bluuebunny/crossref_metadata_2025 huggingface dataset:
Possibility of Reducing Spar-Type FOWT Hydrodynamic Response Using a Torus Structure With Annular Flow
Authors: Murai Motohiko , Liu Xiaolei
Published: October 2021

Gyroscopic motion is considered as an appropriate approach to suppress the shaking motion of rigid bodies. Its spatial orientation is also used to make gyro compasses in the marine industry. In this paper, the floating offshore wind turbine (FOWT) was designed based on potential theory and gyroscopic effect and rotational axis retention effect were also considered, so that FOWT could obtain better hydrodynamic response. However, gyroscopic motion was generated through an annular flow in the internal torus instead of rigid body rotation. The scale of torus and the angular velocity of the annular flow were the design parameters that this article was eager to understand obviously. By vast quantity of calculations, the suitable range of design parameters was obtained.
Comparative Study of Drilling Riser Running/Retrieving Analysis Methodologies
Authors: Vale Leandro , Gallagher Conor , Souza Marcelo , Carneiro Daniel
Published: October 2021

Drilling risers are key components in offshore oil exploration and are present in most of the well construction phases (drilling, casing, cementing and completion). Mobile offshore drilling units can operate in different sites exposed to a range of environmental loadings and water depths. Global riser analyses based on the FE (finite element) method are performed to assess the system feasibility and operating envelopes. In harsh environment and ultradeep water scenarios, the riser running/retrieving operation is one of the most critical due to top-angle limits and riser stress as a result of either contact with the inside of the diverter housing/substructures or loading at the gimbal-spider (API-RP-16Q [1], ISO 13624-1 [2]).

The use of beam-column elements is satisfactory for modelling the riser global response, however it may lead to result uncertainty in terms of local response associated with complex geometry, over-stress, stress concentration and contact modelling (DNV-ST-F201 [3], DNVGL-RP-F203 [4], ISO 13628-7 [5]). The objective of this paper is to compare riser analysis results from a global and a local FE analysis. This comparison is used to identify any limitations associated with the use of a global riser analysis approach for determining structural limits for the riser during deployment/retrieving operations. Several recommendations are also provided regarding the use of the global analysis approach.
System Uncertainty Effects on the Wave Frequency Response Of Floating Vessels Based on Polynomial Chaos Expansion
Authors: Radhakrishnan Gowtham , Han Xu , Sævik Svein , Gao Zhen , Leira Bernt Johan
Published: October 2021

From a mathematical viewpoint, the frequency domain analysis of vessel motion responses due to wave actions incorporates the integration of system dynamics idealized in terms of response amplitude operators (RAOs) for 6 DOF rigid body motions and an input wave spectrum to yield the response spectrum. Various quantities of interest can be deduced from the response spectrum and further used for decision support in marine operations, extreme value and fatigue analysis. The variation of such quantities, owing to the uncertainties associated with the vessel system parameters, can be quantified by performing uncertainty propagation (UP) and consequent sensitivity analysis (SA). This study, emphasizes and proposes a computational-efficient way of assessing the sensitivity of the system model output with respect to the uncertainties residing in the input parameters by operating on a surrogate model representation. In this respect, the global sensitivity analysis is effectively carried out by deploying an efficient non-intrusive polynomial chaos expansion (PCE) surrogate model built using a point collocation strategy. Successively, the coherent and effective Sobol’ indices are obtained from the analytical decomposition of the polynomial coefficients. The indices, eventually, are employed to quantitatively gauge the effects of input uncertainties on the output 6 DOF vessel responses.
Research on the Influences of Broken Ice Parameters on Maneuverable Forces of Ice-Going Ship Oblique Sailing
Authors: Xuan Shenyu , Zhan Chengsheng , Liu Zuyuan , He Binfeng , Zhao Qiaosheng , Guo Wei
Published: October 2021

The broken ice is one of the most common ice conditions for ice-going ships, and the research of ship maneuvering movement in broken ice field can improve sailing safety. In this paper, the discrete element method (DEM) was adopted to study the maneuverable forces, including resistance and transverse force, of ice-going ship oblique sailing in broken ice fields. First, the Araon model tests data of Korea Institute of Ocean Science & Technology (KIOST) was used to verify the ice resistance of direct sailing under different ice sizes and model speeds, and the numerical results are in good agreement with the test results. Second, the influences of broken ice parameters (including concentration, thickness, and shape) on ship-ice interaction and maneuverable forces distribution were researched. The maneuverable forces on the ice-going ships are mainly from the ship-ice interaction. The time history curves of maneuverable forces were analyzed from the average value of maneuverable forces, the average value of peak maneuverable forces, and the number of peaks. Besides, the parameters of broken ice have a heavy influence on the movement of broken ice around the hull, such as accumulating and sliding. The analysis of the broken ice movement contributes to understanding the influences of broken ice parameters on ice-going ships.
Bilinear Fatigue Performance of Composite Marine Risers in Deep Offshore Fields Due to Vortex Induced Vibrations
Authors: Khan Rizwan Ahmad , Ahmad Suhail
Published: October 2021

