bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Simplified Wear Estimation Method Considering Rolling Motion Between Mooring Chain Links for Floating Structures
Authors: Takeuchi Takaaki , Utsunomiya Tomoaki , Gotoh Koji , Sato Iku
Published: October 2021

For the development of floating offshore wind turbines (FOWTs) in Japan, reliability assessment and cost reduction by efficient maintenance on mooring chains are part of the key issues because sites deeper than 60 m require mooring systems for station keeping. In this paper, attempts have been made to simplify the wear estimation method which was previously proposed by using a 3-D rigid-body link model for improvement of accuracy. These investigations are performed about a spar-type floating structure moored with three catenary lines at Goto, Nagasaki prefecture, Japan.

In the previous study, it was confirmed that the estimation method using the 3-D link model can calculate the interlink wear amount closer to the chain diameter measurements and more reasonable than the method using the conventional mass-spring model by removing the rolling distance from the displacement of contact points. However, the estimation method has technical difficulty in terms of calculation of contact properties and analysis costs for the mooring chain design. For this reason, the wear estimation method is simplified and verified by considering the rolling motion between mooring chain links modeled by the widely employed mass-spring model based on the method proposed by Mooring Integrity JIP. Firstly, the wear due to the rolling is reproduced by a three-dimensional FE analysis to investigate the actual wear phenomenon including the effect of the proof load test as well as the idealized configuration. Secondly, the application method is proposed against the response of the mooring chain subjected to irregular waves Finally, a comparison with the measurement is conducted to verify the proposed wear estimation method.
Automatic Tsunami Barrier
Authors: Hamada Eigai , Morita Shoichi , Iiboshi Ayumu , Hiraishi Tetsuya
Published: October 2021

The Anti-Tsunami Laboratory (ATL) invented and developed the Anti-Tsunami Door (ATD) barrier as an automatic tsunami barrier. In September 2018, ATL and Kyoto University tested a mid-scale model of a three-stage ATD unit and confirmed its performance: (1) functioning automatically (refer to Figure 9); (2) achieving reasonable wave height reduction, which is approximately 40%–80% that of a solid barrier of the same height; and (3) demonstrating reasonable strength for a wooden structure under the mid-scale model test conditions. ATL had planned to test a large-scale model of an ATD unit in Oregon State University in May 2020, but that test has been delayed owing to the COVID-19 pandemic. Because the wave pressure on the ATD unit is expected to be high during the large-scale model test, ATL requested that the Explosion Research Institute (ERI) simulate the wave pressure on a large-scale model ATD unit, and based on the results, ATL will reinforce the ATD unit. After testing the large-scale model unit, ATL will install ATD barriers along the coast of Japan, customizing the barrier for specific tsunami hazards.
Application of Deep Learning Technique to Predict Downhole Pressure Differential in Eccentric Annulus of Ultra-Deep Well
Authors: Krishna Shwetank , Ridha Syahrir , Ilyas Suhaib Umer , Campbell Scott , Bhan Uday , Bataee Mahmood
Published: October 2021

Accurate prediction of downhole pressure differential (surge/swab pressure gradient) in the eccentric annulus of ultra-deep wells during tripping operation is a necessity to optimize well geometry, reduction of drilling anomalies, and prevention of hazardous drilling accidents. Therefore, a new predictive model is developed to forecast surge/swab pressure gradient by using feed-forward and backpropagation deep neural networks (FFBP-DNN). A theoretical-based model is developed that follows the physical and mechanical aspects of surge/swab pressure generation in eccentric annulus during tripping operation. The data generated from this model, field data, and experimental data are used to train and test the FFBP-DNN networks. The network is developed used Keras’s deep learning framework. After testing the models, the most optimal arrangement of FFBP-DNN is the ReLU algorithm as an activation function, 4-hidden layers, the learning rate of 0.003, and 2300 of training numbers. The optimum FFBP-DNN model is validated by comparing it with field data (Wells K 470 and K 480, North Sea). It shows an excellent argument between predicted data and field data with an error range of ±7.68 %.
Dynamic Ultimate Strength Characteristics of Stiffened Plates Subjected to the In-Plane Impact Load and Lateral Pressure
Authors: Zhong Qiang , Wang De-yu
Published: October 2021

Dynamic capacity is totally different from quasi-static capacity of ship structural components, although most ultimate strength analyses at present by researchers are performed under quasi-static conditions. To investigate the dynamic ultimate strength characteristics, the dynamic ultimate strength analyses of stiffened plates subjected to impact load were studied based on a 3-D nonlinear explicit finite element method (FEM) in this paper. The impact load in the present work is characterized as a half-sine function. A series of nonlinear finite element analyses are carried out using Budiansky-Roth (B-R) criterion. The influence of impact durations, model ranges, boundary conditions, initial imperfections and impact loads on the dynamic ultimate strength of stiffened plates are discussed. In addition, the ultimate strength of stiffened plates under the in-plane impact combined with lateral pressure was also calculated, which shows lateral pressure has a negligible effect on the dynamic ultimate strength of stiffened plates subjected to the impact load with short durations. Other important conclusions can be obtained from this paper, which are useful insights for the development of ultimate strength theory of ship structures and lay a good foundation for the study of dynamic ultimate strength in the future.
Hybrid Verification of a Deepwater FPSO Using Truncated Model Tests and Numerical Simulations
Authors: Liu Xiangbo , Liong Ching Theng , Kumar Nitesh , Chua Kie Hian , Magee Allan Ross , Choo Yoo Sang
Published: October 2021

