compared to 50% degree of eccentricity. It is also observed in horizontal sections that for the same eccentricity a reduction in fluid viscosity can provide improved cuttings transport efficiency when the drill string is not rotated.
Experimental Study on Local Scour of Triangular Artificial Reef
Authors: Zhao Fenfang , Xu Shiji , Yang Mingda , Tang Yanli , Huang Liuyi , Fang Guangjie
Published: October 2022

Artificial reef (AR) is one of the key methods to restore the offshore fishery resources and ecological environment. To secure its ecological effects, it is of great significance to study the possible instability of the AR, like sinking and reversing caused by change of the submarine topography, water flow and sediment movement. In the present study, the model experiments of the triangular ARs on the mechanism of the local scour are carried out. The prototype of the triangular ARs is used in Xiaoshidao National Marine Ranching in Weihai, Shandong Province. The effects of the heights, the bottom angles and the length of the bottom of the triangular ARs on the scour volume and the equilibrium scour depth are investigated. The results show that for the ARs with the same heights, the scour depth increases with the increasing bottom angles. For the ARs with the same bottom angles, the scour depth increases with the increasing heights. A generalized linear model is used to derive the effect of the bottom angle of the triangular AR on the scour depth. The research results can provide references for the design optimization and deployment of the ARs. This proposed study will provide theoretical support and practical guidance for the optimized engineering design and construction of the ARs.
Nonlinear Reconstruction and Prediction of Regular Waves
Authors: Desmars Nicolas , Hartmann Moritz , Behrendt Jasper , Klein Marco , Hoffmann Norbert
Published: October 2022

A method for the reconstruction of nonlinear ocean surfaces is presented and applied to regular waves. From random samples of surface elevation, the method reconstructs the nonlinear features of the observed waves by means of the High-Order Spectral approach. The reconstructed surface is then propagated to provide a prediction at a later time. The agreement of the reconstructed and predicted surfaces with the reference one is quantified for a wide range of wave steepness. In each case, the accuracy of the surface elevation and surface velocity potential is evaluated for the first-, second- and third-orders of nonlinearity, while the reference surface corresponds to a fourth-order solution. This way, the improvement of the solution pertaining to each order of nonlinearity can be easily identified. The results show that the grid-based method is able to correctly reconstruct highly nonlinear regular waves, providing an accurate initial solution for the surface propagation. Due to the effect of the nonlinear dispersion, it is further shown that the third order of nonlinearity is necessary to obtain an accurate reconstruction/prediction of steep waves.
Hydrodynamic Performance of 3-D Hydrofoil Under the Free Surface Based on Taylor Expansion Boundary Element Method
Authors: Huang Jianghao , Yao Chaobang , Feng Dakui , Sun Xiaoshuai
Published: October 2022

The boundary element method is widely used in solving potential flow problems. This paper uses Taylor expansion boundary element method (TEBEM) to analyze hydrodynamic characteristics of hydrofoils under the free surface, which mainly applies the Taylor expansion to the dipole strength of the boundary integral equation (BIE), and then keeps the first-order derivatives, finally takes the two tangential derivatives with respect to the field points on the boundary to form the closed equations. Combine the equations then solve the potential and its tangential derivatives. The method is applied to three dimensional hydrofoil of the asymmetric NACA4412 profile moving beneath the free surface with constant speed. The free surface condition is linearized in terms of the Double-Body method. Upstream waves are prevented by the use of a one-sided, upstream, finite difference operator for the free surface condition. After solving the doublets on the foil and sources on the free surface, the numerical results of pressure, lift and resistance coefficients and also wave profiles can then be evaluated for different Froude numbers and depths of submergence to demonstrate the influence of free surface and aspect ratio effects on performance of the hydrofoil. Compared to traditional constant panel method (CPM) method, the TEBEM method can extremely improve the accuracy of the tangential derivatives on the non-smooth body surface.
Axial Stiffness and Expansion Behaviour of a Flexible Flowline for Various Extents of Axial Restraint When Subject to Pressure and Thermal Loads
Authors: Tørnes Knut , Nestor Ruairi , Thuen Kristian , Picksley John , Connaire Adrian , Bakken Bård Owe
Published: October 2022

The conditions to which flexible pipes are being exposed are becoming increasingly severe. In particular, flexible flowlines that are fully or partially restrained by back fill or rock cover can become exposed to large axial compression forces under pressure and temperature loading.

A high True axial compression force may lead to a radial outward displacement of the tensile armour which could eventually exceed the allowable limits of API spec 17J if the axial force exceeds a critical level.

Furthermore, when the net Effective axial compressive pipe force exceeds a critical level, the pipe may undergo global buckling either upwards (upheaval buckling) or laterally, which needs to be addressed in detail at design stage, typically by using global finite element (FE) simulations in which equivalent mechanical properties are applied to pipe beam elements to capture the overall behaviour of the flexible pipe.

The overall global mechanical properties of a flexible pipe, such as axial stiffness and thermal and pressure expansion coefficients, which are important parameters in capturing the global buckling behaviour, are dependent on the local behaviour of the various flexible pipe layers.

In this paper an advanced local FE model developed using the industry standard numerical FE tool, Abaqus, together with the assessment methodology is presented in order to study local layer interactions and their influence on the equivalent axial mechanical properties.
A Numerical Investigation on Wave Spectrum Identification and Transformation From Deep to Shallow Waters for the Coastal and Offshore Installations
Authors: Wang Weizhi , Kamath Arun , Pákozdi Csaba , Bihs Hans
Published: October 2022

Nowadays, many aquaculture and marine renewable energy facilities are developed at the shallow and intermediate water areas close to the bathymetric transition to the deep seas. The transition from deep to shallow water has a strong influence on the wave spectrum shape. Consequently, it is challenging to choose the appropriate spectrum for the sites of interest. In this study, a fully nonlinear potential flow (FNPF) model is used to investigate the wave spectrum transformations from deep to shallow water conditions. A series of JONSWAP spectra with different parameters is used as inputs. For each input spectrum, simulations are performed for wave propagations at constant shallow water conditions as well as for wave transformations from deep to shallow water conditions. The resulting spectra at the shallow water regions are compared to each other as well as the transformation (TMA) spectra. The differences are related to wave shoaling, reflection and breaking. The findings are confirmed in a computational fluid dynamics (CFD) domain. The study reveals the correlation between wave transformations and spectrum transformations at bathymetric variations. It is also found that a simulation of the complete wave transformation process produces a more accurate representation of the irregular wave field after the bathymetric transition than directly applying a specific spectrum at the shallow water region.