Risers are an integral part of an offshore oil and gas exploration structures, and that they are prone to vortex-induced vibration (VIV). Although several studies are conducted to analyze the VIV characteristics of risers, the results of amalgamation of multiple parameters and also the relative significance of every parameter on the risers’ VIV characteristics have seldom been considered. Vortex elicited vibration is one of the main causes of the fatigue damage of the riser. In deep sea atmosphere currents sometimes vary in magnitude and direction with depth, thereby causing the likelihood of exciting multiple modes of the riser vibration because of VIV. Vortex elicited vibration analysis has been carried out of a long marine riser for different probable sea locations. To boost the understanding of deepwater environments, the behavior of a composite riser under these forces is investigated. 3D nonlinear dynamic analysis of riser is obtained in time domain using finite part software package ABAQUS/Aqua. The response histories thus obtained are utilized for fatigue safety analyses of the riser. Uncertainty modeling, particularly of crack growth parameters, is undertaken by means of the bi-linear crack growth relationship. Results concerning fatigue safety and crack size evolution are given using Monte Carlo Simulation. The bi-linear crack growth models are found to result in to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has also been investigated.
Numerical Simulations of Sinusoidally Oscillating Cross-Flow Around a Circular Cylinder
Authors: Gamaleldin Muhannad W. , Babanin Alexander V.
Published: October 2021

A numerical study is conducted to investigate a sinusoidal oscillatory cross-flow around a smooth circular cylinder. A numerical model based on the Reynolds-averaged Navier-Stokes (RANS) equations with the k-ω Shear Stress Transport (SST) turbulence model is implemented, using the open source C++ package OpenFOAM®. The study focuses on the level of confidence in using two-dimensional numerical simulations for the predictions of the inherent transient behaviour of the highly nonlinear hydrodynamic induced loads. Simulations are conducted for two values of Keulegan-Carpenter (KC) number corresponding to inertia-dominated and drag-inertia regimes, for a fixed value of the frequency parameter β. Boundary layer separation structures and their temporal evolution are investigated and visualized by means of turbulence kinetic energy contours. Moreover, inline forces inertia and drag coefficients of Morison loads decomposition are found and validated against previous experimental results in literature. Finally, transverse forces and their spectral content is investigated and validated. The study shows that the magnitude and frequency of the unsteady hydrodynamic induced forces coefficients are well reproduced and are in a very good agreement with the experimental observations.
Coupling of Potential Flow and CFD Model for Fluid and Structure Interactions
Authors: Xu Haihua , Zhang Yali , Santo Harrif , Chua Kie Hian , Law Yun Zhi , Chan Eng Soon
Published: October 2021

Computational Fluid Dynamics (CFD) tools are widely used to simulate wave and structure interactions in marine & offshore industry. However, conventional CFD tools require significant computational resources. This is largely due to the requirement of large computational domain to ensure adequate development of nonlinear wave evolutions as well as to avoid boundary effects resulting from wave interacting with any fixed or floating structures in the domain. Furthermore, very fine mesh elements are required to avoid excessive numerical dissipation during wave propagation. All of these factors will significantly increase the computational costs, resulting in the conventional CFD approaches being impractical for simulations of wave-structure interactions over a long duration.

In this paper, a coupled potential flow and CFD model is developed to reduce the simulation cost. The model decomposes the simulation domain into far-field and near-field region. Wave propagation in the far-field region is simulated by a potential flow solver (High-Order Spectral or HOS method), while the wave-structure interactions in the near-field region are simulated by a fully nonlinear, viscous, and two-phase CFD solver (Star-CCM+). A forcing zone is distributed between the two regions to blend the computational outputs from the potential flow into the CFD solvers. The coupling algorithm has been developed to improve the accuracy and efficiency.

The coupled solver is applied to simulate two cases, namely regular wave propagation, and regular wave interaction with a vertical cylinder. Finally, a simulation of a 3D wave encountering an FPSO (Floating Production Storage and Offloading) is presented.
Ship Damage Stability Approval Document Generation by a Amonte Carlo Method
Authors: Krüger Stefan , Aschenberg Katja
Published: October 2021