This paper presents verification of a deep water FPSO with a semi-taut mooring system using model tests and numerical modelling commonly referred to as the hybrid method. The vessel under investigation is a FPSO of 310m in length and 47m in beam with an internal turret mooring system of 12 lines in 2000m water depth. Two configurations of the mooring systems i.e. inline and bisecting are investigated for sea-states up to 1000yr return period. A full depth mooring system has been developed for the FPSO and model tests will be carried out to verify the model. Due to limitations to the size of the model basins, the model tests will be carried out for a truncated mooring setup. Non-linear horizontal stiffness of a single mooring line and the complete mooring system with truncation is compared to that of the existing full depth mooring system. Discrepancies in the vertical forces due to truncation of line length will be discussed in the paper. A numerical model of the truncated set-up will be calibrated using model test results.
Neural Network Meta-Models for FPSO Motion Prediction From Environmental Data
Authors: Cotrim Lucas Pereira , Oliveira Henrique Barros , Queiroz Filho Asdrubal N. , Santos Ismael H. F. , Barreira Rodrigo Augusto , Tannuri Eduardo Aoun , Costa Anna Helena Reali , Gomi Edson Satoshi
Published: October 2021

The current design process of mooring systems for FPSOs is highly dependent on the availability of the platform’s mathematical model and accuracy of dynamic simulations, through which resulting time series motion is evaluated according to design constraints. This process can be time-consuming and present inaccurate results due to the mathematical model’s limitations and overall complexity of the vessel’s dynamics. We propose a Neural Simulator, a set of data-based surrogate models with environmental data as input, each specialized in the prediction of different motion statistics relevant to mooring system design: Maximum Roll, Platform Offset and Fairlead Displacements. The meta-models are trained by real current, wind and wave data measured in 3h periods at the Campos Basin (Brazil) from 2003 to 2010 and the associated dynamic response of a spread-moored FPSO obtained through time-domain simulations using the Dynasim software. A comparative analysis of different model architectures is conducted and the proposed models are shown to correctly capture platform dynamics, providing good results when compared to the statistical analysis of time series motion obtained from Dynasim.
Real Gas Effect on Gas Slippage Phenomenon in Shale
Authors: Chen Yufei , Leung Juliana Y. , Jiang Changbao , Wojtanowicz Andrew K.
Published: October 2021

The past decade has seen the rapid development of shale gas across the world, as the record-breaking success and on-going surge of commercial shale gas production in such unconventional reservoirs pose a tremendous potential to meet the global energy supply. However, questions have been raised about the intricate gas transport mechanisms in the shale matrix, of which the gas slippage phenomenon is one of the key mechanisms for enhancing the fluid transport capacity and, therefore, the overall gas production. Given that shale reservoirs are often naturally deposited in the deep underground formations at high pressure and temperature conditions (much deeper than most typical conventional deposits), the real gas effect cannot be ignored as gas properties may vary significantly under such conditions. The purpose of this study is thus to investigate the real gas effect on the gas slippage phenomenon in shale by taking into account the gas compressibility factor (Z) and Knudsen number (Kn).

This study begins with a specific determination of Z for natural gas at various pressures and temperatures under the real gas effect, followed by several calculations of the gas molecular mean free path at in-situ conditions. Following this, the real gas effect on gas slippage phenomenon in shale is specifically analyzed by examining the change in Knudsen number. Also discussed are the permeability deviation from Darcy flux (non-Darcy flow) due to the combination of gas slippage and real gas effect and the specific range of pressure and pore size for gas slippage phenomenon in shale reservoirs.

The results show that the gas molecular mean free path generally increases with decreasing pressure, especially at relatively low pressures (< 20 MPa). And, increasing temperature will cause the gas molecular mean free path to rise, also at low pressures. Knudsen number of an ideal gas is greater than that of a real gas; while lower than that of a real gas as pressure continues to rise. That is, the real gas effect suppresses the gas slippage phenomenon at low pressures, while enhancing it at high pressures. Also, Darcy’s law starts deviating when Kn > 0.01 and becomes invalid at high Knudsen numbers, and this deviation increases with decreasing pore size. No matter how pore size varies, this deviation increases with decreasing pressure, meaning that the gas slippage effect is significant at low pressures. Finally, slip flow dominates in the various gas transport mechanisms given the typical range of pressure and pore size in shale reservoirs (1 MPa < P < 80 MPa; 3 nm < d < 3000 nm). Gas transport in shale is predominantly controlled by the slippage effect that mostly occurs in micro- or meso-pores (10 to 200 nm). Moreover, considering the real gas effect would improve the accuracy for determining the specific pressure range of the gas slippage phenomenon in shale.
The Use of Mathematical Programming to Determine Optimal Production and Drilling Schedule in an Offshore Oil Field, A Case Study From the Barents Sea
Authors: Lei Guowen , Stanko Milan , Silva Thiago Lima , Widerøe Tom , Skogvang Arnljot
Published: October 2021

A field with two neighboring reservoirs was discovered in the Barents Sea in 2013 and 2014. After a successful extended well test of an appraisal well in 2018 and initial field planning tasks, a preliminary drilling and production schedule was proposed based on cross-domain collaboration and group work involving several disciplines. In this paper, mathematical programming is employed to model and optimize the economic value of the project in order to determine the best drilling and production schedule for the field. The optimization includes some of the technical constraints considered by the field development team while also considering uncertainties such as reservoir size, productivity of well, and cost. These have been systematically evaluated by using simulation-based optimization (sampling). The results were that the use of mathematical programming allows the field planner to evaluate several scenarios within a reasonable time frame, thereby enabling rapid changes in the decisions to respond to new information and risk considerations in a dynamic environment. This paper illustrates the benefits of utilizing mathematical programming in early field planning to optimize the drilling and production schedule.
Helical Flow of Drilling Mud With Cuttings in a Vertical Well
Authors: Ignatenko Yaroslav , Gavrilov Andrey , Bocharov Oleg
Published: October 2021

The paper presents the results of an investigation into drilling mud flow with cuttings in a vertical well. The drilling mud rheology was described with the Herschel-Bulkley model. The axial Reynolds number was around 1000, the flow regime changing together with drill pipe RPM. The investigation covered the flow’s structures, integral parameters and cuttings transport in relation to drill pipe RPM and rate of penetration (ROP). In the laminar flow, most of the particles were localized in the quasi-solid region to move together with the last; the integral parameters had little dependence on drill pipe RPM increase. Increasing drill pipe RPM resulted in formation of the Görtler vortices near the channel’s external and internal walls, whose interaction led to the formation of smaller eddies converting the flow into a turbulent one. Due to the turbulence dispersion, the region taken by the particles widened. Particles suppress the vortex intensity near the channel’s external wall. Under the conditions described, increasing drill pipe RPM and ROP resulted in higher pressure drops and lower transport efficiency.
CFD Gas Explosion Simulation on LNG-Fueled Ship
Authors: Nubli Haris , Sohn Jung Min
Published: October 2021

The International Maritime Organization (IMO) has issued the regulation of the Emission Control Area (ECA). This area was designated to control the air pollutant which emitted by conventional fuel from a ship. Thus, LNG fuel could be an alternative fuel to deal with a new regulation. However, the utilization of LNG fuel in the ship should be proven for its safety and reliability.

The scope of this work was to capture the blast overpressure as an accidental load. The open-deck fuel gas supply system (FGSS) of the hypothetical Oil Tanker was used as a target for the explosion model. The parameters of the scenarios consisted of the gas cloud size and gas cloud center of gravity in X, Y, and Z directions. Each parameter contains a likelihood, and it should be converted as probability density functions (PDF). Thus, it can be utilized to generate 50 scenarios by Latin Hypercube sampling.

This research used the ExSim CFD (Computational Fluid Dynamics) code to simulate a gas explosion. The grid convergence and software validation were also conducted to understand the software performance. Finally, the overpressure and gas explosion frequency from scenarios could be utilized to determine the exceedance frequency diagram. This diagram could be used as a prediction of the gas explosion on the LNG-fueled ship.
Numerical Simulation of the Fixed Barge Barge Interaction Under Irregular Wave Using HOS-StarCCM+ Coupling Tool With Experiment Validation
Authors: Zhang Yali , Xu Haihua , Santo Harrif , Chua Kie Hian , Law Yun Zhi , Chan Eng Soon
Published: October 2021

The interaction between two side-by-side floating vessels has been a subject of interest in recent years due floating liquefied natural gas (FLNG) developments. The safety and operability of these facilities are affected by the free-surface elevation in the narrow gap between the two vessels as well as the relative motions between the vessels. It is common practice in the industry to use potential flow models to estimate the free-surface responses in the gap under various wave conditions. However, it is well-known that any potential flow models require calibration of viscous damping, and model tests are carried out to provide a platform to calibrate the potential flow models.

To improve beyond the potential flow models, Computational Fluid Dynamics (CFD) models will be required. However, the large computational efforts required render the conventional CFD approaches impractical for simulations of wave-structure interactions over a long duration. In this paper, a developed coupled solver between potential flow and Computational Fluid Dynamics (CFD) model is presented. The potential flow model is based on High-Order Spectral method (HOS), while the CFD model is based on fully nonlinear, viscous and two phase StarCCM+ solver. The coupling is achieved using a forcing zone to blend the outputs from the HOS into the StarCCM+ solver. Thus, the efficient nonlinear long time simulation of arbitrary input wave spectrum by HOS can be transferred to the CFD domain, which can reduce the computational domain and simulation time.