The revised SOLAS 2020 damage stability regulations have a strong impact on possible future ship designs. To cope with these requirements, damage stability investigations must become a central part of the initial design phase, and many internal subdivision concepts need to be investigated. Unfortunately, if damage stability calculations are performed in the classical way, they are very time consuming with respect to modelling and computational time. This fact has impeded the consequent subdivision optimization in the past. Therefore, a simulation procedure for damage stability problems was developed which treats damage stability as a stochastic process which was modeled by a Monte Carlo simulation. If statistical damage distributions are once known, the Monte Carlo simulation delivers a population of damages which can be automatically related to certain damage cases. These damage cases can then be investigated with respect to their survivability. Applying this principle to damage stability problems reduces the computational effort drastically where at the same time no more manual modelling is required. This development does especially support the initial design phase of the compartmentation and leads to a safer and more efficient design. If this very efficient simulation principle shall now also be used after the initial design phase for the generation of approval documents, additional information needs to be generated by the simulation method which is not directly obtained during the simulation: This includes detailed individual probabilities in all three directions and the integration of all damage cases into predefined damage zones. This results in fact in a kind of reverse engineering of the manual damage stability process to automatically obtain this required information. It can be demonstrated that the time to obtain the final documents for the damage stability approval can be drastically reduced by implementing this principle.
Comparing Numerical and Analytical Solutions of Solitary Water Waves Over Finite and Variable Depth
Authors: Hallak Thiago S. , Islam Hafizul , Mohapatra Sarat Chandra , Guedes Soares C.
Published: October 2021

In this paper, three methods are used in order to obtain the solution for the propagation of water solitons over finite and variable depth. First, the exact analytical solitary wave solutions of the one-dimensional non-linear Boussinesq equations under shallow water condition are described for constant and variable depth. Second, the three-dimensional Fully Non-linear Potential Flow code OceanWave3D is used in order to obtain the numerical solutions for the solitary waves’ propagation over same depth ranges, providing robust solutions for the potential flow problem. Third, Computational Fluid Dynamics’ tool OpenFOAM is used in order to obtain the viscous solution for the same problem, however, without the accounts of turbulence models. The free-surface profiles are drawn and compared; and the stability of the numerical solutions are assessed. Since the approximations of Boussinesq-type equations depend mainly on the orders of magnitude of amplitude and depth, the numerical-analytical comparison will draw the limits for the validity of the analytical solutions. On the other hand, the comparison will provide the limits where viscous effects start playing an important role, whereas the CFD simulations predict the occurrence of wave breaking. These benchmark cases are compared with past references. After all, results regarding the same phenomena have been described in the literature according to, e.g. Fully Non-linear Boussinesq Models, and Fully Nonlinear Potential Flow schemes solved by Boundary Element Methods. Last but not least, the open source Fully Non-linear Potential Flow code is used in order to provide the potential flow solution for some extra cases of water soliton propagation, in order to capture the trends in weak shoaling scenarios.
Analyzing the Fluid Mechanics of the Dump Bailing Method in the Plug and Abandonment of Oil and Gas Wells
Authors: Akbari Soheil , Taghavi Seyed Mohammad
Published: October 2021

Plug and abandonment (P&A) of oil and gas wells is receiving an increased attention. The P&A operation is performed by placing a barrier, such as a cement plug to avoid reservoir fluids migration toward aquifers. To fulfill these requirements, the desired cement plug should be placed in the wellbore with minimum mixing with the in-situ fluid. A rigless way for placing cement slurry in the wellbore is through the dump bailing method, in which a relatively small amount of cement slurry is injected on a mechanical barrier inside the well to replace the in-situ wellbore fluids (mostly fresh water). The dynamics of the fluid placement is governed by several parameters, such as the flow and geometry parameters, and the fluid properties.

In this study, we analyze the fluid mechanics of the dump bailing method, via experimentally investigating the effects of the viscosity ratio between the replacing and replaced fluids in the process. The viscosities of the fluids involved have significant effects on the mixing and placement flow quality. In our experiments, the fluid placement is carried out in a near-vertical closed-end pipe (i.e. representative of the well casing) to replace an in-situ light fluid. The two fluids are considered to be miscible, and they have a fixed density difference. Our results show that the most efficient placement happens with the injection of the higher viscous fluid. The outcomes of this study can be used for improving the cementing processes in the dump-bailing method of P&A operations.
Experimental Study on the Stability Performance and Turning Motion of Multi-Connection VAWT
Authors: Iwamatsu Saika , Nihei Yasunori , Iijima Kazuhiro , Ikoma Tomoki , Komori Tomoki
Published: October 2021