In this paper, we make reference to the model experiments conducted by Chua et al. (2018), which consist of two identical side-by-side barges of 280 m (length) × 46 m (breadth) × 16.5 m (draught) tested in regular and irregular wave conditions. Our intention is to numerically reproduce the irregular wave conditions and the resulting barge-barge interactions. We first simulate the actual irregular wave conditions based on wave elevations measured by the wave probes using the HOS solver. The outputs are subsequently transferred to the CFD solver through a forcing zone in a 2D computational domain for comparison of the irregular wave conditions without the barges present. Subsequently, a 3D computational domain is set up in the CFD with fixed side-by-side barges modelled, and the interaction under irregular waves is simulated and compared with the experiments. We will demonstrate the applicability of the HOS-StarCCM+ coupling tool in terms of accuracy, efficiency as well as verification and validation of the results.
Algorithms and Models for Smart Well Planning With Emphasis on Trajectory Optimization
Authors: Wiktorski Ekaterina , Sui Dan
Published: October 2021

Well planning is a time-demanding procedure, which integrates knowledge and experience of various field professionals, as drilling engineers, pipe manufacturers, drilling mud specialists, geologists, etc. According to OG21 report (1), time spent for planning a well is on average 2–3 months. Drilling engineers have to design a well at minimum costs maintaining wellbore integrity at any time. The wellbore should also allow for maximum production from the reservoir and minimum tortuosity for successful casing running and completion. Fortunately, in the well-explored geological areas, where stratigraphic sequences and corresponding geopressures are known, the main objective can be narrowed down to optimal trajectory design. Optimal wellbore trajectory considers at least three criteria: shortest possible path, collision avoidance and longest possible contact with reservoir.

Due to large number of modules involved, well planning requires a holistic approach. At the same time, due to complex interaction between the modules and respective physical models, this task implicates a high level of precision. This paper presents a development of an in-house well planning simulator, which integrates all essential well planning modules in a smart way. Central part of the simulator is represented by a trajectory planning and optimization module, which is based on minimization of wellbore length and dogleg severity. Constraints related to anticollision are also included.

Introduction of smart optimization techniques for wellbore trajectory has a real potential of saving time and efforts by providing engineers with multiple options, which satisfy the aforementioned constraints. Our ultimate goal is to automate wellbore planning to the largest possible extent by developing smart optimizers for other vital modules within the well planning simulator.
Validation of a Numerical Model for the Investigation of Tension Leg Platforms With Marine Energy Application Using REEF3D
Authors: Windt Christian , Goseberg Nils , Martin Tobias , Bihs Hans
Published: October 2021

Exploiting the offshore wind resources using floating offshore wind systems at sites with deep water depths requires advanced knowledge of the system behaviour, including the hydro-, areo-, and mooring dynamics. To that end, high-fidelity numerical modelling tools, based on Computational Fluid Dynamics, can support the research and development of floating offshore wind systems by providing high-resolution data sets.

This paper presents the first steps towards the numerical modelling of tension leg platforms for floating offshore wind applications using the open-source Computational Fluid Dynamics toolbox REEF3D. The numerical model of a taut-moored structure is validated against experimental reference data. Results from wave-only test cases highlight the simplicity and effectiveness of the wave generation method, implemented in REEF3D. For the considered wave-structure interaction cases, deviations between the experimental and numerical data can be observed for the surge and pitch displacements, while the heave displacement and the mooring forces are capture with sufficient accuracy. Overall, the numerical results indicate high potential of REEF3D to be used for the modelling of floating offshore wind systems.
Fatigue Assessment of Mooring Chain Considering the Effects Of Mean Load and Corrosion
Authors: Lone Erling N. , Sauder Thomas , Larsen Kjell , Leira Bernt J.
Published: October 2021

Results from full scale fatigue tests of offshore mooring chains performed in recent years have revealed considerable influence of both mean load and corrosion condition on the fatigue capacity. It has been shown that a reduction of the mean load gives an increase in fatigue life, whereas the corrosion experienced by used chains have a significant negative impact. Neither of these effects are properly addressed by current S-N design curves or design practice.