In this study, a series of dedicated water tank tests were conducted in wind and waves to investigate the stability performance and turning motion of Floating Offshore Wind Turbine (FOWT) equipped with two vertical axis wind turbines (VAWT). The FOWT targeted in this study is called Multi-connection VAWT, which is a new type of FOWT moored by Single-Point-Mooring (SPM) system. We designed and manufactured two types of semi-submersible floating bodies. One is a type in which VAWTs are mounted in two places of a right-angled isosceles triangle (Type-A) on a single floater, and the other is two independent units equipped with VAWTs on two separate floaters centered on a moored body. This is a type in which two semi-submersible floating bodies are lined up in a straight line (Type-B). The experimental conditions were determined by scaling down to 1/100 using Froude’s scaling law based on a wind thrust load of 320 kN (rated wind speed of 12 m/s) assuming an actual machine. In the free yawing test in waves, Type-A turned downwards, while Type-B was barely affected by the waves. Furthermore, in the free yawing test in wind, both Type-A and Type-B turned leeward and stabilized at a final point where the wind load was balanced.
Prediction of Nonlinear Acceleration Response of a Large Container Ship and the Validation of Excessive Acceleration Failure Mode
Authors: Duan Fei , Ma Ning , Gu Xiechong , Zhou Yaohua , Shangming Wang
Published: October 2021

The excessive acceleration is one of five stability failure modes for intact stability being discussed at IMO. The excessive acceleration usually occurs in shallow draft state, under which the ship is prone to large nonlinear rolling motion. Therefore, the accurate prediction and evaluation of the acceleration response are required in ship intact stability analysis. This paper proposes a 5-DOF model in time domain to calculate the nonlinear acceleration response of a large container ship. The nonlinear restoring force and wave exciting forces (F-K force) are calculated through pressure integration on instantaneous wetted surfaces. A model test has been carried out to verify the prediction method of ship nonlinear acceleration response in the regular and irregular waves. It turns out the ship nonlinear acceleration response in regular and irregular waves obtained by the nonlinear time domain simulation agrees well with the experimental results. The vulnerability criteria for excessive acceleration are also validated by numerical and experimental results. In addition, the influence factor of ship lateral acceleration is studied. The results show that the prediction accuracy of 5-DOF model is acceptable. However, the accuracy needs to be improved for the condition of short wavelength. The influence of angular velocity can be ignored.
Real-Time Simulation of Hull Structure Using Finite Element in Virtual Reality Applications
Authors: Li Chuntong , Wei Naikun , Luo Xiaomeng , Lv Jianjun , Yang Xuelian , Wang Deyu
Published: October 2021

Visualization post-processing has become the primary means of awareness and understanding of CAE data intuitively and vividly. Visual analysis can help designers extract meaningful features and results from the complex data quickly and efficiently through intuitive visual images. Virtual reality (VR) -based simulation system can provide experience for the decision-makers and inexperienced workers. We propose a novel solution for real-time Finite Element Analysis (FEA) calculation between wave and hull structure. Firstly, an appropriate CAE system with all the FEA results of the hull is established in a single database. Secondly, based on the Unity 3d platform, effective data transmission technology and three-dimensional virtual models are constructed to achieve an immersive interactive experience. Finally, the third important player is hardware, making the Virtual Reality navigation become possible in many different environments. This paper briefly describes the features of this system. The proposed system employs a distributed simulation framework to realize real-time virtual simulation and human-computer interaction (HCI) of hull structures based on the Finite Element (FE) calculations. In addition, the applicability and the accuracy of the proposed virtual simulation method have also been verified by conducting a case study.
Optimization of Depressurization and Hot Water Injection Development for Class III Offshore Hydrate Reservoirs Based on Particle Swarm Optimization
Authors: Bai Yajie , Hou Jian
Published: October 2021

Based on the basic geological parameters of hydrate reservoir at SH7 station in Shenhu sea area of South China Sea, a numerical simulation model of heterogeneous Class III hydrate reservoir is established. Combining the particle swarm optimization with the numerical simulation of gas hydrate reservoir, taking net energy as objective function, an optimization method for the production parameters of Class III hydrate reservoir by depressurization and thermal stimulation is established. After the established optimization model reaches convergence, the net energy of the optimal scheme is increased by 10.976% compared with the initial scheme, which indicates that the development effect can be effectively improved by using particle swarm optimization method to optimize the development parameters of hydrate reservoir. Reservoir heterogeneity has a great impact on the development effect. Injection wells in low permeability area should inject more heat to stimulate hydrate decomposition, and the corresponding gas production rate in this area is small. The establishment of production parameter optimization method of Class III hydrate reservoir by depressurization and thermal stimulation can improve the recovery efficiency, reduce the energy consumption and promote the commercial exploitation process of the offshore hydrate reservoirs.
Parametric Evaluation of Stress Concentration Factor (SCF) at Brace – Chord Intersection of a Ring Stiffened Tubular Joint
Authors: Sai Krishna G. Chandra , Nallayarasu S.
Published: October 2021