This paper suggests an extended S-N curve formulation, that includes the effects of mean load and corrosion condition. The parameters of the extended formulation are estimated empirically from mooring chain test data that includes new and used chains, with various mean loads and with different degrees of corrosion. The fitted capacity model is then used for fatigue calculation for the mooring system of a semi-submersible, showing the importance of using realistic mean loads and mooring chain corrosion in fatigue assessments.
Sensitivity of a Floating Bridge Global Responses to Different Wave Drift Force Models
Authors: Silva de Souza Carlos Eduardo , Fonseca Nuno , Kvittem Marit Irene
Published: October 2021

Floating bridges are a promising solution for replacing ferries in the crossing of Norwegian fjords. Their design involves the adoption of accurate, but at the same time efficient models for the loads the structure is subjected to. Wave drift forces at the bridge’s pontoon may excite the bridge’s lower horizontal modes, with consequences to the loads on the bridge and mooring lines. Newman’s approximation is normally adopted to calculate the wave drift forces in such applications. A common simplification is to assume that the pontoons are fixed in the calculation of wave drift coefficients, while it is known that wave frequency motions may significantly influence drift loads. This paper evaluates the consequences of this simplification, in comparison to coefficients obtained considering the pontoons’ motions. First, the effect of the bridge deflection, due to mean drift, on the pontoon’s motions, is evaluated. It is found that this effect is negligible. Then, the RAOs are used in the calculation of wave drift coefficients, showing very different results than those obtained with fixed pontoons. Time-domain simulations are then performed with wave drift coefficients calculated with both approaches, with focus on the bridge girder moments and mooring line tensions. It is shown that using wave drift coefficients obtained with fixed pontoon is a non-conservative simplification, depending on sea state and wave incidence direction.
A Finite Element Model for Compressive Ice Loads Based on a Mohr-Coulomb Material and the Node Splitting Technique
Authors: Herrnring Hauke , Ehlers Sören
Published: October 2021

This paper presents a finite element model for the simulation of ice-structure interaction problems, which are dominated by crushing at low and medium confinement ratios. The failure mode of ice depends significantly on the strain rate. At very low impact velocities the ice behaves ductile, whereas at high velocities the ice reacts in brittle mode. This paper focuses on the brittle mode, which is the dominating mode for ship-ice interactions.

A multitude of numerical approaches for the simulation of ice can be found in the literature. Nevertheless, the literature approaches do not seem suitable for the simulation of continuous ice-structure interaction processes at low and medium confinement ratios in brittle mode. Therefore, this paper seeks to simulate the ice-structure interaction with the FE method. To preserve mass and energy as much as possible, the node splitting technique is applied, instead of the often used element erosion technique. The intention of the presented model is not to reproduce individual cracks with high accuracy, because this is not possible with a reasonable element size, due to the large number of crack fronts forming during the ice-structure interaction process. The objective of the here introduced Mohr-Coulomb Nodal Split (MCNS) model is to represent the essential material behavior of ice in a efficient formulation. To validate the findings of the model, the simulated maximum ice forces and contact pressures are compared with experiments.
Research on Influencing Factors of Heavy Oil Emulsification
Authors: Liu Yanchi , Wu Guodong , Yao Erdong , Zuo Wei , Zhao Longhao , Li Yuan , Meng Xue
Published: October 2021

In tight heavy oil reservoirs, the formation of W/O emulsion will significantly increase the viscosity of the whole fluid-system. Meanwhile, the emulsion droplets tend to block the core pores, which will reduce the flow oil and water. In this paper, the terms of oil-water ratio, pH and other factors on heavy oil emulsification of tight sandstone in a block of Xinjiang were studied. Furthermore, in order to study the emulsification behavior in large and small pores, a large tube and a small tube are used to investigate how the hole apertures affect heavy oil emulsification. Finally, the demulsification time and dehydration rate were recorded, and the interfacial tension and viscosity were tested. The results show that heavy oil is easy to self-emulsify with water to form W/O emulsion, and it’s extremely stable. When the oil-water ratio is 3:7, the viscosity of the emulsions reaches 307 mPa·s, which is 38 times higher than that of crude oil. Acidic and alkaline conditions are benefit of demulsification and the stability of the emulsions is reduced. In small tube with higher interfacial tension, the demulsification time is shortened, and the stability of the emulsions is reduced.
Interface Risk Reduction in an Integrated SURF-SPS Scope Execution
Authors: Priyadarshi Hemant , Nickel Daniel , Jose Seban
Published: October 2021

The paper provides a detailed estimation of the interfaces that exist in a split SURF-SPS execution model and provides a qualitative comparison to an integrated SURF-SPS execution model. A comprehensive matrix of dependencies between SURF and SPS is presented and is categorized into engineering, procurement, construction/fabrication and installation work packages. The matrix is used to illustrate the exact scope dependencies and thus, the sources of interfaces.

A hypothetical greenfield development has been assumed to develop the interface matrix and to use it for comparison of the two execution models. The comparison also reveals how interfaces are naturally eliminated in an integrated SURF-SPS execution model. In each of the workstreams (E-P-C-I), top risks have been identified and monetary liability estimates for those risks have been provided. By transfer of these risks from company to contractor, monetary liability gets transferred to the contractor, thus, resulting in significant savings for operating companies.