Tubular joints are common in offshore framed structures such as jackets. These joints are subjected to fatigue due to cyclic loads from waves. Stress concentration factor plays a major role in the estimation of fatigue life. Studies have been carried out in the past on stress concentration factors for these joints. However, literature on ring stiffened joints is limited. In the present study, numerical simulations have been carried out on ring stiffened tubular joints, especially the T joints, subjected to axial tension load using finite element method in linear analysis using ABAQUS software. A solid type 20-node quadratic brick element (C3D20R) has been used in the study. Stresses in hotspot locations at brace/chord intersection, ring/chord intersection and ring inner edge are examined. The numerical model has been validated using published experimental data and Lloyd’s register recommendations. Further parametric study has been carried out with 20 models, which includes geometric parameters of ring stiffener such as width of stiffener, thickness of stiffener and spacing between the ring stiffeners. The results of parametric study show a significant reduction of SCF at saddle location by placing ring stiffeners in unstiffened T joint. A set of new parametric equations are developed to calculate SCF for ring stiffened T joint at saddle location for axial tensile load.
Investigation of Model Configuration Parameters for Stick-Slip Modeling
Authors: Wiktorski Ekaterina , Sui Dan
Published: October 2021

Stick-slip vibrations modeling is an important topic within drillstring dynamics. Thus, a number of mathematical models has been suggested to describe behavior of drillstrings under torsional. Most of the models take similar approach with regard to, for instance, drillstring discretization, definition of external forces and velocity-weakening effect.

Commonly, research papers focus on the models’ core — mathematical expressions that describe stick-slip oscillations and inherent to it negative damping. The results are usually presented in terms of downhole rotational velocity or displacement and reaction forces at various surface rotational velocities and applied external forces. However, little attention is paid to discussion and justification of selected model configuration, which includes definition of the following 1) total simulation time, time step, number of masses/elements, etc., 2) initial conditions and boundary conditions, and 3) numerical solver to obtain solution in time. This paper reviews commonly used configurations for stick-slip vibrations modeling and discusses selection criteria provided in the references. It also presents case studies to evaluate effect of the above-mentioned configuration properties on simulations outcome. A simple in-house 1DOF torsional dynamics model was used for that purpose, where one explicit and one implicit numerical solvers were applied to obtain solution in time.

Three case studies are presented, which compare performance of two numerical solvers with respect to convergence and stability. The results from the case studies show, for example, that applied explicit numerical solver (Central Difference Method) introduces numerical damping, while implicit solver (Newton-Raphson Method) does not. Central Difference Method provides convergence when initial force is applied, while damping function has to be defined in case of Newmark-Raphson method to obtain convergence. Stability of the explicit numerical solver is determined by the time step, while selected implicit solver is unconditionally stable. A reasonably small time step has to be selected though to improve the accuracy of the results.

Presented literature review and outcome from the case studies can be used by researchers within this area to select suitable configuration parameters for their models and critically evaluate the outputs. In addition, presented results have application in automated drilling where configuration parameters and calibration factors are updated in real time by control algorithms for continuous modeling of drillstring state with regard to stickslip. Understanding the effects of mentioned properties on system dynamics helps to select suitable combination of operational parameters to stabilize the drillstring.
Validation of Mooring Simulations (for Mooring Integrity Assessment) With In-Service Tension Measurements
Authors: Pauw Willemijn , Hageman Remco , van den Berg Joris , Aalberts Pieter , Yamaji Hironori , Ong Alex
Published: October 2021

Integrity of mooring system is of high importance in the offshore industry. In-service assessment of loads in the mooring lines is however very challenging. Direct monitoring of mooring line loads through load cells or inclinometers requires subsea installation work and continuous data transmission. Other solutions based on GPS and motion monitoring have been presented as solutions to overcome these limitations [1].

Monitoring solutions based on GPS and motion data provide good practical benefits, because monitoring can be conducted from accessible area. The procedure relies on accurate numerical models to model the relation between global motions and response of the mooring system. In this paper, validation of this monitoring approach for a single unit will be presented.

The unit under consideration is a turret-moored unit operating in Australia. In-service measurements of motions, GPS and line tensions are available. A numerical time-domain model of the mooring system was created. This model was used to simulate mooring line tensions due to measured FPSO motions. Using the measured unit response avoids the uncertainty resulting from a prediction of the hydrodynamic response.

Measurements from load cells in various mooring lines are available. These measurements were compared against the results obtained from the simulations for validation of the approach. Three different periods, comprising a total of five weeks of data, were examined in more detail. Two periods are mild weather conditions with different dominant wave directions. The third period features heavy weather conditions.

In this paper, the data set and numerical model are presented. A comparison between the measured and numerically calculated mooring line forces will be presented. Differences between the calculated and measured forces are examined.

This validation study has shown that in-service monitoring of mooring line loads through GPS and motion data provides a new opportunity for mooring integrity assessment with reduced monitoring system complexity.
Water Management and Hydraulic Fracturing Operations in Middle Eastern Tight Gas Reservoirs
Authors: Suboyin Abhijith , Rahman Md Motiur , Haroun Mohamed
Published: October 2021

Tight gas reservoirs in the Middle East are renowned for their extremely low porosity and low permeability along with their high heterogeneity. Over the past few decades, hydraulic fracturing has gained significant attention, particularly to stimulate such formations which were previously considered uneconomical and inefficient.