The following tangible results are provided in the paper: a) % of interface(s) reduced in the E-P-C-I areas; b) Risk reduction in monetary terms for operators – estimated values. This paper justifies the fact that there is a significant interface scope and risk reduction for operators, if they adopt an integrated SURF-SPS execution model.
Simplified Stochastic Modelling of the Force on a Pipe Bend Due to Two-Phase Slug Flow
Authors: Klinkenberg Arnout M. , Tijsseling Arris S.
Published: October 2021

Slug flow, a flow pattern with alternating aerated liquid pockets (slugs) and large gas bubbles, is a commonly observed flow pattern in oil and gas pipelines. Due to its unsteady character, the force on a pipe bend is fluctuating which results in unacceptable motions when the piping is insufficiently supported. To investigate the risk of fatigue failure of the system, finite-element models are used to predict the dynamic stresses required to estimate the fatigue life of the system. The excitation force of the slug flow is the essential input required for accurate fatigue damage predictions.

A new, simplified model of slug forces on a bend is proposed. The model is calculating the slug force by solving the momentum balance over the pipe bend using slug flow properties as liquid holdup and phase velocities. Average properties predicted by a unit slug model cannot predict the stochastic force variations caused by the slug flow. The new approach introduces the stochastic character of slug flow in the force calculations via a log-normal slug length distribution. A Lagrangian slug tracking method is used to solve the governing equations.

The modelled liquid holdup, pressure and predicted forces are compared with available measurements and Computational Fluid Dynamics calculations. The measurements were done under atmospheric conditions and the fluids used were air and water. Whether these measurements are representative for high-pressure oil and gas slug flow is unknown. By using a mechanistic approach where the main equations are based on physical laws instead of fitted measured data, the model is applicable for different fluids and operational conditions. To validate the model for oil and gas flows, the results are compared with Computational Fluid Dynamics calculations done with high gas density and typical oil viscosity.
Experimental, Numerical, and Statistical Investigation of Two Phase Flow in a Cylindrical Perforation Tunnel
Authors: Abobaker Ekhwaiter , Elsanoose Abadelhalim , Rahman Mohammad Azizur , Khan Faisal , Aborig Amer , Butt Stephen
Published: October 2021

Perforation is the final stage in well completion that helps to connect reservoir formations to wellbores during hydrocarbon production. The drilling perforation technique maximizes the reservoir productivity index by minimizing damage. This can be best accomplished by attaining a better understanding of fluid flows that occur in the near-wellbore region during oil and gas operations. The present work aims to enhance oil recovery by modelling a two-phase flow through the near-wellbore region, thereby expanding industry knowledge about well performance. An experimental procedure was conducted to investigate the behavior of two-phase flow through a cylindrical perforation tunnel. Statistical analysis was coupled with numerical simulation to expand the investigation of fluid flow in the near-wellbore region that cannot be obtained experimentally. The statistical analysis investigated the effect of several parameters, including the liquid and gas flow rate, liquid viscosity, permeability, and porosity, on the injection build-up pressure and the time needed to reach a steady-state flow condition. Design-Expert® Design of Experiments (DoE) software was used to determine the numerical simulation runs using the ANOVA analysis with a Box-Behnken Design (BBD) model and ANSYS-FLUENT was used to analyses the numerical simulation of the porous media tunnel by applying the volume of fluid method (VOF). The experimental data were validated to the numerical results, and the comparison of results was in good agreement. The numerical and statistical analysis demonstrated each investigated parameter’s effect. The permeability, flow rate, and viscosity of the liquid significantly affect the injection pressure build-up profile, and porosity and gas flow rate substantially affect the time required to attain steady-state conditions. In addition, two correlations obtained from the statistical analysis can be used to predict the injection build-up pressure and the required time to reach steady state for different scenarios. This work will contribute to the clarification and understanding of the behavior of multiphase flow in the near-wellbore region.
A Unique Approach in Modelling Flow in Tight Oil Unconventional Reservoirs With Viscous, Inertial and Diffusion Forces Contributions
Authors: Aldhuhoori Mohammed , Belhaj Hadi , Ghosh Bisweswar , Fernandes Ryan , Alkuwaiti Hamda , Qaddoura Rabab
Published: October 2021

A model for single-phase fluid flow in tight UCRs was previously produced by modifying the flow Forchheimer’s equation. The new modification addresses the fluid transport phenomena into three scales incorporating a diffusion term. In this study, a new liner model, numerically solved, has been developed and deployed for a gas huff and puff project. The new model has been numerically validated and verified using synthetic data and huff and puff case study. Ideally, the new model suits fluid flow in tight UCRs. The modified Forchheimer’s model presented is solved using the MATLAB numerical method for linear multiphase flow. For the huff & puff case, very simple profiles and flow dynamics of the main flow parameters have been established and a thorough parametric analysis and verifications were performed. It has been observed that the diffusion system becomes more prominent in regulating flow velocity with low permeability of the formation rock and low viscosity of the flowing fluid. The findings indicate a behavioral alignment with a previous hypothesis that matches actual reservoir behavior.
A Coupled Frequency and Time Domain Approach for Hydroelastic Analysis of Very Large Floating Structure
Authors: Chen Dengshuo , Feng Xingya , Hou Chao , Chen Jianfei
Published: October 2021