Even though over a million hydraulic fracturing operations were conducted across the globe, they are still associated with a considerable amount of risk. Studies have shown that an effective, efficient and economical approach coupled with tailored water management strategies are critical for their successful development, especially in arid regions such as the Middle East.

In this research, a realistic field model was constructed and advanced to analyze hydraulic fracture propagation in the presence of natural fractures for a candidate Middle Eastern tight gas reservoir. This flexible simulation model allowed to investigate, identify and characterize the key fracture design parameters that influenced fracture geometry for the candidate field. This further allowed to categorize and propose a unique tailored workflow to highlight the governing parameters for efficient water management strategies for arid regions such as the Middle East. In addition, the results have been extended to current field practices and cases.

The constructed model can greatly assist in streamlining hydraulic fracturing operations and water management strategies in regions such as the Middle East, where resources such as water and proppants can be considered as constraints. In addition, the investigation further highlights the strong need and potential opportunities for the key players in the region to leverage their technology for an efficient water management value chain. The variables and the workflow presented in this study further demonstrates how there is no bespoke solution to a ‘best approach’ in such regions. However, a workflow identifying the key dominant categories, such as a tailored one proposed in this study, may assist in the creation of more efficient and practical strategies while contributing to the overall process chain.
Influence of Pressure on Speed of Sound in Oil-Offloading Hoses
Authors: Buijs Lennert , Meijer Irma , Pereboom Hajo , Garlid Stian , Lunde Knud
Published: October 2021

Pressure surge or water hammer simulations are performed to evaluate a safe design or operation of oil transfer systems. The speed of sound of the transferred fluid plays a key role within pressure surge simulations. Unlike for steel pipe systems, the speed of sound in hoses is not easily determined. In industry, a value of 450 m/s is frequently used for hoses, but this value is often used independent of conveyed fluid, pressure or the type of hose. For that reason, a project was performed that aimed to experimentally reaffirm existing speed of sound data and to extend its usable range by including tests at several static pressure levels.

Speed of sound measurements were performed on two 20”, 12 meter long, water-filled oil offloading hoses. The speed of sound was determined by the initiation of pressure waves in the hoses, while performing pressure measurements on either side of the hose. These experiments were performed at different static pressures up to 18 bar(a).

The measured values depend on the applied method to determine the speed of sound. For both applied methods, the speed of sound is higher than the classically assumed 450 m/s. The method that is considered best applicable for the purpose of the experiments, the speed of sound is significantly higher and can reach values up to 1100 m/s. The consequence of this is that the results from pressure surge studies in which 450 m/s was used, are not conservative.
Numerical Modelling of Ice Rubble Interactions Using Discrete Element Method
Authors: Liu Lei , Bailey Eleanor , Taylor Rocky , King Tony
Published: October 2021

A three-dimensional, freeze-bonded, Discrete Element Method (DEM) numerical model has been developed to simulate various ice rubble/ridge interaction scenarios. The numerical model was validated against the physical tests conducted by C-CORE under the Pipeline Ice Risk Assessment and Mitigation (PIRAM) Joint Industry Project. Accurate representation of ice block geometries and sizes distributions was achieved using clumped particles, rather than the traditional DEM spheres. With the use of clumped ice blocks the numerical model was able to characterize the initial keel conditions (macro porosity and freeze bond contacts) and capture interlocking behavior between ice blocks. A DEM gravel seabed model was then introduced to the clumped ice block model to allow for better representation of soil response during the simulated experiments. The main features of these model developments are described in this paper, along with a comparison of simulated results and large scale physical test results. From this work it was concluded that: (1) clumped ice blocks give more representative ice block shapes for an ice keel than spherical ice blocks, which better capture ice block interactions and overall ridge keel properties and behavior; and (2) a DEM model of the seabed gravel provided a better representation of the seabed than was possible with a continuous stiffness plane, which had important implications for modelling the keel-seabed interactions. The development and inclusion of these two new model features were found to significantly improve the accuracy of the DEM model in reproducing physical test results, while still being sufficiently computationally efficient as to allow for simulation of interactions full-scale ice ridges.
Enabling Technologies for Low Cost Subsea Field Development
Authors: Sevillano Lucas Cantinelli , Faanes Audun , Gjersvik Tor Berge , Sangesland Sigbjørn
Published: October 2021

The oil and gas industry faces many challenges as it is committed to provide energy to a world in transition. Declining prices impose constraints to new developments, either greenfield or brownfield. Additionally, the industry’s commitment to long-term value creation with reduced carbon footprint is confronted with the traditional solutions for well construction, production and processing, which consume significant amount of energy with corresponding high CO2 emissions. In this scenario, subsea production and processing technology has been a key enabler for the exploitation of oil and gas resources.

This paper presents a holistic review of trends in subsea technology development over recent years which have direct impact on the heart of the subsea production system, namely the subsea tree. The technological developments considered are in different subsea applications such as robotic automation, communication systems, and all-electric systems.

The objective of the ongoing research is to perform structural and fundamental analysis of subsea production and injection systems and address the question on how technological developments can be utilized to design an overall better subsea production system so the industry may fully benefit from the economic and ecological impact brought by the joint use of these technologies. Opportunities for reevaluating barrier philosophy to identify technical and economic opportunities for design simplifications of subsea trees that still leave enough pressure barriers in all operational modes are also considered.

The analyses presented indicate the current stage of the examined technologies and their potential at reducing both capital and operational cost of subsea systems. These results will be the basis for the future evaluation of improved and new design solutions within the scope of the ongoing project performed by the Norwegian University of Science and Technology and its industrial partners.
Statistical Description of Nonlinear Waves
Authors: Bitner-Gregersen Elzbieta M. , Gramstad Odin
Published: October 2021

Traditionally, wave parameters and their statistics has been derived from time series measurements of wave elevation. Recently, due to introduction in oceanography of stereo video camera systems, increasing attention has started to be given to spatial wave data and statistics. The present study is addressing temporal and spatial statistics of nonlinear waves giving focus to individual wave parameters. A directionally spread rogue-prone sea state observed in the North Sea is used as an example in the analysis which is based on numerical HOSM (Higher Order Spectral Method) simulations. The nonlinear order in the HOSM solver is set to M = 3, which includes the leading order nonlinear dynamical effects, including the effect of modulational instability. The following wave parameters are investigated: surface elevation, wave crests and wave troughs. The results demonstrate that the maximum spatial crest in a wave record can be up to 70% higher than the temporal crest. Further, the study indicates that the Gram-Charlier series can be used to fit the probability density function of surface elevation. It discusses applicability of the methodology based on the Gram-Charlier series for approximation of distributions of individual wave parameters of extreme and rogue waves and recommends further exploitation of this methodology. The results are discussed in the context of marine structures’ design.
Research on the Hydrodynamic Performance of Zero Speed Fin Stabilizer
Authors: Wei Yuefeng , Yang Yi
Published: October 2021

Nowadays, zero speed fin stabilizer has been initially applied in ship. Whether zero speed fin stabilizer can generate enough lift moment to resist rolling moment or not, determines the anti-rolling effect of ship at zero speed. In the present paper, numerical model is proposed to calculate the lift force and moment of zero speed fin stabilizer. The results of numerical calculation are verified by model test results and the hydrodynamic performance of zero speed fin stabilizer are studied. The numerical results are in good agreement with the model test results. For different swing angular velocity of a zero speed fin stabilizer, the lift force and moment of zero speed fin stabilizer reach the maximum at the same swing angle. For the same swing angle of a zero speed fin stabilizer, the lift force and moment of zero speed fin stabilizer are proportional to the square of angular velocity.
Fibre Spring Mooring Solution for Mooring Floating Offshore Wind Turbines in Shallow Water
Authors: McEvoy Paul , Kim Seojin , Haynes Malak
Published: October 2021

Mooring of Floating Offshore Wind Turbines (FOWT) in shallow water sites (30–80m) is challenging. These sites account for a significant proportion of the nearer to shore potential wind farm locations, and are desirable as they are closer to existing infrastructure and easier to access. Mooring large floating structures in very shallow waters however results in very long heavy mooring lines designed to minimize platform surge and protect the electrical cables. This paper presents an innovative Fibre Spring Mooring (FSM) solution which combines a high modulus, non-stretch, lightweight rope with a compliant nonlinear polymer spring offering a complete semi-taut mooring system which can be connected directly between the platform and the seabed. The paper will present Orcaflex simulation results of a 12MW barge type FOWT platform, moored using a semi-taut FSM mooring at three chosen North Sea locations close to existing wind farms, of 30m, 40m and 50m water depths. Different FSM configurations, with different line lengths, footprint, and ratio of fibre to spring are considered.
Investigation of Multiphase Flow in Porous Media Around Perforation Tunnel Near Wellbore Region, Experimental and Numerical Study
Authors: Elsanoose Abadelhalim , Abobaker Ekhwaiter , Khan Faisal , Rahman Aziz , Aborig Amer
Published: October 2021