This paper develops a practical approach based on Python that couples the hydrodynamic analysis with the structural analysis, in order to solve the hydroelastic problem of Very Large Floating Structure (VLFS). The hydrodynamic analysis is carried out by solving linear 3D diffraction and radiation problems in the frequency domain, while the structural analysis is performed by a time-domain nonlinear finite element model. The coupling is realized by a generalized mode expansion method where the elastic deformation of the VLFS is regarded as extended radiation mode in the water. We consider a pontoon-type floating plate in regular waves. Analytical mode shape functions are used for representing the VLFS elastic deformations. The Mindlin plate theory is used for the finite element model. Convergence study of structure mode shape numbers, hydrodynamic model mesh and finite element model mesh is carefully carried out. Good agreements of the vertical displacement of the floating plate are found compared with experimental data and numerical results in the literature. Our simulation results show that the dynamic response of the VLFS is significantly influenced with consideration of its elastic deformation in the waves, and we see the influence is more pronounced in relatively shorter waves. The proposed approach is shown promising for hydroelastic analysis for more complex VLFS in realistic ocean seastates.
Numerical Investigation of an Experimental Ocean Current Turbine Based on Blade Element Momentum Theory (BEM)
Authors: Sadeqi S. , Rouhi S. , Xiros N. , Aktosun E. , VanZwieten J. , Sultan C. , Ioup J.
Published: October 2021

Ocean currents are one of the alternative sources of green, sustainable, and renewable energy that could generate low-cost electric power without any pollution due to the burning of fossil fuels. Due to the density of the water, ocean currents can produce a significant amount of energy even with a very small current velocity field. In this study, a comprehensive performance analysis of 3-blade horizontal-axis Ocean Current Turbine (OCT) is shown to achieve optimal rpm (revolutions per minute) to match environmental conditions in order to harvest the maximum possible energy from OCT in ocean currents. Our approach is to use Blade Element Momentum (BEM) theory in order to estimate hydrodynamic loads for the turbine; specifically, the design of the OCT blades is based on a FX77-W121 type airfoil. We use JavaFoil to analyze and determine hydrodynamic lift and drag coefficients with respect different angles of attack for the hydrofoil profiles in seawater. After validation of blade design characteristics and obtaining the local coefficients of each hydrofoil cross-sections, we transfer them to our in-house-developed Blade Element Momentum Theory (BEM) code in order to achieve the estimation of performance analysis of the OCT in order to get maximum power and ideal torque and thrust. This performance analysis with BEM model of the OCT is an important step for further analysis due to having different incoming flow speeds in actual time-varying sea conditions. Indeed, the OCT will encounter different incoming ocean current speeds during operation. Therefore, this approach is used to get an accurate brake power estimate of the OCT in different operational current speeds. In addition, this performance analysis of the OCT is going to be utilized in designing and developing a test model for the physical towing tank experiment for later investigation.
Thermal Design of Pipelines – A Challenge for Flow Assurance in the Arctic
Authors: Ponagandla Veerendhar , Liu Liangjian , DeGeer Duane
Published: October 2021

Increasing demand for energy is driving the need to explore the deeper oceans and the far north. While higher temperature, pressure and longer tie-backs are challenges going deep, highly sensitive environment is an issue exploring far north. The discovery of large reserves in the far north has brought the challenges of exploration, production, and transportation in the cold regions like Prudhoe Bay, the Mackenzie Delta, and the Arctic Islands into focus. To transport hydrocarbons to market, pipelines used in the Arctic have unique challenges and stringent design conditions that must be met to ensure reliable operations in such remote and sensitive environments.

To avoid flow assurance risks, the adage “the hotter the better” is in stark contrast to the sensitive nature of the Arctic environment to temperature changes, and where “the colder the better” is more appropriate. Permafrost, and its potential disturbance, is the most important factor to be considered for pipeline thermal design. High temperatures can disturb the in-situ state of the permafrost, causing settlement and instability in the permafrost zone. Also, high pipeline temperatures demand deep trenches to avoid melting the surface ice, challenging installation and increasing CAPEX.

Designing the pipeline to maintain high internal fluid temperatures to reduce flow assurance risks and lower pipeline outer temperatures to minimize the impact on the environment is the best solution. To maintain high fluid temperatures and reduce heat loss to the environment, the conventional idea of a high value insulation like pipe-in-pipe with a vacuum annulus to avoid heat loss to the sensitive Arctic surroundings may seem to be a good solution, but it may not be the optimal solution. This paper discusses a hypothetical scenario (based on field cases) of a multiphase pipeline design and highlights the associated flow assurance/operational risks.
Pre- and Post-Tsunami Depth Changes of Submarine Topography for the Analysis of Submarine Landslide-Induced Tsunami: Proposal of Digitization Method and Application to the Case of the 1923 Great Kanto Earthquake Tsunamis
Authors: Murata Kazuki , Sassa Shinji , Takagawa Tomohiro , Ebisuzaki Toshikazu , Maruyama Shigenori
Published: October 2021

We first propose and examine a method for digitizing analog data of submarine topography by focusing on the seafloor survey records available in the literature to facilitate a detailed analysis of submarine landslides and landslide-induced tsunamis. Second, we apply this digitization method to the seafloor topographic changes recorded before and after the 1923 Great Kanto earthquake tsunami event and evaluate its effectiveness. Third, we discuss the coseismic large-scale seafloor deformation at the Sagami Bay and the mouth of the Tokyo Bay, Japan.