Understanding the behavior of the multiphase flow in the porous media near the wellbore region is essential for increasing wells’ productivity and oil recovery. In this paper, an experimental and numerical study of multiphase flow in porous media near a perforation tunnel is presented. The effect of properties on the flow, such as porosity and permeability, are crucial for increasing oil and gas production. Two-phase flow through a cylindrical porous media with a perforation tunnel samples experimentally and numerically tested. Five sandstone samples were created at Memorial university labs, the sample dimensions are 30.48 cm high, 15.54 cm diameter, and a perforation tunnel has a 25.54 cm depth and 2.54cm diameter. The air and water injected into the sample radially at different flow rates, the water flow rate ranged from 1 to 3 LPM, and the air 3 to 9 LPM. The simulation carried out using ANSYS-Fluent 18.1 commercial software simulates the Volume Of Fluid method VOF coupled with the different turbulent models used to simulate the flow. The results showed that the porous media’s pressure buildup is greatly affected by the gas flow rate and its permeability. The wellbore pressure and porosity have more negligible effect on the pressure buildup profile in the porous media. The dominant factor for the breakthrough of a fluid in a core sample is the gas flow rate. Incorporating the gas flow in a porous system will reduce hydrostatic pressure loss, and less time is required to activate the breakthrough time.
Stochastic Time-Dependent Deterioration Models for Estimating Residual Service Life of Offshore Jacket-Type Platforms
Authors: Srikanth Ishwarya , Arockiasamy M.
Published: October 2021

This paper presents deterioration models for maintenance planning of offshore jacket platform based on two methods: i) stochastic Markov-chain based model and ii) stochastic-mechanistic deterioration models based on steel corrosion rates. Markov-chain models require the estimation of transition probability matrix (TPM), which is typically derived from the inspection data. The global structural health condition of the jacket is computed based on the condition of individual elements and their criticality in terms of failure consequence. The criticality factors are established based on nonlinear static redundancy analyses. This method can model deterioration when routine inspection records of jacket members are available. When there is scarcity of inspection records, stochastic-mechanistic deterioration modeling approach can be used. Monte-Carlo simulations with established corrosion wastage models are utilized to estimate the time-dependent deterioration of jacket legs, horizontal and diagonal bracings in splash and immersion zones. This method is proposed when there is scarcity of inspection records. The deterioration models are further utilized to predict the timing for Maintenance, Repair and Rehabilitation (MRR) actions, and estimate the residual service life of the jacket platform. This study demonstrates the application of the proposed deterioration modeling approaches with a case study of a typical 4-legged offshore jacket platform.
Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice
Authors: Sinsabvarodom Chana , Leira Bernt J. , Chai Wei , Naess Arvid
Published: October 2021

The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking was employed in order to represent a supply vessel equipped with a mooring line system, and the realtime loading during the full-scale measurement was recorded. The second vessel Tor Viking was serving as an ice breaker in order to maintain the physical ice management activities with different ice-breaking schemes, i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns were investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Fatigue assessment based both on Rainflow counting and fitted probabilistic models were performed. For the latter, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress ranges represented by application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the Rainflow counting approach. Among the different scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.
Experimental Investigation of Vortex-Induced Vibrations of a Flexibly Mounted Circular Cylinder in Combined Current and Wave Flows
Authors: Opinel Pierre-Adrien , Srinil Narakorn
Published: October 2021

This paper presents the experimental investigation of vortex-induced vibrations (VIV) of a flexibly mounted circular cylinder in combined current and wave flows. The same experimental setup has previously been used in our previous study (OMAE2020-18161) on VIV in regular waves. The system comprises a pendulum-type vertical cylinder mounted on two-dimensional springs with equal stiffness in in-line and cross-flow directions. The mass ratio of the system is close to 3, the aspect ratio of the tested cylinder based on its submerged length is close to 27, and the damping in still water is around 3.4%. Three current velocities are considered in this study, namely 0.21 m/s, 0.29 m/s and 0.37 m/s, in combination with the generated regular waves. The cylinder motion is recorded using targets and two Qualisys cameras, and the water elevation is measured utilizing a wave probe. The covered ranges of Keulegan-Carpenter number KC are [9.6–35.4], [12.8–40.9] and [16.3–47.8], and the corresponding ranges of reduced velocity Vr are [8–16.3], [10.6–18.4] and [14–20.5] for the cases with current velocity of 0.21 m/s, 0.29 m/s and 0.37 m/s, respectively. The cylinder response amplitudes, trajectories and vibration frequencies are extracted from the recorded motion signals. In all cases the cylinder oscillates primarily at the flow frequency in the in-line direction, and the in-line VIV component additionally appears for the intermediate (0.29 m/s) and high (0.37 m/s) current velocities. The cross-flow oscillation frequency is principally at two or three times the flow frequency in the low current case, similar to what is observed in pure regular waves. For higher current velocities, the cross-flow frequency tends to lock-in with the system natural frequency, as in the steady flow case. The inline and cross-flow cylinder response amplitudes of the combined current and regular wave flow cases are eventually compared with the amplitudes from the pure current and pure regular wave flow cases.