The results confirmed that the latitude / longitude and water depth values recorded by the lead sounding measurement method can be approximately extracted from the sea depth coordinates by triangulation survey through the overlaying of the currently available GIS map data without geometric correction such as affine transformation. Further, this proposed method allows us to obtain mesh data of depth changes in the sea area by using the interpolation method based on the IDW (Inverse Distance Weighted) average method through its application to the case of the 1923 Great Kanto Earthquake. Finally, we analyzed and compared the submarine topography before and after the 1923 tsunami event and the current seabed topography. Consequently, we found that these large-scale depth changes correspond to the valley lines that flow down as the topography of the Sagami Bay and the Tokyo Bay mouth.
3D Laser Scanning for Thickness Measurements of Hull Structures
Authors: Zhang Xi-Ying , Loader Charles , Schilling Spencer , Hernandez Vicente , McSweeney Kevin , Gu Hai
Published: October 2021

3D scanning technology uses lasers to scan and capture object surfaces without physical surface contact. Laser scanning is gaining acceptance by many, including owners of marine or offshore assets as a viable inspection and validation method. Laser technology reduces operational times compared to traditional pit gauging techniques, particularly for large areas of widespread wastage or pitting. This paper studies the use of 3D scanning technology for inspection, thickness gauging, and steel wastage measurements of hull structures.

Pilot tests were conducted on coated and uncorroded plates in Houston, USA, and uncoated and corroded plates and uncoated and deformed plates in Perth, Australia. Manual Ultrasonic Testing (UT) was conducted, which is the method currently accepted by International Association of Classification Societies (IACS) for thickness measurements of hull structures. For the coated plate, the coating thickness was measured on both sides of the plate. The coating thickness was deducted from the total thickness from 3D scanning before the plate thickness was compared with the UT results.

Acceptance criteria are proposed to compare the Manual UT measurements with the 3D scanning measurements to determine if 3D laser scanning is a possible alternative thickness measurement method. The difference of thickness measurements from 3D scanning on coated and uncorroded plates is within 13% when compared with those from UT. The discrepancy is attributed to equipment accuracy tolerances, errors from data post-processing, and measurement errors due to coating surface roughness. For uncoated and corroded plates, the difference reduces to 3%, making the results of 3D scanning acceptable based on acceptance criteria. In addition, the higher accuracy of using 3D scanning to measure plate deformation is demonstrated over traditional methods which use stringlines or laser levels to create a reference surface. Comparisons of the coefficient of variation (CV) on all plates demonstrate the higher precision of 3D scanning technology than that of manual UT. The main limitation of 3D laser scanners is their inability to directly obtain steel thickness for structures that have been coated or painted, especially in watertight/oil-tight structures.

The study identifies capabilities, accuracy, and limitations of using 3D scanning technology for thickness measurements of hull structures in the marine or offshore industries. Scanning technology can support inspections providing fast and precise means of thickness measurements of corroded plates without coating. It provides the potential for producing 3D models and analysis for follow-up inspections. Plausible use cases in the maritime industry include defect analysis, fitness for service assessment, damage assessment, and corrosion monitoring.
Effect of Geometric Parameters of New Semisubmersible Platform on Stability and Hydrodynamic Performance
Authors: Wang Tianying , Zhou Yanjun , Tang Honglin , Zhang Shihua , Tian Haiqing
Published: October 2021

The JCSM concept (short for Jackup Combined Semisubmersible Multifunction Platform) is a new type of semisubmersible platform presented by the first author, which overcomes the shortcomings of the available semisubmersible platforms, and combines the advantages of the traditional semisubmersible platform, the Jackup platform and the new FPSO concept - IQFP. Due to the complicated interaction between stability and hydrodynamic performance, it is necessary to explore the effect of geometrical parameters of the main body on the stability and hydrodynamic performance in order to obtain the optimal design plan of a JCSM platform. Firstly, the structure components and innovations of the JCSM were briefly reviewed in order to facilitate readers to understand its full picture. Then, six independent geometric parameters were selected by carefully studying the shape characteristics of the initial design plan of a JCSM study case. Furthermore, the stability heights and motion responses of various floating bodies of the JCSM case with different geometric parameters in wave were calculated using boundary element method based on potential flow theory. Lastly, effect of the shape parameters on stability and hydrodynamic performance of the JCSM was qualitatively evaluated. The research would shed lights on the shape design of the JCSM main body.